JP5695373B2 - Electrode for electrochemical element and electrochemical element using the same - Google Patents

Description

  The present invention relates to an electrode that can be used for an electrochemical element such as a battery or a capacitor, and an electrochemical element using the electrode.

In recent years, with the development of portable electronic devices such as mobile phones and notebook personal computers, and the practical application of electric vehicles, electrochemical devices such as small batteries, high capacity secondary batteries and capacitors are required. It has become. Currently, LiCoO ₂ , LiNiO ₂ , LiMn ₂ O _{4 and the} like are generally used as positive electrode active materials for high-capacity secondary batteries and capacitors that can meet this requirement.

In particular, LiNiO ₂ can be cited as a positive electrode active material that can constitute a high-capacity battery or capacitor. This is because the stability of the crystal structure in a charged state is lower than that of LiCoO ₂ , and as it is, the safety of the battery or capacitor is improved. It was difficult to be satisfied. Also. LiNiO ₂ was not satisfactory in terms of charge / discharge cycle life due to the low reversibility of the crystal structure.

Under such circumstances, a lithium-containing composite oxide in which a part of Ni is substituted with an element such as Co, Al, or Mg has been proposed in order to maintain the LiNiO ₂ charged crystal structure. Therefore, improvement of safety and reversibility has been attempted (for example, Patent Document 1).

JP 2007-273108 A

  However, the lithium-containing composite oxide as described in Patent Document 1 has a low initial charge / discharge efficiency, so that the capacity drop tends to be large, and since the true density is low, the capacity when used as an electrode is increased. There is still room for improvement in terms of further increasing the capacity of the electrochemical element, and there is also room for improvement in terms of charge / discharge cycle characteristics of the electrochemical element.

  The present invention has been made in view of the above circumstances, and has a high capacity and high stability electrode for an electrochemical element, and the electrode for the electrochemical element, and has a high capacity, charge / discharge cycle characteristics and safety. An excellent electrochemical device is provided.

The electrode for an electrochemical element of the present invention has the following general composition formula (1)
Li _{1 + x} MO ₂ (1)
An electrode for an electrochemical device comprising an electrode mixture layer containing a lithium-containing composite oxide represented by formula (1), wherein −0.3 ≦ x ≦ 0.3 in the general composition formula (1) And M represents an element group of four or more elements including Ni, Mn and Mg and at least one element selected from Nb, Mo, Ga, W and V, When the ratios of Ni, Mn, and Mg to the element amount are a, b, and c in mol% units, respectively, 70 ≦ a ≦ 97, 0.5 <b <30, 0.5 <c <30, −10 <B−c <10 and −8 ≦ (bc) / c ≦ 8, the average valence of Ni is 2.5 to 3.2, and the average valence of Mn is 3.5 to 4. .2 and the average valence of Mg is 1.8 to 2.2.

  The electrochemical device of the present invention is an electrochemical device including a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the positive electrode is the electrode for an electrochemical device.

  ADVANTAGE OF THE INVENTION According to this invention, the electrode for electrochemical elements with high capacity | capacitance and high stability can be provided, and the electrochemical element provided with the electrode for electrochemical elements is high capacity | capacitance, and was excellent in charge / discharge cycling characteristics and safety Can provide.

FIG. 1A is a schematic plan view of a lithium secondary battery according to the present invention, and FIG. 1B is a schematic cross-sectional view of FIG. FIG. 2 is a schematic external view of a lithium secondary battery according to the present invention.

(Embodiment 1)
First, an electrode for an electrochemical element of the present invention (hereinafter sometimes simply referred to as “electrode”) will be described. The electrode for an electrochemical device of the present invention includes an electrode mixture layer containing, as an active material, a lithium-containing composite oxide represented by the general composition formula (1): Li _{1 + x} MO ₂ . In the general composition formula (1), −0.3 ≦ x ≦ 0.3, and M represents an element group containing Ni, Mn, and Mg. Further, when the ratios of Ni, Mn, and Mg contained in the element group M to the total element amount of the element group M are a, b, and c in mol% units, respectively, 70 ≦ a ≦ 97, 0,. 5 <b <30, 0.5 <c <30, −10 <b−c <10, and −8 ≦ (bc) / c ≦ 8. The average valence of Ni is 2.5 to 3.2, the average valence of Mn is 3.5 to 4.2, and the average valence of Mg is 1.8 to 2. .It is bivalent.

  The lithium-containing composite oxide acts as a positive electrode active material for an electrochemical element such as a lithium secondary battery. By using the lithium-containing composite oxide as an active material, the electrochemical element has high capacity and high stability. An electrode can be provided.

<Lithium-containing composite oxide>
Hereinafter, the lithium-containing composite oxide used for the electrode of the present invention will be described. The lithium-containing composite oxide used for the electrode of the present invention contains an element group M containing at least Ni, Mn, and Mg.

  The Ni is a component that contributes to an increase in the capacity of the lithium-containing composite oxide. When the total element amount of the element group M in the general composition formula (1) representing the lithium-containing composite oxide is 100 mol%, the Ni ratio a (mol%) improves the capacity of the lithium-containing composite oxide. From the viewpoint, it is set to 70 mol% or more. However, if the proportion of Ni in the element group M is too large, for example, the amount of Mn or Mg decreases, and the effect of these decreases. Therefore, the Ni ratio a (mol%) is set to 97 mol% or less.

  In the present invention, the capacity of the lithium-containing composite oxide is adjusted to 185 mAh when the driving voltage is 2.5 to 4.3 V based on the lithium metal by adjusting the ratio of Ni in the element group M as described above. / G or more.

  Moreover, the electrical conductivity of lithium containing complex oxide falls, so that the average valence of said Ni becomes small. Therefore, the lithium-containing composite oxide has an average valence (A) of Ni of 2.5 to 3.2 measured by the method shown in the examples described later. In addition, this makes it possible to obtain a high-capacity lithium-containing composite oxide when the driving voltage is 2.5 to 4.3 V based on lithium metal.

In the lithium-containing composite oxide, when the total element amount of the element group M is 100 mol%, the Mn ratio b (mol%) and the Mg ratio c (mol%) are set to 0.5 <b <30. And 0.5 <c <30, and −10 <bc <10 and −8 ≦ (bc) / c ≦ 8, Mn and Mg are present in the crystal lattice. Thereby, when the phase transition of the lithium-containing composite oxide occurs due to the desorption and insertion of Li, the irreversible reaction is relaxed because Mg ²⁺ is transferred to the Li site, and the lithium-containing compound represented by the space group R3-m is contained. The reversibility of the layered crystal structure of the composite oxide is improved. In addition, since tetravalent Mn stabilizes divalent Mg, an electrochemical element having a long charge / discharge cycle life can be formed.

  From the viewpoint of better ensuring the effect of stabilizing divalent Mg by Mn, the ratio b of Mn in all elements of the element group M is preferably 1 mol% or more, and preferably 2 mol% or more. More preferably, it is preferably 10 mol% or less, and more preferably 7 mol% or less. Further, from the viewpoint of better ensuring the effect of improving the reversibility of the crystal structure by Mg, the ratio c of Mg in all elements of the element group M is preferably 1 mol% or more, and preferably 2 mol% or more. More preferably. However, since Mg contributes little to the charge / discharge capacity, if the amount added is large, the capacity may be reduced. Therefore, the ratio c of Mg is preferably 15 mol% or less, more preferably 10 mol% or less, and even more preferably 7 mol% or less. The difference in composition ratio between Mn and Mg is desirably small, preferably −3 ≦ b−c ≦ 3, and more preferably −2 ≦ (bc) / c ≦ 2.

  In the above lithium-containing composite oxide, the average valence of Mg is a value measured by the method shown in Examples below, from the viewpoint of increasing the reversibility of the crystal structure of the lithium-containing composite oxide, and is 1.8-2. .It is bivalent. Further, in the lithium-containing composite oxide, the average valence of Mn is a value measured by the method shown in the examples described later from the viewpoint of stabilizing Mg and effectively exhibiting its action. And 3.5 to 4.2.

  The element group M in the general formula (1) representing the lithium-containing composite oxide includes at least Ni, Mn, and Mg, and may be an element group composed of only these three elements.

  In addition to Ni, Mn and Mg, the element group M further includes Co, Ti, Cr, Fe, Cu, Zn, Al, Ge, Sn, Ag, Ta, Nb, Mo, B, P, Zr, It may be a group of four or more elements including elements such as Ga, Ba, Sr, Ca, Si, W, V and S. When the element group M contains Co, the presence of Co in the crystal lattice of the lithium-containing composite oxide causes a phase of the lithium-containing composite oxide due to Li desorption and insertion during charging and discharging of the electrochemical device. The irreversible reaction resulting from the rearrangement can be further relaxed, and the reversibility of the crystal structure of the lithium-containing composite oxide can be enhanced. Thereby, an electrochemical element having a long charge / discharge cycle life can be configured.

  In the case where the element group M contains Co, when the total element amount of the element group M is 100 mol%, the Co ratio d (mol%) is different from other elements (Ni, Mn, and Mg) constituting the element group M. From the viewpoint of suppressing the effect of these elements from decreasing as the amount of is reduced, 0 <d <30 is preferable. From the viewpoint of better ensuring the effect of improving the reversibility of the crystal structure of the lithium-containing composite oxide by Co, the Co ratio d is more preferably 1 mol% or more.

  Furthermore, the average valence of Co in the lithium-containing composite oxide is a value measured by the method shown in the examples described later, from the viewpoint of ensuring the above-described effect by Co, 2.5 to 3.2. It is preferable that

  The element group M is Ti, Cr, Fe, Cu, Zn, Al, Ge, Sn, Ag, Ta, Nb, Mo, B, P, Zr, Ga, Ba, Sr, Ca, Si, W, When elements such as V and S are included, in order to sufficiently obtain the effects of the present invention, when the total element amount of the element group M is 100 mol%, the ratio of elements other than Ni, Mn, Mg and Co is It is preferably 15 mol% or less, more preferably 7 mol% or less, and particularly preferably 3 mol% or less. In addition, when the element group M contains a plurality of elements other than Ni, Mn, Mg, and Co, the total amount is preferably 15 mol% or less. Elements other than Ni, Mn, Mg, and Co in the element group M may be uniformly distributed in the lithium-containing composite oxide, or may be segregated on the particle surface or the like.

Among the above elements, the element group M preferably contains at least one element selected from Nb, Mo, Ga, W and V. Interlayer distance in the c-axis direction in the crystal lattice of a lithium-containing composite oxide due to solid solution of Ga, V, W, Mo or Nb having a larger ionic radius in the same coordination environment as Ni, Mn, and Co Can be stretched. More specifically, the c-axis lattice constant can be 1.416 to 1.428 nm, and the ratio c / a of the a-axis to c-axis lattice constant can be 4.92 or more. LiNiO ₂ has a layered structure belonging to the space group R3-m, but the charge-discharge process changes the interlayer distance in the transition metal layer and expands and contracts in the c-axis direction. J. et al. Electrochem. soc. , Vol140, No7 (1993). The expansion / contraction of the crystal due to this charge / discharge is one factor that deteriorates the cycle characteristics. By including an element having a larger ionic radius than Ni, such as Nb, Mo, Ga, W, and V, in the lithium-containing composite oxide, the interlayer distance is extended from the beginning, and the The rate of shrinkage can be reduced, and a material with more excellent cycle characteristics can be obtained.

  For example, in a lithium secondary battery using the lithium-containing composite oxide containing Ni, Mn, and Mg as the positive electrode and using graphite, an element that can be alloyed with lithium, or a compound thereof as the negative electrode, Further, when the battery is charged / discharged in a voltage range of 2.8V to 4.2V by including an element such as Nb, the interlayer distance in the c-axis direction of the positive electrode material belonging to the space group R3-m The rate of change can be suppressed to 1.5% or less.

Similarly, in a lithium secondary battery using lithium titanate (Li _4/3 Ti _5/3 O ₄ ) as a negative electrode, when the battery is charged / discharged in a voltage range of 1.0 V to 2.6 V, the space The rate of change of the interlayer distance in the c-axis direction of the positive electrode material belonging to the group R3-m can be suppressed to 1.5% or less.

That is, by adding at least one element selected from Nb, Mo, Ga, W and V to the lithium-containing composite oxide represented by the above general composition formula: Li _{1 + x} MO ₂ , Li _1.00 MO _In charge / discharge corresponding to a change in the Li amount ratio from ₂ to Li _0.25 MO ₂ , the rate of change in the interlayer distance in the c-axis direction of the positive electrode material belonging to the space group R3-m is 1.5% or less. Can be suppressed.

  However, since the above elements do not contribute to the charge / discharge capacity, a large content causes a decrease in capacity. Therefore, the content of Nb, Mo, Ga, W and V is preferably 15 mol% or less, more preferably 7 mol% or less, and more preferably 3 mol% when the total amount of elements in the element group M is 100 mol%. It is particularly preferred that On the other hand, in order to bring about the effect, the content is preferably 0.1 mol% or more.

  The element group M can further contain Zr or Ti. By containing these elements, the charge / discharge cycle characteristics can be further improved. Zr and Ti may be present uniformly in the lithium-containing composite oxide, but are more preferably unevenly distributed on the surface of the lithium composite oxide. This is because the surface activity is suppressed without impairing the electrochemical characteristics of the lithium-containing composite oxide, and the effect of making the active material excellent in charge / discharge cycle characteristics, high-temperature storage characteristics and thermal stability is likely to be exhibited. is there. Therefore, the surface of the lithium-containing composite oxide may be coated with a Zr or Ti compound such as Zr oxide or Ti oxide. Thereby, impurities and by-products on the particle surface of the lithium-containing composite oxide can be reduced, and when forming the electrode mixture layer using a composition such as a paste or slurry containing the lithium-containing composite oxide. The gelation of the composition can be suppressed, and the coating stability can also be improved.

  The content of the Zr or Ti is the entire lithium composite oxide particle containing Zr and Ti in order to prevent the capacity reduction of the lithium-containing composite oxide (if the particle surface has a coating of Zr compound or Ti compound, the coating 5% by mass or less, and more preferably 1% by mass or less of the entire particle including the part. On the other hand, in order to sufficiently exhibit the effect of suppressing the surface activity of the lithium-containing composite oxide, it is preferable to contain 0.001% by mass or more.

In the lithium-containing composite oxide having the above composition, the true density is as large as 4.55 to 4.95 g / cm ³ , the capacity per mass of the active material can be increased, and the reversibility is excellent. Can be a material.

In addition, since the true density of the lithium-containing composite oxide increases particularly when the composition is close to the stoichiometric ratio, in the present invention, in the general composition formula (1), −0.3 ≦ x ≦ 0. .3. By adjusting the value of x in this way, the true density and reversibility can be increased. x is more preferably −0.1 or more and 0.1 or less. In this case, the true density of the lithium-containing composite oxide can be set to a higher value of 4.6 g / cm ³ or more. .

Here, when x <0, that is, when Li is insufficient compared to the stoichiometric ratio, in the synthesis of the lithium-containing composite oxide, Ni enters the Li site of the Li layer constituting the layered structure, and the structure Prone to irregularities. In the X-ray diffraction pattern, if the integrated intensities of the diffraction lines on the (003) plane and the (104) plane are I ₍₀₀₃₎ and I ₍₁₀₄₎ , the value of the ratio is required to obtain a stable structure. [Integral intensity ratio: I ₍₀₀₃₎ / I ₍₁₀₄₎ ] is preferably 1.2 or more, but when the above-described structural irregularity occurs, the integrated intensity ratio becomes smaller than 1.2. The charge / discharge capacity decreases and the cycle characteristics deteriorate.

However, by dissolving Mg in the crystal, the Li layer can be easily formed even when x <0, and Ni can be prevented from entering the Li layer, so that the integrated intensity ratio I _{(003) )} / I ₍₁₀₄₎ can be set to 1.2 or more, the reversibility of the crystal structure is increased, and a lithium-containing composite oxide having a high capacity and excellent cycle characteristics can be obtained.

Further, by designing the composition so that the Li amount ratio is smaller than the stoichiometric ratio, the amount of Li charged can be reduced during the synthesis of the lithium-containing composite oxide, so that excess Li ₂ CO ₃ And LiOH can be prevented from forming or remaining, the deterioration of the quality of the mixture paint caused by the excess compound is suppressed, and the preparation of the paint and the maintenance of the quality are facilitated.

  The lithium-containing composite oxide suppresses gas generation in an electrochemical device using the electrode of the present invention by moderately suppressing the activity of the surface, and in particular, a battery having a rectangular (rectangular cylindrical) outer package. In such a case, it is possible to suppress the deformation of the exterior body and improve the storability and life. From the viewpoint of securing such an effect, the lithium-containing composite oxide preferably has the following form.

First, the lithium-containing composite oxide particles are mainly composed of secondary particles in which primary particles are aggregated, and the volume ratio of the primary particles having a particle size of 1 μm or less to the total volume of the primary particles is 30% by volume or less. It is preferable that it is, and it is more preferable that it is 15 volume% or less. The BET specific surface area of the lithium-containing composite oxide particles is preferably 0.3 m ² / g or less, and more preferably 0.25 m ² / g or less.

  That is, in the lithium-containing composite oxide, when the proportion of primary particles having a particle size of 1 μm or less in all primary particles is too large or the BET specific surface area is too large, the reaction area of the lithium-containing composite oxide is large. As a result, the number of active points increases. Therefore, (1) moisture in the atmosphere, (2) a binder used to form an electrode mixture layer of an electrode using the lithium-containing composite oxide as an active material, and (3) an electrochemical having the electrode An irreversible reaction between the nonaqueous electrolyte of the element and the lithium-containing composite oxide easily occurs. As a result, problems such as generation of gas in the electrochemical element, deformation of the outer package, and gelation of a composition (paste, slurry, etc.) containing a solvent used for forming the electrode mixture layer easily occur. Become.

The lithium-containing composite oxide may not contain any primary particles having a particle size of 1 μm or less, and the ratio of primary particles having a particle size of 1 μm or less may be 0% by volume. Further, the BET specific surface area of the lithium-containing composite oxide is preferably 0.1 m ² / g or more in order to prevent the reactivity from being lowered more than necessary. Furthermore, it is preferable that the number average particle diameter of the whole lithium-containing composite oxide particles composed of non-aggregated primary particles and secondary particles formed by aggregation of the primary particles is 5 to 25 μm. This is because the BET specific surface area can be controlled within an appropriate range within this range.

  The ratio of primary particles having a particle size of 1 μm or less contained in the lithium-containing composite oxide, the number average particle size of the entire lithium-containing composite oxide particles, and the number average particle size of other active materials described later Can be measured by a laser diffraction / scattering particle size distribution analyzer, for example, “Microtrac HRA” manufactured by Nikkiso Co., Ltd. Values shown in the examples described later are values measured by this method. In addition, the BET specific surface area of the lithium-containing composite oxide is measured using a BET equation that is a theoretical equation of multimolecular layer adsorption. Specifically, it is a value obtained as a BET specific surface area using a specific surface area measuring device “Macsorb HM model-1201” by a nitrogen adsorption method manufactured by Mountaintech.

  From the viewpoint of increasing the density of the electrode mixture layer related to the electrode using the lithium-containing composite oxide as an active material, and further increasing the capacity of the electrode and thus the capacity of the electrochemical element, the particle shape is spherical or It is preferably substantially spherical. Thus, in the pressing step (details will be described later) during electrode fabrication, when the lithium-containing composite oxide particles are moved by pressing to increase the density of the electrode mixture layer, the particles are moved without difficulty. , The particles will be rearranged smoothly. Therefore, since the press load can be reduced, it is possible to reduce the damage of the current collector accompanying the press, and to increase the productivity of the electrode. Further, when the lithium-containing composite oxide particles are spherical or substantially spherical, the particles can withstand a larger pressing pressure, and therefore the electrode mixture layer can be made higher in density. .

Further, the lithium-containing composite oxide preferably has a tap density of 2.4 g / cm ³ or more, and preferably 2.8 g / cm ³ or more, from the viewpoint of enhancing the filling property in the electrode mixture layer. More preferred. That is, the ratio of the pores is such that the tap density is high and there are no pores inside the particles, or the area ratio of minute pores of 1 μm or less measured by cross-sectional observation of the particles is 10% or less. By setting it as few particle | grains, the filling property of the lithium containing complex oxide in an electrode mixture layer can be improved.

The tap density of the lithium-containing composite oxide is a value determined as follows using a tap density measuring device “Powder Tester PT-S type” manufactured by Hosokawa Micron. That is, the measurement particles are ground and put into a measuring cup 100 cm ^3, and tapping is performed for 180 seconds while replenishing the reduced volume appropriately. After tapping is completed, excess particles are scraped off with a blade, and then the mass of the measured particles: T (g) is measured, and the tap density is obtained by the following equation.

Tap density (g / cm ³ ) = T / 100

<Method for producing lithium-containing composite oxide>
Next, the manufacturing method of the said lithium containing complex oxide is demonstrated. It is very difficult to obtain the lithium-containing composite oxide with high purity by simply mixing and firing Li-containing compound, Ni-containing compound, Mn-containing compound, Mg-containing compound and the like. This is because Ni, Mn, Mg, etc. have a low diffusion rate in the solid, so that it is difficult to uniformly diffuse them during the synthesis reaction of the lithium-containing composite oxide. It is thought that this is because Ni, Mn, Mg, etc. are difficult to be uniformly distributed therein.

  When producing the lithium-containing composite oxide according to the present invention, at least Ni, Mn, and Mg (in the case where the element group M also includes Co, further Co) as a constituent element, and Li-containing It is preferable to employ a method of calcining the compound, and the lithium-containing composite oxide can be synthesized relatively easily with high purity by such a method. That is, a composite compound containing at least Ni, Mn, and Mg (and Co) is manufactured in advance, and this is baked together with a Li-containing compound. Thus, in the oxide formation reaction, Ni, Mn, and Mg (further Co) is uniformly distributed, and the lithium-containing composite oxide is synthesized with higher purity.

  The method for producing a lithium-containing composite oxide according to the present invention is not limited to the above method, but the physical properties of the lithium composite oxide to be produced, that is, the stability of the structure, depending on the production process. And reversibility of charge / discharge, true density, etc. are presumed to change greatly.

Here, as a composite compound containing at least Ni, Mn and Mg (and Co), for example, a coprecipitation compound containing Ni, Mn and Mg (and Co), a hydrothermally synthesized compound, and a mechanically synthesized compound are used. And compounds obtained by heat-treating them, such as Ni _0.7 Mn _0.1 Mg _0.2 (OH) ₂ , Ni _0.9 Co _0.05 Mn _0.03 Mg _0.02 An oxide or hydroxide of Ni, Mn, and Mg, or an oxide or hydroxide of Ni, Mn, Mg, and Co, such as (OH) ₂ , is preferable.

  The coprecipitated compound can be prepared by adding an aqueous solution in which sulfates, nitrates, and the like of constituent elements such as Ni, Mn, Mg, and Co are dissolved at a predetermined ratio to an alkali hydroxide aqueous solution and reacting them. It can be obtained as a coprecipitated hydroxide of elements.

  Instead of the alkali hydroxide aqueous solution, ammonia water whose pH is adjusted to a range of about 10 to 13 with alkali hydroxide may be used. That is, while keeping the temperature of the ammonia water constant in the range of about 40 to 60 ° C. and adding an alkaline aqueous solution so that the pH of the ammonia water is kept constant within the above range, the sulfate, nitrate, etc. An aqueous solution in which is dissolved is gradually added to precipitate the coprecipitated compound. As a result, the constituent elements of the coprecipitated compound are uniformly distributed, and the average valences of Ni, Mn, and Mg (and Co) of the synthesized lithium-containing composite oxide can be easily controlled within the range of the present invention.

  Part of the element group M includes elements other than Ni, Mn, Mg, and Co, such as Ti, Cr, Fe, Cu, Zn, Al, Ge, Sn, Ag, Ta, Nb, Mo, B, P, The above lithium-containing material containing at least one element selected from the group consisting of Zr, Ga, Ba, Sr, Ca, Si, W, V and S (hereinafter collectively referred to as “element M ′”). When producing a composite oxide, it is produced by mixing and firing a composite compound containing at least Ni, Mn, and Mg (and further Co), a Li-containing compound, and a compound containing element M ′. However, if possible, it is preferable to use a composite compound containing at least Ni, Mn and Mg (further, Co) and further the element M ′. In addition, the amount ratio of Ni, Mn, Mg, and M ′ and the amount ratio of Ni, Mn, Mg, Co, and M ′ in the composite compound are appropriately adjusted according to the composition of the target lithium-containing composite oxide. That's fine.

  As the Li-containing compound that can be used in the production of the lithium-containing composite oxide particles, various lithium salts can be used. For example, lithium hydroxide monohydrate, lithium nitrate, lithium carbonate, lithium acetate, odor Lithium chloride, lithium chloride, lithium citrate, lithium fluoride, lithium iodide, lithium lactate, lithium oxalate, lithium phosphate, lithium pyruvate, lithium sulfate, lithium oxide, etc. Among them, carbon dioxide, Lithium hydroxide monohydrate is preferred in that it does not generate gases that adversely affect the environment, such as nitrogen oxides and sulfur oxides.

  From the above, in order to produce the lithium-containing composite oxide, first, a composite compound containing at least Ni, Mn, and Mg (and a composite compound containing Co and element M ′), a Li-containing compound, and The compound containing the element M ′ used according to the above is mixed at a ratio approximately corresponding to the composition of the target lithium-containing composite oxide. And the said lithium containing complex oxide can be obtained by baking the obtained raw material mixture at 600-1000 degreeC for 1 to 24 hours, for example.

  For example, the following method can be illustrated as a method for producing a lithium-containing composite oxide containing Zr or Ti.

First, an aqueous solution in which sulfates, nitrates, and the like of constituent elements such as Ni, Mn, Mg, and Co are dissolved at a predetermined ratio is added to an alkali hydroxide aqueous solution and reacted to obtain a coprecipitated hydroxide of these constituent elements. . Next, after thoroughly washing and drying, a lithium salt and a compound such as ZrO ₂ or TiO ₂ are added to the coprecipitated hydroxide and sufficiently mixed. Thereafter, the mixture is baked at a predetermined temperature and reacted to obtain a lithium-containing composite oxide.

  Instead of the alkali hydroxide aqueous solution, ammonia water having a pH adjusted to a range of about 10 to 13 with alkali hydroxide as described above may be used.

  Further, it is not a method of mixing and calcining a coprecipitated hydroxide, a lithium salt, a Zr compound or a Ti compound, but by adding a Zr compound or a Ti compound to a reaction solution in which the coprecipitated compound is precipitated, Since a composite in which the coprecipitated hydroxide is coated with a Zr compound or a Ti compound can be formed, a method of baking this together with a lithium salt to form a lithium-containing composite oxide may be used.

  Moreover, as a method of coating the surface of the lithium-containing composite oxide with the Zr compound or Ti compound, the lithium-containing composite oxide and the Zr compound or Ti compound are mixed, and the mixture is fired at a temperature of about 100 to 1000 ° C. The method of doing can be illustrated.

  When firing the raw material mixture, rather than raising the temperature to a predetermined temperature at one time, once heated to a temperature lower than the firing temperature (for example, 250 to 850 ° C.), preheating by holding at that temperature, Thereafter, it is preferable to raise the temperature to the firing temperature to advance the reaction, and it is preferable to keep the oxygen concentration in the firing environment constant.

  This is because, in the process of producing the lithium-containing composite oxide according to the present invention, since trivalent Ni is unstable, it is likely to have a non-stoichiometric composition. Therefore, a composite compound containing at least Ni, Mn, and Mg. (Also, a composite compound containing Co or element M ′), a Li-containing compound, and a lithium-containing product that is produced by causing a stepwise reaction between the compound containing element M ′ used as necessary. This is to increase the homogeneity of the composite oxide and to stably grow the generated lithium-containing composite oxide. That is, when the temperature is raised to the firing temperature at once, or when the oxygen concentration in the firing environment is lowered during firing, a composite compound containing at least Ni, Mn and Mg (further, Co or element M ′ is added). The composite compound containing), the Li-containing compound, and the compound containing the element M ′ used as needed, the reaction tends to be non-uniform, and the generated lithium-containing composite oxide tends to release Li, etc. , The uniformity of the composition tends to be impaired.

  Although there is no restriction | limiting in particular about the time of the said preheating, Usually, what is necessary is just to be about 0.5 to 30 hours.

  The atmosphere at the time of firing the raw material mixture is a gas atmosphere containing oxygen. For example, an air atmosphere, a mixed gas atmosphere of an inert gas (such as argon, helium, or nitrogen) and oxygen gas, an oxygen gas atmosphere, or the like can be used. The oxygen concentration (volume basis) in the atmosphere during firing is preferably 15% or more, and more preferably 18% or more. In addition, in order to maintain a constant oxygen concentration in the atmosphere during firing, it is preferable to perform firing of the raw material mixture in an atmosphere in which the gas containing oxygen is continuously flowed. From the viewpoint of reducing the production cost of the lithium-containing composite oxide and increasing its productivity, and hence the productivity of the electrode, it is more preferable to perform the firing of the raw material mixture in an atmospheric flow.

The flow rate of the gas containing oxygen at the time of firing the raw material mixture is preferably 2 dm ³ / min or more per 100 g of the raw material mixture. If the gas flow rate is too small, that is, if the gas flow rate is too slow, the homogeneity of the composition of the lithium-containing composite oxide may be impaired. The gas flow rate during firing of the raw material mixture is preferably 5 dm ³ / min or less per 100 g of the raw material mixture. Thereby, the gas containing oxygen can be used efficiently.

  In the step of firing the raw material mixture, the dry-mixed mixture may be used as it is, but the raw material mixture is dispersed in a solvent such as ethanol to form a slurry and mixed for about 30 to 60 minutes with a planetary ball mill or the like. It is preferable to use a dried product. By such a method, the homogeneity of the produced lithium-containing composite oxide can be further enhanced.

<Electrode mixture layer>
Next, the electrode mixture layer used for the electrode of the present invention will be described. The electrode of the present invention includes an electrode mixture layer containing the lithium-containing composite oxide according to the present invention as an active material, but the electrode mixture layer may contain other active materials. Examples of other active materials other than the lithium-containing composite oxide according to the present invention include, for example, lithium cobalt oxides such as LiCoO ₂ and LiCo _1-x Ni _x O ₂ ; LiMnO ₂ , Li ₂ MnO ₃ , LiMn ₂ O _4. Lithium manganese oxides such as LiNiO ₂ , LiNi _1-xy Co _x Al _y O ₂ and other nickel nickel oxides; and Li _4/3 Ti _5/3 O ₄ and other spinel lithium-containing composites An oxide; a lithium-containing composite oxide having an olivine structure such as LiFePO ₄ ; an oxide in which the above oxide is a basic composition and its constituent elements are substituted with various elements; and the like can be used. In particular, an active material having a layered structure such as LiCoO ₂ having a higher operating voltage than that of the lithium-containing composite oxide according to the present invention, or an active material having a spinel structure such as LiMn ₂ O ₄ is used. If the battery is configured in combination with an object, for example, repeated charging / discharging in a range where the discharge depth is about 10%, that is, a time corresponding to a condition when a device incorporating the battery is actually used. It becomes possible to improve the charge / discharge cycle characteristics in repeated use (= discharge) and charge. When other active materials other than the lithium-containing composite oxide according to the present invention are used, the ratio of the other active materials is preferably 1% or more of the whole active material by mass ratio, more preferably 5% or more. desirable. On the other hand, in order to clarify the effect of the present invention, the ratio of the other active material is preferably 30% or less, more preferably 20% or less of the entire active material in terms of mass ratio.

Among the other active materials, as the lithium cobalt oxide, in addition to LiCoO ₂ exemplified above, part of Co in LiCoO ₂ is Ti, Cr, Fe, Ni, Mn, Cu, Zn, Al, Ge, Sn. An oxide substituted with at least one element selected from the group consisting of Mg, Ga, W, Ba and Zr (except for the lithium-containing composite oxide according to the present invention) is preferable. This is because these lithium cobalt oxides have a high conductivity of 1.0 × 10 ⁻³ S · cm ⁻¹ or more and can further enhance the load characteristics of the electrode.

Among the other active materials, the spinel-structured lithium-containing composite oxide includes LiMn ₂ O ₄ and Li _4/3 Ti _5/3 O ₄ exemplified above, as well as one of Mn of LiMn ₂ O _4. An oxide in which part is substituted with at least one element selected from the group consisting of Ti, Cr, Fe, Ni, Co, Cu, Zn, Al, Ge, Sn, Mg, Ga, W, Ba, and Zr. preferable. These spinel-structured lithium-containing composite oxides are excellent in safety during overcharge because the amount of lithium that can be extracted is half that of lithium-containing oxides such as lithium cobaltate and lithium nickelate. This is because the safety of the electrochemical device can be further enhanced.

  When the lithium-containing composite oxide according to the present invention is used in combination with another active material, these may be used simply by mixing them, but these particles are used as composite particles integrated by granulation or the like. In this case, the packing density of the active material in the electrode mixture layer is improved, and the contact between the active material particles can be made more reliable. Therefore, the capacity | capacitance and load characteristic of an electrochemical element using the electrode of this invention can be improved further.

  Alternatively, the mixture layer may be formed by a process of dry-mixing the two together and further forming a paint using a biaxial kneader together with a binder or the like.

  Further, in the lithium-containing composite oxide according to the present invention, when the composite particle with the lithium cobalt oxide is used, the lithium cobalt oxide is present on the surface of the lithium-containing composite oxide, so that the composite particle is eluted. Since the Mn and Co thus deposited quickly form a film on the surface of the composite particle, the composite particle is chemically stabilized. As a result, the decomposition of the non-aqueous electrolyte in the electrochemical element due to the composite particles can be suppressed, and further elution of Mn can be suppressed, so that an electrochemical element with more excellent storability and charge / discharge cycle characteristics is configured. Will be able to.

  When the composite particles are used, it is preferable that the number average particle diameter of one of the lithium-containing composite oxide according to the present invention and the other active material is ½ or less of the other number average particle diameter. When composite particles are formed by combining particles having a large number average particle diameter (hereinafter referred to as “large particles”) and particles having a small number average particle diameter (hereinafter referred to as “small particles”). In this case, small particles can be easily dispersed and fixed around the large particles, and composite particles having a more uniform mixing ratio can be formed. Therefore, non-uniform reaction in the electrode can be suppressed, and the charge / discharge cycle characteristics and safety of the electrochemical element can be further enhanced.

  When forming composite particles using large particles and small particles as described above, the number average particle size of the large particles is preferably 10 to 30 μm, and the number average particle size of the small particles is It is preferable that it is 1-15 micrometers.

  The composite particles of the lithium-containing composite oxide and the other active material according to the present invention include, for example, the above-described lithium-containing composite oxide particles and other active material particles in a common uniaxial kneader or biaxial kneader. It is possible to obtain a composite by mixing using various kneaders such as a machine, sliding the particles together and applying a share. The kneading is preferably a continuous kneading method in which raw materials are continuously fed in consideration of the productivity of composite particles.

  During the kneading, it is preferable to further add a binder to each active material particle. Thereby, the shape of the composite particle formed can be kept strong. Further, it is more preferable to add a conductive additive and knead. Thereby, the electroconductivity between active material particles can further be improved.

  As the binder to be added at the time of producing the composite particles, any of a thermoplastic resin and a thermosetting resin can be used as long as it is chemically stable in the electrochemical element. For example, polyethylene (PE), polypropylene (PP), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyhexafluoropropylene (PHFP), styrene butadiene rubber (SBR), tetrafluoroethylene-hexafluoroethylene Polymer, tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoro Ethylene copolymer, ethylene-tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), vinylidene fluoride-pentafluoropropylene copolymer, Pyrene-tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer (ECTFE), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene copolymer A polymer; or an ethylene-acrylic acid copolymer, an ethylene-methacrylic acid copolymer, an ethylene-methyl acrylate copolymer, an ethylene-methyl methacrylate copolymer, and a Na ion crosslinked product of these copolymers. These may be used alone or in combination of two or more. Among these, PVDF, PTFE, and PHFP are preferable in consideration of stability in the electrochemical element and characteristics of the electrochemical element.

  When the composite particles are formed, the amount of the binder added is preferably as small as the composite particles can be stabilized. For example, it is preferably 0.03 to 2 parts by mass with respect to 100 parts by mass of the total active material. .

  The conductive auxiliary agent added during the production of the composite particles may be any one that is chemically stable in the electrochemical element. For example, graphite such as natural graphite and artificial graphite, acetylene black, ketjen black (trade name), carbon black such as channel black, furnace black, lamp black and thermal black; conductive fiber such as carbon fiber and metal fiber; aluminum Metallic powders such as powders; Fluorinated carbon; Zinc oxide; Conductive whiskers made of potassium titanate; Conductive metal oxides such as titanium oxide; Organic conductive materials such as polyphenylene derivatives; One species may be used alone, or two or more species may be used in combination. Among these, highly conductive graphite and carbon black excellent in liquid absorption are preferable. Moreover, the form of the conductive auxiliary agent is not limited to primary particles, and secondary aggregates and aggregated forms such as chain structures can also be used. Such an assembly is easier to handle and has better productivity.

  The amount of the conductive additive added in the case of forming the composite particles is only required to ensure good conductivity and liquid absorbency, and is, for example, 0.1 to 2 parts by mass with respect to 100 parts by mass of the total active material. It is preferable.

  The composite particles preferably have a porosity of 5 to 15%. This is because the composite particles having such a porosity have appropriate contact with the non-aqueous electrolyte (non-aqueous electrolyte solution) and penetration of the non-aqueous electrolyte into the composite particles.

  Furthermore, the shape of the composite particles is also preferably spherical or substantially spherical, similar to the lithium-containing composite oxide according to the present invention. Thereby, the density of the electrode mixture layer can be further increased.

<Method for producing electrode for electrochemical device>
Next, the manufacturing method of the electrode of this invention is demonstrated. The electrode of the present invention can be produced, for example, by forming an electrode mixture layer containing the lithium-containing composite oxide or the composite particles as an active material on one side or both sides of a current collector.

  The electrode mixture layer is prepared by, for example, preparing a paste-like or slurry-like electrode mixture-containing composition by adding the lithium-containing composite oxide or the composite particles, a binder, and a conductive additive to a solvent. And it can form by apply | coating this to the collector surface by various coating methods, drying, and also adjusting the thickness and density of an electrode mixture layer by a press process.

  Examples of the coating method for applying the electrode mixture-containing composition to the surface of the current collector include, for example, a substrate pulling method using a doctor blade; a coater method using a die coater, comma coater, knife coater, etc .; screen printing , Printing methods such as letterpress printing, and the like can be employed.

  As the binder and conductive aid that can be used for the preparation of the electrode mixture-containing composition, the same binders and various conductive aids exemplified as those that can be used for forming the composite particles described above are used. it can.

  In the electrode mixture layer, the total active material including the lithium-containing composite oxide is 80 to 99% by mass, and the binder (including those contained in the composite particles) is 0.5 to 10%. It is preferable to set it as mass% and to make a conductive support agent (including what is contained in a composite particle) into 0.5-10 mass%.

Moreover, it is preferable that the thickness of the said electrode mixture layer is 15-200 micrometers per single side | surface of a collector after press processing. Further, after pressing, the density of the electrode mixture layer is preferably 3.1 g / cm ³ or more, and more preferably 3.52 g / cm ³ or more. By using an electrode having such a high-density electrode mixture layer, higher capacity can be achieved. However, if the density of the electrode mixture layer is too large, the porosity becomes small and the permeability of the non-aqueous electrolyte may decrease, so the density of the electrode mixture layer after the press treatment is 4. It is preferably 0 g / cm ³ or less. As the press treatment, for example, roll pressing can be performed at a linear pressure of about 1 to 100 kN / cm. By such treatment, an electrode mixture layer having the above density can be obtained.

  Moreover, the density of the electrode mixture layer as used in the present specification is a value measured by the following method. First, the electrode is cut into a predetermined area, the mass thereof is measured using an electronic balance having a minimum scale of 0.1 mg, and the mass of the electrode mixture layer is calculated by subtracting the mass of the current collector. On the other hand, the total thickness of the electrode was measured at 10 points with a micrometer having a minimum scale of 1 μm, and the volume of the electrode mixture layer was calculated from the average value obtained by subtracting the thickness of the current collector from these measured values and the area. To do. Then, the density of the electrode mixture layer is calculated by dividing the mass of the electrode mixture layer by the volume.

  The material of the current collector of the electrode is not particularly limited as long as it is a chemically stable electron conductor in the constructed electrochemical device. For example, in addition to aluminum or aluminum alloy, stainless steel, nickel, titanium, carbon, conductive resin, etc., a composite material in which a carbon layer or a titanium layer is formed on the surface of aluminum, aluminum alloy, or stainless steel can be used. . Among these, aluminum or an aluminum alloy is particularly preferable. This is because they are lightweight and have high electron conductivity. As the current collector, for example, a foil, a film, a sheet, a net, a punching sheet, a lath body, a porous body, a foamed body, a fibrous body, or the like made of the above material is used. In addition, the surface of the current collector can be roughened by surface treatment. Although the thickness of a collector is not specifically limited, Usually, it is 1-500 micrometers.

  The electrode of the present invention is not limited to those manufactured by the above manufacturing method, and may be manufactured by other manufacturing methods. For example, when using the composite particles as an active material, without using the electrode mixture-containing composition, the composite particles are directly fixed on the surface of the current collector to form an electrode mixture layer. The obtained electrode may be sufficient.

  Moreover, you may form in the electrode of this invention according to a conventional method the lead body for electrically connecting with the other member in an electrochemical element as needed.

(Embodiment 2)
Next, the electrochemical device of the present invention will be described. The electrochemical element of the present invention includes the electrode for an electrochemical element according to Embodiment 1, a negative electrode, a separator, and a nonaqueous electrolyte as a positive electrode.

  Since the electrochemical device of the present invention includes the electrode for an electrochemical device of Embodiment 1 as a positive electrode, the electrochemical device having high capacity, excellent charge / discharge cycle characteristics and high safety can be obtained. it can.

  The electrochemical element of the present invention is not particularly limited, and includes lithium primary batteries, supercapacitors, and the like in addition to lithium secondary batteries using a non-aqueous electrolyte. Hereinafter, the configuration of a lithium secondary battery, which is a main application, will be described as an example.

  The negative electrode has, for example, a structure having a negative electrode mixture layer made of a negative electrode mixture containing a negative electrode active material and a binder and, if necessary, a conductive additive, on one or both sides of the current collector. Can be used.

Examples of the negative electrode active material include occlusion of Li ions such as graphite, pyrolytic carbons, cokes, glassy carbons, fired bodies of organic polymer compounds, mesocarbon microbeads (MCMB), and carbon fibers. One or a mixture of two or more releasable carbon-based materials is used. In addition, simple substances such as Si, Sn, Ge, Bi, Sb, In and alloys thereof; lithium-containing nitrides; or compounds that can be charged and discharged at a low voltage close to lithium metal such as oxides such as Li ₄ Ti ₅ O ₁₂ ; Alternatively, lithium metal or lithium / aluminum alloy can also be used as the negative electrode active material.

  The negative electrode was formed into a molded body (negative electrode mixture layer) using a negative electrode current collector as a core material and a negative electrode mixture obtained by appropriately adding a conductive additive or a binder as necessary to these negative electrode active materials. Or those obtained by laminating the above-mentioned various alloys or lithium metal foils alone or on the surface of the negative electrode current collector.

  As said binder and said conductive support agent, the thing similar to the various binders illustrated in Embodiment 1 and various conductive support agents can be used.

  The material of the negative electrode current collector is not particularly limited as long as it is an electron conductor that is chemically stable in the constructed battery. For example, in addition to copper or copper alloy, stainless steel, nickel, titanium, carbon, conductive resin, etc., a composite material in which a carbon layer or a titanium layer is formed on the surface of copper, copper alloy, or stainless steel can be used. . Among these, copper or a copper alloy is particularly preferable. This is because they are not alloyed with lithium and have high electron conductivity. As the negative electrode current collector, for example, a foil, a film, a sheet, a net, a punching sheet, a lath body, a porous body, a foamed body, a fibrous body, or the like made of the above materials can be used. In addition, the surface of the negative electrode current collector can be roughened by surface treatment. Although the thickness of the said negative electrode collector is not specifically limited, Usually, it is 1-500 micrometers.

  The negative electrode includes, for example, a negative electrode mixture-containing composition in the form of a paste or slurry in which a negative electrode mixture containing a negative electrode active material and a binder and, if necessary, a conductive additive is dispersed in a solvent. It can obtain by apply | coating to the single side | surface or both surfaces of a collector, and drying and forming a negative mix layer. The above binder may be used by dissolving in a solvent. The said negative electrode is not limited to what was obtained by the said manufacturing method, The thing manufactured by the other method may be used. The thickness of the negative electrode mixture layer is preferably 10 to 300 μm per one side of the negative electrode current collector.

  The separator is preferably a porous film composed of polyolefin such as polyethylene, polypropylene, and ethylene-propylene copolymer; polyester such as polyethylene terephthalate and copolymer polyester; The separator preferably has a property of closing the pores at 100 to 140 ° C., that is, a shutdown function. Therefore, as a separator material, a melting point, that is, a thermoplastic resin having a melting temperature of 100 to 140 ° C. measured using a differential scanning calorimeter (DSC) in accordance with the provisions of Japanese Industrial Standard (JIS) K7121. It is preferable to use a resin. For example, a single layer porous film mainly composed of polyethylene, or a laminated porous film in which 2 to 5 layers of polyethylene and polypropylene are laminated can be used as the separator. When a resin having a melting point of 100 to 140 ° C. such as polyethylene and a resin having a melting point higher than that of polyethylene such as polypropylene are mixed or laminated and used, the resin constituting the porous membrane is 30% by mass or more of polyethylene. Desirably, it is more desirable that it is 50 mass% or more.

  As such a resin porous membrane, for example, a porous membrane composed of the above-exemplified thermoplastic resin used in a conventionally known lithium secondary battery or the like, that is, solvent extraction method, dry type or An ion-permeable porous membrane produced by a wet stretching method or the like can be used.

  The average pore diameter of the separator is preferably 0.01 μm or more, more preferably 0.05 μm or more, preferably 1 μm or less, more preferably 0.5 μm or less.

The air permeability of the separator indicated by the Gurley value is preferably 10 to 500 sec. Here, the Gurley value is measured by a method according to JIS P 8117, and is indicated by the number of seconds that 100 mL of air permeates the membrane under a pressure of 0.879 g / mm ² . If the air permeability is too large, the ion permeability tends to be small, whereas if the air permeability is too small, the strength of the separator tends to be small.

  The strength of the separator is preferably 50 g or more in terms of piercing strength using a needle having a diameter of 1 mm. If the piercing strength of the separator is too small, for example, when lithium dendrite crystals are generated, there is a possibility that a short circuit may occur due to the piercing of the separator.

  Even when the lithium secondary battery according to the present invention has an internal temperature of 150 ° C. or higher, the lithium-containing composite oxide according to the present invention is excellent in thermal stability, so that its safety is maintained. Can do.

  As the non-aqueous electrolyte, a solution (non-aqueous electrolyte) in which an electrolyte salt is dissolved in a solvent can be used. Examples of the solvent include propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), γ-butyrolactone, 2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxymethane, dioxolane derivatives , Sulfolane, 3-methyl-2-oxazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, diethyl ether, 1,3-propane sultone What aprotic organic solvents, and the like, may be used these alone, or in combination of two or more of these. Also, amine imide organic solvents, sulfur-containing or fluorine-containing organic solvents, and the like can be used. Among these, a mixed solvent of EC, MEC, and DEC is preferable. In this case, it is more preferable to include DEC in an amount of 15% by volume to 80% by volume with respect to the total volume of the mixed solvent. This is because such a mixed solvent can enhance the stability of the solvent during high-voltage charging while maintaining the low temperature characteristics and charge / discharge cycle characteristics of the battery high.

As the electrolyte salt related to the non-aqueous electrolyte, lithium perchlorate; organoboron lithium salt; salt of fluorine-containing compound such as trifluoromethanesulfonate; or imide salt is preferably used. Specific examples of the electrolyte salt, for _{example, LiClO 4, LiPF 6, LiBF} 4, LiAsF 6, LiSbF 6, LiCF 3 SO 3, LiC 4 F 9 SO 3, LiCF 3 CO 2, Li 2 C 2 F ₄ (SO ₃ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiC _n F _{2n + 1} SO ₃ (2 ≦ n ≦ 5), LiN (Rf ₃ OSO ₂ ) ₂ , Rf represents a fluoroalkyl group. ], LiB (C ₂ O ₄ ) ₂ [lithium bisoxalate borate (LiBOB)], and the like. These may be used alone or in combination of two or more thereof. Among these, LiPF ₆ and LiBF ₄ are more preferable because of good charge / discharge characteristics. The concentration of the electrolyte salt in the solvent is not particularly limited, but is usually 0.5 to 1.7 mol / L.

  In addition, vinylene carbonates, 1,3-propane sultone, diphenyl disulfide, cyclohexyl benzene, phosphonoacetic acid triethyl and the like for the purpose of improving the characteristics such as safety, charge / discharge cycleability, and high temperature storage property of the non-aqueous electrolyte. Additives such as derivatives, biphenyl, fluorobenzene, and t-butylbenzene may be added as appropriate. Since the surface activity of the active material containing Mn can be stabilized, it is particularly preferable to add an additive containing sulfur element.

  The lithium secondary battery of the present embodiment includes, for example, an electrode laminate in which the electrode (positive electrode) of the present invention and the negative electrode are laminated via the separator, and an electrode winding obtained by winding the electrode in a spiral shape. A body is prepared, and such an electrode body and the non-aqueous electrolyte are enclosed in an exterior body according to a conventional method. As the form of the battery, similarly to the conventionally known lithium secondary battery, a cylindrical battery using a cylindrical (cylindrical or rectangular) outer can, or a flat (circular or rectangular in plan view) Flat type) using an outer can, or a soft package battery using a metal-deposited laminated film as an outer case. The outer can can be made of steel or aluminum.

  Hereinafter, the present invention will be described in detail based on examples. However, the following examples do not limit the present invention.

(Reference Example 1)
<Synthesis of lithium-containing composite oxide>
Aqueous ammonia whose pH was adjusted to about 12 by adding sodium hydroxide was placed in a reaction vessel, and while vigorously stirring, nickel sulfate, manganese sulfate and magnesium sulfate were each added to 3.95 mol / dm ^3. , 0.13 mol ^/ dm 3, a mixed aqueous solution containing a concentration of 0.13 mol / dm ^3, and aqueous ammonia 25% strength by weight, respectively, 23cm ³ / min at a rate of 6.6 cm ³ / min, The mixture was added dropwise using a metering pump to synthesize a coprecipitation compound of Ni, Mn, and Mg (spherical coprecipitation compound). At this time, the temperature of the reaction solution is maintained at 50 ° C., and an aqueous solution of sodium hydroxide having a concentration of 6.4 mol / dm ³ is dropped at the same time so that the pH of the reaction solution is maintained around 12. Gas was bubbled at a flow rate of 1 dm ³ / min.

The coprecipitated compound was washed with water, filtered and dried to obtain a hydroxide containing Ni, Mn and Mg in a molar ratio of 94: 3: 3. 0.196 mol of this hydroxide and 0.204 mol of LiOH.H ₂ O were dispersed in ethanol to form a slurry, and then mixed with a planetary ball mill for 40 minutes and dried at room temperature to obtain a mixture. . Next, the mixture is placed in an alumina crucible, heated to 600 ° C. in a dry air flow of 2 dm ³ / min, kept at that temperature for 2 hours for preheating, and further heated to 700 ° C. to increase oxygen The lithium-containing composite oxide was synthesized by firing for 12 hours in an atmosphere. The obtained lithium-containing composite oxide was pulverized into a powder in a mortar and then stored in a desiccator.

When the composition of the lithium-containing composite oxide powder was measured with an atomic absorption spectrometer, it was found to be a composition represented by Li _1.02 Ni _0.94 Mn _0.03 Mg _0.03 O _2. did.

  In addition, in order to analyze the state of the lithium-containing composite oxide, X-ray absorption spectroscopy (XAS) was performed at the SR Center of Ritsumeikan University using the BL4 beam port of the superconducting small radiation source “Aurora” manufactured by Sumitomo Electric Industries, Ltd. Analysis was carried out. The analysis of the obtained data was performed using analysis software “REX” manufactured by Rigaku Electric Co., Ltd. based on the literature [Journal of the Electronic Society, 146 p2799-2809 (1999)].

  First, based on the state analysis, the K absorption edge positions of Ni, Mn, and Mg of the lithium-containing composite oxide were determined.

Next, in order to determine the average valence of Ni of the lithium-containing composite oxide, NiO and LiNi _0.5 Mn _1.5 O ₄ (both containing Ni with an average valence of 2) are used as standard samples. And a standard sample of a compound containing Ni having an average valence of 3) and LiNi _0.82 Co _0.15 Al _0.03 O ₂ State analysis was performed, and a regression line representing the relationship between the Ni K absorption edge position of each standard sample and the valence of Ni was created. From the position of the K absorption edge of Ni of the lithium-containing composite oxide and the regression line, the average valence of Ni was found to be 3.02.

Further, in order to determine the average valence of Mn of the lithium-containing composite oxide, MnO _2, Li ₂ MnO ₃ and LiNi _0.5 Mn _1.5 O ₄ (all having an average valence of ₄ as standard samples) are used. Standard sample of a compound containing valence Mn), LiMn ₂ O ₄ (standard sample of a compound containing Mn having an average valence of 3.5), LiMnO ₂ and Mn ₂ O ₃ (all having an average valence) A standard sample of a compound containing trivalent Mn) and MnO (a standard sample of a compound containing Mn having an average valence of 2) are used to conduct a state analysis similar to that of a lithium-containing composite oxide. A regression line representing the relationship between the Mn K absorption edge position of the sample and the valence of Mn was prepared. From the K absorption edge position of Mn of the lithium-containing composite oxide and the regression line, the average valence of Mn was found to be 4.02.

Furthermore, in order to determine the average valence of Mg of the lithium-containing composite oxide, as standard samples, MgO and MgAl ₂ O ₄ (both standard samples of compounds containing Mg having an average valence of 2), In addition, the same state analysis as that of the lithium-containing composite oxide is performed using Mg (standard sample of Mg having an average valence of 0), and the relationship between the K absorption edge position of Mg and the valence of Mg of each standard sample is determined. A regression line was created. From the Mg K absorption edge position of the lithium-containing composite oxide and the regression line, the average valence of Mg was found to be 2.01.

The lithium-containing composite oxide powder had a BET specific surface area of 0.24 m ² / g and a tap density of 2.75 g / cm ³ . Furthermore, according to “JIS R1622 General rules for sample size measurement for fine ceramic raw material particle size distribution”, the lithium-containing composite oxide powder is pulverized until it becomes primary particles, and laser diffraction scattering type particle size distribution measurement made by Nikkiso Co., Ltd. When the particle size distribution was measured by the apparatus “Microtrac HRA”, the ratio of primary particles having a particle size of 1 μm or less to the total volume of primary particles was 10% by volume. However, in order to reduce the error, the number of times of crushing was 20 times.

Moreover, the X-ray-diffraction measurement of the said lithium containing complex oxide was performed. Specifically, X-ray diffraction is measured by CuKα rays using an Rigaku X-ray diffraction measurement device “RINT-2500V / PC”, and analysis of the obtained data is performed by Rigaku's analysis software “JADE”. Was used. Here, in the X-ray diffraction pattern, the integrated intensities of the diffraction lines at the (003) plane and the (104) plane are I ₍₀₀₃₎ and I ₍₁₀₄₎ , respectively, and I _{( 003)} and I ₍₁₀₄₎ are respectively And the ratio value I ₍₀₀₃₎ / I ₍₁₀₄₎ was obtained by calculation.

<Preparation of positive electrode>
100 parts by mass of the lithium-containing composite oxide, 20 parts by mass of an N-methyl-2-pyrrolidone (NMP) solution containing PVDF as a binder at a concentration of 10% by mass, and 1 mass of artificial graphite as a conductive assistant Part and 1 part by mass of ketjen black were kneaded using a biaxial kneader, and NMP was added to adjust the viscosity to prepare a positive electrode mixture-containing paste.

The positive electrode mixture-containing paste is applied to both sides of an aluminum foil (positive electrode current collector) having a thickness of 15 μm, and then vacuum-dried at 120 ° C. for 12 hours to form a positive electrode mixture layer on both sides of the aluminum foil. Formed. Thereafter, press treatment was performed to adjust the thickness and density of the positive electrode mixture layer, and a nickel lead body was welded to the exposed portion of the aluminum foil to produce a strip-like positive electrode having a length of 375 mm and a width of 43 mm. . The positive electrode mixture layer in the obtained positive electrode had a thickness of 55 μm per one side, and the density of the positive electrode mixture layer was 3.5 g / cm ³ .

<Production of negative electrode>
To 97.5 parts by mass of natural graphite having a number average particle size of 10 μm as a negative electrode active material, 1.5 parts by mass of styrene butadiene rubber as a binder, and 1 part by mass of carboxymethyl cellulose as a thickener, Were added and mixed to prepare a negative electrode mixture-containing paste.

  The negative electrode mixture-containing paste is applied to both sides of a copper foil (negative electrode current collector) having a thickness of 8 μm, and then vacuum-dried at 120 ° C. for 12 hours to form a negative electrode mixture layer on both sides of the copper foil. Formed. Thereafter, press treatment was performed to adjust the thickness and density of the negative electrode mixture layer, and a nickel lead body was welded to the exposed portion of the copper foil to produce a strip-shaped negative electrode having a length of 380 mm and a width of 44 mm. . The negative electrode mixture layer in the obtained negative electrode had a thickness of 65 μm per one surface.

<Preparation of non-aqueous electrolyte>
A non-aqueous electrolyte was prepared by dissolving LiPF ₆ at a concentration of 1 mol / L in a mixed solvent of EC, MEC, and DEC in a volume ratio of 2: 3: 1.

<Battery assembly>
The strip-shaped positive electrode is overlapped with the strip-shaped negative electrode through a microporous polyethylene separator (porosity: 41%) having a thickness of 16 μm, wound in a spiral shape, and then added so as to become flat. The electrode winding body was pressed into a flat winding structure, and the electrode winding body was fixed with a polypropylene insulating tape. Next, the electrode winding body is inserted into a rectangular battery case made of aluminum alloy having an outer dimension of 4.0 mm in thickness, 34 mm in width, and 50 mm in height, and the lead body is welded. The plate was welded to the open end of the battery case. Thereafter, the non-aqueous electrolyte is injected from the inlet provided in the lid plate, and the inlet is sealed after standing for 1 hour, and the structure shown in FIGS. 1A and 1B is shown in FIG. An external lithium secondary battery was obtained. The design electric capacity of the lithium secondary battery was 900 mAh.

  Here, the battery shown in FIGS. 1A, 1B, and 2 will be described. FIG. 1A is a schematic plan view of the lithium secondary battery, and FIG. 1B is a cross-sectional view of FIG. As shown in FIG. 1 (b), the positive electrode 1 and the negative electrode 2 are spirally wound via a separator 3 and then pressed so as to be flattened. The body 6 is accommodated in a rectangular battery case 4 together with a nonaqueous electrolyte. However, in FIG. 1B, in order to avoid complication, a metal foil, a non-aqueous electrolyte, and the like as a current collector used in manufacturing the positive electrode 1 and the negative electrode 2 are not illustrated.

  The battery case 4 is made of an aluminum alloy and constitutes an outer package of the battery. The battery case 4 also serves as a positive electrode terminal. And the insulator 5 which consists of a polyethylene sheet is arrange | positioned at the bottom part of the battery case 4, and from the flat electrode winding body 6 which consists of the positive electrode 1, the negative electrode 2, and the separator 3, it is in each one end of the positive electrode 1 and the negative electrode 2 The connected positive electrode lead body 7 and negative electrode lead body 8 are drawn out. A stainless steel terminal 11 is attached to a sealing lid plate 9 made of aluminum alloy for sealing the opening of the battery case 4 via a polypropylene insulating packing 10, and an insulator 12 is attached to the terminal 11. A stainless steel lead plate 13 is attached via

  And this cover plate 9 is inserted in the opening part of the battery case 4, and the opening part of the battery case 4 is sealed by welding the joint part of both, and the inside of the battery is sealed. Further, in the battery of FIGS. 1A and 1B, the lid plate 9 is provided with a non-aqueous electrolyte inlet 14, and a sealing member is inserted into the non-aqueous electrolyte inlet 14. For example, the sealing of the battery is ensured by welding and sealing by laser welding or the like. Therefore, in the batteries of FIGS. 1A, 1B, and 2, the nonaqueous electrolyte inlet 14 is actually a nonaqueous electrolyte inlet and a sealing member, but for ease of explanation. , Shown as a non-aqueous electrolyte inlet 14. Further, the lid plate 9 is provided with a cleavage vent 15 as a mechanism for discharging the internal gas to the outside when the temperature of the battery rises.

  In the battery of Reference Example 1, the battery case 4 and the lid plate 9 function as positive terminals by directly welding the positive electrode lead body 7 to the lid plate 9, and the negative electrode lead body 8 is welded to the lead plate 13, By connecting the negative electrode lead body 8 and the terminal 11 through the lead plate 13, the terminal 11 functions as a negative electrode terminal. Depending on the material of the battery case 4 and the like, the battery may be configured so that the sign is reversed.

  FIG. 2 is a schematic external view schematically showing the external appearance of the battery shown in FIG. 1 (a). FIG. 2 is shown for the purpose of showing that the battery is a square battery. In FIG. 2, the battery is schematically shown, and only specific ones of the constituent members of the battery are shown. Also, in FIG. 1B, the inner peripheral side portion of the electrode body is not cross-sectional.

(Reference Example 2)
Nickel sulfate, manganese sulfate and magnesium sulfate, ^{respectively, 3.87mol / dm 3, 0.21mol /} dm 3, except for using a mixed aqueous solution containing a concentration of 0.13 mol / dm ^3, similarly as in Reference Example 1 Thus, a coprecipitation compound was synthesized. And the hydroxide which contains Ni, Mn, and Mg by the molar ratio of 92: 5: 3 was obtained like the reference example 1 except having used the said coprecipitation compound. A lithium-containing composite oxide was synthesized in the same manner as in Reference Example 1 except that 0.196 mol of the hydroxide and 0.204 mol of LiOH.H ₂ O were used. This lithium-containing composite oxide had a BET specific surface area of 0.24 m ² / g and a tap density of 2.7 g / cm ³ . In the lithium-containing composite oxide powder, the ratio of primary particles having a particle size of 1 μm or less to the total volume of primary particles measured in the same manner as in Example 1 was 12% by volume.

And the positive electrode and the lithium secondary battery were produced like the reference example 1 except having used the said lithium containing complex oxide. The density of the positive electrode mixture layer in the positive electrode used for this lithium secondary battery was 3.45 g / cm ³ .

(Reference Example 3)
Nickel sulfate, manganese sulfate, magnesium sulfate and aluminum sulfate, ^{respectively, 3.96mol / dm 3, 0.12mol /} dm 3, 0.08mol / dm 3, a mixed aqueous solution containing a concentration of 0.04 mol / dm ³ A coprecipitated compound was synthesized in the same manner as in Reference Example 1 except that it was used. And the hydroxide which contains Ni, Mn, Mg, and Al by the molar ratio of 94: 3: 2: 1 was obtained like the reference example 1 except having used the said coprecipitation compound. A lithium-containing composite oxide was synthesized in the same manner as in Reference Example 1 except that 0.196 mol of the hydroxide and 0.204 mol of LiOH.H ₂ O were used. This lithium-containing composite oxide had a BET specific surface area of 0.22 m ² / g and a tap density of 2.82 g / cm ³ . In the lithium-containing composite oxide powder, the ratio of particles having a particle size of 1 μm or less to the total volume of primary particles measured in the same manner as in Reference Example 1 was 8% by volume.

And the positive electrode and the lithium secondary battery were produced like the reference example 1 except having used the said lithium containing complex oxide. The density of the positive electrode mixture layer in the positive electrode used for this lithium secondary battery was 3.50 g / cm ³ .

(Reference Example 4)
Nickel sulfate, cobalt sulfate, manganese sulfate and magnesium sulfate, ^{respectively, 3.87mol / dm 3, 0.25mol /} dm 3, 0.04mol / dm 3, a mixed aqueous solution containing a concentration of 0.04 mol / dm ³ A coprecipitated compound was synthesized in the same manner as in Reference Example 1 except that it was used. And the hydroxide which contains Ni, Co, Mn, and Mg by the molar ratio of 92: 6: 1: 1 was obtained like the reference example 1 except having used the said coprecipitation compound. A lithium-containing composite oxide was synthesized in the same manner as in Reference Example 1 except that 0.196 mol of the hydroxide and 0.204 mol of LiOH.H ₂ O were used. This lithium-containing composite oxide had a BET specific surface area of 0.18 m ² / g and a tap density of 2.84 g / cm ³ . In the lithium-containing composite oxide powder, the ratio of particles having a particle size of 1 μm or less to the total volume of primary particles measured in the same manner as in Reference Example 1 was 7% by volume.

And the positive electrode and the lithium secondary battery were produced like the reference example 1 except having used the said lithium containing complex oxide. The density of the positive electrode mixture layer in the positive electrode used for this lithium secondary battery was 3.55 g / cm ³ .

(Reference Example 5)
Ni, Co, Mn, and Mg were mixed at a molar ratio of 90: 5: 3: 2 in the same manner as in Reference Example 4 except that the concentration of the raw material compound in the mixed aqueous solution used for the synthesis of the coprecipitation compound was changed. A lithium-containing composite oxide was synthesized in the same manner as in Reference Example 4 except that the contained hydroxide was synthesized and this hydroxide was used. This lithium-containing composite oxide had a BET specific surface area of 0.20 m ² / g and a tap density of 2.78 g / cm ³ . In the lithium-containing composite oxide powder, the ratio of primary particles having a particle size of 1 μm or less to the total volume of primary particles, which was measured in the same manner as in Reference Example 1, was 8% by volume.

And the positive electrode and the lithium secondary battery were produced like the reference example 1 except having used the said lithium containing complex oxide. The density of the positive electrode mixture layer in the positive electrode used for this lithium secondary battery was 3.54 g / cm ³ .

(Reference Example 6)
Nickel sulfate, manganese sulfate and magnesium sulfate, ^{respectively, 3.87mol / dm 3, 0.21mol /} dm 3, except for using a mixed aqueous solution containing a concentration of 0.13 mol / dm ^3, similarly as in Reference Example 1 Thus, a coprecipitation compound was synthesized. And the hydroxide which contains Ni, Mn, and Mg by the molar ratio of 92: 5: 3 was obtained like the reference example 1 except having used the said coprecipitation compound. A lithium-containing composite oxide was synthesized in the same manner as in Reference Example 1 except that 0.196 mol of this hydroxide and 0.190 mol of LiOH.H ₂ O were used. This lithium-containing composite oxide had a BET specific surface area of 0.22 m ² / g and a tap density of 2.5 g / cm ³ . In the lithium-containing composite oxide powder, the ratio of primary particles having a particle size of 1 μm or less to the total volume of primary particles measured in the same manner as in Reference Example 1 was 12% by volume. A positive electrode and a lithium secondary battery were produced in the same manner as in Reference Example 1 except that the lithium-containing composite oxide was used.

(Reference Example 7)
Ni, Co, Mn, and Mg were mixed at a molar ratio of 90: 5: 3: 2 in the same manner as in Reference Example 4 except that the concentration of the raw material compound in the mixed aqueous solution used for the synthesis of the coprecipitation compound was changed. A lithium-containing composite oxide was synthesized in the same manner as in Reference Example 6 except that the contained hydroxide was synthesized and this hydroxide was used. This lithium-containing composite oxide had a BET specific surface area of 0.20 m ² / g and a tap density of 2.75 g / cm ³ . In the lithium-containing composite oxide powder, the ratio of primary particles having a particle size of 1 μm or less to the total volume of primary particles, which was measured in the same manner as in Reference Example 1, was 8% by volume. A positive electrode and a lithium secondary battery were produced in the same manner as in Reference Example 1 except that the lithium-containing composite oxide was used.

(Reference Example 8)
Ni, Co, Mn, and Mg were mixed at a molar ratio of 93: 3: 2: 2 in the same manner as in Reference Example 4 except that the concentration of the raw material compound in the mixed aqueous solution used for the synthesis of the coprecipitation compound was changed. A lithium-containing composite oxide was synthesized in the same manner as in Reference Example 4 except that the contained hydroxide was synthesized and this hydroxide was used.

This lithium-containing composite oxide had a BET specific surface area of 0.19 m ² / g and a tap density of 2.80 g / cm ³ . In the lithium-containing composite oxide powder, the ratio of primary particles having a particle size of 1 μm or less to the total volume of primary particles, which was measured in the same manner as in Reference Example 1, was 8% by volume.

And the positive electrode and the lithium secondary battery were produced like the reference example 1 except having used the said lithium containing complex oxide. The density of the positive electrode mixture layer in the positive electrode used for this lithium secondary battery was 3.50 g / cm ³ .

Example 1
Ni and Co, Mn, and Mg were synthesized in the same manner as in Reference Example 8 93: 3: 2: hydroxides containing 2 molar ratio: and 0.190 mol, _Ga 2 _{O 3} powder: 0.003 mol and Then, 0.204 mol of LiOH.H ₂ O was dry-mixed, and then a lithium-containing composite oxide in which the proportion of Ga in the element group M was 3 mol% was synthesized in the same manner as in Reference Example 8.

This lithium-containing composite oxide had a BET specific surface area of 0.20 m ² / g and a tap density of 2.83 g / cm ³ . In the lithium-containing composite oxide powder, the ratio of primary particles having a particle size of 1 μm or less to the total volume of primary particles, which was measured in the same manner as in Reference Example 1, was 8% by volume.

And the positive electrode and the lithium secondary battery were produced like the reference example 1 except having used the said lithium containing complex oxide. The density of the positive electrode mixture layer in the positive electrode used for this lithium secondary battery was 3.52 g / cm ³ .

(Example 2)
A lithium-containing composite oxide in which the proportion of V in the element group M was 3 mol% was synthesized in the same manner as in Example 1 except that V ₂ O ₅ powder was used instead of Ga ₂ O ₃ powder.

This lithium-containing composite oxide had a BET specific surface area of 0.18 m ² / g and a tap density of 2.85 g / cm ³ . In the lithium-containing composite oxide powder, the ratio of primary particles having a particle size of 1 μm or less to the total volume of primary particles, which was measured in the same manner as in Reference Example 1, was 8% by volume.

And the positive electrode and the lithium secondary battery were produced like the reference example 1 except having used the said lithium containing complex oxide. The density of the positive electrode mixture layer in the positive electrode used for this lithium secondary battery was 3.54 g / cm ³ .

(Example 3)
A lithium-containing composite oxide in which the ratio of W in the element group M was 3 mol% was synthesized in the same manner as in Example 1 except that 0.006 mol of WO ₃ powder was mixed instead of Ga ₂ O ₃ powder.

This lithium-containing composite oxide had a BET specific surface area of 0.16 m ² / g and a tap density of 2.86 g / cm ³ . In the lithium-containing composite oxide powder, the ratio of primary particles having a particle size of 1 μm or less to the total volume of primary particles, which was measured in the same manner as in Reference Example 1, was 8% by volume.

And the positive electrode and the lithium secondary battery were produced like the reference example 1 except having used the said lithium containing complex oxide. The density of the positive electrode mixture layer in the positive electrode used for this lithium secondary battery was 3.55 g / cm ³ .

Example 4
A lithium-containing composite oxide in which the percentage of Mo in the element group M was 3 mol% was synthesized in the same manner as in Example 1 except that 0.006 mol of MoO ₃ powder was mixed instead of Ga ₂ O ₃ powder.

This lithium-containing composite oxide had a BET specific surface area of 0.16 m ² / g and a tap density of 2.86 g / cm ³ . In the lithium-containing composite oxide powder, the ratio of primary particles having a particle size of 1 μm or less to the total volume of primary particles, which was measured in the same manner as in Reference Example 1, was 8% by volume.

And the positive electrode and the lithium secondary battery were produced like the reference example 1 except having used the said lithium containing complex oxide. The density of the positive electrode mixture layer in the positive electrode used for this lithium secondary battery was 3.55 g / cm ³ .

(Example 5)
A lithium-containing composite oxide in which the proportion of Nb in the element group M was 3 mol% was synthesized in the same manner as in Example 1 except that Nb ₂ O ₅ powder was used instead of Ga ₂ O ₃ powder.

This lithium-containing composite oxide had a BET specific surface area of 0.20 m ² / g and a tap density of 2.89 g / cm ³ . In the lithium-containing composite oxide powder, the ratio of primary particles having a particle size of 1 μm or less to the total volume of primary particles, which was measured in the same manner as in Reference Example 1, was 8% by volume.

And the positive electrode and the lithium secondary battery were produced like the reference example 1 except having used the said lithium containing complex oxide. The density of the positive electrode mixture layer in the positive electrode used for this lithium secondary battery was 3.52 g / cm ³ .

(Example 6)
90 parts by mass of lithium-containing composite oxide (number average particle diameter: 8 μm) synthesized in Example 1 and Li _1.02 Mn _1.95 Al _0.02 Mg _0.02 Ti _0.01 O ₄ (number average particles) (Diameter: 5 μm) After 10 parts by mass of dry mixing, 10 parts by mass of NMP solution containing PVDF as a binder at a concentration of 10% by mass was added and mixed to obtain composite particles.

  A positive electrode and a lithium secondary battery were produced in the same manner as in Example 1 except that this composite particle was used in place of the lithium-containing composite oxide.

(Example 7)
Instead of Li _1.02 Mn _1.95 Al _0.02 Mg _0.02 Ti _0.01 O ₄ , LiCo _0.975 Al _0.01 Mg _0.01 Ti _0.005 O ₂ (number average particle diameter: Composite particles were prepared in the same manner as in Example 6 except that 6 μm) was used, and a positive electrode and a lithium secondary battery were produced in the same manner as in Example 6 except that these composite particles were used.

(Example 8)
Instead of Li _1.02 Mn _1.95 Al _0.02 Mg _0.02 Ti _0.01 O ₄ , LiMn _0.315 Co _0.33 Ni _0.33 Al _0.01 Mg _0.01 Ti _0.005 A composite particle was prepared in the same manner as in Example 6 except that O ₂ (number average particle size: 6 μm) was used, and the positive electrode and lithium secondary were prepared in the same manner as in Example 6 except that this composite particle was used. A battery was produced.

(Comparative Example 1)
A coprecipitated compound was synthesized in the same manner as in Reference Example 1 except that a mixed aqueous solution containing nickel sulfate and cobalt sulfate at concentrations of 3.79 mol / dm ³ and 0.42 mol / dm ³ respectively was used. A hydroxide containing Ni and Co at a molar ratio of 90:10 was obtained in the same manner as in Reference Example 1 except that the coprecipitation compound was used. A lithium-containing composite oxide was synthesized in the same manner as in Reference Example 1 except that 0.196 mol of the hydroxide and 0.204 mol of LiOH.H ₂ O were used. Further, a positive electrode and a lithium secondary battery were produced in the same manner as in Reference Example 1 except that this lithium-containing composite oxide was used.

(Comparative Example 2)
Nickel sulfate, cobalt sulfate and magnesium sulfate, ^{respectively, 3.79mol / dm 3, 0.38mol /} dm 3, except for using a mixed aqueous solution containing a concentration of 0.04 mol / dm ^3, similarly as in Reference Example 1 Thus, a coprecipitation compound was synthesized. And the hydroxide which contains Ni, Co, and Mg by the molar ratio of 90: 9: 1 was obtained like the reference example 1 except having used the said coprecipitation compound. A lithium-containing composite oxide was synthesized in the same manner as in Reference Example 1 except that 0.196 mol of the hydroxide and 0.204 mol of LiOH.H ₂ O were used. Further, a positive electrode and a lithium secondary battery were produced in the same manner as in Reference Example 1 except that this lithium-containing composite oxide was used.

(Comparative Example 3)
Nickel sulfate, cobalt sulfate and a manganese sulfate, ^{respectively, 3.79mol / dm 3, 0.21mol /} dm 3, except for using a mixed aqueous solution containing a concentration of 0.21 mol / dm ^3, similarly as in Reference Example 1 Thus, a coprecipitation compound was synthesized. Then, a hydroxide containing Ni, Co, and Mn at a molar ratio of 90: 5: 5 was synthesized in the same manner as in Reference Example 1 except that the coprecipitation compound was used. A lithium-containing composite oxide was synthesized in the same manner as in Reference Example 1 except that 196 mol and 0.204 mol of LiOH.H ₂ O were used. Further, a positive electrode and a lithium secondary battery were produced in the same manner as in Reference Example 1 except that this lithium-containing composite oxide was used.

(Comparative Example 4)
Nickel sulfate, cobalt sulfate and aluminum sulfate, ^{respectively, 3.79mol / dm 3, 0.21mol /} dm 3, except for using a mixed aqueous solution containing a concentration of 0.21 mol / dm ^3, similarly as in Reference Example 1 Thus, a coprecipitation compound was synthesized. And the hydroxide which contains Ni, Co, and Al by the molar ratio of 90: 5: 5 was obtained like the reference example 1 except having used the said coprecipitation compound. A lithium-containing composite oxide was synthesized in the same manner as in Reference Example 1 except that 0.196 mol of the hydroxide and 0.204 mol of LiOH.H ₂ O were used. Further, a positive electrode and a lithium secondary battery were produced in the same manner as in Reference Example 1 except that this lithium-containing composite oxide was used.

(Comparative Example 5)
A positive electrode and a lithium secondary battery were produced in the same manner as in Reference Example 1 except that commercially available Li _1.02 Ni _0.80 Co _0.15 Al _0.05 O ₂ was used as the lithium-containing composite oxide.

(Comparative Example 6)
Hydroxylation containing Ni, Co, and Mn in a molar ratio of 60:20:20 in the same manner as in Comparative Example 3 except that the concentration of the raw material compound in the mixed aqueous solution used for the synthesis of the coprecipitation compound was changed. A lithium-containing composite oxide was synthesized in the same manner as in Comparative Example 3 except that this hydroxide was used, and the same procedure as in Reference Example 1 was conducted except that this lithium-containing composite oxide was used. A positive electrode and a lithium secondary battery were produced.

(Comparative Example 7)
Hydroxylation containing Ni, Mn and Mg in a molar ratio of 70:20:10 in the same manner as in Reference Example 1 except that the concentration of the raw material compound in the mixed aqueous solution used for the synthesis of the coprecipitation compound was changed. A lithium-containing composite oxide was synthesized in the same manner as in Reference Example 1 except that this hydroxide was used, and the same procedure as in Reference Example 1 was performed except that this lithium-containing composite oxide was used. A positive electrode and a lithium secondary battery were produced.

(Comparative Example 8)
Hydroxylation containing Ni, Mn and Mg in a molar ratio of 94: 3: 3 in the same manner as in Reference Example 1 except that the concentration of the raw material compound in the mixed aqueous solution used for the synthesis of the coprecipitation compound was changed. After synthesizing this product, 0.196 mol of this hydroxide and 0.204 mol of LiOH.H ₂ O were dispersed in ethanol to form a slurry, and then mixed for 40 minutes with a planetary ball mill and dried at room temperature. To obtain a mixture. Next, the mixture is placed in an alumina crucible, heated to 600 ° C. in a dry air flow of 2 dm ³ / min, held at that temperature for 2 hours for preheating, and further heated to 1000 ° C. to the atmosphere. The lithium-containing composite oxide was synthesized by firing in an atmosphere for 12 hours. And the positive electrode and the lithium secondary battery were produced like the reference example 1 except having used this lithium containing complex oxide.

(Comparative Example 9)
Ni, Co, Mn, and Mg were mixed at a molar ratio of 92: 6: 1: 1 in the same manner as in Reference Example 4, except that the concentration of the raw material compound in the mixed aqueous solution used for the synthesis of the coprecipitation compound was changed. After synthesizing the contained hydroxide, 0.196 mol of this hydroxide and 0.204 mol of LiOH.H ₂ O were dispersed in ethanol to form a slurry, and then mixed for 40 minutes with a planetary ball mill, The mixture was dried at room temperature. Next, the mixture is placed in an alumina crucible, heated to 600 ° C. in a dry air flow of 2 dm ³ / min, held at that temperature for 2 hours for preheating, and further heated to 1000 ° C. to the atmosphere. The lithium-containing composite oxide was synthesized by firing in an atmosphere for 12 hours. And the positive electrode and the lithium secondary battery were produced like the reference example 1 except having used this lithium containing complex oxide.

(Comparative Example 10)
A lithium-containing composite oxide was used in the same manner as in Comparative Example 1 except that 0.196 mol of a hydroxide containing Ni and Co at a molar ratio of 90:10 and 0.190 mol of LiOH.H ₂ O were used. Was synthesized. Furthermore, a positive electrode and a lithium secondary battery were produced in the same manner as in Comparative Example 1 except that this lithium-containing composite oxide was used.

(Comparative Example 11)
Lithium was obtained in the same manner as in Comparative Example 3 except that 0.196 mol of a hydroxide containing Ni, Co, and Mn at a molar ratio of 90: 5: 5 and 0.190 mol of LiOH.H ₂ O were used. Containing composite oxide was synthesized. Furthermore, a positive electrode and a lithium secondary battery were produced in the same manner as in Comparative Example 3 except that this lithium-containing composite oxide was used.

The lithium-containing composite oxides used for the positive electrodes of Examples 1 to 5, Reference Examples 2 to 8 and Comparative Examples 1 to 11 were also the same as in Reference Example 1 and included Ni, Co, Mn and Mg as constituent elements. The average valence and the integrated intensity ratio [I ₍₀₀₃₎ / I ₍₁₀₄₎ ] in X-ray diffraction were measured.

Tables 1 and 2 show the compositions of the lithium-containing composite oxides used in the positive electrodes of Examples 1 to 5, Reference Examples 1 to 8 and Comparative Examples 1 to 11, and Tables 3 and 4 show Example 1. -5, the average valences of Ni, Co, Mn and Mg, which are constituent elements of the lithium-containing composite oxide used in the positive electrodes of Reference Examples 1 to 8 and Comparative Examples 1 to 11, and the integrated intensity ratio in X-ray diffraction [I ₍₀₀₃₎ / I ₍₁₀₄₎ ] are shown respectively.

  Furthermore, the following evaluations were performed on the lithium secondary batteries of Examples 1 to 8, Reference Examples 1 to 8, and Comparative Examples 1 to 11. The results are shown in Table 5.

<Standard capacity>
After each battery of Examples 1-8, Reference Examples 1-8 and Comparative Examples 1-11 was stored at 60 ° C. for 7 hours, it was charged at 20 ° C. with a current value of 200 mA for 5 hours, and with a current value of 200 mA. The charge / discharge cycle of discharging until the battery voltage dropped to 2.5V was repeated until the discharge capacity became constant. Next, constant current-constant voltage charging (constant current: 500 mA, constant voltage: 4.2 V, total charging time: 3 hours) is performed, and after discharging for 1 hour, discharging is performed until the battery voltage reaches 2.5 V at a current value of 200 mA. The standard capacity was determined. The standard capacity was measured for 100 batteries for each battery, and the average value was used as the standard capacity for each example and comparative example.

  Further, the positive electrode discharge capacity was calculated by dividing the standard capacity by the mass of the lithium-containing composite oxide contained in the positive electrode.

<Charge / discharge cycle characteristics>
The batteries of Examples 1 to 8, Reference Examples 1 to 8 and Comparative Examples 1 to 11 were charged at a constant current-constant voltage under the same conditions as the standard capacity measurement, and then the battery voltage was at a current value of 200 mA after 1 minute rest. The charge / discharge cycle of discharging until 2.5 V was repeated, the number of cycles until the discharge capacity decreased to 80% of the discharge capacity of the first cycle was determined, and the charge cycle characteristics of each battery were evaluated. The number of cycles in charge / discharge cycle characteristics was measured for 10 batteries for each battery, and the average value was taken as the number of cycles for each of the Examples, Reference Examples, and Comparative Examples.

<Evaluation of safety>
The batteries of Examples 1 to 8, Reference Examples 1 to 8 and Comparative Examples 1 to 11 were subjected to constant current-constant voltage charging (constant current: 600 mA, constant voltage: 4.25 V, total charging time: 3 hours). Then, after putting it in a thermostat, the temperature was raised from 30 ° C. to 170 ° C. at a rate of 5 ° C. per minute, and then allowed to stand at 170 ° C. for 3 hours to measure the surface temperature of the battery. At this time, the battery having a maximum temperature reached 180 ° C. or lower was evaluated as A, and the battery exceeding 180 ° C. was evaluated as B.

  Moreover, the following evaluation was performed about the lithium secondary battery of Examples 1-5 and Reference Examples 1-8. The results are shown in Table 6.

<Change rate of interlayer distance in c-axis direction of positive electrode active material in charge / discharge>
For the batteries of each of the examples, reference examples and comparative examples, the battery in a state discharged to 2.5 V and a state charged to 4.2 V in the measurement conditions of the standard capacity was decomposed in an argon gas atmosphere, and the positive electrode was The sample was taken out and subjected to X-ray diffraction measurement using Cu—Kα rays in an argon gas atmosphere without being exposed to the atmosphere. The obtained diffraction pattern was assigned to the space group R3-m, and the lattice constants of the a axis and the c axis were obtained from this diffraction pattern. The value obtained by dividing the difference between the “c-axis lattice constant in the charged state” and the “c-axis lattice constant in the discharged state” by the “c-axis lattice constant in the discharged state” is the positive electrode in charging and discharging. The change rate of the interlayer distance in the c-axis direction of the active material was used. Also, the value of the lattice constant ratio c / a was determined from the obtained lattice constants of the a-axis and c-axis.

  As is clear from Table 5, the composition and the average valence of Ni, Mn, and Mg (and the average valence of Co) contain a lithium-containing composite oxide, and have a large capacity and excellent thermal stability. In the lithium secondary batteries of Examples 1 to 8 and Reference Examples 1 to 8 having the positive electrode, the interlayer distance in the c-axis direction is extended, and the ratio c / a of the lattice constant of the a-axis to the c-axis is 4 .92 or more, the standard capacity is large, the safety is excellent, and the charge / discharge cycle characteristics are also good.

  In particular, in the batteries of Examples 1 to 8, by containing Nb, Mo, Ga, W, or V, the change rate of the interlayer distance in the c-axis direction could be suppressed to 1.5% or less. The charge / discharge cycle characteristics were further improved as compared with the batteries of Examples 1 to 8.

  In Reference Example 6 and Reference Example 7 in which x in the general composition formula (1) is less than 0 and the amount ratio of Li in the lithium-containing composite oxide is less than the stoichiometric ratio, As compared with the case of using 1 to 5 lithium-containing composite oxides, gelation of the positive electrode mixture-containing paste could be suppressed, and the paint stability could be improved. Further, since a stable crystal structure could be maintained even when x <0, in Reference Example 6 and Reference Example 7, a lithium secondary battery was configured using a lithium-containing composite oxide where x ≧ 0. Excellent characteristics equivalent to those of Reference Examples 1 to 5 were obtained.

  On the other hand, the lithium secondary batteries of Comparative Examples 1 to 7, Comparative Example 10 and Comparative Example 11 having positive electrodes containing a lithium-containing composite oxide whose composition does not satisfy the general formula (1) are charge / discharge cycles. Low characteristics, poor safety, or small standard capacity. In addition, the lithium secondary batteries of Comparative Example 8 and Comparative Example 9 provided with positive electrodes containing lithium-containing composite oxides whose average valences of Ni and Mn are not appropriate have reversibility of the crystal structure of the lithium-containing composite oxides. Since it is low, the standard capacity is small and the charge / discharge cycle characteristics are low.

  Furthermore, the following evaluation was performed about the lithium secondary battery of Example 1 and Examples 6-8. The results are shown in Table 7.

<DOD 10% cycle characteristics>
About each battery of Example 1 and Examples 6-8, after carrying out constant current-constant voltage charge on the same conditions as the time of standard capacity | capacitance measurement, the charging / discharging cycle which discharges for 6 minutes with the electric current value of 1000 mA after 1 minute rest was repeated. . That is, the battery is repeatedly charged and discharged under a discharge condition (discharge amount: 100 mAh) at which the depth of discharge (DOD: Depth of Discharge) is about 10% until the internal resistance of the battery rises to 1.5 times the initial value. The number of cycles was measured. In each example, 10 batteries were tested, and the average value was set to the number of cycles shown in Table 7. The DOD 10% cycle characteristics of each battery were evaluated based on this value.

  From Table 7, in addition to the lithium-containing composite oxide according to the present invention, the batteries of Examples 6 to 8 provided with positive electrodes mixed with other active materials having an operating voltage higher than that of the lithium-containing composite oxide are as follows. It can be seen that excellent cycle characteristics are exhibited in charge and discharge in a shallow region.

  The lithium-containing composite oxide according to the present invention is less stable in the crystal structure in the discharge region where the DOD is up to about 10% than in the case where the discharge depth is deeper than that. When discharging is repeated, the excellent characteristics are not easily exhibited. On the other hand, when an active material having a high operating voltage is used in combination, the active material having a high operating voltage mainly contributes to discharge in the discharge region where the DOD is up to about 10%. Therefore, the above-described crystal structure in the lithium-containing composite oxide according to the present invention. It is considered that the polarization of the electrode due to the instability of the electrode can be reduced.

  The present invention can be implemented in other forms than the above without departing from the spirit of the present invention. The embodiments disclosed in the present application are merely examples, and the present invention is not limited thereto. The scope of the present invention is construed in preference to the description of the appended claims rather than the description of the above specification, and all modifications within the scope equivalent to the claims are construed in the scope of the claims. It is included.

  ADVANTAGE OF THE INVENTION According to this invention, the electrode for electrochemical elements with high capacity | capacitance and high stability can be provided, and the electrochemical element provided with the electrode for electrochemical elements is high capacity | capacitance, and was excellent in charging / discharging cycling characteristics and safety | security. Can provide. The electrochemical device of the present invention is used for power supplies of various electronic devices such as portable electronic devices such as mobile phones and notebook personal computers, as well as electric tools, automobiles, bicycles, and power storages where safety is important. It can also be applied to other uses.

1 Positive electrode 2 Negative electrode 3 Separator

Claims (10)

The following general composition formula (1)
Li _{1 + x} MO ₂ (1)
An electrode for an electrochemical device comprising an electrode mixture layer containing a lithium-containing composite oxide represented by an active material,
In the general composition formula (1),
−0.3 ≦ x ≦ 0.3, and M is four or more elements including Ni, Mn and Mg and at least one element selected from Nb, Mo, Ga, W and V Represents an element group,
When the ratios of Ni, Mn, and Mg to the total element amount of the element group M are a, b, and c in mol% units, respectively, 70 ≦ a ≦ 97, 0.5 <b <30, 0.5 < c <30, −10 <b−c <10 and −8 ≦ (b−c) / c ≦ 8,
The average valence of Ni is 3.0 , the average valence of Mn is 4.0, and the average valence of Mg is 2.0 .
When the integrated intensities of diffraction lines on the (003) plane and (104) plane in the X-ray diffraction measurement of the lithium-containing composite oxide are I ₍₀₀₃₎ and I ₍₁₀₄₎ , respectively , the ratio value I _{( 003)} An electrode for an electrochemical element, wherein / I ₍₁₀₄₎ is 1.2 or more. In the general formula (1), an electrode for an electrochemical element according to claim 1 which is x <0. In the general composition formula (1), the element group M further includes Co,
Wherein when a d in mol% units the ratio of Co to the total amount of elements element group M, 0 <d <30 and an electrode for an electrochemical element according to any one of claims 1 to 2.   The electrode for electrochemical devices according to claim 3, wherein the average valence of Co is 3.0. The lithium-containing composite oxide particles are mainly composed of secondary particles formed by aggregation of primary particles,
The electrode for an electrochemical element according to any one of claims 1 to 4 , wherein a volume ratio of primary particles having a particle diameter of 1 µm or less with respect to a total volume of the primary particles is 30 vol% or less. The BET specific surface area of the lithium-containing composite oxide, an electrode for an electrochemical element according to any one of claims 1 to 5, or less 0.3 m ² / g. The tap density of the lithium-containing composite oxide, 2.4 g / cm ³ or more at which an electrode for an electrochemical element according to any one of claims 1-6. The electrode density of the mixture layer, an electrode for an electrochemical element according to any one of claims 1 to 7 in 3.1 g / cm ³ or more. The electricity according to any one of claims 1 to 8 , wherein a value c / a of a lattice constant of an a-axis to a c-axis of a crystal lattice is 4.92 or more in X-ray diffraction measurement of the lithium-containing composite oxide. Electrode for chemical elements. An electrochemical element comprising a positive electrode, a negative electrode, and a nonaqueous electrolyte, wherein the positive electrode is an electrode for an electrochemical element according to any one of claims 1 to 9 .

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