JP2003092108A - Positive electrode material for lithium secondary battery, positive electrode for lithium secondary battery, and lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the output characteristics at low temperature of a layered lithium nickel manganese composite oxide. SOLUTION: A mixture of a layered lithium nickel manganese composite oxide represented by general formula (I) LiXNiYMnZQ(1- Y- Z) O2 , (in the formula, X is 0<X<=1.2; Y is 0.7<=Y/(1-Y)<=9, and 0<=(1-Y-Z)<=0.5; and Q is at least one selected from the group comprising Al, Co, and Fe.) and a spinel type nickel manganese composite oxide represented by general formula (II) LiX2 Mn(2- Y2) RY2 O4 , (in the formula, X2 is 0<X2<=1.2; Y is 0<=Y<=0.5; R is at least one selected from the group comprising Al, Fe, Ga, Bi, Sn, V, Cr, Co, Ni, Cu, Zn, Mg, Ti, Ge, Nb, Ta, Zr, and Li.) is used in the positive electrode material of the lithium secondary battery.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a composite oxide containing lithium, which is suitable as a positive electrode active material (positive electrode material) of a lithium secondary battery, a positive electrode using the same, and a lithium secondary battery.

[0002]

2. Description of the Related Art Lithium transition metal composite oxides are regarded as promising as a positive electrode active material for providing a practically usable lithium secondary battery. Among these compounds, it is known that high performance battery characteristics can be obtained by using cobalt, nickel and manganese as transition metals, and using lithium cobalt oxide, lithium nickel oxide and lithium manganese oxide as the positive electrode active material. ing. Furthermore, in order to stabilize and increase the capacity of lithium transition metal composite oxides, improve safety, and improve battery characteristics at high temperatures, lithium transition metal composite oxides in which some of the transition metal sites are replaced with other metal elements are used. It is also known to use things. Spinel type lithium manganese oxide LiM as an example of lithium transition metal composite oxide
In the case of n ₂ O ₄ , the Mn valence is formally 3.5 and the valence of 3 and the valence of 4 are mixed together.
By substituting the Mn site with another transition metal having a valence smaller than that of the valence, the Mn valence having Yarn-Teller strain is reduced, the crystal structure is stabilized, and finally the battery characteristics are improved.

When a rare and expensive element such as cobalt is used, it is possible to introduce a substitution element in order to suppress the price of the lithium transition metal composite oxide as a product. For example, LiCo _1-x Ni _x O ₂ (0 <x <1)
Such a lithium-transition metal composite oxide is considered, and studies have been conducted to increase x in order to reduce the ratio of expensive Co and further improve the performance in that direction.

Similarly, when Ni and Mn are compared,
Since Ni is more expensive, LiNi _1-x Mn _x O ₂ (0
Lithium transition metal composite oxides such as <x <1) are also considered. The lithium nickel manganese composite oxide containing such nickel and manganese is an extremely promising material because it has a noteworthy point in terms of battery performance.
However, Solid State Ionics
311-318 (1992) and J. Mater.
Chem. 1149-1155 (1996),
J. Power Sources 629-633
(1997), J. Power Sources
46-53 (1998), the range that can be synthesized as the target product is 0 ≦ x ≦ 0.5, and if x is larger than that, a single phase cannot be obtained.

On the other hand, the 41st Battery Symposium 2D20 (20
00), Ni: Mn = 1: 1 corresponding to x = 0.5.
It has been reported that a highly crystalline single phase having a layered structure of was synthesized by the coprecipitation method. According to it, in this lithium transition metal composite oxide, nickel and manganese are uniformly present in the single-phase crystal, and in order to make nickel and manganese evenly present, the raw material nickel compound and manganese compound are used at the atomic level. Therefore, the coprecipitation method is preferred.

[0006]

However, according to the studies made by the present inventors, the layered lithium nickel manganese composite oxide as described above is inferior in output characteristics at low temperature as an active material of a secondary battery. found. That is, in the layered lithium nickel manganese composite oxide,
The diffusion rate of lithium ions in the crystal is smaller than that of lithium cobalt composite oxide or lithium nickel composite oxide, especially at low temperatures, and dedoping / doping of lithium ion to the active material follows charge / discharge at a high rate. Therefore, when it is used as an active material of a secondary battery, the output characteristics at low temperatures are inferior.

[0007]

Means for Solving the Problems The inventors of the present invention have made earnest studies on a method for improving the output characteristics of the above layered lithium nickel manganese composite oxide at low temperatures, and as a result, in addition to the layered lithium nickel manganese composite oxide, spinel type The inventors have found that the combined use of a lithium-manganese composite oxide significantly improves the output at low temperatures, and completed the present invention.

That is, the gist of the present invention is a positive electrode material for a lithium secondary battery containing a layered lithium nickel manganese composite oxide, which further comprises a spinel type lithium manganese composite oxide. A positive electrode material, a positive electrode for a lithium secondary battery using the same, and a lithium secondary battery.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The layered lithium nickel manganese composite oxide used in the present invention has a layered crystal structure,
It is an oxide containing lithium, nickel and manganese.

Further, the lithium nickel manganese composite oxide used in the present invention has a stable crystal structure and a high capacity,
It is also possible to replace a part of nickel and manganese sites with another metal element for improving safety and improving battery characteristics at high temperature. Various elements can be used as the substituting element, and metal elements such as aluminum, cobalt, and iron are preferable. Among these, aluminum and cobalt are more preferable, and cobalt is the most preferable. Aluminum and cobalt have an advantage that they can be easily solid-dissolved in a layered lithium nickel manganese composite oxide to obtain a single phase. Further, aluminum and cobalt have high performance as a positive electrode active material of a lithium secondary battery. It has the advantage of exhibiting excellent battery characteristics, particularly good discharge capacity retention rate after repeated charging and discharging. Of course, a plurality of these metal elements may be used.

The atomic ratio of the substituting element to the total of the substituting element, nickel and manganese is usually 0.5 or less, preferably 0.4 or less. If the replacement ratio is too large, the capacity tends to decrease when used as a battery material. The layered lithium nickel manganese composite oxide of the present invention is usually represented by the following general formula (I).

[0012]

Embedded image Li _X Ni _Y Mn _Z Q _(1-YZ) O ₂ (I) Here, in the formula (I), X represents a number in the range of 0 <X ≦ 1.2, preferably 0 <X ≦ 1.1. If X is too large, the crystal structure may become unstable, or the battery capacity of the lithium secondary battery using the same may be reduced. Y and Z
Is a number satisfying X + Y ≦ 1, and 0.7 ≦ Y / Z
Represents a number in the range ≦ 9. When the proportion of manganese is relatively large, it becomes difficult to synthesize a single-phase lithium nickel manganese composite oxide. There are several preferable ranges for the value of Y / Z. For example, one of them is that the nickel ratio is small, which is advantageous in terms of cost and can be easily synthesized. In terms of advantage, 0.8 ≦ Y / Z ≦ 1.5, more preferably 0.9 ≦ Y / Z ≦ 1.5. If the Y / Z value is too small, it becomes difficult to synthesize a single-phase lithium nickel manganese composite oxide, and if the Y / Z value is too large, the discharge voltage becomes low. Secondly, the battery capacity is increased by increasing the nickel ratio, the charge / discharge capacity at a high rate is good, and the battery capacity per unit volume is further increased due to the high bulk density. 5 ≦ Y / Z ≦ 9, more preferably Y ≧ 0.6, Y / Z ≦ 9, and (1-Y−Z) ≧
It is a range that satisfies the relationship of 0.075. If the Y value is too small, the capacity does not increase, and the Y / Z value is too large.
Alternatively, if the value of (1-Y-Z) is too small, the stabilization of the crystal structure will be insufficient.

The value of (1-YZ) is 0.5 or less, preferably 0.4 or less. If this value is too large, the amount of the substituting element becomes too large, and the battery capacity of the lithium secondary battery using the lithium nickel manganese composite oxide as the positive electrode active material may be significantly reduced. Q is A
Represents at least one selected from the group consisting of 1, Co and Fe. Of these, more preferable are Al and Co.
And Co is the most preferred. Al and Co are
It can be easily solid-dissolved in the layered lithium nickel manganese composite oxide and can be synthesized as a single-phase lithium transition metal composite oxide. Furthermore, regarding Al and Co,
A lithium secondary battery using the obtained lithium-transition metal composite oxide as a positive electrode active material exhibits high-performance battery characteristics, in particular, good discharge capacity retention rate after repeated charge and discharge. In order to obtain a layered lithium nickel manganese composite oxide having better crystallinity, without forming a solid solution with the layered lithium nickel manganese composite oxide,
A substance that melts during firing to generate a liquid phase (hereinafter referred to as "inert melting agent") may be added. After cooling to room temperature, these inert melting agents are not incorporated in the crystal structure of the layered lithium nickel manganese composite oxide, and are present mainly in the state of coating the surface or depositing on the surface. Examples of the above-mentioned inert melting agent include boron compounds, antimony compounds, halides of potassium, barium and lithium, sulfates, molybdates and the like. Of these, more preferred are boron compounds and antimony compounds. The amount of the inert melting agent added is N
When the total number of moles of i, Mn and the substituting element Q is 1, the molar ratio is usually 0.05 or less, preferably 0.04 or less, more preferably 0.03 or less. If the amount of the inert melting agent added is too large, a sufficient discharge capacity may not be obtained.

In the composition of the general formula (I), the oxygen content may have some non-stoichiometry. The particle morphology of the layered lithium nickel manganese composite oxide is usually
The primary particles are aggregated to form secondary particles. The average primary particle diameter is usually 0.01 μm or more, preferably 0.02 μm or more, more preferably 0.1 μm or more,
It is usually 10 μm or less, preferably 5 μm or less, and more preferably 3 μm or less. The average secondary particle size is usually 1μ
m or more, preferably 4 μm or more, usually 50 μm or less, preferably 40 μm or less.

The preferred BET specific surface area of the lithium nickel manganese composite oxide depends on the composition range.
In the composition range of 0.8 ≦ Y / Z ≦ 1.5, usually 3
m ² / g or more, preferably 4 m ² / g or more, and usually 10 m ² / g or less, preferably 9 m ² / g or less.
In the composition range of 1.5 ≦ Y / Z ≦ 9, usually 0.1
m ² / g or more, preferably 0.2 m ² / g or more, and usually 10 m ² / g or less, preferably 9 m ² / g or less. The size of the primary particles can be controlled by the production conditions such as firing temperature, firing time, firing atmosphere and the like.
Further, the particle size of the secondary particles can be controlled by, for example, manufacturing conditions such as spraying conditions such as a gas-liquid ratio in a spray drying step described later. The specific surface area can be controlled by the particle size of the primary particles and the particle size of the secondary particles,
It is reduced by increasing the particle size of the primary particles and / or the particle size of the secondary particles. If the specific surface area is too small, the rate characteristic tends to be poor, while if it is too large, the rate characteristic and the capacity are deteriorated, and it becomes difficult to produce an electrode when a secondary battery is produced using this. The powder packing density of the lithium nickel manganese composite oxide is a tap density (after 200 taps), usually 0.5 g / cc or more,
It is preferably 0.6 g / cc or more, more preferably 0.
It is 8 g / cc or more. The higher the powder packing density, the higher the energy density per unit volume, but in reality, it is usually 3.0 g / cc or less,
In particular, it is 2.5 g / cc or less.

In the present invention, the specific surface area of the lithium nickel manganese composite oxide is the known BET.
It is measured by a powder specific surface area measuring device. The measurement principle of this method is as follows. That is, the measurement method is the BET one-point method measurement by the continuous flow method, and the adsorption gas and carrier gas used are nitrogen, air, and helium. The powder sample is heated and degassed with the mixed gas at a temperature of 450 ° C. or lower, and then cooled with liquid nitrogen to adsorb the mixed gas. This is heated with water to desorb the adsorbed nitrogen gas, which is detected by a thermal conductivity detector, the amount of which is determined as a desorption peak, and calculated as the specific surface area of the sample.

Lithium nickel manga used in the present invention
Complex oxides include, for example, lithium, nickel, and manganese.
And substitution elements used as necessary, and if necessary
Manufactured by firing with a raw material containing an inert melting agent.
Can be built. With a lithium source used as a raw material
Then, for example, Li₂CO₃, LiNO₃, LiOH,
LiOH / H₂O, lithium dicarboxylate, citric acid
Lithium, lithium fatty acid, alkyl lithium, lithium
Examples of various lithium compounds such as halides
it can. More specifically, for example, Li₂CO₃, LiN
O₃, LiOH, LiOH / H₂O, LiCl, LiI,
Acetic acid Li, Li₂O and the like can be mentioned. These
Among the raw materials for titanium, Li is preferable.₂CO₃, LiNO
₃, LiOH / H₂Water-soluble lithiation of O, Li acetate, etc.
It is a combination. These water-soluble compounds are, for example, dispersion media.
By dissolving in a slurry using water as
Lithium nickel manganese with good properties
A complex oxide can be obtained. Also, during the firing process
Because it does not generate harmful substances such as NOx and SOx,
Lithium compounds containing no elementary or sulfur atoms are preferred.
Yes. The most preferred lithium source is also water-soluble and
LiOH / H containing no nitrogen or sulfur atoms₂O
Is. Needless to say, use multiple types of lithium sources
May be.

As the nickel source, for example, Ni (O
H)₂, NiO, NiOOH, NiCO₃・ 2Ni (O
H)₂・ 4H₂O, NiC₂O_Four・ 2H₂O, Ni (NO₃)
₂・ 6H ₂O, NiSO_Four, NiSO_Four・ 6H₂O, fatty acid
Selected from the group consisting of nickel and nickel halides
You can list at least one that was exposed. In this
Also emits harmful substances such as NOx and SOx during the firing process.
N-containing no nitrogen or sulfur atoms, because it does not grow
i (OH)₂, NiO, NiOOH, NiCO₃・ 2Ni
(OH)₂・ 4H₂O, NiC₂O_Four・ 2H₂D like O
The Heckel compound is preferred. In addition, as an industrial raw material
From the viewpoint of being cheaply available and having high reactivity
Ni (OH) is particularly preferable.₂, NiO, NiO
It is OH. Of course, multiple sources of nickel are used.
May be used.

Examples of manganese sources include Mn ₃ O ₄ and
Mn ₂ O ₃ , MnO ₂ , MnCO ₃ , Mn (NO ₃ ) ₂ , Mn
Examples include SO ₄ , manganese dicarboxylate, manganese citrate, fatty acid manganese, manganese oxyhydroxide, manganese hydroxide, and manganese halide. Among these manganese raw materials, Mn ₂ O ₃ , Mn ₃ O ₄
Is preferable because it has a valence close to the manganese oxidation number of the final target compound oxide. Further, Mn ₂ O ₃ is particularly preferable from the viewpoint of being inexpensively available as an industrial raw material and from the viewpoint of high reactivity. Of course, plural kinds of manganese sources may be used.

As the substitutional element source, the substitution metal
Carbonate in addition to hydroxide, oxide, hydroxide, halogen
Inorganic acid salts such as salts, nitrates, sulfates, acetates, oxalic acid
Examples thereof include organic acid salts such as salts. Concrete aluminum
Examples of the source of nickel include AlOOH and Al₂O₃, A
l (OH)₃, AlCl₃, Al (NO₃)₃・ 9H₂O and
And Al₂(SO_Four)₃Various aluminum compounds such as
You can get it. Above all, NOx and
In terms of not generating harmful substances such as SOx, AlOOH,
Al₂O₃And Al (OH) ₃Is preferred and more preferred
In other words, it is industrially inexpensive and highly reactive.
And AlOOH. Of course, multiple aluminum compounds
It can also be used.

As a concrete cobalt source, for example, C
o (OH) ₂ , CoO, Co ₂ O ₃ , Co ₃ O ₄ , Co (O
_{Ac) 2 · 4H 2 O,} CoCl 2, Co (NO 3) 2 · 6H 2
O, and Co (SO ₄₎ various cobalt compounds such as ₂ · 7H ₂ O and the like. Among them, C is used because it does not generate harmful substances such as NOx and SOx during the firing process.
O (OH) ₂ , CoO, Co ₂ O ₃ , and Co ₃ O ₄ are preferable, and Co (OH) ₂ is more preferable because it is industrially available at low cost and has high reactivity. Of course, a plurality of cobalt compounds can be used.

As a concrete iron source, for example, FeO
(OH), Fe₂O₃, Fe₃O_Four, FeCl₂, FeC
l₃, FeC₂O_Four・ 2H₂O, Fe (NO₃)₃・ 9H
₂O, FeSO _Four・ 7H₂O and Fe₂(SO_Four)₃・ NH₂
Various iron compounds such as O can be mentioned. Above all,
No harmful substances such as NOx and SOx are generated during the firing process.
FeO (OH), Fe₂O₃, Fe₃O_FourIs good
More preferably, it is industrially available at low cost.
FeO (OH), Fe from the viewpoint of high reactivity₂O₃And
It Of course, it is also possible to use a plurality of iron compounds. necessary
Among the inert melting agents added according to, boron compounds
Specifically, Li₂B_FourO₇, Li₂B₂O_Four, L
i₆B_FourO₇Such as lithium borate, Na₂B₆O_Ten, Na₂B
_FourO₇Sodium borate, K, etc.₂B_TenO₁₆, K₂B_FourO₇etc
Potassium borate, B₂O₃, H₃BO₃1 selected from etc.
List of species or mixtures of two or more species and their decomposition products.
You can get it. Similarly added as an inert melting agent
Among the things, the antimony compound, specifically,
Sb₂O₃, Sb₂O_Four, Sb₂O_FiveAntimony oxide, such as L
iSbO₃1 selected from lithium antimonate etc.
There may be mentioned one kind or a mixture of two or more kinds.

These lithium source, nickel source, manganese source and substitutional element source may be dry-mixed and used as a raw material for firing, or may be wet-mixed (that is, in a slurry) and then dried and fired. It may be used as a raw material. When wet-mixing, (1) a slurry containing a nickel source, a manganese source, a lithium source, and a dispersion medium is wet-mixed, spray-dried, and then calcined, or (2) a nickel source, a manganese source, and a dispersion medium. Any method of wet-mixing and spray-drying a slurry containing a and then mixing the slurry with a lithium source and then firing the mixture may be used. Since it is preferable that the respective raw materials are sufficiently mixed before firing, a method of wet mixing at least a nickel source and a manganese source, which allows better mixing, is preferable. The mixing and drying methods in the slurry will be described below. As the dispersion medium used in the slurry, various organic solvents and aqueous solvents can be used, but water is preferable.

The total weight ratio of the lithium source, the nickel source and the manganese source to the total weight of the slurry, or the total weight ratio of the nickel source, the manganese source and the substitutional element source excluding the lithium source is usually 10% by weight or more, preferably It is 12.5% by weight or more, usually 50% by weight or less, and preferably 35% by weight or less. If the weight ratio is less than the above range, the slurry concentration is extremely dilute and the spherical particles generated by spray drying may be smaller than necessary or may be easily broken. When the saturated solubility is exceeded, the lithium source cannot be completely dissolved and it becomes difficult to maintain the uniformity of the slurry.

The average particle size of the solid matter in the slurry is usually 2
μm or less, preferably 1 μm or less, more preferably 0.5 μm or less. If the average particle size of the solid matter in the slurry is too large, not only the reactivity in the firing step is lowered, but also the sphericity is lowered and the final powder packing density tends to be lowered. This tendency is 50μ in average particle size
This becomes particularly noticeable when it is attempted to produce granulated particles of m or less. Further, since making the particles smaller than necessary leads to an increase in the cost of pulverization, the average particle size of the solid is usually 0.01 μm or more, preferably 0.05 μm or more, more preferably 0.1 μm or more.

As a method for controlling the average particle size of the solid matter in the slurry, a raw material compound is previously dry-milled by a ball mill, a jet mill or the like, and this is dispersed in a dispersion medium by stirring or the like, or a raw material compound is dispersed in the dispersion medium. In addition, there may be mentioned a method of carrying out wet pulverization using a medium agitation pulverizer or the like after dispersion by agitation or the like. It is preferable to use a method in which the raw material compound is dispersed in a dispersion medium and then wet-milled by using a medium agitation mill or the like. The effect of the present invention is remarkably exhibited by wet pulverization.

The viscosity of the slurry is usually 50 mPas.
-S or more, preferably 100 mPa-s or more, particularly preferably 200 mPa-s or more, usually 3000 mPa-s
The following is preferably 2000 mPa · s or less, and particularly preferably 1600 mPa · s or less. When the viscosity is less than the above range, a large load is applied to drying before firing,
While the spherical particles produced by drying become unnecessarily small or easily damaged, on the other hand, when it exceeds the above range, it becomes difficult to handle, for example, suction by a tube pump used for slurry transportation during drying becomes impossible. The viscosity of the slurry can be measured using a known BM type viscometer. The BM type viscometer is a measuring method that employs a method of rotating a predetermined metal rotor in a room temperature atmosphere. The viscosity of the slurry is calculated from the resistance force (twisting force) applied to the rotating shaft of the rotor when the rotor is rotated while being immersed in the slurry. However, the room temperature atmosphere means a temperature of 10 ° C to 35 ° C and a relative humidity of 20% RH to 80% RH.
Figure 7 illustrates a normally considered laboratory level environment.

The slurry obtained as described above is usually dried and then subjected to firing treatment. Spray drying is preferred as the drying method. By performing spray drying, a spherical lithium nickel manganese composite oxide can be obtained by a simple method, and as a result, the packing density can be improved. The method of spray drying is not particularly limited, but for example, a droplet of the slurry component from the nozzle by causing a gas flow and a slurry to flow into the tip of the nozzle (this may be simply referred to as “droplet” in this specification). is there.)
Can be used to rapidly dry the scattered droplets by using an appropriate drying gas temperature and blowing amount. Air, nitrogen or the like can be used as the gas supplied as the gas flow, but air is usually used. It is preferable to use these under pressure. The gas flow has a gas linear velocity of usually 100 m / s or more, preferably 20 m / s or more.
The injection is performed at 0 m / s or more, more preferably 300 m / s or more. If it is too small, it becomes difficult to form appropriate droplets. However, since it is difficult to obtain a too high linear velocity,
The normal injection speed is 1000 m / s or less. The nozzle used may have any shape as long as it can eject minute liquid droplets, and a conventionally known one, for example, a liquid droplet described in Japanese Patent No. 2977080 can be miniaturized. Such nozzles can also be used. In addition, it is preferable that the droplets are sprayed in an annular shape from the viewpoint of improving productivity. The scattered droplets are dried. As described above, treatment such as appropriate temperature and air blowing is performed so as to quickly dry the scattered droplets, but it is preferable to introduce the drying gas from the upper part of the drying tower to the lower part by downflow. With such a structure, the throughput per unit volume of the drying tower can be greatly improved. Also,
When spraying liquid droplets in a substantially horizontal direction, by suppressing the liquid droplets sprayed in the horizontal direction with downflow gas, it is possible to greatly reduce the diameter of the drying tower, making it possible to manufacture inexpensively in large quantities. Becomes The dry gas temperature is
It is usually 50 ° C or higher, preferably 70 ° C or higher, and usually 12
The temperature is 0 ° C or lower, preferably 100 ° C or lower. If the temperature is too high, the resulting granulated particles will have many hollow structures, and the packing density of the powder will tend to decrease, while if it is too low, the powder will stick to the powder due to water condensation at the powder outlet. Problems such as blockages may occur.

By spray-drying in this manner, granulated particles as a raw material can be obtained. The average particle size of the granulated particles is preferably 50 μm or less, and more preferably 30 μm or less. However, since it tends to be difficult to obtain a particle size that is too small, it is usually 4 μm or more,
It is preferably at least 5 μm. The particle size of the granulated particles can be controlled by appropriately selecting the spray type, pressurized gas flow supply rate, slurry supply rate, drying temperature and the like.

A raw material containing lithium, manganese, and nickel is calcined. Alternatively, a raw material containing nickel, manganese, etc., obtained by drying a slurry not containing a lithium source, is mixed with a lithium source and then calcined. After the firing treatment, the lithium source may be mixed and further subjected to the firing treatment. As a mixing method, hand shaking mixing,
Mechanical mixing using a ball mill or the like can be mentioned. The firing temperature is usually 700 ° C. or higher, preferably 750 ° C. or higher, and more preferably 800 ° C. or higher, although it varies depending on the types of lithium source, manganese source, and nickel source used as raw materials, the firing time, and the firing atmosphere. ,
It is usually 1050 ° C or lower, preferably 950 ° C or lower. Generally, when the firing temperature is high, the specific surface area of the obtained lithium nickel manganese composite oxide is small. If the temperature is too low, the crystallinity is good, and a long firing time tends to be required to obtain the layered lithium nickel manganese composite oxide having the target specific surface area. Further, if the temperature is too high, a layered lithium nickel manganese composite oxide having a target specific surface area cannot be obtained, a crystal phase other than the target is generated, or a layered lithium nickel manganese composite oxide having many defects is generated. As a result, the battery capacity of a lithium secondary battery using the lithium transition metal composite oxide as a positive electrode active material may decrease, or deterioration due to the collapse of the crystal structure due to charge / discharge may occur.

Although the firing time varies depending on the temperature, it is usually 30 minutes or more and 50 hours or less in the above temperature range. If the firing time is too short, it becomes difficult to obtain a layered lithium nickel manganese composite oxide having good crystallinity, and if it is too long, it is not practical. In order to obtain a layered lithium nickel manganese composite oxide with few crystal defects, it is preferable to cool slowly after the firing reaction,
For example, 5 ° C./min. It is preferable to gradually cool at the following cooling rate.

The atmosphere during firing may be an oxygen-containing gas atmosphere such as air or an inert gas atmosphere such as nitrogen or argon depending on the composition and structure of the compound to be produced. In the case of oxides,
Nickel is preferably air or oxygen because it needs to be oxidized from divalent raw material to trivalent desired product.

The heating device used for firing has the above-mentioned temperature,
There is no particular limitation as long as the atmosphere can be achieved, and for example, a box furnace, a tubular furnace, a tunnel furnace, a rotary kiln or the like can be used. In the present invention, the average particle size of the solid content in the slurry, the average particle size of the granulated particles after spray drying, and the average secondary particle size of the layered lithium nickel manganese composite oxide are known laser diffraction / It is measured by a scattering type particle size distribution measuring device. The measurement principle of this method is as follows. That is, slurry or powder is dispersed in a dispersion medium, the sample solution is irradiated with laser light, and scattered light that is incident on particles and scattered (diffracted) is detected by a detector. The scattering angle θ (angle between the incident direction and the scattering direction) of the detected scattered light is forward scattering (0 <θ <90 °) for large particles, and side scattering or back scattering (90 °) for small particles. ° <θ <180 °). From the measured angular distribution value, the particle size distribution is calculated using information such as the incident light wavelength and the particle refractive index. Further, the average particle size is calculated from the obtained particle size distribution. The dispersion medium used in the measurement may be, for example, a 0.1 wt% sodium hexametaphosphate aqueous solution. The average primary particle diameter of the layered lithium nickel manganese composite oxide can be determined from SEM photographs and the like.

The spinel type lithium manganese composite oxide used in the present invention is an oxide having a spinel type crystal structure and containing lithium and manganese. Further, the spinel type lithium manganese composite oxide of the present invention has a part of manganese site substituted with another metal element in order to stabilize the crystal structure, increase capacity, improve safety, and improve battery characteristics at high temperature. It is also possible to do so.

Various elements can be used as the substituting element, but Al, Fe, Ga, Bi, and
Sn, V, Cr, Co, Ni, Cu, Zn, Mg, T
Metal elements such as i, Ge, Nb, Ta, Zr and Li can be mentioned. Among these, Al, Fe, Ga, C
More preferred are r, Co, Mg, and Ti. Of course, a plurality of these metal elements may be used.

The spinel type lithium manganese composite oxide in the present invention is usually represented by the following general formula (II).

[0037]

Li _X2 Mn _(2-Y2) R _Y2 O ₄ (II) In the formula (II), X2 is in the range of 0 <X2 ≦ 1.2, preferably 0 <X2 ≦ 1.1. Represents a number. If X2 is too large, the crystal structure may become unstable, or the battery capacity of the lithium secondary battery using the same may be reduced. Y
2 is a number representing the substitution amount of manganese by another element,
It is 0.5 or less, preferably 0.35 or less, and more preferably 0.25 or less. The value of Y2 may be 0. If the amount of the substituting element is too large, the battery capacity of the lithium secondary battery using the spinel type lithium manganese composite oxide as the positive electrode active material may be significantly reduced.

R is Al, Fe, Ga, Bi, Sn, V,
Cr, Co, Ni, Cu, Zn, Mg, Ti, Ge, N
It represents at least one selected from the group consisting of b, Ta, Zr and Li. Of these, more preferred is A
1, Fe, Ga, Cr, Co, Mg, Ti, and a lithium secondary battery using the obtained lithium transition metal composite oxide as a positive electrode active material has high performance battery characteristics, especially when repeatedly charged and discharged. The discharge capacity retention ratio of No. 1 shows good performance. In order to obtain a spinel-type lithium-manganese composite oxide having better crystallinity, a substance that does not form a solid solution with the spinel-type lithium-manganese composite oxide and that melts during firing to generate a liquid phase (hereinafter referred to as " It may be added). After cooling to room temperature, these inert melting agents are not taken into the crystal structure of the spinel type lithium manganese composite oxide, and are present mainly in the state of coating the surface or precipitating on the surface. Examples of the above-mentioned inert melting agent include boron compounds, antimony compounds, halides of potassium, barium and lithium, sulfates, molybdates and the like. Of these, more preferred are boron compounds and antimony compounds. When the total number of moles of Mn and the substituting element R is 1, the amount of the inert melting agent added is usually 0.
It is 05 or less, preferably 0.04 or less, and more preferably 0.03 or less. If the amount of the inert melting agent added is too large, a sufficient discharge capacity may not be obtained.

In the composition of the general formula (II), the oxygen content may have some non-stoichiometry. The spinel type lithium manganese composite oxide has an average primary particle diameter of usually 0.01 μm or more, preferably 0.02 μm.
The above is more preferably 0.1 μm or more, usually 10 μm or less, preferably 5 μm or less, and more preferably 3 μm or less. The average secondary particle diameter is usually 1 μm or more, preferably 4 μm or more, usually 50 μm or less, preferably 40
μm or less.

Further, the spinel type lithium manganese composite oxide of the present invention has a BET specific surface area of 0.1 m ² / g or more and 10 m ² / g or less, preferably 0.2 m ² / g or more and 3 m.
² / g or less. The BET specific surface area can be measured by the same method as in the case of measuring the lithium nickel manganese composite oxide described above. The specific surface area, primary particle diameter, and secondary particle diameter of the spinel type lithium manganese composite oxide can be controlled by the same method as in the case of producing the layered lithium nickel manganese composite oxide. If the specific surface area is too small, the rate characteristic tends to be poor, while if it is too large, the rate characteristic and the capacity are deteriorated, and it becomes difficult to produce an electrode when a secondary battery is produced using this. The powder packing density of the spinel type lithium manganese composite oxide is a tap density (after 200 taps), usually 0.5 g / cc or more, preferably 0.6 g / cc or more, and more preferably 0.8 g. / Cc
That is all. The higher the powder packing density, the greater the energy density per unit volume, but
In reality, it is usually 3.0 g / cc or less, especially 2.5.
It is less than or equal to g / cc.

The spinel type lithium manganese composite oxide of the present invention is prepared by the same method as the above-mentioned lithium nickel manganese composite oxide, for example, lithium and manganese, a substitution element optionally used, and an inert melting agent. It can be manufactured by mixing and firing raw materials containing. Lithium source, manganese source,
As the substitute element source and the inert melting agent, the same ones as in the case of the above-mentioned lithium nickel manganese composite oxide can be used.

Besides, the spinel type lithium manganese composite oxide can be manufactured by the same method as in the case of manufacturing the lithium nickel manganese composite oxide described above. The positive electrode material of the present invention is obtained by mixing the lithium nickel manganese composite oxide and the spinel type lithium manganese composite oxide described above and then mixing the lithium transition metal composite oxide. Further, in addition to simply mixing, it may be coated with a spinel type lithium manganese complex oxide with a lithium nickel manganese complex oxide, or after mixing the lithium nickel manganese complex oxide and the spinel type lithium manganese complex oxide. It may be granulated and compounded.

The mixing ratio of the lithium nickel manganese composite oxide and the spinel type lithium manganese composite oxide is such that the content (weight) of the lithium nickel manganese composite oxide is A and the content (weight) of the spinel type lithium manganese composite oxide. When is B, the value (weight ratio) of A / (A + B) is usually 0.05 or more, preferably 0.1 or more,
It is more preferably 0.2 or more, most preferably 0.3 or more, and is usually 0.95 or less, preferably 0.9 or less, more preferably 0.8 or less, most preferably 0.
7 or less. If the value of A / (A + B) is too small, the cycle characteristics at high temperature tend to be poor, and A / (A
If the value of + B) is too large, the output characteristic at low temperature tends to be insufficient.

Lithium nickel manganese composite oxide,
As a method for mixing and forming the spinel type lithium manganese composite oxide, either dry mixing or wet mixing may be used, but dry mixing is particularly preferably used. As the method, a known method such as a ball mill, a Loedige mixer, a mechanofusion, a hybridizer or the like can be used.

A lithium secondary battery can be manufactured using the positive electrode material of the present invention. A lithium secondary battery usually has a positive electrode, a negative electrode, and an electrolyte layer. Examples of the secondary battery of the present invention include a secondary battery consisting of a positive electrode, a negative electrode, an electrolytic solution, and a separator, in which case there is an electrolyte between the positive electrode and the negative electrode, and the separator has a positive electrode and a negative electrode. Placed between them so that they do not touch.

The positive electrode usually contains a positive electrode material containing the lithium nickel manganese composite oxide and the lithium manganese composite oxide, and a binder. In addition, the positive electrode is usually formed by forming a positive electrode layer containing the positive electrode material and a binder on a current collector. Such a positive electrode layer can be produced by applying a slurry of the above positive electrode material, a binder and, if necessary, a conductive agent and the like to a solvent on a positive electrode current collector and drying.

The positive electrode layer occludes lithium ions other than the lithium nickel manganese composite oxide and the lithium manganese composite oxide, such as LiFePO _4.
It may further contain a releasable active material. The proportion of the active material in the positive electrode layer is usually 10% by weight or more, preferably 30% by weight or more, more preferably 50% by weight or more, and usually 99.9% by weight or less, preferably 99% by weight or less. If it is too large, the mechanical strength of the electrode tends to be poor, and if it is too small, the battery performance such as capacity tends to be poor.

Examples of the binder used for the positive electrode include polyvinylidene fluoride, polytetrafluoroethylene, fluorinated polyvinylidene fluoride and EPDM.
(Ethylene-propylene-diene terpolymer), SB
Examples thereof include R (styrene-butadiene rubber), NBR (acrylonitrile-butadiene rubber), fluororubber, polyvinyl acetate, polymethylmethacrylate, polyethylene and nitrocellulose. The proportion of the binder in the positive electrode layer is usually 0.1% by weight or more, preferably 1% by weight or more, more preferably 5% by weight or more, and usually 80% by weight or less, preferably 60% by weight or less, more preferably It is 40% by weight or less, and most preferably 10% by weight or less. If the proportion of the binder is too low, the active material cannot be sufficiently retained and the mechanical strength of the positive electrode is insufficient, which may deteriorate the battery performance such as cycle characteristics, while if it is too high, the battery capacity and conductivity are reduced. Sometimes.

The positive electrode layer usually contains a conductive agent in order to enhance conductivity. Examples of the conductive agent include graphite such as natural graphite and artificial graphite, carbon black such as acetylene black, and carbon materials such as amorphous carbon such as needle coke. The proportion of the conductive agent in the positive electrode is usually 0.01% by weight or more, preferably 0.1% by weight or more, more preferably 1% by weight or more and usually 50% by weight or less, preferably 30% by weight or less, It is preferably 15% by weight or less. If the proportion of the conductive agent is too low, the conductivity may be insufficient, and conversely, if it is too high, the battery capacity may decrease.

The slurry solvent is not particularly limited as long as it dissolves or disperses the binder, but an organic solvent is usually used. For example, N-methylpyrrolidone, dimethylformamide, dimethylacetamide, methylethylketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, NN
-Dimethylaminopropylamine, ethylene oxide,
Tetrahydrofuran etc. can be mentioned. It is also possible to add a dispersant, a thickener and the like to water to make the active material into a slurry with a latex such as SBR.

The thickness of the positive electrode layer is usually 1 to 1000 μm,
It is preferably about 10 to 200 μm. If it is too thick, the conductivity tends to decrease, and if it is too thin, the capacity tends to decrease. As the material of the current collector used for the positive electrode, aluminum, stainless steel, nickel-plated steel or the like is used, and aluminum is preferable. The thickness of the current collector is usually 1 to 1000 μm, preferably 5 to 500 μm
It is a degree. If it is too thick, the capacity of the lithium secondary battery as a whole may be reduced, and if it is too thin, the mechanical strength may be insufficient.

The positive electrode layer obtained by coating and drying is preferably compacted by a roller press or the like in order to increase the packing density of the active material. The negative electrode active material used for the negative electrode of the secondary battery may be lithium or a lithium alloy such as a lithium aluminum alloy, but a carbon material having higher safety and capable of absorbing and releasing lithium is preferable.

The carbon material is not particularly limited, but is not limited to graphite, coal-based coke, petroleum-based coke, coal-based pitch carbide, petroleum-based pitch carbide, or carbide obtained by oxidizing these pitches, needle coke, pitch coke. Examples thereof include phenolic resins, carbides such as crystalline cellulose, and carbon materials obtained by partially graphitizing these, furnace black, acetylene black, pitch-based carbon fibers, and the like.

Further, as the negative electrode active material, SnO, SnO
₂ , Sn _1-x M _x O (M = Hg, P, B, Si, Ge or Sb, where 0 ≦ x <1), Sn ₃ O ₂ (OH) ₂ , S
n _{3- x} M _x O ₂ (OH) ₂ (M = Mg, P, B, Si, G
e, Sb or Mn, where 0 ≦ x <3), LiSi
O _2, can be mentioned SiO ₂ or LiSnO ₂ like. A mixture of two or more selected from these may be used as the negative electrode active material.

As in the case of the positive electrode, the negative electrode is usually formed by forming a negative electrode layer on a current collector. The binder used at this time, and the conductive agent and the like used as necessary and the slurry solvent may be the same as those used for the positive electrode. Further, as the current collector of the negative electrode, copper, nickel, stainless steel, nickel-plated steel or the like is used, and preferably copper is used.

When a separator is used between the positive electrode and the negative electrode, a microporous polymer film is used, and polytetrafluoroethylene, polyester, nylon, cellulose acetate, nitrocellulose, polysulfone, polyacrylonitrile, polyfluorine is used. Polyolefin polymers such as vinylidene, polypropylene, polyethylene and polybutene can be used. Further, a non-woven filter of glass fiber or the like, or a non-woven filter of glass fiber and polymer fiber can also be used. The chemical and electrochemical stability of the separator is an important factor. From this point of view, the polyolefin-based polymer is preferable, and from the viewpoint of the self-closing temperature which is one of the purposes of the battery separator, it is preferable to be made of polyethylene.

In the case of a polyethylene separator, ultrahigh molecular weight polyethylene is preferable from the viewpoint of shape retention at high temperature, and the lower limit of its molecular weight is preferably 500,000, more preferably 1,000,000, and most preferably 1,500,000. On the other hand, the upper limit of the molecular weight is preferably 5,000,000, more preferably 4,000,000, and most preferably 3,000,000. This is because if the molecular weight is too large, the fluidity is so low that the pores of the separator may not be closed when heated.

As the electrolyte constituting the electrolyte layer in the lithium secondary battery of the present invention, for example, a known organic electrolytic solution, polymer solid electrolyte, gel electrolyte, inorganic solid electrolyte or the like can be used, among which, among others, Organic electrolytes are preferred. The organic electrolytic solution is composed of an organic solvent and a solute. The organic solvent is not particularly limited, for example, carbonates, ethers, ketones, sulfolane compounds, lactones, nitriles, chlorinated hydrocarbons,
Ethers, amines, esters, amides, phosphoric acid ester compounds and the like can be used. Typical examples of these are dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, propylene carbonate, ethylene carbonate, butylene carbonate, vinylene carbonate, tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 4-methyl-2. -Pentanone, 1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone, 1,3-dioxolane, 4-methyl-1,3-dioxolane, diethyl ether, sulfolane, methylsulfolane, acetonitrile, propio Nitrile, benzonitrile, butyronitrile, valeronitrile, 1,2-dichloroethane, dimethylformamide, dimethyl sulfoxide, trimethyl phosphate, triethyl phosphate, etc. alone or A mixed solvent of two or more can be used.

The above-mentioned organic solvent preferably contains a high dielectric constant solvent in order to dissociate the electrolyte. Here, the high dielectric constant solvent has a relative dielectric constant of 20 at 25 ° C.
The above compounds are meant. In the high dielectric constant solvent, it is preferable that the electrolytic solution contains ethylene carbonate, propylene carbonate, and a compound in which hydrogen atoms thereof are replaced by another element such as halogen or an alkyl group. The ratio of the high dielectric constant compound in the electrolytic solution is preferably 20.
It is at least 30% by weight, more preferably at least 30% by weight, and most preferably at least 40% by weight. This is because if the content of the compound is small, desired battery characteristics may not be obtained.

The solute to be dissolved in this solvent is not particularly limited, but any conventionally known solute can be used, such as LiClO ₄ , LiAsF ₆ , LiPF ₆ and LiB.
F ₄ , LiB (C ₆ H ₅ ) ₄ , LiCl, LiBr, CH ₃
SO ₃ Li, CF ₃ SO ₃ Li, LiN (SO ₂ CF ₃ ) ₂ ,
LiN (SO ₂ C ₂ F ₅ ) ₂ , LiC (SO ₂ CF ₃ ) ₃ , L
iN (SO ₃ CF ₃ ) _{2 and the} like can be used, and at least one or more of these can be used. Also, C
Gases such as O ₂ , N ₂ O, CO, and SO ₂ and polysulfide S _x ^2-, such as the above additives alone, in any proportion, are additives that form a good film that enables efficient charging and discharging of lithium ions on the negative electrode surface. Alternatively, it may be added to the mixed solvent.

When the polymer solid electrolyte is used, the known polymer can be used. In particular, it is preferable to use a polymer having high ionic conductivity with respect to lithium ions, and for example, polyethylene oxide, polypropylene oxide, polyethyleneimine and the like are preferably used. It is also possible to add the above solvent to the polymer together with the above solute and use it as a gel electrolyte.

Even when an inorganic solid electrolyte is used, this
Use of known crystalline and amorphous solid electrolytes for inorganic substances
You can Examples of the crystalline solid electrolyte include Li
I, Li₃N, Li_{1 + x}M_xTi_2-x(PO_Four)₃(M = A
l, Sc, Y, La), Li_{0.5- 3x}RE_{0.5 + x}TiO
₃(RE = La, Pr, Nd, Sm), etc.
As the crystalline solid electrolyte, for example, 4.9 LiI-3
4.1 Li₂O-61B₂O_Five, 33.3Li₂O-66.
7 SiO₂Oxide glass such as 0.45LiI-0.3
7Li₂S-0.26B₂S₃, 0.30LiI-0.4
2 Li₂S-0.28SiS ₂Such as sulfide glass
To be Use at least one of these
You can

[0063]

EXAMPLES The present invention will be further described below with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist. <Production of Layered Lithium Nickel Manganese Composite Oxide Example 1>
LiOH.H ₂ O, Ni (OH) ₂ , and Mn ₂ O ₃ are respectively contained in the final layered lithium nickel manganese composite oxide, and Li: Ni: Mn = 1.05: 0.50: 0.
It was weighed to be 50 (molar ratio), and pure water was added to this to prepare a slurry having a solid content concentration of 12.5% by weight. While stirring this slurry, a circulation type medium stirring type wet pulverizer (manufactured by Shinmaru Enterprises Co., Ltd .: Dyno Mill K)
DL-A type) was used to grind until the average particle size of the solid content in the slurry became 0.30 μm. The milling time was 6 hours using a 300 ml pot. The viscosity of this slurry was measured with a BM type viscometer (manufactured by Tokimec). The measurement is carried out in the atmosphere at room temperature, a specific metal rotor is fixed to the rotating shaft of the main body of the device, the rotor is immersed below the liquid surface of the slurry, and the rotating shaft is rotated to generate a resistance force (twisting force) on the rotor. The viscosity was calculated. As a result, the initial viscosity was 1510 mPa · s.

Next, this slurry was spray-dried using a two-fluid nozzle type spray dryer (manufactured by Okawara Kakoki Co., Ltd .: L-8 type spray dryer). Air was used as the dry gas at this time, and the amount of the dry gas introduced was 45 m ³ / mi.
n, the drying gas inlet temperature was 90 ° C. Then, the granulated particles obtained by spray drying were fired in air at 900 ° C. for 10 hours to obtain a lithium nickel manganese composite oxide having a molar ratio composition almost charged.

The obtained lithium nickel manganese composite oxide has an average secondary particle diameter of 4.9 μm and a maximum particle diameter of 15 μm.
The particles had a substantially spherical shape. The average particle size of the solid content in the slurry and the average particle size and maximum particle size of the obtained lithium nickel manganese composite oxide are measured by a laser diffraction / scattering particle size distribution measuring device (manufactured by Horiba Ltd .:
The particle size distribution was measured using a LA-920 type particle size distribution measuring device). Specifically, in a room temperature atmosphere, the slurry or the calcined product powder is dispersed in a 0.1% sodium hexametaphosphate aqueous solution by ultrasonic dispersion and stirring, and the transmittance is adjusted between 70% and 95%, and then measured. The average particle size and the maximum particle size were determined from the particle size distribution.

When the powder X-ray diffraction of the obtained lithium nickel manganese composite oxide was measured, the obtained lithium nickel manganese composite oxide Li _1.05 Ni _0.5 Mn _0.5
It was confirmed that O ₂ had a rhombohedral layered structure. 5 g of this powder was placed in a 10-ml glass graduated cylinder, and the powder packing density (tap density) after tapping 200 times was measured and found to be 0.9 g / cc.

The BET specific surface area of this powder was measured and found to be 5.0 m ² / g. The specific surface area can be measured by BE
T type powder specific surface area measuring device (Okura Riken: AMS800
It was determined using a 0 type fully automatic powder specific surface area measuring device). Moreover, the average primary particle diameter determined by the SEM photograph is 0.1 μm.
It was m. <Layered Lithium Nickel Manganese Composite Oxide Production Example 2> LiOH · H ₂ O (manufactured by Honjo Chemical), N
iO ₂ (manufactured by Shodo Kagaku), Mn ₂ O ₃ (manufactured by firing electrolytic manganese dioxide), and Co (OH) ₂ (manufactured by Ise Chemical) in the final layered lithium nickel manganese composite oxide, Li: Ni: Mn: Co = 1.05: 0.
It was weighed to be 65: 0.15: 0.20 (molar ratio), pure water was added to this to prepare a slurry having a solid content concentration of 25% by weight, and the slurry was pulverized in the same manner as in Production Example 1. H ₃ BO ₃ was added to this slurry in a molar ratio of B / (Ni + Mn + Co) = 0.
It was added and dissolved so as to be 01. The obtained slurry was spray dried in the same manner as in Production Example 1 and then calcined at 830 ° C. to obtain a lithium transition metal composite oxide. The average secondary particle diameter and the maximum particle diameter obtained by the same method as in Production Example 1 are 7.
It was 5 μm and 17 μm. The tap density and BET specific surface area were 1.7 g / cc and 0.8 m ² / g, respectively. The average primary particle diameter determined by SEM photograph was 0.2 μm. <Spinel-type lithium manganese complex oxide Production Example _{1> LiOH · H 2 O,} Mn 2 O 3, Al
OOH is the composition in the final spinel type lithium manganese composite oxide, and Li: Mn: Al = 1.04:
Weighed to be 1.88: 0.12 (molar ratio), pure water was added to this to prepare a slurry having a solid content concentration of 35% by weight, and wet pulverization and spraying were carried out in the same procedure as in Comparative Example 1. Granulated particles were obtained by drying. 90% of the granulated particles under a nitrogen stream
5 ° C./min up to 0 ° C. The temperature is raised at 900 ° C., and after reaching 900 ° C., firing is performed for 5 hours in an air stream, and the temperature is 1 ° C./min. At 300 ° C
After cooling to, it was left to cool.

When the powder X-ray diffraction of the obtained lithium manganese composite oxide was measured, the obtained lithium manganese composite oxide Li _1.04 Ni _1.88 Al _0.12 O ₄ had a cubic spinel structure. It was confirmed. The average secondary particle diameter and the maximum particle diameter obtained by the same method as in the production example of the layered lithium nickel manganese composite oxide were 1
It was 6 μm and 34 μm. As a result of obtaining tap density and BET specific surface area, 1.7 g / cc and 0.9 m, respectively.
It was ² / g. The average of 1 obtained by SEM observation
The secondary particle size was 1 μm. <Example 1> The layered lithium nickel manganese composite oxide obtained in Production Example 1 of the layered lithium nickel manganese oxide and the spinel type lithium manganese composite oxide obtained in Production Example 1 of the spinel type lithium manganese complex oxide were prepared. The positive electrode material of the present invention was obtained by mixing in a mortar at a ratio of 1: 1 (weight ratio).

A lithium secondary battery was produced using the obtained positive electrode material by the following method, and the battery was evaluated. A. Measurement of initial discharge capacity 75% by weight of the positive electrode material and 20% of acetylene black
What was weighed in an amount of 5% by weight and 5% by weight of polytetrafluoroethylene powder were thoroughly mixed in a mortar, and a thin sheet was punched out using a 9 mmφ punch. At this time, the total weight was adjusted to be about 8 mg. This was pressed onto an expanded metal of Al to obtain a positive electrode.

A coin cell was assembled with the obtained positive electrode as a test electrode and Li metal as a counter electrode. To this, 0.5 mA
/ MA ² constant current charging, that is, the reaction of releasing lithium ions from the positive electrode is performed at an upper limit of 4.3 V, and 0.5 mA / c
The initial discharge capacity (mAh / g) per unit weight of the positive electrode active material was measured when a constant current discharge of m ² , that is, a reaction of occluding lithium ions in the positive electrode was performed at a lower limit of 3.0V. B. Measurement of Chronopotentiometry In order to evaluate the output at low temperature, chronopotentiometry was measured by the following method.

Average particle size of the negative electrode active material is about 8 to 10 μm.
m graphite powder (d002 = 3.35Å) and polyvinylidene fluoride as a binder in a weight ratio of 92.5:
It was weighed at a ratio of 7.5 and mixed in an N-methylpyrrolidone solution to obtain a negative electrode mixture slurry. This slurry was applied to one side of a copper foil having a thickness of 20 μm, dried to evaporate the solvent, punched out to 12 mmφ, and 0.5 ton /
A negative electrode was obtained by pressing with cm ² . Next, the positive electrode and the negative electrode were combined so that the capacity ratio of the positive electrode to the negative electrode was 1: 1.2, and 1 mol / L as a non-aqueous electrolyte solution.
A coin cell was assembled using a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) having a volume fraction of 3: 7 in which lithium hexafluorophosphate (LiPF ₆ ) was dissolved as an electrolytic solution. The voltage range of charging and discharging was set to the upper limit voltage of 4.2V and the lower limit voltage of 3.0V, and the coin cell adjusted to the charging depth of 40% by 1 / 3C constant current charging / discharging was kept in the low temperature atmosphere of −30 ° C. for 1 hour or more. After that, 1.
Discharge was performed at a constant current of 5 C, and the difference ΔV (V) between the voltage immediately before discharge and the reached voltage 10 seconds after the start of discharge was measured.
It is shown that the smaller ΔV is, the smaller the voltage drop is, and the larger the output is at low temperature. C. 50 ° C / 100 cycle capacity retention measurement A coin cell was assembled using graphite as a negative electrode active material in the same manner as in B above, and a cycle test was performed at 50 ° C by 1C constant current charge / discharge at an upper limit voltage of 4.2V and a lower limit voltage of 3.0V. I went.

At this time, the ratio of the discharge capacity Qh (100) at the 100th cycle to the discharge capacity Qh (1) at the 100th cycle relative to the discharge capacity Qh (1) at the 100th cycle of 1C charge / discharge at 50 ° C.

[0073]

## EQU1 ## P [%] = {Qh (100) / Qh (1)} × 100, and the high temperature characteristics of the batteries were compared with this value. In Table-1,
The evaluation results of A, B and C are shown below. <Example 2> As the layered lithium nickel manganese composite oxide, the one obtained in Production Example 2 of layered lithium nickel manganese composite oxide was used, and the upper limit voltage of charging was 4.2 V when the Li metal was the counter electrode. If graphite is used as the counter electrode,
A lithium secondary battery was prepared and evaluated in the same manner as in Example 1 except that the voltage was 4.1V. The results are shown in Table-1. Comparative Example 1 A lithium secondary battery was produced in the same manner as in Example 1 except that the layered lithium nickel manganese composite oxide obtained in Production Example 1 was used alone as the positive electrode material. ,evaluated.
The results are shown in Table-1. <Comparative Example 2> The layered lithium nickel manganese composite oxide obtained in Production Example 2 of the layered lithium nickel manganese oxide was used alone as a positive electrode material, and a lithium secondary battery was prepared and evaluated in the same manner as in Example 2. did. The results are shown in Table-1.

[0074]

[Table 1] As shown in Table 1, Comparative Examples 1 and 2 were prepared by using the lithium transition metal composite oxide obtained by mixing the layered lithium nickel composite oxide of Examples 1 and 2 and the spinel type lithium nickel composite oxide as the positive electrode active material. In contrast to the case where the layered lithium nickel manganese composite oxide is used alone,
It can be seen that the voltage drop at -30 ° C is small and the output is greatly improved.

[0075]

According to the present invention, it is possible to obtain a positive electrode material for use in a lithium secondary battery, which is excellent in battery performance such as capacity, rate characteristics and cycle characteristics, has high safety, and is inexpensive. In particular, according to the present invention, it is possible to provide a positive electrode material that can be a lithium secondary battery having excellent output characteristics at low temperatures, cycle characteristics at high temperatures, and output characteristics at low temperatures, as compared with conventional methods. .

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Claims (11)

[Claims] 1. A positive electrode material for a lithium secondary battery, which contains a layered lithium nickel manganese composite oxide, further containing a spinel type lithium manganese composite oxide. 2. The positive electrode material for a lithium secondary battery according to claim 1, wherein the layered lithium nickel manganese composite oxide is represented by the following general formula (I). Embedded image Li _X Ni _Y Mn _Z Q _(1-YZ) O ₂ (I) (In the formula, X represents a number in the range of 0 <X ≦ 1.2. Y and Z are 0.7 ≦ Y. / Z ≦ 9, and 0 ≦ (1-Y−Z) ≦
It represents a number that satisfies the relationship of 0.5. Q is Al, Co, Fe
Represents at least one element selected from the group consisting of ) 3. The composition of the layered lithium nickel manganese composite oxide is represented by the above general formula (I), wherein Y and Z satisfy the relationship of 0.7 ≦ Y / Z ≦ 1.5. The positive electrode material for a lithium secondary battery according to claim 2, which is characterized in that. 4. The layered lithium nickel manganese composite oxide has a specific surface area of 3 m ² / g or more and 10 m ² / g or less,
The positive electrode material for a lithium secondary battery according to claim 3, wherein the average primary particle size is 0.01 μm or more and 10 μm or less. 5. The composition of the layered lithium nickel manganese composite oxide is represented by the above general formula (I), wherein Y and Z satisfy the relationship of 1.5 ≦ Y / Z ≦ 9. The positive electrode material for a lithium secondary battery according to claim 2. 6. The composition of the layered lithium nickel manganese composite oxide is represented by the above general formula (I), wherein Y and Z are Y ≧ 0.6, Y / Z ≦ 9, and (1- Y-Z) ≧
The positive electrode material for a lithium secondary battery according to claim 2, which satisfies the relationship of 0.075. 7. The layered lithium nickel manganese composite oxide has a specific surface area of 0.1 m ² / g or more and 10 m ² / g or less, and an average primary particle size of 0.01 μm or more and 10 μm or less. The positive electrode material for a lithium secondary battery according to. 8. The positive electrode material for a lithium secondary battery according to claim 1, wherein the spinel type lithium manganese composite oxide is represented by the following general formula (II). Embedded image Li _X2 Mn _(2-Y2) R _Y2 O ₄ (II) (In the formula, X2 represents a number in the range of 0 <X2 ≦ 1.2. Y
2 represents a number in the range of 0 ≦ Y ≦ 0.5. R is Al, F
e, Ga, Bi, Sn, V, Cr, Co, Ni, Cu,
It represents at least one element selected from the group consisting of Zn, Mg, Ti, Ge, Nb, Ta, Zr and Li. ) 9. When the content of the layered lithium nickel manganese composite oxide is A and the content of the spinel type lithium manganese composite oxide is B, 0.05 ≦ A /
The positive electrode material for a lithium secondary battery according to claim 1, wherein the relationship of (A + B) ≦ 0.95 (weight ratio) is satisfied. 10. A positive electrode for a lithium secondary battery, which uses the positive electrode material for a lithium secondary battery according to claim 1. 11. A lithium secondary battery comprising the positive electrode for a lithium secondary battery according to claim 10, a negative electrode, and an electrolyte.