JP2012181975A - Nonaqueous secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous secondary battery capable of exhibiting superior charge and discharge cycle characteristics even when being charged with high voltage.SOLUTION: The nonaqueous secondary battery comprises: a positive electrode; a negative electrode; and a nonaqueous electrolyte. The positive electrode contains a composite oxide as a cathode active material, which is expressed by the following formula (1): LiNiMMnO(1)[where M is at least one metal element except Ni, Mn, or Li and the formula satisfies 0.4≤x≤0.6 and 0≤y≤0.1]. A part or the whole of a surface of the composite oxide is covered with a material containing F. An atomic concentration ratio F/Mn on the surface of the composite oxide covered with the material containing F is 0.20-1.0.

Description

  The present invention relates to a non-aqueous secondary battery that can exhibit excellent charge / discharge cycle characteristics even when charged to a high voltage.

In recent years, with the development of portable electronic devices such as mobile phones and laptop computers, and the practical application of electric vehicles, secondary batteries with small size, light weight and high capacity have been required. Currently, as a high-capacity secondary battery that can meet this demand, a non-aqueous secondary battery (lithium ion secondary battery) that uses a lithium-containing composite oxide such as LiCoO ₂ as a positive electrode active material and a carbon-based material as a negative electrode active material. Secondary battery) has been commercialized. And with the further development of the application apparatus of a non-aqueous secondary battery, for example, further higher capacity and higher energy density of a non-aqueous secondary battery are required.

As one method for increasing the energy density of a battery, it is conceivable to use a positive electrode active material that can operate at a high potential. Currently, lithium cobalt oxide having a higher end voltage and spinel type lithium manganese oxide of high potential operation type are being studied. Among the latter, the general formula _{LiNi x M y Mn 2-x} -y O 4 (M is at least one transition metal element other than Ni and Mn, 0.4 ≦ x ≦ 0.6,0 ≦ It has been confirmed that the lithium-containing composite oxide represented by y ≦ 0.1) can operate at a potential of 4.5 V or more on the basis of lithium (Patent Document 1, etc.).

However, if a general formula _{LiNi x M y Mn 2-x} -y O wherein the lithium-containing composite oxide represented by ₄ to constitute a battery using the positive electrode active material, as described above, 4.5V based on lithium Since the battery is charged and used at the above high voltage, there is a problem that the non-aqueous electrolyte undergoes an oxidative decomposition reaction on the surface of the positive electrode active material, and the charge / discharge cycle characteristics of the battery deteriorate.

In addition, as a technique for solving such a problem, for example, there is also a proposal of a method of replacing a part of O in LiNi _x M _y Mn _2-xy O ₄ with F (Non-patent Document 2).

JP-A-9-147867

G. Du, Y. et al. Nu Li, J.M. Yung, J. et al. Wang, Mater. Res. Bull. 2008, vol. 43, p. 3607

  However, in the method described in Non-Patent Document 2, although the charge / discharge cycle characteristics of the battery are improved, the transition metal combined with F in the positive electrode active material cannot contribute to charge / discharge. There is a problem that the discharge capacity decreases.

  This invention is made | formed in view of the said situation, The objective is to provide the non-aqueous secondary battery which can exhibit the charging / discharging cycling characteristics excellent even if it charged to high voltage.

The non-aqueous secondary battery of the present invention that has achieved the above object is a non-aqueous secondary battery having a positive electrode, a negative electrode, and a non-aqueous electrolyte. The positive electrode is represented by the following general formula (1) as a positive electrode active material.
_{LiNi x M y Mn 2-x} -y O 4 (1)
[In the general formula (1), M is at least one metal element other than Ni, Mn, and Li, and 0.4 ≦ x ≦ 0.6 and 0 ≦ y ≦ 0.1]
The composite oxide represented by the above, wherein a part or all of the surface of the composite oxide is coated with a material containing F, and the composite oxide is coated with the material containing F The atomic concentration ratio F / Mn between F and Mn on the surface of the object is 0.20 to 1.0.

  According to the present invention, it is possible to provide a non-aqueous secondary battery that can exhibit excellent charge / discharge cycle characteristics even when charged to a high voltage.

LiNi _0.5 Mn _1.5 O ₄ coated with a material containing F used for the non-aqueous secondary battery of Example 3 and LiNi _0.5 Mn used for the non-aqueous secondary battery of Comparative Example 1 It is an XPS spectrum (F1s) of _1.5 O ₄ .

  The positive electrode according to the nonaqueous secondary battery of the present invention has, for example, a structure having a positive electrode mixture layer containing a positive electrode active material, a conductive additive and a binder on one side or both sides of a current collector.

  As the positive electrode active material, a composite oxide represented by the general formula (1) is used. Since this composite oxide can operate at a potential of 4.5 V or more on the basis of lithium, a non-aqueous secondary battery that can be charged at a high voltage of 4.5 V or more on the basis of lithium by using this composite oxide Can be configured. Therefore, it is possible to increase the energy density of the non-aqueous secondary battery.

  In the composite oxide represented by the general formula (1), Ni, Mn, and M (at least one metal element other than Ni, Mn, and Li) are present as positive ions, and O is present as a negative ion. They are connected by ionic bonds to form an oxide crystal lattice called a spinel structure. In order to maintain the skeleton of the spinel structure, the ratio of the total number of Ni atoms, Mn atoms and M atoms to the number of O atoms needs to be around 2: 4.

  In the composite oxide represented by the general formula (1), Mn functions as a main positive ion for maintaining the skeleton of the spinel structure. In the general formula (1) representing the composite oxide, the amount of Mn needs to be “2-xy” in order to balance with the number 4 of O atoms.

  In the composite oxide, Ni is a component that contributes to the improvement of the charge / discharge voltage while maintaining the spinel structure. In the general formula (1) representing the composite oxide, by setting the amount x of Ni to 0.4 or more, it can function even at a high voltage of 4.5 V or more on the basis of lithium. However, if the amount of Ni in the composite oxide is too large, the charge / discharge capacity decreases. Therefore, in the general formula (1) representing the composite oxide, the amount x of Ni is 0.6 or less. .

  Furthermore, in the composite oxide represented by the general formula (1), the crystal structure can be further stabilized by containing a small amount of metal element M other than Ni, Mn and Li in the crystal lattice. . The metal element M is preferably, for example, Cr, Fe, Co, Cu, Zn, Ti, Al, Mg, Ca, Ba, etc. Among these, Fe and Co make the composite oxide have better characteristics. More preferably.

  The composite oxide represented by the general formula (1) may not contain the metal element M, but when the metal element M is contained, the general formula (1) representing the composite oxide. The amount y of the metal element M is 0.6 or less.

  In the positive electrode according to the non-aqueous secondary battery of the present invention, a part or all of the surface of the composite oxide represented by the general formula (1) is covered with a material containing F.

  Since the positive electrode containing the composite oxide has a high voltage of 4.5 V or more during charging, an oxidative decomposition reaction of the non-aqueous electrolyte occurs on the composite oxide surface. At that time, it is considered that the atoms of the composite oxide play a catalytic role and promote the oxidative decomposition of the organic solvent and the electrolyte constituting the nonaqueous electrolytic solution. In the non-aqueous secondary battery of the present invention, since the surface of the composite oxide that is in contact with the non-aqueous electrolyte is coated with a material containing F, direct contact between the atoms of the composite oxide and the non-aqueous electrolyte is possible. Since the contact is reduced and the F-containing material is not easily oxidized and exists as a robust film, the decomposition reaction of the non-aqueous electrolyte can be effectively suppressed.

  In the composite oxide represented by the general formula (1) whose surface is coated with a material containing F, the atomic concentration ratio F / Mn between F and Mn on the surface is coated with the material containing F. From the viewpoint of improving the above-described effect, the value is 0.20 or more. However, if the atomic concentration ratio F / Mn is too large, resistance to insertion of Li ions into the composite oxide and desorption of Li ions from the composite oxide may increase, and battery characteristics may deteriorate. There is. Therefore, the atomic concentration ratio F / Mn is 1.0 or less.

  In addition, the atomic concentration ratio F / Mn of F and Mn on the surface of the composite oxide represented by the general formula (1) whose surface is covered with a material containing F as used in this specification is described in the examples. It is a value measured by the described method.

  The composite oxide represented by the general formula (1) may be covered entirely with the material containing F, or only part of the surface may be covered. It is desirable to adjust the region of the surface of the composite oxide that is covered with the material containing F within a range where the atomic concentration ratio F / Mn satisfies the above preferable value.

  In the surface of the composite oxide represented by the general formula (1) and coated with the material containing F, it is preferable that F atoms are chemically bonded to metal atoms of the composite oxide. Since the metal atom and the F atom are chemically bonded, F is firmly fixed on the surface of the composite oxide. Therefore, even when the battery is repeatedly charged and discharged, the contact between the composite oxide and the non-aqueous electrolyte is performed. Since the effect of preventing the battery persists better, the effect of suppressing the decomposition of the non-aqueous electrolyte and improving the charge / discharge cycle characteristics of the battery is further improved.

  In the nonaqueous secondary battery of the present invention, F exists only in the vicinity of the surface of the composite oxide, and hardly exists in the composite oxide mainly responsible for charge / discharge reactions. Therefore, there is almost no decrease in the charge / discharge capacity of the battery due to metal bonding between the F atoms and the metal atoms of the composite oxide.

  The fact that F atoms and metal atoms are bonded on the surface of the composite oxide can be confirmed by the method described in Examples described later.

  Examples of the method of coating part or all of the surface of the composite oxide represented by the general formula (1) with a material containing F include the following methods (A) and (B).

(A) The composite oxide represented by the general formula (1) is heated in an atmosphere containing fluorine gas. As a result, a material containing F derived from fluorine gas is deposited on the composite oxide and covers the surface thereof.

  The atmosphere for heating the composite oxide may contain only fluorine gas, or may contain fluorine gas and other gases (for example, argon gas, helium gas, neon gas, etc.). When the composite oxide is heated in an atmosphere containing fluorine gas and other gas, the ratio of fluorine gas in 100% by volume of fluorine gas and other gas is preferably 5% by volume or more. .

  When heating the composite oxide, it is preferable that the heating temperature is 150 to 250 ° C. and the heating time is 1 to 5 hours.

  Specific implementation means of the method (A) is not particularly limited. For example, the composite oxide is placed in a heating reaction furnace that can be evacuated, and fluorine gas or fluorine gas is evacuated in the furnace after evacuation. It is possible to employ a means for introducing a mixed gas of the gas and other gas and heating the composite oxide by raising the temperature in the furnace in this state.

(B) The composite oxide represented by the general formula (1) and the fluoride serving as the material of the material containing F are heated while being mixed and stirred. That is, the method (B) is a method of surface-treating the composite oxide using a fluoride, whereby a material containing the fluoride or F derived from the fluoride is treated with the composite oxide. Adhere to the surface.

  Examples of the fluoride used in the method (B) include hexafluoropropene trimer. In addition, a fluoroalkyl radical generated by fluorinating the above fluoride (for example, a perfluoroalkyl radical obtained by fluorinating hexafluoropropylene trimer with fluorine gas) may be used. When an alkyl radical is used, it is more preferable because the radical is highly reactive and can be treated at a relatively low temperature at which damage inside the composite oxide hardly occurs.

  When carrying out the method (B), for example, it is preferable to heat the composite oxide and fluoride (including a fluoroalkyl radical) in a state dissolved in a solvent. Examples of the solvent include fluorine-based organic solvents [“Fluorinert (trade name)” manufactured by 3M, etc.]. Moreover, it is preferable that heating conditions in this case shall be heating temperature 80-150 degreeC, and heating time shall be 1 to 5 hours.

  In order to bond F atoms and metal atoms in the composite oxide on the surface of the composite oxide, for example, the surface of the composite oxide is made of a material containing F by the method (B). It is preferable to coat.

For the positive electrode active material according to the nonaqueous secondary battery of the present invention, only the composite oxide represented by the general formula (1) may be used, and the composite oxide and other positive electrode active materials are used. You may use together. Other positive electrode active materials that can be used in combination with the composite oxide represented by the general formula (1) include, for example, LiCoO ₂ ; a part of Co in LiCoO ₂ , other Ti, Zr, Mg, Al, and the like. And lithium-containing composite oxide substituted with a metal element. These other positive electrode active materials may be used as they are, and in the same manner as the composite oxide represented by the general formula (1), a part or all of the surface thereof is coated with a material containing F. May be used.

  When the composite oxide represented by the general formula (1) and another positive electrode active material are used in combination with the positive electrode active material, the composite oxide represented by the general formula (1) For example, the amount in the total positive electrode active material is preferably 50% by mass or more, and more preferably 80% by mass or more.

  As a normal non-aqueous secondary battery, the conductive additive for the positive electrode is non-crystalline such as graphite; carbon black (acetylene black, ketjen black, etc.) or a carbon material with amorphous carbon formed on the surface. Carbonaceous materials (fibre-grown carbon fibers, carbon fibers obtained by carbonizing after spinning a pitch), carbon nanotubes (various multi-layer or single-wall carbon nanotubes), and the like can be used. As the conductive additive for the positive electrode, those exemplified above may be used alone or in combination of two or more.

  As the binder for the positive electrode, fluororesins such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene; polyacrylic acid; styrene butadiene rubber; and the like can be used.

  In the positive electrode mixture layer according to the positive electrode of the present invention, for example, the positive electrode active material is preferably 70 to 99% by mass, the conductive auxiliary agent is 1 to 20% by mass, and the binder is preferably 1 to 30% by mass. Moreover, it is preferable that the thickness of a positive mix layer is 1-100 micrometers per single side | surface of a collector.

  For the positive electrode current collector, for example, a foil made of aluminum, stainless steel, nickel, titanium, or an alloy thereof, a punched metal, an expanded metal, a net, or the like can be used. Usually, an aluminum foil having a thickness of 10 to 30 μm is used. Are preferably used.

  The non-aqueous secondary battery of the present invention has a positive electrode, a negative electrode, and a non-aqueous electrolyte, and the positive electrode only needs to be the positive electrode described above. Other configurations and structures are conventionally known non-aqueous The configuration and structure employed in the secondary battery can be applied.

  A negative electrode having a structure in which a negative electrode mixture layer containing a negative electrode active material, a binder and the like is provided on one side or both sides of a current collector can be used.

  The negative electrode active material may be any material that can insert and desorb Li ions. For example, graphite, pyrolytic carbons, cokes, glassy carbon, a fired body of an organic polymer compound, mesocarbon microbeads, carbon Examples thereof include carbonaceous materials such as fibers and activated carbon. Moreover, lithium or a lithium-containing compound can also be used as the negative electrode active material. Examples of the lithium-containing compound include tin oxide, silicon oxide, nickel-silicon alloy, magnesium-silicon alloy, tungsten oxide, lithium iron composite oxide, lithium-aluminum, and lithium-lead. Lithium alloys such as lithium-indium, lithium-gallium, and lithium-indium-gallium. Some of these exemplary negative electrode active materials do not contain lithium at the time of manufacture, but are in a state containing lithium at the time of charging.

  Although there is no restriction | limiting in particular about the manufacturing method of a negative electrode, For example, the said negative electrode active material, the conductive support agent (same as the case of a positive electrode) added as needed, and the binder similar to the case of the said positive electrode To prepare a negative electrode mixture, which is dispersed in a solvent to prepare a negative electrode mixture-containing composition (slurry, paste, etc.) (the binder is dissolved or dispersed in a solvent in advance) The negative electrode mixture-containing composition may be applied to the surface of the current collector, dried to form a negative electrode mixture layer, and compression-molded as necessary. In addition, when using lithium or lithium alloy as the negative electrode active material, these foils can be used as they are for the negative electrode, or these foils can be attached to one or both sides of the current collector as a negative electrode agent layer. A negative electrode can be manufactured.

  In the case of the negative electrode having the negative electrode mixture layer, in the negative electrode mixture layer, for example, the negative electrode active material is preferably 70 to 99% by mass, and the polymer binder is preferably 1 to 30% by mass. Moreover, when using a conductive support agent, it is preferable that the quantity of the conductive support agent in a negative mix layer is 1-20 mass%. Furthermore, the thickness of the negative electrode agent layer (including the negative electrode mixture layer) is preferably 1 to 100 μm per one side of the current collector.

  The negative electrode current collector may be, for example, a foil, punched metal, expanded metal, net, or the like made of copper, stainless steel, nickel, titanium, or an alloy thereof. Usually, copper having a thickness of 5 to 30 μm is used. A foil is preferably used.

  The positive electrode of the present invention and the negative electrode are used, for example, in the form of a laminated electrode body laminated with a separator interposed therebetween, or a wound electrode body obtained by winding the separator in a spiral shape.

  As the separator, it is preferable that the separator has sufficient strength and can hold a large amount of the electrolytic solution. From such a viewpoint, a polyethylene, polypropylene, or ethylene-propylene copolymer having a thickness of 10 to 50 μm and an aperture ratio of 30 to 70% is used. A microporous film or a nonwoven fabric containing a polymer is preferable.

  As the non-aqueous electrolyte used in the non-aqueous secondary battery of the present invention, a non-aqueous liquid electrolyte (hereinafter referred to as “electrolytic solution”) is usually used. As the electrolytic solution, a solution obtained by dissolving an electrolyte salt such as a lithium salt in an organic solvent is used. The organic solvent is not particularly limited. For example, chain esters such as dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and methyl propyl carbonate; dielectrics such as ethylene carbonate, propylene carbonate, butylene carbonate, and vinylene carbonate. A cyclic ester having a high rate; a mixed solvent of a chain ester and a cyclic ester; and the like. Particularly, a mixed solvent with a cyclic ester having a chain ester as a main solvent is suitable.

As the electrolyte salt to be dissolved in the organic solvent when preparing the electrolytic solution, for _{example, 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 , LiC _n F _{2n + 1} SO ₃ (n ≧ 2), LiN (RfSO ₂ ) (Rf′SO ₂ ), LiC (RfSO ₂ ) ₃ , LiN (RfOSO ₂ ) ₂ [where Rf , Rf ′ is a fluoroalkyl group] or the like may be used alone or in combination. The concentration of the electrolyte salt in the electrolytic solution is not particularly limited, but is preferably 0.3 mol / l or more, more preferably 0.4 mol / l or more, and 1.7 mol / l. It is preferably 1 or less, and more preferably 1.5 mol / l or less.

  In the battery of the present invention, as the non-aqueous electrolyte, in addition to the electrolyte solution, a gel electrolyte obtained by gelling the electrolyte solution with a gelling agent made of a polymer or a solid electrolyte can be used. As such a solid electrolyte, in addition to an inorganic electrolyte, an organic electrolyte can also be used.

  Moreover, as a form of the battery of this invention, the cylinder shape (square cylinder shape, cylindrical shape, etc.) etc. which used a steel can, an aluminum can, etc. as an exterior can are mentioned. Moreover, it can also be set as the soft package battery which used the laminated film which vapor-deposited the metal as an exterior body.

  The nonaqueous secondary battery of the present invention can exhibit excellent charge / discharge cycle characteristics even when high voltage charging is performed. The battery of the present invention makes use of such characteristics, and uses it as a power source for various devices such as electronic devices (especially portable electronic devices such as mobile phones and laptop computers), power supply systems, vehicles (electric cars, electric bicycles, etc.). For example, it can be preferably used.

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

Example 1
<Preparation of positive electrode>
A positive electrode active material LiNi _0.5 Mn _1.5 O ₄ (average particle size 5 μm) was placed in a heating reactor and evacuated to a fluorine gas diluted with argon gas (fluorine gas in all gases). The concentration was 20 vol%) at a flow rate of 5 ml / min, and the furnace was heated at 200 ° C. for 2 hours while maintaining the normal pressure. Thereby, the surface of LiNi _0.5 Mn _1.5 O ₄ was coated with a material derived from fluorine gas (a material containing F).

LiNi _0.5 Mn _1.5 O ₄ coated with a material containing F: 80 parts by mass, conductive auxiliary agent (acetylene black): 15 parts by mass, PVDF (binder): 5 parts by mass Were mixed to make a positive electrode mixture, which was dispersed in N-methyl-2-pyrrolidone (NMP) to prepare a positive electrode mixture-containing paste. This positive electrode mixture-containing paste was applied to one side of a current collector made of an aluminum foil having a thickness of 15 μm and dried at 85 ° C. to form a positive electrode mixture layer. The sheet-like material after the formation of the positive electrode mixture layer was cut into a 10 cm-wide square and compressed with a roll press machine at a linear pressure of 100 kgf. The sheet-like material after compression was dried at 120 ° C. to evaporate the residual solvent in the positive electrode mixture layer to obtain a sheet-like positive electrode. This sheet-like positive electrode was punched into a circular shape of φ13 mm to obtain a positive electrode for a test battery. In the positive electrode obtained, the thickness of the positive electrode mixture layer was 35 μm.

<Battery assembly>
The battery was assembled in an argon glove box. As the negative electrode, a Li metal electrode obtained by punching a Li foil into a circle having a diameter of 14 mm was used. A porous polyethylene film was used for the separator. A “HS flat cell” manufactured by Hosen Co., Ltd. was used as the battery outer package, and after the stacked body in which the positive electrode, the separator, and the negative electrode were stacked in this order was accommodated in the outer package, 200 μl of electrolyte was injected. As the electrolytic solution, a solution in which LiPF ₆ was dissolved at a concentration of 1.5 mol / l in a mixed solvent of ethylene carbonate and diethyl carbonate in a volume ratio of 1: 3 was used. After the electrolyte solution was injected, the outer package was sealed to obtain a non-aqueous secondary battery.

Example 2
Except for changing the heating time of _LiNi 0.5 _Mn 1.5 _{O 4} in the heating reactor which was introduced fluorine gas diluted with argon gas to 20 minutes, in the same manner as in Example 1 _LiNi 0.5 Mn The surface of _1.5 O ₄ was coated with a material derived from fluorine gas (a material containing F).

A positive electrode was produced in the same manner as in Example 1 except that LiNi _0.5 Mn _1.5 O ₄ coated with the material containing F was used as a positive electrode active material, and this positive electrode was used. Produced a non-aqueous secondary battery in the same manner as in Example 1.

Example 3
A commercially available hexafluoropropene trimer was fluorinated at room temperature according to the following reaction formula to synthesize a perfluoroalkyl radical. This perfluoroalkyl radical is chemically stable because the unpaired electron is located at the center of the molecule, and at this point it is poorly reactive.

Next, the perfluoroalkyl radical was dissolved in a fluorine-based organic solvent [“Fluorinert FC-3283 (trade name)” manufactured by 3 companies] at a concentration of 0.5 mol / l. 50 ml of this solution and 2 g of the same LiNi _0.5 Mn _1.5 O ₄ powder (average particle size 5 μm) used in Example 1 were placed in an ampule and sealed, and then at 100 ° C. for 3 hours. And heated with stirring.

By this treatment, the perfluoroalkyl radical is cleaved to release a trifluoromethyl radical. This trifluoromethyl radical is chemically active and reacts with LiNi _0.5 Mn _1.5 O ₄ to deposit a material containing F derived from the trifluoromethyl radical on its surface _. The surface of ₅ Mn _1.5 O ₄ is coated with a material containing F. At that time, since the F atom has a strong electron-withdrawing property and tends to be a negative ion, it is replaced with O bonded to the metal ion on the surface of the LiNi _0.5 Mn _1.5 O ₄ powder. , F-metal atom bonds are formed.

A positive electrode was produced in the same manner as in Example 1 except that LiNi _0.5 Mn _1.5 O ₄ coated with the material containing F was used as a positive electrode active material, and this positive electrode was used. Produced a non-aqueous secondary battery in the same manner as in Example 1.

Comparative Example 1
A positive electrode was produced in the same manner as in Example 1 except that LiNi _0.5 Mn _1.5 O ₄ was used as a positive electrode active material without covering the surface with a material containing F. A nonaqueous secondary battery was produced in the same manner as in Example 1 except that.

Comparative Example 2
Except for changing the heating time of _LiNi 0.5 _Mn 1.5 _{O 4} in the heating reactor which was introduced fluorine gas diluted with argon gas to 10 minutes, in the same manner as in Example 1 _LiNi 0.5 Mn The surface of _1.5 O ₄ was coated with a material derived from fluorine gas (a material containing F).

A positive electrode was produced in the same manner as in Example 1 except that LiNi _0.5 Mn _1.5 O ₄ coated with the material containing F was used as a positive electrode active material, and this positive electrode was used. Produced a non-aqueous secondary battery in the same manner as in Example 1.

Comparative Example 3
Except for changing the heating time of _LiNi 0.5 _Mn 1.5 _{O 4} in the heating reactor which was introduced fluorine gas diluted with argon gas to 5 hours, in the same manner as in Example 1 _LiNi 0.5 Mn The surface of _1.5 O ₄ was coated with a material derived from fluorine gas (a material containing F).

A positive electrode was produced in the same manner as in Example 1 except that LiNi _0.5 Mn _1.5 O ₄ coated with the material containing F was used as a positive electrode active material, and this positive electrode was used. Produced a non-aqueous secondary battery in the same manner as in Example 1.

LiNi _0.5 Mn _1.5 O ₄ coated with a material containing F used in the non-aqueous secondary batteries of Examples 1 to 3 and Comparative Examples 2 and 3, and LiNi used for the battery of Comparative Example 1 The surface composition and chemical bonding state of _0.5 Mn _1.5 O ₄ were analyzed by the following method, and the charge / discharge characteristics of the nonaqueous secondary batteries of Examples 1 to 3 and Comparative Examples 1 to 3 were as follows: The method was evaluated.

<Analysis of surface composition and chemical bonding state>
LiNi _0.5 Mn _1.5 O ₄ coated with a material containing F used in the non-aqueous secondary batteries of Examples 1 to 3 and Comparative Examples 2 and 3, and the non-aqueous secondary battery of Comparative Example 1 The surface composition and chemical bonding state of LiNi _0.5 Mn _1.5 O ₄ used in the above were analyzed using X-ray photoelectron spectroscopy (XPS).

  For the XPS analysis, an X-ray photoelectron spectrometer (“ESCA5500MC” manufactured by ULVAC-PHI) was used, and each sample powder was analyzed by being bonded and fixed to a sample table with a carbon double-sided tape for vacuum. The analysis aperture diameter was φ800 μm, the X-ray source was AlKα400 W (15 kV), and the photoelectron extraction angle was 45 degrees. The atomic concentration ratio F / Mn was calculated from the spectral intensities of Mn and F detected under these analysis conditions. Moreover, the chemical bond state of F atom was analyzed from the XPS spectrum shape of F1s.

<Charge / discharge characteristics evaluation>
The initial charge / discharge characteristics of the non-aqueous secondary batteries of Examples and Comparative Examples were evaluated. Under a 23 ° C. environment, each battery was charged with a constant current of 0.1 C until the battery voltage of the battery reached 4.9 V, and then discharged with a constant current of 0.1 C until the battery voltage reached 3.0 V. This series of operations was repeated as one cycle, and the charge / discharge characteristics up to three cycles were measured, and the charge / discharge characteristics at the third cycle were defined as initial charge / discharge characteristics.

  Next, the charge / discharge cycle characteristics of the non-aqueous secondary batteries of Examples and Comparative Examples were evaluated. The charge / discharge cycle characteristics were evaluated at a high temperature of 60 ° C. in order to accelerate and evaluate in a severer environment than at room temperature. Each battery installed in a constant temperature room maintained at 60 ° C. is charged with a constant current of 0.1 C until the battery voltage reaches 4.9 V, and then the battery voltage becomes 3.0 V with a constant current of 0.1 C. Discharged until. This series of operations was repeated as one cycle, and charge / discharge characteristics up to 30 cycles were evaluated. Then, from the discharge capacity at 30th cycle (capacity per 1 g of the positive electrode active material) and the initial discharge capacity (capacity per 1 g of the positive electrode active material), the discharge capacity retention rate [= 100 × (60 ° C./30th cycle discharge). Capacity) / (discharge capacity at the third cycle at 23 ° C.)].

  The results are shown in Table 1.

The “F / Mn ratio” in Table 1 is the LiNi _0.5 Mn coated with the material containing F used in these non-aqueous secondary batteries in Examples 1 to 3 and Comparative Examples 2 and 3. The atomic concentration ratio F / Mn on the surface of _1.5 O _{4. In} Comparative Example 1, the atomic concentration ratio F / Mn on the surface of LiNi _0.5 Mn _1.5 O ₄ used in the non-aqueous secondary battery. It is.

As shown in Table 1, an example in which the surface of LiNi _0.5 Mn _1.5 O ₄ was coated with a material containing F and the atomic concentration ratio F / Mn was an appropriate value was used as a positive electrode active material The non-aqueous secondary batteries 1 to 3 have an initial discharge capacity of 133 to 135 mAh / g. This value corresponds to 89.9 to 91.2% with respect to the theoretical discharge capacity (148 mAh / g) of LiNi _0.5 Mn _1.5 O ₄ . Therefore, it can be said that the batteries of Examples 1 to 3 have a high capacity close to the theoretical limit. In addition, the batteries of Examples 1 to 3 have a high discharge capacity retention rate of 87.4 to 92.0% after 60 ° C. and 30 cycles, and have good charge / discharge cycle characteristics.

Comparative In contrast, the battery of Comparative Example 1 that the _LiNi 0.5 _Mn 1.5 _{O 4} that no surface coating was the positive electrode active material, and that those atomic concentration ratio F / Mn is too small and the positive electrode active material The battery of Example 2 has relatively high initial discharge capacities of 132 mAh / g and 130 mAh / g, but has low discharge capacity retention rates of 65.9% and 74.8%, and is inferior in charge / discharge cycle characteristics. In addition, the battery of Comparative Example 3 using a positive electrode active material having an atomic concentration ratio F / Mn that is too large has a low initial discharge capacity of 115 mAh / g.

FIG. 1 shows LiNi _0.5 Mn _1.5 O ₄ coated with a material containing F used in the non-aqueous secondary battery of Example 3, and LiNi ₀ used in the non-aqueous secondary battery of Comparative Example 1. _.5 shows the XPS spectrum (F1s) of Mn _1.5 O ₄ . From the XPS spectrum according to Example 3, in addition to the peak derived from the F—C bond near 687.5 eV, a strong peak derived from the F—metal bond near 684.5 eV is observed. _Therefore, significant percentage of the F present in LiNi _{0.5 Mn} 1.5 _{O 4 surface,} it can be seen that bonded to a metal atom of LiNi _{0.5 Mn} 1.5 _{O 4.}

Claims (4)

A non-aqueous secondary battery having a positive electrode, a negative electrode and a non-aqueous electrolyte,
The positive electrode has the following general formula (1) as a positive electrode active material.
_{LiNi x M y Mn 2-x} -y O 4 (1)
[In the general formula (1), M is at least one metal element other than Ni, Mn, and Li, and 0.4 ≦ x ≦ 0.6 and 0 ≦ y ≦ 0.1]
Containing a complex oxide represented by
Part or all of the surface of the composite oxide is coated with a material containing F;
A non-aqueous secondary battery, wherein an atomic concentration ratio F / Mn between F and Mn on the surface of the composite oxide coated with the material containing F is 0.20 to 1.0.   2. The non-reactor according to claim 1, wherein F atoms are chemically bonded to metal atoms of the composite oxide on the surface of the composite oxide represented by the general formula (1) and coated with a material containing F. 3. Water secondary battery.   The composite oxide represented by the general formula (1) is heated in an atmosphere containing a fluorine gas to coat the surface of the composite oxide with a material containing F. Non-aqueous secondary battery. The composite oxide represented by the general formula (1) is surface-treated with a fluoroalkyl radical, so that the surface of the composite oxide is coated with a material containing F. Non-aqueous secondary battery.

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