JP2002015738A - Nonaqueous electrolyte secondary cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary cell which has less lowering of a discharging capacity when charge and discharge is repeated at temperature exceeding room temperature. SOLUTION: In a nonaqueous electrolyte cell equipped with a positive electrode containing a positive active material, a negative electrode, and a nonaqueous electrolyte, the positive active material consists of active material particles whose composition is given by LixMyM'zO2-wFw, and a protective layer which is formed on at least one part of a surface of the active material particles, and whose composition is given by Me1+aMn2-aO4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a non-aqueous electrolyte secondary battery having an improved positive electrode active material.

[0002]

2. Description of the Related Art In recent years, along with the development of portable information terminals that have become very popular, research and development of lithium ion secondary batteries, which are examples of non-aqueous electrolyte secondary batteries serving as power sources, have been actively conducted and put into practical use. ing. As a lithium ion secondary battery, a lithium ion secondary battery including a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and a nonaqueous electrolyte impregnated in the separator is known.

On the other hand, power supplies for electric vehicles and electric tools,
For new applications such as distributed power storage, research and development on large-sized lithium-ion secondary batteries capable of extracting a larger capacity and a larger current than before has been started. One of the problems in developing such a large lithium ion secondary battery is its temperature characteristics.
That is, in mounting the large-sized lithium ion secondary battery, the large-sized lithium ion secondary battery is arranged in a place close to a heat generating portion such as an internal combustion engine or a power motor, and is likely to be used at a high temperature for a long time. However, when a large-sized lithium-ion secondary battery is manufactured using materials for a lithium-ion secondary battery that has been conventionally developed, and charging and discharging are repeated under the temperature conditions expected when the battery is mounted, the capacity decreases ( (Cycle capacity deterioration).

The reason why a long life cannot be obtained at a high temperature is that a lithium composite oxide (eg, LiCoO ₂
And the non-aqueous electrolyte react with each other to form an inactive layer on the surface of the positive electrode active material, and this inactive layer is considered to inhibit the occlusion and release of lithium in the positive electrode active material. I have. For this reason, attempts have been made to coat the surface of the positive electrode active material with a layered material so that the positive electrode active material and the nonaqueous electrolyte do not come into direct contact.

[0005] However, even if the surface of the positive electrode active material is coated with this layered material to avoid contact between the positive electrode active material and the non-aqueous electrolyte, a lithium-ion secondary battery having a long life under a high temperature environment can be obtained. Was difficult.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a non-aqueous electrolyte secondary battery in which the discharge capacity is less reduced even when charge and discharge are repeated at a temperature exceeding room temperature.

[0007]

A nonaqueous electrolyte secondary battery according to the present invention is a nonaqueous electrolyte secondary battery comprising a positive electrode containing a positive electrode active material, a negative electrode, and a nonaqueous electrolyte. active material, composition of _{Li x M y M 'z O} 2-w F w ( where the M is one or more elements selected Mn, Fe, from the group consisting of Co and Ni, wherein M' is Ti,
V, Cr, Cu, Mg, Al, Si, P, S, Ga, G
one or more elements selected from the group consisting of e and Nb, and the molar ratios x, y, z and w are 0 <x ≦ 1, 0 <y ≦
1, 0 ≦ z ≦ 1, 0 ≦ w ≦ 0.3) and at least a part of the surface of the active material particles, and has a composition of Me _{1 + a} Mn _{2−. a} O ₄ (provided that said Me is Co, more than one kind of element selected from the group consisting of Ni and Cu, the molar ratio a shows a 0 ≦ a ≦ 1) to include a protective layer represented by It is a feature.

[0008] A non-aqueous electrolyte secondary battery according to the present invention is a non-aqueous electrolyte secondary battery comprising a positive electrode containing a positive electrode active material, a negative electrode, and a non-aqueous electrolyte.
The composition is Li _{0.5 + α} Mn _1-α-β T _β O ₂ (however,
Are Fe, Co, Ni, Ti, V, Cr, Cu, Mg,
At least one element selected from the group consisting of Al, Si, P, S, Ga, Ge and Nb, and the molar ratios α and β satisfy 0 <α ≦ 0.05 and 0 ≦ β ≦ 0.1, respectively. And a composition formed on at least a part of the surface of the active material particles and having a composition of Me _{1 + a} Mn _2-a O ₄ (where Me is a group consisting of Co, Ni and Cu). And a protective layer represented by the following formula: wherein the molar ratio a represents 0 ≦ a ≦ 1).

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION A non-aqueous electrolyte secondary battery according to the present invention includes a positive electrode containing a positive electrode active material, a negative electrode, and a non-aqueous electrolyte. The positive active material, the composition is Li _x M _y M _'z O
_2-w F _w (where M is at least one element selected from the group consisting of Mn, Fe, Co and Ni, and M ′
Are Ti, V, Cr, Cu, Mg, Al, Si, P, S,
At least one element selected from the group consisting of Ga, Ge and Nb, wherein the molar ratios x, y, z and w are 0 <x ≦ 1,
0 <y ≦ 1, 0 ≦ z ≦ 1, and 0 ≦ w ≦ 0.3), and at least a part of the surface of the active material particles, and has a composition of Me _{1+ a} Mn _2-a O
₄ (where Me is one or more elements selected from the group consisting of Co, Ni and Cu, and the molar ratio a is 0 ≦ a
≤ 1).

As the non-aqueous electrolyte, for example, a liquid non-aqueous electrolyte (non-aqueous electrolyte) prepared by dissolving an electrolyte in a non-aqueous solvent, and a non-aqueous solvent and an electrolyte are held in a polymer material. Polymer gel nonaqueous electrolytes and the like can be mentioned. As the non-aqueous solvent and the electrolyte contained in each non-aqueous electrolyte, those described in a liquid non-aqueous electrolyte described later can be used.

As the polymer material contained in the gelled nonaqueous electrolyte, for example, polyacrylonitrile, polyacrylate, polyvinylidene fluoride (PVdF), polyethylene oxide (PEO), or acrylonitrile, acrylate, vinylidene fluoride or ethylene oxide can be used. Examples of the polymer include monomers.

Hereinafter, an example of the non-aqueous electrolyte secondary battery according to the present invention will be described.

This non-aqueous electrolyte secondary battery comprises a positive electrode containing the positive electrode active material, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and a liquid non-aqueous electrolyte impregnated in the separator. Have.

The positive electrode, separator, negative electrode and liquid non-aqueous electrolyte will be described in detail.

1) Positive electrode This positive electrode has a current collector and a positive electrode layer supported on the current collector and containing a positive electrode active material.

[0016] The composition of the active material particles constituting the positive active material is represented by _{Li x M y M 'z O} 2-w F w. Here, M is one or more elements selected from the group consisting of Mn, Fe, Co and Ni, and M ′ is Ti, V, C
At least one element selected from the group consisting of r, Cu, Mg, Al, Si, P, S, Ga, Ge and Nb.
The molar ratios x, y, z and w are 0 <x ≦ 1, 0 <y ≦ 1,
0 ≦ z ≦ 1, 0 ≦ w ≦ 0.3, respectively.

In the active material particles, M is preferably Mn. Further, among the above M ′, preferred are Mg and Al. On the other hand, more preferable ranges of the molar ratios x, y, z and w are respectively 0.5 ≦ x ≦
1, 0.5 ≦ y ≦ 1, and 0 ≦ z ≦ 0.3.

The composition of the active material particles is Li _{0.5 + α} Mn
_1-α-β T _β O ₂ (where T is Fe, Co, Ni,
Ti, V, Cr, Cu, Mg, Al, Si, P, S, G
at least one element selected from the group consisting of a, Ge, and Nb, wherein the molar ratios α and β are 0 <α ≦ 0.05, 0 ≦
β ≦ 0.1) are preferred.

The composition of the protective layer formed on at least a part of the surface of the active material particles is represented by Me _{1+ a} Mn _2-a O ₄ . Here, Me is at least one element selected from the group consisting of Co, Ni and Cu. The molar ratio a is 0
≤a≤1. If the molar ratio a is out of the above range, the crystal structure of the oxide and the crystal structure of the active material are significantly different.
The adhesion between the protective layer and the active material particles decreases, and it becomes difficult to improve the cycle life at high temperatures. A more preferable range of the molar ratio a is 0 ≦ a ≦ 0.3.

The protective layer has a thickness of 0.005 to 0.1.
It is preferred to be within the range of μm. This is due to the following reasons. 0.005 μm thick protective layer
If it is less than 3, it is difficult to sufficiently suppress the reaction between the active material and the non-aqueous electrolyte, and it is difficult to sufficiently improve the electron conductivity between the active materials. There is. On the other hand, when the thickness of the protective layer exceeds 0.1 μm, the weight ratio of the active material particles in the positive electrode may decrease relatively, and a high capacity may not be obtained. A more preferred range is 0.01 to 0.08 μm.

The thickness of the layer is measured by the method described below. That is, the positive electrode active material is suspended in the ethanol solution. Then, the solution is dropped on a Cu mesh with a collodion support film. After that, the ethanol is volatilized and dried, and TE
A sample for M observation is prepared. The TEM observation sample was prepared using a high-resolution transmission electron microscope (model name: JEM-4000FX).
And the thickness of the protective layer is measured.

The positive electrode active material may be, for example, the following (1)
Alternatively, it is manufactured by the method described in (2).

(1) The active material particles are immersed in a solution in which a raw material of Me _{1 + a} Mn _2-a O ₄ is dissolved in a solvent, and then the solvent is evaporated to form the raw material on the surface of the active material particles. Is adhered. Subsequently, the raw material adhered to the surface of the active material particles is crystallized by firing at a temperature of 500 ° C. or more in the air or under an oxygen atmosphere, and at least a part of the surface is Me _{1 + a} Mn _2-a Active material particles coated with the O ₄ layer can be obtained.

[0024] Examples of the solvent include water and ethanol.

As a method of evaporating the solvent, for example,
The container containing the solution immersed with the active material particles is
A method in which the solution in which the active material particles are immersed is heated to 0 ° C. to gradually evaporate, or a method in which the solution in which the active material particles are immersed is atomized into a furnace at 150 to 250 ° C. and evaporated in a short time within several seconds. it can.

The firing temperature is preferably in the range of 700 to 800 ° C. When the sintering temperature is within the above range, the layer synthesis conditions are substantially equal to the sintering conditions for synthesizing the active material particles, so that the active material particles are less likely to undergo a change in crystal structure, oxygen deficiency and oxygen excess. Deterioration of the performance of the material particles can be avoided.

(2) After immersing the active material particles in a solution in which a raw material of Me _{1 + a} Mn _2-a O ₄ is dissolved in a solvent, the solution in which the active material particles are immersed is placed in a furnace at 500 ° C. or higher. By spraying the inside of the active material particles in a mist state, it evaporates in a short time within several seconds, and at the same time, Me _{1 + a} Mn _2-a O _{4 is} formed on the surface of the active material particles.
Is crystallized, and at least a part of the surface is Me _{1 + a} Mn _{2- a}
Active material particles coated with the O ₄ layer can be obtained.

The temperature in the furnace is preferably in the range of 700 to 800 ° C. When the temperature in the furnace is within the above range, the conditions for synthesizing the layer are substantially equal to the firing conditions for synthesizing the active material particles, so that a change in the crystal structure, oxygen deficiency and excess oxygen in the active material particles are unlikely to occur. In addition, performance degradation of the active material particles can be avoided.

The positive electrode is produced, for example, by mixing the positive electrode active material, the electric conduction auxiliary agent and the binder and pressing the mixture on a current collector, or by mixing the positive electrode active material, the electric conduction auxiliary agent and It is prepared by suspending a binder in a suitable solvent, applying the suspension to a current collector, and drying.

Examples of the electric conduction aid include acetylene black, carbon black, graphite and the like.

Examples of the binder include polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVd).
F), ethylene-propylene-diene copolymer (EPD
M), styrene-butadiene rubber (SBR) and the like can be used.

The mixing ratio of the positive electrode active material, the electric conduction aid and the binder ranges from 80 to 95% by weight of the positive electrode active material, 3 to 20% by weight of the electric conduction aid and 2 to 7% by weight of the binder. Is preferable. As the current collector, a conductive substrate having a porous structure or a non-porous conductive substrate can be used. Examples of the material constituting the current collector include aluminum, stainless steel, and nickel.

2) Separator As the separator, for example, a synthetic resin nonwoven fabric,
A polyethylene porous film, a polypropylene porous film, or the like can be used.

3) Negative Electrode This negative electrode contains a material capable of occluding (doping) and releasing (undoping) lithium.

As such a material, for example, lithium metal, a Li-containing alloy capable of occluding and releasing lithium, a metal oxide capable of occluding and releasing lithium, and lithium absorbing and releasing lithium can be used. Metal sulfides, metal nitrides capable of storing and releasing lithium, chalcogen compounds capable of storing and releasing lithium, and carbon materials capable of storing and releasing lithium ions. it can. In particular, the negative electrode containing the chalcogen compound or the carbon material has high safety, and can improve the cycle life of the secondary battery,
desirable.

Examples of the carbon material for absorbing and releasing lithium ions include coke, carbon fiber, pyrolytic gas phase carbon material, graphite, resin fired body, mesophase pitch-based carbon fiber, mesophase pitch spherical carbon, and the like. Can be. Carbon materials of the type described above are desirable because they can increase the electrode capacity.

Examples of the chalcogen compound include titanium disulfide, molybdenum disulfide, niobium selenide, tin oxide and the like. When such a chalcogen compound is used for the negative electrode, the capacity of the negative electrode is increased although the battery voltage is reduced, so that the capacity of the secondary battery is improved.

The negative electrode containing the carbon material is produced, for example, by kneading the carbon material and a binder in the presence of a solvent, applying the obtained suspension to a current collector, and drying the resultant. You.

In this case, as the binder, for example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), ethylene-propylene-diene copolymer (EP
DM), styrene-butadiene rubber (SBR) and the like can be used. Further, the mixing ratio of the carbon material and the binder is 90 to 98% by weight of the carbon material and 2 to 10% by weight of the binder.
It is preferable to be within the range. Further, as the current collector, for example, a conductive substrate of aluminum, stainless steel, nickel, or the like can be used. The current collector may have a porous structure or a non-porous structure.

4) Liquid Non-Aqueous Electrolyte (Non-Aqueous Electrolyte) This liquid non-aqueous electrolyte is prepared by dissolving the electrolyte in a non-aqueous solvent.

Examples of the non-aqueous solvent include cyclic carbonates and chain carbonates (eg, ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, etc.), cyclic ethers and chain ethers (eg, , 2−
Dimethoxyethane, 2-methyltetrahydrofuran, etc.), cyclic ester or chain ester (for example, γ-butyrolactone, γ-valerolactone, σ-valerolactone, methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, methyl propionate, propion) Ethylate, propyl propionate, etc.). The non-aqueous solvent includes one or two selected from the types described above.
Up to five types of mixed solvents can be used, but the present invention is not necessarily limited to these.

Examples of the electrolyte include lithium perchlorate (LiClO ₄ ) and lithium hexafluorophosphate (Li
PF ₆ ), lithium borofluoride (LiBF ₄ ), lithium arsenic hexafluoride (LiAsF ₆ ), lithium trifluoromethylsulfonylimide (LiCF ₃ SO ₃ ), lithium bistrifluoromethylsulfonylimide [LiN (CF ₃
SO ₂ ) ₂ ]. As such an electrolyte, one or two or three lithium salts selected therefrom can be used, but the electrolyte is not limited to these.

The amount of the electrolyte dissolved in the non-aqueous solvent is preferably in the range of 0.5 to 2.0 mol / L.

The non-aqueous electrolyte secondary battery according to the present invention, at least a portion of the surface of the active material particles and the active material particles having a composition represented by _{Li x M y M 'z O} 2-w F w described above A positive electrode including a protective layer formed and having a composition represented by the aforementioned Me _{1 + a} Mn _2-a O ₄ , a negative electrode, and a non-aqueous electrolyte are provided. According to such a secondary battery, a long life can be obtained even at a temperature higher than room temperature.

As a result of intensive studies, the present inventors have found that the cycle life in a high-temperature environment is reduced by the mechanism described below.

The positive electrode of the nonaqueous electrolyte secondary battery is formed by binding positive electrode active material particles for inserting and removing lithium ions, an electric conduction auxiliary agent, the active material particles and the electric conduction auxiliary agent to each other, and It is mainly composed of a binder (binder) to be adhered to the metal current collector, and voids (gap between the positive electrode constituting members) are filled with the non-aqueous electrolyte. FIG. 1 schematically shows the state of the positive electrode active material particles, the electric conduction aid, the current collector, and the nonaqueous electrolyte. By the way, electric conduction aid 1
Has a higher electrical conductivity than the positive electrode active material particles 2 and has a function of assisting the transfer of electrons between the active material particles 2 generated during charge and discharge. Therefore, when the amount of the electric conduction aid 1 is increased,
Although the electric conductivity inside the positive electrode increases and a battery excellent in large current characteristics can be obtained, the battery capacity decreases because the amount of the positive electrode active material relatively decreases. Therefore, in order to satisfy both the large current characteristics and the battery capacity, it is necessary to make the amount of the electric conduction aid smaller than that of the positive electrode active material. As a result,
As shown in FIG. 1, most of the positive electrode active material particles 2 did not come into direct contact with the electric conduction auxiliary agent 1 and some of the other positive electrode active material particles 2 did not.
Indirectly comes into contact with the electric conduction auxiliary agent 1 via.
Therefore, most of the electron conduction at the time of charging is performed from the positive electrode active material particles 2 to the electric conduction aid 1 through some other adjacent positive electrode active material particles 2. The reverse is true during discharge. In FIG. 1, the path of electron conduction at the time of charging and discharging is indicated by reference numeral 3.

When the non-aqueous electrolyte secondary battery having such a positive electrode is repeatedly charged and discharged, cycle capacity is deteriorated. That is, the positive electrode active material particles 2 react with the non-aqueous electrolyte 4 present around the positive electrode active material particles 2, causing a change in the composition of the surface of the positive electrode active material particles 2, a change in the crystal structure, or the deposition of electrolyte decomposition precipitates, As a result, the electric conductivity of the surface of the positive electrode active material particles 2 is reduced, so that the electric resistance between the positive electrode active material particles 2 that are in contact with each other increases. Then, the positive electrode active material particles 2 existing at a position distant from the electric conduction aid 1 need to pass through a large number of grain boundaries on the electron transfer path to the positive electrode active material particles 2 and have higher electric resistance. The present inventors have shown by research that the active material particles 2 are in an electrically separated state and cannot participate in charge / discharge, the capacity of the positive electrode is reduced, and the cycle life is shortened.

In the reaction between the positive electrode active material and the non-aqueous electrolyte, which causes an increase in the electric resistance between the positive electrode active material particles in contact with each other, the reaction speed increases as the temperature increases, so , The capacity suddenly decreases.

[0049] As in the present invention, Li _x M _y M described above '
by forming a layer represented by _z O _2-w F Me described above to at least a portion of the surface of the active material particles represented by _{w 1 + a Mn 2-a} O 4, this layer protects the non-aqueous electrolyte Since it functions as a membrane, it is possible to suppress a change in the composition of the positive electrode active material particles due to a reaction with the non-aqueous electrolyte, a change in the crystal structure, and the occurrence of deposition of electrolyte decomposition precipitates. The formation of an electrically insulating film on the particle surface can be suppressed. At the same time, since the layer has electronic conductivity, the electric conductivity of the surface of the positive electrode active material particles can be improved, and the positive electrode indirectly comes into contact with the electric conduction aid via several other positive electrode active material particles. The active material particles can be prevented from being electrically disconnected. As a result, it is possible to realize a non-aqueous electrolyte secondary battery in which a decrease in discharge capacity is small even when charge and discharge are repeated at a temperature exceeding room temperature.

In the secondary battery, the composition of the active material particles is set to Li _{0.5 + α} Mn _{1-α-β TβO 2} so that the crystal structure of the protective layer is similar to that of the active material particles. Since the relations are established or coincide with each other, peeling of the protective layer can be suppressed. As a result, the cycle life of the secondary battery can be further improved.

[0051]

Embodiments of the present invention will be described below in detail.

Example 1 LiOH and MnO ₂ were weighed at a molar ratio of 1.05: 1.95 and sufficiently pulverized and mixed.
Baking was performed at 750 ° C. for 12 hours in an oxygen atmosphere. Further grinding and firing are repeated to obtain a composition of Li _1.05 Mn _1.95 O
₄ (Li _0.525 Mn _0.975 O ₂ ) was obtained. Next, the Li _1.05 Mn _1.95 O ₄ particles were _charged into an aqueous solution in which cobalt nitrate and manganese nitrate were dissolved,
Mix well. At this time, the weight ratio of Li _1.05 Mn _1.95 O ₄ particles, cobalt nitrate and manganese nitrate was 5: 0.6:
1.2. After drying this at 90 ° C., it is baked at 750 ° C. for 2 hours in an oxygen atmosphere to obtain CoMn ₂ O ₄
Li _1.05 Mn _1.95 O ₄ particles covered with a layer consisting of

Then, 80% by weight of the positive electrode active material and 17% by weight of acetylene black as an electric conduction aid were added.
A positive electrode material layer was prepared by mixing polytetrafluoroethylene as a binder at a ratio of 3% by weight. This was press-bonded to a positive electrode current collector consisting of a stainless steel net welded to a battery can in advance to produce a positive electrode.

Further, a negative electrode material layer made of lithium metal was pressure-bonded to a negative electrode current collector made of a nickel net welded to a battery lid to obtain a negative electrode.

On the other hand, ethyl methyl carbonate and ethylene carbonate were mixed at a ratio of 2: 1.
F ₆ was dissolved at a rate of 1 mol / L to prepare a liquid non-aqueous electrolyte.

After laminating a battery can, a positive electrode, a separator made of a polypropylene porous film, a negative electrode, and a battery lid in this order, a liquid non-aqueous electrolyte was injected, and caulked with a gasket to seal the structure. A button-type nonaqueous electrolyte secondary battery having the following was assembled.

That is, the positive electrode current collector 12 is welded to the inner surface of the battery can 11. The positive electrode material layer 13 is pressed on the positive electrode current collector 12. The separator 14 is disposed on the positive electrode material layer 13. On the other hand, battery cover 1
A negative electrode current collector 16 is welded to the inner surface of 5. The negative electrode material layer 17 is pressed on the negative electrode current collector 16.
Such a battery cover 15 is caulked and fixed to the battery can 11 by an insulating gasket 18.

Example 2 The same Li solution as described in Example 1 was added to an aqueous solution in which copper nitrate and manganese nitrate were dissolved.
_1.05 Mn _1.95 O ₄ (Li _0.525 Mn _0.975 O ₂ ) particles were _charged and mixed well. At this time, Li _1.05 Mn _1.95 O ₄
The weight ratio of particles to copper nitrate and manganese nitrate is 5: 0.5:
1.2. After drying this at 90 ° C., it is baked at 750 ° C. for 2 hours in an oxygen atmosphere to obtain CuMn ₂ O ₄
Li _1.05 was coated with a layer consisting of Mn _1. give the ₉₅ O ₄ particles as the positive electrode active material.

A button-type nonaqueous electrolyte secondary battery was assembled in the same manner as in Example 1 except that such a positive electrode active material was used.

Example 3 The same Li _1.05 Mn _1.95 O ₄ (Li _0.525 Mn _0.975 O ₂ ) particles as described in Example 1 were charged into an aqueous solution in which nickel nitrate and manganese nitrate were dissolved, Mixed. At this time, Li _1.05 Mn _1.95
The weight ratio of O ₄ particles to nickel nitrate and manganese nitrate is
5: 0.6: 1.2. After drying at 90 ° C., it is baked at 750 ° C. for 2 hours in an oxygen atmosphere, and Li _1.05 Mn _1.95 O whose surface is covered with a layer made of NiMn ₂ O _4.
Four particles were obtained as a positive electrode active material.

A button type non-aqueous electrolyte secondary battery was assembled in the same manner as in Example 1 except that such a positive electrode active material was used.

Example 4 LiOH, Ni_0.7Co
_0.3(OH)_TwoAre sufficiently weighed in a molar ratio of 1.1: 1.0.
After grinding and mixing, bake at 750 ° C for 12 hours in an oxygen atmosphere.
The composition is LiNi _0.7Co_0.3O_TwoThe living thing represented by
Quality particles were obtained. Then, cobalt nitrate and manganese nitrate
LiNi in ethanol in which_0.7Co_0.3O_Two
The particles were charged and mixed well. At this time, LiNi
_0.7Co_0.3O_TwoWeight of particles and cobalt nitrate and manganese nitrate
The quantitative ratio was 5: 0.3: 0.6. At 80 ° C
After drying, firing at 750 ° C for 2 hours under oxygen atmosphere
And the surface is CoMn_TwoO_FourLiNi covered with a layer consisting of
_0.7Co_0.3O_TwoThe particles were obtained as a positive electrode active material.

A button-type nonaqueous electrolyte secondary battery was assembled in the same manner as in Example 1 except that such a positive electrode active material was used.

Example 5 The same LiNi _0.7 Co _0.3 O ₂ particles as described in Example 4 were charged into ethanol in which copper nitrate and manganese nitrate were dissolved, and mixed well. At this time, the weight ratio of LiNi _0.7 Co _0.3 O ₂ particles, copper nitrate, and manganese nitrate was 5: 0.25: 0.6. This is dried at 80 ° C., and then dried under an oxygen atmosphere for 75 minutes.
The mixture was fired at 0 ° C. for 2 hours to obtain LiNi _0.7 Co _0.3 O ₂ particles whose surface was covered with a layer made of CuMn ₂ O ₄ as a positive electrode active material.

A button-type nonaqueous electrolyte secondary battery was assembled in the same manner as in Example 1 except that such a positive electrode active material was used.

Example 6 The same LiNi _0.7 Co _0.3 O ₂ particles as described in Example 4 were charged into ethanol in which nickel nitrate and manganese nitrate were dissolved, and mixed well. At this time, the weight ratio of LiNi _0.7 Co _0.3 O ₂ particles, nickel nitrate and manganese nitrate was 5: 0.3: 0.6
Met. After this was dried at 90 ° C., in an oxygen atmosphere was calcined 2 hours at 750 ° C., to obtain surface LiNi _0.7 Co _{0 .3} O ₂ particles coated with a layer consisting of NiMn ₂ O ₄ as a positive electrode active material .

A button type non-aqueous electrolyte secondary battery was assembled in the same manner as in Example 1 except that such a positive electrode active material was used.

Example 7 After LiOH and Co ₂ O ₃ were weighed at a molar ratio of 2: 1 and sufficiently pulverized and mixed, the mixture was calcined at 700 ° C. for 12 hours in an oxygen atmosphere to form an active material having a composition represented by LiCoO _2. Material particles were obtained. Next, the LiCoO ₂ particles were charged into an aqueous solution in which cobalt nitrate and manganese nitrate were dissolved, and mixed sufficiently. At this time, LiCoO ₂
The weight ratio of particles to cobalt nitrate and manganese nitrate is 5:
0.3: 0.6. After drying at 90 ° C., it is baked at 750 ° C. for 2 hours in an oxygen atmosphere to obtain a C
LiCoO ₂ particles covered with a layer made of oMn ₂ O ₄ were obtained as a positive electrode active material.

A button-type nonaqueous electrolyte secondary battery was assembled in the same manner as in Example 1 except that such a positive electrode active material was used.

(Embodiment 8) The same LiC as described in Embodiment 7 was added to an aqueous solution in which copper nitrate and manganese nitrate were dissolved.
The oO ₂ particles were charged and mixed well. At this time, Li
The weight ratio of CoO ₂ particles to copper nitrate and manganese nitrate is 5:
0.5: 1.2. After drying at 90 ° C., it is baked at 750 ° C. for 2 hours in an oxygen atmosphere to obtain a C
LiCoO ₂ particles covered with a layer made of uMn ₂ O ₄ were obtained as a positive electrode active material.

A button type non-aqueous electrolyte secondary battery was assembled in the same manner as in Example 1 except that such a positive electrode active material was used.

Example 9 The same LiCoO ₂ particles as described in Example 7 were charged into an aqueous solution in which nickel nitrate and manganese nitrate were dissolved, and mixed sufficiently. At this time, the weight ratio of LiCoO ₂ particles to nickel nitrate and manganese nitrate was 5: 0.6: 1.2. 90 ℃
And then baked at 750 ° C. for 2 hours in an oxygen atmosphere to cover the surface with a layer of NiMn ₂ O ₄ LiCo.
O ₂ particles were obtained as a positive electrode active material.

A button-type nonaqueous electrolyte secondary battery was assembled in the same manner as in Example 1 except that such a positive electrode active material was used.

Example 10 LiOH, MnO ₂ , Al
(NO ₃ ) ₂ .6H ₂ O in a molar ratio of 1.05: 1.9: 0.
After weighing and thoroughly pulverizing and mixing the mixture in an oxygen atmosphere,
Firing at 50 ° C. for 24 hours, the composition is Li _1.05 Mn _1.9 Al
Active material particles represented by _0.05 O ₄ (Li _0.525 Mn _0.95 Al _0.025 O ₂ ) were obtained. Next, the Li _1.05 Mn _1.9 Al was _added to an aqueous solution in which cobalt nitrate and manganese nitrate were dissolved.
_0.05 O ₄ particles were charged and mixed well. At this time,
The weight ratio of Li _1.05 Mn _1.9 Al _0.05 O ₄ particles to cobalt nitrate and manganese nitrate was 5: 0.6: 1.2. After drying this at 90 ° C, it is dried at 750 ° C in an oxygen atmosphere.
For 2 hours to obtain Li _1.05 Mn _1.9 Al _0.05 O ₄ particles whose surface was covered with a layer made of CoMn ₂ O ₄ as a positive electrode active material.

A button type non-aqueous electrolyte secondary battery was assembled in the same manner as in Example 1 except that such a positive electrode active material was used.

Example 11 LiOH, Ni _0.7 Co _0.3
(OH) ₂ , LiF in a molar ratio of 1.0: 0.95: 0.0
5 and crushed and mixed sufficiently, and then 55
The mixture was held at 0 ° C. for 5 hours and calcined at 650 ° C. for 20 hours to obtain active material particles having a composition represented by Li _1.05 Ni _0.7 Co _0.3 O _1.96 F _0.04 . Then, the aqueous solution obtained by dissolving cobalt nitrate and manganese nitrate Li _1.05 Ni _0.7 Co _0.3 O
_1.96 F _0.04 particles were _charged and mixed well. At this time, the weight ratio of Li _1.05 Ni _0.7 Co _0.3 O _1.96 F _0.04 particles to cobalt nitrate and manganese nitrate was 5: 0.3: 0.6.
Met. After drying at 80 ° C., it was baked at 750 ° C. for 2 hours to obtain Li _1.05 Ni _0.7 Co _0.3 O _1.96 F _0.04 particles whose surface was covered with a layer made of CoMn ₂ O ₄ as a positive electrode active material.

A button type non-aqueous electrolyte secondary battery was assembled in the same manner as in Example 1 except that such a positive electrode active material was used.

Comparative Example 1 A button-type nonaqueous electrolyte was prepared in the same manner as in Example 1 except that the same Li _1.05 Mn _1.95 O ₄ particles as described in Example 1 were used as the positive electrode active material. The next battery was assembled.

Comparative Example 2 A button-type nonaqueous electrolyte was produced in the same manner as in Example 1 except that the same LiNi _0.7 Co _0.3 O ₂ particles as described in Example 1 were used as the positive electrode active material. The next battery was assembled.

Comparative Example 3 A button-type nonaqueous electrolyte secondary battery was assembled in the same manner as in Example 1 except that the same LiCoO ₂ particles as those described in Example 1 were used as the positive electrode active material. Was.

The obtained Examples 1 to 15 and Comparative Examples 1 to 3
Was subjected to a charge / discharge cycle test at 60 ° C. That is, 50 charge / discharge cycles were performed in an environment of 60 ° C. The charge and discharge conditions at that time are as follows.
That is, after charging to 4.3 V at 1 mA / cm ² ,
The circuit was opened for 30 minutes, and then discharged at 3.5 mA at 1 mA / cm ² , and then the circuit was opened for 30 minutes, which was one cycle. Then, the discharge capacity in the first cycle is set to 10
The discharge capacity at the 50th cycle, which was set to 0, was measured. This is shown in Table 1 as the capacity retention ratio. Table 1 also shows the weight ratio of the oxide layer in the positive electrode active material and the thickness of the oxide layer in the secondary batteries of Examples 1 to 15.

[0082]

[Table 1]

As is clear from Table 1, the surface was Me _{1 + a}
The secondary batteries of Examples 1 to 3 provided with the positive electrodes including the lithium manganese composite oxide particles coated with the Mn _2-a O ₄ layer were prepared according to Comparative Example 1 including the positive electrodes including the uncoated active material particles. It can be seen that the cycle capacity degradation under a high temperature environment of 60 ° C. can be reduced as compared with the secondary battery. The surface is Me
Examples 4 to 6 provided with a positive electrode containing lithium-containing nickel-cobalt composite oxide particles coated with _{a 1 + a} Mn _2-a O ₄ layer
It can be seen that the secondary battery of Comparative Example 2 can reduce the cycle capacity degradation under a high temperature environment of 60 ° C. as compared with the secondary battery of Comparative Example 2 including the positive electrode including the uncoated active material particles.
Further, the secondary batteries of Examples 7 to 9 each including the positive electrode including the lithium-containing cobalt oxide particles whose surfaces are coated with the Me _{1 + a} Mn _2-a O ₄ layer include the uncoated active material particles. It can be seen that the cycle capacity deterioration under a high temperature environment of 60 ° C. can be reduced as compared with the secondary battery of Comparative Example 3 including the positive electrode.

In the above-described embodiment, an example in which the invention is applied to a button type non-aqueous electrolyte secondary battery has been described. However, the form of the non-aqueous electrolyte secondary battery according to the present invention is not limited to a button type. Instead of a button type, a square type, a cylindrical type, a thin plate type, or the like can be used. In addition, a laminate film can be used as an exterior material instead of a metal can.

[0085]

As described above in detail, according to the present invention, the non-aqueous electrolyte has a small capacity reduction even when charge and discharge are repeated in a high temperature environment which exceeds room temperature but is in a practical use temperature range. A secondary battery can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic diagram for explaining the operation of the present invention.

FIG. 2 is a sectional view showing a button-type nonaqueous electrolyte secondary battery of Example 1.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Electric conduction auxiliary agent, 2 ... Active material particles, 3 ... Electron conduction path at the time of charge / discharge, 4 ... Non-aqueous electrolyte, 11 ... Battery can, 12 ... Positive electrode current collector, 13 ... Positive electrode material layer, 14 ... Separator, 15: Battery cover, 16: Negative electrode current collector, 17: Negative electrode material layer, 18: Insulating gasket.

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Shuji Yamada 1 Tokoba R & D Center, Komukai Toshiba, Saiwai-ku, Kawasaki-shi, Kanagawa F-term (reference) 5H029 AJ03 AJ05 AK03 AL12 AM03 AM04 AM05 AM07 BJ03 BJ13 BJ16 DJ12 DJ16 HJ02 HJ04 5H050 AA07 AA08 CA09 CB12 EA10 EA24 EA28 FA17 FA18 HA02 HA04

Claims (3)

[Claims] A positive electrode containing a positive electrode active material, a negative electrode,
In the nonaqueous electrolyte secondary battery and a nonaqueous electrolyte, wherein the positive active material, composition of _{Li x M y M 'z O} 2-w F w ( where M may Mn, Fe, of Co and Ni At least one element selected from the group consisting of:
V, Cr, Cu, Mg, Al, Si, P, S, Ga, G
one or more elements selected from the group consisting of e and Nb, and the molar ratios x, y, z and w are 0 <x ≦ 1, 0 <y ≦
1, 0 ≦ z ≦ 1, 0 ≦ w ≦ 0.3) and at least a part of the surface of the active material particles, and has a composition of Me _{1+ a} Mn _{2−. a} O ₄ (provided that said Me is Co, more than one kind of element selected from the group consisting of Ni and Cu, the molar ratio a shows a 0 ≦ a ≦ 1) to include a protective layer represented by Characteristic non-aqueous electrolyte secondary battery. 2. A positive electrode containing a positive electrode active material, a negative electrode,
In a non-aqueous electrolyte secondary battery comprising a non-aqueous electrolyte, the positive electrode active material has a composition of Li _{0.5 + α} Mn _1-α-β T _β
O ₂ (where T is Fe, Co, Ni, Ti, V,
At least one element selected from the group consisting of Cr, Cu, Mg, Al, Si, P, S, Ga, Ge and Nb, and the molar ratios α and β are 0 <α ≦ 0.05, 0 ≦ β ≦ 0.
1), and formed on at least a part of the surface of the active material particles, and has a composition of M
e _{1 + a} Mn _2-a O ₄ (where Me is Co, Ni and C
a non-aqueous electrolyte secondary battery comprising at least one element selected from the group consisting of u, wherein the molar ratio a represents 0 ≦ a ≦ 1). 3. The protective layer has a thickness of 0.005 to 0.5.
3. The non-aqueous electrolyte secondary battery according to claim 1, wherein the range is 1 μm.