JP2002075368A - Positive electrode active material, nonaqueous electrolyte battery, and their manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive electrode active material having characteristics of both the Ni composite oxide particles with a large energy density and LiFePO4 particles with the capacity deterioration remaining lesser at the time of charging. SOLUTION: The surfaces of particles expressed by the general formula LiNi1-xMxO2, (where M is element(s) containing at least one of Al, B, Co) are covered with particulates expressed by the general formula LiFePO4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a positive electrode active material and a non-aqueous electrolyte battery using a lithium nickel composite oxide, and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, with the remarkable progress of various electronic devices, research on a rechargeable secondary battery as a power source that can be used conveniently and economically for a long time has been advanced. As typical secondary batteries, lead storage batteries, alkaline storage batteries, lithium secondary batteries, and the like are known. In particular, lithium secondary batteries have advantages such as high output and high energy density. The above lithium secondary battery includes a positive electrode capable of reversibly inserting and removing lithium ions, a negative electrode, and a non-aqueous electrolyte.

In general, as the negative electrode active material, lithium metal, a lithium alloy, a conductive polymer doped with lithium, a layered compound (such as a carbon material or a metal oxide) or a conductive material coexisting with a compound containing lithium is used. A conductive polymer and a layered compound (such as a carbon material and a metal oxide) are used.

On the other hand, a metal oxide, a metal sulfide, a polymer, or the like is used as the positive electrode active material.
Non-lithium-containing compounds such as S ₂ , MoS ₂ , NbSe ₂ , V ₂ O ₅ , and composite oxides already containing lithium such as LiMO ₂ (M = Co, Ni, Mn, Fe, etc.) have been proposed. I have.

As an electrolytic solution, a solution in which a lithium salt is dissolved in an aprotic organic solvent such as propylene carbonate is used.

Further, a polymer film such as polypropylene is used as the separator. In this case, the separator must be as thin as possible in view of lithium ion conductivity and energy density. Usually, a separator of 50 μm or less is considered practical. A battery composed of the above-described positive electrode, negative electrode, and a separator and an electrolyte interposed therebetween can be used as a chargeable / dischargeable secondary battery.

[0007]

The Ni-based positive electrode active material for increasing the capacity of the lithium secondary battery has a larger amount of lithium removed during charging than the conventional Co-based positive electrode active material. Therefore, N
In the i-type positive electrode active material, structural stability is lost,
Capacity deterioration during charging has been observed. On the other hand, LiFeP
O ₄ has excellent structural stability at the time of charging and has little capacity deterioration, but has a low energy density and is difficult to use alone.

In order to obtain a positive electrode active material which has both of these advantages, is excellent in stability during charging, and has a high capacity,
A technique for attaching LiFePO ₄ to the surface of Ni composite oxide particles has been sought. But the effective way is
Not yet found.

The present invention has been proposed in view of the above-described conventional situation, and has a large energy density.
i Composite oxide particles and LiF with small capacity deterioration during charging
An object of the present invention is to provide a positive electrode active material having both characteristics of ePO ₄ particles, a nonaqueous electrolyte battery using the positive electrode active material, and a method for producing the same.

[0010]

Means for Solving the Problems The positive electrode active material of the present invention comprises:
General formula LiNi _1-x M _x O ₂ (where M is Al, B, Co
Is an element containing at least one of the above. ) Is coated with fine particles represented by the general formula LiFePO ₄ .

In the positive electrode active material of the present invention as described above,
Since the surface of the particles represented by the general formula LiNi _1-x M _x O ₂ is coated with the fine particles represented by the general formula LiFePO ₄ , the Ni composite oxide particles having a large energy density and the structural stability are improved. It has both characteristics of excellent LiFePO ₄ particles.

A non-aqueous electrolyte battery according to the present invention includes a positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, and a non-aqueous electrolyte interposed between the positive electrode and the negative electrode. The surface of the particles represented by the general formula LiNi _1-x M _x O ₂ (where M is an element containing at least one of Al, B, and Co) is used as the positive electrode active material.
It is characterized by being coated with fine particles represented by PO ₄ .

In the non-aqueous electrolyte battery according to the present invention as described above, the surface of the particles whose positive electrode active material is represented by the general formula LiNi _1-x M _x O ₂ is made of fine particles represented by the general formula LiFePO ₄ . Coated Ni composite oxide particles with high energy density and LiF with excellent structural stability
It has both properties of ePO ₄ particles.
The nonaqueous electrolyte battery of the present invention using such a positive electrode active material has both high capacity and high charge / discharge cycle characteristics.

Further, the method for producing a positive electrode active material of the present invention comprises:
General formula LiNi _1-x M _x O ₂ (where M is Al, B, Co
Is an element containing at least one of the above. ) And fine particles represented by the general formula LiFePO ₄ are mixed and stirred so that the particle temperature (T) falls within a range of 35 ° C. ≦ T ≦ 45 ° C., thereby obtaining the surface of the particles. Is coated with the fine particles.

In the method for producing a positive electrode active material as described above, by defining the particle temperature when stirring the mixed particles, the surface of the particles represented by the general formula LiNi _1-x M _x O ₂ is A positive electrode active material on which fine particles represented by the formula LiFePO ₄ are adhered is obtained.

Further, the method for producing a nonaqueous electrolyte battery according to the present invention comprises the steps of: forming a positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, and a nonaqueous electrolyte interposed between the positive electrode and the negative electrode. A method for producing a nonaqueous electrolyte battery comprising the steps of: synthesizing the positive electrode active material according to the general formula LiNi _1-x M _x O ₂
(Wherein, M is an element containing at least one of Al, B, and Co) and a general formula LiFeP
Mixed with fine particles represented by O ₄ , and the particle temperature (T) is 3
By stirring so that 5 ° C ≦ T ≦ 45 ° C,
The surface of the particles is coated with the fine particles to form a positive electrode active material.

In the method of manufacturing a non-aqueous electrolyte battery according to the present invention as described above, the particle temperature represented by the general formula LiNi _1-x M _x O ₂ is determined by defining the particle temperature when stirring the mixed particles. Thus, a positive electrode active material having fine particles represented by the general formula LiFePO ₄ adhered to the surface thereof is obtained. In the method for manufacturing a nonaqueous electrolyte battery of the present invention using such a positive electrode active material, a nonaqueous electrolyte battery having both high capacity and high charge / discharge cycle characteristics can be obtained.

[0018]

FIG. 1 shows an example of the configuration of a nonaqueous electrolyte battery according to the present invention. The nonaqueous electrolyte battery 1 includes a negative electrode 2, a negative electrode can 3 containing the negative electrode 2, a positive electrode 4, a positive electrode can 5 containing the positive electrode 4, and a separator disposed between the positive electrode 4 and the negative electrode 2. 6 and an insulating gasket 7. The negative electrode can 3 and the positive electrode can 5 are filled with a non-aqueous electrolyte.

The negative electrode 2 is made of, for example, a metal lithium foil serving as a negative electrode active material. When a material that can be doped and dedoped with lithium is used as the negative electrode active material, the negative electrode 2 is formed by forming a negative electrode active material layer containing the negative electrode active material on a negative electrode current collector. As the negative electrode current collector, for example, a nickel foil or the like is used.

As the negative electrode active material which can be doped with and dedoped with lithium, lithium metal, lithium alloys, conductive polymers doped with lithium, and layered compounds (such as carbon materials and metal oxides) are used.

As the binder contained in the negative electrode active material layer, a known resin material or the like usually used as a binder for the negative electrode active material layer of this type of nonaqueous electrolyte battery can be used.

The negative electrode can 3 houses the negative electrode 2 and serves as an external negative electrode of the nonaqueous electrolyte battery 1.

The positive electrode 4 is formed by forming a positive electrode active material layer containing a positive electrode active material on a positive electrode current collector. As the positive electrode current collector, for example, an aluminum foil or the like is used.

Here, in the present invention, as the positive electrode active material,
General formula LiNi _1-x M _x O ₂ (where M is Al, B, Co
Is an element containing at least one of the above. ) Is used in which the surface of the particles is coated with fine particles of LiFePO ₄ .

As described above, although the Ni composite oxide has a large energy density, there is a problem that a large amount of lithium is released during charging and the structure becomes unstable, thereby causing a capacity deterioration. On the other hand, LiFePO ₄
Although they have excellent structural stability at the time of charging and have little capacity deterioration, they have a problem that their energy density is small and their use alone is difficult.

The Ni composite oxide, whose structure has been destabilized due to lithium desorption during charging, causes a capacity degradation phenomenon due to structural destruction at the interface with the non-aqueous electrolyte inside the battery. In particular, at high temperatures (40 ° C. to 60 ° C.), the degree of deterioration is large. When the surface of this Ni composite oxide is modified to thermally stable LiFePO ₄ , the capacity deterioration at a high temperature is significantly reduced. This is presumably because LiFePO ₄ , which is thermally stable, suppresses surface structural destruction.

Thus, the general formula LiNi _1-x M _x O
₂ (where M is an element containing at least one of Al, B, and Co), by using a positive electrode active material in which the surface of Ni composite oxide particles represented by LiFePO ₄ fine particles is coated. By suppressing the structural deterioration of the Ni composite oxide,
Advantages of Ni composite oxide, high energy density, and LiFePO ₄ , excellent structural stability during charging
The non-aqueous electrolyte battery 1 having the advantages of high capacity and high charge / discharge cycle characteristics can be realized.

As the binder contained in the positive electrode active material layer, a known resin material or the like which is usually used as a binder for the positive electrode active material layer of this type of nonaqueous electrolyte battery can be used.

The positive electrode can 5 houses the positive electrode 4 and serves as an external positive electrode of the nonaqueous electrolyte battery 1.

The separator 6 separates the positive electrode 4 and the negative electrode 2 from each other, and can be formed of a known material which is generally used as a separator of this type of non-aqueous electrolyte battery. A polymer film is used. In addition, the thickness of the separator needs to be as small as possible from the relationship between lithium ion conductivity and energy density. Specifically, the thickness of the separator is suitably, for example, 50 μm or less.

The insulating gasket 7 is integrated into the negative electrode can 3. The insulating gasket 7 is for preventing the nonaqueous electrolyte filled in the negative electrode can 3 and the positive electrode can 5 from leaking.

As the non-aqueous electrolyte, a solution in which an electrolyte is dissolved in an aprotic non-aqueous solvent is used.

Examples of the non-aqueous solvent include propylene carbonate, ethylene carbonate, butylene carbonate, vinylene carbonate, γ-butyl lactone, sulfolane, 1,2-dimethoxyethane, 1,2-diethoxyethane, 2-methyltetrahydrofuran, -Methyl 1,3-dioxolan, methyl propionate, methyl butyrate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate and the like can be used. In particular, from the viewpoint of voltage stability, propylene carbonate,
It is preferable to use cyclic carbonates such as vinylene carbonate, and chain carbonates such as dimethyl carbonate, diethyl carbonate and dipropyl carbonate. In addition, such a non-aqueous solvent may be used alone or as a mixture of two or more.

The electrolyte dissolved in the non-aqueous solvent includes, for example, LiPF ₆ , LiClO ₄ , LiAsF ₆ ,
Lithium salts such as LiBF ₄ , LiCF ₃ SO ₃ , and LiN (CF ₃ SO ₂ ) ₂ can be used. Among these lithium salts, LiPF ₆ and LiBF ₄ are preferably used.

Thus, in the nonaqueous electrolyte battery 1 according to the present invention, the general formula LiNi _1-x M _x O ₂ (where M is Al,
It is an element containing at least one of B and Co. The Ni surface of the composite oxide particles represented as), LiFePO ₄
Since the positive electrode active material coated with fine particles is used, the advantages of the Ni composite oxide, which has a high energy density while suppressing the structural deterioration of the Ni composite oxide, and the advantages of LiFePO ₄ , which has excellent structural stability during charging, are provided. And a battery having both high capacity and high charge / discharge cycle characteristics.

The non-aqueous electrolyte battery 1 is manufactured, for example, as follows.

First, the positive electrode active material according to the present invention as described above is manufactured.

The surface of the LiNi _1-x M _x O ₂ particles has LiFe
In order to deposit the PO ₄ fine particles, for example, the LiNi _1-x
M _x O ₂ particles is reacted with mixed aqueous solution of nitrate and ammonium phosphate, and the like of Fe or Li, by heat _{treatment, LiNi 1-x M x O} 2 -called solution method for forming a LiFePO ₄ surface film on the surface of the particles Can be mentioned.
In the case of this aqueous solution method, the uniformity of the LiFePO ₄ surface film is excellent.
O ₄ single phase cannot be obtained. When the heat treatment is performed in a reducing atmosphere, the LiNi _1-x M _x O ₂ particles cause structural destruction, and the capacity is deteriorated. From such a point, it is difficult to obtain a positive electrode active material that achieves the object of the present invention by the aqueous solution method.

On the other hand, a dry method without heat treatment
Then, the particle hybridization method may be mentioned.
it can. In this particle hybridization method,
Powder collision by mixing and stirring different particles
Generates static electricity, causing fine particles to adhere to the surface of large particles.
You. Since this method does not go through a heating process,
It is possible to carry out a modification. However, the present invention
LiNi used in _1-xM_xO_TwoBecause the particles are brittle,
In the child hybridization method, collision cracking is likely to occur.
No. The degree of this collision cracking_1-xM_xO_TwoOf particles
Hardness, particle size or adhered particles LiFePO_FourHard
Depends on degree and particle size. Therefore, the process in which collision cracking is suppressed
Requirement was required.

Therefore, the present inventor has conducted intensive studies on the conditions under which fine particles of LiFePO ₄ adhere to the surface of the Ni positive electrode particles without causing cracking of the particles. As a result, the LiNi _1-x M the LiFePO ₄ particles on the surface of the _x O ₂ particles when depositing, particle temperature T during the stirring process is that to satisfy the range of 35 ° C. ≦ T ≦ 45 ° C., without causing collision crack, It has been found that good results can be obtained.

The particle temperature T is an index for quantitatively observing the degree of collision of particles during the stirring process. That is, the energy due to the collision between the particles heats the particles,
Since the temperature rises, controlling the particle temperature T is equivalent to controlling the collision energy of the particles.

Specifically, when the particle temperature T is lower than 35 ° C., the collision energy between the particles is not sufficiently high, and the surface of the LiNi _1-x M _x O ₂ particles is covered with the LiFePO ₄ fine particles. I can't wear it. On the other hand, when the particle temperature T is higher than 45 ° C., the collision energy between the particles is too large, which may cause the collision cracking of the particles.

Therefore, LiNi _{1 -x} M _x O ₂ particles and L
By mixing with iFePO ₄ fine particles and stirring under conditions that the particle temperature T during stirring satisfies the range of 35 ° C. ≦ T ≦ 45 ° C., LiNi _1-x M _x O
The positive electrode active material of the present invention can be obtained by attaching LiFePO ₄ fine particles to the surface of the _two particles.

Using the obtained positive electrode active material, a coin-type nonaqueous electrolyte battery is manufactured as follows.

As the positive electrode 4, first, a positive electrode mixture of a slurry is prepared by dispersing a positive electrode active material and a binder in a solvent. Next, the obtained positive electrode mixture is uniformly applied on a positive electrode current collector and dried to form a positive electrode active material layer, whereby the positive electrode 4 is manufactured. Known binders can be used as the binder of the positive electrode mixture, and known additives and the like can be added to the positive electrode mixture.

For the negative electrode 2, first, a negative electrode active material and a binder are dispersed in a solvent to prepare a negative electrode mixture of a slurry. Next, the obtained negative electrode mixture is uniformly applied on a negative electrode current collector and dried to form a negative electrode active material layer, thereby forming a negative electrode 2.
Is produced. As the binder of the negative electrode mixture, a known binder can be used, and a known additive or the like can be added to the negative electrode mixture. Further, metallic lithium serving as a negative electrode active material can be used as the negative electrode 2 as it is.

The non-aqueous electrolyte is prepared by dissolving an electrolyte salt in a non-aqueous solvent.

Then, the negative electrode 2 is accommodated in the negative electrode can 3, the positive electrode 4 is accommodated in the positive electrode can 5, and a separator 6 made of a porous polypropylene film or the like is disposed between the negative electrode 2 and the positive electrode 4. The non-aqueous electrolyte is injected into the negative electrode can 3 and the positive electrode can 5, and the negative electrode can 3 and the positive electrode can 5 are caulked and fixed via the insulating gasket 7, thereby completing the non-aqueous electrolyte battery 1.

In the above-described embodiment, the non-aqueous electrolyte battery 1 using a non-aqueous electrolyte has been described as an example of the non-aqueous electrolyte battery. However, the present invention is not limited to this. Without, a solid electrolyte battery using a polymer solid electrolyte containing a simple substance or a mixture of conductive polymer compounds,
The present invention is also applicable to a gel electrolyte battery using a gel solid electrolyte containing a swelling solvent.

Specific examples of the conductive polymer compound contained in the polymer solid electrolyte and the gel electrolyte include silicon, acryl, acrylonitrile, polyphosphazene-modified polymer, polyethylene oxide, polypropylene oxide, fluorine-based polymer, and the like. Examples thereof include a composite polymer, a crosslinked polymer, and a modified polymer of these compounds. Examples of the fluorine-based polymer include poly (vinylidene fluoride), poly (vinylidene fluoride-co-hexafluoropropylene), poly (vinylidene fluoride-co-tetrafluoroethylene), and poly (vinylidene fluoride-co-trifluorethylene). ) And the like.

Further, in the above-described embodiment, the description has been given by taking the secondary battery as an example. However, the present invention is not limited to this, and can be applied to a primary battery. In addition, the battery of the present invention has a cylindrical shape, a square shape, a coin shape, a button shape, and the like, and its shape is not particularly limited,
In addition, various sizes such as a thin type and a large size can be used.

[0052]

EXAMPLES Next, the present invention was performed to confirm the effects of the present invention.
Examples and comparative examples will be described. In the following embodiments, specific numerical values are described, but it goes without saying that the present invention is not limited to these.

Example 1 First, a positive electrode active material according to the present invention was synthesized as follows.

First, 3 particles of LiNi _0.8 Co _0.2 O ₂ were added.
0.0 g and 1.0 g of LiFePO ₄ fine particles were mixed. Here, the median diameter of the used LiNi _0.8 Co _0.2 O ₂ particles was 11.458 μm, and the median diameter of the LiFePO ₄ fine particles was 0.185 μm. LiNi
FIG. 2 shows the measurement results of the particle size distribution of _0.8 Co _0.2 O ₂ particles.
FIG. 3 shows the particle size distribution measurement results of the FePO ₄ fine particles.

Next, LiNi _0.8 Co _0.2 O ₂ particles and Li
By stirring the mixture with the FePO ₄ fine particles for 5 minutes, the surface of the LiNi _0.8 Co _0.2 O ₂ particles is
Surface modification was performed by attaching O ₄ fine particles to obtain a positive electrode active material. Here, Nara Machinery Co., Ltd.
Using the hybridization system NHS-O,
The rotation speed was adjusted so that the processing temperature T became 36 ° C.

Next, a coin-type non-aqueous electrolyte battery was manufactured using the positive electrode active material obtained as described above.

80% by weight of the obtained positive electrode active material in dry weight, and 15% by weight of graphite (average particle size of 5 μm to 20 μm: trade name KS-15 Lonza) as a conductive agent;
Polyvinylidene fluoride (Aldrich # 1)
300) was mixed with dimethyl fluoride to obtain a positive electrode paste.

Next, this positive electrode paste was applied on an aluminum mesh as a positive electrode current collector, pelletized together with the aluminum mesh, and dried at 100 ° C. for 1 hour in a dry argon stream to obtain a positive electrode. . The positive electrode carries 60 mg of a positive electrode active material per one piece.

Further, a negative electrode was obtained by punching lithium metal into substantially the same diameter as the positive electrode.

Further, 1 mol of LiPF ₆ was added to a mixed solvent of propylene carbonate and dimethyl carbonate in an equal volume.
A non-aqueous electrolyte was prepared by dissolving at a concentration of 1 / l.

Then, the negative electrode obtained as described above was accommodated in a negative electrode can, the positive electrode was accommodated in a positive electrode can, and a separator made of a porous film made of polypropylene or the like was disposed between the negative electrode and the positive electrode. A nonaqueous electrolyte solution was injected into the negative electrode can and the positive electrode can, and the negative electrode can and the positive electrode can were caulked and fixed via an insulating gasket, thereby completing a 2025 coin-type nonaqueous electrolyte battery.

Example 2 Example 1 was repeated except that the rotation speed was adjusted so that the particle temperature T became 38 ° C. when mixing and stirring LiNi _0.8 Co _0.2 O ₂ particles and LiFePO ₄ fine particles. A positive electrode active material was synthesized in the same manner as described above, and a coin-type non-aqueous electrolyte battery was manufactured in the same manner as in Example 1 using the positive electrode active material.

Example 3 Example 1 was repeated except that the rotation speed was adjusted so that the particle temperature T became 40 ° C. when mixing and stirring LiNi _0.8 Co _0.2 O ₂ particles and LiFePO ₄ fine particles. A positive electrode active material was synthesized in the same manner as described above, and a coin-type non-aqueous electrolyte battery was manufactured in the same manner as in Example 1 using the positive electrode active material.

Example 4 Example 1 was repeated except that the rotation speed was adjusted so that the particle temperature T became 42 ° C. when mixing and stirring LiNi _0.8 Co _0.2 O ₂ particles and LiFePO ₄ fine particles. A positive electrode active material was synthesized in the same manner as described above, and a coin-type non-aqueous electrolyte battery was manufactured in the same manner as in Example 1 using the positive electrode active material.

Example 5 Example 1 was repeated except that the rotation speed was adjusted so that the particle temperature T became 44 ° C. when mixing and stirring LiNi _0.8 Co _0.2 O ₂ particles and LiFePO ₄ fine particles. A positive electrode active material was synthesized in the same manner as described above, and a coin-type non-aqueous electrolyte battery was manufactured in the same manner as in Example 1 using the positive electrode active material.

Comparative Example 1 Example 1 was repeated except that the rotation speed was adjusted so that the particle temperature T became 30 ° C. when mixing and stirring LiNi _0.8 Co _0.2 O ₂ particles and LiFePO ₄ fine particles. A positive electrode active material was synthesized in the same manner as described above, and a coin-type non-aqueous electrolyte battery was manufactured in the same manner as in Example 1 using the positive electrode active material.

Comparative Example 2 Example 1 was repeated except that the rotation speed was adjusted so that the particle temperature T became 34 ° C. when mixing and stirring LiNi _0.8 Co _0.2 O ₂ particles and LiFePO ₄ fine particles. A positive electrode active material was synthesized in the same manner as described above, and a coin-type non-aqueous electrolyte battery was manufactured in the same manner as in Example 1 using the positive electrode active material.

Comparative Example 3 Example 1 was repeated except that the rotation speed was adjusted so that the particle temperature T became 46 ° C. when mixing and stirring LiNi _0.8 Co _0.2 O ₂ particles and LiFePO ₄ fine particles. A positive electrode active material was synthesized in the same manner as described above, and a coin-type non-aqueous electrolyte battery was manufactured in the same manner as in Example 1 using the positive electrode active material.

Comparative Example 4 Example 1 was repeated except that the rotation speed was adjusted so that the particle temperature T became 50 ° C. when mixing and stirring LiNi _0.8 Co _0.2 O ₂ particles and LiFePO ₄ fine particles. A positive electrode active material was synthesized in the same manner as described above, and a coin-type non-aqueous electrolyte battery was manufactured in the same manner as in Example 1 using the positive electrode active material.

[0070] without surface modification treatment for <Comparative Example 5> LiNi _0.8 Co _0.2 O ₂ particles, the LiNi _0.8 Co
_A coin-type non-aqueous electrolyte battery was manufactured in the same manner as in Example 1, except that _0.2 O ₂ particles were used as the positive electrode active material.

The load characteristics of the non-aqueous electrolyte battery fabricated as described above were measured. Initial charging is performed at a current density of 500 uA / cell until the open circuit voltage (OCV) reaches 4.2 V and 0.05 V, and discharging is performed at a current density of 5 μA until the closed circuit voltage (CCV) reaches 3.0 V.
Performed at 00 uA / cell.

Further, the battery was charged at the same current density until the OCV became 4.2 V, and stored at 60 ° C. for 24 hours. After storage, the same discharge as in the first cycle was performed at the same current density, and the capacity was measured.

The discharge capacity before storage was defined as Cap (A), and the discharge capacity after storage was defined as Cap (B), and the capacity retention was calculated by the following equation.

Capacity maintenance rate (%) = {Cap (B) / Ca
p (A)｝ × 100 For the nonaqueous electrolyte batteries of Examples 1 to 5 and Comparative Examples 1 to 5, LiNi _0.8 Co _0.2 O ₂ particles and LiF
FIG. 4 shows the relationship between the particle temperature T during stirring with the ePO ₄ fine particles and the capacity retention (%) of the nonaqueous electrolyte battery. In addition,
The horizontal dotted line in FIG. 4 indicates the capacity retention ratio (%) of Comparative Example 5 in which the surface modification treatment was not performed on the LiNi _0.8 Co _0.2 O ₂ particles.

As is apparent from FIG._0.8C
o_0.2O_TwoParticles and LiFePO_FourParticles when stirring with fine particles
Batteries of Comparative Examples 1 and 2 whose temperature T is lower than 35 ° C.
In comparison with Comparative Example 5 in which the surface modification treatment was not performed,
The quantity maintenance rate has decreased. This is the impulse between particles.
Since the impact energy is not high enough, LiNi_1-xM_xO
_TwoLiFePO on the particle surface_FourFine particle deposition
Probably because they could not.

Also, in the batteries of Comparative Examples 3 and 4 having a particle temperature T higher than 45 ° C., the capacity retention ratio was lower than that of Comparative Example 5. This is presumably because the collision energy between the particles was too large, causing collision cracking of the particles.

On the other hand, the batteries of Examples 1 to 5 in which the particle temperature T satisfies the range of 35 ° C. ≦ T ≦ 45 ° C.
A much better capacity retention ratio is obtained as compared with. This is because the collision energy between the particles is controlled to an appropriate range, and thus the particles do not crack and the LiNi _1-x M _x O
It is considered that LiFePO ₄ fine particles could be adhered to the surface of the _two particles. And it turned out that the nonaqueous electrolyte battery using such a positive electrode active material is excellent in high capacity and high charge / discharge cycle characteristics.

[0078]

According to the present invention, the general formula LiNi _1-x M _x O ₂
(In the formula, M is an element containing at least one of Al, B, and Co.) Since the surfaces of the Ni composite oxide particles represented by LiFePO ₄ fine particles are covered, By suppressing structural deterioration, the positive electrode active material has both the advantages of a Ni composite oxide having a high energy density and the advantages of LiFePO ₄ having excellent structural stability during charging, and by using the positive electrode active material, A nonaqueous electrolyte battery having high capacity and excellent charge / discharge cycle characteristics can be realized.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a configuration example of a nonaqueous electrolyte battery according to the present invention.

FIG. 2 is a diagram showing a particle size distribution of LiNi _0.8 Co _0.2 O ₂ particles used in Examples.

FIG. 3 is a view showing a particle size distribution of LiFePO ₄ fine particles used in Examples.

FIG. 4 is a diagram showing a relationship between a stirring temperature T of mixed particles and a capacity retention ratio for a battery prepared in an example.

[Explanation of symbols]

1 non-aqueous electrolyte battery, 2 negative electrode, 3 negative electrode can, 4
Positive electrode, 5 Positive electrode can, 6 Separator, 7 Insulating gasket

Continued on front page F term (reference) 4G048 AA04 AB01 AB04 AC06 AD03 AE05 5H029 AJ03 AJ05 AK03 AM03 AM05 AM07 BJ03 CJ05 CJ08 CJ28 DJ12 DJ16 HJ14 5H050 AA07 AA08 BA17 CA08 CB07 CB12 FA12 FA18 GA07 GA10 GA27 HA02

Claims (4)

[Claims] 1. The surface of a particle represented by a general formula LiNi _1-x M _x O ₂ (where M is an element containing at least one of Al, B and Co) has a general formula LiFePO ₄
A positive electrode active material characterized by being coated with fine particles represented by the formula: 2. A positive electrode having a positive electrode active material, a negative electrode having a negative electrode active material, and a non-aqueous electrolyte interposed between the positive electrode and the negative electrode, wherein the positive electrode active material has a general formula of LiNi _{1 -x} M _x O ₂ (where
M is an element containing at least one of Al, B, and Co. ) Is represented by the general formula LiFePO
A nonaqueous electrolyte battery characterized by being coated with the fine particles represented by ₄ . 3. A particle represented by the general formula LiNi _1-x M _x O ₂ (where M is an element containing at least one of Al, B and Co) and a particle represented by the general formula LiFePO ₄ And the particle temperature (T) is 35 ° C. ≦ T ≦
A method for producing a positive electrode active material, wherein the surface of the particles is covered with the fine particles by stirring the mixture to a temperature of 45 ° C. 4. A method for producing a non-aqueous electrolyte battery comprising: a positive electrode having a positive electrode active material; a negative electrode having a negative electrode active material; and a non-aqueous electrolyte interposed between the positive electrode and the negative electrode. When synthesizing the positive electrode active material, the general formula LiNi _1-x M _x
A particle represented by O ₂ (where M is an element containing at least one of Al, B, and Co);
ePO ₄ is mixed with fine particles, and the particle temperature (T)
A method for producing a non-aqueous electrolyte battery, characterized in that the surface of the particles is covered with the fine particles to form a positive electrode active material by stirring so that the temperature falls within a range of 35 ° C. ≦ T ≦ 45 ° C.