JPH0935715A - Method for producing positive electrode active material and non-aqueous electrolyte secondary battery - Google Patents

Abstract

(57) Abstract: A positive electrode active material having a high electrode packing property and a wide reaction area is manufactured. Further, by using the positive electrode active material obtained by such a manufacturing method, a nonaqueous electrolyte secondary battery having high electrode packing property, high energy density and excellent heavy load cycle characteristics is obtained. . SOLUTION: Composite particles 36 are produced by coating the surface of core particles 34 made of any one of predetermined lithium-containing compounds with fine particles 35 of lithium-containing compounds. Then, the composite particles are used as a positive electrode active material of a battery.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a positive electrode active material and a non-aqueous electrolyte secondary battery using the same.

[0002]

2. Description of the Related Art In recent years, due to remarkable progress in electronic technology, high performance, miniaturization, and portability of electronic devices have been advanced, and batteries used in these electronic devices are required to have high energy. It has become.

Conventionally, secondary batteries used in electronic equipment include aqueous secondary batteries such as nickel-cadmium batteries and lead batteries. However, these aqueous solution type secondary batteries have a low discharge potential, and it is the actual situation that they cannot fully meet the recent demand for improvement in energy density.

On the other hand, recently, as a battery system capable of obtaining a high energy density, a lithium secondary battery using metallic lithium or a lithium alloy as a negative electrode active material has attracted attention,
Research is actively conducted.

However, in this secondary battery,
When metallic lithium is used as the negative electrode active material, when lithium is dissolved and deposited on the negative electrode, metallic lithium crystallizes in a dendrite form from the negative electrode and eventually reaches the positive electrode, which may lead to an internal short circuit. It is highly likely. When a lithium alloy is used as the negative electrode active material, lithium is also dissolved and deposited on the negative electrode, so that the negative electrode is miniaturized and the negative electrode performance is deteriorated. In any case, the lithium secondary battery is recognized as having problems in cycle life, safety, quick charging performance, etc., which is a major obstacle to practical use, and has been partially commercialized as a coin type. Nothing more than.

Therefore, in order to solve such a problem, a non-aqueous electrolyte secondary battery (lithium battery) having a negative electrode active material such as a carbonaceous material capable of doping and dedoping lithium ions is used. Research and development of (ion secondary batteries) are being actively conducted. In this non-aqueous electrolyte secondary battery, since lithium does not exist in a metallic state in the battery system, metallic lithium does not grow in the form of dendrite from the negative electrode, and good cycle characteristics and safety can be obtained. become.

In such a non-aqueous electrolyte secondary battery, the battery voltage is increased by using a lithium-containing compound having a high redox potential as the positive electrode active material.
Energy density is increased. Furthermore, self-discharge is smaller than that of nickel-cadmium batteries, and it exhibits extremely excellent performance as a secondary battery. Since the non-aqueous electrolyte secondary battery using the carbonaceous material as the negative electrode active material has excellent characteristics, it can be used for portable electronic devices such as 8 m / mVTR, CD player, laptop computer, and cellular telephone. Commercialization has started as a power source.

By the way, in portable electronic equipment using a secondary battery, power consumption tends to increase with the diversification of functions. For this reason, with respect to the battery serving as a power source, further improvement in energy density and heavy load cycle characteristics has been demanded.

Here, the heavy duty cycle characteristic of the battery largely depends on the reaction area at the electrode. That is, in the battery,
Good heavy duty cycle characteristics are obtained when the reaction area of the electrode is large.

From this point of view, looking at the cylindrical type battery and the coin type battery which are mainly adopted as the battery type of the lithium ion secondary battery, first, in the cylindrical type battery, the surface of the strip-shaped metal foil serving as a current collector. The thin film positive electrode and the negative electrode on which the electrode mixture layer is formed are laminated with a plurality of layers through a separator, and a wound electrode body formed by winding this is used, which is a so-called jelly roll type. There is. In the case of a negative electrode, the electrode mixture layer is formed by applying a negative electrode mixture slurry in which a powder of a carbonaceous material and a binder are dispersed in an organic solvent to the surface of the current collector and drying the mixture. It is a layer. In the case of the positive electrode, it is a layer formed by applying and drying a positive electrode mixture slurry in which a powder of a lithium-containing compound, a binder and a conductive agent are dispersed in an organic solvent, and drying the same.

The spirally wound electrode body in which a plurality of such thin film electrodes are laminated has a relatively large reaction area, enables rapid charging, and has a long cycle life.

On the other hand, in a coin-type battery, a positive electrode and a negative electrode in pellet form, which are obtained by compression-molding an electrode mixture in accordance with the shape of a battery can, are stacked in a battery can with a separator interposed therebetween. It is stored.

In the case of a battery in which such pellet-shaped electrodes are laminated, it is considered that the electrode reaction is likely to proceed from the surface of the positive electrode and the negative electrode facing the separator, and the electrode reaction becomes slower at the portion farther from this surface. . For this reason, when the electrode thickness is increased, an apparent overvoltage state is likely to occur in the portion far from the surface facing the separator, and the deterioration of the active material progresses. Therefore, sufficient cycle characteristics and load characteristics cannot be obtained.

In order to increase the reaction area of the coin type battery, an electrode structure in which the electrodes are divided in the thickness direction and a current collector is interposed between them is also considered. However, in this case, since the current collector occupies a part of the battery can volume, there is a disadvantage that the filling rate of the electrode mixture is reduced and the battery capacity is reduced accordingly.

[0015]

As described above, in the conventional non-aqueous electrolyte secondary batteries, the degree thereof varies depending on the electrode form, but the problem that the electrode filling property becomes smaller when trying to secure the reaction area of the electrode. Therefore, it is very difficult to improve the heavy load characteristics while maintaining the energy density.

Therefore, the present invention has been proposed in view of the above conventional circumstances, and when an electrode is constructed, a positive electrode active material which can obtain a high electrode packing property and can secure a wide reaction area. It aims at providing the manufacturing method of. Further, by using the positive electrode active material obtained by such a manufacturing method, it is possible to provide a non-aqueous electrolyte secondary battery having high electrode packing property, high energy density, and excellent heavy load cycle characteristics. The purpose is to

[0017]

In order to achieve the above-mentioned object, the method for producing a positive electrode active material of the present invention comprises Li _x CoO ₂ ,
Li _x NiO ₂ , Li _x Mn ₂ O ₄ , Li _x Co _{1- y My} O ₂ ,
_{Li x Ni 1-y M y} O 2, L x Mn 1-y M y O 2 ( where, M is
Ti, V, Cr, Mn, Fe, Al, Co, Ni, C
u, Zn, Mo, Bi, B, at least one element selected, x is 0 <x ≦ 1.2, and y is 0 <y <1). Composite particles are produced by coating the surface of core particles made of the above with fine particles made of any of these lithium-containing compounds.

In producing the positive electrode active material in this manner, the core particles are coated with fine particles, that is, the average particle size r ₁ as the composite particles, the average particle size r ₂ of the core particles, and the core particles. It is important that the average particle size r ₃ of the fine particles that coat the circumference of the core be appropriate.

[0019] That is, the ratio r ₁ / r ₂ of the average particle diameter r ₂ of the average particle diameter r ₁ and its core particles of the composite particles themselves, 1.01 ≦
It is desirable that r ₁ / r ₂ ≦ 2, and the ratio r ₃ / r ₂ of the average particle size r ₃ of the fine particles to the average particle size r ₂ of the core particles is r ₃ / r ₂ ≦
It is more preferably 1/5. However, the average particle size referred to here is the median size, that is, the particle size for 50% of the cumulative distribution.

The produced composite particles may be heat-treated thereafter.

In the non-aqueous electrolyte secondary battery of the present invention, the positive electrode is constituted by using the composite particles thus produced as the positive electrode active material. In this case, the negative electrode is mainly composed of lithium metal, a lithium alloy, or a carbon material capable of doping / dedoping lithium.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION Specific embodiments of the present invention will be described below.

In the method for producing the positive electrode active material of the present invention, the method shown in FIG.
As shown in, Li _x CoO ₂ , Li _x NiO ₂ , Li _x M
n ₂ O ₄ , Li _x Co _{1- y My} O ₂ , Li _x Ni _{1- y My} O ₂ , L
_{x Mn 1-y M y O} 2 ( where, M is, Ti, V, Cr, Mn ,
Fe, Al, Co, Ni, Cu, Zn, Mo, Bi, B
Represents at least one element selected from, and x is 0 <x
≦ 1.2, y is 0 <y <1), and the surface of the core particle 34 made of any of the lithium-containing compounds is represented by the fine particles 35 made of any of these lithium-containing compounds.
The composite particles 36 are produced by coating with.

As a method for coating the surfaces of the core particles 34 made of a lithium-containing compound with the fine particles 35 made of a lithium-containing compound, there is a high-speed air flow impact method.
The high-speed airflow impact method is to disperse a mixture in which powder and fine particles are uniformly mixed in a high-speed airflow, and to repeatedly perform an impact operation to impart mechanical and thermal energy to the powder. It is a thing. By this action, the fine particles are uniformly attached to the surface of the powder, and the surface of the powder is modified. For reference, L not covered with fine particles
A scanning micrograph of iCoO ₂ core particles is shown in FIG.
A scanning micrograph of the composite particles coated with O ₂ fine particles is shown in FIG. In this case, the ratio r ₃ / r ₂ of the average particle size r ₂ of the core particles and the average particle size r ₃ of the fine particles is 0.05. The core particles and the fine particles may be the same kind of lithium-containing compound as described above, or may be different kinds of lithium-containing compounds.

The following effects can be obtained by using, as the positive electrode active material, composite particles of a lithium-containing compound in which the surfaces of the core particles are coated with fine particles.

That is, in general, the packing density of powder particles is
It tends to increase as the particle size increases.
This tendency is also applicable to the case where the positive electrode is made of a lithium-containing compound, and the use of a lithium-containing compound having a larger particle diameter makes it possible to obtain a positive electrode having a high chargeability of the active material.

However, although a lithium-containing compound having a large particle size can have high electrode packing property, its effective surface area contributing to the electrode reaction is small because its specific surface area is small. Therefore, in the positive electrode using such a lithium-containing compound having a large particle size, the portion far from the surface facing the negative electrode is likely to be in an overvoltage state, and the deterioration of the active material progresses.

On the other hand, the composite particles of the lithium-containing compound in which the surface of the core particle is coated with the fine particles have a larger specific surface area than the ordinary lithium-containing compound having the same particle size. Therefore, by increasing the particle size, the filling property is improved, and at the same time, the reaction area that effectively contributes to the electrode reaction is sufficiently ensured.
Therefore, when this composite powder is used for the positive electrode, a high energy can be obtained, and at the same time, a battery excellent in heavy load characteristics and cycle characteristics can be realized.

In order to obtain such an effect effectively, the core particles are covered with fine particles, that is, the average particle size r ₁ of the composite particles, the average particle size r ₂ of the core particles and the average particle size r ₂ of the core particles. It is important that the average particle size r ₃ of the fine particles covering the surroundings is appropriate.

[0030] That is, the ratio r ₁ / r ₂ of the average particle diameter r ₂ of the mean particle size r ₁ and the core particles of the composite particles, 1.01 ≦ r ₁ / r ₂
It is preferable that ≦ 2. When r ₁ / r ₂ is less than 1.01, that is, when the ratio of the coating layer formed by the fine particles is too small, the heavy load cycle characteristics cannot be sufficiently improved. On the other hand, when r ₁ / r ₂ is larger than ₂ , that is, when the ratio of the coating layer formed by the fine particles is too large, the heavy load cycle characteristics deteriorate rather.

The ratio r ₃ / r ₂ of the average particle size r ₃ of the fine particles to the average particle size r ₂ of the core particles is preferably 1/5 or less. When r ₃ / r ₂ is larger than 1/5, that is, when the particle size of the fine particles is too large with respect to the particle size of the core particles,
There is a high possibility that the gap between the core particles and the fine particles is large and the structure of the composite particles is broken.

Among them, the average particle diameter r ₂ of the core particles is preferably 3 μm ≦ r ₂ ≦ 30 μm in terms of handling.

The composite powder of lithium composite oxide in which the surfaces of the core particles are coated with fine particles may be further heat-treated at an appropriate temperature. As a result, the properties such as conductivity of the composite powder are improved, and the composite powder becomes more excellent as a positive electrode active material.

The non-aqueous electrolyte secondary battery of the present invention uses the lithium-containing compound produced as described above as a positive electrode active material. Therefore, a high electrode filling property can be obtained, a sufficient electrode reaction area can be secured, a high energy density can be obtained, and a good heavy load cycle characteristic can be obtained.

On the other hand, as the negative electrode active material of the battery, lithium, a lithium alloy, or a carbon material capable of doping / dedoping lithium is used. As this carbon material, a low crystalline carbon material obtained by firing at a relatively low temperature of 2000 ° C. or lower, or a raw material that easily crystallizes is used.
A highly crystalline carbon material such as artificial graphite or natural graphite obtained by heat treatment at a high temperature near 000 ° C. is used. Specifically, pyrolytic carbons, cokes (pitch coke,
Needle coke, petroleum coke, etc.), graphites, glassy carbons, organic polymer compound fired bodies (carbonized by firing furan resin at an appropriate temperature), carbon fibers, activated carbon and the like. In particular, the surface spacing of the (002) plane is 0.
A carbon material having a characteristic of having a true specific gravity of 370 nm or more and less than 1.70 g / cc and having no exothermic peak at 700 ° C. or more in a differential thermal analysis in an air stream is preferable.

Further, as the electrolytic solution, an electrolytic solution in which a lithium salt is used as a supporting electrolyte and this is dissolved in an organic solvent is used.

As the organic solvent, propylene carbonate, ethylene carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone,
Tetrahydrofuran, 2-methyltetrahydrofuran,
1,3-dioxolane, 4-methyl-1,3-dioxolane, sulfolane, methylsulfolane, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate and the like can be used.

As the supporting electrolyte, LiClO ₄ , Li
AsF ₆ , LiPF ₆ , LiBF ₄ , LiB (C ₆ H ₅ ) ₄ ,
CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, LiN (CF ₃ S
O ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiCl, LiBr
And the like.

[0039]

EXAMPLES Examples of the present invention will be described based on experimental results.

Structure of Battery Produced FIG. 4 shows the structure of the battery produced in each experimental example described later.

In this non-aqueous electrolyte secondary battery, as shown in FIG. 4, a negative electrode 1 formed by coating a negative electrode current collector 10 with a negative electrode active material, and a positive electrode current collector 11 coated with a positive electrode active material. The positive electrode 2 and the positive electrode 2 are wound around the separator 3, and the wound body is housed in the battery can 5 with the insulator 4 placed on the upper and lower sides.

A battery lid 7 is attached to the battery can 5 by caulking through a sealing gasket 6, and is electrically connected to the negative electrode 1 or the positive electrode 2 through a negative electrode lead 12 and a positive electrode lead 13, respectively, It is configured to function as a negative electrode or a positive electrode.

In the battery of this embodiment, the positive electrode lead 13 is welded and attached to the safety valve device 8 having a current cutoff mechanism, and electrically connected to the battery lid 7 via the safety valve device 8. ing.

In the battery having such a structure, when the pressure inside the battery rises, the safety valve device 8 is pushed up and deformed. Then, the positive electrode lead 13 is cut off leaving the portion welded to the safety valve device 8 and the current is cut off.

Example 1 First, a positive electrode active material was produced as follows.

Cobalt carbonate and lithium carbonate were mixed with Li / C
The mixture was mixed so that the o ratio was 1, and the mixture was baked in air at a temperature of 900 ° C. for 5 hours. As a result of X-ray diffraction measurement of this fired product, it was in good agreement with the diffraction pattern of LiCoO _{2 on} the JCPDS card. By crushing this LiCoO ₂ , core particles having an average particle diameter of 3.0 μm and fine particles having an average particle diameter of 0.1 μm were obtained. And this LiCoO ₂
LiCoO ₂ fine particles were coated on the surface of the core particles by a high-speed air current impact method to prepare LiCoO ₂ composite particles. The average particle size of the produced composite particles was 5.9 μm. The average particle diameter is a volume-based median diameter and is measured by a laser diffraction particle size meter (trade name LA- manufactured by Horiba Ltd.
50).

Then, a positive electrode was prepared as follows using the LiCoO ₂ composite particles as a positive electrode active material.

91% by weight of LiCoO ₂ composite particles, 6% by weight of graphite as a conductive agent, and 3% by weight of polyvinylidene fluoride were mixed to prepare a positive electrode mixture, and N-methyl-2 was used.
A positive electrode mixture slurry was prepared by dispersing it in pyrrolidone.

The positive electrode mixture slurry was applied on both sides of an aluminum foil which will be the positive electrode current collector 11, dried, and then compression-molded by a roller press to produce a strip-shaped positive electrode 2.

Next, a negative electrode active material was produced.

Petroleum pitch was used as a starting material, and 10 to 20% of a functional group containing oxygen was introduced (oxygen cross-linking) into the pitch.
Firing was performed at a temperature of 1000 ° C. in an inert gas. as a result,
A non-graphitizable carbon material having properties close to those of a glassy carbon material was obtained.

Negative electrode 1 was prepared as follows using this non-graphitizable carbon material as a negative electrode active material.

90% by weight of a carbon material and 10% by weight of polyvinylidene fluoride as a binder were mixed to prepare a negative electrode mixture, which was dispersed in N-methyl-2-pyrrolidone to obtain a negative electrode mixture slurry.

Then, the negative electrode mixture slurry was applied onto both surfaces of a copper foil which will serve as the negative electrode current collector 10, dried and then compression-molded with a roller press machine to prepare a strip-shaped negative electrode 1.

The strip-shaped negative electrode 1 and the positive electrode 2 produced as described above were laminated with a microporous polypropylene film having a thickness of 25 μm serving as a separator interposed therebetween, and wound a number of times to produce a spiral electrode body. .

Next, the spiral electrode body was housed in a nickel-plated iron battery can 5, and insulating plates 4 were arranged on the upper and lower surfaces of the spiral electrode body. Then, the positive electrode 2 and the negative electrode 1
In order to collect the current, the positive electrode lead 13 made of aluminum is led out from the positive electrode current collector 11 and welded to the safety valve device 8 having a current cutoff device, and the negative electrode lead 12 made of nickel is led out of the negative electrode current collector 10. And welded to the battery can 5.

Then, an electrolytic solution prepared by dissolving LiPF ₆ at a concentration of 1 mol in a mixed solvent of propylene carbonate 50% by volume and methyl ethyl carbonate 50% by volume was injected into the battery can 5. Then, the battery lid 7 and the battery can 5 were fixed by being caulked via the gasket 6 coated with asphalt, to produce a cylindrical battery having a diameter of 18 mm and a height of 65 mm.

[0058] In generating the Example 2 cathode active material, the average particle size of LiCoO ₂ of 15.1μm as the core particles, an average particle diameter using a LiCoO ₂ of 0.7μm as fine particles, the average particle size of 1
A cylindrical battery was produced in the same manner as in Example 1 except that composite particles of 8.4 μm were produced.

[0059] In generating the Example 3 positive electrode active material, the average particle size of LiCoO ₂ of 30.3μm as the core particles, an average particle diameter using a LiCoO ₂ of 3.0μm as fine particles, average particle size 3
A cylindrical battery was produced in the same manner as in Example 1 except that 4.0 μm composite particles were produced.

[0060] In generating a fourth embodiment the positive electrode active material, the average particle size of LiCoO ₂ of 30.3μm as the core particles, an average particle diameter using a LiCoO ₂ of 0.7μm as fine particles, average particle size 3
A cylindrical battery was produced in the same manner as in Example 1 except that composite particles of 3.4 μm were produced.

Comparative Example 1 A cylindrical battery was produced in the same manner as in Example 1 except that LiCoO ₂ having an average particle size of 3.0 μm was used as the positive electrode active material.

Comparative Example 2 A cylindrical battery was produced in the same manner as in Example 1 except that LiCoO ₂ having an average particle size of 15.1 μm was used as the positive electrode active material.

Comparative Example 3 A cylindrical battery was produced in the same manner as in Example 1 except that LiCoO ₂ having an average particle size of 30.3 μm was used as the positive electrode active material.

The battery thus produced was charged under the conditions of a charging voltage of 4.20 V, a charging current of 1000 mA and a charging time of 2.5 hours, and a discharging current of 1200 m.
A, the charge / discharge cycle under heavy load discharge conditions such as discharging under the condition that the final voltage is 2.75 V is repeated, and the ratio of the initial discharge capacity (initial discharge capacity) to the discharge capacity at the 200th cycle (capacity maintenance rate) I asked. Table 1 shows the measurement results of the initial discharge capacity and the capacity retention rate.

[0065]

[Table 1]

In Table 1, first, when comparing the batteries of Comparative Examples 1 to 3 in which LiCoO ₂ not coated with fine particles was directly used as the positive electrode active material, in this case, the average particle size of the positive electrode active material becomes large. It can be seen that the capacity retention rate under heavy load discharge conditions deteriorates.

On the other hand, LiCo coated with fine particles
Comparing Examples 1 to 4 using O ₂ as the positive electrode active material, the battery of Example 3 in which the average particle size of the positive electrode active material is 34.0 μm and the average particle size of the positive electrode active material are 33.4 μm. Even in the battery of Example 4, which is No. 4, a sufficient capacity retention rate was obtained under heavy load discharge conditions.

From this fact, LiC coated with fine particles
It has been found that oO ₂ can impart good heavy load cycle characteristics to the battery even if the average particle size is large, and makes it possible to satisfy both the electrode filling property and the heavy load discharge characteristic.

Example 5 A positive electrode active material was produced as follows.

Cobalt oxide, nickel oxide and lithium hydroxide were mixed so as to have a Li / Ni / Co ratio of 1 / 0.8 / 0.2, and the mixture was heated at 750 ° C. under an atmosphere containing oxygen to give 5
By firing for a time, LiNi _0.8 Co _0.2 O ₂ was produced.

By crushing this LiNi _0.8 Co _0.2 O ₂ , core particles having an average particle size of 15.1 μm were obtained. And
The surface of the core particles of LiNi _0.8 Co _0.2 O ₂ was coated with fine particles of LiCoO ₂ having an average particle size of 0.7 μm by a high-speed air current impact method to obtain LiNi _0.8 Co _0.2 O ₂ and LiC.
Composite particles of oO ₂ were prepared. The average particle size of the composite particles was 18.6 μm.

A cylindrical battery was produced in the same manner as in Example 1 except that the composite particles thus produced were used as the positive electrode active material.

Example 6 A positive electrode active material was produced as follows.

1 mol of manganese dioxide and 0.
LiMn ₂ O ₄ was produced by mixing 25 mol and firing in air at a temperature of 850 ° C. for 5 hours.

By crushing this LiMn ₂ O ₄ , core particles having an average particle size of 15.1 μm were obtained. And this LiM
On the surface of the core particles of n ₂ O ₄ , Li with an average particle size of 0.7 μm
CoO ₂ fine particles were coated by a high-speed air current impact method to prepare composite particles of LiMn ₂ O ₄ and LiCoO ₂ . The average particle size of the composite particles was 18.5 μm.

A cylindrical battery was manufactured in the same manner as in Example 1 except that the composite particles thus produced were used as the positive electrode active material.

Comparative Example 4 A cylindrical battery was produced in the same manner as in Example 1 except that LiNi _0.8 Co _0.2 O ₂ having an average particle size of 15.1 μm was used as the positive electrode active material.

Comparative Example 5 A cylindrical battery was prepared in the same manner as in Example 1 except that LiMn ₂ O ₄ having an average particle size of 15.1 μm was used as the positive electrode active material.

With respect to the battery manufactured as described above, the initial discharge capacity and the discharge capacity at the 200th cycle under heavy load discharge conditions were measured in the same manner as described above, and the capacity retention rate was obtained. The results are shown in Table 2.

[0080]

[Table 2]

As can be seen from Table 2, the batteries of Examples 5 and 6 using LiNi _0.8 Co _0.2 O ₂ or LiMn ₂ O ₄ coated with fine particles as the positive electrode active material were not coated with fine particles. As compared with Comparative Examples 4 and 5 in which LiNi _0.8 Co _0.2 O ₂ or LiMn ₂ O ₄ was directly used as the positive electrode active material, a large initial capacity was obtained and the capacity retention ratio was high. There is.

From this fact, not only LiCoO ₂ but also L
It was found that the coating of iNi _0.8 Co _0.2 O ₂ and LiMn ₂ O ₄ with fine particles is also effective in enhancing the performance as a positive electrode.

Average particle size r ₁ of composite particles, average particle size of core particles
Examination of Diameter r ₂ and Average Particle Size r ₃ of Fine Particles When producing a positive electrode active material, LiCoO ₂ having an average particle size shown in Table 3 was used as core particles and fine particles, and composite particles having an average particle size shown in the same table were used. A cylindrical battery was produced in the same manner as in Example 1 except that

With respect to the manufactured battery, the initial discharge capacity and the 200th cycle discharge capacity under heavy load discharge conditions were measured in the same manner as described above, and the capacity retention rate was obtained. Table 3 shows the results.

[0085]

[Table 3]

As shown in Table 3, the average particle size r of the composite particles
₁ and an average particle size batteries of Experimental Example 7 cells and this value of Example 6 The ratio r ₁ / r ₂ is less than 1.01 to more than two of r ₂ of the core particles, the capacity retention ratio compared to other Is low. Therefore, r ₁ / r ₂ it is seen that that is in the range of _{1.01 ≦ r 1 / r 2 ≦} 2 desirable.

Even if r ₁ / r ₂ is within this range,
Ratio of average particle size r _{3 of} fine particles to average particle size r ₂ of core particles r ₃ /
The battery of Experimental Example 5 in which r ₂ exceeds 1/5 cannot be said to have a sufficient capacity retention rate.

Therefore, when producing composite particles, r ₁ / r ₂ should be within the range of 1.01 ≦ r ₁ / r ₂ ≦ 2, and r ₃ / r ₂ should be 1/5 or less. In addition, it is understood that it is preferable to set the average particle diameter of the core particles and the fine particles and the conditions of the impact method in a high-speed air stream.

In this example, LiCo
O ₂ , LiNi _0.8 CO _0.2 O ₂ , and LiMn ₂ O ₄ were used as the lithium-containing compound. In addition to these, Li _x CoO ₂ , L
i _x NiO ₂ , Li _x Mn ₂ O ₄ , Li _x Co _{1- y My} O ₂ , L
_{i x Ni 1-y MyO 2} , Li x Mn 1-y M y O 2 ( where, M is Ti, V, Cr, Mn, Fe, Al, Co, Ni, C
represents at least one selected from u, Zn, Mo, Bi and B, where x is 0 <x ≦ 1.2 and y is 0 <y <1)
It has been confirmed by experiments that the same effect can be obtained even when the lithium-containing compound represented by

Further, in this embodiment, the positive electrode active material was applied to the cylindrical battery, but the same effect can be obtained when applied to the prismatic, flattened, coin or button type battery. Is.

[0091]

As is clear from the above description, in the method for producing a positive electrode active material of the present invention, the surface of core particles made of a predetermined lithium-containing compound is coated with fine particles made of a lithium-containing compound. When the positive electrode active material produced in this manner is applied to a non-aqueous electrolyte secondary battery, it is possible to secure a large reaction area while enhancing the electrode filling property in the positive electrode, which has high energy and heavy load cycle characteristics. You can acquire excellent secondary batteries.

[Brief description of drawings]

FIG. 1 is a schematic view showing a state in which a surface of a core particle is covered with a composite powder.

FIG. 2 is a scanning micrograph showing the particle structure of LiCoO ₂ core particles.

FIG. 3 is a scanning micrograph showing a particle structure of LiCoO ₂ composite powder.

FIG. 4 is a vertical cross-sectional view showing one structural example of a non-aqueous electrolyte secondary battery to which the present invention is applied.

[Explanation of symbols]

 34 core particles 35 fine particles 36 composite powder

Claims (5)

[Claims] 1. Li _x CoO ₂ , Li _x NiO ₂ , Li _x M
n ₂ O ₄ , Li _x Co _{1- y My} O ₂ , Li _x Ni _{1- y My} O ₂ , L
_{x Mn 1-y M y O} 2 ( where, M is, Ti, V, Cr, Mn ,
Fe, Al, Co, Ni, Cu, Zn, Mo, Bi, B
Represents at least one element selected from, and x is 0 <x
≦ 1.2, y is 0 <y <1, and composite particles are obtained by coating the surface of core particles made of any of the lithium-containing compounds with fine particles made of any of these lithium-containing compounds. A method for producing a positive electrode active material, which comprises: _2. The ratio r ₁ / r ₂ of the average particle size r ₁ of the composite particles and the average particle size r ₂ of the core particles is 1.01 ≦ r ₁ / r ₂ ≦ 2. Item 2. A method for producing a positive electrode active material according to Item 1. 3. The positive electrode active material according to claim ₂ , wherein the ratio r ₃ / r ₂ of the average particle size r _{3 of the} fine particles to the average particle size r ₂ of the core particles is 1/5 or less. Production method. 4. The method for producing a positive electrode active material according to claim 1, wherein the composite particles are heat-treated. 5. A negative electrode comprising a lithium metal, a lithium alloy, or a carbon material capable of being doped or dedoped with lithium as a negative electrode active material, a positive electrode comprising a lithium-containing compound as a positive electrode active material, and a non-aqueous electrolyte solution. In the non-aqueous electrolyte secondary battery formed as described above, the positive electrode active material is Li _x CoO ₂ , Li _x NiO ₂ , Li _x M
n ₂ O ₄ , Li _x Co _{1- y My} O ₂ , Li _x Ni _{1- y My} O ₂ , L
_{x Mn 1-y M y O} 2 ( where, M is, Ti, V, Cr, Mn ,
Fe, Al, Co, Ni, Cu, Zn, Mo, Bi, B
Represents at least one element selected from, and x is 0 <x
≦ 1.2, y is 0 <y <1, and is produced by coating the surface of a core particle made of any of the lithium-containing compounds with fine particles made of any of these lithium-containing compounds. A non-aqueous electrolyte secondary battery characterized in that it is a composite particle.