JP2022115903A - Transition metal-containing composite hydroxide particle and manufacturing method of the same, positive electrode active material for nonaqueous electrolyte secondary battery and manufacturing method of the same, and nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive electrode active material capable of simultaneously improving high capacity characteristics, high output characteristics, especially excellent output characteristics in a low SOC region, and excellent cycle characteristics, and to provide a transition metal-containing composite hydroxide particle as a precursor thereof.

SOLUTION: Provided is a positive electrode active material for a nonaqueous electrolyte secondary battery comprising a secondary particle formed by aggregating a plurality of primary particles. Intermingled in the secondary particle are a large size particle having a structure in which an aggregated portion of the primary particles electrically conducting with an outer shell portion and electrically conducting with each other and a space portion in which the primary particles do not exist are dispersed inside the outer shell portion, and a solid small size particle having a radius equal to a thickness of the outer shell portion of the large size particle or to the aggregated portion of the primary particles. The ratio between the large size particles and the small size particles is the same as a mass ratio in the composite hydroxide particles, and the small size particles exist in a range of 0.05 to 20 in mass ratio to the large size particles.

SELECTED DRAWING: Figure 1

COPYRIGHT: (C)2022,JPO&INPIT

Description

The present invention provides transition metal-containing composite hydroxide particles, a method for producing the same, a positive electrode active material for a non-aqueous electrolyte secondary battery using the transition metal-containing composite hydroxide particles as a precursor, and a method for producing the same, and the non-aqueous electrolyte secondary battery. The present invention relates to a nonaqueous electrolyte secondary battery using a positive electrode active material for a water electrolyte secondary battery as a positive electrode material.

In recent years, with the spread of mobile electronic devices such as mobile phones and laptop computers, there is a strong demand for development of small, lightweight non-aqueous electrolyte secondary batteries with high energy density. Also, there is a strong demand for the development of high-output secondary batteries as power sources for electric vehicles such as hybrid electric vehicles, plug-in hybrid electric vehicles, and battery-powered electric vehicles.

As a secondary battery that satisfies such requirements, there is a lithium ion secondary battery, which is a type of non-aqueous electrolyte secondary battery. This lithium-ion secondary battery is composed of a negative electrode, a positive electrode, a non-aqueous electrolyte, and the like, and the active materials used as materials for the negative electrode and positive electrode are materials capable of desorbing and intercalating lithium. be.

Among these lithium ion secondary batteries, lithium ion secondary batteries using a lithium transition metal-containing composite oxide having a layered rock salt or spinel crystal structure as a positive electrode material can obtain a voltage of 4 V class, so it is high. Batteries with high energy density are currently being extensively researched and developed, and some are even being put to practical use.

As a positive electrode material for such a lithium ion secondary battery, lithium cobalt composite oxide (LiCoO ₂ ) which is relatively easy to synthesize, lithium nickel composite oxide (LiNiO ₂ ) using nickel which is cheaper than cobalt, lithium Nickel-cobalt-manganese composite oxide (
LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ), lithium manganese composite oxide using manganese (LiMn ₂ O ₄ ), lithium nickel manganese composite oxide (LiNi _0.5 Mn _{0
. 5} O ₂ ) and other lithium transition metal-containing composite oxides have been proposed.

In general, high capacity is one of the characteristics required for lithium ion batteries.
In addition, some lithium-ion battery applications require rapid charging and discharging.
Such applications require low resistance and high output characteristics. In particular, it is important to improve output characteristics in a region where the remaining capacity (SOC: State of Charge) is low. This is because it is known that the resistance characteristics of lithium-ion batteries increase as the SOC decreases. Therefore, by reducing the resistance in the low SOC region, the range of SOC in which the desired output characteristics can be obtained is expanded. This is because

One of the measures for obtaining high capacity characteristics is to increase the fillability of the positive electrode active material. By increasing the fillability of the positive electrode active material, the amount of the positive electrode active material per unit volume in the positive electrode mixture constituting the positive electrode is increased, and the lithium ion secondary with excellent volumetric energy density (Wh / L). to get the battery. The fillability of the positive electrode active material is evaluated by the tap density, and the higher the tap density, the higher the fillability. Therefore, by using a positive electrode active material with a higher tap density as a positive electrode material, it is possible to obtain a lithium ion secondary battery with excellent volumetric energy density (Wh/L).

From the knowledge so far, there is a correlation between the average particle size of the positive electrode active material and the tap density. It has been found that the tap density tends to increase as the diameter increases.

On the other hand, as for the output characteristics, it is considered that the more lithium ion insertion/extraction reaction sites in the positive electrode active material, the lower the resistance characteristics of the positive electrode active material and the more the output characteristics are improved. As a means for increasing the number of lithium ion insertion/extraction reaction sites, it is conceivable to increase the specific surface area by reducing the average particle size of the positive electrode active material.

In addition, as one of the causes of deterioration of the positive electrode of a lithium ion secondary battery, a large amount of lithium ions are extracted from certain specific particles in the positive electrode active material due to non-uniformity in the degree of extraction of lithium ions during charging and discharging. , it is conceivable that the deterioration progresses quickly. therefore,
The more uniform the diffusion path length of lithium ions inside each particle of the positive electrode active material, the more uniform the amount of lithium ions present inside the positive electrode active material during charging and discharging, and the more uniform the amount of lithium ions present inside the positive electrode active material. is considered to be good.

In other words, in order to obtain a positive electrode active material with desired battery characteristics such as high capacity characteristics, high output characteristics, and excellent cycle characteristics, it is important to appropriately control the average particle size and particle size distribution. is.

By the way, it is known that the positive electrode active material inherits the properties of the transition metal-containing composite hydroxide particles that serve as its precursor. That is, in order to obtain a positive electrode active material having the battery characteristics described above, it is necessary to appropriately control the average particle size and particle size distribution of the transition metal-containing composite hydroxide particles, which are precursors thereof. .

For example, JP-A-2012-246199, JP-A-2013-147416,
In WO2012/131881 and WO2014/181891,
Manufacture of transition metal-containing composite hydroxide particles, which are the precursors of positive electrode active materials, by a crystallization reaction that is clearly separated into two stages: a nucleation process that mainly produces nuclei and a particle growth process that mainly grows particles. A method for doing so is disclosed. In this method, the pH value of the reaction aqueous solution is adjusted to a liquid temperature of 25°C.
On a standard basis, in the range of 12.0-14.0 for the nucleation process and 10.5-12 for the grain growth process
. Each is controlled within the range of 0. The transition metal-containing composite hydroxide particles obtained by these methods are composed of secondary particles having a small particle size and a narrow particle size distribution.

Further, in the method described in WO2014/181891, the nucleation step and the grain growth step are initially performed in a non-oxidizing atmosphere, and in the grain growth step, after switching the non-oxidizing atmosphere to an oxidizing atmosphere, The atmosphere is controlled at least once by switching back to the non-oxidizing atmosphere.

The transition metal-containing composite hydroxide particles obtained by this method have a small particle size, a narrow particle size distribution, and a central portion formed by aggregation of plate-like or needle-like primary particles. At least one laminated structure in which a low-density layer formed by agglomeration of fine primary particles and a high-density layer formed by agglomeration of plate-like primary particles are alternately laminated on the outside of the and By using such transition metal-containing composite hydroxide particles as a precursor, a space where the primary particles do not exist outside the central part where the primary particles are aggregated, and the primary particles are aggregated, and the central part and the electrical or a structure further comprising an inner shell in which the primary particles are aggregated between the core and the outer shell and electrically conductive to the core and the outer shell can be obtained.

Specifically, the positive electrode active material obtained by the techniques described in these documents has an average particle size of 3 μm.
m to 10 μm or 1 μm to 15 μm, and [(d90−d10)/average particle diameter], which is an index showing the spread of the particle size distribution, is 0.65 or less. In non-aqueous electrolyte secondary batteries using these positive electrode active materials, capacity characteristics,
It is believed that output characteristics and cycle characteristics can be improved.

JP 2012-246199 A JP 2013-147416 A WO2012/131881 WO2014/181891

By the way, as described above, in order to obtain a positive electrode active material having a high tap density required for obtaining a high-capacity lithium ion battery, it is necessary to use large transition metal-containing composite hydroxide particles as a precursor. need to be sized. On the other hand, in order to obtain a high-output lithium-ion battery, it is required to reduce the particle size of the positive electrode active material. That is, the high capacity characteristics and high output characteristics of the positive electrode active material are correlated with the increase in particle size and the decrease in particle size of the particles constituting the precursor and the positive electrode active material, respectively, and are contradictory in terms of particle characteristics. in a relationship.

In view of the above problems, the present invention simultaneously improves high capacity characteristics, high output characteristics, particularly excellent output characteristics in the low SOC region, and excellent cycle characteristics when a secondary battery is configured. It is an object of the present invention to provide a positive electrode active material that can be used as a positive electrode active material, and a transition metal-containing composite hydroxide particle that is a precursor thereof.

Another object of the present invention is to provide a non-aqueous electrolyte secondary battery using such a positive electrode active material and having excellent battery characteristics. A further object of the present invention is to provide a method for easily producing such a positive electrode active material and transition metal-containing composite hydroxide particles on an industrial scale.

The transition metal-containing composite hydroxide particles of the present invention are transition metal-containing composite hydroxide particles that serve as a precursor of a positive electrode active material for non-aqueous electrolyte secondary batteries, comprising a plurality of plate-like primary particles and the plate-like particles. It consists of secondary particles formed by agglomeration of fine primary particles smaller than primary particles.

The transition metal-containing composite hydroxide particles have the general formula (A): Ni _{x Mny} Co _{z Mt} (OH
) _2+a (wherein x+y+z+t=1, 0.3≦x≦0.95, 0.05≦y≦0.55
, 0≦z≦0.4, 0≦t≦0.1, and 0≦a≦0.5, and M is Mg, Ca
, which is one or more additional elements selected from Al, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, and W). .

In particular, in the transition metal-containing composite hydroxide particles of the present invention, the secondary particles are
having a central portion formed by agglomeration of the plate-shaped primary particles, or formed by agglomeration of the plate-shaped primary particles and the fine primary particles, and the fine primary particles aggregating outside the center portion; and at least one laminated structure in which a low-density layer formed by aggregating the plate-like primary particles and a high-density layer formed by aggregating the plate-like primary particles are laminated, and a part of the low-density layer includes the plate-like primary Particles with a large particle size in which there is a high-density part formed by agglomeration of particles;
A high density formed by agglomeration of the plate-shaped primary particles and having a radius of length equivalent to the thickness of the outermost high density layer (outer shell portion) of the high density layers of the large particle size particles. and solid small-sized particles in
It is characterized by being composed of

In the transition metal composite hydroxide particles of the present invention, the secondary particles have an overall average particle size in the range of 1 μm to 15 μm, and are an index showing the spread of the overall particle size distribution [
(d90-d10)/average particle size] is in the range of 0.30 to 0.65.
In addition, the large particle size particles constituting the secondary particles have an average particle size in the range of 4 μm to 15 μm, and are an index showing the spread of the particle size distribution [(d90-d10)/ average particle size] is in the range of 0.30 to 0.65. Further, the small-diameter particles have an average particle diameter in the range of 1 μm to 4 μm, and the half value of the average particle diameter is equal to the thickness of the high-density layer constituting the large-diameter particles, and It is an index showing the spread of the particle size distribution [
(d90-d10)/average particle size] is in the range of 0.30 to 0.65.

Further, in the transition metal-containing composite hydroxide particles, the mass ratio of the large particle size particles and the small particle size particles to the large particle size particles (the small particle size It is characterized by being mixed so that the mass of particles of 1/mass of particles with large particle diameter) is in the range of 0.05 to 20.

It is preferable that the additional element M is uniformly distributed inside the secondary particles and/or uniformly covers the surfaces of the secondary particles.

The transition metal-containing composite hydroxide particles of the present invention can be obtained by the following production method.

In the method for producing transition metal-containing composite hydroxide particles of the present invention, an aqueous solution for nucleation containing at least a metal compound containing a transition metal and an ammonium ion donor is heated to a temperature of 2
A nucleation step in which nucleation is performed while supplying the raw material while controlling the pH value at 5 ° C. to 12.0 to 14.0, and the nuclei obtained in the nucleation step are contained. The pH value of the aqueous solution for particle growth at a liquid temperature of 25° C. is lower than the pH value of the nucleation step, and 1
and a particle growth step of growing the nucleus while supplying the raw material while controlling to be 0.5 to 12.0.

When obtaining large particles among the transition metal-containing composite hydroxide particles of the present invention, the reaction atmosphere at the initial stage of the nucleation step and the particle growth step is a non-oxidizing atmosphere with an oxygen concentration of 5% by volume or less. Then, the reaction atmosphere is controlled at least once by switching from the non-oxidizing atmosphere to an oxidizing atmosphere with an oxygen concentration exceeding 5% by volume, and switching from the oxidizing atmosphere to the non-oxidizing atmosphere.

In this case, the reaction atmosphere is controlled by blowing atmospheric gas into the aqueous solution for nucleation and the aqueous solution for particle growth using a ceramic diffuser. During the switching of the reaction atmosphere, the raw material is continuously supplied.

In this case, the initial stage of the grain growth process is in the range of 2% to 35% of the total grain growth process time from the start of the grain growth process, and the non-oxidizing atmosphere to the oxidizing atmosphere is changed. It is preferable to switch to atmosphere.

When the reaction atmosphere is controlled only once, the crystallization reaction time in the oxidizing atmosphere in the grain growth step is in the range of 1% to 20% of the total grain growth step time. is preferred. On the other hand, when the atmosphere control is performed twice or more, the total crystallization reaction time in the oxidizing atmosphere in the grain growth process is 2% to 30% of the total grain growth process time. and the crystallization reaction time in the oxidizing atmosphere per one time is preferably in the range of 1% to 20% of the entire grain growth process time.

On the other hand, when obtaining particles with a small particle size, the reaction atmosphere is maintained in a non-oxidizing atmosphere with an oxygen concentration of 5% by volume or less throughout the nucleation step and the particle growth step.

In order to make the additive element M uniformly exist inside the secondary particles, it is included in the raw material in the crystallization reaction. On the other hand, in order to uniformly coat the surface of the secondary particles,
A coating step of coating the transition metal-containing composite hydroxide particles with a compound containing the additive element M may be provided after the crystallization reaction (particle growth step) is completed. Part of the additive element M may be included in the raw material so that part of the additive element M is covered.

The positive electrode active material for non-aqueous electrolyte secondary batteries of the present invention comprises secondary particles formed by agglomeration of a plurality of primary particles.

The positive electrode active material has a general formula (B): Li _1+u Ni _{x Mny} Co _z M _t O ₂ (where −
0.05≦u≦0.50, x+y+z+t=1, 0.3≦x≦0.95, 0.05≦y≦
0.55, 0≦z≦0.4, and 0≦t≦0.1, and M is Mg, Ca, Al,
one or more additional elements selected from Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, and W) containing a lithium transition metal having a layered rock salt type hexagonal crystal structure Composed of composite oxide particles.

In the positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention, the secondary particles are provided inside the outer shell and are electrically conductive to the outer shell and to each other. Particles having a large particle size having a structure in which aggregated portions of particles and space portions in which primary particles do not exist are dispersed, and the thickness of the outer shell portion of the large particle size particles or the aggregated portion of the primary particles. It is characterized by a mixture of solid, small-sized particles having radii of equal length.

In the positive electrode active material, the ratio of the large-diameter particles to the small-diameter particles is the same as the mass ratio in the composite hydroxide particles, and the ratio of the small-diameter particles to the large-diameter particles is The particles are mixed so that the mass ratio (mass of small-diameter particles/mass of large-diameter particles) is in the range of 0.05 to 20.

The secondary particles constituting the positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention have an overall average particle size in the range of 1 μm to 15 μm, and are an index showing the spread of the overall particle size distribution. [(d90-d10)/average particle diameter] is in the range of 0.25 to 0.70. In addition, the large particle diameter particles constituting the secondary particles have an average particle diameter of 1 μm to 15 μm
and [(d90−d10)/average particle diameter], which is an index showing the spread of the particle size distribution, is in the range of 0.30 to 0.70. Further, the small particle size particles have an average particle size equal to the thickness of the high-density layer constituting the large particle size particles, and are 1 μm to 4 μm in diameter.
It is in the range of μm and is an index showing the spread of the particle size distribution [(d90-d10)
/average particle diameter] is in the range of 0.30 to 0.70.

The positive electrode active material for a non-aqueous electrolyte secondary battery has a BET specific surface area of 0.7 m ² /g to 4.0 m
It is preferably in the range of ² /g.

The positive electrode active material for non-aqueous electrolyte secondary batteries of the present invention can be obtained by the following manufacturing method.

A first aspect of the method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention comprises:
The transition metal-containing composite hydroxide particles represented by the general formula (A), which are formed by aggregation of plate-like primary particles, or are smaller than the plate-like primary particles and the plate-like primary particles It has a central portion formed by agglomeration of fine primary particles, and a low-density portion formed by agglomeration of the fine primary particles outside the central portion, and a low-density portion formed by agglomeration of the plate-like primary particles on the outside of the center. At least one laminated structure in which a high density portion is laminated, and a high density portion formed by aggregating the plate-like primary particles exists in a part of the low density layer, and the average particle diameter is 1 μm. ~ 15 μm, and [(d90-d10) / average particle diameter], which is an index showing the spread of the particle size distribution, is 0.25 to 0.6
Particles with a large particle size in the range of 5;
The transition metal-containing composite hydroxide particles represented by the general formula (A) are formed by aggregation of the plate-like primary particles, and have a length equivalent to the thickness of the high-density portion of the large-diameter particles. has a radius of
A solid having an average particle size in the range of 1 μm to 4 μm and an index indicating the spread of the particle size distribution [(d90−d10)/average particle size] in the range of 0.25 to 0.65. and particles with a small particle size of
are mixed so that the mass ratio of the small-diameter particles to the large-diameter particles (mass of small-diameter particles/mass of large-diameter particles) is in the range of 0.05 to 20. to obtain a precursor mixture;
mixing the precursor mixture and a lithium compound to form a lithium mixture;
a firing step of firing the lithium mixture at 650° C. to 980° C. in an oxidizing atmosphere;
Prepare.

A second aspect of the method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention includes:
The transition metal-containing composite hydroxide particles represented by the general formula (A), which are formed by aggregation of plate-like primary particles, or are smaller than the plate-like primary particles and the plate-like primary particles It has a central portion formed by agglomeration of fine primary particles, and a low-density portion formed by agglomeration of the fine primary particles outside the central portion, and a low-density portion formed by agglomeration of the plate-like primary particles on the outside of the center. At least one laminated structure in which a high density portion is laminated, and a high density portion formed by aggregating the plate-like primary particles exists in a part of the low density layer, and the average particle diameter is 4 μm. ~ 15 μm, and [(d90-d10) / average particle diameter], which is an index showing the spread of the particle size distribution, is 0.25 to 0.6
Particles with a large particle size in the range of 5;
The transition metal-containing composite hydroxide particles represented by the general formula (A) are formed by aggregation of the plate-like primary particles, and have a length equivalent to the thickness of the high-density portion of the large-diameter particles. has a radius of
A solid having an average particle size in the range of 1 μm to 4 μm and an index indicating the spread of the particle size distribution [(d90−d10)/average particle size] in the range of 0.25 to 0.65. and particles with a small particle size of
a lithium compound;
so that the mass ratio of the small-diameter particles to the large-diameter particles (mass of the small-diameter particles/mass of the large-diameter particles) is in the range of 0.05 to 20, mixing to form a lithium mixture;
a firing step of firing the lithium mixture at 650° C. to 980° C. in an oxidizing atmosphere;
Prepare.

In any aspect, in the mixing step, the lithium mixture is mixed so that the ratio of the sum of the number of metal atoms other than lithium contained in the lithium mixture to the number of lithium atoms is 1:
It is preferable to adjust it to be 0.95 to 1.5.

Further comprising a heat treatment step of heat-treating the precursor mixture or each of the large particle size particles and the small particle size particles at a temperature in the range of 105° C. to 750° C. before the mixing step. is preferred.

The nonaqueous electrolyte secondary battery of the present invention includes a positive electrode, a negative electrode, a separator, and a nonaqueous electrolyte, and the positive electrode active material for a nonaqueous electrolyte secondary battery is used as a positive electrode material for the positive electrode. It is characterized by

According to the present invention, there is provided a positive electrode active material and a precursor thereof that can improve volumetric energy density and output characteristics in a low SOC region without lowering cycle characteristics when a secondary battery is constructed. Transition metal-containing composite hydroxide particles can be provided. In particular, excellent output characteristics in the low SOC region can widen the range of SOC in which desired output can be obtained, and it is possible to provide a positive electrode active material with excellent output characteristics in a wide SOC range.

Further, according to the present invention, it is possible to provide a secondary battery using such a positive electrode active material. Furthermore, according to the present invention, it is possible to provide a method for easily producing such a positive electrode active material and transition metal-containing composite hydroxide particles on an industrial scale.

Therefore, the industrial significance of the present invention is extremely large.

FIG. 1 is an FE-SEM photograph of the surface of secondary particles constituting the positive electrode active material obtained in Example 1. FIG. FIG. 2 is an FE-SEM photograph of a cross section of secondary particles constituting the positive electrode active material obtained in Example 1. FIG. FIG. 3 is a schematic cross-sectional view of a 2032-type coin battery used for battery evaluation. FIG. 4 is a schematic explanatory diagram of an example of impedance evaluation measurement and an equivalent circuit used for analysis.

In order to ensure both high capacity characteristics (fillability) and high output characteristics in the positive electrode active material for non-aqueous electrolyte secondary batteries (hereinafter referred to as “positive electrode active material”), large particle size particles and small particle size particles are used for the positive electrode active material. It is conceivable to have a configuration in which particles of different diameters are mixed.

However, when a lithium ion battery is repeatedly subjected to long-term charge-discharge cycles, lithium ions are preferentially extracted from particles having a short diffusion distance of lithium ions, and the deterioration progresses quickly. In particular, battery cells for applications in which rapid charging and discharging are performed, such as battery cells for hybrid vehicles, are affected more strongly. Therefore, in a positive electrode active material in which large-particle-size particles and small-particle-size particles are mixed, lithium ions are preferentially extracted from small-particle-size particles with a short diffusion distance of lithium ions, and lithium ions are intercalated and deintercalated. There is a problem that the cycle characteristics deteriorate due to non-uniform reaction.

In the case of using a positive electrode active material in which particles of large particle size and particles of small particle size are mixed, in order to obtain a lithium ion battery with little deterioration due to charge-discharge cycles, it is necessary to It is necessary to use a positive electrode active material composed of secondary particles in which the diffusion path length of lithium ions is uniform.

In this way, as a measure to equalize the diffusion path length of lithium ions inside the large-diameter particles and the small-diameter particles, the large-diameter particles have a dispersed space inside the particles, By making it possible to insert and extract lithium ions from the internal space, the diffusion path length of the lithium ions is shortened, and at the same time, the small particle size particles are replaced with the large particle size lithium ions. solid particles with a radius equal to the diffusion path length of .

Further, in order to make the diffusion path length of lithium ions uniform between large-sized particles and between small-sized particles, a narrow particle size distribution is required for each of the large-sized particles and the small-sized particles. is required.

The particle properties of the positive electrode active material inherit the particle properties of the transition metal-containing composite hydroxide particles (hereinafter referred to as "composite hydroxide particles") as a precursor, so that the precursor is dispersed inside the particles. Composite hydroxide particles composed of large-sized particles having a predetermined structure, and the diffusion path length of lithium ions of the large-sized particles, which leads to the structure of the positive electrode active material composed of large-sized particles having a space portion. There is a need for composite hydroxide particles composed of small-sized particles having a predetermined structure that result in a positive electrode active material structure composed of solid small-sized particles having a radius equivalent to .

When producing transition metal-containing composite hydroxide particles, the present inventors clearly separated the crystallization reaction into two stages, a nucleation process and a particle growth process, and then performed nucleation in each of the crystallization processes. It has been found that the particle size distribution of both large-sized particles and small-sized particles can be narrowed by forming the particles for a predetermined short period of time.

In addition, in order to obtain a positive electrode active material composed of large-sized particles having spaces dispersed inside the particles, it is necessary to obtain large-sized particles having a low-density layer, and a nucleation step And the atmosphere control in which the reaction atmosphere in the initial stage of the grain growth process is a non-oxidizing atmosphere, and in the grain growth process, after switching from the non-oxidizing atmosphere to the oxidizing atmosphere, the atmosphere is switched again to the non-oxidizing atmosphere is performed by the ceramic dispersion. The present inventors have found that by blowing the atmospheric gas into the liquid using the trachea at least once, it is possible to obtain particles having a large particle size and having the above-described stratified low-density layer.

In the case of particles having a large particle diameter having such a high density layer and a low density layer, for example, the high density layer and the low density layer are formed by controlling the reaction time while keeping the raw material supply rate constant. It is possible to control the thickness of solid particles with a small particle size. We also found that it is possible to

Based on these findings, large-sized particles with a structure having a low-density layer inside and small-sized solid particles with a radius equivalent to the thickness of the high-density layer inside the large-sized particles with a layered structure , respectively. In addition, by mixing these large-sized particles and small-sized particles in an appropriate ratio, it is possible to obtain transition metal-containing composite hydroxide particles (precursor mixture) in which these particles are mixed. is.

Transition metal-containing composite hydroxide particles composed of large-sized particles and small-sized particles having such a structure, or precursor mixtures in which these large-sized particles and small-sized particles are mixed, In the positive electrode active material obtained by mixing this precursor with a lithium source and firing the mixture as a precursor, each particle inherits the shape of the precursor transition metal-containing composite hydroxide particles. That is, inside the outer shell portion, there are large-sized particles in which the agglomeration portion of the primary particles and the space portion where the primary particles do not exist are dispersed, and the outer shell portion of the large-sized particles and the inside thereof exist. It is possible to obtain a positive electrode active material having a structure in which small-sized solid particles having a radius equal to the thickness of the aggregation portion are mixed.

When a positive electrode active material having such a structure is used as a positive electrode material to form a non-aqueous electrolyte secondary battery,
It was found that the capacity characteristics (filling characteristics) and the output characteristics in the low SOC region can be greatly improved without impairing the cycle characteristics.

The present invention has been completed based on these findings.

1. Transition Metal-Containing Composite Hydroxide Particles (1) Structure of Secondary Particles The composite hydroxide particles of the present invention are composed of secondary particles formed by agglomeration of primary particles. The secondary particles have a central portion formed by aggregation of plate-shaped primary particles or plate-shaped primary particles and fine primary particles, and a low-density layer formed by aggregation of fine primary particles outside the center. and a high-density layer formed by agglomeration of plate-shaped primary particles are laminated, and a high-density part exists in a part of the low-density layer. Particles and high-density solid small-diameter particles having a radius of length equivalent to the thickness of the outermost high-density layer (outer shell portion) of the high-density layers of the large-diameter particles It is characterized by being mixed with particles.

In the present invention, the low-density portion constituting the low-density layer means a portion formed by agglomeration of fine primary particles inside the secondary particles. In addition, the high-density portion that constitutes part of the high-density layer or the low-density layer is a portion formed by aggregation of plate-shaped primary particles that are larger than the fine primary particles and have a thickness inside the secondary particles. means

By using such composite hydroxide particles as a precursor, large-sized particles having a structure in which the space is dispersed inside the secondary particles, and inside the large-sized particles It is possible to obtain a positive electrode active material that has a diffusion path length that is the same as the lithium ion diffusion path length and that is solid and mixed with small-sized particles. The large and small particles can each have a narrow particle size distribution.

In this composite hydroxide particle, the low-density layer does not need to be formed over the entire outer side of the central portion or the entire outer side of the high-density layer. , may be partially formed in the circumferential direction. In addition, even when the low-density layer is formed over the entire outer side of the central portion or the entire outer side of the high-density layer, there is a high-density portion formed by aggregation of plate-like primary particles in the low-density layer. do. More specifically, the low-density layer is located between the surface of aggregates of plate-shaped primary particles that constitute the central portion and the surface of aggregates of plate-shaped primary particles that constitute the high-density layer, or between two high-density layers. Aggregates of fine primary particles are deposited between the surfaces of aggregates of plate-like primary particles that constitute the density layer. , the structure is substantially formed by agglomeration of both plate-like primary particles and fine primary particles. Therefore, in any structure, in the positive electrode active material obtained, the large-sized particles are electrically connected to the outer shell and are electrically connected to each other inside the outer shell. It has a structure in which the primary particles aggregated and the space where the primary particles do not exist are dispersed.

The center portion of the composite hydroxide particles may be composed only of plate-like primary particles, or may have a structure in which plate-like primary particles and fine primary particles are mixed. Further, a structure in which a plurality of aggregated portions of plate-like primary particles are connected may be used. In this case, a laminated structure is formed in which a low-density layer and a high-density layer are laminated on the outer side of the central portion composed of the connected coherent portions.

(2) Thicknesses of central portion, low-density layer, and high-density layer in large particle size particles In the composite hydroxide particles of the present invention, the outer diameter of the central portion, the low By appropriately controlling the density layer and the thickness ratio of each of the high density layer, the outer shell formed by the aggregated primary particles and the aggregated primary particles existing inside the outer shell are formed. In addition, a positive electrode active material is obtained which is composed of secondary particles constituted by aggregated portions electrically conducting to the outer shell portion and a plurality of space portions dispersedly present in the aggregated portions.

In the particles having a large particle diameter that constitute the composite hydroxide particles of the present invention, the low-density portion that constitutes the low-density layer that constitutes the space portion composed of a plurality of pores of uniform size in the positive electrode active material. is properly formed. Therefore, in the cross section of large particle diameter particles obtained by observation with a scanning electron microscope (SEM) such as a field emission scanning electron microscope (FE-SEM) described later, the low density part constituting the low density layer The area ratio is preferably in the range of 5% to 60%, more preferably in the range of 10% to 50%, and in the range of 20% to 40% with respect to the cross-sectional area of the large particle size particles. It is more preferable to be in When the area ratio of the low-density portion exceeds the above range, the structure of the secondary particles in the positive electrode active material is different from the desired structure. More specifically, in the composite hydroxide particles of the present invention, by appropriately controlling the ratio of the outer diameter of the central portion, the thickness of the low-density layer, and the thickness of the high-density layer to the particle size,
It is preferable to set the particle structure of the positive electrode active material within an appropriate range.

In addition, in the large particle size particles, the average ratio of the outer diameter of the central portion to the particle size (hereinafter referred to as the “center particle size ratio”) is preferably in the range of 20% to 60%. % to 55%
more preferably in the range of 30% to 50%.
With such a configuration, it is possible to obtain a desired structure in the obtained positive electrode active material by setting the thicknesses of the low-density layer and the high-density layer to be appropriate. When the size of the central portion exceeds this range, in the large particle size of the composite hydroxide particles,
Since the sizes of the low-density layer and the high-density layer exceed the scope of the present invention, it may not be possible to obtain a structure in which the desired dispersed space portions are provided inside in the positive electrode active material to be obtained.

The average ratio of the thickness of each low-density layer to the particle diameter of large-sized particles (hereinafter referred to as "low-density layer particle size ratio") is preferably in the range of 1% to 30%, preferably 2%. It is preferably in the range of ~20%, more preferably in the range of 3% to 15%. Furthermore, the thickness of the second low-density layer is 50% to 1% of the thickness of the first low-density layer radially inside.
It is preferably in the range of 50%. By controlling in this way, in the obtained positive electrode active material, a space portion having a pore structure composed of a plurality of pores having a uniform and appropriate size can be obtained.

The average ratio of the thickness of each high-density layer to the particle diameter of large-sized particles (hereinafter referred to as "high-density layer particle size ratio") is preferably in the range of 5% to 40%, preferably 10%. It is more preferably in the range of ~30%, and even more preferably in the range of 10% to 20%.

By setting the particle size ratio of the low-density layer and the particle size ratio of the high-density layer within this range, large particles constituting the positive electrode active material obtained using the composite hydroxide particles having such a structure as precursors can be obtained. It is possible to form a structure in which a plurality of space portions (pores) of an appropriate and uniform size are uniformly formed in the particles of the diameter. If the particle size ratio of each low-density layer is too small, the large particle size particles of the resulting positive electrode active material do not have sufficiently large voids during firing of the composite hydroxide particles, resulting in substantially solid particles. There is a possibility that it will be a structure similar to the structure. Conversely, if the particle size ratio of each low-density layer is too large, the low-density layer does not shrink to form a pore structure during firing of the composite hydroxide particles, resulting in a large particle size of the resulting positive electrode active material. In the particles, for example, there is a structure in which large voids exist between the central portion, the high-density layer, and the outer shell portion, and the outer shell portion and the internal cohesive portion are not sufficiently connected or integrated, resulting in the desired structure. may not be obtained. In this case, an electrical conduction path having a sufficient cross-sectional area is not formed between the outer shell portion and the internal agglomerate portion, and the effect of reducing the positive electrode resistance cannot be obtained.

If the particle size ratio of each high-density layer is too small, the predetermined structure of the secondary particles that make up the particles with a large particle size is not maintained during the manufacturing stage or filling stage of the positive electrode active material, and the secondary particles may be destroyed or the secondary particles may There is a possibility that a sufficiently large space may not be formed inside the particles. On the other hand, if the particle size ratio of each high-density layer is too large, a sufficiently large space is not formed inside the secondary particles that constitute the large particle size particles during firing of the composite hydroxide particles. Infiltration of sufficient electrolytic solution and conductive aid into the interior of the secondary particles may be insufficient.

The large-sized particles constituting the composite hydroxide particles of the present invention have at least one layered structure in which a low-density layer and a high-density layer are layered on the outer side of the central portion. The number of laminated structures is arbitrary as long as dispersed spaces are appropriately formed inside the large particle size particles in the positive electrode active material. However, if the number of laminated structures is 1 or more, each low-density layer may not be formed with a sufficient thickness, and the effect of improving the specific surface area may not be sufficiently obtained.

In the large particle size particles constituting the composite hydroxide particles of the present invention, basically When the composite hydroxide particles having such a structure are sintered, the central portion and the high-density layer are substantially integrated due to sintering shrinkage, and there are a plurality of space portions dispersedly generated inside. structure is obtained. The space existing inside can communicate with the outside through grain boundaries or voids between primary particles forming aggregates. Therefore, in such a structure, the electrical conduction path between the primary particles constituting the secondary particles is sufficiently secured while maintaining the difficulty of collapsing of the overall structure of the positive electrode active material obtained, and the space and As a result of sufficiently ensuring communication with the outside, it is possible to further reduce the positive electrode resistance.

Here, the central part particle size ratio, the low density layer particle size ratio, and the high density particle size ratio of the particles with large particle diameters are obtained by measuring the cross section of the composite hydroxide particles, as shown in FIG. type scanning electron microscope (FE
-SEM) or other scanning electron microscope (SEM).
Note that the ratio of the low-density portion can be obtained by binarizing the cross-sectional imaging. Specifically, the cross section of any 10 or more particles is observed with an SEM, binarized, and 1
The cross-sectional area of each grain is determined by calculating the ratio of the total area occupied by the low-density portion in the grain and calculating the average value of these ratios.

Specifically, when obtaining the central particle size ratio, the low density layer particle size ratio, and the high density particle size ratio, first, in a field of view large enough to distinguish the central part of the secondary particles and each layer, Observe the cross-section of the particle for size. The maximum length between any two points on the outer edge of the large particle size particle and the maximum length between any two points on the outer edge of the central part are measured, and those values are used for the large particle size particle. The particle size and the outer diameter of the central part. In addition, the thickness of each layer is measured at three or more arbitrary positions with respect to one large-diameter particle, and the average value is obtained. Here, the thickness of each layer is the length between two points where the length to the outermost edge of the layer is the shortest, when an arbitrary point is selected from the innermost edge of the layer in the cross section of the large particle size particle. Satoru.

By dividing the outer diameter of the central portion and the thickness of each layer by the particle size of the large-sized particles constituting the composite hydroxide particles, the central portion particle size ratio, the low-density layer grain A diameter ratio and a high-density particle size ratio are determined, respectively. Perform similar measurements on 10 or more composite hydroxide particles,
By calculating their average values, it is possible to finally determine the center particle size ratio, the low density layer particle size ratio, and the high density particle size ratio of the large size particles in the entire sample. .

(3) Primary particles [fine primary particles]
The fine primary particles constituting the low-density layer (low-density portion) of the composite hydroxide particles and the fine primary particles present in the center have an average particle size in the range of 0.01 μm to 0.3 μm. and more preferably in the range of 0.1 μm to 0.3 μm. If the average particle size of the fine primary particles is less than 0.01 μm, a sufficiently large low-density portion may not be formed. on the other hand,
When the average particle size of the fine primary particles exceeds 0.3 μm, the shrinkage during firing does not proceed in a low temperature range, and the shrinkage difference between the central portion, the high-density layer, and the high-density portion becomes small, and the positive electrode active material obtained. , it may not be possible to form a sufficiently large space.

The shape of such fine primary particles is preferably plate-like and/or needle-like. By adopting such a shape of the fine primary particles, the density difference between the low-density portion constituting the low-density layer, the central portion, the high-density layer, and the high-density portion can be sufficiently large. A sufficiently large space can be formed in the positive electrode active material obtained.

The average particle diameter of the fine primary particles or the plate-like primary particles described below is determined by embedding the composite hydroxide particles in a resin or the like, making the cross-section observation possible by processing such as a cross-section polisher, and then measuring the cross-section. , can be observed using a scanning electron microscope (SEM) and determined as follows. First, the maximum diameter of 10 or more fine primary particles or plate-like primary particles present in the cross section of the secondary particles is measured, the average value is obtained, and this value is used as the fine primary particles or plate-like particles in the secondary particles. The particle diameter of the primary particles. Next, for 10 or more secondary particles,
Similarly, the particle size of fine primary particles or plate-like primary particles is determined. Finally, by averaging the particle sizes of the fine primary particles or plate-like primary particles in these secondary particles, the average particle size of the fine primary particles or plate-like primary particles can be obtained.

[Plate-like primary particles]
Among the composite hydroxide particles, the plate-like primary particles that constitute the central portion, the high-density layer, and the high-density portion of the large particle size particles, and the small particle size particles have an average particle size of 0.3 μm to It is preferably in the range of 3 μm, more preferably in the range of 0.4 μm to 1.5 μm, and 0.4 μm
It is more preferably in the range of ~1.0 μm. The average particle size of plate-like primary particles is 0.3 μm
If the temperature is less than 100,000, the shrinkage during firing starts from a low temperature region, and the difference in shrinkage from the low-density portion is small, so large-sized particles of the obtained positive electrode active material cannot form a sufficiently large space. Sometimes. On the other hand, when the plate-like primary particles have an average particle size of more than 3 μm, both the large particle size particles and the small particle size particles must be Therefore, it becomes difficult to control the average particle size and particle size distribution of the positive electrode active material within a predetermined range.

(4) Average particle size The large particle size particles constituting the composite hydroxide particles of the present invention have an average particle size of 4 μm to 15 μm.
μm, preferably 5 μm to 12 μm, more preferably 6 μm to 10 μm. In addition, the small-diameter particles constituting the composite hydroxide particles of the present invention have an average particle diameter of 1 μm to 4 μm.
μm, preferably 1.5 μm to 3.5 μm, more preferably 2 μm to 3 μm. The average particle size of the secondary particles correlates with the average particle size of the positive electrode active material whose precursor is the composite hydroxide particles. Therefore, by controlling the average particle size of the secondary particles within such a range, it is possible to control the average particle size of the positive electrode active material having the composite hydroxide particles as a precursor within a predetermined range. Become.

In the composite hydroxide particles of the present invention, the average particle size of the entire secondary particles after mixing the large particle size particles and the small particle size particles is basically the same as that of the large particle size particles. It is almost the same as the average particle size, and by adjusting the average particle size of the large particle size particles and the small particle size particles to the above ranges,
The average particle size is 1 μm to 15 μm, preferably 3 μm to 12 μm, more preferably 3 μm
m to 10 μm.

In the present invention, the average particle size of secondary particles means the volume-based average particle size (MV), which can be obtained from, for example, a volume integrated value measured with a laser beam diffraction/scattering particle size analyzer.

(5) Particle size distribution The composite hydroxide particles of the present invention, both large particle size particles and small particle size particles,
[(d90-d10)/average particle diameter], which is an index showing the spread of the particle size distribution, is 0.65
Below, it is preferably adjusted to 0.55 or less, more preferably 0.50 or less.
In the composite hydroxide particles of the present invention, the spread of the particle size distribution of the secondary particles after mixing the large particle size particles and the small particle size particles is basically the large particle size particles It is almost the same as the spread of the particle size distribution of

The particle size distribution of the positive electrode active material is strongly influenced by its precursor, the composite hydroxide particles. Therefore, when composite hydroxide particles containing many fine particles and coarse particles are used as a precursor, the positive electrode active material also contains many fine particles and coarse particles. ,
Cycle characteristics and output characteristics cannot be sufficiently improved. On the other hand, at the stage of the composite hydroxide particles, both the large particle size particles and the small particle size particles as a whole show the particle size distribution [(d90-d10)/average particle size]. is adjusted to be 0.65 or less, the particle size distribution of the positive electrode active material using this as a precursor can be narrowed.
It is possible to avoid the problems described above. However, assuming industrial-scale production,
It is not practical to use composite hydroxide particles with an excessively small [(d90-d10)/average particle size]. Therefore, considering cost and productivity, [(d90-d
10)/average particle diameter] is preferably about 0.25, about 0.30, or about 0.35.

Note that d10 is the number of particles in each particle size accumulated from the smaller particle size side, and the particle size at which the cumulative volume is 10% of the total volume of all particles, and d90 is the number of particles. , means the particle size whose cumulative volume is 90% of the total volume of all particles. d10 and d90 are
Like the average particle diameter (d50, median diameter), it can be obtained from the volume integrated value measured with a laser beam diffraction scattering particle size analyzer.

(6) Composition As long as the composite hydroxide particles of the present invention have the structure, average particle diameter and particle size distribution described above,
Although its composition is not limited, general formula (A) _{: NixMnyCozMt (} OH _{) 2
+a} (where x + y + z + t = 1, 0.3 ≤ x ≤ 0.95, 0.05 ≤ y ≤ 0.55, 0
≤ z ≤ 0.4, 0 ≤ t ≤ 0.1, and 0 ≤ a ≤ 0.5, and M is Mg, Ca, A
one or more additional elements selected from l, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta and W). By using such composite hydroxide particles as a precursor, it is possible to easily obtain the positive electrode active material represented by the general formula (B) described later, and to achieve higher battery performance.

In addition, in the composite hydroxide particles represented by the general formula (A), nickel constituting this,
The composition range of manganese, cobalt and the additive element M and its critical significance are represented by the general formula (B)
It is the same as the positive electrode active material represented by. Therefore, description of these matters is omitted here.

(7) Ratio of Large Particles to Small Particles The composite hydroxide particles of the present invention have a central portion formed by agglomeration of plate-like primary particles and fine primary particles. A low-density layer formed by agglomeration of fine primary particles and a high-density layer formed by agglomeration of plate-like primary particles are laminated on the outside, and a high-density portion is formed in a part of the low-density layer. Present large sized particles with at least one layered structure and dense solid small sized particles having a radius equal in length to the thickness of the dense layer of large sized particles. Obtained by mixing cities.

In the composite hydroxide particles of the present invention, the mixing ratio of large-sized particles and small-sized particles is in the range of 0.05 to 20 in mass ratio of small-sized particles to large-sized particles. Yes, preferably
It is in the range of 0.1-15, more preferably in the range of 0.5-10. This ratio is determined from the viewpoint of achieving both high capacity characteristics and high output characteristics, especially in the low SOC region. is not sufficiently obtained.

2. Method for Producing Transition Metal-Containing Composite Hydroxide Particles In the method for producing composite hydroxide particles of the present invention, both large-diameter particles and small-diameter particles are subjected to a crystallization reaction to form precursors of positive electrode active materials. A method for producing composite hydroxide particles, comprising: adding an aqueous solution for nucleation containing at least a metal compound containing a transition metal and an ammonium ion donor to a pH value of 12.0 at a liquid temperature of 25° C. 14.0, and the aqueous solution for particle growth containing nuclei obtained in this nucleation step is adjusted to a pH value of nuclei at a liquid temperature of 25 ° C. A particle growth step is provided in which the nuclei are grown by controlling the pH value to be lower than the pH value of the production step and 10.5 to 12.0. Thus, by clearly distinguishing between the nucleation step and the grain growth step, it is possible to appropriately control the average grain size and narrow the spread of the grain size distribution.

For the small-diameter particles among the composite hydroxide particles of the present invention, the reaction atmosphere is controlled so as to maintain a scattering atmosphere with an oxygen concentration of 5% by volume or less throughout the nucleation step and the particle growth step. do. Such a reaction makes it possible to form high-density, solid secondary particles formed by agglomeration of plate-shaped primary particles.

On the other hand, for the large particle size particles among the composite hydroxide particles of the present invention, the reaction atmosphere at the beginning of the nucleation step and the particle growth step is a non-oxidizing atmosphere with an oxygen concentration of 5% by volume or less, and then , switching from a non-oxidizing atmosphere to an oxidizing atmosphere with an oxygen concentration exceeding 5% by volume,
In addition, the reaction atmosphere is controlled at least once by switching from the oxidizing atmosphere to a non-oxidizing atmosphere.

The reaction atmosphere in the process of producing large-diameter particles is controlled by blowing atmosphere gas into the reaction tank, that is, into the aqueous solution for nucleation and the aqueous solution for particle growth using a ceramic diffuser. . During the switching of the reaction atmosphere, the raw material is continuously supplied.

Due to such a reaction, the plate-like primary particles and the fine primary particles have a central portion formed by agglomeration, and the low-density layer formed by agglomeration of the fine primary particles outside the central portion and the plate-like A high-density layer formed by agglomeration of primary particles is laminated, and a high-density part exists in a part of the low-density layer. Next particles can be obtained.

The method for producing composite hydroxide particles of the present invention is limited by the composition of both large-sized particles and small-sized particles, as long as the structure, average particle size, and particle size distribution described above can be realized. However, it can be suitably applied to composite hydroxide particles represented by general formula (A).

(1) Crystallization reaction In the method for producing composite hydroxide particles of the present invention, the crystallization reaction is mainly nucleation regardless of whether large-sized particles or small-sized particles are produced. By clearly separating the two stages of the nucleation step and the grain growth step in which the grains are grown, and by adjusting the crystallization conditions in each step, particularly by changing the reaction atmosphere at a predetermined timing. , it is possible to obtain composite hydroxide particles composed of large-sized particles and small-sized particles having an appropriate particle structure, average particle size, and particle size distribution as described above. In addition, since the operations required for adjusting the crystallization conditions are basically the same as in the prior art, the method for producing composite hydroxide particles of the present invention can be easily applied to industrial-scale production. .

[Nucleation step]
In the nucleation step, regardless of whether large-sized particles or small-sized particles are produced, first, a transition metal compound, which is a raw material in this step, is dissolved in water to prepare a raw material aqueous solution. . In addition, in the method for producing composite hydroxide particles of the present invention, the composition ratio of the obtained composite hydroxide particles is, in principle, the same as the composition ratio of each metal in the raw material aqueous solution. At the same time, an alkaline aqueous solution and an aqueous solution containing an ammonium ion donor are supplied and mixed in the reaction vessel, and the pH value measured at a liquid temperature of 25 ° C. is in the range of 12.0 to 14.0, and the ammonium ion concentration is Prepare a pre-reaction aqueous solution ranging from 3 g/L to 25 g/L. In addition, an inert gas is introduced into the reaction tank to adjust the reaction atmosphere to a non-oxidizing atmosphere with an oxygen concentration of 5% by volume or less. The pH value of the pre-reaction aqueous solution can be measured with a pH meter, and the ammonium ion concentration can be measured with an ion meter.

Next, while stirring the pre-reaction aqueous solution, the raw material aqueous solution is supplied. As a result, an aqueous solution for nucleation, which is a reaction aqueous solution in the nucleation step, is formed in the reaction tank. Since the pH value of the aqueous solution for nucleation is within the range described above, nucleation takes place preferentially with little growth of nuclei in the nucleation step. In the nucleation step, the pH value and the concentration of ammonium ions in the aqueous solution for nucleation change with nucleation. pH 12.0 to 14 based on ℃
. In the range of 0, it is necessary to control the concentration of ammonium ions to be maintained in the range of 3 g/L to 25 g/L.

In the nucleation step, new nuclei are continuously generated by supplying an aqueous solution containing a raw material aqueous solution, an alkaline aqueous solution, and an ammonium ion donor to the nucleating aqueous solution. Then, when a predetermined amount of nuclei is generated in the nucleation aqueous solution, the nucleation step is terminated. At this time, the amount of nuclei generated can be determined from the amount of the metal compound contained in the raw material aqueous solution supplied to the nucleation aqueous solution.

The amount of nuclei generated in the nucleation step is not particularly limited, but in order to obtain composite hydroxide particles with a narrow particle size distribution, It is preferably 0.1 atomic % to 2 atomic %, more preferably 0.1 atomic % to 1.5 atomic %, relative to the metal element in the metal compound.

[Particle growth step]
Regardless of whether large particle size particles or small particle size particles are produced, after the nucleation step is completed, the pH value of the aqueous solution for nucleation in the reaction tank is adjusted to 10.5 at a liquid temperature of 25°C. It is adjusted to a range of up to 12.0 to form an aqueous solution for particle growth, which is a reaction aqueous solution in the particle growth step. The pH value can be adjusted by stopping the supply of the alkaline aqueous solution. Adjusting is preferred. Inorganic acid of the same kind as the acid constituting the metal compound as a raw material is added to the aqueous solution for nucleation,
For example, when sulfate is used as a raw material, sulfuric acid can be supplied.

Next, the supply of the raw material aqueous solution is resumed while stirring the particle growth aqueous solution. On this occasion,
Since the pH value of the aqueous solution for particle growth is within the range described above, almost no new nuclei are generated, nuclei (particles) grow, and composite hydroxide particles having a predetermined particle size are formed. Also in the particle growth process, the pH value and ammonium ion concentration of the aqueous solution for particle growth change as the particles grow. Therefore, the alkaline aqueous solution and the ammonia aqueous solution are supplied at appropriate times to maintain the pH value and the ammonium ion concentration within the above ranges. It is necessary to

When producing small-diameter particles among the composite hydroxide particles of the present invention, a non-oxidizing atmosphere with an oxygen concentration of 5% by volume or less is maintained throughout the nucleation step and the particle growth step. For such solid secondary particles, it is possible to control the particle size by, for example, controlling the reaction time while keeping the raw material supply rate constant.

On the other hand, when producing large-sized particles among the composite hydroxide particles of the present invention, the reaction atmosphere in the early stages of the nucleation step and the particle growth step is a non-oxidizing atmosphere having an oxygen concentration of 5% by volume or less. In addition, in the grain growth process, after switching the reaction atmosphere from a non-oxidizing atmosphere to an oxidizing atmosphere with an oxygen concentration exceeding 5% by volume, the atmosphere is controlled by switching back to a non-oxidizing atmosphere using a ceramic air diffuser. At least 1
By repeating this process, large-sized particles having a predetermined layered structure are obtained. For particles having such a high-density layer and a low-density layer, for example, the thickness of the high-density layer and the low-density layer can be controlled by controlling the reaction time while keeping the raw material supply rate constant. It becomes possible.

Further, by continuing to supply the raw material aqueous solution while switching the reaction atmosphere, it becomes possible to form a high-density portion in a part of the low-density layer. This makes it possible to obtain large-sized particles having the structure described above.

In both the case of large-diameter particles and the case of small-diameter particles, in the method for producing composite hydroxide particles, in the nucleation step and the particle growth step, metal ions are used as nuclei or primary Deposit as particles. Therefore, the ratio of the liquid component to the metal component in the nucleation aqueous solution and the particle growth aqueous solution is increased. As a result, the concentration of the raw material aqueous solution is apparently lowered, and particularly in the particle growth step, the growth of the composite hydroxide particles may be stagnated. Therefore, in order to suppress an increase in the liquid component, it is preferable to discharge a part of the liquid component of the aqueous solution for particle growth to the outside of the reaction tank during the particle growth process after the end of the nucleation process. Specifically, the supply and stirring of the raw material aqueous solution, the alkaline aqueous solution, and the aqueous solution containing the ammonium ion donor are temporarily stopped, and the nuclei and composite hydroxide particles in the particle growth aqueous solution are allowed to settle, and the particle growth aqueous solution is It is preferable to drain the supernatant liquid. Such an operation can increase the relative concentration of the mixed aqueous solution in the aqueous solution for particle growth, thereby preventing stagnation of particle growth and controlling the particle size distribution of the resulting composite hydroxide particles within a suitable range. In addition, the density of the secondary particles as a whole can be improved.

[Particle size control of composite hydroxide particles]
The particle diameter of the composite hydroxide particles obtained as described above is controlled by the time of the particle growth process and the nucleation process, the pH value of the nuclear generation aqueous solution and the particle growth aqueous solution, and the supply amount of the raw material aqueous solution. can be done. For example, by increasing the pH value in the nucleation step or by lengthening the time of the particle generation step, the amount of the metal compound contained in the raw material aqueous solution to be supplied is increased to increase the amount of nuclei generated. Thus, the particle size of the obtained composite hydroxide particles can be reduced. Conversely, by suppressing the amount of nuclei generated in the nucleation step, the particle size of the resulting composite hydroxide particles can be increased.

[Another Embodiment of Crystallization Reaction]
In the method for producing composite hydroxide particles of the present invention, a component-adjusting aqueous solution adjusted to a pH value and an ammonium ion concentration suitable for the particle growth step is prepared separately from the nucleation aqueous solution. , an aqueous solution for nucleation after the nucleation step, preferably an aqueous solution for nucleation after the nucleation step from which part of the liquid component has been removed is added and mixed, and this is used as an aqueous solution for particle growth, and the particle growth step may be performed.

In this case, since the nucleation step and the particle growth step can be separated more reliably, the reaction aqueous solution in each step can be controlled to an optimum state. In particular, since the pH value of the aqueous solution for particle growth can be controlled within the optimum range from the start of the particle growth process,
The resulting composite hydroxide particles can have a narrower particle size distribution.

(2) Supply aqueous solution [raw material aqueous solution]
In the present invention, in principle, the ratio of the metal elements in the raw material aqueous solution is the composition ratio of the resulting composite hydroxide particles. Therefore, it is necessary to appropriately adjust the content of each metal element in the raw material aqueous solution according to the desired composition of the composite hydroxide particles. For example, when trying to obtain the composite hydroxide particles represented by the general formula (A) described above, the ratio of the metal elements in the raw material aqueous solution is changed to Ni:Mn:Co:M=x:y:z;t (However, x + y + z + t = 1
, 0.3≦x≦0.95, 0.05≦y≦0.55, 0≦z≦0.4, 0≦t≦0.1)
It is necessary to adjust so that

The transition metal compound for preparing the raw material aqueous solution is not particularly limited, but it is preferable to use water-soluble nitrates, sulfates, hydrochlorides, etc. from the viewpoint of ease of handling. From the viewpoint of preventing contamination, it is particularly preferable to suitably use a sulfate.

Further, the additive element M (M is Mg, Ca, Al, Ti, V, Cr,
Zr, Nb, Mo, Hf, Ta, and one or more additional elements selected from W), the compound for supplying the additional element M is preferably a water-soluble compound, For example, magnesium sulfate, calcium sulfate, aluminum sulfate, titanium sulfate,
ammonium peroxotitanate, potassium titanium oxalate, vanadium sulfate, ammonium vanadate, chromium sulfate, potassium chromate, zirconium sulfate, niobium oxalate,
Ammonium molybdate, hafnium sulfate, sodium tantalate, sodium tungstate, ammonium tungstate and the like can be preferably used.

The concentration of the raw material aqueous solution is the total of the metal compounds, preferably 1 mol / L to 2.6 mol /
L, more preferably 1.5 mol/L to 2.2 mol/L. The concentration of the raw material aqueous solution is 1
If it is less than mol/L, the amount of crystallized material per reaction vessel is small, resulting in low productivity. On the other hand, when the concentration of the mixed aqueous solution exceeds 2.6 mol / L, it exceeds the saturated concentration at normal temperature,
Crystals of each metal compound may re-precipitate and clog pipes.

The metal compound described above does not necessarily have to be supplied to the reaction tank as an aqueous raw material solution. For example, when a crystallization reaction is performed using a metal compound that reacts to produce a compound other than the target compound when mixed, the metals are individually added so that the total concentration of all the metal compound aqueous solutions is within the above range. An aqueous compound solution may be prepared and supplied to the reaction vessel at a predetermined ratio as an aqueous solution of individual metal compounds.

Further, the supply amount of the raw material aqueous solution is such that the concentration of the product in the particle growth aqueous solution at the end of the particle growth step is preferably 30 g/L to 200 g/L, more preferably 80 g/L to 1 g/L.
50 g/L. If the product concentration is less than 30 g/L, the aggregation of primary particles may be insufficient. On the other hand, if it exceeds 200 g/L, the aqueous metal salt solution for nucleation or the aqueous metal salt solution for particle growth may not sufficiently diffuse into the reaction tank, resulting in uneven particle growth.

[Aqueous alkaline solution]
The alkaline aqueous solution for adjusting the pH value in the reaction aqueous solution is not particularly limited, and a general alkaline metal hydroxide aqueous solution such as sodium hydroxide or potassium hydroxide can be used. Although the alkali metal hydroxide can be added directly to the reaction aqueous solution, it is preferable to add it as an aqueous solution for ease of pH control. In this case, the concentration of the alkali metal hydroxide aqueous solution is preferably 20% by mass to 50% by mass, and 20% by mass
It is more preferable to make it to 30% by mass. By regulating the concentration of the alkali metal aqueous solution within such a range, it is possible to suppress the amount of solvent (water amount) supplied to the reaction system and prevent the pH value from locally increasing at the addition position. , it is possible to efficiently obtain composite hydroxide particles with a narrow particle size distribution.

The method of supplying the alkaline aqueous solution is not particularly limited as long as the pH value of the reaction aqueous solution does not become locally high and is maintained within a predetermined range. For example, while sufficiently stirring the reaction aqueous solution, it may be supplied by a pump capable of controlling the flow rate such as a metering pump.

[Aqueous solution containing ammonium donor]
The aqueous solution containing the ammonium ion donor is also not particularly limited, and for example, ammonia water or an aqueous solution of ammonium sulfate, ammonium chloride, ammonium carbonate, ammonium fluoride, or the like can be used.

When aqueous ammonia is used as the ammonium ion donor, its concentration is preferably 20% to 30% by mass, more preferably 22% to 28% by mass. By limiting the concentration of ammonia water to such a range, loss of ammonia due to volatilization or the like can be minimized, and production efficiency can be improved.

The aqueous solution containing the ammonium ion donor can also be supplied by a pump whose flow rate can be controlled in the same manner as the alkaline aqueous solution.

(3) pH value In the method for producing composite hydroxide particles of the present invention, the pH value at a liquid temperature of 25°C is
12.0 to 14.0 in the nucleation process, and 10.5 to 10.5 in the grain growth process.
Control within the range of 12.0 is required. In any step, the fluctuation range of the pH value during the crystallization reaction is preferably within ±0.2. If the fluctuation range of the pH value is large, the ratio of the amount of nucleation and particle growth will not be constant, making it difficult to obtain composite hydroxide particles with a narrow particle size distribution.

[Nucleation step]
In the nucleation step, the pH value of the reaction aqueous solution (nucleation aqueous solution) is 12.0 to 14.0, preferably 12.3 to 13.5, more preferably 12.5 at a liquid temperature of 25 ° C. ~13
. Control within the range of 3 is required. As a result, it is possible to suppress the growth of nuclei and give priority to nucleation, so that the nuclei generated in this step can be homogeneous and have a narrow particle size distribution. On the other hand, if the pH value is less than 12.0, the growth of nuclei (particles) proceeds along with nucleation, so that the composite hydroxide particles obtained have non-uniform particle diameters and a poor particle size distribution. On the other hand, when the pH value exceeds 14.0, the generated nuclei become too fine, which causes a problem of gelation of the aqueous solution for nucleation.

[Particle growth step]
In the particle growth step, the pH value of the reaction aqueous solution (particle growth aqueous solution) is 10.5 to 12.0, preferably 11.0 to 12.0, more preferably 11.5 to 11.5, based on the liquid temperature of 25 ° C. 1
It is necessary to control it in the range of 2.0. As a result, the generation of new nuclei is suppressed, it becomes possible to give priority to particle growth, and the resulting composite hydroxide particles can be made homogeneous and have a narrow particle size distribution. On the other hand, if the pH value is less than 10.5, the concentration of ammonium ions increases and the solubility of metal ions increases, which not only slows down the crystallization reaction but also increases the amount of metal ions remaining in the reaction aqueous solution. and productivity suffers. On the other hand, if the pH value exceeds 12.0, the amount of nuclei generated during the particle growth process increases, the particle size of the resulting composite hydroxide particles becomes non-uniform, and the particle size distribution deteriorates.

When the pH value is 12.0, it is a boundary condition between nucleation and nucleus growth, so depending on the presence or absence of nuclei in the reaction aqueous solution, the condition may be either the nucleation step or the particle growth step. can be done. That is, when the pH value of the nucleation step is set higher than 12.0 to generate a large amount of nuclei, and then the pH value of the particle growth step is set to 12.0, a large amount of nuclei are present in the reaction aqueous solution, resulting in particles Growth occurs preferentially, and composite hydroxide particles with a narrow particle size distribution can be obtained. On the other hand, when the pH value of the nucleation step is set to 12.0, since there are no growing nuclei in the reaction aqueous solution, nucleation occurs preferentially. ,
The generated nuclei grow to obtain good composite hydroxide particles. In any case, the pH value in the grain growth step should be controlled at a value lower than the pH value in the nucleation step. It is preferably 0.5 or more lower than the pH value of the production step, more preferably 1.0 or more lower.

(4) Reaction Atmosphere The structure of the large-sized particles among the composite hydroxide particles of the present invention controls the pH value of the reaction aqueous solution in the nucleation step and the particle growth step as described above. is formed by appropriately controlling the reaction atmosphere in That is, in the case of producing large-diameter particles, it is important to control the reaction atmosphere as well as control the pH value in each step. That is, after controlling the pH value in each step as described above, the initial reaction atmosphere of the nucleation step and the particle growth step is set to a non-oxidizing atmosphere, so that the central portion where the plate-like primary particles are aggregated, Alternatively, a central portion is formed in which plate-like primary particles and fine primary particles are aggregated. Further, in the middle of the particle growth process, after switching from the non-oxidizing atmosphere to the oxidizing atmosphere, by further switching to the non-oxidizing atmosphere, a low-density layer in which fine primary particles are aggregated outside the central part, A structure is formed in which high-density layers in which plate-like primary particles are aggregated are laminated.

In such control of the reaction atmosphere, the fine primary particles that constitute part of the low-density layer and central portion are usually plate-like and/or needle-like, but depending on the composition of the composite hydroxide particles, they may be rectangular parallelepipeds. Shapes such as elliptical, ellipsoidal, and pyramidal are also possible. In this respect, the same applies to the plate-like primary particles that constitute the central portion, the high-density layer, and the high-density portion. Therefore, when producing particles having a large particle size, it is necessary to appropriately control the reaction atmosphere in each stage according to the composition of the desired composite hydroxide particles.

The reaction atmosphere is controlled by blowing atmospheric gas into the liquid using a ceramic diffuser. Further, by continuing to supply the raw material aqueous solution during atmosphere switching, a high-density portion can be generated in a part of the low-density layer. As for the blowing of the atmosphere gas, the smaller the bubble diameter of the blowing gas, the more efficiently the atmosphere gas can be switched. Therefore, it is desirable that the ceramic air diffuser used for switching the atmosphere has a filter with a small pore size.

[Non-oxidizing atmosphere]
In the production method of the present invention, the atmosphere in all stages of forming small-diameter particles and the reaction atmosphere in the stage of forming the central portion of large-diameter particles and the high-density layer are controlled to non-oxidizing atmospheres. It is necessary to Specifically, the reaction atmosphere is a mixed atmosphere of oxygen and an inert gas so that the oxygen concentration is 5% by volume or less, preferably 2% by volume or less, more preferably 1% by volume or less and a non-oxidizing atmosphere. need to be controlled. As a result, the nuclei generated in the nucleation step can be grown to a certain extent while suppressing unnecessary oxidation. The high-density layer can have a structure in which plate-like primary particles having an average particle size in the range of 0.3 μm to 3 μm and having a narrow particle size distribution are aggregated.

[Oxidizing atmosphere]
On the other hand, at the stage of forming a low-density layer of large-sized particles, it is necessary to control the reaction atmosphere to an oxidizing atmosphere. Specifically, it is necessary to control the oxygen concentration in the reaction atmosphere so that it exceeds 5% by volume, preferably 10% by volume or more, and more preferably an atmospheric atmosphere (oxygen concentration: 21% by volume). becomes. By controlling the oxygen concentration in the reaction atmosphere within such a range, particle growth is suppressed and the average particle size of the primary particles is reduced from 0.01 μm to 0.01 μm.
Since it is controlled within the range of 3 μm, it is possible to form a low-density layer having a sufficient difference in density from the central part and the high-density layer in large-sized particles.

The upper limit of the oxygen concentration in the reaction atmosphere at this stage is not particularly limited. It may not be the size. Therefore, the oxygen concentration is preferably 30% by volume or less.

[Switching reaction atmosphere]
In the grain growth process for producing grains with a large grain size, it is necessary to perform the above-described atmosphere control at an appropriate timing so that secondary grains having the desired grain structure are formed.

For example, when the atmosphere control is performed only once to obtain large-sized particles composed of a central portion, a low-density layer, and a high-density layer (outer shell portion), the start of the particle growth process from time to time in the range of 1% to 30%, preferably in the range of 2% to 20% of the total grain growth step time,
It is necessary to switch from a non-oxidizing atmosphere to an oxidizing atmosphere. Reaction in this range of reaction times in a non-oxidizing atmosphere results in the formation of appropriately sized cores in the large size particles.

The crystallization reaction in the oxidizing atmosphere (including the switching time from the non-oxidizing atmosphere to the oxidizing atmosphere) is preferably in the range of 1% to 30%, more preferably 2% of the total grain growth process time. It should be in the range of ~20%. When the total crystallization reaction time in an oxidizing atmosphere is less than 1% of the total particle growth process time, the size of the space is insufficient in the positive electrode active material using the composite hydroxide particles as a precursor. Sometimes it doesn't work. On the other hand, when it exceeds 30%, the thickness of the outer shell portion of the positive electrode active material becomes excessively thin, which may cause a strength problem.

The crystallization reaction in the non-oxidizing atmosphere (including the time for switching from the oxidizing atmosphere to the non-oxidizing atmosphere) after the start of switching from the oxidizing atmosphere is preferably 15% to 15% of the entire grain growth process time. It should be in the range of 35%, more preferably in the range of 20% to 30%. By the reaction within this range of reaction time in a non-oxidizing atmosphere, the large-diameter particles constituting the positive electrode active material have an appropriate thickness to support the agglomerates and the space of the primary particles dispersed inside. A high-density layer is formed that serves as the shell. After a predetermined time has passed, the introduction of the oxidizing gas into the aqueous reaction solution is started to switch the atmosphere from the non-oxidizing atmosphere to the oxidizing atmosphere, or finally terminate the crystallization reaction.

Atmosphere control is performed twice or more to obtain large-diameter particles having a plurality of laminated structures consisting of a central portion, a low-density layer, and a high-density layer. is preferably in the range of 2% to 20%, more preferably in the range of 3% to 10%, relative to the total grain growth process time. In addition, the crystallization reaction in each oxidizing atmosphere (
(including switching time from non-oxidizing atmosphere to oxidizing atmosphere) is preferably in the range of 1% to 20%, more preferably in the range of 2% to 10%, with respect to the total grain growth process time.
However, it is necessary that the ratio of the total crystallization reaction in the oxidizing atmosphere does not deviate from the range of 2% to 40%. The ratio of the entire crystallization reaction in the oxidizing atmosphere is preferably in the range of 2% to 40%, more preferably in the range of 4% to 20%, with respect to the entire grain growth process time. more preferred. Reaction within this range of reaction time in each oxidizing atmosphere enables the formation of appropriately sized voids that are dispersed inside the secondary particles in the large-diameter particles that make up the positive electrode active material. becomes. After a predetermined period of time has elapsed, introduction of a non-oxidizing gas, that is, an inert gas or a mixed gas of an oxidizing gas and an inert gas is started to switch the oxidizing atmosphere to a non-oxidizing atmosphere.

The crystallization reaction in each non-oxidizing atmosphere (including the switching time from the oxidizing atmosphere to the non-oxidizing atmosphere) after the start of switching from the oxidizing atmosphere is preferably 5 times the total grain growth process time. % to 95%, more preferably 10% to 90%.
However, it is necessary that the ratio of the total crystallization reaction in the non-oxidizing atmosphere does not deviate from the range of 20% to 95%. The ratio of the entire crystallization reaction in the non-oxidizing atmosphere is preferably in the range of 20% to 95%, more preferably in the range of 30% to 90%, with respect to the entire grain growth process time. is more preferred. By the reaction within this range of reaction time in a non-oxidizing atmosphere, the large-diameter particles constituting the positive electrode active material have an appropriate thickness to support the agglomerates and the space of the primary particles dispersed inside. A high-density layer is formed that serves as the shell. It is possible to form a space composed of a large number of pores that can communicate with the outside without lowering the tap density of the secondary particles.

The ratio of the crystallization reaction in the oxidizing atmosphere is defined as the ratio of the amount of metal added in the oxidizing atmosphere to the total amount of metal added in the grain growth step. Similarly, the ratio of crystallization reaction in non-oxidizing atmosphere is defined as the ratio of the amount of metal added in non-oxidizing atmosphere to the total amount of metal added in the grain growth process. In actual operation, by supplying the raw material aqueous solution constantly and making the amount of added metal constant, each crystallization reaction time is set at a predetermined ratio with respect to the entire grain growth process time. can be controlled to be

(5) Ammonium ion concentration The concentration of ammonium ions in the reaction aqueous solution is preferably 3 g/L to 25 g/L, more preferably 5 g/L, for both large and small particles. ~20g
It is held at a constant value within the range of /L.

Since ammonium ions function as a complexing agent in the reaction aqueous solution, if the ammonium ion concentration is less than 3 g/L, the solubility of the metal ions cannot be kept constant, and the reaction aqueous solution tends to gel, and the shape It becomes difficult to obtain composite hydroxide particles having a uniform particle size. On the other hand, when the ammonium ion concentration exceeds 25 g/L, the solubility of the metal ions becomes too high, so that the amount of metal ions remaining in the reaction aqueous solution increases, causing compositional deviation and the like.

If the ammonium ion concentration fluctuates during the crystallization reaction, the solubility of the metal ions fluctuates and uniform composite hydroxide particles are no longer formed. For this reason, it is preferable to control the fluctuation width of the ammonium ion concentration within a certain range through the nucleation step and the grain growth step, and specifically, it is preferable to control the fluctuation width within ±5 g/L.

(6) Reaction temperature The temperature of the reaction aqueous solution (reaction temperature) is preferably 20°C or higher throughout the nucleation step and the particle growth step, both in the case of large particle size particles and in the case of small particle size particles. Preferably, it is necessary to control the temperature within the range of 20°C to 60°C. If the reaction temperature is lower than 20° C., the solubility of the aqueous reaction solution is low, nucleation is likely to occur, and it becomes difficult to control the average particle size and particle size distribution of the resulting composite hydroxide particles. The upper limit of the reaction temperature is not particularly limited, but if it exceeds 60° C., volatilization of ammonia is accelerated, and an ammonium ion supplier is supplied to control the ammonium ions in the reaction aqueous solution within a certain range. The amount of the aqueous solution containing is increased, and the production cost is increased.

(7) Coating step In the method for producing composite hydroxide particles of the present invention, a compound containing the additional element M is added to the raw material aqueous solution for both large particle size particles and small particle size particles. By doing so, it is possible to obtain composite hydroxide particles in which the additional element M is uniformly dispersed inside the particles. However, when trying to obtain the effect of adding the additional element M with a smaller addition amount, the surface of the obtained composite hydroxide particles is coated with a compound containing the additional element M after the particle growth step. It is preferable to

The method of coating the composite hydroxide particles with the compound containing the additive element M is not particularly limited. For example, the composite hydroxide particles are slurried, and the pH value thereof is controlled within a predetermined range. By precipitating the compound containing the additive element M, composite hydroxide particles uniformly coated with the compound containing the additive element M can be obtained.

In this case, an alkoxide solution of the additive element M may be added to the slurried composite hydroxide particles instead of the coating aqueous solution. Alternatively, the composite hydroxide particles may be coated by spraying an aqueous solution or slurry in which a compound containing the additive element M is dissolved without making the composite hydroxide particles into a slurry, followed by drying. Furthermore, by a method of spray drying a slurry in which the composite hydroxide particles and the compound containing the additive element M are suspended, or by mixing the composite hydroxide particles and the compound containing the additive element M by a solid phase method. It can also be coated with

When the surfaces of the composite hydroxide particles are coated with the additive element M, the raw material aqueous solution and the coating It is necessary to adjust the composition of the aqueous solution as appropriate. Moreover, the coating step may be performed on the heat-treated particles after heat-treating the composite hydroxide particles.

(8) Production Apparatus In the method for producing composite hydroxide particles of the present invention, it is preferable to use an apparatus such as a batch reaction tank in which the product is not recovered until the reaction is completed. If such a device
Unlike a continuous crystallizer in which the product is recovered by an overflow system, the growing particles are not recovered simultaneously with the overflow liquid, so composite hydroxide particles with a narrow particle size distribution can be easily obtained.

In addition, in the method for producing composite hydroxide particles of the present invention, it is necessary to control the reaction atmosphere during the crystallization reaction, so it is preferable to use an apparatus capable of controlling the atmosphere, such as a closed type apparatus. With such an apparatus, the reaction atmosphere in the nucleation step and the particle growth step can be appropriately controlled, so that composite hydroxide particles having the above-described particle structure and a narrow particle size distribution can be easily produced. Obtainable.

3. Positive Electrode Active Material for Non-Aqueous Electrolyte Secondary Battery (1) Particle Structure The positive electrode active material of the present invention is composed of secondary particles formed by aggregation of a plurality of primary particles. The secondary particles constituting the positive electrode active material of the present invention include, inside the outer shell portion, agglomeration portions of primary particles electrically conductive with the outer shell portion and electrically conductive with each other, and primary particles large-diameter particles with a structure in which space parts where no , and solid particles having a small particle diameter.

In this positive electrode active material, the structure of the large-diameter particles has a structure in which the space portions are dispersed inside and the aggregation portions of the primary particles including the outer shell portion are electrically connected to each other. other structural elements are optional. For example, in large-sized particles, it is not required that the core be clearly present, but a space is generally formed between the core and the shell, and the core and the shell are separated. It is also possible to employ a structure in which primary particles are dispersedly present in this space and are electrically connected to each other by agglomerates of the primary particles.

The size of each space is also arbitrary as long as the structure is such that the aggregated portion of the primary particles, including the outer shell portion, exists such that the diffusion path length of the lithium ions does not exceed a predetermined length.

It is also possible to adopt a porous structure in which the space inside the outer shell communicates with the outside world by a structure such as a through hole partially formed in the outer shell.

In large-sized particles having such a particle structure, grain boundaries between primary particles, through-holes in the outer shell,
Alternatively, since the electrolyte penetrates into the interior of the secondary particles through the space, lithium can be desorbed and inserted not only on the surface of the secondary particles but also in the interior of the secondary particles. Moreover, in this positive electrode active material, there are many electrically conductive paths inside the secondary particles, and the diffusion path length of lithium ions can be shortened, so that the resistance inside the particles is sufficiently small. becomes possible.

On the other hand, small-sized particles have a solid structure formed by agglomeration of primary particles. Therefore, the resistance inside the particles can be made sufficiently small as in the case of large-diameter particles. With such a structure, the degree of insertion and extraction of lithium ions during the charging and discharging process becomes uniform throughout the positive electrode active material, and selective deterioration of small-sized particles is prevented, resulting in excellent cycle characteristics. It can be a substance.

In addition, since there are many large-sized particles and small-sized particles that fill the gaps between the large-sized particles, the fillability (tap density) of the positive electrode active material as a whole is greatly improved. It is possible to obtain a secondary battery having an excellent volumetric energy density.

Therefore, when the positive electrode active material of the present invention is used, it is possible to obtain a lithium ion secondary battery that has a high volumetric energy density and greatly improved output characteristics in the low SOC region without impairing cycle characteristics. becomes.

(2) Mixing ratio of large-sized particles and small-sized particles The ratio (mass ratio) of large-sized particles and small-sized particles inherits the properties of the precursor composite hydroxide particles. Therefore, it is substantially the same as the composite hydroxide particles. Specifically, the ratio of small-diameter particles to large-diameter particles is in the range of 0.05 to 20 as a mass ratio (mass of small-diameter particles/mass of large-diameter particles). do. This mass ratio is preferably in the range of 0.1-15, more preferably in the range of 0.5-10. If this mass ratio is less than 0.05, it may not be possible to obtain a positive electrode active material with sufficient output characteristics. may not be obtained.

(3) Average Particle Size The average particle size of the secondary particles constituting the positive electrode active material of the present invention is in the range of 1 μm to 15 μm, preferably 3 μm to 12 μm, more preferably 3 μm to 10 μm. adjusted to be In addition, the large particle size particles constituting the secondary particles of the positive electrode active material of the present invention have an average particle size in the range of 4 μm to 15 μm, preferably in the range of 5 μm to 12 μm, more preferably in the range of 6 μm to 10 μm. adjusted to On the other hand, the small-diameter particles that constitute the secondary particles of the positive electrode active material of the present invention have an average particle diameter in the range of 1 μm to 4 μm, preferably in the range of 1.5 μm to 3.5 μm. , more preferably in the range of 2 μm to 3 μm.

If the average particle diameter of the positive electrode active material is in such a range, not only can the battery capacity per unit volume of the secondary battery using this positive electrode active material be increased, but also safety and output characteristics can be improved. can do. On the other hand, if the average particle size of both the large particle size particles and the small particle size particles is less than 1 μm, the fillability of the positive electrode active material decreases, and the battery capacity per unit volume increases. can't On the other hand, even if the particles have a large particle size, when the average particle size exceeds 15 μm, the reaction area of the positive electrode active material decreases, and the interface with the electrolyte solution decreases.
It becomes difficult to improve the output characteristics. The upper limit of the average particle size of the small particle size particles is determined by the average particle size of the large particle size particles and the appropriate diffusion path length of lithium ions in the large particle size particles.

The average particle diameter of the positive electrode active material means the volume-based average particle diameter (MV), as in the case of the composite hydroxide particles described above. can be obtained from the value.

(4) Particle size distribution In the positive electrode active material of the present invention, [(d90-d10)/average particle size], which is an index showing the spread of the particle size distribution, is 0.70 or less, preferably 0.60 or less, more preferably It is composed of lithium transition metal-containing composite oxide particles (hereinafter referred to as "lithium composite oxide particles") having a particle size distribution of 0.55 or less and an extremely narrow particle size distribution. Such a positive electrode active material has a low ratio of fine particles and coarse particles, and a secondary battery using this has excellent safety, cycle characteristics, and output characteristics.

On the other hand, when [(d90-d10)/average particle size] exceeds 0.70, the ratio of fine particles and coarse particles in the positive electrode active material increases. For example, a secondary battery using a positive electrode active material with a large proportion of fine particles generates heat due to local reactions of fine particles, lowers safety, and selectively deteriorates fine particles. , the cycle characteristics are inferior. In addition, a secondary battery using a positive electrode active material with a large proportion of coarse particles cannot secure a sufficient reaction area between the electrolyte and the positive electrode active material, resulting in inferior output characteristics.

On the other hand, assuming industrial-scale production, as a positive electrode active material, [(d90-d10) /
It is not realistic to use particles with an excessively small average particle diameter]. Therefore, considering the cost and productivity, the lower limit of [(d90-d10)/average particle diameter] is about 0.25, 0.25.
About 30 or about 0.35 is preferable.

In addition, for the secondary particles having a large particle diameter constituting the positive electrode active material of the present invention, [(d90-d10)/average particle diameter], which is an index showing the spread of the particle size distribution, is 0.30 to 0.70. range of
It is preferably in the range of 0.30 to 0.65, more preferably in the range of 0.30 to 0.60. On the other hand, for particles with a small particle size, it is an index showing the spread of the particle size distribution [(d90-
d10)/average particle diameter] is in the range of 0.30 to 0.7, preferably in the range of 0.30 to 0.65, more preferably in the range of 0.30 to 0.65. By setting it as such a range, it becomes possible to make the particle size distribution of the whole positive electrode active material into an appropriate range.

In addition, d10 in the index [(d90-d10) / average particle diameter] indicating the spread of the particle size distribution
and d90 and the method of obtaining them are the same as those of the composite hydroxide particles described above, so descriptions thereof will be omitted here.

(5) _{Composition The} composition of the _{positive electrode active material} of the present invention is not limited as long as it has the structure described above. Medium, -0.05≤u≤0
. 50, x+y+z+t=1, 0.3≦x≦0.95, 0.05≦y≦0.55, 0≦z
≦0.4 and 0≦t≦0.1, and M is Mg, Ca, Al, Ti, V, Cr,
one or more additional elements selected from Zr, Nb, Mo, Hf, Ta, and W)
It can be suitably applied to the positive electrode active material represented by. In addition, it is preferable that the composition of the large-diameter particles and the small-diameter particles be the same. In addition to the viewpoint of appropriate control of the composition of the entire positive electrode active material, to reduce the adverse effect on battery characteristics due to variations in the characteristics of the positive electrode active material between large and small particles depending on the composition. is.

In this positive electrode active material, the value of u, which indicates the excess amount of lithium (Li), is preferably -0
. 05 or more and 0.50 or less, more preferably 0 or more and 0.50 or less, more preferably 0 or more and 0
. 35 or less. By limiting the value of u to the above range, the output characteristics and capacity characteristics of a secondary battery using this positive electrode active material as a positive electrode material can be improved. On the other hand, when the value of u is less than −0.05, the positive electrode resistance of the secondary battery becomes large, and the output characteristics cannot be improved. On the other hand, when it exceeds 0.50, not only the initial discharge capacity decreases, but also the positive electrode resistance increases.

Nickel (Ni) is an element that contributes to increasing the potential and capacity of secondary batteries, and the value of x, which indicates the content thereof, is preferably 0.3 or more and 0.95 or less, more preferably 0.3 or more. 3 or more and 0.9 or less. If the value of x is less than 0.3, it is not possible to improve the capacity characteristics of the secondary battery using this positive electrode active material. On the other hand, if the value of x exceeds 0.95, the content of other elements will decrease and the effect cannot be obtained.

Manganese (Mn) is an element that contributes to improving thermal stability, and the value of y, which indicates the content thereof, is preferably 0.05 or more and 0.55 or less, more preferably 0.10 or more and 0.40 or less. and If the value of y is less than 0.05, the thermal stability of the secondary battery using this positive electrode active material cannot be improved. On the other hand, when the value of y exceeds 0.55, Mn is eluted from the positive electrode active material during high-temperature operation, resulting in deterioration of charge-discharge cycle characteristics.

Cobalt (Co) is an element that contributes to the improvement of charge-discharge cycle characteristics, and the value of z indicating its content is preferably 0 or more and 0.4 or less, more preferably 0.10 or more and 0.35 or less. do. When the value of z exceeds 0.4, the initial discharge capacity of the secondary battery using this positive electrode active material is significantly reduced.

In order to further improve the durability and output characteristics of the secondary battery, the positive electrode active material of the present invention may contain an additive element M in addition to the metal elements described above. Such additive elements M include magnesium (Mg), calcium (Ca), aluminum (Al), titanium (Ti), vanadium (V), chromium (Cr), zirconium (Zr), niobium (Nb), molybdenum At least one selected from (Mo), hafnium (Hf), tantalum (Ta), and tungsten (W) can be used.

The value of t indicating the content of the additive element M is preferably 0 or more and 0.1 or less, more preferably 0
. 001 or more and 0.05 or less. If the value of t exceeds 0.1, the metal elements that contribute to the Redox reaction decrease, resulting in a decrease in battery capacity.

The additive element M may be dispersed uniformly inside the particles of the positive electrode active material, or may coat the surface of the particles of the positive electrode active material. Furthermore, the surface may be coated after being uniformly dispersed inside the particles. In any case, it is necessary to control the content of the additive element M to be within the above range.

Further, when further improving the capacity characteristics of a secondary battery using the positive electrode active material represented by the general formula (B), the composition is represented by the general formula (B1): Li _1+u Ni _{x Mny} Co
_z M _t O ₂ (where −0.05≦u≦0.20, x+y+z+t=1, 0.7<x≦0.
95, 0.05≦y≦0.1, 0≦z≦0.2, and 0≦t≦0.1, and M is
one or more additional elements selected from Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, and W). In particular, when achieving compatibility with thermal stability, the value of x in the general formula (B1) is more preferably 0.7 < x ≤ 0.9, and 0.7 < x ≤ 0.85. is more preferred.

On the other hand, when further improving the thermal stability, the composition is represented by the general formula (B2): Li _1+u
Ni _x Mn _y Co _z M _t O ₂ (where −0.05≦u≦0.50, x+y+z+t=1,
0.3≦x≦0.7, 0.1≦y≦0.55, 0≦z≦0.4, and 0≦t≦0.1
and M is one or more additive elements selected from Al, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, and W). preferable.

(6) Specific Surface Area The positive electrode active material of the present invention preferably has a specific surface area of 0.7 m ² /g to 5.0 m ² /g, more preferably 1.8 m ² /g to 5.0 m ² /g. It is more preferable to have A positive electrode active material having a specific surface area within this range has a large contact area with an electrolytic solution, and can greatly improve the output characteristics of a secondary battery using the same. On the other hand, the specific surface area of the positive electrode active material is 0.7 m ² /
If it is less than g, a reaction area with the electrolyte cannot be secured when a secondary battery is constructed,
It becomes difficult to sufficiently improve the output characteristics. On the other hand, the specific surface area of the positive electrode active material is 5.0 m
If it exceeds ² /g, the reactivity with the electrolytic solution becomes too high, which may lower the thermal stability. In addition, if the specific surface area is out of these ranges, the balance between the large particle size particles and the small particle size particles will be unbalanced, and the effect of the present invention of achieving both high capacity characteristics and high output characteristics will be fully exhibited. It will not be possible.

The specific surface area of the positive electrode active material can be measured, for example, by the BET method using nitrogen gas adsorption.

(7) Tap density Increasing the capacity of secondary batteries is an important issue in order to extend the usage time of portable electronic devices and the driving distance of electric vehicles. On the other hand, the thickness of the electrode of the secondary battery is required to be about several microns from the viewpoint of the packing and electronic conductivity of the battery as a whole. For this reason, it is necessary not only to use a high-capacity positive electrode active material, but also to improve the filling property of the positive electrode active material to increase the capacity of the secondary battery as a whole. From this point of view, in the positive electrode active material of the present invention,
The tap density, which is an index of fillability, is preferably 1.0 g/cm ³ or more, and 1.3
g/cm ³ or more is more preferable. If the tap density is less than 1.0 g/cm ³ , the fillability is low, and the capacity characteristics of the entire secondary battery may not be sufficiently improved. on the other hand,
The upper limit of the tap density is not particularly limited, but the upper limit under normal manufacturing conditions is 3
. It becomes about 0 g/cm ³ . In addition, the relationship between the tap density and the ratio of large-diameter particles to small-diameter particles is the same as the specific surface area. This means that the effect of the present invention, which is to achieve both characteristics and high output characteristics, cannot be fully exhibited.

In addition, the tap density is based on JIS Z-2504, and the sample powder collected in the container is
It represents the bulk density after 100 tappings and can be measured using a shaking densimeter.

(8) Surface area per unit volume The positive electrode active material of the present invention has a surface area per unit volume of 0.50 m ² /cm ³ or more. Preferably, the surface area per unit volume ranges from 1.0 m ² /cm ³ to 5.0 m ² /cm ³ , more preferably from 2.0 m ² /cm ³ to 5.0 m ² /cm ³ . Range. In order to improve the output characteristics and capacity characteristics of secondary batteries, it is necessary to increase the specific surface area and tap density, respectively. Represents having a property. The surface area per unit volume can be obtained by multiplying the above-mentioned specific surface area by the measured value of the tap density.

(9) Spatial Ratio Particles of the positive electrode active material of the present invention with large particle diameters require that a plurality of spatial portions be dispersed inside the particles. In the large-diameter particles that constitute the positive electrode active material of the present invention, the area ratio of the entire plurality of spaces measured by cross-sectional observation of the secondary particles is 5% with respect to the cross-sectional area of the secondary particles.
It is in the range of ~60%. As the occupation ratio of the space area to the cross-sectional area of the secondary particles (hereinafter referred to as "space ratio") increases, the specific surface area tends to increase and the diffusion path length of lithium ions tends to decrease. That is, when a secondary battery is constructed, the reaction area with the electrolytic solution is ensured, the diffusion path length of lithium ions inside the large particle size particles and the small particle size particles is uniformly shortened, and the positive electrode resistance is reduced. The reduction leads to improvement in output characteristics in the low SOC region. If the space ratio is below the above range, a sufficient space is not formed, and the effect of providing the space inside cannot be obtained sufficiently. On the other hand, when the above range is exceeded, voids larger than the space exist inside the secondary particles, the ratio of the aggregated portions becomes too low, and electrical conduction between the aggregated portions becomes insufficient. , the desired properties cannot be obtained. This spatial ratio is
It is preferably in the range of 10% to 50%, more preferably in the range of 20% to 40%.

In addition, the space ratio is the cross section of any 10 or more particles of the positive electrode active material.
It can be obtained by performing EM observation, binarizing, calculating the ratio of the total area of the space dispersed in the particle to the cross-sectional area of one particle, and calculating the average value of these. .

4. A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery The method for producing a positive electrode active material of the present invention comprises the above-described large particle size particles and small particle size particles separately, or a composite water obtained by mixing them. There is no particular limitation as long as the oxide particles can be used as a precursor to synthesize a positive electrode active material having a predetermined structure, average particle size and particle size distribution. However, assuming industrial scale production, a predetermined proportion of large and small particles are mixed with the lithium compound, or a predetermined proportion of large and small particles are mixed with the lithium compound. A mixing step of mixing the mixed composite hydroxide particles with a lithium compound to obtain a lithium mixture;
It is preferable to synthesize the positive electrode active material by a manufacturing method including a sintering step of sintering at 0°C. In addition, if necessary, steps such as a heat treatment step and a calcining step may be added to the above-described steps. According to such a manufacturing method, it is possible to easily obtain the positive electrode active material described above, particularly the positive electrode active material represented by the general formula (B).

(1) Heat treatment step In the method for producing a positive electrode active material of the present invention, a heat treatment step is optionally provided before the mixing step to mix large particle size particles, small particle size particles, or these particles. The composite hydroxide particles may be subjected to a predetermined heat treatment to obtain heat-treated particles and then mixed with the lithium compound. Here, the heat-treated particles are composite hydroxide particles (including large particle size particles, small particle size particles, and mixtures thereof, the same applies hereinafter) from which excess moisture has been removed in the heat treatment step.
In addition, transition metal-containing composite oxide particles (hereinafter referred to as "composite oxide particles") in which these particles are converted to oxides by a heat treatment step, or these composite hydroxide particles and composite oxides Mixtures of particles are also included.

The heat treatment step is a step of removing excess moisture contained in the composite hydroxide particles by heating the composite hydroxide particles to 105° C. to 750° C. for heat treatment. As a result, it is possible to reduce the amount of water remaining until after the baking process to a certain amount, and to suppress variation in the composition of the obtained positive electrode active material.

The heating temperature in the heat treatment step is set to 105.degree. C. to 750.degree. If the heating temperature is less than 105° C., excess moisture in the composite hydroxide particles cannot be removed, and variations may not be sufficiently suppressed. On the other hand, even if the heating temperature exceeds 700° C., no further effect can be expected, and the production cost increases.

In the heat treatment step, it is only necessary to remove moisture to the extent that the number of atoms of each metal component in the positive electrode active material and the ratio of the number of Li atoms do not vary. It does not need to be transformed into matter particles. However, the number of atoms of each metal component and Li
In order to reduce the variation in the atomic number ratio, it is necessary to heat to 400 ° C. or higher
It is preferred to convert all composite hydroxide particles to composite oxide particles. Incidentally, by determining the metal components contained in the composite hydroxide particles according to the heat treatment conditions in advance by analysis and determining the mixing ratio with the lithium compound, the above-described variations can be further suppressed.

The atmosphere for the heat treatment is not particularly limited as long as it is a non-reducing atmosphere.
It is preferable to carry out in an air current, which can be easily carried out.

In addition, the heat treatment time is not particularly limited, but from the viewpoint of sufficiently removing excess moisture in the composite hydroxide particles, it is preferably at least 1 hour or longer, more preferably 5 to 15 hours.

(2) Mixing Step The mixing step is a step of mixing the composite hydroxide particles or heat-treated particles described above with a lithium compound to obtain a lithium mixture. In this case, it is possible to separately weigh the large particle size particles and the small particle size particles and mix them with the lithium compound. Alternatively, the composite hydroxide particles of the present invention (mixture of large particle size particles and small particle size particles) can be mixed with a lithium compound.

Specifically, in the first aspect, the transition metal-containing composite hydroxide particles represented by the general formula (A) are formed by aggregation of plate-like primary particles, or plate-like primary particles and a central portion formed by aggregation of fine primary particles smaller than the plate-shaped primary particles, and a low-density portion formed by aggregation of fine primary particles outside the center, and plate-shaped primary particles At least one laminated structure in which high-density portions formed by agglomeration are laminated, and a high-density portion formed by agglomeration of plate-like primary particles exists in a part of the low-density layer, and the average grain size The diameter is in the range of 4 μm to 15 μm, and [(d90-d10) / average particle diameter], which is an index showing the spread of the particle size distribution, is 0.35 to 0.
. 65, and transition metal-containing composite hydroxide particles represented by the general formula (A), which are formed by aggregation of plate-like primary particles and are formed by agglomeration of large particle diameters It has a radius of length equivalent to the thickness of the high-density portion of , the average particle size is in the range of 1 μm to 4 μm, and is an index showing the spread of the particle size distribution [(d90-d10) / average particle size] is in the range of 0.30 to 0.65, and the mass ratio of the small particle size to the large particle size (the mass of the small particle size / Mass of particles with large particle diameter) is mixed so that it is in the range of 0.05 to 20,
A precursor mixture is obtained and then the precursor mixture and the lithium compound are mixed to form a lithium mixture.

In the second aspect, the large particle size particles, the small particle size particles, and the lithium compound are mixed, and the mass ratio of the small particle size particles to the large particle size particles (mass of the small particle size particles/ 0.0 in mass of particles with large diameter)
5 to 20 are mixed together to form a lithium mixture.

In addition, as a third aspect, particles of large particle size and a lithium compound are mixed to obtain a first lithium mixture, and particles of small particle size and a lithium compound are mixed to obtain a second lithium compound. After obtaining the lithium mixture, the first lithium composite oxide particles and the second lithium composite oxide particles are obtained through the calcining step and the firing step, which will be described later. The particles with a small particle size are mixed so that the mass ratio (mass of the particles with a small particle size/mass of the particles with a large particle size) is in the range of 0.05 to 20 to obtain the final positive electrode active material. can also

In any case, in the mixing step, the metal atoms other than lithium in the lithium mixture, specifically, the sum of the number of atoms of nickel, cobalt, manganese and the additive element M (Me), and the number of lithium atoms (Li ) and the ratio (Li/Me) is 0.95 to 1.5, preferably 1.0
~1.5, more preferably 1.0 to 1.35, more preferably 1.0 to 1.2, it is necessary to mix the composite hydroxide particles or heat-treated particles and the lithium compound. . That is, since Li/Me does not change before and after the firing process, Li/Me in the mixing process
It is necessary to mix the composite hydroxide particles or heat-treated particles with the lithium compound so that Me becomes Li/Me in the desired positive electrode active material.

Although the lithium compound used in the mixing step is not particularly limited, it is preferable to use lithium hydroxide, lithium nitrate, lithium carbonate, or a mixture thereof in terms of availability. In particular, considering ease of handling and stability of quality, it is preferable to use lithium hydroxide or lithium carbonate.

It is preferable that the composite hydroxide particles or the heat-treated particles and the lithium compound are sufficiently mixed to the extent that fine powder is not generated. Insufficient mixing may cause variations in Li/Me among individual particles, making it impossible to obtain sufficient battery characteristics. In addition, a general mixer can be used for mixing. For example, shaker mixers, Loedige mixers, Julia mixers, V-blenders, etc. can be used.

(3) Calcination step When lithium hydroxide or lithium carbonate is used as the lithium compound, after the mixing step and before the firing step, the lithium mixture is heated to a temperature lower than the firing temperature described later and at 350 ° C.
A calcining step of calcining at ~800°C, preferably 450°C to 780°C may be performed. As a result, lithium can be sufficiently diffused in the composite hydroxide particles or heat-treated particles, and more uniform lithium composite oxide particles can be obtained.

The holding time at the above temperature is preferably 1 hour to 10 hours, and 3 hours to 6 hours.
Time is preferred. The atmosphere in the calcining step is preferably an oxidizing atmosphere, more preferably an atmosphere with an oxygen concentration of 18% by volume to 100% by volume, as in the firing step described later.

(4) Firing step In the firing step, the lithium mixture obtained in the mixing step is fired under predetermined conditions to diffuse lithium into the composite hydroxide particles or heat-treated particles to obtain lithium composite oxide particles. is.

In this firing step, the fine primary particles that make up the low-density portion in the low-density layer of the composite hydroxide particles or the heat-treated particles have a lower temperature than the plate-like primary particles that make up the central portion, the high-density layer, and the high-density portion. Start sintering from Moreover, the amount of shrinkage is greater than that of the central portion, the high-density layer, and the high-density portion, which are composed of plate-like primary particles. For this reason, the fine primary particles that make up the low-density portion shrink toward the central portion where sintering progresses slowly, the high-density portion of the outer shell, or the high-density portion within the low-density layer, resulting in an appropriate size. is formed.

Furthermore, at the initial stage of the nucleation step in which the central portion is formed, the low-density portion is formed by setting the reaction atmosphere to an oxidizing atmosphere, thereby making it possible to form the central portion into a hollow structure. However, since the structure of the center part changes depending on the composition of the composite hydroxide particles and the firing conditions, etc., after conducting a preliminary test, each condition is appropriately controlled so that the center part has the desired structure. is preferred.

The furnace used in the firing step is not particularly limited as long as it can heat the lithium mixture in the atmosphere or in an oxygen stream. However, from the viewpoint of maintaining a uniform atmosphere in the furnace, an electric furnace that does not generate gas is preferable, and either a batch type or a continuous type electric furnace can be suitably used. This also applies to furnaces used in the heat treatment process and the calcining process.

[Firing temperature]
The firing temperature of the lithium mixture is required to be 650°C to 980°C. If the firing temperature is less than 650 ° C., lithium does not sufficiently diffuse into the composite hydroxide particles or the heat-treated particles, and excess lithium or unreacted composite hydroxide particles or heat-treated particles remain, or the obtained lithium composite In some cases, the crystallinity of the oxide particles becomes insufficient. On the other hand, the firing temperature is 98
When the temperature exceeds 0° C., the lithium composite oxide particles are violently sintered, causing abnormal grain growth and increasing the proportion of amorphous coarse particles.

It should be noted that the firing temperature is preferably 650° C. to 900° C. in order to obtain the positive electrode active material represented by the general formula (B1) described above. On the other hand, when the positive electrode active material represented by the general formula (B2) is to be obtained, the firing temperature is preferably 800°C to 980°C.

In addition, the heating rate in the firing step is preferably 2 ° C./min to 10 ° C./min.
C./min to 10.degree. C./min is more preferable. Furthermore, during the firing step, it is preferable to hold the temperature near the melting point of the lithium compound for preferably 1 to 5 hours, more preferably 2 to 5 hours. Thereby, the composite hydroxide particles or the heat-treated particles and the lithium compound can be reacted more uniformly.

[Baking time]
Of the firing time, the retention time at the firing temperature described above is preferably at least 2 hours or longer, more preferably 4 to 24 hours. When the holding time at the firing temperature is less than 2 hours, lithium does not sufficiently diffuse into the composite hydroxide particles or the heat-treated particles, and excess lithium or unreacted composite hydroxide particles or heat-treated particles remain or are not obtained. The crystallinity of the lithium composite oxide particles obtained may become insufficient.

The cooling rate from the firing temperature to at least 200° C. after the holding time is preferably 2° C./min to 10° C./min, more preferably 33° C./min to 77° C./min. By controlling the cooling rate within such a range, it is possible to prevent damage to equipment such as a sagger due to rapid cooling while ensuring productivity.

[Firing atmosphere]
The atmosphere during firing is preferably an oxidizing atmosphere, and the oxygen concentration is 18% by volume to 10% by volume.
An atmosphere of 0% by volume is more preferable, and a mixed atmosphere of oxygen and an inert gas having the above oxygen concentration is particularly preferable. That is, it is preferable to carry out the calcination in the atmosphere or in an oxygen stream. If the oxygen concentration is less than 18% by volume, the crystallinity of the lithium composite oxide particles may be insufficient.

(5) Crushing step The lithium composite oxide particles obtained by the firing step may be aggregated or slightly sintered. In such a case, it is preferable to pulverize the aggregates or sintered bodies of the lithium composite oxide particles. Thereby, the average particle size and particle size distribution of the obtained positive electrode active material can be adjusted to a suitable range. Crushing means applying mechanical energy to agglomerates consisting of a plurality of secondary particles generated by sintering necking between secondary particles during firing, without almost destroying the secondary particles themselves. It means the operation of separating and loosening aggregates.

As a crushing method, known means can be used, for example, a pin mill or a hammer mill can be used. At this time, it is preferable to adjust the crushing force to an appropriate range so as not to destroy the secondary particles.

5. Non-aqueous Electrolyte Secondary Battery The non-aqueous electrolyte secondary battery of the present invention comprises components such as a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, which are similar to those of general non-aqueous electrolyte secondary batteries. The embodiments described below are merely examples, and the non-aqueous electrolyte secondary battery of the present invention is applied to various modifications and improvements based on the embodiments described herein. It is also possible to

(1) Components (1-a) Positive Electrode Using the positive electrode active material for a non-aqueous electrolyte secondary battery obtained by the present invention, a positive electrode for a non-aqueous electrolyte secondary battery is produced, for example, as follows.

First, a powdered positive electrode active material obtained by the present invention is mixed with a conductive material and a binder, and if necessary, activated carbon and a solvent for viscosity adjustment are added, and these are kneaded to form a positive electrode mixture. Make a material paste. At that time, the mixing ratio of each component in the positive electrode mixture paste is also an important factor that determines the performance of the non-aqueous electrolyte secondary battery. For example, the solid content of the positive electrode mixture excluding the solvent is 1
00 parts by mass, the content of the positive electrode active material is 60 parts by mass to 95 parts by mass, and the content of the conductive material is 1 part by mass to 20 parts by mass, similar to the positive electrode of a general non-aqueous electrolyte secondary battery. , the content of the binder can be 1 part by mass to 20 parts by mass.

The obtained positive electrode mixture paste is applied, for example, to the surface of a current collector made of aluminum foil,
Dry to remove solvent. If necessary, pressure may be applied by a roll press or the like in order to increase the electrode density. Thus, a sheet-like positive electrode can be produced. The sheet-like positive electrode can be cut into an appropriate size depending on the intended battery, and used for manufacturing the battery. However, the method for producing the positive electrode is not limited to the above examples, and other methods may be used.

As the conductive material, for example, graphite (natural graphite, artificial graphite, expanded graphite, etc.) and carbon black-based materials such as acetylene black and ketjen black can be used.

The binder plays a role of binding the active material particles, and examples thereof include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluororubber, ethylene propylene diene rubber, styrene butadiene, cellulose resin and polyacrylic. Acid can be used.

Moreover, if necessary, a solvent for dispersing the positive electrode active material, the conductive material and the activated carbon and dissolving the binder can be added to the positive electrode mixture. Specific examples of solvents include N-methyl-2-
Organic solvents such as pyrrolidone can be used. Activated carbon can also be added to the positive electrode mixture in order to increase the electric double layer capacity.

(1-b) Negative electrode The negative electrode is prepared by mixing a binder with a negative electrode active material such as metal lithium or a lithium alloy, or a negative electrode active material capable of intercalating and deintercalating lithium ions, and adding an appropriate solvent to form a paste. The mixture is applied to the surface of a metal foil current collector such as copper, dried, and compressed to increase the electrode density as required.

Examples of negative electrode active materials include materials containing lithium such as metallic lithium and lithium alloys, natural graphite capable of intercalating and deintercalating lithium ions, artificial graphite, sintered organic compounds such as phenolic resins, and carbon materials such as coke. A powder can be used.
In this case, a fluorine-containing resin such as PVDF can be used as the binder for the negative electrode in the same manner as the binder for the positive electrode. Solvents can be used.

(1-c) Separator The separator is sandwiched between the positive electrode and the negative electrode, and has the function of separating the positive electrode and the negative electrode and retaining the electrolyte. As such a separator, for example, a thin film of polyethylene, polypropylene, or the like and having many fine pores can be used, but there is no particular limitation as long as it has the above function.

(1-d) Non-Aqueous Electrolyte The non-aqueous electrolyte is prepared by dissolving a lithium salt as a supporting salt in an organic solvent.

Organic solvents include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate and trifluoropropylene carbonate; chain carbonates such as diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate and dipropyl carbonate; and ether compounds such as dimethoxyethane, sulfur compounds such as ethyl methyl sulfone and butane sultone, and phosphorus compounds such as triethyl phosphate and trioctyl phosphate. can.

Support salts include LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiN(C
F ₃ SO ₂ ) ₂ , their complex salts, and the like can be used.

Furthermore, the non-aqueous electrolyte may contain a radical scavenger, a surfactant, a flame retardant, and the like.

(2) Non-aqueous Electrolyte Secondary Battery The non-aqueous electrolyte secondary battery of the present invention, which is composed of the positive electrode, negative electrode, separator and non-aqueous electrolyte described above, can be formed in various shapes such as cylindrical and laminated. can.

Regardless of which shape is adopted, the positive electrode and the negative electrode are laminated with a separator interposed to form an electrode body, the obtained electrode body is impregnated with a non-aqueous electrolyte, and communicated with the positive electrode current collector and the outside. The positive electrode terminal and the negative electrode current collector and the negative electrode terminal connected to the outside are connected using a current collecting lead or the like, and sealed in the battery case to complete the non-aqueous electrolyte secondary battery. .

(3) Characteristics of non-aqueous electrolyte secondary battery Since the non-aqueous electrolyte secondary battery of the present invention uses the positive electrode active material of the present invention as a positive electrode material as described above, capacity characteristics, output characteristics and cycle characteristics Excellent for Moreover, in comparison with a secondary battery using a positive electrode active material made of conventional lithium nickel oxide particles,
It can be said that it is excellent in thermal stability and safety.

For example, when the positive electrode active material of the present invention is used to configure a 2032 type coin battery as shown in FIG. A discharge capacity, a positive electrode resistance of 1.2 Ω or less, preferably 1.15 Ω or less, and a 500 cycle capacity retention rate of 75% or more, preferably 80% or more can be achieved simultaneously.

(4) Applications The non-aqueous electrolyte secondary battery of the present invention, as described above, is excellent in capacity characteristics, output characteristics and cycle characteristics. It can be suitably used as a power supply for personal computers, prefectural telephone terminals, etc.). again,
The non-aqueous electrolyte secondary battery of the present invention is excellent in safety, and not only can it be made smaller and higher in output, but it can also simplify the expensive protection circuit, so that the mounting space is limited. It can also be suitably used as a power source for transportation equipment that receives the power.

The present invention will be described in detail below using examples and comparative examples. In the following examples and comparative examples, unless otherwise specified, the composite hydroxide particles and the positive electrode active material were produced by:
Special grade reagent samples manufactured by Wako Pure Chemical Industries, Ltd. were used. In addition, throughout the nucleation step and the particle growth step, the pH value of the reaction aqueous solution was controlled by a pH controller (Nisshin Rika, NPH-690
D), and based on this measured value, the amount of sodium hydroxide aqueous solution supplied was adjusted to control the fluctuation range of the pH value of the reaction aqueous solution in each step within a range of ±0.2.

(Example 1)
(a) Production of composite hydroxide particles (a-1) Production of particles with large particle size [Nucleation step]
First, 14 L of water was put into the reactor, and the temperature inside the reactor was set to 40° C. while stirring. At this time, nitrogen gas was passed through the reaction tank for 30 minutes to make the reaction atmosphere a non-oxidizing atmosphere with an oxygen concentration of 2% by volume or less. Subsequently, an appropriate amount of 25% by mass sodium hydroxide aqueous solution and 25% by mass aqueous ammonia are supplied into the reaction tank so that the pH value is 12.8 at a liquid temperature of 25° C. and the ammonium ion concentration is 10 g/L. to form a pre-reaction aqueous solution.

At the same time, nickel sulfate, cobalt sulfate, and manganese sulfate were dissolved in water so that the molar ratio of the respective metal elements was Ni:Mn:Co=1:1:1 to prepare a 2 mol/L raw material aqueous solution.

Next, this raw material aqueous reaction solution was supplied to the pre-reaction aqueous solution at 100 ml/min to form an aqueous solution for the nucleation step, and nucleation was performed for 0.25 minutes. At this time, a 25% by mass aqueous sodium hydroxide solution and a 25% by mass aqueous ammonia solution were supplied at appropriate times to maintain the pH value and the ammonium ion concentration of the aqueous solution for nucleation within the ranges described above.

[Particle growth step]
After the completion of nucleation, the supply of all the aqueous solutions is temporarily stopped, and sulfuric acid is added to
An aqueous solution for particle growth was formed by adjusting the pH value to 11.6 based on a liquid temperature of 25°C. After confirming that the pH value reached a predetermined value, the raw material aqueous solution was supplied at the same rate as in the nucleation step to grow the nuclei (particles) generated in the nucleation step.

After 24 minutes (2.1% of the entire particle growth process) from the start of the particle growth process, a ceramic diffuser with a filter pore size in the range of 20 μm to 30 μm (manufactured by Kinoshita Rika Kogyo Co., Ltd.)
was used to circulate air in the reaction tank at a flow rate of 3 L/m, and the reaction atmosphere was made an oxidizing atmosphere with an oxygen concentration of 21% by volume (switching operation 1). During this period, the supply of the raw material aqueous solution was continued to grow the particles.

After 5 minutes (0.4% with respect to the entire particle growth process) after the switching operation 1 was performed, nitrogen was circulated in the reaction vessel at a flow rate of 10 L/m using an air diffuser in the same manner. , the reaction atmosphere was a non-oxidizing atmosphere with an oxygen concentration of 2% by volume or less (switching operation 2). During this period, the supply of the raw material aqueous solution was continued to grow the particles.

After 140 minutes (12.3% of the entire grain growth process) after performing the switching operation 2,
Again, using an air diffuser in the reaction tank, air was circulated in the reaction tank at a flow rate of 2 L / m, and the reaction atmosphere was an oxidizing atmosphere with an oxygen concentration of 20% by volume (switching operation 3).

After 17 minutes (1.5% with respect to the entire particle growth process) after performing the switching operation 3, nitrogen was circulated in the reaction vessel at a flow rate of 10 L/m using an air diffuser in the same manner. , the reaction atmosphere was a non-oxidizing atmosphere with an oxygen concentration of 2% by volume or less (switching operation 4).

After 950 minutes (83.6% of the total grain growth process) from switching operation 4, the grain growth process was terminated by stopping the supply of all the aqueous solutions. Thereafter, the obtained product was washed with water, filtered and dried to obtain powdery composite hydroxide particles.

In the particle growth process, 25% by mass sodium hydroxide aqueous solution and 25% by mass ammonia water were supplied at appropriate times throughout the process, and the pH value and ammonium ion concentration of the aqueous solution for particle growth were maintained within the ranges described above. .

(a-2) Production of Particles with Small Particles [Nucleation Step]
First, 14 L of water was put into the reactor, and the temperature inside the reactor was set to 40° C. while stirring. At this time, nitrogen gas was passed through the reaction tank for 30 minutes to make the reaction atmosphere a non-oxidizing atmosphere with an oxygen concentration of 2% by volume or less. Subsequently, an appropriate amount of 25% by mass sodium hydroxide aqueous solution and 25% by mass aqueous ammonia are supplied into the reaction tank so that the pH value is 12.8 at a liquid temperature of 25° C. and the ammonium ion concentration is 10 g/L. to form a pre-reaction aqueous solution.

At the same time, nickel sulfate, cobalt sulfate, manganese sulfate, and zirconium sulfate were dissolved in water so that the molar ratio of the respective metal elements was Ni:Mn:Co=1:1:1, and 2 mol
/L of raw material aqueous solution was prepared.

Next, this raw material aqueous reaction solution was supplied to the pre-reaction aqueous solution at 100 ml/min to form an aqueous solution for the nucleation step, and nucleation was performed for 1 minute. At this time, a 25% by mass aqueous sodium hydroxide solution and a 25% by mass aqueous ammonia solution were supplied at appropriate times to maintain the pH value and the ammonium ion concentration of the aqueous solution for nucleation within the ranges described above.

[Particle growth step]
After the completion of nucleation, the supply of all the aqueous solutions is temporarily stopped, and sulfuric acid is added to
An aqueous solution for particle growth was formed by adjusting the pH value to 11.6 based on a liquid temperature of 25°C. After confirming that the pH value reached a predetermined value, the raw material aqueous solution and the sodium tungstate aqueous solution were supplied to grow the nuclei (particles) generated in the nucleation step. After 100 minutes from the start of grain growth, the grain growth process was completed by stopping the supply of all the aqueous solutions. Thereafter, the resulting product was washed with water, filtered and dried to obtain powdery composite hydroxide particles.

(B) Evaluation of composite hydroxide particles ICP emission spectrometer (Shimadzu Corporation Shimadzu Corporation, ICPE-9000IC
PE-9000), the composite hydroxide particles have the general formula: Ni _0.331 Mn _0.331 Co _0.331 for both large and small particles.
It was confirmed to be represented by W _0.005 (OH) ₂ .

A part of the large-diameter particles is embedded in resin, and after cross-sectional observation is possible by cross-section polishing, 10 or more large-diameter particles are observed with a field emission scanning electron microscope (FE).
-SEM: JSM-6360LA manufactured by JEOL Ltd.).

As a result, large-sized particles have a central portion formed by agglomeration of plate-shaped primary particles, and a low-density particle formed by agglomeration of plate-shaped primary particles and fine primary particles outside the central portion. It has two laminated structures in which a layer and a high-density layer formed by aggregating plate-shaped primary particles are laminated, and the high-density layer is formed by aggregating plate-shaped primary particles in the low-density layer. It was confirmed that the high density part connected with the central part and other high density layers.

Using a laser light diffraction/scattering particle size analyzer (manufactured by Nikkiso Co., Ltd., Microtrac HRA), the average particle size of large particles is measured, and d10 and d90 are measured to indicate the spread of the particle size distribution. [(d90-d10)/average particle size] was calculated. As a result,
It was confirmed that the average particle diameter was 8.1 μm and [(d90−d10)/average particle diameter] was 0.52.

Furthermore, for large grain size particles, the center grain size ratio, the first low density layer grain size ratio, the first high density layer grain size ratio, the second low density layer grain size ratio, and the second The high-density layer (outer shell) grain size ratio was also measured and calculated, and the results were 33%, 7.2%, 8.0%, 5.2%, respectively.
and 14.2%. In addition, the image obtained by SEM observation was binarized, the ratio of the total area occupied by the low-density portion to the cross-sectional area of one particle was obtained, and the average value was calculated. As a result, the area ratio of the low density portion was 35%.

Measurement and calculation of the average particle diameter of the primary particles that constitute the particles with large particle diameters revealed that the average particle diameter of the fine primary particles was 0.08 μm, and that of the plate-like primary particles was 0.3 μm. Met.

On the other hand, when the particles with small particle diameters were similarly measured, it was confirmed that the particles with small particle diameters as a whole had a solid structure formed by agglomeration of plate-like primary particles. The average particle diameter was measured in the same manner as for the large particle diameter particles, and d10 and d90 were measured to calculate [(d90-d10)/average particle diameter], which is an index showing the spread of the particle size distribution. As a result, it was confirmed that the average particle diameter was 3.1 μm and [(d90−d10)/average particle diameter] was 0.51. As a result, it was confirmed that the radius of the small particle size particles is the same as the thickness of the outer shell portion, which is the outermost high-density layer of the large particle size particles. The average particle size of the primary particles, which constitute the small particle size particles, was measured and calculated. 0.28 μm.

(c) Fabrication of positive electrode active material
Volume %) After heat treatment at 120 for 12 hours in an air stream, the mass ratio of large particle size particles: small particle size particles is set to 9: 1, and Li / Me is 1.21. As such, a shaker mixer device (TURBULA Type T2 manufactured by Willie & Bakkofen (WAB)
C) was used to sufficiently mix the large particle size particles, the small particle size particles, and the lithium carbonate to obtain a lithium mixture.

This lithium mixture was placed in a stream of air (oxygen concentration: 21% by volume) at a heating rate of 2.52.
The temperature was raised to 850° C. at a rate of 5° C./min, and the temperature was maintained for 44 hours for firing, followed by cooling to room temperature at a cooling rate of about 4° C./min. Aggregation or mild sintering occurred in the positive electrode active material thus obtained. Therefore, the positive electrode active material was pulverized to adjust the average particle size and particle size distribution.

(d) Evaluation of positive electrode active material By analysis using an ICP emission spectrometer, this positive electrode active material has the general formula: Li _1.21 N
It was confirmed to be represented by i _0.331 Mn _0.331 Co _0.331 W _0.005 O ₂ .

As shown in FIG. 1, it was confirmed that the lithium composite oxide particles constituting the positive electrode active material of the present invention consisted of large particle size particles and small particle size particles. Also, a part of the lithium composite oxide particles was embedded in a resin, and the cross-section was made observable by cross-section polishing, and then observed by SEM (see FIG. 4). As a result, the large-diameter particles are composed of secondary particles formed by agglomeration of a plurality of primary particles, and the secondary particles consist of the outer shell portion,
agglomerates of primary particles that exist dispersedly inside the outer shell and are electrically conductive with the outer shell; and
It was confirmed that there is a space portion in which primary particles do not exist, which exists inside the aggregation portion and is composed of a plurality of pore structures. On the other hand, it was confirmed that the small-diameter particles consist of solid secondary particles formed by aggregation of a plurality of primary particles.

In the SEM observation, the cross section of any 10 or more large particles is observed and binarized, and the ratio of the total area of the space portion to the cross section area of one particle is obtained, It was obtained by calculating the average value of these. As a result, the area ratio of the space was 12%.

In addition, using a laser light diffraction scattering particle size analyzer, the average particle size of the lithium composite oxide particles is measured, and d10 and d90 are measured, which are indices showing the spread of the particle size distribution [
(d90-d10)/average particle diameter] was calculated. Furthermore, the specific surface area was measured by a flow-type gas adsorption method specific surface area measuring device (manufactured by Yuasa Ionics, Multisorb), and a tapping machine (
The tap density was determined by KRS-406 manufactured by Kuramoto Kagaku Kikai Co., Ltd.). These results are shown in Table 1.

(e) Production of secondary battery Positive electrode active material obtained as described above: 52.5 mg, acetylene black: 15 m
g and PTEE: 7.5 mg were mixed, and at a pressure of 100 MPa, a diameter of 11 mm and a thickness of 10
After press-molding to 0 μm, it was dried at 120° C. for 12 hours in a vacuum dryer to prepare a positive electrode (1).

Next, using this positive electrode (1), a 2032-type coin battery (B) was produced in an Ar atmosphere glove box with a controlled dew point of -80°C. The negative electrode of this 2032 type coin battery (
2) uses lithium metal with a diameter of 17 mm and a thickness of 1 mm, and the electrolyte is 1 M LiC
Ethylene carbonate (EC) and diethyl carbonate (DE) with _lO4 as the supporting electrolyte
An equivalent mixture of C) (manufactured by Tomiyama Pharmaceutical Co., Ltd.) was used. Moreover, in the separator (3),
A polyethylene porous membrane with a thickness of 25 μm was used. The 2032-type coin battery (B) has a gasket (4) and is assembled into a coin-shaped battery with a positive electrode can (5) and a negative electrode can (6).

(f) Battery evaluation [initial discharge capacity]
A 2032-type coin battery was left for about 24 hours after it was made, and the open circuit voltage OCV (Ope
n Circuit Voltage) was stabilized, the current density for the positive electrode was changed to 0.1 m
As A/cm ² , charge to a cutoff voltage of 4.3 V, rest for 1 hour, discharge to a cutoff voltage of 3.0 V, and measure the discharge capacity. An initial discharge capacity was determined. At this time, a multi-channel voltage/current generator (R6741A, manufactured by Advantest Co., Ltd.) was used to measure the charge/discharge capacity.

[Positive resistance]
Using a 2032-type coin battery charged at a charging potential of 4.1 V, the resistance value was measured by the AC impedance method. A frequency response analyzer and a potentiogalvanostat (manufactured by Solartron) were used for the measurement, and the Nyquist plot shown in FIG. 4 was obtained. The plot is
Since it appears as the sum of characteristic curves representing solution resistance, negative electrode resistance and capacity, and positive electrode resistance and capacity, fitting calculation was performed using an equivalent circuit to calculate the value of positive electrode resistance.

[Cycle characteristics]
The charge/discharge test described above was repeated, and the 500th cycle capacity retention rate was calculated by measuring the 500th discharge capacity relative to the initial discharge capacity. These results are shown in Table 1.

(Example 2)
The composite hydroxide particles, the positive electrode active material, and the non-aqueous Electrolyte secondary batteries were produced and evaluated.

(Example 3)
The composite hydroxide particles, the positive electrode active material, and Non-aqueous electrolyte secondary batteries were produced and evaluated.

(Comparative example 1)
Composite hydroxide particles, a positive electrode active material, and a non-aqueous electrolyte secondary battery were prepared in the same manner as in Example 1, except that only the large particle size particles obtained in Example 1 were used as the precursor. were produced and these evaluations were performed.

(Comparative example 2)
Composite hydroxide particles, a positive electrode active material, and a non-aqueous electrolyte secondary battery were prepared in the same manner as in Example 1, except that only the small-diameter particles obtained in Example 1 were used as the precursor. were produced and these evaluations were performed.

1 positive electrode (evaluation electrode)
2 negative electrode 3 separator 4 gasket 5 positive electrode can 6 negative electrode can B 2032 type coin battery

By the way, it is known that the positive electrode active material inherits the properties of the transition metal-containing composite hydroxide particles that serve as its precursor. That is, in order to obtain a positive electrode active material having the battery characteristics described above, it is necessary to appropriately control the average particle size and particle size distribution of the transition metal-containing composite hydroxide particles, which are precursors thereof. .

The transition metal-containing composite hydroxide particles obtained by this method have a small particle size, a narrow particle size distribution, and a central portion formed by aggregation of plate-like or needle-like primary particles. At least one laminated structure in which a low-density layer formed by agglomeration of fine primary particles and a high-density layer formed by agglomeration of plate-like primary particles are alternately laminated on the outside of the and By using such transition metal-containing composite hydroxide particles as a precursor, a space where the primary particles do not exist outside the central part where the primary particles are aggregated, and the primary particles are aggregated, and the central part and the electrical or a structure further comprising an inner shell in which the primary particles are aggregated between the core and the outer shell and electrically conductive to the core and the outer shell can be obtained.

[ ( d90-d10)/average particle diameter] is in the range of 0.30 to 0.65. In addition, the large particle size particles constituting the secondary particles have an average particle size in the range of 4 μm to 15 μm, and are an index showing the spread of the particle size distribution [(d90-d10)/ average particle size] is in the range of 0.30 to 0.65. Further, the small-diameter particles have an average particle diameter in the range of 1 μm to 4 μm, and the half value of the average particle diameter is equal to the thickness of the high-density layer constituting the large-diameter particles, and [(d90−d10)/average particle diameter], which is an index showing the spread of the particle size distribution, is in the range of 0.30 to 0.65.

For the small-diameter particles among the composite hydroxide particles of the present invention, the reaction atmosphere is maintained in a non-oxidizing atmosphere with an oxygen concentration of 5% by volume or less throughout the nucleation step and the particle growth step. Control. Such a reaction makes it possible to form high-density, solid secondary particles formed by agglomeration of plate-shaped primary particles.

Next, while stirring the pre-reaction aqueous solution, the raw material aqueous solution is supplied. As a result, an aqueous solution for nucleation, which is a reaction aqueous solution in the nucleation step, is formed in the reaction tank. Since the pH value of the aqueous solution for nucleation is within the range described above, nucleation takes place preferentially with little growth of nuclei in the nucleation step. In the nucleation step, the pH value and the concentration of ammonium ions in the aqueous solution for nucleation change with nucleation. It is necessary to control the pH in the range of 12.0 to 14.0 and the ammonium ion concentration in the range of 3 g/L to 25 g/L on a °C basis.

[Particle size control of composite hydroxide particles]
The particle diameter of the composite hydroxide particles obtained as described above is controlled by the time of the particle growth process and the nucleation process, the pH value of the nuclear generation aqueous solution and the particle growth aqueous solution, and the supply amount of the raw material aqueous solution. can be done. For example, by increasing the pH value in the nucleation step or by lengthening the time of the nucleation step, the amount of metal compound contained in the supplied raw material aqueous solution is increased to increase the amount of nuclei generated. Thus, the particle size of the obtained composite hydroxide particles can be reduced. Conversely, by suppressing the amount of nuclei generated in the nucleation step, the particle size of the resulting composite hydroxide particles can be increased.

Atmosphere control is performed twice or more to obtain large-diameter particles having a plurality of laminated structures consisting of a central portion, a low-density layer, and a high-density layer. is preferably in the range of 2% to 20%, more preferably in the range of 3% to 10%, relative to the total grain growth process time . In addition , the crystallization reaction in each oxidizing atmosphere (including the switching time from the non-oxidizing atmosphere to the oxidizing atmosphere) is preferably in the range of 1% to 20% of the total grain growth process time. More preferably, it should be in the range of 2% to 10%. However, it is necessary that the ratio of the total crystallization reaction in the oxidizing atmosphere does not deviate from the range of 2% to 40%. The ratio of the entire crystallization reaction in the oxidizing atmosphere is preferably in the range of 2% to 40%, more preferably in the range of 4% to 20%, with respect to the entire grain growth process time. more preferred. Reaction within this range of reaction time in each oxidizing atmosphere enables the formation of appropriately sized voids that are dispersed inside the secondary particles in the large-diameter particles that make up the positive electrode active material. becomes. After a predetermined period of time has elapsed, introduction of a non-oxidizing gas, that is, an inert gas or a mixed gas of an oxidizing gas and an inert gas is started to switch the oxidizing atmosphere to a non-oxidizing atmosphere.

On the other hand, small-sized particles have a solid structure formed by agglomeration of primary particles. Therefore, the resistance inside the particles can be made sufficiently small as in the case of large-diameter particles. With such a structure, the degree of insertion and extraction of lithium ions during the charging and discharging process becomes uniform throughout the positive electrode active material, and selective deterioration of small-diameter particles is prevented. It can be a substance.

If the average particle diameter of the secondary particles constituting the positive electrode active material is within such a range, not only can the battery capacity per unit volume of the secondary battery using this positive electrode active material be increased, but also safety can be achieved. performance and output characteristics can also be improved. On the other hand, if the average particle size of both the large particle size particles and the small particle size particles is less than 1 μm, the fillability of the positive electrode active material decreases, and the battery capacity per unit volume increases. can't On the other hand, even if the particles have a large particle size, if the average particle size exceeds 15 μm, the reaction area of the positive electrode active material decreases, and the interface with the electrolyte solution decreases, making it difficult to improve the output characteristics. becomes. The upper limit of the average particle size of the small particle size particles is determined by the average particle size of the large particle size particles and the appropriate diffusion path length of lithium ions in the large particle size particles.

Incidentally, the average particle diameter of the secondary particles constituting the positive electrode active material means the volume-based average particle diameter (MV), as in the case of the composite hydroxide particles described above. It can be obtained from the volume integrated value measured by the meter.

(8) Surface area per unit volume The positive electrode active material of the present invention has a surface area per unit volume of 0.50 m ² /cm ³ or more. Preferably, the surface area per unit volume ranges from 1.0 m ² /cm ³ to 5.0 m ² /cm ³ , more preferably 2.0 m 2 /cm 3 . It ranges from 0 m ² /cm ³ to 5.0 m ² /cm ³ . In order to improve the output characteristics and capacity characteristics of secondary batteries, it is necessary to increase the specific surface area and tap density, respectively. Represents having a property. The surface area per unit volume can be obtained by multiplying the above-mentioned specific surface area by the measured value of the tap density.

Claims (15)

A transition metal-containing composite hydroxide particle comprising a plurality of plate-like primary particles and secondary particles formed by aggregation of fine primary particles smaller than the plate-like primary particles,
The transition metal-containing composite hydroxide particles have the general formula (A): Ni _{x Mny} Co _{z Mt} (OH)
_2+a (wherein x+y+z+t=1, 0.3≦x≦0.95, 0.05≦y≦0.55,
0≦z≦0.4, 0≦t≦0.1, and 0≦a≦0.5, and M is Mg, Ca,
one or more additional elements selected from Al, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, W),
The secondary particles are
having a central portion formed by agglomeration of the plate-shaped primary particles, or formed by agglomeration of the plate-shaped primary particles and the fine primary particles, and the fine primary particles aggregating outside the center portion; and at least one laminated structure in which a low-density layer formed by aggregating the plate-like primary particles and a high-density layer formed by aggregating the plate-like primary particles are laminated, and a part of the low-density layer includes the plate-like primary Particles with a large particle size in which there is a high-density part formed by agglomeration of particles;
A high density formed by agglomeration of the plate-shaped primary particles and having a radius of length equivalent to the thickness of the outermost high density layer (outer shell portion) of the high density layers of the large particle size particles. and solid small-sized particles at
is composed by mixing
The secondary particles have an overall average particle size in the range of 1 μm to 15 μm, and an index showing the spread of the overall particle size distribution [(d90−d10)/average particle size] of 0.25. ~
0.65, and the large particle size has an average particle size in the range of 4 μm to 15 μm, and is an index showing the spread of the particle size distribution [(d90−d10)/average particle size Diameter]
is in the range of 0.25 to 0.65, and the average particle diameter of the small-diameter particles is equal to the thickness of the high-density layer constituting the large-diameter particles, and is 1 μm to 4 μm. in range, and
[(d90-d10) / average particle diameter], which is an index showing the spread of the particle size distribution, is 0.25 to
in the range of 0.65,
The large-diameter particles and the small-diameter particles are present in a mass ratio of the small-diameter particles to the large-diameter particles in the range of 0.05 to 20.
Lithium transition metal composite hydroxide particles. 2. The transition metal-containing composite hydroxide particles according to claim 1, wherein said additive element M is uniformly distributed inside said secondary particles and/or uniformly covers the surfaces of said secondary particles. An aqueous solution for nucleation containing a raw material made of a metal compound containing at least a transition metal and an ammonium ion donor is controlled so that the pH value at a liquid temperature of 25° C. is 12.0 to 14.0. A nucleation step in which nucleation is performed while supplying a raw material, and the aqueous solution for particle growth containing nuclei obtained in the nucleation step is adjusted so that the pH value at a liquid temperature of 25 ° C. is the pH value of the nucleation step. is lower than and controlled to be 10.5 to 12.0, and the nuclei are grown while supplying the raw material, a crystallization step comprising a grain growth step,
The crystallization step is
The reaction atmosphere at the beginning of the nucleation step and the grain growth step is a non-oxidizing atmosphere with an oxygen concentration of 5% by volume or less, and then the non-oxidizing atmosphere is changed to an oxidizing atmosphere with an oxygen concentration exceeding 5% by volume. The reaction atmosphere is controlled at least once by switching and switching from the oxidizing atmosphere to the non-oxidizing atmosphere, and the control of the reaction atmosphere is performed by using a ceramic air diffuser to change the atmosphere gas into the aqueous solution for nucleation. and blowing into the aqueous solution for particle growth, and continuously supplying the raw material during switching of the reaction atmosphere to obtain particles having a layered structure and a large particle size;
a step of obtaining particles having a solid structure and a small particle size by setting the reaction atmosphere to a non-oxidizing atmosphere having an oxygen concentration of 5% by volume or less throughout the nucleation step and the particle growth step;
separately
A method for producing transition metal composite hydroxide particles. In the step of obtaining particles having a large particle diameter, the initial stage of the particle growth step is set to a range of 1% to 30% of the entire particle growth step time from the start of the particle growth step, and the non-oxidized 4. The method for producing transition metal composite hydroxide particles according to claim 3, wherein the atmosphere is switched from the oxidizing atmosphere to the oxidizing atmosphere. When the reaction atmosphere is controlled only once in the step of obtaining particles having a large particle diameter, the crystallization reaction time in the oxidizing atmosphere in the particle growth step is reduced to the entire particle growth step time. 5. The method for producing transition metal composite hydroxide particles according to claim 3 or 4, wherein the range is 1% to 30%. When the atmosphere control is performed twice or more in the step of obtaining particles having a large particle diameter, the total crystallization reaction time in the oxidizing atmosphere in the particle growth step is set to 2 with respect to the entire particle growth step time. % to 40%, and the crystallization reaction time in the oxidizing atmosphere per one time is in the range of 1% to 20% of the entire grain growth process time. The method for producing the transition metal composite hydroxide particles according to 1. the additive element M, after the crystallization reaction is completed, the transition metal-containing composite hydroxide particles,
The method for producing transition metal-containing composite hydroxide particles according to any one of claims 3 to 6, further comprising a coating step of coating with a compound containing the additive element M. General formula (B): Li _1+u Ni _{x Mny} Co _z M _t O ₂ (wherein −0.05≦u≦0.
50, x+y+z+t=1, 0.3≦x≦0.95, 0.05≦y≦0.55, 0≦z≦
0.4 and 0≤t≤0.1 and M is Mg, Ca, Al, Ti, V, Cr, Z
one or more additional elements selected from r, Nb, Mo, Hf, Ta, and W),
Composed of lithium-transition metal-containing composite oxide particles having a layered rock salt type and a hexagonal crystal structure,
The lithium-transition metal-containing composite oxide particles consist of secondary particles formed by aggregation of a plurality of primary particles,
The secondary particles are dispersed in the inner side of the outer shell, in which primary particles are electrically connected to each other and are electrically connected to each other, and a space in which the primary particles are not present. and a solid small particle size having a radius of a length equivalent to the thickness of the outer shell portion of the large particle size particle or the aggregate portion of the primary particles. mixed with particles, and
The ratio of the large-diameter particles to the small-diameter particles is the same as the mass ratio in the composite hydroxide particles, and the mass ratio of the small-diameter particles to the large-diameter particles is 0. present in the range of .05 to 20;
Positive electrode active material for non-aqueous electrolyte secondary batteries. The secondary particles have an overall average particle size in the range of 1 μm to 15 μm, and an index showing the spread of the overall particle size distribution [(d90−d10)/average particle size] of 0.25. ~
In the range of 0.70, the large particle size particles constituting the secondary particles have an average particle size of 1
It is in the range of μm to 15 μm and is an index showing the spread of the particle size distribution [(d90
−d10)/average particle size] is in the range of 0.30 to 0.70, and the average particle size of the small particle size is the thickness of the high-density layer constituting the large particle size. equivalent to 1 μm to 4 μm
m and is an index showing the spread of the particle size distribution [(d90-d10) /
average particle diameter] is in the range of 0.30 to 0.70. Claim 8 or 9, wherein the BET specific surface area is in the range of 0.7 m ² /g to 5.0 m ² /g
3. The positive electrode active material for non-aqueous electrolyte secondary batteries according to . General formula (A): _NixMnyCozMt (OH) _2+a (wherein _x +y+ _z + _t =1,
0.3≦x≦0.95, 0.05≦y≦0.55, 0≦z≦0.4, 0≦t≦0.1, and 0≦a≦0.5, and M is , Mg, Ca, Al, Ti, V, Cr, Zr, Nb,
one or more additive elements selected from Mo, Hf, Ta, and W), which are formed by agglomeration of plate-like primary particles, or Having a central portion formed by aggregation of the plate-like primary particles and fine primary particles smaller than the plate-like primary particles,
At least one laminated structure in which a low-density portion formed by agglomeration of the fine primary particles and a high-density portion formed by agglomeration of the plate-like primary particles are laminated on the outside of the central portion, A high-density portion formed by aggregation of the plate-like primary particles exists in a part of the low-density layer, and has an average particle diameter in the range of 4 μm to 15 μm, and exhibits a broad particle size distribution. is an index [(d9
0-d10)/average particle diameter] is in the range of 0.25 to 0.65, and
The transition metal-containing composite hydroxide particles represented by the general formula (A) are formed by aggregation of the plate-like primary particles, and have a length equivalent to the thickness of the high-density portion of the large-diameter particles. has a radius of
A solid having an average particle size in the range of 1 μm to 4 μm and an index indicating the spread of the particle size distribution [(d90−d10)/average particle size] in the range of 0.25 to 0.65. and particles with a small particle size of
are mixed so that the mass ratio of the small-diameter particles to the large-diameter particles (mass of small-diameter particles/mass of large-diameter particles) is in the range of 0.05 to 20. to obtain a precursor mixture;
mixing the precursor mixture and a lithium compound to form a lithium mixture;
a firing step of firing the lithium mixture at 650° C. to 980° C. in an oxidizing atmosphere;
comprising
A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery. General formula (A): _NixMnyCozMt (OH) _2+a (wherein _x +y+ _z + _t =1,
0.3≦x≦0.95, 0.05≦y≦0.55, 0≦z≦0.4, 0≦t≦0.1, and 0≦a≦0.5, and M is , Mg, Ca, Al, Ti, V, Cr, Zr, Nb,
one or more additive elements selected from Mo, Hf, Ta, and W), which are formed by agglomeration of plate-like primary particles, or Having a central portion formed by aggregation of the plate-like primary particles and fine primary particles smaller than the plate-like primary particles,
At least one laminated structure in which a low-density portion formed by agglomeration of the fine primary particles and a high-density portion formed by agglomeration of the plate-like primary particles are laminated on the outside of the central portion, A high-density portion formed by aggregation of the plate-like primary particles exists in a part of the low-density layer, and has an average particle diameter in the range of 4 μm to 15 μm, and exhibits a broad particle size distribution. is an index [(d9
0-d10)/average particle diameter] is in the range of 0.25 to 0.65, and
The transition metal-containing composite hydroxide particles represented by the general formula (A) are formed by aggregation of the plate-like primary particles, and have a length equivalent to the thickness of the high-density portion of the large-diameter particles. has a radius of
A solid having an average particle size in the range of 1 μm to 4 μm and an index indicating the spread of the particle size distribution [(d90−d10)/average particle size] in the range of 0.25 to 0.65. and particles with a small particle size of
a lithium compound;
so that the mass ratio of the small-diameter particles to the large-diameter particles (mass of the small-diameter particles/mass of the large-diameter particles) is in the range of 0.05 to 20, mixing to form a lithium mixture;
a firing step of firing the lithium mixture at 650° C. to 980° C. in an oxidizing atmosphere;
comprising
A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery. In the mixing step, the lithium mixture is adjusted so that the ratio of the sum of the number of metal atoms other than lithium contained in the lithium mixture to the number of lithium atoms is 1:0.95 to 1.5. 13. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 11 or 12. Further comprising a heat treatment step of heat-treating the precursor mixture or each of the large particle size particles and the small particle size particles at a temperature in the range of 105 ° C. to 750 ° C. before the mixing step, A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 11 to 13. A positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte are provided, and the positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 8 to 10 is used as the positive electrode material of the positive electrode. Non-aqueous electrolyte secondary battery.

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