JP7159697B2 - Method for producing positive electrode active material for lithium ion secondary battery, and method for producing lithium ion secondary battery - Google Patents

Description

The present invention relates to a method for producing a positive electrode active material for a lithium ion secondary battery and a method for producing a lithium ion secondary battery.

In recent years, with the spread of mobile electronic devices such as smart phones, tablet terminals, mobile phones, and laptop computers, there is a strong demand for the development of small, lightweight secondary batteries with high energy density and durability. In addition, there is a strong demand for the development of high-output secondary batteries as batteries for vehicles such as power tools and hybrid vehicles.

As a secondary battery that satisfies such requirements, there is a lithium ion secondary battery. A lithium ion secondary battery is composed of a negative electrode, a positive electrode, an electrolyte, and the like, and a material capable of desorbing and intercalating lithium ions is used as an active material for the negative electrode and the positive electrode.

Lithium-ion secondary batteries are currently being actively researched and developed. Among them, lithium-ion secondary batteries using a layered or spinel-type lithium metal composite oxide as a positive electrode material (positive electrode active material). can obtain a voltage as high as 4 V, and is being put to practical use as a battery with a high energy density.

Currently, lithium-cobalt composite oxide (LiCoO ₂ ), which is relatively easy to synthesize, lithium-nickel composite oxide (LiNiO ₂ ), which uses nickel, which is cheaper than cobalt, is used as a positive electrode active material for lithium-ion secondary batteries. Lithium-nickel-cobalt-manganese composite oxide (LiNi1 _{/ 3Co1} / _3Mn1 / _3O2 ), lithium-manganese composite oxide using manganese ₍ LiMn2O4), lithium _- nickel-manganese composite oxide (LiNi0 _{. 5} Mn _0.5 O ₂ ) have been proposed.

Among these positive electrode active materials, lithium-nickel-cobalt-manganese composite oxide (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ), which has excellent thermal stability and high capacity, has recently attracted attention. . Lithium-nickel-cobalt-manganese composite oxides are layered compounds like lithium-cobalt composite oxides and lithium-nickel composite oxides. Contains a ratio of 1.

In general, the positive electrode resistance (reaction resistance) of a lithium ion secondary battery increases sharply on the low SOC side and the high SOC side with respect to the SOC (States of Charge) representing the state of charge, and when the SOC is around 50% becomes smaller, and the amount of change with respect to SOC also becomes smaller. Therefore, by reducing the positive electrode resistance (reaction resistance) at the beginning of charging (low SOC side) and at the end of charging (high SOC side), the SOC region that can actually be used is widened, and the electric capacity that can actually be used is increased. be able to. For example, in lithium-ion secondary batteries for vehicles, output characteristics are particularly important on the low SOC side.

For example, Patent Document 1 discloses a positive electrode active material having a tap density of 2.0 g/cm ³ or more and an average particle size of 0.01 to 5 μm. Further, for example, Patent Literature 2 discloses a positive electrode active material in which a plurality of primary particles are bonded together to form voids inside. As described in these patent documents, a positive electrode active material with a small particle size and a positive electrode active material having internal voids increase the reaction surface area in the positive electrode of a secondary battery, so that the output characteristics are improved. be able to.

Further, for example, as disclosed in Patent Document 3, attempts have been made to increase the filling rate of the positive electrode active material in the positive electrode by broadening the particle size distribution of the positive electrode active material, thereby improving the electrode density of the positive electrode. ing. By improving the electrode density of the positive electrode, the energy density of the secondary battery can be improved.

JP 2011-187419 A JP 2013-012391 A WO2018/020845

However, in the positive electrode active materials of Patent Documents 1 and 2, although the output characteristics are improved, there is a problem that the production efficiency is low and the manufacturing cost is increased. Due to the presence of voids, it is difficult to increase the electrode density in the positive electrode, resulting in a problem of low energy density.

On the other hand, just by broadening the particle size distribution as in the positive electrode active material of Patent Document 3, compared to the case of using a positive electrode active material having a small diameter or internal voids, the output characteristics of the secondary battery was not sufficient and further improvement was required.

As described above, secondary batteries using conventional positive electrode active materials are required to be improved in either output characteristics or energy density. Development of a positive electrode active material compatible with these has been desired. The present invention has been made in view of these circumstances, and it is an object of the present invention to provide a method for producing a positive electrode active material that can obtain a secondary battery that achieves both high output characteristics and high energy density at a high level. .

In a first aspect of the present invention, there is provided a method for producing a positive electrode active material for a lithium ion secondary battery containing powder of a lithium metal composite oxide having a hexagonal layered structure, comprising nickel, cobalt, and A compound powder containing manganese is classified to separate into at least a first particle group and a second particle group, and the first particle group and a lithium compound are mixed to obtain sintering the first lithium mixture at a temperature of 750° C. or more and 1000° C. or less to obtain a first sintered body; and mixing the second particle group and a lithium compound to obtain a second lithium mixture. at a temperature of 750 ° C. or higher and 1000 ° C. or lower to obtain a second fired body, and mixing the first fired body and the second fired body to obtain a lithium metal composite oxide powder the second particle group has a larger average particle size than the first particle group, and the lithium metal composite oxide powder contains lithium (Li), nickel (Ni), cobalt ( Co), manganese (Mn), and optionally an element M, and the material amount ratio (molar ratio) of each element is Li:Ni:Co:Mn:M=(1+u):(1-xy- z): x: y: z [where u is -0.05 ≤ u ≤ 0.50, x is 0.02 ≤ x ≤ 0.50, y is 0.02 ≤ y ≤ 0.50, z is 0 ≤ z ≤ 0.10, 0.30 ≤ (x + y + z) ≤ 0.95, and M is W, Mo, V, Zr, Ti, Cr, Al, Si, B, Nb, and Ta At least one element selected from] is provided.

Moreover, the volume average particle size Mv of the powder of the compound containing nickel, cobalt and manganese is preferably 5 μm or more and 20 μm or less. Further, the powder of the compound containing nickel, cobalt, and manganese preferably has a variation index [(D90-D10)/volume average particle diameter Mv] of 0.80 or more.

and neutralizing and crystallizing a mixed aqueous solution containing at least nickel, cobalt, and manganese to obtain a powder of a compound containing nickel, cobalt, and manganese, which is a metal composite hydroxide. preferable. Further, a mixed aqueous solution containing at least nickel, cobalt, and manganese is neutralized and crystallized, and the obtained crystallized product is heat-treated to form at least one of a metal composite hydroxide and a metal composite oxide. obtaining a powder of said nickel-, cobalt- and manganese-containing compound. Moreover, neutralization crystallization is preferably carried out using a continuous crystallization method. It is also preferable to heat-treat at least one of the first particle group and the second particle group before mixing with the lithium compound.

A second aspect of the present invention provides a method for manufacturing a lithium ion secondary battery, comprising: obtaining a positive electrode active material by the above manufacturing method, the method including a positive electrode containing the positive electrode active material, a negative electrode, and an electrolyte. be done.

When the manufacturing method of the present invention is used for the positive electrode of a lithium ion secondary battery, it is possible to obtain a positive electrode active material that can achieve both excellent output characteristics and high energy density at a high level. In addition, the production method of the present invention can easily produce the positive electrode active material even in industrial-scale production, and can be said to be of extremely high industrial value.

FIG. 1 is a diagram showing an example of a method for producing a positive electrode active material according to this embodiment. FIG. 2 is a diagram showing an example of a method for producing a precursor powder according to this embodiment. FIG. 3 is a diagram showing a coin-type battery for evaluation used in Examples. FIG. 4 is a graph showing the relationship between the mixing ratio of the second fired body and the tap density. FIG. 5 is a graph showing the relationship between the mixing ratio of the second fired body and the discharge capacity per volume. FIG. 6 is a graph showing the relationship between the mixing ratio of the second sintered body and the positive electrode resistance (80% SOC). 7 is a drawing-substituting photograph showing an SEM image of the positive electrode active material of Example 2. FIG. 8 is a drawing-substituting photograph showing an SEM image of the positive electrode active material of Comparative Example 1. FIG. 9 is a drawing-substituting photograph showing an SEM image of the positive electrode active material of Reference Example 1. FIG. 10 is a drawing-substituting photograph showing an SEM image of the positive electrode active material of Reference Example 2. FIG.

(1) Manufacturing Method of Positive Electrode Active Material for Lithium Ion Secondary Batteries FIG. 1 shows a manufacturing method of a positive electrode active material for lithium ion secondary batteries according to the present embodiment (hereinafter also referred to as "method of manufacturing a positive electrode active material"). ) is a diagram showing an example. Moreover, FIG. 2 is a diagram showing an example of a method for producing powder of a compound containing nickel, cobalt, and manganese according to this embodiment. Hereinafter, a method for producing a positive electrode active material will be described with reference to FIGS. 1 and 2. FIG. In addition, the following description is an example of the manufacturing method of a positive electrode active material, Comprising: The manufacturing method is not limited to the following description.

As shown in FIG. 1, a method for producing a positive electrode active material includes classifying powder of a compound containing nickel, cobalt, and manganese to separate into a first particle group and a second particle group. (Step S10), mixing each of the first particle group and the second particle group with a lithium compound to obtain a first mixture and a second mixture (Step S20a, b); sintering the first mixture and the second mixture to obtain a first sintered body and a second sintered body (step S30a, b); and mixing with the sintered body to obtain a lithium metal composite oxide powder (step S40).

[Classification: Step S10]
First, powder of a compound containing nickel, cobalt, and manganese (hereinafter also referred to as "precursor powder") is classified to separate into at least a first particle group and a second particle group. (step S10). Also, the second particle group has a larger average particle size than the first particle group.

In the manufacturing method according to the present embodiment, the precursor powder is classified (step S10) before firing, and then fired (steps S30a and S30b), thereby sintering the particles during firing. It is possible to obtain a positive electrode active material that is suppressed and has a high tap density. A secondary battery using this positive electrode active material has a high energy density, a reduced positive electrode resistance, and high output characteristics.

The term "classification" as used herein refers to the separation of particles according to their particle sizes by utilizing the difference in the dynamic behavior of particles flowing with a fluid. In step S10, the powder of the precursor of the positive electrode active material is classified into two or more particle groups having different particle size distributions. In the classification (step S10), the precursor powder may be divided into, for example, three groups, or four or more groups. For example, when the precursor powder is divided into three groups, in addition to the first particle group and the second particle group, a third particle group having an average particle size larger than that of the second particle group is separated. good too.

(Particle size distribution of precursor powder)
[(D90−D10)/volume average particle size Mv] (hereinafter sometimes abbreviated as “variation index”), which indicates the index of variation in particle size, of the precursor powder is 0.80 or more. It is preferably 0.90 or more. When the variability index of the precursor powder is within the above range, it indicates that the particle size distribution of the precursor powder is broad. Since the particle size distribution of the powder of the thium metal composite oxide depends on the particle size distribution of the precursor powder, the particle size distribution of the resulting lithium metal composite oxide powder (positive electrode active material) is also broad. Therefore, the energy density can be increased in the positive electrode of the secondary battery using such a positive electrode active material. The upper limit of the variability index of the precursor powder is not particularly limited, but is, for example, 1.20 or less.

Here, D90, D10 and volume average particle diameter Mv are particle diameters where the volume integrated value of the particle amount in the particle size distribution curve in the particle size distribution by the laser diffraction scattering method is 90% of the total from the small particle size side. (D90), 10% of the total particle size (D10), and 50% of the total particle size (volume average particle size Mv).

A precursor powder having such a broad particle size distribution can be produced by a known method. As shown in FIG. It is preferable to manufacture by crystallization (step S1) or heat treatment (step S2). Each step will be described below.

[Neutralization crystallization: Step S1]
The production method according to the present embodiment includes neutralizing and crystallizing a mixed aqueous solution containing at least nickel, cobalt, and manganese to obtain a precursor powder composed of a metal composite hydroxide (step S1). may

Specifically, for example, an aqueous solution of a neutralizing agent is added to a mixed aqueous solution containing at least nickel, cobalt, and manganese in a reaction vessel while stirring to coprecipitate composite hydroxide particles through a neutralization reaction. . A composite hydroxide (metal composite hydroxide) containing at least nickel, cobalt, and manganese can be obtained by neutralization crystallization (step S1).

As the mixed aqueous solution containing at least nickel, cobalt and manganese, for example, nickel, cobalt and manganese sulfate solution, nitrate solution, chloride solution and the like can be used. Moreover, the mixed aqueous solution may contain the element M. The composition of the metal elements contained in the mixed aqueous solution substantially matches the composition of the metal elements contained in the metal composite hydroxide particles obtained. Therefore, the composition of the metal elements in the mixed aqueous solution can be prepared so as to be the same as the composition of the metal elements in the target metal composite hydroxide particles.

The neutralizing agent aqueous solution is not particularly limited, and for example, an alkaline aqueous solution can be used, and an aqueous alkali hydroxide solution is preferably used. More specifically, sodium hydroxide, potassium hydroxide, or the like can be used as the alkali hydroxide.

In addition, a complexing agent may be added to the raw material aqueous solution together with the neutralizing agent aqueous solution. The complexing agent is an aqueous solution in the reaction vessel (a mixed aqueous solution containing at least nickel, cobalt, and manganese, an aqueous solution of a neutralizing agent, and an aqueous solution obtained by mixing a complexing agent when a complexing agent is used) (hereinafter referred to as It is not particularly limited as long as it can bond with metal ions to form a complex in the "reaction aqueous solution"), and known ones can be used. As a complexing agent, for example, an ammonium ion donor can be used. The ammonium ion donor is not particularly limited, but for example, ammonia, ammonium sulfate, ammonium chloride, ammonium carbonate, ammonium fluoride and the like can be used. By adding a complexing agent, the solubility of metal ions in the aqueous reaction solution can be adjusted.

In addition, the conditions for the neutralization crystallization (step S1) are such that metal composite oxide particles are coprecipitated so that the finally obtained lithium metal composite oxide powder (positive electrode active material) has a variation index of 0.80 or more. It is preferable to carry out the reaction under conditions that allow the reaction to occur, and a known method can be used as appropriate. In addition, the neutralization crystallization (step S1) may be performed by, for example, a batch crystallization method or a continuous crystallization method.

The batch-type crystallization method is a method in which the neutralization reaction proceeds in the reaction aqueous solution in the reaction tank, and the particles of the metal composite hydroxide are recovered after reaching a steady state. In the continuous crystallization method, a mixed aqueous solution containing at least nickel, cobalt, and manganese and, if necessary, In this method, an appropriate amount of a complexing agent is added to the reaction aqueous solution, and an aqueous solution containing metal composite hydroxide particles produced by a neutralization reaction in the obtained reaction aqueous solution is recovered from the overflow.

In the production method according to the present embodiment, the neutralization crystallization (step S1) is preferably performed using a continuous crystallization method from the viewpoint of obtaining a precursor powder having a broader particle size distribution. In addition, the continuous crystallization method is suitable for mass production and can reduce manufacturing costs.

In addition, since the particle size distribution of the metal composite oxide obtained by neutralization crystallization (step S1) is reflected in the particle size distribution of the finally obtained lithium metal composite oxide powder, It is preferable to coprecipitate particles of the composite oxide. Therefore, the metal composite hydroxide powder obtained after neutralization crystallization (step S1) has, for example, a variation index [(D90-D10)/volume average particle diameter Mv] of 0.80 or more. is preferred.

In the neutralization crystallization (step S1), the temperature of the reaction aqueous solution, the pH of the reaction aqueous solution, the conditions for stirring the reaction aqueous solution, and other conditions for crystallization are such that the particle size distribution of the resulting metal composite hydroxide particles is The conditions may be appropriately adjusted so as to obtain broad conditions, and for example, known methods and conditions may be used.

In the neutralization crystallization (step S1), the metal composite hydroxide particles recovered after the neutralization reaction may be washed and washed with water to remove impurity components contained in the reaction aqueous solution, filtered and dried. good. For washing, a known method using an alkaline aqueous solution, pure water, or the like may be used. Also, known methods may be used for washing with water, filtration and drying.

[Heat Treatment: Step S2]
In addition, as shown in FIG. 2, in the production method according to the present embodiment, the crystallized product obtained by the neutralization crystallization (step S1) is heat-treated to produce a metal composite hydroxide and a metal composite oxide. obtaining (step S2) a precursor powder consisting of at least one of As will be described later, the heat treatment (step S2) may be performed on the first particle group and/or the second particle group after classification (step S10).

Step S2 is a step of heat-treating the precursor powder to remove at least part of the moisture contained in the precursor powder before mixing with a lithium compound (steps S20a and S20b), which will be described later. By removing at least part of the moisture remaining in the precursor powder, the Li/Me of the lithium metal composite oxide powder (positive electrode active material) obtained in the later-described firing (steps S30a and S30b) is fluctuation can be prevented.

The heat treatment (step S2) sufficiently oxidizes the precursor powder from the viewpoint of further reducing the Li/Me variation, and converts all the hydroxides in the precursor powder to oxides. A metal composite oxide may be obtained. Note that it is not necessary to convert all the metal composite hydroxides into metal oxides, as long as the moisture can be removed to the extent that the Li/Me ratio of the positive electrode active material does not vary.

The heat treatment (step S2) may be performed by heating to a temperature at which at least part of the residual moisture in the precursor powder is removed. Moreover, the atmosphere in which the heat treatment is performed is not particularly limited. For example, from the viewpoint of easy operation, it is preferable to perform the heat treatment in an air current.

(Classification)
Next, the precursor powder is classified into at least a first particle group (small particle size) and a second particle group (large particle size). The classification method used in the present embodiment is not particularly limited, and a known method can be used. For example, dry classification or wet classification may be used. When the fluid is gas, dry classification is performed, and when the fluid is liquid, wet classification is performed. Each classification method will be described in more detail below.

(Dry classification)
In the dry classification, a gas pressurized by a compressor or the like is used as a fluid medium, and the precursor powder (particles) is introduced into the classifier together with this gas. Particles are separated by diameter.

Known classifiers may be used for dry classification. For example, Elbow Jet (manufactured by Nittetsu Mining Co., Ltd.) can be used as the former classifier, and Aerofine Classifier can be used as the latter classifier. (manufactured by Nisshin Engineering Co., Ltd.), Turbo Classifier (manufactured by Nisshin Engineering Co., Ltd.), Microspin (manufactured by Nippon Pneumatic Industry Co., Ltd.), Micron Separator (manufactured by Hosokawa Micron Corporation), Turboflex (manufactured by Hosokawa Micron Corporation), etc. can be used. The fluid medium is not particularly limited, and air, nitrogen or the like can be used, but it is preferable to use air.

(Wet classification)
In wet classification, precursor powder (particles) is dispersed in a medium to form slurry (suspension), and this slurry is introduced into a classifier to separate particles. For example, when a metal composite hydroxide obtained by neutralization crystallization is used as the precursor powder, the slurry after crystallization is subjected to classification as it is after washing as necessary. may

A known classifier may be used for the wet classification, and hydrocyclone (Nihon Kagaku Kikai Seizo Co., Ltd.), Nanocut/Microcut (manufactured by Krettek), and the like can be used. The medium is not particularly limited, and for example, it is preferable to use water. After the wet classification, it is washed with pure water or the like, if necessary, filtered and dried. The methods of washing, filtering, and drying are not particularly limited, and known methods and conditions can be used.

(classification point)
In the classification process, the classification point (cut point) is not particularly limited. It may be appropriately set in consideration of the diameter (particle size distribution).

Specifically, when the particle group is separated into two groups, the first particle group (small particle size) and the second particle group (large particle size), the first particle group: the second The particle groups are classified at a mass ratio of, for example, 5:95 to 95:5, preferably 10:90 to 90:10, more preferably 15:85 to 85:15. can be set. The precursor powder may be separated into three or more groups, and when the particle groups are separated into three or more groups, a plurality of classification points may be set.

When the precursor powder is classified, each particle group obtained after classification has a narrower and sharper particle size distribution than the precursor powder before classification. The index of variation of the first particle group and the second particle group is not particularly limited as long as it is smaller than the index of variation of the precursor powder before classification. For example, it is less than 0.8. may

In addition, the volume average particle diameter Mv of the first particle group (small particle diameter) is not particularly limited as long as it is smaller than the volume average particle diameter Mv of the second particle group (large particle diameter). It may be smaller than the volume average particle diameter Mv of the precursor powder. Further, the volume average particle size Mv of the second particle group (large particle size) may be, for example, larger than the volume average particle size Mv of the precursor powder before classification. The index of variation of the first particle group and the second particle group, and the particle size distribution of each particle group obtained after classification, can be appropriately adjusted according to the desired battery characteristics and the like.

By the way, in the sintering (steps S30a and S30b) described later, the temperature at which sintering starts is generally lower for particles with smaller particle diameters, and it is easier to form a coarse sintered body in which a plurality of particles are bonded at a lower temperature. Become. Therefore, the firing temperature is preferably high in terms of the diffusion of the mixed lithium and the stabilization of the crystal structure. It is required to adjust the firing temperature according to the balance of

Therefore, in the case of a precursor powder before classification or a powder obtained by mixing a plurality of classified particle groups before firing (Steps S30a and S30b), compared with each particle group obtained by classification, Since the particle size distribution is broad, the firing is sometimes performed at a temperature X at which the particles in the first particle group (small particle size) are sintered. In this case, particles with a small particle size may involve particles with a large particle size and be sintered to form an extremely coarse sintered body (FIGS. 8(A) and 8(B), comparative example 1).

On the other hand, when the classified particles of the first particle group (small particle size) and the particles of the second particle group (large particle size) are fired at the same temperature X as above, the second particle group (large particle size 10(A), 10(B), and reference example 2). The first particle group (small particle size) is sintered at this temperature X, but most of the first particle group (small particle size) contains large particle sizes. Therefore, the grain size of the sintered body is naturally restricted, and extremely coarse grains do not occur (see FIGS. 9A and 9B, Reference Example 1).

Therefore, after classifying the precursor powder (step S10), the first particle group and the second particle group are individually fired (step S30a, b), and after firing, the mass ratio at the time of classification is , the first sintered body and the second sintered body are mixed (step S40) and the sample is A, and the sample that is fired without classifying the precursor powder is B, both (samples A and B ), even if all the firing conditions including the firing temperature are the same, sample A has a lower content of coarse sintered bodies than sample B, and the grains become coarser due to sintering. It is possible to suppress the decrease in density and the decrease in electrochemical properties (see FIGS. 7A and 7B, Example 1, and FIGS. 8A and 8B, Comparative Example 1). ).

[Mixing with Lithium Compound: Step S20a, b]
Next, each of the first particle group and the second particle group is mixed with a lithium compound to obtain a first mixture and a second mixture (step S20a, b). Further, in the mixing with the lithium compound (Steps S20a, S20b), a compound containing the element M may be mixed.

The lithium compound is not particularly limited, and a known compound containing lithium can be used, such as lithium carbonate, lithium hydroxide, lithium nitrate, or a mixture thereof. Among these, lithium carbonate, lithium hydroxide, or a mixture thereof is preferable from the viewpoint of being less affected by residual impurities and melting at the firing temperature.

The method of mixing the first particle group or the second particle group, the lithium compound, and optionally the element M is not particularly limited. The particle group or the second particle group, the lithium compound, and optionally the element M should be sufficiently mixed. The conditions for mixing the first particle group and the lithium compound and the conditions for mixing the second particle group and the lithium compound may be the same or different conditions.

As a mixing method, for example, a common mixer can be used for mixing, for example, a shaker mixer, Loedige mixer, Julia mixer, V blender, or the like can be used. It is preferable that the first lithium mixture and the second lithium mixture are sufficiently mixed before firing (steps S30a, g). If the mixture is not sufficiently mixed, the composition of Li and elements other than Li varies among the individual particles of the obtained lithium metal composite oxide powder (positive electrode active material), which causes problems such as insufficient battery characteristics. can occur.

The lithium compound is the molar ratio of lithium (Li) to the total molar amount (Me) of Ni, Co, Mn and element M in the first and second lithium mixtures (hereinafter sometimes referred to as “Li/Me” ) is mixed so as to be 0.95 or more and 1.50 or less. That is, Li/Me in the first lithium mixture and the second lithium mixture are mixed so as to be the same as Li/Me in the obtained lithium metal composite oxide powder (positive electrode active material). Note that the value of Li/Me corresponds to the value of (1+u) in the composition formula described later. This is because the molar ratio of Li/Me and each metal element other than Li does not change before and after firing (steps S30a, b), so the first and This is because Li/Me of the second lithium mixture becomes Li/Me of the positive electrode active material.

Before mixing the first particle group or the second particle group with the lithium compound (step S20a, b), the first particle group or the second particle group is heat-treated. good too. The conditions for the heat treatment can be the same conditions as in step S2 described above.

[Firing: Step S30a, b]
Next, each of the first lithium mixture and the second lithium mixture is fired at a temperature of 750° C. or more and 1000° C. or less in an oxidizing atmosphere to obtain a first fired body and a second fired body. (step S30a, b). When the lithium mixture is fired, the lithium in the lithium compound diffuses into the particles in the particle group (precursor), forming a fired body composed of particles of the lithium metal composite oxide having a polycrystalline structure.

The firing temperature is 750° C. or higher and 1000° C. or lower, preferably 750° C. or higher and 950° C. or lower. If the firing temperature is lower than 750°C, the lithium will not diffuse sufficiently, leaving excess lithium or unreacted particles, or the crystal structure will not be sufficiently arranged, and sufficient battery characteristics will not be obtained. A problem arises. Further, if the firing temperature exceeds 1000° C., intense sintering may occur between particles of the formed lithium metal composite oxide, and abnormal grain growth may occur. If abnormal grain growth occurs, the particles after firing may become coarse and the particle shape may not be maintained, and when the positive electrode active material is formed, the specific surface area decreases and the positive electrode resistance increases. A problem arises that the battery capacity decreases.

The firing atmosphere is preferably an oxidizing atmosphere, and preferably has an oxygen concentration of 20% by volume or more and 100% by volume or less. Moreover, the furnace used for firing is not particularly limited, and a known method can be used. The firing time is not particularly limited, and may be, for example, 1 hour or more and 24 hours or less.

In the first fired body obtained by firing and the second fired body, sintering between particles is relatively suppressed, but coarse particles are formed due to weak sintering and agglomeration. There is In such a case, a step (not shown) of crushing the first fired body and the second fired body may be provided. The sintering and agglomeration can be eliminated by pulverization, and the particle size distribution can be adjusted.

[Mixing of sintered body: step S40]
Next, the first fired body and the second fired body are mixed to obtain a lithium metal composite oxide powder (step S40).

The mixing ratio of the first sintered body and the second sintered body is not particularly limited, and the mixing ratio may be appropriately adjusted according to the desired properties. That is, as shown in FIGS. 4 to 6, the powder characteristics such as tap density, and the electrochemical characteristics such as battery capacity and positive electrode resistance are different between the first sintered body (small particle size) and the second sintered body (large particle size). Since the additivity (linear relationship) is established by the mixing ratio with the particle diameter), the mixing ratio can be appropriately adjusted according to the characteristics required for the positive electrode active material (see FIGS. 4 to 6). see Examples 1 and 2). The mixing ratio of the first fired body and the second fired body is, for example, the first fired body: the second fired body at a mass ratio of 5:95 to 95:5, preferably 10: They may be mixed at a ratio of 90-90:10, more preferably 15:85-85:15. Note that the positive electrode active material obtained by the manufacturing method of the present embodiment has a higher tap than expected from the mixing ratio of the first fired body (small particle size) and the second fired body (large particle size). It can have density, discharge capacity per volume, and low positive electrode resistance (see Examples 1 and 2 in FIGS. 4 to 6).

[Positive electrode active material for lithium ion secondary battery]
Lithium metal composite having a hexagonal layered structure containing lithium (Li), nickel (Ni), cobalt (Co), manganese (Mn), and optionally element M by the production method of the present embodiment described above A positive electrode active material containing oxide powder can be obtained. A secondary battery using this positive electrode active material for the positive electrode can have improved output characteristics and high energy density. The characteristics of the positive electrode active material obtained by the manufacturing method according to this embodiment will be described below.

(composition)
In the lithium metal composite oxide powder, the material amount ratio (molar ratio) of each element is Li:Ni:Co:Mn:M=(1+u):(1-xyz):x:y: z where u is −0.05≦u≦0.50, x is 0.15≦x≦0.50, y is 0.15≦y≦0.50, z is 0≦z≦0. 10, satisfying 0.30≦(x+y+z)≦0.85, and M is at least one selected from W, Mo, V, Zr, Ti, Cr, Al, Si, B, Nb, and Ta species element]. The above composition formula represents the average molar ratio of the entire powder (particles) of the lithium metal composite oxide.

Further, the lithium metal composite oxide powder has a composition formula: Li _1+u Ni _1-xyz Co _x Mn _y M _z O _2+α (wherein M is W, Mo, V, Zr, Ti, at least one element selected from Cr, Al, Si, B, Nb and Ta, and -0.05≤u≤0.50, 0.15≤x≤0.50, 0.15≤y≤ 0.50, 0≦z≦0.10, 0.30≦x+y+z≦0.85, −0.5≦α≦0.5). Note that α in the composition formula may be 0.

In the above molar ratio and composition formula, the range of x indicating the content of Co is 0.15 ≤ x ≤ 0.50, preferably 0.20 ≤ x ≤ 0.50, more preferably 0.20 ≤ x≦0.40. When the value of x is within this range, the secondary battery obtained using the positive electrode active material has a good battery capacity, and the positive electrode resistance (reaction resistance) is reduced, resulting in higher output characteristics. have

In the above molar ratio and composition formula, the range of y indicating the content of Mn is 0.15 ≤ y ≤ 0.50, preferably 0.20 ≤ y ≤ 0.50, more preferably 0.20 ≤ a≤0.40. When the value of y is within this range, the secondary battery obtained using the positive electrode active material not only has good battery capacity and output characteristics, but also has improved thermal stability.

The optionally added element M is at least one element selected from W, Mo, V, Zr, Ti, Cr, Al, Si, B, Nb, and Ta. Also, the element M is preferably an element that can be partially substituted for any one of Ni, Co, and Mn in the crystal.

In the above molar ratio and composition formula, when z indicating the content of the element M exceeds 0, thermal stability and storage characteristics can be improved, preferably 0.0 < z ≤ 0.10. . The element M may be homogeneously dissolved inside the positive electrode active material 10, or may cover the surfaces of the primary particles, cover the surfaces of the secondary particles in the form of a film, or form fine particles on the surfaces of the secondary particles. The distribution may be segregated within the particle, such as being present.

In the above molar ratio and composition formula, the range of (1+u) indicating the content of Li is 0.95 ≤ (1+u) ≤ 1.50, that is, -0.05 ≤ u ≤ 0.50. . When the value of u is within this range, the positive electrode resistance (reaction resistance) is lowered and the output of the battery is improved.

(Volume average particle size)
The powder of the lithium metal composite oxide preferably has a volume average particle diameter Mv of 8 μm or more and 20 μm or less, more preferably 8 μm or more and 15 μm or less. When the volume average particle diameter Mv (hereinafter also referred to as the average particle diameter (Mv)) of the lithium metal composite oxide powder is within the above range, the variation in particle size described later and the composition gradient due to the particle size can be combined. Accordingly, a secondary battery using a positive electrode active material can achieve both high output characteristics and high battery capacity due to high positive electrode filling properties at a higher level.

On the other hand, if the average particle diameter (Mv) of the lithium metal composite oxide powder is less than 8 μm, high filling properties into the positive electrode may not be obtained. Moreover, when the average particle size of the lithium metal composite oxide powder exceeds 20 μm, high output characteristics and high battery capacity may not be obtained. The average particle size (Mv) can be obtained from the volume integrated value measured by a laser beam diffraction/scattering particle size distribution analyzer.

(variation in particle size distribution)
[(D90-D10)/Mv] (hereinafter sometimes abbreviated as "variation index") indicating the particle size variation index of the lithium metal composite oxide powder is 0.80 or more. Here, the variation index is the particle size (D90) at 90% and the particle size (D10) at 10% by volume integration of the particle amount in the particle size distribution curve in the particle size distribution by the laser light diffraction scattering method, and the average It is a value calculated from the particle size (Mv).

When the powder variation index of the lithium metal composite oxide is 0.80 or more, the particle size distribution is relatively broad, so that the filling property of the positive electrode active material in the positive electrode is high, and the secondary battery has a high volumetric energy density. You can get batteries.

In general, when the particle size distribution of the lithium metal composite oxide (positive electrode active material) is broad, fine particles having a smaller particle size than the average particle size (Mv) or particles having an average particle size (Mv) There are many coarse particles with a large particle size. It is well known that a positive electrode active material in which many of these fine particles and coarse particles are mixed has a high packing density, and the energy density per volume can be increased by using such a positive electrode active material. Therefore, when the particle size variation index of the lithium metal composite oxide powder is less than 0.80, the volume energy density may decrease. Although the upper limit of the variation index is not particularly limited, the upper limit is about 1.20 or less when using the manufacturing method of the positive electrode active material described later.

The positive electrode active material according to the present embodiment contains the powder of the lithium metal composite oxide described above, and may be substantially composed of the powder of the lithium metal composite oxide. The powder of the lithium metal composite oxide and the powder of other lithium metal composite oxide may be included within a range that does not impair the effect of (1).

3. Lithium Ion Secondary Battery A method for manufacturing a lithium ion secondary battery according to the present embodiment (hereinafter also referred to as a "method for manufacturing a secondary battery") comprises obtaining a positive electrode active material by the manufacturing method described above, The resulting secondary battery includes a positive electrode containing a positive electrode active material, a negative electrode, and an electrolyte. A lithium ion secondary battery can be composed of the same components as conventionally known lithium ion secondary batteries, and includes, for example, a positive electrode, a negative electrode, and a non-aqueous electrolyte. Also, the secondary battery may be, for example, an all-solid secondary battery comprising a positive electrode, a negative electrode, and a solid electrolyte. Each component other than the positive electrode will be described below.

Note that the embodiments described below are merely examples, and the lithium ion secondary battery according to the present embodiment can be variously modified based on the knowledge of those skilled in the art based on the embodiments described herein. , can be implemented in modified form. Moreover, the lithium-ion secondary battery according to the present embodiment is not particularly limited in its application.

(positive electrode)
A positive electrode for a secondary battery is produced using the positive electrode active material described above. An example of the method for producing the positive electrode will be described below. First, the positive electrode active material (powder), conductive material, and binder are mixed, and if necessary, activated carbon and a solvent for viscosity adjustment are added, and the mixture is kneaded. A positive electrode mixture paste is prepared.

Since the mixing ratio of each material in the positive electrode mixture is a factor that determines the performance of the lithium secondary battery, it can be adjusted according to the application. The mixture ratio of the materials can be the same as that of the positive electrode of a known lithium secondary battery. The content of the conductive material may be 1 part by mass or more and 20 parts by mass or less, and the content of the binder may be 1 part by mass or more and 20 parts by mass or less.

The obtained positive electrode mixture paste is applied, for example, to the surface of a current collector made of aluminum foil, dried to scatter the solvent, and a sheet-like positive electrode is produced. If necessary, pressure may be applied by a roll press or the like in order to increase the electrode density. The sheet-shaped positive electrode thus obtained can be cut into a size suitable for the intended battery, and used for the manufacture of the battery. However, the method for producing the positive electrode is not limited to the above-exemplified method, and other methods may be used.

Examples of conductive materials that can be used include graphite (natural graphite, artificial graphite, expanded graphite, etc.) and carbon black-based materials such as acetylene black and ketjen black.

Binders play a role in binding active material particles, and examples thereof include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluororubber, ethylene propylene diene rubber, styrene butadiene, and cellulose resin. and polyacrylic acid can be used.

If necessary, the positive electrode active material, the conductive material and the activated carbon are dispersed, and a solvent that dissolves the binder is added to the positive electrode mixture. As the solvent, specifically, an organic solvent such as N-methyl-2-pyrrolidone can be used. In addition, activated carbon can be added to the positive electrode mixture in order to increase the electric double layer capacity.

(negative electrode)
Metallic lithium, a lithium alloy, or the like can be used for the negative electrode. In addition, the negative electrode is prepared by mixing a negative electrode active material capable of intercalating and deintercalating lithium ions with a binder, adding an appropriate solvent to make a paste, and applying the negative electrode mixture to the surface of a metal foil current collector such as copper. It may be applied, dried, and compressed to increase the electrode density as necessary.

As the negative electrode active material, for example, natural graphite, artificial graphite, sintered organic compounds such as phenol resin, and powdery carbon substances such as coke 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.

(separator)
A separator is interposed between the positive electrode and the negative electrode. The separator separates the positive electrode from the negative electrode and holds the electrolyte, and a known one can be used. For example, a thin film such as polyethylene or polypropylene having a large number of fine pores can be used. can.

(Non-aqueous electrolyte)
A non-aqueous electrolytic solution can be used as the non-aqueous electrolyte. The non-aqueous electrolytic solution may be, for example, one obtained by dissolving a lithium salt as a supporting salt in an organic solvent. Further, as the non-aqueous electrolytic solution, an ionic liquid in which a lithium salt is dissolved may be used. The ionic liquid refers to a salt composed of cations and anions other than lithium ions and exhibiting a liquid state even at room temperature.

Examples of 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; One selected from ether compounds such as methyltetrahydrofuran and dimethoxyethane, sulfur compounds such as ethylmethylsulfone and butane sultone, and phosphorus compounds such as triethyl phosphate and trioctyl phosphate may be used alone, or two or more may be mixed. can be used as

As the supporting salt, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiN(CF ₃ SO ₂ ) ₂ , composite salts thereof, and the like can be used. Furthermore, the non-aqueous electrolytic solution may contain radical scavengers, surfactants, flame retardants, and the like.

Moreover, when the lithium ion secondary battery is an all-solid secondary battery, a solid electrolyte may be used as the non-aqueous electrolyte. Solid electrolytes have the property of withstanding high voltages. Solid electrolytes include inorganic solid electrolytes and organic solid electrolytes.

As the inorganic solid electrolyte, an oxide-based solid electrolyte, a sulfide-based solid electrolyte, or the like is used.

The oxide-based solid electrolyte is not particularly limited, and can be used as long as it contains oxygen (O) and has lithium ion conductivity and electronic insulation. Examples of oxide-based solid electrolytes include lithium phosphate (Li ₃ PO ₄ ), Li ₃ PO ₄ N _x , LiBO ₂ N _x , LiNbO ₃ , LiTaO ₃ , Li ₂ SiO ₃ , Li ₄ SiO ₄ -Li ₃ PO4, _{Li4SiO4 - Li3VO4} , Li2O _{- B2O3 - P2O5 ,} Li2O _{- SiO2} , Li2O _{- B2O3 -} ZnO, _{Li1 + X AlXTi 2-X} (PO ₄ ) ₃ (0≦X≦1), Li _1+X Al _X Ge _2-X (PO ₄ ) ₃ (0≦X≦1), LiTi ₂ (PO ₄ ) ₃ , Li _3X La _{2/ 3-X} TiO ₃ (0≦X≦2/3), Li ₅ La ₃ Ta ₂ O ₁₂ , Li ₇ La ₃ Zr ₂ O ₁₂ , Li ₆ BaLa ₂ Ta ₂ O ₁₂ , Li _3.6 Si _0.6 P _0.4 O ₄ and the like.

The sulfide-based solid electrolyte is not particularly limited, and any solid electrolyte containing sulfur (S) and having lithium ion conductivity and electronic insulation can be used. Examples of sulfide solid electrolytes include Li ₂ SP ₂ S ₅ , Li ₂ S—SiS ₂ , LiI—Li ₂ S—SiS ₂ , LiI—Li ₂ SP ₂ S ₅ , LiI—Li ₂ S—B ₂ S ₃ , Li ₃ PO ₄ —Li ₂ S—Si ₂ S, Li ₃ PO ₄ —Li ₂ S—SiS ₂ , LiPO ₄ —Li ₂ S—SiS, LiI—Li ₂ S—P ₂ O ₅ , LiI—Li ₃ PO ₄ —P ₂ S ₅ and the like.

Inorganic solid electrolytes other than those described above may be used, such as Li ₃ N, LiI, Li ₃ N--LiI--LiOH, and the like.

The organic solid electrolyte is not particularly limited as long as it is a polymer compound exhibiting ionic conductivity. For example, polyethylene oxide, polypropylene oxide, copolymers thereof, and the like can be used. Moreover, the organic solid electrolyte may contain a supporting salt (lithium salt). When a solid electrolyte is used, the solid electrolyte may also be mixed in the positive electrode material in order to ensure contact between the electrolyte and the positive electrode active material.

(Shape and configuration of secondary battery)
The lithium ion secondary battery according to the present embodiment, which is composed of the positive electrode, the negative electrode, the separator, the non-aqueous electrolyte solution, the positive electrode, the negative electrode, and the solid electrolyte described above, has a cylindrical shape, a laminated shape, and the like. Various shapes are possible.

When a non-aqueous electrolytic solution is used as the non-aqueous electrolyte, the positive electrode and the negative electrode are laminated with a separator interposed to form an electrode body, and the obtained electrode body is impregnated with the non-aqueous electrolytic solution. A lead for current collection is used to connect between the connected positive electrode terminal and between the negative electrode current collector and the negative electrode terminal connected to the outside, and the battery case is sealed to complete the lithium ion secondary battery. .

EXAMPLES Next, the positive electrode active material according to one embodiment of the present invention will be described in detail with reference to examples. However, the present invention is not limited to these examples. Analysis methods and evaluation methods in Examples and Comparative Examples are described below. In this example, unless otherwise specified, samples of special grade reagents manufactured by Wako Pure Chemical Industries, Ltd. were used for manufacturing the metal composite hydroxide particles, the positive electrode active material, and the secondary battery.

[composition]
The composition analysis of the lithium metal composite oxide powder (whole) was performed using an ICP emission spectrometer (ICPS-8100 manufactured by Shimadzu Corporation).

[Dispersion index]
Volume average particle size Mv, D10, D90, etc., which are indicators of particle size distribution, were measured with a laser diffraction particle size distribution analyzer (manufactured by Nikkiso Co., Ltd., trade name: Microtrac). Using each measured value, a variability index represented by [(D90-D10)/Mv] was calculated.

[Particle shape]
The appearance of particles constituting the lithium metal composite oxide powder was observed with a scanning electron microscope (SEM, manufactured by Hitachi High-Technologies Corporation, trade name: S-4700). 7 to 10 show positive electrode active materials obtained in Example 2 (FIG. 7), Comparative Example 1 (FIG. 8), Reference Example 1 (FIG. 9), and Reference Example 2 (FIG. 10), which will be described later. SEM images obtained by

(Evaluation of electrochemical properties)
52.5 mg of the obtained positive electrode active material, 15 mg of acetylene black, and 7.5 mg of polytetrafluoroethylene resin (PTFE) were mixed and press molded at a pressure of 100 MPa to obtain a positive electrode (evaluation electrode) having a diameter of 11 mm and a thickness of 100 μm. A PE was made. After drying the prepared positive electrode PE at 120° C. for 12 hours in a vacuum dryer, a 2032-type coin-type battery CBA was produced using this positive electrode PE in an Ar atmosphere glove box in which the dew point was controlled at −80° C. did. Lithium (Li) metal with a diameter of 17 mm and a thickness of 1 mm is used for the negative electrode NE. Yakuhin Kogyo Co., Ltd.) was used. A polyethylene porous film having a film thickness of 25 μm was used as the separator SE. Moreover, the coin-type battery CBA has a gasket GA and a wave washer WW, and is assembled into a 2032-type coin-type battery CBA with a positive electrode can PC and a negative electrode can NC.

(initial charge/discharge capacity)
After the coin-type battery CBA was left for about 24 hours and the open circuit voltage OCV (Open Circuit Voltage) was stabilized, the current density for the positive electrode PE was set to 0.1 mA/cm ² and the cutoff voltage was 4.3 V. The initial charge capacity was obtained by charging the battery until it became , and the discharge capacity when the battery was discharged to a cutoff voltage of 3.0 V after resting for 1 hour was defined as the initial discharge capacity. A multi-channel voltage/current generator (R6741A, manufactured by Advantest Co., Ltd.) was used to measure the initial charge/discharge capacity.

The initial discharge capacity per volume (mAh/cm ³ ) was calculated by multiplying the discharge capacity per weight (mAh/g) by the tap density (g/cm ³ ).

(positive electrode resistance)
The positive electrode resistance (reaction resistance) was obtained by charging the coin-type battery CBA, which was temperature-controlled to the measurement temperature, at a charging potential of 4.1 V, and measuring the resistance value by the AC impedance method. For measurement, a frequency response analyzer and a potentiogalvanostat (manufactured by Solartron, 1255B) are used to create a Nyquist plot shown in FIG. 4(A), and a fitting calculation is performed using the equivalent circuit shown in FIG. 4(B) Then, the value of the positive electrode resistance (reaction resistance) was calculated.

[Example 1]
(Crystallization step: step S1)
A predetermined amount of pure water was put into a reaction tank (60 L), and the temperature inside the tank was set to 49° C. while stirring. A 2.0 M mixed aqueous solution of nickel sulfate, cobalt sulfate, and manganese sulfate and a 25% by mass hydroxide solution, which is an alkaline solution, were placed in the reaction vessel so that the molar ratio of nickel:cobalt:manganese was 85:5:10. A sodium solution and 25 mass % aqueous ammonia as a complexing agent were simultaneously added continuously to the reactor. At this time, the flow rate was controlled so that the residence time of the mixed aqueous solution was 8 hours, the pH in the reaction tank was adjusted to 12.0 to 12.6, and the ammonia concentration was adjusted to 10 to 14 g/L. After the reactor was stabilized, the slurry containing metal composite hydroxide particles was recovered from the overflow port, and filtered to obtain a metal composite hydroxide cake. Impurities were washed by passing 1 L of pure water through 140 g of the filtered composite hydroxide in Denver.

The filtered powder was dried to obtain metal composite hydroxide particles represented by Ni _0.85 Co _0.05 Mn _0.10 (OH) _2+α (0≦α≦0.4). The volume average particle size Mv of the obtained metal composite hydroxide particles was 12.0 μm, and the particle size variation index was 0.96.

(Classification step: step S10)
Using a dry classifier (Elbow Jet Labo type manufactured by Nittetsu Mining Co., Ltd.), the particles of the obtained metal composite hydroxide are classified so that the mass ratio between the small particle size side and the large particle size side is 30:70. Classification processing was performed by setting a cut point. The obtained first particle group (particle group on the small particle size side: s1) had a volume average particle size Mv of 5.6 μm and a particle size variation index of 0.56. The particle group on the diameter side: s2) had a volume average particle size Mv of 13.4 μm and a particle size variation index of 0.75. The mass ratio of the obtained first particle group (s1) and second particle group (s2) was 28:72. Table 1 shows the particle size, specific surface area, and tap density of the first particle group (s1) and the second particle group (s2).

(Mixing step: step S20a)
The obtained first particle group (s1) was subjected to heat treatment (step S2) in which it was held at 600° C. for 5 hours in an air atmosphere. The first particle group (s1) was converted from metal composite hydroxide to metal composite oxide by heat treatment. For the first particle group (s1) after the heat treatment, lithium hydroxide is added to the atomic ratio of the lithium amount (Li) and the total metal amount (Me) of nickel, cobalt and manganese (hereinafter, represented as Li/Me ) was weighed to 1.02. After that, using a shaker-mixer device (TURBULA Type T2C manufactured by Willie & Bachoffen (WAB)), it was sufficiently mixed with the metal composite hydroxide particles to obtain a first lithium mixture.

(Baking process: step S30a)
The resulting lithium mixture was fired by holding it at 820° C. for 10 hours in an oxygen stream, and then pulverized to obtain a first fired body (lithium metal composite oxide particles).

(Mixing step, baking step: step S20b, step S30b)
Similarly, the second particle group (s2) is heat-treated under the same conditions as the first particle group (s1), mixed with lithium hydroxide, fired, and pulverized to obtain a second fired body (lithium Particles of metal composite oxide) were obtained.

(Mixing step: step S40)
The first fired body and the second fired body are mixed so that the mass ratio of the first fired body (s1): the second fired body (s2) = 28: 72, and the lithium metal composite oxide to obtain a positive electrode active material consisting of a powder of The volume average particle size Mv of the obtained positive electrode active material was 12.2 μm, and the particle size variation index was 0.78. Also, the tap density was 2.61 g/cm ³ .

Table 2 shows the measurement results of the initial charge/discharge capacity and positive electrode resistance (reaction resistance) values (SOC 80% and SOC 20%) of the obtained positive electrode active materials.

(Example 2)
In the mixing step (step S40), a positive electrode active material was produced under the same conditions as in Example 1 except that the mass ratio was mixed so that the first fired body: the second fired body = 50:50. It was submitted for chemical characterization. The volume average particle size Mv of the produced positive electrode active material was 11.2 μm, and the particle size variation index was 0.88. Also, the tap density was 2.53 g/cm ³ . Table 2 shows the measurement results of the electrochemical property evaluation.

(Comparative example 1)
The metal composite hydroxide particles of the first particle group (s1) and the second particle group (s2) obtained in the classification step (step S10) of Example 1 were s1:s2=28:72 in mass ratio. It was mixed so that That is, it is a sample simulating particles of metal composite hydroxide before classification. The particles of this metal composite hydroxide were heat-treated, mixed with lithium hydroxide, and fired under the same conditions as in Example 1, and a positive electrode active material was produced without performing the mixing step of Example 1, and electrochemical properties were obtained. It was used for evaluation.

The volume average particle size Mv of the produced positive electrode active material was 14.5 μm, and the particle size variation index was 0.88. Also, the tap density was 2.20 g/cm ³ . Table 1 shows the measurement results of the electrochemical property evaluation.

(Reference example 1)
Only the first sintered body (s1) obtained in the sintering step (step S30a) of Example 1 was used as a positive electrode active material and subjected to electrochemical property evaluation. The volume average particle size Mv of the produced positive electrode active material was 9.7 μm, and the particle size variation index was 1.01. Also, the tap density was 2.11 g/cm ³ . Table 1 shows the measurement results of the electrochemical property evaluation.

(Reference example 2)
Only the second sintered body (s2) obtained in the sintering step (step S30a) of Example 1 was used as a positive electrode active material and subjected to electrochemical property evaluation. The volume average particle size Mv of the produced positive electrode active material was 13.4 μm, and the particle size variation index was 0.65. Also, the tap density was 2.67 g/cm ³ . Table 1 shows the measurement results of the electrochemical property evaluation.

[Evaluation results]
Compared to the positive electrode active material of Comparative Example 1, the positive electrode active material of Example has a higher tap density and a discharge capacity per volume (mAh/cm ³ ). In addition, as shown in Reference Examples 1 and 2 in FIG. 4, the tap density increases with an increase in the proportion of particles having a large particle diameter. As envisioned, the positive electrode active material of the example has a higher than expected tap density. In addition, as shown in FIG. 5, in the positive electrode active material of the example, similarly to the tap density, the discharge capacity per volume (mAh/cm ³ ) assumed from Reference Examples 1 and 2 is higher. have

Furthermore, the positive electrode active material of Example has a lower positive electrode resistance (SOC 80%, SOC 20%) than the positive electrode active material of Comparative Example 1. As shown in FIG. 6, the positive electrode active material of Example has a lower positive electrode resistance than the positive electrode resistance (SOC 80%) assumed from Reference Examples 1 and 2, and the output characteristics are further improved. was shown.

Claims (10)

A method for producing a positive electrode active material for a lithium ion secondary battery containing powder of a lithium metal composite oxide having a hexagonal layered structure, comprising:
neutralizing and crystallizing a mixed aqueous solution containing at least nickel, cobalt and manganese using a continuous crystallization method to obtain a powder of a compound containing nickel, cobalt and manganese;
Classifying the powder of the compound containing nickel, cobalt, and manganese to separate into at least a first particle group and a second particle group;
mixing the first particle group and a lithium compound, and firing the obtained first lithium mixture at a temperature of 750° C. or more and 1000° C. or less to obtain a first fired body;
mixing the second particle group and a lithium compound, and firing the obtained second lithium mixture at a temperature of 750° C. or more and 1000° C. or less to obtain a second fired body;
mixing the first fired body and the second fired body to obtain a powder of the lithium metal composite oxide,
The second particle group has a larger average particle size than the first particle group,
The lithium metal composite oxide powder contains lithium (Li), nickel (Ni), cobalt (Co), manganese (Mn), and optionally an element M, and the material amount ratio (molar ratio) of each element However, Li: Ni: Co: Mn: M = (1 + u): (1-xyz): x: y: z [where u is -0.05 ≤ u ≤ 0.50, x is 0 .02 ≤ x ≤ 0.50, y is 0.02 ≤ y ≤ 0.50, z is 0 ≤ z ≤ 0.10, and 0.30 ≤ (x + y + z) ≤ 0.95, and M is W, Mo, V, Zr, Ti, Cr, Al, Si, B, Nb, and at least one element selected from Ta],
A method for producing a positive electrode active material for a lithium ion secondary battery. 2. The method for producing a positive electrode active material for a lithium ion secondary battery according to claim 1, wherein the powder of the compound containing nickel, cobalt and manganese has a volume average particle diameter Mv of 5 μm or more and 20 μm or less. The powder of the compound containing nickel, cobalt, and manganese has a variation index [(D90-D10)/volume average particle diameter Mv] of 0.80 or more, according to claim 1 or claim 2 A method for producing the positive electrode active material for a lithium ion secondary battery described. The lithium according to claim 3, wherein the first particle group and the second particle group have a variation index [(D90-D10) / volume average particle diameter Mv] of less than 0.80. A method for producing a positive electrode active material for an ion secondary battery. The powder of the compound containing nickel, cobalt, and manganese is composed of at least one of a metal composite hydroxide and a metal composite oxide, and the crystallized product obtained by the neutralization crystallization is heat-treated. A method for producing the positive electrode active material for a lithium ion secondary battery according to any one of claims 1 to 4, which is obtained . The powder of the compound containing nickel, cobalt and manganese does not contain lithium and contains nickel, cobalt and manganese and optionally the element M, where M is W, Mo, V, Zr, Ti, Cr, Al, Si, B, Nb, and at least one element selected from Ta) is a powder of a compound containing
In the first particle group, the molar ratio (Li/Me) of lithium to the total mole (Me) of nickel, cobalt, manganese, and the element M is 0.95 or more and 1.50 or less, mixed with a lithium compound,
The second particle group is such that the molar ratio (Li/Me) of lithium to the total mole (Me) of nickel, cobalt, manganese, and the element M is 0.95 or more and 1.50 or less, mixed with a lithium compound,
A method for producing a positive electrode active material for a lithium ion secondary battery according to any one of claims 1 to 5. The method for producing a positive electrode active material for a lithium ion secondary battery according to any one of claims 1 to 6, wherein the first fired body and the second fired body contain secondary particles. . The positive electrode active material for a lithium ion secondary battery according to any one of claims 1 to 7, wherein the first lithium mixture and the second lithium mixture are fired at the same temperature. Production method. 9. The method of any one of claims 1 to 8 , comprising heat-treating at least one of the first group of particles and the second group of particles prior to mixing with a lithium compound. A method for producing a positive electrode active material for a lithium ion secondary battery. Obtaining a positive electrode active material by the manufacturing method according to any one of claims 1 to 9 , a lithium ion secondary battery comprising a positive electrode containing the positive electrode active material, a negative electrode, and an electrolyte manufacturing method.

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