JP7408912B2 - Method for producing positive electrode active material for lithium ion secondary batteries - Google Patents

Description

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

In recent years, with the spread of mobile information terminals such as smartphones and tablet PCs, there has been a strong desire to develop small and lightweight non-aqueous electrolyte secondary batteries with high energy density. Furthermore, there is a strong desire to develop 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.

A lithium ion secondary battery is a secondary battery that meets such requirements. This lithium-ion secondary battery consists of a negative electrode, a positive electrode, an electrolyte, etc. The active material used for the negative and positive electrodes is a material that can desorb and insert lithium during charging and discharging. Ru.

Among these lithium ion secondary batteries, lithium ion secondary batteries that use a layered or spinel type lithium transition metal composite oxide as the positive electrode material can obtain a voltage of 4V class, so they can be used as batteries with high energy density. Currently, research and development is being actively carried out, and some are even in the process of being put into practical use.

As positive electrode materials for such lithium ion secondary batteries, lithium cobalt composite oxide (LiCoO ₂ ) particles that are relatively easy to synthesize, lithium nickel composite oxide (LiNiO ₂ ) particles using nickel, which is cheaper than cobalt, Lithium nickel cobalt manganese composite oxide (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) particles, lithium manganese composite oxide (LiMn ₂ O ₄ ) particles using manganese, lithium nickel manganese composite oxide (LiNi Lithium transition metal composite oxide particles such as _0.5 Mn _0.5 O ₂ ) particles have been proposed.

By the way, in order to obtain a lithium ion secondary battery with excellent cycle characteristics and output characteristics, it is necessary that the positive electrode active material is composed of particles having a small particle size and a narrow particle size distribution. This is because particles with a small particle size have a large specific surface area, and when used as a positive electrode active material, they not only can secure a sufficient reaction area with the electrolyte, but also allow the positive electrode to be made thinner, allowing lithium ion This is because the moving distance between the positive electrode and the negative electrode can be shortened, so that the positive electrode resistance can be reduced. In addition, particles with a narrow particle size distribution can equalize the voltage applied to the particles within the electrode, making it possible to suppress a decrease in battery capacity due to selective deterioration of fine particles.

For example, JP2011-116580A, JP2012-246199A, JP2013-147416A, and WO2012/131881A describe a nucleation process that mainly performs nucleation and a particle growth process that mainly performs particle growth. A method is disclosed for producing transition metal composite hydroxide particles, which serve as a precursor of a positive electrode active material, through clearly separated crystallization reactions in two stages of the growth process.

In these methods, precursors with small particle size and narrow particle size distribution are obtained by appropriately adjusting the pH value and reaction atmosphere in the nucleation step and particle growth step. A positive electrode active material with a narrow particle size distribution has been obtained. Furthermore, by controlling the atmosphere in the nucleation step, which mainly involves nucleation, and the particle growth step, which mainly involves particle growth, we can create a low-density center consisting of fine primary particles and a high-density center consisting of plate-shaped or acicular primary particles. Transition metal composite hydroxide particles consisting of a dense outer peripheral portion are obtained, and such a precursor is used to obtain a positive electrode active material having a hollow structure.

Japanese Patent Application Publication No. 2011-116580 Japanese Patent Application Publication No. 2012-246199 Japanese Patent Application Publication No. 2013-147416 WO2012/131881 publication

However, although the manufacturing methods described in these documents can improve the output characteristics by improving the particle structure, they cannot further improve the battery capacity and cycle characteristics that will be required in the future.

SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to provide a positive electrode active material that can further improve battery capacity and cycle characteristics when used in a secondary battery .

A method for manufacturing a positive electrode active material for a lithium ion secondary battery according to one embodiment of the present invention is a method for manufacturing a positive electrode active material for a lithium ion secondary battery, in which general formula (A): Ni _{x Mny} Co _z M _t (OH) _2+a (x+y+z+t=1, 0.3≦x≦0.8, 0.05≦y≦0.55, 0≦z≦0.4, 0≦t≦0.1, 0≦a≦ 0.5, M is one or more additive elements selected from Nb, Mo, Ta, Zr, and W), and [(d90-d10)/MV] is an index indicating the spread of particle size distribution. A mixing step of mixing transition metal composite hydroxide particles having a particle size of 0.65 or less and a lithium compound to form a lithium mixture, and calcining the lithium mixture formed in the mixing step in an oxidizing atmosphere. , a calcination step for obtaining a calcined powder with a (003) plane half width of 0.45° or more, and a calcination step for firing the calcined powder obtained in the calcination step in an oxidizing atmosphere. It is characterized by having.

In this way, when the positive electrode active material for a lithium ion secondary battery is used in a secondary battery, it is possible to provide a positive electrode active material that can further improve battery capacity and cycle characteristics.

At this time, in the calcination step, the carbon content of the calcined powder after the calcination step may be controlled to be 1.0% by mass or less.

In this way, it is possible to further reduce the residual lithium compound, further suppress sintering agglomeration of secondary particles of the lithium transition metal composite oxide in the firing process, and to sufficiently improve crystallinity. .

At this time, in one aspect of the present invention, the calcination step may be performed by holding and firing at 550° C. to 800° C. for 1 to 10 hours in an oxidizing atmosphere.

In this way, lithium can be sufficiently diffused and reacted in the composite hydroxide particles or heat-treated particles, and sintering and agglomeration of the secondary particles can be suppressed.

At this time, in one aspect of the present invention, the firing step may be performed by holding the film at 760° C. to 980° C. for 2 to 24 hours in an oxidizing atmosphere.

In this way, lithium is prevented from sufficiently diffusing into the composite hydroxide particles or heat-treated particles, and excess lithium or unreacted composite hydroxide particles or heat-treated particles remain. The composite oxide particles can have sufficient crystallinity.

At this time, in one aspect of the present invention, the firing step is performed by holding the temperature within the melting point of the lithium compound ±50°C for 1 to 5 hours in an oxidizing atmosphere, and then increasing the temperature to 760°C to 980°C. It may be held for 2 to 24 hours and fired.

In this way, the lithium compound is melted to prevent excess lithium, unreacted composite hydroxide particles, or heat-treated particles from remaining, and the resulting lithium composite oxide particles have sufficient crystallinity. can do.

At this time, in one aspect of the present invention, the method may include a pre-firing crushing process of crushing the calcined powder calcined in the calcining process before the firing process.

In this way, sintering agglomeration of secondary particles constituting the positive electrode active material after the sintering process can be suppressed.

At this time, in one aspect of the present invention, in the mixing step, the lithium mixture is mixed at a ratio of the sum of the number of atoms of metals other than lithium contained in the lithium mixture to the number of lithium atoms of 1:0. The ratio may be adjusted to 95 to 1:1.5.

In this way, the desired lithium content will be achieved.

In this case, one aspect of the present invention may further include a heat treatment step of heat treating the transition metal composite hydroxide particles at 105° C. to 750° C. before the mixing step.

In this way, it is possible to reduce the remaining moisture to a certain amount until after the firing process, and it is possible to suppress variations in the composition of the obtained positive electrode active material.

According to the present invention, it is possible to provide a positive electrode active material that can further improve battery capacity and cycle characteristics .

FIG. 1 is a process diagram schematically showing a positive electrode active material for a lithium ion secondary battery according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view of a coin-shaped battery used for battery evaluation of an example of a positive electrode active material for a lithium ion secondary battery according to an embodiment of the present invention. FIG. 3(A) is a Nyquist plot showing the measurement results of the impedance evaluation of an example of the positive electrode active material for a lithium ion secondary battery according to an embodiment of the present invention, and FIG. FIG. 2 is a schematic explanatory diagram of an equivalent circuit used in the analysis.

The present inventors have worked diligently to further improve the battery capacity and cycle characteristics of a positive electrode active material for lithium ion secondary batteries (hereinafter referred to as "positive electrode active material") based on the conventional technology such as 2013-147416. I did a lot of research. As a result, in the step of firing a mixture of a precursor and a lithium compound, the positive electrode active material is formed by calcination at a specific temperature to adjust the half-width of the calcination to an appropriate range, and then calcination. It was found that the sintering agglomeration of secondary particles can be suppressed, and the characteristics when used in batteries can be improved. The present invention has been completed based on these findings. Hereinafter, preferred embodiments of the present invention will be described.

Note that the present embodiment described below does not unduly limit the content of the present invention described in the claims, and changes can be made without departing from the gist of the present invention. Furthermore, not all of the configurations described in this embodiment are essential as a solution to the present invention. A method for producing a positive electrode active material for a lithium ion secondary battery, a positive electrode active material for a lithium ion secondary battery, and a lithium ion secondary battery according to an embodiment of the present invention will be described in the following order.
1. Transition metal composite hydroxide particles 1-1. Transition metal composite hydroxide particles 1-2. Method for producing transition metal composite hydroxide particles 2. Positive electrode active material for lithium ion secondary batteries 2-1. Positive electrode active material for lithium ion secondary batteries 2-2. Method for producing positive electrode active material for lithium ion secondary battery 3. Lithium ion secondary battery

<1. Transition metal composite hydroxide particles>
<1-1. Transition metal composite hydroxide particles>
In the process of manufacturing the positive electrode active material for lithium ion secondary batteries according to an embodiment of the present invention, transition metal composite hydroxide particles (hereinafter referred to as "composite hydroxide particles") are used for lithium ion secondary batteries. Used as a precursor for positive electrode active material.

It is preferable that the composite hydroxide particles are composed of secondary particles formed by agglomeration of a plurality of plate-shaped primary particles. Furthermore, it is preferable that the secondary particles have a center portion formed by agglomeration of the fine primary particles, and an outer peripheral portion formed by aggregation of the plate-shaped primary particles outside the center portion. More preferably, the center portion contains a higher concentration of the additive element than the outer peripheral portion. By using composite hydroxide particles having such a central portion, it is possible to obtain a positive electrode active material with a hollow structure having higher output characteristics. Further, it is preferable that the average particle size of the secondary particles is 3 μm to 15 μm.

(1) Particle Structure Secondary Particle Structure The composite hydroxide particles suitable for use in the positive electrode active material for a lithium ion secondary battery according to one embodiment of the present invention are formed by agglomeration of a plurality of plate-shaped primary particles. They are approximately spherical secondary particles. Further, it is preferable that the particle has a structure in which the inside of the particle has a center part made of fine primary particles, and an outer peripheral part made of plate-shaped primary particles larger than the fine primary particles outside the center part. Due to this structure in which a plurality of plate-shaped primary particles are aggregated, lithium is sufficiently diffused into the particles during the sintering process to form the lithium nickel manganese composite oxide, which is the positive electrode active material of the present invention. , a good positive electrode active material with uniform lithium distribution can be obtained. Such composite hydroxide particles and methods for producing the same are disclosed in detail in, for example, JP-A-2011-116580 and JP-A-2012-246199.

Here, if the center part has a structure with many gaps in which fine primary particles are connected, the shrinkage due to sintering in the firing step S5 will be smaller than the outer peripheral part made of larger and thicker plate-shaped primary particles. Occurs from low temperatures. Therefore, during firing, sintering progresses from a low temperature, and the particle shrinks from the center toward the outer periphery where sintering progresses slowly, creating a space in the center. Furthermore, since the center is considered to have a low density and has a high shrinkage rate, the center has a sufficiently large space. As a result, the positive electrode active material obtained after firing has a hollow structure.

Furthermore, it is more preferable that the plate-like primary particles aggregate in random directions to form secondary particles. As the plate-shaped primary particles aggregate in random directions, voids are created almost uniformly between the primary particles, and when mixed with a lithium compound and fired, the molten lithium compound spreads into the secondary particles, causing lithium is sufficiently diffused.

In addition, since the composite hydroxide particles having the center part are aggregated in random directions, the center part shrinks evenly in the firing step S5, so that the composite hydroxide particles have a sufficient size inside the positive electrode active material. It is possible to form a space having , which is preferable.

In order to form spaces during the firing, the fine primary particles preferably have an average particle diameter of 0.01 to 0.3 μm, more preferably 0.1 to 0.3 μm. Further, the average particle diameter of the plate-shaped primary particles is preferably 0.3 to 3 μm, more preferably 0.4 to 1.5 μm, and particularly 0.4 to 1.0 μm. preferable.

(2) Average particle size In the composite hydroxide particles used in the positive electrode active material for a lithium ion secondary battery according to an embodiment of the present invention, the average particle size of the secondary particles is preferably 3 μm to 12 μm, more preferably It is adjusted to 3 μm to 10 μm. The average particle size of the secondary particles correlates with the average particle size of the positive electrode active material using the composite hydroxide particles as a precursor. Therefore, by controlling the average particle size of the secondary particles within this range, it is possible to control the average particle size of the positive electrode active material using the composite hydroxide particles as a precursor within a predetermined range. Become.

Note that the average particle size of the secondary particles means a volume-based average particle size (MV), and can be determined from, for example, a volume integrated value measured with a laser beam diffraction scattering particle size analyzer.

(3) Particle size distribution The composite hydroxide particles used in the present invention have an index indicating the spread of particle size distribution [(d90-d10)/average particle size] of 0.65 or less, preferably 0.55 or less, More preferably, it is adjusted to 0.50 or less.

The particle size distribution of the positive electrode active material is strongly influenced by the composite hydroxide particles that are its precursor. 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, and a secondary battery using this Safety, cycle characteristics and output characteristics cannot be sufficiently improved. On the other hand, if [(d90-d10)/average particle size] is adjusted to 0.65 or less at the stage of composite hydroxide particles, the positive electrode active material using this as a precursor can be The particle size distribution can be narrowed, and the above-mentioned problems can be avoided. However, assuming industrial scale production, it is not practical to use composite hydroxide particles having an excessively small [(d90-d10)/average particle size]. Therefore, in consideration of cost and productivity, the lower limit of [(d90-d10)/average particle size] is preferably about 0.25.

In addition, d10 is the particle size at which the number of particles at each particle size is accumulated from the smaller particle size side, and the cumulative volume is 10% of the total volume of all particles, and d90 is the particle size where the number of particles is accumulated in the same way, It means a particle size whose cumulative volume is 90% of the total volume of all particles. Like the average particle diameter, d10 and d90 can be determined from the volume integrated value measured with a laser beam diffraction scattering particle size analyzer.

(4) Composition The composite hydroxide particles used in the positive electrode active material for a lithium ion secondary battery according to an embodiment of the present invention have a general formula (A): Ni _{x Mny} Co _z M _t (OH) _2+a (x+y+z+t =1, 0.3≦x≦0.8, 0.05≦y≦0.55, 0≦z≦0.4, 0≦t≦0.1, 0≦a≦0.5, M is one or more additive elements selected from Nb, Mo, Ta, Zr, and W). By using such composite hydroxide particles as a precursor, a positive electrode active material represented by the general formula (B) described below can be easily obtained, and higher battery performance can be achieved.

In addition, in the composite hydroxide particles represented by the general formula (A), the composition range of nickel, manganese, cobalt, and the additive element M constituting the particles and their critical significance are shown in the general formula (B) below. It is similar to the positive electrode active material used. Therefore, description of these matters will be omitted here.

<1-2. Method for producing transition metal composite hydroxide particles>
Next, a method for producing the above-mentioned transition metal composite hydroxide particles will be explained. The composite hydroxide particles used in the positive electrode active material for a lithium ion secondary battery according to an embodiment of the present invention are prepared by, for example, containing a raw material aqueous solution containing at least a transition metal and an aqueous solution containing an ammonium ion donor in a reaction tank. A reaction aqueous solution is formed by supplying the transition metal composite hydroxide particles, which are then subjected to a crystallization reaction to produce transition metal composite hydroxide particles that serve as a precursor of a positive electrode active material for a lithium ion secondary battery.

In particular, in the crystallization reaction, the pH value of the reaction aqueous solution is adjusted to a range of 12.0 to 14.0 based on the liquid temperature of 25°C, and the nucleation step is performed to generate nuclei, and the nuclei obtained in the nucleation step are A particle growth step in which nuclei are grown by controlling the pH value of the reaction aqueous solution based on a liquid temperature of 25° C. to be lower than the pH value in the nucleation step and between 10.5 and 12.0. It is preferable to clearly distinguish between two stages. In addition, the reaction atmosphere at the beginning of the nucleation step and the particle growth step is adjusted to an oxidizing atmosphere in which the oxygen concentration exceeds 5% by volume, and in the particle growth step, the reaction atmosphere is adjusted from the oxidizing atmosphere to an oxidizing atmosphere with an oxygen concentration of 5% by volume or less. It is preferable to switch to a non-oxidizing atmosphere.

The method for producing composite hydroxide particles is not limited by the composition as long as the structure, average particle size, and particle size distribution described above can be achieved. It can be suitably applied to physical particles.

(1) Crystallization reaction In the above method for producing composite hydroxide particles, the crystallization reaction is clearly separated into two stages: a nucleation step in which nucleation is mainly performed, and a particle growth step in which grains are mainly grown. By adjusting the crystallization conditions in each step, especially by switching the reaction atmosphere in the particle growth step, it is possible to efficiently obtain composite hydroxide particles having the above-mentioned particle structure, average particle size, and particle size distribution. It is possible.

[Nucleation process]
In the nucleation step, first, a transition metal compound serving as a raw material in this step is dissolved in water to prepare a 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 into the reaction tank, and the pH value measured based on the liquid temperature of 25°C is 12.0 to 14.0, and the ammonium ion concentration is 3 g/ Prepare a pre-reaction aqueous solution having a concentration of L to 25 g/L. Note that 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, a raw material aqueous solution is supplied while stirring this pre-reaction aqueous solution. As a result, a nucleation aqueous solution, which is a reaction aqueous solution in the nucleation step, is formed in the reaction tank. Since the pH value of this aqueous solution for nucleation is within the above-mentioned range, in the nucleation step, nucleation occurs preferentially, with almost no nuclei growing. In addition, in the nucleation process, the pH value and ammonium ion concentration of the nucleation aqueous solution change as the nucleation occurs, so the alkaline aqueous solution and the ammonia aqueous solution are supplied in a timely manner so that the pH value of the solution in the reaction tank reaches 25% of the liquid temperature. It is necessary to control the pH to a range of 12.0 to 14.0 and the ammonium ion concentration to a range of 3 g/L to 25 g/L on a temperature basis.

In addition, in the nucleation step, the reaction atmosphere is adjusted to an oxidizing atmosphere in which the oxygen concentration exceeds 5% by volume. As a result, a core formed by agglomeration of fine primary particles can be formed inside the composite hydroxide particles, and by using these composite hydroxide particles as a precursor, a positive electrode active material having a hollow structure can be formed. Therefore, the reaction area with the electrolyte can be further increased.

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 nucleation aqueous solution. Then, when a predetermined amount of nuclei are generated in the aqueous solution for nucleation, the nucleation step is ended.

At this time, the amount of nuclei generated can be determined from the amount of metal compound contained in the raw material aqueous solution supplied to the aqueous solution for nucleation. The amount of nuclei generated in the nucleation process is not particularly limited, but in order to obtain composite hydroxide particles with a narrow particle size distribution, it is necessary to It is preferably 0.1 atomic % to 2 atomic %, more preferably 0.1 atomic % to 1.5 atomic %, based on the metal element in the compound.

[Particle growth process]
After the nucleation process is completed, the pH value of the nucleation aqueous solution in the reaction tank is adjusted to 10.5 to 12.0 based on the liquid temperature of 25°C to form a particle growth aqueous solution that is a reaction aqueous solution in the particle growth process. do. The pH value can also be adjusted by stopping the supply of the alkaline aqueous solution, but in order to obtain composite hydroxide particles with a narrow particle size distribution, it is necessary to temporarily stop the supply of all aqueous solutions and adjust the pH value. It is preferable. Specifically, after stopping the supply of all aqueous solutions, it is preferable to adjust the pH value by supplying the same type of inorganic acid as the acid constituting the metal compound serving as the raw material to the aqueous nucleation solution.

Next, while stirring this particle growth aqueous solution, supply of the raw material aqueous solution is restarted. At this time, since the pH value of the aqueous solution for particle growth is within the above-mentioned range, new nuclei are hardly generated, nuclei (particles) grow, and composite hydroxide particles having a predetermined particle size are formed. Ru. In addition, in the particle growth process, the pH value and ammonium ion concentration of the particle growth aqueous solution change as the particles grow, so the alkaline aqueous solution and ammonia aqueous solution are supplied in a timely manner to maintain the pH value and ammonium ion concentration within the above range. It is necessary to do so.

In particular, in the method for producing composite hydroxide particles of the present invention, the reaction atmosphere is switched from an oxidizing atmosphere to a non-oxidizing atmosphere with an oxygen concentration of 5% by volume or less during the particle growth step. This makes it possible to obtain composite hydroxide particles having the above-mentioned particle structure.

In addition, in such a method for producing composite hydroxide particles, in the nucleation step and the particle growth step, metal ions precipitate as primary particles forming the core or composite hydroxide particles. Therefore, the ratio of the liquid component to the metal component in the aqueous solution for nucleation and the aqueous solution for particle growth increases. As a result, the concentration of the raw material aqueous solution appears to decrease, and the growth of the composite hydroxide particles may stagnate, especially in the particle growth step. Therefore, in order to suppress the 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 after the completion of the nucleation step and during the particle growth step. Specifically, the supply and stirring of the raw material aqueous solution, aqueous alkaline solution, and aqueous solution containing the ammonium ion donor are temporarily stopped, and the nuclei and composite hydroxide particles in the aqueous solution for particle growth are allowed to settle. Preferably, the supernatant liquid is drained. Such operations can increase the relative concentration of the mixed aqueous solution in the particle growth aqueous solution, thereby preventing stagnation of particle growth and controlling the particle size distribution of the resulting composite hydroxide particles within a suitable range. Not only that, but also the density of the secondary particles as a whole can be improved.

[Addition of additive elements]
The concentration of the additive element in the raw material aqueous solution with respect to elements other than the additive element in an oxidizing atmosphere is higher than that in a non-oxidizing atmosphere. The concentration in the oxidizing atmosphere is preferably at least twice the concentration in the non-oxidizing atmosphere, more preferably at least 5 times the concentration in the non-oxidizing atmosphere. Particularly preferably, an aqueous solution containing the additive element is added in an oxidizing atmosphere, and addition of the aqueous solution containing the additive element is stopped in a non-oxidizing atmosphere. When producing the positive electrode active material, the central part where fine primary particles formed in an oxidizing atmosphere agglomerate shrinks inside the outer periphery, which is formed by agglomerating plate-like primary particles formed in a non-oxidizing atmosphere. to form a hollow part. Therefore, additive elements added in an oxidizing atmosphere diffuse to the outer periphery and are present in large quantities on the surface of the primary particles forming the outer shell of the positive electrode active material, whereas additive elements added in a non-oxidizing atmosphere A large amount of the additive element exists inside the primary particles, and a concentrated layer of the additive element is formed on the surface of the primary particles. By forming the concentrated layer on the surface of the primary particles that come into contact with the electrolytic solution, it becomes possible to effectively make the additive element that improves the output characteristics function. By making the concentration of the additive element added in an oxidizing atmosphere higher than the concentration added in a non-oxidizing atmosphere, the amount of the additive element in the concentrated layer can be increased and it can function more effectively. I can do it.

Furthermore, in the particle growth step, the concentration of the additive element is adjusted within a range of 35% to 75% with respect to the time from switching from the oxidizing atmosphere to the non-oxidizing atmosphere until the end of the particle growth step. By making the concentration higher than the above range of 35% to 75%, the concentration of the additive element on the surface side of 50% to 80% of the thickness of the outer peripheral part can be made higher than that on the inner side of the outer peripheral part. By forming such a layer containing a higher concentration of additive elements on the surface side of the outer periphery than on the inside side, it becomes possible to form a concentrated layer in the positive electrode active material more uniformly and improve battery characteristics. .

[Particle size control of composite hydroxide particles]
The particle size of the composite hydroxide particles obtained as described above can be controlled by the time of the particle growth step and nucleation step, the pH value of the nucleation aqueous solution and the particle growth aqueous solution, and the supply amount of the raw material aqueous solution. I can do it. For example, by performing the nucleation step at a high pH value or by lengthening the time of the particle growth step, the amount of metal compounds contained in the supplied raw material aqueous solution can be increased, the amount of nuclei generated can be increased, and the amount of nuclei produced can be increased. The particle size of the composite hydroxide particles can be reduced. On the other hand, 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 used in a positive electrode active material for a lithium ion secondary battery according to an embodiment of the present invention, apart from the nucleation aqueous solution, a pH value and an ammonium ion concentration suitable for the particle growth step are prepared. Prepare the adjusted component adjustment aqueous solution, and add to this component adjustment aqueous solution the nucleation aqueous solution after the nucleation step, preferably the nucleation aqueous solution from which a part of the liquid component has been removed after the nucleation step. The particles may be mixed and used as an aqueous solution for particle growth to perform a particle growth step.

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 optimal state. In particular, since the pH value of the aqueous solution for particle growth can be controlled within the optimal range from the start of the particle growth process, the particle size distribution of the resulting composite hydroxide particles can be made narrower.

(2) Supply aqueous solution a) Raw material aqueous solution The ratio of metal elements in the raw material aqueous solution is approximately the composition ratio of the composite hydroxide particles obtained. Therefore, it is necessary to appropriately adjust the content of each metal element in the raw material aqueous solution depending on the composition of the target composite hydroxide particles. For example, when trying to obtain composite hydroxide particles represented by the above-mentioned general formula (A), the ratio of metal elements in the raw material aqueous solution is changed to Ni:Mn:Co:M=x:y:z ;t (however, adjust so that x+y+z+t=1, 0.3≦x≦0.80, 0.05≦y≦0.55, 0≦z≦0.4, 0≦t≦0.1) It is necessary to do so.

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

In addition, when the additive element M (M is one or more kinds of additive elements selected from Nb, Mo, Ta, Zr, and W) is contained in the composite hydroxide particles, in order to supply the additive element M, Similarly, water-soluble compounds are preferably used as the compound, and for example, niobium oxalate, ammonium molybdate, sodium tantalate, sodium tungstate, ammonium tungstate, etc. can be suitably used.

The concentration of the raw material aqueous solution is preferably 1.0 mol/L to 2.6 mol/L, more preferably 1.5 mol/L to 2.2 mol/L in total of the metal compounds. If the concentration of the raw material aqueous solution is less than 1.0 mol/L, the amount of crystallized material per reaction tank will decrease, resulting in a decrease in productivity. On the other hand, if the concentration of the mixed aqueous solution exceeds 2.6 mol/L, the saturated concentration at room temperature will be exceeded, so that crystals of each metal compound may re-precipitate and clog pipes and the like.

The above-mentioned metal compound does not necessarily need to be supplied to the reaction tank as a raw material aqueous solution. For example, when performing a crystallization reaction using metal compounds that react when mixed to produce compounds other than the desired compound, individually Alternatively, an aqueous solution of the metal compound may be prepared and supplied into the reaction tank at a predetermined ratio as an aqueous solution of each metal compound.

In addition, the supply amount of the raw material aqueous solution is such that the concentration of the product in the particle growth aqueous solution is preferably 30 g/L to 200 g/L, more preferably 80 g/L to 150 g/L at the end of the particle growth step. I will make it happen. If the concentration of the product 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 metal salt aqueous solution for nucleation or the metal salt aqueous solution for particle growth will not be sufficiently diffused in the reaction tank, which may cause uneven particle growth.

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

Note that 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 locally increase and is maintained within a predetermined range. For example, the aqueous reaction solution may be sufficiently stirred and supplied using a pump such as a metering pump that can control the flow rate.

c) Aqueous solution containing ammonium donor The aqueous solution containing ammonium ion donor is not particularly limited, and for example, aqueous ammonia, or an aqueous solution of ammonium sulfate, ammonium chloride, ammonium carbonate, or ammonium fluoride may be used. I can do it.

When aqueous ammonia is used as the ammonium ion donor, its concentration is preferably 20% by mass to 30% by mass, more preferably 22% by mass to 28% by mass. By regulating the concentration of ammonia water within such a range, loss of ammonia due to volatilization etc. can be suppressed to a minimum, thereby making it possible to improve production efficiency.

Note that the aqueous solution containing the ammonium ion donor can also be supplied using a pump that can control the flow rate, similarly to the alkaline aqueous solution.

(3) pH value In the method for producing composite hydroxide particles used in a positive electrode active material for a lithium ion secondary battery according to an embodiment of the present invention, the pH value at a liquid temperature of 25°C is set in the nucleation step. must be controlled within the range of 12.0 to 14.0, and within the range of 10.5 to 12.0 in the particle growth process. In addition, in any step, it is preferable to control the fluctuation range of the pH value during the crystallization reaction to within ±0.2. When the range of pH value fluctuation is large, the ratio of the amount of nucleation to the particle growth is not constant, making it difficult to obtain composite hydroxide particles with a narrow particle size distribution.

a) Nucleation step In the nucleation step, the pH value of the reaction aqueous solution (nucleation aqueous solution) is set to 12.0 to 14.0, preferably 12.3 to 13.5, based on the liquid temperature of 25°C. It is necessary to control it preferably within the range of 12.5 to 13.3. This makes it possible to suppress the growth of nuclei and give priority to nucleation, making it possible to make the nuclei produced in this step homogeneous and with a narrow particle size distribution. On the other hand, if the pH value is less than 12.0, the growth of the nuclei (particles) progresses as well as the nucleation, so that the particle size of the obtained composite hydroxide particles becomes non-uniform and the particle size distribution deteriorates. Moreover, when the pH value exceeds 14.0, the generated nuclei become too fine, resulting in the problem that the aqueous nucleation solution gels.

b) Particle growth step In the particle growth step, the pH value of the reaction aqueous solution (particle growth aqueous solution) is set to 10.5 to 12.0, preferably 11.0 to 12.0, based on the liquid temperature of 25°C. It is necessary to control it preferably within the range of 11.5 to 12.0. This suppresses the generation of new nuclei, allows priority to be given to particle growth, and allows the resulting composite hydroxide particles to be homogeneous and have a narrow particle size distribution. On the other hand, if the pH value is less than 10.5, the ammonium ion concentration increases and the solubility of metal ions increases, which not only slows down the crystallization reaction rate but also increases the amount of metal ions remaining in the reaction aqueous solution. and productivity deteriorates. Moreover, when the pH value exceeds 12.0, the amount of nucleation during the particle growth process increases, the particle size of the obtained composite hydroxide particles becomes non-uniform, and the particle size distribution deteriorates.

In addition, 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, it can be used as a condition for either the nucleation process or the particle growth process. I can do it. That is, if the pH value in the nucleation step is made higher than 12.0 to generate a large amount of nucleation, and then the pH value in the particle growth step is set to 12.0, a large amount of nuclei will be present in the reaction aqueous solution, and the particles will be 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, there are no nuclei to grow in the reaction aqueous solution, so nucleation occurs preferentially. , the generated nuclei grow, and good composite hydroxide particles can be obtained. In either case, the pH value in the particle growth process should be controlled to a value lower than the pH value in the nucleation process, and in order to clearly separate nucleation and particle growth, It is preferable to lower the pH value by 0.5 or more, more preferably by 1.0 or more than the pH value in the production step.

(4) Reaction atmosphere A preferable structure in which the composite hydroxide particles have a central part as described above is such that the pH value of the reaction aqueous solution in the nucleation step and the particle growth step is controlled as described above, and the reaction in these steps is controlled. It is formed by controlling the atmosphere. Therefore, in such a method for producing composite hydroxide particles, the reaction atmosphere is controlled as well as the pH value in each step. In other words, by controlling the pH value in each step as described above and adjusting the initial reaction atmosphere of the nucleation step and particle growth step to an oxidizing atmosphere, a core where fine primary particles aggregate is formed. Ru. In addition, by switching from an oxidizing atmosphere to a non-oxidizing atmosphere during the particle growth process, an outer peripheral area where the plate-shaped primary particles aggregate is formed outside the center area.

In such a reaction atmosphere control, the fine primary particles constituting the center usually have a plate shape and/or a needle shape, but depending on the composition of the composite hydroxide particles, they can have a rectangular parallelepiped shape, an ellipsoid shape, or a rhombohedral shape. It can also take other shapes. Regarding this point, the same applies to the plate-shaped primary particles constituting the outer peripheral portion. Therefore, the reaction atmosphere at each stage is appropriately controlled depending on the composition of the target composite hydroxide particles.

a) Oxidizing atmosphere At the stage of forming the center of the composite hydroxide particles, the reaction atmosphere is controlled to be an oxidizing atmosphere. Specifically, the oxygen concentration in the reaction atmosphere is controlled so as to exceed 5% by volume, preferably 10% by volume or more, and more preferably an atmospheric atmosphere (oxygen concentration: 21% by volume). By controlling the oxygen concentration in the reaction atmosphere within this range, the average particle size of the primary particles will be in the range of 0.01 μm to 0.3 μm, so that a center portion made of fine primary particles can be formed. I can do it.

Note that the upper limit of the oxygen concentration in the reaction atmosphere at this stage is not particularly limited, but if the oxygen concentration is excessively high, the average particle size of the primary particles will be less than 0.01 μm, and the low density layer will not be sufficient. It may not be the same size. For this reason, the oxygen concentration is preferably 30% by volume or less.

b) Non-oxidizing atmosphere On the other hand, the reaction atmosphere at the stage of forming the outer periphery of the composite hydroxide particles is controlled to be a weakly oxidizing atmosphere or a non-oxidizing atmosphere. Specifically, the mixed atmosphere of oxygen and inert gas is controlled so that the oxygen concentration in the reaction atmosphere is 5% by volume or less, preferably 2% by volume or less, more preferably 1% by volume or less. This allows the nuclei generated in the nucleation process to grow to a certain range while suppressing unnecessary oxidation. It is possible to form a structure in which the plate-shaped primary particles are aggregated, and to form an outer peripheral portion having a sufficient difference in primary particle diameter from the above-mentioned central portion.

c) Timing of Atmosphere Control In the particle growth process, the above-mentioned atmosphere control needs to be performed at an appropriate timing so that composite hydroxide particles having the desired particle structure are formed.

The atmosphere in the above particle growth process is changed so that the size of the center of the composite hydroxide particles is so large that the final positive electrode active material has a hollow area that does not cause fine particles to occur and deteriorate the cycle characteristics. The timing will be determined taking into account the For example, it is carried out within a range of 0 to 40%, preferably 0 to 30%, more preferably 0 to 25% of the total particle growth process time from the start of the particle growth process. If the above-mentioned switching is performed at a point exceeding 40% of the total particle growth process time, the formed central part becomes large and the thickness of the outer peripheral part becomes too thin relative to the particle size of the secondary particles. On the other hand, if the above switching is performed before the start of the particle growth process, that is, during the nucleation process, the center portion will become too small or secondary particles having the above structure will not be formed.

d) Switching method Conventionally, the reaction atmosphere during the crystallization process was switched by circulating atmospheric gas in the reaction tank or by inserting a conduit with an inner diameter of about 1 mm to 50 mm into the reaction aqueous solution and bubbling the atmospheric gas. Do it with However, in such conventional techniques, it takes a long time to switch the reaction atmosphere, so it is necessary to stop the supply of the raw material aqueous solution during the switching. Therefore, when switching the reaction atmosphere while supplying the raw material aqueous solution, it is preferable to use a diffuser tube. The diffuser tube is constituted by a conduit having a large number of fine holes on its surface, and can release a large number of fine gases (bubbles) into the liquid, so that it is possible to switch the reaction atmosphere in a short time. Therefore, there is no need to stop the supply of the raw material aqueous solution when switching the reaction atmosphere, and production efficiency can be improved.

As such a diffuser tube, it is preferable to use one made of ceramic, which has excellent resistance in a high pH environment. Furthermore, the smaller the pore diameter of the air diffuser tube, the more fine air bubbles can be emitted, so that the reaction atmosphere can be switched with higher efficiency. In the present invention, it is preferable to use an aeration tube with a pore diameter of 100 μm or less, more preferably an aeration tube with a pore diameter of 50 μm or less.

(5) Ammonium ion concentration The ammonium ion concentration in the reaction aqueous solution is preferably maintained at a constant value within the range of 3 g/L to 25 g/L, more preferably 5 g/L to 20 g/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 metal ions cannot be maintained constant, and the reaction aqueous solution tends to gel, causing the shape to change. It becomes difficult to obtain composite hydroxide particles with a uniform particle size. On the other hand, if the ammonium ion concentration exceeds 25 g/L, the solubility of metal ions becomes too high, and the amount of metal ions remaining in the reaction aqueous solution increases, causing compositional deviation.

Note that if the ammonium ion concentration fluctuates during the crystallization reaction, the solubility of metal ions will fluctuate, making it impossible to form uniform composite hydroxide particles. Therefore, it is preferable to control the fluctuation range of ammonium ion concentration within a certain range through the nucleation step and the particle growth step, and specifically, it is preferable to control the fluctuation range to ±5 g/L.

(6) Reaction Temperature The temperature of the aqueous reaction solution (reaction temperature) needs to be controlled preferably at 20°C or higher, more preferably in the range of 20°C to 60°C, throughout the nucleation step and particle growth step. If the reaction temperature is less than 20° C., nucleation tends to occur due to the low solubility of the reaction aqueous solution, making it 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, the volatilization of ammonia will be accelerated, and the ammonium ion donor supplied to control the ammonium ions in the reaction aqueous solution within a certain range. The amount of aqueous solution containing will increase, and the production cost will increase.

(7) Coating process A coating process may be provided to add additional elements to the positive electrode active material. The coating method is not particularly limited as long as the composite hydroxide particles can be uniformly coated with the compound containing the additive element M. For example, after slurrying composite hydroxide particles and controlling the pH value within a predetermined range, an aqueous solution (aqueous coating solution) in which a compound containing the additive element M is dissolved is added to the surface of the composite hydroxide particles. By precipitating the compound containing the additive element M, composite hydroxide particles uniformly coated with the compound containing the additive element can be obtained. In this case, instead of the aqueous coating solution, an alkoxide solution of the additive element may be added to the slurry of the composite hydroxide particles. Alternatively, the composite hydroxide particles may be coated by spraying and drying an aqueous solution or slurry in which a compound containing an additive element is dissolved, without forming the composite hydroxide particles into a slurry. Furthermore, coating is performed by spray-drying a slurry in which composite hydroxide particles and a compound containing an additive element are suspended, or by mixing the composite hydroxide particles and a compound containing an additive element using a solid phase method. You can also.

In addition, when coating the surface of the composite hydroxide particles with an additive element, the raw material aqueous solution and It is necessary to adjust the composition of the aqueous coating solution as appropriate. Further, the coating step may be performed on heat-treated particles after heat-treating the composite hydroxide particles.

(8) Manufacturing device The crystallizer (reaction tank) for manufacturing the composite hydroxide particles used in the positive electrode active material for a lithium ion secondary battery according to an embodiment of the present invention uses the above-mentioned aeration pipe. There are no particular limitations as long as the reaction atmosphere can be switched. However, it is preferable to use a batch type crystallizer in which the precipitated product is not recovered until the crystallization reaction is completed. With this type of crystallizer, unlike continuous crystallizers that collect products using an overflow method, growing particles are not collected at the same time as the overflow liquid. particles can be easily obtained. Furthermore, in the method for producing composite hydroxide particles of the present invention, it is necessary to appropriately control the reaction atmosphere during the crystallization reaction, and therefore it is preferable to use a closed type crystallizer.

<2. Cathode active material for lithium ion secondary batteries>
<2-1. Cathode active material for lithium ion secondary batteries>
The positive electrode active material for a lithium ion secondary battery according to an embodiment of the present invention has a general formula (B): Li _1+u Ni _{x Mny} Co _z M _t O ₂ (-0.05≦u≦0.50, x+y+z+t =1, 0.3≦x≦0.80, 0.05≦y≦0.55, 0≦z≦0.4, 0≦t≦0.1, M is Nb, Mo, Ta, Zr, A positive electrode active material that is represented by one or more additive elements selected from W), has a hexagonal crystal structure with a layered structure, and is composed of secondary particles formed by agglomeration of multiple primary particles. Yes, when the positive electrode active material is observed using a scanning electron microscope, the ratio of the number of aggregated particles in which five or more secondary particles aggregate to the number of secondary particles within the observation field is 0.7. % or less, and the amount of surplus lithium contained in the positive electrode active material is 0.08% by mass or less.

(1) Particle Structure a) Structure of Secondary Particles A positive electrode active material for a lithium ion secondary battery according to an embodiment of the present invention is composed of secondary particles formed by aggregating a plurality of primary particles. In order to have higher output characteristics, it is preferable that the secondary particles include an outer shell and a hollow section in which no primary particles are present inside the outer shell.

In a positive electrode active material that has a hollow structure, the electrolyte infiltrates through the grain boundaries or voids between the primary particles, and lithium is inserted and extracted at the reaction interface on the primary particle surface on the hollow side inside the particles, so Li ions , the movement of electrons is not hindered, and output characteristics can be improved.

b) Outer shell In a positive electrode active material having a hollow structure, the thickness of the outer shell is preferably 5 to 45%, and preferably 8 to 38%, relative to the particle size of the secondary particles. More preferred. In terms of absolute value, it is more preferably in the range of 0.5 to 2.5 μm, particularly preferably in the range of 0.4 to 2.0 μm. If the ratio of the thickness of the outer shell is less than 5%, the strength of the secondary particles will decrease, so when handling the powder or using it as a battery positive electrode, the particles will be broken and fine particles will be generated, which will deteriorate the characteristics. make worse. On the other hand, when the ratio of the thickness of the outer shell exceeds 45%, the amount of electrolyte decreases from the grain boundaries or voids where the electrolyte can enter the hollow parts inside the particles, and the surface area that contributes to battery reactions becomes smaller. Therefore, the positive electrode resistance increases and the output characteristics deteriorate. Note that the ratio of the thickness of the outer shell to the secondary particle diameter can be determined in the same manner as for the composite hydroxide particles described above.

(2) Average particle size The positive electrode active material for a lithium ion secondary battery according to an embodiment of the present invention is adjusted to have an average particle size of preferably 3 μm to 12 μm, more preferably 3 μm to 10 μm. If the average particle size of the positive electrode active material is within this range, it is possible not only to increase the battery capacity per unit volume of a secondary battery using this positive electrode active material, but also to improve safety and output characteristics. can do. On the other hand, if the average particle diameter is less than 3 μm, the filling properties of the positive electrode active material may be reduced, and the battery capacity per unit volume may not be sufficiently increased. On the other hand, if the average particle size exceeds 15 μm, the reaction area of the positive electrode active material decreases and the interface with the electrolyte decreases, so that the output characteristics may not be sufficiently improved.

Note that the average particle size of the positive electrode active material means the volume-based average particle size (MV), similar to the above-mentioned composite hydroxide particles. It can be determined from the value.

(3) Particle size distribution When the positive electrode active material for a lithium ion secondary battery according to one embodiment of the present invention was observed at a magnification of 1000 times using a scanning electron microscope, five or more secondary particles aggregated. The proportion of aggregated particles in the number of secondary particles in the visual field is 0.7% or less, more preferably 0.4% or less. By reducing the aggregated particles, the distribution of the positive electrode active material particles in the positive electrode becomes uniform, so that the insertion and removal of Li and the flow of current can be made uniform, and the battery capacity and cycle characteristics can be improved. When the number of aggregated particles increases, the distribution of positive electrode active material particles in the positive electrode becomes uneven, making it difficult to improve the battery characteristics.

Further, [(d90-d10)/average particle size], which is an index indicating the spread of particle size distribution, is preferably 0.55 or less, more preferably 0.50 or less, and is composed of particles with an extremely narrow particle size distribution. . Such a positive electrode active material has a small proportion of fine particles and coarse particles, and a secondary battery using this material has better safety, cycle characteristics, and output characteristics.

On the other hand, when [(d90-d10)/average particle size] exceeds 0.55, the proportion of fine particles and coarse particles in the positive electrode active material increases. For example, in a secondary battery that uses a positive electrode active material with a high proportion of fine particles, the secondary battery tends to generate heat due to local reactions of the fine particles, which not only reduces safety but also Selective deterioration of particles may result in poor cycle characteristics. In addition, in a secondary battery using a positive electrode active material with a high proportion of coarse particles, a sufficient reaction area between the electrolyte and the positive electrode active material may not be secured, resulting in poor output characteristics.

On the other hand, assuming industrial scale production, it is not practical to use a cathode active material that has an extremely small [(d90-d10)/average particle size]. Therefore, in consideration of cost and productivity, the lower limit of [(d90-d10)/average particle size] is preferably about 0.25.

Note that the meanings of d10 and d90 in the index showing the spread of particle size distribution [(d90-d10)/average particle diameter] and how to obtain them are the same as for the composite hydroxide particles described above, so they will be explained here. The explanation of is omitted.

(4) Crystallite diameter The positive electrode active material for a lithium ion secondary battery according to an embodiment of the present invention preferably has a crystallite diameter of 100 nm to 160 nm, more preferably 110 nm to 150 nm. By controlling the crystallite diameter within the above range, cycle characteristics and output can be further improved.

(5) Composition The positive electrode active material for a lithium ion secondary battery according to an embodiment of the present invention has the general formula (B): Li _1+u Ni _{x Mny} Co _z M _t O ₂ (-0.05≦u≦0 .50, x+y+z+t=1, 0.3≦x≦0.80, 0.05≦y≦0.55, 0≦z≦0.4, 0≦t≦0.1, M is Nb, Mo, It can be suitably applied to a positive electrode active material represented by one or more additive elements selected from Ta, Zr, and W.

In the positive electrode active material for a lithium ion secondary battery according to an embodiment of the present invention, the value of u indicating the excess amount of lithium (Li) is preferably -0.05 or more and 0.50 or less, more preferably 0 or more and 0 or less. .50 or less, more preferably 0 or more and 0.35 or less. By regulating the value of u within the above range, it is possible to improve the output characteristics and battery capacity of a secondary battery using this positive electrode active material as a positive electrode material. On the other hand, if the value of u is less than -0.05, the positive electrode resistance of the secondary battery increases, making it impossible to improve the output characteristics. 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 high potential and high capacity of secondary batteries, and the value of x indicating its content is 0.3 or more and 0.80 or less, more preferably 0.3 or more. It shall be 0.60 or less. If the value of x is less than 0.3, the battery capacity of a secondary battery using this positive electrode active material cannot be improved. On the other hand, when the value of x exceeds 0.80, the content of other elements decreases, making it impossible to obtain the effects thereof.

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

Cobalt (Co) is an element that contributes to improving 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. If the value of z exceeds 0.4, the initial discharge capacity of a secondary battery using this positive electrode active material will be significantly reduced.

The positive electrode active material for a lithium ion secondary battery according to an embodiment of the present invention may contain an additive element M in addition to the above-mentioned metal elements in order to further improve the durability and output characteristics of the secondary battery. good. Such additive elements M include magnesium (Mg), calcium (Ca), aluminum (Al), titanium (Ti), vanadium (V), chromium (Cr), zirconium (Zr), niobium (Nb), and molybdenum. (Mo), hafnium (Hf), tantalum (Ta), lanthanum (La), and tungsten (W).

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. When the value of t exceeds 0.1, the metal elements contributing to the Redox reaction decrease, resulting in a decrease in battery capacity.

(6) Surplus Lithium In the positive electrode active material for a lithium ion secondary battery according to one embodiment of the present invention, the amount of surplus lithium (Li) is 0.8% by mass or less. The amount of excess Li can be evaluated by titrating Li eluted from the positive electrode active material. Add 10 ml of pure water to 1 g of the obtained positive electrode active material, stir for 1 minute, and add 1 mol/liter of hydrochloric acid while measuring the pH of the filtered filtrate. The amount of surplus Li is evaluated by analyzing the state of the compound, and the amount of Li calculated from the neutralization point (shoulder) of the first stage from the high alkaline side of the titration curve is defined as the amount of surplus Li. Usually, two stages of neutralization points are observed in the titration curve, with the first stage neutralization point indicating the amount of LiOH, and the second stage neutralization point indicating the amount of Li ₂ CO ₃ .

In the positive electrode active material for a lithium ion secondary battery according to an embodiment of the present invention, by setting the amount of excess Li to 0.80% by mass or less, preferably 0.75% by mass or less, it is possible to It is possible to suppress elution of Li from the positive electrode active material and suppress gelation of the paste. This makes it possible to manufacture a uniform positive electrode, improving battery capacity and cycle characteristics. In addition, the high crystallinity suppresses the elution of Li, preventing excessive extraction of lithium from the crystals of the positive electrode active material, maintaining high crystallinity and improving battery capacity and cycle characteristics. do.

(6) Specific surface area The positive electrode active material for a lithium ion secondary battery according to an embodiment of the present invention preferably has a specific surface area of 0.3 m ² /g to 5.0 m ² /g, and 0.3 m 2 /g. ² /g to 4.0 m ² /g is more preferable, and even more preferably 0.5 m ² /g to 3.0 m ² /g. A positive electrode active material having a specific surface area within this range has a large contact area with an electrolytic solution, and can significantly improve the output characteristics of a secondary battery using the positive electrode active material. On the other hand, if the specific surface area of the positive electrode active material is less than 0.3 m ² /g, it will not be possible to secure enough reaction area with the electrolyte when forming a secondary battery, and the output characteristics will not be sufficiently improved. It becomes difficult to do so. On the other hand, when the specific surface area of the positive electrode active material exceeds 4.0 m ² /g, the reactivity with the electrolytic solution becomes too high, so that thermal stability may decrease.

Note that 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 has become 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 a secondary battery is required to be approximately several microns due to the packing of the entire battery and problems with electronic conductivity. Therefore, it is necessary not only to use a high-capacity cathode active material, but also to improve the filling properties of the cathode active material to increase the capacity of the secondary battery as a whole. From this point of view, in the positive electrode active material for a lithium ion secondary battery according to an embodiment of the present invention, it is preferable that the tap density, which is an index of filling property, is 1.0 g/cm ³ or more. More preferably, it is 2 g/cm ³ or more. If the tap density is less than 1.0 g/cm ³ , the filling property is low and the battery capacity 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 about 3.0 g/cm ³ .

Note that the tapped density refers to the bulk density after a sample powder collected in a container is tapped 100 times based on JIS Z-2504, and can be measured using a shaking specific gravity meter.

<2-2. Manufacturing method of positive electrode active material for lithium ion secondary battery>
Next, a method for manufacturing a positive electrode active material for a lithium ion secondary battery according to an embodiment of the present invention will be described with reference to the drawings. As shown in FIG. 1, a method for producing a positive electrode active material for a lithium ion secondary battery according to an embodiment of the present invention includes mixing at least the above-described composite hydroxide particles with a lithium compound to obtain a lithium mixture. Step S2, a calcination step S3 of calcining the obtained lithium mixture at 750° C. to 900° C. in an oxidizing atmosphere, and a calcination step S3 of calcining the lithium mixture calcined in the calcination step S3. A positive electrode active material is synthesized by a manufacturing method comprising a firing step S5 of firing at 850° C. to 980° C. in an oxidizing atmosphere. Note that, if necessary, steps such as a heat treatment step S1 and a crushing step may be added to the above-mentioned steps. According to such a manufacturing method, the above-mentioned positive electrode active material, particularly the positive electrode active material represented by general formula (B), can be easily obtained. Each step will be explained in detail below.

(1) Heat treatment step S1
In the method for producing a positive electrode active material for a lithium ion secondary battery according to an embodiment of the present invention, a heat treatment step S1 is optionally provided before the mixing step S2, and after the composite hydroxide particles are heat treated particles. May be mixed with lithium compounds. Here, the heat-treated particles include not only composite hydroxide particles from which excess moisture has been removed in the heat treatment step S1, but also transition metal composite oxide particles (hereinafter referred to as "composite oxide particles") converted into oxides in the heat treatment step S1. Also included are particles (referred to as "particles") or mixtures thereof.

The heat treatment step S1 is a step in which excess water contained in the composite hydroxide particles is removed by heating the composite hydroxide particles to 105° C. to 750° C. and heat-treating them. Thereby, it is possible to reduce the remaining moisture to a certain amount until after the firing step S5, and it is possible to suppress variations in the composition of the obtained positive electrode active material.

The heating temperature in the heat treatment step S1 is 105°C to 750°C. If the heating temperature is less than 105° C., excess water 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., not only no further effect can be expected, but also production costs increase.

In addition, in the heat treatment step S1, it is sufficient to remove water to the extent that there is no variation in the number of atoms of each metal component in the positive electrode active material and the ratio of the number of Li atoms, so it is not necessary to remove all the composite hydroxide particles. There is no need for conversion to oxide particles. However, in order to reduce the variation in the number of atoms of each metal component and the ratio of the number of Li atoms, all composite hydroxide particles are converted to composite oxide particles by heating to 400°C or higher. It is preferable to do so. Note that the above-mentioned variations can be further suppressed by determining the metal components contained in the composite hydroxide particles under heat treatment conditions in advance by analysis and determining the mixing ratio with the lithium compound.

The atmosphere in which the heat treatment is carried out is not particularly limited, and may be any non-reducing atmosphere, but it is preferable to carry out the heat treatment in an air stream because it can be easily carried out. Further, 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, and more preferably from 5 hours to 15 hours.

(2) Mixing step S2
The mixing step S2 is a step of mixing a lithium compound with the above-described composite hydroxide particles or heat-treated particles to obtain a lithium mixture.

In the mixing step S2, the ratio of the sum of the numbers of metal atoms other than lithium in the lithium mixture (Me), specifically nickel, cobalt, manganese, and the additional element M, to the number of atoms of lithium (Li) is determined. (Li/Me) is 1:0.95 to 1:1.5, preferably 1:1.0 to 1:1.5, more preferably 1:1.0 to 1:1.35, even more preferably It is necessary to mix the composite hydroxide particles or heat-treated particles and the lithium compound so that the ratio is 1:1.0 to 1:1.2. That is, since Li/Me does not change before and after the firing step S5, the composite hydroxide particles or heat-treated particles and lithium are mixed so that the Li/Me in the mixing step S2 becomes the desired Li/Me of the positive electrode active material. It is necessary to mix the compounds.

The lithium compound used in the mixing step S2 is not particularly limited, but from the viewpoint of availability, it is preferable to use lithium hydroxide, lithium nitrate, lithium carbonate, or a mixture thereof. In particular, in consideration of ease of handling and stability of quality, it is preferable to use lithium hydroxide or lithium carbonate, and more preferably to use lithium carbonate.

It is preferable that the composite hydroxide particles or the heat-treated particles and the lithium compound are sufficiently mixed to such an extent that no fine powder is generated. If mixing is insufficient, Li/Me may vary between individual particles, and sufficient battery characteristics may not be obtained. Note that a general mixer can be used for mixing. For example, a shaker mixer, Loedige mixer, Julia mixer, V blender, etc. can be used.

(3) Calcining process S3
The lithium mixture formed in the mixing step S2 is calcined at 550°C to 800°C, preferably 580°C to 720°C in an oxidizing atmosphere. Thereby, lithium can be sufficiently diffused and reacted in the composite hydroxide particles or the heat-treated particles, and sintering agglomeration of the secondary particles in the next firing step S5 can be suppressed. That is, by calcination, the lithium compound is consumed by reaction with the composite hydroxide particles or the heat-treated particles, and the amount of lithium compound remaining after calcination is significantly reduced. In the next firing step S5, in order to improve the crystallinity of the lithium-transition metal composite oxide particles, it is necessary to hold them at a high temperature. During this holding, the lithium compound melts and the secondary particles of the lithium-transition metal composite oxide are formed. Sintering agglomeration progresses rapidly. By significantly reducing the remaining lithium compound through calcination, sintering agglomeration of secondary particles can be suppressed.

Note that the holding time at the above temperature is preferably 1 hour to 10 hours, more preferably 3 hours to 6 hours. Further, the atmosphere in the calcination step S3 is preferably an oxidizing atmosphere, similar to the later-described firing step S5, and more preferably an atmosphere with an oxygen concentration of 18% by volume to 100% by volume.

In the method for producing a positive electrode active material for a lithium ion secondary battery according to an embodiment of the present invention, the half width of the (003) plane of the calcined powder obtained by calcining is 0.45° or more, preferably 0. It is 50° or more. As a result, calcined powder with relatively low crystallinity, ie, lithium transition metal composite oxide particles, is obtained, and highly crystalline lithium transition metal composite oxide particles are obtained in the subsequent firing step S5. The (003) plane half width of the calcined powder is preferably 0.80° or less, more preferably 0.75° or less, from the perspective of reducing the amount of lithium carbonate remaining in the calcined powder. preferable. The half value width can be easily controlled by adjusting the amount of oxygen supplied to the calcination step S3, the temperature and time at which it is held. For example, by reducing the amount of oxygen supplied by reducing the flow rate of the atmospheric gas, it is possible to delay the formation reaction of the lithium-transition metal composite oxide and cause the lithium carbonate to react while suppressing a decrease in the half value width.

In the positive electrode active material for a lithium ion secondary battery according to an embodiment of the present invention, by particularly controlling the above-mentioned half width, when the positive electrode active material for a lithium ion secondary battery is configured into a secondary battery, , battery capacity and cycle characteristics can be further improved.

Furthermore, the carbon content of the particles after calcination is controlled to preferably be 1.0% by mass or less, preferably 0.8% by mass or less, and more preferably 0.30% by mass to 0.75% by mass. . Thereby, it is possible to further reduce the remaining lithium compound, further suppress sintering agglomeration of the secondary particles of the lithium transition metal composite oxide in the firing step S5, and to sufficiently improve crystallinity. The carbon content can be easily controlled by adjusting the temperature and time of calcination.

(4) Pre-firing crushing step S4
In the pre-firing crushing step S4, the lithium mixture calcined in the calcining step S3 is crushed before the firing step S5 described below. Since the calcination step S3 is carried out at a high temperature of 750°C to 900°C in an oxidizing atmosphere, the lithium composite oxide particles obtained by the calcination step S3 may have coarse particles of LiOH etc. that are not sufficiently loosened. Since areas with high lithium concentration tend to aggregate, agglomeration or slight sintering may occur. In such a case, if the firing is performed at a high temperature as it is, the sintering will become strong, and even after the post-firing crushing step performed after the firing step S5, aggregated particles will still remain. Therefore, in the present embodiment, the average particle size and particle size distribution of the positive electrode active material obtained by crushing the aggregates or sintered bodies of the calcined lithium composite oxide particles generated in the calcining step S3 can be adjusted to a suitable range.

In this manner, in this embodiment, the lithium mixture calcined in the calcining step S3 is crushed to suppress sintering agglomeration of the secondary particles constituting the positive electrode active material after the sintering step. Note that the crushing referred to here refers to the process of applying mechanical energy to an agglomerate of multiple secondary particles generated due to sinter necking between secondary particles during calcination to destroy the secondary particles themselves. It means an operation that loosens aggregates by separating them without destroying them. Moreover, as a method of crushing, a known means can be used, and for example, a pin mill, a hammer mill, etc. 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) Firing process S5
The firing step S5 is a step of increasing the crystallinity of the calcined powder obtained by calcining the lithium mixture under predetermined conditions to obtain highly crystalline lithium transition metal composite oxide particles.

Composite hydroxide particles are secondary particles that have a center portion formed by agglomeration of fine primary particles, and an outer peripheral portion formed by aggregation of the plate-shaped primary particles outside the center portion. In some cases, in this calcination step S5 and the previous calcination step S3, the center and high-density layer of the composite hydroxide particles and heat-treated particles undergo sintering shrinkage to form an agglomerated portion of primary particles in the positive electrode active material. do. On the other hand, since the low-density layer is composed of fine primary particles, it begins to sinter at a lower temperature than the center and high-density layer, which are composed of plate-like single particles larger than the fine primary particles. Furthermore, the amount of shrinkage in the low-density layer is greater than that in the center and the high-density layer. Therefore, the fine primary particles constituting the low-density layer shrink toward the center where sintering progresses slowly and toward the high-density layer, and a space of an appropriate size is formed. At this time, the high-density part within the low-density layer shrinks by sintering while maintaining connection with the center and the high-density layer, so in the resulting positive electrode active material, the outer shell part and the agglomerated part are electrically electrical conduction, and a sufficient cross-sectional area of the path can be ensured. As a result, the internal resistance of the positive electrode active material is significantly reduced, and when a secondary battery is constructed, it becomes possible to improve the output characteristics without impairing the battery capacity or cycle characteristics.

The particle structure of such a positive electrode active material is basically determined according to the particle structure of the composite hydroxide particles that are the precursor, but it may be affected by its composition, firing conditions, etc. It is preferable to conduct a preliminary test and then adjust each condition as appropriate to obtain the desired structure.

Note that the furnace used in the firing step S5 is not particularly limited, and may be any furnace that 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. Regarding this point, the same applies to the furnace used in the heat treatment step S1 and the calcination step S3.

a) Firing temperature The firing temperature of the calcined powder needs to be higher than the calcining temperature and 760°C to 1050°C, preferably 790°C to 1000°C. If the firing temperature is less than 760°C, lithium will not diffuse sufficiently into the composite hydroxide particles or heat-treated particles, and excess lithium or unreacted composite hydroxide particles or heat-treated particles may remain, or the resulting lithium composite may The crystallinity of the oxide particles becomes insufficient. On the other hand, when the firing temperature exceeds 1050° C., lithium composite oxide particles are violently sintered, abnormal grain growth is caused, and the proportion of irregularly shaped coarse particles increases.

Further, the temperature increase rate in the firing step S5 is preferably 2° C./min to 10° C./min, more preferably 5° C./min to 10° C./min. Furthermore, during the firing step S5, it is preferable to maintain the temperature near the melting point of the lithium compound for preferably 1 to 5 hours, more preferably 2 to 5 hours. Thereby, the crystallinity of the calcined powder can be improved more uniformly.

b) Firing time Among the firing times, the holding time at the above-mentioned firing temperature is preferably at least 1 hour, more preferably from 2 hours to 24 hours. If the holding time at the firing temperature is less than 2 hours, the resulting lithium composite oxide particles may have insufficient crystallinity.

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 3°C/min to 7°C/min. By controlling the cooling rate within such a range, it is possible to ensure productivity and prevent equipment such as saggers from being damaged due to rapid cooling.

c) Firing atmosphere The atmosphere during firing is preferably an oxidizing atmosphere, more preferably an atmosphere with an oxygen concentration of 18% to 100% by volume, and a mixed atmosphere of oxygen and an inert gas with the above oxygen concentration. It is particularly preferable that That is, the firing is preferably performed 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.

In the firing step S5, the material is held in an oxidizing atmosphere at a temperature range of ±50°C, the melting point of the lithium compound, for 1 to 5 hours, and then raised to a temperature of 760°C to 980°C, held for 2 to 24 hours, and fired. This is particularly preferred. The melting point of a lithium compound ±50°C is a temperature range of ±50°C of the melting point of each lithium compound, although the melting point varies depending on the lithium compound.

(6) Post-firing crushing step S6
The lithium composite oxide particles obtained in the firing step S5 may be agglomerated or slightly sintered. In such a case, it is preferable to crush the aggregate or sintered body of 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. Note that crushing is a process in which mechanical energy is applied to an aggregate consisting of multiple secondary particles that is generated due to sinter necking between secondary particles during firing, without destroying the secondary particles themselves. It means the operation of separating and loosening aggregates.

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

<3. Lithium ion secondary battery>
The positive electrode active material for a lithium ion secondary battery according to an embodiment of the present invention is not limited to the secondary battery used, but can be suitably used, for example, in a lithium ion secondary battery. A lithium ion secondary battery includes the same constituent members as a general lithium ion secondary battery, such as a positive electrode, a negative electrode, a separator, and a nonaqueous electrolyte. Note that the embodiments described below are merely examples, and the lithium ion secondary battery of the present invention can be applied to forms with various changes and improvements based on the embodiments described in this specification. It is also possible.

(1) Components a) Positive electrode Using the above-described positive electrode active material for a lithium ion secondary battery, a positive electrode for a lithium ion secondary battery is produced, for example, as follows.

First, a conductive material and a binder are mixed with the positive electrode active material of the present invention, and if necessary, activated carbon and a solvent for adjusting viscosity are added, and the mixture is kneaded to prepare a positive electrode mixture paste. At this time, the mixing ratio of each component in the positive electrode mixture paste is also an important factor that determines the performance of the lithium ion secondary battery. For example, when the solid content of the positive electrode mixture excluding the solvent is 100 parts by mass, the content of the positive electrode active material is 60 parts by mass to 95 parts by mass, similar to the positive electrode of a general lithium ion secondary battery. The content of the conductive material can be 1 part by mass to 20 parts by mass, and the content of the binder can be 1 part by mass to 20 parts by mass.

The obtained positive electrode mixture paste is applied to the surface of a current collector made of aluminum foil, for example, and dried to scatter the solvent. If necessary, pressure may be applied using a roll press or the like to increase the electrode density. In this way, 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 battery production. Note that the method for producing the positive electrode is not limited to the one exemplified above, 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 in binding the active material particles, and includes, for example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluororubber, ethylene propylene diene rubber, styrene butadiene, cellulose resin, or polyacrylic resin. Acids can be used.

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

b) Negative electrode Metallic lithium, lithium alloy, etc. can be used for the negative electrode. In addition, a negative electrode mixture made by mixing a binder with a negative electrode active material that can absorb and deintercalate lithium ions and adding an appropriate solvent to form a paste is applied to the surface of a metal foil current collector such as copper. , dried and compressed to increase the electrode density if necessary.

Examples of negative electrode active materials include materials containing lithium such as metallic lithium and lithium alloys, natural graphite that can absorb and desorb lithium ions, fired organic compounds such as artificial graphite and phenol resin, and carbon materials such as coke. Powder can be used. In this case, as the negative electrode binder, a fluororesin such as PVDF can be used as in the positive electrode, and as the solvent for dispersing these active materials and the binder, an organic resin such as N-methyl-2-pyrrolidone can be used. Solvents can be used.

c) Separator The separator is placed 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 or polypropylene having many fine pores can be used, but there is no particular limitation as long as it has the above-mentioned functions.

d) Non-aqueous electrolyte The non-aqueous electrolyte may be one in which a lithium salt as a supporting salt is dissolved in an organic solvent. Further, as the non-aqueous electrolyte, an ionic liquid in which a lithium salt is dissolved may be used. Note that the ionic liquid refers to a salt that is composed of cations and anions other than lithium ions and remains in 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, linear carbonates such as diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate and dipropyl carbonate, and also tetrahydrofuran and 2-methyltetrahydrofuran. and ether compounds such as dimethoxyethane, sulfur compounds such as ethylmethylsulfone and butane sultone, and phosphorus compounds such as triethyl phosphate and trioctyl phosphate, etc., may be used alone or in combination of two or more. can.

As the supporting salt, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiN(CF ₃ SO ₂ ) ₂ , complex salts thereof, and the like can be used. Furthermore, the nonaqueous electrolyte may contain a radical scavenger, a surfactant, a flame retardant, and the like.

Furthermore, a solid electrolyte may be used as the non-aqueous electrolyte. A solid electrolyte has the property of being able to withstand high voltage. Examples of solid electrolytes include inorganic solid electrolytes and organic solid electrolytes. As the inorganic solid electrolyte, oxide-based solid electrolytes, sulfide-based solid electrolytes, etc. are used.

The oxide-based solid electrolyte is not particularly limited, and any material that contains oxygen (O) and has lithium ion conductivity and electronic insulation can be used. Examples of oxide _- based solid electrolytes include lithium _phosphate ( _{Li 3} PO _{4 ) , Li 3} PO ₄ N _X , _{LiBO 2 N} PO ₄ , Li ₄ SiO ₄ -Li ₃ VO ₄ , Li ₂ O-B ₂ O ₃ -P ₂ O ₅ , Li ₂ O-SiO ₂ , Li ₂ O-B ₂ O ₃ -ZnO, Li _1+X Al _X Ti _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 3 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 Examples include P _0.4 O ₄ and the like.

The sulfide-based solid electrolyte is not particularly limited, and any material that contains sulfur (S) and has lithium ion conductivity and electronic insulation can be used. Examples of the sulfide solid electrolyte 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.

Note that as the inorganic solid electrolyte, other than those mentioned above may be used, for example, Li ₃ N, LiI, Li ₃ N-LiI-LiOH, etc. may be used.

The organic solid electrolyte is not particularly limited as long as it is a polymer compound that exhibits ionic conductivity, and for example, polyethylene oxide, polypropylene oxide, copolymers thereof, etc. can be used. Moreover, the organic solid electrolyte may contain a supporting salt (lithium salt).

(2) Lithium ion secondary battery The lithium ion secondary battery of the present invention, which is composed of the above positive electrode, negative electrode, separator, and non-aqueous electrolyte, can be formed into various shapes such as a cylindrical shape and a stacked shape.

Regardless of the shape, the positive electrode and negative electrode are laminated with a separator in between to form an electrode body, the obtained electrode body is impregnated with a non-aqueous electrolyte, and the positive electrode current collector is connected to the outside. Connections are made between the positive electrode terminal and between the negative electrode current collector and the negative electrode terminal communicating with the outside using current collection leads, and the battery case is sealed to complete a lithium ion secondary battery.

(3) Characteristics of lithium ion secondary battery As described above, the lithium ion secondary battery according to one embodiment of the present invention uses the positive electrode active material of the present invention as a positive electrode material, and therefore has battery capacity and output characteristics. and excellent cycle characteristics. Moreover, it can be said that it is superior in terms of thermal stability and safety when compared with secondary batteries using conventional positive electrode active materials made of lithium-nickel composite oxide particles.

(4) Applications As mentioned above, the lithium ion secondary battery according to an embodiment of the present invention has excellent battery capacity, output characteristics, and cycle characteristics, and is used in small portable electronic devices that require these characteristics at a high level. It can be suitably used as a power source for devices (notebook personal computers, mobile phones, etc.). In addition, the lithium ion secondary battery of the present invention has excellent safety, and not only can it be made smaller and have higher output, but also can simplify the expensive protection circuit, which limits the installation space. It can also be suitably used as a power source for transportation equipment that receives the battery.

Hereinafter, the present invention will be explained in detail using Examples and Comparative Examples. In the Examples and Comparative Examples below, unless otherwise specified, each sample of reagent special grade manufactured by Wako Pure Chemical Industries, Ltd. was used to prepare the composite hydroxide particles and the positive electrode active material. In addition, throughout the nucleation process and particle growth process, the pH value of the reaction aqueous solution is measured by a pH controller (manufactured by Nisshin Rika, NPH-690D), and based on this measurement value, the supply amount of the sodium hydroxide aqueous solution is adjusted. In this way, the fluctuation width of the pH value of the reaction aqueous solution in each step was controlled within the range of ±0.2.

(Example 1)
(Production of transition metal composite hydroxide particles)
(Nucleation process)
First, a reaction tank (34 L) was filled with water up to half its volume, and the temperature inside the tank was set at 40° C. while stirring. At this time, the inside of the reaction tank was set to an atmospheric atmosphere (oxygen concentration: 21% by volume). Add appropriate amounts of 25% by mass sodium hydroxide aqueous solution and 25% by mass aqueous ammonia to the water in this reaction tank, and adjust the pH value of the reaction solution in the tank to 13.0 based on the liquid temperature of 25°C. did. Furthermore, the ammonia concentration in the reaction solution was adjusted to 10 g/L to obtain a pre-reaction aqueous solution.

At the same time, nickel sulfate, cobalt sulfate, manganese sulfate, and zirconium sulfate were added to water so that the molar ratio of each metal element was Ni:Mn:Co:Zr=33.1:33.1:33.1:0.2. to prepare a 1.8 mol/L raw material aqueous solution.

This mixed aqueous solution was added to the pre-reaction aqueous solution in the reaction tank at a rate of 88 ml/min to form a reaction aqueous solution. At the same time, 25% by mass aqueous ammonia and 25% by mass aqueous sodium hydroxide solution were also added to this aqueous reaction solution at a constant rate, and while the ammonia concentration in the aqueous reaction solution (aqueous solution for nucleation) was maintained at the above value, the pH was adjusted. Nucleation was performed by crystallizing for 2 minutes and 30 seconds while controlling the pH value to 13.0 (nucleation pH value).

(Particle growth process)
After the nucleation is completed, the supply of all aqueous solutions is temporarily stopped, and sulfuric acid is added to adjust the pH value to 11.6 based on the liquid temperature of 25°C. Formed. To the reaction aqueous solution (particle growth aqueous solution), the supply of the raw material aqueous solution and the 25 mass% sodium hydroxide aqueous solution was restarted, and an additional sodium tungstate aqueous solution was supplied as the raw material aqueous solution, and the ammonia concentration was raised to the above level with 25 mass% ammonia water. The pH value was maintained at the above value, crystallization was continued, and particle growth was performed. The concentration and flow rate of the sodium tungstate aqueous solution were adjusted to match the composition. After 30 minutes of particle growth, the supply of liquid was once stopped, and nitrogen gas was allowed to flow at 5 L/min until the oxygen concentration in the reaction tank became a non-oxidizing atmosphere of 0.2% by volume or less. Thereafter, the supply of the raw material aqueous solution and the sodium tungstate aqueous solution was restarted, and crystallization was performed for a total of 2 hours from the start of growth while maintaining the ammonia concentration and pH value.

When the inside of the reaction tank became full of liquid, crystallization was stopped, stirring was stopped, and the reactor was left standing to promote precipitation of the product. After that, half of the supernatant liquid was extracted from the reaction tank, and crystallization was restarted. After crystallization was performed for 2 hours (4 hours in total), crystallization was terminated.

Then, the product was washed with water, filtered, and dried to obtain composite hydroxide particles. Note that the above-mentioned switching from the atmospheric atmosphere to the nitrogen atmosphere was performed at a time point of 12.5% of the entire particle growth process time from the start of the particle growth process.

In the above crystallization, the pH was controlled by adjusting the supply flow rate of the sodium hydroxide aqueous solution using a pH controller, and the fluctuation range was within a range of 0.2 above and below the set value.

(Analysis of composite hydroxide)
A sample of the obtained composite hydroxide was dissolved in an inorganic acid and then chemically analyzed by ICP emission spectroscopy, and the composition was found to be Ni _0.331 Mn _0.331 Co _0.331 Zr _{0. 002} W _0.005 (OH) _2+a (0≦a≦0.5).

In addition, for this composite hydroxide, the average particle size and particle size distribution [(d90-d10)/average particle size] values were measured using a laser diffraction scattering particle size distribution analyzer (Microtrack HRA, manufactured by Nikkiso Co., Ltd.). It was calculated from the volume integrated value measured using As a result, the average particle size was 4.5 μm, and the [(d90-d10)/average particle size] value was 0.48.

Next, the obtained composite hydroxide particles were observed by SEM (scanning electron microscope S-4700 manufactured by Hitachi High-Technologies Corporation) (magnification: 1000 times), and the composite hydroxide particles were found to be It was confirmed that the particles were approximately spherical in shape and the particle size was approximately uniform.

In addition, when a sample of the obtained composite hydroxide particles was embedded in resin and subjected to cross-section polisher processing, SEM observation results were performed at a magnification of 10,000 times, and the composite hydroxide particles were is composed of secondary particles, and the secondary particles have a central part consisting of needle-shaped, flaky fine primary particles (particle size approximately 0.3 μm), and an outer part of the central part that is larger than the fine primary particles. It was confirmed that the outer peripheral portion was composed of plate-shaped primary particles (particle size approximately 0.6 μm). The thickness of the outer shell portion relative to the secondary particle diameter was determined from SEM observation of this cross section to be 12%.

(Manufacture of positive electrode active material)
Lithium hydroxide was weighed and mixed with the composite hydroxide particles so that Li/Me=1.12 to prepare a lithium mixture. The mixing was performed using a shaker mixer device (TURBULA Type T2C, manufactured by Willy & Backofen (WAB)).

The obtained lithium mixture was calcined at 650° C. for 4 hours in the atmosphere (oxygen: 21% by volume) using a furnace capable of controlling the atmosphere. Atmospheric gas was supplied to the furnace at a rate of 5 L/min. The obtained calcined powder had a (003) half width of 0.55° and a carbon content of 0.71% by mass. After crushing the calcined powder, the temperature was increased at a rate of 5° C./min and fired at 970° C. for 3 hours, and after cooling, the powder was crushed to obtain a positive electrode active material.

(Analysis of positive electrode active material)
When the particle size distribution of the obtained positive electrode active material was measured in the same manner as the composite hydroxide particles, the average particle size was 4.9 μm, and the [(d90-d10)/average particle size] value was 0. It was .50.

In addition, when the positive electrode active material was subjected to SEM observation and cross-sectional SEM observation in the same manner as the composite hydroxide particles, the obtained positive electrode active material was approximately spherical, and the particle size was almost uniform. This was confirmed. Further, when observed using a scanning electron microscope at a magnification of 1000 times, the ratio of the number of aggregated particles in which five or more secondary particles aggregated was 0.7% or less.

The amount of eluted Li was determined from the neutralization point that appeared by adding 10 ml of pure water to 1 g of the positive electrode active material, stirring for 1 minute, and then adding 1 mol/liter of hydrochloric acid while measuring the pH of the filtered filtrate. . The amount of eluted Li was 0.07% by mass.

The specific surface area of the obtained cathode active material was measured using a flow-type gas adsorption specific surface area measuring device (Multisorb, manufactured by Yuasa Ionics Co., Ltd.), and the tap density was measured using a tapping machine (KRS-406, manufactured by Kuramochi Scientific Instruments Manufacturing Co., Ltd.). , were measured respectively. As a result, it was confirmed that the specific surface area was 1.5 m ² /g and the tap density was 1.20 g/cm ³ .

In addition, the obtained positive electrode active material was analyzed by powder X-ray diffraction using Cu-Kα rays using an X-ray diffraction device (Panalytical, X'Pert PRO), and the crystal structure of the positive electrode active material was was confirmed to consist of a single phase of hexagonal layered crystal lithium nickel manganese composite oxide. From the obtained X-ray diffraction pattern, the (003) plane crystallite diameter using Scherrer's equation was found to be 115 nm.

Further, analysis using an ICP emission spectrometer revealed that this positive electrode active material was expressed by the general formula: Li _1.12 Ni _0.331 Mn _0.331 Co _0.331 Zr _0.002 W _0.005 O ₂ It was confirmed that this is the case.

(Manufacture of coin-type batteries and evaluation of battery characteristics)
52.5 mg of a positive electrode active material for a non-aqueous electrolyte secondary battery, 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 a diameter of 11 mm and a thickness of 100 μm. Positive electrode 1 (evaluation electrode) shown in was produced. The produced positive electrode 1 was dried in a vacuum dryer at 120° C. for 12 hours. Then, using this positive electrode 1, a 2032 type coin-shaped battery 10 was manufactured in a glove box with an Ar atmosphere whose dew point was controlled at -80°C.

For the negative electrode 2, we used a negative electrode sheet in which copper foil was coated with graphite powder with an average particle size of about 20 μm punched out into a disc shape of 14 mm in diameter and polyvinylidene fluoride, and 1M LiPF ₆ was used as the electrolyte. A mixed solution of equal amounts of ethylene carbonate (EC) and diethyl carbonate (DEC) (manufactured by Toyama Pharmaceutical Co., Ltd.) was used. As the separator 3, a polyethylene porous film with a film thickness of 25 μm was used. Further, the coin-shaped battery 10 had a gasket 4 and a wave washer 5, and was assembled into a coin-shaped battery with a positive electrode can 6 and a negative electrode can 7. The initial discharge capacity and positive electrode resistance, which indicate the performance of the manufactured coin-type battery 10, were evaluated as follows.

a) Initial discharge capacity The initial discharge capacity is determined by setting the current density to the positive electrode to 0.1 mA/cm ² after the coin-type battery 10 is left for about 24 hours after manufacturing and the open circuit voltage OCV (Open Circuit Voltage) is stabilized. The initial discharge capacity was defined as the capacity when the battery was charged to a cutoff voltage of 4.3V and discharged to a cutoff voltage of 3.0V after a 1-hour rest.

b) Positive electrode resistance In addition, the positive electrode resistance is measured by the AC impedance method using a frequency response analyzer and a potentiogalvanostat (manufactured by Solartron, 1255B) after charging the coin-type battery 10 at a charging potential of 4.1 V at 25°C. Then, the Nyquist plot shown in FIG. 3 is obtained. This Nyquist plot is expressed as the sum of characteristic curves showing the solution resistance, the negative electrode resistance and its capacity, and the positive electrode resistance and its capacity, so based on this Nyquist plot, a fitting calculation is performed using an equivalent circuit, and the positive electrode resistance is The value of was calculated.

Table 1 shows the characteristics of the composite hydroxide and calcined powder obtained in this example, and Table 2 shows the characteristics of the positive electrode active material and the evaluation of the coin-type battery 10 manufactured using this positive electrode active material. show. Furthermore, Tables 1 and 2 show the same contents for Examples 2 to 6 and Comparative Example 1 below.

(Example 2)
In the particle growth process, the flow rate of the sodium tungstate aqueous solution was adjusted so that the concentration of tungsten in the non-oxidizing atmosphere was 20% of the concentration of the additive element (tungsten) in the raw material aqueous solution in the oxidizing atmosphere. In the same manner as in Example 1, a positive electrode active material for a non-aqueous electrolyte secondary battery was obtained and evaluated. It was confirmed that the composition of the obtained positive electrode active material was represented by Li _1.12 Ni _0.331 Mn _0.331 Co _0.331 Zr _0.002 W _0.005 O ₂ .

(Example 3)
A positive electrode active material for a non-aqueous electrolyte secondary battery was obtained and evaluated in the same manner as in Example 1, except that the calcination time was 8 hours.

(Example 4)
A positive electrode active material for a non-aqueous electrolyte secondary battery was obtained and evaluated in the same manner as in Example 1, except that the calcination temperature was 700°C and the firing temperature was 990°C.

(Example 5)
A positive electrode active material for a non-aqueous electrolyte secondary battery was obtained and evaluated in the same manner as in Example 1, except that the calcination temperature was 600°C and the firing temperature was 980°C.

(Example 6)
A positive electrode active material for a non-aqueous electrolyte secondary battery was obtained and evaluated in the same manner as in Example 1, except that during firing the calcined powder was held at a temperature near the melting point of the lithium compound for 2 hours in the firing step S5. went.

(Comparative example 1)
A non-aqueous electrolyte secondary A battery positive electrode active material was obtained and evaluated.

(evaluation)
In the transition metal composite hydroxide particles and the positive electrode active material for a lithium ion secondary battery according to an embodiment of the present invention, both the positive electrode active materials had little aggregation and had low surplus lithium. Therefore, coin-type batteries using these positive electrode active materials for lithium ion secondary batteries have high initial discharge capacity and low positive electrode resistance, and are batteries with excellent characteristics. Therefore, it was possible to provide a positive electrode active material that can further improve battery capacity and cycle characteristics. Further, the present invention was able to provide a secondary battery with further improved battery capacity and cycle characteristics using this positive electrode active material.

Although each embodiment and each example of the present invention has been described in detail as above, those skilled in the art will appreciate that many modifications can be made without substantially departing from the novelty and effects of the present invention. , it will be easy to understand. Therefore, all such modifications are included within the scope of the present invention.

For example, a term that appears at least once in the specification or drawings together with a different term with a broader or synonymous meaning may be replaced by that different term anywhere in the specification or drawings. In addition, the method for manufacturing a positive electrode active material for a lithium ion secondary battery, the positive electrode active material for a lithium ion secondary battery, and the structure and operation of the lithium ion secondary battery are also limited to those described in each embodiment and each example of the present invention. However, various modifications are possible.

S1 Heat treatment process, S2 Mixing process, S3 Calcination process, S4 Pre-firing crushing process, S5 Firing process, S6 Post-baking crushing process 1 Positive electrode (evaluation battery), 2 Negative electrode, 3 Separator, 4 Gasket, 5 Wave washer , 6 positive electrode can, 7 negative electrode can, 10 coin type battery

Claims (8)

A method for producing a positive electrode active material for a lithium ion secondary battery, the method comprising:
General formula (A): Ni _{x Mny} Co _z M _t (OH) _2+a (x+y+z+t=1, 0.3≦x≦0.8, 0.05≦y≦0.55, 0≦z≦0.4 , 0≦t≦0.1, 0≦a≦0.5, M is one or more additive elements selected from Nb, Mo, Ta, Zr, and W), indicating a spread of particle size distribution A mixing step of forming a lithium mixture by mixing transition metal composite hydroxide particles whose index [(d90-d10)/MV] is 0.65 or less and a lithium compound;
a calcination step of calcining the lithium mixture formed in the mixing step in an oxidizing atmosphere to obtain a calcined powder having a (003) plane half width of 0.45° or more;
a firing step of firing the calcined powder obtained in the calcining step in an oxidizing atmosphere;
A method for producing a positive electrode active material for a lithium ion secondary battery, comprising: The positive electrode for a lithium ion secondary battery according to claim 1, wherein in the calcination step, the carbon content of the calcined powder after the calcination step is controlled to be 1.0% by mass or less. Method for producing active material. The production of a positive electrode active material for a lithium ion secondary battery according to claim 1 or 2, wherein the calcination step is performed by holding and firing at 550° C. to 800° C. for 1 to 10 hours in an oxidizing atmosphere. Method. The positive electrode for a lithium ion secondary battery according to any one of claims 1 to 3, wherein the firing step is performed by holding and firing at 760° C. to 980° C. for 2 to 24 hours in an oxidizing atmosphere. Method for producing active material. In the firing step, the lithium compound is maintained at a temperature within the melting point of the lithium compound ±50°C for 1 to 5 hours in an oxidizing atmosphere, and then the temperature is raised to 760°C to 980°C for 2 to 24 hours and fired. The method for producing a positive electrode active material for a lithium ion secondary battery according to any one of claims 1 to 4. The lithium ion powder according to any one of claims 1 to 5, further comprising a pre-calcination crushing process of crushing the calcined powder calcined in the calcining process, before the calcining process. A method for producing a positive electrode active material for a next battery. In the mixing step, the lithium mixture is mixed so that the ratio of the sum of the atoms of metals other than lithium contained in the lithium mixture to the number of lithium atoms is 1:0.95 to 1:1.5. The method for producing a positive electrode active material for a lithium ion secondary battery according to any one of claims 1 to 6, characterized in that the positive electrode active material for a lithium ion secondary battery is adjusted to: The lithium ion dihydride according to any one of claims 1 to 7, further comprising a heat treatment step of heat-treating the transition metal composite hydroxide particles at 105° C. to 750° C. before the mixing step. A method for producing a positive electrode active material for a next battery.