JP2020129498A - Method for producing positive electrode active material for lithium ion secondary battery, positive electrode active material for lithium ion secondary battery, and lithium ion secondary battery - Google Patents

Abstract

To provide a method for producing a positive electrode active material for lithium ion secondary batteries, the positive electrode active material being high in nickel ratio and excellent in cycle characteristics.SOLUTION: There is provided a method for producing a positive electrode active material for lithium ion secondary batteries. The method includes: a first step of preparing a raw material mixture by mixing an alkaline solution containing a tungsten compound and a lithium metal composite oxide which has a layered crystal structure and contains, by the ratio of the amount of substance, Li, Ni, Co and an element M in a ratio of Li:Ni:Co:M=z:(1-x-y):x:y (where, 0≤x<0.10, 0≤y<0.10, 0≤x+y<0.10 and 0.97≤z≤1.20 are satisfied, and the element M represents at least one element selected from among Mn, V, Mg, Mo, Nb, Ti and Al); and a second step of subjecting the raw material mixture to heat treatment. The tungsten concentration of the alkaline solution containing a tungsten compound is 0.05 mol/L or more and 1.8 mol/L or less.SELECTED DRAWING: None

Description

The present invention relates to 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.

In recent years, with the spread of portable electronic devices such as mobile phones and notebook computers, development of small and lightweight non-aqueous electrolyte secondary batteries having high energy density has been strongly desired. Further, development of a high-power secondary battery as a battery for an electric vehicle such as a hybrid vehicle is strongly desired.

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

Lithium ion secondary batteries are currently being actively researched and developed. Among them, lithium ion secondary batteries using a layered or spinel type lithium metal composite oxide as a positive electrode material have a high voltage of 4V class. Therefore, it is being put to practical use as a battery having a high energy density.

The positive electrode materials that have been proposed so far include a lithium cobalt composite oxide (LiCoO ₂ ) that is relatively easy to synthesize, a lithium nickel composite oxide (LiNiO ₂ ) that uses nickel that is cheaper than cobalt, and lithium nickel. Examples thereof include cobalt manganese composite oxide (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ), lithium manganese composite oxide using manganese (LiMn ₂ O ₄ ), and the like.

Lithium-ion secondary batteries are used for many applications such as electric vehicles as described above, so in recent years, lithium-ion secondary batteries have been required to have higher capacity and lower cost. Has been. Therefore, as the positive electrode material, a lithium metal composite oxide having a high nickel ratio can be obtained, which has a high capacity when used in a lithium ion secondary battery and has a lower cost than nickel as a main component as compared with cobalt. It has been attracting attention in recent years.

For example, Patent Document 1 discloses positive electrode active material particles represented by Li _a Ni _x Co _y M _z O ₂ . In the above chemical formula, M is aluminum (Al), manganese (Mn), chromium (Cr), iron (Fe), vanadium (V), magnesium (Mg), titanium (Ti), zirconium (Zr), niobium. (Nb), molybdenum (Mo), tungsten (W), copper (Cu), zinc (Zn), gallium (Ga), indium (In), tin (Sn), lanthanum (La), cerium (Ce). It is one or more metal elements selected from the group, and a, x, y, z are 0.20≦a≦1.20, 0.80≦x<1.00, 0.00< The values are in the range of y≦0.20 and 0.00≦z≦0.10, and there is a relationship of x+y+z=1 between x, y and z.

JP, 2006-100101, A

However, when a lithium metal composite oxide having a high nickel ratio is used in a lithium ion secondary battery, there is a problem that cycle characteristics are deteriorated.

Therefore, in view of the problems of the above-mentioned conventional techniques, it is an object of one aspect of the present invention to provide a method for producing a positive electrode active material for a lithium ion secondary battery having a high nickel ratio and excellent cycle characteristics.

According to an aspect of the present invention for solving the above problems,
Lithium (Li), nickel (Ni), cobalt (Co), and element M (M) in the ratio of the amount of substances, Li:Ni:Co:M=z:(1-x-y):x:y. (However, 0≦x<0.10, 0≦y<0.10, 0≦x+y<0.10, 0.97≦z≦1.20, and the element M is Mn, V, Mg, Mo, A lithium metal composite oxide containing at least one element selected from Nb, Ti and Al) and having a layered crystal structure is mixed with an alkali solution containing a tungsten compound to obtain a raw material mixture. The first step,
A second step of heat treating the raw material mixture,
A method for producing a positive electrode active material for a lithium ion secondary battery, wherein the tungsten concentration of the alkali solution containing the tungsten compound is 0.05 mol/L or more and 1.8 mol/L or less.

According to one aspect of the present invention, it is possible to provide a method for producing a positive electrode active material for a lithium ion secondary battery, which has a high nickel ratio and is excellent in cycle characteristics.

It is sectional drawing of the coin type battery used for battery evaluation.

Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings, but the present invention is not limited to the following embodiments, and the following embodiments without departing from the scope of the present invention Can be variously modified and replaced.
(1) Positive Electrode Active Material for Lithium Ion Secondary Battery The positive electrode active material for the lithium ion secondary battery of the present embodiment (hereinafter, also simply referred to as “positive electrode active material”) is lithium (Li), nickel (Ni), Cobalt (Co), element M (M), and tungsten (W), in the ratio of the amount of materials, Li:Ni:Co:M:W=d:(1-ab):a:b:c It can be contained in a ratio. Note that a, b, c, d are 0≦a<0.10, 0≦b<0.10, 0.001≦c≦0.03, 0≦a+b<0.10, 0.97≦. It is preferable to satisfy d≦1.20. Further, the element M can be at least one element selected from Mn, V, Mg, Mo, Nb, Ti and Al.

In the positive electrode active material of the present embodiment, a representing the content ratio of cobalt is more preferably 0≦a≦0.06, and b representing the content ratio of the element M is 0≦b≦0.06. Is more preferable. Further, c, which represents the content ratio of tungsten, is more preferably 0.005≦c≦0.025. It is more preferable that d indicating the content ratio of lithium is 0.97≦d≦1.05.

In the positive electrode active material of this embodiment, the total of a+b, which is the sum of a indicating the content of cobalt and b indicating the content of the element M, is 0 or more and less than 0.1. Therefore, 1-ab, which is the content of nickel, is higher than 0.9 and 1.0 or less, which is a high content ratio. By increasing the content ratio of nickel in this way, the charge/discharge capacity can be increased.

The positive electrode active material of the present embodiment can increase the nickel ratio by containing each element in the above ratio as a whole. Further, when used in a lithium ion secondary battery, its cycle characteristics can be made excellent.

Although the specific structure of the positive electrode active material of the present embodiment is not particularly limited, for example, particles serving as a base material (hereinafter, also referred to as “base material particles”) and a coating material arranged on the surface of the base material particles And particles containing tungsten and lithium (hereinafter, also referred to as “coated particles”). Further, the positive electrode active material of the present embodiment can also be composed of base material particles and coated particles arranged on the surfaces of the base material particles.

Hereinafter, the positive electrode active material of the present embodiment will be described by taking as an example the case where the base material particles and the coating particles arranged on the surfaces of the base material particles are used, but the present invention is not limited thereto. By having the composition described above as the whole positive electrode active material, the nickel ratio is high, and the cycle characteristics can be made excellent when used in a lithium ion secondary battery.

Further, the base material particles and the coated particles do not need to be clearly distinguishable, and the base material particles and the coated particles exist in the vicinity of their boundaries by mixing at least a part of the components constituting each particle. May be. Further, for example, some of the elements constituting the coated particles, such as tungsten, may be mixed or solid-dissolved in the base material particles.

In the positive electrode active material of this embodiment, a lithium metal composite oxide having a high nickel ratio can be used as a raw material for the base material particles. Thereby, the nickel ratio of the positive electrode active material can be increased, the amount of expensive metal such as cobalt used can be suppressed, and the cost can be reduced. In addition, a high charge/discharge capacity can be obtained. Furthermore, by disposing the coating particles on the surface of the base material particles, the cycle characteristics can be improved while maintaining the charge/discharge capacity.

As described above, when a lithium metal composite oxide having a high nickel ratio is used in a lithium ion secondary battery, the charge/discharge capacity can be improved, but the charge/discharge capacity decreases when repeatedly charged/discharged. That is, that is, the cycle characteristics are deteriorated. When the lithium metal composite oxide having a high nickel ratio is used, the reason why the cycle characteristics are deteriorated is that the NiO layer is formed on the particle surface of the lithium metal composite oxide having a high nickel ratio and the resistance increases. In this way, the NiO layer is formed on the surface of the particles of the lithium metal composite oxide, and the resistance is increased, so that the extraction of lithium locally occurs, and the deterioration of the particles of the lithium metal composite oxide progresses. It is considered that the characteristics are degraded.

Therefore, the inventors of the present invention conducted further studies, and found that base material particles using a lithium metal composite oxide having a high nickel ratio as a raw material and composite particles in which coated particles were arranged on the surface of the base material particles. It was found that the use of particles can improve the cycle characteristics particularly.

It is considered that this is because it is possible to suppress the resistance of the surface of the base material particles and uniformly extract lithium from the surface of the base material particles by forming the composite particles in which the base material particles and the coated particles are combined. To be In this way, by combining the base material particles and the coated particles into the composite particles, it is possible to suppress the deterioration of the base material particles and particularly improve the cycle characteristics, which is a previously unknown effect. Can be demonstrated.

In general, if the surface of the positive electrode active material is completely covered with a heterogeneous compound, the movement (intercalation) of lithium ions is greatly restricted, resulting in a high lithium metal composite oxide. It is also possible that the advantage of capacity will be erased.

However, in the positive electrode active material of the present embodiment, the coated particles arranged on the surface of the base material particles contain tungsten and lithium, so that the lithium ion conductivity (conductivity) is high and the effect of promoting the movement of lithium ions is high. is there. Therefore, by disposing the coated particles on the surface of the base material particles, a lithium conduction path can be formed at the interface with the electrolyte, and the charge/discharge capacity of the base material particles can be maintained.

Further, on the surface of the base material particles, by forming the composite particles in which the coating particles are arranged, since the coating particles have the effect of promoting the movement of lithium ions as described above, the reaction resistance of the positive electrode active material of the present embodiment is increased. It is also possible to reduce and improve output characteristics.

The base material particles included in the positive electrode active material of the present embodiment may include primary particles and secondary particles formed by aggregating the primary particles.

The lithium metal composite oxide that can be preferably used as a raw material of the base material particles when manufacturing the positive electrode active material of the present embodiment includes, for example, lithium (Li), nickel (Ni), cobalt (Co), and elements. M(M) can be contained in a ratio of the amounts of materials of Li:Ni:Co:M=z:(1-x-y):x:y. It is preferable that x, y, and z satisfy 0≦x<0.10, 0≦y<0.10, 0≦x+y<0.10, and 0.97≦z≦1.20. Further, the element M can be at least one element selected from Mn, V, Mg, Mo, Nb, Ti and Al. The lithium metal composite oxide may have a layered crystal structure. The lithium metal composite oxide preferably has a layered crystal structure of hexagonal rock salt type structure. The base material particles contained in the positive electrode active material of the present embodiment may contain the lithium metal composite oxide.

More preferably, x representing the content ratio of cobalt is 0≦x≦0.06, and y representing the content ratio of the element M is more preferably 0≦y≦0.06. Further, z indicating the content ratio of lithium is more preferably 0.97≦z≦1.05.

In the lithium metal composite oxide, the sum of x+y, which is the sum of x indicating the content of cobalt and y indicating the content of the element M, is 0 or more and less than 0.1. Therefore, 1-xy, which is the content of nickel, is higher than 0.9 and 1.0 or less, which is a high content ratio. As described above, by using the lithium metal composite oxide having a high nickel content rate as the raw material of the base material particles, the nickel content rate is increased even in the entire positive electrode active material, and the composition described above is obtained and the charge/discharge capacity is increased. can do.

Lithium metal composite oxide can be suitably used as a raw material of the base particles can be represented for example by the general formula _{Li z Ni 1-x-y} Co x M y O 2 + α. Since x, y, z and the element M have already been described, the description thereof will be omitted here. α is preferably −0.2≦α≦0.2, for example.

Here, when the surface of the base material particles is coated only with the layered material that is a thick film, the specific surface area may decrease. Therefore, when the surface of the base material particles is coated only with a layered material that is a thick film, the contact area with the electrolyte becomes small even if the coating material has high lithium ion conductivity, and as a result, the charge/discharge capacity is increased. And the reaction resistance may increase.

On the other hand, in the positive electrode active material of the present embodiment, it is possible to form composite particles in which coating particles are arranged on the surface of the base material particles. Therefore, unlike the case where only the layered material that is the above-described thick film is arranged, the contact area between the composite particles including the base material particles and the electrolyte is sufficient, and the lithium ion conductivity can be effectively improved. In addition, it is possible to suppress a decrease in charge/discharge capacity and a reaction resistance.

The particle size of the coated particles is not particularly limited, but the particle size is preferably 1 nm or more and 100 nm or less.

By setting the particle size of the coated particles to 1 nm or more, it is possible to have particularly high lithium ion conductivity. Further, by setting the particle size of the coated particles to 100 nm or less, the coated particles can form a particularly uniform coating on the surface of the base material particles, and in particular, improve cycle characteristics and suppress reaction resistance. be able to.

Further, the contact between the base material particles and the electrolyte occurs on the surface of the primary particle of the base material particles, and therefore it is preferable that the coated particles are formed on the surface of the primary particle of the base material particles. Here, the primary particle surface in the base material particles, the primary particle surface exposed at the outer surface of the secondary particles and the secondary particles outside the surface of the secondary particles through which the electrolyte can penetrate into It includes the exposed primary particle surface. Further, even the grain boundaries between the primary particles are included if the binding of the primary particles is incomplete and the electrolyte is permeable.

The contact with the electrolyte is not only the outer surface of the secondary particles formed by agglomeration of the primary particles of the base material particles, but also the voids in the vicinity of the surface of the secondary particles and inside, and also in the incomplete grain boundary. Occurs. Therefore, it is preferable to dispose the coated particles on the surfaces of the primary particles to promote the movement of lithium ions. Therefore, by disposing the coated particles on the entire surface of the primary particles, it becomes possible to particularly improve the cycle characteristics of the positive electrode active material and further reduce the reaction resistance.

Here, the coated particles do not have to be completely formed on the entire surface of the primary particles of the base material particles, and may be in a scattered state. Even in the scattered state, if the coated particles are formed on the outer surface of the base material particles and the surface of the primary particles exposed in the voids inside, the effect of improving the cycle characteristics and reducing the reaction resistance can be obtained. ..

The properties of the primary particle surface of the base material particles can be determined by, for example, observing with a field emission scanning electron microscope, and for the positive electrode active material of the present embodiment, the surface of the primary particle of the base material particles is coated. It is confirmed that particles are formed.

On the other hand, when the coated particles are formed unevenly among the base material particles of the positive electrode active material of the present embodiment, the movement of lithium ions between the base material particles becomes non-uniform, so that the specific base material particles May be overloaded. Therefore, it is preferable that the coated particles are uniformly formed between the base material particles.

The coated particles included in the positive electrode active material of the present embodiment are preferably particles containing tungsten and lithium. Tungsten and lithium contained in the coated particles included in the positive electrode active material of the present embodiment may exist, for example, as a simple substance or may form a compound, and may be contained in any form. However, it is preferable that at least part of the tungsten and lithium contained in the positive electrode active material of the present embodiment exist in the form of lithium tungstate. Therefore, the coated particles are preferably particles containing lithium tungstate, for example.

By forming the lithium tungstate, the lithium ion conductivity is further increased, and the effect of improving the cycle characteristics and reducing the reaction resistance becomes greater.

Further, the amount of tungsten indicating the ratio of the number of atoms of tungsten contained in the positive electrode active material of the present embodiment to the total number of atoms of nickel, cobalt, and element M is 0.1 atom% or more and 3 atom% or less. Is preferable, and more preferably 0.5 at% or more and 2.5 at% or less. By setting the amount of tungsten in the above range, the charge/discharge capacity and the cycle characteristics can be particularly improved and both can be achieved.

When the amount of tungsten is 0.1 atomic% or more, cycle characteristics can be particularly improved. Further, by setting the amount of tungsten to 3.0 atom% or less, it is possible to suppress the formation of the coated particles excessively, enhance the lithium conduction between the base material particles and the electrolyte, and particularly enhance the charge/discharge capacity. be able to.

As described above, the coated particles are preferably particles containing, for example, tungsten and lithium. In this case, the amount of lithium contained in the coated particles is not particularly limited, and if the coated particles contain lithium, an effect of improving lithium ion conductivity can be obtained. Usually, excess lithium is present on the surface of the lithium metal composite oxide used as the raw material of the positive electrode active material of the present embodiment, and when mixed with an alkaline solution, the lithium supplied to the particles containing tungsten and lithium by the excess lithium. The amount may be sufficient, but it is preferable that the amount is sufficient to form lithium tungstate.

Further, when the ratio “Li/Me” of the total number of atoms (Me) of nickel, cobalt, and element M in the positive electrode active material and the number of atoms (Li) of lithium is 0.97 or more and 1.20 or less. Preferably. By setting Li/Me to 0.97 or more, the reaction resistance of the positive electrode in the lithium ion secondary battery using the positive electrode active material can be particularly suppressed, and the output of the battery can be increased. Further, by setting Li/Me to 1.20 or less, the initial discharge capacity of the lithium ion secondary battery using the positive electrode active material can be particularly increased, and the reaction resistance of the positive electrode can be suppressed.

The powder characteristics such as the particle size and tap density of the positive electrode active material of the present embodiment are not particularly limited, and can be arbitrarily selected according to the characteristics required for the lithium ion secondary battery to be used.

According to the positive electrode active material of the present embodiment described above, by having a predetermined composition, it is possible to improve the cycle characteristics and the charge/discharge capacity of a lithium ion secondary battery using the positive electrode active material. ..
(2) Method for Manufacturing Positive Electrode Active Material for Lithium Ion Secondary Battery A method for manufacturing the positive electrode active material for lithium ion secondary battery of the present embodiment will be described. According to the method for producing a positive electrode active material for a lithium ion secondary battery of the present embodiment, the above-described positive electrode active material can be produced, and therefore, a part of the already described matters will be omitted.

The method for producing a positive electrode active material for a lithium ion secondary battery of the present embodiment (hereinafter, also simply referred to as a “method for producing a positive electrode active material”) can include the following steps.

Lithium (Li), nickel (Ni), cobalt (Co), and element M (M) in the ratio of the amount of substances, Li:Ni:Co:M=z:(1-x-y):x:y. The first step of mixing the lithium metal composite oxide having a layered crystal structure with an alkali solution containing a tungsten compound to obtain a raw material mixture.
Second step of heat treating the raw material mixture.

In addition, x, y, and z in the above formula showing the material amount ratio of the lithium metal composite oxide are 0≦x<0.10, 0≦y<0.10, 0≦x+y<0.10, 0. It is preferable that 97≦z≦1.20. Further, the element M can be at least one element selected from Mn, V, Mg, Mo, Nb, Ti and Al.

Further, the tungsten concentration of the alkaline solution containing the tungsten compound can be set to 0.05 mol/L or more and 1.8 mol/L or less.

The method for producing the positive electrode active material of the present embodiment will be described in detail below for each step.
(First step)
In the first step, a lithium metal composite oxide having a layered crystal structure is mixed with an alkali solution containing a tungsten compound (hereinafter, the alkali solution containing a tungsten compound is also referred to as “alkali solution (W)”). It is a process to do.

By performing the first step, tungsten can be dispersed on the surface of the primary particles of the lithium metal composite oxide that can come into contact with the electrolyte.

When only the solid tungsten compound is added to and mixed with the lithium metal composite oxide, not only the dispersion of tungsten is insufficient, but also lithium may not be eluted from the lithium metal composite oxide powder. Therefore, in this case, when a tungsten compound that does not contain lithium is used as the tungsten compound, a tungsten compound that does not contain lithium, for example, tungsten oxide, may be formed on the particle surface of the lithium metal composite oxide. There is.

Therefore, in the first step, it is preferable to add the tungsten compound as an alkaline solution containing the tungsten compound. The alkaline solution containing the tungsten compound can be prepared, for example, by dissolving the tungsten compound in the alkaline solution.

The dissolution method may be an ordinary powder dissolution method, and for example, the tungsten compound may be added and dissolved while stirring the alkaline solution using a reaction vessel equipped with a stirrer. It is preferable to completely dissolve the tungsten compound in the alkaline solution from the viewpoint of uniform dispersion.

As the tungsten compound, one that can be dissolved in an alkaline solution can be preferably used, and one or more selected from tungsten oxide, lithium tungstate, ammonium tungstate, and the like can be preferably used.

The amount of tungsten to be added to the alkaline solution is not particularly limited, but in the first step, nickel, cobalt, and It is preferable to add it so that the ratio of the number of atoms of the element M to the total number of atoms is 0.1 atom% or more and 3.0 atom% or less, and more preferably 0.5 atom% or more and 2.5 atom% or less. preferable.

In the method for producing the positive electrode active material of the present embodiment, the raw material mixture obtained in the first step can be directly used in the second step. That is, the lithium metal composite oxide and the alkaline solution (W) can be subjected to the second step without solid-liquid separation after mixing. Therefore, the total amount of tungsten in the alkaline solution (W) is dispersed and adhered to the surface of the primary particles of the lithium metal composite oxide. Therefore, the amount of tungsten added to the alkaline solution used in the first step may be the amount necessary to form particles containing tungsten and lithium on the surface of the lithium metal composite oxide particles.

However, when the positive electrode active material obtained after the heat treatment in the second step is crushed, the particles containing tungsten and lithium formed on the surface of the particles of the lithium metal composite oxide are peeled off, and the positive electrode active material The tungsten content may decrease. In such a case, the amount of tungsten to be added to the alkaline solution may be determined in anticipation of the reduction amount during crushing. In this case, for example, the ratio of the number of atoms of tungsten added to the alkaline solution to the total number of atoms of nickel, cobalt and the element M contained in the mixed lithium metal composite oxide is further 5 atom% or more within the range described above. It can be added in an amount of 20 atomic% or more.

Moreover, the tungsten concentration of the alkaline solution (W) is preferably 0.05 mol/L or more and 1.8 mol/L or less, and more preferably 0.05 mol/L or more and 1.5 mol/L or less. By setting the tungsten concentration to 0.05 mol/L or more, it is possible to prevent the raw material mixture from being slurried when mixed with the lithium metal composite oxide, and to mix the lithium metal composite oxide with the lithium metal composite oxide. It is possible to suppress the elution of lithium contained in the layered lattice of the object. By setting the tungsten concentration to 1.8 mol/L or less, it is possible to secure a sufficient amount of the alkaline solution as a solvent and to particularly uniformly disperse the tungsten on the particle surface of the lithium metal composite oxide, which is preferable.

The alkali used in the alkaline solution (W) is not particularly limited, but it is preferable to use a general alkaline solution containing no impurities harmful to the positive electrode active material in order to obtain a high charge/discharge capacity. Specifically, for example, ammonia, lithium hydroxide, or the like, which is unlikely to be mixed with impurities, can be used, but lithium hydroxide is preferably used from the viewpoint of not interfering with lithium intercalation. That is, it is preferable that the alkaline solution containing the tungsten compound is a solution of the tungsten compound in an aqueous lithium hydroxide solution. When lithium hydroxide is used, Li/Me in the raw material mixture obtained after mixing is the sum of the numbers of atoms of nickel, cobalt, and element M (Me) in the positive electrode active material, which has already been described for the positive electrode active material. It is preferable to adjust the addition amount so that the ratio (Li/Me) with the number of lithium atoms (Li) is satisfied. When lithium hydroxide is used as the alkali, for example, it is preferable that the number of lithium atoms in the added lithium hydroxide is 4.5 or more and 15.0 or less in atomic ratio with respect to the number of tungsten atoms. This is because lithium is eluted from the lithium metal composite oxide and supplied, but by using lithium hydroxide in the above range, it is possible to supply lithium in an amount sufficient to form lithium tungstate.

Further, the alkaline solution is preferably an aqueous solution. In order to disperse the tungsten on the entire surface of the primary particles of the lithium metal composite oxide, it is preferable to penetrate into voids and incomplete grain boundaries inside the secondary particles of the lithium metal composite oxide, and alcohol having high volatility is used. This is because when a solvent such as the above is used, the solvent may evaporate and not sufficiently penetrate before the alkaline solution (W) penetrates into the voids inside the secondary particles.

The pH of the alkaline solution may be a pH at which the tungsten compound dissolves, but is preferably 9 or more and 12 or less. By adjusting the pH to 9 or more, it is possible to prevent the lithium elution amount from the lithium metal composite oxide from becoming excessively large when mixed with the lithium metal composite oxide, and to obtain the obtained positive electrode active material as a lithium ion secondary oxide. When used in a battery, the battery characteristics can be particularly improved. In addition, by setting the pH to 12 or less, the excess alkaline component remaining in the lithium metal composite oxide is sufficiently suppressed, and the battery characteristics are particularly high when the obtained positive electrode active material is used in a lithium ion secondary battery. can do.

The composition of the lithium metal composite oxide used as the raw material of the base material particles in the first step is not particularly limited, and can be selected according to the components added in the manufacturing step and the composition of the intended positive electrode active material. For example, when lithium hydroxide is used as an alkali when preparing an alkaline solution as described above, the lithium content increases due to the addition of the lithium hydroxide. Therefore, the amount of the lithium hydroxide added and the target positive electrode It can be selected according to the composition of the active material.

Examples of the lithium metal composite oxide to be used as the raw material of the base material particles include lithium (Li), nickel (Ni), cobalt (Co), and element M (M) in a ratio of the amount of material, Li:Ni:Co. :M=z:(1-x-y):x:y The lithium metal composite oxide contained in the ratio can be used. In addition, x, y, and z in the above formula showing the material amount ratio of the lithium metal composite oxide are 0≦x<0.10, 0≦y<0.10, 0≦x+y<0.10, 0. It is preferable that 97≦z≦1.20. Further, the element M can be at least one element selected from Mn, V, Mg, Mo, Nb, Ti and Al. The lithium metal composite oxide may have a layered crystal structure. The lithium metal composite oxide preferably has a layered crystal structure of hexagonal rock salt type structure.

Lithium-metal composite oxide serve as raw material for the base particles can be represented for example by the general formula _{Li z Ni 1-x-y} Co x M y O 2 + α. Since x, y, z and the element M have already been described, the description thereof will be omitted here. α is preferably −0.2≦α≦0.2, for example.

Further, since increasing the contact area with the electrolyte is advantageous for improving the output characteristics, the lithium metal composite oxide includes primary particles and secondary particles formed by aggregating the primary particles. It is preferable to use a lithium metal composite oxide. In addition, it is preferable that the lithium metal composite oxide has voids and grain boundaries through which the electrolyte can permeate secondary particles.

In the first step, the lithium metal composite oxide and the alkaline solution (W) can be mixed as described above. At this time, for example, the alkaline solution (W) can be added to and mixed with the powder of the lithium metal composite oxide.

The alkaline solution (W) is preferably a liquid. In the first step, it is preferable that the lithium metal composite oxide and the alkali solution containing the tungsten compound are mixed at a temperature of 50°C or lower. It is preferable that the alkaline solution (W) is a liquid as described above, since it is preferable that the alkaline solution (W) permeates the voids and the grain boundaries of the secondary particles of the lithium metal composite oxide.

Moreover, by mixing at 50° C. or lower, the drying rate of the alkaline solution can be suppressed, and the alkaline solution can be sufficiently permeated into the voids and grain boundaries of the secondary particles of the lithium metal composite oxide. By suppressing the drying rate of the alkaline solution, it is possible to sufficiently elute lithium from the particles of the lithium metal composite oxide, the surface of the particles of the lithium metal composite oxide, tungsten containing a sufficient amount of lithium and Particles containing lithium can be formed.

It is preferable that the lithium metal composite oxide and the alkaline solution (W) are sufficiently mixed to uniformly disperse tungsten. A general mixer can be used for the mixing, and for example, a shaker mixer, a Loedige mixer, a Julia mixer, a V blender, or the like is used to such an extent that the particles of the lithium metal composite oxide particles are not destroyed. It is preferable that the lithium metal composite oxide and the alkaline solution (W) are sufficiently mixed. By mixing the lithium metal composite oxide and the alkali solution (W) in the first step, tungsten in the alkali solution (W) can be uniformly distributed on the surface of the primary particles of the lithium metal composite oxide. ..

The lithium metal composite oxide used in the first step may be washed with water before it is used in the first step. That is, the method for manufacturing the positive electrode active material of the present embodiment may further include a water washing step of washing the lithium metal composite oxide with water before the first step. By washing with water, the battery capacity and stability of the obtained positive electrode active material can be particularly enhanced.

Washing with water may be performed by known methods and conditions, and is preferably performed in a range in which lithium is not excessively eluted from the lithium metal composite oxide and battery characteristics are not deteriorated. In the case of washing with water, any method may be used, such as drying and then mixing with the alkaline solution (W), or mixing with the alkaline solution (W) only by solid-liquid separation without drying. In the case of only solid-liquid separation, the water content after mixing with the alkali solution (W) is the maximum water content of the mixture of the dried lithium metal composite oxide and the alkali solution (W), that is, the alkali having the lowest tungsten concentration. It is preferable not to exceed the water content when mixed with the solution (W). By preventing the water content from becoming excessively high, the lithium eluted from the lithium metal composite oxide is suppressed, and when the obtained positive electrode active material is used as a lithium ion secondary battery, its battery characteristics are particularly It is preferable because it can be increased.
(Second step)
In the second step, the raw material mixture obtained in the first step can be heat treated. Thereby, the particles of the lithium metal composite oxide are formed by the tungsten supplied from the alkali solution (W), the lithium eluted from the lithium metal composite oxide, and the lithium supplied by the alkali solution (W) in some cases. Particles containing tungsten and lithium can be formed on the surface.

The heat treatment condition of the second step is not particularly limited, but from the viewpoint of particularly improving the electrical characteristics of the obtained positive electrode active material, it is preferable to perform the heat treatment at a temperature of 100° C. or higher and 600° C. or lower in an oxygen atmosphere or a vacuum atmosphere. ..

By setting the heat treatment temperature to 100° C. or higher, the water contained in the raw material mixture can be sufficiently evaporated, and the particles containing tungsten and lithium can be sufficiently formed.

In addition, by setting the heat treatment temperature to 600° C. or lower, it is possible to suppress the sintering of the primary particles of the lithium metal composite oxide and the solid solution of some tungsten in the layered structure of the lithium metal composite oxide. .. Therefore, when the obtained positive electrode active material is used in a lithium secondary battery, its charge/discharge capacity can be particularly increased.

The atmosphere during the heat treatment is preferably an oxidizing atmosphere such as an oxygen atmosphere or a vacuum atmosphere as described above in order to avoid reaction with moisture or carbonic acid in the atmosphere. The oxygen atmosphere here may be, for example, a mixed atmosphere of oxygen and an inert gas, or an atmosphere composed of only oxygen.

The heat treatment time is not particularly limited, but is preferably 5 hours or more and 15 hours or less in order to sufficiently evaporate the water content of the alkaline solution (W) to form particles containing tungsten and lithium.
(3) Lithium Ion Secondary Battery The lithium ion secondary battery of the present embodiment (hereinafter, also referred to as “secondary battery”) can have a positive electrode containing the positive electrode active material described above.

Hereinafter, one configuration example of the secondary battery of the present embodiment will be described for each component. The secondary battery of the present embodiment includes, for example, a positive electrode, a negative electrode and a non-aqueous electrolyte, and is composed of the same components as a general lithium ion secondary battery. Note that the embodiments described below are merely examples, and the lithium ion secondary battery of the present embodiment is implemented in various modifications and improvements based on the knowledge of those skilled in the art, including the following embodiments. can do. Moreover, the secondary battery is not particularly limited in its use.
(Positive electrode)
The positive electrode included in the secondary battery of the present embodiment may include the above-described positive electrode active material.

An example of the method for manufacturing the positive electrode will be described below. First, the above-mentioned positive electrode active material (powder), a conductive material and a binder (binder) are mixed to form a positive electrode mixture, and further activated carbon or a solvent for the purpose of adjusting viscosity, etc. is added, if necessary. This can be kneaded to produce a positive electrode mixture paste.

The mixing ratio of each material in the positive electrode mixture is a factor that determines the performance of the lithium ion secondary battery, and thus can be adjusted according to the application. The mixing ratio of the materials can be the same as that of the positive electrode of a known lithium ion secondary battery. For example, when the total mass of the solid content of the positive electrode mixture excluding the solvent is 100% by mass, the positive electrode active material is It may be contained in an amount of 60% by mass or more and 95% by mass or less, a conductive material in an amount of 1% by mass or more and 20% by mass or less, and a binder in a ratio of 1% by mass or more and 20% by mass or less.

The obtained positive electrode mixture paste is applied to the surface of a current collector made of, for example, an aluminum foil, dried, and the solvent is scattered to produce a sheet-shaped positive electrode. If necessary, pressure can be applied by a roll press or the like to increase the electrode density. The sheet-shaped positive electrode thus obtained can be cut into an appropriate size according to the intended battery and used for the production of the battery.

As the conductive material, for example, graphite (natural graphite, artificial graphite, expanded graphite, or the like) or a carbon black-based material such as acetylene black or Ketjen Black (registered trademark) can be used.

The binder (binder) plays a role of binding the active material particles together, and includes, for example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluororubber, ethylene propylene diene rubber, styrene butadiene, and cellulosics. One or more selected from resins and polyacrylic acid can be used.

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

The method for producing the positive electrode is not limited to the above-described examples, and other methods may be used. For example, it can be manufactured by press-molding the positive electrode mixture and then drying it in a vacuum atmosphere.
(Negative electrode)
For the negative electrode, metallic lithium, lithium alloy, or the like can be used. For the negative electrode, a negative electrode active material capable of absorbing and desorbing lithium ions is mixed with a binder, and a suitable solvent is added to form a paste negative electrode mixture material on the surface of a metal foil current collector such as copper. You may use what was formed by apply|coating, drying, and compressing in order to raise electrode density as needed.

As the negative electrode active material, for example, a sintered body of an organic compound such as natural graphite, artificial graphite and phenol resin, or a powdery body of a carbon material such as coke can be used. In this case, a fluorine-containing resin such as PVDF can be used as the negative electrode binder as in the positive electrode, and a solvent for dispersing these active materials and the binder can be an organic material such as N-methyl-2-pyrrolidone. A solvent can be used.
(Separator)
If necessary, a separator may be sandwiched between the positive electrode and the negative electrode. The separator is for separating the positive electrode and the negative electrode and holding the electrolyte, and a known material can be used.For example, a thin film such as polyethylene or polypropylene, which has a large number of minute holes, may be used. it can.
(Non-aqueous electrolyte)
As the non-aqueous electrolyte, for example, a non-aqueous electrolytic solution can be used.

As the non-aqueous electrolytic solution, for example, a solution in which a lithium salt as a supporting salt is dissolved in an organic solvent can be used. Further, as the non-aqueous electrolyte solution, an ionic liquid in which a lithium salt is dissolved may be used. The ionic liquid is a salt that is composed of cations and anions other than lithium ions and is liquid even at room temperature.

Examples of the organic solvent include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate and trifluoropropylene carbonate, chain carbonates such as diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate and dipropyl carbonate, and tetrahydrofuran and 2-methyltetrahydrofuran. And one compound selected from ether compounds such as dimethoxyethane, sulfur compounds such as ethylmethyl sulfone and butane sultone, phosphorus compounds such as triethyl phosphate and trioctyl phosphate, etc. may be used alone or in combination of two or more. It can also be used.

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

A solid electrolyte may be used as the non-aqueous electrolyte. The solid electrolyte has the property of withstanding a high voltage. Examples of the solid electrolyte include inorganic solid electrolytes and organic solid electrolytes.

Examples of the inorganic solid electrolyte include oxide-based solid electrolytes and sulfide-based solid electrolytes.

The oxide-based solid electrolyte is not particularly limited and, for example, one containing oxygen (O) and having lithium ion conductivity and electronic insulation can be suitably used. The oxide-based solid electrolyte, for example, lithium phosphate _{(Li 3 PO 4), Li} 3 PO 4 N X, LiBO 2 N X, LiNbO 3, LiTaO 3, Li 2 SiO 3, Li 4 SiO 4 -Li 3 _{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 3X La 2 / _3-X TiO ₃ (0≦X≦2/3), Li ₅ La ₃ Ta ₂ O ₁₂ , Li ₇ La ₃ Zr ₂ O ₁₂ , Li ₆ BaLa ₂ Ta ₂ O ₁₂ , Li _3.6 Si _0.6. One or more selected from P _0.4 O _{4 and the} like can be used.

The sulfide-based solid electrolyte is not particularly limited, and one containing, for example, sulfur (S) and having lithium ion conductivity and electronic insulation can be suitably used. The sulfide-based solid electrolyte, for _{example, Li 2 S-P 2 S} 5, Li 2 S-SiS 2, LiI-Li 2 S-SiS 2, LiI-Li 2 S-P 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 can be used one or more selected from ₅ or the like.

As the inorganic solid electrolyte, those other than the above may be used, and for example, Li ₃ N, LiI, Li ₃ N-LiI-LiOH, or the like may be used.

The organic solid electrolyte is not particularly limited as long as it is a polymer compound exhibiting ion conductivity, and for example, polyethylene oxide, polypropylene oxide, copolymers thereof, or the like can be used. Further, the organic solid electrolyte may contain a supporting salt (lithium salt).
(Shape and configuration of secondary battery)
The lithium-ion secondary battery of the present embodiment described above can be formed into various shapes such as a cylindrical shape and a laminated shape. Whichever shape is adopted, if the secondary battery of the present embodiment uses a non-aqueous electrolyte solution as the non-aqueous electrolyte, the positive electrode and the negative electrode, the electrode body by laminating via a separator, The obtained electrode body is impregnated with a non-aqueous electrolyte solution, and a lead for current collection is provided between the positive electrode current collector and the positive electrode terminal communicating with the outside, and between the negative electrode current collector and the negative electrode terminal communicating with the outside. It is possible to make a structure in which the battery case is connected and sealed in the battery case.

Incidentally, as described above, the secondary battery of the present embodiment is not limited to a form using a non-aqueous electrolyte solution as the non-aqueous electrolyte, for example, a secondary battery using a solid non-aqueous electrolyte, that is, all It can also be a solid state battery. In the case of an all-solid-state battery, the configuration other than the positive electrode active material can be changed as necessary.

Since the secondary battery of the present embodiment uses the above-described positive electrode active material, it can have low cost, high capacity, and excellent cycle characteristics. In addition, the reaction resistance at the positive electrode can be suppressed and the output can be increased.

Therefore, it can be suitably used in various applications requiring low capacity, high capacity, high output, and high cycle characteristics. Specifically, for example, it is suitable as a power source for small portable electronic devices (notebook personal computers, mobile phone terminals, etc.) that always require high capacity, and is also suitable as a power source for electric vehicles that requires high output. ..

In addition, the secondary battery of the present embodiment is suitable for an electric vehicle power source that is restricted in mounting space because it can be downsized and high output. The secondary battery of the present embodiment can be used not only as a power source for an electric vehicle that is driven purely by electric energy, but also as a power source for a so-called hybrid vehicle that is used in combination with a combustion engine such as a gasoline engine or a diesel engine. it can.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples. As described below, a battery was manufactured using the positive electrode active material prepared in each of Examples and Comparative Examples, and evaluation was performed. First, a battery manufacturing method and a battery evaluation method will be described.
(Battery manufacturing and evaluation)
For the evaluation of the positive electrode active material, 2032 type coin type battery 10 (hereinafter referred to as coin type battery) shown in FIG. 1 was used.

As shown in FIG. 1, the coin-type battery 10 includes a case 11 and an electrode 12 housed in the case 11.

The case 11 has a positive electrode can 11a that is hollow and has one end opened, and a negative electrode can 11b that is arranged in the opening of the positive electrode can 11a. When the negative electrode can 11b is arranged in the opening of the positive electrode can 11a. A space for accommodating the electrode 12 is formed between the negative electrode can 11b and the positive electrode can 11a.

The electrode 12 includes a positive electrode 12a, a separator 12c, and a negative electrode 12b, which are stacked in this order. The positive electrode 12a contacts the inner surface of the positive electrode can 11a via a current collector 13, and the negative electrode 12b is collected. It is housed in the case 11 so as to come into contact with the inner surface of the negative electrode can 11 b via the electric body 13. The current collector 13 is also arranged between the positive electrode 12a and the separator 12c.

The case 11 is provided with a gasket 11c, and relative movement is fixed by the gasket 11c so that the positive electrode can 11a and the negative electrode can 11b are kept in non-contact with each other. Further, the gasket 11c also has a function of sealing the gap between the positive electrode can 11a and the negative electrode can 11b to shut off the inside and the outside of the case 11 in a gas-tight and liquid-tight manner.

The coin-type battery 10 shown in FIG. 1 was manufactured as follows.

First, 52.5 mg of the positive electrode active material for lithium ion secondary batteries prepared in the following Examples and Comparative Examples, 15 mg of acetylene black, and 7.5 mg of polytetrafluoroethylene resin (PTFE) were mixed, and the diameter was 11 mm at a pressure of 100 MPa. Then, the positive electrode 12a was manufactured by press molding to a thickness of 100 μm. The produced positive electrode 12a was dried in a vacuum dryer at 120° C. for 12 hours.

Using the positive electrode 12a, the negative electrode 12b, the separator 12c, and the electrolytic solution, the coin-type battery 10 described above was produced in a glove box in an Ar atmosphere whose dew point was controlled at -80°C.

As the negative electrode 12b, there was used a negative electrode sheet in which a copper foil was coated with graphite powder having an average particle size of about 20 μm, which was punched into a disk shape with a diameter of 14 mm.

A 25-μm-thick polyethylene porous film was used as the separator 12c. As an electrolytic solution, a mixed solution (manufactured by Toyama Pharmaceutical Co., Ltd.) of ethylene carbonate (EC) and diethyl carbonate (DEC) using 1M LiClO ₄ as a supporting electrolyte was used.

The initial discharge capacity and cycle characteristics showing the performance of the manufactured coin type battery 10 were evaluated as follows.

The initial discharge capacity was left for about 24 hours after the coin-type battery 10 was manufactured, and after the open circuit voltage OCV (Open Circuit Voltage) became stable, the current density to the positive electrode was set to 0.1 mA/cm ² and the cut-off voltage 4 The capacity at the time of charging to 0.3 V, discharging for 1 hour, and then discharging to a cut-off voltage of 3.0 V was taken as the initial discharge capacity.

The cycle characteristics of the obtained coin-type battery were evaluated as battery evaluation. The cycle characteristics were evaluated by measuring the capacity retention rate after 200 cycles of charge and discharge. Specifically, the produced coin-type battery was charged to a cutoff voltage of 4.3 V at a current density of 0.3 mA/cm ² in a constant temperature bath kept at 25° C., and after a 1-hour rest, cut. After performing a conditioning in which a cycle of discharging to an off voltage of 3.0 V was repeated for 5 cycles, the battery was charged to a cutoff voltage of 4.3 V with a current density of 2.0 mA/cm ² in a constant temperature bath maintained at 60°C. After a rest of 1 hour, a cycle of discharging to a cut-off voltage of 3.0 V was repeated 200 times, and the discharge capacity of each cycle was measured for evaluation.

The discharge capacity obtained in the first cycle after conditioning the coin-type battery was divided by the discharge capacity obtained in the 200th cycle after conditioning, and the capacity retention ratio was the raw material of the base material particles. It was judged that the cycle characteristics were excellent when it was higher than when evaluated only with a certain lithium metal composite oxide powder.

In each of the following Examples and Comparative Examples, each sample of Wako Pure Chemical Industries, Ltd. special reagent grade was used to manufacture the positive electrode active material and the secondary battery.

Hereinafter, each condition of Examples and Comparative Examples will be described.
[Example 1]
(First step)
Layered hexagonal crystal represented by Li _1.016 Ni _0.91 Co _0.05 Al _0.04 O ₂ obtained by mixing oxide powder containing Ni as a main component and lithium hydroxide and firing the mixture. A lithium metal composite oxide powder having a crystal structure of a base rock salt structure was used as a raw material for the base material particles. This lithium metal composite oxide powder had an average particle diameter of 11.6 μm and a specific surface area of 0.9 m ² /g. In addition, the average particle diameter was evaluated by using a volume integrated average value in a laser diffraction scattering method, and the specific surface area was evaluated by using a BET method by nitrogen gas adsorption. The average particle size of the used lithium metal composite oxide powder is shown in Table 1 as the average particle size of the base material particle raw material.

0.183 g of tungsten oxide (WO ₃ ) was added to an aqueous solution in which 0.2 g of lithium hydroxide (LiOH) was dissolved in 3 mL of pure water, and the mixture was stirred at 25° C. to obtain a tungsten concentration of 0.1. An alkaline solution containing a 26 mol/L tungsten compound was obtained. Next, an alkaline solution (W) was added to 15 g of a lithium metal composite oxide powder used as a raw material for the base material particles, and a shaker mixer device (TURBULA Type T2C manufactured by Willy e Bakkofen (WAB)) was used. Mix well at 25°C. At this time, the ratio of the number of atoms of tungsten contained in the alkali solution containing the tungsten compound to the total number of atoms of nickel, cobalt and the element M (aluminum in this example) contained in the mixed lithium metal composite oxide. The amount of tungsten is 0.5 atom %. In Table 1, the amount is expressed as the amount of tungsten.

By the above operation, a raw material mixture which is a mixture of the alkaline solution (W) and the lithium metal composite oxide powder was obtained.
(Second step)
The resulting raw material mixture was placed in a magnesia firing container, heated in a 100% by volume oxygen stream to a heat treatment temperature of 500° C. at a heating rate of 2.8° C./min, and heat-treated at 500° C. for 10 hours. Then, the furnace was cooled to room temperature.

The composition of the positive electrode active material obtained after the heat treatment was analyzed by the ICP method.

As a result, it was confirmed that the composition of the positive electrode active material was represented by Li _1.069 Ni _0.91 Co _0.05 Al _0.04 W _0.005 O ₂ .
[Battery evaluation]
The battery characteristics of the coin-type battery 10 shown in FIG. 1 having a positive electrode manufactured by using the obtained positive electrode active material were evaluated.

As a result, the initial discharge capacity was 212.8 mAh/g, the discharge capacity after 200 cycles was 173.3 mAh/g, and the capacity retention ratio before and after the cycle was 81.4%.

Hereinafter, for Examples 2 to 5 and Comparative Examples 1 to 6, only the substances and conditions changed from those of Example 1 are shown. Table 1 shows the initial discharge capacities of Examples 1 to 5 and Comparative Examples 1 to 6, the discharge capacity after 200 cycles, and the capacity retention rate after 200 cycles.
[Example 2]
A positive electrode active material was obtained in the same manner as in Example 1 except that WO ₃ used was 0.915 g. The tungsten concentration of the alkaline solution containing the tungsten compound used in the first step was 1.32 mol/L.

It was confirmed that the composition of the obtained positive electrode active material was Li _1.071 Ni _0.91 Co _0.05 Al _0.04 W _0.025 O ₂ . The results of the battery characteristic evaluation are shown in Table 1.
[Example 3]
The raw material of the base material particles is represented by Li _1.018 Ni _0.94 Co _0.01 Al _0.05 O ₂ , and has a layered hexagonal rock salt type crystal structure and an average particle diameter of 11.9 μm. A positive electrode active material was obtained in the same manner as in Example 1 except that the lithium metal composite oxide powder having a specific surface area of 0.9 m ² /g was used. It was confirmed that the composition was Li _1.068 Ni _0.94 Co _0.01 Al _0.05 W _0.005 O ₂ . The results of the battery characteristic evaluation are shown in Table 1.
[Example 4]
As the raw material of the base material particles, Li _1.032 Ni _0.92 Co _0.02 Al _0.05 Mn _0.01 O ₂ is represented, and has a crystal structure of a layered hexagonal rock salt type structure, and an average particle size. Was 11.2 μm and the specific surface area was 0.6 m ² /g, and a positive electrode active material was obtained in the same manner as in Example 1 except that the lithium metal composite oxide powder was used. It was confirmed that the composition was Li _1.084 Ni _0.92 Co _0.02 Al _0.05 Mn _0.01 W _0.005 O ₂ . The results of the battery characteristic evaluation are shown in Table 1.
[Example 5]
The raw material of the base material particles is represented by Li _1.015 Ni _0.91 Co _0.05 Al _0.04 O ₂ , and has a layered hexagonal rock salt type crystal structure and an average particle diameter of 5.2 μm. A positive electrode active material was obtained in the same manner as in Example 1 except that the lithium metal composite oxide powder having a specific surface area of 1.2 m ² /g was used. It was confirmed that the composition was Li _1.071 Ni _0.91 Co _0.05 Al _0.04 W _0.005 O ₂ . The results of the battery characteristic evaluation are shown in Table 1.
[Comparative Example 1]
The raw material of the base material particles used in Example 1 was directly used as the positive electrode active material. Table 1 shows the evaluation results of the positive electrode active material.
[Comparative Example 2]
The raw material of the base material particles used in Example 3 was directly used as the positive electrode active material. Table 1 shows the evaluation results of the positive electrode active material.
[Comparative Example 3]
The raw material of the base material particles used in Example 4 was directly used as the positive electrode active material. Table 1 shows the evaluation results of the positive electrode active material.
[Comparative Example 4]
The raw material of the base material particles used in Example 5 was directly used as the positive electrode active material. Table 1 shows the evaluation results of the positive electrode active material.
[Comparative Example 5]
A positive electrode active material was obtained in the same manner as in Example 1 except that WO ₃ used was 0.029 g. The tungsten concentration of the alkaline solution containing the tungsten compound used in the first step was 0.04 mol/L.

It was confirmed that the composition of the obtained positive electrode active material was Li _1.069 Ni _0.91 Co _0.05 Al _0.04 W _0.0008 O ₂ . The results of the battery characteristic evaluation are shown in Table 1.
[Comparative Example 6]
A positive electrode active material was obtained in the same manner as in Example 1 except that WO ₃ used was 1.28 g. The tungsten concentration of the alkaline solution containing the tungsten compound used in the first step was 1.84 mol/L.

It was confirmed that the composition of the obtained positive electrode active material was Li _1.069 Ni _0.91 Co _0.05 Al _0.04 W _0.035 O ₂ . The results of the battery characteristic evaluation are shown in Table 1.

実施例１〜実施例５においては、対応する母材粒子の原料であるリチウム金属複合酸化物のみの場合、すなわち実施例１、２に関しては比較例１、実施例３〜５については、それぞれ比較例２〜比較例４と比較して、サイクル特性が向上することを確認できた。

In Examples 1 to 5, only the lithium metal composite oxide that is the raw material of the corresponding base material particles, that is, Comparative Examples 1 and 2 and Comparative Examples 1 and 2, respectively, are compared. It was confirmed that the cycle characteristics were improved as compared with Examples 2 to 4.

Further, comparing the results of Example 1, Example 2, Comparative Example 5, and Comparative Example 6 using the same lithium metal composite oxide as the raw material of the base material particles, the content ratio of tungsten is the positive electrode active material of the present embodiment. It was confirmed that the cycle characteristics of Examples 1 and 2 satisfying the composition of the substance were significantly improved as compared with Comparative Examples 5 and 6.

Claims (10)

Lithium (Li), nickel (Ni), cobalt (Co), and element M (M) in the ratio of the amount of substances, Li:Ni:Co:M=z:(1-x-y):x:y. (However, 0≦x<0.10, 0≦y<0.10, 0≦x+y<0.10, 0.97≦z≦1.20, and the element M is Mn, V, Mg, Mo, A lithium metal composite oxide containing at least one element selected from Nb, Ti and Al) and having a layered crystal structure is mixed with an alkali solution containing a tungsten compound to obtain a raw material mixture. The first step,
A second step of heat treating the raw material mixture,
A method for producing a positive electrode active material for a lithium ion secondary battery, wherein the tungsten concentration of the alkali solution containing the tungsten compound is 0.05 mol/L or more and 1.8 mol/L or less. The method for producing a positive electrode active material for a lithium ion secondary battery according to claim 1, further comprising a water washing step of washing the lithium metal composite oxide with water before the first step. In the first step, the ratio of the number of atoms of tungsten contained in the alkaline solution containing the tungsten compound to the total number of atoms of nickel, cobalt, and the element M contained in the mixed lithium metal composite oxide is And 0.1 at% or more and 3.0 at% or less, The method for producing a positive electrode active material for a lithium ion secondary battery according to claim 1 or 2. The production of a positive electrode active material for a lithium ion secondary battery according to any one of claims 1 to 3, wherein the alkaline solution containing the tungsten compound is obtained by dissolving the tungsten compound in an aqueous lithium hydroxide solution. Method. The lithium ion according to any one of claims 1 to 4, wherein in the first step, the lithium metal composite oxide and the alkali solution containing the tungsten compound are mixed at a temperature of 50°C or lower. A method for producing a positive electrode active material for a secondary battery. The positive electrode active material for a lithium ion secondary battery according to claim 1, wherein the heat treatment in the second step is performed at 100° C. or higher and 600° C. or lower in an oxygen atmosphere or a vacuum atmosphere. Production method. Lithium (Li), nickel (Ni), cobalt (Co), element M (M), and tungsten (W) are expressed as Li:Ni:Co:M:W=d:(1-a -B): a:b:c (where 0≤a<0.10, 0≤b<0.10, 0.001≤c≤0.03, 0≤a+b<0.10, 0.97≤ d≦1.20, the element M is a positive electrode active material for a lithium ion secondary battery, which is contained at a ratio of at least one element selected from Mn, V, Mg, Mo, Nb, Ti and Al. The lithium ion secondary battery according to claim 7, wherein the ratio of the number of atoms of tungsten contained to the total number of atoms of nickel, cobalt, and the element M is 0.5 atom% or more and 2.5 atom% or less. Positive electrode active material. The positive electrode active material for a lithium ion secondary battery according to claim 7, wherein at least part of the contained tungsten and lithium is present in the form of lithium tungstate. A lithium ion secondary battery having a positive electrode containing the positive electrode active material for a lithium ion secondary battery according to any one of claims 7 to 9.

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