JP7271891B2 - Positive electrode active material for lithium ion secondary battery, method for producing positive electrode active material for lithium ion secondary battery - Google Patents

Description

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

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

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

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

As positive electrode active materials mainly proposed so far, lithium cobalt composite oxide (LiCoO ₂ ) which is relatively easy to synthesize, lithium nickel composite oxide (LiNiO ₂ ) using nickel which is cheaper than cobalt, Lithium-nickel-cobalt-manganese composite oxide (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ), lithium-manganese composite oxide (LiMn ₂ O ₄ ) using manganese, and the like can be mentioned.

Of these, lithium-nickel composite oxides are attracting attention as materials from which high battery capacity can be obtained. Furthermore, in recent years, emphasis has been placed on reducing the resistance necessary for increasing the output. Addition of different elements is used as a method for realizing the above-mentioned low resistance. In particular, addition of transition metals such as W, Mo, Nb, Ta, and Re, which can take high numbers, is considered useful.

Further, in recent years, there has been a demand for higher output, and various studies have been made.

For example, in Patent Document 1, the general formula Li _z Ni _1-xy Co _x M _y O ₂ (where 0.10≦x≦0.35, 0≦y≦0.35, 0.97≦z≦ 1.20, M is at least one element selected from Mn, V, Mg, Mo, Nb, Ti and Al) from primary particles and secondary particles formed by agglomeration of the primary particles A lithium metal composite oxide comprising fine particles containing lithium tungstate represented by any one of Li ₂ WO ₄ , Li ₄ WO ₅ and Li ₆ W ₂ O ₉ on the surface of the lithium metal composite oxide A positive electrode active material for a non-aqueous electrolyte secondary battery is disclosed, which is characterized by having

In the positive electrode active material for a non-aqueous electrolyte secondary battery disclosed in Patent Document 1, by forming fine particles containing the lithium tungstate on the surface of the lithium metal composite oxide powder, lithium is formed at the interface with the electrolyte. Since it forms a conduction path, it is said that the reaction resistance of the active material can be reduced and the output characteristics can be improved.

JP 2013-125732 A

However, as disclosed in Patent Document 1, when a positive electrode active material for a non-aqueous electrolyte secondary battery in which lithium tungstate is arranged on the surface of a lithium metal composite oxide is applied to a non-aqueous electrolyte secondary battery, lithium tungstate In some cases, a decrease in battery capacity was observed compared to the case where no

For this reason, there is a demand for a positive electrode active material for a lithium ion secondary battery, which has a coating made of lithium tungstate and has an excellent battery capacity when used as a lithium ion secondary battery.

Therefore, in view of the above-mentioned problems of the prior art, in one aspect of the present invention, a positive electrode active material for a lithium ion secondary battery having a coating made of lithium tungstate, which has excellent battery capacity when used as a lithium ion secondary battery intended to provide

In order to solve the above problems, according to one aspect of the present invention, there is provided a positive electrode active material for a lithium ion secondary battery containing a film-containing lithium metal composite oxide powder,
The film-containing lithium metal composite oxide powder is
General formula: Li _z Ni _1-x-y Co _x My _{O 2+α} (where 0 < x ≤ 0.35, 0 ≤ y ≤ 0.35, 0.95 ≤ z ≤ 1.30, 0 ≤ α ≤ 0.15, M is at least one element selected from Mn, V, Mg, Mo, Nb, Ti and Al), and the crystal structure is a layered lithium metal composite oxide particle;
a coating of lithium tungstate disposed on the surface of the lithium metal composite oxide particles;
The ratio of the amount of lithium contained in the lithium compound other than lithium tungstate present on the surface of the coating-containing lithium metal composite oxide particles to the total amount of lithium contained in the coating-containing lithium metal composite oxide particles is 0.01. Provided is a positive electrode active material for a lithium ion secondary battery having a mass % or more and 0.05 mass % or less.

ADVANTAGE OF THE INVENTION According to one aspect of the present invention, it is possible to provide a positive electrode active material for a lithium ion secondary battery having a coating made of lithium tungstate, which has excellent battery capacity when used as a lithium ion secondary battery.

Explanatory drawing of the structure of the coin-type battery produced in an Example and a comparative example. Explanatory drawing of the structure of the lamination-type battery produced in an Example and a comparative example.

Hereinafter, the embodiments for carrying out the present invention will be described with reference to the drawings. Various modifications and substitutions can be made to.
[Positive active material for lithium ion secondary battery]
A configuration example of the positive electrode active material for a lithium ion secondary battery according to the present embodiment will be described below.

The positive electrode active material for lithium ion secondary batteries of the present embodiment (hereinafter also simply referred to as "positive electrode active material") contains a film-containing lithium metal composite oxide powder.
The coating-containing lithium metal composite oxide powder is a coating-containing lithium metal composite oxide having lithium metal composite oxide particles and a lithium tungstate coating disposed on the surfaces of the lithium metal composite oxide particles. Contains particles.
The lithium metal composite oxide has the general formula: Li _z Ni _1-x-y Co _x M _y O _2+α (where 0 < x ≤ 0.35, 0 ≤ y ≤ 0.35, 0.95 ≤ z ≤1.30, 0≤α≤0.15, M is at least one element selected from Mn, V, Mg, Mo, Nb, Ti and Al), and the crystal structure is a layered structure.
The ratio of the amount of lithium contained in the lithium compound other than lithium tungstate present on the surface of the coating-containing lithium metal composite oxide particles to the total amount of lithium contained in the coating-containing lithium metal composite oxide particles is 0.01. It is more than mass % and below 0.05 mass %.

The inventors of the present invention have found that when a positive electrode active material for a lithium ion secondary battery having a coating made of lithium tungstate is applied to a lithium ion secondary battery, the battery capacity decreases compared to when the coating is not provided. We investigated the cause of the occurrence of such cases. As a result, when a coating of lithium tungstate is formed on the surface of the lithium metal composite oxide particles, the lithium ions inside the particles of the lithium metal composite oxide may be extracted, and the amount of lithium inside the particles decreases. The present inventors have found that this is the cause of the decrease in capacity, and completed the present invention.

The positive electrode active material of this embodiment contains the film-containing lithium metal composite oxide powder as described above. The positive electrode active material of the present embodiment can also be composed of a film-containing lithium metal composite oxide powder.

The film-containing lithium metal composite oxide powder is a film-containing lithium metal composite oxide having particles of lithium metal composite oxide as a base material and a film (coating) of lithium tungstate disposed on the surface of the base material. can contain particles. The film-containing lithium metal composite oxide powder can also be composed of a plurality of film-containing lithium metal composite oxide particles.

As the base material, the general formula: Li _z Ni _1-x-y Co _x M _y O _2+α (where 0 < x ≤ 0.35, 0 ≤ y ≤ 0.35, 0.95 ≤ z ≤ 1.30 , 0 ≤ α ≤ 0.15, M is at least one element selected from Mn, V, Mg, Mo, Nb, Ti and Al), a lithium metal composite oxide with a layered crystal structure Particles can be used. A high charge/discharge capacity can be obtained by using such lithium metal composite oxide particles.

In order to obtain a higher charge/discharge capacity, it is preferable to satisfy x+y≦0.2 and 0.95≦z≦1.10 in the above general formula. If high thermal stability is required, x+y>0.2 is preferred.

The particles of the lithium metal composite oxide preferably have a form composed of primary particles and secondary particles formed by aggregation of the primary particles. The film-containing lithium metal composite oxide particles preferably have a lithium tungstate film on part or all of the surfaces of the primary particles of the lithium metal composite oxide particles.

In general, it is considered that if the surfaces of the particles of the positive electrode active material are completely covered with a foreign compound, the movement (intercalation) of lithium ions is greatly restricted.

However, lithium tungstate has high lithium ion conductivity and has the effect of promoting movement of lithium ions. Therefore, by arranging lithium tungstate on the surface of the primary particles of the lithium metal composite oxide particles, it is possible to form a lithium conduction path at the interface with the electrolyte. In addition, the reaction resistance of the positive electrode active material, that is, the positive electrode resistance, can be reduced to improve the output characteristics of the battery.

Since the reaction resistance is reduced, the voltage lost in the battery is reduced, and the voltage actually applied to the load side is relatively increased, resulting in high output. In addition, since the lithium is sufficiently inserted and removed from the positive electrode by increasing the voltage applied to the load side, the charge/discharge capacity of the battery, that is, the battery capacity can also be improved.

Lithium tungstate has many forms such as Li ₂ WO ₄ , Li ₄ WO ₅ and Li ₆ W ₂ O ₉ , and any state of lithium tungstate may be contained in the film.

Since contact between the electrolyte and the positive electrode active material occurs on the surface of the primary particles of the lithium metal composite oxide contained in the positive electrode active material, lithium tungstate is preferably arranged on the surface of the primary particles of the lithium metal composite oxide. . Here, the primary particle surface refers to the surface of the primary particles exposed on the outer surface of the secondary particles, the portion that can contact the electrolyte through the exterior of the secondary particles, for example, when the electrolyte is an electrolyte, the electrolyte It includes primary particle surfaces exposed in the vicinity of the surface of permeable secondary particles and internal voids, as well as the surfaces of primary particles that exist alone. In addition, even if the grain boundary between the primary particles, the portion where the bonding of the primary particles is incomplete and can be in contact with the electrolyte, for example, if the electrolyte is an electrolyte, the surface of the primary particles is in a state where the electrolyte can permeate. include.

The contact between the positive electrode active material and the electrolyte occurs not only on the outer surface of the secondary particles formed by aggregation of the primary particles of the lithium metal composite oxide contained in the positive electrode active material, but also on the vicinity of the surface of the secondary particles and the inner primary particles. Voids between grains and even imperfect grain boundaries occur. For this reason, it is preferable to dispose a film of lithium tungstate on the surfaces of the primary particles to promote movement of lithium ions. In this way, by arranging the lithium tungstate film on most of the surfaces of the primary particles of the lithium metal composite oxide that can come into contact with the electrolyte, the reaction resistance of the positive electrode active material can be further reduced. preferable.

Although the form of the lithium tungstate forming the film is not particularly limited, it is preferably in the form of fine particles, for example.

Lithium tungstate is preferably particles having a particle diameter of, for example, 1 nm or more and 200 nm or less. This is because lithium tungstate having a particle size of 1 nm or more can exhibit sufficient lithium ion conductivity. In addition, by setting the particle size of lithium tungstate to 200 nm or less, it is possible to form a particularly uniform coating on the surface of the lithium metal composite oxide particles, thereby particularly suppressing the reaction resistance.

When lithium tungstate exists in the form of particles, it is not necessary that all the particles are distributed in the range of particle diameters of 1 nm or more and 200 nm or less. , 50% or more in number preferably have a size of 1 nm or more and 200 nm or less.

Lithium tungstate does not need to be arranged on the entire surface of the lithium metal composite oxide particles, and may be in a scattered state, for example.

Lithium tungstate may be present in the form of a thin film on the surfaces of the particles of the lithium metal composite oxide. By coating the surface of the lithium metal composite oxide particles with a thin film, it is possible to form a lithium conduction path at the interface with the electrolyte while suppressing the decrease in the specific surface area, further improving the battery capacity and reducing the reaction resistance. The effect of doing is obtained.

When the lithium tungstate is arranged in the form of a thin film on the surface of the lithium metal composite oxide particles, the thin film preferably has a thickness of 1 nm or more and 150 nm or less.

This is because when lithium tungstate exists in the form of a thin film, the lithium tungstate thin film can exhibit sufficient lithium ion conductivity by setting the thickness of the film to 1 nm or more and 150 nm or less.

Even when the lithium tungstate is present in the form of a thin film, it does not need to be arranged on the entire surface of the lithium metal composite oxide particles, and may be present only partially, for example. In addition, the entire lithium tungstate coating need not have a thickness of 1 nm or more and 150 nm or less, and for example, a part of the lithium tungstate coating may have the thickness described above.

Lithium tungstate may be in a plurality of states, for example, the fine particle state described above and the thin film state.

The properties of lithium tungstate on the particle surface of such a lithium metal composite oxide can be determined, for example, by observation with a field emission scanning electron microscope (SEM).

Then, the ratio of the amount of lithium contained in the lithium compound other than lithium tungstate present on the surface of the coating-containing lithium metal composite oxide particles to the total amount of lithium contained in the coating-containing lithium metal composite oxide particles (hereinafter simply (also referred to as "unreacted lithium content ratio") is preferably 0.05% by mass or less. More preferably, the content of unreacted lithium is 0.03% by mass or less. Moreover, the content of unreacted lithium is preferably 0.01% by mass or more.

According to the study of the inventors of the present invention, the lithium compound other than lithium tungstate present on the surface of the film-containing lithium metal composite oxide particles is an unreacted lithium compound that remains when the lithium tungstate film is formed. caused by. Lithium compounds other than lithium tungstate present on the surfaces of the film-containing lithium metal composite oxide particles are considered to be mainly composed of lithium hydroxide and lithium carbonate.

By controlling the content of unreacted lithium within a predetermined range, it is possible to suppress a decrease in battery capacity due to extraction of lithium ions from the inside of the lithium metal composite oxide particles during the formation of the lithium tungstate coating. In addition, by controlling the unreacted lithium content ratio within a predetermined range, for example, in the case of a lithium ion secondary battery, gas is generated due to the reaction between the lithium compound other than lithium tungstate and the binder inside the battery. can be suppressed.

Specifically, when the unreacted lithium content is 0.01% by mass or more as described above, tungstic acid Sufficient excess lithium was present to form lithium. Therefore, it is possible to suppress the decrease in battery capacity caused by the extraction of lithium ions from the inside of the particles of the lithium metal composite oxide powder during the formation of the lithium tungstate film.

Further, when the content of unreacted lithium is 0.05% by mass or less, the content of lithium compounds other than lithium tungstate present on the surfaces of the film-containing lithium metal composite oxide particles is sufficiently suppressed. . Therefore, in the case of a lithium ion secondary battery, the reaction between the lithium compound other than lithium tungstate present on the surface of the film-containing lithium metal composite oxide particles and the binder or the like can be suppressed, and gas generation can be suppressed. .

The content of unreacted lithium can be analyzed by neutralization titration and ICP emission spectroscopy/mass spectrometry.

Specifically, first, the film-containing lithium metal composite oxide particles are gas-treated with carbon dioxide gas to carbonate lithium hydroxide among lithium compounds other than lithium tungstate. Then, the film-containing lithium metal composite oxide particles gas-treated with carbon dioxide gas are added to pure water, stirred for a certain period of time, filtered, barium chloride is added to the filtrate, and neutralization titration is performed with hydrochloric acid. By performing neutralization titration with hydrochloric acid, the amount of lithium contained in the lithium compound other than lithium tungstate present on the surface of the film-containing lithium metal composite oxide particles can be specified from the second neutralization point.

In addition, the total amount of lithium contained in the film-containing lithium metal composite oxide particles can be determined by dissolving predetermined film-containing lithium metal composite oxide particles with acid and performing ICP emission spectroscopy/mass spectrometry.

As described above, the amount of lithium contained in the lithium compound other than lithium tungstate present on the surface of the coating-containing lithium metal composite oxide particles obtained by neutralization titration and ICP emission spectroscopy/mass spectrometry, and the coating content The unreacted lithium content can be calculated from the total amount of lithium contained in the lithium metal composite oxide particles.

According to the positive electrode active material of this embodiment described above, the content of unreacted lithium is controlled within a predetermined range. That is, it is possible to suppress the extraction of lithium ions from the inside of the particles of the lithium metal composite oxide when forming the lithium tungstate film. In addition, lithium compounds other than lithium tungstate present on the surface of the film-containing lithium metal composite oxide particles are suppressed.

Therefore, it is possible to obtain a positive electrode active material having a lithium tungstate film and having excellent battery capacity. Furthermore, when it is used as a lithium ion secondary battery, generation of gas can be suppressed.
[Method for producing positive electrode active material for lithium ion secondary battery]
Next, a method for manufacturing the positive electrode active material for a lithium ion secondary battery of the present embodiment (hereinafter also referred to as "method for manufacturing a positive electrode active material") will be described.

The manufacturing method of the positive electrode active material of this embodiment can have the following steps.

A mixing step of mixing the lithium metal composite oxide powder and the tungsten compound to prepare a raw material mixture.
A heat treatment process for heat-treating the raw material mixture.
The lithium metal composite oxide powder has the general formula: Li _z Ni _1-xy Co _x M _y O _2+α (where 0 < x ≤ 0.35, 0 ≤ y ≤ 0.35, 0.95 ≤ z ≤ 1.30, 0 ≤ α ≤ 0.15, M is at least one element selected from Mn, V, Mg, Mo, Nb, Ti and Al), and the crystal structure is a layered structure The lithium metal composite oxide particles are included, and the total amount of eluted lithium is 0.20% by mass or more and 1.00% by mass or less.

Each step will be described below.
(1) Mixing Step In the mixing step, the lithium metal composite oxide powder and the tungsten compound can be mixed to prepare a raw material mixture.

Each raw material used in the mixing step will be described.
(lithium metal composite oxide powder)
The lithium metal composite oxide powder has a general formula: Li _z Ni _1-xy Co _x M _y O _2+α (where 0 < x ≤ 0.35, 0 ≤ y ≤ 0.35, 0.95 ≤ z ≤ 1.30, 0 ≤ α ≤ 0.15, M is at least one element selected from Mn, V, Mg, Mo, Nb, Ti and Al) Lithium metal having a layered crystal structure Contains composite oxide particles. The lithium metal composite oxide powder can also be composed of a plurality of particles of the lithium metal composite oxide.

In order to obtain a higher charge/discharge capacity, it is preferable to satisfy x+y≦0.2 and 0.95≦z≦1.10 in the above general formula. If high thermal stability is required, x+y>0.2 is preferred.

Further, the lithium metal composite oxide powder preferably has a total dissolved lithium amount of 0.20% by mass or more and 1.00% by mass or less. Here, the total amount of eluted lithium means the amount of lithium calculated by adding pure water to the lithium metal composite oxide powder, stirring the mixture for a certain period of time, and then performing neutralization titration on the filtered filtrate. Specifically, the compound state of eluted lithium can be evaluated from the neutralization point that appears by adding hydrochloric acid while measuring the pH of the filtrate, and the total amount of eluted lithium can be calculated.

The total amount of eluted lithium indicates the ratio of excess lithium adhering to the surface of the lithium metal composite oxide particles to the lithium metal composite oxide particles. It can be said that it has a sufficient amount of surplus lithium for the reaction with Therefore, when a heat treatment is performed after mixing with the tungsten compound, the reaction between the tungsten compound and the surplus lithium sufficiently proceeds, and extraction of internal lithium ions can be sufficiently suppressed. However, even if the total amount of eluted lithium is greater than 1.00% by mass, there is no significant difference in suppressing the extraction of internal lithium ions, so the total amount of eluted lithium is 1.00% by mass or less. Preferably. Further, by setting the total amount of eluted lithium to 1.00% by mass or less, it is possible to sufficiently suppress the unreacted lithium content in the film-containing lithium metal composite oxide particles of the obtained positive electrode active material. Therefore, when a lithium ion secondary battery is produced using the obtained positive electrode active material, the lithium compound other than lithium tungstate present on the surface of the film-containing lithium metal composite oxide particles reacts with the binder and the like. can be suppressed, and the generation of gas can be suppressed.

A lithium metal composite oxide powder can be obtained by firing a mixture of a lithium compound and a metal composite hydroxide or metal composite oxide, which is a precursor of the lithium metal composite oxide. The temperature at which the mixture is fired can be selected according to the composition and the like, and is not particularly limited, but is preferably higher than 700°C and lower than 800°C. The atmosphere during firing is preferably an oxidizing atmosphere. As the oxidizing atmosphere, an oxygen-containing gas atmosphere can be preferably used, and for example, an atmosphere with an oxygen concentration of 18 vol % or more and 100 vol % or less is more preferable.

The metal composite oxide is represented by, for example, Ni _1-xy Co _x M _y O _1+β . Also, the metal composite hydroxide is represented by, for example, Ni _1-xy Co _x M _y (OH) _2+γ . Since x, y, and the element M in the formula are the same as in the case of the lithium metal composite oxide described above, their description is omitted here. Note that β preferably satisfies 0≦β≦0.15 and γ satisfies 0≦γ≦0.15.

The metal composite hydroxide can be prepared by a crystallization method or the like, and the metal composite oxide can be prepared, for example, by roasting the metal composite hydroxide.

In the method for producing a positive electrode active material of the present embodiment, before the mixing step, if necessary, the mixture of the metal composite hydroxide or metal composite oxide and the lithium compound is baked to obtain a lithium metal composite It can also have a lithium metal composite oxide powder preparation step of preparing an oxide powder.

Then, if the surface of the lithium metal composite oxide particles contained in the lithium metal composite oxide powder contains excessive lithium, for example, after performing a water washing step of washing the lithium metal composite oxide powder with water, mixing It can also be used for the process. In the water washing step, for example, the lithium metal composite oxide powder and water are mixed to form a slurry, whereby water washing can be performed. After washing with water, the water content of the resulting lithium metal composite oxide powder (cake) can be adjusted by solid-liquid separation. The moisture content of the cake and the raw material mixture to be described later can be measured with a general moisture meter.
(tungsten compound)
The tungsten compound is preferably water-soluble and dissolves in water contained in the raw material mixture, in order to allow the tungsten compound to permeate to the surface of the primary particles inside the secondary particles of the lithium metal composite oxide. However, even if the tungsten compound is difficult to dissolve in water at room temperature, any compound that dissolves in water upon heating during heat treatment may be used. Furthermore, since the water in the raw material mixture becomes alkaline due to the contained lithium, it may be a compound that is soluble in alkali.

The state of the tungsten compound is not particularly limited, and may be, for example, a solid state or an aqueous solution state.

As described above, the tungsten compound is not limited as long as it is soluble in water, but preferably one or more selected from tungsten oxide, lithium tungstate, ammonium tungstate, and sodium tungstate. In particular, one or more selected from tungsten oxide, lithium tungstate, and ammonium tungstate, which are less likely to be contaminated with impurities, is more preferable, and one or more selected from tungsten oxide and lithium tungstate is even more preferable.

Then, the raw material mixture can be prepared by mixing the lithium metal composite oxide powder and the tungsten compound as described above.

The content of water in the raw material mixture with respect to the lithium metal composite oxide powder is preferably 2% by mass or more. By setting the water content in the above range, voids between primary particles communicating with the outside of the secondary particles of the lithium metal composite oxide contained in the lithium metal composite oxide powder and imperfect grain boundaries are filled with water. The tungsten in the tungsten compound can be infiltrated. Therefore, it is possible to disperse a sufficient amount of tungsten on the surfaces of the primary particles. However, if the water content is excessively high, the heat treatment efficiency in the post-process is lowered, so the water content is preferably 20% by mass or less. The content of water in the raw material mixture with respect to the lithium metal composite oxide powder is more preferably 3% by mass or more and 15% by mass or less, and even more preferably 3% by mass or more and 10% by mass or less.

By setting the content of water in the raw material mixture within the above range, the pH rises due to the amount of lithium eluted in the water, thereby exhibiting the effect of suppressing excessive elution of lithium. The molar ratio of Co and M in the lithium metal composite oxide powder is maintained up to the positive electrode active material.

The moisture content of the raw material mixture can be adjusted by adjusting the moisture content of the cake obtained when the lithium-nickel composite oxide powder is washed with water, as described above. Moreover, it can also be adjusted by, for example, adding water to the raw material mixture.

In the case where the lithium metal composite oxide powder is added after being added as a cake containing water by the above-described water washing step, Li (lithium) contained in the water content of the cake relative to W (tungsten) in the raw material mixture obtained in the mixing step is preferably 1.5 or more and less than 3.0. This is because by setting the molar ratio of Li contained in the moisture of the cake to W in the raw material mixture to be 1.5 or more, a sufficient amount of lithium can be supplied for the reaction with the tungsten compound, and less than 3.0 This is because the amount of surplus lithium that has not reacted with W after the heat treatment can be suppressed. Depending on the amount of the tungsten compound to be added, the molar ratio of Li contained in the moisture of the cake to W in the raw material mixture may be less than 1.5. should be supplemented. As the lithium compound to be added, a water-soluble lithium compound such as lithium hydroxide is preferable. The number of moles of Li contained in the water content of the cake can be obtained, for example, from the Li concentration in the filtrate obtained when solid-liquid separation is performed in the above-described water washing step and the water content of the cake. The lithium concentration in the filtrate can be determined by neutralization titration with hydrochloric acid.

Furthermore, the amount of tungsten contained in the raw material mixture is preferably 3.0 atomic % or less, and 0.0 atomic % or less, relative to the total number of atoms of Ni, Co and M contained in the lithium metal composite oxide powder. It is more preferable to make it 05 atomic % or more and 2.0 atomic % or less. As a result, the amount of tungsten contained in the lithium tungstate in the positive electrode active material can be set within a more preferable range, and both high charge/discharge capacity and output characteristics of the positive electrode active material can be achieved.
(2) Heat Treatment Step The heat treatment step is a step of heat-treating the prepared raw material mixture.

As a result, lithium tungstate is formed on the surface of the lithium metal composite oxide particles from the lithium and tungsten contained in the water content of the raw material mixture, and a positive electrode active material is obtained.

The heat treatment conditions in the heat treatment step are not particularly limited as long as they are selected so that lithium tungstate is formed. However, in order to prevent deterioration of electrical properties when used as a positive electrode active material, the reaction with moisture and carbonic acid in the atmosphere should be avoided, and an oxidizing atmosphere such as an oxygen atmosphere or a decarboxylated air atmosphere, Alternatively, it is preferable to carry out in a vacuum atmosphere.

The heat treatment temperature in the heat treatment step is also not particularly limited, but the heat treatment temperature is preferably 100° C. or higher and 600° C. or lower, for example.

This is because by setting the heat treatment temperature to 100° C. or higher, the moisture contained in the raw material mixture can be sufficiently evaporated, and the lithium tungstate production reaction can be sufficiently advanced. On the other hand, if the heat treatment temperature exceeds 600°C, the primary particles of the lithium metal composite oxide may be sintered, and some tungsten may dissolve in the lithium metal composite oxide, so it should be 600°C or less. is preferred.

The heat treatment time in the heat treatment step is also not particularly limited, but is preferably 3 hours or more and 20 hours or less, more preferably 5 hours or more and 15 hours or less.
[Lithium ion secondary battery]
Next, one structural example of the lithium ion secondary battery of this embodiment will be described.

The lithium ion secondary battery (hereinafter also referred to as "secondary battery") of the present embodiment 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 this embodiment includes, for example, a positive electrode, a negative electrode, and a non-aqueous electrolyte, and is composed of components similar to those of a general lithium ion secondary battery. It should be noted that the embodiments described below are merely examples, and the lithium ion secondary battery of the present embodiment is implemented in a form in which various changes and improvements are made based on the knowledge of those skilled in the art, including the following embodiments. can do. Moreover, the lithium-ion secondary battery of this embodiment is not particularly limited in its application.
(1) Positive Electrode The positive electrode included in the secondary battery of the present embodiment can contain the positive electrode active material described above.

An example of the method for producing the positive electrode will be described below. First, the above-described positive electrode active material (powder), conductive material and binder are mixed to form a positive electrode mixture. By kneading this, a positive electrode mixture paste can be produced.

Since the mixing ratio of each material in the positive electrode mixture is a factor that determines the performance of the lithium ion secondary battery, it can be adjusted according to the application. The mixture ratio of the materials can be the same as that of the positive electrode of a known lithium ion secondary battery. It can contain 60% by mass or more and 95% by mass or less, 1% by mass or more and 20% by mass or less of the conductive material, and 1% by mass or more and 20% by mass or less of the binder.

The obtained positive electrode mixture paste is applied, for example, to the surface of a current collector made of aluminum foil, dried to scatter the solvent, and a sheet-like positive electrode is produced. If necessary, pressure may be applied by a roll press or the like in order to increase the electrode density. The sheet-shaped positive electrode thus obtained can be cut into a size suitable for the intended battery, and used for the manufacture of the battery.

As the conductive material, for example, graphite (natural graphite, artificial graphite, expanded graphite, etc.), one or more carbon black-based materials selected from acetylene black, Ketjenblack (registered trademark), etc. can be used. .

The binding agent (binder) plays a role of binding the active material particles, and examples thereof include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluororubber, ethylene propylene diene rubber, styrene butadiene, and cellulose. One or more selected from resins, polyacrylic acid, and the like can be used.

If necessary, a solvent for dispersing the positive electrode active material, the conductive material and the activated carbon and dissolving the binder can be added to the positive electrode mixture. As the solvent, specifically, an organic solvent such as N-methyl-2-pyrrolidone can be used. Activated carbon can also be added to the positive electrode mixture in order 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 produced by press-molding a positive electrode mixture and then drying it in a vacuum atmosphere.
(2) Negative Electrode Metallic lithium, lithium alloys, or the like can be used for the negative electrode. In addition, the negative electrode is prepared by mixing a negative electrode active material capable of intercalating and deintercalating lithium ions with a binder, adding an appropriate solvent to make a paste, and applying the negative electrode mixture to the surface of a metal foil current collector such as copper. It may be applied, dried, and compressed to increase the electrode density as necessary.

As the negative electrode active material, for example, natural graphite, artificial graphite, sintered organic compounds such as phenol resin, and powdery carbon substances such as coke can be used. In this case, a fluorine-containing resin such as PVDF can be used as the binder for the negative electrode in the same manner as the binder for the positive electrode. Solvents can be used.
(3) Separator Between the positive electrode and the negative electrode, a separator can be interposed and arranged as necessary. The separator separates the positive electrode from the negative electrode and holds the electrolyte, and a known one can be used. For example, a thin film such as polyethylene or polypropylene having a large number of fine pores can be used. can.
(4) 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 obtained by dissolving a lithium salt as a supporting salt in an organic solvent can be used. Further, as the non-aqueous electrolytic 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 that is liquid even at room temperature.

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

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

A solid electrolyte may be used as the non-aqueous electrolyte. Solid electrolytes have the property of withstanding high voltages. Solid electrolytes include inorganic solid electrolytes and organic solid electrolytes.

Examples of inorganic solid electrolytes 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 preferably used. Examples of oxide-based solid electrolytes include lithium phosphate (Li ₃ PO ₄ ), Li ₃ PO ₄ N _x , LiBO ₂ N _x , LiNbO ₃ , LiTaO ₃ , Li ₂ SiO ₃ , Li ₄ SiO ₄ -Li _{3 PO4} , _Li4SiO4 - _Li3VO4 , _{Li2O - B2O3 - P2O5} , _{Li2O - SiO2 , Li2O} - _{B2O3 -} ZnO, Li1 _{+X AlXTi 2-X} (PO ₄ ) ₃ (0≦X≦1), Li _1+X Al _X Ge _2-X (PO ₄ ) ₃ (0≦X≦1), LiTi ₂ (PO ₄ ) ₃ , Li _3X La _{2/ 3-X} TiO ₃ (0≦X≦2/3), Li ₅ La ₃ Ta ₂ O ₁₂ , Li ₇ La ₃ Zr ₂ O ₁₂ , Li ₆ BaLa ₂ Ta ₂ O ₁₂ , Li _3.6 Si _0.6 One or more selected from P _0.4 O ₄ and the like can be mentioned.

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

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

The organic solid electrolyte is not particularly limited as long as it is a polymer compound exhibiting ion conductivity. For example, polyethylene oxide, polypropylene oxide, copolymers thereof, and the like can be used. Moreover, the organic solid electrolyte may contain a supporting salt (lithium salt).
(Shape and configuration of secondary battery)
The lithium-ion secondary battery of this embodiment described above can have various shapes such as a cylindrical shape and a laminated shape. Regardless of which shape is adopted, if the secondary battery of the present embodiment uses a non-aqueous electrolyte as a non-aqueous electrolyte, the positive electrode and the negative electrode are laminated with a separator interposed to form an electrode body, The obtained electrode body is impregnated with a non-aqueous electrolytic solution, and a current collecting lead is formed between the positive electrode current collector and the positive electrode terminal connected to the outside, and between the negative electrode current collector and the negative electrode terminal connected to the outside. etc., and sealed in the battery case.

As described above, the secondary battery of the present embodiment is not limited to the form using a non-aqueous electrolyte as a non-aqueous electrolyte. For example, a secondary battery using a solid non-aqueous electrolyte, that is, a 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.

The lithium-ion secondary battery of this embodiment includes a positive electrode using the positive electrode active material described above as a positive electrode material. Therefore, a lithium-ion secondary battery having excellent battery capacity can be obtained. Furthermore, a lithium ion secondary battery in which gas generation is suppressed can be obtained.

In addition, since the positive electrode active material includes a film made of lithium tungstate, a lithium ion secondary battery with low reaction resistance and excellent output characteristics can be obtained.

Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples.
(Evaluation method)
First, evaluation methods in the following examples and comparative examples will be described.
(1) Total eluted lithium amount of lithium metal composite oxide powder The total eluted lithium amount of the lithium metal composite oxide powder was evaluated by the Warder method, which is one of the neutralization titration methods. From the evaluation results, the amounts of lithium hydroxide (LiOH) and lithium carbonate (Li ₂ CO ₃ ) were calculated, and the sum of these lithium amounts was defined as the surplus lithium amount.

Specifically, pure water was added to the lithium metal composite oxide powder prepared for the mixing step in each of the following examples and comparative examples, and after stirring, hydrochloric acid was added while measuring the pH of the filtered filtrate. It was calculated by evaluating the compound state of lithium eluted from the neutralization point that appears as the temperature increases.

Note that the above titration was measured up to the second neutralization point. The alkali content neutralized with hydrochloric acid up to the second neutralization point is regarded as the amount of lithium derived from lithium hydroxide (LiOH) and lithium carbonate (Li ₂ CO ₃ ), and the amount of hydrochloric acid added dropwise up to the second neutralization point. The amount of lithium in the filtrate was calculated from the amount and the concentration of hydrochloric acid.

Then, the calculated amount of lithium in the filtrate is divided by the amount of the sample of the lithium metal composite oxide powder used in preparing the filtrate, and the unit is converted to % by mass to obtain the total amount of the lithium metal composite oxide powder. The amount of eluted lithium was determined.
(2) Unreacted Lithium Content Ratio The unreacted lithium content of the film-containing lithium metal composite oxide particles was evaluated by neutralization titration.

Specifically, first, the obtained film-containing lithium metal composite oxide particles (powder), which is the positive electrode active material, is gas-treated with carbon dioxide gas, and unreacted lithium compounds, that is, lithium compounds other than lithium tungstate, are hydroxylated. Carbonates lithium.

15 g of the film-containing lithium metal composite oxide particles that have been gas-treated with carbon dioxide gas are added to 75 mL of pure water and stirred for 15 minutes. Neutralization titration was performed with hydrochloric acid.

By performing neutralization titration with hydrochloric acid, the amount of lithium contained in the unreacted lithium compound existing on the surface of the coating-containing lithium metal composite oxide particles from the second neutralization point, that is, the amount of lithium compounds other than lithium tungstate The amount of lithium contained was evaluated.

Further, the total amount of lithium contained in the film-containing lithium metal composite oxide particles was determined by dissolving the film-containing lithium metal composite oxide particles with an acid and performing ICP emission spectroscopy/mass spectrometry.

The amount of lithium contained in the lithium compound other than lithium tungstate present on the surface of the film-containing lithium metal composite oxide particles obtained by the above neutralization titration and ICP emission spectroscopy/mass spectrometry, and the film-containing lithium metal composite The unreacted lithium content ratio was calculated from the total amount of lithium contained in the oxide particles.

In the following examples and comparative examples, since no additive other than the target component was added to the positive electrode active material, the positive electrode active material was made of film-containing lithium metal composite oxide particles. It is composed of metal composite oxide powder. Therefore, the positive electrode active material thus obtained is evaluated as described above.
(3) Discharge capacity A 2032-type coin-type battery 10 (hereinafter referred to as "coin-type battery") shown in Fig. 1 was used to evaluate the positive electrode active materials obtained in the following examples and comparative examples. bottom. FIG. 1 shows a perspective view and a cross-sectional view of a coin-type battery.

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

The case 11 has a hollow positive electrode can 11a with one end open, and a negative electrode can 11b 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 consists of a positive electrode 12a, a separator 12c and a negative electrode 12b, which are stacked in this order. It is housed in the case 11 so as to come into contact with the inner surface of the can 11b through the current collector 13. As shown in FIG. A current collector 13 is also arranged between the positive electrode 12a and the separator 12c.

The case 11 is provided with a gasket 11c, which restricts relative movement between the positive electrode can 11a and the negative electrode can 11b so as to maintain a non-contact state. The gasket 11c also has the function of sealing the gap between the positive electrode can 11a and the negative electrode can 11b to seal the inside of the case 11 from the outside in an air-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, 15 mg of acetylene black, and 7.5 mg of polytetrafluoroethylene (PTFE) resin were mixed, and the resulting positive electrode mixture was press molded at a pressure of 100 MPa to have a diameter of 11 mm and a thickness of 100 μm. Thus, the positive electrode 12a was produced. 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 above-described coin-type battery 10 was produced in an Ar atmosphere glove box in which the dew point was controlled at -80°C.

A lithium (Li) metal having a diameter of 17 mm and a thickness of 1 mm was used for the negative electrode 12b. A polyethylene porous film having a film thickness of 25 μm was used for the separator 12c.

An electrolytic solution is used as the electrolyte, and the electrolytic solution is an equal volume mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) with 1 M LiClO ₄ as a supporting electrolyte (supporting salt) (manufactured by Toyama Pharmaceutical Co., Ltd.). Using.

The discharge capacity (initial discharge capacity) indicating the performance of the manufactured coin-type battery 10 was evaluated as follows.

After the coin-type battery 10 shown in FIG. 1 was produced and allowed to stand for about 24 hours, and after the open circuit voltage OCV (open circuit voltage) was stabilized, the current density to the positive electrode was set to 0.1 mA/cm ² and the cutoff voltage was 4. Charged up to 3V. After resting for 1 hour, the capacity when the battery was discharged to a cutoff voltage of 3.0 V was taken as the discharge capacity. A multi-channel voltage/current generator (R6741A, manufactured by Advantest Co., Ltd.) was used to measure the discharge capacity.
(4) Evaluation of gas generation Using the obtained positive electrode active material, the laminate type battery 20 shown in FIG. 2 was produced. Note that FIG. 2 is a perspective view so that the internal structure of the laminate type battery 20 can be seen.

The laminate-type battery 20 has a structure in which a laminate of a positive electrode film 21 , a separator 22 , and a negative electrode film 23 is impregnated with an electrolytic solution and sealed with a laminate 24 . A positive electrode tab 25 is connected to the positive electrode film 21 and a negative electrode tab 26 is connected to the negative electrode film 23 , respectively.

A slurry obtained by dispersing 20.0 g of the obtained positive electrode active material, 2.35 g of acetylene black, and 1.18 g of polyvinylidene fluoride in N-methyl-2-pyrrolidone (NMP) was applied to a positive electrode per 1 cm ² of Al foil. It was applied so that 7.3 mg of active material was present. Next, the Al foil coated with the slurry containing the positive electrode active material was dried in the atmosphere at 120° C. for 30 minutes to remove NMP. The Al foil coated with the positive electrode active material was cut into strips with a width of 66 mm, and roll-pressed with a load of 1.2 t to prepare a positive electrode film. Then, the positive electrode film was cut into a rectangle of 50 mm×30 mm, dried in a vacuum dryer at 120° C. for 12 hours, and used as the positive electrode film 21 of the laminate type battery 20 .

In addition, a negative electrode film 23 was prepared by coating a copper foil with a negative electrode mixture paste, which is a mixture of graphite powder having an average particle size of about 20 μm and polyvinylidene fluoride. The separator 22 is a polyethylene porous film with a thickness of 25 μm, and the electrolyte is a 3:7 mixed solution of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) with 1M LiPF ₆ as a supporting electrolyte (Ube Industries, Ltd.) company) was used.

In a dry room controlled at a dew point of −80° C., the laminate of the positive electrode film 21, the separator 22, and the negative electrode film 23 is impregnated with an electrolytic solution and sealed with a laminate 24 to produce a laminate type battery 20. bottom.

The produced laminate type battery was stored in a constant temperature bath (Cosmopia) manufactured by Hitachi Appliances, Inc. set at 25° C. for 12 hours.

After storing for 12 hours, while being housed in a constant temperature bath, using a charge/discharge device (manufactured by Hokuto Denko Co., Ltd.: HJ1001SD8), a constant current mode of 0.2 C in the range of 3.0 V to 4.3 V was charged and discharged three times. After charging and discharging, the battery was charged to 4.6 V in a constant current mode of 1 C, and left in a constant temperature bath for 72 hours.

After being left in the constant temperature bath, the laminate was evaluated as A when no swelling was observed and gas generation was suppressed, and B when the laminate was confirmed to be swelling and gas was generated. bottom.
[Example 1]
(lithium metal composite oxide powder preparation step)
First, a lithium metal composite oxide powder to be subjected to the mixing step was prepared by the following procedure.

Anhydrous lithium hydroxide and a metal composite oxide represented by Ni _0.88 Co _0.09 Al _0.03 O are the atomic ratios of lithium (Li) and metals other than lithium (Me) They were weighed and mixed so that the Li/Me ratio was 1.05.

Metals other than lithium mean metal components contained in metal composite oxides, that is, Ni, Co, and Al. As the metal composite oxide, one prepared by roasting a metal composite hydroxide produced by a crystallization method at 500° C. in an air atmosphere (oxygen: 21 vol %) was used.

Next, the mixture was placed in a sagger and fired in an atmosphere with an oxygen concentration of 80 vol % or higher at 780° C. for 220 minutes using a roller hearth kiln to produce a lithium-nickel composite oxide. The obtained lithium metal composite oxide powder was evaluated for the total amount of eluted lithium. Table 1 shows the evaluation results. Further, when the powder X-ray diffraction pattern of the obtained lithium metal composite oxide powder was measured, it was confirmed that the powder had a layered crystal structure.

Ion-exchanged _{water was} added to the obtained particles ( _powder ) of the lithium metal _composite oxide represented by _{Li1.05Ni0.88Co0.09Al0.03O2} so that the slurry concentration was 1500 g/L. was added and slurried.

The electrical conductivity of the ion-exchanged water used was 5 μS/cm.

After stirring the slurry for 20 minutes, it was filtered by a filter press to obtain a cake containing lithium metal composite oxide powder and water.

(Mixing process)
A cake containing a lithium metal composite oxide powder and water is added with trioxide so that the ratio of the number of tungsten atoms to the number of atoms of metal components other than lithium contained in the lithium metal composite oxide powder is 0.15%. Tungsten was added. A raw material mixture was prepared by mixing for 5 minutes at room temperature (25° C.). A shaker mixer was used for mixing.

The content ratio of water to the lithium metal composite oxide powder in the obtained raw material mixture was 4.5% by mass.
(Heat treatment process)
Next, the raw material mixture was heat-treated at 150° C. for 10 hours in a decarbonated air atmosphere to obtain a positive electrode active material.

The unreacted lithium content ratio of the obtained positive electrode active material was evaluated. Table 1 shows the evaluation results.

The obtained positive electrode active material and the lithium metal composite oxide powder subjected to the mixing step were observed with a scanning electron microscope (model: JSM-7001F manufactured by JEOL Ltd.).

As a result, it was confirmed that the lithium metal composite oxide particles contained in the lithium metal composite oxide powder had secondary particles formed by agglomeration of primary particles. In addition, it was confirmed by observation using backscattered electrons that the positive electrode active material was a film-containing lithium metal composite oxide particle in which a film was formed on the surface of the primary particles of the lithium metal composite oxide. By comparing with the analysis results of powder X-ray diffraction, it was confirmed that the coating was composed of lithium tungstate. In addition, the same thing could be confirmed in Examples 2 and 3 below.

A lithium ion secondary battery was produced using the obtained positive electrode active material, and evaluation of discharge capacity and evaluation of gas generation were performed. Table 1 shows the evaluation results.
[Example 2, Example 3]
In the lithium metal composite oxide powder preparation step, the positive electrode active material and A lithium ion secondary battery was produced and evaluated. Table 1 shows the evaluation results.

In each case, a lithium metal composite oxide powder having the same composition as in Example 1 was obtained. In addition, it was confirmed that the prepared lithium metal composite oxide powder had a layered crystal structure [Comparative Examples 1 and 2].
In the lithium metal composite oxide powder preparation step, the positive electrode active material and the A lithium ion secondary battery was produced and evaluated. Table 1 shows the evaluation results.

表１に示した結果から、未反応リチウム含有割合を０．０１質量％以上０．０５質量％以下とすることで、放電容量が２１０ｍＡｈ／ｇ以上であり、リチウムイオン二次電池とした場合に、電池容量に優れた、タングステン酸リチウムによる被膜を備えた正極活物質とすることができることを確認できた。

From the results shown in Table 1, by setting the unreacted lithium content ratio to 0.01% by mass or more and 0.05% by mass or less, the discharge capacity is 210 mAh / g or more, and when it is a lithium ion secondary battery , it was confirmed that a positive electrode active material having a coating made of lithium tungstate, which is excellent in battery capacity, can be obtained.

It was also confirmed that by setting the unreacted lithium content ratio within the above range, it is possible to suppress gas generation in the case of a lithium ion secondary battery.

Claims (2)

A positive electrode active material for a lithium ion secondary battery comprising a film-containing lithium metal composite oxide powder,
The film-containing lithium metal composite oxide powder is
General formula: Li _z Ni _1-x-y Co _x My _{O 2+α} (where 0 < x ≤ 0.35, 0 ≤ y ≤ 0.35, 0.95 ≤ z ≤ 1.30, 0 ≤ α ≤ 0.15, M is at least one element selected from Mn, V, Mg, Mo, Nb, Ti and Al), and the crystal structure is a layered lithium metal composite oxide particle;
a coating of lithium tungstate disposed on the surface of the lithium metal composite oxide particles;
The ratio of the amount of lithium contained in the lithium compound other than lithium tungstate present on the surface of the coating-containing lithium metal composite oxide particles to the total amount of lithium contained in the coating-containing lithium metal composite oxide particles is 0.01. A positive electrode active material for a lithium-ion secondary battery having a mass % or more and 0.05 mass % or less. A method for producing a positive electrode active material for a lithium ion secondary battery according to claim 1,
General formula: Li _z Ni _1-x-y Co _x My _{O 2+α} (where 0 < x ≤ 0.35, 0 ≤ y ≤ 0.35, 0.95 ≤ z ≤ 1.30, 0 ≤ α ≤ 0.15, M is at least one element selected from Mn, V, Mg, Mo, Nb, Ti and Al) Lithium containing particles of a lithium metal composite oxide having a layered crystal structure A mixing step of mixing a metal composite oxide powder and a tungsten compound to prepare a raw material mixture;
and a heat treatment step of heat-treating the raw material mixture,
The lithium metal composite oxide powder has a total eluted lithium amount of 0.20% by mass or more and 1.00% by mass or less,
The method for producing a positive electrode active material for a lithium ion secondary battery, wherein the total amount of eluted lithium is a ratio of the amount of surplus lithium evaluated by the Warder method for the lithium metal composite oxide powder to the lithium metal composite oxide powder.

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