WO2016084931A1 - Positive electrode active material for nonaqueous electrolyte secondary cell, method for manufacturing same, and nonaqueous electrolyte secondary cell in which said positive electrode active material is used - Google Patents

Abstract

Provided is a positive electrode active material for a nonaqueous electrolyte secondary cell with which high capacity and greater output is obtained when used as a positive electrode material. A method for manufacturing the positive electrode active material for a nonaqueous electrolyte secondary cell, the method having: a mixing step in which is obtained a W mixture of Li metal composite oxide particles comprising primary particles represented by the general formula Li_zNi_1-x-yCo_xM_yO₂ (O < x ≤ 0.35, 0 ≤ y ≤ 0.35, 0.95 ≤ z ≤ 1.30, and M is at least one element selected from Mn, V, Mg, Mo, Nb, Ti, and Al) and secondary particles in which the primary particles are aggregated, 2 mass% or more of liquid in relation to the oxide particles, and a W compound or a W compound and an Li compound, the molar ratio of the total amount of Li contained in the W compound, or the W compound and Li compound, of the liquid and solid portions, in relation to the amount of W contained, being 3-5; and a heat treatment step for heat-treating the W mixture, and forming lithium tungstate on the surface of the primary particles of the Li metal composite oxide particles.

Description

Positive electrode active material for non-aqueous electrolyte secondary battery, method for producing the same, and non-aqueous electrolyte secondary battery using the positive electrode active material

The present invention relates to a positive electrode active material for a non-aqueous electrolyte secondary battery, a manufacturing method thereof, and a non-aqueous electrolyte secondary battery using the positive electrode active material.

In recent years, with the widespread use of portable electronic devices such as mobile phones and laptop computers, the development of small and lightweight non-aqueous electrolyte secondary batteries having high energy density is strongly desired. In addition, development of a high output secondary battery is strongly desired as a battery for electric vehicles including hybrid vehicles.

As a secondary battery satisfying such requirements, there is a lithium ion secondary battery.
This 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 the active material of the negative electrode and the positive electrode. Such a lithium ion secondary battery is currently being actively researched and developed. Among them, a lithium ion secondary battery using a layered or spinel type lithium metal composite oxide as a positive electrode material, Since a high voltage of 4V class can be obtained, practical use is progressing as a battery having a high energy density.

The materials mainly proposed so far include 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, and lithium nickel. Examples thereof include cobalt manganese composite oxide (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) and lithium manganese composite oxide (LiMn ₂ O ₄ ) using manganese.
Among these, lithium nickel composite oxide has attracted attention as a material that can provide a high battery capacity. Further, in recent years, low resistance necessary for high output is regarded as important.
Addition of foreign elements is used as a method for realizing the low resistance, and transition metals capable of taking high numbers such as W, Mo, Nb, Ta, Re, etc. are particularly useful.

For example, Patent Document 1 contains at least one element selected from Mo, W, Nb, Ta, and Re in an amount of 0.1 to 5 mol% with respect to the total molar amount of Mn, Ni, and Co. Lithium transition metal compound powder for a lithium secondary battery positive electrode material has been proposed, and Mo, W, Nb, Ta, and Li in the surface portion of primary particles and the total of metal elements other than Mo, W, Nb, Ta, and Re The total atomic ratio of Re is preferably 5 times or more of the atomic ratio of the entire primary particle.

According to this proposal, it is possible to achieve both low cost and high safety of the lithium transition metal compound powder for the lithium secondary battery positive electrode material, high load characteristics, and improved powder handling properties.
However, the lithium transition metal compound powder is obtained by pulverizing raw materials in a liquid medium, spray-drying a slurry in which these are uniformly dispersed, and firing the resulting spray-dried body. Therefore, a part of different elements such as Mo, W, Nb, Ta, and Re is replaced with Ni arranged in a layer, and there is a problem that battery characteristics such as battery capacity and cycle characteristics are deteriorated. It was.

Patent Document 2 discloses a positive electrode active material for a non-aqueous electrolyte secondary battery having at least a layered lithium transition metal composite oxide, the lithium transition metal composite oxide being composed of primary particles and aggregates thereof. A non-aqueous electrolyte having a compound which is present in the form of a particle composed of one or both of secondary particles and has at least one selected from the group consisting of molybdenum, vanadium, tungsten, boron and fluorine on at least the surface of the particle A positive electrode active material for a secondary battery has been proposed.

As a result, it is said that a positive electrode active material for a non-aqueous electrolyte secondary battery having excellent battery characteristics even under a more severe use environment can be obtained, and in particular, the surface of the particle is composed of molybdenum, vanadium, tungsten, boron and fluorine. By having a compound having at least one selected from the group, the initial characteristics are improved without impairing the improvement of thermal stability, load characteristics and output characteristics.

However, the effect of at least one additive element selected from the group consisting of molybdenum, vanadium, tungsten, boron and fluorine is considered to be an improvement in initial characteristics, that is, initial discharge capacity and initial efficiency, and refers to output characteristics. is not. Further, according to the disclosed manufacturing method, since the additive element is mixed with the hydroxide that has been heat-treated at the same time as the lithium compound and fired, a part of the additive element is replaced with nickel arranged in layers. There was a problem that caused the battery characteristics to deteriorate.

Further, Patent Document 3 discloses a metal including at least one selected from Ti, Al, Sn, Bi, Cu, Si, Ga, W, Zr, B, and Mo around the positive electrode active material and / or a plurality of these. A positive electrode active material coated with an intermetallic compound and / or oxide obtained by a combination has been proposed.
Such a coating can absorb oxygen gas and ensure safety, but no output characteristics are disclosed. Further, the disclosed manufacturing method is a method of coating using a planetary ball mill, and such a coating method causes physical damage to the positive electrode active material, resulting in deterioration of battery characteristics.

In Patent Document 4, a composite oxide particle mainly composed of lithium nickelate is subjected to heat treatment by adhering a tungstic acid compound, and the content of carbonate ions is 0.15% by weight or less. A positive electrode active material has been proposed.
According to this proposal, there is a tungstic acid compound or a decomposition product of the tungstic acid compound on the surface of the positive electrode active material, and the oxidation activity on the surface of the composite oxide particles in a charged state is suppressed. Although gas generation can be suppressed, the output characteristics are not disclosed at all.

Furthermore, the disclosed production method preferably comprises a composite oxide particle heated to a boiling point or higher of a solution in which an adherent component is dissolved, and a sulfuric acid compound, a nitric acid compound, a boric acid compound, or a phosphoric acid compound as well as a tungstate compound. Since the solution dissolved in the solvent is applied as the adhering component, and the solvent is removed in a short time, the tungsten compound is not sufficiently dispersed on the surface of the composite oxide particles, so that there is a problem that it is not uniformly applied. .

In addition, improvements relating to higher output of the lithium nickel composite oxide have been made. For example, Patent Document 5 discloses a lithium metal composite oxide including primary particles and secondary particles formed by aggregation of the primary particles, and Li ₂ WO ₄ , Li _{4 A} positive electrode active material for a non-aqueous electrolyte secondary battery having fine particles containing lithium tungstate represented by either WO ₅ or Li ₆ W ₂ O ₉ has been proposed, and high output is obtained with high capacity. Yes. However, although the output is increased while maintaining a high capacity, a further increase in capacity is required.

JP 2009-289726 A JP 2005-251716 A Japanese Patent Laid-Open No. 11-16566 JP 2010-40383 A JP 2013-125732 A

In view of the above problems, the present invention provides a positive electrode active material for a non-aqueous electrolyte secondary battery that, when used in a positive electrode material, has a high capacity and suppresses an increase in the amount of gas generated while obtaining a higher output. The purpose is to do.

In order to solve the above-mentioned problems, the present inventors have intensively studied the influence on the powder characteristics of the lithium metal composite oxide used as the positive electrode active material for the non-aqueous electrolyte secondary battery and the output characteristics of the battery. In addition, by forming lithium tungstate having a specific form on the surfaces of primary particles and secondary particles constituting the lithium metal composite oxide, the positive electrode resistance of the positive electrode active material is reduced and the output characteristics of the battery are improved. I found that it was possible. Furthermore, as a manufacturing method thereof, it has been found that the form of the lithium tungstate can be controlled by heat-treating a mixture in which lithium and tungsten outside the particles of the lithium metal composite oxide are controlled to a specific ratio. The present invention has been completed.

That is, the first invention of the present invention have the general _{formula: Li z Ni 1-x-} y Co x M y O 2 ( however, 0 <x ≦ 0.35,0 ≦ y ≦ 0.35,0.95 ≦ z ≦ 1.30, M is at least one element selected from Mn, V, Mg, Mo, Nb, Ti and Al), and secondary particles formed by agglomeration of primary particles Lithium metal composite oxide powder having a layered crystal structure composed of secondary particles, 2% by mass or more of moisture with respect to the lithium metal composite oxide powder, and tungsten of tungsten compound or tungsten compound and lithium compound The total lithium contained in the water and solid tungsten compound or the water and solid tungsten compound and lithium compound relative to the amount of tungsten contained. A mixing step of obtaining a tungsten mixture having a molar ratio of 3 to 5; and a heat treatment step of heat-treating the obtained tungsten mixture to form lithium tungstate on the primary particle surface of the lithium metal composite oxide. And a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery.

According to a second aspect of the present invention, in the method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to the first aspect, a lithium metal composite oxide powder is mixed with water to form a slurry. A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, comprising: a water washing step of washing the oxide powder with water; and then a solid-liquid separation step of solid-liquid separation after the water washing step as a pre-process of the mixing step. is there.

A third invention of the present invention is for a non-aqueous electrolyte secondary battery, wherein the concentration of the lithium metal composite oxide powder contained in the slurry according to the second invention is 200 to 5000 g with respect to 1 L of water. It is a manufacturing method of a positive electrode active material.

According to a fourth aspect of the present invention, in the method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to the second and third aspects, the tungsten compound is added at least during the water washing step and after the solid-liquid separation step. A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, wherein a tungsten mixture is obtained.

According to a fifth aspect of the present invention, in the fourth aspect of the present invention, the water washing step forms a slurry in which the lithium metal composite oxide powder is mixed with an aqueous solution of a tungsten compound to form a positive electrode active for a non-aqueous electrolyte secondary battery. It is a manufacturing method of a substance.

A sixth invention of the present invention is a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, wherein the tungsten compound according to the fourth invention is in a powder state.

A seventh invention of the present invention is a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, wherein the heat treatment in the first to sixth inventions is performed at 100 to 600 ° C.

According to an eighth aspect of the present invention, the amount of tungsten contained in the tungsten mixture according to the first to seventh aspects is 0 with respect to the total number of Ni, Co and M atoms contained in the lithium metal composite oxide powder. A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, characterized by comprising 0.05 to 2.0 atomic%.

According to a ninth aspect of the present invention, there is provided a nonaqueous electrolyte secondary battery comprising a lithium metal composite oxide powder having a layered crystal structure composed of primary particles and secondary particles formed by aggregation of the primary particles. a use positive electrode active material, the general _{formula: Li z Ni 1-x-} y Co x M y W a O 2 + α ( although, 0 <x ≦ 0.35,0 ≦ y ≦ 0.35,0.95 ≦ z ≦ 1.30, 0 <a ≦ 0.03, 0 ≦ α ≦ 0.15, and M is at least one element selected from Mn, V, Mg, Mo, Nb, Ti and Al) The lithium metal composite oxide has lithium tungstate on the surface of primary particles, and the abundance ratio of Li ₄ WO ₅ contained in the lithium tungstate is 50 to 90 mol%, for a non-aqueous electrolyte secondary battery It is a positive electrode active material.

In a tenth aspect of the present invention, the amount of lithium contained in a lithium compound other than lithium tungstate present on the surface of the lithium metal composite oxide particles in the ninth aspect is 0.08 with respect to the total amount of the positive electrode active material. A positive electrode active material for a non-aqueous electrolyte secondary battery, characterized in that the content is not more than mass%.

According to an eleventh aspect of the present invention, the amount of tungsten contained in the lithium tungstate according to the ninth and tenth aspects of the present invention is W relative to the total number of Ni, Co and M atoms contained in the lithium metal composite oxide. The positive electrode active material for a non-aqueous electrolyte secondary battery is characterized in that the number of atoms is 0.05 to 2.0 atomic%.

According to a twelfth aspect of the present invention, the lithium tungstate according to the ninth to eleventh aspects of the present invention is present on the primary particle surface of the lithium metal composite oxide as fine particles having a particle diameter of 1 to 200 nm. It is a positive electrode active material for electrolyte secondary batteries.

A thirteenth aspect of the present invention is a nonaqueous system characterized in that the lithium tungstate according to the ninth to eleventh aspects is present on the primary particle surface of the lithium metal composite oxide as a film having a thickness of 1 to 150 nm. It is a positive electrode active material for electrolyte secondary batteries.

According to a fourteenth aspect of the present invention, the lithium tungstate according to the ninth to eleventh aspects is the primary particle of the lithium metal composite oxide as both fine particles having a particle diameter of 1 to 200 nm and a film having a thickness of 1 to 150 nm. A positive electrode active material for a non-aqueous electrolyte secondary battery, characterized by being present on the surface.

A fifteenth aspect of the present invention is a non-aqueous electrolyte secondary battery comprising a positive electrode containing the positive electrode active material for a non-aqueous electrolyte secondary battery according to the ninth to fourteenth aspects.

ADVANTAGE OF THE INVENTION According to this invention, when used for the positive electrode material of a battery, the positive electrode active material for nonaqueous electrolyte secondary batteries which can implement | achieve high output with a high capacity | capacitance is suppressed, suppressing gas generation amount.
Furthermore, the manufacturing method is easy and suitable for production on an industrial scale, and its industrial value is extremely large.

It is a schematic explanatory drawing of the measurement example of impedance evaluation, and the equivalent circuit used for analysis. It is a schematic sectional drawing of the 2032 type coin battery 1 used for battery evaluation. It is an example which shows the cross-sectional observation result by the scanning microscope of the positive electrode active material obtained in the Example. It is a schematic explanatory drawing of the laminate cell 4 used for battery evaluation. It is a schematic explanatory drawing which shows the evaluation method of the gas generation amount which pressurizes the lamination cell 4 with the hydraulic press machine PA.

Hereinafter, after describing the positive electrode active material of the present invention first, the production method and the nonaqueous electrolyte secondary battery using the positive electrode active material according to the present invention will be described.

(1) Positive electrode active material The positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention is a lithium metal having a layered structure crystal structure composed of primary particles and secondary particles formed by agglomeration of primary particles. a positive electrode active material for a non-aqueous electrolyte secondary battery comprising a composite oxide having a composition of general formula of the positive electrode active _{material: Li z Ni 1-x-} y Co x M y W a O 2 + α ( although, 0 <x ≦ 0.35, 0 ≦ y ≦ 0.35, 0.95 ≦ z ≦ 1.30, 0 <a ≦ 0.03, 0 ≦ α ≦ 0.15, M is Mn, V, Mg, Mo, Lithium tungstate is present on the surface of the primary particle of the lithium metal composite oxide, and Li ₄ WO ₅ is present in the lithium tungstate, represented by at least one element selected from Nb, Ti and Al) The ratio is 50 to 90 mol% It is an.

In the present invention, the general formula as a base material _{Li z Ni 1-x-y} Co x M y O 2 ( however, 0 <x ≦ 0.35,0 ≦ y ≦ 0.35,0.95 ≦ z ≦ 1 .30, M is a lithium metal composite oxide represented by (at least one element selected from Mn, V, Mg, Mo, Nb, Ti and Al), thereby obtaining a high charge / discharge capacity. is there. In order to obtain a higher charge / discharge capacity, it is preferable to satisfy x + y ≦ 0.2 and 0.95 ≦ z ≦ 1.10. When high thermal stability is required, it is preferable to satisfy x + y> 0.2.
Further, a lithium metal composite oxide powder whose base material is composed of primary particles and secondary particles formed by agglomeration of primary particles (hereinafter, secondary particles and primary particles present alone are combined to form “lithium” The abundance ratio of Li ₄ WO ₅ contained in the lithium tungstate formed on the surface of the primary particle (hereinafter referred to as the Li ₄ WO ₅ abundance ratio). Is from 50 to 90 mol%, it suppresses an increase in the amount of gas generated and improves the output characteristics while maintaining the charge / discharge capacity.

In general, when the surface of the positive electrode active material is completely covered with a different compound, the movement (intercalation) of lithium ions is greatly limited, resulting in a high capacity of the lithium nickel composite oxide. The advantages are erased.
On the other hand, in the present invention, lithium tungstate is formed on the surface of the lithium metal composite oxide particles and on the surface of the primary particles inside, but this lithium tungstate has high lithium ion conductivity and the movement of lithium ions. Has the effect of prompting. For this reason, since the lithium tungstate is formed on the primary particle surface of the lithium metal composite oxide particles, a Li conduction path is formed at the interface with the electrolytic solution, so that the reaction resistance of the positive electrode active material (hereinafter, positive electrode) The output characteristics of the battery are improved by reducing the resistance.
That is, by reducing the positive electrode resistance, the voltage lost in the battery is reduced, and the voltage actually applied to the load side becomes relatively high, so that a high output can be obtained. Further, since the voltage applied to the load side is increased, lithium is sufficiently inserted into and extracted from the positive electrode, so that the charge / discharge capacity of the battery (hereinafter sometimes referred to as “battery capacity”) is also improved. is there.

Here, in this lithium tungstate, it is important that the abundance ratio of Li ₄ WO ₅ is 50 to 90 mol%.
That is, lithium tungstate has many forms such as Li ₂ WO ₄ , Li ₄ WO ₅ and Li ₆ W ₂ O _9, but Li ₄ WO ₅ has high lithium ion conductivity, and Li on the surface of the primary particles. _Since the reaction resistance of the positive electrode active material is greatly reduced by the presence of ₄ WO ₅ , a greater effect of improving the output characteristics can be obtained. Further, the battery capacity can be improved by reducing the positive electrode resistance.

However, if lithium tungstate is only Li ₄ WO _{5, the} amount of gas generated during high-temperature storage of the battery increases, which causes a safety problem. The details of the cause of the increased gas generation amount are unknown, but Li ₄ WO ₅ is considered to be because Li is easily dissociated by a solvent, particularly moisture.

Therefore, in the present invention, by setting the abundance ratio of Li ₄ WO ₅ to 50 to 90 mol%, preferably 50 to 80 mol%, an effect of greatly reducing the reaction resistance can be obtained while suppressing an increase in gas generation amount. Yes.
On the other hand, Li ₂ WO ₄ is not as high as Li ₄ WO _5, but has high lithium ion conductivity and is not easily dissociated by moisture. Therefore, the effect of suppressing the amount of gas generated during high-temperature storage of the battery is high.

Therefore, the abundance ratio of Li ₂ WO ₄ contained in the lithium tungstate formed on the surface of the primary particles (hereinafter referred to as Li ₂ WO ₄ abundance ratio) is 10 to 50 mol%, and Li ₄ WO ₅ and Li ₂ The total abundance ratio of WO ₄ is preferably 90 mol% or more. In this situation, a large effect of reducing the reaction resistance can be obtained while further suppressing an increase in the amount of gas generated.

The existence form of lithium tungstate can be measured as long as the existence form can be specified by a molar ratio, and can be measured by instrumental analysis using an X-ray or an electron beam. Alternatively, it may be calculated by pH titration analysis with hydrochloric acid.

Furthermore, since contact with the electrolytic solution occurs on the surface of the primary particles, it is important that lithium tungstate (hereinafter sometimes referred to as “LWO”) is formed on the surface of the primary particles. Here, the primary particle surface in the present invention means the surface of the primary particle exposed at the outer surface of the secondary particle and the surface of the secondary particle that can penetrate the electrolyte through the outside of the secondary particle and the inside of the secondary particle. It includes the surface of primary particles exposed in the voids. Furthermore, even a grain boundary between primary particles is included as long as the primary particles are not completely bonded and the electrolyte solution can penetrate.

The contact with the electrolytic solution is not limited to the outer surface of the secondary particles formed by agglomeration of the primary particles, but also the gap between the primary particles in the vicinity of the inner surface of the secondary particles and the incomplete grain boundary. However, since it also occurs, it is necessary to form LWO also on the surface of the primary particles to promote the movement of lithium ions. Therefore, the reaction resistance of the positive electrode active material can be further reduced by forming LWO on more primary particle surfaces that can be contacted with the electrolytic solution.

Furthermore, the form of the LWO on the primary particle surface is such that when the surface of the primary particle is coated with a layered material, the contact area with the electrolytic solution becomes small. When the layered material is formed, the formation of the compound is specified. It tends to result in concentration on the primary particle surface. That is, although the layered material as the coating has high lithium ion conductivity, the effects of improving the charge / discharge capacity and reducing the positive electrode resistance can be obtained, but there is room for improvement.

Therefore, in order to obtain a higher effect, LWO is preferably present on the primary particle surface of the lithium metal composite oxide as fine particles having a particle diameter of 1 to 200 nm.
By adopting such a configuration, the lithium ion conductivity can be effectively improved with a sufficient contact area with the electrolytic solution, thereby improving the charge / discharge capacity and more effectively reducing the positive electrode resistance. Can do. If the particle diameter is less than 1 nm, fine particles may not have sufficient lithium ion conductivity. On the other hand, if the particle diameter exceeds 200 nm, the formation of fine particles on the primary particle surface becomes non-uniform, and the higher effect of reducing positive electrode resistance may not be obtained.

Here, the fine particles do not have to be completely formed on the entire surface of the primary particles, but may be scattered. Even in the scattered state, if the fine particles are formed on the outer surface and the inner primary particle surface of the lithium metal composite oxide particles, the effect of reducing the reaction resistance of the positive electrode can be obtained.

Further, it is not necessary for all the fine particles to be present as fine particles having a particle diameter of 1 to 200 nm. Preferably, 50% or more of the fine particles formed on the surface of the primary particles are formed in a particle diameter range of 1 to 200 nm. High effect can be obtained.

On the other hand, when the primary particle surface is covered with a thin film, a conduction path of Li can be formed at the interface with the electrolytic solution while suppressing a decrease in specific surface area, which means higher charge / discharge capacity and reduced positive electrode resistance. An effect is obtained. When the surface of the primary particles is coated with such a thin film-like LWO, it is preferably present on the primary particle surface of the lithium metal composite oxide as a film having a thickness of 1 to 150 nm.
If the film thickness is less than 1 nm, the film may not have sufficient lithium ion conductivity. Moreover, when a film thickness exceeds 150 nm, lithium ion conductivity will fall and the higher effect of positive electrode resistance reduction may not be acquired.

However, this coating may be partially formed on the primary particle surface, and the film thickness range of all coatings may not be 1 to 150 nm. If a film having a film thickness of 1 to 150 nm is formed at least partially on the primary particle surface, a high effect can be obtained.
Furthermore, even when the fine particle form and the thin film form form are mixed and LWO is formed on the primary particle surface, a high effect on the battery characteristics can be obtained.

On the other hand, when lithium tungstate is formed non-uniformly between lithium metal composite oxide particles, the movement of lithium ions between lithium metal composite oxide particles becomes non-uniform. Particles are loaded, and cycle characteristics and output characteristics are likely to deteriorate.
Therefore, it is preferable that lithium tungstate is uniformly formed between the lithium metal composite oxide particles.

The property of the primary particle surface of such a lithium metal composite oxide can be judged, for example, by observing with a field emission scanning electron microscope (SEM). For the positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention, It has been confirmed that lithium tungstate is formed on the surface of primary particles made of lithium metal composite oxide.
Therefore, it is necessary that the amount of lithium tungstate formed is sufficient to reduce the reaction resistance and to ensure a sufficient primary particle surface that can be contacted with the electrolytic solution. .

The amount of lithium contained in the lithium compound other than lithium tungstate present on the surface of such lithium metal composite oxide particles (hereinafter referred to as excess lithium amount) is 0.08 mass relative to the total amount of the positive electrode active material. % Or less, and more preferably 0.05% by mass or less.
By making the amount of excess lithium 0.08% by mass or less, it is possible to more effectively suppress gas generation at high temperatures.
That is, lithium hydroxide and lithium carbonate exist in addition to lithium tungstate on the primary particle surface of the lithium metal composite oxide, and the amount of excess lithium present on the surface of the lithium metal composite oxide is controlled, thereby Generation of gas during high-temperature storage of the battery caused by lithium and lithium carbonate can be more effectively suppressed.

Further, the amount of tungsten contained in the lithium tungstate is 3.0 atomic% or less, preferably 0.05 to 2.0%, based on the total number of Ni, Co and M atoms contained in the lithium metal composite oxide. Atomic%. Thereby, the improvement effect of an output characteristic is acquired. Furthermore, by setting the content to 0.05 to 2.0 atomic%, the amount of LWO formed is sufficient to reduce the positive electrode resistance, and a sufficient primary particle surface capable of contact with the electrolyte is ensured. It is possible to make the amount as high as possible, and it is possible to further achieve both high charge / discharge capacity and output characteristics.
If the amount of tungsten is less than 0.05 atomic%, the effect of improving the output characteristics may not be sufficiently obtained. If the amount of tungsten exceeds 3.0 atomic%, the amount of lithium tungstate to be formed increases so that lithium Lithium conduction between the metal complex oxide and the electrolyte may be hindered, and the charge / discharge capacity may be reduced.

Further, the total amount of lithium in the positive electrode active material increases by the amount of lithium contained in the lithium tungstate, but the ratio of the sum of the number of atoms Ni, Co and M (Me) in the positive electrode active material to the number of Li atoms. “Li / Me” is 0.95 to 1.30, preferably 0.97 to 1.25, and more preferably 0.97 to 1.20. Thereby, Li / Me of the lithium metal composite oxide particles as the core material is preferably 0.95 to 1.25, more preferably 0.95 to 1.20, and a high battery capacity is obtained, and formation of the LW compound is achieved. A sufficient amount of lithium can be secured. In order to obtain a higher battery capacity, it is preferable that Li / Me of the positive electrode active material as a whole is 0.95 to 1.15, and Li / Me of the lithium metal composite oxide particles is 0.95 to 1.10. preferable. Here, the core material is lithium metal composite oxide particles that do not contain an LW compound, and becomes a positive electrode active material by forming an LW compound on the primary particle surface of the lithium metal composite oxide particles.
If the Li / Me is less than 0.95, the reaction resistance of the positive electrode in the non-aqueous electrolyte secondary battery using the obtained positive electrode active material increases, and the output of the battery decreases. On the other hand, when Li / Me exceeds 1.30, the initial discharge capacity of the positive electrode active material decreases and the reaction resistance of the positive electrode also increases.

The positive electrode active material of the present invention has improved output characteristics by forming lithium tungstate on the primary particle surface of the lithium metal composite oxide, and the powder characteristics such as particle size and tap density as the positive electrode active material are as follows: What is necessary is just to be in the range of the positive electrode active material used normally.

(2) Method for Producing Positive Electrode Active Material Hereinafter, the method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention will be described in detail for each step.

[Mixing process]
The mixing step includes a lithium metal composite oxide powder having a layered crystal structure composed of primary particles and secondary particles formed by aggregation of the primary particles, and 2 masses with respect to the lithium metal composite oxide powder. % Of water and a tungsten compound, or a mixture of a tungsten compound and a lithium compound, and the water and solid tungsten compound or the water and solid tungsten compound and lithium with respect to the amount of tungsten (W) contained This is a step of obtaining a tungsten mixture in which the molar ratio of the total amount of lithium (Li) contained in the compound (hereinafter referred to as Li molar ratio) is 3 to 5.

The moisture content of the lithium metal composite oxide powder in the tungsten mixture (hereinafter simply referred to as the mixture) is 2% by mass or more. Thereby, tungsten contained in the tungsten compound penetrates into the voids between the primary particles communicating with the outside of the secondary particles and imperfect grain boundaries together with moisture, and a sufficient amount of W can be dispersed on the surface of the primary particles. . The amount of moisture may be 2% by mass or more. However, if the amount of moisture is excessively large, the efficiency of the heat treatment in the subsequent process is reduced, or the elution of lithium from the lithium metal composite oxide particles is increased, resulting in a mixture. Since the Li molar ratio in the inside becomes excessively high and battery characteristics when the obtained positive electrode active material is used for the positive electrode of the battery may be deteriorated, the amount of water is preferably 20% by mass or less. More preferably, it is set to ˜15% by mass, and further preferably 3 to 10% by mass.
By setting the amount of water within the above range, the pH rises due to the lithium content eluted in the water, and the effect of suppressing the elution of excessive lithium is exhibited. The molar ratio of Co and M in the lithium metal composite oxide powder is maintained up to the positive electrode active material.

The tungsten compound to be used is preferably water-soluble so as to dissolve in the water contained in the mixture in order to penetrate the surface of the primary particles inside the secondary particles. That is, the tungsten compound used includes a tungsten compound in an aqueous solution state.

Since the tungsten compound existing in the state of the aqueous solution only needs to have an amount that can penetrate to the surface of the primary particles inside the secondary particles, a part thereof may be mixed in a solid state. Moreover, even if it is difficult to dissolve in water at room temperature, any compound that dissolves in water by heating during heat treatment may be used. Furthermore, since the water in the mixture becomes alkaline due to the contained lithium, it may be a compound that is soluble in alkali.

As described above, the tungsten compound is not limited as long as it can be dissolved in water, but tungsten oxide, lithium tungstate, ammonium tungstate, sodium tungstate, and the like are preferable, and tungsten oxide, which is less likely to be mixed with impurities, Lithium tungstate and ammonium tungstate are more preferable, and tungsten oxide and lithium tungstate are more preferable.

The Li molar ratio of this mixture is set to 3.0 or more and 5.0 or less.
Thereby, the Li ₄ WO ₅ abundance ratio of the obtained positive electrode active material can be 50 to 90 mol%. When the Li molar ratio is less than 3.0, the Li ₄ WO ₅ abundance ratio is less than 50 mol%, and when the Li molar ratio exceeds 5.0, the Li ₄ WO ₅ abundance ratio exceeds 90 mol% and surplus lithium The amount exceeds 0.08% by mass with respect to the total amount of the positive electrode active material.
Therefore, from the viewpoint of controlling the abundance ratio of Li ₄ WO ₅ and reducing the amount of excess lithium, the Li molar ratio is preferably less than 4.5, and more preferably 4.0 or less. Depending on the tungsten compound to be added, the Li molar ratio may be less than 3.0. In this case, the lithium compound may be added to compensate for the shortage. Water-soluble compounds such as LiOH) are preferred.

Furthermore, the amount of tungsten contained in this mixture is preferably 3.0 atomic percent or less with respect to the total number of Ni, Co and M atoms contained in the lithium metal composite oxide powder, More preferably, it is set to ˜2.0 atomic%. Thereby, the amount of tungsten contained in the lithium tungstate in the positive electrode active material can be within a preferable range, and the high charge / discharge capacity and the output characteristics of the positive electrode active material can be further compatible.

In this mixing step, water may be supplied and mixed together with the tungsten compound so that the water content of the mixture becomes 2% by mass or more, and an aqueous solution of tungsten compound or a tungsten compound and water may be supplied individually.
On the other hand, the lithium metal composite oxide powder obtained by firing the metal composite hydroxide or the metal composite oxide and the lithium compound has secondary particles or unreacted lithium compounds on the surface of the primary particles. . For this reason, the amount of lithium present in the water constituting the mixture becomes excessive, and it may be difficult to control the Li molar ratio.

Therefore, it is preferable to provide a water washing step in which the lithium metal composite oxide powder is mixed with water to make a slurry and washed with water before obtaining the mixture. It is preferable to provide.
By providing this water washing step, the amount of lithium present in the water in the mixture can be reduced to facilitate the control of the Li molar ratio.

The water washing conditions in the water washing step are sufficient to reduce unreacted lithium compounds, for example, preferably 0.08% by mass or less, more preferably 0.05% by mass or less, based on the total amount of lithium metal composite oxide particles. In order to form a slurry, it is preferable to stir the lithium metal composite oxide powder contained in the slurry at a concentration of 200 to 5000 g with respect to 1 L of water.
By setting the concentration of the lithium metal composite oxide powder within this range, unreacted lithium compounds can be more sufficiently reduced while suppressing deterioration due to elution of lithium from the lithium metal composite oxide particles.
The washing time and washing temperature may be in a range where the unreacted lithium compound can be sufficiently reduced. For example, the washing time is preferably 5 to 60 minutes and the washing temperature is preferably in the range of 10 to 40 ° C.

In the present invention, if a mixture as described above is obtained, the step of adding the tungsten compound is not limited. However, when a water washing step is provided, the mixing step is preferably completed after the water washing step. If the mixture is obtained before the water washing step, the tungsten compound is washed away by water washing, so that the amount of tungsten in the mixture may be insufficient.
Therefore, when a water washing process is provided, it is preferable to obtain a predetermined mixture by adding a tungsten compound at least during the water washing process and after the solid-liquid separation process.

Therefore, when the tungsten compound is added in the water washing step, the tungsten compound may be added to water mixed with the lithium metal composite oxide powder in advance to form an aqueous solution or suspension, or may be added after slurrying. In order to easily control the total amount of lithium, the tungsten compound is preferably a tungsten compound that is completely dissolved in the slurry during washing with water. In addition, it is preferable to use a tungsten compound that is hardly soluble in water or a compound that does not contain lithium.
As a result, the influence of lithium dissolved from the solid tungsten compound in the mixture can be reduced, and the total amount of lithium in the mixture can be easily controlled.

On the other hand, when the tungsten compound is added after the solid-liquid separation step, the tungsten compound may be in an aqueous solution state or a powder state. When added after the solid-liquid separation step, there is no lithium or tungsten removed together with the liquid components, and all the tungsten compounds remain in the mixture, so that the Li molar ratio can be easily controlled.

Further, when the tungsten compound is added during the washing step, the tungsten compound may be in an aqueous solution state or a powder state, and a uniform mixture can be obtained by adding the tungsten compound to the slurry and stirring. .
When a tungsten compound used is in the form of an aqueous solution or a water-soluble compound, the tungsten compound dissolved in the slurry is removed together with the liquid components of the slurry in the solid-liquid separation step after washing with water. However, the tungsten dissolved in the water in the mixture can make the amount of tungsten in the mixture sufficient.

The amount of tungsten in the mixture becomes stable along with the amount of water depending on the washing conditions and the solid-liquid separation conditions. Therefore, these conditions may be determined together with the type and amount of the tungsten compound by preliminary tests.
The total amount of lithium contained in the water and the tungsten compound relative to tungsten in the mixture (hereinafter referred to as the total amount of lithium) can also be determined by a preliminary test in the same manner as the amount of tungsten.

The amount of tungsten in the mixture when the tungsten compound is added in the water washing step can be determined by ICP emission spectroscopy. Further, the amount of lithium contained in the water of the mixture can be determined from the analysis value of lithium and the amount of water by ICP emission spectroscopy in the liquid component separated into solid and liquid after washing with water.
On the other hand, the amount of lithium contained in the solid tungsten compound is determined by adding the tungsten compound to a lithium hydroxide aqueous solution having the same concentration as the liquid component after water washing, stirring under the same conditions as in water washing, and remaining tungsten as a residue. The amount remaining as a solid content in the mixture can be calculated from the ratio of the compounds, and can be determined from the tungsten compound remaining as a solid content.

Further, the amount of tungsten contained in the mixture when the tungsten compound is added after the solid-liquid separation step can be determined from the amount of the tungsten compound to be added. On the other hand, the total amount of lithium in the mixture is the amount of lithium contained in the moisture determined from the analysis value of lithium by ICP emission spectroscopy and the amount of moisture of the liquid component solid-liquid separated after washing with water, the amount of tungsten compound added, or the amount of tungsten compound And may be calculated as the sum of lithium amounts obtained from the lithium compound amount.

When the tungsten compound is added as an aqueous solution after the solid-liquid separation step, it is necessary to adjust the aqueous solution so that the water content preferably does not exceed 20% by mass as described above. It is preferable that the concentration be 05 to 2 mol / L.
Thereby, the required amount of tungsten can be added while suppressing the moisture of the mixture. If the amount of water exceeds 20% by mass, the liquid may be adjusted again by solid-liquid separation, but the amount of tungsten and lithium in the removed liquid component should be determined to confirm the Li molar ratio of the mixture. Is required.

In order to make the amount of water contained in the mixture 2% by mass or more, the mixing after the solid-liquid separation step is preferably performed at a temperature of 50 ° C. or less. If the temperature exceeds 50 ° C., the moisture content may be less than 2% by mass due to drying during mixing.

The mixing with the tungsten compound is not limited as long as it is a device capable of mixing uniformly, and a general mixer can be used. For example, the mixture may be sufficiently mixed with the tungsten compound using a shaker mixer, a Laedige mixer, a Julia mixer, a V blender, or the like so that the shape of the lithium metal composite oxide particles is not destroyed.

In the production method of the present invention, the composition of the positive electrode active material obtained is only tungsten added and added in the mixing step from the lithium metal composite oxide as a base material and lithium added as necessary. , lithium-metal composite oxide as a base material, a high capacity and in view of the low reaction resistance, the composition is known formula _{Li z Ni 1-x-y} Co x M y O 2 ( however, 0 <x ≦ 0 .35, 0 ≦ y ≦ 0.35, 0.95 ≦ z ≦ 1.25, and M is at least one element selected from Mn, V, Mg, Mo, Nb, Ti, and Al) Lithium metal composite oxide is used.

On the other hand, in the case of washing with water, Li / Me (corresponding to z in the general formula) decreases due to lithium elution at the time of washing with water. A lithium metal composite oxide in which / Me is adjusted may be used. The decrease amount of Li / Me due to general water washing conditions is about 0.03 to 0.08.
In addition, even when a small amount of water is supplied in the mixing step, lithium elutes though a small amount. Therefore, z indicating Li / Me of the lithium metal composite oxide as a base material is preferably 0.95 ≦ z ≦ 1.30, and preferably 0.97 ≦ z ≦ 1.20.

Furthermore, since it is advantageous for improving the output characteristics to increase the contact area with the electrolytic solution, the primary particles and secondary particles formed by agglomeration of the primary particles are formed. It is preferable to use a lithium metal composite oxide powder having voids and grain boundaries that can be penetrated.

[Heat treatment process]
The heat treatment step is a step of heat treating the produced mixture.
Thereby, lithium tungstate is formed on the primary particle surface of the lithium metal composite oxide from lithium and tungsten contained in the moisture of the mixture, and a positive electrode active material for a non-aqueous electrolyte secondary battery is obtained.
If LWO is formed, the heat treatment method is not particularly limited, but in order to prevent deterioration of electrical characteristics when used as a positive electrode active material for a non-aqueous electrolyte secondary battery, a reaction with moisture or carbonic acid in the atmosphere is performed. Avoid heat treatment in an oxidizing atmosphere such as an oxygen atmosphere or in a vacuum atmosphere at a temperature of 100 to 600 ° C.

If the heat treatment temperature is less than 100 ° C., the evaporation of moisture is not sufficient and LWO may not be formed sufficiently. On the other hand, when the heat treatment temperature exceeds 600 ° C., primary particles of the lithium metal composite oxide are sintered and some tungsten is dissolved in the layered structure of the lithium metal composite oxide. The discharge capacity may decrease.

On the other hand, when the tungsten compound contained in the mixture remains as a solid, particularly when the tungsten compound is added as a powder after the solid-liquid separation step, the temperature rises until the temperature exceeds, for example, 90 ° C. while the dissolution is sufficiently performed. The temperature rate is preferably 0.8 to 1.2 ° C./min. Even in the mixing step, the tungsten compound powder is dissolved in the water in the mixture. By setting the temperature increase rate, the solid tungsten compound is sufficiently dissolved during the temperature increase, and the primary particles inside the secondary particles. It can penetrate to the particle surface.

When the solid tungsten compound is dissolved, it is preferable to perform heat treatment in a sealed container so that moisture does not volatilize while the dissolution is sufficiently performed.
The heat treatment time is not particularly limited, but is preferably 3 to 20 hours, and more preferably 5 to 15 hours in order to sufficiently evaporate the water in the mixture to form LWO.

(3) Non-aqueous electrolyte secondary battery The non-aqueous electrolyte secondary battery of the present invention includes a positive electrode, a negative electrode, a non-aqueous electrolyte solution, and the like, and includes the same components as those of a general non-aqueous electrolyte secondary battery. The embodiment described below is merely an example, and the nonaqueous electrolyte secondary battery of the present invention can be variously modified based on the knowledge of those skilled in the art based on the embodiment described in the present specification. It can be implemented in an improved form. Moreover, the use of the nonaqueous electrolyte secondary battery of the present invention is not particularly limited.

(A) Positive electrode Using the positive electrode active material for a non-aqueous electrolyte secondary battery described above, for example, a positive electrode of a non-aqueous electrolyte secondary battery is produced as follows.
First, a powdered positive electrode active material, a conductive material, and a binder are mixed, and, if necessary, a target solvent such as activated carbon and viscosity adjustment is added and kneaded to prepare a positive electrode mixture paste.
Each mixing ratio in the positive electrode mixture paste is also an important factor for determining the performance of the non-aqueous electrolyte secondary battery. When the total mass of the solid content of the positive electrode mixture excluding the solvent is 100 parts by mass, the content of the positive electrode active material is 60 to 95 parts by mass in the same manner as the positive electrode of a general non-aqueous electrolyte secondary battery, and the conductive material The content of is desirably 1 to 20 parts by mass, and the content of the binder is desirably 1 to 20 parts by mass.

The obtained positive electrode mixture paste is applied to the surface of a current collector made of, for example, an aluminum foil and dried to disperse the solvent. If necessary, pressurization may be performed by a roll press or the like to increase the electrode density.
In this way, a sheet-like positive electrode can be produced. The sheet-like positive electrode can be cut into an appropriate size or the like according to the target battery and used for battery production. However, the method for manufacturing the positive electrode is not limited to the illustrated one, and other methods may be used.

In producing the positive electrode, as the conductive agent, for example, graphite (natural graphite, artificial graphite, expanded graphite, etc.), carbon black materials such as acetylene black, ketjen black (registered trademark), and the like can be used.
The binder plays a role of anchoring the active material particles. For example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluorine rubber, ethylene propylene diene rubber, styrene butadiene, cellulosic resin, polyacrylic. An acid or the like can be used.
If necessary, a positive electrode active material, a conductive material, and activated carbon are dispersed, and a solvent that dissolves the binder is added to the positive electrode mixture. Specifically, an organic solvent such as N-methyl-2-pyrrolidone can be used as the solvent. Also

(B) Negative electrode A negative electrode mixture in which a negative electrode active material capable of occluding and desorbing lithium ions is mixed with a binder and an appropriate solvent is added to the negative electrode. Is applied to the surface of a metal foil current collector such as copper, dried, and compressed to increase the electrode density as necessary.
As the negative electrode active material, for example, a fired organic compound such as natural graphite, artificial graphite, or phenol resin, or a powdery 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 case of the positive electrode, and a solvent for dispersing these active materials and the binder can be N-methyl-2-pyrrolidone or the like. Organic solvents can be used.

(C) Separator A separator is interposed between the positive electrode and the negative electrode. The separator separates the positive electrode and the negative electrode and retains the electrolyte, and a thin film such as polyethylene or polypropylene and a film having many minute holes can be used.

(D) Non-aqueous electrolyte The non-aqueous electrolyte is obtained by dissolving a lithium salt as a supporting salt in an organic solvent.
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, ethyl methyl carbonate, and dipropyl carbonate; -A single compound selected from ether compounds such as methyltetrahydrofuran and dimethoxyethane, sulfur compounds such as ethyl methyl sulfone and butane sultone, phosphorus compounds such as triethyl phosphate and trioctyl phosphate, or a mixture of two or more. Can be used.

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

(E) Battery shape and configuration As described above, the shape of the nonaqueous electrolyte secondary battery of the present invention composed of the positive electrode, the negative electrode, the separator, and the nonaqueous electrolytic solution described above is various, such as a cylindrical type and a laminated type. can do.
In any case, the positive electrode and the negative electrode are laminated via a separator to form an electrode body, and the obtained electrode body is impregnated with a non-aqueous electrolyte and communicated with the positive electrode current collector and the outside. The positive electrode terminal and the negative electrode current collector and the negative electrode terminal communicating with the outside are connected using a current collecting lead or the like and sealed in a battery case to complete a non-aqueous electrolyte secondary battery. .

(F) Characteristics The nonaqueous electrolyte secondary battery using the positive electrode active material of the present invention has a high capacity and a high output.
The non-aqueous electrolyte secondary battery using the positive electrode active material according to the present invention obtained in a particularly preferred form is, for example, a high initial discharge capacity of 165 mAh / g or more and a low positive electrode when used for the positive electrode of a 2032 type coin battery. Resistance is obtained, and further, high capacity and high output. Moreover, it can be said that it has high thermal stability and is excellent in safety.

In addition, the measurement method of the positive electrode resistance in the present invention is a solution resistance, a negative electrode resistance and a negative electrode capacity, and a positive electrode resistance when the frequency dependence of the battery reaction is measured by a general AC impedance method as an electrochemical evaluation method. A Nyquist diagram based on the positive electrode capacity is obtained as shown in FIG.

The battery reaction at the electrode consists of a resistance component accompanying the charge transfer and a capacity component due to the electric double layer. When these are expressed as an electric circuit, it becomes a parallel circuit of resistance and capacity. It is represented by an equivalent circuit in which circuits are connected in series. Fitting calculation is performed on the Nyquist diagram measured using this equivalent circuit, and each resistance component and capacitance component can be estimated. The positive electrode resistance is equal to the diameter of the semicircle on the low frequency side of the obtained Nyquist diagram.
From the above, the positive electrode resistance can be estimated by performing AC impedance measurement on the manufactured positive electrode and performing fitting calculation on the obtained Nyquist diagram with an equivalent circuit.

About the secondary battery which has a positive electrode using the positive electrode active material obtained by this invention, the performance (initial stage discharge capacity, positive electrode resistance) was measured.
Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples.

(Battery manufacture and evaluation)
For the evaluation of the initial discharge capacity and the positive electrode resistance of the positive electrode active material, a 2032 type coin battery 1 (hereinafter referred to as a coin type battery) shown in FIG. 2 was used.
As shown in FIG. 2, the coin-type battery 1 is composed of a case 2 and an electrode 3 accommodated in the case 2.
The case 2 has a positive electrode can 2a that is hollow and open at one end, and a negative electrode can 2b that is disposed in the opening of the positive electrode can 2a. When the negative electrode can 2b is disposed in the opening of the positive electrode can 2a, A space for accommodating the electrode 3 is formed between the negative electrode can 2b and the positive electrode can 2a. The electrode 3 includes a positive electrode 3a, a separator 3c, and a negative electrode 3b, which are stacked in this order. The positive electrode 3a contacts the inner surface of the positive electrode can 2a, and the negative electrode 3b contacts the inner surface of the negative electrode can 2b. As shown in FIG.

The case 2 includes a gasket 2c, and relative movement is fixed by the gasket 2c so as to maintain a non-contact state between the positive electrode can 2a and the negative electrode can 2b. Further, the gasket 2c also has a function of sealing a gap between the positive electrode can 2a and the negative electrode can 2b to block the inside and outside of the case 2 in an airtight and liquid tight manner.

The coin type battery 1 shown in FIG. 2 was manufactured as follows.
First, 52.5 mg of a positive electrode active material for a non-aqueous electrolyte secondary battery, 15 mg of acetylene black, and 7.5 mg of polytetrafluoroethylene resin (PTFE) are mixed, and press-molded to a diameter of 11 mm and a thickness of 100 μm at a pressure of 100 MPa. A positive electrode 3a was produced. The produced positive electrode 3a was dried in a vacuum dryer at 120 ° C. for 12 hours.
Using the positive electrode 3a, the negative electrode 3b, the separator 3c, and the electrolyte, the coin-type battery 1 shown in FIG. 2 was produced in a glove box in an Ar atmosphere in which the dew point was controlled at −80 ° C.

As the negative electrode 3b, a negative electrode sheet in which graphite powder having an average particle diameter of about 20 μm punched into a disk shape with a diameter of 14 mm and polyvinylidene fluoride were applied to a copper foil was used.
As the separator 3c, a polyethylene porous film having a film thickness of 25 μm was used.
As the electrolytic solution, an equivalent 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 positive electrode resistance showing the performance of the manufactured coin battery 1 were evaluated as follows.
The initial discharge capacity is left for about 24 hours after the coin-type battery 1 is manufactured, and after the open circuit voltage OCV (Open Circuit Voltage) is stabilized, the current density with respect to the positive electrode is set to 0.1 mA / cm ² and the cut-off voltage 4 The capacity when the battery was charged to 3 V, discharged after a pause of 1 hour to a cutoff voltage of 3.0 V was defined as the initial discharge capacity.

The positive electrode resistance is a Nyquist plot shown in FIG. 1 when the coin-type battery 1 is charged at a charging potential of 4.1 V and measured by an AC impedance method using a frequency response analyzer and a potentiogalvanostat (Solartron, 1255B). Is obtained. Since this Nyquist plot is represented as the sum of the solution resistance, the negative electrode resistance and its capacity, and the characteristic curve indicating the positive electrode resistance and its capacity, the fitting calculation was performed using an equivalent circuit based on this Nyquist plot, and the positive resistance The value of was calculated.

Moreover, the lamination cell 4 shown in the schematic explanatory drawing of FIG. 4 was used for evaluation of the gas generation amount of a positive electrode active material.
The laminate cell 4 is manufactured by pasting a positive electrode active material on an aluminum current collector foil (thickness: 0.02 mm), leaving a conductive portion connected to the outside, and drying, so that the basis weight of the positive electrode active material is 7 mg. A positive electrode sheet 5 on which a positive electrode active material layer of / cm ² was formed was produced.
Also, carbon powder (acetylene black) was pasted as a negative electrode active material on a copper current collector foil (thickness 0.02 mm), and a negative electrode active material layer having a negative electrode active material weight of 5 mg / cm ² was formed in the same manner. A negative electrode sheet 6 was produced.

A laminated sheet was formed between the produced positive electrode sheet 5 and negative electrode sheet 6 with a separator 7 made of a polypropylene microporous film (thickness 20.7 μm, porosity density 43.9%) interposed. Then, this laminated sheet is sandwiched between two aluminum laminate sheets 8 (thickness 0.05 mm), and the three sides of the aluminum laminate sheet are heat-sealed and sealed to assemble a laminate cell having a structure as shown in FIG. It was.

Thereafter, an electrolytic solution manufactured by Ube Industries Co., Ltd., in which LiPF ₆ (1 mol / L) and cyclohexylbenzene (2 wt%) were dissolved in a mixed solvent of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate (volume ratio 3: 3: 4). 260 μl was injected, and the remaining one side was heat-sealed to produce a gas generation test laminate cell 4 for evaluating the gas generation amount shown in FIG. The size of the produced laminate cell 4 was 60 mm long and 90 mm wide.

(Gas generation test)
The produced laminate cell 4 was stored for 12 hours in a constant temperature bath (Cosmo Pier) manufactured by Hitachi Appliances, Ltd. set at 25 ° C.
After storing for 12 hours, using a charge / discharge device (Hokuto Denko Co., Ltd .: HJ1001SD8) while being housed in a thermostatic chamber, a constant current mode of 0.2 C in the range of 3.0 to 4.3 V The battery was charged and discharged three times. After charging and discharging, the battery was charged in a constant current mode of 1 C up to 4.6 V, and then left in a constant temperature bath for 72 hours to generate gas in the laminate cell 4.
At this time, the laminate cell 4 was sandwiched and held between a pair of plate-like members (made of stainless steel), and an exposed portion was formed by exposing a width of 1 cm from the end of the laminate cell from the pair of plate-like members.

(Evaluation of the amount of gas generated)
The gas generation test-laminated laminate cell (hereinafter referred to as a “tested laminate cell”) 4a is taken out of the thermostatic bath, and marking is performed with an oil-based magic at a position 1 cm wide from the end of the tested laminate cell 4a. It was.
Thereafter, as shown in the schematic explanatory diagram of the gas generation amount evaluation method in FIG. 5, the tested laminate cell 4a is placed on the table T of the manual hydraulic press machine PA4 (manufactured by NPA Corporation: model number TB-50H). Te, on the post-test laminate cell 4a, (part of the portion marked to the end of the post-test laminate cell 4a, the non-pressing portion UPA width L ₁₎ width 1cm minutes from the end leaving a pressurized A rectangular parallelepiped pressing plate (made of stainless steel) to be the member PP was placed.
In addition, a rectangular parallelepiped measurement plate (made of stainless steel) is disposed in the non-pressurized portion UPA as the mounting member MP, and a dial gauge Ga is formed on the upper surface of one end portion (portion placed on the non-pressurized portion) of the measurement plate. (CITIZEN, Inc .: 2A-104) was installed.

After that, as shown in FIG. 5, the pressure member PP is pressed by the manual hydraulic press machine PA and a pressure of 4 kN is applied to the tested laminate cell 4a, and the gas in the tested laminate cell 4a is collected in the non-pressurized part UPA. The non-pressurized part UPA was swollen by the collected gas, and one end part of the mounting member MP was moved upward.
Finally, the value of the dial gauge Ga was read, the amount of movement of one end of the mounting member MP was measured, and the amount of generated gas was evaluated.

In this example, each reagent-grade sample manufactured by Wako Pure Chemical Industries, Ltd. was used for producing composite hydroxide, producing a positive electrode active material, and a secondary battery.

A lithium metal composite represented by Li _1.030 Ni _0.82 Co _0.15 Al _0.03 O ₂ obtained by a known technique of mixing and baking oxide powder containing Ni as a main component and lithium hydroxide A powder of oxide particles was used as a base material. This lithium metal composite oxide powder had an average particle size of 12.4 μm and a specific surface area of 0.3 m ² / g. In addition, the average particle diameter was evaluated using the volume integrated average value in the laser diffraction scattering method, and the specific surface area was evaluated using the BET method based on nitrogen gas adsorption.

An aqueous solution of a tungsten compound was obtained by adding and stirring 15.6 g of tungsten oxide (WO ₃ ) in an aqueous solution in which 5.6 g of lithium hydroxide (LiOH) was dissolved in 100 ml of pure water.

Next, 75 g of lithium metal composite oxide powder as a base material was immersed in the aqueous solution and further mixed by stirring for 10 minutes, and at the same time, the lithium metal composite oxide powder was washed with water. Then, it solid-liquid-separated by carrying out suction filtration using Nutsche, and obtained the tungsten mixture which consists of lithium metal complex oxide particle | grains, a liquid component, and a tungsten compound.

This mixture was dried, and the water content with respect to the lithium metal composite oxide particles determined from the mass before and after drying was 7.6% by mass.
When analyzed by ICP emission spectroscopy, the Li concentration of the liquid component was 2.62 mol / L, the tungsten content of the mixture was 0.0039 mol, and the Li molar ratio was 3.9.

The obtained mixture was put into a stainless steel (SUS) firing container, heated in a vacuum atmosphere at a heating rate of 2.8 ° C./min to 210 ° C. and heat-treated for 13 hours, and then cooled to room temperature.
Finally, the mixture was pulverized through a sieve having an aperture of 38 μm to obtain a positive electrode active material having lithium tungstate on the primary particle surfaces.

When the tungsten content and Li / Me of the obtained positive electrode active material were analyzed by ICP emission spectroscopy, Ni: Co: Al was an atomic ratio of 82: 15: 3, and the tungsten content was Ni, Co. And it was confirmed that the composition was 0.5 atomic% with respect to the total number of atoms of M, the Li / Me was 0.994, and the Li / Me of the core material was 0.992.
Li / Me was determined by analyzing a lithium metal composite oxide powder washed with water under the same conditions by ICP emission spectroscopy using a lithium hydroxide solution containing Li at the same concentration as in washing with water.

[Analysis of lithium tungstate and surplus lithium]
The presence state of lithium tungstate in the obtained positive electrode active material was evaluated by titrating Li eluted from the positive electrode active material. After adding pure water to the obtained positive electrode active material and stirring for a certain period of time, when evaluating the compound state of lithium eluted from the neutralization point that appears by adding hydrochloric acid while measuring the pH of the filtered filtrate The presence of Li ₄ WO ₅ was confirmed in lithium tungstate, and the abundance ratio of Li ₄ WO ₅ contained was calculated to be 60 mol%.

On the other hand, W in tungsten oxide and Li in lithium hydroxide were mixed so as to have the same Li molar ratio (3.9) to produce lithium tungstate, and the lithium tungstate produced by X-ray diffraction was confirmed. However, since only Li ₄ WO ₅ and Li ₂ WO ₄ were confirmed, in the lithium tungstate in the positive electrode active material, the abundance ratio of Li ₄ WO ₅ is 60 mol%, and the abundance ratio of Li ₂ WO ₄ is It was thought to be 40 mol%. Moreover, the excess lithium was 0.03 mass% with respect to the whole quantity of a positive electrode active material.

[Morphological analysis of lithium tungstate]
The obtained positive electrode active material was embedded in a resin and subjected to a cross section polisher to prepare an observation sample. When the cross section was observed by SEM using the sample at a magnification of 5000 times, the primary particles and secondary particles formed by agglomeration of the primary particles were formed, and fine particles of lithium tungstate were formed on the primary particle surface. It was confirmed that the particle diameter of the fine particles was 20 to 145 nm.
In addition, secondary particles with lithium tungstate formed on the primary particle surface account for 90% of the observed number of secondary particles, and it was confirmed that lithium tungstate was uniformly formed between the secondary particles. It was.

Further, when the vicinity of the surface of the primary particles of the obtained positive electrode active material was observed with a transmission electron microscope (TEM), a lithium tungstate film having a thickness of 2 to 85 nm was formed on the surface of the primary particles, and the coating was made of tungsten. It was confirmed to be lithium acid lithium.

[Battery evaluation]
The battery characteristics of the coin-type battery 1 shown in FIG. 2 having a positive electrode produced using the obtained positive electrode active material were evaluated. In addition, the positive electrode resistance used the relative value which set Example 1 as 100 as the evaluation value. The initial discharge capacity was 204.6 mAh / g.

[Evaluation of gas generation]
A laminate cell 4 was prepared using the obtained positive electrode active material as a positive electrode material, a gas generation test was performed, and the amount of gas generated was evaluated. In the evaluation, the amount of gas generated was evaluated as a relative value with Example 1 as 100.

Hereinafter, for Examples 2 to 6 and Comparative Examples 1 to 5, only the substances and conditions changed from those in Example 1 are shown.
Table 1 shows the morphological analysis results of the lithium tungstates of Examples 1 to 6 and Comparative Examples 1 to 5, and the evaluation values of the initial discharge capacity and the positive electrode resistance.

A positive electrode active material for a non-aqueous electrolyte secondary battery was obtained under the same conditions as in Example 1 except that 3.5 g of LiOH and 10.5 g of WO ₃ were used.
The tungsten mixture after solid-liquid separation was dried, and the water content with respect to the lithium metal composite oxide particles determined from the mass before and after the drying was 6.8% by mass.
When analyzed by ICP emission spectroscopy, the Li concentration of the liquid component was 1.74 mol / L, the tungsten content of the tungsten mixture was 0.0023 mol, and the Li molar ratio was 3.8.

When the tungsten content and Li / Me of the obtained positive electrode active material were analyzed by ICP emission spectroscopy, the tungsten content was a composition of 0.3 atomic% with respect to the total number of Ni, Co and M atoms. It was confirmed that the Li / Me was 0.994 and the core material Li / Me was 0.992.
Moreover, when the obtained positive electrode active material was titrated and analyzed, the presence of Li ₄ WO ₅ was confirmed in the lithium tungstate, and the abundance ratio of Li ₄ WO ₅ contained in the lithium tungstate was calculated. Met.

On the other hand, W in tungsten oxide and Li in lithium hydroxide were mixed so as to have the same Li molar ratio (3.8) to produce lithium tungstate, and the lithium tungstate produced by X-ray diffraction was confirmed. However, since only Li ₄ WO ₅ and Li ₂ WO ₄ were confirmed, in the lithium tungstate in the positive electrode active material, the abundance ratio of Li ₄ WO ₅ is 60 mol%, and the abundance ratio of Li ₂ WO ₄ is It was thought to be 40 mol%.
Furthermore, the excess lithium was 0.02 mass% with respect to the total amount of the positive electrode active material.
The morphology analysis and evaluation of lithium tungstate were performed in the same manner as in Example 1, and the evaluation results are shown in Table 1 together with the battery characteristics.

A positive electrode active material for a non-aqueous electrolyte secondary battery was obtained under the same conditions as in Example 1 except that 7.0 g of LiOH and 19.3 g of WO ₃ were used.
The tungsten mixture after solid-liquid separation was dried, and the water content with respect to the lithium metal composite oxide particles determined from the mass before and after the drying was 7.3% by mass.
When analyzed by ICP emission spectroscopy, the Li concentration of the liquid component was 3.19 mol / L, the tungsten content of the mixture was 0.0046 mol, and the Li molar ratio was 3.8.

When the tungsten content and Li / Me of the obtained positive electrode active material were analyzed by ICP emission spectroscopy, the tungsten content was a composition of 0.6 atomic% with respect to the total number of Ni, Co and M atoms. It was confirmed that the Li / Me was 0.995 and the Li / Me of the core material was 0.993.
Moreover, when the obtained positive electrode active material was titrated and analyzed, the presence of Li ₄ WO ₅ was confirmed in the lithium tungstate, and the abundance ratio of Li ₄ WO ₅ contained in the lithium tungstate was calculated. Met.

On the other hand, W in tungsten oxide and Li in lithium hydroxide were mixed so as to have the same Li molar ratio (3.8) to produce lithium tungstate, and the lithium tungstate produced by X-ray diffraction was confirmed. However, since only Li ₄ WO ₅ and Li ₂ WO ₄ were confirmed, in the lithium tungstate in the positive electrode active material, the abundance ratio of Li ₄ WO ₅ is 60 mol%, and the abundance ratio of Li ₂ WO ₄ is It was thought to be 40 mol%.
Furthermore, the excess lithium was 0.04 mass% with respect to the total amount of the positive electrode active material.
The morphology analysis and evaluation of lithium tungstate were performed in the same manner as in Example 1, and the evaluation results are shown in Table 1 together with the battery characteristics.

300 g of lithium metal composite oxide powder as a base material was immersed in 400 ml of pure water and washed with water. After solid-liquid separation, 4.6 g of lithium hydroxide (LiOH) and 1.44 g of tungsten oxide (WO ₃ ) were added. Using a shaker mixer apparatus (TURBULA Type T2C manufactured by Willy et Bacofen (WAB)), the mixture was sufficiently mixed at 30 ° C. to obtain a tungsten mixture, and until the temperature of the mixture reached 90 ° C. in the heat treatment step. A positive electrode active material for a non-aqueous electrolyte secondary battery was obtained under the same conditions as in Example 1 except that the temperature was raised at 1 ° C./min.

The tungsten mixture was dried, and the water content with respect to the lithium metal composite oxide particles determined from the mass before and after drying was 7.5% by mass.
When analyzed by ICP emission spectroscopy, the Li concentration of the liquid component during solid-liquid separation was 0.31 mol / L, the tungsten content of the mixture was 0.062 mol, and the Li molar ratio was 3.2. .

When the tungsten content and Li / Me of the obtained positive electrode active material were analyzed by ICP emission spectroscopy, the tungsten content was a composition of 2.0 atomic% with respect to the total number of Ni, Co and M atoms. It was confirmed that the Li / Me was 0.990 and the Li / Me of the core material was 0.988.
Moreover, when the obtained positive electrode active material was subjected to titration analysis, the presence of Li ₄ WO ₅ was confirmed in the lithium tungstate, and the abundance ratio of Li ₄ WO ₅ contained in the lithium tungstate was calculated to be 55 mol%. Met.

On the other hand, W in tungsten oxide and Li in lithium hydroxide were mixed so as to have the same Li molar ratio (3.2) to produce lithium tungstate, and the lithium tungstate produced by X-ray diffraction was confirmed. However, since only Li ₄ WO ₅ and Li ₂ WO ₄ were confirmed, in the lithium tungstate in the positive electrode active material, the abundance ratio of Li ₄ WO ₅ is 55 mol%, and the abundance ratio of Li ₂ WO ₄ is It was thought to be 45 mol%. Moreover, the excess lithium was 0.03 mass% with respect to the whole quantity of a positive electrode active material.
The morphology analysis and evaluation of lithium tungstate were performed in the same manner as in Example 1, and the evaluation results are shown in Table 1 together with the battery characteristics.

300 g of lithium metal composite oxide powder as a base material was immersed in 400 ml of pure water and washed with water. After solid-liquid separation, 31.2 g of lithium tungstate (Li ₄ WO _A positive electrode active material for a nonaqueous electrolyte secondary battery was obtained under the same conditions as in Example 1 except that an aqueous solution in which ₅ ) was dissolved was added to obtain a tungsten mixture.

The tungsten mixture was dried, and the water content with respect to the lithium metal composite oxide particles determined from the mass before and after drying was 6.4% by mass.
Further, when analyzed by ICP emission spectroscopy, the Li concentration of the liquid component at the time of solid-liquid separation after addition of lithium tungstate was 1.36 mol / L, the tungsten content of the mixture was 0.0065 mol, Li The molar ratio was 4.0.

When the tungsten content and Li / Me of the obtained positive electrode active material were analyzed by ICP emission spectroscopy, the tungsten content was a composition of 0.2 atomic% with respect to the total number of Ni, Co and M atoms. It was confirmed that the Li / Me was 0.992 and the core material Li / Me was 0.989.
Moreover, when the obtained positive electrode active material was subjected to titration analysis, the presence of Li ₄ WO ₅ was confirmed in the lithium tungstate, and the abundance ratio of Li ₄ WO ₅ contained in the lithium tungstate was calculated to be 75 mol%. Met.

On the other hand, W in tungsten oxide and Li in lithium hydroxide were mixed so as to have the same Li molar ratio (4.0) to produce lithium tungstate, and the lithium tungstate produced by X-ray diffraction was confirmed. However, since only Li ₄ WO ₅ and Li ₂ WO ₄ were confirmed, the lithium tungstate in the positive electrode active material had an abundance ratio of Li ₄ WO ₅ of 75 mol%, and the abundance ratio of Li ₂ WO ₄ was It was thought to be 25 mol%.
Furthermore, the excess lithium was 0.02 mass% with respect to the total amount of the positive electrode active material.
The morphology analysis and evaluation of lithium tungstate were performed in the same manner as in Example 1, and the evaluation results are shown in Table 1 together with the battery characteristics.

The average particle size obtained by a known technique of mixing and firing oxide powder composed of Ni, Co and Mn and lithium hydroxide is 5.6 μm, the specific surface area is 0.7 m ² / g, Li _{1 .175 For} non-aqueous electrolyte secondary batteries in the same manner as in Example 1 except that the powder of lithium metal composite oxide particles represented by Ni _0.34 Co _0.33 Mn _0.33 O ₂ was used as a base material. A positive electrode active material was obtained. The mixture after solid-liquid separation was dried, and the water content with respect to the lithium metal composite oxide particles determined from the mass before and after drying was 7.8% by mass.
When analyzed by ICP emission spectroscopy, the Li concentration of the liquid component was 2.24 mol / L, the tungsten content of the mixture was 0.0039 mol, and the Li molar ratio was 3.8.

When the tungsten content and Li / Me of the obtained positive electrode active material were analyzed by ICP emission spectroscopy, the tungsten content was a composition of 0.5 atomic% with respect to the total number of Ni, Co and M atoms. It was confirmed that the Li / Me was 1.146, and the core material Li / Me was 1.144.
Moreover, when the obtained positive electrode active material was titrated and analyzed, the presence of Li ₄ WO ₅ and Li ₂ WO ₄ was confirmed in the lithium tungstate, and the abundance ratio of Li ₂ WO ₄ contained in the lithium tungstate was determined. When calculated, the abundance ratio of Li ₄ WO ₅ was 60 mol%, and the abundance ratio of Li ₂ WO ₄ was considered to be 40 mol%.
Furthermore, the excess lithium was 0.02 mass% with respect to the total amount of the positive electrode active material.
The morphology analysis and evaluation of lithium tungstate were performed in the same manner as in Example 1, and the evaluation results are shown in Table 1 together with the battery characteristics.

(Comparative Example 1)
A positive electrode active material for a non-aqueous electrolyte secondary battery was obtained under the same conditions as in Example 1 except that the aqueous solution of the tungsten compound was changed to pure water and washed.
When Li / Me of the obtained positive electrode active material was analyzed by ICP emission spectroscopy, Li / Me was 0.991. Excess lithium was 0.03% by mass relative to the total amount of the positive electrode active material.
The morphology analysis and evaluation of lithium tungstate were performed in the same manner as in Example 1, and the evaluation results are shown in Table 1 together with the battery characteristics.

(Comparative Example 2)
A positive electrode active material for a non-aqueous electrolyte secondary battery was obtained under the same conditions as in Example 1 except that 9.5 g of LiOH and 15.6 g of WO ₃ were used.
The tungsten mixture after the solid-liquid separation was dried, and the water content with respect to the lithium metal composite oxide particles determined from the mass before and after the drying was 7.6% by mass.
When analyzed by ICP emission spectroscopy, the Li concentration of the liquid component was 4.22 mol / L, the tungsten content of the mixture was 0.0039 mol, and the Li molar ratio was 6.3.

When the tungsten content and Li / Me of the obtained positive electrode active material were analyzed by ICP emission spectroscopy, the tungsten content was a composition of 0.5 atomic% with respect to the total number of Ni, Co and M atoms. It was confirmed that the Li / Me was 0.996 and the core material Li / Me was 0.993.
Moreover, when the obtained positive electrode active material was subjected to titration analysis, the presence of Li ₄ WO ₅ was confirmed in the lithium tungstate, and the abundance ratio of Li ₄ WO ₅ contained in the lithium tungstate was calculated to be 95 mol%. Met.

On the other hand, W in tungsten oxide and Li in lithium hydroxide were mixed so as to have the same Li molar ratio (6.3) to produce lithium tungstate, and the lithium tungstate produced by X-ray diffraction was confirmed. However, since only Li ₄ WO ₅ was confirmed, the lithium tungstate in the positive electrode active material had an abundance ratio of Li ₄ WO ₅ of 95 mol% and an abundance ratio of Li ₂ WO ₄ of 0 mol%. it was thought.
Furthermore, the excess lithium was 0.08 mass% with respect to the total amount of the positive electrode active material.
The morphology analysis and evaluation of lithium tungstate were performed in the same manner as in Example 1, and the evaluation results are shown in Table 1 together with the battery characteristics.

(Comparative Example 3)
A positive electrode active material for a non-aqueous electrolyte secondary battery was obtained under the same conditions as in Example 1, except that 4.0 g of LiOH and 15.6 g of WO ₃ were used.
The tungsten mixture after the solid-liquid separation was dried, and the water content with respect to the lithium metal composite oxide particles determined from the mass before and after the drying was 7.6% by mass.
When analyzed by ICP emission spectroscopy, the Li concentration of the liquid component was 1.95 mol / L, the tungsten content of the mixture was 0.0039 mol, and the Li molar ratio was 2.9.

When the tungsten content and Li / Me of the obtained positive electrode active material were analyzed by ICP emission spectroscopy, the tungsten content was a composition of 0.5 atomic% with respect to the total number of Ni, Co and M atoms. It was confirmed that the Li / Me was 0.994 and the core material Li / Me was 0.992.
Moreover, when the obtained positive electrode active material was subjected to titration analysis, the presence of Li ₄ WO ₅ was confirmed in the lithium tungstate, and the abundance ratio of Li ₄ WO ₅ contained in the lithium tungstate was calculated to be 35 mol. %Met.

On the other hand, W in tungsten oxide and Li in lithium hydroxide were mixed so as to have the same Li molar ratio (2.9) to produce lithium tungstate, and the lithium tungstate produced by X-ray diffraction was confirmed. However, since only Li ₄ WO ₅ and Li ₂ WO ₄ were confirmed, in the lithium tungstate in the positive electrode active material, the abundance ratio of Li ₄ WO ₅ is 35 mol%, and the abundance ratio of Li ₂ WO ₄ is It was thought to be 65 mol%.
Moreover, the excess lithium was 0.02 mass% with respect to the whole quantity of a positive electrode active material.
The morphology analysis and evaluation of lithium tungstate were performed in the same manner as in Example 1, and the evaluation results are shown in Table 1 together with the battery characteristics.

(Comparative Example 4)
The aqueous solution of the tungsten compound was changed to pure water, washed with water, separated into solid and liquid, and dried. After drying, 15.1 g of lithium tungstate (Li ₄ WO ₅ ) was added, and the shaker mixer apparatus (Willy et al. -A positive electrode active material for a non-aqueous electrolyte secondary battery was obtained under the same conditions as in Example 1 except that the mixture was thoroughly mixed, stirred and heat-treated using TURBULA Type T2C manufactured by Bacofen (WAB). The water content after solid-liquid separation and drying was less than 1.0% by mass.

When the tungsten content and Li / Me of the obtained positive electrode active material were analyzed by ICP emission spectroscopy, the tungsten content was a composition of 0.5 atomic% with respect to the total number of Ni, Co and M atoms. It was confirmed that the Li / Me was 0.992, and the Li / Me of the core material was 0.991.

Moreover, when the obtained positive electrode active material was subjected to titration analysis, it was confirmed that Li ₄ WO ₅ was present in the lithium tungstate, and the abundance ratio of Li ₄ WO ₅ contained in the lithium tungstate was calculated to be 98 mol%. The excess lithium was 0.03% by mass relative to the total amount of the positive electrode active material.

Observation by SEM and TEM confirmed that lithium tungstate was attached only to the surface of the positive electrode active material particles and was not present on the surface of the primary particles inside.
The morphology analysis and evaluation of lithium tungstate were performed in the same manner as in Example 1, and the evaluation results are shown in Table 1 together with the battery characteristics.

(Comparative Example 5)
A positive electrode active material for a non-aqueous electrolyte secondary battery was obtained in the same manner as in Example 6 except that it was changed to pure water and washed without using an aqueous solution of a tungsten compound.
When Li / Me of the obtained positive electrode active material was analyzed by ICP emission spectroscopy, Li / Me was 1.138.
Excess lithium was 0.04 mass% with respect to the total amount of the positive electrode active material.
The morphology analysis and evaluation of lithium tungstate were performed in the same manner as in Example 1, and the evaluation results are shown in Table 1 together with the battery characteristics.

[Evaluation]
As is apparent from Table 1, since the positive electrode active materials of Examples 1 to 6 were manufactured according to the present invention, the initial discharge capacity was lower than those of Comparative Examples 1 and 5 in which the positive electrode resistance was low and lithium tungstate was not formed. Therefore, the battery has excellent characteristics.
FIG. 3 shows an example of a cross-sectional observation result of the positive electrode active material obtained in the example of the present invention using a scanning microscope. The obtained positive electrode active material is composed of primary particles and primary particles aggregated. It was confirmed that fine particles containing lithium tungstate were formed on the primary particle surface. The fine particles containing lithium tungstate are indicated by arrows in FIG.

In Comparative Example 1, since lithium tungstate is not formed on the primary particle surfaces, the positive electrode resistance is significantly high, and it is difficult to meet the demand for higher output.
In Comparative Examples 2 and 3, the amount of tungsten with respect to the number of Ni, Co, and M atoms contained in the positive electrode active material is similar to that in Example 1, but Comparative Example 2 has a large proportion of Li ₄ WO ₅ . The positive electrode resistance is about the same as that of the example, but the amount of gas generation is increased. On the other hand, since the ratio of Li ₄ WO ₅ is small in Comparative Example 3, the amount of gas generation is small, but the positive electrode resistance is high.
Since Comparative Example 4 was mixed with the tungsten compound in a dry state, lithium tungstate was not formed on the surface of the primary particles inside the secondary particles, the positive electrode resistance was high, and the lithium tungstate was Li ₄ WO ₅ . It can be seen that the amount of gas generation is also increasing.
In Comparative Example 5, since lithium tungstate is not formed on the primary particle surface, the positive electrode resistance is significantly high, and it is difficult to meet the demand for higher output.

The non-aqueous electrolyte secondary battery of the present invention is suitable for a power source of a small portable electronic device (such as a notebook personal computer or a mobile phone terminal) that always requires a high capacity, and an electric vehicle battery that requires a high output. Also suitable.
In addition, the nonaqueous electrolyte secondary battery of the present invention has excellent safety, and can be downsized and increased in output, and thus is suitable as a power source for an electric vehicle subject to restrictions on mounting space. The present invention can be used not only as a power source for an electric vehicle driven purely by electric energy but also as a power source for a so-called hybrid vehicle used in combination with a combustion engine such as a gasoline engine or a diesel engine.

DESCRIPTION OF SYMBOLS 1 Coin type battery 2 Case 2a Positive electrode can 2b Negative electrode can 2c Gasket 3 Electrode 3a Positive electrode 3b Negative electrode 3c Separator 4 Laminate cell 4a Gas generation tested laminate cell 5 Positive electrode sheet 6 Negative electrode sheet 7 Separator 8 Aluminum laminate sheet PA Manual hydraulic press machine UPA Non-pressurizing part L ₁ (non-pressurizing part) width PP pressure member MP mounting member Ga dial gauge T table

Claims (15)

1. General _{formula: Li z Ni 1-x-} y Co x M y O 2 ( however, 0 <x ≦ 0.35,0 ≦ y ≦ 0.35,0.95 ≦ z ≦ 1.30, M is, Mn , V, Mg, Mo, Nb, Ti, and Al), and a layered crystal structure composed of secondary particles formed by aggregation of primary particles. A lithium metal composite oxide powder, a moisture of 2% by mass or more based on the lithium metal composite oxide powder, and a tungsten compound or a tungsten mixture of a tungsten compound and a lithium compound,
   Mixing step of obtaining a tungsten mixture in which the molar ratio of the total amount of lithium contained in the moisture and solid tungsten compound or the total amount of lithium contained in the moisture and solid tungsten compound and the lithium compound with respect to the contained tungsten amount When,
   Producing a positive electrode active material for a non-aqueous electrolyte secondary battery, characterized by having a heat treatment step of heat-treating the obtained tungsten mixture to form lithium tungstate on the primary particle surface of the lithium metal composite oxide Method.
2. 2. The method of manufacturing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the lithium metal composite oxide powder is mixed with water to form a slurry, and the lithium metal composite oxide powder is washed with water. A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, comprising a water washing step and a solid-liquid separation step of solid-liquid separation after the water washing step as a pre-step of the mixing step.
3. 3. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 2, wherein the concentration of the lithium metal composite oxide powder contained in the slurry is 200 to 5000 g with respect to 1 L of water.
4. 4. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 2 or 3, wherein a tungsten compound is added at least during the water washing step or after the solid-liquid separation step to obtain the tungsten mixture. A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery.
5. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 4, wherein the water washing step forms a slurry in which lithium metal composite oxide powder is mixed with an aqueous solution of a tungsten compound.
6. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 4, wherein the tungsten compound is in a powder state.
7. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 6, wherein the heat treatment is performed at 100 to 600 ° C.
8. The amount of tungsten contained in the tungsten mixture is 0.05 to 2.0 atomic% with respect to the total number of Ni, Co and M atoms contained in the lithium metal composite oxide particles. The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 7.
9. A positive electrode active material for a non-aqueous electrolyte secondary battery comprising a lithium metal composite oxide powder having a layered crystal structure composed of primary particles and secondary particles formed by aggregation of primary particles,
   General _{formula: Li z Ni 1-x-} y Co x M y W a O 2 + α ( although, 0 <x ≦ 0.35,0 ≦ y ≦ 0.35,0.95 ≦ z ≦ 1.30,0 < a ≦ 0.03, 0 ≦ α ≦ 0.15, and M is at least one element selected from Mn, V, Mg, Mo, Nb, Ti and Al), and the lithium metal composite oxide A positive electrode active material for a non-aqueous electrolyte secondary battery, characterized in that it has lithium tungstate on the surface of primary particles and the abundance ratio of Li ₄ WO ₅ contained in the lithium tungstate is 50 to 90 mol%.
10. The amount of lithium contained in a lithium compound other than lithium tungstate present on the surface of the lithium metal composite oxide is 0.08% by mass or less based on the total amount of the positive electrode active material. The positive electrode active material for nonaqueous electrolyte secondary batteries as described.
11. The amount of tungsten contained in the lithium tungstate is 0.05 to 2.0 atomic% of W atoms with respect to the total number of Ni, Co and M atoms contained in the lithium metal composite oxide. The positive electrode active material for non-aqueous electrolyte secondary batteries according to claim 9 and 10.
12. The non-aqueous electrolyte secondary according to any one of claims 9 to 11, wherein the lithium tungstate is present on the primary particle surface of the lithium metal composite oxide as fine particles having a particle diameter of 1 to 200 nm. Positive electrode active material for batteries.
13. The non-aqueous electrolyte secondary according to any one of claims 9 to 11, wherein the lithium tungstate is present on the primary particle surface of the lithium metal composite oxide as a film having a thickness of 1 to 150 nm. Positive electrode active material for batteries.
14. 12. The lithium metal composite oxide according to claim 9, wherein the lithium tungstate is present on the primary particle surface of the lithium metal composite oxide in both forms of fine particles having a particle diameter of 1 to 200 nm and a film having a thickness of 1 to 150 nm. The positive electrode active material for non-aqueous electrolyte secondary batteries according to claim 1.
15. A non-aqueous electrolyte secondary battery comprising a positive electrode containing the positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 9 to 14.

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