JP7069534B2 - Positive electrode active material for non-aqueous electrolyte secondary battery and non-aqueous electrolyte secondary battery using the positive electrode active material - Google Patents

Description

The present invention relates to a positive electrode active material for a non-aqueous electrolyte secondary battery 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 notebook computers, the development of small and lightweight secondary batteries having a high energy density is strongly desired. In addition, the development of high-output secondary batteries as batteries for electric vehicles such as hybrid vehicles is also strongly desired.

As a secondary battery satisfying such a requirement, there is a non-aqueous electrolyte secondary battery represented by a lithium ion secondary battery. This lithium ion secondary battery is composed of a negative electrode, a positive electrode, an electrolytic solution and the like, and the active material of the negative electrode and the positive electrode is a material capable of desorbing and inserting lithium.
Such non-aqueous electrolyte secondary batteries are currently being actively researched and developed. Among them, lithium ion secondary batteries using a layered or spinel type lithium nickel composite oxide as a positive electrode material are used. Since a high voltage of 4V class can be obtained, it is being put into practical use as a battery having a high energy density.

The materials that have been mainly proposed so far are 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 a cobalt manganese composite oxide (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) and a lithium manganese composite oxide using manganese (LiMn ₂ O ₄ ).
Of these, lithium-nickel composite oxides are attracting attention as materials that have good cycle characteristics and can obtain high output with low resistance, and in recent years, low resistance required for high output has been emphasized.

Addition of a foreign element is used as a method for achieving the above-mentioned low resistance, and a transition metal such as W, Mo, Nb, Ta, and Re, which can take an expensive number, is particularly useful.
For example, Patent Document 1 contains 0.1 to 5 mol% of one or more elements selected from Mo, W, Nb, Ta and Re with respect to the total molar amount of Mn, Ni and Co. Lithium transition metal compound powders for positive electrode materials for lithium secondary batteries have been proposed, and Mo, W, Nb, Ta and Mo, W, Nb, Ta and Mo, W, Nb, Ta and the total of metal elements other than Li and Mo, W, Nb, Ta and Re on the surface of the primary particles have been proposed. It is said that the total atomic ratio of Re is preferably 5 times or more the atomic ratio of the entire primary particles.
According to this proposal, it is possible to achieve both low cost and high safety, high load characteristics, and improved powder handling of lithium transition metal compound powders for positive electrode materials of lithium secondary batteries. ..

However, the lithium transition metal-based compound powder is obtained by pulverizing a raw material in a liquid medium, spray-drying a slurry in which these are uniformly dispersed, and firing the obtained spray-dried material. Therefore, there is a problem that some of the different elements such as Mo, W, Nb, Ta and Re are replaced with Ni arranged in layers, and the battery characteristics such as the capacity and cycle characteristics of the battery are deteriorated. rice field.

Further, Patent Document 2 describes a positive electrode active material for a non-aqueous electrolyte secondary battery having at least a layered structure of a lithium transition metal composite oxide, wherein the lithium transition metal composite oxide is a primary particle and an aggregate thereof. A non-aqueous electrolyte present in the form of particles consisting of one or both of certain secondary particles and having a compound on at least the surface of the particles comprising at least one selected from the group consisting of molybdenum, vanadium, tungsten, boron and fluorine. Positive electrode active materials for secondary batteries have 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 can be obtained even in an even more severe usage environment, and in particular, the surface of the particles is composed of molybdenum, vanadium, tungsten, boron and fluorine. By having a compound having at least one selected from the group, it is said that 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 said to be in improving the initial characteristics, that is, the initial discharge capacity and the initial efficiency, and the output characteristics are mentioned. It's not a thing. 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 the battery characteristics were deteriorated.

Further, Patent Document 3 describes a metal containing 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. Intermetallic compounds obtained by combination and / or oxide-coated positive electrode active materials have been proposed.
It is said that such a coating can absorb oxygen gas and ensure safety, but the output characteristics are not disclosed at all. Further, the disclosed manufacturing method uses a planetary ball mill for coating, and such a coating method causes physical damage to the positive electrode active material and deteriorates battery characteristics.

Further, in Patent Document 4, a composite oxide particle mainly composed of lithium nickelate is coated with a tungstic acid compound and heat-treated, and the content of carbonate ions is 0.15% by weight or less. Positive positive active materials have been proposed.
According to this proposal, a tungstate compound or a decomposition product of a tungstate compound is present on the surface of the positive electrode active material, and in order to suppress the oxidative activity on the surface of the composite oxide particles in a charged state, the decomposition of a non-aqueous electrolytic solution or the like is carried out. It is said that gas generation can be suppressed, but the output characteristics are not disclosed at all.

Further, Patent Document 5 describes a mixture of a lithium composite oxide powder and a composite oxide containing at least one element selected from the group consisting of Mo and W and Li at a temperature of about 650 to about 950 ° C. For a lithium secondary battery characterized by having a surface layer containing at least one element selected from the group consisting of Mo and W and Li on the surface of the lithium composite oxide powder obtained by the heat treatment in 1. Positive positive active materials have been proposed.
According to this proposal, a positive electrode active material for a lithium secondary battery having better thermal stability than the conventionally proposed positive electrode active material can be obtained without significantly deteriorating the high initial discharge capacity. No properties are disclosed.

In addition, improvements have been made regarding increasing the output of the lithium-nickel composite oxide.
For example, Patent Document 6 describes a lithium metal composite oxide composed of primary particles and secondary particles formed by aggregating the primary particles, and Li ₂ WO ₄ is provided on the surface of the lithium metal composite oxide. A positive electrode active material for a non-aqueous electrolyte secondary battery having fine particles containing lithium tungstate represented by either Li ₄ WO ₅ or Li ₆ W ₂ O ₉ has been proposed, and it is said that high capacity and high output can be obtained. ing.
However, although the output is increased while maintaining the high capacity, further increase in capacity is required.

Japanese Unexamined Patent Publication No. 2009-289726 Japanese Unexamined Patent Publication No. 2005-25716 Japanese Unexamined Patent Publication No. 11-16566 Japanese Unexamined Patent Publication No. 2010-40383 Japanese Unexamined Patent Publication No. 2002-73567 Japanese Unexamined Patent Publication No. 2013-125732

In view of the above problems, an object of the present invention is to provide a positive electrode active material for a non-aqueous electrolyte secondary battery, which can obtain high capacity and high output when used as a positive electrode material.

In order to solve the above problems, the present inventors have diligently studied the powder characteristics of lithium nickel composite oxide used as a positive electrode active material for a non-aqueous electrolyte secondary battery and the influence on the positive electrode resistance of the battery. , Forming a compound containing tungsten and lithium on the surface of the primary particles constituting the lithium nickel composite oxide powder, and using a lithium compound other than the compound containing tungsten and lithium present on the surface of the primary particle of the lithium nickel composite oxide powder. It has been found that by reducing the amount, it is possible to reduce the positive electrode resistance of the battery and improve the output characteristics.

Further, as a manufacturing method thereof, a lithium nickel composite oxide and a lithium-free tungsten compound are mixed and heat-treated to form a tungsten and a lithium-containing compound on the surface of the primary particles of the lithium nickel composite oxide. We have found that it is possible to reduce lithium compounds other than compounds containing lithium, and have completed the present invention.

The first invention of the present invention has a general formula: Liz Ni _{1-x-y Co x} My O ₂ (where _{0.00≤x≤0.35} , 0.00≤y≤0.35, 0". .95 ≦ z ≦ 1.20, M is composed of a primary particle represented by Mn, V, Mg, Mo, Nb, Ti and Al) and a secondary particle in which the primary particles are aggregated. A positive electrode active material for a non-aqueous electrolyte secondary battery composed of lithium nickel composite oxide particles, which has a compound containing tungsten and lithium on the surface of the primary particles of the lithium nickel composite oxide particles, and the lithium nickel composite. The amount of lithium contained in all the compounds containing lithium present on the surface of the primary particles of the oxide particles is 0.05 to 0.35% by mass with respect to the total amount of the positive electrode active material, except for the compounds containing tungsten and lithium. The amount of lithium contained in the lithium-containing compound is 0.01% by mass or more and 0.05% by mass or less with respect to the total amount of the positive electrode active material, and the amount of lithium contained in the lithium carbonate in the lithium-containing compound is The amount of tungsten contained in the positive electrode active material is 0.03% by mass or less with respect to the total amount of the positive electrode active material, and the amount of tungsten contained in the lithium tungstenate and the compound containing tungsten is the lithium nickel. It is a positive electrode active material for a non-aqueous electrolyte secondary battery, characterized in that it is 0.05 to 0.30 atomic% with respect to the total number of atoms of Ni, Co and M contained in the composite oxide particles.

The second invention of the present invention is a positive electrode active material for a non-aqueous electrolyte secondary battery, wherein the compound containing tungsten and lithium in the first invention is lithium tungstate.

A third aspect of the present invention is a non-aqueous electrolyte secondary battery characterized by having a positive electrode containing a positive electrode active material for a non-aqueous electrolyte secondary battery obtained in the first or second invention .

According to the present invention, a positive electrode active material for a non-aqueous electrolyte secondary battery capable of achieving high capacity and high output when used as a positive electrode material of a battery can be obtained.
Further, the manufacturing method is easy and suitable for production on an industrial scale and has high productivity, and its industrial value is extremely large.

It is a schematic explanatory diagram of the measurement example of impedance evaluation and the equivalent circuit used for analysis. It is the schematic sectional drawing of the coin type battery B used for the battery evaluation. It is a cross-sectional SEM photograph (observation magnification 10000 times) of the lithium nickel composite oxide of this invention.

Hereinafter, the present invention will be described first with respect to the positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention, and then a method for producing the same and a non-aqueous electrolyte secondary battery using the positive electrode active material according to the present invention.

(1) Positive particle active material for non-aqueous electrolyte secondary battery The positive particle active material for non-aqueous electrolyte secondary battery of the present invention has a general formula: _Liz Ni _{1-xy Co x My} O ₂ (however, 0. 00 ≦ x ≦ 0.35, 0.00 ≦ y ≦ 0.35, 0.95 ≦ z ≦ 1.20, M is at least one selected from Mn, V, Mg, Mo, Nb, Ti and Al. A non-aqueous system composed of lithium nickel composite oxide particles (hereinafter, may be simply referred to as “composite oxide particles”) composed of primary particles represented by (element) and secondary particles in which the primary particles are aggregated. It is a positive electrode active material for an electrolyte secondary battery (hereinafter, may be simply referred to as “positive electrode active material”), and is the surface of the secondary particles of the lithium nickel composite oxide particles and the surface of the internal primary particles (hereinafter, hereinafter. The surface of the secondary particle and the surface of the internal primary particle are sometimes simply referred to as the "primary particle surface"), and the compound containing tungsten and lithium is present on the surface of the primary particle of the lithium nickel composite oxide. , The amount of lithium contained in all the compounds containing lithium is 0.05 to 0.35% by mass or less based on the total amount of the positive electrode active material, and is contained in compounds containing lithium other than tungsten and compounds containing lithium. The amount of lithium is 0.05% by mass or less with respect to the total amount of the positive electrode active material, and the amount of lithium contained in lithium carbonate in the lithium-containing compound is 0.03% by mass or less with respect to the total amount of the positive electrode active material. It is characterized by that.

In the present invention, the core material is a general formula: Liz Ni _{1-x-y Co x} My O ₂ (where _{0.00≤x≤0.35} , 0.00≤y≤0.35, 0. 95 ≦ z ≦ 1.20, M is at least one element selected from Mn, V, Mg, Mo, Nb, Ti and Al), and high charge / discharge is achieved by using a lithium nickel composite oxide. It gains capacity.
Further, the amount of lithium contained in the tungsten- and lithium-containing compounds formed on the surface of the primary particles of the lithium-nickel composite oxide particles and all the lithium-containing compounds present on the surface of the lithium-nickel composite oxide is the positive electrode. The amount of lithium contained in compounds containing lithium other than tungsten and lithium-containing compounds is 0.05 to 0.35% by mass or less with respect to the total amount of the active material, and 0.05% by mass or less with respect to the positive electrode active material. By setting the amount of lithium contained in lithium carbonate in the lithium-containing compound to 0.03% by mass or less with respect to the total amount of the positive electrode active material, the output characteristics are improved while maintaining the charge / discharge capacity, and the cycle is further improved. It has improved characteristics.

Generally, when the surface of the positive electrode active material is completely covered with a different compound, the movement (intercalation) of lithium ions is greatly restricted, resulting in the high capacity of the lithium nickel composite oxide. The advantages are erased.
On the other hand, in the positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention (hereinafter, simply referred to as “positive electrode active material”), lithium (Li) and tungsten (W) are applied to the surface of the lithium nickel composite oxide particles. A compound containing the compound (hereinafter, may be referred to as “LiW compound”) is formed, and this compound has a high lithium ion conductivity and has an effect of promoting the movement of lithium ions. Therefore, by forming the above compound on the surface of the lithium nickel composite oxide particles, a conduction path of Li is formed at the interface with the electrolytic solution, so that the reaction resistance of the positive electrode active material (hereinafter referred to as “positive electrode resistance”). In some cases), the output characteristics are improved.

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 is 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 and removed from the positive electrode, so that the battery capacity is also improved. Further, by reducing the reaction resistance, the load of the active material at the time of charging / discharging is also reduced, so that the cycle characteristics can be improved.

Therefore, such a LiW compound has a high Li ion conductivity and has an effect of promoting the movement of Li ions by containing Li and W. However, this LiW compound is Li ₂ WO ₄ or Li ₄ WO ₅ . It is preferable that it exists in the form of.

Here, since contact with the electrolytic solution occurs on the surface of the primary particle, it is important that this compound is formed on the surface of the primary particle.
The surface of the primary particle in the present invention is exposed to the voids near and inside the surface of the secondary particle through which the electrolytic solution can permeate through the surface of the primary particle exposed on the outer surface of the secondary particle and the outside of the secondary particle. It includes the surface of primary particles. Further, even the grain boundaries between the primary particles are included if the bonds of the primary particles are incomplete and the electrolytic solution can penetrate.

That is, the contact between this compound and the electrolytic solution is not only the outer surface of the secondary particles formed by agglomerating the primary particles, but also the voids near and inside the surface of the secondary particles, and the incomplete grain boundary. However, it is necessary to form a compound on the surface of the primary particles to promote the movement of lithium ions.
Therefore, by forming the LiW compound on most of the surfaces of the primary particles that can come into contact with the electrolytic solution, the reaction resistance of the lithium nickel composite oxide particles can be further reduced.

Here, the LiW compound does not have to be formed on the entire surface of the primary particles that can be completely contacted with the electrolytic solution, and may be in a partially covered state or a scattered state. If the compound is formed on the surface of the primary particles that can be in contact with the electrolytic solution even in a partially coated or scattered state, the effect of reducing the reaction resistance can be obtained.
In particular, on the surface of the primary particles inside near the surface of the secondary particles, the positive electrode resistance contributes greatly due to the effect of promoting the movement of lithium ions, and the LiW compound is at least on the surface of the primary particles near the surface of the secondary particles. By forming the particles, a great effect on reducing the positive electrode resistance can be obtained. Here, the vicinity of the surface is, for example, a range from the surface of the secondary particles to about 1 to 3 μm.

Further, in the form of the LiW compound on the surface of the primary particles, when the surface of the primary particles is coated with a layered material, the contact area with the electrolytic solution becomes small. Further, the formation of a layered substance tends to result in the formation of the LiW compound concentrated on the surface of a specific primary particle. Therefore, since the layered material as a coating material has high lithium ion conductivity, the effects of improving the charge / discharge capacity and reducing the reaction resistance can be obtained, but there is room for improvement.
Therefore, in order to obtain a higher effect, the LiW compound is preferably present on the surface of the primary particles of the lithium nickel composite oxide as fine particles having a particle diameter of 1 to 300 nm.

By adopting such a form, the contact area with the electrolytic solution can be made sufficient and the lithium ion conduction can be effectively improved, so that the charge / discharge capacity can be improved and the reaction resistance can be reduced more effectively. can. If the particle size is less than 1 nm, the fine particles may not have sufficient lithium ion conductivity.
However, if the particle size exceeds 300 nm, the formation of the fine particles on the surface becomes non-uniform, and a higher effect of reducing the reaction resistance may not be obtained.
However, the LiW compound does not have to exist as fine particles having a particle diameter of 1 to 300 nm, and preferably 50% or more of the fine particles formed on the surface of the primary particles are formed in the particle diameter range of 1 to 300 nm. If it is done, a high effect can be obtained.

On the other hand, if the surface of the primary particles is coated with a thin film, a conduction path of Li can be formed at the interface with the electrolytic solution while suppressing a decrease in the specific surface area, which is said to improve the charge / discharge capacity and reduce the reaction resistance. The effect is obtained. When the surface of the primary particles is coated with such a thin-film LiW compound, it is preferably present on the surface of the primary particles of the lithium nickel composite oxide as a film having a film thickness of 1 to 200 nm.
If the film thickness is less than 1 nm, the film may not have sufficient lithium ion conductivity. Further, if the film thickness exceeds 200 nm, the lithium ion conductivity is lowered, and an effect higher than the reaction resistance reducing effect may not be obtained.

However, this film may be partially formed on the surface of the primary particles, and the film thickness range of all the films may not be 1 to 200 nm. A high effect can be obtained if a film having a film thickness of 1 to 200 nm is formed on the surface of the primary particles at least partially. When a LiW compound is formed as a film, by controlling the amount of tungsten contained in the LiW compound within the above range, a film having a film thickness of 1 to 200 nm sufficient to obtain an effect is formed. To.
Further, even when the LiW compound is formed on the surface of the primary particles by mixing the fine particle form and the thin film film form, a high effect on the battery characteristics can be obtained.

In the positive electrode active material of the present invention, the amount of lithium contained in all the compounds including lithium present on the surface of the primary particles of the lithium nickel composite oxide particles is the total amount of the positive electrode active material. On the other hand, it is 0.05 to 0.35% by mass, preferably 0.08 to 0.30% by mass.
By setting the total of all the compounds containing lithium, that is, the LiW compound and the compounds containing lithium other than the LiW compound in the above range, the shortage of the amount of Li in the lithium nickel composite oxide particles is suppressed, and the capacity is high and high. A positive electrode active material for output can be obtained, and cycle characteristics can be improved.

The amount of lithium contained in the lithium-nickel composite oxide present on the surface of the primary particles of the composite oxide particles and the lithium-containing compound other than the LiW compound (hereinafter referred to as "surplus lithium amount") is the positive electrode active material. It is 0.05% by mass or less, preferably 0.03% by mass or less, based on the total amount.

By limiting the amount of excess lithium in this way, high charge / discharge capacity and output characteristics are obtained, and cycle characteristics are improved.
In addition to the LiW compound, lithium hydroxide and lithium carbonate are present on the surface of the secondary particles and the surface of the primary particles of the composite oxide particles, and the lithium-containing compound whose abundance can be expressed as the amount of excess lithium thereof is a compound. The conductivity of lithium is poor, hindering the movement of lithium ions from the lithium-nickel composite oxidant.

That is, by reducing the amount of surplus lithium, the effect of promoting the movement of lithium ions by the LiW compound can be enhanced, the load on the lithium nickel composite oxide during charging and discharging can be reduced, and the cycle characteristics can be improved.
In addition, by controlling the amount of excess lithium, the movement of lithium ions between the composite oxide particles is made uniform, the load on specific composite oxide particles is suppressed, and the cycle characteristics can be improved. ..
Too little excess lithium indicates that excess lithium is extracted from the crystals of the composite oxide particles when the LiW compound is formed. Therefore, the amount of excess lithium is preferably 0.01% by mass or more in order to suppress deterioration of battery characteristics.

Further, in the positive electrode active material of the present invention, the amount of lithium contained in lithium carbonate present on the surface of the composite oxide particles is 0.03% by mass or less, preferably 0.02% by mass, based on the total amount of the positive electrode active material. % Or less, more preferably 0.015% by mass or less.
If it exceeds 0.02% by mass, the amount of lithium carbonate present on the surface of the composite oxide particles increases, and the amount of gas generated in the process of repeating charging and discharging may increase. In this way, lithium carbonate By limiting the amount, gas generation can be suppressed, deterioration of battery performance can be suppressed, and safety can be ensured. Further, when the amount of lithium carbonate is large, the conduction of Li ions between the electrolytic solution and the positive electrode active material is hindered, which causes problems such as an increase in the reaction resistance of the positive electrode active material and a decrease in the charge capacity.

The content of lithium carbonate is determined by, for example, measuring the total carbon element (C) content in the positive electrode active material with a carbon sulfur analyzer, and assuming that the measured carbon element (C) content is all derived from lithium carbonate. The amount of lithium contained can be obtained from lithium carbonate by converting it into lithium carbonate.
On the other hand, the lithium-nickel composite oxide particles have very few surface deterioration layers due to excessive elution of lithium, so that high battery characteristics can be obtained. That is, the deteriorated layer on the surface has high resistance, which is one of the factors that increase the positive electrode resistance. Therefore, by reducing the deteriorated layer, the positive electrode resistance is lowered, the output characteristics are improved, and the battery capacity is also high. can get.

The amount of tungsten contained in the LiW compound is preferably 0.05 to 3.0 atomic% with respect to the total number of atoms of Ni, Co and M contained in the lithium nickel composite oxide, and is preferably 0.05 to 3.0 atomic%. It is more preferably 2.0 atomic%, further preferably 0.1 to 1.0 atomic%, and particularly preferably 0.1 to 0.5 atomic%. This makes it possible to 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, and if the amount of tungsten exceeds 3.0 atomic%, the amount of the LiW compound formed becomes too large and lithium. Lithium conduction between the nickel compound oxide and the electrolytic solution may be hindered, and the charge / discharge capacity may decrease.

As for the amount of lithium in the entire positive electrode active material, the ratio "Li / Me" of the sum of the atomic numbers of Ni, Co and M (Me) in the positive electrode active material to the number of atoms of Li is 0.95 to 1. It is 20, and "Li / Me" is preferably in the range of 0.97 to 1.15.
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 becomes large, so that the output of the battery becomes low. Further, when Li / Me exceeds 1.20, the initial discharge capacity of the positive electrode active material decreases and the reaction resistance of the positive electrode also increases. Since the lithium content contained in the LiW compound is supplied from the lithium-nickel composite oxide particles as the base material, the amount of lithium in the entire positive electrode active material does not change before and after the formation of the LiW compound. Here, the base material is lithium nickel composite oxide particles used as a raw material before forming a LiW compound, and the core material is lithium nickel composite oxide particles having a LiW compound formed on the surface of the primary particles thereof. ..

That is, since the Li / Me of the lithium nickel composite oxide particles as the core material after the formation of the LiW compound is less than that before the formation, setting it to 0.97 or more provides better charge / discharge capacity and reaction resistance. Obtainable.
Therefore, the total amount of lithium in the positive electrode active material is more preferably 0.97 to 1.15.

The positive electrode active material of the present invention is composed of a lithium nickel composite oxide which is a hexagonal layered compound, and has a cobalt (Co) content in the above general formula showing the composition of the lithium nickel composite oxide which is a core material. The indicated x is 0.00 ≦ x ≦ 0.35, preferably 0.03 ≦ x ≦ 0.35, and more preferably 0.03 ≦ x ≦ 0.20.
When the cobalt content is in the above range, excellent cycle characteristics and thermal stability can be obtained. Although the cycle characteristics of the positive electrode active material can be improved by increasing the cobalt content, the cobalt content is preferably 0.2 or less from the viewpoint of increasing the capacity of the positive electrode active material.

Further, y indicating the content of M, which is at least one element selected from Mn, V, Mg, Mo, Nb, Ti and Al, is 0.00 ≦ y ≦ 0.35, preferably 0. 0.01 ≦ y ≦ 0.35. When the content of M is in the above range, excellent cycle characteristics and thermal stability can be obtained.
If y exceeds 0.35, it becomes difficult to increase the capacity of the positive electrode active material. When the effect of improving the battery characteristics is obtained, it is preferable to add M, and in order to sufficiently obtain the effect of improving the battery characteristics, it is more preferable to set y to 0.01 or more.

In the positive electrode active material of the present invention, a LiW compound is provided on the surface of the secondary particles and the surface of the primary particles of the lithium nickel composite oxide particles to improve the output characteristics and the cycle characteristics, and the particle size and tap as the positive electrode active material. The powder properties such as density may be within the range of the positive electrode active material usually used.
Further, the effect of providing the LiW compound on the surface of the secondary particles and the surface of the primary particles of the lithium nickel composite oxide particles is, for example, a lithium cobalt-based composite oxide, a lithium manganese-based composite oxide, and a lithium nickel-cobalt manganese-based. It can be applied not only to powders such as composite oxides and the positive electrode active material described in the present invention, but also to commonly used positive electrode active materials for lithium secondary batteries.

(2) Method for Producing Positive Electrode Active Material 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 below for each step.

[Mixing process]
The mixing step is a step of mixing a tungsten compound powder with lithium nickel composite oxide particles as a base material to obtain a tungsten mixture of lithium nickel composite oxide particles and tungsten compound particles (hereinafter, simply referred to as a mixture).
By mixing the lithium-free tungsten compound powder with the composite oxide particles, the tungsten-free compound present on the surface of the primary particles of the composite oxide particles of the base material and the tungsten compound are present in the next heat treatment step. The particles can be reacted. That is, as will be described later, a tungsten-free lithium-containing compound existing on the surface of the primary particle is reacted with a lithium-free tungsten compound to disperse it on the surface of the primary particle, and further heat is applied to bring the LiW compound to the surface of the primary particle. To form.

The water content of the composite oxide particles before mixing is preferably less than 0.2% by mass. This makes it possible to shorten the storage time in a wet state, and further suppress excessive elution of lithium from the composite oxide particles.
Further, the composite oxide particles before mixing are preferably left in a calcined state. By using the composite oxide particles in the fired state, it is possible to secure a sufficient amount of the lithium compound present on the surface of the primary particles to react with the tungsten compound, and it is extracted from the composite oxide particles by reacting with the tungsten compound. Lithium can be reduced to suppress the formation of a deteriorated layer on the surface of the primary particles.

Since the tungsten compound powder is uniformly dispersed on the surface of the primary particles, it is preferably fine, and the average particle size of the volume integration in the particle size distribution measurement by the laser diffraction / scattering method is more preferably 0.05 to 5 μm. Further, since it reacts with the excess Li content on the surface of the primary particles, a compound having good reactivity with the lithium compound is preferable. Since the mixture is heated in the heat treatment step of the subsequent step, even if it is difficult to react at room temperature, the mixture may be one that reacts by heating at the time of heat treatment.

As described above, as the tungsten compound, a lithium-free tungsten compound is used in order to react with the lithium compound existing on the surface of the lithium-nickel composite oxide to reduce excess lithium. For example, a compound that easily reacts with lithium, such as tungsten oxide, tungstic acid, ammonium tungstate, and sodium tungstate, is preferable, and tungsten oxide (WO ₃ ) or tungstic acid (WO ₃ · H) having a low possibility of contamination with impurities is preferable. ₂ O) is more preferable. With the lithium-containing tungsten compound, the LiW compound can be formed on the surface of the primary particles, but the excess lithium cannot be sufficiently reduced.

Further, the amount of tungsten contained in this mixture is preferably 0.05 to 3.0 atomic% with respect to the total number of atoms of Ni, Co and M contained in the composite oxide particles. It is more preferably 05 to 2.0 atomic%, further preferably 0.1 to 1.0 atomic%, and particularly preferably 0.1 to 0.5 atomic%.
As a result, the amount of tungsten contained in the LiW compound in the positive electrode active material can be set in a preferable range, and the high charge / discharge capacity and output characteristics of the positive electrode active material can be further achieved at the same time.

When mixing the lithium nickel composite oxide and the tungsten compound, a general mixer can be used. For example, a shaker mixer, a Ladyge mixer, a Julia mixer, a V-blender, or the like may be used to sufficiently mix the lithium-nickel composite oxide to the extent that the skeleton is not destroyed.

[Heat treatment process]
The heat treatment step is a step of heat-treating the tungsten mixture, and further reacts the tungsten-free lithium compound existing on the surface of the primary particles of the lithium nickel composite oxide particles with the tungsten compound particles to disperse them on the surface of the primary particles, and then disperse the primary particles. It forms a lithium-tungsten compound on the surface.

Here, it is important to react the lithium compound with the tungsten compound to disperse the tungsten and further form the LiW compound on the surface of the primary particles.
By heating the tungsten mixture in the heat treatment step, the lithium compound remaining on the surface of the secondary particles reacts with the tungsten compound particles. Since the lithium compound remaining on the surface of the primary particles contains lithium hydroxide, water is generated when the compound reacts with the tungsten compound, and the generated water and tungsten and lithium are at least near the surface of the secondary particles. It penetrates to the surface of the primary particles and disperses, and the reaction between the lithium compound and the tungsten compound continues. When further heating is continued, the water evaporates to form a LiW compound. By forming this LiW compound, the battery characteristics can be improved. In addition, the excess lithium in the obtained positive electrode active material is significantly reduced, and the battery characteristics can be further improved.

Furthermore, the tungsten compound also has the effect of reacting with the excess lithium in the composite oxide particles and extracting the excess lithium present in the composite oxide particles, as well as reducing the excess lithium on the surface of the primary particles. By extracting lithium, the crystallinity of the lithium nickel composite oxide particles is improved, and the battery characteristics can be further enhanced.

Here, the temperature in the heat treatment is preferably 100 to 600 ° C. By adjusting the temperature to 100 to 600 ° C., the reaction between the above-mentioned lithium compound and the tungsten compound is sufficiently advanced during the temperature rise to sufficiently disperse the tungsten on the surface of the primary particles, and further form the LiW compound. Excess lithium from the composite oxide particles can be reduced.
Below 100 ° C, the LiW compound may not be sufficiently formed. On the other hand, when the temperature is higher than 600 ° C., the elution of lithium from the composite oxide particles accelerates too much, or the structure of the composite oxide itself is destroyed by cation mixing inside the composite oxide, resulting in sufficient battery characteristics. It may not be obtained.

The heating time in the heat treatment step is not particularly limited, but is preferably 0.5 hours or more because the lithium compound and the tungsten compound are reacted to sufficiently disperse the tungsten to form the LiW compound.

In order to react the lithium compound with the tungsten compound in this way and disperse the tungsten on the surface of the primary particles, it is preferable to allow the reaction to proceed sufficiently and heat the particles until they are further dispersed. Therefore, in the heat treatment step, the tungsten mixture is heat-treated to react the lithium compound present on the surface of the primary particles of the lithium nickel composite oxide particles with the tungsten compound particles, and the tungsten is dispersed on the surface of the primary particles. By heat-treating at a temperature higher than that of the first heat treatment step for forming the composite oxide particles and the first heat treatment step performed after the first heat treatment step, tungsten and tungsten and the surface of the primary particles of the lithium nickel composite oxide particles are formed. It is preferable to have a second heat treatment step for forming lithium nickel composite oxide particles provided with a compound containing lithium.

For example, the heat treatment temperature in the first heat treatment step is preferably 60 to 80 ° C. As a result, the lithium compound and the tungsten compound can be reacted, and the evaporation of the generated water can be suppressed, so that the tungsten can be more sufficiently dispersed on the surface of the primary particles.
On the other hand, if the heat treatment temperature is less than 60 ° C., the reaction between the lithium compound and the tungsten compound present on the surface of the primary particles of the lithium nickel composite oxide may not sufficiently occur. If the temperature is higher than 80 ° C., the water evaporates too quickly, and the dispersion of tungsten on the surface of the primary particles may not proceed sufficiently.
The heating time in the first heat treatment step is not particularly limited, but is preferably 0.5 to 2 hours because the lithium compound and the tungsten compound react with each other to sufficiently disperse the tungsten.

In the second heat treatment step, the water in the mixture is sufficiently evaporated by heat treatment at a temperature higher than the heat treatment temperature of the first heat treatment step, and a LiW compound is formed on the surface of the primary particles of the lithium nickel composite oxide particles. The heat treatment temperature is preferably 100 to 600 ° C. as in the heat treatment step described above.
The heat treatment time in the second heat treatment step is not particularly limited, but is preferably 1 to 15 hours in order to sufficiently evaporate the water content to form the LiW compound, and preferably 5 to 12 hours.

The atmosphere in the heat treatment step is preferably decarbonized air, an inert gas or a vacuum atmosphere in order to avoid the reaction between moisture and carbon dioxide in the atmosphere and lithium on the surface of the lithium nickel composite oxide particles. In particular, when decarboxylated air is used, it is desirable because it does not deteriorate the lithium nickel composite oxide as compared with the inert gas and the vacuum atmosphere, and has an advantage in terms of cost.
Here, decarboxylated air will be described. The normal atmosphere contains a small amount of carbon dioxide gas (CO ₂ ), but the decarboxylated air of the present invention is obtained by decarboxylating the content of this carbon dioxide gas to 10 ppm or less, which is lower than that of the normal atmosphere.

(3) Non-aqueous electrolyte secondary battery The non-aqueous electrolyte secondary battery of the present invention comprises a positive electrode, a negative electrode, a non-aqueous electrolyte solution, and the like, and is composed of the same components as a general non-aqueous electrolyte secondary battery. The embodiments described below are merely examples, and the non-aqueous electrolyte secondary battery of the present invention may be modified in various ways based on the embodiments described in the present specification and based on the knowledge of those skilled in the art. It can be carried out in an improved form. Further, the non-aqueous electrolyte secondary battery of the present invention is not particularly limited in its use.

(A) Positive electrode Using the positive electrode active material for the non-aqueous electrolyte secondary battery described above, for example, the positive electrode of the non-aqueous electrolyte secondary battery is produced as follows.
First, a powdery positive electrode active material, a conductive material, and a binder are mixed, and if necessary, activated carbon, a solvent for viscosity adjustment and the like is added, and the mixture is kneaded to prepare a positive electrode mixture paste.
The mixing ratio of each of the positive electrode mixture pastes is also an important factor in 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, as in the case of the positive electrode of a general non-aqueous electrolyte secondary battery, and the conductive material. The content of the binder is preferably 1 to 20 parts by mass, and the content of the binder is preferably 1 to 20 parts by mass.

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

In the production of 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 binding the active material particles, for example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluororubber, ethylene propylene diene rubber, styrene butadiene, cellulose resin, and polyacrylic acid. Acids and the like can be used.

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

(B) Negative electrode The negative electrode is a negative electrode mixture made into a paste by mixing a binder with a negative electrode active material that can occlude and desorb lithium ions, such as metallic lithium or lithium alloy, and adding an appropriate solvent. Is applied to the surface of a metal leaf current collector such as copper, dried, and if necessary, compressed to increase the electrode density.

As the negative electrode active material, for example, an organic compound fired body such as natural graphite, artificial graphite, or phenol resin, or a powdery body of a carbon substance such as coke can be used. In this case, as the negative electrode binder, a fluororesin such as PVDF can be used as in the positive electrode, and as the solvent for dispersing these active substances and the binder, N-methyl-2-pyrrolidone or the like can be used. An organic solvent can be used.

(C) Separator A separator is sandwiched between the positive electrode and the negative electrode.
The separator separates the positive electrode and the negative electrode and retains an electrolyte, and a thin film such as polyethylene or polypropylene, which has a large number of fine pores, can be used.

(D) Non-aqueous electrolyte solution The non-aqueous electrolyte solution is obtained by dissolving a lithium salt as a supporting salt in an organic solvent.
Examples of the organic solvent used include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate and trifluoropropylene carbonate, chain carbonates such as diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate and dipropyl carbonate, and tetrahydrofuran. One selected from 2-methyl tetrahydrofuran, ether compounds such as dimethoxyethane, sulfur compounds such as ethylmethyl sulfone and butane sulton, phosphorus compounds such as triethyl phosphate and trioctyl phosphate, etc., alone or in admixture 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 , etc., and a composite salt thereof can be used.
Further, the non-aqueous electrolyte solution may contain a radical scavenger, a surfactant, a flame retardant and the like.

(E) Battery shape and configuration The shape of the non-aqueous electrolyte secondary battery of the present invention, which is composed of the positive electrode, the negative electrode, the separator and the non-aqueous electrolyte solution described above, may be various, such as a cylindrical type and a laminated type. can do.
Regardless of which shape is adopted, 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 solution to communicate with the positive electrode current collector and the outside. A non-aqueous electrolyte secondary battery is completed by connecting between the positive electrode terminal and the negative electrode current collector and the negative electrode terminal leading to the outside using a current collecting lead or the like and sealing the battery case. ..

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

An example of the method for measuring the positive electrode resistance in the present invention is as follows.
When the frequency dependence of the battery reaction is measured by the AC impedance method, which is a general electrochemical evaluation method, the Nyquist diagram based on the solution resistance, the negative electrode resistance and the negative electrode capacity, and the positive electrode resistance and the positive electrode capacity is shown in FIG. Obtained like this.
The battery reaction at the electrode consists of a resistance component due to charge transfer and a capacitance component due to the electric double layer. When these are represented by an electric circuit, it is a parallel circuit of resistance and capacitance, and the battery as a whole is a solution resistance, a negative electrode, and a positive electrode in parallel. It is represented by an equivalent circuit in which circuits are connected in series.

Fitting calculation can be 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 resulting semicircle on the low frequency side of the Nyquist diagram.
From the above, the positive electrode resistance can be estimated by measuring the AC impedance of the manufactured positive electrode and calculating the fitting with the equivalent circuit to the obtained Nyquist diagram.

The performance (initial discharge capacity, positive electrode resistance, cycle characteristics) of the secondary battery having a positive electrode using the positive electrode active material obtained by the present invention was measured.
Hereinafter, the present invention will be specifically described with reference to examples of the present invention, but the present invention is not limited to these examples.

(Battery manufacturing and evaluation)
The evaluation of the obtained positive electrode active material for a non-aqueous electrolyte secondary battery was performed by preparing a battery as follows and measuring the charge / discharge capacity.
52.5 mg of the 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. The positive electrode 1 (evaluation electrode) shown in the above was produced. The prepared positive electrode 1 was dried in a vacuum dryer at 120 ° C. for 12 hours. Then, using this positive electrode 1, a 2032 type coin-type battery B was produced in a glove box having an Ar atmosphere with a dew point controlled at −80 ° C.
For the Li metal negative electrode 2, a negative electrode sheet in which graphite powder having an average particle size of about 20 μm punched into a disk shape having a diameter of 14 mm and polyvinylidene fluoride was coated on a copper foil was used, and 1 M LiPF ₆ was used as the electrolytic solution. A 3: 7 mixed solution of ethylene carbonate (EC) and diethyl carbonate (DEC) as a supporting electrolyte (manufactured by Toyama Yakuhin Kogyo Co., Ltd.) was used. A polyethylene porous membrane having a film thickness of 25 μm was used for the separator 3. Further, the coin-type battery B has a gasket 4 and a wave washer 5, and the positive electrode can 6 and the negative electrode can 7 are assembled into a coin-shaped battery.
The initial discharge capacity and positive electrode resistance indicating the performance of the manufactured coin-type battery B were evaluated as follows.

The initial discharge capacity is the cutoff voltage with the current density for the positive electrode set to 0.1 mA / cm ² after the open circuit voltage OCV (Open Circuit Voltage) is stabilized by leaving it for about 24 hours after manufacturing the coin-type battery B. The capacity when the battery was charged to 3 V, paused for 1 hour, and then discharged to a cutoff voltage of 3.0 V was defined as the initial discharge capacity.
A multi-channel voltage / current generator (manufactured by Fujitsu Access Limited) was used to measure the charge / discharge capacity.

The positive electrode resistance is measured by the AC impedance method using a frequency response analyzer and a potato galvanostat (1255B, manufactured by Solartron) after charging the coin-type battery B with a charging potential of 4.1 V. Is obtained.
Since this Nyquist plot is expressed as the sum of solution resistance, negative electrode resistance and its capacitance, and positive electrode resistance and its capacitance, fitting calculation is performed using an equivalent circuit based on this Nyquist plot, and positive electrode resistance is performed. The value of was calculated.

The evaluation of the cycle characteristics was performed based on the capacity retention rate and the increase rate of the positive electrode resistance after the cycle test. The cycle test was paused for 10 minutes after the initial discharge capacity measurement, and the charge / discharge cycle was repeated 500 cycles (charge / discharge) including the initial discharge capacity measurement in the same manner as the initial discharge capacity measurement. The discharge capacity at the 500th cycle was measured, and the percentage of the discharge capacity at the 500th cycle with respect to the discharge capacity at the first cycle (initial discharge capacity) was determined as the capacity retention rate (%). Further, the positive electrode resistance after 500 cycles was measured and evaluated by the rate of increase (times) from the positive electrode resistance before the cycle test.

In this example, each sample of Wako Pure Chemical Industries, Ltd.'s reagent special grade was used for the production of the composite hydroxide, the positive electrode active material, and the secondary battery.

Lithium-nickel composite oxidation represented by Li _1.025 Ni _0.91 Co _0.06 Al _0.03 O ₂ obtained by a known technique of mixing and firing an oxide containing Ni as a main component and lithium hydroxide. The base material was powder of physical particles.
1.08 g of tungsten oxide (WO ₃ ) is added to 150 g of the base material so that the W amount is 0.30 atomic% with respect to the total number of atoms of Ni, Co and Al contained in the lithium nickel composite oxide. Then, the mixture was sufficiently mixed using a shaker mixer device (TURBULA Type T2C manufactured by Willy et Bacoffen (WAB)) to obtain a mixed powder.

The obtained mixed powder was transferred to a SUS container, placed in an electric furnace purged with decarboxylated air, heated to 500 ° C. for 3 hours, and then cooled in the furnace. The amount of carbon dioxide (CO ₂ ) in the decarboxylated air used was 10 ppm or less.

Finally, it was sieved with a mesh opening of 38 μm and crushed to obtain a positive electrode active material having a LiW compound on the surface of the primary particles.
When the tungsten content of the obtained positive electrode active material was analyzed by the ICP method, it was confirmed that the tungsten content was 0.30 atomic% with respect to the total number of atoms of Ni, Co and Al.

[Total lithium amount]
It was determined by adding 10 ml of pure water to 1 g of the obtained positive electrode active material, stirring for 1 minute, separating the solid and liquid, and analyzing Li eluted in the liquid by the ICP method. The total amount of lithium was 0.09% by mass with respect to the total amount of the positive electrode active material.

[Amount of surplus lithium]
The surplus lithium of the obtained positive electrode active material was evaluated by titrating Li eluted from the positive electrode active material. Add 10 ml of pure water to 1 g of the obtained positive electrode active material, stir for 1 minute, and then add hydrochloric acid while measuring the pH of the filtered filtrate to analyze the compound state of lithium that elutes from the neutralization point that appears. When the amount of surplus lithium was evaluated, the amount of surplus lithium was 0.02% by mass with respect to the total amount of the positive electrode active material.

[Amount of Li in lithium carbonate]
The amount of lithium carbonate present on the surface of the obtained positive electrode active material was measured by a carbon sulfur analyzer (CS-600 manufactured by LECO) to measure the total carbon element (C) content, and the measured amount of total carbon element. Was calculated by converting to lithium carbonate (Li ₂ CO ₃ ), and the amount of Li in lithium carbonate was calculated from the obtained amount of lithium carbonate. The amount of Li in lithium carbonate present on the surface of the obtained positive electrode active material was 0.012% by mass with respect to the mass of the positive electrode active material.

[Morphological analysis of compounds containing lithium and tungsten]
When the obtained positive electrode active material was embedded in a resin and processed so that the cross section could be observed, the cross section was observed by SEM at a magnification of 5000 times, and the primary particles and the primary particles were aggregated. It was confirmed that the particles were composed of secondary particles, and fine particles of a compound containing lithium and tungsten were formed on the surface of the primary particles, and the particle size of the fine particles was 20 to 170 nm. Further, after embedding the obtained positive electrode active material in a resin and making it possible to observe the cross section of the secondary particles with a transmission electron microscope (TEM), the vicinity of the surface of the primary particles was observed by TEM. A thin film of a compound containing lithium and tungsten having a film thickness of 2 to 90 nm was formed on the surface, and it was confirmed that the compound was lithium tungsten.

[Battery evaluation]
The battery characteristics of the coin-type battery B shown in FIG. 2, which has a positive electrode manufactured by using the obtained positive electrode active material, were evaluated. As the positive electrode resistance before the cycle test, the relative value of Example 1 as "1.00" was used as the evaluation value.
The initial discharge capacity was 214 mAh / g.
Hereinafter, for Examples and Comparative Examples, only the substances and conditions changed from those of Example 1 are shown. Table 1 also shows the evaluation values of the initial discharge capacity, the positive electrode resistance, and the cycle characteristics of Example 1.

Implemented except that 0.52 g of tungsten oxide (WO ₃ ) was added so that the W amount was 0.15 atomic% with respect to the total number of atoms of Ni, Co and Al contained in the lithium nickel composite oxide. The positive electrode active material was obtained and the battery characteristics were evaluated in the same manner as in Example 1.
The results are shown in Table 1.

Implemented except that 0.36 g of tungsten oxide (WO ₃ ) was added so that the W amount was 0.10 atomic% with respect to the total number of atoms of Ni, Co and Al contained in the lithium nickel composite oxide. The positive electrode active material was obtained and the battery characteristics were evaluated in the same manner as in Example 1.
The results are shown in Table 1.

Tungsten oxide (WO ₃ ) was set to 0 so that the heat treatment temperature was 650 ° C. and the W amount was 0.15 atomic% with respect to the total number of atoms of Ni, Co and Al contained in the lithium nickel composite oxide. Except for the addition of .54 g, a positive electrode active material was obtained and the battery characteristics were evaluated in the same manner as in Example 1.
The results are shown in Table 1.

(Comparative Example 1)
The base material used in Example 1 was evaluated as it was as a positive electrode active material.
The results are shown in Table 1.

(Comparative Example 2)
Tungsten oxide (WO ₃ ) was 0 so that the heat treatment temperature was 60 ° C. and the W amount was 0.15 atomic% with respect to the total number of atoms of Ni, Co and Al contained in the lithium nickel composite oxide. Except for the addition of .54 g, a positive electrode active material was obtained and the battery characteristics were evaluated in the same manner as in Example 1.
The results are shown in Table 1.

(Comparative Example 3)
Except for the addition of lithium tungstate (LWO: Li ₂ WO ₄ ) so that the amount of W is 0.15 atomic% with respect to the total number of atoms of Ni, Co and Al contained in the lithium nickel composite oxide. Obtained a positive electrode active material and evaluated it in the same manner as in Example 1.
The results are shown in Table 1.

[evaluation]
As is clear from Table 1, since the positive electrode active materials of Examples 1 to 4 were produced according to the present invention, the initial discharge capacity was higher, the positive electrode resistance was lower, and the cycle was higher than that of the comparative example. The characteristics are also good, and the battery has excellent characteristics.
Further, FIG. 3 shows an example of cross-sectional SEM observation results of the positive electrode active material obtained in the examples of the present invention. The obtained positive electrode active material is a secondary particle composed of primary particles and primary particles aggregated together. It was confirmed that the LiW compound was formed on the surface of the primary particles. The position where the LiW compound was confirmed is indicated by a black arrow in FIG.

In Example 4, since the heat treatment temperature was high, it is considered that the crystallinity of the obtained active material was lowered, and the battery characteristics were slightly deteriorated as compared with Examples 1 to 3.

On the other hand, in Comparative Example 1, since the LiW compound according to the present invention is not formed on the surface of the primary particles, the positive electrode resistance is significantly high, and it is difficult to meet the demand for high output.
Further, in Comparative Example 2, the reaction between the lithium compound and the tungsten compound is not sufficient due to the low heat treatment temperature, and the positive electrode resistance is lowered because lithium tungstate is not uniformly present on the surface of the primary particles of the positive electrode active material. The effect is small, and it is difficult to meet the demand for high output.
Further, in Comparative Example 3, since lithium tungstate was added, the reaction between the lithium compound and the tungsten compound present on the surface of the primary particles of the lithium nickel composite oxide did not sufficiently occur, and the battery characteristics were not sufficiently improved.

The non-aqueous electrolyte secondary battery of the present invention is suitable as a power source for small portable electronic devices (notebook personal computers, mobile phone terminals, etc.) that always require high capacity, and is a battery for electric vehicles that requires high output. It is also suitable for.

Further, the non-aqueous electrolyte secondary battery of the present invention has excellent safety, can be miniaturized and has a high output, and is therefore suitable as a power source for an electric vehicle whose mounting space is restricted. The present invention can be used not only as a power source for an electric vehicle driven by purely 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.

1 Positive electrode (evaluation electrode)
2 Li metal negative electrode 3 separator 4 gasket 5 wave washer 6 positive electrode can 7 negative electrode can B coin type battery

Claims (3)

General formula: Li _z Ni _{1-x-y Co x} My O ₂ (where 0.00≤x≤0.35, 0.00≤y≤0.35, 0.95≤z≤1.20, M is composed of lithium nickel composite oxide particles composed of primary particles represented by (at least one element selected from Mn, V, Mg, Mo, Nb, Ti and Al) and secondary particles in which the primary particles are aggregated. It is a positive electrode active material for non-aqueous electrolyte secondary batteries.
The lithium nickel composite oxide particles have a compound containing tungsten and lithium on the surface of the primary particles, and have
The amount of lithium contained in all the compounds containing lithium present on the surface of the primary particles of the lithium nickel composite oxide particles is 0.05 to 0.35% by mass with respect to the total amount of the positive electrode active material, and tungsten and lithium. The amount of lithium contained in the lithium-containing compound other than the lithium-containing compound is 0.01% by mass or more and 0.05% by mass or less with respect to the total amount of the positive electrode active material, and is contained in the lithium carbonate in the lithium-containing compound. The amount of lithium is 0.03% by mass or less with respect to the total amount of the positive electrode active material.
The amount of tungsten contained in the positive electrode active material is the amount of tungsten contained in lithium, which is lithium tungstate, and a compound containing tungsten, and the total number of atoms of Ni, Co, and M contained in the lithium nickel composite oxide particles. A positive electrode active material for a non-aqueous electrolyte secondary battery, characterized in that it is 0.05 to 0.30 atomic% with respect to the amount. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the compound containing tungsten and lithium is lithium tungstate. A non-aqueous electrolyte secondary battery comprising a positive electrode containing the positive electrode active material for the non-aqueous electrolyte secondary battery according to claim 1 or 2.

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