JP6860962B2 - 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. - Google Patents

Description

The present invention is a positive electrode active material for a non-aqueous electrolyte secondary battery, it relates to a nonaqueous electrolyte secondary battery using the Contact and positive electrode active material.

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

A secondary battery that meets this requirement is 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 lithium ion secondary batteries are currently being actively researched and developed. Among them, lithium ion secondary batteries using a layered or spinel type lithium metal composite oxide as a positive electrode material 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} ), which uses 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 oxide and lithium nickel cobalt manganese composite oxide are attracting attention as materials that have good cycle characteristics and can obtain high output with low resistance. In recent years, it has been important to reduce the resistance required for high output. It is being viewed.
Addition of a different element is used as a method for achieving the above-mentioned low resistance, and a transition metal capable of taking an expensive number such as W, Mo, Nb, Ta, and Re 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 Patent Document 1, it is possible to achieve both low cost and high safety, high load characteristics, and improved powder handleability of the lithium transition metal compound powder for the positive electrode material of the lithium secondary battery.
However, this 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. It was.

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 that exists in the form of particles consisting of one or both of certain secondary particles and has a compound on at least the surface of the particles having 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 mentions the output characteristics. is not it. Further, according to the disclosed production 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 positive electrode active materials coated with oxides 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 the 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 carbonate ion content is 0.15% by weight or less. Positive electrode active materials have been proposed.
According to this proposal, a tungstate compound or a decomposition product of the tungstate compound is present on the surface of the positive electrode active material, and in order to suppress the oxidizing activity on the surface of the composite oxide particles in the charged state, the decomposition of a non-aqueous electrolyte solution or the like is performed. Although it is said that gas generation can be suppressed, the output characteristics are not disclosed at all.

Further, in the disclosed production method, a sulfuric acid compound, a nitrate compound, a boric acid compound or a phosphoric acid compound is coated with a tungstate compound on a composite oxide particle which is preferably heated to a temperature higher than the boiling point of a solution in which an adherend component is dissolved. It is said that the tungsten compound is not sufficiently dispersed on the surface of the composite oxide particles and is uniformly adhered to the surface of the composite oxide particles because the solution dissolved in the solvent is adhered as an adhesion component and the solvent is removed in a short time. It's difficult.

A positive electrode active material for a non-aqueous electrolyte secondary battery to which tungsten is added for the purpose of improving output characteristics is also being studied. For example, Patent Document 5, the general formula _{Li z Ni 1-x-y} Co x M y O 2 ( however, 0.10 ≦ x ≦ 0.35,0 ≦ y ≦ 0.35,0.97 ≦ z ≤1.20, M is a primary particle represented by (at least one element selected from Mn, V, Mg, Mo, Nb, Ti and Al) and a secondary particle formed by aggregating the primary particles. A positive electrode active material for a non-aqueous electrolyte secondary battery has been proposed, wherein the primary particles of the lithium metal composite oxide have fine particles containing W and Li on the surface. However, although the positive electrode active material in this document can obtain a high capacity, a higher capacity is required.

On the other hand, as a positive electrode active material capable of obtaining a high capacity, lithium nickel-cobalt-manganese composite oxide to which lithium is excessively added has attracted attention, and it has been studied to improve output characteristics by further adding tungsten. For example, Patent Document 6, the general _{formula: Li 1 + u Ni x Co} y Mn z M t O 2 + α (0.05 ≦ u ≦ 0.95, x + y + z + t = 1,0 ≦ x ≦ 0.5,0 ≦ y ≦ 0.5, 0.5 ≦ z <0.8, 0 ≦ t ≦ 0.1, M is an additive element and is selected from Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo and W. It is a lithium metal composite oxide composed of primary particles represented by one or more elements) and secondary particles formed by aggregating the primary particles, and is formed on the surface or grain boundary of the lithium metal composite oxide. A positive electrode active material for a non-aqueous electrolyte secondary battery having a compound layer having a layer thickness of 20 nm or less containing lithium in which tungsten is concentrated has been proposed.

However, although the resistance value of the positive electrode active material described in Patent Document 6 is reduced, the lithium nickel-cobalt-manganese composite oxide to which lithium is excessively added has a high resistance value by nature, and therefore is further reduced. Improvement of output characteristics by resistance is required.

Japanese Unexamined Patent Publication No. 2009-289726 Japanese Unexamined Patent Publication No. 2005-251716 Japanese Unexamined Patent Publication No. 11-16566 Japanese Unexamined Patent Publication No. 2010-40383 Japanese Unexamined Patent Publication No. 2012-79464 International Publication WO2012 / 165654

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

In order to solve the above problems, the present inventors have diligently studied the powder characteristics of the lithium nickel cobalt manganese composite oxide used as the positive electrode active material for the non-aqueous electrolyte secondary battery and the influence on the positive electrode resistance of the battery. As a result, by forming fine particles containing W and Li on the surface of the primary particles of the lithium nickel cobalt manganese composite oxide, the positive electrode resistance of the battery is further reduced, the output characteristics are improved, and a high capacity can be obtained. I found.
Further, as a method for producing the same, it is possible to form fine particles containing W and Li on the entire surface of the primary particles by mixing an alkaline solution containing tungsten and a lithium nickel cobalt manganese composite oxide solution and heat-treating the mixture. This has led to the completion of the present invention.

The first aspect of the present invention have the general _{formula: Li 1 + u Ni x Co} y Mn z M t O 2 + α (0.40 ≦ u <0.60, (z-x> 0.4 z-x ≦ u when , Z <0.6, u ≦ z), 0 ≦ x ≦ 0.5, 0 ≦ y ≦ 0.5, 0.5 ≦ z <0.8, 0 <x + y, x + y + z + t = 1, z−x <0.6, 0.4≤α <0.6, M are additive elements, and one or more elements selected from Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, and W. ) Is a lithium metal composite oxide composed of primary particles and secondary particles formed by aggregating primary particles, and the fine particles containing W and Li are only the fine particles, and the lithium metal composite oxide thereof. It is a positive electrode active material for a non-aqueous electrolyte secondary battery, characterized in that it is dispersed and scattered on the surface of primary particles.

In the second invention of the present invention, the amount of tungsten contained in the fine particles in the first invention is W atoms with respect to the total number of atoms of Ni, Co, Mn and M contained in the lithium metal composite oxide. It is a positive electrode active material for a non-aqueous electrolyte secondary battery, characterized in that the number is 0.1 to 3.0 atomic%.

A third invention 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 according to the first and second inventions.

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

It is the schematic sectional drawing of the coin-type battery 1 used for battery evaluation.

Hereinafter, regarding the present invention, first, the positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention (hereinafter, simply referred to as a positive electrode active material) will be described, and then the production method thereof and the non-aqueous system using the positive electrode active material according to the present invention The electrolyte secondary battery will be described.

(1) the positive electrode active material of the positive electrode active material present invention have the general _{formula: Li 1 + u Ni x Co} y Mn z M t O 2 + α (0.40 ≦ u <0.60, (z-x> when 0.4 When z−x ≦ u, z <0.6, u ≦ z ) , 0 ≦ x ≦ 0.5, 0 ≦ y ≦ 0.5, 0.5 ≦ z <0.8, 0 <x + y, x + y + z + t = 1, z-x <0.6, 0.4≤α <0.6, M are additive elements and are selected from Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo and W. A lithium metal composite oxide composed of primary particles represented by one or more elements) and secondary particles formed by aggregating the primary particles is used as a base material, and the surface of the primary particles of the lithium metal composite oxide is used as a base material. It is characterized by having fine particles containing W and Li that are present in a dispersed state.

In the present invention, the general formula as the base _{material: Li 1 + u Ni x Co} y Mn z M t O 2 + α (0.40 ≦ u <0.60, (z-x> 0.4 z-x ≦ u when, When z <0.6, u ≦ z ) , 0 ≦ x ≦ 0.5, 0 ≦ y ≦ 0.5, 0.5 ≦ z <0.8, 0 <x + y, x + y + z + t = 1, z−x < 0.6, 0.4 ≦ α <0.6, M is an additive element, and one or more elements selected from Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, and W) By using the lithium metal composite oxide represented by, an extremely high charge / discharge capacity can be obtained.
Furthermore, the output characteristics are improved while maintaining the charge / discharge capacity by the fine particles containing W (tungsten) and Li (lithium) formed in a dispersed state on the surface of the primary particles of the lithium metal composite oxide of the base material. is there.

In general, if the surface of the positive electrode active material is completely covered with a dissimilar compound, the movement (intercalation) of lithium ions is greatly restricted, resulting in a high capacity of the lithium metal composite oxide. The advantages are erased.
On the other hand, in the present invention, only fine particles containing W and Li are formed in a dispersed state without forming a layer on the surface of the primary particles of the lithium metal composite oxide used as the base material. Since the lithium ion conductivity is high and has the effect of promoting the movement of lithium ions, by forming these fine particles in a dispersed state on the surface of the lithium metal composite oxide powder, the conduction path of Li at the interface with the electrolytic solution Therefore, the reaction resistance of the active material is reduced, the output characteristics are improved, and the cycle characteristics can be further improved.

Here, when the surface of the positive electrode active material is coated with a layered material, the specific surface area is lowered regardless of the coating thickness, and even if the coating material has high lithium ion conductivity, the electrolytic solution The contact area with the battery becomes smaller, which tends to cause a decrease in charge / discharge capacity and an increase in reaction resistance. However, by forming only the fine particles so as to exist in a dispersed state without forming a layered substance as in the present invention, the contact area with the electrolytic solution can be made sufficient and the lithium ion conduction can be effectively improved. Therefore, it is possible to suppress a decrease in charge / discharge capacity and reduce reaction resistance.

In particular, the lithium nickel-cobalt-manganese composite oxide to which lithium is excessively added used in the present invention originally has high resistance and is disadvantageous in output characteristics, so that a greater effect can be obtained by reducing the reaction resistance. Moreover, since the decrease in charge / discharge capacity is suppressed, it is possible to fully utilize the extremely high charge / discharge capacity of the lithium nickel-cobalt-manganese composite oxide.

Such fine particles preferably have a particle size of 1 to 100 nm.
If the particle size is less than 1 nm, the fine particles may not have sufficient lithium ion conductivity. Further, if the particle size exceeds 100 nm, the formation of fine particles existing in a dispersed state on the surface becomes non-uniform, and the effect of reducing the reaction resistance may not be sufficiently obtained.

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

Contact with this electrolytic solution occurs not only on the outer surface of the secondary particles formed by agglomeration of the primary particles, but also on the voids near and inside the surface of the secondary particles, and also on the incomplete grain boundary, so that the primary particles It is necessary to form fine particles on the surface to promote the movement of lithium ions.
Therefore, it is possible to further reduce the reaction resistance of the lithium metal composite oxide particles by forming the fine particles so as to exist in a dispersed state on the entire surface of the primary particles.

Here, it is preferable that the fine particles are scattered. In particular, it is preferable that the particles are scattered in a dispersed state.
Even when the fine particles are scattered, if the fine particles are formed on the outer surface of the secondary particles of the lithium metal composite oxide and on the surface of the primary particles exposed to the voids inside, the effect of reducing the reaction resistance can be obtained. ..
On the other hand, if the fine particles are completely formed in the form of a layered material on the entire surface or a part of the primary particles, the contact with the electrolytic solution is reduced, and the effect of reducing the reaction resistance may not be sufficiently obtained.

The surface properties of such a lithium metal composite oxide powder can be determined by, for example, observing with an electric field radiation type scanning electron microscope, and the positive electrode active material of the present invention is a primary particle made of a lithium metal composite oxide. It has been confirmed that fine particles containing W and Li are formed on the surface in a dispersed state.
On the other hand, when fine particles are formed non-uniformly among the lithium metal composite oxide particles, the movement of lithium ions between the lithium metal composite oxide powders becomes non-uniform, so that specific lithium metal composite oxide particles can be obtained. A load is applied, which tends to cause deterioration of cycle characteristics and an increase in reaction resistance. Therefore, it is preferable that the fine particles are uniformly formed even among the lithium metal composite oxide particles.

The fine particles formed on the surface of the primary particles of the present invention may contain W and Li, but it is preferable that W and Li are in the form of lithium tungstate. By forming this lithium tungstate, the lithium ion conductivity is further increased, and the effect of reducing the reaction resistance is further enhanced.
The amount of tungsten contained in the fine particles is 0.1 to 3.0 atomic% with respect to the total number of atoms of nickel (Ni), cobalt (Co), manganese (Mn) and M contained in the lithium metal composite oxide. Is preferable. As a result, both high charge / discharge capacity and output characteristics can be achieved at the same time.

If the amount of tungsten is less than 0.1 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 fine particles formed becomes too large and the lithium metal is formed. Lithium conduction between the composite oxide and the electrolytic solution may be hindered and the charge / discharge capacity may decrease.

The amount of lithium contained in the fine particles is not particularly limited, and if the fine particles contain lithium, the effect of improving the lithium ion conductivity can be obtained. Normally, excess lithium is present on the surface of the lithium metal composite oxide, and the amount of lithium supplied to the fine particles by the excess lithium when mixed with an alkaline solution may be sufficient, but an amount sufficient to form lithium tungstate. Is preferable.

Further, the amount of lithium in the entire positive electrode active material is such that the ratio "Li / Me" of the sum of the atomic numbers of Ni, Co, Mn and M (Me) in the positive electrode active material to the number of atomic numbers of Li is 1.4 or more. , Preferably less than 1.6. _{If the Li / Me is less than 1.4, the amount of the compound of Li 2} MnO ₃ decreases in the non-aqueous electrolyte secondary battery using the obtained positive electrode active material, and the discharge capacity decreases. Further, when Li / Me becomes 1.6 or more, 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 is obtained by forming fine particles containing W and Li on the surface of the primary particles of the lithium metal composite oxide to improve the output characteristics, and is a powder such as particle size and tap density as the positive electrode active material. The body characteristics may be within the range of the positive electrode active material usually used.

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

[First step]
In the first step, an alkaline solution in which a tungsten compound is dissolved in a lithium metal composite oxide composed of primary particles and secondary particles formed by aggregating the primary particles (hereinafter, an alkaline solution in which the tungsten compound is dissolved is alkaline). This is a step of adding and mixing the solution (W).
As a result, W can be dispersed on the surface of the primary particles of the lithium metal composite oxide that can come into contact with the electrolytic solution.

In this first step, the tungsten compound is first dissolved in an alkaline solution.
The dissolution method may be an ordinary powder dissolution method. For example, a tungsten compound is added while stirring the solution using a reaction vessel equipped with a stirrer, and the solution is completely dissolved in an alkaline solution to obtain a uniform dispersion state. To do.

The tungsten compound may be any compound that can be dissolved in an alkaline solution, and it is preferable to use a tungsten compound that is easily soluble in alkali, such as tungsten oxide, lithium tungstate, and ammonium tungstate.
The amount of tungsten dissolved in the alkaline solution is preferably 0.1 to 3.0 atomic% with respect to the total number of atoms of Ni, Co, Mn and M contained in the mixed lithium metal composite oxide.

If solid-liquid separation is not performed after mixing with the alkaline solution, the total amount of tungsten in the alkaline solution (W) is dispersed and adhered to the surface of the primary particles of the lithium metal composite oxide, so that fine particles are formed on the surface of the primary particles. The amount may be the amount required to make it.

In the case of solid-liquid separation, the amount of the alkaline solution retained in the powder of the lithium metal composite oxide after the solid-liquid separation may be confirmed by a preliminary test and adjusted by the amount of tungsten in the retained alkaline solution.

However, when the lithium metal composite oxide powder is crushed after the heat treatment, the fine particles containing W and Li formed on the surface of the primary particles are peeled off, and the tungsten content of the obtained positive electrode active material is reduced. Sometimes. In such a case, the amount of tungsten to be dissolved in the alkaline solution may be determined in anticipation of the amount of decrease, that is, 5 to 20 atomic% with respect to the amount of tungsten to be added.

The tungsten concentration of the alkaline solution (W) is preferably 0.05 mol / L or more. If it is less than 0.05 mol / L, a large amount of alkaline solution to be mixed with a low tungsten concentration is required, so that the slurry is formed when mixed with the lithium metal composite oxide. Slurry elutes Li contained in the layered lattice of the lithium metal composite oxide, which is not preferable because it causes deterioration of battery characteristics. On the other hand, in the case of solid-liquid separation, if the tungsten concentration exceeds 2 mol / L, the amount of alkaline solution is small, and W may not be uniformly dispersed on the surface of the primary particles.

As the alkali used for the alkaline solution, a general alkaline solution containing no impurities harmful to the positive electrode active material is used in order to obtain a high charge / discharge capacity.
Ammonia and lithium hydroxide that are not likely to be mixed with impurities can be used, but lithium hydroxide is preferably used from the viewpoint of not inhibiting the intercalation of Li.
When lithium hydroxide is used, the amount of lithium contained in the positive electrode active material after mixing needs to be within the range of Li / M of the general formula, but the amount of lithium hydroxide is atomized with respect to W. The ratio is preferably 4.5 to 15.0. Li is supplied by eluting from a lithium metal composite oxide, and by using lithium hydroxide in this range, a sufficient amount of Li can be supplied to form lithium tungstate.

Further, the alkaline solution is preferably an aqueous solution.
In order to disperse W on the surface of the primary particles constituting the secondary particles, it is necessary to permeate the voids inside the secondary particles and the incomplete grain boundaries, and if a solvent such as alcohol having high volatility is used, , The solvent may evaporate and not penetrate sufficiently before the alkaline solution permeates the voids inside the secondary particles.

The pH of the alkaline solution may be any pH at which the tungsten compound dissolves, but is preferably 9 to 12.
If the pH is less than 9, the amount of lithium eluted from the lithium metal composite oxide may become too large and the battery characteristics may deteriorate. On the other hand, if the pH exceeds 12, the excess alkali remaining in the lithium metal composite oxide may become too large and the battery characteristics may deteriorate.

In the production method of the present invention, the composition of the obtained positive electrode active material is only a trace amount of lithium that increases by adding it as an alkaline solution from the lithium metal composite oxide as the base material. Therefore, the lithium metal composite of the base material From the viewpoint of high capacity, the oxide used is a lithium nickel cobalt manganese composite oxide to which lithium is excessively added, for example, the lithium nickel cobalt manganese composite oxide disclosed in International Publication WO2012 / 165654, and the general formula: Li. _{1 + u Ni x Co y Mn} z M t O 2 + α (0.40 ≦ u <0.60, (z-x> z-x ≦ u when 0.4, u ≦ z when z <0.6), 0 ≦ x ≦ 0.5, 0 ≦ y ≦ 0.5, 0.5 ≦ z <0.8, 0 <x + y, x + y + z + t = 1, z−x <0.6, 0.4 ≦ α <0. 6 and M are additive elements, and a lithium metal composite oxide represented by Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, W (one or more elements selected from them) is used. ..

Here, when the excess amount of Mn with respect to Ni, that is, "z-x" is larger than 0.4, u needs to be (z-x) or more. When u is less than (z-x), the _{amount of Li 2} MnO ₃ formed decreases, and the battery capacity decreases. Further, when z indicating the amount of Mn is less than 0.6 and the amount of Li exceeds the amount of Mn, the _{excess Li that does not form Mn and Li 2} MnO ₃ increases, so that the battery capacity decreases.

At least one type of Ni and Co is preferable, x indicating the amount of Ni is 0 ≦ x ≦ 0.5, and y indicating the amount of Co is 0 ≦ y ≦ 0.5. When either x or y exceeds 0.5, the _{amount of Li 2} MnO ₃ formed decreases, and the battery capacity decreases. On the other hand, when both x and y become 0, LiMO ₂ is not formed and the battery capacity decreases.

Z indicating the amount of Mn is 0.5 ≦ z <0.8, and when z is less than 0.5, Li ₂ MnO ₃ is not sufficiently produced and unreacted Li is present. Battery characteristics deteriorate. On the other hand, when z is 0.8 or more, Li _{required for forming Li 2} MnO ₃ and LiMO ₂ is insufficient, so that a spinel phase such as _{LiNi 0.5} Mn _1.5 O _{4 is generated.} Therefore, the battery characteristics are deteriorated. In order to suppress the generation of the spinel phase, this (zx) is preferably 0.6 or less.

Further, α in the general formula is a numerical value indicating an excess amount of O (oxygen), and needs to be in the same numerical range as u in order to form _{Li 2} MnO ₃ and _{Li MO 2.}
Further, since increasing the contact area with the electrolytic solution is advantageous for improving the output characteristics, the primary particles and the secondary particles formed by aggregating the primary particles are composed of the secondary particles of the electrolytic solution. Use a lithium metal composite oxide powder with permeable voids and grain boundaries.

Next, the lithium metal composite oxide powder is added to the alkaline solution (W) prepared with stirring and mixed.
The mixing is preferably carried out at a temperature where the alkaline solution (W) is a liquid and the temperature is 50 ° C. or lower. The alkaline solution (W) needs to penetrate into the voids and grain boundaries of the secondary particles, and needs to be a liquid. Further, when the temperature exceeds 50 ° C., the alkaline solution dries quickly, so that it may not sufficiently penetrate into the voids and grain boundaries of the secondary particles. Further, if the drying is fast, the elution of Li from the lithium metal composite oxide powder cannot be expected, and particularly when the alkaline solution (W) does not contain Li, the fine particles formed on the surface may not contain Li.

The lithium metal composite oxide powder and the alkaline solution (W) are sufficiently mixed in order to make the dispersion of W uniform, and a general mixer can be used for the mixing.
For example, a shaker mixer, a radige mixer, a Julia mixer, a V blender, or the like may be used to sufficiently mix the lithium metal composite oxide powder with the alkaline solution (W) to the extent that the skeleton is not destroyed. As a result, W in the alkaline solution (W) can be uniformly distributed on the surface of the primary particles of the lithium metal composite oxide.

[Second step]
The second step is a step of heat-treating a mixture of the alkaline solution (W) and the lithium metal composite oxide powder.
By this heat treatment, tungsten (from W supplied from the alkaline solution (W), elution of lithium from the lithium metal composite oxide powder of the alkaline solution (W), or lithium (Li) supplied by both of them, is used. Positive active material for non-aqueous electrolyte secondary batteries, which forms fine particles containing W) and lithium (Li) and has fine particles containing W and Li scattered on the surface of the primary particles of a lithium metal composite oxide in a dispersed state. Is obtained.

The heat treatment method is not particularly limited, but it is preferable to heat-treat at a temperature of 100 to 600 ° C.
If the heat treatment temperature is less than 100 ° C., the evaporation of water is not sufficient and fine particles may not be sufficiently formed. On the other hand, when the heat treatment temperature exceeds 600 ° C., the primary particles of the lithium metal composite oxide cause sintering and some W is dissolved in the layered structure of the lithium metal composite oxide, so that the battery is charged. The discharge capacity may decrease.

The atmosphere during the heat treatment is preferably an oxidizing atmosphere such as an oxygen atmosphere or a vacuum atmosphere in order to avoid reaction with moisture and carbonic acid in the atmosphere.
The heat treatment time is not particularly limited, but is preferably 5 to 15 hours in order to sufficiently evaporate the water content of the alkaline solution to form fine particles.

(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 powdered positive electrode active material, a conductive material, and a binder are mixed, and if necessary, activated carbon, a solvent for viscosity adjustment or 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 and the conductive material is similar to the positive electrode of a general non-aqueous electrolyte secondary battery. It is desirable that the content of the binder is 1 to 20 parts by mass and the content of the binder is 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 produced. 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 producing the positive electrode, for example, graphite (natural graphite, artificial graphite, expanded graphite, etc.), carbon black material such as acetylene black, ketjen black, or the like can be used as the conductive agent.
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, polyacrylic. 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 metallic lithium, a lithium alloy, or a negative electrode active material capable of occluding and desorbing lithium ions, and adding an appropriate solvent. Is applied to the surface of a metal foil current collector such as copper, dried, and if necessary, compressed to increase the electrode density.

As the negative electrode active material, for example, a calcined product of an organic compound such as natural graphite, artificial graphite, or phenol resin, or a powdered material 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 a 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 the 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 include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate and trifluoropropylene carbonate, chain carbonates such as diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate and dipropyl carbonate, and tetrahydrofuran and 2-. One selected from ether compounds such as methyl tetrahydrofuran and dimethoxyethane, sulfur compounds such as ethyl methyl sulfone and butane sulton, and phosphorus compounds such as triethyl phosphate and trioctyl phosphate are used alone or in combination of two or more. be able to.

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 composed of the positive electrode, the negative electrode, the separator and the non-aqueous electrolyte solution described above is various, such as cylindrical type and laminated type. Can be.
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 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.
The non-aqueous electrolyte secondary battery using the positive electrode active material according to the present invention obtained in a particularly preferable form can obtain a high initial discharge capacity of 250 mAh / g or more when used for the positive electrode of a 2032 type coin battery, for example. In addition, it has low resistance, high output, and excellent cycle characteristics. In addition, it can be said that it has high thermal stability and is also excellent in safety.

The performance (initial discharge capacity, positive electrode resistance) of a 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)
A 2032 type coin battery (hereinafter referred to as a coin type battery) shown in FIG. 1 was used for the evaluation of the positive electrode active material.
The coin-type battery is composed of a case and electrodes housed in the case.
The case has a positive electrode can 6 which is hollow and has one end opened, and a negative electrode can 7 which is arranged in the opening of the positive electrode can 6. When the negative electrode can 7 is arranged in the opening of the positive electrode can 6, A space for accommodating the electrodes is formed between the negative electrode can 7 and the positive electrode can 6.

The electrode is composed of a positive electrode 1, a separator 3, and a negative electrode 2, and is laminated so as to be arranged in this order. The positive electrode 1 contacts the inner surface of the positive electrode can 6, and the negative electrode 2 is on the inner surface of the negative electrode can 7 with a wave washer 5. It is housed in a case so that it comes into contact with each other.
The case is provided with a gasket 4, and the gasket 4 fixes the relative movement between the positive electrode can 6 and the negative electrode can 7 so as to maintain a non-contact state. Further, the gasket 4 also has a function of sealing the gap between the positive electrode can 6 and the negative electrode can 7 to seal the inside and the outside of the case in an airtight and liquid-tight manner.

The coin-type battery shown in FIG. 1 above was manufactured as follows.
First, 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, thinned to a weight of about 10 mg with a diameter of 10 mm, and the positive electrode is formed. 1 was prepared. The prepared positive electrode 1 was dried in a vacuum dryer at 120 ° C. for 12 hours.
Using the positive electrode 1, the negative electrode 2, the separator 3, and the electrolytic solution, the above-mentioned coin-type battery was produced in a glove box having an Ar atmosphere with a dew point controlled at −80 ° C.

As the negative electrode 2, a negative electrode sheet in which graphite powder having an average particle diameter of about 20 μm punched into a disk shape having a diameter of 14 mm and polyvinylidene fluoride was applied to a copper foil was used.
A polyethylene porous membrane having a film thickness of 25 μm was used for the separator 3. As the electrolytic solution, a 3: 7 mixed solution of ethylene carbonate (EC) and diethyl carbonate (DEC) using _{1M LiPF 6 as a supporting electrolyte (manufactured by Tomiyama Pure Chemical Industries, Ltd.) was used.}

The initial discharge capacity and positive electrode resistance, which indicate the performance of the manufactured coin-type battery, were evaluated as follows.
^{The initial discharge capacity is set to 0.1 mA / cm 2} for the current density with respect to the positive electrode after the open circuit voltage OCV (Open Circuit Voltage) is stabilized by leaving it for about 24 hours after manufacturing the coin-type battery, and the cutoff voltage is 4. The initial discharge capacity was defined as the capacity when the battery was charged to 8 V and discharged to a cutoff voltage of 3.0 V after a one-hour rest.

To measure the positive electrode resistance, perform constant current-low voltage charging, adjust the potential to 4.5V, pass a current of 1.3mA for 10 seconds, and subtract the potential after 10 seconds from 4.5V to obtain ΔV. , ΔV was passed, and the resistance (Ω) was calculated by dividing by 1.3 mA, which is the current value. 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.

The cycle capacity retention rate (cycle characteristics) is the discharge capacity after repeating the cycle of charging to 4.7 V and discharging to 3.0 V 200 times, assuming that the current density with respect to the positive electrode is ^{2 mA / cm 2.} And the ratio of the initial discharge capacity was calculated and used as the capacity retention rate.

(Making the base material)
First, half the amount of pure water is put into the reaction tank, and while stirring, nitrogen gas is circulated to lower the oxygen concentration in the reaction tank, the temperature in the tank is set to 40 ° C. Add an appropriate amount of sodium hydroxide aqueous solution and 25% by mass ammonia water, adjust the pH of the solution to 12.8 based on the liquid temperature of 25 ° C (all pH is adjusted based on the liquid temperature of 25 ° C), and adjust the concentration of ammonia in the liquid to 10 g / L. The reaction solution was prepared. Here, a 1.8 mol / L aqueous solution (mixed aqueous solution A) obtained by dissolving nickel sulfate, cobalt sulfate, and manganese sulfate (Ni: Co: Mn = 2: 1: 7 in molar ratio of metal elements) in pure water , Aqueous ammonia solution and aqueous sodium hydroxide solution were added at a constant rate, and crystallization was carried out for 2 minutes and 30 seconds while controlling the pH value to 12.8 (nuclear pH).

After that, only the supply of the sodium hydroxide aqueous solution is suspended until the pH reaches 11.6 (nuclear growth pH), and after reaching the pH value of 11.6, the supply of the sodium hydroxide aqueous solution is restarted again. did. Then, while controlling the pH to 11.6, crystallization was continued for 2 hours, and when the inside of the reaction vessel became full, crystallization was stopped, stirring was stopped, and the mixture was allowed to settle to promote precipitation of the product. did. After extracting half of the supernatant, crystallization was restarted. After further crystallization for 2 hours (4 hours in total), crystallization was completed and the product was washed with water, filtered and dried.

By the method described above, _{a composite hydroxide represented by Ni 0.20} Co _0.10 Mn _0.70 OH) _{2 + β} (0 ≦ β ≦ 0.5) was obtained.
The obtained composite hydroxide is heat-treated at 150 ° C. for 12 hours in an air atmosphere, and then lithium carbonate is weighed so that Li / Me = 1.5, and a shaker mixer device (Willie et Bacoffen (WB)) is used. A mixture of the heat-treated composite hydroxide and lithium carbonate was obtained using TURBULA Type T2C).
This mixture was calcined in an air (oxygen: 21% by volume) air stream at 900 ° C. for 10 hours and further crushed to obtain a lithium metal composite oxide as a base material.

When the crystal structure of the obtained lithium metal composite oxide was confirmed by an X-ray diffraction (XRD) apparatus, Li ₂ MnO ₃ and LiM'O ₂ (M'indicates Ni, Co and Mn) from the XRD pattern. The existence of was confirmed. The ratio of Li ₂ MnO ₃ and LiM'O ₂ is 0.5: 0.5 when calculated from the composition.
The average particle size of the obtained lithium metal composite oxide was evaluated by using the volume integrated average value in the laser diffraction / scattering method, and the specific surface area was evaluated by using the BET method. The average particle size of this lithium metal composite oxide powder was 5.2 μm, and the specific surface area was 1.1 m ² / g.

(First step)
An alkali containing tungsten is obtained by adding _{0.183 g of tungsten oxide (WO 3} ) to an alkaline solution of an aqueous solution of 0.2 g of lithium hydroxide (LiOH) dissolved in 3 ml of pure water and stirring the mixture. A solution (W) was obtained.
Next, an alkaline solution (W) was added to 15 g of the prepared lithium metal composite oxide powder, and further, a shaker mixer device (TURBULA Type T2C manufactured by Willy et Bacoffen (WAB)) was sufficiently used. Mixing gave a mixture of alkaline solution (W) and lithium metal composite oxide.

(Second step)
The obtained mixture was placed in a firing vessel made of magnesia, heated to 500 ° C. at a heating rate of 2.8 ° C./min in a 100% oxygen stream, heat-treated for 10 hours, and then cooled to room temperature.
When the tungsten content of the lithium metal composite oxide powder after the heat treatment was analyzed by the ICP method, it was found that the tungsten content was 0.5 atomic% with respect to the total number of atoms of Ni, Co and Mn. confirmed. From this, it was confirmed that the composition of the mixture of the alkaline solution (W) and the lithium metal composite oxide and the composition after the heat treatment were equivalent.

Finally, a positive electrode active material was obtained by sieving through a sieve having a mesh size of 38 μm and crushing the mixture.
When the cross section of the obtained positive electrode active material was observed with a scanning electron microscope, it was confirmed that fine particles containing W and Li were formed on the surface of the primary particles of the lithium metal composite oxide in a dispersed state. did.

(Battery evaluation)
The initial discharge capacity, the positive electrode resistance, and the cycle capacity retention rate were evaluated using the coin-type battery 1 shown in FIG. 1 having a positive electrode prepared by using the obtained positive electrode active material. The resistance was evaluated by the reduction rate from Comparative Example 2. The results are shown in Table 1.

(Comparative Example 1)
It was carried out except that tungsten oxide was added and fired so that the tungsten content was 0.5 atomic% with respect to the total number of atoms of Ni, Co and Mn at the time of firing instead of the first step and the second step. A positive electrode active material was obtained and evaluated in the same manner as in Example 1. Table 1 shows the results of the initial discharge capacity, positive electrode resistance, and cycle capacity retention rate.
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 0.5 atomic% with respect to the total number of atoms of Ni, Co and Al. It was. Further, when the surface of the primary particles of the lithium metal composite oxide constituting the positive electrode active material was observed by SEM, a layered substance containing W and Li was observed.

(Comparative Example 2)
For the lithium metal composite oxide obtained in Example 1, the first step and the second step were omitted, and a positive electrode active material containing only the base material without providing fine particles on the surface of the primary particles was obtained and evaluated. .. Table 1 shows the results of the initial discharge capacity, positive electrode resistance, and cycle capacity retention rate.

(Comparative Example 3)
A positive electrode active material was obtained in the same manner as in Example 1 except that the lithium metal composite oxide powder represented by _{Li 1.060} Ni _0.76 Co _0.14 Al _0.10 O _{2 was used as the base material.} Evaluation was performed. The average particle size of this lithium metal composite oxide powder was 5.0 μm, and the specific surface area was 0.9 m ² / g. Further, when the tungsten content of the lithium metal composite oxide powder after the heat treatment was analyzed by the ICP method, the tungsten content was 0.5 atomic% with respect to the total number of atoms of Ni, Co and Al. It was confirmed that. From this, it was confirmed that the composition of the mixture of the alkaline solution (W) and the lithium metal composite oxide and the composition after the heat treatment were equivalent.
Table 1 shows the results of the initial discharge capacity, positive electrode resistance, and cycle capacity retention rate.

From Table 1, the positive electrode active material of the present invention has almost the same initial discharge capacity as that of Comparative Example 2 in which only the base material having no fine particles containing W and Li on the surface of the primary particles is used. It was confirmed that the positive electrode resistance was significantly reduced and the cycle characteristics were excellent. Further, it was confirmed that the positive electrode resistance was reduced and the cycle characteristics were good as compared with Comparative Example 1 in which W was added by the oxide.

Further, when compared with Comparative Example 3 using a lithium metal composite oxide having a different composition as a base material, it can be seen that the positive electrode resistance is significantly reduced and the cycle characteristics are good while increasing the initial discharge capacity.

From the above, it can be seen that the positive electrode active material of the present invention has a high discharge capacity of more than 250 mAh / g, can significantly reduce the positive electrode resistance, and has excellent battery characteristics.

Since the non-aqueous secondary battery of the present invention has high capacity and excellent electrical characteristics, it is suitable as a small power supply device that requires high energy density in recent portable electronic devices such as mobile phones and notebook computers. is there.
Further, since the non-aqueous secondary battery of the present invention has excellent safety, it is an electric vehicle driven by purely electric energy, a hybrid vehicle or a plug-in hybrid used in combination with a combustion engine such as a gasoline engine or a diesel engine. It can also be suitably used as a large power supply device for automobiles and the like.

1 Positive electrode (evaluation electrode)
2 Carbon negative electrode 3 Separator 4 Gasket 5 Wave washer 6 Positive electrode can 7 Negative electrode can

Claims (3)

_{Formula: Li 1 + u Ni x Co} y Mn z M t O 2 + α (0.40 ≦ u <0.60, (z-x> when z-x ≦ u, z < 0.6 when 0.4 u ≦ z), 0 ≦ x ≦ 0.5, 0 ≦ y ≦ 0.5, 0.5 ≦ z <0.8, 0 <x + y, x + y + z + t = 1, z−x <0.6, 0.4 ≦ α <0.6, M is an additive element, and is a primary particle represented by Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, W) and the above. A lithium metal composite oxide composed of secondary particles composed of aggregated primary particles.
Microparticles containing W and Li are in only the fine particles, the positive electrode active material for a non-aqueous electrolyte secondary battery, characterized by dotted distributed on the surface of the primary particles of the lithium metal composite oxide. The amount of tungsten contained in the fine particles is such that the number of atoms of W is 0.1 to 3.0 atomic% with respect to the total number of atoms of Ni, Co, Mn and M contained in the lithium metal composite oxide. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the present material is present. 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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