JP2017050056A - Positive electrode active material for nonaqueous electrolyte secondary battery, manufacturing method thereof, and nonaqueous electrolyte secondary battery arranged by use thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a positive electrode active material for a nonaqueous electrolyte secondary battery, which enables the achievement of a high capacity and a high output power when used as a positive electrode material even with a simple process.SOLUTION: A method for manufacturing a positive electrode active material for a nonaqueous electrolyte secondary battery material comprises: a mixing step for obtaining a mixture by mixing particles of a nickel composite oxide expressed by the general formula, NiCoMO(where 0≤x≤0.35, 0≤y≤0.35, and M represents at least one element selected from Mn and others), a lithium compound of which the ratio Li/Me of a number of lithium atoms to a total number Me of Ni, Co and M atoms included in the nickel composite oxide particles is 0.95-1.20, and a tungsten compound of which the number of tungsten atoms to the total number Me is 0.06-0.50 atom%; and a sintering step for sintering the mixture at 600-800°C under an oxidizing atmosphere.SELECTED DRAWING: Figure 1

Description

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

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

  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 includes a negative electrode, a positive electrode, an electrolyte, and the like, and a material capable of detaching and inserting lithium is used as an active material for the negative electrode and the positive electrode.

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

  Among them, a lithium ion secondary battery using layered or spinel type lithium nickel composite oxide particles as a positive electrode material is being put to practical use as a battery having a high energy density because a high voltage of 4V class can be obtained. In other words, lithium nickel composite oxide particles have been attracting attention as a material with good cycle characteristics and low resistance and high output. In recent years, the lithium nickel composite oxide particles have a low resistance necessary for high output of the lithium nickel composite oxide particles. Research is regarded as important.

  Addition of foreign elements is used as a method for realizing the low resistance, and transition metals capable of taking high numbers such as W, Mo, Nb, Ta, Re, etc. are particularly useful.

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

  According to this proposal, it is said that it is possible to achieve both low cost and high safety of lithium transition metal-based compound powder for lithium secondary battery positive electrode material, high load characteristics, and improved powder handleability. . However, in Patent Document 1, the firing temperature is as high as 800 ° C. or higher as described in paragraph 0157, and some of W and the like are dissolved in the lithium nickel composite oxide, or partially lithium nickel composite oxide. There is a problem that the sintering of the secondary particles of the product progresses and becomes coarse, and it is impossible to increase the output of the lithium nickel composite oxide particles.

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

  As a result, it is said that a positive electrode active material for a non-aqueous electrolyte secondary battery having excellent battery characteristics even under a severer usage environment can be obtained. 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, the initial characteristics are improved without impairing the improvement of thermal stability, load characteristics and output characteristics.

  However, the effect of at least one additive element selected from the group consisting of molybdenum, vanadium, tungsten, boron and fluorine is considered to be an improvement in initial characteristics, that is, initial discharge capacity and initial efficiency, and refers to output characteristics. It is not a thing. In addition, according to the disclosed manufacturing method, since the additive element is mixed with the hydroxide that has been heat-treated simultaneously with the lithium compound and fired, the molybdenum nickel compound oxide is formed and then the molybdenum compound is added. There has been a problem that the process of obtaining lithium nickel composite oxide particles becomes complicated.

  Further, Patent Document 3 discloses a metal including at least one selected from Ti, Al, Sn, Bi, Cu, Si, Ga, W, Zr, B, and Mo around the positive electrode active material and / or a plurality of these. There has been proposed a positive electrode active material coated with an intermetallic compound and / or an oxide obtained by combining the above.

  Such a coating can absorb oxygen gas and ensure safety, but no output characteristics are disclosed. Further, the disclosed manufacturing method is a method of coating using a planetary ball mill, and in such a coating method, physical damage is caused to the positive electrode active material, so that a low power necessary for high output is obtained. There was a problem that resistance was difficult.

  In Patent Document 4, a composite oxide particle mainly composed of lithium nickelate is subjected to heat treatment by adhering a tungstic acid compound, and the content of carbonate ions is 0.15% by weight or less. A positive electrode active material has been proposed.

  According to this proposal, there is a tungstic acid compound or a decomposition product of the tungstic acid compound on the surface of the positive electrode active material, and the oxidation activity on the surface of the composite oxide particles in the charged state is suppressed. Although gas generation can be suppressed, the output characteristics are not disclosed at all.

  Further, the disclosed production method preferably comprises applying a sulfate compound, a nitrate compound, a borate compound or a phosphate compound together with a tungstic acid compound to the composite oxide particles heated to a temperature equal to or higher than the boiling point of the solution in which the deposition component is dissolved. A solution dissolved in a solvent is applied as an adhesion component, and the solvent is removed in a short time. Therefore, the tungsten compound is not sufficiently dispersed on the surface of the composite oxide particles and is not uniformly applied. As a result, there is a problem that it is difficult to reduce the resistance required for high output.

In addition, improvements relating to higher output of lithium nickel composite oxide particles have also been made.
For example, Patent Document 5 discloses lithium nickel composite oxide particles composed of primary particles and secondary particles formed by agglomerating the primary particles, and Li ₂ WO on the surface of the lithium nickel composite oxide particles. ₄ , a positive electrode active material for a non-aqueous electrolyte secondary battery having fine particles containing lithium tungstate represented by any one of Li ₄ WO ₅ and Li ₆ W ₂ O ₉ is proposed, and high output is obtained with high capacity It is said that.

  However, in Patent Document 5, since the tungsten compound is added after the lithium nickel composite oxide is formed, there is a problem that the process of obtaining the lithium nickel composite oxide particles is complicated. Moreover, since tungsten is dissolved in an alkaline solution containing lithium and added by mixing with lithium-nickel composite oxide, there is a problem that excessive lithium deteriorates battery characteristics.

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

  In view of the above circumstances, an object of the present invention is to provide a positive electrode active material for a non-aqueous electrolyte secondary battery that can provide a high output with a high capacity when used in a positive electrode. Another object of the present invention is to provide a production method capable of obtaining the positive electrode active material even in a simple process.

In order to solve the above-mentioned problems, the present inventor has conducted intensive research on the powder characteristics of lithium nickel composite oxide particles 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. When a positive electrode active material having high battery capacity (charge / discharge capacity) and output characteristics can be obtained by forming a lithium tungsten compound on the surface of primary particles of lithium nickel composite oxide particles and suppressing the formation of lithium carbonate I got the knowledge. In addition, the inventors have obtained the knowledge that the positive electrode active material can be obtained by mixing a nickel compound oxide particle with a lithium compound and a tungsten compound and firing the mixture, thereby completing the present invention.
The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery of the first invention, the general _{formula: Li a Ni 1-x-} y Co x M y W c O 2 + α ( although, 0 ≦ x ≦ 0.35,0 ≦ y ≦ 0.35, 0.0006 ≦ c ≦ 0.0050, 0.95 ≦ a ≦ 1.20, 0 ≦ α ≦ 0.20, M is Mn, V, Mg, Mo, Nb, Ti and A positive electrode for a non-aqueous electrolyte secondary battery composed of lithium metal composite oxide particles composed of primary particles and secondary particles formed by agglomeration of primary particles, represented by at least one element selected from Al) a method of manufacturing an active material, the general _{formula: Ni 1-x-y Co} x M and nickel composite oxide particles represented by y _{O 2,} Ni contained in the nickel composite oxide particles, Co and M The ratio Li / Me between the total number of atoms Me and the number of lithium atoms is 0.9. A mixing step of mixing a lithium compound having a molecular weight of ˜1.20 and a tungsten compound having a tungsten atom number of 0.06 to 0.50 atomic% with respect to Me to obtain a mixture; And firing at 600 to 800 ° C. to obtain lithium nickel composite oxide particles in which a lithium tungsten compound is formed on the surface of the primary particles.
The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to the second invention is characterized in that, in the first invention, the lithium tungsten compound is in the form of fine particles, and the particle diameter of the fine particles is 1 to 500 nm.
A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to a third invention is characterized in that, in the first invention, the lithium tungsten compound is in a film form, and the thickness of the film is 1 to 100 nm.
According to a fourth aspect of the present invention, there is provided a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery. In the first aspect, the lithium tungsten compound is in the form of fine particles and a film, and the fine particles have a particle size of 1 to 500 nm. The thickness of the film is 1 to 100 nm.
The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to a fifth aspect of the present invention is the first to fourth aspects, wherein the lithium compound is at least one selected from lithium hydroxide, lithium carbonate, and lithium acetate. It is characterized by that.
According to a sixth aspect of the present invention, there is provided a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, wherein the tungsten compound is at least one selected from tungsten oxide, tungstic acid, and ammonium paratungstate in the first to fifth inventions. It is characterized by being.
The positive electrode active material for a non-aqueous electrolyte secondary battery of the seventh aspect of the present invention have the general _{formula: Li a Ni 1-x-} y Co x M y W c O 2 + α ( although, 0 ≦ x ≦ 0.35,0 ≦ y ≦ 0.35, 0.0006 ≦ c ≦ 0.005, 0.95 ≦ a ≦ 1.20, 0 ≦ α ≦ 0.20, M is selected from Mn, V, Mg, Mo, Nb, Ti, and Al A positive electrode active material for a non-aqueous electrolyte secondary battery composed of lithium metal composite oxide particles composed of primary particles and secondary particles formed by aggregation of primary particles. Then, a lithium tungsten compound is formed on the surface of the primary particle of the lithium metal composite oxide, and the amount of lithium contained in the lithium carbonate present on the surface of the lithium nickel composite oxide particle is 0 with respect to the positive electrode active material. 0.02% by mass or less It is characterized by.
The positive electrode active material for a non-aqueous electrolyte secondary battery according to an eighth aspect of the invention is characterized in that, in the seventh aspect, the lithium tungsten compound is in the form of fine particles, and the particle diameter of the fine particles is 1 to 500 nm.
A positive electrode active material for a non-aqueous electrolyte secondary battery according to a ninth invention is characterized in that, in the seventh invention, the lithium tungsten compound is in a film form, and the thickness of the film is 1 to 100 nm.
A positive electrode active material for a non-aqueous electrolyte secondary battery according to a tenth aspect of the present invention is the positive electrode active material according to the seventh aspect, wherein the lithium tungsten compound is in the form of fine particles and a film, and the particle diameter of the fine particles is 1 to 500 nm. Is 1 to 100 nm.
A non-aqueous electrolyte secondary battery according to an eleventh aspect of the invention includes a positive electrode including the positive electrode active material for non-aqueous electrolyte secondary batteries according to the seventh to eleventh aspects of the invention.

According to the first invention, there is a mixing step in which nickel composite oxide particles, a lithium compound, and a tungsten compound are simultaneously mixed to obtain a mixture. The complicated process in which is added can be simplified.
Also, nickel composite oxide particles general _{formula: Ni 1-x-y Co} x M y O 2 ( however, 0 ≦ x ≦ 0.35,0 ≦ y ≦ 0.35, M is Mn, V, Mg, The ratio of the total number of atoms of Ni, Co, and M in which the lithium compound is contained in the nickel composite oxide particles to the number of lithium atoms, and at least one element selected from Mo, Nb, Ti, and Al) When Li / Me is 0.95 to 1.20, the amount of Li for synthesizing the lithium nickel composite oxide particles and the lithium tungsten compound can be within a preferable range, and is high even when the process is simplified. Charge / discharge capacity and sufficient output characteristics can be obtained.
In addition, when the tungsten compound has a number of tungsten atoms with respect to Me of 0.06 to 0.50 atomic%, the amount of tungsten for synthesizing the lithium tungsten compound can be within a preferable range, and a high charge / discharge capacity and Sufficient output characteristics can be obtained.
Furthermore, the mixture is baked at 600 to 800 ° C. in an oxidizing atmosphere to obtain lithium nickel composite oxide particles in which a lithium tungsten compound is formed on the surface of the primary particles, and the formation of the lithium tungsten compound. As a result, surplus lithium can be prevented from remaining, resistance can be reduced, and a high-capacity positive electrode active material manufacturing process can be provided.
According to the second invention, the lithium tungsten compound is in the form of fine particles, and the positive electrode active material capable of reducing the resistance is obtained when the fine particles have a particle diameter of 1 to 500 nm. That is, if the particle diameter is less than 1 nm, fine particles may not have sufficient lithium ion conductivity. If the particle diameter exceeds 500 nm, the formation of a coating with fine particles becomes non-uniform, and the reaction resistance is reduced. Is not enough.
According to the third invention, the positive electrode active material capable of reducing the resistance can be obtained when the lithium tungsten compound is in the form of a film and the thickness of the film is 1 to 100 nm. That is, when the film thickness is less than 1 nm, lithium ion conductivity may not be obtained. When the film thickness exceeds 100 nm, the contact area with the electrolytic solution is reduced due to a decrease in specific surface area, and the effect of reducing reaction resistance is sufficient I can't get it.
According to the fourth invention, the lithium tungsten compound is in the form of fine particles and a film, the particle diameter of the fine particles is 1 to 500 nm, and the thickness of the film is 1 to 100 nm. A possible positive electrode active material is obtained.
According to the fifth invention, the lithium compound is at least one selected from lithium hydroxide, lithium carbonate, and lithium acetate, whereby a high-capacity positive electrode active material can be obtained. That is, when a halide or lithium oxide is considered as a lithium compound, an element may enter as an impurity in a halide or a reaction may be insufficient with lithium oxide, whereas lithium hydroxide or lithium carbonate. This is not the case with lithium acetate.
According to the sixth invention, when the tungsten compound is at least one selected from tungsten oxide, tungstic acid, and ammonium paratungstate, a high-capacity positive electrode active material capable of reducing the resistance can be obtained. That is, when a halide, sodium tungstate, or the like is considered as a tungsten compound, it is difficult to reduce the resistance because the halogen element or sodium remains as an impurity, and the battery capacity is reduced. Tungsten oxide, tungstic acid, paratungsten This is not the case with ammonium acid.
According to the seventh invention, the lithium tungsten compound is formed on the surface of the primary particle of the lithium nickel composite oxide particle, and the amount of lithium contained in the lithium carbonate existing on the surface is 0.02 with respect to the positive electrode active material. By making the mass% or less, low resistance and high capacity are possible, the amount of gas generated in the process of repeated charge and discharge can be suppressed, the performance deterioration of the secondary battery can be suppressed, and the battery Safety can be improved.
According to the eighth aspect of the present invention, the lithium tungsten compound is in the form of fine particles, and the particle diameter of the fine particles is 1 to 500 nm, whereby a positive electrode active material capable of lowering the resistance can be obtained. That is, if the particle diameter is less than 1 nm, fine particles may not have sufficient lithium ion conductivity. If the particle diameter exceeds 500 nm, the formation of a coating with fine particles becomes non-uniform, and the reaction resistance is reduced. Is not enough.
According to the ninth invention, the lithium tungsten compound is in the form of a film, and the thickness of the film is 1 to 100 nm, whereby a positive electrode active material capable of further reducing the resistance is obtained. That is, when the film thickness is less than 1 nm, the lithium ion conductivity may not be obtained. When the film thickness exceeds 100 nm, the specific surface area decreases, the contact area with the electrolytic solution decreases, and the reaction resistance is reduced. Not enough.
According to the tenth invention, the lithium tungsten compound is in the form of fine particles and a film, the particle diameter of the fine particles is 1 to 500 nm, and the thickness of the film is 1 to 100 nm. A possible positive electrode active material is obtained.
According to the eleventh aspect of the present invention, a nonaqueous electrolyte secondary battery having a high capacity and good output characteristics can be obtained by having the positive electrode containing the positive electrode active material for a nonaqueous electrolyte secondary battery.

It is a flowchart of the manufacturing method which concerns on embodiment of this invention. It is an enlarged view of the surface of the positive electrode active material particle manufactured by the manufacturing method which concerns on embodiment of this invention. It is an example of the cross-sectional SEM observation result (observation magnification 30000 times) of the lithium nickel complex oxide manufactured with the manufacturing method which concerns on embodiment of this invention. It is a schematic explanatory drawing of the measurement example of impedance evaluation, and the equivalent circuit used for analysis. It is a schematic sectional drawing of the coin-type battery 1 used for battery evaluation.

  Hereinafter, after describing the positive electrode active material for a nonaqueous electrolyte secondary battery according to the present invention, the method for producing a positive electrode active material for a nonaqueous electrolyte secondary battery according to the present invention and the produced positive electrode active material were used. A non-aqueous electrolyte secondary battery will be described.

(1) Positive electrode active material for a non-aqueous electrolyte secondary battery of the positive electrode active material present invention for a nonaqueous electrolyte secondary battery, the general _{formula: Li a Ni 1-x-} y Co x M y W c O 2 + α ( where 0 ≦ x ≦ 0.35, 0 ≦ y ≦ 0.35, 0.0006 ≦ c ≦ 0.0050, 0.95 ≦ a ≦ 1.20, 0 ≦ α ≦ 0.20, M is Mn, V, At least one element selected from Mg, Mo, Nb, Ti, and Al), and composed of lithium metal composite oxide particles composed of primary particles and secondary particles formed by aggregation of primary particles. A positive electrode active material for a non-aqueous electrolyte secondary battery, wherein a lithium tungsten compound is formed on the surface of the lithium nickel composite oxide particles, and the amount of lithium contained in the lithium carbonate present on the surface of the lithium nickel composite oxide particles Lithium nickel It is characterized in that the weight of Le composite oxide particles is 0.02 mass% or less.

In the present invention, the general formula _{Li b Ni 1-x-y} Co x M y O 2 as a substrate to form a lithium tungsten compound on the surface of the primary particles (where, 0 ≦ x ≦ 0.35,0 ≦ y ≦ 0.35, 0.95 ≦ b ≦ 1.20, and M is at least one element selected from Mn, V, Mg, Mo, Nb, Yi, and Al). Thus, a high charge / discharge capacity is obtained.

  In the above general formula, x represents an atomic ratio of Co when a metal element other than Li (Ni, Co, and M) is 1. The range of x is 0 ≦ x ≦ 0.35, and preferably 0 <x ≦ 0.35. By including cobalt in the positive electrode active material, good cycle characteristics can be obtained. This is because by replacing a part of nickel in the crystal lattice with cobalt, the expansion and contraction behavior of the crystal lattice due to lithium desorption due to charge / discharge can be reduced.

  The range of x is preferably 0.03 ≦ x ≦ 0.35 and more preferably 0.05 ≦ x ≦ 0.30 from the viewpoint of improving the cycle characteristics of the secondary battery. In addition, the range of x is preferably 0.03 ≦ x ≦ 0.15, more preferably 0.05 ≦ x ≦ 0.10, from the viewpoint of increasing the capacity of the secondary battery. On the other hand, when importance is attached to thermal stability, the range of x is preferably 0.07 ≦ x ≦ 0.25, and more preferably 0.10 ≦ x ≦ 0.20.

  In the above general formula, y represents an atomic ratio of M (additive element) when a metal element other than Li (Ni, Co, and M) is 1. M is at least one element selected from Mn, V, Mg, Mo, Nb, Ti and Al. The range of y is 0 ≦ y ≦ 0.35, and by adding M to the positive electrode active material, the durability characteristics and safety of the secondary battery containing this positive electrode active material can be improved. On the other hand, if y exceeds 0.35, the metal element contributing to the oxidation-reduction reaction (Redox reaction) decreases, and the battery capacity decreases. Moreover, when M is aluminum, the safety | security of a positive electrode active material improves more. From the viewpoint of increasing the capacity of the battery, the range of y is preferably 0 <y ≦ 0.10 including M, and more preferably 0 <y ≦ 0.05.

  In the above general formula, b represents the element ratio of Li when the metal elements (Ni, Co, and M) other than Li in the lithium nickel composite oxide are set to 1. The range of b is 0.95 ≦ b ≦ 1.20. When b is less than 0.95, the lithium in the lithium metal composite oxide is insufficient, the reaction resistance of the positive electrode is increased, and the output characteristics may be deteriorated. Moreover, since the amount of Li necessary for synthesizing the lithium tungsten compound is insufficient, the output characteristics may be deteriorated. On the other hand, when b exceeds 1.20, the safety of the secondary battery may be lowered. From the viewpoint of a balance between battery output and safety, the range of b is preferably 0.95 ≦ b ≦ 1.15. From the viewpoint of increasing the capacity of the battery, when 0.03 ≦ x ≦ 0.15 and 0 <y ≦ 0.10, the range of b may be 0.95 ≦ b ≦ 1.05. Preferably, 0.95 ≦ b ≦ 1.00 is more preferable.

  Further, the base material is composed of primary particles and secondary particles composed of aggregated primary particles. Lithium metal composite oxide particles (hereinafter secondary particles and primary particles present alone are simply combined with “lithium metal”. This is a composite oxide particle.) And the lithium tungsten compound formed on the surface of the primary particle (primary particle surface) realizes higher battery performance in terms of battery capacity and output characteristics. is there.

  Here, 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 limited, and as a result, the lithium nickel composite oxide has The advantage of high capacity is lost.

  On the other hand, in the positive electrode active material for non-aqueous electrolyte secondary batteries of the present invention (hereinafter simply referred to as “positive electrode active material”), a lithium tungsten compound is formed on the surface of the lithium metal composite oxide particles. This lithium tungsten compound has a high lithium ion conductivity and has an effect of promoting the movement of lithium ions. Therefore, by forming a lithium tungsten compound on the surface of the lithium metal composite oxide particles, a Li conduction path is formed at the interface with the electrolytic solution, so that the reaction resistance of the positive electrode active material (hereinafter referred to as “positive electrode resistance”). In other words, 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 becomes relatively high, so that a high output can be obtained. Moreover, since the applied voltage to the load side becomes high, lithium is sufficiently inserted and extracted from the positive electrode, so that the battery capacity is also improved. Furthermore, since the load of the active material at the time of charge / discharge is reduced by reducing the reaction resistance, cycle characteristics can also be improved.

Thus, this lithium tungsten compound contains lithium (Li) and tungsten (W), and thus has a high Li ion conductivity and has an effect of promoting the movement of Li ions. % Or more is preferably present in the form of Li ₄ WO ₅ , and more preferably 65% or more of W is present in the form of Li ₄ WO ₅ .

That is, Li ₄ WO ₅ has many Li ion conduction paths among compounds containing Li and W, and has a high effect of promoting the movement of Li ions, so that 50% or more of W exists in the form of Li ₄ WO _5. As a result, an even higher reaction resistance reduction effect can be obtained.

  Here, since the 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.

  In the present invention, the primary particle surface is exposed to the primary particle surface exposed at the surface of the secondary particle, and the vicinity of the surface of the secondary particle through which the electrolyte solution can permeate through the outside of the secondary particle and the internal space. The primary particle surface is included. Furthermore, even if it is the grain boundary between primary particles, as long as the coupling | bonding of primary particles is incomplete and the electrolyte solution can permeate | transmit, it will be contained in the primary particle surface in this invention.

  That is, the contact between the lithium tungsten compound and the electrolytic solution is not limited to the outer surface of the secondary particles formed by agglomeration of the primary particles, but also in the vicinity of the surface of the secondary particles, the internal voids, and the secondary particles. Therefore, it is necessary to promote the movement of lithium ions by forming a compound on the surface of such primary particles.

  Therefore, the reaction resistance of the lithium metal composite oxide particles can be further reduced by forming the lithium tungsten compound on many primary particle surfaces that can come into contact with the electrolytic solution.

  Furthermore, the form of the lithium tungsten compound on the primary particle surface is such that when the surface of the primary particle is coated with a layered material, the contact area with the electrolytic solution is reduced. It tends to result in formation being concentrated on the surface of certain primary particles. Therefore, although the layered material as the coating has high lithium ion conductivity, the effects of improving the charge / discharge capacity and reducing the reaction resistance can be obtained, but there is still room for improvement.

  Therefore, in order to obtain a higher effect, the lithium tungsten compound is preferably in the form of fine particles and present on the surface of the primary particles of the lithium metal composite oxide as fine particles having a particle diameter of 1 to 500 nm.

  By adopting such a form, it is possible to effectively improve lithium ion conduction with a sufficient contact area with the electrolytic solution, thereby improving the charge / discharge capacity and reducing the reaction resistance more effectively. it can. If the particle diameter is less than 1 nm, fine particles may not have sufficient lithium ion conductivity.

  However, if the particle diameter exceeds 500 nm, the formation of fine particles on the surface becomes non-uniform, and a higher effect of reducing reaction resistance may not be obtained. In order to obtain a high effect by making the formation more uniform, the particle diameter is more preferably 300 nm or less, and further preferably 200 nm or less.

  However, it is not necessary for all lithium tungsten compounds to be present as fine particles having a particle diameter of 1 to 500 nm, and preferably 50% or more of the fine particles formed on the surface of the primary particles are formed in a particle diameter range of 1 to 500 nm. If it is done, a high effect can be obtained.

  On the other hand, when the surface of the primary particles is coated in a film shape, it is possible to form a Li conduction path at the interface with the electrolytic solution while suppressing a decrease in specific surface area, thereby improving higher charge / discharge capacity and reducing reaction resistance. The effect is obtained. When the primary particle surface is coated with such a film-like compound, it is preferably present on the primary particle surface of the lithium metal composite oxide as a thin film having a thickness of 1 to 100 nm.

  If the film thickness is less than 1 nm, the lithium tungsten compound may not have sufficient lithium ion conductivity. On the other hand, if the film thickness exceeds 100 nm, the lithium ion conductivity is lowered, and a higher effect than the reaction resistance reducing effect may not be obtained.

  However, this film-like lithium tungsten compound may be partially formed on the primary particle surface, and the film thickness range of all lithium tungsten compounds may not be 1 to 100 nm. If a film having a thickness of 1 to 100 nm is formed at least partially on the primary particle surface, a high effect can be obtained. When a lithium tungsten compound is formed as a thin film, by controlling the amount of tungsten contained in the lithium tungsten compound within the above range, a film having a film thickness of 1 to 100 nm sufficient to obtain an effect can be obtained. It is formed.

  Furthermore, even when the fine particle form and the film form are mixed and a lithium tungsten compound is formed on the primary particle surface, a high effect on the battery characteristics can be obtained.

  On the other hand, when lithium tungsten compounds are formed unevenly between lithium metal composite oxide particles, the movement of lithium ions between lithium metal composite oxide particles becomes nonuniform, so that certain lithium metal composite oxides Particles are loaded and tend to cause deterioration of cycle characteristics and increase of reaction resistance.

  Therefore, it is preferable that the lithium tungsten compound is uniformly formed between the lithium metal composite oxide particles.

  The formation state of the lithium tungsten compound in such lithium metal composite oxide particles can be determined by observing with, for example, an electrolytic emission scanning electron microscope or a transmission electron microscope. It has been confirmed that the lithium tungsten compound is formed in the form described above on the surface of the primary particles of the composite oxide particles.

  For example, when observing 50 or more particles (secondary particles) arbitrarily extracted in an arbitrary observation field of at least two or more by observation with a constant magnification in observation with a field emission scanning electron microscope, the primary When the number of lithium metal composite oxide particles containing lithium tungsten compound on the surface of the particles is 90% or more of the observed number of particles, the lithium tungsten compound is uniformly formed between the lithium metal composite oxide particles. It can be said that.

  The amount of lithium tungsten compound formed can be controlled by the amount of tungsten contained in the lithium tungsten compound, and the amount of tungsten is based on the total number of Ni, Co and M atoms contained in the positive electrode active material. The number of W atoms is 0.06 to 0.50 atomic%, preferably 0.08 to 0.50 atomic%, and more preferably 0.10 to 0.50 atomic%.

  Thereby, a sufficient amount of the lithium tungsten compound can be formed while securing the surface of the primary particles that can be contacted with the electrolytic solution, and the reaction resistance of the positive electrode active material can be reduced. Moreover, since it can contribute to charging / discharging efficiently to the inside of a secondary particle, a battery capacity can also be improved.

  When the amount of tungsten contained in the lithium tungsten compound is less than 0.06 atomic% with respect to the total number of Ni, Co and M atoms contained in the positive electrode active material, the formation of the lithium tungsten compound The amount is small, and the reaction resistance of the positive electrode active material cannot be sufficiently reduced. On the other hand, when the amount of tungsten exceeds 0.50 atomic%, the primary particle surface that can be contacted with the electrolyte solution is reduced, and the efficiency of charging / discharging inside the secondary particles is reduced, thereby improving the battery capacity. This reduces the effect of In addition, lithium is consumed in the lithium tungsten compound, and the lithium necessary for the lithium nickel composite oxide particles may be insufficient, and the battery capacity and output characteristics of the base material itself may be deteriorated.

  Furthermore, in the positive electrode active material of the present invention, the amount of lithium contained in lithium carbonate present on the surface of the lithium nickel composite oxide particles is 0.02% by mass or less, preferably 0.017% by mass with respect to the positive electrode active material. % Or less. If it exceeds 0.02 mass%, the amount of lithium carbonate present on the surface of the lithium nickel composite oxide particles increases, and the amount of gas generated in the process of repeated charge and discharge may increase. By limiting the amount of lithium carbonate, gas generation can be suppressed, battery performance deterioration can be suppressed, and safety can be ensured. In addition, when the amount of lithium carbonate increases, the conduction of Li ions in the electrolytic solution and the positive electrode active material is hindered, causing problems such as an increase in reaction resistance of the positive electrode active material and a decrease in charge capacity.

  As for the content of lithium carbonate, for example, the total carbon element (C) content in the positive electrode active material is measured with a carbon sulfur analyzer, and the measured carbon element (C) content is all derived from lithium carbonate. Converted to lithium carbonate, the amount of lithium contained from lithium carbonate can be determined.

  The positive electrode active material of the present invention is a material in which a lithium tungsten compound is formed on the surface of primary particles constituting the lithium metal composite oxide particles as a base material to reduce the reaction resistance of the positive electrode and improve the battery characteristics. The powder characteristics such as particle diameter and tap density as a substance may be within the range of a positive electrode active material that is usually used.

  The effects of providing a lithium tungsten compound on the surfaces of secondary particles and primary particles of lithium nickel composite oxide particles and reducing lithium carbonate include, for example, lithium cobalt composite oxide, lithium manganese composite oxide, lithium The present invention can be applied not only to powders such as nickel-cobalt-manganese-based composite oxides, but also to positive electrode active materials for lithium secondary batteries that are generally used as well as the positive electrode active materials listed in the present invention.

(2) Method for Producing Positive Electrode Active Material for Nonaqueous Electrolyte Secondary Battery Hereinafter, a method for producing a positive electrode active material for a nonaqueous electrolyte secondary battery of the present invention will be described with reference to FIG.

[Mixing process]
The mixing step is a step of obtaining a mixture by mixing nickel composite oxide particles, a lithium compound, and a tungsten compound at a time.

In the mixing step, the general _{formula: Ni 1-x-y Co} x M y O 2 ( however, 0 ≦ x ≦ 0.35,0 ≦ y ≦ 0.35, M is Mn, V, Mg, Mo, Nb, Nickel composite oxide particles represented by at least one element selected from Ti and Al are used. The nickel composite oxide particles may be used in the form of a composite hydroxide. The composition ratio of the metal elements (Ni, Co and M) in the nickel composite oxide particles is also maintained in the obtained positive electrode active material. Therefore, a positive electrode active material having a target composition ratio can be obtained by using nickel composite oxide particles having a metal element composition ratio equivalent to that of the positive electrode active material to be obtained.

  The lithium compound to be mixed is preferably lithium hydroxide, lithium carbonate, lithium acetate or the like, more preferably lithium hydroxide having high reactivity. The ratio Li / Me between the number of lithium atoms contained in the lithium compound and the total number of Me atoms of Ni, Co and M contained in the nickel composite oxide particles is 0.95 to 1.20, preferably 0.95. ˜1.15. Thereby, the amount of lithium for synthesizing the lithium nickel composite oxide particles and the lithium tungsten compound can be within a preferable range, and even when the process is simplified, high charge / discharge capacity and sufficient output characteristics can be obtained. .

  Although it is possible to use halides and lithium oxides as lithium compounds, elements may enter impurities as impurities in lithium halides, while lithium oxides may cause inadequate reaction. Lithium and lithium acetate do not contain impurities, and a higher capacity positive electrode active material can be obtained. Moreover, when the ratio of nickel is high, lithium hydroxide is more preferable. This is because the firing temperature described later can be lowered.

  The tungsten compound to be used is preferably tungsten oxide, tungstic acid, ammonium tungstate, sodium tungstate, or the like, and more preferably tungsten oxide or tungstic acid with a low possibility of impurity contamination. The number of tungsten atoms contained in the tungsten compound is 0.06 to 0.50 atomic%, preferably 0.08 to 0.5% with respect to the total Me of the number of Ni, Co and M atoms contained in the nickel composite oxide particles. 0.05 atomic%, more preferably 0.10 to 0.50 atomic%. Thereby, the amount of tungsten for synthesizing the lithium tungsten compound can be within a preferable range, and a high battery capacity and sufficient output characteristics can be obtained.

  When considering halides, sodium tungstate, etc. as tungsten compounds, it is difficult to reduce resistance due to residual halogen elements and sodium as impurities, and the battery capacity decreases. Tungsten oxide, tungstic acid, paratungstic acid This is not the case with ammonium. Accordingly, a positive electrode active material having a higher capacity and a lower capacity can be obtained.

  When mixing the nickel composite oxide particles, the lithium compound, and the tungsten compound, a general mixer can be used. For example, it may be mixed sufficiently using a shaker mixer, a Laedige mixer, a Julia mixer, a V blender, or the like so that the shape of the nickel composite oxide particles is not destroyed.

[Baking process]
The firing step is a step in which a mixture of nickel composite oxide particles, a lithium compound and a tungsten compound is fired to obtain lithium nickel composite oxide particles in which a lithium tungsten compound is formed on the secondary particle surface and the primary particle surface.

  Firing is performed in an oxidizing atmosphere, and the firing temperature is 600 to 800 ° C, preferably 650 to 790 ° C. By setting the firing temperature to 600 to 800 ° C., the synthesis reaction of the lithium nickel composite oxide is sufficiently performed, the battery characteristics such as the battery capacity and output characteristics of the base material itself are improved, and the synthesized lithium nickel composite oxide A lithium tungsten compound is formed on the surface of the primary particles of the product particles, and a high reaction resistance reduction effect can be obtained. If it is less than 600 degreeC, the synthesis | combination reaction of lithium nickel complex oxide is not fully performed. When the temperature exceeds 800 ° C., part or all of tungsten is dissolved in the lithium nickel composite oxide to lower the battery capacity, and the formation of the lithium tungsten compound becomes insufficient, and the effect of reducing the reaction resistance is also lowered. Moreover, the sintering of lithium nickel composite oxide particles partially proceeds and becomes coarse, which may deteriorate battery characteristics.

  Furthermore, an unreacted lithium compound can be reduced by mixing and baking a tungsten compound with a lithium compound. The lithium carbonate present on the surface of the lithium nickel composite oxide particles is generated by the reaction between the unreacted lithium and carbon dioxide in the atmosphere when unreacted lithium remains in the firing step. The amount of lithium contained in the lithium carbonate can be reduced by setting the tungsten compound mixed in the mixing step to an appropriate amount. That is, if the tungsten compound is an appropriate amount, the tungsten compound easily reacts with the lithium compound, so that the unreacted lithium can be converted into a lithium tungsten compound. By reducing the lithium carbonate, the amount of lithium contained in the lithium carbonate can be reduced. Can be reduced. Thereby, as described above, the battery characteristics can be improved.

  In addition, since lithium in the lithium compound easily diffuses into the nickel composite oxide, the tungsten in the tungsten compound mixed with the lithium compound also diffuses with the lithium to form a primary inside the secondary particle of the lithium nickel composite oxide. It diffuses to the particle surface to form a lithium tungsten compound. In particular, when lithium compounds such as lithium hydroxide and lithium carbonate that melt during firing are used, the tungsten compound penetrates into the primary particle surface inside the secondary particles together with the molten lithium compound, and the surface of the primary particles more uniformly. A lithium tungsten compound can be formed on the substrate.

  By firing in an oxidizing atmosphere, the synthesis reaction of the lithium nickel composite oxide is promoted, and the battery characteristics of the substrate itself can be enhanced. As the oxidizing atmosphere, a mixed gas atmosphere with an inert gas containing 18% by volume or more of oxygen is preferable, and an air atmosphere or an oxygen atmosphere (containing an oxygen concentration of 90% by volume or more) is more preferable. In addition, if carbon dioxide gas is contained in the atmosphere, the amount of lithium carbonate present on the surface of the fired lithium nickel composite oxide particles increases. For example, a decarbonizing atmosphere in which the carbon dioxide concentration is 50 ppm by volume or less It is preferable that

  The firing time is preferably 10 to 20 hours, and more preferably 10 to 15 hours. If it is less than 10 hours, the synthesis reaction of the lithium nickel composite oxide is not sufficiently performed, and the charge / discharge capacity and output characteristics of the core material itself may be deteriorated. When it exceeds 20 hours, productivity will fall remarkably.

  Further, after firing, the surface of the primary particles of the lithium metal composite oxide may be washed with water to such an extent that the necessary amount of lithium tungsten compound can be maintained. By washing with water, lithium carbonate present on the surface of the lithium nickel composite oxide particles can be further reduced. Washing conditions can be selected from known washing conditions.

[Crushing process]
The lithium nickel composite oxide particles after firing may be aggregated or slightly sintered. In this case, the aggregate or sintered body of lithium nickel composite oxide particles can be crushed. Thereby, since the lithium nickel composite oxide particles can be handled as a powder having an appropriate particle size, the filling property when used as the positive electrode active material can be improved. Note that pulverization means that mechanical energy is applied to an aggregate composed of a plurality of secondary particles generated by sintering necking between secondary particles during firing, and the secondary particles themselves are hardly destroyed. This is an operation of separating the secondary particles and loosening the aggregates.

  When crushing, a general crusher can be used. For example, a pin mill or a hammer mill can be used. At this time, the crushing force is adjusted to an appropriate range so as not to destroy the secondary particles.

(3) Non-aqueous electrolyte secondary battery A non-aqueous electrolyte secondary battery using a positive electrode active material produced by the production method of the present invention comprises a positive electrode, a negative electrode, a non-aqueous electrolyte, and the like, and is a general non-aqueous electrolyte. It is comprised by the component similar to a secondary battery. The embodiment described below is merely an example, and the nonaqueous electrolyte secondary battery is subjected to various changes and improvements based on the knowledge of those skilled in the art based on the embodiment described in this specification. Can be implemented. Further, the disclosed nonaqueous electrolyte secondary battery is not particularly limited in its application.

(A) Positive electrode Using the positive electrode active material for a non-aqueous electrolyte secondary battery described above, for example, a positive electrode of a non-aqueous electrolyte secondary battery is produced as follows.

  First, a powdered positive electrode active material, a conductive material, and a binder are mixed, and, if necessary, a target solvent such as activated carbon and viscosity adjustment is added and kneaded to prepare a positive electrode mixture paste.

  Each mixing ratio in the positive electrode mixture paste is also an important factor for determining the performance of the non-aqueous electrolyte secondary battery. When the total mass of the solid content of the positive electrode mixture excluding the solvent is 100 parts by mass, the content of the positive electrode active material is 60 to 95 parts by mass in the same manner as the positive electrode of a general non-aqueous electrolyte secondary battery, and the conductive material The content of is 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 the surface of a current collector made of, for example, an aluminum foil and dried to disperse the solvent. If necessary, pressurization may be performed by a roll press or the like to increase the electrode density. In this way, a sheet-like positive electrode can be produced.

  The sheet-like positive electrode can be cut into an appropriate size or the like according to the target battery and used for battery production. However, the method for manufacturing the positive electrode is not limited to the illustrated one, and other methods may be used.

  In producing the positive electrode, as the conductive agent, for example, graphite (natural graphite, artificial graphite, expanded graphite, etc.), carbon black materials such as acetylene black, ketjen black (registered trademark), and the like can be used.

  The binder plays a role of anchoring the active material particles. For example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluorine rubber, ethylene propylene diene rubber, styrene butadiene, cellulosic resin, polyacrylic. An acid or the like can be used. If necessary, a positive electrode active material, a conductive material, and activated carbon are dispersed, and a solvent that dissolves the binder is added to the positive electrode mixture.

  Specifically, an organic solvent such as N-methyl-2-pyrrolidone can be used as the solvent. Activated carbon can be added to the positive electrode mixture in order to increase the electric double layer capacity.

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

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

(D) Non-aqueous electrolyte The non-aqueous electrolyte is obtained by dissolving a lithium salt as a supporting salt in an organic solvent. Examples of the organic solvent used include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and trifluoropropylene carbonate, chain carbonates such as diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, and dipropyl carbonate, and tetrahydrofuran, A single compound selected from ether compounds such as 2-methyltetrahydrofuran and dimethoxyethane, sulfur compounds such as ethyl methyl sulfone and butane sultone, phosphorus compounds such as triethyl phosphate and trioctyl phosphate, or a mixture of two or more. Can be used.

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

(E) Battery shape and configuration As described above, the shape of the nonaqueous electrolyte secondary battery of the present invention composed of the positive electrode, the negative electrode, the separator, and the nonaqueous electrolyte solution described above is various, such as a cylindrical type and a laminated type. can do. In any case, the positive electrode and the negative electrode are laminated through a separator to form an electrode body, and the obtained electrode body is impregnated with a non-aqueous electrolyte and communicated with the positive electrode current collector and the outside. Connect between the positive electrode terminal and between the negative electrode current collector and the negative electrode terminal leading to the outside using a current collecting lead, etc., and seal the battery case to complete the non-aqueous electrolyte secondary battery. .

(F) Characteristics The nonaqueous electrolyte secondary battery using the positive electrode active material of the present invention has a high capacity and a high output. 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 low when used for the positive electrode of a 2032 type coin battery, for example. A positive electrode resistance is obtained, and a high capacity and a high output are obtained. Moreover, 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 is as follows.
When the frequency dependence of the battery reaction is measured by a general AC impedance method as an 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. Is obtained as follows. The battery reaction at the electrode consists of a resistance component accompanying the charge transfer and a capacity component due to the electric double layer. When these are expressed as an electric circuit, it becomes a parallel circuit of resistance and capacity. It is represented by an equivalent circuit in which circuits are connected in series.

  Fitting calculation is performed on the Nyquist diagram measured using this equivalent circuit, and each resistance component and capacitance component can be estimated. The positive electrode resistance is equal to the diameter of the semicircle on the low frequency side of the obtained Nyquist diagram.

  From the above, the positive electrode resistance can be estimated by performing AC impedance measurement on the manufactured positive electrode and performing fitting calculation on the obtained Nyquist diagram with an equivalent circuit.

  About the secondary battery which has a positive electrode using the positive electrode active material obtained by this invention, the performance (initial stage discharge capacity, positive electrode resistance) was measured.

  Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples.

(Battery manufacture and evaluation)
For the evaluation of the positive electrode active material, a 2032 type coin battery 1 (hereinafter referred to as a coin type battery) shown in FIG. 5 was used. As shown in FIG. 5, the coin-type battery 1 includes a case 2 and an electrode 3 accommodated in the case 2.

  The case 2 has a positive electrode can 2a that is hollow and open at one end, and a negative electrode can 2b that is disposed in the opening of the positive electrode can 2a. When the negative electrode can 2b is disposed in the opening of the positive electrode can 2a, A space for accommodating the electrode 3 is formed between the negative electrode can 2b and the positive electrode can 2a. The electrode 3 includes a positive electrode 3a, a separator 3c, and a negative electrode 3b, which are stacked in this order. The positive electrode 3a contacts the inner surface of the positive electrode can 2a, and the negative electrode 3b contacts the inner surface of the negative electrode can 2b. As shown in FIG.

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

The coin type battery 1 shown in FIG. 5 was manufactured as follows.
First, 52.5 mg of a positive electrode active material for a non-aqueous electrolyte secondary battery, 15 mg of acetylene black, and 7.5 mg of polytetrafluoroethylene resin (PTFE) are mixed and press-molded to a diameter of 11 mm and a thickness of 100 μm at a pressure of 100 MPa. A positive electrode 3a was produced. The produced positive electrode 3a was dried at 120 ° C. for 12 hours in a vacuum dryer.

  Using the positive electrode 3a, the negative electrode 3b, the separator 3c, and the electrolyte, the coin-type battery 1 shown in FIG. 5 was produced in a glove box in an Ar atmosphere in which the dew point was controlled at −80 ° C. As the negative electrode 3b, a negative electrode sheet in which graphite powder having an average particle diameter of about 20 μm punched into a disk shape with a diameter of 14 mm and polyvinylidene fluoride were applied to a copper foil was used.

As the separator 3c, a polyethylene porous film having a film thickness of 25 μm was used. As the electrolytic solution, an equivalent mixed solution (manufactured by Toyama Pharmaceutical Co., Ltd.) of ethylene carbonate (EC) and diethyl carbonate (DEC) using 1M LiClO ₄ as a supporting electrolyte was used.

The initial discharge capacity and positive electrode resistance showing the performance of the manufactured coin battery 1 were evaluated as follows. The initial discharge capacity is left for about 24 hours after the coin-type battery 1 is manufactured, and after the open circuit voltage OCV (Open Circuit Voltage) is stabilized, the current density with respect to the positive electrode is set to 0.1 mA / cm ² and the cut-off voltage 4 The capacity when the battery was charged to 3 V, discharged after a pause of 1 hour to a cutoff voltage of 3.0 V was defined as the initial discharge capacity.

  When the positive electrode resistance is measured by the AC impedance method using a frequency response analyzer and a potentiogalvanostat (manufactured by Solartron, 1255B) after charging the coin-type battery 1 at a charging potential of 4.1 V, the Nyquist plot shown in FIG. can get.

  Since this Nyquist plot is expressed as the sum of the characteristic curve indicating the solution resistance, the negative electrode resistance and its capacity, and the positive electrode resistance and its capacity, the fitting calculation is performed using an equivalent circuit based on this Nyquist plot, and the positive resistance The value of was calculated.

  In this example, each of the reagent special grades manufactured by Wako Pure Chemical Industries, Ltd. was used for producing the composite hydroxide, the positive electrode active material, and the secondary battery.

Example 1
Li / Me is 1.00 and W / Me (× 100%) is 0.15 atomic% to 100 g of nickel composite oxide represented by Ni _0.91 Co _0.06 Al _0.03 O _2. Then, 31.7 g of lithium hydroxide and 0.46 g of tungsten oxide were added, and the mixture was sufficiently mixed using a shaker mixer apparatus (TURBURA Type T2C manufactured by Willy et Bacofen (WAB)) to obtain a mixture.

  The obtained mixture was put in a magnesia firing container, heated to 750 ° C. in a 100% oxygen stream, fired for 10 hours, and then cooled to room temperature. After furnace cooling, it was crushed and finally passed through a sieve having an opening of 38 μm to obtain a positive electrode active material. When Li / Me and W / Me (× 100%) of the obtained positive electrode active material were analyzed by ICP method, Li / Me was 1.00 and W / Me (× 100%) was 0.15 atomic%. It was confirmed that there was.

[Li content in lithium carbonate]
The amount of lithium carbonate present on the surface of the obtained positive electrode active material was measured for the total carbon element (C) content with a carbon sulfur analyzer (LE-CO CS-600), and the amount of the total carbon element measured. Was converted into lithium carbonate (Li ₂ CO ₃ ), and the amount of Li in the lithium carbonate was calculated from the obtained amount of lithium carbonate. The amount of Li in the lithium carbonate present on the surface of the obtained positive electrode active material was 0.015% by mass with respect to the mass of the positive electrode active material.

[Morphological analysis of lithium tungsten compounds]
When the obtained positive electrode active material was embedded in a resin and subjected to cross-section polisher, cross-sectional observation by SEM with a magnification of 5000 times was performed. As a result, the primary particles and the primary particles were agglomerated. It was confirmed that fine particles of a lithium tungsten compound were formed on the primary particle surface, and the particle size of the fine particles was 20 to 120 nm. Further, when the cross section of any 50 or more secondary particles was observed at a magnification of 5000 times, the ratio of the secondary particles having a lithium tungsten compound on the surface of the primary particles inside the secondary particles to the observed number of secondary particles (compound The abundance ratio) was 96%.

  Furthermore, when the vicinity of the surface of the primary particle of the obtained positive electrode active material was observed with a transmission electron microscope (TEM), a coating of a lithium tungsten compound having a film thickness of 1 to 70 nm was formed on the surface of the primary particle, and the compound was tungsten. It was confirmed to be lithium acid lithium.

Further, the presence state of lithium tungstate in the positive electrode active material was evaluated by titrating Li eluted from the positive electrode active material. After adding pure water to the obtained positive electrode active material and stirring for 30 minutes, the compound state of lithium eluting from the neutralization point that appears by adding hydrochloric acid while measuring the pH of the filtered filtrate was evaluated. The presence of Li ₄ WO ₅ and Li ₂ WO ₄ was confirmed in the lithium tungstate, and the abundance ratio of Li ₄ WO ₅ contained was calculated to be 87 mol%.

[Battery evaluation]
The battery characteristics of the coin-type battery 1 shown in FIG. 5 having a positive electrode produced using the obtained positive electrode active material were evaluated. For the positive electrode resistance before the cycle test, the relative value where Example 1 was “1.00” was used as the evaluation value. The initial discharge capacity was 210 mAh / g.

  Hereinafter, about an Example and a comparative example, only the substance and conditions which changed with Example 1 are shown. Table 1 shows the initial discharge capacity, positive electrode resistance, and evaluation values for the amount of Li in lithium carbonate in Example 1.

(Example 2)
Example 1 except that 30.1 g of lithium hydroxide was added to 100 g of nickel composite oxide represented by Ni _0.91 Co _0.06 Al _0.03 O _{2 so} that Li / Me was 0.95. Similarly, a positive electrode active material was obtained, and battery characteristics and lithium carbonate amount were evaluated. The results are shown in Table 1.

(Example 3)
Example 1 except that 32.7 g of lithium hydroxide was added to 100 g of nickel composite oxide represented by Ni _0.91 Co _0.06 Al _0.03 O _{2 so} that Li / Me was 1.03. Similarly, a positive electrode active material was obtained, and battery characteristics and lithium carbonate amount were evaluated. The results are shown in Table 1.

Example 4
0.31 g of tungsten oxide is added to 100 g of nickel composite oxide represented by Ni _0.91 Co _0.06 Al _0.03 O _{2 so} that W / Me (× 100%) is 0.10 atomic%. A positive electrode active material was obtained in the same manner as in Example 1 except that the battery characteristics and the amount of lithium carbonate were evaluated. Since the lithium tungsten compound was not confirmed in the cross-sectional observation by SEM, the compound presence rate was evaluated by TEM observation. The results are shown in Table 1.

(Example 5)
Add 0.92 g of tungsten oxide to 100 g of nickel composite oxide represented by Ni _0.91 Co _0.06 Al _0.03 O _{2 so} that W / Me (× 100%) is 0.30 atomic%. A positive electrode active material was obtained in the same manner as in Example 1 except that the battery characteristics and the amount of lithium carbonate were evaluated. The results are shown in Table 1.

(Example 6)
0.50 g of tungstic acid was added to 100 g of nickel composite oxide represented by Ni _0.91 Co _0.06 Al _0.03 O _{2 so} that W / Me (× 100%) was 0.15 atomic%. A positive electrode active material was obtained in the same manner as in Example 1 except that the battery characteristics and the amount of lithium carbonate were evaluated. The results are shown in Table 1.

(Example 7)
Addition of 0.39 g of tungsten oxide to 100 g of nickel composite oxide represented by Ni _0.91 Co _0.06 Al _0.03 O _{2 so} that W / Me (× 100%) is 0.125 atomic% A positive electrode active material was obtained in the same manner as in Example 1 except that the battery characteristics and the amount of lithium carbonate were evaluated. The results are shown in Table 1.

(Example 8)
1.38 g of tungsten oxide is added to 100 g of nickel composite oxide represented by Ni _0.91 Co _0.06 Al _0.03 O _{2 so} that W / Me (× 100%) is 0.45 atomic%. A positive electrode active material was obtained in the same manner as in Example 1 except that the battery characteristics and the amount of lithium carbonate were evaluated. The results are shown in Table 1.

Example 9
The addition of tungsten oxide or the like to 100 g of the nickel composite oxide represented by Ni _0.91 Co _0.06 Al _0.03 O ₂ is the same as in Example 1, except that the firing temperature is 630 ° C. and the positive electrode active material is used. The battery characteristics and the amount of lithium carbonate were evaluated. The results are shown in Table 1.

(Example 10)
The addition of tungsten oxide or the like to 100 g of nickel composite oxide represented by Ni _0.91 Co _0.06 Al _0.03 O ₂ is the same as in Example 1, but the firing temperature is set to 680 ° C. and the positive electrode active material is used. The battery characteristics and the amount of lithium carbonate were evaluated. The results are shown in Table 1.

(Example 11)
The addition of tungsten oxide or the like to 100 g of nickel composite oxide represented by Ni _0.91 Co _0.06 Al _0.03 O ₂ is the same as in Example 1, except that the firing temperature is 730 ° C. and the positive electrode active material is used. The battery characteristics and the amount of lithium carbonate were evaluated. The results are shown in Table 1.

(Example 12)
The addition of tungsten oxide or the like to 100 g of nickel composite oxide represented by Ni _0.91 Co _0.06 Al _0.03 O ₂ is the same as in Example 1, except that the firing temperature is 780 ° C. and the positive electrode active material is used. The battery characteristics and the amount of lithium carbonate were evaluated. The results are shown in Table 1.

(Comparative Example 1)
A positive electrode active material was obtained and battery characteristics were obtained in the same manner as in Example 1 except that no tungsten compound was added to 100 g of nickel composite oxide represented by Ni _0.91 Co _0.06 Al _0.03 O _2. And the amount of lithium carbonate was evaluated. The results are shown in Table 1.

(Comparative Example 2)
0.16 g of tungsten oxide is added to 100 g of nickel composite oxide represented by Ni _0.91 Co _0.06 Al _0.03 O _{2 so} that W / Me (× 100%) is 0.05 atomic%. A positive electrode active material was obtained in the same manner as in Example 1 except that the battery characteristics and the amount of lithium carbonate were evaluated. The results are shown in Table 1.

(Comparative Example 3)
2.30 g of tungsten oxide is added to 100 g of nickel composite oxide represented by Ni _0.91 Co _0.06 Al _0.03 O _{2 so} that W / Me (× 100%) is 0.75 atomic%. A positive electrode active material was obtained in the same manner as in Example 1 except that the battery characteristics and the amount of lithium carbonate were evaluated. The results are shown in Table 1.

(Comparative Example 4)
The addition of tungsten oxide or the like to 100 g of nickel composite oxide represented by Ni _0.91 Co _0.06 Al _0.03 O ₂ is the same as in Example 1, but the firing temperature is set to 550 ° C. and the positive electrode active material is used. The battery characteristics and the amount of lithium carbonate were evaluated. The results are shown in Table 1.

(Comparative Example 5)
The addition of tungsten oxide or the like to 100 g of nickel composite oxide represented by Ni _0.91 Co _0.06 Al _0.03 O ₂ is the same as in Example 1, except that the firing temperature is 820 ° C. The battery characteristics and the amount of lithium carbonate were evaluated. The results are shown in Table 1.

(Comparative Example 6)
An alkaline solution (W) containing tungsten by adding and stirring 0.055 g of tungsten oxide (WO ₃ ) in an aqueous solution in which 0.06 g of lithium hydroxide (LiOH) is dissolved in 3 ml of pure water. Got. Next, an alkaline solution (W) is added to 15 g of the lithium metal composite oxide powder obtained in Comparative Example 1, and a shaker mixer apparatus (TURBULA Type T2C manufactured by Willy et Bacofen (WAB)) is used. The mixture was sufficiently mixed to obtain a mixture of the alkaline solution (W) and the lithium metal composite oxide powder.

  The obtained mixture is put in a magnesia baking vessel, heated to 500 ° C. at a temperature rising rate of 2.8 ° C./min in a 100% oxygen stream, heat-treated for 10 hours, then cooled to room temperature and furnace-cooled. By crushing, a positive electrode active material was obtained, and battery characteristics and lithium carbonate amount were evaluated. The results are shown in Table 1.

[Evaluation]
As can be seen from Table 1, since the positive electrode active materials of Examples 1 to 12 were produced according to the present invention, the initial discharge capacity was generally higher than 206 mAh / g compared to the comparative example, and the positive electrode resistance was generally 1.26 or less. In addition, the amount of lithium carbonate, which is a factor of gas generated in the process of repeated charge and discharge, is also suppressed to approximately 0.018 wt% or less.

  FIG. 3 shows an example of a cross-sectional SEM observation result of the positive electrode active material obtained in the example of the present invention, and FIG. 2 shows an image diagram of FIG. The obtained positive electrode active material is composed of primary particles 12 and secondary particles 11 formed by agglomerating the primary particles 12, and the surface of the primary particles 12 is observed on the surface of the primary particles 12 by SEM observation and TEM observation of the cross section. It was confirmed that the lithium tungsten compound 13 was formed. The positions where the lithium tungsten compounds 13 and 14 are confirmed are indicated by arrows in FIG.

  On the other hand, in Comparative Example 1, since the lithium tungsten compound according to the present invention is not formed on the secondary particle surface and the primary particle surface, the positive electrode resistance is significantly high, and it is difficult to meet the demand for higher output. is there.

  The non-aqueous electrolyte secondary battery of the present invention is suitable for a power source of a small portable electronic device (such as a notebook personal computer or a mobile phone terminal) that always requires a high capacity, and an electric vehicle battery that requires a high output. Also suitable.

  In addition, the nonaqueous electrolyte secondary battery of the present invention has excellent safety, and can be downsized and increased in output, and thus is suitable as a power source for an electric vehicle subject to restrictions on mounting space. The present invention can be used not only as a power source for an electric vehicle driven purely by electric energy but also as a power source for a so-called hybrid vehicle used in combination with a combustion engine such as a gasoline engine or a diesel engine.

DESCRIPTION OF SYMBOLS 1 Coin type battery 2 Case 2a Positive electrode can 2b Negative electrode can 2c Gasket 3 Electrode 3a Positive electrode 3b Negative electrode 3c Separator 11 Secondary particle 12 Primary particle 13 Film-like lithium tungsten compound 14 Fine particle lithium tungsten compound

Claims (11)

General _{formula: Li a Ni 1-x-} y Co x M y W c O 2 + α ( although, 0 ≦ x ≦ 0.35,0 ≦ y ≦ 0.35,0.0006 ≦ c ≦ 0.0050,0. 95 ≦ a ≦ 1.20, 0 ≦ α ≦ 0.20, where M is at least one element selected from Mn, V, Mg, Mo, Nb, Ti and Al), and primary particles and primary particles A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery comprising lithium metal composite oxide particles comprising secondary particles formed by aggregation of
General _formula: and nickel composite oxide particles represented by _{Ni 1-x-y Co x} M y O 2,
A lithium compound having a ratio Li / Me of the total number of atoms of Ni, Co and M contained in the nickel composite oxide particles to the number of lithium atoms of 0.95 to 1.20;
A mixing step of mixing a tungsten compound with which the number of tungsten atoms with respect to Me is 0.06 to 0.50 atomic% to obtain a mixture;
Firing the mixture in an oxidizing atmosphere at 600 to 800 ° C. to obtain lithium nickel composite oxide particles in which a lithium tungsten compound is formed on the surface of the primary particles.
The manufacturing method of the positive electrode active material for non-aqueous electrolyte secondary batteries characterized by the above-mentioned. The lithium tungsten compound is in the form of fine particles,
The particle diameter of the fine particles is 1 to 500 nm.
The manufacturing method of the positive electrode active material for non-aqueous electrolyte secondary batteries of Claim 1 characterized by the above-mentioned. The lithium tungsten compound is in the form of a film;
The thickness of the film is 1 to 100 nm,
The manufacturing method of the positive electrode active material for non-aqueous electrolyte secondary batteries of Claim 1 characterized by the above-mentioned. The lithium tungsten compound is in the form of fine particles and a film,
The particle diameter of the fine particles is 1 to 500 nm, and the thickness of the film is 1 to 100 nm.
The manufacturing method of the positive electrode active material for non-aqueous electrolyte secondary batteries of Claim 1 characterized by the above-mentioned. The lithium compound is at least one selected from lithium hydroxide, lithium carbonate, and lithium acetate;
The manufacturing method of the positive electrode active material for non-aqueous electrolyte secondary batteries of any one of Claims 1-4 characterized by the above-mentioned. The tungsten compound is at least one selected from tungsten oxide, tungstic acid, and ammonium paratungstate.
The manufacturing method of the positive electrode active material for nonaqueous electrolyte secondary batteries of any one of Claims 1-5 characterized by the above-mentioned. General _{formula: Li a Ni 1-x-} y Co x M y W c O 2 + α ( although, 0 ≦ x ≦ 0.35,0 ≦ y ≦ 0.35,0.0006 ≦ c ≦ 0.0050,0. 95 ≦ a ≦ 1.20, 0 ≦ α ≦ 0.20, where M is at least one element selected from Mn, V, Mg, Mo, Nb, Ti and Al), and primary particles and primary particles A positive electrode active material for a non-aqueous electrolyte secondary battery composed of lithium metal composite oxide particles comprising secondary particles formed by agglomeration,
A lithium tungsten compound is formed on the surfaces of the primary particles of the lithium metal composite oxide, and the amount of lithium contained in the lithium carbonate present on the surfaces of the lithium nickel composite oxide particles is 0.02 mass relative to the positive electrode active material. % Positive electrode active material for non-aqueous electrolyte secondary battery, The lithium tungsten compound is in the form of fine particles, and the particle diameter of the fine particles is 1 to 500 nm.
The positive electrode active material for a nonaqueous electrolyte secondary battery according to claim 7. The lithium tungsten compound is in the form of a film, and the thickness of the film is 1 to 100 nm.
The positive electrode active material for a nonaqueous electrolyte secondary battery according to claim 7. The lithium tungsten compound is in the form of fine particles and a film, the particle diameter of the fine particles is 1 to 500 nm, and the thickness of the film is 1 to 100 nm.
The positive electrode active material for a nonaqueous electrolyte secondary battery according to claim 7. It has a positive electrode containing the positive electrode active material for nonaqueous electrolyte secondary batteries of any one of Claims 7-10.
A non-aqueous electrolyte secondary battery.