JP2005302507A - Cathode active material for nonaqueous electrolyte secondary battery, and nonaqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cathode active material for a nonaqueous electrolyte secondary battery which can be manufactured stably and a nonaqueous electrolyte secondary battery using it as the cathode, and in which reduction of inner resistance of the battery and generation of high power become possible. <P>SOLUTION: This material is composed of a powdered lithium metal compound oxide expressed by LiNi<SB>1-X</SB>M<SB>X</SB>O<SB>2</SB>(provided, M expresses at least one kind or more of metal elements selected from a group consisting of Co, Al, Mg, Mn, Ti, Fe, Cu, Zn and Ga, and 0<x≤0.25 is satisfied), wherein the powder is constituted of primary particles of lithium metal compound oxide together with secondary particles formed by a plurality of the assembled primary particles, the shape of the secondary particles is spherical or ellipsoidal, the diameter of the powder is 40 μm or less, the powder contains 0.5 to 7.0 vol% of particles of particle diameter 1 μm or less, the surface area ratio of the powder is larger by 0.3m<SP>2</SP>/g at the maximum than that of the powder consisting excluding the particles of powder diameter 1 μm or less, while the tap density of the powder is smaller by 0.2 g/cm<SP>3</SP>at the maximum than that of the powder consisting of the particles excluding the powder having diameter 1 μm or less. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a positive electrode active material for a non-aqueous electrolyte secondary battery, and a non-aqueous electrolyte secondary battery using the positive electrode active material as a positive electrode. More specifically, the present invention relates to a reduction in internal resistance and a high non-aqueous electrolyte secondary battery. The present invention relates to a positive electrode active material for a non-aqueous electrolyte secondary battery that can be improved, and a non-aqueous electrolyte secondary battery using the positive electrode active material as a positive electrode.

  With the widespread use of portable devices such as mobile phones and laptop computers, small and lightweight secondary batteries with high energy density are required. As such a secondary battery, there is a lithium ion secondary battery that uses a substance capable of detaching and inserting Li, such as lithium metal, lithium alloy, metal oxide, or carbon, as a negative electrode. It has been broken.

  Also in the automobile field, demand for electric vehicles has increased due to resource and environmental problems, and lithium-ion batteries that are inexpensive, have a large capacity, and have good cycle characteristics and output characteristics as motor drive batteries for electric cars and hybrid cars. There is a need for secondary batteries.

As a positive electrode active material of a lithium ion secondary battery which is a non-aqueous electrolyte secondary battery, a lithium metal composite oxide composed of a lithium oxide and another metal oxide, particularly a lithium cobalt composite oxide that is relatively easy to synthesize A lithium ion secondary battery using (LiCoO ₂ ) is expected to be a battery having a high energy density because a high voltage of 4V class is obtained, and its practical application is progressing. In the lithium ion secondary battery using the lithium cobalt composite oxide, many developments have been made so far to obtain excellent initial capacity characteristics and cycle characteristics, and various results have already been obtained. .

  However, since the lithium cobalt composite oxide uses an expensive cobalt compound as a main raw material, the cost of the active material and the battery is increased, and improvement of the active material is desired. The unit price per capacity of a battery using this lithium cobalt composite oxide is about four times as high as that of a nickel-metal hydride battery already used as a secondary battery. is there.

  Therefore, reducing the cost of active materials and making it possible to manufacture cheaper lithium ion secondary batteries is not only used for small secondary batteries for portable devices, but also for power storage and electric vehicles. It is possible to expand the application to large-sized secondary batteries such as, and this is industrially significant.

Here, as a new material of the positive electrode active material for the lithium ion secondary battery, lithium nickel composite oxide (LiNiO ₂ ) using nickel cheaper than cobalt can be given. Lithium nickel composite oxides can be expected to have higher capacity than lithium cobalt composite oxides, and because of the high battery voltage similar to lithium ion secondary batteries using lithium cobalt composite oxide as the positive electrode active material, It is actively performed.

  However, the lithium ion secondary battery using this lithium nickel composite oxide as the positive electrode active material has the following drawbacks. That is, when compared with a lithium ion secondary battery using a lithium cobalt composite oxide as a positive electrode active material, the cycle performance is inferior, and the battery performance is relatively impaired when used or stored in a high temperature environment. It had the disadvantage of being easy to get.

  Therefore, various proposals have been made for the lithium metal composite oxide with the aim of solving these drawbacks.

For example, in Japanese Patent Application Laid-Open No. 8-213015, Li _x Ni _a Co _b M _c O ₂ (provided that 0.8 ≦ x ≦ for the purpose of improving the self-discharge characteristics and cycle characteristics of a lithium ion secondary battery. 1.2, 0.01 ≦ a ≦ 0.99, 0.01 ≦ b ≦ 0.99, 0.01 ≦ c ≦ 0.3, 0.8 ≦ a + b + c ≦ 1.2, M is Al, V, Lithium metal composite oxides represented by at least one element selected from Mn, Fe, Cu and Zn have been proposed.

Japanese Patent Laid-Open No. 8-45509 discloses Li _w Ni _x Co _y B _z O ₂ (however, in the case of 0. 5) as a positive electrode active material capable of maintaining good battery performance during storage and use in a high temperature environment. 05 ≦ w ≦ 1.10, 0.5 ≦ x ≦ 0.995, 0.005 ≦ z ≦ 0.20, x + y + z = 1) and the like are proposed.

  The lithium metal composite oxides proposed in these publications have both higher charge capacity and higher discharge capacity than the lithium cobalt composite oxide, and improved cycle characteristics compared to the lithium nickel composite oxide. .

  However, these lithium metal composite oxides were not sufficient in output characteristics. This is mainly due to the low conductivity of the positive electrode active material and the insufficient diffusibility of Li. Therefore, when configuring the battery, the amount of the conductive material mixed with the positive electrode active material must be increased in order to ensure sufficient conductivity, and as a result, the capacity per unit mass and volume per unit of the battery is small. There was a problem of becoming.

Further, JP 2001-52704, the general formula _{Li w A v Q x Co y} O 2 ( where, A is a Ge, Y, Si, Zr, at least one or more selected from Ti, Q Is at least one selected from Ni, Mn, Fe, and Al, and w, v, x, and y are 0 ≦ w ≦ 1.2, 0.02 ≦ v ≦ 0.125, 0.01, respectively. ≦ x ≦ 0.175, 0.01x / y ≦ 0.25), and the composite oxide mainly has a hexagonal and / or monoclinic crystal structure. Moreover, a high-power capacity positive electrode material and a secondary battery are provided by having a mixed phase structure in which two or more types of phases having the same crystal form but having different lattice constants are in contact with each other across grain boundaries. It is described. However, the synthesis is complicated and it takes a long time to synthesize, and it is difficult to produce while maintaining the above structure, resulting in unstable performance.

Japanese Patent Laid-Open No. 2000-82466 achieves an optimal packing density of lithium metal composite oxide particles and is used in a state of close packing as a positive electrode active material. In order to improve battery performance as compared with the case where physical particles are used, the general formula Li _x M _{1 -y} N _y O _{2 -z} (wherein M represents Co, Ni or Mn, and N is M Represents one or more elements selected from the group consisting of different transition metal elements or elements having an atomic number of 11 or more, x represents a number in the range of 0.2 ≦ x ≦ 1.2, and y is Represents a number in the range of 0 ≦ y ≦ 0.5, and z represents a number in the range of 0 ≦ z ≦ 1.0), or the general formula Li _a Mn _2-b N _b O _4-c ( In the formula, N is as defined above, a represents a number in the range of 0 <a <2.0, and b represents a number in the range of 0 ≦ b ≦ 0.6. C represents a number in the range of 0 ≦ c ≦ 2.0), and the average particle size of the lithium composite oxide particles is 0.1 to There are two or more peaks in the particle size distribution of the lithium composite oxide particles within the range of 50 μm, specifically, the particles having the larger particle size and the smaller particle size. A positive electrode active material having a diameter ratio of 1.4 or more, or a lithium metal composite having a larger average particle diameter and having two different average particle diameters in the range of an average particle diameter of 0.1 to 50 μm A positive electrode active material has been proposed in which the compounding ratio of the oxide particles is 60 to 80% by mass and the compounding ratio of the lithium metal composite oxide particles having the smaller average particle diameter is 20 to 40% by mass.

  However, in this positive electrode active material, lithium composite oxide particles having a small average particle size are mixed in a large amount of 20 to 40% by mass, so that the specific surface area becomes too large and the tap density becomes too small, resulting in a unit volume. There was a drawback that the charge / discharge capacity of the hit battery decreased.

Japanese Patent Laid-Open No. 8-213015

JP-A-8-45509

JP 2001-52704 A

JP 2000-82466 A

  An object of the present invention is to provide a positive electrode active material for a non-aqueous electrolyte secondary battery that can be stably manufactured, and can reduce the internal resistance and increase the output of the battery, and a non-aqueous electrolyte secondary battery using the positive electrode as a positive electrode It is to provide.

In the present invention, the first invention is LiNi _1-X M _X O ₂ (where M is at least one selected from the group consisting of Co, Al, Mg, Mn, Ti, Fe, Cu, Zn, Ga) The metal element is a lithium metal composite oxide powder represented by 0 <x ≦ 0.25), and the powder is composed of primary particles of a lithium metal composite oxide and a plurality of the primary particles. The secondary particles are spherical or elliptical spherical, and the powder has a particle size of 40 μm or less, and the powder has a particle size of 1 μm or less of 0.5 to 0.5 μm. 7.0% by volume, and the specific surface area of the powder is 0.3 m ² / g larger than the specific surface area of the powder formed by removing particles having a particle diameter of 1 μm or less from the powder. The tap density is the same as that obtained by removing particles having a particle diameter of 1 μm or less from the powder. It is the most 0.2 g / cm ³ less than the tap density of the powder to provide a positive active material for non-aqueous electrolyte secondary battery, characterized.

In the present invention, the second invention is LiNi _1-X M _X O ₂ (where M is at least one selected from the group consisting of Co, Al, Mg, Mn, Ti, Fe, Cu, Zn, Ga) The metal element is a lithium metal composite oxide powder represented by 0 <x ≦ 0.25), and the powder is composed of primary particles of a lithium metal composite oxide and a plurality of the primary particles. The secondary particles are spherical or elliptical spherical, and the powder has a particle size of 40 μm or less, and the powder has a particle size of 1 μm or less of 0.5 to 0.5 μm. 7.0% by volume, and the specific surface area of the powder is 0.3 m ² / g larger than the specific surface area of the powder formed by removing particles having a particle diameter of 1 μm or less from the powder. The tap density is the same as that obtained by removing particles having a particle diameter of 1 μm or less from the powder. The non-aqueous electrolyte is characterized in that the powder has a specific resistance of 250 Ωcm or less when measured under a pressure of 100 kg / cm ^{2 at} a maximum of 0.2 g / cm ³ smaller than the tap density of the formed powder. A positive electrode active material for a secondary battery is provided.

  Furthermore, the present invention provides a non-aqueous electrolyte secondary battery comprising a positive electrode using the positive electrode active material for a non-aqueous electrolyte secondary battery.

  The positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention constitutes a positive electrode of a lithium ion secondary battery (non-aqueous electrolyte secondary battery), and the lithium ion secondary battery is charged and discharged. In the curve obtained by differentiating the capacity of the ion secondary battery with respect to the voltage, the voltage at the rising edge of the obtained first peak is 3.56 V or less and the voltage at the first peak position is 3.65 V or less.

Furthermore, the present invention relates to LiNi _1-X M _X O ₂ (where M is at least one metal element selected from the group consisting of Co, Al, Mg, Mn, Ti, Fe, Cu, Zn, and Ga). And satisfying 0 <x ≦ 0.25), and the particles constituting the powder were formed by aggregating a plurality of primary particles of the lithium metal composite oxide. Preparing a powder that is substantially composed of secondary particles, the shape of the secondary particles is spherical or oval, and the particle diameter of the particles constituting the powder is substantially within the range of 1 μm to 40 μm; By pulverizing the powder, particles having a particle diameter of 1 μm or less are prepared, and the particles having a particle diameter of 1 μm or less are mixed with the powder at a ratio of 0.5 to 7.0% by volume. Specific surface area before mixing of particles having a particle diameter of 1 μm or less Up to 0.3 m ² / g greater than the product, a non-aqueous system, characterized in that the tap density of the powder, reduce 0.2 g / cm ³ at maximum than the tap density before mixing of the particle size 1μm or less of the particles A method for producing a positive electrode active material for an electrolyte secondary battery is provided.

The positive electrode active material for a non-aqueous electrolyte secondary battery obtained by the present invention has a general formula: LiNi _1-X M _X O ₂ (where M is Co, Al, Mg, Mn, Ti, Fe, Cu, Zn, Ga At least one metal element selected from the group consisting of: lithium metal composite oxide powder represented by 0 <x ≦ 0.25), wherein the powder is a primary particle of the composite oxide And secondary particles in which a plurality of the primary particles are combined, and the shape of the secondary particles is spherical or elliptical. Moreover, this powder contains 0.5 volume%-7.0 volume% of fine powder of a lithium complex oxide of 1 micrometer or less. And the specific surface area of the said powder which comprises the positive electrode active material for non-aqueous electrolyte secondary batteries is 0.01 m < ² > /g-0.O from the specific surface area of the powder when the particle diameter is 1 micrometer or less. 3m ² / g increased and tap density is not at most than the tap density 0.2 g / cm ³ less when not contained the following particle diameter 1 [mu] m. As a result, when the whole of the powder constituting the positive electrode active material for the non-aqueous electrolyte secondary battery is pulverized, there is no inconvenience in production such as generation of dust, and capacity reduction due to a decrease in packing density. By increasing the contact area between the liquid and the positive electrode active material and increasing the number of places where Li ions diffuse, it is possible to provide a secondary battery capable of increasing the output.

  When a nonaqueous electrolyte secondary battery is used as a power source for a hybrid vehicle or an electric vehicle, output characteristics are particularly important.

  The charge / discharge reaction of the battery proceeds by reversibly entering and exiting Li ions in the positive electrode active material. Since Li ions enter and exit from the surface of the positive electrode active material through the electrolytic solution, the current density per unit area of the active material decreases as the specific surface area of the positive electrode active material increases with the same amount of current, and the diffusion of Li Works for you. Therefore, the positive electrode active material has a particle size as small as possible, a material with a large specific surface area is excellent in Li diffusibility, and a decrease in capacity when current density is increased (excellent load characteristics) is expected to improve output characteristics. it can. However, simply reducing the particle size of the positive electrode active material and making it fine powder causes inconveniences in production such as generation of dust, and also causes a decrease in packing density when it is used as an electrode. The capacity is reduced.

  As a result of repeated studies on positive electrode active materials synthesized by various methods, the present inventors have found the following.

(1) LiNi _1-X M _X O ₂ (where M is at least one metal element selected from the group consisting of Co, Al, Mg, Mn, Ti, Fe, Cu, Zn, Ga, 0 <X ≦ 0.25 is satisfied), the powder is conventionally formed by aggregating a plurality of primary particles of the lithium metal composite oxide. Secondary particles, the shape of the secondary particles is spherical or elliptical, the particle diameter of the powder is 40 μm or less, the average particle diameter is 5 to 11 μm, and the particle diameter is 1 μm or less (See the particle size distribution in FIG. 4).

(2) In addition to the powder composed of secondary particles having an average particle diameter of several μm that mainly constitute the positive electrode active material as described above, 0.5 to 7.0% by volume of complex oxide fine particles of 1 μm or less are allowed to exist. Thus, the specific surface area of the powder can be increased to improve the output characteristics, there is no inconvenience in handling, and the packing density is not significantly reduced. Composite oxide fine particles of 1 μm or less can be obtained, for example, by pulverizing the powder.

As a result of further research, the present inventors have measured the specific resistance of powder measured by applying a pressure of 100 kg / cm ² or more to the composite oxide, in which the optimum amount of composite oxide fine particles of 1 μm or less is measured. I found that it was relatively easy to estimate.

  That is, for example, the lithium metal composite oxide having a particle size of 40 μm or less, an average particle size of 5 to 11 μm, a normal particle size distribution, and substantially no amount of particles having a particle size of 1 μm or less. When the fine powder of lithium metal composite oxide of 1 μm or less is mixed in an amount of 0.5 to 7.0% by volume to increase the fine powder, the fine powder is filled between the particles, and per unit volume. It has been found that the number of grain boundaries present increases and the electrical resistance increases. Utilizing this, the fine powder content of the lithium metal composite oxide powder can be evaluated, and the optimum amount of mixed fine powder can reduce the internal resistance of the battery and increase the output without substantially reducing the powder filling rate. It has been found that a positive electrode active material for a non-aqueous electrolyte secondary battery can be obtained, and the present invention has been achieved.

That is, the positive electrode active material for a non-aqueous electrolyte secondary battery according to the first aspect of the present invention is LiNi _1-X M _X O ₂ (where M is Co, Al, Mg, Mn, Ti, Fe, Cu, At least one metal element selected from the group consisting of Zn and Ga, satisfying 0 <x ≦ 0.25), and the powder is lithium metal composite oxide A primary particle of the product and secondary particles formed by aggregating a plurality of the primary particles, the shape of the secondary particles is spherical or elliptical, and the particle diameter of the powder is 40 μm or less, The powder contains 0.5 to 7.0% by volume of particles having a particle size of 1 μm or less, and the specific surface area of the powder is the ratio of the powder constituted by excluding particles having a particle size of 1 μm or less from the powder. up to 0.3m ² / g larger than the surface area, the powder of the tap Once again, characterized in maximum by 0.2 g / cm ³ less than the tap density of the formed powder except for the following particle the particle size 1μm from powder.

The positive electrode active material for a non-aqueous electrolyte secondary battery according to the second invention of the present invention is LiNi _1-X M _X O ₂ (where M is Co, Al, Mg, Mn, Ti, Fe, Cu, Zn, At least one metal element selected from the group consisting of Ga and satisfying 0 <x ≦ 0.25), and the powder is made of a lithium metal composite oxide. A primary particle and secondary particles formed by aggregating a plurality of the primary particles, the shape of the secondary particles is spherical or elliptical, and the particle diameter of the powder is 40 μm or less, and the powder Contains 0.5 to 7.0% by volume of particles having a particle diameter of 1 μm or less, and the specific surface area of the powder is less than the specific surface area of the powder constituted by removing the particles having a particle diameter of 1 μm or less from the powder. up to 0.3 m ² / g greater, the tap density of the powder, said Up to 0.2 g / cm ³ less than the tap density of the powder made except for the following particle the particle size 1μm from end, and the powder specific resistance when measured under a pressure of 100kg / cm ² 250Ωcm It is characterized by the following.

  Furthermore, the present invention provides a non-aqueous electrolyte secondary battery comprising a positive electrode using the positive electrode active material for a non-aqueous electrolyte secondary battery.

The positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention constitutes a positive electrode of a lithium ion secondary battery (non-aqueous electrolyte secondary battery), and the charge / discharge of the lithium ion secondary battery is reduced to a current density of 0 for the positive electrode. In the curve obtained by differentiating the capacity of the lithium ion secondary battery with respect to the voltage when it is set at 0.5 mA / cm ² , the first peak rise voltage is 3.56 V or less, and the first peak A position voltage of 3.65 V or less is obtained.

Furthermore, the manufacturing method of the positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention is LiNi _1-X M _X O ₂ (where M is Co, Al, Mg, Mn, Ti, Fe, Cu, Zn, Ga). And at least one metal element selected from the group consisting of lithium metal composite oxide powders satisfying 0 <x ≦ 0.25, wherein the particles constituting the powder are lithium metal It is substantially composed of secondary particles formed by aggregating a plurality of primary particles of the composite oxide, the shape of the secondary particles is spherical or elliptical, and the particle diameter of the particles constituting the powder is substantially A powder in the range of 1 μm to 40 μm is prepared, and the powder is pulverized to prepare particles having a particle diameter of 1 μm or less. The particles having a particle diameter of 1 μm or less are added to the powder in an amount of 0.5 to 7.0 volumes. %, And thereby the specific surface area of the powder is The specific surface area before mixing of the particles having a particle diameter of 1 μm or less is 0.3 m ² / g at maximum, and the tap density of the powder is 0.2 g at most than the tap density before mixing of the particles having a particle diameter of 1 μm or less. Reduce / cm ³ .

  The non-aqueous electrolyte secondary battery, that is, the lithium ion secondary battery according to the present invention is composed of the same components as those of a general lithium ion secondary battery, such as a positive electrode, a negative electrode, and a non-aqueous electrolyte. Hereinafter, embodiments of the lithium ion secondary battery of the present invention will be described in detail for each of the items such as the positive electrode, the negative electrode, and other components.

1. The positive electrode active material for a non-aqueous electrolyte secondary battery according to the cathode active material present _{invention, LiNi 1-X M X O} 2 ( where, M is Co, Al, Mg, Mn, Ti, Fe, Cu, Zn, Ga, And at least one metal element selected from the group consisting of a powder of a lithium metal composite oxide represented by 0 <x ≦ 0.25, and the particles constituting the powder are composed of the composite oxide A plurality of primary particles of the product are aggregated to form secondary particles. The shape of the secondary particles is spherical or elliptical, and the particle diameter of the particles is 40 μm or less, and fine particles having a particle diameter of 1 μm or less are reduced to 0. The specific surface area increases up to 0.3 m ² / g with respect to the specific surface area of the powder when it is 5 to 7.0% by volume and does not contain fine particles having a particle diameter of 1 μm or less. For tap density when fine particles with a diameter of 1 μm or less are not contained, Wherein the reduction value of the density is 0.2 g / cm ³ at maximum.

  The particles constituting the powder of the positive electrode active material according to the present invention are mainly composed of secondary particles formed by aggregating a plurality of primary particles, and the particles are fine particles of 1 μm or less in an amount of 0.5 volume% to 7.0 volume%. By including, the contact area with the electrolytic solution increases, the instantaneous diffusion of Li ions between the powder and the electrolytic solution becomes faster, and the output characteristics can be improved.

  If the amount of fine particles is increased outside the above range, the specific surface area becomes too large, the tap density is decreased, and the charge / discharge capacity of the battery per unit volume is also not preferable. The fine particles having a particle diameter of 1 μm or less are typically obtained by pulverizing the positive electrode active material powder.

  The particle size distribution of the positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention (see FIG. 3) is essentially a single distribution, and there is no small particle size peak, or even if it exists, it is around 1 μm or less. It is small. Since there is no peak of a small particle size portion at a particle diameter larger than 1 μm, battery characteristics can be improved without greatly affecting the specific surface area and tap density.

  The specific surface area is measured by a specific surface area meter Kantasorb (manufactured by Yuasa Ionics Co., Ltd.), and the tap density is measured by JIS R 1628.

  When the additive element M is x> 0.25, not only a layered rock salt structure but also a second phase such as a spinel structure is formed, and a battery having good cycle characteristics cannot be formed.

  The additive element M is at least one metal element selected from the group consisting of Co, Al, Mg, Mn, Ti, Fe, Cu, Zn, and Ga.

Co and Mn mainly serve to stabilize the crystal structure of the lithium nickel composite oxide. By stabilizing the crystal structure, the cycle characteristics of the non-aqueous electrolyte secondary battery are kept good, and the deterioration of the battery capacity due to charging / discharging at high temperature and storage at high temperature is suppressed. In particular, Co has the advantage that the reduction in capacity due to element substitution is suppressed, and the resulting composite oxide Li (Co, Ni) O ₂ is completely solid solution type, so that the decrease in crystallinity is minimized. It is preferable to do this.

  Further, Al, Mg, Mn, Ti, Fe, Cu, Zn, and Ga mainly play a role of suppressing thermal decomposition due to oxygen release and improving thermal stability. Among these elements, it is more desirable to use Al. This is because Al has the advantage of minimizing capacity reduction while improving thermal stability.

The powder of the positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention has a specific resistance of 250 Ωcm or less measured by applying a pressure of 100 kg / cm ^{2 to} the lithium metal composite oxide powder. Is preferred.

LiNi _1-X M _X O ₂ (wherein M is a group consisting of Co, Al, Mg, Mn, Ti, Fe, Cu, Zn, Ga), which is a positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention In order to produce a lithium metal composite oxide represented by 0 <x ≦ 0.25 with at least one selected metal element, a lithium compound, a nickel compound, and an additive element compound are respectively provided. It is possible to synthesize by quantitative mixing and baking in an oxygen stream at a temperature of about 650 ° C. to 850 ° C. for about 20 hours.

  When the temperature is lower than 650 ° C., the reaction with the lithium compound does not proceed sufficiently, and it becomes difficult to synthesize a lithium nickel composite oxide having a desired layered structure. On the other hand, when the temperature exceeds 850 ° C., Ni is mixed into the Li layer and Li is mixed into the Ni layer, so that the layered structure is disturbed and the lithium seat occupation ratio at the 3a site is lowered.

  Accordingly, the disorder of the crystal structure can be reduced by setting the heat treatment temperature to 650 ° C. or more and 850 ° C. or less, and preferably the crystal structure with less disorder can be realized by setting the heat treatment temperature to 700 ° C. or more and 800 ° C. or less.

  As the lithium compound, lithium hydroxide, lithium carbonate and the like are preferable. As the nickel compound, nickel oxide, nickel carbonate, nickel nitrate, nickel hydroxide, nickel oxyhydroxide and the like can be used. As the additive element compound, an oxide, a carbonate or the like is used.

  In the lithium metal composite oxide powder of the present invention, it is preferable that a plurality of primary particles of the composite oxide are aggregated to form secondary particles, and the shape of the secondary particles is spherical or elliptical. In order to easily obtain such a particle shape, it is desirable to use nickel hydroxide among the above raw materials. There is a method in which nickel hydroxide is produced by a precipitation method and at the same time an additive is added as a precipitate. This coprecipitation method is preferable because the additive elements can be mixed uniformly. Further, the obtained hydroxide has a plurality of primary particles aggregated to form secondary particles, and the shape of the secondary particles is spherical or elliptical, and the hydroxide is used as a raw material to form a lithium metal composite. If an oxide is produced, the powder particles of the lithium metal composite oxide are formed by aggregating a plurality of primary particles of the composite oxide to form secondary particles, and the shape of the secondary particles is spherical or elliptical.

  The positive electrode is formed from a positive electrode mixture containing a positive electrode active material, a conductive material, and a binder. Specifically, a powdered positive electrode active material and a conductive material are mixed, a binder is added thereto, and if necessary, a solvent is added for the purpose of adjusting the viscosity to adjust the positive electrode mixture paste. By applying the material paste onto the surface of a current collector made of, for example, an aluminum foil, drying, and pressing as necessary, a sheet-like positive electrode can be produced.

  The conductive material is for securing the electrical conductivity of the positive electrode, and for example, a material obtained by mixing one or more carbon material powders such as carbon black, acetylene black, and graphite can be used. .

  The binder plays a role of anchoring the active material particles. For example, a fluorine-containing resin such as polytetrafluoroethylene, polyvinylidene fluoride, or fluororubber, or a thermoplastic resin such as polypropylene or polyethylene can be used. . An organic solvent such as N-methyl-2-pyrrolidone can be used as a solvent added to the positive electrode mixture as needed, that is, as a solvent for dispersing the active material and the conductive material and dissolving the binder.

  The above active material, conductive material, and binder are mixed, and if necessary, the above activated carbon and solvent are added and kneaded to prepare a positive electrode mixture paste. The respective mixing ratios in the positive electrode mixture are also important factors that determine the performance of the lithium secondary battery. When the total solid content (meaning excluding solvent) of the positive electrode mixture is 100% by mass, the active material is 60 to 95% by mass and the conductive material is 1 to 20 as in the case of the positive electrode of a general lithium secondary battery. The mass% and the binder are desirably 1 to 20 mass%.

  The positive electrode is, for example, applied to the surface of a metal foil current collector made of aluminum or the like, the above-mentioned positive electrode mixture paste sufficiently kneaded, dried to disperse the solvent, and then, if necessary, a roll to increase the electrode density By compressing with a press or the like, a sheet-like material can be formed. The sheet-like positive electrode can be cut into an appropriate size according to the intended battery and used for battery production.

2. Negative electrode For the negative electrode, metallic lithium, lithium alloy, etc. Also, a negative electrode mixture made by mixing a binder with a negative electrode active material capable of occluding and desorbing lithium ions, and adding a suitable solvent, is made of copper, etc. The metal foil current collector is coated, dried, and compressed as necessary to increase the electrode density. At this time, as the negative electrode active material, for example, a fired organic compound such as natural graphite, artificial graphite, or a 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 polyvinylidene fluoride is used as in the positive electrode, and an organic solvent such as N-methyl-2-pyrrolidone is used as a solvent for dispersing these active materials and the binder. be able to.

3. A separator is sandwiched and loaded between the positive electrode and the negative electrode of the separator. The separator separates the positive electrode and the negative electrode and retains the electrolyte, and a thin microporous film such as polyethylene or polypropylene can be used.

4). Nonaqueous electrolyte The nonaqueous electrolyte is obtained by dissolving a lithium salt as a supporting salt in an organic solvent. Examples of the organic solvent include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and trifluoropropylene carbonate; chain carbonates such as diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, and dipropyl carbonate; and tetrahydrofuran, 2- 1 type selected from ether compounds such as methyltetrahydrofuran and dimethoxyethane, sulfur compounds such as ethylmethylsulfone and butanesultone, phosphorus compounds such as triethyl phosphate, triethyl phosphate and trioctyl phosphate alone or in combination of 2 or more types It can be used by mixing.

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

  The lithium secondary battery of the present invention is configured as described above, and the shape thereof can be various, such as a cylindrical type and a laminated type. Even if any shape is adopted, the positive electrode and the negative electrode are laminated via a separator to form an electrode body, and between the positive electrode current collector and the negative electrode current collector to the positive electrode terminal and the negative electrode terminal, The battery can be completed by connecting with a current collecting lead or the like, impregnating the electrode body with the non-aqueous electrolyte, and sealing the battery case.

5). Non-aqueous electrolyte secondary battery The non-aqueous electrolyte secondary battery obtained by the above method includes a positive electrode using the positive electrode active material for the non-aqueous electrolyte secondary battery, and shows a charge curve when charging is performed. In the curve differentiated by voltage (dQ / dV curve), the voltage at the rising edge of the first peak obtained can be 3.56 V or less, and the voltage at the first peak position can be 3.65 V or less.

  This is due to the effect of the fine powder, that is, the particle diameter is 40 μm or less, and the powder having an average particle diameter of 5 to 11 μm (particle size distribution is a normal distribution), the fine powder of 1 μm or less is 0.5% by volume to 7%. 0.0 vol% means that the contact area between the electrolyte and the positive electrode active material is increased, and as a result, the overvoltage is lowered. When the Li diffusion barrier is increased, the overvoltage is increased and the output is reduced. turn into.

  The dQ / dV curve can be obtained by numerically differentiating the measured charge / discharge curve using a personal computer or the like, but the analysis software attached to the secondary battery charge / discharge tester (for example, BTS2000 manufactured by Nagano Co., Ltd.). It can also be calculated using a series).

6). The embodiments described above are merely examples, and the non-aqueous electrolyte secondary battery of the present invention is implemented in various modifications and improvements based on the knowledge of those skilled in the art including the above-described embodiments. can do.

  Moreover, the use of the nonaqueous electrolyte secondary battery of the present invention is not particularly limited.

  Utilizing the merit of the non-aqueous electrolyte secondary battery of the present invention, which has excellent output characteristics, makes it suitable for use as a power source for a device that receives a large amount of instantaneous energy and outputs a large amount of energy instantaneously. In other words, it is preferably used as a power source for applications that are charged with a large current from the start of charging and discharged with a large current from the start of discharging. Considering that a power source for an electric vehicle needs to regenerate a large amount of energy instantaneously, such as when decelerating, and that a large amount of power needs to be output at the time of start, sudden start, sudden acceleration, etc. The lithium secondary battery of the present invention is suitable as a power source for electric vehicles. The electric vehicle power source means not only an electric vehicle driven purely by electric energy but also a so-called hybrid car power source used in combination with a combustion engine such as a gasoline engine or a diesel engine. .

  Hereinafter, an embodiment according to the present invention will be described in detail with reference to the preferred drawings.

(Example 1)
In order to synthesize LiNi _0.82 Co _0.15 Al _0.03 O _{2 in} which 15 atomic% of Ni is substituted with Co and 3 atomic% with Al, a plurality of primary particles of 1 μm or less are aggregated to form spherical secondary particles. A metal composite hydroxide formed by solid solution with a molar ratio of cobalt and aluminum of 82: 15: 3 was prepared by coprecipitation.

  After weighing this metal composite hydroxide and commercially available lithium hydroxide monohydrate (manufactured by FMC) so that the molar ratio of lithium to metal is 1: 1, a mixer (Fuji Powder Co., Ltd.) The mixture was sufficiently mixed using a Spartan Luther manufactured and calcined at 350 ° C. for 2 hours in an oxygen atmosphere, then baked at 680 ° C. for 20 hours, and cooled to room temperature.

  When the obtained fired product was analyzed by X-ray diffraction, it was confirmed that it was a desired positive electrode active material having a hexagonal layered structure.

The obtained fired product had a particle size of 1.0 μm to 24.0 μm, and an average particle size of about 10.0 μm (A powder). This powder had a BET specific surface area of 0.50 m ² / g and a tap density of 2.5 g / cm ³ .

Part of the obtained positive electrode active material was pulverized with a pin mill (Coroplex 160Z manufactured by Sagano Sangyo Co., Ltd.) to 1 μm or less so that the fine powder (B powder) was 3.5 vol% in the positive electrode active material. Mixed with A powder. The BET specific surface area of the obtained mixed powder was 0.61 m ² / g, which was 0.10 m ² / g larger than that of the A powder.

The tap density was 2.5 g / cm ³ . Furthermore, the specific resistance of the obtained positive electrode active material was measured. The measurement was performed using a cylindrical plastic with two convex copper jigs formed in a center of a plate having a diameter of 15 mm and a height of 15 mm and a plate having a diameter of 50 mm and a thickness of 3 mm and a hole having a diameter of 15 mm. A plastic tube was placed on one jig, 1 g of the positive electrode active material was put therein, another jig was put on the top, and the positive electrode active material was sandwiched from above and below by the jig. In this state, the resistance of the positive electrode active material when a pressure of 100 kg / cm ² was applied was measured by connecting terminals to the upper and lower jigs. Further, when pressure was applied, the thickness of the positive electrode active material was measured using calipers, and the specific resistance was calculated using the following formula.

Formula 1

  Here, A represents the specific resistance (Ωcm), X represents the resistance value (Ω), and L represents the thickness (cm) of the powder when pressure is applied.

  Table 1 shows the average value of the results of three measurements. Table 1 shows the results of measurement of the specific surface area and tap density of the same positive electrode active material sample.

Next, the battery characteristics evaluation by the active material was performed as follows. 90% by mass of the active material powder obtained above was mixed with 5% by mass of acetylene black and 5% by mass of PVDF (polyvinylidene fluoride), and NMP (n-methylpyrrolidone) was added to make a paste. This paste was applied to an aluminum foil having a thickness of 20 μm so that the mass of the active material after drying was 0.05 g / cm ² , vacuum-dried at 120 ° C., and punched into a disk shape having a diameter of 1 cm to obtain a positive electrode. . The above operation was performed in the atmosphere except for vacuum drying.

A mixed solution of equal amounts of ethylene carbonate (EC) and diethyl carbonate (DEC) using Li metal as the negative electrode and 1M LiClO ₄ as the supporting salt was used as the electrolyte. A 2032 type coin battery as shown in FIG. 1 was produced in an Ar atmosphere glove box whose dew point was controlled at −80 ° C.

The produced battery was allowed to stand for about 24 hours, and after the OCV was stabilized, the current density with respect to the positive electrode was set to 0.5 mA / cm ² and charge / discharge was performed in the range of a cutoff voltage of 3.0 to 4.3 V. The charge / discharge curve was differentiated by potential to obtain a dQ / dV curve. The obtained dQ / dV curve is shown in FIG.

(Example 2)
In the same manner as in Example 1, LiNi _0.82 Co _0.15 Al _0.03 O ₂ was synthesized. It was confirmed that the obtained fired product was a desired positive electrode active material having a hexagonal layered structure. A part of the fired product is pulverized to a fine powder of 1 μm or less, and the fine powder is mixed so that the content ratio of the powder of 1 μm or less is 0.5% by volume. The results of measuring the surface area and tap density are shown in Table 1, and the dQ / dV curve is shown in FIG.

(Example 3)
In the same manner as in Example 1, LiNi _0.82 Co _0.15 Al _0.03 O ₂ was synthesized, and the obtained fired product was confirmed to be a desired positive electrode active material having a hexagonal layered structure. The results of measuring the specific resistance, specific surface area, and tap density in the same manner as in Example 1 were mixed with fine powder so that the content of powder of 1 μm or less was 7.0% by volume, and the dQ / dV curve is shown in Table 1. Is shown in FIG.

(Comparative Example 1)
In the same manner as in Example 1, LiNi _0.82 Co _0.15 Al _0.03 O ₂ was synthesized. As in Example 1, the obtained fired product had a particle size of 1.0 μm to 24.0 μm, and an average particle size of about 10.0 μm. This powder had a BET specific surface area of 0.51 m ² / g and a tap density of 2.5 g / cm ³ . It was confirmed that the fired product obtained by firing in the same manner as in Example 1 was a desired positive electrode active material having a hexagonal layered structure.

  The obtained fired product was used as it was, that is, the fine powder amount was 0.0% by volume, and the results of specific resistance, specific surface area and tap density measured by the same method as in Example 1 are shown in Table 1, dQ / dV curve Is shown in FIG.

(Comparative Example 2)
LiNi _0.82 Co _0.15 Al _0.03 O ₂ was synthesized in the same manner as in Example 1. It was confirmed that the obtained fired product was a desired positive electrode active material having a hexagonal layered structure. Table 1 shows the results of specific resistance, specific surface area, and tap density measured in the same manner as in Example 1 with the addition of 8.0% by volume of fine powder to the fired product, and the dQ / dV curve Shown in 2 (b).

(Comparative Example 3)
LiNi _0.82 Co _0.15 Al _0.03 O ₂ was synthesized in the same manner as in Example 1. It was confirmed that the obtained fired product was a desired positive electrode active material having a hexagonal layered structure. Table 1 shows the results of specific resistance, specific surface area, and tap density measured in the same manner as in Example 1 with 50% by volume of fine powder added to the fired product, and the dQ / dV curve is shown in FIG. Shown in b).

"Evaluation"
From Table 1, it can be seen that the specific resistance value increases as the amount of fine powder increases. Further, the tap density representing the particle packing density is hardly changed by the increase in the specific resistance, and the packing density is not changed. On the other hand, when the fine powder of Comparative Example 3 is 50% by volume, the grain boundary increases due to the fine powder. The specific resistance value is increased, and the tap density indicating the packing density is considerably reduced to 1.5 g / cm ^2, which is not preferable because the amount of the positive electrode active material packed in the unit volume is reduced.

  In Comparative Example 1, since there is no fine powder, the grain boundary is small and the specific resistance is small. However, as apparent from the dQ / dV curve of FIG. 2A, the dQ / dV curves of the positive electrode active materials of Examples 1 to 3 and Comparative Examples 2 to 3 shown in FIG. Whereas the peak rising voltage is 3.55 V or less and the first peak position is 3.65 V or less, in the case of the positive electrode active material of Comparative Example 1 having no fine powder, the first peak rising voltage is 3 .57V and 3.56V or more, and the first peak position is 3.7V and 3.65V or more.

  That is, it can be seen that as the fine powder content increases, the contact area between the electrolyte and the powder increases, and the rising voltage of the first peak and the voltage at the first peak position decrease.

Further, it has been found that when the rising voltage of the first peak is 3.55 V or less and the voltage at the position of the first peak is 3.65 V or less, output characteristics that are not practically problematic can be obtained. From the above, by mixing 0.5 to 7.0% by volume of fine powder, the specific surface area can be increased without lowering the packing density, and the output characteristics of the battery can be increased. It turns out that it can evaluate by using a specific resistance value.

It is sectional drawing of the coin battery which was in battery evaluation. (A) dQ / dV curve of an Example and (b) dQ / dV curve of a comparative example. It is a graph which shows the particle size distribution of the powder of the positive electrode active material for non-aqueous electrolyte secondary batteries by one Example of this invention. It is a graph which shows the particle size distribution of the powder of the conventional positive electrode active material for non-aqueous electrolyte secondary batteries.

Explanation of symbols

1 Lithium metal negative electrode 2 Separator (electrolyte impregnation)
3 Positive electrode (Evaluation electrode)
4 Gasket 5 Negative electrode can 6 Positive electrode can 7 Current collector

Claims (6)

LiNi _1-X M _X O ₂ (where M is at least one metal element selected from the group consisting of Co, Al, Mg, Mn, Ti, Fe, Cu, Zn, Ga, and 0 <x ≦ The particles constituting the powder are mainly composed of secondary particles formed by aggregating a plurality of primary particles of the lithium metal composite oxide. The shape of the secondary particles is spherical or oval, the particle diameter of the particles constituting the powder is 40 μm or less, and the powder is 0.5 to 7.0% by volume of particles having a particle diameter of 1 μm or less. And the specific surface area of the powder is 0.3 m ² / g larger than the specific surface area of the powder formed by removing particles having a particle diameter of 1 μm or less from the powder, and the tap density of the powder is The particles having a particle diameter of 1 μm or less are removed from the powder. The positive electrode active material for a non-aqueous electrolyte secondary battery comprising up by 0.2 g / cm ³ less than the tap density of the powder is. LiNi _1-X M _X O ₂ (where M is at least one metal element selected from the group consisting of Co, Al, Mg, Mn, Ti, Fe, Cu, Zn, Ga, and 0 <x ≦ The particles constituting the powder are mainly composed of secondary particles formed by aggregating a plurality of primary particles of the lithium metal composite oxide. The shape of the secondary particles is spherical or oval, the particle diameter of the particles constituting the powder is 40 μm or less, and the powder is 0.5 to 7.0% by volume of particles having a particle diameter of 1 μm or less. And the specific surface area of the powder is 0.3 m ² / g larger than the specific surface area of the powder formed by removing particles having a particle diameter of 1 μm or less from the powder, and the tap density of the powder is The particles having a particle diameter of 1 μm or less are removed from the powder. A maximum than the tap density of the powder 0.2 g / cm ³ less to be, and non-aqueous electrolyte secondary specific resistance of the powder is equal to or less than 250Ωcm when measured under a pressure of 100 kg / cm ² Positive electrode active material for batteries. The positive electrode of a lithium ion secondary battery is configured, and the capacity of the lithium ion secondary battery is measured by voltage when charging and discharging the lithium ion secondary battery at a current density of 0.5 mA / cm ² with respect to the positive electrode. 3. The curve obtained by differentiating, wherein the obtained first peak rising voltage is 3.56 V or less and the first peak position voltage is 3.65 V or less. The positive electrode active material for non-aqueous electrolyte secondary batteries. A non-aqueous electrolyte secondary battery comprising a positive electrode using the positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1. A non-aqueous electrolyte secondary battery using the positive electrode active material according to any one of claims 1 and 2 for a positive electrode, wherein a curve obtained by differentiating the capacity when performing charge and discharge with voltage, A nonaqueous electrolyte secondary battery, wherein the obtained first peak rising voltage is 3.56 V or less and the first peak position voltage is 3.65 V or less. LiNi _1-X M _X O ₂ (where M is at least one metal element selected from the group consisting of Co, Al, Mg, Mn, Ti, Fe, Cu, Zn, Ga, and 0 <x ≦ 0.25 satisfying 0.25), and the particles constituting the powder are substantially composed of secondary particles formed by aggregating a plurality of primary particles of the lithium metal composite oxide. And preparing a powder in which the shape of the secondary particles is spherical or elliptical and the particle diameter of the particles constituting the powder is substantially within the range of 1 μm to 40 μm, and pulverizing the powder To prepare particles having a particle size of 1 μm or less, and mixing the particles having a particle size of 1 μm or less with respect to the powder in a proportion of 0.5 to 7.0% by volume. 0 maximum from the specific surface area before mixing of particles with a diameter of 1 μm or less 3m ² / g greater, the tap density of the powder, a positive electrode for a nonaqueous electrolyte secondary battery, which comprises up to 0.2 g / cm ³ less than the tap density before mixing of the particle size 1μm or less of the particles The manufacturing method of the active material.

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