JP5332121B2 - Positive electrode active material powder - Google Patents

Description

  The present invention relates to a positive electrode active material powder. More specifically, the present invention relates to a positive electrode active material powder used for a non-aqueous electrolyte secondary battery.

  The positive electrode active material powder is used in non-aqueous electrolyte secondary batteries such as lithium secondary batteries. Non-aqueous electrolyte secondary batteries have already been put to practical use as power sources for mobile phones and notebook computers, and are also being applied to medium and large applications such as automobiles and power storage.

  As a conventional positive electrode active material powder, Patent Document 1 discloses a powder having an average primary particle diameter of 0.54 μm to 2.02 μm and an average secondary particle diameter of 3.6 μm to 10 μm, and Patent Document 2 discloses an average primary particle. Specifically, powders each having a diameter of 0.17 μm to 0.7 μm and a median diameter of secondary particles of 6 to 12 μm are described.

JP-A-6-325791 Japanese Patent Laid-Open No. 2005-141983

  However, the non-aqueous electrolyte secondary battery obtained by using the conventional positive electrode active material powder has few problems with respect to the discharge capacity, but is used for applications that require high output at a high current rate, that is, automotive applications, electric tools, etc. It is not sufficient for power tool applications. An object of the present invention is to provide a positive electrode active material powder useful for a non-aqueous electrolyte secondary battery that exhibits a high discharge capacity and can exhibit a high output at a high current rate.

  As a result of various studies in view of the above circumstances, the present inventors have shown that a nonaqueous electrolyte secondary battery obtained by using a specific positive electrode active material powder exhibits a high discharge capacity and a high output at a high current rate. The present invention has been found to be possible.

That is, this invention is comprised from the following invention.
<1> A positive electrode active material powder composed of primary particles and agglomerated particles of primary particles, wherein the primary particles and the agglomerated particles of the primary particles in the powder have a volume-based average particle size of 0.1 μm or more and 3 μm or less. The percentage of the sum of the volume of particles having a particle size of 5 μm or more] / [the sum of the volumes of all particles] is 10% or less, and the BET specific surface area of the powder is more than 2 m ² / g and not more than 7 m ² / g Active material powder.
<2> The positive electrode active material powder according to <1>, wherein the composition of the positive electrode active material is represented by the formula (1).
Li _x1 Ni _1-y1 M ¹ _y1 O ₂ (1)
(In formula (1), x1 and y1 are 0.9 ≦ x1 ≦ 1.2 and 0 ≦ y1 ≦ 0.5, respectively, and M ¹ is Co.)
<3> The positive electrode active material powder according to <1>, wherein the composition of the positive electrode active material is represented by the formula (2).
Li _x2 Ni _1-y2 M ² _y2 O ₂ (2)
(In the formula (2), x2 and y2 are 0.9 ≦ x2 ≦ 1.2 and 0.3 ≦ y2 ≦ 0.9, respectively, and M ² is Co and Mn.)
<4> A positive electrode for a non-aqueous electrolyte secondary battery comprising the positive electrode active material powder according to any one of <1> to <3>.
<5> The positive electrode for a nonaqueous electrolyte secondary battery according to <4>, which has a conductive material.
<6> The positive electrode for a nonaqueous electrolyte secondary battery according to <5>, wherein the conductive material contains a fibrous carbon material.
<7> A nonaqueous electrolyte secondary battery comprising the positive electrode for a nonaqueous electrolyte secondary battery according to any one of <4> to <6>.

  When the positive electrode active material powder of the present invention is used in a non-aqueous electrolyte secondary battery, it exhibits a high discharge capacity and a high output at a high current rate. Therefore, the positive electrode active material powder of the present invention is a non-aqueous electrolyte secondary battery. It can be used for batteries, especially for non-aqueous electrolyte secondary batteries for applications requiring high output at high current rates, that is, for power tools such as automobiles and power tools. The present invention is extremely useful industrially.

The positive electrode active material powder of the present invention is a positive electrode active material powder comprising primary particles and aggregated particles of primary particles, and the volume-based average particle size of the primary particles and aggregated particles of the primary particles in the powder is 0.1 μm or more. The percentage of [sum of the volume of particles having a particle size of 5 μm or more] / [sum of the volume of all particles] is 10% or less, and the BET specific surface area of the powder exceeds 2 m ² / g and is 7 m ^2. / G or less.

  In the present invention, the volume-based average particle size of the primary particles and the aggregated particles of the primary particles in the positive electrode active material powder is the cumulative particle size distribution of the aggregated particles obtained by aggregating the primary particles and the primary particles. It means the particle size (D50) seen from the fine particle side when 50% is accumulated, and the value of D50 is used as a value measured by a laser diffraction scattering method particle size distribution measuring apparatus. In the positive electrode active material powder of the present invention, primary particles and agglomerated particles of the primary particles are mixed. Therefore, when the particle size of the positive electrode active material powder is measured using a laser diffraction scattering method particle size distribution measuring device, The particle sizes of the aggregated particles of the particles and the primary particles are summed and measured, and an average value of the particle sizes is obtained as a value (D50). Further, in the present invention, the non-aqueous electrolyte secondary battery can exhibit high discharge capacity and high output at a high current rate by setting the average particle size to 0.1 μm or more and 3 μm or less. Positive electrode active material powder for use. The average particle size is preferably 0.1 μm or more and 2 μm or less, more preferably 0.1 μm or more and 1.5 μm or less. By setting the average particle size in the above range, a positive electrode active material powder for a nonaqueous electrolyte secondary battery exhibiting a higher discharge capacity can be obtained. On the other hand, if the average particle size is less than 0.1 μm, the compatibility between the positive electrode active material powder and the conductive material and binder described later is not good, and the binding property between the positive electrode current collector described later decreases, resulting in In addition, the discharge capacity and cycle performance of the nonaqueous electrolyte secondary battery are undesirably reduced. On the other hand, when the average particle size exceeds 3 μm, it is not preferable because the obtained nonaqueous electrolyte secondary battery does not sufficiently exhibit high output at a high current rate.

  In the present invention, the [sum of the volume of particles having a particle diameter of 5 μm or more] / [sum of the volume of all particles] is 10% or less, preferably 7% or less, more preferably 5% or less. Here, as the percentage, a value measured by a laser diffraction / scattering particle size distribution measuring apparatus similar to the above is used. Here, the particles refer to primary particles and aggregated particles of primary particles. When the percentage exceeds 10%, it is not preferable because the obtained nonaqueous electrolyte secondary battery is not sufficient to exhibit high output at a high current rate. Further, by reducing the percentage to 7% or less and 5% or less, a higher output non-aqueous electrolyte secondary battery tends to be obtained.

In the present invention, the BET specific surface area of the powder is more than 2 m ² / g and 7 m ² / g or less. By setting the BET specific surface area of the powder within the above range, a positive electrode active material powder for a non-aqueous electrolyte secondary battery that exhibits a high discharge capacity and can exhibit a high output at a high current rate is obtained. it can. Furthermore, the BET specific surface area of the powder is preferably 2.5 m ² / g or more and 7 m ² / g or less, more preferably 3 m ² / g, in order to obtain a nonaqueous electrolyte secondary battery exhibiting high discharge capacity and high output. This is 4 m ² / g or less. If the BET specific surface area of the powder is 2.0 m ² / g or less, it is not preferable in terms of the discharge capacity of the nonaqueous electrolyte secondary battery, and if it exceeds 7 m ² / g, the storage characteristics of the powder and the connection with the positive electrode current collector are not preferable. It is not preferable in terms of operability such as wearability.

  Moreover, as a composition of the positive electrode active material powder of this invention, the following representative compositions, ie, the composition represented by Formula (1), the composition represented by Formula (2), can be mentioned.

Li _x1 Ni _1-y1 M ¹ _y1 O ₂ (1)
(In formula (1), x1 and y1 are 0.9 ≦ x1 ≦ 1.2 and 0 ≦ y1 ≦ 0.5, respectively, and M ¹ is Co.)
Here, in order to increase the discharge capacity, x1 is preferably 1.0 or more and 1.1 or less, and more preferably 1.0 or more and 1.05 or less. In the same meaning, y1 is preferably 0.05 or more and 0.3 or less, more preferably 0.1 or more and 0.2 or less.

Li _x2 Ni _1-y2 M ² _y2 O ₂ (2)
(In the formula (2), x2 and y2 are 0.9 ≦ x2 ≦ 1.2 and 0.3 ≦ y2 ≦ 0.9, respectively, and M ² is Co and Mn.)
Here, in order to increase the discharge capacity, x2 is preferably 1.0 or more and 1.1 or less, and more preferably 1.0 or more and 1.05 or less. In the same meaning, y2 is preferably 0.4 or more and 0.8 or less, and more preferably 0.5 or more and 0.7 or less. M ² is preferably in the range of 50:50 to 20:80, more preferably in the range of 40:60 to 30:70, in terms of molar ratio of Co: Mn.

Further, a part of the elements of M ¹ and M ² may be B, Al, Ga, In, Si, Ge, Sn, Mg, Sc, Y, Ti, Zr, and Hf within a range not impairing the effects of the present invention. V, Nb, Ta, Cr, Mo, W, Tc, Fe, Ru, Rh, Ir, Pd, Cu, Ag, Zn, and the like may be substituted.

In addition, regarding the positive electrode active material powder of the present invention, the crystal structure specified by powder X-ray diffraction measurement is usually a NaFeO ₂ type crystal structure.

  Further, with the positive electrode active material powder of the present invention as a core material, the surface of the particles further contains one or more elements selected from B, Al, Ga, In, Si, Ge, Sn, Mg and transition metal elements You may make it adhere with the compound to do. Among the above elements, one or more selected from B, Al, Mg, Co, Cr, Mn and Fe are preferable, and Al is more preferable from the viewpoint of operability. Examples of the compound include oxides, hydroxides, oxyhydroxides, carbonates, nitrates, organic acid salts, and mixtures of the above elements. Of these, oxides, hydroxides, oxyhydroxides, carbonates or mixtures thereof are preferred. In addition, in the case of heat treatment after the above-described deposition treatment, the BET specific surface area of the powder after the deposition heat treatment is equal to the BET specific surface area of the positive electrode active material powder of the present invention, although it depends on the temperature of the heat treatment. In some cases, the range of the BET specific surface area of the positive electrode active material powder in the present invention is that before deposition.

Next, a method for producing the positive electrode active material powder of the present invention will be described.
The positive electrode active material powder of this invention can be manufactured by baking the metal compound mixture which can become the positive electrode active material powder of this invention by baking. That is, a compound containing a corresponding metal element is weighed so as to have a predetermined composition and can be produced by firing a metal compound mixture obtained after mixing. For example, a composite oxide represented by Li _1.08 [Ni _0.35 Mn _0.44 Co _0.21 ] O ₂ , which is one of the preferred compositions, includes lithium hydroxide, dinickel trioxide, manganese carbonate, and cobalt oxide in Li: Ni: Mn. : Co can be obtained by firing the metal compound mixture obtained by weighing and mixing so that the molar ratio of Co is 1.08: 0.35: 0.44: 0.21.

  As the compound containing the metal element, for example, a compound containing a metal element of Li, Al, Ni, Mn, Co, Fe, an oxide is used, or hydroxide, oxyhydroxide, carbonic acid is used. A salt, nitrate, acetate, halide, oxalate, alkoxide, or the like that can be decomposed and / or oxidized to form an oxide at a high temperature can be used. Among these, a hydroxide and / or carbonate is preferable as the compound containing Li, a hydroxide and / or oxide is preferable as the compound containing Al, and a hydroxide is used as the compound containing Ni. And / or oxides are preferred, carbonates and / or oxides are preferred as compounds containing Mn, oxides and / or hydroxides are preferred as compounds containing Co, and compounds containing Fe are preferred as compounds containing Fe Hydroxides and / or oxides are preferred. Moreover, you may use the composite compound containing 2 or more types of said metal element as a compound containing a metal element.

  In order to increase the crystallinity of the positive electrode active material powder, the metal compound mixture before firing may further contain a compound containing boron. The content of the boron-containing compound may be usually 0.00001 mol% or more and 5 mol% or less in terms of boron with respect to the total mol of the metal element excluding lithium in the metal compound mixture. . Preferably, it is 0.0001 mol% or more and 3 mol% or less in terms of boron. Examples of the compound containing boron include boron oxide and boric acid, and boric acid is preferable. The boron further contained in the metal compound mixture here may remain in the fired positive electrode active material powder of the present invention, or may be removed by washing, evaporation or the like.

  The compound containing the metal element may be mixed by either dry mixing or wet mixing, but simpler dry mixing is preferable, and examples of the dry mixing apparatus include a V-type mixer, a W-type mixer, and a ribbon mixer. , Drum mixer, dry ball mill and the like.

  In addition, from the viewpoint of promoting the solid phase reaction during firing, the volume-based average particle diameter of the metal compound mixture is preferably a value in the range of 1 μm to 20 μm. Here, the volume-based average particle diameter of the metal compound mixture is measured by the same laser diffraction scattering method particle size distribution measuring apparatus as described above.

  After the metal compound mixture is compression-molded as necessary, a fired product is obtained by, for example, holding and firing in a temperature range of 700 ° C. or more and 1200 ° C. or less for 2 to 30 hours. In firing, it is preferable to rapidly reach the holding temperature as long as the firing vessel containing the metal compound mixture is not damaged. As the firing atmosphere, although depending on the composition, air, oxygen, nitrogen, argon, or a mixed gas thereof can be used, but an atmosphere containing oxygen is preferable.

  Next, the fired product can be pulverized using a pulverizer to obtain the positive electrode active material powder of the present invention. From the viewpoint of setting the percentage of [sum of volume of particles having a particle diameter of 5 μm or more] / [sum of volumes of all particles] in the present invention to 10% or less, it is preferable to use a jet mill as the pulverizer. In the case of a jet mill, since the particles constituting the fired product are accelerated by a jet stream and pulverized by collision between particles, there is little distortion of the crystal structure due to collision, and pulverization is easy in a short time. Generation of particles other than the intended purpose can be suppressed. In place of the jet mill, pulverization may be performed using a vibration mill or a dry ball mill. However, in that case, the process may be complicated, for example, requiring an air classification operation. Moreover, it is more preferable to use a fluidized bed jet mill with a built-in classifier as the jet mill. Examples of the jet mill include a counter jet mill (manufactured by Hosokawa Micron Corporation, product name).

  Next, a method for producing a positive electrode for a non-aqueous electrolyte secondary battery having the positive electrode active material powder of the present invention will be described. The positive electrode can be produced by supporting a positive electrode mixture containing the positive electrode active material powder of the present invention, a conductive material and a binder on a positive electrode current collector, and the positive electrode for a non-aqueous electrolyte secondary battery has a conductive material.

  A carbonaceous material can be used as the conductive material, and examples of the carbonaceous material include graphite powder, carbon black, acetylene black, and fibrous carbon material. Since carbon black and acetylene black are fine particles and have a large surface area, adding a small amount to the positive electrode mixture can increase the conductivity inside the positive electrode and improve the charge / discharge efficiency and rate characteristics. This decreases the binding property between the positive electrode mixture and the positive electrode current collector by the binder, and causes an increase in internal resistance. Usually, the ratio of the conductive material in the positive electrode mixture is 5 parts by weight or more and 20 parts by weight or less with respect to 100 parts by weight of the positive electrode active material powder. When a fibrous carbon material is used as the conductive material, this ratio can be lowered.

In order to further increase the conductivity of the positive electrode for a nonaqueous electrolyte secondary battery, the conductive material preferably contains a fibrous carbon material. When the fibrous carbon material is contained, a / b is usually 20 to 1000, where a is the length of the fibrous carbon material and b is the diameter of the cross section perpendicular to the length direction of the material. Further, when the length of the fibrous carbon material is a and the volume-based average particle diameter (D50) of the primary particles and the aggregated particles of the primary particles in the positive electrode active material powder of the present invention is c, the value of a / c is , Usually 2-10, preferably 2-5. When a / c is less than 2, conductivity between particles in the positive electrode active material powder may not be sufficient, and when it exceeds 10, the binding property between the positive electrode mixture and the positive electrode current collector is lowered. There is a case. Moreover, in the fibrous carbon material, it is better that the electric conductivity is high. The electrical conductivity of the fibrous carbon material is measured on a sample obtained by molding the fibrous carbon material so as to have a density of 1.0 to 1.5 g / cm ^{3. In} this case, the electrical conductivity is usually 1 S / cm. It is above, Preferably it is 2 S / cm or more.

  Specific examples of the fibrous carbon material include graphitized carbon fiber and carbon nanotube. The carbon nanotube may be either a single wall or a multi-wall. As the fibrous carbon material, a commercially available material may be pulverized and prepared so as to be in the range of the above a / b and a / c. The pulverization may be either dry or wet. Examples of the dry pulverization include pulverization using a ball mill, a rocking mill, and a planetary ball mill. Examples of the wet pulverization include pulverization using a ball mill and a disperser. Examples of the disperser include Dispermat (product name, manufactured by Eiko Seiki Co., Ltd.).

  In the positive electrode for a non-aqueous electrolyte secondary battery of the present invention, when a fibrous carbon material is used, the proportion of the fibrous carbon material is based on 100 parts by weight of the positive electrode active material powder in order to further increase the conductivity of the positive electrode. It is preferable that it is 0.1 to 10 weight part. Further, as the conductive material, a fibrous carbon material and other carbonaceous materials (graphite powder, carbon black, acetylene black, etc.) may be used in combination. In this case, the other carbonaceous material is preferably spherical and fine. When other carbonaceous materials are used in combination, the proportion of the material is 0.1 to 10 parts by weight with respect to 100 parts by weight of the positive electrode active material powder.

  As the binder, a thermoplastic resin can be used. Specifically, polyvinylidene fluoride (hereinafter sometimes referred to as PVDF), polytetrafluoroethylene (hereinafter sometimes referred to as PTFE), and four fluorine. Fluoropolymers such as fluorinated ethylene / hexafluoropropylene / vinylidene fluoride copolymers, propylene hexafluoride / vinylidene fluoride copolymers, tetrafluoroethylene / perfluorovinyl ether copolymers, polyethylene, polypropylene, etc. Polyolefin resin and the like. Moreover, you may mix and use these 2 or more types.

  Further, by using a fluororesin and a polyolefin resin as a binder, the ratio of the fluororesin to the positive electrode mixture is 1 to 10% by weight, and the ratio of the polyolefin resin is 0.1 to 2% by weight, It is preferable because a positive electrode mixture having excellent binding properties with the positive electrode current collector can be obtained.

  As the positive electrode current collector, Al, Ni, stainless steel or the like can be used, but Al is preferable in that it is easily processed into a thin film and is inexpensive. As a method of supporting the positive electrode mixture on the positive electrode current collector, there is a method of pressure molding, or a method of pasting using an organic solvent or the like, applying onto the positive electrode current collector, drying and pressing to fix the positive electrode current collector. Can be mentioned. When making a paste, a slurry composed of a positive electrode active material, a conductive material, a binder, and an organic solvent is prepared. Examples of the organic solvent include amine solvents such as N, N-dimethylaminopropylamine and diethylenetriamine, ether solvents such as tetrahydrofuran, ketone solvents such as methyl ethyl ketone, ester solvents such as methyl acetate, dimethylacetamide, 1-methyl- Examples include amide solvents such as 2-pyrrolidone.

  Examples of the method for applying the positive electrode mixture to the positive electrode current collector include a slit die coating method, a screen coating method, a curtain coating method, a knife coating method, a gravure coating method, and an electrostatic spray method. By the method mentioned above, the positive electrode for nonaqueous electrolyte secondary batteries in this invention can be manufactured.

Next, a non-aqueous electrolyte secondary battery having the positive electrode for a non-aqueous electrolyte secondary battery of the present invention will be described using a lithium secondary battery as an example of the battery.
A lithium secondary battery is a separator, a negative electrode in which a negative electrode mixture is supported on a negative electrode current collector, and an electrode group obtained by laminating and winding the above positive electrode in a battery can, It can be produced by impregnating an electrolytic solution composed of an organic solvent containing an electrolyte.

  As the shape of the electrode group, for example, a shape in which the cross section when the electrode group is cut in a direction perpendicular to the winding axis is a circle, an ellipse, a rectangle, a rectangle with rounded corners, etc. Can be mentioned. In addition, examples of the shape of the battery include a paper shape, a coin shape, a cylindrical shape, and a square shape.

As the negative electrode, a negative electrode mixture containing a material capable of doping and dedoping lithium ions supported on a negative electrode current collector, lithium metal or lithium alloy, etc. can be used, and lithium ions can be doped and dedoped. Specific examples of such materials include carbonaceous materials such as natural graphite, artificial graphite, cokes, carbon black, pyrolytic carbons, carbon fibers, and fired organic polymer compounds, and have a lower potential than the positive electrode. It is also possible to use chalcogen compounds such as oxides and sulfides that can be doped and dedoped with lithium ions. As the carbonaceous material, a carbonaceous material mainly composed of graphite such as natural graphite or artificial graphite is preferable because of high potential flatness and low average discharge potential. The shape of the carbonaceous material may be, for example, a flake shape such as natural graphite, a spherical shape such as mesocarbon microbeads, a fibrous shape such as graphitized carbon fiber, or an aggregate of fine powder.
In the case where the electrolytic solution does not contain ethylene carbonate, which will be described later, when a negative electrode mixture containing polyethylene carbonate is used, the cycle characteristics and large current discharge characteristics of the resulting battery are preferably improved.

  The negative electrode mixture may contain a binder as necessary. Examples of the binder include a thermoplastic resin, and specific examples include PVDF, thermoplastic polyimide, carboxymethyl cellulose, polyethylene, and polypropylene.

  The chalcogen compounds such as oxides and sulfides used as a material capable of doping and dedoping lithium ions contained in the negative electrode mixture are mainly composed of elements of Groups 13, 14, and 15 of the periodic table. Examples thereof include chalcogen compounds such as crystalline or amorphous oxides and sulfides, and specific examples include amorphous compounds mainly composed of tin oxide. These can contain a carbonaceous material as a conductive material as required.

Examples of the negative electrode current collector include Cu, Ni, and stainless steel. Cu is preferable because it is difficult to form an alloy with lithium and it can be easily processed into a thin film.
The method of supporting the negative electrode mixture on the negative electrode current collector is the same as in the case of the positive electrode. The method is a method of pressure molding, pasted using a solvent, etc., coated on the negative electrode current collector, dried, pressed and pressed. And the like.

  As the separator, for example, a material having a form such as a porous membrane, a nonwoven fabric, a woven fabric made of a polyolefin resin such as polyethylene and polypropylene, a fluororesin, a nitrogen-containing aromatic polymer, and the like can be used. Moreover, it is good also as a separator which used 2 or more types of these materials. Examples of the separator include separators described in JP 2000-30686 A, JP 10-324758 A, and the like. The thickness of the separator is preferably as thin as possible as long as the mechanical strength is maintained in that the volume energy density of the battery is increased and the internal resistance is reduced, and is preferably about 10 to 200 μm, more preferably about 10 to 30 μm. .

In the electrolyte, the _{electrolyte, LiClO 4, LiPF 6, LiAsF} 6, LiSbF 6, LIBF 4, LiCF 3 SO 3, LiN (SO 2 CF 3) 2, LiC (SO 2 CF 3) 3, Li 2 B Examples thereof include lithium salts such as ₁₀ Cl ₁₀ , a lower aliphatic carboxylic acid lithium salt, and LiAlCl _4, and a mixture of two or more of these may be used. The lithium salt is selected from the group consisting of fluorine-containing LiPF ₆ , LiAsF ₆ , LiSbF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (SO ₂ CF ₃ ) ₂ and LiC (SO ₂ CF ₃ ) ₃ among these. It is preferable to use those containing at least one kind.

In the electrolytic solution, examples of the organic solvent include propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, 4-trifluoromethyl-1,3-dioxolan-2-one, 1,2-di ( Carbonates such as methoxycarbonyloxy) ethane; 1,2-dimethoxyethane, 1,3-dimethoxypropane, pentafluoropropyl methyl ether, 2,2,3,3-tetrafluoropropyl difluoromethyl ether, tetrahydrofuran, 2-methyl Ethers such as tetrahydrofuran; esters such as methyl formate, methyl acetate and γ-butyrolactone; nitriles such as acetonitrile and butyronitrile; N, N-dimethylformamide, N, N-dimethylacetate Amides such as amides; Carbamates such as 3-methyl-2-oxazolidone; Sulfur-containing compounds such as sulfolane, dimethyl sulfoxide and 1,3-propane sultone, or those obtained by further introducing a fluorine substituent into the above organic solvent Usually, two or more of these are mixed and used. Among these, a mixed solvent containing carbonates is preferable, and a mixed solvent of cyclic carbonate and acyclic carbonate or cyclic carbonate and ether is more preferable.
The mixed solvent of cyclic carbonate and non-cyclic carbonate has a wide operating temperature range, excellent load characteristics, and is hardly decomposable even when a graphite material such as natural graphite or artificial graphite is used as the negative electrode active material. In addition, a mixed solvent containing ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate is preferable.
Further, in view of particularly excellent safety improving effect is obtained, it is preferable to use an electrolytic solution containing an organic solvent having a lithium salt and a fluorine substituent containing fluorine such as LiPF _6. A mixed solvent containing ethers having fluorine substituents such as pentafluoropropyl methyl ether and 2,2,3,3-tetrafluoropropyl difluoromethyl ether and dimethyl carbonate has excellent high-current discharge characteristics, preferable.

A solid electrolyte may be used instead of the above electrolytic solution.
As the solid electrolyte, for example, a polymer electrolyte such as a polyethylene oxide polymer compound, a polymer compound including at least one of a polyorganosiloxane chain or a polyoxyalkylene chain can be used. Moreover, what is called a gel type which hold | maintained the nonaqueous electrolyte solution in the polymer | macromolecule can also be used. The _{Li 2 S-SiS 2, Li} 2 S-GeS 2, Li 2 S-P 2 S 5, Li 2 sulfide electrolyte such as S-B ₂ S _3, or _{Li 2 S-SiS 2 -Li 3} PO 4 When an inorganic compound electrolyte containing a sulfide such as Li ₂ S—SiS ₂ —Li ₂ SO ₄ is used, safety may be further improved.

  Hereinafter, the present invention will be described in more detail with reference to examples. Unless otherwise specified, the electrodes for the charge / discharge test and the flat battery were prepared by the following method. The particle size distribution measurement of the positive electrode active material powder and the BET specific surface area of the positive electrode active material powder were measured by the following methods.

(1) Particle size distribution measurement of positive electrode active material powder Measurement was performed using a master sizer 2000 manufactured by Malvern as a laser diffraction scattering particle size distribution measuring apparatus. As the dispersion medium, an aqueous 0.2 wt% sodium hexametaphosphate solution was used. As the volume-based average particle diameter, a particle diameter value (D50 value) at a point of 50% of the total particle volume was used.

(2) Measurement of BET specific surface area of positive electrode active material powder 1 g of the powder was dried in a nitrogen stream at 150 ° C. for 15 minutes, and then measured using Flowsorb II2300 manufactured by Micromeritics.
(3) Measurement of powder packing density of positive electrode active material powder 10 g of the positive electrode active material powder was put into a 10 ml glass graduated cylinder, tapped 200 times, and the powder packing density (tap density) was measured. This measurement was repeated twice, and the average value of the measured values was defined as the powder packing density.

(4) Production of flat battery for charge / discharge test 1-methyl-2-pyrrolidone (hereinafter referred to as NMP) of PVDF as a binder and a mixture of flaky natural graphite and acetylene black serving as a positive electrode active material powder and conductive material The solution is mixed and kneaded so that the active material: flake graphite: acetylene black: PVDF has a weight ratio of 87: 9: 1: 3 to obtain a positive electrode mixture paste, and a positive electrode current collector The paste is applied to an Al foil having a thickness of 20 μm and dried at 60 ° C. for 1 hour in a hot air dryer, followed by vacuum drying at 50 ° C. for 8 hours, and consolidation treatment by a roll press. A positive electrode was obtained by cutting into a size of 5 cm × 2 cm. The weight of the obtained positive electrode was measured, the weight of the Al foil was subtracted from the weight of the positive electrode, the weight of the positive electrode mixture was calculated, and the weight of the positive electrode active material powder was calculated from the weight ratio of the paste-like positive electrode mixture. .
The obtained positive electrode, and ethylene carbonate (hereinafter sometimes referred to as EC), dimethyl carbonate (hereinafter sometimes referred to as DMC), and ethyl methyl carbonate (hereinafter sometimes referred to as EMC) as an electrolytic solution. A 30:35:35 (volume ratio) mixture of LiPF ₆ dissolved to 1 mol / liter (hereinafter sometimes referred to as LiPF ₆ / EC + DMC + EMC), a polyethylene porous membrane as a separator, Further, metallic lithium was used as a counter electrode and a reference electrode, and these were combined to produce a flat battery.

Example 1
(1) Synthesis of positive electrode active material powder Nickel hydroxide (manufactured by Kansai Catalysts Chemical Co., Ltd.), manganese oxide (manufactured by high purity chemical), lithium carbonate (manufactured by Honjo Chemical Co., Ltd.), cobalt oxide (manufactured by Shodo Chemical Co., Ltd.), After weighing boric acid (Yoneyama Chemical) so that the molar ratio of each element is Li: Ni: Mn: Co: B = 1.07: 0.35: 0.44: 0.21: 0.03 The powder was obtained by pulverizing and mixing for 4 hours (circumferential speed 0.7 m / s) by a dry ball mill using 15 mmφ alumina balls as media. This powder was put into a tunnel-type continuous furnace and fired in air at 1040 ° C. for 4 hours to obtain a fired product. The fired product is coarsely pulverized with a roll crusher, and then subjected to main pulverization using a jet mill (spiral jet mill NPK100 type manufactured by Nippon Pneumatic Co., Ltd.) under the conditions of a powder supply amount of 2 kg / h and a pressure of 4 kg / cm ^2. As a result, a pulverized powder was obtained. Coarse particles were removed from the pulverized powder with a sieve having an opening of 45 μm to obtain a positive electrode active material powder. The positive electrode active material powder has an average particle size of 1.3 μm, [sum of volume of particles having a particle size of 5 μm or more] / [sum of volumes of all particles] is 3%, specific surface area is 3.3 m ² / g, The powder packing density was 1.1 g / cc.

(2) Evaluation of charge / discharge performance when used as a positive electrode active material for a lithium secondary battery A flat battery was prepared using the obtained positive electrode active material powder, and charged by constant current and constant voltage charge and constant current discharge under the following conditions. A discharge test was performed. The obtained results are shown in Table 1.
Charging / discharging conditions:
The current value per unit weight of the positive electrode active material is set to 1C = 150 mA / g, and the current value of 1C is calculated by multiplying the weight of the positive electrode active material powder obtained as described above.
Charging is performed under conditions of maximum charging voltage 4.3V, charging time 8 hours, charging current 0.2C, and discharging is performed under conditions of minimum discharging voltage 3.0V, discharging currents 0.2C, 1C, 5C and 10C. It was. In addition, before each discharge test, it charged on the same conditions.

Example 2
(1) Synthesis of positive electrode active material powder Except that the molar ratio of each element is Li: Ni: Mn: Co: B = 1.10: 0.36: 0.42: 0.21: 0.03 Shows the average particle size, [sum of the volume of particles having a particle size of 5 μm or more] / [sum of the volume of all particles], specific surface area, powder, of the positive electrode active material powder obtained in the same manner as in Example 1. When the packing density was measured, the same result as in Example 1 was obtained. Further, a flat battery was produced using the positive electrode active material powder, and a charge / discharge test by constant current and constant voltage charge and constant current discharge was conducted in the same manner as in Example 1. As a result, the same results as in Example 1 were obtained. Obtained.

Comparative Example 1
(1) Synthesis of positive electrode active material powder Nickel hydroxide (manufactured by Kansai Catalysts Chemical Co., Ltd.), manganese oxide (manufactured by high purity chemical), lithium carbonate (manufactured by Honjo Chemical Co., Ltd.), cobalt oxide (manufactured by Shodo Chemical Co., Ltd.), After weighing boric acid (Yoneyama Chemical) so that the molar ratio of each element is Li: Ni: Mn: Co: B = 1.08: 0.35: 0.44: 0.21: 0.03 The powder was obtained by pulverizing and mixing for 4 hours (circumferential speed 0.7 m / s) by a dry ball mill using 15 mmφ alumina balls as media. This powder was put into a tunnel-type continuous furnace and fired in air at 1040 ° C. for 4 hours to obtain a fired product. The fired product was pulverized for 7 hours (peripheral speed 0.7 m / s) with a dry ball mill using 15 mmφ alumina balls as media, and coarse particles were removed with a sieve having an opening of 45 μm to obtain a positive electrode active material powder. . The positive electrode active material powder has an average particle size of 3.2 μm, a percentage of [sum of volume of particles having a particle size of 5 μm or more] / [sum of volumes of all particles] of 43%, and a specific surface area of 1.7 m ^2. / G, the powder packing density was 1.8 g / cc.
(2) Evaluation of charge / discharge performance in the case of using as the positive electrode active material of a lithium secondary battery A flat battery was produced using the obtained positive electrode active material, and constant current and constant voltage charging and constant charging were performed under the same conditions as in Example 1. A charge / discharge test using current discharge was performed. The obtained results are shown in Table 1.

Comparative Example 2
(1) Synthesis of positive electrode active material powder A fired product was obtained by the same method as in Example 1, and the fired product was pulverized for 13 hours (circumferential speed 0.7 m / s) by a dry ball mill using 15 mmφ alumina balls as media. The coarse particles were removed with a sieve having an opening of 45 μm to obtain a positive electrode active material powder.
The positive electrode active material powder has an average particle size of 2.5 μm, a percentage of [sum of volume of particles having a particle size of 5 μm or more] / [sum of volume of all particles] of 39% and a specific surface area of 1.7 m. ² / g, the powder packing density was 1.8 g / cc.
(2) Evaluation of charge / discharge performance in the case of using as the positive electrode active material of a lithium secondary battery A flat battery was produced using the obtained positive electrode active material, and constant current and constant voltage charging and constant charging were performed under the same conditions as in Example 1. A charge / discharge test using current discharge was performed. The obtained results are shown in Table 1.

  From the discharge capacity data in Example 1, Comparative Example 1 and Comparative Example 2 shown in Table 1 and the data of 0.2C versus rate characteristics, the battery using the positive electrode active material powder of Example 1 has a high discharge current. Even so (for example, 10 C), it can be seen that the discharge capacity is large and the output is high.

Claims (6)

A positive electrode active material powder comprising primary particles and agglomerated particles of primary particles, wherein the primary particles and the agglomerated particles of the primary particles in the powder have a volume-based average particle size of 0.1 μm or more and 3 μm or less, and a particle size of 5 μm or percentages of the sum of the volume of the particle] / [sum of the volumes of all particles] is 10% or less state, and are 7m ² / g or less BET specific surface area of greater than 2m ² / g of powder, the composition The positive electrode active material powder for nonaqueous electrolyte secondary batteries represented by Formula (1) .
Li _x1 Ni _1-y1 M ¹ _y1 O ₂ (1)
(In formula (1), x1 and y1 are 0.9 ≦ x1 ≦ 1.2 and 0 ≦ y1 ≦ 0.5, respectively, and M ¹ is Co.) A positive electrode active material powder comprising primary particles and agglomerated particles of primary particles, wherein the primary particles and the agglomerated particles of the primary particles in the powder have a volume-based average particle size of 0.1 μm or more and 3 μm or less, and a particle size of 5 μm or percentages of the sum of the volume of the particle] / [sum of the volumes of all particles] is 10% or less state, and are 7m ² / g or less BET specific surface area of greater than 2m ² / g of powder, the composition The positive electrode active material powder for nonaqueous electrolyte secondary batteries represented by Formula (2) .
Li _x2 Ni _1-y2 M ² _y2 O ₂ (2)
(In the formula (2), x2 and y2 are 0.9 ≦ x2 ≦ 1.2 and 0.3 ≦ y2 ≦ 0.9, respectively, and M ² is Co and Mn.) The positive electrode for nonaqueous electrolyte secondary batteries which has the positive electrode active material powder for nonaqueous electrolyte secondary batteries of Claim 1 or 2 . The positive electrode for a nonaqueous electrolyte secondary battery according to claim 3, which has a conductive material. The positive electrode for a nonaqueous electrolyte secondary battery according to claim 4, wherein the conductive material contains a fibrous carbon material. Non-aqueous electrolyte secondary battery having a non-aqueous electrolyte secondary battery positive electrode according to any one of claims 3-5.