Nonaqueous electrolyte secondary battery

Abstract

Provided is a non-aqueous electrolyte secondary battery having high capacity and suppressed peeling of a positive electrode mixture layer. A non-aqueous electrolyte secondary battery according to one embodiment of the present invention is provided with a positive electrode, a negative electrode, and a non-aqueous electrolyte, the positive electrode having a positive electrode collector and a positive electrode mixture layer formed on the surface of the positive electrode collector, the positive electrode mixture layer containing a first positive electrode active material and a second positive electrode active material having a smaller average particle diameter than the first positive electrode active material, the particle diameter ratio (R1 / R2) of the average particle diameter (R1) of the first positive electrode active material to the average particle diameter (R2) of the second positive electrode active material is 3-9, the volume ratio (V1 / V2) of the volume (V1) of the first positive electrode active material to the volume (V2) of the second positive electrode active material is 3-15, and the density of the positive electrode mixture layer is 3.35-3.70 g / cm3.

Description

Technical Field

[0001] The present invention relates to a non-aqueous electrolyte secondary battery. Background Art

[0002] Heretofore, a lithium transition metal composite oxide containing Ni, Co, etc. has been used as a high-capacity positive electrode active material. For example, in Patent Document 1, a technique for improving battery capacity and rate characteristics by using a positive electrode active material obtained by mixing two lithium cobalt oxides having different compositions and average particle diameters at a prescribed volume ratio is disclosed.

[0003] Prior Art Documents

[0004] Patent Documents

[0005] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2006-156004 Summary of the Invention

[0006] In recent years, there has been an increasing demand for high capacity, and studies have been made on increasing the proportion of the positive electrode active material in the positive electrode mixture layer. However, if the content of the binder in the positive electrode mixture layer is too small, the positive electrode mixture layer may peel off from the positive electrode current collector. Patent Document 1 does not study the peeling of the positive electrode mixture layer, and there is still room for improvement.

[0007] An object of the present invention is to provide a non-aqueous electrolyte secondary battery having high capacity and suppressing peeling of the positive electrode mixture layer.

[0008] A non-aqueous electrolyte secondary battery according to one aspect of the present invention is characterized by including a positive electrode, a negative electrode, and a non-aqueous electrolyte. The positive electrode has a positive electrode current collector and a positive electrode mixture layer formed on the surface of the positive electrode current collector. The positive electrode mixture layer contains a first positive electrode active material and a second positive electrode active material having an average particle diameter smaller than that of the first positive electrode active material. The particle size ratio R1 / R2 of the average particle diameter R1 of the first positive electrode active material to the average particle diameter R2 of the second positive electrode active material is 3 or more and 9 or less, and the volume ratio V1 / V2 of the volume V1 of the first positive electrode active material to the volume V2 of the second positive electrode active material is 3 or more and 15 or less. The density of the positive electrode mixture layer is 3.35 g / cm 3 or more and 3.70 g / cm 3 or less.

[0009] The non-aqueous electrolyte secondary battery of the present invention has high capacity and excellent adhesion of the positive electrode mixture layer. Brief Description of the Drawings

[0010] Figure 1 is an axial sectional view of a cylindrical secondary battery as an example of an embodiment. Detailed Description of the Invention

[0011] Hereinafter, with reference to the accompanying drawings, an example of an embodiment of the cylindrical secondary battery of the present invention will be described in detail. In the following description, specific shapes, materials, numerical values, directions, etc. are examples for facilitating the understanding of the present invention and can be appropriately changed according to the specifications of the secondary battery. In addition, although a cylindrical secondary battery in which a wound electrode body is housed in a cylindrical outer package is illustrated below, the electrode body is not limited to the wound type and may be a laminated type in which a plurality of positive electrodes and a plurality of negative electrodes are alternately laminated piece by piece with a spacer interposed therebetween. The outer package is not limited to a cylindrical shape and may be, for example, a square shape, a button shape, etc. In addition, the outer package may also be a soft package type composed of a laminated sheet including a metal layer and a resin layer. In addition, in this specification, the description of "numerical value (A) to numerical value (B)" means equal to or greater than numerical value (A) and equal to or less than numerical value (B).

[0012] Figure 1 is a cross-sectional view of a cylindrical secondary battery 10 as an example of an embodiment. As Figure 1 shown, the secondary battery 10 includes a wound electrode body 14, a non-aqueous electrolyte, and an outer package can 16 that houses the electrode body 14 and the non-aqueous electrolyte. The electrode body 14 has a positive electrode 11, a negative electrode 12, and a spacer 13, and has a wound structure in which the positive electrode 11 and the negative electrode 12 are wound in a spiral shape with the spacer 13 interposed therebetween. The outer package can 16 is a bottomed cylindrical metal container that is open on one axial side, and the opening of the outer package can 16 is sealed by a sealing body 17. Hereinafter, for the convenience of description, the side of the battery where the sealing body 17 is located is set as the upper side, and the bottom side of the outer package can 16 is set as the lower side.

[0013] The positive electrode 11, the negative electrode 12, and the spacer 13 that constitute the electrode body 14 are all strip-shaped long bodies, and are alternately laminated in the radial direction of the electrode body 14 by being wound in a spiral shape. The spacer 13 isolates the positive electrode 11 and the negative electrode 12 from each other. In order to prevent the precipitation of lithium, the negative electrode 12 is formed with a size one turn larger than that of the positive electrode 11. That is, the negative electrode 12 is formed to be longer than the positive electrode 11 in the length direction and the width direction (short side direction). Two spacers 13 are formed with a size at least one turn larger than that of the positive electrode 11, and are arranged, for example, in a manner of sandwiching the positive electrode 11. The electrode body 14 includes a positive electrode lead 20 connected to the positive electrode 11 by welding or the like and a negative electrode lead 21 connected to the negative electrode 12 by welding or the like.

[0014] Insulating plates 18 and 19 are respectively arranged above and below the electrode body 14. Figure 1In the example shown, the positive electrode lead 20 extends toward the sealing body 17 side through the through-hole of the insulating plate 18, and the negative electrode lead 21 extends toward the bottom side of the outer packaging can 16 through the outside of the insulating plate 19. The positive electrode lead 20 is connected to the lower surface of the internal terminal plate 23 inside the sealing body 17 by welding or the like, and the cap 27, which is the top plate of the sealing body 17 and is electrically connected to the internal terminal plate 23, becomes the positive electrode terminal. The negative electrode lead 21 is connected to the inner surface of the bottom of the outer packaging can 16 by welding or the like, and the outer packaging can 16 becomes the negative electrode terminal.

[0015] A gasket 28 is provided between the outer packaging can 16 and the sealing body 17 to ensure the airtightness inside the battery. A slotted portion 22 for supporting the sealing body 17 is formed in a part of the side surface of the outer packaging can 16 bulging inward. The slotted portion 22 is preferably formed in a ring shape along the circumferential direction of the outer packaging can 16, and the sealing body 17 is supported by its upper surface. The sealing body 17 is fixed to the upper part of the outer packaging can 16 by using the slotted portion 22 and the opening end portion of the outer packaging can 16 caulked to the sealing body 17.

[0016] The sealing body 17 has a structure in which an internal terminal plate 23, a lower valve body 24, an insulating member 25, an upper valve body 26, and a cap 27 are laminated in sequence from the side of the electrode body 14. Each member constituting the sealing body 17 has, for example, a disc shape or a ring shape, and the members other than the insulating member 25 are electrically connected to each other. The lower valve body 24 and the upper valve body 26 are connected at their respective central portions, and the insulating member 25 is sandwiched between their respective peripheral portions. When the internal pressure of the battery rises due to abnormal heat generation, the lower valve body 24 deforms and breaks in a manner of pushing the upper valve body 26 toward the cap 27 side, thereby blocking the current path between the lower valve body 24 and the upper valve body 26. When the internal pressure further rises, the upper valve body 26 breaks, and gas is discharged from the opening of the cap 27.

[0017] Hereinafter, the positive electrode 11, the negative electrode 12, the separator 13, and the non-aqueous electrolyte constituting the secondary battery 10 will be described in detail, particularly the positive electrode 11.

[0018] [Positive Electrode]

[0019] The positive electrode 11 has a positive electrode current collector and a positive electrode mixture layer formed on the surface of the positive electrode current collector. The positive electrode mixture layer is preferably formed on both surfaces of the positive electrode current collector. As the positive electrode current collector, a foil of a metal such as aluminum or aluminum alloy that is stable in the potential range of the positive electrode 11, a film having the metal disposed on the surface layer, or the like can be used.

[0020] The positive electrode mixture layer contains, for example, a positive electrode active material, a binder, and a conductive agent. The content of the positive electrode active material in the positive electrode mixture layer is, for example, 85% by mass to 99% by mass with respect to the total mass of the positive electrode mixture layer. For example, a positive electrode mixture slurry containing a positive electrode active material, a binder, a conductive agent, etc. is coated on the surface of the positive electrode current collector, and after the coating film is dried, the coating film is calendered using a roller or the like, whereby the positive electrode 11 can be manufactured.

[0021] The density of the positive electrode mixture layer is preferably 3.35 g / cm 3 or more and 3.70 g / cm 3 or less, more preferably 3.40 g / cm 3 or more and 3.65 g / cm 3 or less. The density of the positive electrode mixture layer can be obtained by dividing the mass of the positive electrode mixture layer by the mass of the positive electrode mixture layer.

[0022] Examples of the conductive agent contained in the positive electrode mixture layer include carbon-based particles such as carbon black (CB), acetylene black (AB), Ketjen black, carbon nanotubes (CNT), graphene, and graphite. They can be used alone or in combination of two or more. The content of the conductive agent relative to the mass of the positive electrode active material is, for example, 0.1% by mass to 10% by mass.

[0023] Examples of the binder contained in the positive electrode mixture layer include fluorine-based resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), polyimide-based resins, acrylic-based resins, polyolefin-based resins, and polyacrylonitrile (PAN). They can be used alone or in combination of two or more. The content of the binder relative to the mass of the positive electrode active material is preferably 0.1% by mass to 5% by mass, more preferably 0.1% by mass to 1% by mass, and particularly preferably 0.1% by mass to 0.5% by mass. By reducing the content of the binder, the content of the positive electrode active material increases, and the battery capacity can be increased.

[0024] The positive electrode active material contained in the positive electrode mixture layer is, for example, a lithium transition metal composite oxide. The lithium transition metal composite oxide can have, for example, a layered structure belonging to the space group R-3m, a layered structure belonging to the space group C2 / m, etc. Among them, from the viewpoints of high capacity and crystal structure stability, etc., a layered structure belonging to the space group R-3m is preferred. The layered structure of the lithium transition metal composite oxide can include a transition metal layer, a Li layer, and an oxygen layer.

[0025] The lithium transition metal composite oxide is, for example, represented by the general formula Li a Ni x M1 y M2 z O b(wherein 0.9 ≤ a ≤ 1.2, 0.33 ≤ x ≤ 0.96, 0 ≤ y ≤ 0.67, 0 ≤ z ≤ 0.67, 1.9 ≤ b ≤ 2.1, x + y + z = 1, M1 is one or more elements selected from Co, Al, and Mn, and M2 is one or more elements selected from Nb, Ti, Zr, W, and Si). The molar percentage of the metal elements contained in the lithium transition metal composite oxide can be measured, for example, by inductively coupled plasma (ICP) optical emission spectrometry.

[0026] The lithium transition metal composite oxide, for example, contains secondary particles formed by aggregation of primary particles. The particle size of the primary particles constituting the secondary particles of the lithium transition metal composite oxide is, for example, 0.02 μm to 2 μm. The particle size of the primary particles is measured as the diameter of the circumscribed circle in the particle image observed by a scanning electron microscope (SEM).

[0027] The positive electrode active material contains a first positive electrode active material and a second positive electrode active material having an average particle size smaller than that of the first positive electrode active material. The particle size ratio R1 / R2 of the average particle size R1 of the first positive electrode active material to the average particle size R2 of the second positive electrode active material is preferably 3 or more and 9 or less, more preferably 4 or more and 8 or less. Here, the average particle size means the median diameter (D50) based on the volume of the secondary particles. D50 means the particle size at which the cumulative frequency in the particle size distribution based on the volume reaches 50% starting from the smaller particle size side, and is also called the median diameter. The particle size distribution of the secondary particles of the lithium transition metal composite oxide can be measured using a laser diffraction type particle size distribution measuring device (for example, MT3000II manufactured by Microtrac Bel Co., Ltd.) with water as the dispersion medium. The average particle size R1 is, for example, 1 μm to 50 μm, and the average particle size R2 is, for example, 0.2 μm to 10 μm.

[0028] The volume ratio V1 / V2 of the volume V1 of the first positive electrode active material to the volume V2 of the second positive electrode active material is preferably 3 or more and 15 or less, more preferably 4 or more and 12 or less.

[0029] By controlling the density of the positive electrode binder layer to be in the range of 3.35 g / cm 3 to 3.70 g / cm 3 while using the first positive electrode active material and the second positive electrode active material that satisfy the particle size ratio R1 / R2 of 3 to 9 and the volume ratio V1 / V2 of 3 to 15, since the binder spreads between the positive electrode active materials, it is possible to achieve both high capacity and suppression of peeling of the positive electrode binder layer.

[0030] [Negative electrode]

[0031] The negative electrode 12 has, for example, a negative electrode current collector and a negative electrode mixture layer formed on the surface of the negative electrode current collector. The negative electrode mixture layer is preferably formed on both sides of the negative electrode current collector. As the negative electrode current collector, a foil of a metal stable in the potential range of the negative electrode such as copper, or a film having the metal disposed on the surface layer can be used.

[0032] The negative electrode mixture layer contains, for example, a negative electrode active material and a binder. The content of the negative electrode active material in the negative electrode mixture layer is, for example, 80% by mass to 99% by mass relative to the total mass of the negative electrode mixture layer. For example, a negative electrode mixture slurry containing a negative electrode active material, a binder, etc. is coated on the surface of the negative electrode current collector, and after the coating film is dried, the coating film is calendered using a roll or the like, whereby the negative electrode 12 can be manufactured.

[0033] The negative electrode active material contained in the negative electrode mixture layer is not particularly limited as long as it can reversibly occlude and release Li ions, and generally a carbon material such as graphite is used. The graphite can be any of natural graphite such as flake graphite, massive graphite, and earthy graphite, massive artificial graphite, graphitized mesophase carbon microspheres, and other artificial graphite. In addition, a metal that alloyizes with Li such as Si or Sn, a metal compound containing Si or Sn, a lithium titanium composite oxide, etc. can also be used as the negative electrode active material. For example, a silicon oxide represented by SiO x (where x is 0.5 to 1.6), a silicon-containing material in which fine particles of Si are dispersed in a lithium silicate phase represented by Li 2y SiO （2＋y） (0 < y < 2), a silicon-containing material in which fine particles of Si are dispersed in a carbon phase, etc. can be used in combination with graphite.

[0034] Examples of the binder contained in the negative electrode mixture layer include styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber (NBR), carboxymethyl cellulose (CMC) or its salts (CMC-Na, CMC-K, CMC-NH4, etc., and also partially neutralized salts), polyacrylic acid (PAA) or its salts (PAA-Na, PAA-K, etc., and also partially neutralized salts), polyvinyl alcohol (PVA), etc. They can be used alone or in combination of two or more.

[0035] [Spacer]

[0036] The spacer 13 is, for example, a porous sheet having ion permeability and insulation properties, such as a microporous film, woven fabric, non-woven fabric, etc. Specific examples of the porous sheet include microporous films, woven fabrics, non-woven fabrics, etc. As the material of the spacer, olefin resins such as polyethylene and polypropylene, cellulose, etc. are suitable. The spacer 13 may also be a laminate having a cellulose fiber layer and a thermoplastic resin fiber layer such as an olefin resin. In addition, it may be a multilayer spacer including a polyethylene layer and a polypropylene layer, or a spacer having a material such as an aromatic polyamide resin or ceramic coated on the surface of the spacer 13.

[0037] [Non-aqueous electrolyte]

[0038] The non-aqueous electrolyte has lithium ion conductivity. The non-aqueous electrolyte may be a liquid electrolyte (electrolyte solution) or a solid electrolyte.

[0039] The liquid electrolyte (electrolyte solution) contains a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. As the non-aqueous solvent, esters, ethers, nitriles such as acetonitrile, amides such as dimethylformamide, and a mixed solvent of two or more of them are used, for example. The non-aqueous solvent may also contain a halogen-substituted product in which at least a part of the hydrogen of these solvents is substituted with a halogen atom such as fluorine.

[0040] Examples of the above esters include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, chain carbonates such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl propyl carbonate, ethyl propyl carbonate, methyl isopropyl carbonate, cyclic carboxylic acid esters such as γ-butyrolactone, γ-valerolactone, chain carboxylic acid esters such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate (MP), ethyl propionate, etc.

[0041] Examples of the above ethers include cyclic ethers such as 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, propylene oxide, 1,2-epoxybutane, 1,3-dioxane, 1,4-dioxane, 1,3,5-trioxane, furan, 2-methylfuran, 1,8-cineole, crown ether, chain ethers such as 1,2-dimethoxyethane, diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, dihexyl ether, ethyl vinyl ether, butyl vinyl ether, methyl phenyl ether, ethyl phenyl ether, butyl phenyl ether, pentyl phenyl ether, methoxytoluene, benzyl ethyl ether, diphenyl ether, dibenzyl ether, o-dimethoxybenzene, 1,2-diethoxyethane, 1,2-dibutoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, 1,1-dimethoxymethane, 1,1-diethoxyethane, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, etc.

[0042] Preferably, fluorinated cyclic carbonates such as fluoroethylene carbonate (FEC), fluorinated linear carbonates, fluorinated linear carboxylates such as methyl fluoropropionate (FMP), etc. are used as the above-mentioned halogen substituents.

[0043] The electrolyte salt is preferably a lithium salt. Examples of the lithium salt include LiBF4, LiClO4, LiPF6, LiAsF6, LiSbF6, LiAlCl4, LiSCN, LiCF3SO3, LiCF3CO2, Li(P(C2O4)F4), LiPF 6-x (C n F 2n＋1 ) x (1 < x < 6, n is 1 or 2), LiB 10 Cl 10 ., LiCl, LiBr, LiI, lithium chloroborane, lithium lower aliphatic carboxylate, borate salts such as Li2B4O7, Li(B(C2O4)F2), etc., imide salts such as LiN(SO2CF3)2, LiN(C1F 2l＋1 SO2)(C m F 2m＋1 SO2){l, m are integers of 1 or more}, etc. These lithium salts can be used alone or in combination of multiple kinds. Among them, from the viewpoints of ionic conductivity, electrochemical stability, etc., LiPF6 is preferably used. The concentration of the lithium salt is preferably set to 0.8 to 1.8 mol per 1 L of the solvent.

[0044] As the solid electrolyte, for example, solid or gel-like polymer electrolytes, inorganic solid electrolytes, etc. can be used. As the inorganic solid electrolyte, known materials in all-solid-state lithium ion secondary batteries, etc. (for example, oxide-based solid electrolytes, sulfide-based solid electrolytes, halogen-based solid electrolytes, etc.) can be used. The polymer electrolyte contains, for example, a lithium salt and a matrix polymer, or contains a non-aqueous solvent, a lithium salt, and a matrix polymer. As the matrix polymer, for example, a polymer material that gels after absorbing a non-aqueous solvent is used. Examples of the polymer material include fluororesins, acrylic resins, polyether resins, etc.

[0045] Examples

[0046] Hereinafter, the present invention will be further described using examples, but the present invention is not limited to these examples.

[0047] <Example 1-1>

[0048] [Fabrication of positive electrode]

[0049] Using those with an average particle size of 10.2 μm and a composition of LiNi 0.88 Co 0.04 Mn 0.08The lithium transition metal composite oxide represented by O2 is used as the first positive electrode active material. Using a lithium transition metal composite oxide represented by O2 with an average particle size of 2.0 μm and a composition of LiNi 0.88 Co 0.07 Al 0.05 O2 as the second positive electrode active material. Accordingly, the particle size ratio R1 / R2 is 5.1. The first positive electrode active material and the second positive electrode active material are mixed such that the volume ratio V1 / V2 is 9.3, and this is used as the positive electrode active material. This positive electrode active material, carbon black, and polyvinylidene fluoride (PVDF) are mixed at a mass ratio of 100:0.5:0.7, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) is added as a dispersion medium to prepare a positive electrode mixture paste. Then, this positive electrode mixture paste is coated on both sides of a positive electrode current collector made of aluminum foil, the coating film is dried, calendered, and cut into a specified electrode size to produce a positive electrode having a positive electrode mixture layer formed on both sides of the positive electrode current collector. The density of the positive electrode mixture layer is 3.50 g / cm 3 . It should be noted that a exposed portion exposing the surface of the positive electrode current collector is provided in a part of the positive electrode.

[0050] [Fabrication of negative electrode]

[0051] 100 parts by mass of artificial graphite, 1 part by mass of sodium carboxymethylcellulose (CMC-Na), 1.2 parts by mass of styrene-butadiene rubber (SBR), and water are mixed to prepare a negative electrode mixture paste. Then, this negative electrode mixture paste is coated on both sides of a negative electrode current collector made of copper foil, the coating film is dried, calendered, and cut into a specified electrode size to produce a negative electrode having a negative electrode mixture layer formed on both sides of the negative electrode current collector. It should be noted that a exposed portion exposing the surface of the negative electrode current collector is provided in a part of the negative electrode.

[0052] [Preparation of non-aqueous electrolyte]

[0053] Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed at a volume ratio of 3:7 to prepare a mixed solvent. Lithium hexafluorophosphate (LiPF6) is dissolved to a concentration of 1 mol / L with respect to this mixed solvent to prepare a non-aqueous electrolyte.

[0054] [Fabrication of test battery]

[0055] An aluminum positive electrode lead is installed at the exposed portion of the positive electrode, and a nickel negative electrode lead is installed at the exposed portion of the negative electrode. A winding-type electrode body is produced by winding the positive electrode and the negative electrode spirally with a spacer made of a polyethylene microporous membrane interposed therebetween. The electrode body is housed in a bottomed cylindrical outer packaging can, the negative electrode lead is welded to the inner surface of the bottom of the outer packaging can, and the positive electrode lead is welded to the internal terminal plate of the sealing body. Thereafter, the non-aqueous electrolyte is injected into the outer packaging can, and the open end portion of the outer packaging can is tightly fixed to the sealing body to produce a cylindrical test battery.

[0056] [Evaluation of the adhesion of the positive electrode mixture layer]

[0057] The positive electrode is cut to produce a test piece with a width of 15 mm and a length of 80 mm. A double-sided tape (manufactured by Nitto Denko Corporation) is pasted on the positive electrode mixture layer on one surface of the test piece and fixed to a stainless steel substrate with a smooth surface. The stainless steel substrate with the test piece fixed is set horizontally. One end of the positive electrode current collector in the length direction of the test piece is fixed to the movable jig of a tensile testing machine (trade name: TENSILON universal testing machine RTC1210, manufactured by A&D Company, Limited), and it is set in such a way that the positive electrode current collector is peeled off in a direction of 90° with respect to the substrate surface of the stainless steel substrate. Thereafter, the movable jig is moved, and the positive electrode mixture layer and the positive electrode current collector of the test piece are peeled off at a speed of 20 mm / min. At this time, the tensile direction is maintained at 90° with respect to the substrate surface of the stainless steel substrate on which the test piece is fixed. The value of the stable tensile strength when the test piece is peeled off by 30 mm or more is read as the peeling strength (N / m) of the positive electrode mixture layer from the positive electrode current collector.

[0058] [Evaluation of the battery discharge capacity]

[0059] After charging the above test battery at a constant current of 1C to a battery voltage of 4.2V in a temperature environment of 25°C, it is charged at a constant voltage of 4.2V until the current value becomes 0.02C. Thereafter, it is discharged at a constant current of 1C until the battery voltage reaches 2.5V, and the discharge capacity at this time is set as the battery discharge capacity.

[0060] <Example 1-2>

[0061] Except that in the production of the positive electrode, the first positive electrode active material and the second positive electrode active material are mixed in such a way that the volume ratio V1 / V2 is 6.1, the positive electrode and the test battery are produced in the same manner as in Example 1-1 and evaluated.

[0062] <Example 1-3>

[0063] Except that in the production of the positive electrode, the first positive electrode active material and the second positive electrode active material are mixed in such a way that the volume ratio V1 / V2 is 12.2, a positive electrode and a test battery are produced in the same manner as in Example 1-1 and evaluated.

[0064] <Example 1-4>

[0065] Except that in the production of the positive electrode, the line pressure during calendering coating is reduced, a positive electrode and a test battery are produced in the same manner as in Example 1-1 and evaluated. The density of the positive electrode mixture layer is 3.45 g / cm 3 .

[0066] <Example 1-5>

[0067] Except that in the production of the positive electrode, the line pressure during calendering coating is increased, a positive electrode and a test battery are produced in the same manner as in Example 1-1 and evaluated. The density of the positive electrode mixture layer is 3.55 g / cm 3 .

[0068] <Comparative Example 1-1>

[0069] Except that in the production of the positive electrode, only the first positive electrode active material is used and set as the positive electrode active material, a test battery is produced in the same manner as in Example 1-1 and evaluated.

[0070] <Comparative Example 1-2>

[0071] Except that in the production of the positive electrode, a lithium transition metal composite oxide represented by an average particle size of 1.0 μm and a composition of LiNi 0.88 Co 0.07 Al 0.05 O2 is used as the second positive electrode active material, and the first positive electrode active material and the second positive electrode active material are mixed in such a way that the volume ratio V1 / V2 is 7.2, a test battery is produced in the same manner as in Example 1-1 and evaluated.

[0072] <Comparative Example 1-3>

[0073] Except that in the production of the positive electrode, the first positive electrode active material and the second positive electrode active material are mixed in such a way that the volume ratio V1 / V2 is 1.9, a positive electrode and a test battery are produced in the same manner as in Example 1-1 and evaluated.

[0074] <Comparative Example 1-4>

[0075] Except that in the production of the positive electrode, the line pressure during calendering coating is further lower than that in Example 1-4, a positive electrode and a test battery are produced in the same manner as in Example 1-1 and evaluated. The density of the positive electrode mixture layer is 3.30 g / cm 3 .

[0076] <Examples 2-1 to 2-5, Comparative Examples 2-1 to 2-4>

[0077] Except that in the production of the positive electrode, the amount of PVDF mixed was changed to 0.4 parts by mass relative to 100 parts by mass of the positive electrode active material, the positive electrode and the test battery were produced in the same manner as in Examples 1-1 to 1-5 and Comparative Examples 1-1 to 1-4, respectively, and evaluated.

[0078] The evaluation results of the test batteries of the examples and comparative examples are shown in Table 1. In Table 1, the results of the peel strength and discharge capacity of Examples 1-1 to 1-5, 2-1 to 2-5 and Comparative Examples 1-2 to 1-4, 2-1 to 2-4 are shown as relative values when the respective results of the peel strength and discharge capacity of the test battery of Comparative Example 1-1 are set to 100.

[0079]

[0080] Both the peel strength and the discharge capacity of the test battery of the example were better than those of the test battery of Comparative Example 1-1, and it was found that the adhesion of the positive electrode mixture layer was excellent. Particularly in Example 2-1, even when the amount of PVDF as a binder was reduced to 0.5 parts by mass, the peel strength was significantly improved compared to Comparative Example 1-1.

[0081] The present invention will be further described by the following embodiments.

[0082] Constitution 1:

[0083] A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte,

[0084] The positive electrode has a positive electrode current collector and a positive electrode mixture layer formed on the surface of the positive electrode current collector,

[0085] The positive electrode mixture layer contains a first positive electrode active material and a second positive electrode active material having an average particle diameter smaller than that of the first positive electrode active material,

[0086] The particle size ratio R1 / R2 of the average particle diameter R1 of the first positive electrode active material to the average particle diameter R2 of the second positive electrode active material is 3 or more and 9 or less,

[0087] The volume ratio V1 / V2 of the volume V1 of the first positive electrode active material to the volume V2 of the second positive electrode active material is 3 or more and 15 or less,

[0088] The density of the positive electrode mixture layer is 3.35 g / cm 3 or more and 3.70 g / cm 3 or less.

[0089] Constitution 2:

[0090] The non-aqueous electrolyte secondary battery according to Configuration 1, wherein the particle size ratio R1 / R2 is 4 or more and 8 or less, the volume ratio V1 / V2 is 4 or more and 12 or less, and the density of the positive electrode mixture layer is 3.40 g / cm 3 or more and 3.65 g / cm 3 or less.

[0091] Configuration 3:

[0092] The non-aqueous electrolyte secondary battery according to Configuration 1 or 2, wherein the first positive electrode active material and the second positive electrode active material are lithium transition metal composite oxides represented by the general formula Li a Ni x M1 y M2 z O b (where 0.9 ≤ a ≤ 1.2, 0.33 ≤ x ≤ 0.96, 0 ≤ y ≤ 0.67, 0 ≤ z ≤ 0.67, 1.9 ≤ b ≤ 2.1, x + y + z = 1, M1 is one or more elements selected from Co, Al, and Mn, and M2 is one or more elements selected from Nb, Ti, Zr, W, and Si).

[0093] Description of Reference Numerals

[0094] 10 Secondary battery, 11 Positive electrode, 12 Negative electrode, 13 Spacer, 14 Electrode body, 16 Outer packaging can, 17 Sealing body, 18, 19 Insulating plate, 20 Positive electrode lead, 21 Negative electrode lead, 22 Grooved portion, 23 Internal terminal plate, 24 Lower valve body, 25 Insulating member, 26 Upper valve body, 27 Cap, 28 Gasket.

Claims

1. A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the positive electrode has a positive electrode current collector and a positive electrode mixture layer formed on the surface of the positive electrode current collector, the positive electrode mixture layer contains a first positive electrode active material and a second positive electrode active material having an average particle size smaller than that of the first positive electrode active material, a particle size ratio R1 / R2 of an average particle size R1 of the first positive electrode active material to an average particle size R2 of the second positive electrode active material is 3 or more and 9 or less, a volume ratio V1 / V2 of a volume V1 of the first positive electrode active material to a volume V2 of the second positive electrode active material is 3 or more and 15 or less, The density of the positive electrode mixture layer is 3.35 g / cm 3 or more and 3.70 g / cm 3 or less.

2. The non-aqueous electrolyte secondary battery according to claim 1, wherein, The particle size ratio R1 / R2 is 4 or more and 8 or less, the volume ratio V1 / V2 is 4 or more and 12 or less, and the density of the positive electrode mixture layer is 3.40 g / cm 3 or more and 3.65 g / cm 3 or less.

3. The non-aqueous electrolyte secondary battery according to claim 1, wherein, The first positive electrode active material and the second positive electrode active material are lithium transition metal composite oxides represented by the general formula Li a Ni x M1 y M2 z O b where 0.9 ≤ a ≤ 1.2, 0.33 ≤ x ≤ 0.96, 0 ≤ y ≤ 0.67, 0 ≤ z ≤ 0.67, 1.9 ≤ b ≤ 2.1, x + y + z = 1, M1 is one or more elements selected from Co, Al, and Mn, and M2 is one or more elements selected from Nb, Ti, Zr, W, and Si.

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