Non-aqueous electrolyte secondary battery

Abstract

A nonaqueous electrolyte secondary battery has an electrode body in which a positive electrode and a negative electrode are wound with a separator interposed therebetween in a flat shape, and a nonaqueous electrolyte, the positive electrode having a positive electrode composite layer containing a positive electrode active material. The positive electrode composite layer has added thereto 0.10 to 0.30 mass% of ceramic particles, the median particle diameter (D50) of the ceramic particles on a volume basis is 0.5 μm or less, the air permeability of the separator is 165 to 310 seconds / 100 ml, and the air permeability of a flat portion of the separator relative to the air permeability of a curved portion of the separator is 120 to 140%.

Description

Technical Field

[0001] The present disclosure relates to a nonaqueous electrolyte secondary battery. Background Art

[0002] The addition of ceramic particles to the positive electrode composite material layer of non-aqueous electrolyte secondary batteries is known. For example, Patent Document 1 discloses a non-aqueous electrolyte secondary battery in which alumina particles are coated on the positive electrode active material to improve thermal stability during charging and cycle characteristics.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 2001-143703 Summary of the Invention

[0006] In non-aqueous electrolyte secondary batteries, due to repeated charge and discharge, the positive electrode active material expands and contracts as lithium ions are inserted and removed. As a result, the adhesion between the positive electrode and the separator is weakened, and the distance between the positive electrode and the negative electrode becomes uneven, thereby reducing the cycle characteristics. As a solution, for example, a solution is considered to pressurize the wound electrode body into a flat shape to enhance the adhesion between the positive electrode and the separator. However, in this case, the pores of the separator are crushed, the air permeability of the separator increases, and the power characteristics are reduced.

[0007] A non-aqueous electrolyte secondary battery as one embodiment of the present invention comprises: an electrode body in which a positive electrode and a negative electrode are wound into a flat shape via a separator, and a non-aqueous electrolyte, the positive electrode having a positive electrode composite material layer containing a positive electrode active material, 0.10 to 0.30 mass % of ceramic particles are added to the positive electrode composite material layer, the volume-based median particle size (D50) of the ceramic particles is less than 0.5 μm, the permeability of the separator is 165 to 310 seconds / 100 ml, and the permeability of the flat portion of the separator is 120 to 140% relative to the permeability of the curved portion of the separator.

[0008] According to one embodiment of the present disclosure, cycle characteristics can be improved, and power characteristics can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 It is a perspective view showing a nonaqueous electrolyte secondary battery as an example of an embodiment.

[0010] Figure 2 It is a perspective view showing an electrode body as an example of an embodiment.

[0011] Figure 3 Schematic diagram showing the state of ceramic particles added to the positive electrode active material.

[0012] Figure 4 It is a schematic diagram showing the state in which the positive electrode slurry is kneaded.

[0013] Figure 5 It is a schematic diagram showing another state in which the positive electrode slurry is kneaded.

[0014] Figure 6 Schematic diagram showing the state of the positive electrode active material after the positive electrode composite material layer is compressed.

[0015] Figure 7 Schematic diagram showing the state of the positive electrode active material and separator after the electrode assembly is press-molded. DETAILED DESCRIPTION

[0016] The following drawings illustrate embodiments of the present disclosure. The shapes, materials, and numbers described below are examples and may be modified as appropriate based on the specifications of the non-aqueous electrolyte secondary battery. In all drawings, identical elements are denoted by the same reference numerals.

[0017] [Non-aqueous electrolyte secondary battery]

[0018] Figure 1 : is a perspective view of a non-aqueous electrolyte secondary battery 10 as an example of this embodiment. The non-aqueous electrolyte secondary battery 10 includes an electrode body 11 (see FIG. 1 ) in which a positive electrode and a negative electrode are stacked and wound with a separator 40 interposed therebetween. Figure 2 ), and a non-aqueous electrolyte impregnated into the electrode body 11. Figure 1 As shown, the nonaqueous electrolyte secondary battery 10 includes an outer can 12 having a bottomed cylindrical rectangular parallelepiped shape and a rectangular opening at the top, and a sealing member 13 that closes the rectangular opening of the outer can 12 .

[0019] The outer can 12 is a square can with a rectangular opening, formed from a metal material such as aluminum or an aluminum alloy, integrally molded into a predetermined shape. The sealing member 13 includes two external terminals: a positive electrode external terminal 15 and a negative electrode external terminal 16; an inlet 17 for injecting non-aqueous electrolyte into the outer can 12; and a gas outlet 18 for releasing internal gas to the outside of the non-aqueous electrolyte secondary battery 10 in the event of an abnormality caused by an increase in internal pressure.

[0020] [Electrode body]

[0021] Figure 2 is a three-dimensional diagram of the electrode body 11. Figure 2As shown, electrode body 11 is obtained by stacking and winding a positive electrode and a negative electrode with a separator 40 interposed therebetween to form a wound electrode body, applying pressure in a predetermined direction to the wound electrode body, and forming the wound electrode body into a flat shape. Electrode body 11 has a flat portion 11A that is compression-formed by the pressure application, and a curved portion 11B that is continuous with flat portion 11A and is not compression-formed by the pressure application.

[0022] [Non-aqueous electrolyte]

[0023] The nonaqueous electrolyte comprises a nonaqueous solvent and an electrolyte salt dissolved in the nonaqueous solvent. The nonaqueous electrolyte may comprise nitriles. Examples of nitriles include acetonitrile, propionitrile, butyronitrile, valeronitrile, n-heptanenitrile, succinonitrile, glutaronitrile, adiponitrile, pimelonitrile, 1,2,3-propanetricarboxylic acid nitrile, and 1,3,5-pentanetricarboxylic acid nitrile.

[0024] [Non-aqueous solvent]

[0025] Examples of non-aqueous solvents include cyclic carbonates, chain carbonates, and carboxylates. Specifically, examples include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, and vinylene carbonate; chain carbonates such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl propyl carbonate, ethyl propyl carbonate, and methyl isopropyl carbonate; chain carboxylates such as methyl propionate (MP), ethyl propionate, methyl acetate, ethyl acetate, and propyl acetate; and cyclic carboxylates such as γ-butyrolactone (GBL) and γ-valerolactone (GVL).

[0026] The non-aqueous solvent may contain ethers. Examples of the ethers include 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, propylene oxide, 1,2-butylene oxide, 1,3-dioxane, 1,4-dioxane, 1,3,5-trioxane, furan, 2-methylfuran, 1,8-cineole, and cyclic ethers such as crown ether; ethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, dihexyl ether, and ethyl ether. Chain ethers such as propylene glycol, 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, and tetraethylene glycol dimethyl ether.

[0027] The non-aqueous solvent may contain a halogen-substituted substance. Examples of the halogen-substituted substance include fluorinated cyclic carbonates such as 4-fluoroethylene carbonate (FEC), fluorinated chain carbonates, and fluorinated chain carboxylates such as methyl 3,3,3-trifluoropropionate (FMP).

[0028] [Electrolyte salt]

[0029] The electrolyte salt is preferably a lithium salt. Among the lithium salts, substances commonly used as supporting salts in conventional non-aqueous electrolyte secondary batteries can be used. Examples include LiBF4, LiClO4, LiPF6, LiAsF6, LiSbF6, LiAlCl4, LiSCN, LiCF3SO3, LiC(C2F5SO2)3, LiCF3CO2, Li(P(C2O4)F4), Li(P(C2O4)2F2), 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, Li2B4O7, Li(B(C2O4)2)[lithium bis(oxalatoborate)(LiBOB)], Li(B(C2O4)F2) and other borates, LiN(FSO2)2, LiN(C l F 2l+1 SO2)(C m F 2m+1 SO2) {l, m is an integer greater than 1} and other imide salts, Li x P y O z F α (x is an integer of 1 to 4, y is 1 or 2, z is an integer of 1 to 8, and α is an integer of 1 to 4), etc. Among them, LiPF6, Li x P y O z F α (x is an integer of 1 to 4, y is 1 or 2, z is an integer of 1 to 8, and α is an integer of 1 to 4). x P y O z F α Examples thereof include lithium monofluorophosphate and lithium difluorophosphate. These lithium salts may be used alone or in combination of two or more.

[0030] [positive electrode]

[0031] The positive electrode comprises a positive electrode core and a positive electrode composite material layer disposed on the positive electrode core. The positive electrode core can be made of a metal foil, such as aluminum, that is stable within the positive electrode potential range, or a thin film with the metal disposed on the surface. The positive electrode composite material layer comprises a positive electrode active material 21, a conductive material, and a binder 23, and is preferably disposed on both surfaces of the positive electrode core. Ceramic particles 22, described in detail below, are added to the positive electrode active material 21.

[0032] [Active substance]

[0033] The positive electrode active material 21 is a metal oxide containing at least lithium and a transition metal element, for example, a metal oxide having the general formula Li x Me y O2 represents. In the above general formula, Me is a transition metal element such as nickel, cobalt and manganese. x is, for example, not less than 0.8 and not more than 1.2. y varies depending on the type and oxidation number of Me, but is, for example, not less than 0.7 and not more than 1.3. As a lithium-containing transition metal oxide, lithium nickel cobalt manganese oxide containing Ni, Co and Mn is particularly preferred. In addition, it is preferred that the positive electrode active material 21 contains 10 to 40 mol% of manganese relative to the total amount of the transition metal.

[0034] The added elements of the transition metal oxide containing lithium are not limited to nickel, cobalt and manganese, and other added elements may also be included. As other added elements, for example, alkali metal elements other than lithium, transition metal elements other than Mn, Ni and Co, alkaline earth metal elements, Group 12 elements, Group 13 elements and Group 14 elements can be cited. As specific examples of other added elements, for example, zirconium (Zr), boron (B), magnesium (Mg), aluminum (Al), titanium (Ti), iron (Fe), copper (Cu), zinc (Zn), tin (Sn), sodium (Na), potassium (K), barium (Ba), strontium (Sr) and calcium (Ca) can be cited. Among them, Zr is suitable. It is believed that by containing Zr, the crystal structure of the transition metal oxide containing lithium is stabilized, and the durability and cyclability of the positive electrode composite material layer at high temperature are improved. The Zr content in the lithium-containing transition metal oxide is preferably 0.05 mol% to 10 mol%, more preferably 0.1 mol% to 5 mol%, particularly preferably 0.2 mol% to 3 mol%, based on the total amount of metals excluding Li.

[0035] [Ceramic particles]

[0036] Figure 3 Schematic diagram showing the state of ceramic particles 22 added to the positive electrode active material 21. Figure 3 As shown, ceramic particles 22 are added to the positive electrode active material 21 so that the ceramic particles 22 adhere closely to the surface of the positive electrode active material 21. The ceramic particles 22 are preferably dispersed on the surface of the positive electrode active material 21.

[0037] Ceramic particles 22 are insulating ceramics, preferably made of a high-resistance insulating material. They can be nitride-based or oxide-based ceramics. They contain at least one oxide selected from titanium oxide, aluminum oxide, and zirconium dioxide. The amount of ceramic particles 22 added to the positive electrode composite material layer is preferably 0.10 to 0.30 wt%, more preferably 0.20 to 0.30 wt%.

[0038] The volume-based median diameter (D50) of the ceramic particles 22 is preferably 0.5 μm or less, more preferably 0.05 μm to 0.1 μm. When the D50 of the ceramic particles 22 is set to 1, the ratio of the D50 of the positive electrode active material 21 is preferably 10 to 200, more preferably 15 to 25. The median diameter refers to the median diameter at which the volume cumulative value of the particle size distribution measured by a laser diffraction and scattering particle size distribution analyzer (e.g., HORIBA LA-750) reaches 50%.

[0039] Figure 4 and Figure 5 Schematic diagram showing the state of kneading the positive electrode slurry. Figure 4 As shown in FIG, a binder 23 is added during the kneading of the positive electrode slurry to improve the adhesion between the positive electrode active material 21 and the ceramic particles 22. Figure 5 As shown, the binder 23 dissolves in the solvent and changes from a solid phase to a liquid phase. Therefore, the binder 23 is incorporated between the positive electrode active material 21 and the ceramic particles 22 , further improving the adhesion between the positive electrode active material 21 and the ceramic particles 22 .

[0040] Figure 6 Schematic diagram showing the state of the positive electrode active material 21 after the positive electrode composite material layer is compressed. Figure 6 As shown, the ceramic particles 22 are pressed and bite into the surface of the positive electrode active material 21, further improving the adhesion between the positive electrode active material 21 and the ceramic particles 22. As described in detail later, after the positive electrode and the negative electrode are stacked and wound with the separator 40 interposed therebetween, the ceramic particles 22 of the positive electrode active material 21 bite into the separator 40, which can improve the adhesion between the positive electrode and the separator 40.

[0041] [Conductive materials]

[0042] Examples of the conductive material include carbon materials such as carbon black, acetylene black, Ketjen black, and graphite, etc. These may be used alone or in combination of two or more.

[0043] [Bonding material]

[0044] Examples of the adhesive material 23 include fluorine-based resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide-based resins, acrylic resins, and polyolefin-based resins. Furthermore, these resins can be used in combination with carboxymethyl cellulose (CMC) or its salts (CMC-Na, CMC-K, CMC-NH4, and partially neutralized salts), polyethylene oxide (PEO), and the like. These can be used alone or in combination of two or more.

[0045] [negative electrode]

[0046] The negative electrode is preferably composed of a negative electrode current collector formed of, for example, a metal foil, and a negative electrode composite material layer formed on one or both sides of the current collector. The negative electrode current collector may be a foil of a metal that is stable within the potential range of the negative electrode, or a thin film having the metal disposed on the surface. The negative electrode composite material layer preferably includes a binder in addition to the negative electrode active material.

[0047] [Active substance]

[0048] As the negative electrode active material, for those that can reversibly absorb and release lithium ions, for example, graphite-based carbon materials such as natural graphite and artificial graphite, amorphous carbon materials, metals such as Si and Sn alloyed with lithium, alloy materials or metal composite oxides, etc. can be mentioned. In addition, they can be used alone or in combination of two or more. From the perspective of easily forming a low-resistance film on the negative electrode surface, it is particularly preferred to use a carbon material comprising a graphite-based carbon material and an amorphous carbon material fixed to the surface of the graphite-based carbon material.

[0049] Graphite-based carbon materials refer to carbon materials with a well-developed graphite crystal structure, and examples thereof include natural graphite and artificial graphite. They may be in the form of flakes, or may be sphericalized to form spheres. Artificial graphite may be produced by heat-treating petroleum, coal pitch, coke, or the like at 2000 to 3000°C or above in an Acheson furnace, a graphite heating furnace, or the like. The d(002) plane spacing based on X-ray diffraction is preferably 0.338 nm or less, and the thickness of the crystal in the c-axis direction (Lc(002)) is preferably 30 to 1000 nm.

[0050] Amorphous carbon materials refer to carbon materials with underdeveloped graphite crystal structures, and are carbon materials in an amorphous or microcrystalline state with a turbostratic structure. More specifically, they refer to materials with a d(002) plane spacing of 0.342 nm or more based on X-ray diffraction. Examples of amorphous carbon materials include hard carbon (difficult to graphitize carbon), soft carbon (easy to graphitize carbon), carbon black, carbon fibers, activated carbon, and the like. Their production methods are not particularly limited. For example, they can be obtained by carbonizing a resin or a resin composition, and phenolic thermosetting resins, thermoplastic resins such as polyacrylonitrile, petroleum or coal-based tar, asphalt, and the like can be used. In addition, for example, carbon black is obtained by thermal cracking of hydrocarbons as raw materials, and examples of thermal cracking methods include thermal methods and acetylene decomposition methods. Examples of incomplete combustion methods include contact methods, lamp / pine soot methods, gas furnace methods, and oil furnace methods. Specific examples of carbon black produced by these production methods include acetylene black, Ketjen black, thermal cracking carbon black, and furnace black. In addition, the surfaces of these amorphous carbon materials may be further covered with other non-crystalline and amorphous carbon.

[0051] In addition, the amorphous carbon material is preferably present in a state of being fixed to the surface of the graphite-based carbon material. Here, fixed refers to a state of being chemically / physically bonded, meaning that even if the negative electrode active material of the present disclosure is stirred in water or an organic solvent, the graphite-based carbon material and the amorphous carbon material do not separate.

[0052] By attaching an amorphous carbon material having a larger reaction area than graphite carbon and a multi-oriented structure to the surface of the graphite carbon material, a film with a low reaction overvoltage is formed on the surface of the amorphous carbon material. Therefore, it is believed that the reaction overvoltage of the graphite carbon material as a whole for Li insertion / extraction reactions is reduced. Furthermore, since the amorphous carbon material has a higher reaction potential than the graphite carbon material, it preferentially reacts with the Group 5 / Group 6 elements dissolved from the positive electrode, forming a high-quality film with better lithium ion permeability on the surface of the amorphous carbon material. Therefore, it is believed that the reaction resistance of the graphite carbon material as a whole for Li insertion / extraction reactions is further reduced.

[0053] The ratio of the graphite-based carbon material to the amorphous carbon material is not particularly limited. A higher proportion of the amorphous carbon material, which has excellent Li storage properties, is preferred. The proportion of the amorphous carbon material is more preferably 0.5 wt% or greater, and preferably 2 wt% or greater, of the active material. However, if the amorphous carbon material becomes excessive, it will not be uniformly fixed to the graphite surface. Therefore, it is preferable to determine an upper limit taking this into consideration.

[0054] As methods for fixing amorphous carbon to graphite-based carbon materials, there are the following methods: a method of adding petroleum-based or coal-based tar, asphalt, etc. to the amorphous carbon material, mixing it with the graphite-based carbon material, and then heat treating it; a mechanical fusion method of applying compressive shear stress between graphite particles and solid amorphous carbon to cover them; a solid phase method of covering by sputtering method, etc.; a liquid phase method of dissolving amorphous carbon in a solvent such as toluene and impregnating graphite, and then heat treating it; etc.

[0055] From the perspective of Li diffusion distance, the primary particle size of amorphous carbon is preferably small. In addition, the reaction surface area for Li storage reaction becomes larger, so the larger the specific surface area, the more preferred. However, if it is too large, excessive reaction occurs at the surface, resulting in an increase in resistance. Therefore, the specific surface area of ​​amorphous carbon is preferably 5m 2 / g and above~200m 2 From the viewpoint of reducing excess specific surface area, the primary particle size is preferably 20 nm to 1000 nm, more preferably 40 nm to 100 nm, and preferably does not have a hollow structure with a cavity within the particle.

[0056] [Bonding material]

[0057] As the binder, fluorine-based resins, PAN, polyimide-based resins, acrylic resins, polyolefin-based resins, etc. can be used in the same manner as in the case of the positive electrode. When an aqueous solvent is used to prepare the negative electrode composite material slurry, styrene-butadiene rubber (SBR), CMC or its salts, polyacrylic acid (PAA) or its salts (PAA-Na, PAA-K, etc., and partially neutralized salts), polyvinyl alcohol (PVA), etc. are preferably used.

[0058] [Separator]

[0059] A porous sheet having ion permeability and insulation is used as the separator 40. Specific examples of the porous sheet include microporous films, woven fabrics, non-woven fabrics, and the like. Suitable materials for the separator 40 include olefin resins such as polyethylene and polypropylene, and cellulose. The separator 40 may be a laminate having a cellulose fiber layer and a thermoplastic resin fiber layer such as an olefin resin. In addition, a multilayer separator comprising a polyethylene layer and a polypropylene layer may be used, or a separator obtained by coating the surface of the separator 40 with a resin such as an aramid resin may be used. Among these materials, polyolefin resins are preferably used.

[0060] For example, the separator 40 made of a polyolefin resin can be formed with pores by a known method such as a dry method or a wet method. The air permeability (air permeability) of the separator 40 can be adjusted by adjusting the size and number of the pores. The air permeability can be measured using a Gurley tester method (according to JIS P8117).

[0061] Then, when the separator / positive electrode / separator / negative electrode are stacked, wound, and press-formed into a flat shape to form the electrode body 11, the pores of the separator 40 are crushed due to the press-forming, thereby changing the air permeability of the separator 40 constituting the electrode body 11.

[0062] The air permeability of the separator 40 is preferably 165 to 310 sec / 100 ml, more preferably 180 to 310 sec / 100 ml. The air permeability of the separator 40 is adjusted so that D50 of the ceramic particles 22 is sufficiently larger than the diameter of the pores 40A of the separator 40 .

[0063] The air permeability of the flat portion of the separator 40 (the portion facing the flat portion 11A of the electrode body 11) is preferably 120-140%, and more preferably 130-140%, relative to the air permeability of the curved portion of the separator 40 (the portion facing the curved portion 11B of the electrode body 11). The curved portion of the separator 40 is not compressed by the pressurizing pressure. Therefore, the curved portion of the separator 40 has the same air permeability as the separator 40 before press molding, and the flat portion of the separator 40 has the same air permeability as the separator 40 after press molding. In other words, the air permeability of the separator 40 after press molding is preferably 120-140%, and more preferably 130-140%, relative to the air permeability of the separator 40 before press molding.

[0064] Figure 7 Schematic diagram showing the state of the positive electrode active material 21 and the separator 40 after the electrode body 11 is press-formed. Figure 7 As shown, the ceramic particles 22 adhered to the positive electrode active material 21 bite into the separator 40, thereby acting as an anchoring effect, thereby enhancing the close adhesion between the positive electrode active material 21 and the separator 40. This can suppress the formation of gaps between the separator 40 and the positive electrode due to expansion or contraction of the positive electrode active material 21 during cycling, and can improve the cycle characteristics of the non-aqueous electrolyte secondary battery 10.

[0065] It should be noted that, in this embodiment, D50 of the ceramic particles 22 is sufficiently larger than the diameter of the pores 40A of the separator 40 . Therefore, the ceramic particles 22 are not incorporated into the pores 40A of the separator 40 .

[0066] For example, in order to improve the adhesion strength between the separator 40 and the positive electrode active material 21 without adding ceramic particles 22, a solution of increasing the pressurization pressure is considered. However, if the pressurization pressure is increased, the air permeability of the separator 40 becomes higher, and the power characteristics of the non-aqueous electrolyte secondary battery 10 are reduced. In addition, if the amount of ceramic particles 22 added is excessive, the lithium ion diffusion reaction is hindered, thereby reducing the power characteristics of the non-aqueous electrolyte secondary battery 10. In this embodiment, by adding an appropriate amount of ceramic particles 22, the cycle characteristics can be improved without reducing the power characteristics of the non-aqueous electrolyte secondary battery 10.

[0067] Furthermore, in this embodiment, a small gap is formed near the contact surface between the separator 40 and the ceramic particles 22, and the electrolyte penetrates into and retains the electrolyte. This prevents deterioration in the cycle characteristics of the non-aqueous electrolyte secondary battery 10 due to electrolyte depletion during cycling.

[0068] It should be noted that the present invention is not limited to the above-described embodiment and its modifications, and various changes and improvements can be made within the scope of the features described in the claims of the present application.

[0069] <Example>

[0070] Hereinafter, the present disclosure will be further described based on examples, but the present disclosure is not limited to these examples.

[0071] <Example 1>

[0072] [Production of positive electrode]

[0073] As the positive electrode active material, a lithium nickel cobalt manganese composite oxide (LiNi) was added with 0.20 wt% of ceramic particles with a D50 of 0.5 μm or less. 0.35 Co 0.35 Mn 0.30 O2), polyvinylidene fluoride as a binding material, carbon black as a conductive material, and N-methyl-2-pyrrolidone as a dispersion medium are mixed to prepare a positive electrode active material composite material slurry. In addition, in the above-mentioned positive electrode active material composite material slurry, the mass ratio of lithium nickel cobalt manganese composite oxide: polyvinylidene fluoride: carbon black is made to be 90:3:7. Then, using a die coater, the above-mentioned positive electrode active material composite material slurry is applied to the surface of both sides of an aluminum foil with a thickness of 15μm as a positive electrode core. Thereafter, the positive electrode active material composite material slurry is dried, and the N-methyl-2-pyrrolidone as a dispersion medium is removed to form a positive electrode active material composite material layer on the positive electrode core. Thereafter, a compression roller is used to compress the positive electrode active material composite material layer to a specified filling density (2.5g / cm 3), and cut into a predetermined size so as to form a positive electrode core exposed portion on one side in the longitudinal direction of the positive electrode plate to obtain a positive electrode plate.

[0074] [Production of negative electrode]

[0075] Graphite as a negative electrode active material, styrene butadiene rubber (SBR) as a binder, carboxymethyl cellulose (CMC) as a thickening material, and water as a dispersion medium are mixed in a mass ratio of graphite:SBR:CMC of 99.2:0.6:0.2 to prepare a negative electrode active material composite material slurry. The negative electrode active material composite material slurry is applied to both sides of a copper foil with a thickness of 8 μm as a negative electrode core using a die coater. The negative electrode active material composite material slurry is then dried to remove water from the negative electrode active material composite material slurry, forming a negative electrode active material composite material layer on the core. Thereafter, a compression roller is used to compress the negative electrode active material composite material layer to a specified filling density (1.2 g / cm 3 ), a negative electrode core exposed portion is formed on one side of the negative electrode plate in the longitudinal direction, and the positive electrode plate is cut into a predetermined size.

[0076] [Production of Electrode Body]

[0077] The positive electrode plate produced by the above method and the negative electrode plate produced by the above method are wound with a separator made of polypropylene having a thickness of 18 μm and an air permeability of 140 seconds / 100 ml, and then press-formed into a flat shape to produce a flat wound electrode body. The separator / positive electrode / separator / negative electrode stacked in this order is wound on a cylindrical winding core to form a wound body. In addition, the positive electrode and the negative electrode are wound in such a way that the exposed parts of their respective cores are located on opposite sides of the wound body in the axial direction. At this time, the air permeability of the separator blank before press forming is measured in advance, the flat wound electrode body after press forming is disassembled, the air permeability of the separator at the position after press forming is measured on the flat part, and the air permeability of the separator before and after press forming is compared. The air permeability after press forming is 168 seconds / 100 ml, and the air permeability increase rate after press forming is 120%. The air permeability is measured by Gurley permeability (according to JIS P8117).

[0078] [Preparation of non-aqueous electrolyte]

[0079] A mixed solvent of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 3:3:4 (25°C, 1 atm) was prepared. LiPF6 was added as a solute at a concentration of 1.15 mol / L to this mixed solvent, and 1% by mass of lithium fluorosulfonate was further added to form a non-aqueous electrolyte.

[0080] [Fabrication of non-aqueous electrolyte secondary battery]

[0081] After welding the positive current collector plate to the exposed portion of the positive electrode core and the negative current collector plate to the exposed portion of the negative electrode core, the electrode assembly was inserted into the rectangular outer can and the current collector plates were connected to the corresponding terminals. A sealing plate was installed at the opening of the outer can. The non-aqueous electrolyte was injected through the electrolyte injection hole in the sealing plate and then sealed with a sealing plug to produce a non-aqueous electrolyte secondary battery with a rated capacity of 4.1 Ah.

[0082] <Example 2>

[0083] In the production of the electrode assembly, a battery was produced in the same manner as in Example 1 except that the air permeability of the separator after press molding was 182 sec / 100 ml and the air permeability increase rate of the separator after press molding was 130%.

[0084] <Example 3>

[0085] In the production of the electrode assembly, a battery was produced in the same manner as in Example 1 except that the air permeability of the separator after press molding was 196 sec / 100 ml and the air permeability increase rate of the separator after press molding was 140%.

[0086] <Example 4>

[0087] In the production of the positive electrode, a battery was produced in the same manner as in Example 2 except that 0.10 wt % of ceramic particles having a D50 of 0.5 μm or less were added.

[0088] <Example 5>

[0089] In the production of the positive electrode, a battery was produced in the same manner as in Example 2 except that 0.30 wt % of ceramic particles having a D50 of 0.5 μm or less were added.

[0090] <Example 6>

[0091] A separator having a Gurley air permeability of 220 sec / 100 ml was prepared. In the preparation of the electrode assembly, a battery was prepared in the same manner as in Example 1 except that the air permeability of the separator after press molding was 264 sec / 100 ml and the air permeability increase rate of the separator after press molding was 120%.

[0092] <Example 7>

[0093] In the production of the electrode assembly, a battery was produced in the same manner as in Example 6 except that the air permeability of the separator after press molding was 286 sec / 100 ml and the air permeability increase rate of the separator after press molding was 130%.

[0094] <Example 8>

[0095] In the production of the electrode assembly, a battery was produced in the same manner as in Example 6 except that the air permeability of the separator after press molding was 308 sec / 100 ml and the air permeability increase rate of the separator after press molding was 140%.

[0096] Comparative Example 1

[0097] In the production of the positive electrode, no ceramic particles were added. In the production of the electrode body, the air permeability of the separator after pressurization was 154 seconds / 100 ml, and the air permeability increase rate of the separator after pressurization was 110%. Except for this, the battery was produced in the same manner as in Example 1.

[0098] Comparative Example 2

[0099] In the production of the electrode assembly, a battery was produced in the same manner as in Comparative Example 1, except that the air permeability of the separator after press molding was 168 sec / 100 ml and the air permeability increase rate of the separator after press molding was 120%.

[0100] Comparative Example 3

[0101] In the production of the electrode assembly, a battery was produced in the same manner as in Comparative Example 1, except that the air permeability of the separator after press molding was 182 sec / 100 ml and the air permeability increase rate of the separator after press molding was 130%.

[0102] <Comparative Example 4>

[0103] In the production of the electrode assembly, a battery was produced in the same manner as in Comparative Example 1, except that the air permeability of the separator after press molding was 196 sec / 100 ml and the air permeability increase rate of the separator after press molding was 140%.

[0104] <Comparative Example 5>

[0105] In the production of the electrode assembly, a battery was produced in the same manner as in Comparative Example 1, except that the air permeability of the separator after press molding was 210 sec / 100 ml and the air permeability increase rate of the separator after press molding was 150%.

[0106] <Comparative Example 6>

[0107] In the production of the positive electrode, a battery was produced in the same manner as in Comparative Example 1, except that 0.20 wt % of ceramic particles having a D50 of 0.5 μm or less were added.

[0108] <Comparative Example 7>

[0109] In the production of the positive electrode, a battery was produced in the same manner as in Comparative Example 5, except that 0.20 wt % of ceramic particles having a D50 of 0.5 μm or less were added.

[0110] <Comparative Example 8>

[0111] In the production of the positive electrode, a battery was produced in the same manner as in Comparative Example 3 except that 0.05 wt % of ceramic particles having a D50 of 0.5 μm or less were added.

[0112] <Comparative Example 9>

[0113] In the production of the positive electrode, a battery was produced in the same manner as in Comparative Example 3 except that 0.4 wt % of ceramic particles having a D50 of 0.5 μm or less were added.

[0114] <Comparative Example 10>

[0115] A separator having a Gurley air permeability of 220 sec / 100 ml was prepared. In the preparation of the electrode assembly, a battery was prepared in the same manner as in Comparative Example 6 except that the air permeability of the separator after press molding was 242 sec / 100 ml and the air permeability increase rate of the separator after press molding was 110%.

[0116] <Comparative Example 11>

[0117] In the production of the electrode assembly, a battery was produced in the same manner as in Comparative Example 10 except that the air permeability of the separator after press molding was 330 sec / 100 ml and the air permeability increase rate of the separator after press molding was 150%.

[0118] [Moldability]

[0119] It was confirmed whether the electrode body was molded so as to fall within a predetermined height and predetermined thickness.

[0120] [Power characteristics]

[0121] For non-aqueous electrolyte secondary batteries, CCCV charging is performed at a charging current of 1 / 10 It under the condition of 25°C until the state of charge (SOC) becomes 50%. For non-aqueous electrolyte secondary batteries, CCCV charging is performed at a charging current of 1 / 10 It under the condition of 25°C until the state of charge (SOC) becomes 50%. Then, the non-aqueous electrolyte secondary batteries are placed under the condition of 25°C for 2 hours. After that, under the condition of 25°C, discharge is performed for 10 seconds at currents of 1 It, 2 It, 4 It, 8 It, 10 It, 12 It and 16 It, and the voltage of each battery is measured. Each current value and battery voltage are plotted, and the power (W) is calculated from the IV characteristics during discharge as the room temperature power characteristics. It should be noted that the state of charge deviated by discharge is restored to the original state of charge by charging at a constant current of 1 It. Table 1 shows the relative values ​​when the power characteristics of the battery of Comparative Example 1 are 100 as power characteristics.

[0122] [Cycle characteristics]

[0123] At 25°C, constant current charging was performed at a constant current of 1It until the battery voltage reached 4.10V. Thereafter, constant voltage charging was performed at a constant voltage of 4.10V for 1.5 hours. After a pause of 10 seconds, the battery was discharged at a constant current of 1It until the battery voltage reached 2.5V. The discharge capacity at this time was referred to as the battery capacity before the cycle. Then, the following charge and discharge cycles were performed 400 times at 25°C. Charge at a constant current of 2It until the battery voltage reached 4.10V. After a pause of 10 seconds, discharge at a constant current of 2It until the battery voltage reached 3.0V. This was referred to as one cycle. After 400 cycles, constant current charging was performed at 25°C at a constant current of 1It until the battery voltage reached 4.1V. Thereafter, constant voltage charging was performed at a constant voltage of 4.1V for 1.5 hours. After a pause of 10 seconds, discharge at a constant current of 1It until the battery voltage reached 2.5V. The discharge capacity at this time was referred to as the battery capacity after high-temperature cycling. Then, the capacity retention rate after high-temperature cycling was calculated according to the following formula: Table 1 shows relative values ​​when the cycle characteristics of the battery of Comparative Example 1 are regarded as 100 as cycle characteristics.

[0124] Capacity retention rate = (battery capacity after cycle (Ah) / battery capacity before cycle (Ah))

[0125] [Table 1]

[0126]

[0127] As shown in Table 1, the batteries of Examples 1 to 8 were excellent in both power characteristics and cycle characteristics.

[0128] In Examples 1-3, while the air permeability and rise rate of the separator after press molding were the same as those of Comparative Examples 2-4, it was confirmed that the moldability was improved, and the cycle characteristics were significantly improved. This is believed to be because the addition of ceramic particles enhanced the adhesion between the positive electrode composite material layer and the separator during press molding, and suppressed capacity degradation during charge-discharge cycles.

[0129] In the case of Examples 4-5, compared with Comparative Example 3, it was confirmed that the moldability, power characteristics, and cycle characteristics were improved by adding the ceramic particles.

[0130] In the case of Examples 6-8, it was confirmed that the formability, power characteristics and cycle characteristics after press molding showed the same tendency as in Examples 1-3. When separators with different air permeabilities were used, the air permeability increase rate of the separators after press molding was also preferably in the range of 120-140%.

[0131] In Comparative Examples 1 to 5, it was confirmed that increasing the pressurization pressure caused the separator pores to be crushed, and the air permeability of the separator to increase and deteriorate. Furthermore, the moldability was also insufficient in Comparative Example 5, where the pressurization pressure was the highest.

[0132] In the case of Comparative Example 6, the moldability was insufficient due to insufficient pressurization, and even when ceramic particles were added, the cycle characteristics were not improved when the separator air permeability increase rate was 110%.

[0133] In Comparative Example 7, the pressurization pressure was the highest and the moldability was sufficient, but the power characteristics and cycle characteristics were lower than those of Examples 1 to 3. This is believed to be because the high pressurization pressure resulted in excessive adhesion between the positive electrode composite material layer and the separator, making it difficult for the electrolyte to penetrate, and thus failing to improve the power characteristics and cycle characteristics.

[0134] In Comparative Example 8, 0.05 wt% of ceramic particles were added to the positive electrode active material. However, the power and cycle characteristics remained largely unchanged compared to Comparative Example 3. Adding inorganic particles did not improve these characteristics. This is believed to be due to the small amount of inorganic particles added.

[0135] In the case of Comparative Example 9, it is considered that the amount of ceramic particles added was excessive (addition amount 0.40 wt %), and the ceramic particles became a resistance component in the positive electrode material layer, thereby deteriorating the power characteristics.

[0136] In the case of Comparative Examples 10-11, as in Comparative Examples 6, 7, and Examples 1-3, it was confirmed that the formability, power characteristics, and cycle characteristics after press molding showed the same tendency. Even when separators with different air permeabilities were used, the air permeability increase rate of the separators after press molding was preferably in the range of 120-140%.

[0137] Description of Reference Numerals

[0138] 10 Non-aqueous electrolyte secondary batteries

[0139] 11 Electrode body

[0140] 11A Flat part

[0141] 11B curved face

[0142] 12 shell tank

[0143] 13 Sealing body

[0144] 15 Positive external terminal

[0145] 16 Negative external terminal

[0146] 18 Gas exhaust port

[0147] 20 positive electrode

[0148] 21. Positive electrode active material

[0149] 21. Positive electrode core

[0150] 22 Ceramic particles

[0151] 23 Adhesive material

[0152] 40 dividers

[0153] 40A hole

Claims

1. A non-aqueous electrolyte secondary battery comprising: an electrode body in which a positive electrode and a negative electrode are wound into a flat shape with a separator interposed therebetween; and a non-aqueous electrolyte, wherein the positive electrode comprises a positive electrode composite material layer containing a positive electrode active material. The positive electrode composite material layer contains 0.10-0.30% by mass of ceramic particles. The volume-based median particle size (D50) of the ceramic particles is 0.5 μm or less, The air permeability of the separator is 165-310 seconds / 100 ml, The air permeability of the flat portion of the separator is 120-140% of the air permeability of the curved portion of the separator. The ceramic particles are insulating ceramics, and are closely attached to the surface of the positive electrode active material. The ceramic particles closely attached to the positive electrode active material are engaged with the separator.

2. The nonaqueous electrolyte secondary battery according to claim 1, wherein The ratio of D50 of the positive electrode active material when D50 of the ceramic particles is set to 1 is 10-200.

3. The non-aqueous electrolyte secondary battery according to claim 1, wherein The positive electrode active material contains 10 to 40 mol % of manganese relative to the total amount of transition metals.

4. The nonaqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein The ceramic particles include at least one oxide selected from the group consisting of titanium oxide, aluminum oxide, and zirconium dioxide.

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