Non-aqueous electrolyte secondary battery

Abstract

This non-aqueous electrolyte secondary battery has: an electrode body formed by winding, in a flat shape, a positive electrode and a negative electrode with a separator interposed therebetween; and a non-aqueous electrolyte. The positive electrode has a positive electrode mixture layer containing a positive electrode active material. In the positive electrode mixture layer, 0.10-0.30 mass% of ceramic particles are added, the volume-based median size (D50) of the ceramic particles is 0.5 μm or less, the air permeability of the separator is 165-310 sec / 100 ml, and the air permeability of a flat portion of the separator with respect to the air permeability of a curved portion of the separator is 120-140%.

Description

[Technical field]

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

[0002] It is known to add ceramic particles to the positive electrode composite layer of a nonaqueous electrolyte secondary battery. For example, in the nonaqueous electrolyte secondary battery disclosed in Patent Document 1, the positive electrode active material is coated with alumina particles to improve thermal stability during charging and cycle characteristics. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2001-143703 A Summary of the Invention

[0004] In non-aqueous electrolyte secondary batteries, the positive electrode active material expands and contracts with the insertion and desorption of lithium ions as the battery is repeatedly charged and discharged. 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, resulting in a deterioration in cycle characteristics. As a solution to this problem, for example, a rolled electrode body may be pressed into a flat shape to strengthen the adhesion between the positive electrode and the separator. However, in this case, the pores of the separator are crushed, increasing the air permeability of the separator, resulting in a deterioration in output characteristics.

[0005] A nonaqueous electrolyte secondary battery according to one embodiment of the present disclosure is a nonaqueous electrolyte secondary battery comprising an electrode assembly in which a positive electrode and a negative electrode are wound flatly with a separator interposed therebetween, and a nonaqueous electrolyte, in which the positive electrode has a positive electrode mixture layer containing a positive electrode active material, in which 0.10 to 0.30 mass % of ceramic particles are added to the positive electrode mixture layer, the volume-based median diameter (D50) of the ceramic particles is 0.5 μm or less, the air permeability of the separator is 165 to 310 sec / 100 ml, and the air permeability of the flat portions of the separator is 120 to 140% of the air permeability of the curved portions of the separator.

[0006] According to one aspect of the present disclosure, it is possible to improve cycle characteristics and output characteristics. [Brief description of the drawings]

[0007] [Figure 1] FIG. 1 is a perspective view showing a nonaqueous electrolyte secondary battery as an example of the embodiment. [Diagram 2] FIG. 2 is a perspective view showing an electrode assembly according to an embodiment. [Diagram 3] FIG. 3 is a schematic diagram showing the state of ceramic particles added to the positive electrode active material. [Figure 4] FIG. 4 is a schematic diagram showing the state in which the positive electrode slurry is kneaded. [Diagram 5] FIG. 5 is a schematic diagram showing another state in which the positive electrode slurry is kneaded. [Figure 6] FIG. 6 is a schematic diagram showing the state of the positive electrode active material after the positive electrode mixture layer is compressed. [Figure 7] FIG. 7 is a schematic diagram showing the state of the positive electrode active material and the separator after the electrode body has been press-molded. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. The shapes, materials, and quantities described below are merely examples and can be changed as appropriate according to the specifications of the non-aqueous electrolyte secondary battery. In the following, the same reference numerals are used to denote equivalent elements in all drawings.

[0009] [Nonaqueous electrolyte secondary battery] Fig. 1 is a perspective view of a nonaqueous electrolyte secondary battery 10 as an example of this embodiment. The nonaqueous electrolyte secondary battery 10 has an electrode assembly 11 (see Fig. 2) in which a positive electrode and a negative electrode are stacked and wound with a separator 40 interposed therebetween and wound into a flat shape, and a nonaqueous electrolyte impregnated in the electrode assembly 11. As shown in Fig. 1, the nonaqueous electrolyte secondary battery 10 also has an outer can 12 in the shape of a cylindrical rectangular parallelepiped with a bottom having a rectangular opening on the ceiling side, and a sealing body 13 that closes the rectangular opening of the outer can 12.

[0010] The exterior can 12 is a square can body having a rectangular opening, and is made by integrally molding a metal material such as aluminum or an aluminum alloy into a predetermined shape. The sealing body 13 includes two external terminals, a positive electrode external terminal 15 and a negative electrode external terminal 16, a liquid injection port 17 for injecting a nonaqueous electrolyte into the exterior can 12, and a gas exhaust port 18 for releasing internal gas to the outside of the nonaqueous electrolyte secondary battery 10 when the internal pressure increases in the event of an abnormality in the nonaqueous electrolyte secondary battery 10.

[0011] [Electrode body] Fig. 2 is a perspective view of the electrode body 11. As shown in Fig. 2, the electrode body 11 is formed by applying a press pressure in a predetermined direction to a wound electrode body in which a positive electrode and a negative electrode are stacked and wound with a separator 40 interposed therebetween, and molding the wound electrode body into a flat shape. The electrode body 11 has a flat portion 11A that is compression molded by the press pressure, and a curved portion 11B that is formed continuously with the flat portion 11A and is not compression molded by the press pressure.

[0012] [Non-aqueous electrolyte] The non-aqueous electrolyte includes a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. The non-aqueous electrolyte may include nitriles. Examples of nitriles include acetonitrile, propionitrile, butyronitrile, valeronitrile, n-heptanenitrile, succinonitrile, glutaronitrile, adiponitrile, pimelonitrile, 1,2,3-propanetricarbonitrile, and 1,3,5-pentanetricarbonitrile.

[0013] [Non-aqueous solvent] Examples of the non-aqueous solvent include cyclic carbonates, chain carbonates, and carboxylates.Specific 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).

[0014] The non-aqueous solvent may contain an ether. Examples of the ether include cyclic ethers such as 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 crown ether; diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, dihexyl ether, ethyl vinyl ether, butyl vinyl ether, methyl phenyl ether, and ethyl and chain ethers such as diphenyl ether, butylphenyl ether, pentylphenyl 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.

[0015] The non-aqueous solvent may contain a halogen-substituted product. Examples of the halogen-substituted product 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).

[0016] [Electrolyte salt] The electrolyte salt is preferably a lithium salt. The lithium salt may be any salt that is generally used as a supporting salt in conventional non-aqueous electrolyte secondary batteries. For example, LiBF 4 , LiClO 4 , LiPF 6 , LiAsF 6 , LiSbF 6 , LiAlCl 4 , LiSCN, LiCF 3 SO 3 , LiC(C 2 F 5 SO 2 ) 3 , LiCF 3 CO 2 , Li(P(C 2 O 4 )F 4 ), Li(P(C 2 O 4 ) 2 F 2 ), 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, Li 2 B 4 O 7 , Li(B(C 2 O 4 ) 2 ) [Lithium bis(oxalato)borate (LiBOB)], Li(B(C 2 O 4 )F 2 ) and other borates, LiN(FSO 2 ) 2, LiN(C l F 2l+1 SO 2 )(C m F 2m+1 SO 2 ) {l and m are integers of 1 or more}, imide salts such as Li x P y O z F α (wherein 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). Among these, LiPF 6 Or Li x P y O z F α (wherein 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) are preferred. x P y O z F α Examples of the lithium salt include lithium monofluorophosphate, lithium difluorophosphate, etc. The lithium salt may be used alone or in combination of two or more kinds.

[0017] [Positive electrode] The positive electrode has a positive electrode core and a positive electrode composite layer provided on the positive electrode core. For the positive electrode core, a foil of a metal such as aluminum that is stable in the potential range of the positive electrode, or a film with the metal disposed on the surface layer, can be used. The positive electrode composite layer contains a positive electrode active material 21, a conductive material, and a binder 23, and is preferably provided on both sides of the positive electrode core. Ceramic particles 22, which will be described in detail later, are added to the positive electrode active material 21.

[0018] [Active material] The positive electrode active material 21 is a metal oxide containing at least lithium and a transition metal element, for example, a metal oxide represented by the general formula Li x Me y O 2In the above general formula, Me is a transition metal element such as nickel, cobalt, or manganese. x is, for example, 0.8 or more and 1.2 or less. y varies depending on the type and oxidation number of Me, but is, for example, 0.7 or more and 1.3 or less. As the lithium-containing transition metal oxide, lithium nickel cobalt manganese oxide containing Ni, Co, and Mn is particularly preferable. In addition, the positive electrode active material 21 preferably contains 10 to 40 mol % of manganese with respect to the total amount of transition metals.

[0019] The additive element of the lithium-containing transition metal oxide is not limited to nickel, cobalt, and manganese, and may contain other additive elements. Examples of the other additive elements include 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. Specific examples of the other additive elements include 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). Among these, Zr is preferred. It is believed that the inclusion of Zr stabilizes the crystal structure of the lithium-containing transition metal oxide, improving the durability and cycleability at high temperatures of the positive electrode mixture layer. 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 %, and particularly preferably 0.2 mol % to 3 mol %, based on the total amount of metals excluding Li.

[0020] [Ceramic particles] Fig. 3 is a schematic diagram showing the state of ceramic particles 22 added to positive electrode active material 21. As shown in Fig. 3, ceramic particles 22 are added to positive electrode active material 21, and ceramic particles 22 are adhered to the surface of positive electrode active material 21. Ceramic particles 22 are preferably scattered on the surface of positive electrode active material 21.

[0021] The ceramic particles 22 are insulating ceramics, and an insulating material having high electrical resistance is selected. The ceramic particles 22 may be a nitride-based ceramic or an oxide-based ceramic. The ceramic particles 22 contain at least one oxide selected from titanium oxide, aluminum oxide, and zirconium dioxide. The amount of the ceramic particles 22 added is preferably 0.10 to 0.30 wt %, and more preferably 0.20 to 0.30 wt %, based on the positive electrode mixture layer.

[0022] The volume-based median diameter (D50) of ceramic particles 22 is preferably 0.5 μm or less, and more preferably 0.05 μm to 0.1 μm. When D50 of ceramic particles 22 is taken as 1, the ratio of D50 of positive electrode active material 21 is preferably 10 to 200, and more preferably 15 to 25. The median particle diameter means the median diameter at which the volume integrated value is 50% in the particle size distribution measured by a laser diffraction scattering type particle size distribution measuring device (for example, LA-750 manufactured by HORIBA).

[0023] 4 and 5 are schematic diagrams showing a state in which the positive electrode slurry is kneaded. As shown in Fig. 4, the binder 23 is added during the kneading of the positive electrode slurry, thereby improving the adhesion between the positive electrode active material 21 and the ceramic particles 22. Furthermore, as shown in Fig. 5, after the binder 23 is dissolved in the solvent and changes from a solid phase to a liquid phase, the binder 23 enters between the positive electrode active material 21 and the ceramic particles 22, thereby further improving the adhesion between the positive electrode active material 21 and the ceramic particles 22.

[0024] Fig. 6 is a schematic diagram showing the state of the positive electrode active material 21 after the positive electrode composite layer is compressed. As shown in Fig. 6, the ceramic particles 22 bite into the surface of the positive electrode active material 21 due to the pressing pressure, further improving the adhesion between the positive electrode active material 21 and the ceramic particles 22. As a result, as will be described in detail later, after press molding of a wound electrode body in which the positive electrode and the negative electrode are laminated and wound with the separator 40 interposed therebetween, the ceramic particles 22 of the positive electrode active material 21 bite into the separator 40, improving the adhesion between the positive electrode and the separator 40.

[0025] [Conductive material] Examples of the conductive material include carbon materials such as carbon black, acetylene black, ketjen black, graphite, etc. These may be used alone or in combination of two or more kinds.

[0026] [Binding material] Examples of the binder 23 include fluorine-based resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide resins, acrylic resins, and polyolefin resins. In addition, the binder 23 may be a combination of these resins and carboxymethylcellulose (CMC) or its salts (CMC-Na, CMC-K, CMC-NH 4 etc., or may be partially neutralized salts), polyethylene oxide (PEO), etc. may be used in combination. These may be used alone or in combination of two or more kinds.

[0027] [Negative electrode] The negative electrode is preferably composed of a negative electrode current collector made of, for example, a metal foil and a negative electrode composite 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 in the potential range of the negative electrode, or a film having the metal disposed on the surface layer. The negative electrode composite layer preferably contains a binder and the like in addition to the negative electrode active material.

[0028] [Active material] The negative electrode active material can reversibly store and release lithium ions, and examples thereof include graphite-based carbon materials such as natural graphite and artificial graphite, amorphous carbon materials, metals that are alloyed with lithium such as Si and Sn, alloy materials, and metal composite oxides. These may be used alone or in combination of two or more. In particular, it is preferable to use a carbon material containing a graphite-based carbon material and an amorphous carbon material fixed to the surface of the graphite-based carbon material, because a low-resistance coating is easily formed on the surface of the negative electrode.

[0029] Graphite-based carbon materials are carbon materials with a developed graphite crystal structure, and examples thereof include natural graphite and artificial graphite. These may be in the form of flakes, or may be subjected to a spheroidizing treatment to process them into spheres. Artificial graphite is produced by subjecting petroleum, coal pitch, coke, or the like as raw materials to a heat treatment at 2000 to 3000°C or higher in an Acheson furnace or a graphite heater furnace. The d(002) interplanar spacing determined by X-ray diffraction is preferably 0.338 nm or less, and the crystal thickness in the c-axis direction (Lc(002)) is preferably 30 to 1000 nm.

[0030] Amorphous carbon materials are carbon materials in which the graphite crystal structure is not developed, and are in an amorphous or microcrystalline turbostratic state, and more specifically, mean that the d(002) plane spacing determined by X-ray diffraction is 0.342 nm or more. Examples of amorphous carbon materials include hard carbon (hardly graphitizable carbon), soft carbon (easily graphitizable carbon), carbon black, carbon fiber, activated carbon, and the like. There is no particular limitation on the manufacturing method for these. For example, they can be obtained by carbonizing a resin or a resin composition, and can be made of phenol-based thermosetting resins, thermoplastic resins such as polyacrylonitrile, petroleum-based or coal-based tar or pitch, and the like. For example, carbon black can be obtained by pyrolyzing a hydrocarbon as a raw material, and examples of the pyrolysis method include the thermal method and the acetylene decomposition method. Examples of the incomplete combustion method include the contact method, the lamp-pine smoke method, the gas furnace method, and the oil furnace method. Specific examples of carbon black produced by these manufacturing methods include acetylene black, ketjen black, thermal black, furnace black, and the like. Furthermore, the surface of these amorphous carbon materials may be further coated with another amorphous or irregular carbon.

[0031] 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" means a state of being chemically / physically bonded, and means that the graphite-based carbon material and the amorphous carbon material are not separated even when the negative electrode active material of the present disclosure is stirred in water or an organic solvent.

[0032] By adhering an amorphous carbon material, which has a larger reaction area and a multi-oriented structure compared to graphite-based carbon, to the surface of a graphite-based carbon material, a coating with a low reaction overvoltage is formed on the surface of the amorphous carbon material, which is believed to reduce the reaction overvoltage of the entire graphite-based carbon material against Li insertion / desorption reactions. Furthermore, because the amorphous carbon material has a more noble reaction potential than the graphite-based carbon material, it reacts preferentially with the Group 5 / Group 6 elements eluted from the positive electrode, forming a high-quality coating with better lithium ion permeability on the surface of the amorphous carbon material, which is believed to further reduce the reaction resistance of the entire graphite-based carbon material against Li insertion / desorption reactions.

[0033] The ratio of the graphite-based carbon material to the amorphous carbon material is not particularly limited, but it is preferable that the ratio of the amorphous carbon material having excellent Li-storage properties is high, and the ratio of the amorphous carbon material is 0.5 wt% or more in the active material, more preferably 2 wt% or more. However, if the amorphous carbon material is excessive, it will not be able to be uniformly fixed to the graphite surface, so it is preferable to set the upper limit taking this into consideration.

[0034] Methods for fixing amorphous carbon to graphite-based carbon materials include a method in which petroleum-based or coal-based tar, pitch, etc. are added to the amorphous carbon material, mixed with the graphite-based carbon material, and then heat-treated; a mechanofusion method in which compressive shear stress is applied between graphite particles and solid amorphous carbon to coat them; a solid-phase method in which coating is performed by a sputtering method or the like; and a liquid-phase method in which amorphous carbon is dissolved in a solvent such as toluene, graphite is immersed in the solution, and then heat-treated.

[0035] The primary particle size of the amorphous carbon is preferably small from the viewpoint of the diffusion distance of Li, and the specific surface area is preferably large because the reactive surface area for the Li absorption reaction is large. However, if it is too large, excessive reaction occurs on the surface, leading to an increase in resistance. For this reason, the specific surface area of ​​the amorphous carbon is set to 5 m 2 / g or more ~200m 2In order to reduce an excessive specific surface area, the primary particle size is preferably 20 nm or more and 1000 nm or less, more preferably 40 nm or more and 100 nm or less, and the particles preferably do not have a hollow structure in which cavities exist within the particles.

[0036] [Binding material] As in the case of the positive electrode, the binder may be a fluorine-based resin, PAN, a polyimide-based resin, an acrylic resin, a polyolefin-based resin, or the like. When preparing the negative electrode mixture slurry using an aqueous solvent, it is preferable to use styrene-butadiene rubber (SBR), CMC or a salt thereof, polyacrylic acid (PAA) or a salt thereof (PAA-Na, PAA-K, or the like, or a partially neutralized salt), polyvinyl alcohol (PVA), or the like.

[0037] [Separator] The separator 40 is made of a porous sheet having ion permeability and insulation properties. Specific examples of the porous sheet include a microporous thin film, a woven fabric, and a nonwoven fabric. The separator 40 is preferably made of an olefin resin such as polyethylene or polypropylene, or cellulose. The separator 40 may be a laminate having a cellulose fiber layer and a thermoplastic resin fiber layer such as an olefin resin. The separator 40 may also be a multi-layer separator including a polyethylene layer and a polypropylene layer, and a separator 40 having a resin such as an aramid resin applied to the surface thereof may also be used. Among these materials, it is preferable to use a polyolefin resin.

[0038] For example, in the separator 40 using a polyolefin resin, pores are formed by a known method such as a dry method or a wet method. The size and number of the pores can be adjusted to adjust the air permeability (air permeability) of the separator 40. The air permeability can be measured by the Gurley tester method (in accordance with JIS P8117).

[0039] Then, when the electrode body 11 is produced by stacking and winding the separator / positive electrode / separator / negative electrode in that order and pressing them into a flat shape, the pores of the separator 40 are crushed by the press molding, thereby changing the air permeability of the separator 40 formed into the electrode body 11.

[0040] The air permeability of the separator 40 is preferably 165 to 310 sec / 100 ml, and 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.

[0041] 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 to 140%, and more preferably 130 to 140%, of the air permeability of the curved portion of the separator 40 (the portion facing the curved portion 11B of the electrode body 11). Since the curved portion of the separator 40 is not compressed by the press pressure, 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 to 140%, and more preferably 130 to 140%, of the air permeability of the separator 40 before press molding.

[0042] Fig. 7 is a schematic diagram showing the state of the positive electrode active material 21 and the separator 40 after the electrode body 11 has been press-molded. As shown in Fig. 7, the ceramic particles 22 that are in close contact with the positive electrode active material 21 act as an anchor effect by being embedded in the separator 40, thereby strengthening the adhesion between the positive electrode active material 21 and the separator 40. This makes it possible to suppress the generation 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 improves the cycle characteristics of the nonaqueous electrolyte secondary battery 10.

[0043] In this embodiment, since the D50 of the ceramic particles 22 is sufficiently larger than the diameter of the pores 40A of the separator 40, the ceramic particles 22 do not enter the pores 40A of the separator 40.

[0044] For example, it is conceivable to increase the adhesive strength between the separator 40 and the positive electrode active material 21 without adding the ceramic particles 22 by increasing the pressing pressure. However, increasing the pressing pressure increases the air permeability of the separator 40, and the output characteristics of the nonaqueous electrolyte secondary battery 10 decrease. Furthermore, if the amount of ceramic particles 22 added is excessive, the lithium ion diffusion reaction is inhibited, thereby decreasing the output characteristics of the nonaqueous electrolyte secondary battery 10. In this embodiment, by adding an appropriate amount of ceramic particles 22, it is possible to improve the cycle characteristics without decreasing the output characteristics of the nonaqueous electrolyte secondary battery 10.

[0045] Furthermore, in this embodiment, minute gaps are formed near the contact surfaces between the separator 40 and the ceramic particles 22, and the electrolyte solution permeates into the gaps and is retained therein, thereby making it possible to avoid deterioration of the cycle characteristics of the nonaqueous electrolyte secondary battery 10 due to electrolyte drying up during cycles.

[0046] It should be noted that the present invention is not limited to the above-described embodiment and its modified examples, and various modifications and improvements are possible within the scope of the claims of this application.

[0047] <Example> The present disclosure will be further described below with reference to examples, but the present disclosure is not limited to these examples.

[0048] <Example 1> [Preparation of positive electrode] The positive electrode active material is a lithium nickel cobalt manganese composite oxide (LiNi 0.35 Co 0.35 Mn 0.30 O 2), polyvinylidene fluoride as a binder, carbon black as a conductive material, and N-methyl-2-pyrrolidone as a dispersion medium were kneaded to prepare a positive electrode active material composite slurry. The positive electrode active material composite slurry was adjusted so that the mass ratio of lithium nickel cobalt manganese composite oxide: polyvinylidene fluoride: carbon black was 90: 3: 7. Next, the positive electrode active material composite slurry was applied to both surfaces of an aluminum foil having a thickness of 15 μm as a positive electrode core by a die coater, and then the positive electrode active material composite slurry was dried, and N-methyl-2-pyrrolidone as a dispersion medium was removed to form a positive electrode active material composite layer on the positive electrode core. Then, the positive electrode active material composite layer was compressed to a predetermined packing density (2.5 g / cm 3 ) using a compression roller. 3 ) and cut to a predetermined size so that a positive electrode substrate exposed portion was formed on one longitudinal side of the positive electrode plate to obtain a positive electrode plate.

[0049] [Preparation of negative electrode] Graphite as the negative electrode active material, styrene butadiene rubber (SBR) as the binder, carboxymethyl cellulose (CMC) as the thickener, and water as the dispersion medium were kneaded so that the mass ratio of graphite:SBR:CMC was 99.2:0.6:0.2 to prepare a negative electrode active material composite slurry. The negative electrode active material composite slurry was applied to both sides of a copper foil having a thickness of 8 μm as a negative electrode core body using a die coater, and then the negative electrode active material composite slurry was dried to remove water from the negative electrode active material composite slurry, forming a negative electrode active material composite layer on the core body. Then, the negative electrode active material composite layer was compressed to a predetermined packing density (1.2 g / cm) using a compression roller. 3 ) and cut to a predetermined size so that a negative electrode substrate exposed portion was formed on one longitudinal side of the negative electrode plate to obtain a positive electrode plate.

[0050] [Preparation of electrode body] The positive electrode plate prepared by the above method and the negative electrode plate prepared by the above method were wound through a polypropylene separator having a thickness of 18 μm and an air permeability of 140 sec / 100 ml, and then pressed into a flat shape to prepare a flat wound electrode body. The wound body was formed by stacking separator / positive electrode / separator / negative electrode in this order and winding it around a cylindrical winding core. The positive electrode and negative electrode were wound so that their core exposed parts were located on the axial opposite sides of the wound body. At this time, the air permeability of the separator raw sheet before press molding was measured in advance, the press-molded flat wound electrode body was disassembled, and the separator air permeability of the part press-molded at the flat part was measured, and the separator air permeability before and after press molding was compared. The air permeability after press molding was 168 sec / 100 ml, and the air permeability increase rate after press molding was 120%. The air permeability was measured using the Gurley air permeability (based on JIS P8117).

[0051] [Preparation of non-aqueous electrolyte] A mixed solvent was prepared by mixing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 3:3:4 (at 25°C and 1 atm). 6 was added at a concentration of 1.15 mol / L, and further 1 mass % of lithium fluorosulfonate was added to prepare a nonaqueous electrolyte solution.

[0052] [Preparation of non-aqueous electrolyte secondary battery] A positive electrode current collector was welded to the exposed portion of the positive electrode core, and a negative electrode current collector was welded to the exposed portion of the negative electrode core, and then the electrode assembly was inserted into a rectangular outer can and each current collector was connected to a corresponding terminal. A sealing plate was attached to the opening of the outer can, and the nonaqueous electrolyte was poured through the electrolyte injection hole of the sealing plate, and the injection hole was sealed with a sealing plug to obtain a nonaqueous electrolyte secondary battery with a rated capacity of 4.1 Ah.

[0053] <Example 2> A battery was produced in the same manner as in Example 1, except that in the preparation of the electrode body, the air permeability of the separator after press molding was 182 sec / 100 ml and the increase rate of the air permeability of the separator after press molding was 130%.

[0054] <Example 3> In the production of the electrode body, 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%.

[0055] <Example 4> 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 with a D50 of 0.5 μm or less was added.

[0056] <Example 5> 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 with a D50 of 0.5 μm or less was added.

[0057] <Example 6> A separator with a Gurley air permeability of 220 sec / 100 ml was prepared. In the production of the electrode body, a battery was produced 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%.

[0058] <Example 7> In the production of the electrode body, 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%.

[0059] <Example 8> In the production of the electrode body, 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%.

[0060] <Comparative Example 1> A battery was fabricated in the same manner as in Example 1, except that in the preparation of the positive electrode, no ceramic particles were added, and in the preparation of the electrode body, the air permeability of the separator after press molding was 154 sec / 100 ml, and the increase rate of the air permeability of the separator after press molding was 110%.

[0061] <Comparative Example 2> A battery was produced in the same manner as in Comparative Example 1, except that in the preparation of the electrode body, 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%.

[0062] <Comparative Example 3> A battery was produced in the same manner as in Comparative Example 1, except that in the preparation of the electrode body, the air permeability of the separator after press molding was 182 sec / 100 ml and the increase rate of the air permeability of the separator after press molding was 130%.

[0063] <Comparative Example 4> A battery was produced in the same manner as in Comparative Example 1, except that in the preparation of the electrode body, the air permeability of the separator after press molding was 196 sec / 100 ml and the increase rate of the air permeability of the separator after press molding was 140%.

[0064] <Comparative Example 5> A battery was produced in the same manner as in Comparative Example 1, except that in the preparation of the electrode body, 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%.

[0065] <Comparative Example 6> A battery was fabricated in the same manner as in Comparative Example 1, except that in the fabrication of the positive electrode, 0.20 wt % of ceramic particles having a D50 of 0.5 μm or less was added.

[0066] <Comparative Example 7> A battery was fabricated in the same manner as in Comparative Example 5, except that in the fabrication of the positive electrode, 0.20 wt % of ceramic particles having a D50 of 0.5 μm or less was added.

[0067] <Comparative Example 8> A battery was fabricated in the same manner as in Comparative Example 3, except that in the fabrication of the positive electrode, 0.05 wt % of ceramic particles having a D50 of 0.5 μm or less was added.

[0068] <Comparative Example 9> A battery was fabricated in the same manner as in Comparative Example 3, except that in the fabrication of the positive electrode, 0.4 wt % of ceramic particles having a D50 of 0.5 μm or less was added.

[0069] <Comparative Example 10> A separator with a Gurley air permeability of 220 sec / 100 ml was prepared. A battery was produced in the same manner as in Comparative Example 6, except that in the production of the electrode body, the separator had an air permeability of 242 sec / 100 ml after press molding, and the increase rate of the separator's air permeability after press molding was 110%.

[0070] <Comparative Example 11> A battery was produced in the same manner as in Comparative Example 10, except that in the preparation of the electrode body, 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%.

[0071] [Moldability] It was confirmed whether the electrode body was formed to have a specified height and thickness.

[0072] [Output characteristics] The nonaqueous electrolyte secondary battery was CCCV charged at a charging current of 1 / 10 It under the condition of 25 ° C. until the depth of charge (SOC) was 50%. The nonaqueous electrolyte secondary battery was CCCV charged at a charging current of 1 / 10 It under an environment of 25 ° C. until the depth of charge (SOC) was 50%. Then, the nonaqueous electrolyte secondary battery was left in an environment of 25 ° C. for 2 hours. Then, in an environment of 25 ° C., discharge was performed for 10 seconds at currents of 1 It, 2 It, 4 It, 8 It, 10 It, 12 It and 16 It, and each battery voltage was measured. Each current value and battery voltage were plotted, and the output (W) was calculated from the IV characteristics during discharge to obtain the room temperature output characteristics. The charge depth that was shifted by discharge was returned to the original charge depth by charging at a constant current of 1 It. Table 1 shows the relative values ​​when the output characteristics of the battery of Comparative Example 1 are set to 100 as the output characteristics.

[0073] [Cycle characteristics] Under the condition of 25 ° C, constant current charging was performed at a constant current of 1 It until the battery voltage reached 4.10 V. Then, constant voltage charging was performed at a constant voltage of 4.10 V for 1.5 hours. After a 10-second pause, the battery was discharged at a constant current of 1 It until the battery voltage reached 2.5 V. The discharge capacity at this time was taken as the battery capacity before cycling. Next, under the condition of 25 ° C, the following charge and discharge cycle was performed 400 cycles. The battery was charged at a constant current of 2 It until the battery voltage reached 4.10 V. After a 10-second pause, the battery was discharged at a constant current of 2 It until the battery voltage reached 3.0 V. This is taken as one cycle. After the 400 cycles, constant current charging was performed at a constant current of 1 It until the battery voltage reached 4.1 V under the condition of 25 ° C. Then, constant voltage charging was performed at a constant voltage of 4.1 V for 1.5 hours. After a 10-second pause, the battery was discharged at a constant current of 1 It until the battery voltage reached 2.5 V. The discharge capacity at this time was taken as the battery capacity after high-temperature cycling. The capacity retention rate after the high-temperature cycle was calculated from the following formula: Table 1 shows the cycle characteristics relative to the cycle characteristics of the battery of Comparative Example 1, which is set at 100.

[0074] Capacity retention rate = (battery capacity after cycling (Ah) / battery capacity before cycling (Ah))

[0075] [Table 1]

[0076] As shown in Table 1, all of the batteries of Examples 1 to 8 have excellent output characteristics and cycle characteristics.

[0077] In the case of Example 1-3, although the separator air permeability and the increase rate after press molding were the same as those in Comparative Example 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 strengthened the adhesion between the positive electrode mixture layer and the separator during press molding and suppressed the capacity deterioration during charge-discharge cycles.

[0078] In the case of Examples 4-5, it was confirmed that, compared with Comparative Example 3, the moldability, output characteristics, and cycle characteristics were improved by the addition of ceramic particles.

[0079] In the case of Examples 6-8, the moldability, output characteristics, and cycle characteristics after press molding tended to be the same as in Examples 1-3, and it was confirmed that even when separators having different air permeabilities were used, the separator air permeability increase rate after press molding is preferably in the range of 120-140%.

[0080] In the case of Comparative Examples 1-5, it was confirmed that increasing the pressing pressure caused the separator pores to collapse, increasing the separator air permeability, and thus deteriorating the separator. Furthermore, even in Comparative Example 5, which had the highest pressing pressure, the moldability was insufficient.

[0081] In the case of Comparative Example 6, the moldability was insufficient due to insufficient pressing, and even though ceramic particles were added, the cycle characteristics were not improved when the separator air permeability increase rate was 110%.

[0082] In the case of Comparative Example 7, the pressing pressure was the highest and the moldability was sufficient, but the output characteristics and cycle characteristics were lower than those of Examples 1 to 3. This is thought to be because the pressing pressure was too high, which caused the adhesion between the positive electrode mixture layer and the separator to be too strong, making it difficult for the electrolyte to penetrate, and therefore no improvement was obtained in the output characteristics and cycle characteristics.

[0083] In the case of Comparative Example 8, 0.05 wt of ceramic particles was added to the positive electrode active material, but the output characteristics and cycle characteristics were almost unchanged compared to Comparative Example 3, and the output characteristics and cycle characteristics were not improved by adding inorganic particles. This is thought to be due to the small amount of inorganic particles added.

[0084] In the case of Comparative Example 9, the amount of ceramic particles added was excessive (addition amount 0.40 wt %), and it is believed that the ceramic particles became a resistance component in the positive electrode mixture layer, resulting in a decrease in output characteristics.

[0085] In the case of Comparative Examples 10-11, the moldability, output characteristics, and cycle characteristics after press molding tended to be the same as those of Comparative Examples 6 and 7 and Examples 1-3, and it was confirmed that even when separators with different air permeabilities were used, the separator air permeability increase rate after press molding is preferably in the range of 120-140%. [Explanation of symbols]

[0086] 10 Nonaqueous electrolyte secondary battery 11 Electrode body 11A Flat part 11B Curved section 12 Outer can 13 Sealing body 15 Positive external terminal 16 Negative external terminal 18 Gas exhaust port 20 positive electrode 21 Cathode active material 21 Positive electrode core 22 Ceramic particles 23 Binding material 40 Separator 40A pore

Claims

1. A non-aqueous electrolyte secondary battery comprising an electrode assembly in which a positive electrode and a negative electrode are wound in a flat shape with a separator interposed therebetween, and a non-aqueous electrolyte, the positive electrode having a positive electrode mixture layer containing a positive electrode active material, The positive electrode mixture layer contains 0.10 to 0.30 mass % of ceramic particles, The ceramic particles have a volume-based median diameter (D50) of 0.5 μm or less, The separator has an air permeability of 165 to 310 sec / 100 ml, the air permeability of the flat portion of the separator relative to the air permeability of the curved portion of the separator is 120 to 140%, The ceramic particles have insulating properties and are present on the surface of the positive electrode active material. Nonaqueous electrolyte secondary battery.

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

3. 3. The nonaqueous electrolyte secondary battery according to claim 1, The positive electrode active material contains 10 to 40 mol % manganese based on the total amount of transition metals. Nonaqueous electrolyte secondary battery.

4. 4. The nonaqueous electrolyte secondary battery according to claim 1, The ceramic particles include at least one oxide selected from titanium oxide, aluminum oxide, and zirconium dioxide; Nonaqueous electrolyte secondary battery.

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