Non-aqueous electrolyte secondary battery

Abstract

Provided is a non-aqueous electrolyte secondary battery that has improved cycle characteristics. A non-aqueous electrolyte secondary battery, which is one aspect of the present disclosure, comprises: a wound electrode body in which a positive electrode and a negative electrode are wound, with a first separator that is disposed on the winding inner side of the positive electrode and a second separator that is disposed on the winding outer side of the positive electrode being interposed therebetween; an electrolytic solution; and an exterior body which accommodates the electrode body and the electrolytic solution, wherein the first separator has a first base material layer and a first coating layer that is formed on the surface of the first base material layer which faces the positive electrode, the second separator has a second base material layer and a second coating layer that is formed on the surface of the second base material layer which faces the positive electrode, the first coating layer and the second coating layer each include a filler and an organic material, and the content of the filler in the first coating layer is higher than the content of the filler in the second coating layer.

Description

[Technical Field]

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

[0002] For a long time, non-aqueous electrolyte secondary batteries have been widely used, in which wound electrode bodies, consisting of strip-shaped positive and negative electrodes wound around a separator, are housed in a metal casing. The separator prevents short circuits from occurring due to contact between the positive and negative electrodes.

[0003] Patent Document 1 discloses a technology that enhances the adhesion between the separator and the electrode while ensuring the safety of the battery, by laminating two coating layers on the surface of a porous substrate layer and making the binder content in the surface coating layer higher than the binder content in the substrate layer coating layer.

[0004] Patent Document 2 discloses a technology for preventing battery runaway at high temperatures by laminating coating layers on both sides of a substrate layer which is a microporous film, and by making the binder content in the coating layer located on the negative electrode side higher than the binder content in the coating layer located on the positive electrode side. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2013-235824 [Patent Document 2] Japanese Patent Publication No. 2015-88430 [Overview of the project] [Problems that the invention aims to solve]

[0006] Incidentally, in a secondary battery, suppressing a decrease in battery capacity due to repeated charge and discharge and improving cycle characteristics are important issues. As a result of intensive studies by the inventors of the present application, it has been found that in a wound electrode body, charge and discharge reactions do not easily proceed uniformly between the inner and outer sides of the positive electrode winding, so that cycle characteristics are likely to deteriorate. The amount of electrolyte retained on the inner side of the positive electrode winding is presumed to be smaller than the amount retained on the outer side of the positive electrode winding. The techniques disclosed in Patent Document 1 and Patent Document 2 do not consider the deterioration of cycle characteristics due to the difference in electrolyte retention between the inner and outer sides of the positive electrode winding, and there is still room for improvement. electrolyte This is presumably because the amount of the electrolyte retained on the inner side of the positive electrode winding is smaller than the amount retained on the outer side of the positive electrode winding. The techniques disclosed in Patent Document 1 and Patent Document 2 do not consider the deterioration of cycle characteristics due to the difference in electrolyte retention between the inner and outer sides of the positive electrode winding, and there is still room for improvement.

[0007] An object of the present disclosure is to provide a non-aqueous electrolyte secondary battery with improved cycle characteristics.

Means for Solving the Problems

[0008] A non-aqueous electrolyte secondary battery according to an aspect of the present disclosure includes a wound electrode body in which a positive electrode and a negative electrode are wound via a first separator disposed on the inner side of the positive electrode winding and a second separator disposed on the outer side of the positive electrode winding, an electrolyte, and an exterior body that houses the electrode body and the electrolyte. The first separator has a first base material layer and a first coating layer formed on the surface of the first base material layer facing the positive electrode. The second separator has a second base material layer and a second coating layer formed on the surface of the second base material layer facing the positive electrode. The first coating layer and the second coating layer each contain a filler and an organic material, and the content of the filler in the first coating layer is larger than the content of the filler in the second coating layer.

Advantages of the Invention

[0009] According to the non-aqueous electrolyte secondary battery according to the present disclosure, cycle characteristics can be improved.

Brief Description of the Drawings

[0010] [Figure 1] It is a longitudinal sectional view of a cylindrical battery which is an example of an embodiment. [Figure 2]It is a cross-sectional view in the lateral direction of a wound electrode body included in the cylindrical battery shown in FIG. 1.

Embodiments for Carrying Out the Invention

[0011] Hereinafter, an example of an embodiment of a non-aqueous electrolyte secondary battery according to the present disclosure will be described in detail with reference to the drawings. Hereinafter, a cylindrical battery in which a wound electrode body is housed in a cylindrical outer package will be exemplified, but the outer package is not limited to a cylindrical shape, and may be, for example, a rectangular shape, a coin shape, or the like. Further, the outer package may be a pouch type composed of a laminate sheet including a metal layer and a resin layer. In the following description, specific shapes, materials, numerical values, directions, etc. are examples for facilitating the understanding of the present disclosure, and can be appropriately changed according to the specifications of the non-aqueous electrolyte secondary battery. Further, in the following description, when a plurality of embodiments and modified examples are included, it is assumed from the beginning that their characteristic parts are used in appropriate combination <00001​​​​​As the non-aqueous solvent (organic solvent) for the electrolyte, carbonates, lactones, ethers, ketones, esters, etc., can be used, and two or more of these solvents can be used in mixture form. When using a mixture of two or more solvents, it is preferable to use a mixed solvent containing cyclic carbonates and linear carbonates. For example, ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc. can be used as cyclic carbonates, and dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC), etc. can be used as linear carbonates. As esters, it is preferable to use carbonate esters such as methyl acetate (MA) and methyl propionate (MP). The non-aqueous solvent may contain halogen-substituted products in which at least some of the hydrogen atoms of these solvents are substituted with halogen atoms such as fluorine. As halogen-substituted compounds, it is preferable to use, for example, fluoroethylene carbonate (FEC) and methyl fluoropropionate (FMP). As the electrolyte salt of the electrolyte solution, LiPF6, LiBF4, LiCF3SO3, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, and mixtures thereof can be used. The solubility of the electrolyte salt in the non-aqueous solvent is, for example, 0.5 mol / L to 2.0 mol / L.

[0014] The inside of the cylindrical battery 10 is sealed by closing the open end of the outer casing 15 with the sealing body 16. Insulating plates 17 and 18 are provided above and below the electrode body 14, respectively. The positive electrode lead 19 extends upward from the upper end face of the electrode body 14 through a through hole in the insulating plate 17 and is welded to the lower surface of the filter 22, which is the bottom plate of the sealing body 16. In the cylindrical battery 10, the cap 26, which is the top plate of the sealing body 16 electrically connected to the filter 22, becomes the positive electrode terminal. On the other hand, the negative electrode lead 20 extends from the lower end face of the electrode body 14 through the outside of the insulating plate 18 to the bottom side of the outer casing 15 and is welded to the inner surface of the bottom of the outer casing 15. In the cylindrical battery 10, the outer casing 15 becomes the negative electrode terminal.

[0015] The outer casing 15 is, for example, a bottomed cylindrical metal outer casing. A gasket 27 is provided between the outer casing 15 and the sealing body 16 to ensure airtightness inside the cylindrical battery 10. The outer casing 15 has grooves 21 formed, for example, by pressing the side surface from the outside. The grooves 21 are preferably formed in an annular shape along the circumferential direction of the outer casing 15, and their upper surface supports the sealing body 16 via the gasket 27.

[0016] The sealing body 16 has a filter 22, a lower valve body 23, an insulating member 24, an upper valve body 25, and a cap 26, which are stacked in order from the electrode body 14 side. Each component of the sealing body 16 has, for example, a disc shape or a ring shape, and each component except the insulating member 24 is electrically connected to one another. The lower valve body 23 and the upper valve body 25 are connected to each other at their respective centers, with the insulating member 24 interposed between their respective peripheries. If the internal pressure of the battery rises due to abnormal heat generation, for example, the lower valve body 23 may rupture, causing the upper valve body 25 to bulge towards the cap 26 and separate from the lower valve body 23, thereby interrupting the electrical connection between the two. If the internal pressure rises further, the upper valve body 25 may rupture, and gas may be discharged from the through hole 26a of the cap 26.

[0017] The electrode body 14 will be described in detail below with reference to Figure 2. Figure 2 is a lateral cross-sectional view of the wound electrode body 14 included in the cylindrical battery 10 shown in Figure 1. In the electrode body 14, a first separator 13a is placed on the inside of the winding of the positive electrode 11, and a second separator 13b is placed on the outside of the winding of the positive electrode 11. The negative electrode 12, the first separator 13a, the positive electrode 11, and the second separator 13b are all formed in a strip shape and are stacked in this order and wound in a spiral around the winding axis, which is the winding center of the electrode body 14, so that they are alternately stacked in the radial direction of the electrode body 14. In the electrode body 14, the longitudinal direction of the positive electrode 11 and the negative electrode 12 is the winding direction, and the width direction of the positive electrode 11 and the negative electrode 12 is the winding axis direction. Note that the inside of the winding means the inside (winding axis side) in the radial direction of the electrode body 14, and the outside of the winding means the outside in the radial direction of the electrode body 14.

[0018] The positive electrode 11 has a positive electrode current collector and a positive electrode mixture layer formed on the surface of the positive electrode current collector. For the positive electrode current collector, a foil of a metal stable within the potential range of the positive electrode such as aluminum, a film having the metal disposed on the surface layer, etc. can be used. The thickness of the positive electrode current collector is, for example, 10 μm to 30 μm.

[0019] The positive electrode mixture layer is preferably formed on both surfaces of the positive electrode current collector. The thickness of the positive electrode mixture layer is, for example, 10 μm to 150 μm on one side of the positive electrode current collector. The positive electrode mixture layer contains, for example, a positive electrode active material, a conductive agent, and a binder. The positive electrode can be produced, for example, by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, a binder, etc. on both surfaces of the positive electrode current collector, drying the coating film, and then rolling the coating film using a roller or the like.

[0020] Examples of the positive electrode active material contained in the positive electrode mixture layer include lithium transition metal oxides containing transition metal elements such as Co, Mn, and Ni. The lithium transition metal oxide is, for example, Li 2-y CoO2, Li x NiO2, Li x MnO2, Li x Co y Ni 1-y O2, Li x Co y M 1-y O z 、Li x Ni 1-y M y O z 、Li x Mn2O4, Li x Mn 2-y M y O4, LiMPO4, Li2MPO4F (M is at least one of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, B, 0 < x ≤ 1.2, 0 < y ≤ 0.9, 2.0 ≤ z ≤ 2.3). These may be used alone or in combination of multiple kinds. In terms of achieving a higher capacity of the non-aqueous electrolyte secondary battery, the positive electrode active material is Li<000​​​​​​Ni 1-y M y O z (M is at least one of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, B, 0 < x ≤ 1.2, 0 < y ≤ 0.9, 2.0 ≤ z ≤ 2.3), etc., and it is preferable to contain a lithium nickel composite oxide.

[0021] As the conductive agent contained in the positive electrode mixture layer, for example, carbon-based particles such as carbon black (CB), acetylene black (AB), ketjen black, carbon nanotube (CNT), graphene, graphite, etc. can be mentioned. These may be used alone or in combination of two or more kinds.

[0022] As the binder contained in the positive electrode mixture layer, for example, fluorine-based resins such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polyimide-based resins, acrylic resins, polyolefin-based resins, etc. can be mentioned. These may be used alone or in combination of two or more kinds.

[0023] The negative electrode 12 has a negative electrode current collector and a negative electrode mixture layer formed on the surface of the negative electrode current collector. For the negative electrode current collector, a foil of a metal stable within the potential range of the negative electrode such as copper, a film having the metal disposed on the surface layer, etc. can be used. The thickness of the negative electrode current collector is, for example, 5 μm to 30 μm.

[0024] The negative electrode mixture layer is preferably formed on both sides of the negative electrode current collector. The thickness of the negative electrode mixture layer is, for example, 10 μm to 150 μm on one side of the negative electrode current collector. The negative electrode mixture layer contains, for example, a negative electrode active material and a binder. The negative electrode can be produced, for example, by applying a negative electrode mixture slurry containing a negative electrode active material, a binder, etc. on both sides of the negative electrode current collector, drying the coating film, and then rolling the coating film using a roller or the like.

[0025] As the negative electrode active material contained in the negative electrode binder layer, any material that can reversibly occlude and release lithium ions is not particularly limited, and generally carbon materials such as graphite are used. Graphite may be any of natural graphite such as flake graphite, massive graphite, and earthy graphite, artificial massive graphite, and artificial graphite such as graphitized mesophase carbon microbeads. Further, as the negative electrode active material, metals that alloy with Li such as Si and Sn, metal compounds containing Si, Sn, etc., and lithium titanium composite oxides may be used. For example, SiO x (0.5 ≦ x ≦ 1.6), or Li 2y SiO (2+y) A Si-containing compound in which fine particles of Si are dispersed in a lithium silicate phase represented by (0 < y < 2), etc., may be used in combination with graphite.

[0026] Examples of the binder contained in the negative electrode binder layer include styrene-butadiene rubber (SBR), nitrile-butadiene rubber (NBR), carboxymethyl cellulose (CMC) or its salts, polyacrylic acid (PAA) or its salts (PAA-Na, PAA-K, etc., and partially neutralized salts may also be used), polyvinyl alcohol (PVA), etc. These may be used alone or in combination of two or more.

[0027] As shown in FIG. 2, the first separator 13a is disposed inside the winding of the positive electrode 11, and the second separator 13b is disposed outside the winding of the positive electrode 11. That is, in the electrode body 14, the first separator 13a is disposed so as to be sandwiched between the negative electrode 12 on the radially inner side and the positive electrode 11 on the radially outer side, and the second separator 13b is disposed so as to be sandwiched between the positive electrode 11 on the radially inner side and the negative electrode 12 on the radially outer side. The first separator 13a and the second separator 13b are interposed between the positive electrode 11 and the negative electrode 12 to physically and electrically separate the positive electrode 11 and the negative electrode 12.

[0028] The first separator 13a has a first base material layer 30 and a first coating layer 32 formed on the surface of the first base material layer 30 facing the positive electrode 11, and the second separator 13b has a second base material layer 34 and a second coating layer 36 formed on the surface of the second base material layer 34 facing the positive electrode 11.

[0029] For example, porous substrates having ion permeability and insulating properties are used as the first substrate layer 30 and the second substrate layer 34. Specific examples of porous substrates include microporous thin films, woven fabrics, and nonwoven fabrics. The materials for the first substrate layer 30 and the second substrate layer 34 include polyethylene, polypropylene, and polyolefins such as copolymers of polyethylene and α-olefin. Aqua Examples include yl resin, polystyrene, polyester, and cellulose. The thickness of the first substrate layer 30 and the second substrate layer 34 is, for example, 3 μm to 20 μm.

[0030] The first coating layer 32 and the second coating layer 36 each contain a filler and an organic material, and the filler content in the first coating layer 32 is greater than the filler content in the second coating layer 36. Here, the filler content in the first coating layer 32 is the ratio of the mass of the filler contained in the first coating layer 32 to the mass of the first coating layer 32, and the filler content in the second coating layer 36 is the ratio of the mass of the filler contained in the second coating layer 36 to the mass of the second coating layer 36.

[0031] Because the filler has a high affinity for the electrolyte, the first coating layer 32 has better electrolyte retention than the second coating layer 36. By placing the first coating layer 32 on the inside of the positive electrode 11 winding and the second coating layer 36 on the outside of the positive electrode 11 winding, the difference in electrolyte retention between the inside and outside of the positive electrode 11 winding can be reduced, thereby improving the cycle characteristics.

[0032] The filler content in the first coating layer 32 is preferably 75% by mass or more, and more preferably 85% by mass or more. The upper limit of the filler content in the first coating layer 32 is, for example, 95% by mass.

[0033] The filler content in the second coating layer 36 is preferably 60% by mass or less, and more preferably 50% by mass or less. The lower limit of the filler content in the second coating layer 36 is, for example, 10% by mass.

[0034] The thicknesses of the first coating layer 32 and the second coating layer 36 are not particularly limited, but for example, they are 1 μm to 10 μm each. Furthermore, the method for forming the first coating layer 32 and the second coating layer 36 is not particularly limited, but for example, the coating layers may be formed on at least one main surface of the first substrate layer 30 and the second substrate layer 34 using a doctor blade method, gravure coating method, transfer method, or die coating method.

[0035] The presence of fillers in the first coating layer 32 and the second coating layer 36 preferably results in a melting point or thermal softening point of 150°C or higher, and more preferably 200°C or higher. This provides a thermal shrinkage suppression effect to the separator. Examples of fillers include metal oxide particles, metal nitride particles, metal fluoride particles and metal carbide particles, sulfide particles, etc. Examples of metal oxide particles include aluminum oxide (e.g., α-Al2O3), titanium oxide, magnesium oxide, zirconium oxide, nickel oxide, silicon oxide, manganese oxide, etc. Examples of metal nitride particles include titanium nitride, boron nitride, aluminum nitride, magnesium nitride, silicon nitride, etc. Examples of metal fluoride particles include aluminum fluoride, lithium fluoride, sodium fluoride, magnesium fluoride, calcium fluoride, barium fluoride, etc. Examples of metal carbide particles include silicon carbide, boron carbide, titanium carbide, and tungsten carbide. Examples of sulfide particles include barium sulfate. In addition, fillers include zeolite (M 2 / n Porous aluminosilicates such as O·Al2O3·xSiO2·yH2O (where M is a metal element, x≧2, y≧0), talc (Mg3Si4O 10Layered silicates such as (OH)2), minerals such as barium titanate (BaTiO3) and strontium titanate (SrTiO3) may also be used. These may be used individually or in combination of two or more.

[0036] The BET specific surface area of ​​the filler is not particularly limited, but 1m 2 / g~20m 2 A range of / g is preferred, and 3m 2 / g~15m 2 A range of / g is more preferable. The average particle size of the filler is not particularly limited, but is preferably 0.1 μm to 5 μm, and more preferably 0.2 μm to 1 μm.

[0037] The organic material is a material that can form a film on the substrate layer. Furthermore, it is preferable that the organic material has the function of bonding individual fillers to each other and to the substrate layer. The organic material is preferably a polymer material, and examples include fluororesins such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE), polyimide resins, polyamide resins, acrylic resins, polyolefin resins, styrene-butadiene rubber (SBR), nitrile-butadiene rubber (NBR), carboxymethylcellulose (CMC) or its salts, polyacrylic acid (PAA) or its salts, and polyvinyl alcohol (PVA). These may be used individually or in combination of two or more types. [Examples]

[0038] The present disclosure will be further illustrated by the following examples, but the present disclosure is not limited to these examples.

[0039] <Examples> 1 > [Fabrication of the positive electrode] As the positive electrode active material, LiNi 0.88 Co 0.09 Al 0.03 Lithium nickel-cobalt oxide containing aluminum, represented by O2, was used. 98 parts by mass of LiNi 0.88 Co 0.09 Al0.03 O2, 1 part by mass of acetylene black, and 1 part by mass of polyvinylidene fluoride (PVDF, average molecular weight 1.1 million) were mixed, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) was added to prepare a positive electrode mixture slurry. Next, the positive electrode mixture slurry was applied to both sides of a strip-shaped positive electrode current collector made of 15 μm thick aluminum foil, dried, rolled, and cut to a predetermined electrode plate size to produce a positive electrode in which a positive electrode mixture layer was formed on both sides of the positive electrode current collector. A positive electrode exposed portion was provided approximately in the center of the longitudinal direction of the positive electrode, where there was no mixture layer and the surface of the current collector was exposed, and an aluminum positive electrode lead was welded to the positive electrode exposed portion.

[0040] [Fabrication of the negative electrode] A negative electrode mixture slurry was prepared by mixing 95 parts by mass of graphite, 5 parts by mass of Si oxide, 1 part by mass of carboxymethylcellulose (CMC), and 1.2 parts by mass of styrene-butadiene rubber (SBR), and adding an appropriate amount of water. Next, the negative electrode mixture slurry was applied to both sides of a strip-shaped negative electrode current collector made of copper foil with a thickness of 8 μm, dried, rolled, and cut to a predetermined electrode plate size to produce a negative electrode in which a negative electrode mixture layer was formed on both sides of the negative electrode current collector. A negative electrode exposed portion was provided at the outer end of the negative electrode winding, where the mixture layer was absent and the surface of the current collector was exposed, and a nickel negative electrode lead was welded to the negative electrode exposed portion.

[0041] [Preparation of Separator A] A porous polyethylene substrate with a thickness of 12 μm was used as the base layer. α-Al2O3 powder as a filler and an acrylic ester-based binder emulsion as an organic material were mixed in a solid content mass ratio of 95:5. Then, an appropriate amount of water was added to adjust the solid content concentration to 10% by mass to prepare dispersion A. Dispersion A was applied to the entire surface of one side of the porous substrate using a microgravure coater, and the coating film was dried to form a coating layer A with an average thickness of 4 μm on one side of the substrate.

[0042] [Preparation of Separator B] A porous polyethylene substrate with a thickness of 12 μm was used as the substrate layer. Para-aramid was polymerized by adding terephthalic acid dichloride (TPC) to a solution of paraphenylenediamine and calcium chloride dissolved in NMP to obtain a para-aramid solution with a solid content concentration of 2% by mass. Dispersion B was prepared by mixing α-Al2O3 powder as a filler and the para-aramid solution so that the solid content mass ratio of α-Al2O3 powder as a filler to para-aramid as an organic material was 50:50. Dispersion B was applied to the entire surface of one side of the porous substrate using a microgravure coater, and the coating film was dried to form a coating layer B with an average thickness of 4 μm on one side of the substrate.

[0043] [Preparation of electrolyte solution] 100 parts by mass of a mixed solvent consisting of ethylene carbonate (EC) and dimethylmethyl carbonate (DMC) (volume ratio EC:DMC = 1:3) was mixed with 5 parts by mass of vinylene carbonate (VC). LiPF6 was dissolved in this mixed solvent to a concentration of 1 mol / L to prepare an electrolyte.

[0044] [Manufacturing of secondary batteries] A wound electrode body was fabricated by spirally winding the positive and negative electrodes via separator A as a first separator and separator B as a second separator. Separator A was placed on the inside of the winding of the positive electrode so that coating layer A faced the positive electrode, and separator B was placed on the outside of the winding of the positive electrode so that coating layer B faced the positive electrode. Insulating plates were placed above and below the electrode body, and the electrode body was housed in an outer casing. The negative electrode lead was welded to the bottom of the bottomed cylindrical outer casing, and the positive electrode lead was welded to the sealing body. Electrolyte was injected into the outer casing, and the opening of the outer casing was sealed with the sealing body via a gasket to fabricate a secondary battery.

[0045] [Evaluation of capacity retention rate] The above-mentioned secondary battery was charged at a constant current of 0.1It at 25°C until the battery voltage reached 4.2V, and then charged again at a constant voltage of 4.2V until the current value reached 0.05It. Afterward, it was discharged at a constant current of 0.5It until the battery voltage reached 2.5V. This charge-discharge cycle was considered one cycle, and 500 cycles were performed. The capacity retention rate of the secondary battery during the charge-discharge cycle was calculated using the following formula. Capacity retention rate = (Discharge capacity at 500 cycles / Discharge capacity at 1 cycle) × 100

[0046] <Example 2> [Fabrication of Separator C] A porous polyethylene substrate with a thickness of 12 μm was used as the base layer. α-Al2O3 powder as a filler and an acrylic ester-based binder emulsion as an organic material were mixed in a solid content mass ratio of 85:15. Then, an appropriate amount of water was added to prepare dispersion C, resulting in a solid content concentration of 10% by mass. Dispersion C was applied to the entire surface of one side of the porous substrate using a microgravure coater, and the coating film was dried to form a coating layer C with an average thickness of 4 μm on one side of the substrate.

[0047] In the fabrication of the secondary battery, a separator C was used as the first separator, and the separator C was placed on the inside of the winding of the positive electrode so that the coating layer C faced the positive electrode. The secondary battery was fabricated in the same manner as in Example 1, and the capacity retention rate was evaluated.

[0048] <Comparative Example 1> In the fabrication of the secondary battery, separator C was used as the first and second separators, and the separator C was positioned on the inside and outside of the winding of the positive electrode so that both coating layers C faced the positive electrode. The secondary battery was fabricated in the same manner as in Example 1, and the capacity retention rate was evaluated.

[0049] <Comparative Example 2> In the fabrication of the secondary battery, separator B was used as the first separator, and separator B was placed on the inside of the positive electrode winding so that the coating layer B faced the positive electrode. Separator A was used as the second separator, and separator A was placed on the outside of the positive electrode winding so that the coating layer A faced the positive electrode. A secondary battery was then fabricated in the same manner as in Example 1, and the capacity retention rate was evaluated.

[0050] <Comparative Example 3> In the fabrication of the secondary battery, separator B was used as the first separator, and separator B was placed on the inside of the positive electrode winding so that the coating layer B faced the positive electrode. Separately, separator C was used as the second separator, and separator C was placed on the outside of the positive electrode winding so that the coating layer C faced the positive electrode. The secondary battery was then fabricated in the same manner as in Example 1, and the capacity retention rate was evaluated.

[0051] The evaluation results of the secondary batteries for the examples and comparative examples are shown in Table 1. Table 1 also includes the filler content in the first and second coating layers, respectively.

[0052] [Table 1]

[0053] The secondary battery in the example has a higher capacity retention rate and improved cycle characteristics compared to the secondary battery in the comparative example. This is presumed to be because increasing the filler content in the first coating layer facing the positive electrode on the inside of the winding compared to the filler content in the second coating layer facing the positive electrode on the outside of the winding improved the electrolyte retention on the inside of the positive electrode, thereby improving the uniformity of the charge-discharge reaction on both sides of the positive electrode. [Explanation of symbols]

[0054] 10 Cylindrical battery, 11 Positive electrode, 12 Negative electrode, 13a First separator, 13b Second separator, 14 Electrode body, 15 Outer casing, 16 Sealing body, 17,18 Insulating plate, 19 Positive electrode lead, 20 Negative electrode lead, 21 Grooved section, 22 Filter, 23 Lower valve body, 24 Insulating member, 25 Upper valve body, 26 Cap, 27 Gasket, 30 First base layer, 32 First coating layer, 34 Second base layer, 36 Second coating layer

Claims

1. A wound electrode body in which a positive electrode and a negative electrode are wound around each other via a first separator positioned on the inside of the winding of the positive electrode and a second separator positioned on the outside of the winding of the positive electrode, Electrolyte and The electrode body and the outer casing that houses the electrolyte are provided, The first separator comprises a first substrate layer and a first coating layer formed on the surface of the first substrate layer facing the positive electrode. The second separator comprises a second substrate layer and a second coating layer formed on the surface of the second substrate layer facing the positive electrode. The first coating layer and the second coating layer each contain a filler and a polymer material. The filler is one or more compound particles selected from metal oxide particles, metal nitride particles, metal fluoride particles, metal carbide particles, and sulfide particles. A non-aqueous electrolyte secondary battery wherein the content of the filler in the first coating layer is greater than the content of the filler in the second coating layer.

2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the filler content in the first coating layer is 75% by mass or more, and the filler content in the second coating layer is 60% by mass or less.

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