Nonaqueous electrolyte secondary battery

Abstract

Provided is a non-aqueous electrolyte secondary battery having high capacity and excellent durability. A non-aqueous electrolyte secondary battery according to one embodiment of the present invention is provided with: an electrode body including a first electrode and a second electrode having different polarities from each other; an electrolyte; the first electrode has a rectangular shape and has a current collector and a mixture layer formed on the surface of the current collector, and the mixture layer has a first region, a second region, and a third region in this order from one end portion toward the other end portion in the width direction of the first electrode. The width of each of the first region and the third region in the width direction of the first electrode is 1-20% of the length of the first electrode in the width direction, the mixture layer contains an electrolyte salt, and the content of the electrolyte salt in each of the first region and the third region is higher than the content of the electrolyte salt in each of the second region.

Description

Technical Field

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

[0002] The positive electrode and the negative electrode, which are electrodes of a non-aqueous electrolyte secondary battery, each have a current collector and a mixture layer formed on the surface of the current collector. The mixture layer contains an active material that can reversibly absorb and release Li ions.

[0003] Patent Document 1 discloses a technique for pre-incorporating a portion of the electrolyte salt in the final desired electrolyte solution into the positive electrode from the viewpoint of improving the liquid injection property during the manufacture of the secondary battery. Patent Document 2 discloses a technique for pre-incorporating an electrolyte into the positive electrode in order to suppress the reduction in the electrolyte salt concentration inside the positive electrode after repeated charge and discharge cycles.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Publication No. 2011-192561

[0007] Patent Document 2: International Publication No. 2018 / 025469 Summary of the invention

[0008] In recent years, secondary batteries are required to further improve battery characteristics such as durability and battery capacity. The inventors have repeatedly conducted in-depth research and found that even if the electrodes contain electrolyte salts, the reduction in battery capacity caused by the charge and discharge cycle cannot be fully suppressed. In addition, if the content of electrolyte salts in the electrodes is increased, the content of active materials in the electrodes is relatively reduced, and the battery capacity is reduced. The technology disclosed in Patent Documents 1 and 2 has not been studied for the balance between battery capacity and durability of secondary batteries, and there is still room for improvement.

[0009] An object of the present invention is to provide a nonaqueous electrolyte secondary battery having a high capacity and excellent durability.

[0010] A non-aqueous electrolyte secondary battery as one embodiment of the present invention is characterized in that it comprises: an electrode body comprising a first electrode and a second electrode having different polarities; an electrolyte; and an outer packaging body for containing the electrode body and the electrolyte, wherein the first electrode is rectangular in shape and has a current collector and a mixture layer formed on the surface of the current collector, the mixture layer having a first region, a second region, and a third region in sequence from one end toward the other end in the width direction of the first electrode, the widths of the first region and the third region in the width direction of the first electrode are respectively 1% to 20% of the length of the first electrode in the width direction, the mixture layer contains an electrolyte salt, and the contents of the electrolyte salt in the first region and the third region are respectively higher than the content of the electrolyte salt in the second region.

[0011] According to the nonaqueous electrolyte secondary battery which is one embodiment of the present invention, it is possible to achieve both high capacity and high durability. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 This is an axial cross-sectional view of a cylindrical secondary battery as an example of an embodiment.

[0013] Figure 2 It is a front view showing a positive electrode according to an example of the embodiment in a developed state. DETAILED DESCRIPTION

[0014] Hereinafter, an example of an embodiment of a cylindrical secondary battery of the present invention will be described in detail with reference to the accompanying drawings. In the following description, specific shapes, materials, numerical values, directions, etc. are examples for facilitating the understanding of the present invention and can be appropriately changed to match the specifications of the secondary battery. In addition, although a cylindrical secondary battery in which a wound electrode body is contained in a cylindrical outer packaging body is exemplified below, the electrode body is not limited to a wound type, but may also be a stacked type in which a plurality of positive electrodes and a plurality of negative electrodes are alternately stacked one by one with a separator. The outer packaging body is not limited to a cylindrical shape, for example, it may also be a square, button-shaped, etc. In addition, the outer packaging body may also be a soft-pack type composed of a laminated sheet comprising a metal layer and a resin layer. In addition, in this specification, the recording of "value (A) to value (B)" means above value (A) and below value (B).

[0015] Figure 1 FIG. 1 is an axial cross-sectional view of a cylindrical secondary battery 10 as an example of an embodiment. Figure 1As shown, the secondary battery 10 includes a wound electrode body 14, an electrolyte, and an outer package 16 for accommodating the electrode body 14 and the electrolyte. The electrode body 14 includes a positive electrode 11, a negative electrode 12, and a separator 13, and has a winding structure in which the positive electrode 11 and the negative electrode 12 are wound in a spiral shape with the separator 13 interposed therebetween. The outer package 16 is a metal container in a bottomed cylindrical shape with one side open in the axial direction, and the opening of the outer package 16 is sealed by a sealing body 17. In the following, for the convenience of explanation, the sealing body 17 side of the battery is set as the upper side, and the bottom side of the outer package 16 is set as the lower side.

[0016] The positive electrode 11, the negative electrode 12 and the separator 13 constituting the electrode body 14 are all rectangular strips, which are alternately stacked along the radial direction of the electrode body 14 by being wound into a spiral shape along the length direction. The separator 13 separates the positive electrode 11 and the negative electrode 12 from each other. In order to prevent the precipitation of lithium, the negative electrode 12 is formed to be one circle larger than the positive electrode 11. That is, the negative electrode 12 is formed longer than the positive electrode 11 in the length direction and the width direction. The two separators 13 are formed to be at least one circle larger than the positive electrode 11, for example, arranged in a manner of sandwiching the positive electrode 11. The electrode body 14 includes a positive electrode lead 20 connected to the positive electrode 11 by welding or the like, and a negative electrode lead 21 connected to the negative electrode 12 by welding or the like. In the electrode body 14, the length 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 axial direction. That is, the end faces of the positive electrode 11 and the negative electrode 12 in the width direction form the end faces of the electrode body 14 in the axial direction.

[0017] Insulating plates 18 and 19 are disposed above and below the electrode body 14 , respectively. Figure 1 In the example shown, the positive electrode lead 20 extends toward the sealing body 17 through the through hole of the insulating plate 18, and the negative electrode lead 21 extends toward the bottom side of the outer package 16 through the outer side of the insulating plate 19. The positive electrode lead 20 is connected to the lower surface of the internal terminal plate 23 of the sealing body 17 by welding or the like, and the cover 27 as the top plate of the sealing body 17 electrically connected to the internal terminal plate 23 serves as the positive terminal. The negative electrode lead 21 is connected to the inner surface of the bottom of the outer package 16 by welding or the like, and the outer package 16 serves as the negative terminal.

[0018] A gasket 28 is provided between the outer package 16 and the sealing body 17 to ensure the airtightness of the battery interior. A groove 22 is formed in the outer package 16, in which a part of the side surface bulges inward and supports the sealing body 17. The groove 22 is preferably formed in an annular shape along the circumferential direction of the outer package 16, and the sealing body 17 is supported by its upper surface. The sealing body 17 is fixed to the upper part of the outer package 16 by the groove 22 and the open end of the outer package 16 that is caulked to the sealing body 17.

[0019] The sealing body 17 has a structure in which an internal terminal plate 23, a lower valve body 24, an insulating member 25, an upper valve body 26 and a cover 27 are stacked in order from the electrode body 14 side. The components constituting the sealing body 17 have, for example, a disc shape or a ring shape, and the components except the insulating member 25 are electrically connected to each other. The lower valve body 24 and the upper valve body 26 are connected at their respective central portions, and an insulating member 25 is sandwiched between their respective peripheral portions. When the internal pressure of the battery rises due to abnormal heat, the lower valve body 24 is deformed and broken in a manner that pushes the upper valve body 26 toward the cover 27 side, thereby blocking the current path between the lower valve body 24 and the upper valve body 26. When the internal pressure rises further, the upper valve body 26 breaks, and gas is discharged from the opening of the cover 27.

[0020] The positive electrode 11, the negative electrode 12, the separator 13 and the electrolyte are described in detail below. Hereinafter, an example in which the positive electrode 11 is the first electrode and the negative electrode 12 is the second electrode is described. It should be noted that the present embodiment is not limited to this example. For example, the negative electrode 12 may be the first electrode. In addition, the second electrode may have the same characteristics as the first electrode, and both the positive electrode 11 and the negative electrode 12 may have the characteristics of the first electrode.

[0021] [positive electrode]

[0022] In reference Figure 2 At the same time, the positive electrode 11 will be described. Figure 2 1 is a front view showing a positive electrode 11 of an example of an embodiment in a developed state. The positive electrode 11 includes a positive electrode collector 30 and a positive electrode mixture layer 32 formed on the surface of the positive electrode collector 30. The positive electrode mixture layer 32 is preferably formed on both sides of the positive electrode collector 30. The positive electrode collector 30 can be made of a foil of a metal such as aluminum or an aluminum alloy that is stable in the potential range of the positive electrode 11, or a film having the metal disposed on the surface.

[0023] The positive electrode mixture layer 32 has a first region 32a, a second region 32b, and a third region 32c in order from one end toward the other end in the width direction of the positive electrode 11. In this embodiment, one end is located on the upper side of the secondary battery 10, and the other end is located on the lower side of the secondary battery 10.

[0024] The width t1 of the first region 32a and the width t3 of the third region 32c in the width direction of the positive electrode 11 are respectively 1% to 20% of the length in the width direction of the positive electrode 11. The width t1 of the first region 32a and the width t3 of the third region 32c may be different from each other, but are preferably the same. It should be noted that the width t2 of the second region 32b is 60% to 98% of the length in the width direction of the positive electrode 11.

[0025] The positive electrode mixture layer 32 includes an electrolyte salt. The positive electrode mixture layer 32 further includes, for example, a positive electrode active material, a binder, and a conductive agent. The content of the electrolyte salt in the first region 32a and the third region 32c is respectively higher than the content of the electrolyte salt in the second region 32b. Thus, high capacity and high durability can be taken into account. Here, the content of the electrolyte salt in the first region 32a is the ratio of the mass of the electrolyte salt to the total mass of the first region 32a, and the content of the electrolyte salt in the second region 32b and the third region 32c is also defined in the same way.

[0026] The content of the electrolyte salt in the first region 32a and the third region 32c is preferably 0.1% by mass to 10% by mass, more preferably 0.1% by mass to 5% by mass, and even more preferably 0.1% by mass to 1% by mass.

[0027] The content of the electrolyte salt in the second region 32b is, for example, less than 0.1% by mass. Preferably, no electrolyte salt is contained in the second region 32b. This can increase the content of the positive electrode active material in the second region 32b and increase the battery capacity. The content of the positive electrode active material in each of the first region 32a, the second region 32b, and the third region 32c is, for example, 80% to 99% by mass relative to the total mass of each region.

[0028] The electrolyte salt contained in the positive electrode mixture layer 32 is preferably a lithium salt. Examples of lithium salts include LiBF 4 、LiClO 4 、LiPF 6 、LiAsF 6 、LiSbF 6 、LiAlCl 4 、LiSCN、LiCF 3 SO 3 、LiCF 3 CO 2 、Li(P(C 2 O 4 )F 4 )、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 )F 2 ) and other borates, LiN (SO2 CF 3 ) 2 、LiN(C 1 F 2l＋1 SO 2 ) (C m F 2m＋1 SO 2 ){l, m is an integer greater than 1} and other imide salts. The lithium salt may be used alone or in combination. Among them, LiPF 6 The electrolyte salt contained in the positive electrode mixture layer 32 may be the same as the electrolyte salt contained in the electrolytic solution described later.

[0029] As the positive electrode active material contained in the positive electrode mixture layer 32, a lithium transition metal composite oxide containing a transition metal element such as Ni can be exemplified. The lithium transition metal composite oxide preferably contains Ni and at least one element selected from Mn, Co and Al. The content of Ni in the lithium transition metal composite oxide is, for example, 60 mol% to 95 mol% relative to the total molar number of metal elements excluding Li. The lithium transition metal composite oxide can be, for example, in the general formula Li a Ni x M1 y M2 z O 2-b (wherein, 0.8≤a≤1.2, 0.6≤x≤0.95, 0.05≤y≤0.4, 0≤z≤0.15, 0≤b<0.05, x+y+z=1, M1 is at least one element selected from Mn, Co and Al, and M2 is at least one element selected from Fe, Ti, Si, Nb, Zr, Mo and Zn).

[0030] Examples of the conductive agent contained in the positive electrode mixture layer 32 include carbon black (CB), acetylene black (AB), Ketjen black, carbon nanotubes (CNT), graphene, graphite and other carbon particles, etc. These may be used alone or in combination of two or more.

[0031] Examples of the binder contained in the positive electrode mixture layer 32 include fluorine-based resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), polyimide-based resins, acrylic resins, polyolefin-based resins, and polyacrylonitrile (PAN). These may be used alone or in combination of two or more.

[0032] The positive electrode active material, the conductive agent, and the binder contained in the first region 32 a , the second region 32 b , and the third region 32 c may be different from each other, but are preferably the same.

[0033] The method for producing the positive electrode 11 is not particularly limited, and the positive electrode 11 can be produced, for example, as follows.

[0034] (1) Prepare a first positive electrode mixture slurry for the first region 32a and the third region 32c and a second positive electrode mixture slurry for the second region 32b. For example, only the first positive electrode mixture slurry contains an electrolyte salt. The first positive electrode mixture slurry and the second positive electrode mixture slurry both contain a positive electrode active material, a conductive agent, and a binder.

[0035] (2) The first positive electrode mixture slurry and the second positive electrode mixture slurry are applied in stripes along the longitudinal direction and adjacent to each other in the width direction of the positive electrode 11. At this time, the positive electrode exposed portion 34 is provided by, for example, intermittent application of the first positive electrode mixture slurry without applying the first positive electrode mixture slurry to a part of the positive electrode current collector 30.

[0036] (3) After the applied slurry is dried, the coating is rolled using a rolling roll to produce the positive electrode 11 .

[0037] [negative electrode]

[0038] The negative electrode 12 includes, for example, a negative electrode current collector and a negative electrode mixture layer formed on the surface of the negative electrode current collector. The negative electrode mixture layer is preferably formed on both sides of the negative electrode current collector. The negative electrode current collector can be made of a foil of a metal such as copper that is stable in the potential range of the negative electrode, or a film having the metal disposed on the surface.

[0039] The negative electrode mixture layer includes, for example, a negative electrode active material and a binder. The content of the negative electrode active material in the negative electrode mixture layer is, for example, 80% to 99% by mass relative to the total mass of the negative electrode mixture layer. For example, a negative electrode mixture slurry including a negative electrode active material, a binder, etc. is applied to the surface of the negative electrode current collector, and after the coating is dried, the coating is rolled using a roller or the like, thereby manufacturing the negative electrode 12.

[0040] The negative electrode active material contained in the negative electrode mixture layer is not particularly limited as long as it is a material that can reversibly absorb and release Li ions. Carbon materials such as graphite are generally used. Graphite can be any of natural graphites such as flaky graphite, blocky graphite, and earthy graphite, blocky artificial graphite, and artificial graphites such as graphitized mesophase carbon microbeads. In addition, as the negative electrode active material, metals such as Si and Sn alloyed with Li, metal compounds containing Si, Sn, etc., lithium-titanium composite oxides, etc. can also be used. For example, SiO x (x is 0.5 to 1.6) represented by silicon oxide, Li 2y SiO （2＋y） A silicon-containing material in which Si fine particles are dispersed in a lithium silicate phase, a silicon-containing material in which Si fine particles are dispersed in a carbon phase, or the like represented by (0<y<2) is used in combination with graphite.

[0041] Examples of the binder contained in the negative electrode mixture layer include styrene butadiene rubber (SBR), acrylonitrile butadiene rubber (NBR), carboxymethyl cellulose (CMC) or its salts (CMC-Na, CMC-K, CMC-NH 4 etc., and partially neutralized salts may also be used), 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.

[0042] [Spacer]

[0043] The spacer 13 may be, for example, a porous sheet having ion permeability and insulation. Specific examples of the porous sheet include microporous films, woven fabrics, nonwoven fabrics, and the like. Suitable materials for the spacer include olefin resins such as polyethylene and polypropylene, and cellulose. The spacer 13 may also be a laminate having a cellulose fiber layer and a thermoplastic resin fiber layer such as an olefin resin. In addition, a multilayer spacer including a polyethylene layer and a polypropylene layer may be used, and a spacer having a material such as an aramid resin or ceramics coated on the surface of the spacer 13 may also be used.

[0044] [Electrolyte]

[0045] The electrolyte is a liquid electrolyte containing a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. The non-aqueous solvent may be, for example, esters, ethers, nitriles such as acetonitrile, amides such as dimethylformamide, and mixed solvents of two or more thereof. The non-aqueous solvent may also contain a halogen substituted product in which at least a portion of the hydrogen atoms of these solvents are replaced with halogen atoms such as fluorine.

[0046] Examples of the esters include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), and butylene 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; cyclic carboxylates such as γ-butyrolactone and γ-valerolactone; and chain carboxylates such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate (MP), and ethyl propionate.

[0047] 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, cyclic ethers such as crown ether, 1,2-dimethoxyethane, diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, dihexyl ether. , ethyl vinyl ether, butyl vinyl ether, methyl phenyl ether, ethyl phenyl ether, butyl phenyl ether, pentyl phenyl ether, methoxytoluene, benzyl ethyl ether, diphenyl ether, dibenzyl ether, o-dimethoxybenzene, 1,2-diethoxyethane, 1,2-dibutoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, 1,1-dimethoxymethane, 1,1-diethoxyethane, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether and other chain ethers, etc.

[0048] As the halogen-substituted substance, fluorinated cyclic carbonates such as fluoroethylene carbonate (FEC), fluorinated chain carbonates, fluorinated chain carboxylates such as fluoromethyl propionate (FMP), and the like are preferably used.

[0049] The electrolyte salt contained in the electrolytic solution may be different from the electrolyte salt contained in the positive electrode 11, but is preferably the same as the electrolyte salt contained in the positive electrode 11. The electrolyte salt contained in the electrolytic solution preferably contains a lithium salt, more preferably contains LiPF 6 The concentration of the lithium salt is preferably 0.5 mol to 2.0 mol per 1 L of the solvent.

[0050] Example

[0051] Hereinafter, the present invention will be further described using examples; however, the present invention is not limited to these examples.

[0052] [Production of positive electrode]

[0053] Use LiNi 0.80 Co 0.15 Al 0.05 O 2 The lithium composite oxide represented by is used as the first positive electrode active material. The first positive electrode active material, acetylene black (AB), polyvinylidene fluoride (PVDF) and lithium hexafluorophosphate (LiPF 6 ) were mixed in a mass ratio of 100:1:0.9:0.5, and kneaded while adding N-methylpyrrolidone (NMP) to prepare a first positive electrode mixture slurry. In addition, the first positive electrode active material, acetylene black (AB) and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 100:1:0.9, and kneaded while adding N-methylpyrrolidone (NMP) to prepare a second positive electrode mixture slurry.

[0054] On the surface of a rectangular positive electrode collector made of aluminum foil, the first positive electrode mixture slurry and the second positive electrode mixture slurry are applied in stripes in the longitudinal direction and dried. The back side is also applied and dried in the same manner. After the dried coating film is rolled using a roller, it is cut into a specified electrode plate size to produce a positive electrode having a positive electrode mixture layer formed on both sides of the positive electrode collector. The positive electrode mixture layer is Figure 2 The same form is formed by applying the first positive electrode mixture slurry to the first region and the third region, and applying the second positive electrode mixture slurry to the second region. In the width direction of the positive electrode, the ratio of the width of the first region to the width of the second region to the width of the third region is 5:90:5. In addition, in the approximate center of the longitudinal direction of the positive electrode, the positive electrode exposure portion is provided by intermittently applying the first positive electrode mixture slurry and the second positive electrode mixture slurry, and the aluminum positive electrode lead is welded to the positive electrode exposure portion.

[0055] [Production of negative electrode]

[0056] 98 parts by mass of graphite, 1 part by mass of carboxymethyl cellulose (CMC) and 1 part by mass of styrene butadiene rubber (SBR) were mixed, and an appropriate amount of water was added to prepare a negative electrode mixture slurry. Then, the negative electrode mixture slurry was applied to both sides of a rectangular negative electrode collector made of copper foil in such a way that a negative electrode exposure portion of the negative electrode collector was exposed at the end of the winding end side. After the coating was dried, it was rolled and cut into a specified electrode plate size to produce a negative electrode with a negative electrode mixture layer formed on both sides of the negative electrode collector, and a nickel negative electrode lead was welded to the negative electrode exposure portion.

[0057] [Preparation of electrolyte]

[0058] Lithium hexafluorophosphate (LiPF) was dissolved in a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) (EC:EMC=3:7 by volume). 6 ), so that the concentration is 1.5 mol / L to prepare an electrolyte.

[0059] [Manufacturing of secondary batteries]

[0060] The positive electrode and the negative electrode are wound with a spacer made of a polyolefin resin to produce an electrode body. Insulating plates are arranged on the upper and lower parts of the electrode body, and the electrode body is contained in a cylindrical outer package. Then, the negative electrode lead is welded to the bottom of the outer package, and the positive electrode lead is welded to the sealing body. After that, the electrolyte is injected into the interior of the outer package by decompression, and the open end of the outer package is sealed by clamping the gasket to the sealing body to produce a secondary battery.

[0061] <Example 2>

[0062] A secondary battery was produced in the same manner as in Example 1 except that the ratio of the width of the first region, the width of the second region, and the width of the third region in the width direction of the positive electrode was changed to 2.5:95:2.5.

[0063] <Example 3>

[0064] A secondary battery was produced in the same manner as in Example 1 except that the ratio of the width of the first region, the width of the second region, and the width of the third region in the width direction of the positive electrode was changed to 10:80:10.

[0065] <Comparative Example 1>

[0066] A secondary battery was produced in the same manner as in Example 1, except that in the production of the positive electrode, only the second positive electrode mixture slurry was applied to the entire surface of the positive electrode current collector except for the positive electrode exposed portion.

[0067] <Comparative Example 2>

[0068] A secondary battery was produced in the same manner as in Example 1, except that in the production of the positive electrode, only the first positive electrode mixture slurry was applied to the entire surface of the positive electrode current collector except for the positive electrode exposed portion.

[0069] [Evaluation of initial battery capacity and capacity retention rate]

[0070] At an ambient temperature of 25°C, the secondary batteries of the embodiments and comparative examples were charged at a constant current of 0.3C until the battery voltage was 4.2V, and then charged at a constant voltage of 4.2V until the current value was 0.01C. Thereafter, they were discharged at a constant current of 0.5C to 2.5V. The charge and discharge were set as 1 cycle, and 100 cycles were performed. The capacity retention rate of the charge and discharge cycle of the secondary batteries of each embodiment and each comparative example was calculated using the following formula. In addition, the discharge capacity of the first cycle was set as the initial battery capacity.

[0071] Capacity retention rate = (discharge capacity at the 200th cycle / discharge capacity at the 1st cycle) × 100

[0072] The evaluation results of the secondary batteries of the examples and comparative examples are shown in Table 1. It should be noted that in Table 1, the initial battery capacities of Examples 1 to 3 and Comparative Example 1 are expressed as relative values ​​with the value of the initial battery capacity of Comparative Example 2 being 100. In addition, in Table 1, the capacity retention rates of Examples 1 to 3 and Comparative Example 2 are expressed as relative values ​​with the value of the capacity retention rate of Comparative Example 1 being 100.

[0073]

[0074] The initial battery capacity and capacity retention rate of the secondary batteries of Examples 1 to 3 are high, and both high capacity and high durability can be achieved. On the other hand, the capacity retention rate of the secondary battery of Comparative Example 1 is low, and the initial battery capacity of the secondary battery of Comparative Example 2 is low. It can be seen that by making the content of the electrolyte salt in the specified range near the two ends in the width direction greater than the content of the electrolyte salt in the central part in the width direction in the mixture layer, a secondary battery with high capacity and excellent durability can be obtained.

[0075] The present invention can be further described by the following embodiments.

[0076] Composition 1:

[0077] A non-aqueous electrolyte secondary battery comprises: an electrode body including a first electrode and a second electrode having different polarities; an electrolyte; and an outer package for accommodating the electrode body and the electrolyte.

[0078] The first electrode is rectangular in shape and includes a current collector and a mixture layer formed on a surface of the current collector.

[0079] The mixture layer includes a first region, a second region, and a third region in order from one end toward the other end in the width direction of the first electrode.

[0080] The widths of the first region and the third region in the width direction of the first electrode are respectively 1% to 20% of the length of the first electrode in the width direction.

[0081] The above-mentioned mixture layer contains electrolyte salt,

[0082] The content of the electrolyte salt in the first region and the third region is higher than the content of the electrolyte salt in the second region.

[0083] Composition 2:

[0084] The nonaqueous electrolyte secondary battery according to claim 1, wherein in the electrode body, the first electrode and the second electrode are wound with a separator interposed therebetween.

[0085] Composition 3:

[0086] The nonaqueous electrolyte secondary battery according to configuration 1 or 2, wherein the first electrode is a positive electrode.

[0087] Composition 4:

[0088] The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 3, wherein the electrolyte salt contains lithium hexafluorophosphate.

[0089] Composition 5:

[0090] The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 4, wherein the second region does not contain the electrolyte salt.

[0091] Description of Reference Numerals

[0092] 10 secondary battery, 11 positive electrode, 12 negative electrode, 13 separator, 14 electrode body, 16 outer packaging body, 17 sealing body, 18, 19 insulating plate, 20 positive electrode lead, 21 negative electrode lead, 22 slotted portion, 23 internal terminal plate, 24 lower valve body, 25 insulating member, 26 upper valve body, 27 cover, 28 gasket, 30 positive electrode collector, 32 positive electrode mixture layer, 32a first region, 32b second region, 32c third region, 34 positive electrode exposed portion.

Claims

1. A non-aqueous electrolyte secondary battery comprising: an electrode body including a first electrode and a second electrode having different polarities; an electrolyte; and an outer package for accommodating the electrode body and the electrolyte, The first electrode is rectangular in shape and includes a current collector and a mixture layer formed on a surface of the current collector. The mixture layer includes a first region, a second region, and a third region in order from one end toward the other end in the width direction of the first electrode. The widths of the first region and the third region in the width direction of the first electrode are respectively 1% to 20% of the length of the first electrode in the width direction. The mixture layer comprises an electrolyte salt, The content rates of the electrolyte salt in the first region and the third region are respectively higher than the content rate of the electrolyte salt in the second region.

2. The nonaqueous electrolyte secondary battery according to claim 1, wherein In the electrode body, the first electrode and the second electrode are wound with a separator interposed therebetween.

3. The nonaqueous electrolyte secondary battery according to claim 1, wherein The first electrode is a positive electrode.

4. The nonaqueous electrolyte secondary battery according to claim 1, wherein The electrolyte salt includes lithium hexafluorophosphate.

5. The nonaqueous electrolyte secondary battery according to claim 1, wherein The second region does not contain the electrolyte salt.

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