Non-aqueous electrolyte secondary batteries

Abstract

To provide a non-aqueous electrolyte secondary battery capable of suppressing an increase of a reaction resistance of a center part of an electrode body while maintaining a volume capacitance.SOLUTION: An electrolyte contains: a solvent; a lithium salt; and an addition agent. The addition agent contains at least one kind selected from a group formed by a boron chemical compound having an oxalate group and a chemical compound including a fluorosulfonyl group, and a BET specific surface area of a negative electrode active material layer is 1.8 m2 / g or more and 3.0 m2 / g or less. The negative electrode active material layer contains a particle group formed by negative electrode active material particles. An average spherical level of particle groups is 0.87 or more. In the case where the electrode body is a winding type electrode body, when a length of the negative electrode active material layer in a direction that is parallel to a winding shaft direction of the electrode body is 180 mm or more, and the electrode body is a lamination type electrode body, the minimum distance of the negative electrode active material layer at least one of opposite end parts in view of a lamination direction is 180 mm or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a non-aqueous electrolyte secondary battery (hereinafter also referred to as a battery). [Background technology]

[0002] Japanese Patent Laid-Open Publication No. 2007-179883 (Patent Document 1) and International Publication No. 2014 / 157591 (Patent Document 2) disclose additives used in electrolyte solutions to suppress an increase in reaction resistance of non-aqueous electrolyte secondary batteries. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-179883 [Patent Document 2] International Publication No. 2014 / 157591 Summary of the Invention [Problem to be solved by the invention]

[0004] Even when the additives described in Patent Documents 1 and 2 are used in the electrolyte solution of a nonaqueous electrolyte secondary battery, if the width of the electrode body is increased in order to improve the battery capacity per volume (hereinafter also referred to as volumetric capacity), the reaction resistance in the center of the electrode body may increase, resulting in a deterioration in battery characteristics. This is presumably because the additive penetrates into the center of the electrode body more slowly than the solvent of the electrolyte solution or the lithium salt, so the protective coating formed by the additive in the center of the electrode body is smaller than that at the edges of the electrode body, and as a result, the resistance in the center of the electrode body is more likely to increase.

[0005] The object of the present disclosure is to maintain the volume capacity while center The present invention provides a non-aqueous electrolyte secondary battery capable of suppressing an increase in reaction resistance in the battery. [Means for solving the problem]

[0006] The present invention provides the following nonaqueous electrolyte secondary battery. [1] A nonaqueous electrolyte secondary battery including an electrode assembly and an electrolyte solution, The electrode assembly includes a positive electrode plate, a negative electrode plate, and a separator, the electrolyte solution includes a solvent, a lithium salt, and an additive; the additive comprises at least one selected from the group consisting of a boron compound having an oxalate group and a compound having a fluorosulfonyl group, the negative electrode plate includes a negative electrode core material and a negative electrode active material layer containing negative electrode active material particles, The BET specific surface area of the negative electrode active material layer is 1.8 m 2 / g or more 3.0m 2 / g or less, the negative electrode active material layer includes a particle group made of the negative electrode active material particles, and the particle group has an average sphericity of 0.87 or more; The electrode body is a wound type electrode body or a stacked type electrode body, When the electrode body is a wound electrode body, the length of the negative electrode active material layer in a direction parallel to the winding axis direction of the electrode body is 180 mm or more, A nonaqueous electrolyte secondary battery, wherein when the electrode body is a laminated electrode body, the shortest distance between at least one opposing end of the negative electrode active material layer when viewed in the lamination direction is 180 mm or more. [2] The nonaqueous electrolyte secondary battery according to [1], wherein the electrode assembly has a width dimension of 300 mm or less. [3] The nonaqueous electrolyte secondary battery according to [1] or [2], wherein the content of the additive in the electrolyte solution is 0.001% by mass or more and 10% by mass or less. [4] The nonaqueous electrolyte secondary battery according to any one of [1] to [3], wherein the particle group has an average particle diameter D50 of 10 μm or more and 30 μm or less. [5] The nonaqueous electrolyte secondary battery according to any one of [1] to [4], wherein the average sphericity is 0.9 or more. [Effects of the Invention]

[0007] According to the present disclosure, the volume capacity is maintained while the inside of the electrode body center It is possible to provide a non-aqueous electrolyte secondary battery capable of suppressing an increase in reaction resistance in the battery. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram showing an example of the configuration of a nonaqueous electrolyte secondary battery according to this embodiment. [Figure 2] FIG. 2 is a schematic diagram showing an example of the configuration of the electrode body in this embodiment. [Figure 3] FIG. 3 is a schematic cross-sectional view showing an example of the configuration of the electrode body in this embodiment. [Figure 4] FIG. 4 is a schematic diagram showing an example of the configuration of the electrode body in this embodiment. [Figure 5] FIG. 5 is a schematic diagram showing the layer structure of the laminate produced in the example. [Figure 6] FIG. 6 is a schematic diagram illustrating a sample used for evaluating reaction resistance in the examples. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to the following embodiments. In all of the drawings, the scales of the components are appropriately adjusted to make them easier to understand, and the scales of the components shown in the drawings do not necessarily match the scales of the actual components.

[0010] FIG. 1 is a schematic diagram showing an example of the configuration of a nonaqueous electrolyte secondary battery according to this embodiment. The battery 100 can be used for any purpose. For example, the battery 100 may be used as a main power source or a power source for power assist in an electric vehicle or the like. A battery module or a battery pack may be formed by connecting a plurality of batteries 100. The battery 100 may have a rated capacity of, for example, 1 to 200 Ah.

[0011] The battery 100 includes an exterior body 90. The exterior body 90 is rectangular (flattened rectangular parallelepiped). The exterior body 90 may be made of, for example, an aluminum (Al) alloy. The exterior body 90 houses the electrode assembly 50 and an electrolyte (not shown). That is, the battery 100 includes the electrode assembly 50 and the electrolyte.

[0012] The exterior body 90 may include, for example, a sealing plate 91 and an exterior can 92. The sealing plate 91 closes the opening of the exterior can 92. For example, the sealing plate 91 and the exterior can 92 may be joined by laser processing or the like. The exterior body 90 may have any shape. For example, the exterior body 90 may be in the shape of a pouch. That is, the exterior body 90 may be a pouch made of an Al laminate film or the like.

[0013] The sealing plate 91 is provided with a positive electrode terminal 81 and a negative electrode terminal 82. The sealing plate 91 may further be provided with an injection port (not shown), a gas exhaust valve (not shown), etc. An electrolyte can be injected into the exterior body 90 through the injection port. The injection port can be closed with, for example, a sealing plug. The positive electrode current collecting member 71 connects the positive electrode terminal 81 and the electrode body 50. The positive electrode current collecting member 71 may be, for example, an Al plate. The negative electrode current collecting member 72 connects the negative electrode terminal 82 and the electrode body 50. The negative electrode current collecting member 72 may be, for example, a copper (Cu) plate.

[0014] The electrode assembly 50 includes a positive electrode plate, a separator, and a negative electrode plate. The electrode assembly 50 may be, for example, a wound type or a laminated type. When the electrode assembly 50 is a wound type, the positive electrode plate, the negative electrode plate, and the separator may each be, for example, a laminated body having a strip-like planar shape. A wound body can be formed by spirally winding the strip-like laminated body. The wound body can be, for example, cylindrical. A flat electrode assembly 50 can be formed by radially compressing the cylindrical wound body. The dimension of the electrode assembly 50 in the width direction (W-axis direction in FIG. 1 ) can be, for example, 300 mm or less, or 180 mm or more and 300 mm or less.

[0015] FIG. 2 is a schematic diagram showing an example of the configuration of an electrode assembly in this embodiment. The electrode assembly 50 in FIG. 2 is a wound electrode assembly having a winding axis parallel to the W-axis direction. The electrode assembly 50 includes a laminate 40. The electrode assembly 50 may essentially consist of the laminate 40. The laminate 40 includes a positive electrode plate 10, a negative electrode plate 20, and a separator 30. At least a portion of the separator 30 is interposed between the positive electrode plate 10 and the negative electrode plate 20. The separator 30 separates the positive electrode plate 10 and the negative electrode plate 20. The laminate 40 may include only one separator 30. The laminate 40 may include two separators 30. For example, the positive electrode plate 10 may be sandwiched between two separators 30. For example, the negative electrode plate 20 may be sandwiched between two separators 30. The laminate 40 may be formed by, for example, laminating a separator 30 (first separator), a negative electrode plate 20, a separator 30 (second separator), and a positive electrode plate 10 in this order.

[0016] FIG. 3 is a schematic cross-sectional view showing an example of the configuration of an electrode assembly in this embodiment. The electrode assembly 50 in FIG. 3 is a wound electrode assembly. FIG. 3 shows a cross section perpendicular to the winding axis. The electrode assembly 50 includes a curved portion 51 and a flat portion 52. The laminate 40 is curved at the curved portion 51. At the curved portion 51, the laminate 40 may be arc-shaped. At the flat portion 52, the laminate 40 is flat. The flat portion 52 is sandwiched between two curved portions 51. The flat portion 52 connects the two curved portions 51. The thickness of the laminate 40 refers to the total thickness of the positive electrode plate 10, the negative electrode plate 20, and the separator 30 included in the laminate 40. The laminate 40 may have a thickness of, for example, 100 to 200 μm, or may have a thickness of 1 to 100 mm.

[0017] FIG. 4 is a schematic cross-sectional view showing an example of the configuration of an electrode assembly in this embodiment. The electrode assembly 50 in FIG. 4 is a laminated electrode assembly. When the electrode assembly 50 is a laminated type, each of the positive electrode plate, the negative electrode plate, and the separator may be a laminate having, for example, a rectangular planar shape. As shown in FIG. 4, the electrode assembly 50 can be formed by stacking a plurality of laminates in a predetermined direction (D-axis direction). The laminated electrode assembly 50 is essentially composed of the flat portion of the laminate 40 described above. The laminated electrode assembly may have a thickness of, for example, 100 to 200 μm, or may have a thickness of 1 to 100 mm.

[0018] In the electrode assembly 50, the positive electrode plates 10 may have any number of layers. The number of layers of the positive electrode plates 10 indicates the number of times a line that cuts across the electrode assembly 50 in the layering direction intersects with the positive electrode plates 10. The layering direction indicates the direction in which the positive electrode plates 10, negative electrode plates 20, and separators 30 are layered in the electrode assembly 50. The layering direction in the wound electrode assembly 50 is parallel to the thickness direction of the positive electrode plates 10, negative electrode plates 20, and separators 30 in the flat portion 52 (the D-axis direction in FIG. 3). The layering direction in the layered electrode assembly 50 is parallel to the thickness direction of the positive electrode plates 10, negative electrode plates 20, and separators 30 (the D-axis direction in FIG. 4).

[0019] The positive electrode plates 10 may have a stacking number of, for example, 2 to 100. The negative electrode plates 20 may have a stacking number of, for example, 2 to 100. The separators 30 may have a stacking number of, for example, 4 to 200. The stacking numbers of the negative electrode plates 20 and separators 30 can be counted in the same way as the stacking number of the positive electrode plates 10. When the electrode body 50 is a stacked type, the stacking numbers of the positive electrode plates 10, negative electrode plates 20, and separators 30 indicate the numbers of the positive electrode plates 10, negative electrode plates 20, and separators 30, respectively.

[0020] In FIG. 1, when the electrode assembly 50 is a wound electrode assembly, the length of the negative electrode active material layer in a direction parallel to the winding axis direction (W-axis direction) of the electrode assembly 50 is 180 mm or more, for example, 200 mm or more or 220 mm or more, and may be 300 mm or less. In FIG. 1, when the electrode assembly 50 is a stacked electrode assembly, the shortest distance between at least one opposing end of the negative electrode active material layer when viewed from the stacking direction (D-axis direction) is 180 mm or more, for example, 200 mm or more or 220 mm or more, and may be 300 mm or less. In the case of a stacked electrode assembly having a rectangular shape when viewed from the stacking direction, the shortest distance is the shorter distance between one opposing end. In FIG. 4, the shortest distance is the distance in the W-axis direction.

[0021] The positive electrode plate 10 includes a positive electrode core material 11 and a positive electrode active material layer 12 (see FIG. 2). The positive electrode core material 11 is a conductive sheet. The positive electrode core material 11 may include, for example, pure Al foil or Al alloy foil. The positive electrode core material 11 may have a thickness of, for example, 10 to 30 μm. When the electrode body 50 is a wound electrode body, the positive electrode core material 11 may be exposed at one end in the width direction of the electrode body 50 (W-axis direction in FIG. 2). When the electrode body 50 is a laminated electrode body, the positive electrode core material 11 may be exposed at one end in the direction perpendicular to the width direction of the electrode body 50 (H-axis direction in FIG. 4). A positive electrode current collecting member 71 may be joined to the exposed portion of the positive electrode core material 11 (see FIG. 1).

[0022] The positive electrode active material layer 12 may be disposed on only one surface of the positive electrode core material 11. The positive electrode active material layer 12 may be disposed on both the front and back surfaces of the positive electrode core material 11. When the electrode body 50 is a wound type, the thickness of the positive electrode active material layer 12 refers to the total thickness of the positive electrode active material layers 12 included in the laminate 40. When the electrode body 50 is a laminate type, the thickness of the positive electrode active material layer 12 refers to the total thickness of the positive electrode active material layers 12 included in the electrode body 50. For example, when the positive electrode active material layers 12 are formed on both surfaces of the positive electrode plate 10, the thickness of the positive electrode active material layer 12 refers to the total thickness of the positive electrode active material layers 12 on both surfaces (two). The positive electrode active material layer 12 may have a thickness of, for example, 100 μm or more and 260 μm or less, or may have a thickness of 20 to 60 μm, or may have a thickness of 30 to 50 μm. The thickness of the positive electrode active material layer 12 on one surface (one layer) may be, for example, 10 to 30 μm, or 15 to 25 μm.

[0023] The positive electrode active material layer 12 contains positive electrode active material particles. The positive electrode active material particles may contain any component. The positive electrode active material particles may contain, for example, at least one selected from the group consisting of LiCoO2, LiNiO2, LiMnO2, LiMn2O4, Li(NiCoMn)O2, Li(NiCoAl)O2, and LiFePO4. For example, in a composition formula such as "Li(NiCoMn)O2," the sum of the composition ratios in parentheses is 1. That is, "C Ni +C Co +C Mn =1" relationship is satisfied. For example, "C Ni " indicates the composition ratio of Ni. As long as the total composition ratio is 1, the composition ratio of each component is arbitrary.

[0024] The positive electrode active material layer 12 may further contain, in addition to the positive electrode active material particles, for example, a conductive material, a binder, an additive, etc. For example, the positive electrode active material layer 12 may be substantially composed of, by mass fraction, 0.1 to 10% of a conductive material, 0.1 to 10% of a binder, and the remainder being positive electrode active material particles. The conductive material may contain, for example, acetylene black, etc. The binder may contain any component. The binder may contain, for example, polyvinylidene fluoride (PVdF), etc. Details of the additives will be described later.

[0025] The separator 30 includes a porous resin layer. The separator 30 may be essentially composed of the porous resin layer. The porous resin layer is in direct contact with the negative electrode active material layer 22. The absence of any intervening material between the porous resin layer and the negative electrode active material layer 22 is expected to improve output, for example. The separator 30 may or may not include a protective layer on the surface that contacts the positive electrode active material layer 12.

[0026] The porous resin layer may have a thickness of, for example, 10 to 50 μm, 10 to 30 μm, or 14 to 20 μm.

[0027] The porous resin layer has electrical insulation properties. The porous resin layer contains a polyolefin-based material. The porous resin layer may, for example, be substantially made of a polyolefin-based material. The polyolefin-based material may, for example, contain at least one material selected from the group consisting of polyethylene (PE) and polypropylene (PP).

[0028] The negative electrode plate 20 includes a negative electrode core material 21 and a negative electrode active material layer 22 (see FIG. 2). The negative electrode active material layer 22 may be disposed on the surface of the negative electrode core material 21. The negative electrode active material layer 22 may be disposed on only one side of the negative electrode core material 21. The negative electrode active material layer 22 may be disposed on both the front and back sides of the negative electrode core material 21. The negative electrode core material 21 is a conductive sheet. The negative electrode core material 21 may include, for example, pure Cu foil or Cu alloy foil. The negative electrode core material 21 may have a thickness of, for example, 5 to 30 μm. When the electrode body 50 is a wound electrode body, the negative electrode core material 21 may be exposed at one end in the width direction of the negative electrode plate 20 (W-axis direction in FIG. 2). When the electrode body 50 is a stacked electrode body, the negative electrode core material 21 may be exposed at one end in the direction perpendicular to the width direction of the electrode body 50 (H-axis direction in FIG. 4). A negative electrode current collecting member 72 can be joined to the exposed portion of the negative electrode core material 21 (see FIG. 1).

[0029] The BET specific surface area of the negative electrode active material layer 22 (hereinafter also referred to as the electrode plate BET) is 1.8 m2 / g or more 3.0m 2 / g or less. When the electrode plate BET is reduced, the surface area through which lithium enters and leaves decreases, resulting in an increase in reaction resistance. However, when a specific additive is contained in the electrolyte, an increase in the electrode plate BET tends to increase the reaction resistance in the center of the electrode body compared to the periphery. This is thought to be because, when a specific additive is contained, the interaction between the electrode plate surface and the additive slows the transport of the additive to the center compared to the solvent or salt. When the electrode plate BET is within the above range, the increase in reaction resistance in the center of the electrode body tends to be easily suppressed. The electrode plate BET is preferably 2.0 m 2 / g or more 3.0m 2 / g or less. The BET of the electrode plate is measured according to the method described in the Examples section below. The central part of the electrode body may be, for example, a circular region with a diameter of 10 mm centered on the geometric center of a plane when viewed from the stacking direction of the electrode body (the D-axis direction in FIG. 1).

[0030] When the electrode assembly 50 is a wound type, the thickness of the negative electrode active material layer 22 refers to the total thickness of the negative electrode active material layers 22 included in the laminate 40. When the electrode assembly 50 is a laminate type, the thickness of the negative electrode active material layer 22 refers to the total thickness of the negative electrode active material layers 22 included in the electrode assembly 50. For example, when the negative electrode active material layers 22 are formed on both sides of the negative electrode plate 20, the thickness of the negative electrode active material layer 22 refers to the total thickness of the negative electrode active material layers 22 on both sides (two). The negative electrode active material layer 22 may have a thickness of, for example, 100 μm or more and 260 μm or less, or may have a thickness of 40 to 80 μm, or may have a thickness of 50 to 70 μm. The thickness of the negative electrode active material layer 22 on one side (one side) may be, for example, 20 to 40 μm, or 25 to 35 μm.

[0031] The negative electrode active material layer 22 includes negative electrode active material particles. The negative electrode active material layer 22 may be substantially composed of negative electrode active material particles. Examples of the negative electrode active material particles include natural graphite, artificial graphite, silicon, silicon oxide, tin, tin oxide, and Li4Ti5O 12The negative electrode active material particles may contain at least one selected from the group consisting of: The negative electrode active material particles may be, for example, composite particles. The negative electrode active material particles may contain, for example, a substrate particle and a coating. The coating may cover the surface of the substrate particle. The substrate particle may contain, for example, natural graphite, etc. The coating may contain, for example, amorphous carbon, etc.

[0032] The negative electrode active material layer may contain particle groups composed of negative electrode active material particles. The particle groups have an average sphericity of 0.87 or more. When the average sphericity of the particle groups is within the above range, the particles are less likely to be crushed by compression, and the flow paths through which the electrolyte permeates the negative electrode plate tend to be wider. This reduces the influence of the surface of the negative electrode active material layer on the permeation of specific additives toward the center of the electrode plate, and tends to reduce the reaction resistance in the center of the electrode body. The particle groups preferably have a sphericity of 0.90 or more and typically 1.00 or less. The average sphericity of the particle groups is measured according to the method described in the Examples section below.

[0033] The average particle diameter D50 (hereinafter also referred to as D50) of the particle group consisting of negative electrode active material particles may be, for example, 10 μm or more and 30 μm or less. The average particle diameter D50 represents the particle diameter at which the cumulative particle volume from the small particle diameter side in the volume-based particle size distribution is 50% of the total particle volume. The average particle diameter D50 can be measured by a laser diffraction / scattering method.

[0034] The negative electrode active material layer 22 may further contain a conductive material, a binder, etc. in addition to the negative electrode active material particles. For example, the negative electrode active material layer 22 may essentially be composed of 0 to 10% by mass of a conductive material, 0.1 to 10% by mass of a binder, and the remainder being negative electrode active material particles. The conductive material may contain any component. The conductive material may contain, for example, carbon black, carbon nanotubes, etc. The binder may contain any component. The binder may contain, for example, at least one selected from the group consisting of carboxymethyl cellulose (CMC) and styrene butadiene rubber (SBR).

[0035] The electrolyte is a liquid electrolyte. The electrolyte contains a solvent, a lithium salt (hereinafter also referred to as Li salt), and an additive. The solvent is aprotic. The solvent may contain any component. For example, the solvent may contain at least one selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), 1,2-dimethoxyethane (DME), methyl formate (MF), methyl acetate (MA), methyl propionate (MP), and γ-butyrolactone (GBL).

[0036] The Li salt is dissolved in a solvent. The Li salt may include, for example, at least one selected from the group consisting of LiPF, LiBF, and LiN(FSO). The Li salt may have a molar concentration of, for example, 0.2 to 2.0 M (mol / L).

[0037] The content of the additive in the electrolyte solution may be, for example, 0.001% by mass or more and 10% by mass or less. The additive includes at least one selected from the group consisting of a boron compound having an oxalate group and a compound having a -SO2F group. Examples of the boron compound having an oxalate group include lithium bis(oxalato)borate (LiBOB). Examples of the compound having a fluorosulfonyl group (-SO2F group) include lithium fluorosulfonate (FS03Li), lithium bis(fluorosulfonyl)imide, and compounds represented by the following formula: [ka] [In the formula, R1 is an alkyl group, alkenyl group, or alkynyl group having 1 to 10 carbon atoms which may be substituted with a halogen atom, or an aromatic hydrocarbon group having 6 to 20 carbon atoms which may be substituted with a halogen atom, and n is an integer of 0 to 1.] and the like.

[0038] The present invention will be described in more detail below with reference to examples. In the examples, "%" and "parts" are by mass % and mass parts unless otherwise specified. [Example]

[0039] Example 1 [Preparation of negative electrode plate] As the negative electrode active material, graphite having an average sphericity of 0.9 and an average particle diameter D50 of 17 μm was used. When compressed to a predetermined thickness, the negative electrode plate had a BET of 2.5 mm. 2 The active material was selected so that the average particle size was 1 / g. A negative electrode mixture slurry was prepared by mixing a mixture with a graphite:SBR:CMC=100:1:1 wt% with water. The negative electrode mixture slurry was applied to the copper foil of a negative electrode current collector, dried, compressed to a predetermined thickness, and cut to a predetermined width to produce a negative electrode plate consisting of a copper foil portion on which a negative electrode active material layer was formed and a portion on which no active material layer was formed. The length of the negative electrode active material layer in the direction parallel to the winding axis of the electrode body (hereinafter also referred to as the width of the negative electrode active material layer) was 180 mm. [Preparation of positive electrode plate] A positive electrode mixture slurry was prepared by mixing a mixture with LiNiCoMnO2:AB:PVdF = 100:1:1 wt% with NMP. This mixture was applied to an aluminum foil positive electrode current collector, dried, compressed to a predetermined thickness, and cut to a predetermined width to produce a positive electrode plate with a widthwise portion of the aluminum foil where the positive electrode active material layer was formed and a portion where the active material layer was not formed. The length of the positive electrode active material layer in the direction parallel to the winding axis of the electrode body (hereinafter also referred to as the width of the positive electrode active material layer) was 176 mm. [Preparation of electrode body] As shown in FIG. 5, a positive electrode plate 10 and a negative electrode plate 20 were stacked with a separator 30 made of three layers of polypropylene / polyethylene / polypropylene in between so that the aluminum foil of the positive electrode plate and the copper foil of the negative electrode plate were exposed at both ends, to produce a laminate, and one end of the laminate was wound around the winding axis R to produce a wound electrode body 50. [Fabrication of non-aqueous electrolyte secondary battery] The aluminum foil of the positive current collector was welded to the aluminum plate used for external current collection of the electrode body, and the copper foil of the negative current collector was welded to the copper plate used for external current collection of the electrode body. The electrode was then inserted into an outer case of an aluminum laminate film, and electrolyte was poured in according to the electrolyte pouring method described below. The laminate film was then sealed to prepare a nonaqueous electrolyte secondary battery. The results are shown in Table 1. [Electrolyte injection method] The first electrolyte solution [1.2M LiPF6EC / EMC (volume ratio 1:3), additive: LiBOB 0.5 wt%] was prepared and left for 3 hours after injection. After that, the battery was charged to 2.5 V at a current of 0.05 C in a 25°C environment and left for 1 hour. Next, activation treatment was performed.

[0040] <Example 2> A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 1, except that a second electrolyte solution [1.2M LiPFEC / EMC (volume ratio 1:3), additive: LiSOF 1.0 wt%] was used instead of the first electrolyte solution used in Example 1. The results are shown in Table 1.

[0041] Example 3 A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 1, except that the width of the negative electrode active material layer was 300 mm and the width of the positive electrode active material layer was 296 mm. The results are shown in Table 1.

[0042] Example 4 As the negative electrode active material, graphite having an average particle diameter D50 of 15 μm and an average sphericity of 0.93 was used, and when compressed to a predetermined thickness, the negative electrode plate BET was 2.0 mm. 2 / g, a nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 1. The results are shown in Table 1.

[0043] <Example 5> As the negative electrode active material, graphite having an average particle diameter D50 of 15 μm and an average sphericity of 0.92 was used, and when compressed to a predetermined thickness, the electrode plate BET of the negative electrode plate was 3.0 mm. 2 / g, a nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 1. The results are shown in Table 1.

[0044] <Comparative Example 1> A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 1, except that the width of the negative electrode active material layer was 78 mm and the width of the positive electrode active material layer was 74 mm. The results are shown in Table 1.

[0045] <Comparative Example 2> A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 1, except that the third electrolytic solution [1.2M LiPFEC / EMC (volume ratio 1:3), no additives] was used instead of the first electrolytic solution used in Example 1. The results are shown in Table 1.

[0046] <Comparative Example 3> As the negative electrode active material, graphite having an average particle diameter D50 of 14 μm and an average sphericity of 0.86 was used, and when compressed to a predetermined thickness, the electrode plate BET of the negative electrode plate was 3.0 mm. 2 / g, a nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 1. The results are shown in Table 1.

[0047] <Comparative Example 4> As the negative electrode active material, graphite having an average particle diameter D50 of 25 μm and an average sphericity of 0.92 was used, and when compressed to a predetermined thickness, the electrode plate BET of the negative electrode plate was 1.7 m. 2 / g, a nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 1. The results are shown in Table 1.

[0048] <Comparative Example 5> As the negative electrode active material, graphite having an average particle diameter D50 of 14 μm and an average sphericity of 0.90 was used, and when compressed to a predetermined thickness, the electrode plate BET of the negative electrode plate was 3.5 mm. 2 / g, a nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 1. The results are shown in Table 1.

[0049] <Measuring method for electrode plate BET> A predetermined weight of negative electrode plate was punched out, cut into small pieces, and placed in a cell for BET measurement. The cell for BET measurement was heated to expel the adsorbed gas, then immersed in liquid nitrogen to cool. N2 gas was passed through the cell to measure P / P0 from the pressure loss, and the following BET equation was used: P / {V(P0-P)}=1 / V m C+(C-1) / V m C×P / P0 [In the formula, V, P, P0, V m and C respectively represent the gas adsorption amount, pressure, saturated vapor pressure, monolayer adsorption amount (amount of gas adsorbed in a monolayer), and condensation coefficient of the adsorbed molecules when the gas molecules (adsorbate) are adsorbed on a solid surface. The specific surface area was calculated according to the following.

[0050] <Method for measuring average sphericity> From the image analysis of multiple particles, the sphericity of each particle was calculated using the following formula, and the average sphericity was obtained by averaging the results. Sphericity = (perimeter of a circle equivalent to the particle area) / total perimeter of the particle

[0051] <Volumetric capacity evaluation method> The battery was charged at a constant current of 1 / 3 C to 4.2 V, then charged at a constant voltage of 0.05 C, and then discharged at a constant current of 1 / 3 C to 2.5 V. The capacity per volume was calculated by dividing the discharge capacity by the volume of the battery. Table 1 shows the relative values when the value for Example 1 is set to 100.

[0052] <Reaction resistance evaluation method> As shown in FIG. 6 , the nonaqueous electrolyte secondary batteries of each Example were disassembled after initial activation. The negative electrode plate facing the inner periphery of the first turn of the positive electrode at the start of winding the electrode assembly was cut out, washed with dimethyl carbonate (DMC), and then dried under reduced pressure. A φ10 mm hole (the length of CR in the figure) was punched out from the center of the cut-out negative electrode plate to obtain a sample 23 for reaction resistance evaluation. One side of the negative electrode was peeled off, and a φ11 mm Li metal plate was placed opposite the negative electrode plate via a φ13 mm PP / PE / PP separator to create a coin cell. The negative electrode of the coin cell was charged to 50% SOC, and then AC impedance was measured at 25°C with an amplitude of 10 mV in the range of 1 MHz to 0.1 Hz. The data in the range of 1 kHz to 1 Hz was used as the reaction resistance. Table 1 shows relative values, with the value for Example 1 set to 100.

[0053] [Table 1]

[0054] As shown in Table 1, in Examples 1 to 5, the volumetric capacity was maintained while the inside of the electrode body center The increase in reaction resistance in the negative electrode active material layer was suppressed. The use of a boron compound containing an oxalate group (LiBOB) or a compound containing SO2F (FSO3Li) was confirmed to reduce reaction resistance. It was also confirmed that, although the volumetric capacity tends to increase as the width of the negative electrode active material layer increases, the reaction resistance in the center of the electrode body tends to increase. This is presumably due to the interaction between the surface of the negative electrode active material layer and the additive, which allows the additive to penetrate more slowly than solvents or salts. As a result, the protective film formed by the additive in the negative electrode active material layer becomes unevenly distributed, reducing the protective film in the center of the electrode body, causing the reaction to become uneven and resulting in an increase in reaction resistance. [Explanation of symbols]

[0055] 10 positive electrode plate, 11 positive electrode core material, 12 positive electrode active material layer, 20 negative electrode plate, 21 negative electrode core material, 22 negative electrode active material layer, 23 reaction resistance evaluation sample, 30 separator, 40 laminate, 50 electrode body, 51 curved portion, 52 flat portion, 71 positive electrode current collecting member, 72 negative electrode current collecting member, 81 positive electrode terminal, 82 negative electrode terminal, 90 exterior body, 91 sealing plate, 92 exterior can, 100 battery, W width direction, R winding axis, S start of winding, E end of winding, CR diameter.

Claims

1. A non-aqueous electrolyte secondary battery including an electrode assembly and an electrolyte solution, The electrode assembly includes a positive electrode plate, a negative electrode plate, and a separator, the electrolyte solution includes a solvent, a lithium salt, and an additive; the additive includes at least one selected from the group consisting of a boron compound having an oxalate group and a compound having a fluorosulfonyl group, the negative electrode plate includes a negative electrode core material and a negative electrode active material layer containing negative electrode active material particles, The BET specific surface area of the negative electrode active material layer is 1.8 m ２ / g or more 3.0m ２ / g or less, the negative electrode active material layer includes a particle group made of the negative electrode active material particles, and the particle group has an average sphericity of 0.9 or more; The particle group has an average particle diameter D50 of 10 μm or more and 30 μm or less, The electrode body is a wound type electrode body or a stacked type electrode body, When the electrode body is a wound electrode body, the length of the negative electrode active material layer in a direction parallel to the winding axis direction of the electrode body is 180 mm or more, When the electrode body is a laminated electrode body, the shortest distance between at least one opposing end of the negative electrode active material layer when viewed in the lamination direction is 180 mm or more.

2. 2. The nonaqueous electrolyte secondary battery according to claim 1, wherein the electrode assembly has a width of 300 mm or less.

3. 2. The nonaqueous electrolyte secondary battery according to claim 1, wherein the content of the additive in the electrolyte solution is 0.001% by mass or more and 10% by mass or less.

4. A non-aqueous electrolyte secondary battery as described in claim 1, wherein the electrode body is a wound-type electrode body.

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