Nonaqueous electrolyte secondary battery, battery pack, and battery module

Abstract

To provide a nonaqueous electrolyte secondary battery which includes a wide electrode body and is subjected to pressure in the electrode plate stacking direction of the electrode body, and which has low output resistance and suppresses deterioration of cycle characteristics, and to provide a battery pack and a battery module including the same.SOLUTION: A nonaqueous electrolyte secondary battery includes a wound-type electrode body and an electrolyte, and a positive electrode plate includes a positive electrode active material layer, and a negative electrode plate includes a negative electrode active material layer, at least one of the positive electrode active material layer and the negative electrode active material layer has a dimension of 150 mm or more in a winding axis direction of an electrode body, the electrolyte includes an electrolyte salt and LiFSO3, the electrolyte salt comprises at least one of LiPF6 and LiBF4, a ratio A / B of a total concentration A (mol / L) of LiPF6 and LiBF4 to a concentration B (mol / L) of LiFSO3 in the electrolyte is 5 or more and 12 or less, and the electrode body is subjected to a pressure of 0.5 MPa or more in a stacking direction of the electrode plates.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a non-aqueous electrolyte secondary battery, and further to a battery pack and a battery module including the same. [Background technology]

[0002] For the purpose of improving the input / output characteristics and impedance characteristics after endurance testing of a nonaqueous electrolyte secondary battery, Patent Document 1 proposes a nonaqueous electrolyte solution containing LiPF6 and LiFSO3, and Patent Document 2 proposes setting the ratio of the molar content of FSO3 to the molar content of PF6 within a specific range. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-152956 [Patent Document 2] Japanese Patent Application Laid-Open No. 2011-187440 Summary of the Invention [Problem to be solved by the invention]

[0004] In non-aqueous electrolyte secondary batteries containing wide electrode assemblies (e.g., active material layers with a longitudinal dimension of 15 cm or more), when pressure is applied to the electrode assemblies in the direction of electrode plate stacking, salt concentration unevenness is likely to occur during high-rate cycling, resulting in a large increase in positive electrode potential and a tendency for capacity degradation to occur. When an electrolyte containing LiFSO3 is used, SO3F - is adsorbed on the surface of the positive electrode active material, which tends to inhibit the formation of a LiF film derived from the electrolyte salt, and when the cell size is large, the salt concentration unevenness due to high-rate charging cycles becomes significant, and the salt concentration at the edge of the plate tends to decrease. As a result, the potential at the edge of the positive plate increases, and the positive electrode active material and the highly acidic SO3F -This is presumably because the potential reaches a point at which the transition metal reacts with the cathode active material, causing the transition metal to dissolve from the cathode active material on which the LiF coating is insufficient, and deposit on the anode plate.

[0005] An object of the present disclosure is to provide a nonaqueous electrolyte secondary battery that includes a wide electrode assembly and is subjected to pressure in the electrode plate stacking direction of the electrode assembly, and that has low output resistance and suppressed deterioration in cycle characteristics, as well as a battery pack and a battery module that include the same. [Means for solving the problem]

[0006] The present disclosure provides the following nonaqueous electrolyte secondary battery, battery pack, and battery module. [1] A battery comprising an electrode body and an electrolyte solution, the electrode body is a wound electrode body in which a positive electrode plate and a negative electrode plate are wound with a separator interposed therebetween, The positive electrode plate includes a positive electrode active material layer, the negative electrode plate includes a negative electrode active material layer, At least one of the positive electrode active material layer and the negative electrode active material layer has a dimension of 150 mm or more in the winding axis direction of the electrode body, The electrolyte solution contains an electrolyte salt and LiFSO3, the electrolyte salt contains at least one of LiPF6 and LiBF4, When the total concentration of LiPF6 and LiBF4 in the electrolyte is A (mol / L) and the concentration of LiFSO3 is B (mol / L), the A / B ratio, which is the ratio of A to B, is 5 or more and 12 or less; A non-aqueous electrolyte secondary battery, wherein the electrode assembly is subjected to a pressure of 0.5 MPa or more in the electrode plate stacking direction. [2] The nonaqueous electrolyte secondary battery according to [1], wherein the A / B ratio is 6.7 or more and 10 or less. [3] The nonaqueous electrolyte secondary battery according to [1] or [2], wherein the total concentration A of LiPF6 and LiBF4 in the electrolyte solution is 1 to 1.5 mol / L. [4] The nonaqueous electrolyte secondary battery according to any one of [1] to [3], wherein the concentration B of LiFSO3 in the electrolyte solution is 0.1 to 0.25 mol / L. [5] The nonaqueous electrolyte secondary battery according to any one of [1] to [4], wherein the electrode body has a length parallel to the winding axis of 180 mm or more. [6] A battery pack comprising the nonaqueous electrolyte secondary battery according to any one of [1] to [5]. [7] A battery module comprising the nonaqueous electrolyte secondary battery according to any one of [1] to [5]. [Effects of the Invention]

[0007] According to the present disclosure, it is possible to provide a nonaqueous electrolyte secondary battery that includes a wide electrode assembly and is subjected to pressure in the electrode plate stacking direction of the electrode assembly, and that has low output resistance and suppressed deterioration in cycle characteristics, as well as a battery pack and a battery module that include the same. [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 perspective view showing an example of a battery pack according to this embodiment. [Figure 6] FIG. 6 is a perspective view showing an example of a battery module according to the present embodiment. [Figure 7] FIG. 7 is a schematic diagram for explaining a method for restraining a battery in an embodiment. 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] In this specification, elements expressed in the singular include the plural unless otherwise specified. For example, a "particle" can mean not only "one particle" but also "an aggregate of particles (powder, powder, particle group)."

[0011] FIG. 1 is a schematic diagram showing an example of the configuration of a battery in 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 multiple batteries 100. Battery modules and battery packs will be described later. The battery 100 may have a rated capacity of, for example, 1 to 300 Ah.

[0012] The battery 100 includes an electrode assembly 50 and an electrolyte. As shown in FIG. 1, the battery 100 may further include an exterior body 90. The exterior body 90 houses the electrode assembly 50 and the electrolyte (not shown). The exterior body 90 is rectangular (flattened rectangular parallelepiped). The exterior body 90 may be made of, for example, an aluminum (Al) alloy. A pressure of 0.5 MPa or more is applied to the electrode assembly 50 in the electrode plate stacking direction (the D-axis direction in FIG. 1). The pressure may be applied from outside the electrode assembly 50. The pressure applied to the electrode assembly may be an area indicated by the electrode assembly area S in FIG. 4. An explanation of FIG. 4 will be given later. The electrode assembly 50 may be constrained within the exterior body 90. The force constraining the electrode assembly 50 may be the pressure described above. The force constraining the electrode assembly 50 may be, for example, a force constraining multiple batteries and inter-cell separators in a battery module described later.

[0013] 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.

[0014] 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.

[0015] The electrode assembly 50 is a wound electrode assembly in which a positive electrode plate and a negative electrode plate are wound with a separator interposed therebetween. The positive electrode plate, the negative electrode plate, and the separator may form, for example, a laminate having a strip-like planar shape. A wound assembly may be formed by spirally winding the strip-like laminate. The wound assembly may be, for example, cylindrical. A flat electrode assembly 50 may be formed by radially compressing the cylindrical wound assembly. The dimension of the electrode assembly 50 in the winding axis direction (hereinafter also referred to as the width direction) (W-axis direction in FIG. 1) may be, for example, 180 mm or more, or may be 180 mm or more and 300 mm or less.

[0016] 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 R 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 positive electrode plate 10 and the negative electrode plate 20 may each be bonded to a separator 30. The laminate 40 may include a single separator 30 alone. 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.

[0017] FIG. 3 is a schematic cross-sectional view showing an example of the configuration of an electrode assembly in this embodiment. 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 400 μm, or may have a thickness of 1 to 300 μm. The thickness of the laminate 40 is the thickness in the electrode assembly stacking direction (the D-axis direction in FIG. 3).

[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 (the D-axis direction in FIG. 3 ) of the positive electrode plates 10, negative electrode plates 20, and separators 30 in the flat portion 52.

[0019] As shown in FIG. 4, the electrode body 50 can be produced by stacking a positive electrode plate 10 and a negative electrode plate 20 with a separator 30 interposed therebetween so that the aluminum foil of the positive electrode plate and the copper foil of the negative electrode plate are exposed at both ends to produce a laminate, and then winding the laminate around one end of the laminate as the winding axis R.

[0020] The positive electrode plate 10 may have a stacking number of, for example, 2 to 100. The negative electrode plate 20 may have a stacking number of, for example, 2 to 100. The separator 30 may have a stacking number of, for example, 4 to 200. The stacking numbers of the negative electrode plate 20 and the separator 30 can be counted in the same way as the stacking number of the positive electrode plate 10.

[0021] The positive electrode plate 10 includes a positive electrode active material layer. In Fig. 1, the dimension of the positive electrode active material layer in a direction parallel to the winding axis direction (W-axis direction) of the electrode body 50 is 150 mm or more, and may be, for example, 180 mm or more, 200 mm or more, or 220 mm or more, or 300 mm or less. The positive electrode active material layer will be described later.

[0022] The negative electrode plate 20 includes a negative electrode active material layer. In Fig. 1, the dimension of the negative electrode active material layer in a direction parallel to the winding axis direction (W-axis direction) of the electrode body 50 is 150 mm or more, and may be, for example, 180 mm or more, 200 mm or more, or 220 mm or more, or 300 mm or less. The negative electrode active material layer will be described later.

[0023] 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 active material layer 12 may be disposed on the surface of the positive electrode core material 11. The positive electrode active material layer 12 may be disposed on only one side of the positive electrode core material 11. The positive electrode active material layer 12 may be disposed on both the front and back sides of the positive electrode core material 11. The positive electrode core material 11 is a conductive sheet. The positive electrode core material 11 may include, for example, pure Al foil, Al alloy foil, or the like. The positive electrode core material 11 may have a thickness of, for example, 10 to 30 μm. The positive electrode core material 11 may be exposed at one end in the width direction of the electrode body 50 (the W-axis direction in FIG. 2). A positive electrode current collecting member 71 may be joined to the exposed portion of the positive electrode core material 11 (see FIG. 1). The thickness of the positive electrode plate 10 may be, for example, 20 to 290 μm, 50 to 250 μm, or 100 to 200 μm. The longitudinal dimension of the positive electrode plate 10 may be, for example, 0.5 to 10 m, or 1 to 5 m.

[0024] 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. For example, when the positive electrode active material layers 12 are formed on both sides of the positive electrode plate 10, the thickness of the positive electrode active material layers 12 refers to the total thickness of the positive electrode active material layers 12 on both sides (two). The positive electrode active material layers 12 may have a thickness of, for example, 10 to 260 μm, 20 to 60 μm, or 30 to 50 μm. The thickness of the positive electrode active material layer 12 on one side (one side) may be, for example, 5 to 130 μm, 10 to 30 μm, or 15 to 25 μm.

[0025] The positive electrode active material layer 12 may contain a lithium transition metal composite oxide. The lithium transition metal composite oxide may contain 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. The composition ratio of each component is arbitrary as long as the total of the composition ratios is 1. The positive electrode active material layer 12 may contain positive electrode active material particles. The positive electrode active material particles may contain any component. The positive electrode active material particles may contain the above-mentioned lithium transition metal composite oxide.

[0026] The positive electrode active material layer 12 may further contain, for example, a conductive material, a binder, etc. in addition to the positive electrode active material particles. 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, a carbon material, etc. The binder may contain any component. The binder may contain, for example, polyvinylidene fluoride (PVdF), etc. The packing density (after compression) of the positive electrode active material layer 12 is, for example, 2.0 g / cm. 3 More than 4.0g / cm 3 It may be the following:

[0027] 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, Cu alloy foil, or the like. The negative electrode core material 21 may have a thickness of, for example, 5 to 30 μm. The negative electrode core material 21 may be exposed at one end in the width direction (W-axis direction in FIG. 2) of the negative electrode plate 20. A negative electrode current collecting member 72 may be joined to the exposed portion of the negative electrode core material 21 (see FIG. 1). The thickness of the negative electrode plate 20 may be, for example, 20 to 290 μm, 50 to 250 μm, or 100 to 200 μm. The longitudinal dimension of the negative electrode plate 20 may be, for example, 0.5 to 10 m, or 1 to 5 m.

[0028] 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. 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 layers 22 refers to the total thickness of the negative electrode active material layers 22 on both sides (two). The negative electrode active material layers 22 may have a thickness of, for example, 10 to 260 μm, 40 to 80 μm, or 50 to 70 μm. The thickness of the negative electrode active material layer 22 on one side (one) may have a thickness of, for example, 5 to 130 μm, 20 to 40 μm, or 25 to 35 μm. The packing density (after compression) of the negative electrode active material layers 22 is, for example, 1.0 g / cm. 3 More than 1.8g / cm 3 It may be the following:

[0029] The negative electrode active material layer 22 is made of, for example, graphite, silicon, silicon oxide, tin, tin oxide, and Li4Ti5O 12 The negative electrode active material layer 22 may contain at least one selected from the group consisting of the negative electrode active material. The negative electrode active material layer 22 may contain negative electrode active material particles. The negative electrode active material particles may contain the above-mentioned negative electrode active material. The negative electrode active material layer 22 may essentially consist of negative electrode active material particles. The negative electrode active material particles may be, for example, composite particles. The negative electrode active material particles may include, 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, graphite, etc. The coating may contain, for example, amorphous carbon, etc.

[0030] 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 be substantially 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, a carbon material. 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).

[0031] The separator 30 includes a resin film. The separator 30 may be substantially composed of a resin film. The separator 30 may have a single-layer structure made of one resin film, or a multilayer structure made of two or more resin films. When the separator 30 has a multilayer structure, the resin films may be different types of resin films. The resin film may be substantially made of, for example, a polyolefin-based material. The polyolefin-based material may include, for example, at least one selected from the group consisting of polyethylene (PE) and polypropylene (PP). When the separator 30 has a multilayer structure, the separator 30 may have a three-layer structure made of, for example, a resin film made of PP / a resin film made of PE / a resin film made of PP. The resin film may have a thickness of, for example, 10 to 50 μm, 10 to 30 μm, or 10 to 20 μm. The resin film may be porous.

[0032] The electrolyte is a liquid electrolyte. The electrolyte contains an electrolyte salt and LiFSO3. The electrolyte salt may be dissolved in a solvent described below in the electrolyte.

[0033] The electrolyte salt contains at least one of LiPF6 and LiBF4. The electrolyte salt may contain LiPF6 alone, LiBF4 alone, or both LiPF6 and LiBF4. When the total concentration of LiPF6 and LiBF4 in the electrolyte is A (mol / L) and the concentration of LiFSO3 is B (mol / L), the A / B ratio, which is the ratio of A to B, is 5 to 12. By setting A / B within the above range, at least one of LiPF6 and LiBF4 is present in sufficient proportion to LiFSO3, a sufficient LiF film is formed on the surface of the positive electrode active material, and leaching of the active material transition metal due to LiFSO3 is suppressed. As a result, it is presumed that a battery exhibiting low output resistance and good cycle characteristics can be obtained. From the viewpoint of output resistance and cycle characteristics, the A / B ratio is preferably 5 to 10, more preferably 6.7 to 10.

[0034] The total concentration A of LiPF6 and LiBF4 in the electrolyte may be, for example, 1.0 to 1.5 mol / L. The concentration B of LiFSO3 in the electrolyte may be, for example, 0.1 to 0.25 mol / L.

[0035] The electrolyte may contain a solvent. The solvent is aprotic. The solvent may contain any component. The solvent may contain at least one selected from the group consisting of carbonate-based solvents, 1,2-dimethoxyethane (DME), methyl formate (MF), methyl acetate (MA), methyl propionate (MP), and γ-butyrolactone (GBL). The solvent preferably contains a carbonate-based solvent. Examples of carbonate-based solvents include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC).

[0036] The battery of the present disclosure can have a capacity retention rate of 90% or more in an evaluation of cycle characteristics. When the cycle capacity retention rate is 90% or more, the battery can have good cycle characteristics. The evaluation of cycle characteristics is carried out according to the method described in the Examples section below.

[0037] A method for manufacturing a battery can include, for example, an accommodation step of accommodating the electrode body in an outer case and an injection step of injecting an electrolyte. In the accommodation step, the aluminum foil of the positive current collector and the aluminum plate for external current collection of the electrode body are welded, and the copper foil of the negative current collector and the copper plate for external current collection of the electrode body are welded, and the resultant can be inserted into an outer case of an aluminum laminate film. In the injection step, the above-mentioned electrolyte can be injected. After the injection, the can is sealed and welded to obtain a battery.

[0038] (Battery pack) Fig. 5 is a perspective view of a battery pack 200. The battery pack 200 shown in Fig. 5 includes batteries 100 and inter-cell separators 201. The batteries 100 and the inter-cell separators 201 are arranged alternately along the Y-axis direction (first direction).

[0039] The batteries 100 are rectangular battery cells, and a plurality of batteries 100 are provided along the Y-axis direction. The plurality of batteries 100 are electrically connected to one another via bus bars (not shown).

[0040] Inter-cell separators 201 are provided between multiple batteries 100. The inter-cell separators 201 prevent unintended electrical conduction between adjacent batteries 100. The inter-cell separators 201 ensure electrical insulation between adjacent batteries 100.

[0041] (battery module) 6 is a perspective view of a battery module 300. As shown in FIG. 3, the battery module 300 includes batteries 100, inter-cell separators 201, binding members 301, and end plates 302.

[0042] The batteries 100 and inter-cell separators 201 arranged alternately along the Y-axis direction (first direction) are pressed by the end plates 302 and are constrained between the two end plates 302.

[0043] The end plates 302 are arranged at both ends in the Y-axis direction. The end plates 302 are fixed to a base such as a case that houses the battery module 300. The restraining member 301 connects the two end plates 302 to each other and restrains the multiple batteries 100 and inter-cell separators 201 along the Y-axis direction.

[0044] When a compressive force in the Y-axis direction is applied to the stack of batteries 100, inter-cell separators 201, and end plates 302, and the restraining members 301 are fixed to the end plates 302, and the compressive force is then released, a tensile force acts on the restraining members 301 connecting the two end plates 302. In reaction to this, the restraining members 301 press the two end plates 302 in a direction that brings them closer to each other. This completes the construction of the battery module 300.

[0045] A battery pack is constructed by housing the battery modules 300 in a pack case (cell-module-pack structure). Alternatively, a structure may be used in which the battery assembly 200 shown in Fig. 5 is directly supported by the wall of the pack case (cell-to-pack structure). [Example]

[0046] 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.

[0047] Example 1 [Preparation of positive electrode plate] A cathode active material layer mixture with a composition of LiNiCoMnO2:AB:pVdF = 100:1:1 wt% was mixed with NMP to prepare a cathode mixture slurry. The mixture was applied to an aluminum foil cathode current collector, dried, compressed to a specified thickness, and cut to a specified width to produce a cathode plate consisting of a portion of the aluminum foil on which the cathode active material layer was formed and a portion without the active material layer. The width of the cathode active material layer was 150 mm. [Preparation of negative electrode plate] Graphite was used as the negative electrode active material. A negative electrode active material layer mixture with a composition of graphite:SBR:CMC=100:1:1 wt% was mixed with water to prepare a negative electrode mixture slurry. The negative electrode mixture slurry was applied to the copper foil of the negative electrode current collector, dried, compressed to a predetermined thickness, and cut to a predetermined width to prepare a negative electrode plate consisting of a portion on the copper foil where the negative electrode active material layer was formed and a portion where the active material layer was not formed. The width of the negative electrode active material layer formed was 154 mm. [Preparation of electrode body] An electrode assembly having the configuration shown in Fig. 4 was fabricated as follows: A positive electrode plate and a negative electrode plate were laminated with a separator consisting of three layers of polypropylene / polyethylene / polypropylene in between so that the positive electrode aluminum foil and the negative electrode copper foil were exposed at both ends to produce a laminate, and the laminate was wound around one end of the laminate as a winding axis to produce the electrode assembly.

[0048] [Fabrication of non-aqueous electrolyte secondary battery] The aluminum foil of the positive current collector was welded to an aluminum plate for external current collection, and the copper foil of the negative current collector was welded to a copper plate for external current collection. These were then inserted into the outer shell of an aluminum laminate film, and the following electrolyte 1 was poured into it, and the laminate film was sealed. (electrolyte 1) Solvent: EC / EMC (volume ratio 1:3) LiPF6 concentration (concentration A): 1mol / L LiFSO3 concentration (concentration B): 0.1mol / L

[0049] Next, as shown in FIG. 7, both side surfaces of the battery that are perpendicular to the winding axis of the electrode body were sandwiched between stainless steel restraint plates, and the four corners of these restraint plates were fastened together with screws and nuts. The load was adjusted so that a restraint pressure of 0.5 MPa was applied to the electrode body area S (the width direction is the width where the positive electrode active material layer is formed) shown in FIG. 4, and the battery was restrained to produce a nonaqueous electrolyte secondary battery.

[0050] <Comparative Example 1> A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 1, except that in the fabrication of the positive electrode plate, the width over which the positive electrode active material layer was formed was set to 100 mm, in the fabrication of the negative electrode plate, the width over which the negative electrode active material layer was formed was set to 104 mm, and the electrolytic solution 1 was changed to the following electrolytic solution 2. (electrolyte 2) Solvent: EC / EMC (volume ratio 1:3) LiPF6 concentration (concentration A): 1mol / L LiFSO3: None

[0051] <Comparative Example 2> A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 1, except that in the fabrication of the positive electrode plate, the width over which the positive electrode active material layer was formed was set to 100 mm, in the fabrication of the negative electrode plate, the width over which the negative electrode active material layer was formed was set to 104 mm, and the electrolytic solution 1 was changed to the following electrolytic solution 3. (Electrolyte 3) Solvent: EC / EMC (volume ratio 1:3) LiPF6 concentration (concentration A): 1mol / L LiFSO3 concentration (concentration B): 0.08mol / L

[0052] <Comparative Example 3> A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 1, except that in the fabrication of the positive electrode plate, the width over which the positive electrode active material layer was formed was set to 100 mm, in the fabrication of the negative electrode plate, the width over which the negative electrode active material layer was formed was set to 104 mm, and the electrolytic solution 1 was changed to the following electrolytic solution 4. (electrolyte 4) Solvent: EC / EMC (volume ratio 1:3) LiPF6 concentration (concentration A): 1mol / L LiFSO3 concentration (concentration B): 0.1mol / L

[0053] <Comparative Example 4> A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 1, except that in the fabrication of the positive electrode plate, the width over which the positive electrode active material layer was formed was set to 100 mm, in the fabrication of the negative electrode plate, the width over which the negative electrode active material layer was formed was set to 104 mm, and the electrolytic solution 1 was changed to the following electrolytic solution 5. (electrolyte 5) Solvent: EC / EMC (volume ratio 1:3) LiPF6 concentration (concentration A): 1mol / L LiFSO3 concentration (concentration B): 0.2mol / L

[0054] <Comparative Example 5> A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 1, except that in the fabrication of the positive electrode plate, the width over which the positive electrode active material layer was formed was set to 100 mm, in the fabrication of the negative electrode plate, the width over which the negative electrode active material layer was formed was set to 104 mm, and the electrolytic solution 1 was changed to the following electrolytic solution 6. (electrolyte 6) Solvent: EC / EMC (volume ratio 1:3) LiPF6 concentration (concentration A): 1mol / L LiFSO3 concentration (concentration B): 0.25mol / L

[0055] <Comparative Example 6> A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 1, except that the electrolytic solution 1 in Example 1 was changed to the electrolytic solution 2.

[0056] <Comparative Example 7> A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 1, except that the electrolytic solution 1 in Example 1 was changed to the electrolytic solution 3.

[0057] <Example 2> A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 1, except that the electrolytic solution 1 in Example 1 was changed to the following electrolytic solution 7. (electrolyte 7) Solvent: EC / EMC (volume ratio 1:3) LiPF6 concentration (concentration A): 1mol / L LiFSO3 concentration (concentration B): 0.15mol / L

[0058] Example 3 A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 1, except that the electrolytic solution 1 in Example 1 was changed to the electrolytic solution 5.

[0059] <Comparative Example 8> A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 1, except that the electrolytic solution 1 in Example 1 was changed to the electrolytic solution 6.

[0060] Example 4 A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 1, except that the electrolytic solution 1 in Example 1 was changed to the following electrolytic solution 8. (electrolyte 8) Solvent: EC / EMC (volume ratio 1:3) LiPF6 concentration (concentration A): 1.5mol / L LiFSO3 concentration (concentration B): 0.25mol / L

[0061] <Example 5> A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 1, except that the electrolytic solution 1 in Example 1 was changed to the following electrolytic solution 9. (electrolyte 9) Solvent: EC / EMC (volume ratio 1:3) Concentration A=1.0mol / L LiPF6 concentration: 0.9mol / L LiBF4 concentration: 0.1mol / L LiFSO3 concentration (concentration B): 0.2mol / L

[0062] <Comparative Example 9> A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 1, except that the electrolytic solution 1 in Example 1 was changed to the electrolytic solution 7 and the battery was not constrained.

[0063] <Initial activation of non-aqueous electrolyte secondary batteries> After preparing a non-aqueous electrolyte secondary battery using the method described in each example, the battery was initially activated by charging it at a current of 4.2 Vccccv at C / 10 in a 25°C environment, storing it at 60°C for 24 hours, and discharging it to 3 V at a current of C / 10.

[0064] <Evaluation method for non-aqueous electrolyte secondary batteries> [Output resistance measurement] In an environment of 25°C, charge the battery to SOC 50% at a current value of C / 3, and measure the battery voltage after 30 minutes of rest (=V0). Then, discharge the battery for 10 seconds at a current value of 2C in an environment of 25°C. Measure the battery voltage at the 10th second (=V1) and calculate it using the following formula: Resistance = (V0-V1) / 2C current value The output resistance of the battery was calculated according to the following formula: The output resistance of Comparative Examples 1 to 5 is shown in Table 1 as a relative value with Comparative Example 1 set to 100%, and the output resistance of Examples 1 to 5 and Comparative Examples 6 to 9 is shown as a relative value with Comparative Example 6 set to 100%.

[0065] [Evaluation of cycle characteristics] After measuring the output resistance, a cycle test was conducted. The cycle test conditions were as follows: charging at a current of 2C to 4.2Vcccv in a 25°C environment, and discharging to 3V at a current of C / 2. This cycle was repeated. The cycle capacity retention rate was defined as the ratio of the discharge capacity at the 500th cycle to the discharge capacity at the first cycle. Capacity retention rate = (500th cycle discharge capacity / 1st cycle discharge capacity) x 100 (%) The results are shown in Table 1.

[0066] [Table 1]

[0067] In Comparative Examples 1 to 5, the width of the positive electrode active material layer was 100 mm, and the electrode width was relatively narrow. Therefore, increasing the LiFSO3 concentration reduced output resistance and improved cycle capacity retention, but no specific effect of the A / B ratio was observed. This is presumably because the electrode width was relatively narrow, which reduced the salt concentration across the width of the electrode, even during a relatively high-rate charge cycle of 2C. Consequently, the positive electrode potential was less likely to rise, reducing transition metal elution from the positive electrode active material. The addition of LiFSO3 reduced resistance and slightly improved cycle capacity retention. In Comparative Examples 1 to 5, at least no decrease in cycle retention was observed.

[0068] In Comparative Examples 6 to 8 and Examples 1 to 5, where the width of the positive electrode active material layer was 150 mm and the electrode body width was relatively wide, increasing the LiFSO3 concentration tended to reduce output resistance and improve cycle capacity retention. In Examples 1 to 3, where the A / B ratio was in the range of 5 to 10, a specific output resistance reduction effect was achieved, along with a cycle capacity retention of 90% or more. Within the A / B ratio range of Examples 1 to 3, a reduction in LiFSO3 output resistance and an improvement in cycle capacity retention were achieved. On the other hand, in Comparative Example 8, where the LiFSO3 concentration was relatively high and the A / B ratio was 4.0, the cycle capacity retention rate significantly decreased. This is presumably because the width of the positive electrode active material layer was as wide as 150 mm, which resulted in significant salt concentration unevenness across the cell width due to the relatively high 2C charge cycle, resulting in an increase in the positive electrode potential during charge. In contrast to this, in Examples 1 to 3, the LiPF6 concentration was sufficient relative to the LiFSO3 concentration, so a sufficient LiF coating was formed on the surface of the positive electrode active material, which is presumed to have resulted in suppressing the elution of transition metals from the positive electrode active material and maintaining a high cycle capacity retention rate. On the other hand, in Comparative Example 8, the LiPF6 concentration was low relative to the LiFSO3 concentration, so it is predicted that the LiF coating on the surface of the positive electrode active material was insufficient, resulting in a high degree of interaction between the positive electrode active material and the highly acidic SO3F - It is presumed that the reaction potential reached 1000 kJ / s, and where the LiF coating was insufficient, the transition metal in the positive electrode active material eluted and accumulated on the negative electrode, resulting in a decrease in capacity retention. In Examples 1 to 3, where the A / B ratio was in the range of 5 to 10, a cycle capacity retention of 90% or more was obtained along with a decrease in output resistance. Furthermore, good results were also obtained in Examples 4 and 5.

[0069] In Comparative Example 9, where the battery was not constrained, the A / B ratio was 6.7, but the output resistance was high and the cycle capacity retention rate was also low. This is presumably because the unconstrained battery allowed the electrolyte to flow smoothly, making it less likely for salt concentration to vary during the cycle test. However, because the battery was not constrained, the gap between the electrodes was more likely to widen, resulting in higher resistance and, further, greater capacity degradation during the cycle test. [Explanation of symbols]

[0070] 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, 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, 111 negative electrode external terminal, 112 positive electrode external terminal, 113 restraining plate, 114 screw, 200 battery pack, 201 inter-cell separator, 300 battery module, 301 restraining member, 302 end plate, W width direction, R winding axis, S electrode body area.

Claims

1. An electrode assembly and an electrolyte solution are included. the electrode body is a wound electrode body in which a positive electrode plate and a negative electrode plate are wound with a separator interposed therebetween, The positive electrode plate includes a positive electrode active material layer, the negative electrode plate includes a negative electrode active material layer, At least one of the positive electrode active material layer and the negative electrode active material layer has a dimension of 150 mm or more in the winding axis direction of the electrode body, The electrolyte solution contains an electrolyte salt and LiFSO ３ and The electrolyte salt is LiPF ６ and LiBF ４ and LiPF in the electrolyte ６ and LiBF ４ The total concentration of LiFSO is A (mol / L). ３ When the concentration of the solution is B (mol / L), the A / B ratio, which is the ratio of A to B, is 5 or more and 12 or less, the total concentration A of LiPF 6 and LiBF 4 in the electrolyte solution is 1 to 1.5 mol / L; The concentration B of LiFSO 3 in the electrolyte solution is 0.1 to 0.25 mol / L, A non-aqueous electrolyte secondary battery, wherein a pressure of 0.5 MPa or more is applied to the electrode assembly in the electrode plate stacking direction.

2. 2. The nonaqueous electrolyte secondary battery according to claim 1, wherein the A / B ratio is 6.7 or more and 10 or less.

3. 2. The nonaqueous electrolyte secondary battery according to claim 1, wherein the electrode body has a length parallel to the winding axis of 180 mm or more.

4. A non-aqueous electrolyte secondary battery as described in claim 1, wherein the positive electrode active material layer contains a lithium transition metal composite oxide.

5. A battery pack comprising the nonaqueous electrolyte secondary battery according to claim 1.

6. A battery module comprising the nonaqueous electrolyte secondary battery according to claim 1 .

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