Nonaqueous electrolyte secondary battery and battery pack

Abstract

To provide a non-aqueous electrolyte liquid secondary battery in which a high-rate deterioration is suppressed.SOLUTION: A non-aqueous electrolyte liquid secondary battery comprises: a non-aqueous electrolyte liquid; a wound electrode body 20 to which a positive electrode, a negative electrode, and a separator are overlapped and wound; and a rectangular type battery case housing them. The wound electrode body includes: a pair of flat surface parts 20f formed so as to oppose each other while nipping a winding shaft; and a pair of R parts 20r where a front surface formed between the pair of flat surface parts is a curve surface. Here, in a state where the wound electrode body is restricted with a restraint pressure of 4.5kN from a thickness direction, both of the following formulas are satisfied: 0.282<a / b and c / d<1.91, where a total of the outermost peripheral length of the pair of R parts of the wound electrode body in a cross section orthogonal to the winding shaft of the wound electrode body is a (mm); the outermost peripheral length of the wound electrode body in the cross section is b (mm); a width of the positive electrode active material layer is c (mm); and a height of the wound electrode body is d (mm).SELECTED DRAWING: Figure 3

Description

[Technical field]

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

[0002] Secondary batteries such as lithium-ion secondary batteries are lightweight and have high energy density, and therefore are favored as high-output power sources for driving vehicles such as electric vehicles (BEVs) and hybrid electric vehicles (HEVs), and demand for them is expected to continue to increase in the future.

[0003] As secondary batteries become more powerful, there is a demand for the development of technology that suppresses the deterioration of battery characteristics (high-rate deterioration) caused by high-rate charging and discharging. For example, Patent Document 1 discloses a secondary battery equipped with an electrolyte swelling layer as such technology. Patent Document 2 discloses a configuration of a wound electrode body in which the inter-plate distance falls within a predetermined range. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2019-185991 A [Patent Document 2] JP 2020-177858 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, the technology of Patent Document 1 requires the addition of an electrolyte swelling layer and a large amount of excess liquid to impregnate the electrolyte swelling layer with the electrolyte, so there is room for improvement in terms of cost and energy density. In addition, the technology of Patent Document 2 may not be sufficiently effective in a usage environment where a restraining load is continuously applied to the electrode body. Therefore, the development of further technology to suppress high-rate degradation is desired.

[0006] In view of the above circumstances, the present invention has been made, and a main object of the present invention is to provide a nonaqueous electrolyte secondary battery in which high-rate degradation is suppressed, and another object of the present invention is to provide a battery pack including such a nonaqueous electrolyte secondary battery. [Means for solving the problem]

[0007] The nonaqueous electrolyte secondary battery disclosed herein includes a nonaqueous electrolyte, a sheet-shaped positive electrode having a positive electrode active material layer formed in a strip shape along the longitudinal direction on a long positive electrode current collector, a sheet-shaped negative electrode having a negative electrode active material layer formed in a strip shape along the longitudinal direction on a long negative electrode current collector, a flat-shaped wound electrode body formed by overlapping and winding in the longitudinal direction a separator interposed between the positive electrode and the negative electrode, and a rectangular battery case that contains the nonaqueous electrolyte and the wound electrode body. The wound electrode body has a pair of flat parts formed to face each other across a winding axis, and a pair of R parts formed between the pair of flat parts and having curved surfaces. Here, in a state in which the entire flat portion of the wound electrode body is restrained by applying a restraining pressure of 4.5 kN from the opposing direction of the flat portion, the sum of the outermost perimeter lengths of the pair of R portions of the wound electrode body in a cross section perpendicular to the winding axis of the wound electrode body is a (mm), the outermost perimeter length of the wound electrode body in the cross section is b (mm), the length in the width direction perpendicular to the longitudinal direction of the positive electrode active material layer is c (mm), and the height of the wound electrode body, which is the distance between the vertices of the pair of R portions in the cross section, is d (mm), the following condition is satisfied: 0.282 c / d<1.91; The present invention is characterized in that it has all of the above.

[0008] The wound electrode body of the nonaqueous electrolyte secondary battery having such a configuration has a high ratio of R parts, which are parts that contribute to the electrolyte retention function, and therefore can improve the nonuniformity of the salt concentration of the electrolyte in the wound electrode body. In addition, by setting the height of the wound electrode body to the positive electrode coating width at a predetermined ratio or more, nonuniformity of the salt concentration of the electrolyte in the width direction is less likely to occur. This makes it possible to suppress high-rate deterioration of the nonaqueous electrolyte secondary battery.

[0009] ​ In a preferred embodiment of the nonaqueous electrolyte secondary battery disclosed herein, the condition: 1.66≦c / d≦1.72 is further satisfied, which makes it possible to more suitably suppress high-rate degradation.

[0010] In one embodiment of the nonaqueous electrolyte secondary battery disclosed herein, the height d of the wound electrode body may be 50 mm or more and 55 mm or less. A wound electrode body of such a size can more suitably suppress high-rate degradation.

[0011] The present disclosure also provides a battery pack including the nonaqueous electrolyte secondary battery disclosed herein. The battery pack disclosed herein is a battery pack in which a plurality of unit cells are electrically connected to one another and arranged, and at least one of the unit cells is the nonaqueous electrolyte secondary battery disclosed herein. This makes it possible to realize a battery pack in which high-rate degradation is suppressed. [Brief description of the drawings]

[0012] [Figure 1] 1 is a cross-sectional view illustrating a schematic configuration of a nonaqueous electrolyte secondary battery according to one embodiment. [Diagram 2] FIG. 2 is an exploded view showing a schematic configuration of a wound electrode body of a nonaqueous electrolyte secondary battery according to one embodiment. [Diagram 3] 1 is a cross-sectional view that illustrates a cross section perpendicular to the winding axis of a wound electrode body when a pressure of 4.5 kN is applied from the thickness direction of the wound electrode body. FIG. [Figure 4] 1 is a perspective view showing a schematic configuration of a battery pack according to an embodiment; [Diagram 5] 1 is a graph showing the relationship between the value of the outermost periphery length of the R portion when restrained / the outermost periphery length of the wound electrode body when restrained and the high-rate resistance increase rate. [Figure 6] 1 is a graph showing the relationship between the positive electrode coating width / height of the wound electrode body when restrained (c / d) and the high-rate resistance increase rate. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] The technology disclosed herein will be described in detail below. Matters necessary for implementation other than those specifically mentioned in this specification can be understood as design matters for a person skilled in the art based on the prior art in the field. The content of the technology disclosed herein can be implemented based on the content disclosed in this specification and common technical knowledge in the field.

[0014] In addition, each drawing is a schematic drawing, and the dimensional relationship (length, width, thickness, etc.) does not reflect the actual dimensional relationship. In addition, in the drawings described below, the same reference numerals are used for members and parts having the same function, and duplicated explanations may be omitted or simplified. Furthermore, in this specification, when a numerical range is described as A to B (where A and B are arbitrary numerical values), this is interpreted as being the same as in the general sense, meaning A or more and B or less, and including a range above A and below B.

[0015] In this specification, the term "secondary battery" refers to a general electricity storage device in which charge and discharge reactions occur by the movement of charge carriers between a pair of electrodes (positive and negative electrodes) via an electrolyte. .Ma In addition, in this specification, the term "lithium ion secondary battery" refers to a secondary battery that uses lithium ions as a charge carrier and realizes charging and discharging by the transfer of charge associated with the lithium ions between positive and negative electrodes.

[0016] Hereinafter, an embodiment of the nonaqueous electrolyte secondary battery disclosed herein will be described. FIG. 1 is a cross-sectional view that shows a schematic configuration of a nonaqueous electrolyte secondary battery 100 according to an embodiment. The nonaqueous electrolyte secondary battery 100 is a lithium ion secondary battery. The nonaqueous electrolyte secondary battery 100 is a rectangular sealed battery constructed by accommodating a flat wound electrode body 20 and a nonaqueous electrolyte (not shown) inside a battery case 30. The battery case 30 is provided with a positive electrode terminal 42 and a negative electrode terminal 44 for external connection. In addition, a thin-walled safety valve 36 is provided that is set to release the internal pressure when the internal pressure of the battery case 30 rises to a predetermined level or higher. Furthermore, the battery case 30 is provided with an injection port (not shown) for injecting the nonaqueous electrolyte. The material of the battery case 30 is preferably a metal material that is high in strength, lightweight, and has good thermal conductivity. Examples of such metal materials include aluminum and steel.

[0017] FIG. 2 is an exploded view showing a schematic configuration of a wound electrode body 20 of a nonaqueous electrolyte secondary battery 100 according to an embodiment. As shown in FIG. 2, the wound electrode body 20 is formed by stacking (stacking) a long sheet-like positive electrode 50 and a long sheet-like negative electrode 60 with two long sheet-like separators 70 interposed therebetween, and wound in the longitudinal direction around a winding axis WL. The positive electrode 50 includes a long sheet-like positive electrode collector 52 and a positive electrode active material layer 54 formed along the longitudinal direction on one or both sides (both sides here) of the positive electrode collector 52. At one edge of the positive electrode collector 52 in the winding axis WL direction (i.e., the sheet width direction perpendicular to the longitudinal direction), a portion where the positive electrode collector 52 is exposed without the positive electrode active material layer 54 being formed in a strip shape along the edge (i.e., the positive electrode collector exposed portion 52a) is provided. The negative electrode 60 also includes a long sheet-like negative electrode collector 62 and a negative electrode active material layer 64 formed along the longitudinal direction of one or both sides (both sides in this case) of the negative electrode collector 62. The other edge of the negative electrode collector 62 in the winding axis WL direction is provided with a portion (i.e., a negative electrode collector exposed portion 62a) where the negative electrode active material layer 64 is not formed in a strip shape along the edge and the negative electrode collector 62 is exposed. A positive electrode collector plate 42a is joined to the positive electrode collector exposed portion 52a, and a negative electrode collector plate 44a is joined to the negative electrode collector exposed portion 62a (see FIG. 1). The positive electrode collector plate 42a is electrically connected to a positive electrode terminal 42 for external connection, realizing electrical continuity between the inside and the outside of the battery case 30. Similarly, the negative electrode current collector 44a is electrically connected to a negative electrode terminal 44 for external connection, realizing electrical continuity between the inside and outside of the battery case 30 (see FIG. 1).

[0018] The positive electrode current collector 52 constituting the positive electrode 50 may be, for example, an aluminum foil. The positive electrode active material included in the positive electrode active material layer 54 may be, for example, a lithium composite metal oxide having a layered structure or a spinel structure, for example, a lithium composite metal oxide having a composition formula: Li α (Ni x Co y Mn z)O2 (wherein 1≦α≦1.2, 0≦x≦1, 0≦y≦1, 0≦z≦1, and x+y+z=1 are satisfied). As such a lithium composite metal oxide, for example, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNiO2, LiCoO2, etc.

[0019] The content of the positive electrode active material in the positive electrode active material layer 54 (i.e., the content of the positive electrode active material relative to the total mass of the positive electrode active material layer 54) is not particularly limited, but is preferably 80 mass % or more, and more preferably 90 mass % or more. When the content of the positive electrode active material in the positive electrode active material layer 54 is within the above range, a battery with high energy density can be provided.

[0020] The positive electrode active material layer 54 may also contain a conductive material, a binder, etc. As the conductive material, for example, carbon black such as acetylene black (AB), carbon nanotubes such as single-walled carbon nanotubes and multi-walled carbon nanotubes, and other carbon materials (such as graphite) can be suitably used. As the binder, for example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), etc. can be used.

[0021] The basis weight of the positive electrode active material layer 54 is not particularly limited, but is, for example, 10 mg / cm 2 More than 15mg / cm 2 Less than or equal to 11 mg / cm 2 More than 13.3mg / cm 2 The electrode thickness of the positive electrode 50 is not particularly limited, but may be, for example, 50 μm or more and 65 μm or less, and may be 52 μm or more and 61 μm or less.

[0022] The positive electrode active material layer 54 can be formed by dispersing the positive electrode active material and materials (conductive material, binder, etc.) used as necessary in an appropriate solvent (e.g., N-methyl-2-pyrrolidone: NMP) to prepare a paste-like (or slurry-like) composition (positive electrode active material layer forming paste), applying an appropriate amount of the composition to the surface of the positive electrode current collector 52, and drying it. During such application, the basis weight, thickness (or thickness of the positive electrode 50) and application width of the positive electrode active material layer 54 can be adjusted.

[0023] The negative electrode current collector 62 constituting the negative electrode 60 may be, for example, copper foil. The negative electrode active material layer 64 includes the negative electrode active material disclosed herein. As the negative electrode active material, one or more of various materials known to be usable for the negative electrode of a non-aqueous electrolyte secondary battery may be used without any particular limitation. Suitable examples include carbon materials such as graphite, hard carbon, and soft carbon. The negative electrode active material may be amorphous-coated graphite in which the surface of granular natural graphite is coated with amorphous carbon, for example, carbon black.

[0024] The content of the negative electrode active material in the negative electrode active material layer 64 (i.e., the content of the negative electrode active material relative to the total mass of the negative electrode active material layer 64) is not particularly limited, but is preferably 90 mass% or more, more preferably 95 mass% or more, and even more preferably 98 mass% or more.

[0025] The negative electrode active material layer 64 may further contain a binder, a thickener, etc. As the binder, for example, styrene butadiene rubber (SBR) etc. may be used. As the thickener, for example, carboxymethyl cellulose (CMC) etc. may be used.

[0026] The weight of the negative electrode active material layer 64 is not particularly limited, but is, for example, 5 mg / cm 2 More than 10mg / cm 2 Less than 7 mg / cm 2 More than 8.5mg / cm 2The electrode thickness of the negative electrode 60 is not particularly limited, but may be, for example, 60 μm or more and 90 μm or less, and may be 65 μm or more and 85 μm or less.

[0027] The negative electrode active material layer 64 can be formed, for example, by dispersing the negative electrode active material and materials (such as a binder) used as necessary in an appropriate solvent (such as ion-exchanged water) to prepare a paste-like (or slurry-like) composition (negative electrode active material layer forming paste), applying an appropriate amount of the composition to the surface of the negative electrode current collector 62, and drying it. During such application, the basis weight, thickness (or thickness of the negative electrode 60), application width, etc. of the negative electrode active material layer 64 can be adjusted.

[0028] As the separator 70, various microporous sheets similar to those conventionally used in nonaqueous electrolyte secondary batteries can be used, such as microporous resin sheets made of resins such as polyethylene (PE) and polypropylene (PP). Such microporous resin sheets may have a single-layer structure or a multi-layer structure of two or more layers (for example, a three-layer structure in which PP layers are laminated on both sides of a PE layer). In addition, a heat-resistant layer (HRL) may be formed on the surface of the separator 70.

[0029] The thickness of the separator 70 is not particularly limited, but may be, for example, 5 μm to 30 μm, preferably 10 μm to 25 μm, and more preferably 15 μm to 20 μm. Within such a range, the strength of the separator 70 can be increased and the weight of the wound electrode body 20 can be reduced.

[0030] The length (width) of the separator 70 in the width direction (i.e., the direction perpendicular to the longitudinal direction) is not particularly limited, but is typically set to be longer than the coating width of at least the positive electrode active material layer 54 and the negative electrode active material layer 64 in order to ensure insulation between the positive electrode 50 and the negative electrode 60. The width of the separator 70 can be, for example, 10 mm or more and 300 mm or less, 50 mm or more and 150 mm or less, or 90 mm or more and 120 mm or less.

[0031] The non-aqueous electrolyte can be the same as that used in conventional lithium ion secondary batteries. For example, a non-aqueous electrolyte containing a supporting salt in an organic solvent (nonaqueous solvent) can be used. As the non-aqueous solvent, aprotic solvents such as carbonates, esters, ethers, etc. can be used. Among them, carbonates, for example, ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), etc., can be preferably used. Alternatively, fluorine-based solvents such as fluorinated carbonates, such as monofluoroethylene carbonate (MFEC), difluoroethylene carbonate (DFEC), monofluoromethyl difluoromethyl carbonate (F-DMC), trifluorodimethyl carbonate (TFDMC), etc. can be preferably used. Such non-aqueous solvents can be used alone or in appropriate combination of two or more. As the supporting salt, for example, lithium salts such as LiPF6, LiBF4, LiClO4, etc. can be preferably used. The concentration of the supporting salt is not particularly limited, but is preferably about 0.7 mol / L or more and 1.3 mol / L or less.

[0032] The nonaqueous electrolyte may contain components other than the nonaqueous solvent and supporting salt described above, so long as the effects of the present technology are not significantly impaired, and may contain various additives such as a gas generating agent, a film forming agent, a dispersing agent, a thickener, etc. Specific examples of such additives include fluorophosphates (preferably difluorophosphates, e.g., lithium difluorophosphate represented by LiPO2F2) and oxalato complex compounds such as lithium bis(oxalato)borate (LiBOB).

[0033] FIG. 3 is a cross-sectional view showing a cross section perpendicular to the winding axis WL of the wound electrode body 20 when a pressure of 4.5 kN is applied from the thickness direction T of the wound electrode body 20. The wound electrode body 20 has a pair of flat portions 20f formed to face each other across the winding axis. The pair of flat portions 20f may face each other in the thickness direction T of the wound electrode body 20. The wound electrode body 20 also has a pair of R portions 20r formed between the pair of flat portions 20f. The R portions 20r are formed so that their surfaces are curved. The R portions 20r are portions that are easy to retain non-aqueous electrolyte. Therefore, if the proportion of the R portions 20r in the entire wound electrode body 20 is increased, more non-aqueous electrolyte is retained inside the wound electrode body 20. As a result, even during high-rate charging and discharging, non-uniformity in the distribution of salt concentration is less likely to occur inside the wound electrode body 20, making it possible to suppress high-rate deterioration.

[0034] However, in general, when the height of the wound electrode body is reduced in order to increase the proportion of the R portion in the wound electrode body, the battery capacity is reduced by the amount of the reduced height. On the other hand, when the length of the wound electrode body in the width direction (i.e., the winding axis direction) is increased to widen the coating width of the positive electrode active material layer in order to compensate for the reduced battery capacity, the salt concentration tends to become non-uniform inside the wound electrode body during high-rate charging and discharging, which creates a trade-off in that high-rate deterioration is likely to be promoted.

[0035] Therefore, the present disclosure provides a wound electrode body 20 that can appropriately suppress high-rate deterioration. In a state in which a pressure (confining pressure) of 4.5 kN is applied to the entire flat portions 20f of the wound electrode body 20 from the opposing directions of the pair of flat portions 20f of the wound electrode body 20 as shown in FIG. 3, the wound electrode body 20 can be characterized by the sum a (mm) of the outermost perimeter of the pair of R portions 20r of the wound electrode body 20 in a cross section perpendicular to the winding axis WL of the wound electrode body 20, the outermost perimeter b (mm) of the wound electrode body 20, the height d (mm) of the wound electrode body 20, which is the distance between the vertices P1, P2 of the pair of R portions 20r, and the length c (mm) of the positive electrode active material layer 54 in the width direction (i.e., the direction of the winding axis WL) perpendicular to the longitudinal direction of the positive electrode current collector 52. In this specification, unless otherwise specified, the term "constrained state" refers to a state in which the wound electrode body 20 is constrained by applying a pressure (constraining pressure) of 4.5 kN to the entire flat portions 20f from the opposing directions of the pair of flat portions 20f of the wound electrode body 20. The constraining pressure can allow for unavoidable errors due to the performance of the constraining jig that applies the constraining pressure, and may be in the range of 4.5±0.1 kN.

[0036] The value (a / b) obtained by dividing the total outer periphery length a (mm) of the pair of R portions 20r of the wound electrode body 20 by the outer periphery length b (mm) of the wound electrode body 20 is an index showing the proportion of the R portions 20r in the entire wound electrode body 20.

[0037] The total outer periphery length a (mm) of the pair of R portions 20r of the wound electrode body 20 is not particularly limited, but is, for example, 30 mm to 40 mm, and preferably 33 mm to 37 mm. In this specification, the total outer periphery length a (mm) of the pair of R portions 20r refers to the length of a circumference whose diameter is the thickness of the wound electrode body 20 in a restrained state.

[0038] ​The outermost peripheral length b (mm) of the wound electrode body 20 is not particularly limited. For example, it is 110 mm or more and 130 mm or less, preferably 115 mm or more and 120 mm or less. The outermost peripheral length b (mm) of the wound electrode body 20 can be calculated by various methods. For example, it can be calculated as the sum of the measured value of the length of the flat portion 20f and the sum a of the above pair of outermost peripheral lengths. Also, for example, it can be calculated by obtaining the length of the circumference using the diameter when wound around the core used as the winding axis WL (the sum of the diameter of the core (core diameter) and the thickness of the electrode bodies facing each other across the core).

[0039] The value (c / d) obtained by dividing the length c (mm) in the width direction orthogonal to the longitudinal direction of the positive electrode current collector 52 of the positive electrode active material layer 54 by the height d (mm) of the wound electrode body 20, which is the distance between the vertices P1 and P2 of the pair of R portions 20r, can be an index indicating the ratio of the width to the height of the wound electrode body 20. From the viewpoint of suppressing the non-uniformity of the salt concentration in the width direction of the wound electrode body 20 during high-rate charge and discharge, it is preferably c / d < 1.91, more preferably c / d ≤ 1.77, and even more preferably c / d ≤ 1.72. Also, although not particularly limited, from the viewpoint of suppressing the non-uniformity of the salt concentration in the height direction of the wound electrode body 20 during high-rate charge and discharge, for example, 1.59 < c / d, and preferably 1.63 ≤ c / d, and more preferably 1.66 ≤ c / d.

[0040] The length c (mm) in the width direction orthogonal to the longitudinal direction of the positive electrode current collector 52 of the positive electrode active material layer 54 is not particularly limited. For example, it is 60 mm or more and 120 mm or less, may be 80 mm or more and 100 mm or less, and can be 85 mm or more and 90 mm or less.

[0041] The length of the negative electrode active material layer 64 in the width direction perpendicular to the longitudinal direction of the negative electrode current collector 62 is not particularly limited, but is typically set to be greater than the length of the positive electrode active material layer 54 in the width direction. This allows the negative electrode active material layer 64 to sufficiently accept the lithium ions released from the positive electrode active material layer 54, thereby suppressing the deposition of metallic lithium. The length of the negative electrode active material layer 64 in the width direction perpendicular to the longitudinal direction of the negative electrode current collector 62 is, for example, 70 mm or more and 120 mm or less, may be 80 mm or more and 110 mm or less, or may be 90 mm or more and 100 mm or less.

[0042] The length c (mm) of the positive electrode active material layer 54 in the width direction perpendicular to the longitudinal direction of the positive electrode current collector 52 can be measured using a commercially available width measuring device. The length of the negative electrode active material layer 64 in the width direction perpendicular to the longitudinal direction of the negative electrode current collector 62 can be measured in the same manner.

[0043] The height d (mm) of the wound electrode body 20, which is the distance between the vertices P1 and P2 of the pair of R parts 20r, is not particularly limited, but is preferably 50 mm or more and 55 mm or less, and may be 52 mm or more and 54 mm or less. With such a height, the ratio of the R parts 20r of the wound electrode body 20 is suitably adjusted, so that high-rate deterioration can be more suitably suppressed. The height d (mm) of the wound electrode body 20 can be measured, for example, by removing the wound electrode body 20 from the battery case and restraining it from the thickness direction T (the opposing direction of the pair of flat parts 20f) with a pressure of 4.5 kN, and measuring the height of the center part in the width direction of the wound electrode body 20 using a commercially available laser displacement meter.

[0044] The thickness of the wound electrode body 20 in the restrained state is not particularly limited, but may be, for example, 10 mm to 12 mm, and may be 10.6 mm to 11.7 mm. The thickness of the wound electrode body 20 can be measured, for example, using a commercially available laser displacement meter.

[0045] The number of stacked positive electrodes 50 in the wound electrode body 20 is not particularly limited, but may be 30-40, or 31-35, for example.

[0046] In a preferred embodiment of the nonaqueous electrolyte secondary battery 100 disclosed herein, the above a, b, c, and d satisfy the condition:

[0047] The nonaqueous electrolyte secondary battery 100 disclosed herein can be preferably used as a single cell included in the battery pack 10. FIG. 4 is a perspective view showing a schematic configuration of the battery pack 10 according to one embodiment. As shown in FIG. 4, the nonaqueous electrolyte secondary batteries 100 are used as a plurality of single cells constituting the battery pack 10, and the plurality of nonaqueous electrolyte secondary batteries are electrically connected to each other and arranged. The nonaqueous electrolyte secondary batteries 100 are arranged in a mutually arranged manner while being inverted one by one, so that the positive electrode terminals 42 and the negative electrode terminals 44 are arranged alternately in the arrangement direction. A spacer 12 is sandwiched between the arranged nonaqueous electrolyte secondary batteries 100. The spacer 12 can function as a heat dissipation means for efficiently dissipating heat, a length adjustment means, or the like. A pair of end plates (restraint plates) 17 are arranged at both ends of the arranged nonaqueous electrolyte secondary batteries 100. In addition, a tightening beam material 18 is attached so as to bridge between the two end plates 17. The ends of the beam material 18 are fastened and fixed to the end plates 17 with screws 19. This restrains the multiple nonaqueous electrolyte secondary batteries 100 so that a predetermined restraining load is applied in the arrangement direction of the nonaqueous electrolyte secondary batteries 100 (the thickness direction of the wound electrode body 20).

[0048] ​The battery pack 10 includes a bus bar 14 that connects the positive electrode terminal 42 of one cell (non-aqueous electrolyte secondary battery 100) to the negative electrode terminal 44 of the other cell (non-aqueous electrolyte secondary battery 100) between two adjacently arranged non-aqueous electrolyte secondary batteries 100. This electrically connects the multiple non-aqueous electrolyte secondary batteries 100 to each other. Here, the multiple non-aqueous electrolyte secondary batteries 100 are connected in series, but they may also be connected in parallel. In addition, the single cells that make up the battery pack 10 need only include at least one non-aqueous electrolyte secondary battery 100 disclosed herein, and all the single cells may be composed of the non-aqueous electrolyte secondary batteries 100 disclosed herein.

[0049] The nonaqueous electrolyte secondary battery 100 and the battery pack 10 according to one embodiment have been described above. The nonaqueous electrolyte secondary battery 100 and the battery pack 10 can be used for various applications. Specific applications include power sources for driving vehicles such as electric vehicles (BEVs), hybrid vehicles (HEVs), and plug-in hybrid vehicles (PHEVs); storage batteries for small power storage devices, and the like; among these, power sources for driving vehicles are preferred.

[0050] In another embodiment, the nonaqueous electrolyte secondary battery 100 may have an exterior film for ensuring insulation between the wound electrode body 20 and the battery case 30. The exterior film is made of a material that can function as an insulating member, and examples of the exterior film include various thermoplastic resins, typically polyolefin resin materials such as polypropylene (PP) and polyethylene (PE). The shape of the exterior film is not particularly limited, but may be, for example, a bag-like shape with an open upper end and a bottom. In the case of such a bag-like exterior film, the wound electrode body 20 can be housed in the exterior film from the opening of the exterior film.

[0051] Hereinafter, examples of the technology disclosed herein will be described, but it is not intended that the technology disclosed herein be limited to those shown in these examples.

[0052] Electrode assemblies of Examples 1 to 17 were prepared, and the structure of each electrode assembly and the high-rate resistance increase rate were compared.

[0053] <Preparation of positive electrode> Lithium nickel cobalt manganese composite oxide (LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2), multi-walled carbon nanotubes as a conductive material, and polyvinylidene fluoride (PVdF) as a binder were mixed in a weight ratio of positive electrode active material:conductive material:binder=91:6:3, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) was added as a solvent to prepare a slurry for forming a positive electrode active material layer. This slurry for forming a positive electrode active material layer was applied to a positive electrode current collector made of aluminum foil in a predetermined width so as to have a predetermined basis weight. Thereafter, drying and roll pressing were performed to prepare a positive electrode. The positive electrode active material layer was formed on both sides of the positive electrode current collector. The basis weight, electrode thickness, application width, and electrode length of the positive electrodes in Examples 1 to 17 are shown in Table 1.

[0054] <Preparation of negative electrode> Amorphous coated natural graphite as the negative electrode active material, styrene butadiene rubber (SBR) as the binder, and carboxymethyl cellulose (CMC) as the thickener were mixed to a weight ratio of negative electrode active material:binder:thickener=98:1:1, and an appropriate amount of ion-exchanged water was added as a solvent to prepare a slurry for forming a negative electrode active material layer. This slurry for forming a negative electrode active material layer was applied to a copper foil negative electrode current collector to a predetermined width so as to have a predetermined basis weight. Thereafter, drying and roll pressing were performed to prepare a negative electrode. The negative electrode active material layer was formed on both sides of the negative electrode current collector. The basis weight, electrode thickness, coating width, and electrode length of the negative electrodes in Examples 1 to 17 are shown in Table 1. In each of Examples 1 to 17, the positive and negative electrodes were prepared so that the cell capacity was 4.1 Ah.

[0055] As the separator, a microporous polyolefin sheet having a three-layer structure of PP / PE / PP was prepared. The thickness, width, and length of the separator in Examples 1 to 17 are shown in Table 1.

[0056] <Preparation of wound electrode body> In each example, a separator, a negative electrode, a separator, and a positive electrode were stacked in this order from the bottom to prepare a laminate. This laminate was wound in the longitudinal direction around a winding core (see Table 1) having a predetermined diameter. This wound laminate was compressed from the stacking direction at 6.9 kN for 3 seconds, then compressed at 2 kN for 1 second, and then further compressed at a speed of 1 mm / min. Then, it was compressed until the restraining load reached 4 kN, and a flat-shaped wound electrode body was produced. The thickness of the wound electrode body at this time (i.e., the distance between the flat parts) was measured with a laser displacement meter (manufactured by Keyence Corporation, product name: LK-G157).

[0057] Next, the current collector plate connected to the lid was welded to the wound electrode body, and the wound electrode body was then housed in an exterior film made of PP and housed in the case body. Then, the boundary between the lid and the case body was welded to assemble the test cell, and non-aqueous electrolyte was poured into the test cell through the injection port. The non-aqueous electrolyte was a mixed solvent containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of EC:EMC:DMC=30:35:35, with LiPF6 dissolved as a supporting salt at a concentration of 1.1 mol / L. Then, the injection port was sealed to obtain a square test cell.

[0058] <Measurement of wound electrode thickness when restrained> The test cell was clamped by a pair of restraining jigs made of SUS303. At this time, the restraining jigs were set to clamp the electrode body from the thickness direction. Next, the test cell clamped by the restraining jigs was set in an autograph (manufactured by Shimadzu Corporation, product name: AG-IS (50 kN)). The autograph applied a pressure of 4.5 kN in the thickness direction of the electrode body, and the thickness of the cell after 60 seconds under the pressure (the sum of the thickness of the electrode body under pressure, the thickness of the side wall of the battery case, and the thickness of the exterior film) was measured with a laser displacement meter (manufactured by Keyence Corporation, product name: LK-G157). Then, the thickness of the electrode body under a pressure of 4.5 kN (the thickness of the wound electrode body when restrained) was calculated by subtracting the thickness of the wall of the battery case and the thickness of the exterior film from the thickness of the cell. It was assumed that there was no change in the thickness of the side wall of the battery case and the thickness of the insulating film under a pressure of 4.5 kN.

[0059] <Measurement of high-rate resistance increase rate> The test cell was adjusted to a state of charge (SOC) of 60% in a 25°C environment, and the initial resistance value was calculated from the voltage drop ΔV and current value I when the test cell was discharged at a current of 30C for 10 seconds. After that, the test cell was adjusted again to an SOC of 60% in a 25°C environment. Then, 2000 cycles of pulse charging and discharging were performed, with pulse charging at 30C for 10 seconds, resting for 10 seconds, pulse discharging at 30C for 30 seconds, and resting for 10 seconds as one cycle. Then, the resistance value after 2000 cycles was calculated from the voltage drop and current value during pulse discharging at the 2000th cycle. The resistance increase rate after high-rate charging and discharging (high-rate resistance increase rate) was calculated from the ratio of the initial resistance value to the resistance value after 2000 cycles. The results are shown in Table 1. Note that "1C" refers to the magnitude of the current that changes the SOC from 0% to 100% in one hour.

[0060] <Measurement of the height (d) of the wound electrode body when restrained> After measuring the high-rate resistance increase rate, the wound electrode body was removed from the test cell, and a pressure of 4.5 kN was applied from the thickness direction of the wound electrode body for 60 seconds using the above-mentioned autograph. Then, the height of the wound electrode body under pressure after 60 seconds was measured using a width measurement sensor (manufactured by Keyence Corporation, product name: LK-G157). The height of the wound electrode body was taken as the distance between the vertices of the R part at the center of the width direction of the wound electrode body. The results are shown in Table 1.

[0061] <Calculation of the outermost circumference (a) of the wound electrode body when restrained> In a cross section perpendicular to the winding axis of the wound electrode body, the outermost perimeter of a pair of R parts when a pressure of 4.5 kN is applied in the thickness direction of the wound electrode body is assumed to be the same as the circumference of a circle whose diameter is the thickness of the wound electrode body when restrained, and the outermost perimeter of the R part of the wound electrode body when restrained is Formula: Thickness of the wound electrode body when restrained as above × π The results are shown in Table 1.

[0062] <Calculation of the outermost circumference (b) of the wound electrode body when restrained> The outermost circumference (b) of the wound electrode body when restrained in a cross section perpendicular to the winding axis of the wound electrode body is Formula: (Coil diameter + thickness of the wound electrode body when the wound electrode body is manufactured) × π The results are shown in Table 1.

[0063] The values ​​of the outermost perimeter of the R portion when restrained / the outermost perimeter of the wound electrode body when restrained (a / b) and the positive electrode coating width / the height of the wound electrode body when restrained (c / d) were calculated. The results are shown in Table 1. Figure 5 shows a graph of the relationship between the values ​​of the outermost perimeter of the R portion when restrained / the outermost perimeter of the wound electrode body when restrained and the high-rate resistance increase rate. Figure 6 shows a graph of the relationship between the positive electrode coating width / the height of the wound electrode body when restrained (c / d) and the high-rate resistance increase rate.

[0064] [Table 1]

[0065] As shown in Table 1 and Figures 5 and 6, 0.282

[0066] Although specific examples of the technology disclosed herein have been described in detail above, these are merely examples and do not limit the scope of the claims. The technology disclosed herein includes various modifications and variations of the above specific examples. [Explanation of symbols]

[0067] 10 Battery pack 12 Spacer 14 Bus bar 17 End Plate 18 Beam material 19 Bis 20 Wound electrode body 20f flat part 20r R part 30 Battery case 36 Safety valve 42 Positive terminal 42a Positive current collector 44 Negative terminal 44a Negative current collector plate 50 positive electrode 52 Positive electrode current collector 52a Exposed part of positive electrode current collector 54 Cathode active material layer 60 negative electrode 62 Negative electrode current collector 62a Exposed part of negative electrode current collector 64 Negative electrode active material layer​ 70 separator 100 non-aqueous electrolyte secondary battery

Claims

1. A non-aqueous electrolyte; a sheet-shaped positive electrode including a positive electrode active material layer formed in a band shape along the longitudinal direction on a long positive electrode current collector, a sheet-shaped negative electrode including a negative electrode active material layer formed in a band shape along the longitudinal direction on a long negative electrode current collector, and a separator interposed between the positive electrode and the negative electrode, which are stacked and wound in the longitudinal direction to form a flat wound electrode body; a rectangular battery case that accommodates the nonaqueous electrolyte and the wound electrode body; A non-aqueous electrolyte secondary battery comprising: The wound electrode body has a pair of flat portions formed to face each other across a winding axis, and a pair of R portions having curved surfaces formed between the pair of flat portions, Here, in a state in which a restraining pressure of 4.5 kN is applied to the entire planar portion of the wound electrode body from the opposing direction of the planar portion, In a cross section perpendicular to the winding axis of the wound electrode body, The sum of the outermost peripheral lengths of the pair of R portions of the wound electrode body is a (mm), The outermost peripheral length of the wound electrode body is b (mm), The length of the positive electrode active material layer in a width direction perpendicular to the longitudinal direction is c (mm), The height of the wound electrode body, which is the distance between the vertices of the pair of R portions in the cross section, is d (mm), When The following conditions: 0.287≦a / b≦0.32; and 1.63≦c / d≦1.77; A non-aqueous electrolyte secondary battery comprising:

2. 2. The nonaqueous electrolyte secondary battery according to claim 1, further satisfying the condition: 1.66≦c / d≦1.

72.

3. 3. The nonaqueous electrolyte secondary battery according to claim 1, wherein the height d of the wound electrode body is 50 mm or more and 55 mm or less.

4. A battery pack in which a plurality of unit cells are electrically connected to each other and arranged, 4. A battery pack, wherein at least one of the cells is the nonaqueous electrolyte secondary battery according to claim 1.

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