Secondary battery and method for manufacturing the same

Abstract

The present invention relates to a secondary battery and a method for manufacturing the secondary battery. According to the present disclosure, there is provided a secondary battery capable of more appropriately suppressing the precipitation of metallic lithium. The secondary battery (100) disclosed herein includes a wound electrode body (40) and a battery case (50) that houses the wound electrode body (40). In the vicinity of the positive electrode starting end in the flat portion (40f) of the wound electrode body (40) of the secondary battery (100), a lamination shortage region (48) is formed in which the total number of lamination layers of the positive electrode plate and the negative electrode plate in the thickness direction of the wound electrode body (40) is smaller than that in other regions of the flat portion (40f). Further, in the secondary battery (100), a protruding portion (52e) that protrudes toward at least a part of the lamination shortage region (48) is formed on the inner surface of the battery case (50). Thereby, it is possible to prevent poor pressing in the lamination shortage region (48) and suppress the precipitation of metallic Li caused by an increase in the local inter-pole distance.

Description

Technical Field

[0001] The present invention relates to a secondary battery and a method for manufacturing the secondary battery. Background Art

[0002] A secondary battery such as a lithium-ion secondary battery has an electrode body including a pair of electrode plates (a positive electrode plate and a negative electrode plate). As an example of the electrode body, a wound electrode body obtained by winding a long strip-shaped positive electrode plate and a negative electrode plate with a separator interposed therebetween can be cited. In this wound electrode body, one end (starting end) of each electrode plate is disposed inside the electrode body, and the other end (terminal end) is disposed outside the electrode body. In addition, the outer shape of such a wound electrode body is sometimes formed into a flat shape. The flat-shaped wound electrode body has a pair of curved portions with a curved outer surface and a flat portion with a flat outer surface connecting the pair of curved portions.

[0003] Patent Document 1 discloses an example of a secondary battery including the above-described flat-shaped wound electrode body. In the secondary battery described in Patent Document 1, a wound inner end of the positive electrode (positive electrode starting end) and a wound inner end of the negative electrode (negative electrode starting end) are disposed inside the flat portion of the wound electrode body. Moreover, the wound inner end of the negative electrode has an extending portion extending toward the curved portion side with respect to the wound inner end of the positive electrode, and the extending portion of the negative electrode is folded back within a range where it does not overlap with the positive electrode. According to the secondary battery described in Patent Document 1, the deviation of the thickness of the flat portion of the electrode body is suppressed, and thus, the electrode body can be easily accommodated in the battery case. In addition, the deviation of the distance between the positive electrode and the negative electrode (inter-pole distance) can also be suppressed, and thus, there is also an effect of suppressing the precipitation of metallic lithium (metallic Li) caused by the deviation of the charge and discharge reaction.

[0004] Prior Art Documents

[0005] Patent Documents

[0006] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2019-169353 Summary of the Invention

[0007] Problems to be Solved by the Invention

[0008] However, in recent years, the requirements for the durability and long life of secondary batteries have been increasing, and a technique capable of appropriately suppressing the precipitation of metallic lithium as compared with the past has been demanded. The present invention has been completed in view of the above requirements, and an object thereof is to provide a technique capable of appropriately suppressing the precipitation of metallic lithium.

[0009] Means for Solving the Problems

[0010] In order to achieve the above object, a secondary battery having the following structure is provided by the technique disclosed herein.

[0011] The secondary battery disclosed herein includes a flat wound electrode body formed by winding a positive electrode plate and a negative electrode plate with a separator interposed therebetween, and a battery case that houses the wound electrode body. The flat wound electrode body of this secondary battery has a pair of curved portions with curved outer surfaces and a flat portion with a flat outer surface that connects the pair of curved portions. In addition, one end in the length direction of the positive electrode plate is disposed inside the wound electrode body as the positive electrode starting end, and the other end is disposed outside the wound electrode body as the positive electrode terminal end. Further, one end in the length direction of the negative electrode plate is disposed inside the wound electrode body as the negative electrode starting end, and the other end is disposed outside the wound electrode body as the negative electrode terminal end. Moreover, the positive electrode starting end is disposed inside the flat portion, and the negative electrode starting end extends closer to one of the pair of curved portions than the positive electrode starting end. And in the vicinity of the positive electrode starting end in the flat portion, a stacking deficiency region where the number of stacked layers of the positive electrode plate and the negative electrode plate in the thickness direction of the wound electrode body is smaller than that in other regions of the flat portion is formed. Furthermore, in the secondary battery disclosed herein, a protruding portion that protrudes toward at least a part of the stacking deficiency region is formed on the inner surface of the battery case, or a spacer is disposed between at least a part of the stacking deficiency region and the battery case.

[0012] This secondary battery is usually used in a state where pressure is applied to the flat portion of the wound electrode body from the outside of the battery case to reduce the distance (inter-pole distance) between the positive electrode plate and the negative electrode plate inside the electrode body. However, in a flat-shaped wound electrode body, in the vicinity of the positive electrode starting end disposed in the flat portion, a stacking deficiency region where the total number of stacked layers of the electrode plates (positive electrode plate, negative electrode plate) is smaller and the thickness is thinner than other regions of the flat portion may be generated. In this case, an appropriate pressure is not applied to the stacking deficiency region, resulting in an increase in the local inter-pole distance. Therefore, the precipitation of metallic Li may be promoted. In contrast, in the secondary battery disclosed herein, a protruding portion (or spacer) that centrally presses at least a part of the stacking deficiency region is provided. Thereby, it is possible to prevent poor pressing in the stacking deficiency region and suppress the precipitation of metallic Li caused by an increase in the local inter-pole distance.

[0013] In one aspect of the secondary battery disclosed herein, the stacking deficiency region is formed between the positive electrode starting end and the negative electrode starting end in the direction along the flat portion. According to the technology disclosed herein, it is possible to appropriately suppress the precipitation of metallic Li in the vicinity of the stacking deficiency region.

[0014] In one aspect of the secondary battery disclosed herein, the protruding portion or the spacer extends along the winding axis of the wound electrode body. Thereby, it is possible to more appropriately prevent poor pressing in the stacking deficiency region and further improve the Li precipitation resistance.

[0015] In one embodiment of the secondary battery disclosed herein, the length of the stacking deficiency region in the direction of the flat portion is 5 mm or less. By manufacturing the wound electrode body in such a manner that the stacking deficiency region is narrowed, the Li precipitation resistance can be further improved. Further, the protrusion or the spacer in the direction of the flat portion preferably has a size corresponding to the length of the stacking deficiency region. That is, in the embodiment where the length of the stacking deficiency region is 5 mm or less, the size of the protrusion or the spacer is preferably 5 mm or less.

[0016] In one embodiment of the secondary battery disclosed herein, the protruding dimension of the protrusion protruding from the inner surface of the battery case or the thickness of the spacer is 0.04 mm or more. Thereby, it is possible to appropriately prevent poor pressing in the stacking deficiency region and more appropriately improve the Li precipitation resistance.

[0017] In one embodiment of the secondary battery disclosed herein, a plurality of wound electrode bodies are housed in the battery case. According to the technology disclosed herein, in a secondary battery having such a plurality of wound electrode bodies, precipitation of metallic Li can also be appropriately suppressed.

[0018] Further, in the embodiment using the plurality of wound electrode bodies, it is preferable to dispose an intermediate spacer between the stacking deficiency regions of two adjacent wound electrode bodies. Thereby, it is possible to appropriately press the stacking deficiency regions of the plurality of wound electrode bodies, respectively, and further improve the Li precipitation resistance.

[0019] In one embodiment of the secondary battery disclosed herein, a recess corresponding to the protrusion is formed on the outer surface of the battery case. In other words, the protrusion is preferably formed by pressing the battery case from the outer surface side by stamping to deform it. Thereby, it is possible to suppress the positional deviation between the stacking deficiency region and the protrusion in the manufacturing process, and appropriately exhibit the effect of suppressing Li precipitation obtained by the protrusion. In addition, since the accommodation of the wound electrode body into the battery case becomes easy, it is also possible to contribute to an improvement in manufacturing efficiency.

[0020] In one embodiment of the secondary battery disclosed herein, the spacer is an adhesive tape adhered to the outer surface of the flat portion of the wound electrode body. Thereby, it is possible to reliably prevent the positional deviation between the stacking deficiency region and the spacer, and appropriately exhibit the effect of suppressing Li precipitation obtained by the spacer.

[0021] In one embodiment of the secondary battery disclosed herein, the wound electrode body is housed in the battery case in a state of being covered with an electrode body holder made of an insulating resin sheet, and the spacer is a protrusion formed on the electrode body holder. In this embodiment, it is also possible to prevent poor pressing in the stacking deficiency region and suppress the precipitation of metallic Li.

[0022] Further, as another aspect of the technology disclosed herein, a method for manufacturing a secondary battery is provided. The manufacturing method is a method for manufacturing a secondary battery in which a wound electrode body is housed inside a battery case, and includes: a winding step of manufacturing a cylindrical wound body in which a positive electrode plate and a negative electrode plate are wound with a separator therebetween; a forming step of subjecting the cylindrical wound body to pressure forming to manufacture a flat wound electrode body; and a housing step of housing the flat wound electrode body inside the battery case. Moreover, the flat wound electrode body has: a pair of bent portions with a curved outer surface and a flat portion with a flat outer surface connecting the pair of bent portions. One end in the length direction of the positive electrode plate is disposed inside the wound electrode body as a positive electrode starting end, and the other end is disposed outside the wound electrode body as a positive electrode terminal end. Also, one end in the length direction of the negative electrode plate is disposed inside the wound electrode body as a negative electrode starting end, and the other end is disposed outside the wound electrode body as a negative electrode terminal end. Further, the positive electrode starting end is disposed inside the flat portion, and the negative electrode starting end extends closer to one of the pair of bent portions than the positive electrode starting end. In the vicinity of the positive electrode starting end in the flat portion, a lamination shortage region where the total number of laminations of the positive electrode plate and the negative electrode plate in the thickness direction of the wound electrode body is smaller than in other regions of the flat portion is formed. Moreover, in the manufacturing method disclosed herein, it is characterized in that, after the housing step, a pressing step is performed, and in the pressing step, the lamination shortage region of the wound electrode body housed inside the battery case is pressed from the outside of the battery case to deform the battery case, thereby forming a protruding portion protruding toward the lamination shortage region.

[0023] According to the manufacturing method having the above configuration, a protruding portion that locally presses the lamination shortage region to suppress the precipitation of metallic Li can be easily formed. Also, by forming the protruding portion in the pressing step after the housing step, when the wound electrode body is housed in the battery case, the positional deviation between the lamination shortage region and the protruding portion can be suppressed, and thus, the Li precipitation resistance can be further improved. In addition, the housing of the wound electrode body inside the battery case becomes easy, and thus, it can also contribute to an improvement in manufacturing efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is a perspective view schematically showing a secondary battery according to the first embodiment.

[0025] Figure 2 is along Figure 1 in the schematic longitudinal sectional view taken along line II-II in

[0026] Figure 3 is along Figure 1 in the schematic longitudinal sectional view taken along line III-III in

[0027] Figure 4is a schematic cross-sectional view along Figure 1 the IV-IV line in

[0028] Figure 5 is a perspective view schematically showing the electrode body mounted on the sealing plate.

[0029] Figure 6 is a perspective view schematically showing the electrode body provided with the positive electrode second current collector part and the negative electrode second current collector part.

[0030] Figure 7 is a schematic view showing the structure of the wound electrode body of a secondary battery according to an embodiment.

[0031] Figure 8 is schematically showing Figure 7 the front view of the wound electrode body of

[0032] Figure 9 is a schematic longitudinal cross-sectional view along Figure 8 the IX-IX line in

[0033] Figure 10 is a schematic longitudinal cross-sectional view schematically showing another example of the wound electrode body.

[0034] Figure 11 is a schematic longitudinal cross-sectional view of a secondary battery according to a second embodiment.

[0035] Figure 12 is a schematic longitudinal cross-sectional view of a secondary battery according to a third embodiment.

[0036] Figure 13 is a front view schematically showing the wound electrode body of a secondary battery according to a third embodiment.

[0037] Figure 14 is a schematic longitudinal cross-sectional view of a secondary battery according to a fourth embodiment.

[0038] Figure 15 is a photograph showing the result of the Li precipitation resistance evaluation of Sample 1.

[0039] Figure 16 is a photograph showing the result of the Li precipitation resistance evaluation of Sample 2.

[0040] Figure 17 is a photograph showing the result of the Li precipitation resistance evaluation of Sample 3.

[0041] Explanation of Reference Numerals

[0042] 10 Positive electrode plate

[0043] 10e Positive electrode terminal part

[0044] 10s Positive electrode starting end part

[0045] 20 Negative electrode plate

[0046] 20e Negative electrode terminal part

[0047] 20s Negative electrode starting part

[0048] 30 Separator

[0049] 40 Wound electrode body

[0050] 40f Flat part

[0051] 40r Bent part

[0052] 48 Laminating insufficient area

[0053] 50 Battery case

[0054] 52 Outer package

[0055] 52a Bottom wall

[0056] 52b Long side wall

[0057] 52c Short side wall

[0058] 52d Concave part

[0059] 52e Protruding part

[0060] 54 Sealing plate

[0061] 80 Spacer

[0062] 85 Intermediate spacer

[0063] 100 Secondary battery Detailed implementation manners

[0064] Hereinafter, embodiments of the technology disclosed herein will be described with reference to the drawings. It should be noted that matters required for implementing the technology disclosed herein other than those specifically mentioned in this specification (for example, detailed materials of each component) can be grasped as design matters of those skilled in the art based on the prior art in this field. The technology disclosed herein can be implemented based on the content disclosed in this specification and common general knowledge in this field. It should be noted that the expression "A to B" indicating a range in this specification includes the meaning of "A or more and B or less", and includes the meanings of "preferably greater than A" and "preferably less than B".

[0065] It should be noted that in this specification, a "secondary battery" generally refers to a power storage device in which a charge-discharge reaction occurs by the movement of charge carriers between a pair of electrodes (a positive electrode and a negative electrode) via an electrolyte. The technology disclosed herein can be applied to those using lithium ions (Li +)A secondary battery (typically, a lithium-ion secondary battery) in which charge carriers can be deposited in the form of metallic lithium (Li metal) as charge carriers and accompany charge and discharge reactions.

[0066] In addition, in the respective figures referred to in this specification, the reference numeral X in the drawings represents the "depth direction", the reference numeral Y represents the "width direction", and the reference numeral Z represents the "height direction". Further, F in the depth direction X represents "front", and Rr represents "rear". L in the width direction Y represents "left", and R represents "right". Further, U in the height direction Z represents "upper", and "D" represents lower. However, these directions are determined for convenience of explanation and are not intended to limit the setting method when using the secondary battery disclosed herein.

[0067] <First Embodiment>

[0068] 1. Structure of the secondary battery

[0069] Hereinafter, with reference to Figures 1 to 9 One embodiment of the secondary battery disclosed herein will be described. Figure 1 FIG. is a perspective view schematically showing the secondary battery of this embodiment. Figure 2 is along Figure 1 A schematic longitudinal sectional view taken along line II-II in Figure 3 is along Figure 1 A schematic longitudinal sectional view taken along line III-III in Figure 4 is along Figure 1 A schematic cross-sectional view taken along line IV-IV in Figure 5 FIG. is a perspective view schematically showing the electrode body mounted on the sealing plate. Figure 6 FIG. is a perspective view schematically showing the electrode body on which the positive electrode second current collector and the negative electrode second current collector are mounted. Figure 7 FIG. is a schematic view showing the structure of the wound electrode body of the secondary battery of this embodiment. Figure 8 is schematically showing Figure 7 The front view of the wound electrode body of Figure 9 is along Figure 8 A schematic longitudinal sectional view taken along line IX-IX in Figure 9 It should be noted that, for convenience of explanation, in Figure 7 etc., the description of the separator 30 (see

[0070] As Figure 2 shown, the secondary battery 100 of this embodiment includes a wound electrode body 40 and a battery case 50 that houses the wound electrode body 40. Hereinafter, the specific structure of the secondary battery 100 will be described.

[0071] (1) Battery case

[0072] The battery case 50 is a housing that houses the wound electrode body 40. Although not shown, a non-aqueous electrolyte is also housed inside the battery case 50. As Figure 1 shown, the battery case 50 in the present embodiment has an outer shape of a flat and bottomed rectangular parallelepiped (square). It should be noted that the battery case 50 can be made of a conventionally well-known material without particular limitation. For example, the battery case 50 can be made of metal. As an example of the material of the battery case 50, aluminum, aluminum alloy, iron, iron alloy, etc. can be cited.

[0073] The battery case 50 includes an outer package 52 and a sealing plate 54. The outer package 52 is a flat bottomed square container having an opening 52h on its upper surface. As Figure 1 and Figure 2 shown, the outer package 52 includes: a bottom wall 52a having a substantially rectangular plane; a pair of long side walls 52b extending upward in the height direction Z from the long sides of the bottom wall 52a; and a pair of short side walls 52c extending upward in the height direction Z from the short sides of the bottom wall 52a. In addition, as will be described in detail later, a linear recess 52d extending along the width direction Y is formed in the long side wall 52b of the outer package 52 in the present embodiment. On the other hand, the sealing plate 54 is a plate-like member having a substantially rectangular plane that closes the opening 52h of the outer package 52. Moreover, the outer peripheral edge portion of the sealing plate 54 is joined (e.g., welded) to the outer peripheral edge portion of the opening 52h of the outer package 52. Thus, the battery case 50 with its interior hermetically sealed is fabricated. In addition, a liquid injection hole 55 and a gas discharge valve 57 are provided in the sealing plate 54. The liquid injection hole 55 is a through hole provided for injecting the non-aqueous electrolyte into the interior of the sealed battery case 50. It should be noted that the liquid injection hole 55 is sealed by a sealing member 56 after the injection of the non-aqueous electrolyte. In addition, the gas discharge valve 57 is a thin wall portion designed to break (open) and discharge the gas when a large amount of gas is generated inside the battery case 50.

[0074] (2) Non-aqueous electrolyte

[0075] As described above, inside the battery case 50, in addition to the wound electrode body 40, a non-aqueous electrolyte (not shown) is also housed. The non-aqueous electrolyte can be a conventionally well-known non-aqueous electrolyte used in secondary batteries without particular limitation. For example, the non-aqueous electrolyte is prepared by dissolving a supporting electrolyte in a non-aqueous solvent. As an example of the non-aqueous solvent, carbonate solvents such as ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate can be cited. As an example of the supporting electrolyte, fluorine-containing lithium salts such as LiPF6 can be cited.

[0076] (3) Electrode terminal

[0077] In addition, on one side in the width direction Y of the sealing plate 54 ( Figure 1 , Figure 2At the end on the left side (in the figure) of [], a positive terminal 60 is installed. This positive terminal 60 is connected to a plate-shaped positive external conductive member 62 outside the battery case 50. On the other hand, on the other side ( Figure 1 , Figure 2 the right side in the figure) of the end of the sealing plate 54, a negative terminal 65 is installed. A plate-shaped negative external conductive member 67 is installed on this negative terminal 65. These external conductive members (the positive external conductive member 62 and the negative external conductive member 67) are connected to other secondary batteries and external devices via external connection members (bus bars, etc.). It should be noted that the external conductive members are preferably made of metals with excellent conductivity (such as aluminum, aluminum alloy, copper, copper alloy, etc.).

[0078] (4) Electrode current collector

[0079] As Figures 3 to 5 shown, in the secondary battery 100 of the present embodiment, a plurality (three) of wound electrode bodies 40 are housed in the battery case 50. As will be described in detail later, a positive electrode tab group 42 and a negative electrode tab group 44 are provided on each wound electrode body 40. The positive terminal 60 is connected to the positive electrode tab groups 42 of the plurality of wound electrode bodies 40 via a positive electrode current collector 70. Specifically, the positive electrode current collector 70 is housed inside the battery case 50. As Figure 2 and Figure 5 shown, this positive electrode current collector 70 includes: a plate-shaped conductive member that extends in the width direction Y along the inner surface of the sealing plate 54, namely the positive electrode first current collector 71; and a plate-shaped conductive member that extends in the height direction Z, namely a plurality of positive electrode second current collectors 72. Moreover, the lower end portion 60c of the positive terminal 60 is inserted into the inside of the battery case 50 through the terminal insertion hole 58 of the sealing plate 54 and connected to the positive electrode first current collector 71 (refer to Figure 2 ). On the other hand, as Figures 4 to 6 shown, in this secondary battery 100, the number of positive electrode second current collectors 72 corresponding to the number of wound electrode bodies 40 is provided. Each positive electrode second current collector 72 is connected to the positive electrode tab group 42 of the wound electrode body 40. Moreover, as Figure 4 and Figure 5 shown, the positive electrode tab group 42 of the wound electrode body 40 is bent so that the positive electrode second current collector 72 faces one side surface 40a of the wound electrode body 40. Thereby, the upper end portion of the positive electrode second current collector 72 is electrically connected to the positive electrode first current collector 71.

[0080] On the other hand, the negative terminal 65 is connected to the negative electrode tab groups 44 of the plurality of wound electrode bodies 40 via the negative electrode current collector portion 75. The connection structure on the negative electrode side is substantially the same as the connection structure on the positive electrode side described above. Specifically, the negative electrode current collector portion 75 includes: a plate-shaped conductive member, i.e., the negative electrode first current collector portion 76, which extends in the width direction Y along the inner surface of the sealing plate 54; and a plurality of plate-shaped conductive members, i.e., the negative electrode second current collector portions 77, which extend in the height direction Z (refer to Figure 2 and Figure 5 ). Moreover, the lower end portion 65c of the negative terminal 65 is inserted into the inside of the battery case 50 through the terminal insertion holes 59 and is connected to the negative electrode first current collector portion 76 (refer to Figure 2 ). On the other hand, the plurality of negative electrode second current collector portions 77 are respectively connected to the negative electrode tab groups 44 of the wound electrode bodies 40 (refer to Figures 4 to 6 ). Moreover, the negative electrode tab group 44 is bent so that the negative electrode second current collector portion 77 faces the other side surface 40b of the wound electrode body 40. Thereby, the upper end portion of the negative electrode second current collector portion 77 is electrically connected to the negative electrode first current collector portion 76. In addition, the electrode current collector portions (the positive electrode current collector portion 70 and the negative electrode current collector portion 75) may preferably be made of a metal with excellent conductivity (such as aluminum, aluminum alloy, copper, copper alloy, etc.).

[0081] (5) Insulating member

[0082] In addition, in this secondary battery 100, various insulating members for preventing conduction between the wound electrode body 40 and the battery case 50 are installed. Specifically, an external insulating member 92 is interposed between the positive electrode external conductive member 62 (negative electrode external conductive member 67) and the outer side surface of the sealing plate 54 (refer to Figure 1 ). Thereby, conduction between the positive electrode external conductive member 62, the negative electrode external conductive member 67 and the sealing plate 54 can be prevented. In addition, washers 90 are respectively installed in the terminal insertion holes 58, 59 of the sealing plate 54 (refer to Figure 2 ). Thereby, conduction between the positive terminal 60 (or negative terminal 65) inserted into the terminal insertion holes 58, 59 and the sealing plate 54 can be prevented. In addition, an internal insulating member 94 is disposed between the positive electrode first current collector portion 71 (or negative electrode first current collector portion 76) and the inner side surface of the sealing plate 54. The internal insulating member 94 includes a plate-shaped base portion 94a interposed between the positive electrode first current collector portion 71 (or negative electrode first current collector portion 76) and the inner side surface of the sealing plate 54. Thereby, conduction between the positive electrode first current collector portion 71, the negative electrode first current collector portion 76 and the sealing plate 54 can be prevented. And the internal insulating member 94 includes an insulating protrusion 94b protruding from the inner side surface of the sealing plate 54 toward the wound electrode body 40 (refer to Figure 2 and Figure 3). Thus, the movement of the wound electrode body 40 in the height direction Z can be restricted, and the wound electrode body 40 can be prevented from directly contacting the sealing plate 54. In addition, the plurality of wound electrode bodies 40 are held by an electrode body holder 98 (see FIG. 1 ) made of an insulating resin sheet. Figure 3 ) is contained inside the battery case 50 in a covered state. Thus, it is possible to prevent the wound electrode body 40 from directly contacting the outer casing 52. It should be noted that the materials of the above-mentioned insulating components are not particularly limited as long as they have the specified insulation properties. As an example, synthetic resin materials such as polyolefin resins (such as polypropylene (PP), polyethylene (PE)), fluorine resins (such as perfluoroalkoxyalkane (PFA), polytetrafluoroethylene (PTFE)) can be used.

[0083] (6) Wound electrode body

[0084] like Figure 7 As shown in the figure, the electrode body used in the secondary battery 100 of the present embodiment is a wound electrode body 40 in which the positive electrode plate 10 and the negative electrode plate 20 are wound with the separator 30 interposed therebetween. The wound electrode body 40 is housed in the battery case 50 in such a manner that the winding axis WL of the wound electrode body 40 is substantially consistent with the width direction Y of the secondary battery 100. That is, the "winding axis direction" in the following description is substantially the same direction as the width direction Y in the figure. The structure of the wound electrode body 40 is described in detail below.

[0085] (a) Positive plate

[0086] like Figure 7 As shown, the positive electrode plate 10 is a long strip-shaped component. The thickness of the positive electrode plate 10 is preferably 28μm to 420μm, more preferably 50μm to 178μm, and further preferably 112μm to 165μm. The positive electrode plate 10 includes a positive electrode core 12 as a strip-shaped metal foil and a positive electrode active material layer 14 formed on the surface of the positive electrode core 12. It should be noted that, from the perspective of battery performance, the positive electrode active material layer 14 is preferably formed on both sides of the positive electrode core 12. In addition, in the positive electrode plate 10, the positive electrode tab 12t extends from the end edge on one side of the winding axis direction (width direction Y) toward the outside ( Figure 7 ) protrudes on the left side. Moreover, the positive electrode tab 12t is formed in plurality at predetermined intervals in the longitudinal direction L of the long strip-shaped positive electrode plate 10. The positive electrode tab 12t is an area where the positive electrode active material layer 14 is not formed and the positive electrode core 12 is exposed. In addition, in an area adjacent to the end edge on the positive electrode tab 12t side of the positive electrode plate 10, a protective layer 16 extending along the longitudinal direction L of the positive electrode plate 10 is formed. In addition, the width of the positive electrode active material layer 14 in the width direction Y is preferably 200 mm to 400 mm, more preferably 250 mm to 350 mm, and further preferably 260 mm to 300 mm.

[0087] The positive electrode core 12 is preferably made of a metal material having a specified conductivity. For example, the positive electrode core 12 is preferably made of aluminum, an aluminum alloy, or the like. In addition, the thickness of the positive electrode core 12 is preferably 8 μm to 20 μm, more preferably 10 μm to 18 μm, and still more preferably 12 μm to 15 μm.

[0088] The positive electrode active material layer 14 is a layer containing a positive electrode active material. The positive electrode active material uses a material that can reversibly occlude and release charge carriers. In addition, the positive electrode active material layer 14 may contain additives such as a conductive material and an adhesive in addition to the positive electrode active material. It should be noted that each material (positive electrode active material, conductive material, adhesive, etc.) contained in the positive electrode active material layer 14 can be used without particular limitation as a conventionally known material that can be used in a typical secondary battery (for example, a lithium ion secondary battery), and is not limited to the technology disclosed herein. Therefore, detailed description is omitted. It should be noted that when the total solid content of the positive electrode active material layer 14 is set to 100% by mass, the content of the positive electrode active material is approximately 80% by mass or more, typically 90% by mass or more. In addition, the thickness of the positive electrode active material layer 14 on one side of the positive electrode core 12 is preferably 10 μm to 100 μm, more preferably 20 μm to 80 μm, and still more preferably 50 μm to 75 μm. It should be noted that the "thickness of the positive electrode active material layer" in this specification refers to the size of the positive electrode active material layer in the direction perpendicular to the flat portion 40f of the wound electrode body 40 (i.e., the depth direction X).

[0089] The protective layer 16 is formed in such a way that its conductivity is lower than that of the positive electrode active material layer 14. By providing the protective layer 16 in a region adjacent to the edge of the positive electrode plate 10, it is possible to prevent an internal short circuit caused by direct contact between the positive electrode core 12 and the negative electrode active material layer 24 when the separator 30 is damaged. For example, as the protective layer 16, a layer containing insulating ceramic particles and an adhesive is preferably formed. Regarding the materials (ceramic particles, adhesive, etc.) contained in the protective layer 16, they can also be used without particular limitation as conventionally known materials that can be used in a typical secondary battery (for example, a lithium ion secondary battery), and are not limited to the technology disclosed herein. Therefore, detailed description is omitted. It should be noted that the protective layer is not an essential component of the positive electrode plate in the technology disclosed herein. That is, in the secondary battery disclosed herein, a positive electrode plate without a protective layer may also be used.

[0090] (b) Negative electrode plate

[0091] As Figure 7As shown, the negative electrode plate 20 is a long strip-shaped component. The thickness of the negative electrode plate 20 is preferably 24 μm to 420 μm, more preferably 106 μm to 215 μm, and further preferably 158 μm to 185 μm. The negative electrode plate 20 includes a negative electrode core 22 that is a strip-shaped metal foil and a negative electrode active material layer 24 formed on the surface of the negative electrode core 22. It should be noted that, from the perspective of battery performance, the negative electrode active material layer 24 is preferably formed on both sides of the negative electrode core 22. And, on the negative electrode plate 20, a negative electrode tab 22t protruding outward from one end edge in the winding axis direction (width direction Y) ( Figure 7 the right side in the figure) is provided. A plurality of the negative electrode tabs 22t are provided at a prescribed interval in the length direction L of the negative electrode plate 20. The negative electrode tab 22t is a region where the negative electrode core 22 is exposed without the negative electrode active material layer 24 formed thereon. In addition, the width of the negative electrode active material layer 24 in the width direction Y is preferably 200 mm to 400 mm, more preferably 250 mm to 350 mm, and further preferably 260 mm to 300 mm.

[0092] The negative electrode core 22 can preferably use a metal material having a prescribed conductivity. The negative electrode core 22 is preferably composed of, for example, copper, a copper alloy, or the like. In addition, the thickness of the negative electrode core 22 is preferably 4 μm to 20 μm, more preferably 6 μm to 15 μm, and further preferably 8 μm to 10 μm.

[0093] The negative electrode active material layer 24 is a layer containing a negative electrode active material. The negative electrode active material uses a material that can reversibly occlude and release charge carriers in relation to the above-mentioned positive electrode active material. In addition, the negative electrode active material layer 24 may contain additives such as a binder and a tackifier in addition to the negative electrode active material. Regarding each material (negative electrode active material, binder, tackifier, etc.) contained in the negative electrode active material layer 24, conventionally known materials that can be used in a normal secondary battery (for example, a lithium ion secondary battery) can be used without particular limitation, and the technology disclosed herein is not limited, so detailed description is omitted. It should be noted that when the total solid content of the negative electrode active material layer 24 is set to 100% by mass, the content of the negative electrode active material is approximately 30% by mass or more, typically 50% by mass or more. It should be noted that the negative electrode active material may account for 80% by mass or more of the negative electrode active material layer 24, or may account for 90% by mass or more. In addition, the thickness of the negative electrode active material layer 24 on one side of the negative electrode core 22 is preferably 10 μm to 200 μm, more preferably 20 μm to 100 μm, and further preferably 75 μm to 85 μm.

[0094] (c) Separator

[0095] The wound electrode body 40 in this embodiment includes two separator membranes 30. These separator membranes 30 are interposed between the positive electrode plate 10 and the negative electrode plate 20. Thereby, contact between the positive electrode plate 10 and the negative electrode plate 20 can be prevented. In addition, the separator membrane 30 has a function of allowing charge carriers (such as lithium ions) to pass through. As an example of such a separator membrane 30, an insulating sheet formed with a plurality of fine pores through which charge carriers can pass can be cited. It should be noted that regarding the separator membrane 30, a separator membrane used in a conventionally known secondary battery can be used without particular limitation, and the technology disclosed herein is not limited, so detailed description is omitted. It should be noted that the thickness of the separator membrane 30 is preferably 4 μm to 30 μm, more preferably 6 μm to 20 μm, and further preferably 8 μm to 16 μm.

[0096] (d) Structure of the wound electrode body

[0097] Next, the specific structure of the wound electrode body 40 including the positive electrode plate 10, the negative electrode plate 20, and the separator membrane 30 will be described. The wound electrode body 40 is manufactured by laminating and winding the positive electrode plate 10 and the negative electrode plate 20 with two separator membranes 30 interposed therebetween. Specifically, first, a laminate (refer to Figure 7 ) is manufactured by laminating the separator membrane 30, the negative electrode plate 20, the separator membrane 30, and the positive electrode plate 10 in this order. At this time, the lamination position in the width direction Y of each sheet member is adjusted such that only the positive electrode tab 12t of the positive electrode plate 10 protrudes from the side edge on one side ( Figure 7 the left side in Figure 7 ) of the width direction Y and only the negative electrode tab 22t of the negative electrode plate 20 protrudes from the side edge on the other side ( Figure 8 the right side in

[0098] ). Next, the manufactured laminate is wound to manufacture a cylindrical body. The number of windings at this time is preferably appropriately adjusted in consideration of the performance of the target wound electrode body 40, manufacturing efficiency, etc. As an example, the number of windings of the wound electrode body 40 is preferably 10 to 60 times, more preferably 30 to 40 times. Next, by performing pressure forming on this cylindrical body, a wound electrode body 40 having a flat shape is manufactured. As shown in Figure 9As shown, in the wound electrode body 40 after production, one end of the strip-shaped positive electrode plate 10 in the length direction L is disposed as the positive electrode starting end portion 10s inside the wound electrode body 40. Moreover, the other end of the positive electrode plate 10 is disposed as the positive electrode terminal end portion 10e outside the wound electrode body 40. Similarly, one end of the strip-shaped negative electrode plate 20 is disposed as the negative electrode starting end portion 20s inside the wound electrode body 40. In addition, the other end of the negative electrode plate 20 is disposed as the negative electrode terminal end portion 20e outside the wound electrode body 40. It should be noted that although not shown in Figure 9 for the sake of simplicity, the positive electrode active material layer 14 is formed up to both ends in the length direction L of the positive electrode plate 10 (the positive electrode starting end portion 10s and the positive electrode terminal end portion 10e) (refer to Figure 7 ). Similarly, the negative electrode active material layer 24 is formed up to both ends in the length direction L of the negative electrode plate 20 (the negative electrode starting end portion 20s and the negative electrode terminal end portion 20e) (refer to Figure 7 ).

[0099] In addition, as Figure 8 shown, at one end of the wound electrode body 40 in the winding axis direction (width direction Y) after production, a positive electrode tab group 42 in which a plurality of positive electrode tabs 12t exposing the positive electrode core 12 are laminated is formed. On the other hand, at the other end of the wound electrode body 40 in the winding axis direction (width direction Y), a negative electrode tab group 44 in which a plurality of negative electrode tabs 22t exposing the negative electrode core 22 are laminated is formed. On the other hand, at the central portion of the wound electrode body 40 in the width direction Y, a core portion 46 where the positive electrode active material layer 14 faces the negative electrode active material layer 24 is formed. This core portion 46 becomes the main place where the charge and discharge reaction occurs. Here, as described above, in the present embodiment, after the positive electrode tab group 42 is connected to the positive electrode second current collector 72, it is bent so that the positive electrode second current collector 72 faces the side surface 40a of the wound electrode body 40 (refer to Figures 4 to 6 ). Similarly, after the negative electrode tab group 44 is connected to the negative electrode second current collector 77, it is bent so that the negative electrode second current collector 77 faces the side surface 40b of the wound electrode body 40. By providing the positive electrode tab group 42 (and the negative electrode tab group 44) that can be bent in this way, the volume of the core portion 46 (charge and discharge region) with respect to the internal volume of the battery case 50 can be increased. Therefore, it is possible to contribute to the improvement of battery performance.

[0100] As described above, the wound electrode body 40 in the present embodiment is formed into a flat shape by stamping. As Figure 3 and Figure 9 shown, this flat-shaped wound electrode body 40 has a pair of curved portions 40r with curved outer surfaces and a flat portion 40f with a flat outer surface connecting the pair of curved portions 40r. As Figure 3As shown, when the wound electrode body 40 is housed in the battery case 50, the flat portion 40f faces the long side wall 52b of the exterior body 52 (i.e., the flat surface of the battery case 50). In addition, the upper bent portion 40r faces the sealing plate 54, and the lower bent portion 40r faces the bottom wall 52a of the exterior body 52.

[0101] Here, as Figure 9 shown, in the wound electrode body 40 having the above structure, there may be a stacking deficiency region 48 where the number of stacked layers of the positive electrode plate 10 or the negative electrode plate 20 is smaller than that in other regions in the flat portion 40f, and the precipitation of metallic Li is promoted near the stacking deficiency region 48. Specifically, when manufacturing the flat-shaped wound electrode body 40, it is very difficult to align and arrange both the positive electrode starting end portion 10s and the negative electrode starting end portion 20s (especially the positive electrode starting end portion 10s) within the bent portion 40r. Therefore, in such a wound electrode body 40, there is a high possibility of generating a stacking deficiency region 48 where the total number of stacked electrode plates is smaller than that in other regions in the flat portion 40f near the positive electrode starting end portion 10s of the flat portion 40f. Moreover, such a secondary battery 100 is usually used in a state where the flat surface of the battery case 50 (the long side wall 52b of the exterior body 52) is sandwiched and the flat portion 40f of the wound electrode body 40 is pressurized. As a result, the inter-pole distance between the positive electrode plate 10 and the negative electrode plate 20 inside the wound electrode body 40 becomes smaller, and thus the resistance decreases. However, for the above stacking deficiency region 48, since the pressure from the outside of the battery case 50 cannot be sufficiently transmitted, the inter-pole distance locally increases and the resistance becomes high. As a result, current concentration occurs around the stacking deficiency region 48, and metallic Li precipitates on the surface of the negative electrode active material layer 24. In addition, in a region where the inter-pole distance is large, gases formed by the decomposition of the non-aqueous electrolyte are likely to accumulate. Therefore, if charge and discharge are repeated, the resistance in the stacking deficiency region 48 further increases, further promoting the precipitation of metallic Li. In contrast, in the secondary battery 100 of the present embodiment, as Figure 3 shown, a protruding portion 52e protruding toward the stacking deficiency region 48 of the wound electrode body 40 is formed on the inner surface of the battery case 50 (exterior body 52). Since the protruding portion 52e locally presses the stacking deficiency region 48, it is possible to prevent the local increase in the inter-pole distance caused by poor pressurization of the stacking deficiency region 48. As a result, it is possible to prevent current concentration from occurring around the stacking deficiency region 48 and to appropriately suppress the precipitation of metallic Li.

[0102] It should be noted that, as will be described later in detail, in the present embodiment, after the wound electrode body 40 is housed in the battery case 50, a stamping process of pressing the lamination shortage region 48 from the outside of the battery case 50 is performed, thereby forming the protrusion 52e. Therefore, a recess 52d corresponding to the protrusion 52e is formed on the outer surface of the battery case 50 in the present embodiment (refer to Figure 1 and Figure 3 ). Thereby, the positional deviation between the lamination shortage region 48 and the protrusion 52e can be suppressed, and thus the Li precipitation resistance can be further improved.

[0103] In addition, as described above, the lamination shortage region 48 is formed near the positive electrode starting end 10s in the flat portion 40f, and thus extends along the winding axis (width direction Y) of the wound electrode body 40 as shown in Figure 8 . From the viewpoint of appropriately preventing poor pressing in the lamination shortage region 48, the protrusion 52e is preferably formed so as to extend along the winding axis (width direction Y) of the wound electrode body 40. In this case, as shown in Figure 1 , a linear recess 52d extending along the width direction Y is formed on the long side wall 52b of the outer package 52. However, the formation region of the protrusion 52e in the width direction Y is not particularly limited and can be appropriately changed. For example, a plurality of protrusions 52e may be arranged at a predetermined interval along the width direction Y. Even in the case where such a dotted-line-shaped protrusion 52e is formed, poor pressing in the lamination shortage region 48 can be sufficiently prevented. In addition, the protrusion 52e may be formed only in a part of the width direction Y. In this way, when the protrusion 52e is formed only in a part of the width direction Y, it is preferable to form the protrusion 52e at the center portion in the width direction Y.

[0104] In addition, the protruding portion 52e is formed so as to be able to press at least a part of the stacking shortage region 48 in the direction along the flat portion 40f (height direction Z). That is, the size of the protruding portion 52e in the height direction Z may be larger or smaller than the size of the stacking shortage region 48 in the height direction Z. It should be noted that, from the viewpoint of efficiently eliminating the poor pressing of the stacking shortage region 48, it is preferable that the height dimension of the protruding portion 52e is of the same degree as the height dimension of the stacking shortage region 48. For example, the ratio of the height dimension of the protruding portion 52e to the height dimension of the stacking shortage region 48 is preferably 0.25 to 1.75, more preferably 0.5 to 1.5, further preferably 0.75 to 1.25, and particularly preferably 0.9 to 1.1. In addition, if the respective height dimensions are exemplified, the height dimension of the stacking shortage region 48 is preferably 5 mm or less, more preferably 4.5 mm or less, and particularly preferably 4 mm or less. As the height dimension of the stacking shortage region 48 becomes smaller, there is a tendency that the precipitation of metallic Li is less likely to occur. It should be noted that the lower limit value of the height dimension of the stacking shortage region 48 is not particularly limited and may be 1 mm or more or 1.5 mm or more. On the other hand, the height dimension of the protruding portion 52e is preferably 5 mm or less, more preferably 4.5 mm or less, and particularly preferably 4 mm or less. Thus, local stress is easily applied to the stacking shortage region 48, and therefore, the Li precipitation resistance can be further improved. On the other hand, from the viewpoint of appropriately pressing the stacking shortage region 48, the lower limit value of the height dimension of the protruding portion 52e is preferably 1.5 mm or more, and particularly preferably 2 mm or more.

[0105] In addition, the formation positions of the stacking shortage region and the protruding portion in the technology disclosed herein are not particularly limited as long as they are near the positive electrode starting end portion. For example, in Figure 9 the wound electrode body 40 having the structure shown, a stacking shortage region 48 is formed between the positive electrode starting end portion 10s and the negative electrode starting end portion 20s in the direction in which the flat portion 40f extends (that is, the height direction Z). In this case, by providing the protruding portion 52e so as to press between the positive electrode starting end portion 10s and the negative electrode starting end portion 20s, an increase in the inter-pole distance in the stacking shortage region 48 can be prevented, and the precipitation of metallic Li can be appropriately suppressed. It should be noted that, in Figure 9 the wound electrode body 40 having the structure shown, a stacking shortage region 48 is generated near the bent portion 40r on the lower side in the height direction Z. However, the position where the stacking shortage region 48 is formed is not limited to the vicinity of the lower bent portion 40r. For example, in the case where the wound electrode body is manufactured in such a manner that the positive electrode starting end portion is disposed near the upper bent portion, the stacking shortage region is formed near the upper bent portion. In this case, by forming the protruding portion so as to press the vicinity of the upper bent portion, the precipitation of metallic Li can be appropriately suppressed. In addition, asFigure 10 As shown, even in the case of adopting a structure in which the negative electrode plate 20 is folded back at the bent portion 40r, a stacking shortage region 48 is formed near the positive electrode start end portion 10s. Specifically, in Figure 10 the wound electrode body 40 shown, a stacking shortage region 48 where the total number of stacked electrode plates is insufficient is generated between the negative electrode start end portion 20s of the folded-back negative electrode plate 20 and the positive electrode start end portion 10s. Therefore, in the wound electrode body 40 having this structure, the protruding portion 52e can also be formed in such a manner as to be able to press the vicinity of the positive electrode start end portion 10s. Thereby, precipitation of metallic Li in the vicinity of the stacking shortage region 48 can be appropriately suppressed.

[0106] In addition, the protruding dimension of the protruding portion 52e is preferably adjusted appropriately in consideration of the thickness of the positive electrode plate 10. Specifically, as Figure 9 and Figure 10 shown, in the stacking shortage region 48, generally, the number of stacked positive electrode plates 10 is one less than that in other regions. Therefore, the protruding dimension of the protruding portion 52e is preferably adjusted to be about the same as the thickness of the positive electrode plate 10. Thereby, poor pressing in the stacking shortage region 48 can be appropriately eliminated, and precipitation of metallic Li can be more appropriately suppressed. For example, the ratio of the protruding dimension of the protruding portion 52e to the thickness of the positive electrode plate 10 is preferably 0.25 to 1.75, more preferably 0.5 to 1.5, still more preferably 0.75 to 1.25, and particularly preferably 0.9 to 1.1. It should be noted that specifically, the protruding dimension of the protruding portion 52e is preferably 0.04 mm or more, more preferably 0.05 mm or more, still more preferably 0.07 mm or more, and particularly preferably 0.1 mm or more. On the other hand, from the viewpoint of reliably preventing breakage of the wound electrode body 40 caused by the protruding portion 52e, the upper limit of the protruding dimension of the protruding portion 52e is preferably 1 mm or less, more preferably 0.5 mm or less, still more preferably 0.3 mm or less. It should be noted that the "protruding dimension of the protruding portion" in this specification refers to the height of the apex of the protruding portion with respect to the straight line connecting the upper end and the lower end of the long side wall of the outer package.

[0107] In addition, as described above, in the wound electrode body 40 in the present embodiment, the positive electrode start end portion 10s is disposed near the bent portion 40r on the lower side in the height direction Z (refer to Figure 9)。In this case, the positive electrode terminal portion 10e is preferably disposed at a position close to the upper bending portion 40r. Thereby, it is possible to prevent the positive electrode start end portion 10s from approaching the positive electrode terminal portion 10e in the circumferential direction of the wound electrode body 40. Therefore, it is possible to make the surface pressure distribution uniform with respect to the flat portion 40f and generate a stable charge and discharge reaction. It should be noted that the relationship between the start end portion and the terminal end portion described above is the same for the negative electrode plate 20. That is, when the negative electrode start end portion 20s is disposed near the lower bending portion 40r in the height direction Z, the negative electrode terminal portion 20e is preferably disposed at a position close to the upper bending portion 40r.

[0108] It should be noted that, as in the present embodiment, the positive electrode terminal portion 10e and the negative electrode terminal portion 20e are preferably disposed at the bending portion 40r (for example, the upper bending portion 40r). Thereby, it is possible to prevent steps caused by the positive electrode terminal portion 10e and the negative electrode terminal portion 20e from being generated on the surface of the flat portion 40f. Therefore, it is possible to make the surface pressure distribution of the flat portion 40f more uniform. It should be noted that at the outermost periphery of the wound electrode body 40, the negative electrode terminal portion 20e preferably extends from the positive electrode terminal portion 10e in such a manner that the positive electrode terminal portion 10e is covered by the negative electrode plate 20. By making the negative electrode plate 20 longer than the positive electrode plate 10 in this way, the occlusion performance of the charge carriers on the negative electrode side is sufficiently ensured, and thus the Li precipitation resistance can be further improved. In addition, when the positive electrode start end portion 10s and the negative electrode start end portion 20s are disposed at the bending portion 40r, it is preferable to form an adhesive layer on the surface of the separator 30 (refer to Figure 7 ). Thereby, in the wound electrode body 40 after production, it is possible to prevent the positive electrode start end portion 10s and the negative electrode start end portion 20s from shifting from the bending portion 40r.

[0109] 2. Manufacturing method of secondary battery

[0110] Above, the structure of the secondary battery 100 of the present embodiment has been described. Next, an example of the manufacturing method of the secondary battery 100 will be described. It should be noted that the manufacturing method of the secondary battery 100 of the present embodiment includes (1) a winding step, (2) a forming step, (3) a housing step, and (4) a stamping step.

[0111] (1) Winding step

[0112] In this step, a cylindrical wound body is produced by winding the positive electrode plate 10 and the negative electrode plate 20 with the separator 30 interposed therebetween. Specifically, first, a laminate (refer to Figure 7)。At this time, the lamination positions of the respective sheet members are adjusted such that the positive electrode tab 12t protrudes from one side edge of the laminate and the negative electrode tab 22t protrudes from the other side edge. Then, the laminate is wound to produce a cylindrical wound body (cylindrical body).

[0113] (2) Forming process

[0114] In this process, the wound cylindrical body is press-formed to flatten the cylindrical body. Thereby, a flat wound electrode body 40 having a pair of bent portions 40r and a flat portion 40f is produced (refer to Figure 9 ). Then, as shown in Figure 8 , a winding fixing band 38 is pasted on the terminal portion 30e of the separator 30 disposed on the outermost peripheral surface. Thereby, the shape of the flat wound electrode body 40 is maintained. Here, in the conventional method for manufacturing a secondary battery, as a result of flattening the wound body in this process, the arrangement positions of the positive electrode start end portion 10s and the negative electrode start end portion 20s are displaced, and a lamination shortage region 48 where the total number of laminated electrode plates is insufficient is generated near the positive electrode start end portion 10s.

[0115] (3) Accommodation process

[0116] In this process, the flat wound electrode body 40 is accommodated inside the battery case 50. Specifically, as shown in Figure 6 , a positive electrode second current collector 72 is connected to the positive electrode tab group 42 of the wound electrode body 40, and a negative electrode second current collector 77 is connected to the negative electrode tab group 44. Then, as shown in Figure 5 , a plurality of (three in the figure) wound electrode bodies 40 are arranged with the flat portions 40f facing each other. Then, a sealing plate 54 is disposed above the plurality of wound electrode bodies 40, and the positive electrode tab group 42 of each wound electrode body 40 is bent so that the positive electrode second current collector 72 faces one side surface 40a of the wound electrode body 40. Thereby, the positive electrode first current collector 71 is connected to the positive electrode second current collector 72. Similarly, the negative electrode tab group 44 of each wound electrode body 40 is bent so that the negative electrode second current collector 77 faces the other side surface 40b of the wound electrode body 40. Thereby, the negative electrode first current collector 76 is connected to the negative electrode second current collector 77. As a result, the wound electrode body 40 is mounted on the sealing plate 54 via the positive electrode current collector 70 and the negative electrode current collector 75.

[0117] Next, the surface of the wound electrode body 40 mounted on the sealing plate 54 is covered with an electrode body holding member 98 (refer to Figure 3) It is housed inside the outer package 52 after covering. Moreover, the flat portion 40f of the wound electrode body 40 housed inside the outer package 52 faces the long side wall 52b (i.e., the flat surface of the battery case 50). After that, after blocking the opening 52h on the upper surface of the outer package 52 with the sealing plate 54, the battery case 50 is constructed by joining (welding) the outer package 52 and the sealing plate 54. After that, the electrolyte is injected into the inside of the battery case 50 from the liquid injection hole 55 of the sealing plate 54, and the liquid injection hole 55 is blocked with the sealing member 56. Thus, the inside of the battery case 50 is sealed.

[0118] (4) Stamping process

[0119] Next, in the manufacturing method of the present embodiment, a stamping process is performed in which the lamination shortage region 48 of the wound electrode body 40 housed in the battery case 50 is pressed from the outside of the battery case 50 to deform the battery case 50. As a result of performing this stamping process, a protruding portion 52e protruding toward the lamination shortage region 48 is formed on the inner surface of the battery case 50 (refer to Figure 3 ). In addition, a concave portion 52d corresponding to the protruding portion 52e is formed on the outer surface of the battery case 50 (refer to Figure 1 ). In this way, by forming the protruding portion 52e after housing the wound electrode body 40 in the battery case 50, it is possible to suppress the positional deviation between the lamination shortage region and the protruding portion during the housing process. Therefore, the Li precipitation resistance can be further improved. In addition, compared with the method of previously forming the protruding portion on the inner surface of the battery case (outer package), the housing of the wound electrode body into the inside of the battery case becomes easier. Therefore, it is also possible to contribute to the improvement of the manufacturing efficiency.

[0120] It should be noted that the pressing force in this process is preferably appropriately adjusted in such a way as to form a protruding portion with an appropriate protruding size in consideration of the rigidity of the battery case 50, etc. For example, in the case of using an aluminum battery case with a thickness of 0.8 mm, the pressing force in this process is preferably 3 kN or more, more preferably 6 kN or more, further preferably 8 kN or more, and particularly preferably 10 kN or more. On the other hand, the upper limit value of the pressing force in this process is not particularly limited as long as it is within the range where the battery case and the wound electrode body are not damaged. For example, the upper limit value of the pressing force can be 100 kN or less, can also be 50 kN or less, and can also be 30 kN or less.

[0121] <Other embodiments>

[0122] Above, one embodiment of the technology disclosed herein has been described. It should be noted that the above first embodiment shows an example of applying the technology disclosed herein and does not limit the technology disclosed herein. Hereinafter, other embodiments of the technology disclosed herein will be described.

[0123] (1) Second Embodiment

[0124] As described above, in the secondary battery 100 of the first embodiment, the protruding portion 52e is formed by performing stamping processing for pressing the lamination shortage region 48 from the outside of the battery case 50. Therefore, a recess 52d corresponding to the protruding portion 52e is formed on the outer surface of the battery case 50 (outer package 52) (see Figure 1 and Figure 3 ). However, the protruding portion 52e only needs to protrude toward at least a part of the lamination shortage region 48, and the forming means thereof is not particularly limited. For example, in the secondary battery 100A of the second embodiment shown in Figure 11 , the protruding portion 52e is mounted on the inner surface of the long side wall 52b of the outer package 52. In the secondary battery 100A having this structure, a recess as shown in Figure 3 is not formed on the outer surface of the battery case 50 (long side wall 52b of the outer package 52). Moreover, in the secondary battery 100A of this second embodiment, it is also possible to prevent poor pressing in the lamination shortage region 48 and appropriately suppress the precipitation of metallic Li.

[0125] (2) Third Embodiment

[0126] In addition, in the above first to second embodiments, the structure in which the protruding portion 52e provided on the battery case 50 presses the lamination shortage region 48 is adopted. However, the secondary battery disclosed herein only needs to have a structure capable of appropriately pressing the lamination shortage region of the wound electrode body, and a structure other than the protruding portion may also be adopted. Specifically, in the secondary battery 100B of the third embodiment shown in Figure 12 , a spacer 80 is disposed between the lamination shortage region 48 of the wound electrode body 40 and the battery case 50 (long side wall 52b of the outer package 52). In the secondary battery 100B of this third embodiment, when pressing in such a manner as to sandwich the long side wall 52b of the outer package 52, the lamination shortage region 48 is locally pressed by the spacer 80. Thereby, it is possible to prevent poor pressing in the lamination shortage region 48 and appropriately suppress the precipitation of metallic Li.

[0127] It should be noted that the material of the spacer 80 is not particularly limited, and a raw material having a prescribed rigidity can be used without particular limitation. It should be noted that if the possibility of internal short circuit is considered, the spacer 80 is preferably made of an insulating resin material. As a preferred example of the material of this spacer 80, hard resins such as polypropylene and polyethylene can be cited. In addition, as Figure 13As shown, the spacer 80 is preferably an adhesive tape 82 made of resin adhered to the outer surface of the flat portion 40f of the wound electrode body 40. By using such an adhesive tape 82 as the spacer 80, the positional deviation of the spacer 80 can be reliably prevented, and the poor pressurization of the insufficient lamination region 48 can be more reliably prevented. In addition, the dimensions (height dimension, thickness, width dimension) of the spacer 80 are preferably adjusted appropriately from the viewpoint of appropriately pressing the insufficient lamination region 48. It should be noted that the specific dimensions of the spacer 80 are the same as those of the protrusion 52e described above, so the detailed description is omitted. Figure 3 ) Similarly, from the viewpoint of appropriately pressing the insufficient lamination region 48, it is preferably adjusted appropriately.

[0128] In addition, the spacer may be formed on the electrode body holder (refer to the reference numeral 98 in Figure 12 ) that houses the wound electrode body. Such an electrode body holder is usually manufactured by folding an insulating resin sheet. At this time, by folding the resin sheet in such a way that a plurality of resin sheets are laminated at positions facing the insufficient lamination region, a spacer for pressing the insufficient lamination region can be easily formed. In addition, in the structure shown in Figure 12 , a spacer 80 is disposed between the electrode body holder 98 and the wound electrode body 40, but the spacer may also be disposed between the battery case (outer package) and the electrode body holder. Even in this case, the insufficient lamination region can be appropriately pressed via the electrode body holder, so the precipitation of metallic Li can be appropriately suppressed.

[0129] (4) Fourth Embodiment

[0130] In the above first to third embodiments, protrusions 52e or spacers 80 are provided on both outer sides in the depth direction X, and the insufficient lamination regions 48 of a plurality of wound electrode bodies 40 are pressed in such a way as to be sandwiched from both outer sides in the depth direction X. Even in this case, an appropriate pressure can be applied to the insufficient lamination regions 48 of each of the plurality of wound electrode bodies 40, and the precipitation of metallic Li can be sufficiently suppressed. However, from the viewpoint of directly pressing the insufficient lamination region of the wound electrode body arranged in the center in the depth direction and further improving the Li precipitation resistance, it is preferable to arrange an intermediate spacer between the insufficient lamination regions of two adjacent wound electrode bodies. Specifically, in Figure 14In the secondary battery 100C of the fourth embodiment shown, three wound electrode bodies 40A to 40C are housed in the battery case 50. Moreover, an intermediate spacer 85 is disposed between the wound electrode bodies 40A and 40B, and an intermediate spacer 85 is disposed between the wound electrode bodies 40B and 40C. Thereby, it is possible to directly press the stacking shortage regions 48 of the plurality of wound electrode bodies 40A to 40B, respectively, and thus it is possible to more appropriately suppress the precipitation of metallic Li. Note that, similar to the above-described spacer 80, the intermediate spacer 85 can be made of a raw material having a predetermined rigidity (e.g., a hard resin) without particular limitation. In addition, the specific dimensions of the intermediate spacer 85 overlap with the specific dimensions of the above-described protrusion 52e and spacer 80, and thus detailed description thereof is omitted.

[0131] (5) Regarding other structures

[0132] The secondary battery disclosed herein may also appropriately modify various structures other than the above-described protrusion and spacer. For example, the technology disclosed herein can be particularly suitable for high-capacity secondary batteries. Specifically, in order to construct a high-capacity secondary battery, it is required to increase the packing density of the positive electrode active material layer and increase the positive electrode capacity. In this case, the ratio of the capacity of the negative electrode to the capacity of the positive electrode (opposite capacity ratio: negative electrode capacity / positive electrode capacity) decreases, and thus metallic Li is likely to precipitate on the surface of the negative electrode active material layer. In contrast, according to the technology disclosed herein, it is possible to improve the Li precipitation resistance, and thus it is possible to achieve a high density of the positive electrode active material layer, which has been difficult to achieve in the past, and contribute to the construction of a high-capacity secondary battery. For example, according to the technology disclosed herein, even in the case of using a wound electrode body having a packing density of the positive electrode active material layer of 3.4 g / cc or more (e.g., 3.6 g / cc) and an opposite capacity ratio of 1.1 or less (e.g., 1.08), it is possible to appropriately suppress the precipitation of metallic Li.

[0133] In addition, in the case of constructing a high-capacity secondary battery, the winding electrode body is also enlarged. In such a large winding electrode body 40, it is difficult to apply uniform surface pressure to the entire flat portion 40f with an increased area, and thus, precipitation of metallic Li is likely to occur. However, according to the technology disclosed herein, even when using such a large winding electrode body 40, poor pressing in the insufficient lamination region 48 can be prevented, and thus, precipitation of metallic Li can be suppressed. As an example, the width dimension of the above-mentioned large winding electrode body 40 is preferably 200 mm to 400 mm, more preferably 250 mm to 350 mm, still more preferably 260 mm to 320 mm, and, for example, about 300 mm. In addition, the height dimension is preferably 60 mm to 120 mm, more preferably 70 mm to 110 mm, particularly preferably 80 mm to 100 mm, and, for example, about 85 mm. In addition, the thickness is preferably 5 mm to 25 mm, more preferably 8 mm to 20 mm, particularly preferably 10 mm to 15 mm. It should be noted that the "width dimension of the winding electrode body" refers to the length of the coating region of the positive electrode active material layer in the direction in which the winding axis WL extends (i.e., the width direction Y). In addition, the "height dimension of the winding electrode body" refers to the dimension in the direction perpendicular to the winding axis and perpendicular to the thickness direction (depth direction X) (i.e., the height direction Z).

[0134] [Test Example]

[0135] Hereinafter, test examples related to the technology disclosed herein will be described. It should be noted that the content of the test examples described below is not intended to limit the technology disclosed herein.

[0136] 1. Fabrication of Each Sample

[0137] (1) Sample 1

[0138] In this experiment, a laminate was fabricated by laminating a positive electrode plate and a negative electrode plate with two separator films in between, and the laminate was wound and then press-formed to produce a flat-shaped wound electrode body. First, a positive electrode plate was prepared, on both sides of which a positive electrode active material layer (with a thickness of 60 μm and a width of 280 mm) was formed on a positive electrode core (aluminum foil with a thickness of 13 μm). In the positive electrode active material layer of this positive electrode plate, the positive electrode active material, a conductive material, and a binder were contained in a ratio of 97.5:1.5:1.0. It should be noted that the positive electrode active material used was a lithium nickel cobalt manganese-based composite oxide (NCM). In addition, the conductive material used was acetylene black (AB). Moreover, the binder used was polyvinylidene fluoride (PVdF). On the other hand, a negative electrode plate was used, on both sides of which a negative electrode active material layer (with a thickness of 80 μm and a width of 285 mm) was formed on a negative electrode core (copper foil with a thickness of 8 μm). In the negative electrode active material layer of this negative electrode plate, the negative electrode active material, a thickening agent, and a binder were contained in a ratio of 98.3:0.7:1.0. It should be noted that the negative electrode active material used was graphite, the thickening agent used was carboxymethyl cellulose (CMC), and the binder used was styrene butadiene rubber (SBR). Moreover, the separator used was a resin sheet made of polyethylene (PE).

[0139] Next, a laminate was fabricated by laminating a positive electrode plate and a negative electrode plate with a separator film in between, and the laminate was wound to produce a cylindrical body. It should be noted that the number of winding times in this experiment was set to 33 times. Next, press-forming was carried out to flatten the wound cylindrical body, thereby producing a flat-shaped wound electrode body. Here, in the wound electrode body 40 of this experiment, as Figure 9 shown, the negative electrode starting end portion 20s was extended toward the bending portion 40r side, and a lamination shortage region 48 was generated near the positive electrode starting end portion 10s. Next, after connecting the wound electrode body 40 to an electrode terminal, it was housed in a battery case. Next, after injecting a non-aqueous electrolyte into the battery case, the battery case was sealed, thereby constructing a test-use lithium ion secondary battery. It should be noted that the non-aqueous electrolyte used in this experiment was prepared by dissolving a supporting electrolyte (LiPF6) at a concentration of 1 mol / L in a non-aqueous solvent obtained by mixing EC, DMC, and EMC in a volume ratio of 3:4:3.

[0140] Next, in this experiment, for the lamination shortage region of the constructed test-use battery, linear press-working was carried out from the outside of the battery case along the width direction. Here, in Sample 1, the pressure of the press-working was set to 3 kN. However, no deformation was confirmed in the battery case after the press-working.

[0141] (2) Sample 2

[0142] In Sample 2, a test battery was constructed in the same steps as in Sample 1, except that the stamping pressure was changed to 6 kN. In the battery of this Sample 2, it was confirmed that a recess with a depth of 0.044 mm was formed on the outer surface of the battery case after stamping. That is, it can be understood that a protrusion with a protrusion size of 0.044 mm was formed on the inner surface of the battery case of Sample 2.

[0143] (3) Sample 3

[0144] In Sample 3, a test battery was constructed in the same steps as in Samples 1 and 2, except that the stamping pressure was changed to 10 kN. In the battery of this Sample 3, it was confirmed that a recess with a depth of 0.101 mm was formed on the outer surface of the battery case after stamping. That is, it can be understood that a protrusion with a protrusion size of 0.101 mm was formed on the inner surface of the battery case of Sample 3.

[0145] 2. Evaluation test

[0146] In this evaluation, the test batteries of each sample were placed in an environment of 20 °C, and the cycle charge and discharge of repeatedly performing CC charge and CC discharge under specified conditions were repeated 1,000 times. It should be noted that in the CC charge in this evaluation test, charging was performed at a charging rate of 1C for 100 seconds. On the other hand, in the CC discharge, discharging was performed at a discharging rate of 1C for 100 seconds. Then, after performing the above cycle charge and discharge, the battery was discharged until the SOC became 0%, and the test battery was disassembled to recover the negative electrode plate. Then, it was visually observed whether metallic Li was precipitated on the surface of the negative electrode active material layer. The test results are as Figures 15 to 17 shown. It should be noted that Figure 15 is a photograph showing the result of the Li precipitation resistance evaluation of Sample 1. In addition, Figure 16 is a photograph showing the result of the Li precipitation resistance evaluation of Sample 2. Moreover, Figure 17 is a photograph showing the result of the Li precipitation resistance evaluation of Sample 3.

[0147] First, as Figure 15 shown, in Sample 1, it was confirmed that a large amount of metallic Li was precipitated on the surface of the negative electrode active material layer in a manner along the stacking deficiency region extending in the winding axis direction. On the other hand, as Figure 16 and Figure 17 shown, in Samples 2 and 3, the precipitation of metallic Li in the stacking deficiency region was suppressed. From this, it can be known that by forming a protrusion on the inner surface of the battery case and locally pressing the stacking deficiency region with this protrusion, the precipitation of metallic Li near the stacking deficiency region can be suppressed. And, as Figure 17As shown, in Sample 3, the precipitation of metallic Li was not confirmed at all. From this, it can be seen that the protruding height of the protruding portion is preferably 0.05 mm or more, more preferably 0.1 mm or more.

[0148] The present invention has been described in detail above, but the above description is merely illustrative. That is, the technology disclosed herein includes technologies obtained by various modifications and changes to the above specific examples.

Claims

1. A secondary battery, comprising: a flat wound electrode body formed by winding a positive electrode plate and a negative electrode plate with a separator interposed therebetween, and a battery case housing the wound electrode body, characterized in that the flat wound electrode body has: a pair of bent portions with a curved outer surface and a flat portion with a flat outer surface connecting the pair of bent portions; one end in the longitudinal direction of the positive electrode plate is disposed inside the wound electrode body as a positive electrode starting end, and the other end is disposed outside the wound electrode body as a positive electrode terminal end, and one end in the longitudinal direction of the negative electrode plate is disposed inside the wound electrode body as a negative electrode starting end, and the other end is disposed outside the wound electrode body as a negative electrode terminal end; the positive electrode starting end is disposed inside the flat portion; the negative electrode starting end extends closer to one of the pair of bent portions than the positive electrode starting end; in the vicinity of the positive electrode starting end in the flat portion, a lamination shortage region where the total number of laminations of the positive electrode plate and the negative electrode plate in the thickness direction of the wound electrode body is less than that in other regions of the flat portion is formed; a protrusion protruding toward at least a part of the lamination shortage region is formed on the inner surface of the battery case and a recess corresponding to the protrusion is formed on the outer surface of the battery case, or a spacer is disposed between at least a part of the lamination shortage region and the battery case and the spacer is an adhesive tape adhered to the outer surface of the flat portion of the wound electrode body, or a spacer is disposed between at least a part of the lamination shortage region and the battery case and the wound electrode body is housed inside the battery case in a state of being covered by an electrode body holding member made of an insulating resin sheet and the spacer is a protrusion formed on the electrode body holding member.

2. The secondary battery according to claim 1, characterized in that the lamination shortage region is formed between the positive electrode starting end and the negative electrode starting end in the direction along the flat portion.

3. The secondary battery according to claim 1 or 2, characterized in that the protrusion or the spacer extends along the winding axis of the wound electrode body.

4. The secondary battery according to claim 1 or 2, characterized in that the length of the lamination shortage region in the direction along the flat portion is 5 mm or less.

5. The secondary battery according to claim 4, characterized in that the size of the protrusion or the spacer in the direction along the flat portion is 5 mm or less.

6. The secondary battery according to claim 1 or 2, characterized in that the protruding size of the protrusion protruding from the inner surface of the battery case or the thickness of the spacer is 0.04 mm or more.

7. The secondary battery according to claim 1 or 2, characterized in that a plurality of the wound electrode bodies are housed in the battery case.

8. The secondary battery according to claim 7, characterized in that an intermediate spacer is disposed between the lamination shortage regions of two adjacent wound electrode bodies.

9. A method for manufacturing a secondary battery, which is a method for manufacturing a secondary battery in which a wound electrode body is housed inside a battery case, characterized in that, The manufacturing method of the secondary battery includes: a winding step of manufacturing a cylindrical wound body obtained by winding a positive electrode plate and a negative electrode plate with a separator therebetween; a forming step of subjecting the cylindrical wound body to pressure forming to manufacture a flat wound electrode body; and a housing step of housing the flat wound electrode body inside the battery case, wherein the flat wound electrode body has a pair of curved portions with curved outer surfaces and a flat portion with a flat outer surface connecting the pair of curved portions, one end in the length direction of the positive electrode plate is disposed inside the wound electrode body as a positive electrode starting end, and the other end is disposed outside the wound electrode body as a positive electrode terminal end, and one end in the length direction of the negative electrode plate is disposed inside the wound electrode body as a negative electrode starting end, and the other end is disposed outside the wound electrode body as a negative electrode terminal end, the positive electrode starting end is disposed inside the flat portion, the negative electrode starting end extends closer to one of the pair of curved portions than the positive electrode starting end, in the vicinity of the positive electrode starting end in the flat portion, a stacking shortage region where the total number of stacked layers of the positive electrode plate and the negative electrode plate in the thickness direction of the wound electrode body is smaller than in other regions of the flat portion is formed, here, after the housing step, a pressing step is performed, in which the stacking shortage region of the wound electrode body housed in the battery case is pressed from the outside of the battery case to deform the battery case, thereby forming a protruding portion protruding toward the stacking shortage region.

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