Secondary battery

Abstract

According to the present disclosure, a secondary battery capable of more appropriately suppressing precipitation of metallic lithium is provided. The secondary battery disclosed herein has a flat wound electrode body (40). The wound electrode body has a pair of curved portions (40r1, 40r2) and a flat portion (40f). Also, a positive electrode initial end portion (20s) inside the wound electrode body has a first region (17) extending along the flat portion. On the other hand, a negative electrode initial end portion inside the wound electrode body has a second region (27) extending along the flat portion, a turn-back portion (28) turned back from an end portion of the second region, and a third region (29) extending along the flat portion from an end portion of the turn-back portion. Also, the wound electrode body has an electrode initial end laminated portion (48) in which the first region, the second region, and the third region overlap. According to this structure, it is possible to prevent local poor pressing in the flat portion and to suppress precipitation of metallic lithium.

Description

Technical Field

[0001] This invention relates to secondary batteries. Background Technology

[0002] Secondary batteries, such as lithium-ion batteries, have an electrode body with a pair of electrode plates (positive and negative). As an example of this electrode body, a wound electrode body can be described as one formed by winding a long strip of positive and negative electrode plates together with a separator. In this wound electrode body, one end (starting end) of each electrode plate is disposed inside the electrode body, and the other end (ending end) is disposed outside the electrode body. Furthermore, the shape of this wound electrode body can be formed into a flat shape. This flat wound electrode body has a pair of curved portions with a bent outer surface and a flat portion connecting the pair of curved portions with a flat outer surface.

[0003] Patent Document 1 discloses an example of a secondary battery having the aforementioned flat-shaped wound electrode body. In the secondary battery described in Patent Document 1, the inner winding end of the positive electrode (positive electrode start end) and the inner winding end of the negative electrode (negative electrode start end) are disposed inside the flat portion of the wound electrode body. Furthermore, the inner winding end of the negative electrode has an extension that extends towards the curved portion side compared to the inner winding end of the positive electrode, and this extension of the negative electrode is folded back within a range that does not overlap with the positive electrode. According to the secondary battery described in Patent Document 1, since the thickness deviation at the flat portion of the electrode body is suppressed, the electrode body can be easily housed in the battery casing. In addition, deviations in the distance (inter-electrode distance) between the positive and negative electrodes can also be suppressed, thus also having the effect of suppressing the deposition of metallic lithium (metallic Li) caused by deviations in the charge-discharge reaction.

[0004] Existing technical documents

[0005] Patent documents

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

[0007] The problem that the invention aims to solve

[0008] Furthermore, in recent years, there has been an increasing demand for improved durability and longer lifespan in secondary batteries, requiring technologies that can more effectively suppress lithium metal deposition. This invention was made in view of these requirements, and its object is to provide a secondary battery capable of effectively suppressing lithium metal deposition.

[0009] Technical solutions for solving the problem

[0010] To achieve the above objectives, a secondary battery with the following structure is provided using the technology 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 separated by a separator, and a battery casing housing the wound electrode body. The flat wound electrode body of the secondary battery has a pair of curved portions with a curved outer surface and a flat portion connecting the pair of curved portions and having a flat outer surface. One end of the positive electrode plate along its long side is disposed inside the wound electrode body as the positive electrode start end, and the other end is disposed outside the wound electrode body as the positive electrode end. Similarly, one end of the negative electrode plate along its long side is disposed inside the wound electrode body as the negative electrode start end, and the other end is disposed outside the wound electrode body as the negative electrode end. Furthermore, in the secondary battery disclosed herein, the positive electrode start end has a first region extending along the flat portion, the negative electrode start end has a second region extending along the flat portion, a folded-back portion folded back from the end of the second region along the curved portion, and a third region extending along the flat portion from the end of the folded-back portion. The wound electrode body has an electrode start end stacked portion where the first, second, and third regions overlap in the thickness direction.

[0012] Such secondary batteries are typically used by pressurizing the flat portion of the wound electrode body from the outside of the battery casing to reduce the distance (inter-electrode distance) between the positive and negative electrode plates inside the electrode body. However, in flat wound electrode bodies, the flat portion near the bend sometimes has a lower number and thinner layer of sheet-like components (positive electrode plate, negative electrode plate, separator) compared to other areas. In this case, poor pressurization occurs in a part of the flat portion, which may promote the precipitation of metallic Li due to the local increase in the inter-electrode distance. In contrast, in the secondary battery disclosed here, the negative electrode plate (the beginning of the negative electrode) is folded back along the bend to form an electrode beginning stack where the first region of the positive electrode plate, the second region of the negative electrode plate, and the third region of the negative electrode plate overlap. This prevents poor pressurization in the flat portion near the bend and suppresses the precipitation of metallic Li due to the local increase in the inter-electrode distance.

[0013] In one embodiment of the secondary battery disclosed herein, the length of the electrode start-layer stack in the long side direction of the positive electrode plate is 0.5 mm to 10 mm. This allows for more appropriate prevention of localized poor pressurization at the flat portion and more appropriate improvement in Li precipitation resistance.

[0014] In one embodiment of the secondary battery disclosed herein, a plurality of wound electrode bodies are housed within a battery casing. An increase in the inter-electrode distance caused by the aforementioned localized pressurization defects may occur in each of the plurality of wound electrode bodies. Therefore, the technology disclosed herein can be suitably applied to high-capacity secondary batteries having a plurality of wound electrode bodies.

[0015] Furthermore, in the configuration of having multiple wound electrode bodies, it is preferable that the length of the electrode start-layer stack in the long side direction of the positive electrode plate is different in each of the multiple wound electrode bodies. This helps to uniformly distribute the surface pressure at the flat portions of each wound electrode body when pressure is simultaneously applied to all the multiple wound electrode bodies from the outside of the battery casing.

[0016] In one embodiment of the secondary battery disclosed herein, the positive electrode starting end is positioned close to one of the bends of a pair of bends, and the positive electrode terminal end is positioned closer to the other bend than the positive electrode starting end. This prevents thickness variations caused by the proximity of the positive electrode starting end and the positive electrode terminal end, contributing to the homogenization of surface pressure distribution in the flat portion. Furthermore, in this embodiment, it is preferable that at least one of the positive electrode terminal end and the negative electrode terminal end is positioned at the bend of the other. This prevents step differences from forming on the surface of the flat portion of the wound electrode body, thus further contributing to the homogenization of surface pressure distribution in the flat portion.

[0017] In one embodiment of the secondary battery disclosed herein, the separator has a porous substrate layer made of resin and a porous surface layer formed on the surface of the porous substrate layer and comprising ceramic particles and a binder. In this embodiment, it is preferable that the porosity of the porous surface layer in the region not facing the negative and positive electrode plates is 30% to 60%. The separator, having a porous surface layer with a porosity in the range of 30% to 60%, is deformed by being flattened during the stamping process of the wound electrode body, and can function as a buffer to absorb thickness deviations of the wound electrode body. Therefore, by using a separator with a porous surface layer having the aforementioned porosity, step differences can be prevented on the surface of the flat portion of the wound electrode body, thus contributing to the homogenization of surface pressure distribution in the flat portion. Furthermore, the porosity of the porous surface layer of the separator before stamping can be investigated by measuring the porosity of the porous surface layer in the region not facing the negative and positive electrode plates.

[0018] Furthermore, in the use of a separator with a porous surface layer, it is preferable that the thickness of the porous substrate layer in the separator sandwiched between the positive and negative electrode plates is 60% or less of the thickness of the porous substrate layer in the region not facing the negative and positive electrode plates. By performing stamping in such a way that the thickness of the porous substrate layer after pressurization is 60% or less of that before pressurization, deviations in the thickness of the wound electrode body can be appropriately absorbed.

[0019] In one embodiment of the secondary battery disclosed herein, the wound electrode body is manufactured by winding a laminate in which a first separator, a negative electrode plate, a second separator, and a positive electrode plate are sequentially stacked. Furthermore, in this embodiment, it is preferable that a first extension extending from the negative electrode starting end is formed at one end of the first separator along its long side, and a second extension extending from the negative electrode starting end is formed at one end of the second separator along its long side. This allows for a more uniform surface pressure distribution across the entire flat area, improving the Li precipitation resistance of the entire flat surface.

[0020] Furthermore, in the method of forming the first extension and the second extension, it is preferable that each of the first extension and the second extension is folded back along at least one of the pair of bends to form a diaphragm stack where only the first diaphragm and the second diaphragm are stacked. This allows for further homogenization of the surface pressure distribution at the flat portion, further improving Li precipitation resistance.

[0021] Furthermore, in the method of forming the diaphragm stack, it is preferable that the first diaphragm layer has three or more layers and the second diaphragm layer has two or more layers. This allows for a more uniform surface pressure distribution in the flat portion.

[0022] Furthermore, in the embodiment comprising a first diaphragm and a second diaphragm, it is preferable to have an adhesive layer provided on the surface of at least one of the first diaphragm and the second diaphragm. This prevents diaphragm positional displacement from occurring inside the wound electrode body. Additionally, in this embodiment, it is preferable to form mesh-like protrusions on the surface of the adhesive layer. This facilitates deformation of the adhesive layer during stamping, thereby absorbing thickness deviations in the wound electrode body.

[0023] In one embodiment of the secondary battery disclosed herein, a separator is sandwiched between a second region and a third region at the beginning of the negative electrode, and the distance between the second and third regions in the thickness direction of the electrode body is smaller than the thickness of the negative electrode plate. By reducing the gap between the second and third regions in this way, the structural pressure applied to the electrode body can be made more uniform.

[0024] Furthermore, in the method of sandwiching the diaphragm between the second and third regions, it is preferable that the value obtained by subtracting the total thickness of the diaphragm sandwiched between the second and third regions from the distance between the second and third regions in the thickness direction of the wound electrode body is 50 μm or less. This further reduces the gap between the second and third regions. Additionally, in this method, it is preferable that three or more diaphragm layers are sandwiched between the second and third regions at the beginning of the negative electrode.

[0025] In one embodiment of the secondary battery disclosed herein, the positive electrode plate comprises a positive electrode core as a strip-shaped metal foil and a positive electrode active material layer applied to the surface of the positive electrode core, and the negative electrode plate comprises a negative electrode core as a strip-shaped metal foil and a negative electrode active material layer applied to the surface of the negative electrode core. In this embodiment, it is preferable to form a positive electrode tab assembly with exposed positive electrode tabs of the positive electrode core stacked at one end in the winding axis direction of the winding electrode body, and a negative electrode tab assembly with exposed negative electrode tabs of the negative electrode core stacked at the other end in the winding axis direction of the winding electrode body. This increases the volume of the charge / discharge region relative to the internal capacity of the battery casing, thus contributing to improved battery performance.

[0026] Furthermore, in the embodiment of the above-described positive electrode active material layer, it is preferable that the width of the positive electrode active material layer is 200 mm to 400 mm. The technology disclosed herein is particularly suitable for secondary batteries having wound electrode bodies of this size.

[0027] In one embodiment of the secondary battery disclosed herein, the height of the wound electrode body is 60 mm to 120 mm. The technology disclosed herein is particularly suitable for secondary batteries having wound electrode bodies of this size.

[0028] In one embodiment of the secondary battery disclosed herein, the thickness of the wound electrode body is 5 mm to 25 mm. The technology disclosed herein is particularly suitable for secondary batteries having wound electrode bodies of this size.

[0029] The thickness of the positive electrode plate is 65% to 95% of the thickness of the negative electrode plate. This allows for the achievement of optimal electrode thickness and pressure. Attached Figure Description

[0030] Figure 1 This is a perspective view schematically illustrating one embodiment of a secondary battery.

[0031] Figure 2 It is along Figure 1 A schematic longitudinal section view of line II-II in the diagram.

[0032] Figure 3 It is along Figure 1 A schematic longitudinal section view of line III-III in the diagram.

[0033] Figure 4 It is along Figure 1 A schematic cross-sectional view of line IV-IV in the diagram.

[0034] Figure 5 It is a schematic perspective view of the electrode body installed on the sealing plate.

[0035] Figure 6 It is a perspective view schematically showing an electrode body with a positive second collector and a negative second collector installed.

[0036] Figure 7 This is a schematic diagram showing the structure of a wound electrode body of a secondary battery according to one embodiment.

[0037] Figure 8 It is shown schematically. Figure 7 Front view of the wound electrode body.

[0038] Figure 9 It is along Figure 8 A schematic longitudinal section view of the IX-IX line.

[0039] Figure 10 This is a schematic longitudinal sectional view of the wound electrode body of a secondary battery according to another embodiment.

[0040] Figure 11 This is a schematic longitudinal sectional view of the wound electrode body of a secondary battery according to another embodiment.

[0041] Figure 12 This is a schematic longitudinal sectional view showing the vicinity of the bend in a conventionally wound electrode body.

[0042] Figure 13 This is a schematic cross-sectional view showing the area near the bend of a conventionally wound electrode.

[0043] Figure 14 This is a photograph of pressure-sensitive paper showing the results of the surface pressure distribution evaluation of sample 1.

[0044] Figure 15 This is a photograph of pressure-sensitive paper showing the results of the surface pressure distribution evaluation of sample 2.

[0045] Figure 16 This is a photograph of pressure-sensitive paper showing the results of the surface pressure distribution evaluation of sample 3.

[0046] Figure 17 This is a photograph of pressure-sensitive paper showing the results of the surface pressure distribution evaluation of sample 4.

[0047] Explanation of reference numerals in the attached figures

[0048] 10 Positive electrode plate

[0049] 10e Positive terminal section

[0050] 10s Positive electrode start end

[0051] 17 First District

[0052] 20 Negative electrode plate

[0053] 20e Negative terminal section

[0054] 20s negative electrode start end

[0055] 27 Second Region

[0056] 28 Turnaround Section

[0057] 29 Third District

[0058] 30 Diaphragm

[0059] 32 First diaphragm

[0060] 32e First Extension

[0061] 34 Second diaphragm

[0062] 34e Second Extension

[0063] 40. Winded electrode body

[0064] 40f Flat section

[0065] The curved part on the upper side of 40r1

[0066] The curved part on the lower side of 40r2

[0067] 48 Electrode start-up stack

[0068] 49. Diaphragm laminate

[0069] 50 Battery casing

[0070] 100 Secondary Battery. Detailed Implementation

[0071] The embodiments of the technology disclosed herein will now be described with reference to the accompanying drawings. It should be noted that matters necessary for implementing the technology disclosed herein, other than those specifically mentioned in this specification (e.g., the general structure and manufacturing process of a battery), can be understood by those skilled in the art based on prior art in this field. This invention can be implemented based on the content disclosed in this specification and common technical knowledge in this field. Furthermore, the expression "A to B" indicating scope in this specification includes the meaning of "A or more and B or less," and also includes the meanings of "preferably greater than A" and "preferably less than B."

[0072] Furthermore, in this specification, "secondary battery" refers to an energy storage device that generates a charging and discharging reaction by the movement of charge carriers via an electrolyte between a pair of electrodes (positive and negative). The technology disclosed herein can be applied to the use of lithium-ion batteries (Li... +As a charge carrier, it can be used as a secondary battery (typically a lithium-ion secondary battery) to deposit metallic lithium (Li) through charge-discharge reactions.

[0073] In addition, in the figures referenced in this specification, reference numeral X indicates "depth direction," reference numeral Y indicates "width direction," and reference numeral Z indicates "height direction." Furthermore, in the depth direction X, F indicates "front," and Rr indicates "rear." In the width direction Y, L indicates "left," and R indicates "right." And in the height direction Z, U indicates "up," and D indicates "down." However, these directions are determined for ease of explanation and are not intended to limit the installation method when using the secondary battery disclosed herein.

[0074] Secondary batteries

[0075] The following is for reference Figures 1-9 One embodiment of the secondary battery disclosed herein will be described. Figure 1 This is a schematic perspective view of the secondary battery according to this embodiment. Figure 2 It is along Figure 1 A schematic longitudinal section view of line II-II in the diagram. Figure 3 It is along Figure 1 A schematic longitudinal section view of line III-III in the diagram. Figure 4 It is along Figure 1 A schematic cross-sectional view of line IV-IV in the diagram. Figure 5 It is a schematic perspective view of the electrode body installed on the sealing plate. Figure 6 It is a perspective view schematically showing an electrode body with a positive second collector and a negative second collector installed. Figure 7 This is a schematic diagram showing the structure of the wound electrode body of the secondary battery according to this embodiment. Figure 8 It is shown schematically. Figure 7 Front view of the wound electrode body. Figure 9 It is along Figure 8 A schematic longitudinal sectional view of line IX-IX in the diagram. Furthermore, for ease of explanation, in... Figure 9 The diaphragm 30 is omitted (see reference). Figure 7 Records (etc.).

[0076] like Figure 2 As shown, the secondary battery 100 of this embodiment includes a wound electrode body 40 and a battery casing 50 that houses the wound electrode body 40. The specific structure of this secondary battery 100 will be described below.

[0077] (1) Battery casing

[0078] The battery casing 50 is a frame that houses the wound electrode body 40. Although not shown in the diagram, a non-aqueous electrolyte is also contained inside the battery casing 50. Figure 1 As shown, the battery casing 50 in this embodiment has a flat, bottomed cuboid shape (square). Furthermore, conventionally known materials can be used in the battery casing 50 without particular limitations. For example, the battery casing 50 can be made of metal. Examples of materials for the battery casing 50 include aluminum, aluminum alloys, iron, and iron alloys.

[0079] The battery casing 50 includes an outer body 52 and a sealing plate 54. The outer body 52 is a flat, bottomed, square container with an opening 52h on its upper surface. Figure 1 and Figure 2 As shown, the outer casing 52 has a generally rectangular bottom wall 52a, a pair of long side walls 52b extending upward in the height direction Z from the long side of the bottom wall 52a, and a pair of short side walls 52c extending upward in the height direction Z from the short side of the bottom wall 52a. On the other hand, the sealing plate 54 is a generally rectangular plate-shaped member that closes the opening 52h of the outer casing 52. Furthermore, the outer periphery of the sealing plate 54 is joined (e.g., welded) to the outer periphery of the opening 52h of the outer casing 52. Thus, a battery casing 50 with its interior airtightly sealed is created. Additionally, the sealing plate 54 is provided with an injection hole 55 and a gas vent valve 57. The injection hole 55 is a through hole provided for injecting a non-aqueous electrolyte into the sealed battery casing 50. Furthermore, the injection hole 55 is sealed by the sealing member 56 after the non-aqueous electrolyte is injected. In addition, the gas discharge valve 57 is a thin-walled part designed to break (open) and discharge the gas when a large amount of gas is generated inside the battery casing 50.

[0080] (2) Non-aqueous electrolyte

[0081] As described above, inside the battery casing 50, in addition to the wound electrode body 40, a non-aqueous electrolyte (not shown) is also contained. For the non-aqueous electrolyte, conventionally known non-aqueous electrolytes used in secondary batteries can be used without particular limitation. For example, the non-aqueous electrolyte is prepared by dissolving a supporting salt in a non-aqueous solvent. Examples of non-aqueous solvents include carbonate solvents such as ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate. Examples of supporting salts include fluorinated lithium salts such as LiPF6.

[0082] (3) Electrode terminals

[0083] Additionally, on one side of the width direction Y of the sealing plate 54 ( Figure 1 , Figure 2A positive terminal 60 is mounted on the left end of the battery casing 50. This positive terminal 60 is connected to a plate-shaped external positive electrode conductive member 62 on the outside of the battery casing 50. On the other hand, on the other side of the sealing plate 54 in the width direction Y... Figure 1 , Figure 2 A negative terminal 65 is installed at the right end of the battery. A plate-shaped external conductive member 67 is installed on the negative terminal 65. These external conductive members (positive external conductive member 62 and negative external conductive member 67) are connected to other secondary batteries and external devices via external connecting members (busbars, etc.). Furthermore, the external conductive members are preferably made of a metal with excellent conductivity (aluminum, aluminum alloy, copper, copper alloy, etc.).

[0084] (4) Electrode collector

[0085] like Figures 3-5 As shown, in the secondary battery 100 of this embodiment, a plurality (3) of wound electrode bodies 40 are housed within the battery casing 50. Each wound electrode body 40 is provided with a positive electrode tab group 42 and a negative electrode tab group 44, the details of which will be described later. The positive terminal 60 is connected to the positive electrode tab group 42 of each of the plurality of wound electrode bodies 40 via a positive current collector 70. Specifically, the positive current collector 70 is housed inside the battery casing 50. Figure 2 and Figure 5 As shown, the positive electrode current collector 70 includes a plate-shaped conductive member extending along the inner side of the sealing plate 54 in the width direction Y, namely the first positive electrode current collector 71, and plate-shaped conductive members extending along the height direction Z, namely a plurality of second positive electrode current collectors 72. Furthermore, the lower end 60c of the positive terminal 60 is inserted into the battery casing 50 through the terminal insertion hole 58 of the sealing plate 54, and connected to the first positive electrode current collector 71 (see reference). Figure 2 On the other hand, such as Figures 4-6 As shown, in this secondary battery 100, a number of positive electrode second current collectors 72 are provided, corresponding to the number of wound electrode bodies 40. Each positive electrode second current collector 72 is connected to the positive electrode tab group 42 of the wound electrode body 40. Furthermore, as... Figure 4 and Figure 5 As shown, the positive electrode tab assembly 42 of the wound electrode body 40 is bent such that the second positive electrode current collector 72 faces one side 40a of the wound electrode body 40. Thus, the upper end of the second positive electrode current collector 72 is electrically connected to the first positive electrode current collector 71.

[0086] On the other hand, the negative terminal 65 is connected to the negative electrode tabs 44 of each of the plurality of wound electrode bodies 40 via the negative electrode current collector 75. The connection structure on the negative side is substantially the same as the connection structure on the positive side described above. Specifically, the negative electrode current collector 75 has a plate-shaped conductive member extending along the inner side of the sealing plate 54 in the width direction Y, namely the negative electrode first current collector 76, and plate-shaped conductive members extending along the height direction Z, namely the plurality of negative electrode second current collectors 77 (see reference). Figure 2 and Figure 5 Furthermore, the lower end 65c of the negative terminal 65 is inserted into the interior of the battery casing 50 through the terminal insertion hole 59 and connected to the negative first current collector 76 (see reference). Figure 2 On the other hand, each of the multiple negative electrode second current collectors 77 is connected to the negative electrode tab assembly 44 of the wound electrode body 40 (see reference). Figures 4-6 Furthermore, the negative electrode tab assembly 44 is bent such that the second negative electrode current collector 77 faces the other side 40b of the wound electrode body 40. Thus, the upper end of the second negative electrode current collector 77 is electrically connected to the first negative electrode current collector 76. Additionally, the electrode current collectors (positive electrode current collector 70 and negative electrode current collector 75) can be made of metals with excellent conductivity (aluminum, aluminum alloy, copper, copper alloy, etc.).

[0087] (5) Insulating components

[0088] Furthermore, the secondary battery 100 is equipped with various insulating components to prevent the winding electrode body 40 from conducting through the battery casing 50. Specifically, an external insulating component 92 (see reference) is sandwiched between the positive electrode external conductive component 62 (negative electrode external conductive component 67) and the outer surface of the sealing plate 54. Figure 1 This prevents the positive electrode external conductive component 62 and the negative electrode external conductive component 67 from conducting with the sealing plate 54. Additionally, washers 90 are installed in the terminal insertion holes 58 and 59 of the sealing plate 54 (see reference). Figure 2 This prevents the positive terminal 60 (or negative terminal 65) inserted into the terminal insertion holes 58 and 59 from conducting with the sealing plate 54. Furthermore, an internal insulating member 94 is disposed between the positive first current collector 71 (or negative first current collector 76) and the inner surface of the sealing plate 54. This internal insulating member 94 has a plate-shaped base 94a sandwiched between the positive first current collector 71 (or negative first current collector 76) and the inner surface of the sealing plate 54. This prevents the positive first current collector 71, the negative first current collector 76, and the sealing plate 54 from conducting with each other. Moreover, the internal insulating member 94 has a protrusion 94b protruding from the inner surface of the sealing plate 54 toward the winding electrode body 40 (see reference). Figure 2 and Figure 3This restricts the movement of the wound electrode body 40 in the height direction Z, preventing direct contact between the wound electrode body 40 and the sealing plate 54. Furthermore, the plurality of wound electrode bodies 40 are held by an electrode body holder 98 made of an insulating resin sheet (see reference). Figure 3 The electrode body 40 is contained within the battery casing 50 in a covered state. This prevents direct contact between the wound electrode body 40 and the outer casing 52. Furthermore, the materials of the aforementioned insulating components are not particularly limited as long as they possess the predetermined insulating properties. For example, synthetic resin materials such as polyolefin resins (e.g., polypropylene (PP), polyethylene (PE)) and fluorine resins (e.g., perfluoroalkoxyalkane (PFA), polytetrafluoroethylene (PTFE)) can be used.

[0089] (6) Winding the electrode body

[0090] like Figure 7 As shown, the electrode body used in the secondary battery 100 of this embodiment is a flat wound electrode body 40 formed by winding the positive electrode plate 10 and the negative electrode plate 20 with a separator 30 in between. This wound electrode body 40 is housed within the battery casing 50 such that the winding axis WL of the wound electrode body 40 is substantially aligned with the width direction Y of the secondary battery 100. That is, the "winding axis direction" in the following description is the same as the width direction Y shown in the figure. The structure of the wound electrode body 40 will be described in detail below.

[0091] (a) Positive electrode plate

[0092] like Figure 7 As shown, the positive electrode plate 10 is a long strip-shaped component. The positive electrode plate 10 includes a positive electrode core 12, which is a strip-shaped metal foil, and a positive electrode active material layer 14 applied to the surface of the positive electrode core 12. Furthermore, from the viewpoint of battery performance, the positive electrode active material layer 14 is preferably applied to both sides of the positive electrode core 12. Additionally, in this positive electrode plate 10, the positive electrode tab 12t extends outward from one end edge in the winding axis direction (width direction Y). Figure 7 The positive electrode tab 12t protrudes from the left side of the elongated strip-shaped positive electrode plate 10. Furthermore, multiple positive electrode tabs 12t are formed at predetermined intervals along the long side L of the strip-shaped positive electrode plate 10. The positive electrode tabs 12t are the areas where the positive electrode active material layer 14 is not applied and the positive electrode core 12 is exposed. Additionally, a protective layer 16 extending along the long side L of the positive electrode plate 10 is formed in the region adjacent to the end edge of the positive electrode tab 12t side of the positive electrode plate 10.

[0093] The components constituting the positive electrode plate 10 can be made of conventionally known materials that are also used in general secondary batteries (e.g., lithium-ion secondary batteries) without particular limitation. For example, the positive electrode core 12 can preferably be made of a metallic material with a predetermined conductivity. The positive electrode core 12 is preferably made of aluminum, aluminum alloy, etc. 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 even more preferably 12 μm to 15 μm.

[0094] Furthermore, the positive electrode active material layer 14 is a layer containing the positive electrode active material. The positive electrode active material is a material capable of reversibly absorbing and releasing charge carriers. From the viewpoint of stably manufacturing a high-performance positive electrode plate 10, the positive electrode active material is preferably a lithium transition metal composite oxide. Among the lithium transition metal composite oxides, as the transition metal, lithium transition metal composite oxides containing at least one of the group consisting of nickel (Ni), cobalt (Co), and manganese (Mn) are particularly preferred. Specific examples include lithium nickel cobalt manganese composite oxide (NCM), lithium nickel composite oxide, lithium cobalt composite oxide, lithium manganese composite oxide, lithium nickel manganese composite oxide, lithium nickel cobalt aluminum composite oxide (NCA), and lithium iron nickel manganese composite oxide. In addition, as a preferred example of a lithium transition metal composite oxide that does not contain Ni, Co, and Mn, lithium iron phosphate composite oxide (LFP) is an example. Furthermore, the term "lithium nickel cobalt manganese composite oxide" in this specification is used to include oxides containing additive elements in addition to the main constituent elements (Li, Ni, Co, Mn, O). Examples of added elements include transition metal elements such as Mg, Ca, Al, Ti, V, Cr, Si, Y, Zr, Nb, Mo, Hf, Ta, W, Na, Fe, Zn, and Sn, as well as typical metallic elements. Additionally, added elements can also be half-metal elements such as B, C, Si, and P, or non-metallic elements such as S, F, Cl, Br, and I. While detailed descriptions are omitted, this applies to other lithium transition metal composite oxides described as "~ series composite oxides." Furthermore, the positive electrode active material layer 14 may also contain additives other than the positive electrode active material. Examples of such additives include conductive materials and binders. Specific examples of conductive materials include carbon materials such as acetylene black (AB). Specific examples of binders include resin binders such as polyvinylidene fluoride (PVdF). Moreover, when the 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.

[0095] Furthermore, the width dimension of the positive electrode active material layer 14 is preferably 200 mm to 400 mm, more preferably 250 mm to 350 mm, and even more preferably 260 mm to 300 mm, for example, about 280 mm. In relatively large wound electrode bodies 40 with a width dimension of 200 mm or more for the positive electrode active material layer 14, there is a tendency for Li precipitation to easily occur due to localized poor pressure, as described later. However, according to the technology disclosed herein, even in such large wound electrode bodies 40, localized poor pressure can be prevented in the flat portion 40f, and the precipitation of metallic Li can be suppressed. 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 even more preferably 50 μm to 75 μm. Furthermore, in this specification, the "width dimension" of the wound electrode body and the constituent members of the wound electrode body refers to the dimension in the direction in which the winding axis WL extends (i.e., the width direction Y). In addition, the “thickness” of the wound electrode body and the constituent components of the wound electrode body refers to the dimension in the direction perpendicular to the flat portion 40f of the wound electrode body 40 (i.e., the depth direction X).

[0096] On the other hand, the protective layer 16 is configured to have a lower conductivity than the positive electrode active material layer 14. By placing this protective layer 16 in the region adjacent to the end edge of the positive electrode plate 10, it is possible to prevent internal short circuits 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, the protective layer 16 is preferably formed as a layer containing insulating ceramic particles. Examples of such ceramic particles include inorganic oxides such as alumina (Al2O3), magnesium oxide (MgO), silicon dioxide (SiO2), and titanium dioxide (TiO2), nitrides such as aluminum nitride and silicon nitride, metal hydroxides such as calcium hydroxide, magnesium hydroxide, and aluminum hydroxide, mica, talc, boehmite, zeolite, apatite, and kaolin, and glass fiber. Considering insulation and heat resistance, alumina, boehmite, aluminum hydroxide, silicon dioxide, and titanium dioxide are preferred among the above materials. Alternatively, the protective layer 16 may also contain an adhesive for fixing the ceramic particles onto the surface of the positive electrode core 12. Examples of such adhesives include resin adhesives such as polyvinylidene fluoride (PVdF). Furthermore, the protective layer is not a necessary component of the positive electrode plate. That is, in the secondary battery disclosed herein, a positive electrode plate without a protective layer may also be used.

[0097] (b) Negative electrode plate

[0098] like Figure 7As shown, the negative electrode plate 20 is a long strip-shaped component. This negative electrode plate 20 includes a negative electrode core 22 as a strip-shaped metal foil and a negative electrode active material layer 24 applied to the surface of the negative electrode core 22. Furthermore, from the viewpoint of battery performance, the negative electrode active material layer 24 is preferably applied to both sides of the negative electrode core 22. Moreover, the negative electrode plate 20 has an edge extending outward from one end edge in the winding axis direction (width direction Y). Figure 7 The negative electrode tab 22t protrudes from the right side of the negative electrode plate 20. Multiple negative electrode tabs 22t are provided at predetermined intervals along the long side L of the negative electrode plate 20. These negative electrode tabs 22t are the areas where the negative electrode active material layer 24 is not applied and the negative electrode core 22 is exposed.

[0099] The components constituting the negative electrode plate 20 can be made of conventionally known materials that are also used in general secondary batteries (e.g., lithium-ion secondary batteries) without particular limitations. For example, the negative electrode core 22 can preferably be made of a metallic material with a predetermined conductivity. The negative electrode core 22 is preferably made of copper, copper alloy, etc. In addition, the thickness of the negative electrode core 22 is preferably 4μm to 20μm, more preferably 6μm to 15μm, and even more preferably 8μm to 10μm.

[0100] Furthermore, the negative electrode active material layer 24 is a layer containing the negative electrode active material. For the negative electrode active material, there are no particular limitations as long as it can reversibly absorb and release charge carriers in relation to the aforementioned positive electrode active material; materials that can be used in conventional secondary batteries can be used without particular restriction. Examples of such negative electrode active materials include carbon materials and silicon-based materials. Examples of carbon materials include graphite, hard carbon, soft carbon, and amorphous carbon. Alternatively, graphite with amorphous carbon coating can be used. On the other hand, examples of silicon-based materials include silicon and silicon oxide (silicon dioxide). Silicon-based materials may also contain other metallic elements (e.g., alkaline earth metals) and their oxides. Additionally, the negative electrode active material layer 24 may contain additives other than the negative electrode active material. Examples of such additives include adhesives and tackifiers. Specific examples of adhesives include rubber-based adhesives such as styrene-butadiene rubber (SBR). Specific examples of tackifiers include carboxymethyl cellulose (CMC). Furthermore, when the 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. Additionally, the negative electrode active material can account for 80% by mass or more, or even 90% by mass or more, of the negative electrode active material layer 24. Furthermore, the width of the negative electrode active material layer 24 is preferably 200mm to 400mm, more preferably 250mm to 350mm, and even more preferably 260mm to 300mm, for example, approximately 285mm. Furthermore, the thickness of the negative electrode active material layer 24 on one side of the negative electrode core 22 is preferably 10μm to 200μm, more preferably 50μm to 100μm, and even more preferably 75μm to 85μm.

[0101] (c) diaphragm

[0102] The wound electrode body 40 in this embodiment includes two separators 30. Hereinafter, for ease of explanation, the separator 30 disposed on the outer side of the negative electrode plate 20 will be referred to as the "first separator 32," and the separator 30 disposed between the negative electrode plate 20 and the positive electrode plate 10 will be referred to as the "second separator 34." These separators 30 are sheet-like components that prevent contact between the positive electrode plate 10 and the negative electrode plate 20 and allow charge carriers (e.g., lithium ions) to pass through. As an example of such separator 30, an insulating sheet with multiple fine pores allowing charge carriers to pass through can be cited.

[0103] As the separator 30, any separator used in conventionally known secondary batteries can be used without particular limitation. A preferred example of the separator 30 is a separator comprising a porous substrate layer made of a resin such as a polyolefin resin (e.g., polyethylene (PE), polypropylene (PP)). Furthermore, it is preferable to form a porous surface layer containing an insulating inorganic material on the surface of this porous substrate layer. This porous surface layer has excellent heat resistance, thus suppressing shrinkage and breakage of the separator 30 caused by temperature rise. Examples of inorganic materials for this porous surface layer include ceramic particles such as alumina, boehmite, aluminum hydroxide, and titanium dioxide. Additionally, the porous surface layer contains an adhesive for bonding the ceramic particles. Resin adhesives such as polyvinylidene fluoride (PVdF) and acrylic resins can be used. Furthermore, the two separators 30 used in this embodiment (first separator 32 and second separator 34) can be made of the same material or different materials. In addition, the thickness of each diaphragm 30 is preferably 4μm to 30μm, more preferably 6μm to 20μm, and even more preferably 8μm to 16μm.

[0104] Furthermore, the porous substrate layer of the separator 30 is particularly preferably a porous substrate layer with a porosity in the range of 30% to 60%. The separator 30, having such a porosity, deforms by being flattened during the stamping of the wound electrode body 40, and can function as a buffer to absorb thickness deviations in the wound electrode body 40. That is, by using the separator 30 with the aforementioned porosity, step differences can be prevented on the surface of the flat portion 40f of the wound electrode body 40, contributing to improved Li precipitation resistance due to the homogenization of surface pressure distribution in the flat portion 40f. Moreover, the aforementioned porosity of the porous surface layer refers to the porosity before the manufacture of the wound electrode body 40 (before stamping). In the wound electrode body 40 after stamping, by measuring the porosity of the porous surface layer of the separator 30 disposed in the region not facing the negative electrode plate 20 and the positive electrode plate 10, the porosity of the porous surface layer before stamping can be investigated. Furthermore, as the "region that does not face the negative electrode plate 20 and the positive electrode plate 10" here, examples include the "region 30a where only the diaphragm 30 extends" formed on both sides of the wound electrode body 40 in the winding axis direction.

[0105] Furthermore, when the diaphragm 30 with the porous surface layer functions as a buffer, it is preferable to perform the stamping process in such a way that the thickness of the porous substrate layer after pressurization is reduced to 70% or less (more preferably 60% or less, and even more preferably 50% or less) of the thickness before pressurization. By sufficiently deforming the porous surface layer in this way, deviations in the thickness of the wound electrode body 40 can be adequately absorbed. In addition, in the manufactured wound electrode body 40, in order to investigate the reduction rate of the thickness of the porous substrate layer based on stamping, the thickness of the porous surface layer of the diaphragm 30 sandwiched between the positive electrode plate 10 and the negative electrode plate 20, and the thickness of the porous surface layer in the region not facing the negative electrode plate 20 and the positive electrode plate 10 can be investigated.

[0106] Furthermore, it is preferable to provide an adhesive layer on at least one surface of each separator 30. This adhesive layer is a layer containing a resin adhesive such as polyvinylidene fluoride (PVdF) or acrylic resin, and is bonded to the positive electrode plate 10 and the negative electrode plate 20 by pressure, heat, etc. This prevents the positional displacement of the sheet members (positive electrode plate 10, negative electrode plate 20, and separator 30) inside the wound electrode body 40. The secondary battery 100 of this embodiment suppresses the precipitation of metallic Li by adjusting the arrangement positions of the beginning ends (positive electrode beginning end 10s and negative electrode beginning end 20s) of the positive electrode plate 10 and the negative electrode plate 20, as will be described in detail later. Therefore, by using a separator 30 with an adhesive layer to prevent positional displacement of the positive electrode plate 10 and the negative electrode plate 20, the aforementioned Li precipitation suppression effect can be performed more stably. Furthermore, from the viewpoint of more appropriately preventing positional displacement of the sheet members, the adhesive layer is preferably formed on both sides of the separator 30. Furthermore, when the adhesive layer is formed only on one side of the separator 30, it is preferable to form the adhesive layer on the surface in contact with the positive electrode plate 10. This is because the positive electrode plate 10 tends to shift more easily than the negative electrode plate 20. Additionally, in the case of a separator 30 having the aforementioned porous surface layer, an adhesive layer can be formed separately on the surface of the porous surface layer, or the porous surface layer can also function as an adhesive layer. This porous surface layer, which also functions as an adhesive layer, can be formed by increasing the proportion of adhesive. For example, when the total weight of the porous surface layer is 100% by mass, the proportion of adhesive can be set to 5% by mass or more (preferably 10% by mass or more). This allows for the formation of a porous surface layer that exhibits sufficient adhesiveness and functions as an adhesive layer.

[0107] Furthermore, it is preferable that the surface of the adhesive layer has protrusions that appear mesh-like when viewed from above. These mesh-like protrusions are easily deformed during the stamping process of the wound electrode body 40, thus functioning as a buffer between sheet-like components. As a result, it can absorb thickness variations in the wound electrode body 40 within the surface of the flat portion 40f after stamping, more appropriately suppressing the precipitation of metallic Li. Furthermore, the adhesive layer is not limited to the above-described manner. For example, the adhesive layer itself can also be formed in a mesh-like shape. In other words, an adhesive layer that appears mesh-like when viewed from above can also be formed on the surface of a porous substrate layer or a porous surface layer. Such a mesh-like adhesive layer can also function as a buffer.

[0108] (d) Construction of the wound electrode body

[0109] Next, the specific structure of the wound electrode body 40, which includes the aforementioned positive electrode plate 10, negative electrode plate 20, and separator 30, will be described. This wound electrode body 40 is manufactured by winding the positive electrode plate 10 and negative electrode plate 20 together with two separators 30 in between. Specifically, firstly, a laminated body consisting of a first separator 32, a negative electrode plate 20, a second separator 34, and a positive electrode plate 10 is fabricated (see reference). Figure 7 At this point, adjust the stacking position of each sheet component in the width direction Y so that only the positive electrode tab 12t of the positive electrode plate 10 is positioned from one side of the width direction Y. Figure 7 The left side of the negative electrode plate 20 protrudes from the other side, and only the negative electrode tab 22t of the negative electrode plate 20 protrudes from the other side. Figure 7 The right side edge of the layered body protrudes. Then, the fabricated laminate is wound to form a cylindrical body. The number of turns is preferably adjusted appropriately considering the performance and manufacturing efficiency of the desired wound electrode body 40. For example, the number of turns for the wound electrode body 40 is preferably 10 to 60 times, more preferably 30 to 40 times. Then, the cylindrical body is stamped to form a flat wound electrode body 40. Furthermore, as... Figure 8 As shown, a first diaphragm 32 is disposed on the outermost peripheral surface of the fabricated wound electrode body 40. The shape of the wound electrode body 40 is maintained by attaching a winding fixing tape 38 to the terminal portion 32a of the first diaphragm 32.

[0110] like Figure 9 As shown, in the manufactured wound electrode body 40, one end of the positive electrode plate 10 along its long side L is disposed inside the wound electrode body 40 as the positive electrode start end 10s. The other end of the positive electrode plate 10 is disposed outside the wound electrode body 40 as the positive electrode terminal portion 10e. Similarly, one end of the negative electrode plate 20 is disposed inside the wound electrode body 40 as the negative electrode start end 20s. The other end of the negative electrode plate 20 is disposed outside the wound electrode body 40 as the negative electrode terminal portion 20e. Furthermore, although in Figure 9The illustration is omitted, but the positive electrode plate 10 is endowed with a positive electrode active material layer 14 (see reference). Figure 7 ) up to the two ends in the long side direction L (positive electrode starting end 10s and positive electrode terminal end 10e). Similarly, the negative electrode plate 20 is endowed with a negative electrode active material layer 24 (see reference). Figure 7 ) Until the two ends of the long side direction L (the negative electrode starting end 20s and the negative electrode terminal part 20e).

[0111] Furthermore, a positive electrode tab assembly 42 is formed at one end of the wound electrode body 40 along the winding axis direction (width direction Y), where multiple positive electrode cores 12 are exposed. On the other hand, a negative electrode tab assembly 44 is formed at the other end of the wound electrode body 40 along the winding axis direction (width direction Y), where multiple negative electrode cores 22 are exposed. Meanwhile, a core portion 46 is formed at the center of the wound electrode body 40 along the width direction Y, where the positive electrode active material layer 14 and the negative electrode active material layer 24 face each other. This core portion 46 becomes the main site for generating the charge-discharge reaction. Here, as described above, in this embodiment, after the positive electrode tab assembly 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 (see reference). Figures 4-6 Similarly, after the negative electrode tab assembly 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 40b of the wound electrode body 40. By providing such a bendable positive electrode tab assembly 42 (and negative electrode tab assembly 44), the volume of the core 46 (charge / discharge area) relative to the internal capacity of the battery casing 50 can be increased, thus contributing to improved battery performance.

[0112] As described above, the wound electrode body 40 in this embodiment is formed into a flat shape by stamping. Figure 9 As shown, the flat-shaped wound electrode body 40 has a pair of curved portions 40r1, 40r2 with curved outer surfaces and a flat portion 40f that connects the pair of curved portions 40r1, 40r2 and has a flat outer surface. Figure 3 As shown, when the wound electrode body 40 is housed within the battery casing 50, the flat portion 40f faces the long sidewall 52b of the outer casing 52 (i.e., the flat surface of the battery casing 50). Furthermore, the upper curved portion 40r1 faces the sealing plate 54, and the lower curved portion 40r2 faces the bottom wall 52a of the outer casing 52.

[0113] Here, if a region with a thinner thickness than other regions is formed within the surface of the flat portion 40f of the aforementioned wound electrode body 40, the precipitation of metallic Li will be promoted near this region. Specifically, this secondary battery 100 is typically pressed into the flat surface (long sidewall 52b of the outer casing 52) of the battery casing 50 and used while the flat portion 40f of the wound electrode body 40 is under pressure. As a result, the inter-electrode distance between the positive electrode plate 10 and the negative electrode plate 20 inside the wound electrode body 40 becomes smaller, thus reducing the resistance. However, since the aforementioned locally thinner region cannot adequately transmit the pressure when the flat portion 40f is pressed, it becomes a region with a locally larger inter-electrode distance, resulting in higher resistance. Furthermore, around this region with a locally larger inter-electrode distance, due to current concentration, metallic Li is easily deposited on the surface of the negative electrode active material layer 24. In addition, in the region with a locally larger inter-electrode distance, since gases from the decomposition of non-aqueous electrolyte tend to accumulate, the resistance further increases during repeated charge and discharge cycles, making the precipitation of metallic Li more likely.

[0114] As an example, Figure 12 The conventional wound electrode body 140 shown tends to have an insufficient number of sheet members stacked in the flat portion 140f near the bend 140r, easily resulting in localized thickness deficiencies. Specifically, when forming the flat-shaped wound electrode body 140, it is very difficult to arrange both the positive electrode start end 110s and the negative electrode start end 120s (especially the positive electrode start end 110s) within the bend 140r and to make the number of electrode plates (positive electrode plate 110 and negative electrode plate 120) in the plane of the flat portion 140f the same. Therefore, in such a wound electrode body 140, a region 141 is typically formed near the bend 140r where the number of electrode plate stacks is less than in other areas of the flat portion 140f. In this case, poor pressurization occurs in the region 141 where the number of stacks is insufficient, easily leading to the precipitation of metallic Li due to the localized increase in inter-electrode distance. Furthermore, this precipitation of metallic Li may also promote… Figure 13 The structure shown is generated in the wound electrode body 240. Specifically, in Figure 13 In the wound electrode body 240 shown, a structure is adopted in which the negative electrode starting end 220s extends towards the bending portion 240r and the region (extension portion) in the negative electrode plate 220 that does not overlap with the positive electrode plate 210 is folded back. However, even with this structure, since a region 241 with insufficient electrode plate stacking is generated in the flat portion 240f, metallic Li tends to precipitate around this region 241.

[0115] In contrast, in the secondary battery 100 of this embodiment, from the viewpoint of preventing localized pressure failure at the flat portion 40f of the wound electrode body 40, the respective arrangement positions of the positive electrode start end 10s and the negative electrode start end 20s are adjusted. Specifically, as Figure 9 As shown, the positive electrode starting end 10s of the positive electrode plate 10 in this embodiment has a first region 17 extending along the flat portion 40f of the wound electrode body 40. On the other hand, the negative electrode starting end 20s of the negative electrode plate 20 has: a second region 27 extending along the flat portion 40f, a folded-back portion 28 folded back from the end of the second region 27 along the bend 40r2, and a third region 29 extending along the flat portion 40f from the end of the folded-back portion 28. In the wound electrode body 40 of this structure, an electrode starting layer stack 48 is formed in the region including the flat portion 40f near the bend 40r2, where the first region 17, the second region 27, and the third region 29 overlap in the thickness direction (depth direction X). As a result, localized poor pressure application can be prevented in the flat portion 40f near the bend 40r2, and thus the precipitation of metallic Li due to the local increase in inter-electrode distance can be appropriately suppressed.

[0116] Furthermore, in this specification, each of the first region 17, the second region 27, and the third region 29 is described as "extending along the flat portion 40f". However, this description does not limit the first region 17, the second region 27, and the third region 29 to being parallel to the outer surface of the flat portion 40f. That is, the first region 17, the second region 27, and the third region 29 may also be slightly inclined relative to the outer surface of the flat portion 40f. In addition, the first region 17, the second region 27, and the third region 29 may not be strictly straight; they may be curved or meandering. Similarly, the fold-back portion 28 does not need to be parallel to the outer surface of the curved portion 40r2; it may also be meandering, etc.

[0117] Furthermore, the length of the electrode start-end stacked portion 48 in the height direction Z is preferably 0.5 mm to 10 mm, preferably 1 mm to 10 mm, preferably 1 mm to 7 mm, and for example, about 3 mm. This allows for more appropriate prevention of localized pressurization problems at the flat portion 40f, and more appropriate improvement in Li precipitation resistance. Moreover, as in this embodiment, in the secondary battery 100 having multiple wound electrode bodies 40, it is preferable that the lengths of the electrode start-end stacked portions 48 of each wound electrode body 40 are different. This allows for the application of pressure to all the multiple wound electrode bodies 40 from the outside of the battery casing 50, which helps to homogenize the surface pressure distribution at the flat portion 40f of each wound electrode body 40, thus appropriately improving the Li precipitation resistance of the entire surface of the flat portion 40f.

[0118] In addition, such as Figure 9As shown, in the wound electrode body 40 of this embodiment, the positive electrode starting end portion 10s is disposed near the lower curved portion 40r2 in the height direction Z. In contrast, the positive electrode terminal portion 10e is disposed at a position closer to the upper curved portion 40r1 than the positive electrode starting end portion 10s. This prevents the positive electrode starting end portion 10s and the positive electrode terminal portion 10e from approaching each other in the circumferential direction of the wound electrode body 40, thus contributing to the uniformity of the surface pressure distribution in the flat portion 40f. Furthermore, in this embodiment, the negative electrode terminal portion 20e of the negative electrode plate 20 is also similarly disposed at a position closer to the upper curved portion 40r1 than the negative electrode starting end portion 20s. This further enhances the uniformity of the surface pressure distribution in the flat portion 40f.

[0119] More specifically, in this embodiment, a positive electrode terminal 10e and a negative electrode terminal 20e are disposed on the upper curved portion 40r1. In this case, the step difference caused by the positive electrode terminal 10e and the negative electrode terminal 20e can be prevented from occurring on the surface of the flat portion 40f, thus further homogenizing the surface pressure distribution at the flat portion 40f. Furthermore, at the outermost periphery of the wound electrode body 40, it is preferable that the negative electrode terminal 20e extends from the positive electrode terminal 10e in such a way that the positive electrode terminal 10e is covered by the negative electrode plate 20. For example, as Figure 9 As shown, when the positive electrode terminal 10e is disposed in the region between 9 and 12 o'clock in the arc of the upper curved portion 40r1, the negative electrode terminal 20e is preferably disposed in the region between 12 and 3 o'clock. By making the negative electrode plate 20 longer than the positive electrode plate 10, the absorption performance of the charge carrier on the negative electrode side is sufficiently ensured, and the resistance to Li precipitation can be further improved. In addition, when the positive electrode starting end 10s and the negative electrode starting end 20s are disposed in the curved portion 40r1, a diaphragm 30 with an adhesive layer is preferably used. This prevents the positive electrode starting end 10s and the negative electrode starting end 20s from shifting away from the curved portion 40r1.

[0120] Furthermore, the height dimension of the wound electrode body 40 in this embodiment is preferably 60mm to 120mm, more preferably 80mm to 110mm, particularly preferably 90mm to 100mm, for example, about 95mm. Additionally, the thickness of the wound electrode body 40 is preferably 5mm to 25mm, more preferably 8mm to 20mm, and particularly preferably 10mm to 15mm. The Li precipitation suppression effect of the technology disclosed herein is particularly suitable in secondary batteries having a wound electrode body 40 with the aforementioned dimensions. Furthermore, the "height dimension" here refers to the dimension in the direction perpendicular to the winding axis WL and perpendicular to the thickness direction (depth direction X) (i.e., the height direction Z).

[0121] Furthermore, the ratio of the thickness of the positive electrode plate 10 to the thickness of the negative electrode plate 20 is preferably 65% ​​to 95%, more preferably 70% to 90%, and particularly preferably 75% to 85%. This allows for the attainment of optimal electrode body thickness and structural pressure. Additionally, the term "thickness of the electrode plate (positive or negative electrode plate)" in this specification refers to the combined thickness of the electrode active material layer and the electrode core. For example, in an electrode plate where electrode active material layers are formed on both sides of the electrode core, the combined thickness of the two electrode active material layers and the electrode core is termed "thickness of the electrode plate."

[0122] <Other Implementation Methods>

[0123] The above description illustrates one embodiment of the technology disclosed herein. Furthermore, the above embodiment demonstrates an example of applying the technology disclosed herein and does not limit the scope of the technology disclosed herein. Other embodiments of the technology disclosed herein will be described below.

[0124] (1) Number of wound electrode bodies

[0125] For example, the secondary battery 100 of the above embodiment is a high-capacity secondary battery in which three wound electrode bodies 40 are housed inside the battery casing 50. However, the number of electrode bodies housed in one battery casing is not particularly limited; it can be two or more, or it can be one. Furthermore, in a secondary battery having multiple wound electrode bodies, localized pressure defects may occur near the bends of each wound electrode body, thus tending to cause the precipitation of metallic Li. In contrast, in the technology disclosed herein, since each of the multiple wound electrode bodies can be constructed to prevent localized pressure defects, the precipitation of metallic Li can be appropriately suppressed.

[0126] (2) Capacity of secondary batteries

[0127] Furthermore, to construct high-capacity secondary batteries, it is necessary to increase the filling density of the positive electrode active material layer, which carries the charge during charging, thereby increasing the positive electrode capacity. In this case, the ratio of the negative electrode capacity to the positive electrode capacity (phase capacity ratio: negative electrode capacity / positive electrode capacity) decreases, thus making it easier for metallic Li to deposit on the surface of the negative electrode plate. In contrast, according to the technology disclosed herein, by improving the configuration of the positive and negative electrode start-up positions, Li deposition resistance can be improved. Therefore, it is possible to achieve a high density of the positive electrode active material layer, which is difficult to obtain from the perspective of Li deposition resistance, thus contributing to the high capacity of the secondary battery. For example, according to the technology disclosed herein, even when using a wound electrode body with a positive electrode active material layer filling density of 3.4 g / cc or more (e.g., 3.6 g / cc) and a phase capacity ratio of 1.1 or less (e.g., 1.08), the deposition of metallic Li can be appropriately suppressed.

[0128] (3) Position of the starting end of each electrode

[0129] In the above embodiment, the positive electrode start-end portion 10s and the negative electrode start-end portion 20s are arranged near the lower curved portion 40r2, and the positive electrode terminal portion 10e and the negative electrode terminal portion 20e are arranged in the upper curved portion 40r1. However, if an electrode start-end stack is formed in the flat portion of the wound electrode body, the arrangement positions of the start-end and terminal portions of the positive and negative electrode plates are not particularly limited. That is, in the technology disclosed here, the positive electrode start-end portion and the negative electrode start-end portion can also be arranged near the upper curved portion, and the electrode start-end stack is formed in the flat portion near the upper curved portion. In this case, local pressure failure can also be prevented, and Li deposition can be sufficiently suppressed. However, the area near the positive electrode tab group and the negative electrode tab group tends to generate power concentration. Considering this, it is preferable that the positive electrode start-end portion and the negative electrode start-end portion are arranged near the curved portion on the side away from the positive electrode tab group and the negative electrode tab group. That is, as Figure 2 As shown, in the wound electrode body 40 in which a positive electrode tab group 42 and a negative electrode tab group 44 are formed in the upper part in the height direction Z, the positive electrode beginning end 10s and the negative electrode beginning end 20s are preferably arranged near the lower bending portion 40r2.

[0130] (4) The beginning end of the diaphragm

[0131] like Figure 9As shown, in the secondary battery 100 of the above embodiment, the deposition of metallic Li is suppressed by adjusting the arrangement positions of the positive electrode start-end 10s and the negative electrode start-end 20s in such a way as to form the electrode start-end stack 48. Here, in order to further suppress the deposition of metallic Li appropriately, it is preferable to adjust the arrangement position of the start-end of the separator in addition to the start-ends of the positive and negative electrode plates. Hereinafter, an embodiment of adjusting the arrangement position of the start-end of the separator will be described. Figure 10 This is a schematic cross-sectional view of the wound electrode body of a secondary battery according to another embodiment.

[0132] like Figure 10 As shown, in this embodiment, the starting ends 30s of the two separators 30 extend from the negative electrode starting end 20s. Specifically, one end of the first separator 32 in the long side direction (the starting end 30s of the first separator 32) has a first extension 32e extending from the negative electrode starting end 20s. Similarly, one end of the second separator 34 (the starting end 30s of the second separator 34) has a second extension 34e extending from the negative electrode starting end 20s. By extending the starting ends 30s of the separators 30 from the negative electrode starting end 20s, it is possible to prevent step differences caused by the negative electrode starting end 20s from occurring in the region adjacent to the electrode starting end stack 48. As a result, the surface pressure distribution at the flat portion 40f of the wound electrode body 40 can be made more uniform, thereby improving the Li precipitation resistance of the entire surface of the flat portion 40f.

[0133] In addition, Figure 10 In the illustrated embodiment, the first extension 32e and the second extension 34e are each folded back along the upper bend 40r1. This forms a membrane stack 49 inside the wound electrode body 40, consisting only of the first membrane 32 and the second membrane 34. As a result, the surface pressure distribution at the flat portion 40f can be further homogenized, and the Li precipitation resistance of the entire surface of the flat portion 40f can be improved more appropriately. Furthermore, the number of membrane layers 30 in the membrane stack 49 is preferably adjusted appropriately considering the thickness of the negative electrode plate 20 and the thickness of the membrane 30. Specifically, it is preferable to adjust the number of membrane layers 30 in the wound electrode body 40 before pressurization so that the membrane stack 49 is slightly thicker than the negative electrode plate 20. As an example, in the membrane stack 49, it is preferable to have at least three layers of the first membrane 32 and at least two layers of the second membrane. Therefore, when the wound electrode body 40 is pressurized, the diaphragm stack 49 deforms in a flattened manner, which can appropriately suppress the generation of step difference caused by the negative electrode beginning end 20s.

[0134] Furthermore, as in this embodiment, when the starting end 30s of the diaphragm 30 extends from the starting end 20s of the negative electrode, it is preferable to form an adhesive layer on the surface of each diaphragm 30. In other words, it is preferable that the first extension 32e extending from the first diaphragm 32 and the second extension 34e extending from the second diaphragm 34 are each bonded together by the adhesive layer. This prevents positional displacement of the diaphragm 30 from occurring inside the wound electrode body 40 (particularly in the diaphragm stack 49).

[0135] In addition, such as Figure 10 As shown, in this embodiment, a separator 30 (second separator 34) is sandwiched between the second region 27 and the third region 29 of the electrode start-end stack 48. In this case, it is preferable that the distance between the second region 27 and the third region 29 in the thickness direction (depth direction X) is smaller than the thickness of the negative electrode plate 20. Specifically, when the separator 30 is disposed between the second region 27 and the third region 29, the separator 30 in the electrode start-end stack 48 is deformed by being flattened due to pressure from outside the battery casing 50. At this time, by adjusting the thickness of the separator 30 and the pressure relative to the winding electrode body 40 in a way that reduces the distance between the second region 27 and the third region 29, the gap between the second region 27 and the third region 29 is reduced, thus enabling the uniformity of the structural pressure applied to the electrode body. For example, the gap between the second region 27 and the third region 29 in the electrode start-end stack 48 is preferably 50 μm or less, more preferably 30 μm or less, and particularly preferably 20 μm or less. By setting the space between the second region 27 and the third region 29 to a state with almost no gap, the effect of homogenizing the pressure can be more effectively achieved. Furthermore, the "gap between the second and third regions in the electrode beginning stack" in this specification is a value obtained by subtracting the total thickness of the diaphragm sandwiched between the second and third regions from the distance between the second and third regions.

[0136] In addition, Figure 10 In the illustrated embodiment, the diaphragm 30 sandwiched between the second region 27 and the third region 29 of the electrode beginning stack 48 is only the second diaphragm 34. However, the diaphragm sandwiched between the second and third regions is not limited to the second diaphragm. For example, in Figure 11 In the illustrated embodiment, a first diaphragm 32 and a second diaphragm 34 are sandwiched between the second region 27 and the third region 29 of the electrode beginning stack 48. Specifically, in Figure 11In the illustrated embodiment, the first extension 32e of the first diaphragm 32 and the second extension 34e of the second diaphragm 34 are each folded back along the upper bend 40r1 and inserted between the second region 27 and the third region 29. According to this structure, three or more layers of diaphragms 30 can be disposed between the second region 27 and the third region 29. This further facilitates reducing the gap between the second region 27 and the third region 29 present in the electrode beginning stack 48. Furthermore, as... Figure 11 As shown, the first extension 32e and the second extension 34e inserted between the second region 27 and the third region 29 can also be folded back along the fold-back portion 28 of the negative electrode plate 20. This allows four or more layers of diaphragms to be sandwiched between the second region 27 and the third region 29, further reducing the gap between the second region 27 and the third region 29.

[0137] [Experimental Example]

[0138] The following describes experimental examples related to this invention. Furthermore, the content of the experimental examples described below is not intended to limit the invention.

[0139] 1. Preparation of each sample

[0140] In this experiment, four types of wound electrodes (samples 1-4) were fabricated with different configuration positions of the positive and negative electrode starting ends. The following is a detailed description of each sample.

[0141] (1) Sample 1

[0142] In this experiment, a laminate consisting of a positive electrode plate and a negative electrode plate separated by two separators was fabricated. This laminate was then wound and stamped to create a flat, wound electrode body. First, as the positive electrode plate, a positive electrode plate with a positive active material layer (60 μm thick, 280 mm wide) applied to both sides of a positive electrode core (13 μm thick aluminum foil) was prepared. The positive active material layer of this positive electrode plate contained positive active material, conductive material, and binder in a ratio of 97.5:1.5:1.0. Furthermore, lithium nickel cobalt manganese composite oxide (NCM) was used as the positive active material. Acetylene black (AB) was used as the conductive material. Polyvinylidene fluoride (PVdF) was used as the binder. On the other hand, as the negative electrode plate, a negative electrode plate with a negative active material layer (80 μm thick, 285 mm wide) applied to both sides of a negative electrode core (8 μm thick copper foil) was used. In the negative electrode active material layer of this negative electrode plate, negative electrode active material, tackifier, and binder are contained in a ratio of 98.3:0.7:1.0. Furthermore, graphite is used as the negative electrode active material, carboxymethyl cellulose (CMC) as the tackifier, and styrene-butadiene rubber (SBR) as the binder. As a separator, a porous surface layer containing alumina powder and polyvinylidene fluoride (PVdF) is formed on the surface of a porous polyethylene (PE) substrate layer. In this experiment, the PVdF content in the porous surface layer was adjusted to 25% by mass so that the porous surface layer of the separator functions as an adhesive layer.

[0143] Next, a laminate consisting of positive and negative electrode plates stacked with a separator was fabricated, and this laminate was wound to create a cylindrical body. Furthermore, the number of windings in this experiment was set to 33. Then, a stamping process was performed to flatten the wound cylindrical body, thereby creating a flat wound electrode body. Here, in the wound electrode body 240 of sample 1, as shown... Figure 13 As shown, a structure is adopted in which the negative electrode starting end 220s extends towards the bending portion 240r and the region (extension) of the negative electrode plate 220 that does not overlap with the positive electrode plate 210 is folded back. Specifically, after fabricating a laminated body in which the negative electrode plate 220 extends from the positive electrode starting end 210s, the extended negative electrode plate 220 is bent in a manner that does not overlap with the positive electrode plate 210. Then, the laminated body is wound and stamped to form a product. Figure 13 The wound electrode body 240 shown has the following structure.

[0144] (2) Sample 2

[0145] In Sample 2, the wound electrode body was manufactured under the same conditions as Sample 1, except that the positions of the positive and negative electrode starting ends were different. Specifically, in Sample 2, a laminate was manufactured by overlapping the positive and negative electrode starting ends, and then the laminate was wound to form a cylindrical body. Then, the wound electrode body was manufactured by stamping with the positive and negative electrode starting ends positioned at the bend. Furthermore, when the cross-section of the manufactured wound electrode body was examined, as shown... Figure 12 As shown, neither the positive electrode start-end 110s nor the negative electrode start-end 120s reaches the bend 140r, and the flat portion 140f is disposed near the bend 140r. Moreover, the positions of the positive electrode start-end 110s and the negative electrode start-end 120s are inconsistent, and the negative electrode plate 220 extends slightly from the positive electrode start-end 210s.

[0146] (3) Sample 3

[0147] In Sample 3, except that the stamping positions were adjusted so that the positive and negative electrode starting ends were positioned on the flat portion, the wound electrode body was manufactured under the same conditions as Sample 2. When the cross-section of the manufactured wound electrode body was checked, both the positive and negative electrode starting ends were positioned on the flat portion, but similar to Sample 2, the positions of the positive and negative electrode starting ends were not the same, and the negative electrode plate extended slightly from the positive electrode starting end.

[0148] (4) Sample 4

[0149] In sample 4, the wound electrode body was fabricated under the same conditions as in sample 1, except that the positions of the positive and negative electrode start ends were different. Specifically, in sample 4, as... Figure 9 As shown, a wound electrode body 40 is fabricated by forming an electrode beginning stack 48 in which a first region 17, a second region 27, and a third region 29 overlap in a flat portion 40f near the bending portion 40r2. Specifically, after fabricating a stack extending from the positive electrode beginning 10s to the negative electrode plate 20, the extended negative electrode plate 20 is bent so that the top portion of the negative electrode plate 20 (corresponding to the third region 29) overlaps with the positive electrode plate 10. Then, after winding the stack, a cylindrical body is stamped with the bending position (foldback portion) of the negative electrode plate 20 positioned at the bending portion, thereby fabricating a wound electrode body 40. Figure 9 The wound electrode body 40 shown has the following structure.

[0150] 2. Evaluation Test

[0151] (1) Evaluation of surface pressure distribution

[0152] In this evaluation, the surface pressure distribution when pressing the flat portion of the wound electrode body of each sample was investigated. Specifically, firstly, a pair of pressure-sensitive papers (manufactured by Fujifilm) were attached to the flat portion of the wound electrode body used as the test subject. Then, using a pressing clamp with a flat pressing surface, pressure was applied to the flat portion of the wound electrode body. The pressure was set to 125 kN, and the pressing time was set to 3 seconds. Afterward, the pressure-sensitive paper was removed from the wound electrode body, and the discolored portion (the pressed portion) of the pressed paper was visually observed. Figures 14-17 The results are shown in the figure. Figure 14 This is a photograph of pressure-sensitive paper showing the results of the surface pressure distribution evaluation of sample 1. Figure 15 This is a photograph of pressure-sensitive paper showing the results of the surface pressure distribution evaluation of sample 2. Figure 16 This is a photograph of pressure-sensitive paper showing the results of the surface pressure distribution evaluation of sample 3. Figure 17 This is a photograph of pressure-sensitive paper showing the results of the surface pressure distribution evaluation of sample 4.

[0153] (2) Evaluation of Li precipitation resistance

[0154] In this evaluation, lithium-ion secondary batteries using the wound electrode bodies of each sample were constructed, and their Li deposition resistance was evaluated. Specifically, for each sample, three wound electrode bodies were fabricated, and each wound electrode body was connected to the electrode terminals and housed within a battery casing. Then, a non-aqueous electrolyte was injected into the battery casing, and the casing was sealed, thereby constructing the lithium-ion secondary battery for testing. Furthermore, the non-aqueous electrolyte used in this evaluation was prepared by dissolving the supporting salt (LiPF6) at a concentration of 1 mol / L in a non-aqueous solvent containing EC, DMC, and EMC in a volume ratio of 3:4:3.

[0155] Then, the constructed test battery was placed in an environment of 20°C and subjected to 1000 cycles of charge-discharge cycling, which repeatedly performed CC charging and CC discharging under predetermined conditions. Furthermore, in the CC charging of this evaluation test, the battery was charged at a rate of 1C for 100 seconds. Conversely, in the CC discharging, the battery was discharged at a rate of 1C for 100 seconds. After performing the above-described charge-discharge cycles, the battery was discharged until the State of Charge (SOC) reached 0%, and the test battery was disassembled and the negative electrode plate was recovered. Then, it was visually observed whether metallic Li was deposited on the surface of the negative electrode active material layer.

[0156] (3) Test Results

[0157] First, such as Figures 14-16As shown, as a result of the surface pressure distribution evaluation, unpressurized areas A were confirmed to occur locally in samples 1-3, where the pressure-sensitive paper remained almost unchanged in color after the test (without applied pressure). Specifically, it was found that in samples 1-3, linear unpressurized areas A along the winding axis of the winding electrode body were formed in the flat portion near the curved portion. Furthermore, as a result of the Li precipitation resistance evaluation, metallic Li was precipitated on the surface of the negative electrode active material layer near these unpressurized areas A. In particular, in sample 3, an unpressurized area A larger than that in samples 1 and 2 was formed, and more metallic Li precipitation was confirmed.

[0158] On the other hand, such as Figure 17 As shown, in the surface pressure distribution evaluation of sample 4, sufficient pressure was applied to the flat portion near the bend, and the unpressurized region A, as seen in samples 1-3, was not produced. Furthermore, as a result of the Li precipitation resistance evaluation, almost no metallic Li precipitation was detected in sample 4. From the above results, it can be concluded that... Figure 9 As shown, by adjusting the arrangement of the positive electrode start-end portion 10s and the negative electrode start-end portion 20s in such a way as to form an electrode start-end stack 48 that overlaps the first region 17 of the positive electrode plate 10, the second region 27 of the negative electrode plate 20 and the third region 29 of the negative electrode plate 20, the precipitation of metallic Li can be appropriately suppressed.

[0159] 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 alterations to the specific examples described above.

Claims

1. A secondary battery, the secondary battery comprising a flat wound electrode body formed by winding a positive electrode plate and a negative electrode plate separated by a separator, and a battery casing housing the wound electrode body, wherein, The flat, wound electrode body has a pair of curved portions with a bent outer surface and a flat portion connecting the pair of curved portions with a flat outer surface. The negative electrode plate comprises a negative electrode core as a strip-shaped metal foil and a layer of negative electrode active material applied to the surface of the negative electrode core. One end of the positive electrode plate, along its long side, is positioned inside the wound electrode body as the positive electrode starting end, while the other end is positioned outside the wound electrode body as the positive electrode ending end. One end of the negative electrode plate, along its long side, is positioned inside the wound electrode body as the negative electrode starting end, while the other end is positioned outside the wound electrode body as the negative electrode ending end. The positive electrode starting end has a first region extending along the flat portion to one end in the long side direction of the positive electrode plate. The negative electrode starting end has a second region extending along the flat portion, a folded-back portion that folds back from the end of the second region along the curved portion, and a third region extending from the end of the folded-back portion along the flat portion to one end in the long side direction of the negative electrode plate. The wound electrode body has an electrode start-end stack where the first region, the second region, and the third region overlap in the thickness direction. In the thickness direction of the wound electrode body, the second region is located between the first region and the third region. A negative electrode tab assembly is formed at one end of the winding axis of the wound electrode body, on which the negative electrode tab of the negative electrode core is exposed.

2. The secondary battery according to claim 1, wherein, The length of the electrode start-end stack in the long side direction of the positive electrode plate is 0.5 mm to 10 mm.

3. The secondary battery according to claim 1 or 2, wherein, The battery casing contains a plurality of the wound electrode bodies.

4. The secondary battery according to claim 3, wherein, In each of the plurality of wound electrode bodies, the length of the electrode beginning stack in the long side direction of the positive electrode plate is different.

5. The secondary battery according to claim 1 or 2, wherein, The positive electrode starting end is positioned close to one of the two bends, and the positive electrode terminal end is positioned on the other bend.

6. The secondary battery according to claim 5, wherein, At least one of the positive terminal portion and the negative terminal portion is disposed on the curved portion of the other.

7. The secondary battery according to claim 1 or 2, wherein, The diaphragm has a porous resin substrate layer and a porous surface layer formed on the surface of the porous substrate layer and comprising ceramic particles and an adhesive. The porosity of the porous surface layer in the region not facing the positive and negative electrode plates is 30% to 60%.

8. The secondary battery according to claim 7, wherein, The thickness of the porous surface layer in the separator sandwiched between the positive electrode plate and the negative electrode plate is less than 60% of the thickness of the porous surface layer in the region not facing the positive electrode plate and the negative electrode plate.

9. The secondary battery according to claim 1 or 2, wherein, The wound electrode body is manufactured by winding a stack of layers consisting of a first diaphragm, the negative electrode plate, a second diaphragm, and the positive electrode plate in sequence.

10. The secondary battery according to claim 9, wherein, A first extension portion extending from the negative electrode starting end is formed at one end of the first diaphragm along its long side, and a second extension portion extending from the negative electrode starting end is formed at one end of the second diaphragm along its long side.

11. The secondary battery according to claim 10, wherein, The first extension and the second extension are each folded back along at least one of the pair of bends to form a diaphragm stack consisting only of the first diaphragm and the second diaphragm.

12. The secondary battery according to claim 11, wherein, In the membrane stack, the first membrane layer has three or more layers, and the second membrane layer has two or more layers.

13. The secondary battery according to claim 9, wherein, An adhesive layer is provided on the surface of at least one of the first diaphragm and the second diaphragm.

14. The secondary battery according to claim 13, wherein, The adhesive layer has protrusions that appear as a mesh when viewed from above.

15. The secondary battery according to claim 1 or 2, wherein, The diaphragm is sandwiched between the second region and the third region of the electrode initial stack, and the distance between the second region and the third region in the thickness direction of the wound electrode body is smaller than the thickness of the negative electrode plate.

16. The secondary battery according to claim 15, wherein, The value obtained by subtracting the total thickness of the diaphragm sandwiched between the second and third regions from the distance between the second and third regions in the thickness direction of the wound electrode body is 50 μm or less.

17. The secondary battery according to claim 15, wherein, Three or more layers of the diaphragm are sandwiched between the second region and the third region at the beginning of the negative electrode.

18. The secondary battery according to claim 1 or 2, wherein, The positive electrode plate has a positive electrode core as a strip of metal foil and a layer of positive electrode active material applied to the surface of the positive electrode core.

19. The secondary battery according to claim 18, wherein, A positive electrode tab assembly is formed at the other end of the winding axis of the wound electrode body, on which the positive electrode tab of the positive electrode core is exposed.

20. The secondary battery according to claim 18, wherein, The width of the positive electrode active material layer is 200mm to 400mm.

21. The secondary battery according to claim 1 or 2, wherein, The height of the wound electrode body is 60mm to 120mm.

22. The secondary battery according to claim 1 or 2, wherein, The thickness of the wound electrode body is 5mm to 25mm.

23. The secondary battery according to claim 1 or 2, wherein, The thickness of the positive electrode plate is in the range of 65% to 95% relative to the thickness of the negative electrode plate.

24. A secondary battery, the secondary battery comprising a flat wound electrode body formed by winding a positive electrode plate and a negative electrode plate separated by a separator, and a battery casing housing the wound electrode body, wherein, The flat, wound electrode body has a pair of curved portions with a bent outer surface and a flat portion connecting the pair of curved portions with a flat outer surface. One end of the positive electrode plate, along its long side, is positioned inside the wound electrode body as the positive electrode starting end, while the other end is positioned outside the wound electrode body as the positive electrode ending end. One end of the negative electrode plate, along its long side, is positioned inside the wound electrode body as the negative electrode starting end, while the other end is positioned outside the wound electrode body as the negative electrode ending end. The positive electrode starting end has a first region extending along the flat portion to one end in the long side direction of the positive electrode plate. The positive electrode starting end is positioned close to one of the two bends, and the positive electrode terminal end is positioned at the other bend. The negative electrode starting end has a second region extending along the flat portion, a folded-back portion that folds back from the end of the second region along the curved portion, and a third region extending from the end of the folded-back portion along the flat portion to one end in the long side direction of the negative electrode plate. The wound electrode body has an electrode start-end stack where the first region, the second region, and the third region overlap in the thickness direction. In the thickness direction of the wound electrode body, the second region is located between the first region and the third region.

25. The secondary battery according to claim 24, wherein, The length of the electrode start-end stack in the long side direction of the positive electrode plate is 0.5 mm to 10 mm.

26. The secondary battery according to claim 24 or 25, wherein, The battery casing contains a plurality of the wound electrode bodies.

27. The secondary battery according to claim 26, wherein, In each of the plurality of wound electrode bodies, the length of the electrode beginning stack in the long side direction of the positive electrode plate is different.

28. The secondary battery according to claim 24, wherein, At least one of the positive terminal portion and the negative terminal portion is disposed on the curved portion of the other.

29. The secondary battery according to claim 24 or 25, wherein, The diaphragm has a porous resin substrate layer and a porous surface layer formed on the surface of the porous substrate layer and comprising ceramic particles and an adhesive. The porosity of the porous surface layer in the region not facing the positive and negative electrode plates is 30% to 60%.

30. The secondary battery according to claim 29, wherein, The thickness of the porous surface layer in the separator sandwiched between the positive electrode plate and the negative electrode plate is less than 60% of the thickness of the porous surface layer in the region not facing the positive electrode plate and the negative electrode plate.

31. The secondary battery according to claim 24 or 25, wherein, The wound electrode body is manufactured by winding a stack of layers consisting of a first diaphragm, the negative electrode plate, a second diaphragm, and the positive electrode plate in sequence.

32. The secondary battery according to claim 31, wherein, A first extension portion extending from the negative electrode starting end is formed at one end of the first diaphragm along its long side, and a second extension portion extending from the negative electrode starting end is formed at one end of the second diaphragm along its long side.

33. The secondary battery according to claim 32, wherein, The first extension and the second extension are each folded back along at least one of the pair of bends to form a diaphragm stack consisting only of the first diaphragm and the second diaphragm.

34. The secondary battery according to claim 33, wherein, In the membrane stack, the first membrane layer has three or more layers, and the second membrane layer has two or more layers.

35. The secondary battery according to claim 31, wherein, An adhesive layer is provided on the surface of at least one of the first diaphragm and the second diaphragm.

36. The secondary battery according to claim 35, wherein, The adhesive layer has protrusions that appear as a mesh when viewed from above.

37. The secondary battery according to claim 24 or 25, wherein, The diaphragm is sandwiched between the second region and the third region of the electrode initial stack, and the distance between the second region and the third region in the thickness direction of the wound electrode body is smaller than the thickness of the negative electrode plate.

38. The secondary battery according to claim 37, wherein, The value obtained by subtracting the total thickness of the diaphragm sandwiched between the second and third regions from the distance between the second and third regions in the thickness direction of the wound electrode body is 50 μm or less.

39. The secondary battery according to claim 37, wherein, Three or more layers of the diaphragm are sandwiched between the second region and the third region at the beginning of the negative electrode.

40. The secondary battery according to claim 24 or 25, wherein, The positive electrode plate comprises a positive electrode core as a strip-shaped metal foil and a layer of positive electrode active material applied to the surface of the positive electrode core. The negative electrode plate has a negative electrode core as a strip of metal foil and a layer of negative electrode active material applied to the surface of the negative electrode core.

41. The secondary battery according to claim 40, wherein, A positive electrode tab assembly is formed at one end of the wound electrode body along the winding axis direction, with the positive electrode tabs of the positive electrode core exposed. A negative electrode tab assembly is formed at the other end of the winding axis of the wound electrode body, on which the negative electrode tab of the negative electrode core is exposed.

42. The secondary battery according to claim 40, wherein, The width of the positive electrode active material layer is 200mm to 400mm.

43. The secondary battery according to claim 24 or 25, wherein, The height of the wound electrode body is 60mm to 120mm.

44. The secondary battery according to claim 24 or 25, wherein, The thickness of the wound electrode body is 5mm to 25mm.

45. The secondary battery according to claim 24, wherein, The negative terminal portion is disposed on the curved portion of the other party.

46. ​​The secondary battery according to claim 24 or 25, wherein, The thickness of the positive electrode plate is in the range of 65% to 95% relative to the thickness of the negative electrode plate.

47. A secondary battery, the secondary battery comprising a flat wound electrode body formed by winding a positive electrode plate and a negative electrode plate separated by a separator, and a battery casing housing the wound electrode body, wherein, The flat, wound electrode body has a pair of curved portions with a bent outer surface and a flat portion connecting the pair of curved portions with a flat outer surface. One end of the positive electrode plate, along its long side, is positioned inside the wound electrode body as the positive electrode starting end, while the other end is positioned outside the wound electrode body as the positive electrode ending end. One end of the negative electrode plate, along its long side, is positioned inside the wound electrode body as the negative electrode starting end, while the other end is positioned outside the wound electrode body as the negative electrode ending end. The positive electrode starting end has a first region extending along the flat portion to one end in the long side direction of the positive electrode plate. The negative electrode starting end has a second region extending along the flat portion, a folded-back portion that folds back from the end of the second region along the curved portion, and a third region extending from the end of the folded-back portion along the flat portion to one end in the long side direction of the negative electrode plate. The wound electrode body has an electrode start-end stack where the first region, the second region, and the third region overlap in the thickness direction. In the thickness direction of the wound electrode body, the second region is located between the first region and the third region. The battery casing houses a plurality of wound electrode bodies, and in each of the plurality of wound electrode bodies, the length of the electrode beginning stack in the long side direction of the positive electrode plate is different.

48. The secondary battery according to claim 47, wherein, The length of the electrode start-end stack in the long side direction of the positive electrode plate is 0.5 mm to 10 mm.

49. The secondary battery according to claim 47, wherein, The positive electrode starting end is positioned close to one of the two bends, and the positive electrode terminal end is positioned on the other bend.

50. The secondary battery according to claim 49, wherein, At least one of the positive terminal portion and the negative terminal portion is disposed on the curved portion of the other.

51. The secondary battery according to claim 47 or 48, wherein, The diaphragm has a porous resin substrate layer and a porous surface layer formed on the surface of the porous substrate layer and comprising ceramic particles and an adhesive. The porosity of the porous surface layer in the region not facing the positive and negative electrode plates is 30% to 60%.

52. The secondary battery according to claim 51, wherein, The thickness of the porous surface layer in the separator sandwiched between the positive electrode plate and the negative electrode plate is less than 60% of the thickness of the porous surface layer in the region not facing the positive electrode plate and the negative electrode plate.

53. The secondary battery according to claim 47 or 48, wherein, The wound electrode body is manufactured by winding a stack of layers consisting of a first diaphragm, the negative electrode plate, a second diaphragm, and the positive electrode plate in sequence.

54. The secondary battery according to claim 53, wherein, A first extension portion extending from the negative electrode starting end is formed at one end of the first diaphragm along its long side, and a second extension portion extending from the negative electrode starting end is formed at one end of the second diaphragm along its long side.

55. The secondary battery according to claim 54, wherein, The first extension and the second extension are each folded back along at least one of the pair of bends to form a diaphragm stack consisting only of the first diaphragm and the second diaphragm.

56. The secondary battery according to claim 55, wherein, In the membrane stack, the first membrane layer has three or more layers, and the second membrane layer has two or more layers.

57. The secondary battery according to claim 53, wherein, An adhesive layer is provided on the surface of at least one of the first diaphragm and the second diaphragm.

58. The secondary battery according to claim 57, wherein, The adhesive layer has protrusions that appear as a mesh when viewed from above.

59. The secondary battery according to claim 47 or 48, wherein, The diaphragm is sandwiched between the second region and the third region of the electrode initial stack, and the distance between the second region and the third region in the thickness direction of the wound electrode body is smaller than the thickness of the negative electrode plate.

60. The secondary battery according to claim 59, wherein, The value obtained by subtracting the total thickness of the diaphragm sandwiched between the second and third regions from the distance between the second and third regions in the thickness direction of the wound electrode body is 50 μm or less.

61. The secondary battery according to claim 59, wherein, Three or more layers of the diaphragm are sandwiched between the second region and the third region at the beginning of the negative electrode.

62. The secondary battery according to claim 47 or 48, wherein, The positive electrode plate comprises a positive electrode core as a strip-shaped metal foil and a layer of positive electrode active material applied to the surface of the positive electrode core. The negative electrode plate has a negative electrode core as a strip of metal foil and a layer of negative electrode active material applied to the surface of the negative electrode core.

63. The secondary battery according to claim 62, wherein, A positive electrode tab assembly is formed at one end of the wound electrode body along the winding axis direction, with the positive electrode tabs of the positive electrode core exposed. A negative electrode tab assembly is formed at the other end of the winding axis of the wound electrode body, on which the negative electrode tab of the negative electrode core is exposed.

64. The secondary battery according to claim 62, wherein, The width of the positive electrode active material layer is 200mm to 400mm.

65. The secondary battery according to claim 47 or 48, wherein, The height of the wound electrode body is 60mm to 120mm.

66. The secondary battery according to claim 47 or 48, wherein, The thickness of the wound electrode body is 5mm to 25mm.

67. The secondary battery according to claim 47 or 48, wherein, The thickness of the positive electrode plate is in the range of 65% to 95% relative to the thickness of the negative electrode plate.

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