Secondary battery

Abstract

The present invention provides a secondary battery having a wound electrode body wound with high precision. The secondary battery (100) includes a wound electrode body (40) formed by winding a positive electrode plate (10) and a negative electrode plate (20) with a separator (30) interposed therebetween, and a battery case (50) housing the wound electrode body (40). The separator (30) has a strip-shaped base material layer (32) and a surface layer (34) formed on the surface of the base material layer (32) and having a network structure made of polyvinylidene fluoride. The separator (30) is disposed outside the negative electrode terminal portion (20e) of the negative electrode plate (20), and the distance between the negative electrode terminal portion (20e) and the separator terminal portion (30e) of the separator (30) is 30 mm or less.

Description

Technical Field

[0001] The present invention relates to a secondary battery. Background Art

[0002] Secondary batteries such as lithium ion secondary batteries generally include: an electrode body having a pair of electrode plates (a positive electrode plate and a negative electrode plate); a battery case housing the electrode body; and electrode terminals (a positive electrode terminal and a negative electrode terminal) exposed to the outside of the battery case. Moreover, each electrode plate constituting the electrode body includes, for example, an electrode core (a positive electrode core and a negative electrode core) as a foil-shaped metal member and an electrode active material layer (a positive electrode active material layer and a negative electrode active material layer) formed on the surface of the electrode core.

[0003] As an example of the electrode body of such a secondary battery, a wound electrode body in which a positive electrode plate and a negative electrode plate are wound with a separator interposed therebetween can be cited. As the separator of such a wound electrode body, a porous strip-shaped film having a base material layer made of a resin material such as polyethylene (PE) is generally used. In addition, from the viewpoint of improving the safety of the secondary battery, a separator having a heat-resistant surface layer formed on the surface of the base material layer is sometimes used. For example, in Patent Document 1, a separator having a porous resin layer (base material layer) and a porous heat-resistant layer (surface layer) laminated on at least one surface of the resin layer is disclosed. Moreover, the heat-resistant layer includes a filler made of an inorganic material and a binder. The separator having such a heat-resistant layer suppresses thermal shrinkage when the temperature rises, and thus can prevent the occurrence of an internal short circuit and improve the safety of the secondary battery.

[0004] Prior Art Documents

[0005] Patent Documents

[0006] Patent Document 1: International Publication No. 2012 / 124093 Summary of the Invention

[0007] Problems to be Solved by the Invention

[0008] In addition, sometimes polyvinylidene fluoride is used as the binder constituting the surface layer. The surface layer formed of polyvinylidene fluoride has a network structure and a relatively large specific surface area. Therefore, the electrode plate in contact with the surface layer of the separator is bonded to the surface layer, thereby suppressing the winding deviation of the entire electrode body. Here, when winding the electrode plate and the separator to form a wound electrode body, it is necessary to make the separator longer than the electrode plate so that the separator is located on the outermost periphery of the electrode body. The separator having a surface layer made of polyvinylidene fluoride has a property of being relatively easily charged. Therefore, when the separator is wound alone using a winding device (such as a winding roller), the separator itself may be charged and stick to the winding device or the like, or creases and wrinkles may occur in the separator during the winding of the separator, resulting in inaccurate winding. In a secondary battery manufactured using a wound electrode body in which the electrode plate and the separator are not accurately wound, uneven pressure is generated on the electrode body, the reaction during charge and discharge becomes uneven, and lithium may precipitate.

[0009] The present invention has been completed in view of the above circumstances, and an object thereof is to provide a secondary battery including a wound electrode body that is accurately wound.

[0010] Means for Solving the Problem

[0011] According to the present invention, there is provided a secondary battery including a wound electrode body formed by winding a positive electrode plate and a negative electrode plate with a separator interposed therebetween, and a battery case for housing the wound electrode body. The positive electrode plate has a strip-shaped positive electrode core and a positive electrode active material layer formed on at least one surface of the positive electrode core. The negative electrode plate has a strip-shaped negative electrode core and a negative electrode active material layer formed on at least one surface of the negative electrode core. The separator has a strip-shaped base material layer and a surface layer formed on at least one surface of the base material layer and having a network structure made of polyvinylidene fluoride. One end in the length direction of the negative electrode plate, i.e., the negative electrode starting end, is located inside the wound electrode body, and the other end in the length direction of the negative electrode plate, i.e., the negative electrode terminal end, is located outside the wound electrode body. One end in the length direction of the separator, i.e., the separator starting end, is located inside the wound electrode body, and the other end in the length direction of the separator, i.e., the separator terminal end, is located outside the wound electrode body. The separator is disposed outside the negative electrode terminal end, and the distance between the negative electrode terminal end and the separator terminal end is 30 mm or less.

[0012] The inventors of the present application have conducted various studies. As a result, it has been found that when the distance between the winding end portion of the negative electrode plate (negative electrode terminal portion) and the winding end portion of the separator (separator terminal portion) is too long, the separator is further charged, and it is easy for the separator to generate creases and wrinkles. Therefore, it has been found that by further shortening the distance between the negative electrode terminal portion and the separator terminal portion, the occurrence of the above problems can be suppressed. That is, the distance between the negative electrode terminal portion and the separator terminal portion is set to 30 mm or less. By shortening the distance between the negative electrode terminal portion and the separator terminal portion in this way, the length of the separator wound alone becomes shorter. Thereby, the generation of creases and wrinkles in the separator is suppressed. In addition, when the separator is wound alone, the contact time between the separator and the winding device becomes shorter. Therefore, the charging of the separator is suppressed. Thereby, it is possible to suppress the separator from sticking to the winding device or the like, and the separator or the like can be wound with high precision. According to the above, by setting the distance between the negative electrode terminal portion and the separator terminal portion to 30 mm or less, a secondary battery having a wound electrode body wound with high precision can be obtained.

[0013] In a preferred embodiment of the secondary battery disclosed herein, the wound electrode body is formed in a flat shape and has a pair of curved portions with a curved outer surface and a flat portion with a flat outer surface connecting the pair of curved portions. When the direction perpendicular to the winding axis direction of the wound electrode body and perpendicular to the thickness direction of the wound electrode body is set as the height direction, the dimension of the wound electrode body in the height direction is 80 mm or more. When the wound electrode body is pressed into a flat shape, the surface layer made of polyvinylidene fluoride and the electrode plates (here, the positive electrode plate and the negative electrode plate) in contact with it are firmly bonded. Thereby, the rebound of the wound electrode body after pressing is suppressed, and the flat shape can be appropriately maintained. In addition, when the dimension of the wound electrode body in the height direction is 80 mm or more, the influence caused by the length of the distance between the negative electrode terminal portion and the separator terminal portion is particularly significant. Therefore, the effect brought about by setting the distance between the negative electrode terminal portion and the separator terminal portion to 30 mm or less is further exerted.

[0014] In a preferred embodiment of the secondary battery disclosed herein, when the direction parallel to the winding axis direction of the wound electrode body and perpendicular to the thickness direction of the wound electrode body is set as the width direction, the dimension of the wound electrode body in the width direction is 200 mm or more. When the dimension of the wound electrode body in the width direction is 200 mm or more, the influence caused by the size of the exposed area of the separator (the area exposed in the winding axis direction) is particularly significant. Therefore, the effect brought about by setting the distance between the negative electrode terminal portion and the separator terminal portion to 30 mm or less is further exerted.

[0015] In a preferred embodiment of the secondary battery disclosed herein, when the distance between the negative electrode terminal portion and the separator terminal portion is A and the dimension in the height direction of the flat portion of the wound electrode body is B, the following formula is satisfied: A < 0.4B. Thereby, when manufacturing the wound electrode body, generation of creases and wrinkles in the separator is suppressed, and charging of the separator is suppressed. As a result, a secondary battery including a wound electrode body wound with high precision can be obtained.

[0016] In a preferred embodiment of the secondary battery disclosed herein, the negative electrode terminal portion is located at the bent portion. Thereby, the separator can be further shortened.

[0017] In a preferred embodiment of the secondary battery disclosed herein, a winding fixing tape for pasting the terminal portion of the separator to the outermost surface of the wound electrode body is provided. When the distance between the negative electrode terminal portion and the separator terminal portion is A and the length of the winding fixing tape is C, the following formula is satisfied: 20 ≤ C ≤ 40, A ≥ 1 / 2C. Thereby, loosening of the winding of the wound electrode body can be suppressed, and since the winding fixing tape does not overlap with the negative electrode terminal portion, a height difference caused by the thickness of the winding fixing tape can be reduced.

[0018] In a preferred embodiment of the secondary battery disclosed herein, a winding fixing tape for pasting the terminal portion of the separator to the outermost circumference of the wound electrode body is provided. The separator terminal portion is located in the central region in the length direction of the winding fixing tape, and the winding fixing tape does not overlap with the negative electrode terminal portion. Thereby, loosening of the winding of the wound electrode body can be suppressed, and since the winding fixing tape does not overlap with the negative electrode terminal portion, a height difference caused by the thickness of the winding fixing tape can be reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a perspective view schematically showing a secondary battery according to an embodiment.

[0020] Figure 2 is along Figure 1 a schematic longitudinal sectional view taken along line II-II in

[0021] Figure 3 is along Figure 1 a schematic longitudinal sectional view taken along line III-III in

[0022] Figure 4 is along Figure 1 a schematic transverse sectional view taken along line IV-IV in

[0023] Figure 5 is a perspective view schematically showing an electrode body mounted on a sealing plate.

[0024] Figure 6It is a perspective view schematically showing an electrode body equipped with a second positive current collector and a second negative current collector.

[0025] Figure 7 It is a schematic diagram showing the structure of a wound electrode body of a secondary battery according to an embodiment.

[0026] Figure 8 It schematically shows Figure 7 a front view of the wound electrode body.

[0027] Figure 9 It is a schematic longitudinal sectional view along the IX-IX line in Figure 8 the above.

[0028] Figure 10 It is an enlarged view schematically showing the interface of the positive electrode plate, negative electrode plate and separator of the wound electrode body of a secondary battery according to an embodiment.

[0029] Explanation of reference numerals

[0030] 10 Positive electrode plate

[0031] 12 Positive electrode core

[0032] 14 Positive electrode active material layer

[0033] 16 Protective layer

[0034] 20 Negative electrode plate

[0035] 20e Negative electrode terminal part

[0036] 22 Negative electrode core

[0037] 24 Negative electrode active material layer

[0038] 30 Separator

[0039] 30e Separator terminal part

[0040] 32 Substrate layer

[0041] 34 Surface layer

[0042] 38 Winding fixing band

[0043] 40 Wound electrode body

[0044] 40f Flat part

[0045] 40r Bending part

[0046] 42 Positive electrode tab group

[0047] 44 Negative electrode tab group

[0048] 50 Battery case

[0049] 60 Positive terminal

[0050] 65 Negative terminal

[0051] 70 Positive current collector

[0052] 75 Negative current collector

[0053] 100 Secondary battery. Detailed implementation manners

[0054] Hereinafter, embodiments of the technology disclosed herein will be described with reference to the accompanying drawings. In addition, matters required for implementing the technology disclosed herein other than those specifically mentioned in this specification (for example, the general structure and manufacturing process of the battery) can be grasped as design matters made by those skilled in the art based on the prior art in this field. The technology disclosed herein can be implemented based on the content disclosed in this specification and the common general knowledge in this field. In addition, in this specification, the expression "A to B" indicating a range means "A or more and B or less", and includes the meaning of "preferably greater than A" and "preferably less than B".

[0055] In addition, in this specification, a "secondary battery" refers to a general electrical storage device in which a charge-discharge reaction occurs by the movement of charge carriers between a pair of electrodes (a positive electrode and a negative electrode) via an electrolyte. In addition to so-called storage batteries such as lithium-ion secondary batteries, nickel-metal hydride batteries, and nickel-cadmium batteries, this secondary battery also includes capacitors such as electric double layer capacitors. Hereinafter, embodiments in the case of taking the lithium-ion secondary battery among the above secondary batteries as an object will be described.

[0056] In addition, in the respective drawings referred to in this specification, the reference numeral X in the drawings represents the "depth direction", the reference numeral Y represents the "width direction", and the reference numeral Z represents the "height direction". In addition, F in the depth direction X represents "front", and Rr represents "rear". L in the width direction Y represents "left", and R represents "right". Moreover, U in the height direction Z represents "up", and D represents "down". However, these directions are determined for the convenience of explanation and are not intended to limit the installation method when using the secondary battery disclosed herein.

[0057] <First Embodiment>

[0058] 1. Structure of the secondary battery

[0059] Hereinafter, with reference to Figures 1 to 10 An embodiment of the secondary battery disclosed herein will be described. Figure 1 is a schematic perspective view showing the secondary battery of this embodiment. Figure 2 is along Figure 1 in the schematic longitudinal sectional view taken along line II-II in Figure 3is along Figure 1 a schematic longitudinal sectional view taken along line III-III in Figure 4 is along Figure 1 a schematic transverse sectional view taken along line IV-IV in Figure 5 is a perspective view schematically showing an electrode body mounted on a sealing plate. Figure 6 is a perspective view schematically showing an electrode body on which a positive second current collector and a negative second current collector are mounted. Figure 7 is a schematic view showing the structure of a wound electrode body of a secondary battery according to the present embodiment. Figure 8 is schematically showing Figure 7 a front view of the wound electrode body. Figure 9 is along Figure 8 a schematic longitudinal sectional view taken along line IX-IX in Figure 10 is an enlarged view schematically showing an interface between a positive electrode plate, a negative electrode plate, and a separator of a wound electrode body of a secondary battery according to the present embodiment.

[0060] As Figure 2 shown, the secondary battery 100 according to the present embodiment includes a wound electrode body 40 and a battery case 50 that houses the wound electrode body 40. Hereinafter, the specific structure of the secondary battery 100 will be described.

[0061] (1) Battery case

[0062] The battery case 50 is a housing that houses the wound electrode body 40. Although not shown, a non-aqueous electrolyte is also housed inside the battery case 50. As Figure 1 shown, the battery case 50 in the present embodiment has an outer shape of a flat and bottomed rectangular parallelepiped (square) shape. In addition, as the battery case 50, conventionally known materials can be used without particular limitation. For example, the battery case 50 can be made of metal. As an example of the material of the battery case 50, aluminum, aluminum alloy, iron, iron alloy, etc. can be cited.

[0063] As Figure 1 and Figure 2As shown, the battery case 50 includes an outer package 52 and a sealing plate 54. The outer package 52 is a flat bottomed square container having an opening 52h on its upper surface. The outer package 52 includes a bottom wall 52a that is substantially rectangular in plan view, a pair of long side walls 52b that extend upward in the height direction Z from the long sides of the bottom wall 52a, and a pair of short side walls 52c that extend upward in the height direction Z from the short sides of the bottom wall 52a. On the other hand, the sealing plate 54 is a plate-like member that closes the opening 52h of the outer package 52 and is substantially rectangular in plan view. Moreover, the outer peripheral edge portion of the sealing plate 54 is joined (e.g., welded) to the outer peripheral edge portion of the opening 52h of the outer package 52. Thus, a battery case 50 that is hermetically sealed inside is produced. In addition, a liquid injection hole 55 and a gas discharge valve 57 are provided in the sealing plate 54. The liquid injection hole 55 is a through hole provided for injecting a non-aqueous electrolyte into the interior of the sealed battery case 50. In addition, the liquid injection hole 55 is sealed by a sealing member 56 after the injection of the non-aqueous electrolyte. Further, the gas discharge valve 57 is a thin wall portion designed to break (open) and discharge the gas when a large amount of gas is generated inside the battery case 50.

[0064] (2) Electrolyte

[0065] As described above, inside the battery case 50, in addition to the wound electrode body 40, an electrolyte (not shown) is also accommodated. As the electrolyte, an electrolyte used in a conventional secondary battery can be used without particular limitation. For example, as the electrolyte, a non-aqueous electrolyte in which a supporting salt is dissolved in a non-aqueous solvent can be used. As an example of the non-aqueous solvent, carbonate solvents such as ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate can be cited. As an example of the supporting salt, fluorine-containing lithium salts such as LiPF 6 and the like can be cited.

[0066] (3) Electrode terminals

[0067] In addition, a positive electrode terminal 60 is mounted on one end ( Figure 1 , Figure 2 the left side in) of the sealing plate 54 in the width direction Y. The positive electrode terminal 60 is connected to a plate-like positive electrode external conductive member 62 outside the battery case 50. On the other hand, a negative electrode terminal 65 is mounted on the other end ( Figure 1 , Figure 2 the right side in) of the sealing plate 54 in the width direction Y. A plate-like negative electrode external conductive member 67 is mounted on the negative electrode terminal 65. These external conductive members (the positive electrode external conductive member 62 and the negative electrode external conductive member 67) are connected to other secondary batteries and external devices via an external connection member (such as a bus bar). In addition, the external conductive member is preferably made of a metal (aluminum, aluminum alloy, copper, copper alloy, etc.) having excellent conductivity.

[0068] (4) Electrode current collector

[0069] As Figures 3 to 5 shown, in the secondary battery 100 of the present embodiment, a plurality (three) of wound electrode bodies 40 are housed in the battery case 50. Although the detailed structure will be described later, a positive electrode tab group 42 and a negative electrode tab group 44 are provided on each of the wound electrode bodies 40 (refer to Figure 7 and Figure 8 ). As Figure 4 shown, these electrode tab groups (positive electrode tab group 42 and negative electrode tab group 44) are bent in a state where the electrode current collectors (positive electrode current collector 70 and negative electrode current collector 75) are joined.

[0070] Specifically, the positive electrode tab group 42 of each of the plurality of wound electrode bodies 40 is connected to the positive electrode terminal 60 via the positive electrode current collector 70. The positive electrode current collector 70 is housed inside the battery case 50. As Figure 2 and Figure 5 shown, the positive electrode current collector 70 includes a positive electrode first current collector 71 and a plurality of positive electrode second current collectors 72. The positive electrode first current collector 71 is a plate-shaped conductive member extending in the width direction Y along the inner side surface of the sealing plate 54, and the positive electrode second current collector 72 is a plate-shaped conductive member extending in the height direction Z. Moreover, the lower end portion 60c of the positive electrode terminal 60 is inserted into the inside of the battery case 50 through the terminal insertion hole 58 of the sealing plate 54 and connected to the positive electrode first current collector 71 (refer to Figure 2 ). On the other hand, as Figures 4 to 6 shown, in this secondary battery 100, the same number of positive electrode second current collectors 72 as the number of wound electrode bodies 40 is provided. Each positive electrode second current collector 72 is connected to the positive electrode tab group 42 of the wound electrode body 40. Moreover, as Figure 4 and Figure 5 shown, the positive electrode tab group 42 of the wound electrode body 40 is bent so that the positive electrode second current collector 72 faces one side surface 40a of the wound electrode body 40. Thereby, the upper end portion of the positive electrode second current collector 72 is electrically connected to the positive electrode first current collector 71.

[0071] On the other hand, the negative electrode tab group 44 of each of the plurality of wound electrode bodies 40 is connected to the negative electrode terminal 65 via the negative electrode current collector 75. The connection structure on the negative electrode side is substantially the same as the connection structure on the positive electrode side described above. Specifically, the negative electrode current collector 75 includes a negative electrode first current collector 76 and a plurality of negative electrode second current collectors 77. The negative electrode first current collector 76 is a plate-shaped conductive member extending in the width direction Y along the inner side surface of the sealing plate 54, and the negative electrode second current collector 77 is a plate-shaped conductive member extending in the height direction Z (refer to Figure 2 and Figure 5)。Moreover, the lower end portion 65c of the negative terminal 65 is inserted into the interior of the battery case 50 through the terminal insertion holes 59 and is connected to the negative first current collector 76 (see Figure 2 ). On the other hand, the plurality of negative second current collectors 77 are respectively connected to the negative electrode tab group 44 of the wound electrode body 40 (see Figures 4 to 6 ). Moreover, the negative electrode tab group 44 is bent so that the negative second current collector 77 faces the other side surface 40b of the wound electrode body 40. Thus, the upper end portion of the negative second current collector 77 is electrically connected to the negative first current collector 76. In addition, as the electrode current collectors (the positive current collector 70 and the negative current collector 75), metals (such as aluminum, aluminum alloy, copper, copper alloy, etc.) with excellent conductivity can also be preferably used.

[0072] (5) Insulating member

[0073] In addition, in this secondary battery 100, various insulating members are installed to prevent conduction between the wound electrode body 40 and the battery case 50. Specifically, an external insulating member 92 is interposed between the positive external conductive member 62 (negative external conductive member 67) and the outer side surface of the sealing plate 54 (see Figure 1 ). Thus, conduction between the positive external conductive member 62, the negative external conductive member 67 and the sealing plate 54 can be prevented. In addition, gaskets 90 are respectively installed in the terminal insertion holes 58, 59 of the sealing plate 54 (see Figure 2 ). Thus, conduction between the positive terminal 60 (or negative terminal 65) inserted into the terminal insertion holes 58, 59 and the sealing plate 54 can be prevented. In addition, an internal insulating member 94 is disposed between the positive first current collector 71 (or negative first current collector 76) and the inner side surface of the sealing plate 54. The internal insulating member 94 includes a plate-shaped base portion 94a interposed between the positive first current collector 71 (or negative first current collector 76) and the inner side surface of the sealing plate 54. Thus, conduction between the positive first current collector 71, the negative first current collector 76 and the sealing plate 54 can be prevented. And the internal insulating member 94 includes a protruding portion 94b protruding from the inner side surface of the sealing plate 54 toward the wound electrode body 40 (see Figure 2 and Figure 3 ). Thus, movement of the wound electrode body 40 in the height direction Z can be restricted, and direct contact between the wound electrode body 40 and the sealing plate 54 can be prevented. In addition, the plurality of wound electrode bodies 40 are supported by an electrode body support 98 made of an insulating resin sheet (see Figure 3) The covered state is stored inside the battery case 50. Thereby, direct contact between the wound electrode body 40 and the exterior body 52 can be prevented. In addition, the material of each of the above-described insulating members is not particularly limited as long as it has a prescribed insulation property. As an example, synthetic resin materials such as polyolefin resins (e.g., polypropylene (PP), polyethylene (PE)), fluorine resins (e.g., perfluoroalkoxy alkane (PFA), polytetrafluoroethylene (PTFE)) can be used.

[0074] (6) Wound electrode body

[0075] As Figure 7 shown, the electrode body used in the secondary battery 100 of the present embodiment is a flat wound electrode body 40 formed by winding a positive electrode plate 10 and a negative electrode plate 20 with a separator 30 interposed therebetween. Moreover, the flat wound electrode body 40 has a pair of bent portions 40r whose outer surfaces are bent and a flat portion 40f whose outer surface connects the pair of bent portions 40r. In addition, in the secondary battery 100, the wound electrode body 40 is stored in the battery case 50 such that the winding axis WL of the wound electrode body 40 substantially coincides with the width direction Y of the secondary battery 100 (see Figure 2 ). That is, the “winding axis direction” in the following description is substantially the same direction as the width direction Y in the drawing. The thickness t1 of the wound electrode body 40 (see Figure 9 ) is preferably 10 mm or more. The thickness t1 is, for example, preferably 10 mm to 25 mm, more preferably 11 mm to 15 mm. The “thickness of the wound electrode body” means the distance between a pair of flat portions 40f. That is, the “thickness of the wound electrode body” means the length of the wound electrode body 40 in the depth direction X. The dimension h1 in the height direction Z of the wound electrode body 40 (see Figure 8 ) is preferably 80 mm or more. The dimension h1 is, for example, preferably 80 mm to 100 mm, more preferably 90 mm to 95 mm. The “dimension in the height direction of the wound electrode body” means the length of the wound electrode body 40 in a direction perpendicular to the winding axis direction of the wound electrode body 40 and perpendicular to the thickness direction of the wound electrode body 40. That is, the “dimension in the height direction of the wound electrode body” means the length of the wound electrode body 40 in the height direction Z. The dimension WX in the width direction Y of the wound electrode body 40 (see Figure 7 ) is preferably 200 mm or more. The dimension WX is, for example, preferably 200 mm to 400 mm, more preferably 275 mm to 300 mm. The “dimension in the width direction of the wound electrode body” means the length of the wound electrode body 40 in a direction perpendicular to the winding axis direction of the wound electrode body 40 and perpendicular to the thickness direction of the wound electrode body 40. That is, the “dimension in the width direction of the wound electrode body” means the length of the wound electrode body 40 in the width direction Y.

[0076] (a) Positive electrode plate

[0077] As Figure 7 and Figure 10 shown, the positive electrode plate 10 is a long strip-shaped member. 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. In addition, 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. Further, in this positive electrode plate 10, a positive electrode tab 12t protrudes outward from one end edge in the winding axis direction (width direction Y) ( Figure 7 the left side in). Moreover, a plurality of the positive electrode tabs 12t are formed at a predetermined interval in the length direction of the long strip-shaped positive electrode plate 10. The positive electrode tab 12t is a region where the positive electrode core 12 is exposed without applying the positive electrode active material layer 14. Further, in a region adjacent to the end edge on the positive electrode tab 12t side of the positive electrode plate 10, a protective layer 16 extending in the length direction of the positive electrode plate 10 is formed.

[0078] As each member constituting the positive electrode plate 10, conventionally known materials that can be used in general secondary batteries (for example, lithium ion secondary batteries) can be used without particular limitation. For example, as the positive electrode core 12, a metal material having a predetermined conductivity can be preferably used. The positive electrode core 12 is preferably composed of, for example, aluminum, an aluminum alloy, or the like.

[0079] In addition, the positive electrode active material layer 14 is a layer containing a positive electrode active material. The positive electrode active material is a granular material capable of reversibly occluding 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 above lithium transition metal composite oxides, as the transition metal, a lithium transition metal composite oxide containing at least one of the group consisting of nickel (Ni), cobalt (Co), and manganese (Mn) is particularly preferred. Specific examples include lithium nickel cobalt manganese composite oxides (NCM), lithium nickel composite oxides, lithium cobalt composite oxides, lithium manganese composite oxides, lithium nickel manganese composite oxides, lithium nickel cobalt aluminum composite oxides (NCA), lithium iron nickel manganese composite oxides, etc. In addition, as a preferred example of a lithium transition metal composite oxide not containing Ni, Co, and Mn, a lithium iron phosphate composite oxide (LFP), etc. can be cited. In addition, the term "lithium nickel cobalt manganese composite oxide" in this specification is a term for an oxide containing elements added in addition to the main constituent elements (Li, Ni, Co, Mn, O). Examples of such 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, Sn, etc., typical metal elements, etc. In addition, the added element may also be a semi-metal element such as B, C, Si, P, etc., or a non-metal element such as S, F, Cl, Br, I, etc. Although detailed description is omitted, this also applies to other lithium transition metal composite oxides described as "~ composite oxide". In addition, the positive electrode active material layer 14 may also contain additives other than the positive electrode active material. As an example of such an additive, a conductive material, a binder, etc. can be cited. As a specific example of the conductive material, a carbon material such as acetylene black (AB) can be cited. As a specific example of the binder, a resin binder such as polyvinylidene fluoride (PVdF) can be cited. In addition, when the total solid content of the positive electrode active material layer 14 is set to 100% by mass, the content of the positive electrode active material is approximately 80% by mass or more, typically 90% by mass or more.

[0080] The width dimension w1 of the positive electrode active material layer 14 (refer to Figure 7 ) is preferably 100 mm or more. The width dimension w1 of the positive electrode active material layer 14 is preferably 100 mm to 350 mm, more preferably 275 mm to 300 mm. As the width dimension w1 of the positive electrode active material layer 14 becomes longer, the wound electrode body 40 becomes larger, and thus, there is a tendency for static electricity to easily be generated in the separator 30 and for creases and wrinkles to easily be generated in the separator 30 at the end of winding the separator 30. In addition, the above "width dimension of the positive electrode active material layer" refers to the length of the positive electrode active material layer in the direction in which the winding axis of the wound electrode body extends (winding axis direction).

[0081] On the other hand, the protective layer 16 is configured to have a lower conductivity than the positive electrode active material layer 14. By disposing the protective layer 16 in a region adjacent to the edge of the positive electrode plate 10, it is possible to prevent an internal short circuit caused by direct contact between the positive electrode core 12 and the negative electrode active material layer 24 when the separator 30 is damaged. For example, as the protective layer 16, a layer containing insulating ceramic particles is preferably formed. Examples of such ceramic particles include alumina (Al 2 O 3 ), magnesium oxide (MgO), silicon dioxide (SiO 2 ), titanium dioxide (TiO 2 ) and other inorganic oxides, nitrides such as aluminum nitride and silicon nitride, metal hydroxides such as calcium hydroxide, magnesium hydroxide, and aluminum hydroxide, clay minerals such as mica, talc, boehmite, zeolite, apatite, and kaolin, and glass fibers. Considering insulation and heat resistance, among the above materials, alumina, boehmite, aluminum hydroxide, silicon dioxide, and titanium dioxide are preferred. In addition, the protective layer 16 may also contain a binder for fixing the above ceramic particles to the surface of the positive electrode core 12. Examples of such a binder include resin binders such as polyvinylidene fluoride (PVdF). In addition, the protective layer is not an essential component of the positive electrode plate. That is, in the secondary battery disclosed herein, a positive electrode plate without a protective layer can also be used.

[0082] In addition, the thickness t2 of the positive electrode plate 10 (see Figure 10 ) is preferably 80 μm or more, more preferably 100 μm or more, and still more preferably 120 μm or more. Since the positive electrode plate 10 having such a sufficient thickness has a large elastic effect after stamping, there may be springback in which the flat portion 40f expands due to the elastic effect remaining in the bent portion 40r, and the interelectrode distance is likely to increase. Details will be described later, but according to the technology disclosed herein, it is also possible to appropriately suppress the increase in the interelectrode distance caused by springback. In addition, from the viewpoint of easily preventing springback, the thickness of the positive electrode plate 10 is preferably 200 μm or less, more preferably 180 μm or less, and still more preferably 160 μm or less. In addition, the "thickness of the positive electrode plate" in this specification is the total thickness of the positive electrode core and the positive electrode active material layer.

[0083] (b) Negative electrode plate

[0084] As shown in Figure 7 and Figure 10 , the negative electrode plate 20 is a long strip-shaped member. The negative electrode plate 20 includes a negative electrode core 22 that is a strip-shaped metal foil and a negative electrode active material layer 24 applied to the surface of the negative electrode core 22. In addition, 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. And, in the negative electrode plate 20, there is provided a portion that extends outward from one end edge in the winding axis direction (width direction Y)Figure 7 The protruding negative electrode tab 22t on the right side in []. A plurality of the negative electrode tabs 22t are provided at a predetermined interval in the longitudinal direction of the negative electrode plate 20. The negative electrode tab 22t is an area where the negative electrode core 22 is exposed without applying the negative electrode active material layer 24.

[0085] As each member constituting the negative electrode plate 20, conventionally known materials that can be used in general secondary batteries (for example, lithium ion secondary batteries) can be used without particular limitation. For example, as the negative electrode core 22, a metal material having a predetermined conductivity is preferably used. The negative electrode core 22 is preferably made of copper, a copper alloy, or the like.

[0086] In addition, the negative electrode active material layer 24 is a layer containing a negative electrode active material. As the negative electrode active material, there is no particular limitation as long as it can reversibly occlude and release charge carriers in relation to the above-mentioned positive electrode active material, and materials that can be used in conventional general secondary batteries can be used without particular limitation. Examples of the negative electrode active material include carbon materials and silicon-based materials. As the carbon material, for example, graphite, hard carbon, soft carbon, amorphous carbon, etc. can be used. In addition, amorphous carbon-coated graphite in which the surface of graphite is coated with amorphous carbon can also be used. On the other hand, examples of the silicon-based materials include silicon, silicon oxide (silicon dioxide), etc. In addition, the silicon-based materials may contain other metal elements (for example, alkaline earth metals) and their oxides. In addition, the negative electrode active material layer 24 may contain additives other than the negative electrode active material. As an example of the additive, a binder, a thickener, etc. can be cited. As a specific example of the binder, a rubber-based binder such as styrene-butadiene rubber (SBR) can be cited. In addition, as a specific example of the thickener, carboxymethyl cellulose (CMC) etc. can be cited. In addition, when the total solid content of the negative electrode active material layer 24 is set to 100% by mass, the content of the negative electrode active material is approximately 30% by mass or more, typically 50% by mass or more. In addition, the negative electrode active material may account for 80% by mass or more of the negative electrode active material layer 24, or may account for 90% by mass or more. In addition, the width dimension w2 of the negative electrode active material layer 24 (refer to Figure 7 ) is preferably 120 mm or more. The width dimension w2 of the negative electrode active material layer 24 is preferably 120 mm to 370 mm, more preferably 280 mm to 305 mm.

[0087] In addition, the thickness t3 of the negative electrode plate 20 (refer to Figure 10)Preferably 100 μm or more, more preferably 130 μm or more, and further preferably 160 μm or more. Similar to the above-described positive electrode plate 10, if the negative electrode plate 20 becomes thicker, it may promote an increase in the interelectrode distance caused by springback. However, according to the technology disclosed herein, even when using a negative electrode plate 20 having such a thickness, the occurrence of springback can be appropriately suppressed. On the other hand, from the viewpoint of easily preventing springback, the thickness of the negative electrode plate 20 is preferably 250 μm or less, more preferably 220 μm or less, and further preferably 190 μm or less. In addition, the "thickness of the negative electrode plate" in this specification is the total thickness of the negative electrode core and the negative electrode active material layer.

[0088] (c) Separator

[0089] As Figure 7 and Figure 9 shown, the wound electrode body 40 in the present embodiment includes two separators 30. Each separator 30 is an insulating sheet formed with a plurality of minute through-holes through which charge carriers can pass. By interposing the separator 30 between the positive electrode plate 10 and the negative electrode plate 20, contact between the positive electrode plate 10 and the negative electrode plate 20 can be prevented, and charge carriers (e.g., lithium ions) can move between the positive electrode plate 10 and the negative electrode plate 20.

[0090] As Figure 10 shown, the separator 30 in the present embodiment has a strip-shaped base material layer 32 and surface layers 34 formed on the surfaces (both sides) of the base material layer 32. The detailed functions will be described later, but in the present embodiment, one surface layer 34 of the separator 30 having the above structure is bonded to the positive electrode plate 10, and the other surface layer 34 is bonded to the negative electrode plate 20. Thereby, the interelectrode distance maintaining function provided by the separator 30 is sufficiently exerted. In addition, the flat portion 40f of the wound electrode body 40 (refer to Figure 9 ) is restricted from expanding in the thickness direction (depth direction X), and therefore, an increase in the interelectrode distance caused by springback can also be suppressed. Hereinafter, the separator 30 having this structure will be described.

[0091] First, the base material layer 32 can be used without particular limitation as the base material layer used in a conventionally known separator for a secondary battery. For example, the base material layer 32 is preferably a porous sheet-like member containing a polyolefin resin or the like. Thereby, the flexibility of the separator 30 can be sufficiently ensured, and the production (winding and stamping) of the wound electrode body 40 can be easily performed. In addition, as the polyolefin resin, polyethylene (PE), polypropylene (PP), or the like, or a mixture thereof can be used. The base material layer 32 is preferably made of polyethylene. In addition, the thickness t4 of the base material layer 32 (refer to Figure 10)Preferably, it is 5 μm to 25 μm, more preferably 12 μm to 20 μm. In addition, the air permeability of the base material layer 32 is preferably 50 seconds / 100 cc to 300 seconds / 100 cc, more preferably 100 seconds / 100 cc to 250 seconds / 100 cc. The air permeability is measured, for example, by the Gurley test method. In addition, the porosity of the base material layer 32 is preferably 20% to 70%, more preferably 30% to 60%, and further preferably 40% to 50%. Thereby, charge carriers can be appropriately moved between the positive electrode plate 10 and the negative electrode plate 20. In addition, in this specification, the "porosity" represents the porosity before stamping as long as not particularly mentioned. In addition, the "porosity before stamping" can be obtained by taking as the measurement object the separator disposed in the region not facing the positive electrode plate and the negative electrode plate. As the "region not facing the positive electrode plate and the negative electrode plate", examples include Figure 7 the "region 30a where only the separator 30 protrudes" formed at both side edges of the wound electrode body 40 in

[0092] As Figure 10 shown, the surface layer 34 in this embodiment is a layer formed on both surfaces of the base material layer 32. The surface layer 34 contains inorganic particles and polyvinylidene fluoride (PVdF) as a binder. As the inorganic particles, ceramic particles containing ceramics such as alumina, silica, titanium dioxide, boehmite, aluminum hydroxide, magnesium carbonate, magnesium oxide, zirconia, zinc oxide, iron oxide, cerium dioxide, and yttrium oxide as main components can be cited. The surface layer 34 containing such inorganic particles has excellent heat resistance. Thereby, the thermal shrinkage of the separator 30 when the temperature rises can be suppressed, which helps to improve the safety of the secondary battery 100. In addition, among the above-mentioned ceramic particles, alumina particles and boehmite particles are particularly preferred from the viewpoint of suppressing the thermal shrinkage of the separator 30. In addition, the average particle size of the inorganic particles is preferably 0.05 μm to 3.0 μm, more preferably 0.1 μm to 1.0 μm, for example. In addition, the specific surface area of the inorganic particles is preferably about 2 m 2 / g to 13 m 2 / g. In addition, the "average particle size" in this specification refers to the particle size (D 50 particle size) at the cumulative value of 50% in the particle size distribution obtained by the laser diffraction / scattering method. In addition, the thickness t5 of the surface layer 34 (refer to Figure 10 ) is preferably 1 μm to 4 μm, more preferably 1.5 μm to 3 μm. PVdF can more appropriately exhibit the adhesiveness to the electrode plate. In addition, since PVdF is used for the surface layer 34, it is preferable that PVdF is contained as a binder in the positive electrode active material layer 14 of the positive electrode plate 10 facing the surface layer 34. Thereby, the adhesive strength between the surface layer 34 and the positive electrode plate 10 can be further improved.

[0093] In addition, the surface layer 34 preferably adjusts the content of the inorganic particles so as to exhibit a predetermined adhesiveness with respect to the positive electrode plate 10 (or the negative electrode plate 20). For example, the content of the inorganic particles in the surface layer 34 is preferably less than 90% by mass, more preferably 85% by mass or less, and particularly preferably 80% by mass or less (for example, 75% by mass). If the content of the inorganic particles in the surface layer 34 is made to be a certain amount or less, the surface layer 34 is likely to be deformed during stamping, and thus, the effect of maintaining the interelectrode distance brought about by the fitting (adhesion) of the positive electrode plate 10 (or the negative electrode plate 20) and the surface layer 34 can be appropriately exhibited. On the other hand, if the content of the inorganic particles in the surface layer 34 is excessively reduced, the content of the resin material such as the binder relatively increases, and thus, adhesiveness may occur in the surface layer 34 before stamping. In such a case, it may be difficult to wind the positive electrode plate 10 and the negative electrode plate 20 with the separator 30 interposed therebetween. From this viewpoint, the content of the inorganic particles in the surface layer 34 is preferably 60% by mass or more, more preferably 65% by mass or more, and particularly preferably 70% by mass or more (for example, 75% by mass). In addition, by forming the surface layer 34 containing a certain amount or more of the inorganic particles in this way, it is also possible to appropriately prevent an internal short circuit caused by the heat shrinkage of the separator 30. In addition, the "content of the inorganic particles" in the present specification is the mass ratio of the inorganic particles to the total mass of the surface layer.

[0094] In addition, the surface layer 34 has a network structure including a plurality of voids and made of polyvinylidene fluoride. In the surface layer 34, the inorganic particles are dispersed inside the polyvinylidene fluoride solidified into a network. The surface layer 34 having this network structure has high flexibility, and thus, is deformed in a flattened manner during stamping. As a result, the deviation of the thickness t1 of the wound electrode body 40 can be absorbed by the separator 30, and thus, the precipitation of charge carriers due to the deviation of the interelectrode distance can be suppressed. In addition, the porosity of the network structure of the surface layer 34 is preferably 30% to 90%, more preferably 40% to 80%, and particularly preferably 55% to 75%. Thereby, appropriate flexibility can be imparted to the surface layer 34 to suppress the deviation of the thickness t1 of the wound electrode body 40, and the strength of the separator 30 can be maintained.

[0095] Next, a method for manufacturing the flat wound electrode body 40 will be described. This manufacturing method includes (1) a winding step and (2) a stamping step.

[0096] (1) Winding step

[0097] In this step, first, a laminate (see Figure 7 ) is produced by laminating the separator 30, the negative electrode plate 20, the separator 30, and the positive electrode plate 10 in this order. At this time, the lamination position in the width direction Y of each sheet member is adjusted so that only the positive electrode tab 12t of the positive electrode plate 10 protrudes from one side in the width direction Y (Figure 7 The side edge on the left side (in the figure) protrudes, and only the negative electrode tab 22t of the negative electrode plate 20 protrudes from the side edge of the other side ( Figure 7 the right side in the figure). Then, a cylindrical wound electrode body 40 is produced by winding the produced laminate. The number of windings at this time is preferably adjusted appropriately in consideration of the performance, manufacturing efficiency, etc. of the secondary battery 100 as the purpose. In addition, for ease of explanation, Figure 9 the wound electrode body 40 shown in the figure shows a structure with a significantly reduced number of windings. That is, Figure 9 the number of windings of the wound electrode body 40 shown in the figure is not limited to the number of windings of the wound electrode body disclosed herein.

[0098] Here, the positive electrode plate 10, the negative electrode plate 20, and the separator 30 constituting the wound electrode body 40 increase in length in the length direction in the order of the positive electrode plate 10, the negative electrode plate 20, and the separator 30. That is, the separator 30 is the longest. As Figure 9 shown, the separator 30 is disposed outside the negative electrode terminal portion 20e of the negative electrode plate 20. The distance A (that is, the circumferential distance A) between the negative electrode terminal portion 20e and the separator terminal portion 30e of the separator 30 is set to 30 mm or less (for example, 10 mm or more and 30 mm or less). For example, the length in the length direction of the separator 30 can be appropriately adjusted by cutting the separator 30, etc. In addition, the separator terminal portion 30e is the terminal portion of the outer separator 30A among the two separators 30. In addition, the inner separator 30B among the two separators 30 may be shorter than the outer separator 30A. As described above, since the separator 30 is the longest, only the separator 30 is wound when the winding of the laminate is about to be completed. Therefore, it is possible that the separator 30 becomes charged and adheres to other members, or the separator 30 generates creases and wrinkles before the winding is completed. However, according to the technology disclosed herein, by making the distance A between the negative electrode terminal portion 20e and the separator terminal portion 30e 30 mm or less, the occurrence of the above problems can be suppressed, and a wound electrode body 40 wound with high precision can be produced. When the winding of the separator 30 is completed, the separator terminal portion 30e is adhered to the outermost periphery (here, the separator 30A) of the wound electrode body 40 by the winding fixing tape 38. The winding fixing tape 38 is adhered to prevent the winding of the wound electrode body 40 from coming loose. The winding fixing tape 38 is located at the flat portion 40f. The length C in the length direction (circumferential direction of the wound electrode body 40 or height direction Z) of the winding fixing tape 38 is, for example, 20 mm or more and 40 mm or less. The separator terminal portion 30e is located in the central region in the length direction of the winding fixing tape 38. Here, the central region in the length direction of the winding fixing tape 38 means the region including the length of ±10% from the center in the length direction of the winding fixing tape 38. The winding fixing tape 38 does not overlap with the negative electrode starting end portion 20s and the negative electrode terminal portion 20e.

[0099] (2) Stamping process

[0100] In this process, the wound electrode body 40 is pressed to produce a wound electrode body 40 having a flat shape (see Figure 9 ). As Figure 9 shown, the wound electrode body 40 having a flat shape after press forming has a pair of bent portions 40r with a curved outer surface and a flat portion 40f with a flat outer surface connecting the pair of bent portions 40r. In the present embodiment, in the press forming, the surface layer 34 of the separator 30 is bonded to the positive electrode plate 10 and the negative electrode plate 20. Specifically, in the press forming, the wound electrode body 40 is flattened, and as a result, a large pressure is applied to each of the sheet-like members (the positive electrode plate 10, the negative electrode plate 20, and the separator 30) located in the flat portion 40f. At this time, in the present embodiment, by adjusting the content of the inorganic particles in the surface layer 34, the pressure in the press forming, etc., the surface layer 34 is deformed in conformity with the unevenness of the surface of the positive electrode active material layer 14 (or the negative electrode active material layer 24). Thereby, at the interface between the separator 30 and the positive electrode plate 10 and the negative electrode plate 20 in the flat portion 40f of the wound electrode body 40, the separator 30 is fitted and bonded to the positive electrode plate 10 and the negative electrode plate 20, and thus, the separator 30 holds the inter-pole distance between the positive electrode plate 10 and the negative electrode plate 20. In addition, an increase in the inter-pole distance caused by springback can be suppressed.

[0101] As Figure 9As shown, in the wound electrode body 40 after stamping, one end in the length direction of the strip-shaped positive electrode plate 10, i.e., the positive electrode start end 10s, is located inside the wound electrode body 40. The other end in the length direction of the positive electrode plate 10, i.e., the positive electrode terminal end 10e, is located outside the wound electrode body 40. The positive electrode start end 10s is located on the flat portion 40f of the wound electrode body 40. The positive electrode terminal end 10e is located on the first bending portion 40r1 of the wound electrode body 40. Here, the first bending portion 40r1 is the portion located behind when the bending portion 40r is bisected in the depth direction X, and is the portion that bends downward from the front to the back. In addition, one end in the length direction of the strip-shaped negative electrode plate 20, i.e., the negative electrode start end 20s, is located inside the wound electrode body 40. The other end in the length direction of the negative electrode plate 20, i.e., the negative electrode terminal end 20e, is located outside the wound electrode body 40. The negative electrode start end 20s is located on the flat portion 40f of the wound electrode body 40. The negative electrode terminal end 20e is located on the second bending portion 40r2 of the wound electrode body 40. Here, the second bending portion 40r2 is the portion located in front when the bending portion 40r is bisected in the depth direction X, and is the portion that bends downward from the back to the front. In addition, one end in the length direction of the strip-shaped separator 30, i.e., the separator start end 30s, is located inside the wound electrode body 40. The other end in the length direction of the separator 30, i.e., the separator terminal end 30e, is located outside the wound electrode body 40. Both the separator start end 30s and the separator terminal end 30e are located on the flat portion 40f of the wound electrode body 40.

[0102] As Figure 9 shown, in the flat-shaped wound electrode body 40, when the distance between the negative electrode terminal end 20e and the separator terminal end 30e is set as A and the dimension in the height direction Z of the flat portion 40f of the wound electrode body 40 is set as B, the following formula is satisfied: A < 0.4B. Thereby, generation of creases and wrinkles in the separator 30 during the production of the wound electrode body 40 is suppressed, and charging of the separator 30 is suppressed. In addition, when the length in the length direction (circumferential direction or height direction Z of the wound electrode body 40) of the winding fixing band 38 is set as C, the following formula is satisfied: 20 ≤ C ≤ 40, A ≥ 1 / 2C. Thereby, loosening of the winding of the wound electrode body 40 can be suppressed, and since the winding fixing band 38 does not overlap with the negative electrode terminal end 20e, the height difference caused by the thickness of the winding fixing band 38 can be reduced.

[0103] <Other Embodiments>

[0104] Above, one embodiment of the technology disclosed herein has been described. In addition, the above-described embodiment shows an example of applying the technology disclosed herein and does not limit the technology disclosed herein. Hereinafter, other embodiments of the technology disclosed herein will be described.

[0105] (1) Formation surface of the surface layer

[0106] In the above-described embodiment, surface layers 34 are formed on both surfaces of the base material layer 32. However, the surface layers do not need to be formed on both surfaces of the base material layer, and it is sufficient if they are formed on at least one of the surfaces of the base material layer. However, considering the adhesiveness between the separator and the electrode body, suppression of thermal shrinkage of the separator, etc., it is preferable to form the surface layers on both surfaces of the base material layer. Further, as described above, the surface layer has a tendency of having more excellent adhesiveness with respect to the positive electrode plate than the negative electrode plate. Considering this point, when the surface layer is formed only on one of the surfaces of the base material layer, it is preferable to form the surface layer on the surface on the side in contact with the positive electrode plate.

[0107] (2) Number of wound electrode bodies

[0108] In the secondary battery 100 of the above-described embodiment, three wound electrode bodies 40 are housed inside the battery case 50. However, the number of electrode bodies housed in one battery case is not particularly limited, and may be two or more (a plurality), or may be one.

[0109] (3) Dimensions of wound electrode bodies

[0110] The technology disclosed herein can be preferably applied to a secondary battery 100 having a wound electrode body 40 with the following outer dimensions. The distance A between the negative electrode terminal portion 20e and the separator terminal portion 30e of the separator 30 is within 250% of the thickness t1 of the wound electrode body 40 (i.e., A ≤ 2.5t1) of the wound electrode body 40. The distance A between the negative electrode terminal portion 20e and the separator terminal portion 30e of the separator 30 is within 150% of the circumferential length E (refer to Figure 9 ) of the bent portion 40r of the wound electrode body 40 (i.e., A ≤ 1.5E) of the wound electrode body 40. The distance A between the negative electrode terminal portion 20e and the separator terminal portion 30e of the separator 30 is within 30% of the dimension h1 in the height direction Z of the wound electrode body 40 (i.e., A ≤ 0.3h1) of the wound electrode body 40. The area of the separator 30 exposed from the negative electrode terminal portion 20e is 0.009 m 2 or less with respect to the area of the flat portion 40f of the wound electrode body 40.

[0111] 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 deformations and changes of the above-described specific examples.

Claims

1. A secondary battery, the secondary battery comprising a wound electrode body formed by winding a positive electrode plate and a negative electrode plate with a separator therebetween, and a battery case housing the wound electrode body, wherein, the positive electrode plate has a strip-shaped positive electrode core body and a positive electrode active material layer formed on at least one surface of the positive electrode core body, the negative electrode plate has a strip-shaped negative electrode core body and a negative electrode active material layer formed on at least one surface of the negative electrode core body, the separator has a strip-shaped base material layer and a surface layer formed on at least one surface of the base material layer and having a network structure made of polyvinylidene fluoride, the wound electrode body is formed in a flat shape and has a pair of curved portions with curved outer surfaces and a flat portion with a flat outer surface connecting the pair of curved portions, one end in the length direction of the negative electrode plate, i.e., the negative electrode starting end, is located inside the wound electrode body, and the other end in the length direction of the negative electrode plate, i.e., the negative electrode terminal end, is located outside the wound electrode body, one end in the length direction of the separator, i.e., the separator starting end, is located inside the wound electrode body, and the other end in the length direction of the separator, i.e., the separator terminal end, is located in the flat portion outside the wound electrode body, the separator is disposed outside the negative electrode terminal end, the distance between the negative electrode terminal end and the separator terminal end is 30 mm or less, the secondary battery includes a winding fixing band that pastes the separator terminal end to the outermost surface of the wound electrode body, the winding fixing band is located in the flat portion, when a direction perpendicular to the winding axis direction of the wound electrode body and perpendicular to the thickness direction of the wound electrode body is defined as the height direction, the distance between the negative electrode terminal end and the separator terminal end is defined as A, and the dimension in the height direction of the flat portion of the wound electrode body is defined as B, the following formula is satisfied: A < 0.4B.

2. The secondary battery according to claim 1, wherein, the dimension in the height direction of the wound electrode body is 80 mm or more.

3. The secondary battery according to claim 2, wherein, when a direction parallel to the winding axis direction of the wound electrode body and perpendicular to the thickness direction of the wound electrode body is defined as the width direction, the dimension in the width direction of the wound electrode body is 200 mm or more.

4. The secondary battery according to claim 2 or 3, wherein, the negative electrode terminal end is located in the curved portion.

5. The secondary battery according to any one of claims 1 to 3, wherein, when the distance between the negative electrode terminal end and the separator terminal end is defined as A and the length of the winding fixing band is defined as C, the following formula is satisfied: 20 ≤ C ≤ 40, A ≥ 1 / 2C.

6. The secondary battery according to any one of claims 1 to 3, wherein, the separator terminal end is located in the central region in the length direction of the winding fixing band, the winding fixing band does not overlap with the negative electrode terminal end.

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