Secondary battery

Abstract

To provide a battery in which reaction irregularities are suppressed.SOLUTION: A secondary battery 100 disclosed herein includes a wound electrode assembly 20 including a first flat outer surface FO1, a first curved outer surface RO1, and a second curved outer surface RO2. A tape 28 is attached to the first flat outer surface FO1, and the end of the tape 28 on the first curved outer surface RO1 side is located closer to the first flat outer surface FO1 than the apex T1 of the first curved outer surface RO1, and the end of the tape 28 on the second curved outer surface RO2 side is located closer to the first flat outer surface FO1 than the apex T2 of the second curved outer surface RO2. When the area of the first flat outer surface FO1 that overlaps with the positive electrode active material layer is S1 and the area of the area to which the tape 28 is attached is S2, the ratio of S2 to S1 is 95% or more.SELECTED DRAWING: Figure 5

Description

[Technical Field]

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

[0002] Conventionally, secondary batteries have been known that include a wound electrode assembly in which a strip-shaped positive electrode having a positive electrode active material layer and a strip-shaped negative electrode having a negative electrode active material layer are stacked with a strip-shaped separator interposed therebetween and wound (see Patent Documents 1 to 4). For example, Patent Document 1 discloses a secondary battery in which a plurality of stop tapes are attached at intervals along the winding axis direction to the winding end portion of the wound electrode assembly to prevent loosening of the winding. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-076036 [Patent Document 2] Patent Publication No. 2022-137789 [Patent Document 3] Japanese Patent Application Laid-Open No. 2009-146749 [Patent Document 4] Japanese Patent Application Laid-Open No. 2003-178792 Summary of the Invention [Problem to be solved by the invention]

[0004] According to the inventors' investigations, the thickness of the area where the tape is applied increases locally, creating a step on the outer surface of the wound electrode assembly. As a result, when pressure is applied to the wound electrode assembly during the battery manufacturing process or use, the area where the tape is applied is pressed strongly, resulting in a local increase in surface pressure. As a result, it has been newly discovered that this makes it more likely that the charge / discharge reaction will become uneven.

[0005] The present invention has been made in view of the above circumstances, and has an object to provide a battery in which unevenness in charge / discharge reactions is suppressed. [Means for solving the problem]

[0006] The present invention provides a secondary battery comprising a wound electrode assembly formed by stacking and winding a strip-shaped positive electrode having a positive electrode active material layer and a strip-shaped negative electrode having a negative electrode active material layer with a strip-shaped separator interposed therebetween, and a battery case that houses the wound electrode assembly. The wound electrode assembly includes a first flat outer surface and a second flat outer surface that are arranged to face each other, a first curved outer surface that connects one end of the first flat outer surface to one end of the second flat outer surface, and a second curved outer surface that connects the other end of the first flat outer surface to the other end of the second flat outer surface. A tape is attached to the first flat outer surface, and the tape covers at least a portion of the winding terminal end of the separator, the end of the tape on the first curved outer surface side is located closer to the first flat outer surface than the apex of the first curved outer surface, and the end of the tape on the second curved outer surface side is located closer to the first flat outer surface than the apex of the second curved outer surface, and when viewed from a direction perpendicular to the first flat outer surface, an area of ​​the first flat outer surface that overlaps with the positive electrode active material layer is S1 and an area of ​​the area to which the tape is attached is S2, the ratio of S2 to S1 is 95% or more.

[0007] By covering substantially the entire area (95% or more) of the first flat outer surface of the wound electrode body that overlaps with the positive electrode active material layer with tape, steps are less likely to occur on the first flat outer surface. This makes it possible to homogenize the surface pressure on the first flat outer surface and suppress uneven reactions during charge and discharge. This in turn suppresses the deposition of metallic lithium (dendrites). Furthermore, by applying tape so as not to cover the two vertices of the wound electrode body, distortion of the electrodes or the wound electrode body can be suppressed even when the wound electrode body expands and contracts due to charge and discharge. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a perspective view schematically showing a battery according to one embodiment. [Figure 2] FIG. 2 is a schematic vertical cross-sectional view taken along line II-II in FIG. [Figure 3] FIG. 3 is a schematic vertical cross-sectional view taken along line III-III in FIG. [Figure 4] FIG. 4 is a schematic diagram showing the configuration of a wound electrode body. [Figure 5] FIG. 5 is a cross-sectional view that schematically shows a wound electrode body. [Figure 6] FIG. 6 is a front view that schematically shows a wound electrode body. [Figure 7] FIG. 7(A) is an explanatory diagram of the winding step, and FIG. 7(B) is an explanatory diagram of the forming step. DETAILED DESCRIPTION OF THE INVENTION

[0009] Preferred embodiments of the technology disclosed herein will be described below with reference to the drawings as appropriate. Matters other than those specifically mentioned in this specification that are necessary for implementing the technology disclosed herein (e.g., the general configuration and manufacturing process of secondary batteries that do not characterize the technology disclosed herein) can be understood as design matters for those skilled in the art based on prior art in the relevant field. The technology disclosed herein can be implemented based on the content disclosed in this specification and common technical knowledge in the relevant field. Furthermore, the expression "A to B" indicating a range in this specification means greater than or equal to A and less than or equal to B, and also encompasses the meanings of "preferably greater than A" and "preferably smaller than B."

[0010] <Secondary battery 100> FIG. 1 is a perspective view of a secondary battery 100. FIG. 2 is a schematic longitudinal cross-sectional view taken along line II-II in FIG. 1, showing the internal structure of the secondary battery 100. FIG. 3 is a schematic longitudinal cross-sectional view taken along line III-III in FIG. 1. In the following description, the same reference numerals are used to designate components and parts that perform the same functions, and redundant descriptions may be omitted or simplified. Furthermore, the reference numerals F, Rr, L, R, U, and D in the drawings represent front, rear, left, right, top, and bottom, and the reference numerals X, Y, and Z in the drawings represent the short side direction of the secondary battery 100, the long side direction perpendicular to the short side direction, and the up-down direction, respectively. However, these directions are merely used for convenience of explanation and do not limit the installation form of the secondary battery 100 in any way.

[0011] As shown in FIG. 1, the secondary battery 100 here is a prismatic secondary battery having a hexahedral polygonal shape (specifically, a rectangular parallelepiped shape). As shown in FIG. 2, the secondary battery 100 includes a battery case 10, a wound electrode assembly 20, a positive electrode terminal 30, and a negative electrode terminal 40. The secondary battery 100 here also includes an electrolyte (not shown). The secondary battery 100 is preferably a non-aqueous electrolyte secondary battery such as a lithium-ion secondary battery. In this specification, the term "secondary battery" refers to a general power storage device that can be repeatedly charged and discharged, and is a concept that encompasses lithium-ion secondary batteries, nickel-metal hydride batteries, lithium-ion capacitors, etc.

[0012] The battery case 10 is a housing that houses the wound electrode assembly 20 and the electrolyte. As shown in FIG. 1, the battery case 10 has a flat, bottomed, rectangular parallelepiped (rectangular) outer shape. The material of the battery case 10 may be the same as that conventionally used, and is not particularly limited. The battery case 10 is preferably made of metal, more preferably aluminum, aluminum alloy, iron, iron alloy, or the like. As shown in FIG. 2, in this embodiment, the battery case 10 includes a bottomed rectangular (box-shaped) case body 12 having an opening 12h on one side (here, the upper side) and a sealing plate (lid) 14 that closes the opening 12h of the case body 12. The sealing plate 14 is joined (e.g., welded) to the periphery of the opening 12h of the case body 12, thereby forming an integrated battery case 10. The battery case 10 is hermetically sealed.

[0013] As shown in Fig. 1, the case body 12 has a substantially rectangular bottom surface 12a having a pair of short sides and a pair of long sides, a pair of long side surfaces 12b extending from the pair of long sides of the bottom surface 12a and facing each other, and a pair of short side surfaces 12c extending from the pair of short sides of the bottom surface 12a and facing each other. The bottom surface 12a faces the opening 12h. In a plan view, the area of ​​the long side surfaces 12b is larger than the area of ​​the short side surfaces 12c. In this specification, the term "substantially rectangular" is intended to encompass not only a perfect rectangular shape (rectangular shape) but also shapes in which the corners connecting the long and short sides of the rectangle are rounded or have notches at the corners.

[0014] As shown in FIG. 2 , the sealing plate 14 is a plate-shaped member that closes the opening 12h of the case body 12. The sealing plate 14 faces the bottom surface 12a of the case body 12. Here, the sealing plate 14 constitutes the upper wall of the battery case 10. The sealing plate 14 is generally rectangular in plan view. The sealing plate 14 is provided with a liquid inlet 15, a drain valve 17, and two terminal outlet holes 18 and 19. The liquid inlet 15 is for injecting electrolyte into the battery case 10 after the sealing plate 14 is assembled to the case body 12. The liquid inlet 15 is sealed with a sealing member 16 after the electrolyte is injected. The drain valve 17 is configured to break when the pressure inside the battery case 10 exceeds a predetermined value, thereby discharging gas inside the battery case 10 to the outside. The terminal outlet holes 18 and 19 penetrate the sealing plate 14 in the vertical direction Z. The terminal pull-out holes 18, 19 have inner diameters large enough to allow the positive electrode terminal 30 and the negative electrode terminal 40 to be inserted therethrough before being attached to the sealing plate 14 (before being crimped).

[0015] The positive electrode terminal 30 is disposed at one end of the sealing plate 14 in the long side direction Y (the left end in FIGS. 1 and 2). As shown in FIG. 2, the positive electrode terminal 30 extends from the inside to the outside of the sealing plate 14 through the terminal outlet hole 18. Here, the positive electrode terminal 30 is crimped to the peripheral portion of the sealing plate 14 surrounding the terminal outlet hole 18 by crimping. A crimped portion 30c is formed at the end of the positive electrode terminal 30 on the side of the case body 12 (the lower end in FIG. 2). The positive electrode terminal 30 is preferably made of metal, and more preferably made of aluminum or an aluminum alloy. Inside the battery case 10, the positive electrode terminal 30 is electrically connected to the positive electrode tab group 23 of the wound electrode assembly 20 via the positive electrode current collector 50. The positive electrode terminal 30 is insulated from the sealing plate 14 by an internal insulating member 80 and a gasket 90.

[0016] The negative electrode terminal 40 is disposed at the other end of the sealing plate 14 in the long side direction Y (the right end in FIGS. 1 and 2). As shown in FIG. 2, the negative electrode terminal 40 extends from the inside to the outside of the sealing plate 14 through the terminal lead-out hole 19. Here, the negative electrode terminal 40 is crimped to the peripheral portion of the sealing plate 14 surrounding the terminal lead-out hole 19 by crimping. A crimped portion 40c is formed at the end of the negative electrode terminal 40 on the side of the case body 12 (the lower end in FIG. 2). The negative electrode terminal 40 is preferably made of metal, and more preferably made of copper or a copper alloy, for example. Inside the battery case 10, the negative electrode terminal 40 is electrically connected to the negative electrode tab group 25 of the wound electrode assembly 20 via the negative electrode current collecting portion 60. The negative electrode terminal 40 is insulated from the sealing plate 14 by an internal insulating member 80 and a gasket 90.

[0017] The electrolyte is accommodated inside the battery case 10 together with the wound electrode assembly 20. The electrolyte may be the same as a conventional one and is not particularly limited. The electrolyte is typically a liquid (electrolytic solution). The electrolytic solution is, for example, a non-aqueous electrolytic solution containing a non-aqueous solvent and a supporting salt. However, the electrolytic solution may also be an aqueous electrolytic solution containing an aqueous solvent. The non-aqueous solvent includes, for example, carbonates such as ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate. The supporting salt is, for example, a fluorine-containing lithium salt such as lithium hexafluorophosphate (LiPF6). The electrolytic solution may further contain additives as necessary. The electrolyte may be a solid (solid electrolyte) and may be integrated with the wound electrode assembly 20.

[0018] The wound electrode assembly 20 is housed inside the battery case 10. As shown in FIG. 3, in this embodiment, multiple (specifically, three) wound electrode assemblies 20 are housed inside one battery case 10. When multiple (e.g., three) wound electrode assemblies 20 are housed inside one battery case 10, the effect of the step is more than doubled (e.g., tripled). Therefore, it is particularly preferable to apply the technology disclosed herein. However, the number of wound electrode assemblies 20 housed inside one battery case 10 is not particularly limited, and may be one. The wound electrode assembly 20 is disposed inside the case main body 12 while being covered with an electrode assembly holder 29 made of a resin sheet, here.

[0019] FIG. 4 is a schematic diagram showing the configuration of the wound electrode body 20. The wound electrode body 20 is configured by stacking a strip-shaped positive electrode 22 and a strip-shaped negative electrode 24 with at least one strip-shaped separator 26 interposed therebetween and winding them around a winding axis WL. The wound electrode body 20 preferably includes a strip-shaped positive electrode 22, a strip-shaped first separator 26, a strip-shaped negative electrode 24, and a strip-shaped second separator 26. The wound electrode body 20 has a flat shape. The configuration and shape of the wound electrode body 20 may be the same as those of a conventional electrode, and are not particularly limited. As shown in FIG. 2, in this embodiment, the wound electrode body 20 is disposed inside the case body 12 with the winding axis WL (see FIG. 4) oriented approximately parallel to the long side direction Y. The wound electrode body 20 is disposed inside the case body 12 so that the winding axis WL is aligned with the bottom surface 12a and the sealing plate .

[0020] 3, the wound electrode body 20 has a flat portion 20f, a first curved portion 20r1 provided at one end (here, the upper end) of the flat portion 20f, and a second curved portion 20r2 provided at the other end (here, the lower end) of the flat portion 20f. Here, the flat portion 20f faces the pair of long side surfaces 12b of the case body 12. Here, the first curved portion 20r1 faces the sealing plate 14. Here, the second curved portion 20r2 faces the bottom surface 12a of the case body 12.

[0021] As shown in FIG. 4, the positive electrode 22 includes a positive electrode current collector 22c, and a positive electrode active material layer 22a and a positive electrode protective layer 22p fixed to at least one surface (preferably both surfaces) of the positive electrode current collector 22c. However, the positive electrode protective layer 22p is not essential and may be omitted in other embodiments. The configuration and shape of the positive electrode 22 may be the same as conventional ones and are not particularly limited. The positive electrode current collector 22c is strip-shaped. The positive electrode current collector 22c is made of a conductive metal such as aluminum, an aluminum alloy, nickel, or stainless steel. In this example, the positive electrode current collector 22c is a metal foil, specifically, an aluminum foil.

[0022] A plurality of positive electrode tabs 22t are provided at one end of the positive electrode current collector 22c in the long side direction Y (the left end in FIG. 4). The plurality of positive electrode tabs 22t are convex and protrude toward one side in the long side direction Y (the left side in FIG. 4). The positive electrode tabs 22t are part of the positive electrode current collector 22c and are made of metal foil (aluminum foil). However, the position of the positive electrode tabs 22t is not particularly limited. In other embodiments, the positive electrode tabs 22t may be provided at the other end in the long side direction Y (the right end in FIG. 4) or at both ends in the long side direction Y. The plurality of positive electrode tabs 22t are stacked at one end in the long side direction Y (the left end in FIG. 4) to form a positive electrode tab group 23. The positive electrode tab group 23 is electrically connected to the positive electrode terminal 30 via the positive electrode current collector 50.

[0023] 4, the positive electrode active material layer 22a is provided in a strip shape along the longitudinal direction of the strip-shaped positive electrode current collector 22c. The positive electrode active material layer 22a contains a positive electrode active material (e.g., a lithium transition metal composite oxide such as a lithium nickel cobalt manganese composite oxide) that can reversibly store and release charge carriers. The positive electrode active material layer 22a may contain any component other than the positive electrode active material, such as a conductive material (e.g., a carbon material), a binder, various additive components, etc.

[0024] Although not particularly limited, in a high-capacity secondary battery 100 used in a vehicle or the like, the length L1 of the positive electrode active material layer 22a in the long side direction Y is preferably approximately 15 cm or more, for example, 20 cm or more, or even 25 cm or more. The length L1 of the positive electrode active material layer 22a may be approximately 40 cm or less, for example, 35 cm or less. In addition, in a high-capacity secondary battery 100, the thickness of the positive electrode 22 (the average value of the total thickness of the positive electrode current collector 22c and the positive electrode active material layer 22a in the region where the positive electrode active material layer 22a is formed) is preferably 50 to 200 μm, more preferably 100 to 180 μm, and even more preferably 120 to 160 μm.

[0025] As shown in FIG. 4, the positive electrode protective layer 22p is provided at the boundary between the positive electrode current collector 22c and the positive electrode active material layer 22a in the long side direction Y. Here, the positive electrode protective layer 22p is provided at one end of the positive electrode current collector 22c in the long side direction Y (the left end in FIG. 4). However, in other embodiments, the positive electrode protective layer 22p may be provided at both end portions in the long side direction Y. The positive electrode protective layer 22p is provided in a strip shape along the positive electrode active material layer 22a. The positive electrode protective layer 22p preferably contains an insulating inorganic filler (e.g., alumina). The positive electrode protective layer 22p may contain optional components other than the inorganic filler, such as a conductive material, a binder, and various additive components.

[0026] As shown in FIG. 4, the negative electrode 24 has a negative electrode current collector 24c and a negative electrode active material layer 24a fixed to at least one surface (preferably both surfaces) of the negative electrode current collector 24c. The configuration and shape of the negative electrode 24 may be the same as conventional ones and are not particularly limited. The negative electrode current collector 24c is strip-shaped. The negative electrode current collector 24c is made of a conductive metal such as copper, a copper alloy, nickel, or stainless steel. In this example, the negative electrode current collector 24c is a metal foil, specifically a copper foil.

[0027] A plurality of negative electrode tabs 24t are provided at one end of the negative electrode current collector 24c in the long side direction Y (the right end in FIG. 4). Here, the plurality of negative electrode tabs 24t are convex and protrude toward one side in the long side direction Y (the right side in FIG. 4). Here, the negative electrode tabs 24t are part of the negative electrode current collector 24c and are made of metal foil (copper foil). However, the position of the negative electrode tabs 24t is not particularly limited. In other embodiments, the negative electrode tabs 24t may be provided at the other end in the long side direction Y (the left end in FIG. 4), or may be provided at both ends in the long side direction Y. Here, the plurality of negative electrode tabs 24t are stacked at one end in the long side direction Y (the right end in FIG. 4) to form a negative electrode tab group 25. The negative electrode tab group 25 is provided at a position symmetrical to the positive electrode tab group 23 in the long side direction Y. The negative electrode tab group 25 is electrically connected to the negative electrode terminal 40 via the negative electrode current collector 60.

[0028] 4, the negative electrode active material layer 24a is provided in a strip shape along the longitudinal direction of the strip-shaped negative electrode current collector 24c. The negative electrode active material layer 24a contains a negative electrode active material (e.g., a carbon material such as graphite) that can reversibly store and release charge carriers. The negative electrode active material layer 24a may contain optional components other than the negative electrode active material, such as a binder, a dispersant, and various additive components.

[0029] In the long side direction Y, the length L2 of the negative electrode active material layer 24a is preferably longer than the length L1 of the positive electrode active material layer 22a. The negative electrode active material layer 24a preferably covers the positive electrode active material layer 22a at both ends in the long side direction Y. Although not particularly limited, the length L2 of the negative electrode active material layer 24a is preferably 20 to 45 cm, and more preferably 25 to 35 cm. In the high-capacity secondary battery 100, the thickness of the negative electrode 24 (the average value of the total thickness of the negative electrode current collector 24c and the negative electrode active material layer 24a in the region where the negative electrode active material layer 24a is formed) is preferably 100 to 250 μm, more preferably 130 to 220 μm, and even more preferably 160 to 200 μm.

[0030] The separator 26 is a member that insulates the positive electrode active material layer 22a of the positive electrode 22 from the negative electrode active material layer 24a of the negative electrode 24. The separator 26 is an insulating sheet formed with a plurality of fine through-holes through which charge carriers can pass. The separator 26 forms the outer surface of the wound electrode body 20. Here, two separators 26 are used per wound electrode body 20. The configuration and shape of the separators 26 may be the same as conventional ones and are not particularly limited. Furthermore, the configurations of the two separators 26 may be the same or different.

[0031] The separator 26 is preferably a porous resin sheet made of a polyolefin resin such as polyethylene (PE) or polypropylene (PP). The separator 26 preferably has a resin separator substrate and one or more functional layers formed on at least one surface of the separator substrate. The functional layer is a layer that imparts a desired function to the separator substrate (e.g., improved heat resistance, adhesiveness, strength, etc.). Suitable examples of the functional layer include a heat resistance layer (HRL) and an adhesive layer. The heat resistance layer is a layer containing an inorganic filler. Examples of inorganic fillers that can be used include alumina, boehmite, aluminum hydroxide, and titania.

[0032] In the long side direction Y, the length L3 of the separator 26 is preferably longer than the length L2 of the negative electrode active material layer 24a. The separator 26 preferably covers the negative electrode active material layer 24a at both ends in the long side direction Y. The thickness of the separator 26 is typically smaller than the thickness of the positive electrode 22 and the thickness of the negative electrode 24. Although not particularly limited, the thickness (average thickness) of the separator 26 is preferably 1 to 30 μm, more preferably 4 to 28 μm, even more preferably 8 to 24 μm, and particularly preferably 12 to 20 μm.

[0033] FIG. 5 shows a cross section of the wound electrode assembly 20 in a direction perpendicular to the winding axis WL. For ease of explanation, FIG. 5 shows a significantly reduced number of windings of the wound electrode assembly 20. As shown in FIG. 5, the flat portion 20f of the wound electrode assembly 20 includes a first flat outer surface FO1 and a second flat outer surface FO2 that are arranged to face each other. The first flat outer surface FO1 and the second flat outer surface FO2 each extend along the long side surface 12b (see FIG. 3). The first curved portion 20r1 of the wound electrode assembly 20 includes a first curved outer surface RO1 that connects one end (here, the upper end) of the first flat outer surface FO1 to one end (here, the upper end) of the second flat outer surface FO2. The first curved outer surface RO1 faces the sealing plate 14 (see FIG. 3). The second curved portion 20r2 of the wound electrode assembly 20 includes a second curved outer surface RO2 that connects the other end (here, the lower end) of the first flat outer surface FO1 to the other end (here, the lower end) of the second flat outer surface FO2. The second curved outer surface RO2 faces the bottom surface 12a of the case body 12 (see FIG. 3).

[0034] In this embodiment, the winding start end 22s, which is one end in the longitudinal direction of the strip-shaped positive electrode 22, is located on the flat portion 20f of the wound electrode body 20. The winding start end 24s, which is one end in the longitudinal direction of the strip-shaped negative electrode 24, is located on the flat portion 20f of the wound electrode body 20. Furthermore, the winding start end 26s, which is one end in the longitudinal direction of the two strip-shaped separators 26, is located on the flat portion 20f of the wound electrode body 20. Here, the winding start end 22s of the positive electrode 22, the winding start end 24s of the negative electrode 24, and the winding start ends 26s of the two separators 26 are aligned in the vertical direction Z.

[0035] The winding terminal end 22e, which is the other longitudinal end of the strip-shaped positive electrode 22, is preferably located in the first curved portion 20r1 of the wound electrode body 20. Specifically, when the first curved portion 20r1 is divided into two equal parts in the short side direction X into a first region A1 located on the front F side (i.e., curved downward from the rear Rr toward the front F) and a second region A2 located on the rear Rr side (i.e., curved downward from the front F toward the rear Rr), the winding terminal end 22e of the positive electrode 22 is located in the second region A2 here. The outside (surface side) of the winding terminal end 22e of the positive electrode 22 is covered with the negative electrode 24 and two separators 26 here. The outside of the winding terminal end 22e of the positive electrode 22 is not covered with the tape 28.

[0036] The winding terminal end 24e, which is the other longitudinal end of the strip-shaped negative electrode 24, is located closer to the outer periphery of the winding than the winding terminal end 22e of the positive electrode 22. The winding terminal end 24e of the negative electrode 24 is preferably located in the first curved portion 20r1 of the wound electrode body 20. More specifically, the winding terminal end 24e of the negative electrode 24 is located in the first region A1 here. The outside (surface side) of the winding terminal end 24e of the negative electrode 24 here is covered with two separators 26 and a tape 28. By positioning the winding terminal end 22e of the positive electrode 22 and / or the winding terminal end 24e of the negative electrode 24 (preferably both) in the first curved portion 20r1, the occurrence of a step in the flat portion 20f (more specifically, the first flat outer surface FO1) can be relatively suppressed compared to when the winding terminal end 22e and / or the winding terminal end 24e are positioned in the flat portion 20f.

[0037] The winding end 26e of each of the two strip-shaped separators 26, which is the other longitudinal end, is located closer to the outer periphery of the winding than the winding end 22e of the positive electrode 22 and the winding end 24e of the negative electrode 24. It is preferable that at least the winding end 26e of the outer separator 26 is located on the flat portion 20f (more specifically, the first flat outer surface FO1) of the wound electrode assembly 20. This more effectively prevents the wound electrode assembly 20 from loosening. Here, the winding end 26e of each of the two separators 26 is located on the flat portion 20f (more specifically, the first flat outer surface FO1) of the wound electrode assembly 20. As described above, the thickness of the separator 26 is typically smaller than the thickness of the positive electrode 22 and the thickness of the negative electrode 24. Therefore, winding end 26e of separator 26 may be located in flat portion 20f. However, in other embodiments, winding end 26e of separator 26 may be located in, for example, first curved portion 20r1 or second curved portion 20r2.

[0038] A tape 28 is attached to the first flat outer surface FO1 of the wound electrode assembly 20. The tape 28 covers at least a portion of the winding end portion 26e of the separator 26. This prevents the wound electrode assembly 20 from loosening. An end portion 281 (here, the upper end portion) of the tape 28 on the first curved outer surface RO1 side is located closer to the first flat outer surface FO1 (here, lower) than the apex portion (here, the upper end portion) T1 of the first curved outer surface RO1. An end portion 282 (here, the lower end portion) of the tape 28 on the second curved outer surface RO2 side is located closer to the first flat outer surface FO1 (here, higher) than the apex portion (here, the lower end portion) T2 of the second curved outer surface RO2. This prevents distortion of the electrodes (positive electrode 22 and / or negative electrode 24) or the wound electrode assembly 20 even if the wound electrode assembly 20 expands and contracts due to charging and discharging.

[0039] In particular, in a high-capacity secondary battery 100 used in a vehicle or the like, the positive electrode 22 and / or negative electrode 24 are thick, and the wound electrode body 20 swells significantly during charge and discharge. If the apex T1 of the first curved outer surface RO1 and / or the apex T2 of the second curved outer surface RO2 are covered by the tape 28, the wound electrode body 20 cannot swell in the vertical direction Z. This causes so-called buckling, and the inter-electrode distance between the positive electrode 22 and the negative electrode 24 becomes wider in some areas. As a result, dendrites are more likely to form due to repeated charge and discharge. The above configuration can effectively suppress the occurrence of such buckling.

[0040] The end 281 of the tape 28 on the first curved outer surface RO1 side is preferably located on the first curved outer surface RO1. The end 282 of the tape 28 on the second curved outer surface RO2 side is preferably located on the second curved outer surface RO2. This more effectively prevents unevenness from occurring on the first flat outer surface FO1. During the manufacturing process or use of the secondary battery 100, the pair of long sides 12b may be clamped by a restraining mechanism and the secondary battery 100 may be pressed from the long side direction Y. In such cases, if the unevenness on the first flat outer surface FO1 is reduced, the surface pressure on the first flat outer surface FO1 can be made uniform, preventing localized application of large pressure. As a result, reaction irregularities during charging and discharging are less likely to occur, and ultimately, dendrite formation can be suppressed. This allows the effects of the technology disclosed herein to be achieved at a higher level.

[0041] The configuration of the tape 28 may be the same as conventional ones and is not particularly limited. The tape 28 preferably has a tape base and an adhesive layer formed on the surface of the tape base. The tape base may be, for example, a film made of a resin such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), polyvinyl chloride, polypropylene (PP), polyarylate, polyurethane, polycarbonate, polyamide, polyimide (PI), polyphenylene sulfide (PPS), or polytetrafluoroethylene, or a composite thereof. The adhesive layer is a layer containing an adhesive. Examples of the adhesive that may be used include rubber-based, silicone-based, acrylic-based, and acrylate-based adhesives. Among these, it is preferable that the tape contain an acrylic and / or rubber-based adhesive.

[0042] The thickness of tape 28 (if an adhesive layer is provided, the average value of the total thickness of the tape base portion and the adhesive layer in the area where the adhesive layer is formed) is typically smaller than the thickness of positive electrode 22 and the thickness of negative electrode 24. The thickness of tape 28 is typically larger than the thickness of separator 26. The thickness of tape 28 is generally 50 μm or less, for example, preferably 40 μm or less, and more preferably 30 μm or less.

[0043] FIG. 6 is a front view of the wound electrode assembly 20 (viewed from a direction perpendicular to the first flat outer surface FO1). As shown in FIG. 6, the tape 28 here has a rectangular shape having long and short sides. The tape 28 is arranged so that the long side of the rectangle is along the long side direction Y. The length Ly of the long side of the tape 28 (here, the length in the long side direction Y; in other words, the length in the direction along the winding axis WL) here is longer than the length L1 of the positive electrode active material layer 22a. The length Ly of the long side of the tape 28 here is longer than the length L2 of the negative electrode active material layer 24a. The length Ly of the long side of the tape 28 here is approximately the same as the length L3 of the separator 26. However, in other embodiments, the length Ly of the long side of the tape 28 may be shorter than, for example, the length L2 of the negative electrode active material layer 24a or the length L3 of the separator 26. The length Lz of the short side of the tape 28 (here, the length in the vertical direction Z, in other words, the length in the direction perpendicular to the winding axis WL) is longer than the length in the vertical direction Z of the first flat outer surface FO1.

[0044] In this embodiment, when the area of ​​the region of the first flat outer surface FO1 overlapping with the positive electrode active material layer 22a (i.e., the area of ​​the region overlapping with the first flat outer surface FO1 and the positive electrode active material layer 22a) is S1 and the area of ​​the region to which the tape 28 is attached (i.e., the area of ​​the tape 28 overlapping the region overlapping with the first flat outer surface FO1) is S2, the ratio of S2 to S1 (S2 / S1) is 95% or more. The ratio (S2 / S1) is preferably 98% or more, and more preferably 100% or more. In the embodiment of FIG. 6, it exceeds 100%. The region of the first flat outer surface FO1 overlapping with the positive electrode active material layer 22a is the thickest region here. By setting the ratio (S2 / S1) to a predetermined ratio or more, the tape 28 can cover substantially the entire thickest region, making it less likely that steps will occur on the first flat outer surface FO1. This makes it possible to homogenize the surface pressure applied to the first flat outer surface FO1 and prevent localized application of large pressure during the manufacturing process or use of the secondary battery 100. As a result, reaction irregularities during charging and discharging are less likely to occur, and ultimately, the generation of dendrites can be prevented.

[0045] In addition, when the area of the region of the first flat outer surface FO1 that overlaps with the negative electrode active material layer 24a is denoted as S3 (not shown in the figure), it is preferable that the area S3 is the same as or larger than the area S1 of the region that overlaps with the positive electrode active material layer 22a. In the present embodiment, the length L2 of the negative electrode active material layer 24a is longer than the length L1 of the positive electrode active material layer 22a. Therefore, the area S3 of the region that overlaps with the negative electrode active material layer 24a is larger than the area S1 of the region that overlaps with the positive electrode active material layer 22a. In such a mode, the effects of the technology disclosed herein can be exerted at a higher level.

[0046] <Method for manufacturing secondary battery 100> The method for manufacturing the secondary battery 100 is characterized by including the manufacturing process of manufacturing the wound electrode body 20 as described above. Other manufacturing processes may be the same as those in the prior art. The wound electrode body 20 can be manufactured by a manufacturing method including, for example, (1) a winding process and (2) a forming process in this order. Further, the manufacturing method disclosed herein may further include other processes at any stage.

[0047] FIG. 7(A) is an explanatory view of (1) the winding process. In the winding process, a cylindrical wound body (cylindrical body) 20X is manufactured. Specifically, first, a strip-shaped first separator 26, a strip-shaped negative electrode 24, a strip-shaped second separator 26, and a strip-shaped positive electrode 22 are laminated in this order and wound around the axis 200 as shown in FIG. 7(A). Thereby, the cylindrical body 20X is manufactured. Then, a tape 28 is attached to the outer surface of the wound electrode body 20. When the diameter of the axis 200 is D and the thickness of the cylindrical body 20X is H, the height of the flat portion 20f of the wound electrode body 20 to be manufactured is expressed as D×π / 2 (half of the circumferential length of the axis 200). It is preferable that the length Ly in the long side direction Y of the tape 28 to be attached satisfies the following formula: D×π / 2 < Ly < (D×π / 2) + H×π;

[0048] FIG. 7(B) is an explanatory diagram of the (2) molding step. In the molding step, the cylindrical body is crushed by, for example, pressure molding. This produces a flat wound electrode body 20 having a flat portion 20f, a first curved portion 20r1, and a second curved portion 20r2, as shown in FIGS. 4-6. Furthermore, by setting the length Ly of the tape 28 in the long side direction Y to fall within the above range, it is possible to achieve a configuration in which the tape 28 covers substantially the entire surface of one flat surface (first flat outer surface FO1), and the vertices T1 and T2 protrude beyond the tape 28, as in the technology disclosed herein. In this manner, a flat wound electrode body 20 can be produced.

[0049] <Uses of the secondary battery 100> The secondary battery 100 can be used for various purposes, but can be suitably used, for example, as a power source (driving power source) for a motor mounted on a vehicle such as a passenger car, truck, etc. The type of vehicle is not particularly limited, but examples include a plug-in hybrid electric vehicle (PHEV), a hybrid electric vehicle (HEV), and a battery electric vehicle (BEV).

[0050] Although the preferred embodiment of the present invention has been described above, the above embodiment is merely an example. The present invention can be implemented in various other forms. The present invention can be implemented based on the contents disclosed in this specification and the technical common sense in the relevant field. The technology described in the claims includes various modifications and alterations of the above-exemplified embodiment. For example, it is possible to replace part of the above-described embodiment with other modifications, or to add other modifications to the above-described embodiment. Furthermore, if a technical feature is not described as essential, it may be deleted as appropriate.

[0051] As described above, specific aspects of the technology disclosed herein include those described in the following sections. Item 1: A wound electrode body is provided, which is formed by stacking a strip-shaped positive electrode having a positive electrode active material layer and a strip-shaped negative electrode having a negative electrode active material layer with a strip-shaped separator interposed therebetween and winding them, and a battery case that houses the wound electrode body, wherein the wound electrode body includes a first flat outer surface and a second flat outer surface that are arranged to face each other, a first curved outer surface that connects one end of the first flat outer surface to one end of the second flat outer surface, and a second curved outer surface that connects the other end of the first flat outer surface to the other end of the second flat outer surface, and a tape is attached to the first flat outer surface, and the tape a tape covering at least a part of a winding terminal end of the separator, an end of the tape on the first curved outer surface side being located closer to the first flat outer surface than apexes of the first curved outer surface, and an end of the tape on the second curved outer surface side being located closer to the first flat outer surface than apexes of the second curved outer surface, wherein, when viewed from a direction perpendicular to the first flat outer surface, an area of ​​a region of the first flat outer surface that overlaps with the positive electrode active material layer is S1 and an area of ​​a region to which the tape is attached is S2, a ratio of S2 to S1 is 95% or more. Item 2: The secondary battery described in Item 1, wherein the wound electrode body has a flat portion, a first curved portion provided at one end of the flat portion, and a second curved portion provided at the other end of the flat portion, one outer surface of the flat portion being the first flat outer surface and the other outer surface being the second flat outer surface, the outer surface of the first curved portion being the first curved outer surface, and the outer surface of the second curved portion being the second curved outer surface. Item 3: The secondary battery according to item 2, wherein the winding terminal end of the positive electrode and the winding terminal end of the negative electrode are located in the first curved portion. Item 4: The secondary battery according to any one of Items 1 to 3, wherein the winding end of the separator is located on the first flat outer surface. Item 5: A secondary battery according to any one of items 1 to 4, wherein an end of the tape on the side of the first curved outer surface is located on the first curved outer surface, and an end of the tape on the side of the second curved outer surface is located on the second curved outer surface. [Explanation of symbols]

[0052] 10 Battery case 20 Wound electrode body 20f flat area FO1 1st flat outer surface FO2 2nd flat outer surface 20r1 First curved section RO1 First curved outer surface 20r2 Second curved section RO2 Second curved outer surface 22 Positive electrode 22a Cathode active material layer 24 Negative electrode 26 Separator 28 Tape 100 Secondary battery

Claims

1. a wound electrode body formed by stacking a strip-shaped positive electrode having a positive electrode active material layer and a strip-shaped negative electrode having a negative electrode active material layer with a strip-shaped separator interposed therebetween and winding the stack; a battery case that houses the wound electrode body; Equipped with The wound electrode body is a first flat outer surface and a second flat outer surface disposed oppositely; a first curved outer surface connecting one end of the first flat outer surface and one end of the second flat outer surface; a second curved outer surface connecting the other end of the first flat outer surface and the other end of the second flat outer surface; Including, a tape is attached to the first flat outer surface; the tape covers at least a portion of the winding terminal end of the separator, an end portion of the tape on the first curved outer surface side is located closer to the first flat outer surface than a vertex portion of the first curved outer surface; an end portion of the tape on the second curved outer surface side is located closer to the first flat outer surface than a vertex portion of the second curved outer surface; When viewed from a direction perpendicular to the first flat outer surface, an area of ​​the first flat outer surface that overlaps with the positive electrode active material layer is defined as S1, and an area of ​​the area to which the tape is attached is defined as S2, and a ratio of S2 to S1 is 95% or more. Secondary battery.

2. the wound electrode body has a flat portion, a first curved portion provided at one end of the flat portion, and a second curved portion provided at the other end of the flat portion, one outer surface of the flat portion is the first flat outer surface, and the other outer surface is the second flat outer surface; The outer surface of the first curved portion is the first curved outer surface, and the outer surface of the second curved portion is the second curved outer surface. The secondary battery according to claim 1 .

3. a winding terminal end of the positive electrode and a winding terminal end of the negative electrode are located in the first curved portion; The secondary battery according to claim 2 .

4. The winding end of the separator is located on the first flat outer surface. The secondary battery according to claim 1 .

5. an end portion of the tape on the first curved outer surface side is located on the first curved outer surface, an end portion of the tape on the second curved outer surface side is located on the second curved outer surface; The secondary battery according to claim 1 .

Images