Secondary battery and method for manufacturing secondary battery

Abstract

According to this disclosure, a secondary battery and a method for manufacturing the secondary battery are provided to suppress the generation of springback in a wound electrode body with a specific external dimension. The secondary battery disclosed herein includes a flat wound electrode body and a battery casing housing the wound electrode body. The spacer (30) of the secondary battery has a strip-shaped substrate layer (32) and a surface layer (34) containing inorganic particles and a binder. Furthermore, at least one of the positive electrode plate (10) and the negative electrode plate (20) is bonded to the surface layer (34) of the spacer (30). In addition, the width dimension of the positive electrode active material layer (14) in the secondary battery (100) disclosed herein is 200 mm or more, the thickness dimension of the wound electrode body is 8 mm or more, and the height dimension of the wound electrode body is 120 mm or less. According to the technology disclosed herein, even when using a wound electrode body with such an external dimension that is prone to springback, the generation of springback can be appropriately suppressed.

Description

Technical Field

[0001] This invention relates to secondary batteries and methods for manufacturing secondary batteries. Background Technology

[0002] Secondary batteries, such as lithium-ion batteries, typically include an electrode body with a pair of electrode plates (positive and negative plates) and a battery casing housing the electrode body. As an example of the electrode body of such a secondary battery, a wound electrode body in which the positive and negative plates are wound with spacers between them can be cited. As the spacer for such a wound electrode body, a porous strip film or the like, having a substrate layer made of a resin material such as polyethylene (PE), is commonly used. Furthermore, from the viewpoint of improving the safety of secondary batteries, spacers with a heat-resistant layer formed on the surface of the substrate layer are sometimes used. For example, Patent Document 1 discloses a spacer having a porous resin layer (substrate layer) and a porous heat-resistant layer laminated on at least one side of the resin layer. This heat-resistant layer contains fillers and binders made of inorganic materials. Since spacers with such heat-resistant layers can suppress thermal shrinkage during temperature rise, they can prevent internal short circuits and improve the safety of the secondary battery.

[0003] Prior art literature

[0004] Patent documents

[0005] Patent Document 1: International Publication No. 2012 / 124093 Summary of the Invention

[0006] The problem that the invention aims to solve

[0007] As an example of the shape of the aforementioned wound electrode body, a flat shape can be cited. This flat-shaped wound electrode body is manufactured by stamping a cylindrical wound electrode body (cylindrical body) made by winding a positive electrode plate and a negative electrode plate with spacers between them. The wound electrode body has a pair of curved portions with curved outer surfaces and a flat portion with a flat outer surface connecting the pair of curved portions. Since the distance between the positive and negative electrode plates (inter-electrode distance) is narrowed in the flat portion of the flat-shaped wound electrode body, the movement of charge carriers between the electrodes can be promoted.

[0008] Furthermore, in recent years, various studies have been conducted on the external dimensions of wound electrode bodies with the aim of increasing the capacity of secondary batteries. Based on the present invention, it has been learned that wound electrode bodies with specific external dimensions are difficult to fully plastically deform during stamping. Due to the elastic effect remaining in the bent portions, frequent springback due to expansion of the flat portions occurs. When this springback occurs, the inter-electrode distance expands in a portion of the flat portion, potentially leading to increased battery resistance and charge carrier deposition. Additionally, since wound electrode bodies that have experienced springback are difficult to accommodate into the battery casing, this may also be a major cause of reduced production efficiency.

[0009] The present invention was made to solve the above-mentioned problems, and its purpose is to provide a secondary battery that suppresses the generation of springback in a wound electrode body with a specific external dimension.

[0010] Technical solutions for solving the problem

[0011] To achieve the above objectives, a secondary battery having the following structure is provided by means of the technology disclosed herein.

[0012] The secondary battery disclosed herein includes a flat wound electrode body formed by winding a positive electrode plate and a negative electrode plate with spacers between them, and a battery casing housing the wound electrode body. The flat wound electrode body has a pair of curved portions on its outer surface and a flat portion connecting the pair of curved portions on its outer surface. 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. Furthermore, in the secondary battery disclosed herein, the spacer has a strip-shaped substrate layer and a surface layer formed on at least one surface of the substrate layer containing inorganic particles and a binder. At least one of the positive and negative electrode plates in the flat portion is bonded to the surface layer of the spacer. In this secondary battery, the width of the positive electrode active material layer is 200 mm or more, the thickness of the wound electrode body is 8 mm or more, and the height of the wound electrode body is 120 mm or less.

[0013] First, in this specification, "the width dimension of the positive electrode active material layer" refers to the length of the positive electrode active material layer in the direction of the winding axis extending from the winding axis of the winding electrode body (winding axis direction). Since the winding electrode body becomes larger as the width dimension of the positive electrode active material layer increases, there is a tendency for the elastic force exerted from the curved portion on the flat portion after stamping to increase. Next, "the thickness dimension of the winding electrode body" refers to the length of the flat portion in the direction perpendicular to the flat portion. Similar to the width dimension of the positive electrode active material layer, even when the thickness dimension of the winding electrode body increases, there is a tendency for the elastic force after stamping to increase. Furthermore, "the height dimension of the winding electrode body" refers to the length from the upper end of one curved portion to the lower end of the other curved portion. When the height dimension of the winding electrode body is shorter, since the pair of curved portions are close together, the elastic force generated from each curved portion easily acts on the entire flat portion. That is, the technology disclosed herein targets a wound electrode body with a shape that is prone to springback, having a width of 200 mm or more, a thickness of 8 mm or more, and a height of 120 mm or less for the positive electrode active material layer.

[0014] Here, the inventors conducted various studies and discovered that using spacers with heat-resistant layers to improve safety further promotes the springback of the wound electrode body. Regarding this, the inventors investigated as follows: Conventional spacers are formed by stamping, pressing and deforming them along the uneven surfaces of the electrode plates (positive and negative plates) and fitting them into the electrode plates. When the spacer is bonded to the electrode plates in this way, springback is suppressed. On the other hand, spacers with heat-resistant layers have higher strength and are less prone to deformation such as when fitting into the electrode plates. That is, spacers with heat-resistant layers lose the springback suppression function of conventional spacers. The secondary battery disclosed herein is based on this insight. Specifically, the spacer of the secondary battery with the above structure has a surface layer containing inorganic particles and a binder to prevent internal short circuits caused by thermal shrinkage. However, the surface layer in the technology disclosed herein differs from the heat-resistant layer in the prior art, having adhesiveness to the extent that it is fitted and bonded to the electrode plates by stamping. Therefore, since the rebound suppression effect generated by the bonding between the spacer and the electrode plate can be properly utilized, even when using a wound electrode body with the above-mentioned dimensions, the generation of rebound can be suppressed without reducing the improvement in safety.

[0015] In a preferred embodiment of the secondary battery disclosed herein, the content of inorganic particles relative to the total mass of the surface layer is 70% to 80% by mass. As the content of inorganic particles in the surface layer decreases, it becomes easier to achieve a rebound suppression effect based on the adhesion between the electrode plate and the surface layer. On the other hand, if the content of inorganic particles in the surface layer is excessively reduced, adhesion may occur in the surface layer, potentially making it difficult to manufacture the wound electrode body. Furthermore, by adding a certain amount of inorganic particles to the surface layer, thermal shrinkage of the spacer can be appropriately prevented. From these viewpoints, the content of inorganic particles in the surface layer is preferably in the range of 70% to 80% by mass.

[0016] In one embodiment of the secondary battery disclosed herein, the surface layer comprises at least one of alumina particles and boehmite particles as inorganic particles. This allows for appropriate prevention of thermal shrinkage of the spacer.

[0017] In one embodiment of the secondary battery disclosed herein, the surface layer comprises polyvinylidene fluoride (PVDF) as a binder. This facilitates the effective rebound suppression caused by the adhesion between the electrode plates and the surface layer.

[0018] In one embodiment of the secondary battery disclosed herein, the surface layer has a mesh-like structure containing multiple voids. This allows for greater flexibility in the surface layer, enabling the uniformity of the thickness of the flat portion of the wound electrode body and contributing to the suppression of deviations in the inter-electrode distance.

[0019] In the scheme of forming the above-mentioned mesh-like surface layer, it is preferable that the porosity of the surface layer of the spacer disposed in the area not opposite to the positive and negative electrode plates is 50% or more. This allows the surface layer to possess appropriate softness, and more effectively suppresses deviations in the inter-electrode distance. Furthermore, in this specification, "the porosity of the surface layer of the spacer disposed in the area not opposite to the positive and negative electrode plates" refers to the porosity of the surface layer of the spacer before stamping.

[0020] In one embodiment of the secondary battery disclosed herein, a plurality of wound electrodes are housed within a battery casing. In this secondary battery, springback may occur in each of the plurality of wound electrodes. In this case, the impact of springback on the overall battery performance of the secondary battery can easily become significant. In contrast, since the technology disclosed herein can suppress the springback of each of the plurality of wound electrodes, it is suitable for application to secondary batteries having multiple wound electrodes.

[0021] Furthermore, in the embodiment with the aforementioned multiple wound electrode bodies, it is preferable to have a spacer provided on the outermost periphery of the wound electrode body, with adjacent wound electrode bodies bonded to each other via the surface layer of the spacer. This restricts the movement of the wound electrode bodies inside the battery casing, thus preventing damage to the wound electrode bodies caused by external impacts or vibrations.

[0022] In one embodiment of the secondary battery disclosed herein, a positive electrode tab assembly with stacked positive electrode tabs exposing a positive electrode core is formed at one end in the winding axis direction of the wound electrode body, and a negative electrode tab assembly with stacked negative electrode tabs exposing a negative electrode core is formed at the other end in the winding axis direction of the wound electrode body. The positive electrode tab assembly is bent in a state of engagement with a positive current collector, which is a plate-shaped conductive member, and the negative electrode tab assembly is bent in a state of engagement with a negative current collector, which is a plate-shaped conductive member. In the wound electrode body with the above structure, when bending the electrode tab assemblies (positive electrode tab assembly and negative electrode tab assembly), an increase in the inter-electrode distance may occur in the region near the electrode tab assemblies. In contrast, in the technology disclosed herein, since the spacer is bonded to the electrode plate, an increase in the inter-electrode distance in the region near the electrode tab assemblies can also be prevented.

[0023] In one embodiment of the secondary battery disclosed herein, a spacer is disposed on the outermost periphery of the wound electrode body. The end portion of the spacer is attached to the outermost surface of the wound electrode body using a winding fixing tape, which is positioned on a straight line connecting the positive electrode tab group and the negative electrode tab group. This prevents the winding of the wound electrode body from unwinding, thereby suppressing the increase in the inter-electrode distance in the vicinity of the electrode tab group and achieving a stable connection between the electrode tab group and the electrode current collectors (positive and negative current collectors).

[0024] In one embodiment of the secondary battery disclosed herein, a spacer is disposed on the outermost periphery of the wound electrode body. The terminal portion of the spacer is attached to the outermost surface of the wound electrode body using a winding fixing tape. The thickness of the surface layer of the spacer sandwiched between the positive and negative electrode plates is 0.9 or less relative to the thickness of the surface layer of the spacer disposed in the region not opposite to the positive and negative electrode plates. This prevents the formation of steps in the flat portion due to the thickness of the winding fixing tape, and prevents a decrease in battery performance caused by deviations in surface pressure relative to the flat portion.

[0025] In one embodiment of the secondary battery disclosed herein, one end of the positive electrode plate, along its long side, is disposed inside the flat portion of the wound electrode body as the positive electrode start end, and the other end, along its long side, is disposed outside the flat portion of the wound electrode body as the positive electrode end end. Similarly, one end of the negative electrode plate, along its long side, is disposed inside the flat portion of the wound electrode body as the negative electrode start end, and the other end, along its long side, is disposed outside the flat portion of the wound electrode body as the negative electrode end end. With this structure, in a flat wound electrode body, the start ends of both the positive and negative electrode plates can be disposed inside the flat portion, and the end ends can be disposed outside the flat portion.

[0026] In the configuration where the positive electrode start-end and positive electrode end-end are arranged on the flat portion, it is preferable that the adhesion strength between the positive electrode start-end and the surface layer is greater than the adhesion strength between the positive electrode end-end and the surface layer. In this way, by relatively strengthening the adhesion strength inside the wound electrode body, the rebound suppression effect can be more appropriately achieved.

[0027] In the configuration where the positive electrode start-end and negative electrode end-end are positioned on the flat portion, it is preferable that the adhesion strength between the positive electrode end-end and the surface layer is greater than that between the negative electrode end-end and the surface layer. This improves the permeability of the electrolyte into the interior of the wound electrode body.

[0028] In the embodiment where the positive electrode start-end and negative electrode terminal end are disposed inside the flat portion, it is preferable that a plurality of wound electrode bodies are housed within the battery casing, and a spacer is disposed at the outermost periphery of each wound electrode body. When adjacent wound electrode bodies are bonded together via the surface layer of the spacer, the bonding strength between adjacent wound electrode bodies is greater than the bonding strength between the positive electrode terminal end and the surface layer. This allows for more reliable restriction of movement of the wound electrode bodies within the battery casing and more appropriate prevention of damage to the wound electrode bodies.

[0029] Furthermore, as another aspect of the technology disclosed herein, a method for manufacturing a secondary battery is provided. This method includes: a step of forming a cylindrical body by winding a positive electrode plate and a negative electrode plate with a spacer between them; a step of stamping the cylindrical body to form a flat wound electrode body; and a step of housing the wound electrode body inside a battery casing. In this manufacturing method, the wound electrode body is any of the wound electrode bodies described above. According to this manufacturing method, a secondary battery capable of appropriately suppressing the rebound of the wound electrode body can be manufactured. Attached Figure Description

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

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

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

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

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

[0035] Figure 6 It is a schematic three-dimensional view of an electrode body with a positive second current collector and a negative second current collector installed.

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

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

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

[0039] Figure 10 This is an enlarged view schematically showing the interface of the positive electrode plate, negative electrode plate, and spacer of a wound electrode body of a secondary battery according to one embodiment.

[0040] Explanation of reference numerals in the attached figures

[0041] 10 Positive electrode plate

[0042] 12 Positive electrode core

[0043] 14 Positive electrode active material layer

[0044] 16 protective layers

[0045] 20 Negative electrode plate

[0046] 22 Negative electrode core

[0047] 24 Negative electrode active material layer

[0048] 30 spacers

[0049] 32 Substrate layer

[0050] 34 Surface layer

[0051] 38. Winding fixing tape

[0052] 40. Winded electrode body

[0053] 40f Flat section

[0054] 40r bend

[0055] 42 Positive electrode tabs

[0056] 44 Negative electrode tabs

[0057] 50 Battery casing

[0058] 60 Positive extremes

[0059] 65 Negative extremes

[0060] 70 Positive current collector

[0061] 75 Negative current collector

[0062] 100 Secondary Battery. Detailed Implementation

[0063] Hereinafter, embodiments of the technology disclosed herein will be described with reference to the accompanying drawings. Furthermore, matters necessary for implementing the technology disclosed herein, other than those specifically mentioned in this specification (e.g., the general structure and manufacturing process of a battery), can be understood by those skilled in the art based on prior art in this field. The technology disclosed herein can be implemented based on the content disclosed in this specification and common technical knowledge in this field. Furthermore, the expression "A to B" indicating a range in this specification includes the meaning of "A or more and B or less," and also includes the meanings of "preferably larger than A" and "preferably smaller than B."

[0064] Furthermore, in this specification, "secondary battery" refers to a general energy storage device that generates a charge-discharge reaction by moving charge carriers between a pair of electrodes (positive and negative electrodes) via an electrolyte. This secondary battery includes not only so-called storage batteries such as lithium-ion secondary batteries, nickel-metal hydride batteries, and nickel-cadmium batteries, but also capacitors such as electric double-layer capacitors. Hereinafter, an embodiment will be described using a lithium-ion secondary battery as an example.

[0065] In addition, in the figures referenced in this specification, reference numeral X indicates "depth direction," reference numeral Y indicates "width direction," and reference numeral Z indicates "height direction." Furthermore, in the depth direction X, F indicates "front," and Rr indicates "rear." In the width direction Y, L indicates "left," and R indicates "right." And in the height direction Z, U indicates "up," and D indicates "down." However, these directions are determined for ease of explanation and are not intended to limit the installation configuration when using the secondary battery disclosed herein.

[0066] <First Implementation>

[0067] 1. Structure of a secondary battery

[0068] The following is for reference Figures 1-10 An embodiment of the secondary battery disclosed herein will be described. Figure 1 This is a schematic perspective view of the secondary battery according to this embodiment. Figure 2 It is along Figure 1 A schematic longitudinal section view of line II-II in the diagram. Figure 3 It is along Figure 1 A schematic longitudinal section view of line III-III in the diagram. Figure 4 It is along Figure 1 A schematic cross-sectional view of line IV-IV in the diagram. Figure 5 It is a schematic perspective view of the electrode body installed on the sealing plate. Figure 6 It is a schematic three-dimensional view of an electrode body with a positive second current collector and a negative second current collector installed. Figure 7 This is a schematic diagram showing the structure of the wound electrode body of the secondary battery according to this embodiment. Figure 8 It is shown schematically. Figure 7 Front view of the wound electrode body. Figure 9 It is along Figure 8 A schematic longitudinal section view of the IX-IX line. Figure 10 This is an enlarged view schematically showing the interface between the positive electrode plate, the negative electrode plate, and the spacer of the wound electrode body of the secondary battery according to this embodiment.

[0069] like Figure 2 As shown, the secondary battery 100 of this embodiment includes a wound electrode body 40 and a battery casing 50 that houses the wound electrode body 40. The specific structure of this secondary battery 100 will be described below.

[0070] (1) Battery casing

[0071] The battery casing 50 is a frame that houses the wound electrode body 40. Although not shown in the figure, a non-aqueous electrolyte is also contained inside the battery casing 50. Figure 1 As shown, the battery casing 50 in this embodiment has a flat, bottomed cuboid shape (square). Furthermore, conventionally known materials can be used in the battery casing 50 without particular limitations. For example, the battery casing 50 can be made of metal. Examples of materials for the battery casing 50 include aluminum, aluminum alloys, iron, and iron alloys.

[0072] like Figure 1 and Figure 2As shown, the battery casing 50 includes an outer body 52 and a sealing plate 54. The outer body 52 is a flat, bottomed, square container with an opening 52h on its upper surface. The outer body 52 has a bottom wall 52a with a generally rectangular planar shape, a pair of long side walls 52b extending upward in the height direction Z from the long side of the bottom wall 52a, and a pair of short side walls 52c extending upward in the height direction Z from the short side of the bottom wall 52a. On the other hand, the sealing plate 54 is a plate-shaped member with a generally rectangular planar shape that blocks the opening 52h of the outer body 52. ​​Furthermore, the outer periphery of the sealing plate 54 is joined (e.g., welded) to the outer periphery of the opening 52h of the outer body 52. ​​Thus, a battery casing 50 with its interior airtightly sealed is produced. In addition, an injection hole 55 and a gas venting valve 57 are provided in the sealing plate 54. The injection hole 55 is a through hole provided for injecting a non-aqueous electrolyte into the interior of the sealed battery casing 50. Furthermore, the injection port 55 is sealed by the sealing member 56 after the non-aqueous electrolyte is injected. Additionally, the gas vent valve 57 is a thin-walled portion designed to break (open) and release a large amount of gas generated within the battery casing 50.

[0073] (2) Electrolyte

[0074] As described above, in addition to the wound electrode body 40, an electrolyte (not shown) is also contained inside the battery casing 50. As the electrolyte, electrolytes used in conventionally known secondary batteries can be used without particular limitation. For example, a non-aqueous electrolyte containing a supporting salt dissolved in a non-aqueous solvent can be used. Examples of such non-aqueous solvents include carbonate solvents such as ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate. Examples of such supporting salts include fluorinated lithium salts such as LiPF6.

[0075] (3) Electrode terminals

[0076] Additionally, on one side of the width direction Y of the sealing plate 54 ( Figure 1 , Figure 2 A positive terminal 60 is mounted on the left end of the battery casing 50. This positive terminal 60 is connected to a plate-shaped external positive electrode conductive member 62 on the outside of the battery casing 50. On the other hand, on the other side of the sealing plate 54 in the width direction Y... Figure 1 , Figure 2 A negative terminal 65 is installed at the right end of the battery. A plate-shaped external conductive member 67 is installed on the negative terminal 65. The external conductive members (positive external conductive member 62 and negative external conductive member 67) are connected to other secondary batteries and external devices via external connecting members (busbars, etc.). Furthermore, the external conductive members are preferably made of a metal with excellent conductivity (aluminum, aluminum alloy, copper, copper alloy, etc.).

[0077] (4) Electrode current collector

[0078] like Figures 3-5 As shown, in the secondary battery 100 of this embodiment, a plurality (three) of wound electrode bodies 40 are housed within the battery casing 50. Detailed construction will be described later, but each wound electrode body 40 is provided with a positive electrode tab group 42 and a negative electrode tab group 44 (see reference). Figure 7 and Figure 8 ).like Figure 2 As shown, the positive terminal 60 is connected to the positive electrode tabs 42 of each of the plurality of wound electrode bodies 40 via a positive current collector 70. The positive current collector 70 is housed inside the battery casing 50. Figure 2 and Figure 5 As shown, the positive current collector 70 includes a first positive current collector 71 and a plurality of second positive current collectors 72. The first positive current collector 71 is a plate-shaped conductive member extending along the inner side of the sealing plate 54 in the width direction Y, and the plurality of second positive current collectors 72 are plate-shaped conductive members extending along the height direction Z. Furthermore, the lower end 60c of the positive terminal 60 is inserted into the battery casing 50 through the terminal insertion hole 58 of the sealing plate 54 and connected to the first positive current collector 71 (see reference). Figure 2 On the other hand, such as Figures 4-6 As shown, the secondary battery 100 is provided with a number of positive electrode second current collectors 72 corresponding to the plurality of wound electrode bodies 40. Each positive electrode second current collector 72 is connected to the positive electrode tab group 42 of the wound electrode body 40. Furthermore, as... Figure 4 and Figure 5 As shown, the positive electrode tab assembly 42 of the wound electrode body 40 is bent so that the positive second current collector 72 is opposite to one side 40a of the wound electrode body 40. Thus, the upper end of the positive second current collector 72 is electrically connected to the positive first current collector 71.

[0079] On the other hand, the negative terminal 65 is connected to the negative electrode tabs 44 of each of the plurality of wound electrode bodies 40 via the negative electrode current collector 75. The connection structure on the negative side is substantially the same as the connection structure on the positive side described above. Specifically, the negative electrode current collector 75 includes a first negative electrode current collector 76 and a plurality of second negative electrode current collectors 77. The first negative electrode current collector 76 is a plate-shaped conductive member extending along the inner side surface of the sealing plate 54 in the width direction Y, and the plurality of second negative electrode current collectors 77 are plate-shaped conductive members extending along the height direction Z (see reference). Figure 2 and Figure 5 Furthermore, the lower end 65c of the negative terminal 65 is inserted into the interior of the battery casing 50 through the terminal insertion hole 59 and connected to the negative first current collector 76 (see reference). Figure 2 On the other hand, multiple negative electrode second current collectors 77 are respectively connected to the negative electrode tab group 44 of the wound electrode body 40 (see reference). Figures 4-6Furthermore, the negative electrode tab assembly 44 is bent so that the second negative current collector 77 faces the other side 40b of the wound electrode body 40. Thus, the upper end of the second negative current collector 77 is electrically connected to the first negative current collector 76. Additionally, metals with excellent conductivity (aluminum, aluminum alloys, copper, copper alloys, etc.) can preferably be used in the electrode current collectors (positive current collector 70 and negative current collector 75).

[0080] (5) Insulating components

[0081] Furthermore, in this secondary battery 100, various insulating components are installed to prevent the wound electrode body 40 from conducting with the battery casing 50. Specifically, an external insulating component 92 (see reference) is sandwiched between the positive electrode external conductive component 62 (negative electrode external conductive component 67) and the outer side of the sealing plate 54. Figure 1 This prevents the positive electrode external conductive member 62 and the negative electrode external conductive member 67 from conducting with the sealing plate 54. Additionally, gaskets 90 are installed in the terminal insertion holes 58 and 59 of the sealing plate 54 (see reference). Figure 2 This prevents the positive terminal 60 (or negative terminal 65) inserted into the terminal insertion holes 58 and 59 from conducting with the sealing plate 54. Furthermore, an internal insulating member 94 is disposed between the positive first current collector 71 (or negative first current collector 76) and the inner surface of the sealing plate 54. This internal insulating member 94 has a plate-shaped base 94a sandwiched between the positive first current collector 71 (or negative first current collector 76) and the inner surface of the sealing plate 54. This prevents the positive first current collector 71, the negative first current collector 76, and the sealing plate 54 from conducting with each other. Moreover, the internal insulating member 94 has a protrusion 94b protruding from the inner surface of the sealing plate 54 toward the winding electrode body 40 (see reference). Figure 2 and Figure 3 Therefore, the 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. Furthermore, the multiple wound electrode bodies 40 are held in place by an electrode body holder 98 (see reference 54) made of an insulating resin sheet. Figure 3 The electrode body 40 is housed inside the battery casing 50 while covered. This prevents direct contact between the wound electrode body 40 and the outer casing 52. Furthermore, the materials of the aforementioned insulating components are not particularly limited, as long as they have the specified insulation properties. For example, synthetic resin materials such as polyolefin resins (e.g., polypropylene (PP), polyethylene (PE)) and fluorinated resins (e.g., perfluoroalkoxyalkane (PFA), polytetrafluoroethylene (PTFE)) can be used.

[0082] (6) Winding the electrode body

[0083] like Figure 7As shown, the electrode body used in the secondary battery 100 of this embodiment is a flat wound electrode body 40 formed by winding the positive electrode plate 10 and the negative electrode plate 20 with spacers 30 between them. In this secondary battery 100, the wound electrode body 40 is housed in the battery casing 50 in such a way that the winding axis WL of the wound electrode body 40 is substantially aligned with the width direction Y of the secondary battery 100 (see reference). Figure 2 That is, the "winding axis direction" in the following description is the same as the width direction Y in the figure.

[0084] (a) External dimensions

[0085] First, the wound electrode body 40 in this embodiment has the following external dimensions (width, thickness, height). Furthermore, as in this embodiment, in a secondary battery having multiple wound electrode bodies, the external dimensions of each wound electrode body can be the same or different. Additionally, it is not necessary for all of the multiple wound electrode bodies to have the following external dimensions; it is sufficient for at least one wound electrode body to have the following external dimensions. Even in this case, the springback suppression effect based on the technology disclosed herein can be achieved. However, when all of the multiple wound electrode bodies have the following external dimensions, springback is more likely to occur in each wound electrode body; therefore, the effect of the technology disclosed herein can be achieved more appropriately.

[0086] First, in this embodiment, the width dimension w1 of the positive electrode active material layer 14 (refer to...) Figure 7 The thickness t1 of the positive electrode active material layer 14 is 200 mm or more. Since the wound electrode body 40 becomes larger as the width w1 of the positive electrode active material layer 14 increases, there is a tendency for the elastic effect generated from the bent portion 40r after stamping to increase. Furthermore, the width w1 of the positive electrode active material layer 14 is preferably 200 mm to 400 mm, more preferably 250 mm to 350 mm, and even more preferably 260 mm to 300 mm, for example, about 280 mm. Secondly, in this embodiment, the thickness t1 of the wound electrode body 40 (refer to...) Figure 9 The thickness t1 of the wound electrode body 40 is 8mm or more. When the thickness t1 of the wound electrode body 40 increases, the elastic effect from the bent portion 40r after stamping also increases. The thickness t1 of the wound electrode body 40 is preferably 8mm to 25mm, more preferably 8mm to 20mm, and even more preferably 10mm to 15mm, for example, about 12mm. Third, in this embodiment, the height h1 of the wound electrode body 40 (refer to...) Figure 8The height h1 of the wound electrode body 40 is 120 mm or less. Since the pair of bent portions 40r approach each other when the height h1 of the wound electrode body 40 becomes shorter, the elastic effect generated from each bent portion 40r easily acts on the entire flat portion 40f. The height h1 of the wound electrode body 40 is preferably 60 mm to 120 mm, more preferably 80 mm to 110 mm, and even more preferably 90 mm to 100 mm, for example, about 94 mm.

[0087] As described above, the wound electrode body 40 in this embodiment has an external dimension that easily generates a large elastic force in the bent portion 40r after stamping, and the elastic force from the bent portion 40r easily acts on the flat portion 40f. In contrast, the secondary battery 100 of this embodiment has a structure that can appropriately suppress springback even when using a wound electrode body 40 with such an external dimension that easily generates springback. Hereinafter, the specific structure of the wound electrode body 40 in this embodiment will be described.

[0088] (b) Positive electrode plate

[0089] like Figure 7 and Figure 10 As shown, the positive electrode plate 10 is a long strip-shaped component. The positive electrode plate 10 includes a positive electrode core 12 as a strip-shaped metal foil and a positive electrode active material layer 14 applied to the surface of the positive electrode core 12. Furthermore, from the viewpoint of battery performance, it is preferable to apply the positive electrode active material layer 14 to both sides of the positive electrode core 12. Additionally, in this positive electrode plate 10, the positive electrode tab 12t extends outward from one end edge in the winding axis direction (width direction Y). Figure 7 (The left side of the image is protruding). Furthermore, multiple positive electrode tabs 12t are formed at predetermined intervals along the long side L of the elongated strip-shaped positive electrode plate 10. These positive electrode tabs 12t are the areas where the positive electrode core 12 is exposed without the positive electrode active material layer 14. Additionally, a protective layer 16 extending along the long side L of the positive electrode plate 10 is formed in the region adjacent to the end edge of the positive electrode tab 12t side of the positive electrode plate 10.

[0090] In the components constituting the positive electrode plate 10, conventionally known materials that can be used in general secondary batteries (e.g., lithium-ion secondary batteries) can be used without particular restriction. For example, a metallic material with a specified conductivity can be preferably used in the positive electrode core 12. The positive electrode core 12 is preferably made of, for example, aluminum, aluminum alloy, etc.

[0091] Furthermore, the positive electrode active material layer 14 is a layer containing the positive electrode active material. The positive electrode active material is a particulate material capable of reversibly absorbing and releasing charge carriers. From the viewpoint of stably producing a high-performance positive electrode plate 10, the positive electrode active material is preferably a lithium transition metal composite oxide. Among the aforementioned lithium transition metal composite oxides, lithium transition metal composite oxides containing at least one of the group consisting of nickel (Ni), cobalt (Co), and manganese (Mn) as transition metals are particularly preferred. Specific examples include lithium nickel cobalt manganese composite oxide (NCM), lithium nickel composite oxide, lithium cobalt composite oxide, lithium manganese composite oxide, lithium nickel manganese composite oxide, lithium nickel cobalt aluminum composite oxide (NCA), and lithium iron nickel manganese composite oxide. Furthermore, as a preferred example of a lithium transition metal composite oxide that does not contain Ni, Co, and Mn, lithium iron phosphate composite oxide (LFP) is an example. Furthermore, the term "lithium nickel cobalt manganese composite oxide" in this specification refers to oxides containing additive elements in addition to the main constituent elements (Li, Ni, Co, Mn, O). Examples of such additive elements include transition metal elements and typical metal elements such as Mg, Ca, Al, Ti, V, Cr, Si, Y, Zr, Nb, Mo, Hf, Ta, W, Na, Fe, Zn, and Sn. Additionally, additive elements can also be half-metal elements such as B, C, Si, and P, or non-metal elements such as S, F, Cl, Br, and I. Although detailed explanations are omitted, this also applies to other lithium transition metal composite oxides described as "~type composite oxides". Furthermore, the positive electrode active material layer 14 may also contain additives other than the positive electrode active material. Examples of such additives include conductive materials and binders. Specific examples of conductive materials include carbon materials such as acetylene black (AB). Specific examples of binders include resin binders such as polyvinylidene fluoride (PVdF). Furthermore, when the solid composition 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.

[0092] On the other hand, the protective layer 16 is configured to have a lower conductivity than the positive electrode active material layer 14. By providing this protective layer 16 in the region adjacent to the end edge of the positive electrode plate 10, internal short circuits caused by direct contact between the positive electrode core 12 and the negative electrode active material layer 24 can be prevented when the spacer 30 is damaged. For example, the protective layer 16 is preferably formed as a layer containing insulating ceramic particles. Examples of such ceramic particles include inorganic oxides such as alumina (Al2O3), magnesium oxide (MgO), silicon dioxide (SiO2), and titanium dioxide (TiO2), nitrides such as aluminum nitride and silicon nitride, metal hydroxides such as calcium hydroxide, magnesium hydroxide, and aluminum hydroxide, mica, talc, boehmite, zeolite, apatite, and kaolin, as well as glass fibers. Considering insulation and heat resistance, alumina, boehmite, aluminum hydroxide, silicon dioxide, and titanium dioxide are also preferred among the above-mentioned ceramic particles. Alternatively, the protective layer 16 may also contain an adhesive for fixing the aforementioned ceramic particles onto the surface of the positive electrode core 12. Examples of such adhesives include resin adhesives such as polyvinylidene fluoride (PVdF). Furthermore, the protective layer is not a necessary component of the positive electrode plate. That is, in the secondary battery disclosed herein, a positive electrode plate without a protective layer can also be used.

[0093] In addition, the thickness t2 of the positive electrode plate 10 (refer to) Figure 10 The thickness of the positive electrode plate 10 is preferably 80 μm or more, more preferably 100 μm or more, and even more preferably 120 μm or more. Since a positive electrode plate 10 with such a sufficient thickness exhibits greater elasticity after stamping, it could potentially be a major cause of springback. However, according to the technology disclosed herein, even when using a positive electrode plate 10 of such thickness, springback can be appropriately suppressed. On the other hand, 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 even more preferably 160 μm or less. Furthermore, the term "thickness of the positive electrode plate" in this specification refers to the combined thickness of the positive electrode core and the positive electrode active material layer.

[0094] Furthermore, the surface roughness of the positive electrode plate 10 (typically the surface roughness of the positive electrode active material layer 14) is preferably 0.01 μm or more, and more preferably 0.02 μm or more. Details will be described later, but in this embodiment, by deforming and fitting the surface layer 34 of the spacer 30 to match the unevenness of the surface of the positive electrode plate 10, the spacer 30 is bonded to the positive electrode plate 10, thereby suppressing springback. From the viewpoint of appropriately achieving bonding between the spacer 30 and the positive electrode plate 10, it is preferable that the positive electrode plate 10 has a certain or higher surface roughness. On the other hand, the upper limit of the surface roughness of the positive electrode plate 10 is not particularly limited, and it may also be 3 μm or less. Furthermore, "surface roughness" in this specification refers to the arithmetic mean roughness Ra.

[0095] Furthermore, preferably, the positive electrode active material layer 14 contains large positive electrode active material particles with a peak particle size in the range of 10 μm to 20 μm and small positive electrode active material particles with a peak particle size in the range of 2 μm to 6 μm, as analyzed by laser diffraction-scattering. By mixing two types of positive electrode active material particles with different particle diameters, and forming fine irregularities on the surface of the positive electrode active material layer 14, the bonding between the positive electrode plate 10 and the spacer 30 can be achieved more appropriately. Moreover, the aforementioned large and small particles can be either the same type of lithium transition metal composite oxide or different types of lithium transition metal composite oxides.

[0096] Furthermore, in recent years, from the viewpoint of improving battery capacity, attempts have been made to form a positive electrode active material layer with a filling density of 2 g / cc or higher. However, since such a high-density positive electrode active material layer exerts a large reaction force on stamping, it may become a major cause of springback in the wound electrode body. However, according to the technology disclosed herein, even when a high-density positive electrode active material layer of 2 g / cc or higher (preferably 2.5 g / cc or higher) is formed, springback in the wound electrode body can be appropriately suppressed. In other words, according to the technology disclosed herein, a high-density positive electrode active material layer that is difficult to use in conventional technologies can be easily used, contributing to the improvement of battery capacity. In addition, from the viewpoint of appropriately preventing springback, the filling density of the positive electrode active material layer 14 is preferably 4 g / cc or lower.

[0097] (c) Negative electrode plate

[0098] like Figure 7 and Figure 10 As shown, the negative electrode plate 20 is a long strip-shaped component. This negative electrode plate 20 includes a negative electrode core 22 as a strip-shaped metal foil and a negative electrode active material layer 24 applied to the surface of the negative electrode core 22. Furthermore, from the viewpoint of battery performance, it is preferable to apply the negative electrode active material layer 24 to both sides of the negative electrode core 22. Moreover, the negative electrode plate 20 has an end edge extending outward from the winding axis direction (width direction Y). Figure 7 The negative electrode tab 22t protrudes from the right side of the negative electrode plate 20. Multiple negative electrode tabs 22t are provided at predetermined intervals along the long side L of the negative electrode plate 20. These negative electrode tabs 22t represent the areas where the negative electrode core 22 is exposed without being endowed with the negative electrode active material layer 24.

[0099] In the components constituting the negative electrode plate 20, conventionally known materials that can be used in general secondary batteries (e.g., lithium-ion secondary batteries) can be used without particular restriction. For example, a metallic material with a specified conductivity can preferably be used in the negative electrode core 22. The negative electrode core 22 is preferably made of, for example, copper, copper alloy, etc.

[0100] Furthermore, the negative electrode active material layer 24 is a layer containing the negative electrode active material. The negative electrode active material is not particularly limited as long as it can reversibly absorb and release charge carriers in relation to the aforementioned positive electrode active material; materials commonly used in conventional secondary batteries can be used without particular restriction. Examples of negative electrode active materials include carbon materials and silicon-based materials. Examples of carbon materials include graphite, hard carbon, soft carbon, and amorphous carbon. Alternatively, graphite with amorphous carbon coating can be used. On the other hand, examples of silicon-based materials include silicon and silicon dioxide. Silicon-based materials may also contain other metallic elements (e.g., alkaline earth metals) and their oxides. Additionally, the negative electrode active material layer 24 may contain additives other than the negative electrode active material. Examples of such additives include binders and thickeners. Specific examples of binders include rubber-based binders such as styrene-butadiene rubber (SBR). Specific examples of thickeners include carboxymethyl cellulose (CMC). Furthermore, when the solid content of the negative electrode active material layer 24 is set to 100% by mass, the content of the negative electrode active material is approximately 30% by mass or more, typically 50% by mass or more. Additionally, the negative electrode active material can occupy either 80% or more by mass of the negative electrode active material layer 24, or 90% or more by mass. Furthermore, the width w2 of the negative electrode active material layer 24 is preferably 200mm to 450mm, more preferably 250mm to 350mm, and even more preferably 260mm to 320mm.

[0101] Additionally, the thickness t3 of the negative electrode plate 20 (refer to...) Figure 10 The thickness of the negative electrode plate 20 is preferably 100 μm or more, more preferably 130 μm or more, and even more preferably 160 μm or more. Similar to the positive electrode plate 10 described above, a thicker negative electrode plate 20 may promote springback. However, according to the technology disclosed herein, even when using a negative electrode plate 20 of such thickness, 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 even more preferably 190 μm or less. Furthermore, the term "thickness of the negative electrode plate" in this specification refers to the combined thickness of the negative electrode core and the negative electrode active material layer.

[0102] Furthermore, similar to the surface roughness of the positive electrode plate 10, from the viewpoint of appropriately achieving adhesion between the spacer 30 and the negative electrode plate 20, it is preferable to also adjust the surface roughness of the negative electrode plate 20 (typically the surface roughness of the negative electrode active material layer 24). For example, the surface roughness of the negative electrode plate 20 is preferably 0.05 μm or more, more preferably 0.1 μm or more. This allows for proper adhesion between the spacer 30 and the negative electrode plate 20, and enables a more appropriate rebound suppression effect. Furthermore, the upper limit of the surface roughness of the negative electrode plate 20 is not particularly limited, and it can also be 5 μm or less.

[0103] (d) Spacer

[0104] like Figure 7 and Figure 9 As shown, the wound electrode body 40 in this embodiment includes two spacers 30. Each spacer 30 is an insulating sheet with multiple fine through holes through which charge carriers can pass. By sandwiching the spacer 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.

[0105] like Figure 10 As shown, the spacer 30 in this embodiment has a strip-shaped substrate layer 32 and a surface layer 34 formed on both sides of the substrate layer 32. Detailed functions will be described later, but in this embodiment, one surface layer 34 of the spacer 30 with 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. Therefore, due to the flat portion 40f of the wound electrode body 40 (refer to...) Figure 9 Expansion along the thickness direction (depth direction X) is restricted, thus suppressing springback. The spacer 30 of this structure will be described below.

[0106] First, the substrate layer 32 can be used without particular limitation in substrate layers used in conventionally known secondary battery spacers. For example, the substrate layer 32 is preferably a porous sheet-like member containing a polyolefin resin, etc. This ensures sufficient flexibility of the spacer 30, making it easy to manufacture (wound and stamped) the wound electrode body 40. Furthermore, polyethylene (PE), polypropylene (PP), or mixtures thereof can be used as the polyolefin resin. Additionally, the porosity of the substrate layer 32 is preferably 20% to 70%, more preferably 30% to 60%. This allows the charge carrier to move appropriately between the positive electrode plate 10 and the negative electrode plate 20. Furthermore, the term "porosity" in this specification refers to the porosity before stamping unless otherwise specified. This "porosity before stamping" can be obtained by measuring a spacer disposed in a region not opposite to the positive and negative electrode plates. Examples of such "regions not opposite to the positive and negative electrode plates" include those formed in… Figure 7 The "region 30a where only the spacer 30 protrudes" on both sides of the wound electrode body 40.

[0107] like Figure 10 As shown, the surface layer 34 in this embodiment is a layer formed on both sides of the substrate layer 32. This surface layer 34 contains inorganic particles and a binder. Examples of inorganic particles include ceramic particles containing alumina, silicon dioxide, titanium dioxide, boehmite, aluminum hydroxide, magnesium carbonate, magnesium oxide, zirconium oxide, zinc oxide, iron oxide, cerium dioxide, yttrium oxide, etc., as main components. The surface layer 34 containing such inorganic particles exhibits excellent heat resistance. This suppresses the thermal shrinkage of the spacer 30 during temperature rise, contributing to improved safety of the secondary battery 100. Furthermore, from the viewpoint of suppressing the thermal shrinkage of the spacer 30, alumina particles and boehmite particles are particularly preferred among the aforementioned ceramic particles. Additionally, the average particle diameter of the inorganic particles is preferably, for example, 0.15 μm to 2 μm, more preferably 0.3 μm to 0.7 μm, and even more preferably 0.3 μm to 0.5 μm. Furthermore, the specific surface area of ​​the inorganic particles is preferably, for example, 2 m². 2 / g~13m 2 Approximately / g. Furthermore, the "average particle diameter" in this specification refers to the particle diameter at which the cumulative value of the particle size distribution determined by laser diffraction-scattering method reaches 50% (D). 50 Particle diameter).

[0108] Next, conventionally known resin materials with a certain degree of adhesion can be used in the adhesive of the surface layer 34 without particular limitation. For example, the adhesive of the surface layer 34 is preferably an acrylic resin, a polyolefin resin, a cellulose resin, a fluorinated resin, or other resin materials. As an acrylic resin, resins with polymers of acrylates as the main component can be used. As a polyolefin resin, polyethylene (PE), polypropylene (PP), etc., can be used. As a cellulose resin, carboxymethyl cellulose (CMC), etc., can be used. As a fluorinated resin, polyvinylidene fluoride (PVdF), etc., can be used. In addition, the surface layer 34 may also contain two or more of the above-mentioned adhesive resins. Furthermore, among the above-mentioned adhesive resins, PVdF can more appropriately exert its adhesion to the electrode plate. In addition, the surface layer 34 preferably contains an adhesive of the same type as the adhesive of the electrode active material layer of the opposing electrode plate. As an example, when the positive electrode active material layer 14 contains PVdF, it is preferable to use PVdF as an adhesive for the surface layer 34 opposite to the positive electrode active material layer 14. This further improves the adhesion strength between the surface layer 34 and the positive electrode plate 10.

[0109] Furthermore, the content of inorganic particles in the surface layer 34 is preferably adjusted in a manner that provides a predetermined adhesiveness to the positive electrode plate 10 (or negative electrode plate 20). For example, the content of inorganic particles in the surface layer 34 is preferably less than 90% by mass, more preferably less than 85% by mass, and particularly preferably less than 80% by mass. In this way, since the surface layer 34 is easily deformed during stamping when the content of inorganic particles in the surface layer 34 is set to a certain level, the springback suppression effect generated by the interlocking (adhesion) between the positive electrode plate 10 (or negative electrode plate 20) and the surface layer 34 can be appropriately exerted. On the other hand, since the content of inorganic particles in the surface layer 34 is excessively reduced, the content of resin materials such as binders becomes relatively higher, and therefore, adhesiveness may occur in the surface layer 34 before stamping. In such a case, it may become difficult to wind the positive electrode plate 10 and the negative electrode plate 20 with the spacer 30 in between. From this perspective, the content of 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. Furthermore, by forming a surface layer 34 containing a certain amount or more of inorganic particles, it is also possible to appropriately prevent internal short circuits caused by the thermal shrinkage of the spacer 30. In addition, the term "content of inorganic particles" in this specification refers to the mass ratio of inorganic particles relative to the total mass of the surface layer.

[0110] Furthermore, the surface layer 34 preferably has a mesh-like structure containing multiple voids. In this surface layer 34, inorganic particles are dispersed within the binder resin that has been hardened in a mesh-like manner. Because the surface layer 34 with this mesh-like structure has high flexibility, it deforms in a flattened manner during stamping. As a result, since the spacer 30 can absorb the thickness t1 deviation of the wound electrode body 40, the deposition of charge carriers caused by the deviation of the inter-electrode distance can be suppressed. In addition, the porosity of the surface layer 34 with the mesh-like structure is preferably 50% or more, more preferably 60% or more, and particularly preferably 70% or more. As a result, the surface layer 34 can be given appropriate flexibility, and the deviation of the thickness t1 of the wound electrode body 40 can be suppressed. On the other hand, considering the strength of the spacer 30, the porosity of the surface layer 34 is preferably 90% or less, more preferably 80% or less.

[0111] Furthermore, preferably, the surface layer 34 with the aforementioned mesh structure is formed such that the filling density on the electrode plate side (outer side of the spacer 30) is higher than the filling density on the substrate layer 32 side (inner side of the spacer 30). Therefore, since the surface layer 34 on the substrate layer 32 side preferentially undergoes pressing deformation during stamping, the collapse of voids in the surface layer 34 on the electrode plate side can be prevented. This suppresses the decrease in electrolyte permeability to the vicinity of the electrode plate and contributes to preventing liquid depletion.

[0112] Additionally, the thickness t4 of spacer 30 (refer to...) Figure 10 The thickness t4 of the spacer 30 is preferably 4 μm or more, more preferably 8 μm or more, and even more preferably 12 μm or more. Similar to the positive electrode plate 10 and the negative electrode plate 20 described above, as the thickness t4 of the spacer 30 increases, there is a tendency to promote springback. However, according to the technology disclosed herein, even when using a spacer 30 of sufficient thickness as described above, springback can be appropriately suppressed. On the other hand, from the viewpoint of easily preventing springback, the thickness of the spacer 30 is preferably 28 μm or less, more preferably 24 μm or less, and even more preferably 20 μm or less. Furthermore, the "thickness t4 of the spacer 30" in this specification refers to the combined thickness of the substrate layer 32 and the surface layer 34.

[0113] 2. Manufacturing method of secondary batteries

[0114] The structure of the secondary battery 100 of this embodiment has been described above. Next, while describing the manufacturing steps of the secondary battery 100, the rebound suppression effect based on the technology disclosed herein will be specifically explained. Furthermore, the manufacturing method of the secondary battery 100 of this embodiment includes (1) a winding process, (2) a stamping process, and (3) a housing process.

[0115] (1) Winding process

[0116] In this process, firstly, a laminate consisting of spacer 30, negative electrode plate 20, spacer 30, and positive electrode plate 10 stacked sequentially is fabricated (see reference). Figure 7 At this point, the stacking position of each component in the width direction Y is adjusted so that only the positive electrode tab 12t of the positive electrode plate 10 is positioned in one direction in the width direction Y. Figure 7 The left side of the negative electrode plate 20 protrudes from the other side, and only the negative electrode tab 22t of the negative electrode plate 20 protrudes from the other side. Figure 7 The right side of the stacked body protrudes. Furthermore, a cylindrical wound body (cylindrical body) is produced by winding the manufactured stacked body. Preferably, the number of windings is appropriately adjusted considering the performance and manufacturing efficiency of the target secondary battery 100. Furthermore, according to the technology disclosed herein, a wound electrode body 40 with more than 20 windings can be easily manufactured. Specifically, since a wound electrode body 40 with more than 20 windings is particularly prone to springback after stamping (described later), stable manufacturing is difficult. However, according to the technology disclosed herein, since springback can be appropriately suppressed, a wound electrode body 40 with more than 20 windings can be stably manufactured. Furthermore, for ease of explanation, Figure 9 The wound electrode body 40 shown illustrates an electrode body with a significantly reduced number of windings. That is, Figure 9 The number of times the wound electrode body 40 is shown is not limited to the number of times the wound electrode body is disclosed herein.

[0117] (2) Stamping process

[0118] In this process, a flat-shaped wound electrode body 40 is produced by stamping the wound cylindrical body (see reference). Figure 9 ).like Figure 9 As shown, the flat-shaped wound electrode body 40 after stamping has a pair of curved portions 40r with a bent outer surface and a flat portion 40f connecting the pair of curved portions 40r with a flat outer surface. Additionally, as... Figure 7 and Figure 8 As shown, a positive electrode tab group 42, in which positive electrode tabs 12t are stacked, is formed at one end of the flat, stamped wound electrode body 40 in the width direction Y, and a negative electrode tab group 44, in which negative electrode tabs 22t are stacked, is formed at the other end. Furthermore, a core portion 46, in which the positive electrode active material layer 14 and the negative electrode active material layer 24 face each other, is formed at the center of the wound electrode body 40 in the width direction Y.

[0119] In this embodiment, the surface layer 34 of the spacer 30 is bonded to the positive electrode plate 10 (negative electrode plate 20) during stamping. Specifically, the result of flattening the wound body during stamping is that greater pressure is applied to each of the sheet-like members (positive electrode plate 10, negative electrode plate 20, and spacer 30) located in the flat portion 40f. In this embodiment, by adjusting the content of inorganic particles in the surface layer 34, the pressure during stamping, etc., the surface layer 34 is deformed to match the unevenness of the surface of the positive electrode active material layer 14 (or negative electrode active material layer 24). As a result, at the interface between the spacer 30 in the flat portion 40f of the wound electrode body 40 and the positive electrode plate 10 (or negative electrode plate 20), the spacer 30 is fitted into the positive electrode plate 10 (negative electrode plate 20) and bonded thereto. As a result, even when an elastic force is applied from the curved portion 40r to the flat portion 40f after stamping, the expansion of the flat portion 40f can be limited and springback suppressed.

[0120] Furthermore, the adhesion strength between the surface layer 34 of the flat portion 40f of the wound electrode body 40 disposed before being housed in the battery casing 50 and the electrode plate (typically the positive electrode plate 10) is preferably 0.5 N / m or more, more preferably 0.75 N / m or more, and even more preferably 1.0 N / m or more. Preferably, the content of inorganic particles in the surface layer 34 and the pressure during stamping are adjusted in such a way as to ensure appropriate adhesion strength between the surface layer 34 and the electrode plate. As a result, the springback of the wound electrode body 40 after stamping can be more appropriately suppressed. In addition, the "adhesion strength" in this specification is based on the 90° peel strength of JIS Z0237.

[0121] And, as Figure 8 and Figure 9 As shown, in this embodiment, a spacer 30 is disposed on the outermost peripheral surface of the stamped wound electrode body 40. The shape of the wound electrode body 40 is maintained by attaching the winding fixing strip 38 to the terminal portion 30e of the spacer 30. Furthermore, it is preferable that the winding fixing strip 38 is disposed on a straight line connecting the positive electrode tab group 42 and the negative electrode tab group 44. As a result, since the unwinding of the wound electrode body 40 can be prevented, the expansion of the flat portion 40f near the electrode tab group (positive electrode tab group 42, negative electrode tab group 44) can be suppressed, and the engagement of the electrode tab group with the current collector (positive current collector 70, negative current collector 75) can be stably implemented.

[0122] Furthermore, when the winding fixing tape 38 is attached to the terminal portion 30e of the spacer 30, it is preferable to adjust the softness of the surface layer 34 and the stamping pressure by reducing the ratio of the thickness of the surface layer 34 before stamping to the thickness of the surface layer 34 after stamping to 0.9 or less (more preferably 0.8 or less, further preferably 0.7 or less, and particularly preferably 0.6 or less). This allows the thickness of the winding fixing tape 38 to be absorbed by the pressing deformation of the surface layer 34, preventing the formation of large steps in the flat portion 40f. As a result, the reduction in battery performance caused by deviations in surface pressure relative to the flat portion 40f can be suppressed. This effect is particularly suitable in secondary batteries 100 having multiple wound electrode bodies 40 as in this embodiment. Furthermore, similar to the "porosity before stamping" mentioned above, the "thickness of the surface layer before stamping" can be adjusted by controlling the area not opposite to the negative and positive electrode plates (e.g., the area opposite to the negative and positive electrode plates). Figure 7 The area marked 30a in the attached figure is used as the measurement object for testing. On the other hand, the "thickness of the surface layer after stamping" is measured based on the thickness of the surface layer 34 of the spacer 30 sandwiched between the positive electrode plate 10 and the negative electrode plate 20 (for example, near the center of the flat portion 40f).

[0123] In addition, such as Figure 9 As shown, in the stamped and formed wound electrode body 40, one end of the strip-shaped positive electrode plate 10, as the positive electrode start end 10s, is disposed inside the wound electrode body 40. The other end of the positive electrode plate 10, as the positive electrode terminal portion 10e, is disposed outside the wound electrode body 40. Similarly, one end of the strip-shaped negative electrode plate 20, as the negative electrode start end 20s, is disposed inside the wound electrode body 40. The other end of the negative electrode plate 20, as the negative electrode terminal portion 20e, is disposed outside the wound electrode body 40. Furthermore, in this wound electrode body 40, the aforementioned positive electrode start end 10s, positive electrode terminal portion 10e, negative electrode start end 20s, and negative electrode terminal portion 20e are all disposed on the flat portion 40f of the wound electrode body 40.

[0124] Furthermore, in Figure 9 In the wound electrode body 40 with the structure shown, preferably, the positive electrode starting end 10s and the surface layer 34 (see reference) Figure 10 The bonding strength between the positive electrode terminal 10e and the surface layer 34 is greater than that between the positive electrode terminal 10e and the surface layer 34. Therefore, since the bonding strength inside the wound electrode body 40 is stronger, the effect of suppressing springback can be more effectively achieved. Furthermore, when the wound electrode body 40 is manufactured in a manner that strengthens the internal bonding strength, the thickness of the surface layer 34 bonded to the positive electrode start point 10s inside the electrode body is thinner than the thickness of the surface layer 34 bonded to the positive electrode terminal 10e.

[0125] In addition, Figure 9 In the wound electrode body 40 shown, it is preferable that the adhesion strength between the positive electrode terminal 10e and the surface layer 34 is greater than the adhesion strength between the negative electrode terminal 20e and the surface layer 34. This allows the electrolyte to easily penetrate to the vicinity of the surface of the negative electrode plate 20, which is preferable from the viewpoint of preventing electrolyte depletion. Furthermore, when the wound electrode body 40 is manufactured in a manner that relatively reduces the adhesion strength between the negative electrode terminal 20e and the surface layer 34, the thickness of the surface layer 34 bonded to the positive electrode terminal 10e is thinner than the thickness of the surface layer 34 bonded to the negative electrode terminal 20e.

[0126] Furthermore, regarding the adhesion strength between the positive electrode terminal 10e and the surface layer 34, it is preferable that the adhesion strength at the central portion in the winding axis direction (width direction Y) is greater than that at the two side edges. This further strengthens the restriction of expansion at the central portion of the flat portion 40f, appropriately suppressing springback. Specifically, it is preferable that the adhesion strength at the central portion in the winding axis direction is approximately 1.03 to 1.1 times the adhesion strength at the two side edges. Additionally, in this structure of the wound electrode body 40, the thickness of the surface layer 34 located at the central portion in the width direction Y is smaller than the thickness of the surface layers 34 located at the two side ends.

[0127] Furthermore, during stamping, minimal pressure is applied to the bent portion 40r of the wound electrode body 40. Therefore, the surface layer 34 of the spacer 30 located at the bent portion 40r tends to be thicker than the surface layer 34 of the spacer 30 located at the flat portion 40f. Specifically, the thickness of the surface layer 34 at the bent portion 40r can be 1.5 to 3 times the thickness of the surface layer 34 at the flat portion 40f. More specifically, the thickness of the surface layer 34 at the bent portion 40r tends to be approximately 1 μm thicker than the surface layer 34 at the flat portion 40f.

[0128] (3) Containment procedures

[0129] In this process, the wound electrode body 40, formed in the stamping process, is housed inside the battery casing 50. Specifically, as follows: Figure 6 As shown, a positive electrode second current collector 72 is connected to the positive electrode tab group 42 of the wound electrode body 40, and a negative electrode second current collector 77 is connected to the negative electrode tab group 44. Furthermore, as... Figure 5As shown, multiple (three in the figure) wound electrode bodies 40 are arranged with their flat portions 40f facing each other. A sealing plate 54 is positioned above the multiple wound electrode bodies 40, and the positive electrode tabs 42 of each wound electrode body 40 are bent so that the positive second current collector 72 faces one side 40a of the wound electrode body 40. This connects the positive first current collector 71 and the positive second current collector 72. Similarly, the negative electrode tabs 44 of each wound electrode body 40 are bent so that the negative second current collector 77 faces the other side 40b of the wound electrode body 40. This connects the negative first current collector 76 and the negative second current collector 77. As a result, the wound electrode bodies 40 are mounted on the sealing plate 54 via the positive current collector 70 and the negative current collector 75.

[0130] In the connection between the sealing plate 54 and the wound electrode body 40, stress is applied to the flat portion 40f near the electrode tabs (positive electrode tab 42 and negative electrode tab 44) when bending the electrode tabs. As a result, the inter-electrode distance increases in the flat portion 40f near the electrode tabs, which may lead to the deposition of charge carriers. However, in this embodiment, since the electrode plate and the spacer 30 are bonded together, the inter-electrode distance can be prevented from increasing even when stress is applied when bending the electrode tabs. Therefore, according to this embodiment, a stable connection between the electrode tabs and the electrode current collector can also be achieved.

[0131] Next, in this process, the electrode body holder 98 (see reference) is used. Figure 3 After the wound electrode body 40, which is mounted on the sealing plate 54, is covered, it is housed inside the outer casing 52. As a result, the flat portion 40f of the wound electrode body 40 faces the long sidewall 52b of the outer casing 52 (i.e., the flat surface of the battery casing 50). In addition, the upper curved portion 40r faces the sealing plate 54, and the lower curved portion 40r faces the bottom wall 52a of the outer casing 52. After the opening 52h on the upper surface of the outer casing 52 is blocked by the sealing plate 54, the battery casing 50 is constructed by joining (welding) the outer casing 52 to the sealing plate 54. Then, electrolyte is injected into the interior of the battery casing 50 through the injection hole 55 of the sealing plate 54, and the injection hole 55 is blocked by the sealing member 56. The secondary battery 100 of this embodiment is manufactured through the above process. As described above, since the secondary battery 100 bonds the spacer 30 to the electrode plate via the surface layer 34, springback after stamping can be suppressed. Therefore, the increase in battery resistance and charge carrier deposition caused by the increase in inter-electrode distance can be suppressed. Furthermore, since the thickness t1 of the wound electrode body 40 after stamping can be maintained, and the reception of the wound electrode body 40 into the outer casing 52 is facilitated, it also contributes to improved manufacturing efficiency.

[0132] <Other Implementation Methods>

[0133] The above describes one embodiment of the technology disclosed herein. Furthermore, the above embodiment illustrates an example of applying the technology disclosed herein and does not limit the scope of the technology disclosed herein. Hereinafter, other embodiments of the technology disclosed herein will be described.

[0134] (1) Formation surface of the surface layer

[0135] In the above embodiment, a surface layer 34 is formed on both sides of the substrate layer 32. However, the surface layer does not need to be formed on both sides of the substrate layer; it is sufficient to form it on at least one side of the substrate layer. However, when considering the adhesion between the spacer and the electrode body, and the suppression of thermal shrinkage of the spacer, it is preferable to form the surface layer on both sides of the substrate layer. Furthermore, as mentioned above, the surface layer tends to have better adhesion to the positive electrode plate than the negative electrode plate. Considering this, when the surface layer is formed only on one side of the substrate layer, it is preferable to form the surface layer on the side that is in contact with the positive electrode plate.

[0136] (2) Number of wound electrode bodies

[0137] The secondary battery 100 of the above embodiment houses three wound electrode bodies 40 inside the battery casing 50. However, the number of electrode bodies housed in one battery casing is not particularly limited; it can be two or more, or it can be one. Furthermore, in the presence of… Figure 3 In a secondary battery 100 with multiple wound electrode bodies 40 as shown, springback may occur at each of the wound electrode bodies 40. In this case, the impact of springback on the overall performance of the secondary battery 100 can easily become significant. In contrast, according to the technology disclosed herein, a structure capable of suppressing springback can be adopted for each of the multiple wound electrode bodies 40. Therefore, the technology disclosed herein is particularly suitable for application to a secondary battery 100 having multiple wound electrode bodies 40.

[0138] Furthermore, as described in the above embodiment, in a secondary battery 100 having multiple wound electrode bodies 40, it is preferable to have a spacer 30 having a surface layer 34 disposed at the outermost periphery of the wound electrode bodies 40. This way, since adjacent wound electrode bodies 40 are bonded together via the outermost periphery spacer 30, movement of the wound electrode bodies 40 inside the battery casing 50 can be restricted. As a result, damage to the wound electrode bodies 40 caused by external impacts or vibrations (external forces) can be prevented. For example, such as... Figure 6As shown, when the wound electrode body 40 is connected to the electrode current collectors (positive electrode second current collector 72, negative electrode second current collector 77) via electrode tabs (positive electrode tab 42, negative electrode tab 44), the electrode tabs may break because the wound electrode body 40 may move due to external force. In contrast, by bonding multiple wound electrode bodies 40 via spacers 30, the movement of each wound electrode body 40 can be restricted, preventing damage to the electrode tabs. Furthermore, it is preferable that when multiple wound electrode bodies 40 are bonded via spacers 30, the bonding strength between adjacent wound electrode bodies 40 is greater than that of the positive electrode terminal portion 10e (see reference). Figure 9 The bonding strength between the winding electrode body 40 and the surface layer 34 is high. As a result, the movement of the winding electrode body 40 can be more reliably restricted, and damage to the winding electrode body 40 (e.g., electrode tab assembly) can be more properly prevented.

[0139] Furthermore, when the spacer 30 is positioned at the outermost periphery of the wound electrode body 40, the two outermost wound electrode bodies 40 in the depth direction X can be bonded to the electrode body retainer 98 via the surface layer 34 of the spacer 30. Therefore, since the movement of the wound electrode body 40 within the battery casing 50 can be more reliably restricted, damage to the wound electrode body 40 can be further appropriately prevented.

[0140] The present invention has been described in detail above, but the above description is merely illustrative. That is, the technology disclosed herein includes solutions obtained by various modifications and alterations to the above specific examples.

Claims

1. A secondary battery, the secondary battery comprising a flat wound electrode body formed by winding a positive electrode plate and a negative electrode plate with spacers between them, and a battery casing housing the wound electrode body, wherein, The flat-shaped wound electrode body has a pair of curved portions on its outer surface and a flat portion on its outer surface that connects the pair of curved portions. 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 spacer has a strip-shaped substrate layer and a surface layer formed on at least one surface of the substrate layer and comprising inorganic particles and a binder. At least one of the positive electrode plate and the negative electrode plate of the flat portion is bonded to the surface layer of the spacer. The width of the positive electrode active material layer is 200 mm or more, the thickness of the wound electrode body is 8 mm or more, and the height of the wound electrode body is 120 mm or less. One end of the positive electrode plate, along its long side, is positioned inside the flat portion of the wound electrode body as the positive electrode starting end, and the other end, positioned outside the flat portion of the wound electrode body as the positive electrode ending end. One end of the negative electrode plate, along its long side, is positioned inside the flat portion of the wound electrode body as the negative electrode starting end, while the other end is positioned outside the flat portion of the wound electrode body as the negative electrode ending end. The adhesion strength between the positive electrode terminal and the surface layer is greater than that between the negative electrode terminal and the surface layer. The adhesion strength between the positive electrode starting end and the surface layer is greater than the adhesion strength between the positive electrode terminal end and the surface layer.

2. The secondary battery according to claim 1, wherein, The battery casing houses a plurality of the wound electrode bodies. The spacer is disposed on the outermost periphery of the wound electrode body, and adjacent wound electrodes bodies are bonded to each other via the surface layer of the spacer.

3. The secondary battery according to claim 2, wherein, The adhesion strength between adjacent wound electrode bodies is greater than the adhesion strength between the positive electrode terminal and the surface layer.

4. The secondary battery according to any one of claims 1 to 3, wherein, The content of the inorganic particles relative to the total mass of the surface layer is 70% to 80% by mass.

5. The secondary battery according to any one of claims 1 to 3, wherein, As the inorganic particles, the surface layer comprises at least one of alumina particles and boehmite particles.

6. The secondary battery according to any one of claims 1 to 3, wherein, As the adhesive, the surface layer comprises polyvinylidene fluoride and has a mesh-like structure containing a plurality of voids.

7. The secondary battery according to any one of claims 1 to 3, wherein, The negative electrode plate has a strip-shaped negative electrode core and a layer of negative electrode active material formed on at least one surface of the negative electrode core. A positive electrode tab assembly is formed at one end of the wound electrode body along the winding axis direction, consisting of positive electrode tabs stacked on top of the exposed positive electrode core; and a negative electrode tab assembly is formed at the other end of the wound electrode body along the winding axis direction, consisting of negative electrode tabs stacked on top of the exposed negative electrode core. The positive electrode tab is formed with multiple, partially protruding portions spaced apart along the long side of the positive electrode plate, and the negative electrode tab is formed with multiple, partially protruding portions spaced apart along the long side of the negative electrode plate. The spacer is disposed on the outermost periphery of the wound electrode body, and the end portion of the spacer is attached to the outermost surface of the wound electrode body by a winding fixing tape. The winding fixing tape is positioned on a straight line connecting the positive electrode tab group and the negative electrode tab group.

8. A method for manufacturing a secondary battery, wherein, The method for manufacturing the secondary battery comprises: The process of manufacturing a cylindrical body by winding the positive and negative electrode plates with spacers in between; The process of stamping the cylindrical body to produce a flat, wound electrode body; and The process of housing the wound electrode body inside the battery casing. The wound electrode body is the wound electrode body according to any one of claims 1 to 7.

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