Rectangular secondary battery

Abstract

A battery (10) comprises: a flat electrode body (13) in which a positive electrode and a negative electrode are wound with a separator therebetween; and a flat outer can (14) which accommodates the electrode body (13), the flat outer can having a bottomed cylindrical-shape. A first protruding part (31) protrudes in the minor-axis direction of the electrode body (13) and extends in the winding axis direction of the electrode body (13). The first protruding part is provided at both ends, in the major-axis direction of the electrode body (13), of at least one inner surface (14b) of a pair of main surface parts (14a) that are part of the outer can (14) and that face each other in the minor-axis direction of the electrode body (13).

Description

Prismatic secondary battery

[0001] The present disclosure relates to a prismatic secondary battery.

[0002] A conventional prismatic secondary battery is described in Patent Document 1. This prismatic secondary battery is a lithium-ion secondary battery that includes a flat electrode assembly and a flat, cylindrical, bottomed outer can that houses the flat electrode assembly. The flat electrode assembly is joined to the outer can via a positive electrode tab and to a negative electrode terminal that is stationary relative to the outer can via a negative electrode tab. This prismatic secondary battery is intended to be installed primarily in mobile electronic devices such as smartphones, laptops, and MP3 players.

[0003] Special table 2016-531403 publication

[0004] In the above-described prismatic secondary battery, the electrode assembly is connected to the outer can and the negative terminal via easily deformable positive and negative tabs. Therefore, if a mobile electronic device or the like equipped with a prismatic secondary battery is accidentally dropped, the flat electrode assembly may move within the outer can due to the impact of the drop, resulting in damage caused by the force from the outer can. In light of this background, the present inventors discovered that if the central portion of the main surface of the electrode assembly is pressed by the inner surface of the outer can to prevent the flat electrode assembly from moving within the outer can, the flat electrode assembly's thickness in the minor axis direction of the prismatic secondary battery increases significantly as the flat electrode assembly expands after charge / discharge cycles. Therefore, an object of the present disclosure is to provide a prismatic battery that can suppress damage to the flat electrode assembly when subjected to impact and also suppresses an increase in the electrode assembly's minor axis thickness after cycling.

[0005] In order to solve the above problems, the prismatic secondary battery according to the present disclosure comprises a flat electrode body in which an elongated positive electrode and an elongated negative electrode are wound with a separator interposed therebetween, and a flat, cylindrical outer can with a bottom that houses the electrode body, and when portions of the outer can that face each other in the minor axis direction of the electrode body are defined as a pair of main surface portions, a first protrusion that protrudes in the minor axis direction of the electrode body and extends in the direction of the winding axis of the electrode body is provided on both ends in the major axis direction of the electrode body on the inner surface of at least one of the pair of main surface portions.

[0006] The prismatic secondary battery according to the present disclosure can suppress damage to the flat electrode body when subjected to an impact, and can also suppress an increase in the thickness of the battery after charge / discharge cycles.

[0007] FIG. 1 is a cross-sectional view of a prismatic secondary battery according to a first embodiment cut along a plane including the winding axis direction and the center in the major axis direction. FIG. 2 is a top view of a sealing plate as viewed from above in the winding axis direction. FIG. 3 is a top view of a spacer as viewed from above in the winding axis direction. FIG. 4 is a cross-sectional view taken along line A-A in FIG. 1. FIG. 5 is a diagram illustrating the structure of an outer can. FIG. 6 is a diagram illustrating the structure of a first protrusion in an outer can of a prismatic secondary battery of a modified example. FIG. 7 is a diagram illustrating the structure of an outer can of a prismatic secondary battery according to a second embodiment. FIG. 8 is a diagram illustrating the structure of an outer can of a prismatic secondary battery of Comparative Example 1. FIG. 9 is a diagram illustrating the structure of an outer can of a prismatic secondary battery of Comparative Example 2.

[0008] Hereinafter, with reference to the drawings, an embodiment of a prismatic secondary battery according to the present disclosure will be described in detail. The prismatic secondary battery according to the present disclosure may be a battery using an aqueous electrolyte or a battery using a nonaqueous electrolyte. Hereinafter, a nonaqueous electrolyte secondary battery (lithium ion battery) using a nonaqueous electrolyte will be exemplified as a prismatic secondary battery 10 according to one embodiment, but the prismatic secondary battery according to the present disclosure is not limited thereto.

[0009] It is anticipated from the beginning that new embodiments may be constructed by appropriately combining the features of the embodiments and variations described below. In the following embodiments, the same components are denoted by the same reference numerals in the drawings, and redundant explanations will be omitted. Furthermore, multiple drawings include schematic views, and the dimensional ratios of the length, width, height, etc. of each component between different drawings do not necessarily match.

[0010] In this specification, the side of the sealing plate 17 in the winding axis direction of the flat electrode body 13 of the prismatic secondary battery 10 is referred to as the "top," and the side of the bottom 29 of the outer can 14 in the winding axis direction is referred to as the "bottom." In the following description and drawings, the X direction is the major axis direction of the flat electrode body 13, the Y direction is the minor axis direction of the flat electrode body 13, and the Z direction is the winding axis direction of the flat electrode body 13. The X direction, Y direction, and Z direction are perpendicular to one another. In the following description, the prismatic secondary battery will be simply referred to as a battery.

[0011] Among the components described below, those not recited in the independent claims showing the highest concepts are optional components and are not essential components. Furthermore, the present disclosure is not limited to the following embodiments and their modifications, and various improvements and modifications are possible within the scope of the claims of this application and their equivalents.

[0012] First Embodiment Fig. 1 is a cross-sectional view of a battery 10 taken along a plane that includes the Z and X directions and passes through the center in the Y direction. The Z direction corresponds to the winding axis direction of the flat electrode body 13. The X and Y directions correspond to the major and minor axis directions of the flat electrode body 13, respectively. Fig. 2 is a top view of a sealing plate 17 as viewed from above in the Z direction, and Fig. 3 is a top view of a spacer 15 as viewed from above in the Z direction. As shown in Fig. 1, the battery 10 includes a flat electrode body (hereinafter simply referred to as the electrode body) 13, a nonaqueous electrolyte (not shown), a flat, cylindrical outer can 14 with a bottom that accommodates the electrode body 13 and the nonaqueous electrolyte, a sealing plate 17 that seals the opening of the outer can 14, an insulating plate 26 that contacts the underside of the sealing plate 17, and a plate-like spacer 15 that is disposed above the electrode body 13 and made of an insulating material.

[0013] The electrode assembly 13 is formed into a flat shape by winding a long positive electrode and a long negative electrode with two long separators interposed therebetween, and then pressing in the Y direction. The positive electrode is disposed on the outermost periphery of the electrode assembly 13. The sealing plate 17 is fitted into the opening of the exterior can 14. The fitting portion between the exterior can 14 and the sealing plate 17 is welded, for example, by laser welding, to seal the interior of the battery 10.

[0014] The non-aqueous electrolyte has ion conductivity (e.g., lithium ion conductivity). The non-aqueous electrolyte is composed of a liquid electrolyte (electrolytic solution). The liquid electrolyte (electrolytic solution) includes a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of the non-aqueous solvent include esters, ethers, nitriles, amides, and mixed solvents of two or more of these. Examples of the non-aqueous solvent include ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and mixed solvents of these. The non-aqueous solvent may contain a halogen-substituted compound (e.g., fluoroethylene carbonate) in which at least a portion of the hydrogen atoms of these solvents are substituted with halogen atoms such as fluorine. The electrolyte salt may include, for example, LiPF ６ Lithium salts such as

[0015] The positive electrode has a positive electrode core and positive electrode mixture layers formed on both sides of the positive electrode core. The positive electrode core can be made of a metal foil, such as aluminum or an aluminum alloy, that is stable within the potential range of the positive electrode, or a film with such a metal disposed on the surface. The positive electrode mixture layer contains a positive electrode active material, a conductive agent, and a binder. The positive electrode can be produced, for example, by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, a binder, etc., onto the positive electrode core, drying the coating, and then compressing it to form positive electrode mixture layers on both sides of the positive electrode core.

[0016] The positive electrode active material is mainly composed of a lithium-containing metal composite oxide. Examples of metal elements contained in the lithium-containing metal composite oxide include Ni, Co, Mn, Al, B, Mg, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Zr, Nb, In, Sn, Ta, and W. An example of a preferred lithium-containing metal composite oxide is a composite oxide containing at least one of Ni, Co, Mn, and Al.

[0017] Examples of conductive agents contained in the positive electrode mixture layer include carbon black such as acetylene black and ketjen black, and carbon materials such as graphite. Examples of binders contained in the positive electrode mixture layer include fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide resins, acrylic resins, and polyolefin resins. These resins may be used in combination with cellulose derivatives such as carboxymethyl cellulose (CMC) or its salts, polyethylene oxide (PEO), and the like.

[0018] The negative electrode has a negative electrode core and a negative electrode mixture layer formed on both sides of the negative electrode core. The negative electrode core can be made of a metal foil, such as copper or a copper alloy, that is stable within the potential range of the negative electrode, or a film with such a metal disposed on the surface layer. The negative electrode mixture layer contains a negative electrode active material and a binder. The negative electrode can be produced, for example, by applying a negative electrode mixture slurry containing a negative electrode active material and a binder to the negative electrode core, drying the coating, and then compressing it to form a negative electrode mixture layer on both sides of the core.

[0019] The negative electrode active material generally uses a carbon material that reversibly absorbs and releases lithium ions. Preferred carbon materials are graphites such as natural graphite, such as flake graphite, lump graphite, and amorphous graphite, and artificial graphite, such as lump artificial graphite and graphitized mesophase carbon microbeads. The negative electrode mixture layer may contain a silicon (Si) material as the negative electrode active material. In addition, the negative electrode active material may be a metal other than Si that alloys with lithium, an alloy containing such a metal, or a compound containing such a metal.

[0020] The binder contained in the negative electrode mixture layer may be, as in the case of the positive electrode, a fluororesin, PAN, polyimide resin, acrylic resin, polyolefin resin, etc., but is preferably styrene-butadiene rubber (SBR) or a modified product thereof. The negative electrode mixture layer may contain, in addition to SBR, for example, CMC or a salt thereof, polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol, etc.

[0021] The separator is a porous sheet having ion permeability and insulating properties. Specific examples of the porous sheet include a microporous thin film, a woven fabric, and a nonwoven fabric. Preferred materials for the separator include polyolefin resins such as polyethylene and polypropylene, and cellulose. The separator may have either a single-layer structure or a laminated structure. A heat-resistant layer or the like may be formed on the surface of the separator.

[0022] As shown in FIG. 1 , the positive electrode tab 11 and the negative electrode tab 12 extend upward in the Z direction from the electrode body 13. The spacer 15 has two slit-shaped openings 18, 20 (see FIG. 3 ) spaced apart in the X direction. The negative electrode tab 12 passes through the opening 18 and is joined to the underside of a metal rivet 21 that penetrates an insulating plate 26. The rivet 21 is joined to the inner circumferential surface of an annular negative electrode terminal plate 19a and is electrically connected to it. The negative electrode terminal plate 19a and the rivet 21 constitute the negative electrode terminal 19.

[0023] Fig. 4 is a cross-sectional view taken along line A-A in Fig. 1. As shown in Fig. 4, the positive electrode tab 11 passes between the spacer 15 and the outer can 14. The positive electrode tab 11 has a bent portion between the spacer 15 and the insulating plate 26. The end of the positive electrode tab 11 is sandwiched between the outer can 14 and the sealing plate 17, and is welded integrally with the outer can 14 and the sealing plate 17. The sealing plate 17 and the outer can 14 electrically joined to the positive electrode constitute a positive electrode terminal.

[0024] As shown in FIG. 2 , the sealing plate 17 is provided with a safety valve 22 and a nonaqueous electrolyte injection hole 23. The nonaqueous electrolyte injection hole 23 is sealed with a sealing material (not shown). As shown in FIG. 1 , a negative electrode terminal plate 19a and an insulating annular gasket 24 are placed on the sealing plate 17. The gasket 24 is made of an insulating material, such as polyolefin. The gasket 24 insulates and seals the negative electrode terminal 19 from the sealing plate 17. The rivet 21 is inserted into the sealing plate 17 from below via an insulating plate 26. The tip of the rivet 21 is then crimped to integrate the rivet 21, the insulating plate 26, the sealing plate 17, the gasket 24, and the negative electrode terminal plate 19a. A recess is formed on the underside of the insulating plate 26, and the lower end of the rivet 21 is received in the recess. As a result, the rivet 21 does not protrude toward the electrode body 13.

[0025] As shown in FIG. 3 , the spacer 15 has a main body 15a occupying the center and end portions 15b provided on both sides in the X direction. The main body 15a is made of an insulating material such as polypropylene. Meanwhile, the end portions 15b are made of an insulating material with shock-absorbing properties, such as styrene-butadiene rubber. The main body 15a and end portions 15b are arranged in close contact with each other. Insulating tape 16 is attached to the main body 15a and end portions 15b so as to surround the entire periphery of the main body 15a and end portions 15b. This integrates the main body 15a and end portions 15b. The positive electrode side current collecting structure and the negative electrode side current collecting structure may be any current collecting structure used in prismatic batteries and are not limited to the current collecting structures described using FIGS. 1 to 4 .

[0026] FIG. 5 is a diagram illustrating the structure of the outer can 14. More specifically, FIG. 5(a) is a cross-sectional view of the battery 10 taken along a plane including the Z and X directions and passing through one end of the battery 10 in the Y direction. FIG. 5(b) is a cross-sectional view taken along line C-C in FIG. 5(a). FIG. 5(c) is a cross-sectional view taken along line D-D in FIG. 5(a), and FIG. 5(d) is a cross-sectional view taken along line E-E in FIG. 5(a). In FIGS. 5(a) and 5(b), the cross-section indicated by dots is a partial region of the outer can 14, i.e., the cross-section of the first protrusion 31. In FIG. 5(a), the cross-section indicated by dashed-dotted lines is another partial region of the outer can 14, i.e., the cross-section of the second protrusion 41. FIG. 5 shows the battery 10 initially charged to 30% capacity after fabrication. In FIG. 5, the sealing plate 17 and insulating plate 26 are illustrated as a single, integrated component. The cross-sectional view taken along line FF in FIG. 5(b) coincides with FIG. 5(a).

[0027] 5( a) to 5(d), in the present disclosure, the portions of the exterior can 14 that face the outside of the body in the Y direction are defined as a pair of main surface portions 14a. First protrusions 31 that protrude in the Y direction and extend in the Z direction are provided on both ends in the X direction of a pair of inner surfaces 14b of the pair of main surface portions 14a. One end of the electrode body 13 in the X direction is sandwiched between a pair of first protrusions 31 in the Y direction, and the other end of the electrode body 13 in the X direction is also sandwiched between another pair of first protrusions 31 in the Y direction.

[0028] 5( a) and 5(d), second protrusions 41 extending in the X direction are provided on the pair of inner surfaces 14b at the ends on the bottom 29 side in the Z direction. The center in the X direction of the lower end of the electrode body 13 in the Z direction is sandwiched between the pair of second protrusions 41. The first protrusions 31 and the second protrusions 41 are connected at the ends of the pair of inner surfaces 14b on the bottom 29 side in the Z direction.

[0029] Next, the effects of the battery 10 of the present disclosure will be described. Conventionally, when a mobile electronic device or the like equipped with a prismatic secondary battery is accidentally dropped, the flat electrode body moves within the outer can due to the impact of the drop and is easily damaged by the force from the outer can. In other words, by clamping the electrode body in the Y direction on the inner surface of the outer can, movement of the electrode body can be suppressed, and damage to the electrode body can be suppressed.

[0030] However, as will be explained in detail later, the present inventors have experimentally found that the central portions of the flat electrode assembly in the Y and Z directions expand significantly during charge and discharge. Therefore, if the central portions of the electrode assembly in the Y and Z directions are clamped in the Y direction by the inner surface of the outer can to prevent the electrode assembly from moving, the thickness of the prismatic secondary battery in the Y direction will increase significantly as the electrode assembly expands after charge and discharge cycles.

[0031] In view of this background, according to the battery 10 of the first embodiment, both Y-direction ends of the electrode body 13 and the lower Z-direction end of the electrode body 13 are sandwiched by the inner surface 14b of the outer can 14. Therefore, movement of the electrode body 13 can be suppressed, and damage to the electrode body 13 can be suppressed. Furthermore, since the first protrusion 31 and the second protrusion 41 are provided at positions facing both Y-direction ends of the electrode body 13 and the lower Z-direction end of the electrode body 13, which have a relatively small amount of expansion, expansion of the battery 10 in the Y direction after charge / discharge cycles can be suppressed.

[0032] 5( c), the Y-direction thickness t1 of the outer can 14 at a first location 32 on the inner surface 14b where the first protrusion 31 is provided is greater than the Y-direction thickness t2 of the outer can 14 at a second location 33 on the main surface 14a that is spaced apart in the X-direction from the first protrusion 31. Therefore, the rigidity of the outer can 14 at the first location 32 is increased, and the pair of first protrusions 31 can firmly sandwich the electrode body 13 in the Y direction.

[0033] 5(c) and 5(d), the Y-direction thickness t3 of the outer can 14 at a third location 42 on the main surface 14a where the second protruding portion 41 is provided is greater than the Y-direction thickness t4 of the outer can 14 at a fourth location 43 on the main surface 14a that is spaced apart in the Z-direction from the second protruding portion 41. Therefore, the rigidity of the outer can 14 at the third location 42 is increased, and the pair of second protruding portions 41 can firmly sandwich the electrode body 13 in the Y direction.

[0034] In order to effectively suppress expansion of the battery 10 in the Y direction after charge / discharge cycles, it is preferable that the first protrusion 31 be located within a range from an end P1 (see FIG. 5(c)) in the X direction of the main surface 14a of the outer can 14 (see FIG. 5(c)), which is located toward the center in the X direction and a length that is 20% of the X direction length of the main surface 14a (see FIG. 5(c)). Furthermore, in order to effectively suppress movement of the electrode body 13, it is preferable that the X direction length of the first protrusion 31 be 5% or more of the X direction length of the main surface 14a of the outer can 14.

[0035] In order to effectively suppress expansion of the battery 10 in the Y direction after charge / discharge cycles, it is preferable that the second protrusion 41 be located within a range from a lower end P3 (see FIG. 5(b)) in the Y direction of the main surface 14a of the outer can 14 to a first position P4 (see FIG. 5(b)), which is located 20% of the Z direction length of the main surface 14b toward the center in the Z direction. Furthermore, in order to effectively suppress movement of the electrode body 13, it is preferable that the Z direction length of the second protrusion 41 be 5% or more of the Z direction length of the main surface 14a of the outer can 14.

[0036] In the battery 10, the first protrusions 31 are provided on both X-direction end portions of the inner surfaces 14b of both of the pair of principal surface portions 14a facing each other in the Y direction. However, the first protrusions may be provided on both X-direction end portions of only one of the pair of principal surface portions. The second protrusions 41 extending in the X direction are provided on the Z-direction lower end portions of both of the inner surfaces 14b of the pair of principal surface portions 14a facing each other in the Y direction. However, the second protrusions extending in the X direction may be provided on the Z-direction lower end portion of only one of the pair of principal surface portions facing each other in the Y direction.

[0037] The Y-direction thickness t1 was greater than the Y-direction thickness t2. However, the Y-direction thickness of the outer can at a first location on the main surface where the first protruding portion is provided may be the same as the Y-direction thickness of the outer can at a second location on the main surface that is spaced apart in the X-direction from the first protruding portion, or may be smaller than the Y-direction thickness of the outer can at the second location. Furthermore, the Y-direction thickness t3 was greater than the Y-direction thickness t4. However, the Y-direction thickness of the outer can at a third location on the inner surface where the second protruding portion is provided may be the same as the Y-direction thickness of the outer can at a fourth location on the inner surface that is spaced apart in the Z-direction from the second protruding portion, or may be smaller than the Y-direction thickness of the outer can at the fourth location.

[0038] Although the case where the first protrusion 31 and the second protrusion 41 are continuously connected in the X direction has been described, the first protrusion and the second protrusion do not have to be connected. Also, as shown in Fig. 5C, the first protrusion 31 extends in the Z direction from the X-direction end of the main surface 14a. However, the first protrusion may be provided at a position spaced apart in the X direction from the X-direction end of the main surface.

[0039] As shown in Fig. 5(b), the Y-direction end faces 36 of the first protrusions 31 are located at approximately the same Y-direction position. However, as shown in Fig. 6, that is, a cross-sectional view of a modified battery 110 corresponding to Fig. 5(b), the Y-direction end face 136 of the first protrusions 131 may include an inclined surface portion 136a that is inclined in the Z direction so that the inner diameter of the outer can 114 increases from the bottom 129 side of the outer can 114 in the Z direction toward the end on the opening side of the outer can 114. In this way, the electrode body 13 can be smoothly inserted into the outer can 114.

[0040] Second Embodiment FIG. 7 is a diagram illustrating the structure of the outer can 214. More specifically, FIG. 7( a) is a cross-sectional view of the battery 210 taken along a plane including the Z and X directions and passing through one end of the battery 210 in the Y direction. FIG. 7( b) is a cross-sectional view taken along line G-G in FIG. 7( a). FIG. 7( c) is a cross-sectional view taken along line H-H in FIG. 7( a). In FIG. 7( a), the cross-section indicated by dots is a partial region of the outer can 214, i.e., the cross-sectional region of the first protrusion 31. FIG. 7 shows the battery 210 in a state where it is initially charged to 30% capacity after fabrication. In FIG. 7, the sealing plate 17 and insulating plate 26 are also illustrated as a single, integrated member. The cross-sectional view taken along line I-I in FIG. 7( b) corresponds to FIG. 7( a). In the battery 210, the outer can 214 has the first protrusion 31 but does not have the second protrusion 41 (see FIG. 5 ). Even in such a battery 210, damage to the electrode body 13 when subjected to an impact can be suppressed, and an increase in the thickness of the battery 210 in the Y direction after charge / discharge cycles can also be suppressed.

[0041] Example 1 The outer can 14 of the battery 10 of the first embodiment was fabricated by drawing an aluminum plate so that the Y-direction thickness was partially increased. The thicknesses of the thick portions (t1 and t3) were 0.45 mm, and the thicknesses of the thin portions (t2 and t4) were 0.32 mm. The thick portions corresponded to the first location 32 and the third location 42 of the outer can 14. A flat electrode assembly 13 was fabricated by winding the positive electrode and negative electrode with a separator interposed therebetween, pressing them in the Y direction, and securing the winding end with polypropylene tape. The Y-direction thickness of the electrode assembly 13 was 3.6 mm. The fabricated electrode assembly 13 was placed in the outer can 14, poured with electrolyte, and sealed to fabricate the battery 10 of the first embodiment.

[0042] The tension ratio of the electrode body 13 immediately after fabrication ([Y-direction thickness of the electrode body 13] / [distance between the pair of inner surfaces 14b]) was 87% in the thin-walled portion and 92% in the thick-walled portion. The tension ratio of the electrode body 13 immediately after fabrication, after being charged to 30% of its capacity, was 94% in the thin-walled portion and 101% in the thick-walled portion. The tension ratio of 101% in the thick-walled portion was calculated by simulating the Y-direction thickness of the electrode body 13 after expansion due to charging, assuming that no force is applied from the pair of inner surfaces 14b, and dividing the calculated Y-direction thickness by the distance between the pair of inner surfaces 14b.

[0043] Example 2 A battery 210 of the second embodiment was fabricated using the same method as that described for the battery 10 of Example 1. The various dimensions of the battery 210 of Example 2 corresponding to those of the battery 10 of Example 1, such as the thickness of the thick and thin portions, were the same as those of the battery 10 of Example 1.

[0044] <Comparative Example 1> Figure 8 is a diagram illustrating the structure of the exterior can 314 of Comparative Example 1. More specifically, Figure 8(a) is a cross-sectional view of the battery 310 of Comparative Example 1 cut along a plane that includes the Z direction and the X direction and passes through one end of the battery in the Y direction, and Figure 8(b) is a cross-sectional view taken along line I-I in Figure 8(a). Also, Figure 8(c) is a cross-sectional view taken along line J-J in Figure 8(a). The cross-sectional view of line K-K in Figure 8(b) coincides with Figure 8(a).

[0045] The battery 310 of Comparative Example 1 is identical to the battery 10 of Example 1 except that the first protrusion 31 and the second protrusion 41 are not present.

[0046] <Comparative Example 2> Figure 9 is a diagram illustrating the structure of the exterior can 414 of Comparative Example 2. More specifically, Figure 9(a) is a cross-sectional view of the battery 410 of Comparative Example 2 cut along a plane that includes the Z direction and the X direction and passes through one end of the battery 410 in the Y direction, and Figure 9(b) is a cross-sectional view taken along line L-L in Figure 9(a). Figure 9(c) is a cross-sectional view taken along line M-M in Figure 9(a). The cross-sectional view taken along line N-N in Figure 9(b) coincides with Figure 9(a). In Figure 9(a), the cross-sectional area indicated by a dot is the cross-sectional area of ​​a protrusion 431, which will be described below.

[0047] In the battery 410 of Comparative Example 2, a protrusion 431 that protrudes inward in the Y direction from the upper end in the Z direction to the lower end in the Z direction is provided in the X direction center of a pair of inner surfaces 414b (see FIG. 9(c)) of a pair of main surface portions 414a of the outer can 414 that face each other in the Y direction. The portion of the outer can 414 where the protrusion 431 is provided is a thick portion that is thick in the Y direction. The various dimensions of the battery 410 of Comparative Example 2 that correspond to those of the battery 10 of Example 1, such as the thickness of the thick and thin portions, are the same as those of the battery 10 of Example 1.

[0048] (Drop Test) Five batteries each of Examples 1 and 2 and Comparative Examples 1 and 2 were prepared, and each battery was charged to 30% of its capacity. Each battery was dropped from a height of 1.5 m. The drop test was repeated 15 times while monitoring the voltage of each battery. A voltage drop of a predetermined voltage or more was deemed to have occurred.

[0049] (Cycle Test) Three batteries were prepared for each of Examples 1 and 2 and Comparative Examples 1 and 2. Before the cycle test, the average maximum thickness in the Y direction of each battery was the same for Examples 1 and 2 and Comparative Examples 1 and 2. Each battery was charged at a constant current of 0.5 C at room temperature until the voltage reached 4.2 V, and then charged at a constant voltage of 4.2 V until the current reached 0.02 C. Subsequently, the battery was discharged at a constant current of 1.0 C until the voltage reached 2.75 V. This charge / discharge cycle was counted as one cycle, and the charge / discharge cycle was repeated 500 times. The maximum thickness in the Y direction of each battery was then measured. The average maximum thickness in the Y direction of each Example and Comparative Example was calculated.

[0050] The test results are shown in Table 1. As shown in Table 1, in the drop test, a short circuit was confirmed in one battery in Comparative Example 1, which did not have a protruding portion (thick portion). On the other hand, in Examples 1 and 2 and Comparative Example 2, which had a protruding portion, no short circuit was confirmed in any of the batteries. This confirmed that providing a protruding portion can suppress damage to the electrode body.

[0051] Furthermore, with regard to the cycle test, the average value of the maximum Y-direction thickness after the cycle test was the largest in Comparative Example 2, in which a pair of protrusions was provided on a pair of inner surfaces so as to sandwich the central portion of the electrode body in the Y and Z directions. On the other hand, the average value of the maximum Y-direction thickness after the cycle test of the batteries of Examples 1 and 2, in which protrusions were provided on a pair of inner surfaces so as to sandwich the portion other than the central portion of the electrode body in the Y and Z directions, was approximately the same as the average value of the maximum Y-direction thickness after the cycle test of the battery of Comparative Example 1, in which no protrusions were provided.

[0052] Therefore, it was confirmed that providing a pair of protrusions on a pair of inner surfaces so as to sandwich the electrode body in the Y direction and other than the central portion in the Z direction not only suppresses damage to the electrode body, but also suppresses the increase in the Y direction thickness of the battery after charge / discharge cycles.

[0053] The prismatic secondary battery of the present disclosure may also have the following configurations. Configuration 1: A prismatic secondary battery including: a flat electrode assembly formed by winding a long positive electrode and a long negative electrode with a separator interposed therebetween; and a bottomed, cylindrical, flat outer can housing the electrode assembly, wherein, when portions of the outer can facing each other in the short diameter direction of the electrode assembly are defined as a pair of main surface portions, first protrusions that protrude in the short diameter direction and extend in the direction of the winding axis of the electrode assembly are provided on both ends in the long diameter direction of the inner surface of at least one of the pair of main surface portions. Configuration 2: The prismatic secondary battery according to Configuration 1, wherein the first protrusions are provided on the inner surfaces of both of the pair of main surface portions. Configuration 3: The prismatic secondary battery according to Configuration 1 or 2, wherein the thickness of the outer can at a first location on the main surface portion where the first protrusion is provided is greater than the thickness of the outer can at a second location on the main surface portion that is spaced apart from the first protrusion in the long diameter direction. Configuration 4: The prismatic secondary battery according to any one of Configurations 1 to 3, wherein a second protrusion extending in the major axis direction is provided on an end of at least one of the main surface portions on the bottom side of the exterior can.Configuration 5: The prismatic secondary battery according to Configuration 4, wherein the second protrusion is provided on both of the pair of main surface portions.Configuration 6: The prismatic secondary battery according to Configuration 4 or 5, wherein the thickness of the exterior can at a third location on the main surface portion where the second protrusion is provided is greater than the thickness of the exterior can at a fourth location on the main surface portion that is spaced apart from the second protrusion in the winding axis direction.Configuration 7: The prismatic secondary battery according to any one of Configurations 1 to 6, wherein an end face in the minor axis direction of the first protrusion includes an inclined surface portion that is inclined so that the inner diameter of the exterior can increases from the bottom side of the exterior can to the end on the opening side of the exterior can in the winding axis direction. Configuration 8: The prismatic secondary battery according to any one of Configurations 1 to 7, wherein the first protrusion is located within a range of 20% of the length of the principal surface portion in the major axis direction from an end of the principal surface portion in the major axis direction.Configuration 9: The prismatic secondary battery according to any one of Configurations 1 to 8, wherein the length of the first protrusion in the major axis direction is 5% or more of the length of the principal surface portion in the major axis direction.Configuration 10: The prismatic secondary battery according to any one of Configurations 4 to 6, wherein the second protrusion is located within 20% of the length of the main surface portion in the winding axis direction from the end of the main surface portion on the bottom side.Configuration 11: The prismatic secondary battery according to Configurations 4, 5, 6, or 10, wherein the length of the second protrusion in the winding axis direction is 5% or more of the length of the main surface portion in the winding axis direction.

[0054] 10,110,210 Battery, 11 Positive electrode tab, 12 Negative electrode tab, 13 Electrode body, 14,114,214 Outer can, 14a Main surface portion, 14b Inner surface of main surface portion, 15 Spacer, 16 Insulating tape, 17 Sealing plate, 18,20 Opening, 19 Negative electrode terminal, 19a Negative electrode terminal plate, 21 Rivet, 22 Safety valve, 23 Non-aqueous electrolyte injection hole, 24 Gasket, 26 Insulating plate, 29,129 Bottom portion, 31,131 First protrusion portion, 36,136 End surface of first protrusion portion, 41 Second protrusion portion, 136a Inclined surface portion.

Claims

1. A prismatic secondary battery comprising: a flat electrode assembly in which a long positive electrode and a long negative electrode are wound with a separator interposed therebetween; and a flat, cylindrical outer can with a bottom that houses the electrode assembly; wherein, when portions of the outer can that face each other in the short diameter direction of the electrode assembly are defined as a pair of main surfaces, a first protrusion is provided on both ends in the long diameter direction of the electrode assembly on the inner surface of at least one of the pair of main surfaces, the first protrusion protruding in the short diameter direction and extending in the direction of the winding axis of the electrode assembly.

2. The prismatic secondary battery according to claim 1, wherein the first protrusions are provided on the inner surfaces of both of the pair of main surface portions.

3. A prismatic secondary battery according to claim 1 or 2, wherein the thickness of the outer can at a first location on the main surface where the first protrusion is provided is greater than the thickness of the outer can at a second location on the main surface that is spaced apart from the first protrusion in the major axis direction.

4. The prismatic secondary battery according to claim 1 or 2, wherein a second protrusion extending in the major axis direction is provided on an end of at least one of the main surface portions on the bottom side of the exterior can.

5. The prismatic secondary battery according to claim 4, wherein the second protrusions are provided on both of the pair of main surface portions.

6. The prismatic secondary battery according to claim 4, wherein the thickness of the outer can at a third location on the main surface where the second protrusion is provided is greater than the thickness of the outer can at a fourth location on the main surface that is spaced apart from the second protrusion in the direction of the winding axis.

7. A prismatic secondary battery according to claim 1 or 2, wherein the end face of the first protrusion in the minor axis direction includes an inclined surface portion that slopes in the direction of the winding axis so that the inner diameter of the outer can increases from the bottom side of the outer can toward the end of the opening side of the outer can.

8. The prismatic secondary battery according to claim 1 or 2, wherein the first protrusion is located within a range of 20% of the length of the main surface portion in the major axis direction from the end of the main surface portion in the major axis direction.

9. The prismatic secondary battery according to claim 1 or 2, wherein the length of the first protrusion in the major axis direction is 5% or more of the length of the main surface portion in the major axis direction.

10. The prismatic secondary battery according to claim 4, wherein the second protrusion is located within a range of 20% of the length of the main surface portion in the direction of the winding axis from the end of the main surface portion on the bottom side.

11. The prismatic secondary battery according to claim 4, wherein the length of the second protruding portion in the direction of the winding axis is 5% or more of the length of the main surface portion in the direction of the winding axis.

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