Flat battery

Abstract

To provide a flat battery with excellent sealing performance.SOLUTION: A flat battery disclosed herein includes a battery container and a power generation element housed in the battery container. The battery container includes an outer can having a bottom portion and a peripheral wall portion, a sealing body, and an annular gasket disposed between the outer can and the sealing body. The outer peripheral side of the gasket is in contact with the inner surface of the peripheral wall of the outer can. The gasket is made of a resin having a tensile modulus of elasticity of 1000 MPa or more as a base material, and the surface of the outer peripheral side of the gasket is composed of a resin having a lower tensile modulus of elasticity than that of the base material.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present application relates to a flat battery with excellent sealing properties. [Background technology]

[0002] Conventionally, flat batteries called coin batteries or button batteries have been known. In such flat batteries, a gasket is interposed between an outer can and a sealing body, and a battery container is used that is formed by crimping the open end of the outer can inward. In such flat batteries, a gasket is placed between the outer can and the sealing body and crimped to seal the battery container.

[0003] However, in flat batteries in which the battery container is sealed using a gasket, gas and electrolyte generated by the electrochemical reaction of the battery can leak through small gaps in the sealing part, which can degrade battery performance and compromise safety.

[0004] Various proposals have been made to solve the above problems. For example, Patent Document 1 proposes a sealed battery in which the surface of a first resin that forms the base of an insulating packing equivalent to the above-mentioned gasket is covered with a second resin layer that is more flexible than the first resin and is formed by chemical vapor deposition. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 5-121058 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the effects of the sealed battery proposed in Patent Document 1 were confirmed when applied to a cylindrical battery, and further study is required for application to a flat battery. The inventors then performed a structural analysis of a flat battery using an outer can and a gasket, and found that the contact pressure between the outer can and the gasket can be improved if certain conditions are met, making it clear that a flat battery with improved airtightness and leakage resistance can be realized.

[0007] The present application has been made under the above circumstances, and aims to provide a flat battery with excellent sealing properties. [Means for solving the problem]

[0008] The flat battery of the present application includes a battery container and a power generating element housed within the battery container, the battery container being composed of an outer can having a bottom portion and a peripheral wall portion, a sealing body, and an annular gasket arranged between the outer can and the sealing body, the outer peripheral side of the gasket being in contact with the inner surface of the peripheral wall portion of the outer can, the gasket being composed of a resin having a tensile modulus of elasticity of 1000 MPa or more as a base material, and the surface portion of the outer peripheral side of the gasket being composed of a resin having a tensile modulus of elasticity lower than that of the base material. Effect of the Invention

[0009] According to the present application, a flat battery with excellent sealing properties can be provided. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a cross-sectional view that illustrates a flat battery according to an embodiment. [Diagram 2] FIG. 2 is an enlarged view of part A in FIG. [Diagram 3] FIG. 3A is a partial cross-sectional view showing structure 1 before crimping for structural analysis using an outer can and a gasket, and FIG. 3B is a partial cross-sectional view showing structure 2 before crimping for structural analysis using an outer can and a gasket. [Figure 4]FIG. 4A shows the results of calculating the contact pressure between the outer can and the gasket when the tensile modulus of the resin in the surface portion of Structure 1 is changed, and FIG. 4B shows the results of calculating the contact pressure between the outer can and the gasket when the tensile modulus of the resin in the surface portion of Structure 2 is changed. [Diagram 5] FIG. 5A is a cross-sectional view of the structure 1 in a state where ref is crimped, and FIG. 5B is a cross-sectional view of the structure 1 in a state where case1-1 is crimped. [Figure 6] FIG. 6A is a cross-sectional view of the structure 2 in a state where the ref is crimped, and FIG. 6B is a cross-sectional view of the structure 2 in a state where the case2-1 is crimped. [Figure 7] FIG. 7A shows the results of calculating the maximum contact pressure between the outer can and the gasket by changing the tensile modulus of elasticity of the resin in the surface portion of Structure 1, and FIG. 7B shows the results of calculating the maximum contact pressure between the outer can and the gasket by changing the tensile modulus of elasticity of the resin in the surface portion of Structure 2. [Figure 8] FIG. 8A shows the results of calculating the integral value of the contact pressure between the outer can and the gasket by changing the tensile modulus of the resin of the surface portion of Structure 1, and FIG. 8B shows the results of calculating the integral value of the contact pressure between the outer can and the gasket by changing the tensile modulus of the resin of the surface portion of Structure 2. [Figure 9] 9A to 9D are diagrams in which the entire thickness of the end portion T of the structure 1 is set to 0.3 mm, and the thickness of the surface portion of the end portion T is changed from 0.05 to 0.2 mm. [Figure 10] FIG. 10A is a diagram showing the relationship between the tensile modulus of elasticity and the thickness of the surface portion of the resin of structure 1 shown in FIGS. 9A to 9D and the maximum contact pressure between the outer can and the gasket, expressed as a relative ratio based on the reference gasket. FIG. 10B is a diagram showing the relationship between the tensile modulus of elasticity and the thickness of the surface portion of the resin of structure 1 shown in FIGS. 9A to 9D and the integrated value of contact pressure between the outer can and the gasket, expressed as a relative ratio based on the reference gasket. [Figure 11]FIG. 11A shows the results of calculating the maximum contact pressure between the outer can and the gasket when two types of base materials for the gasket of Structure 1, PP and PPS, are used and the tensile modulus of the resin in the surface portion of each is changed. FIG. 11B shows the results of calculating the integrated value of the contact pressure between the outer can and the gasket when two types of base materials for the gasket of Structure 1, PP and PPS, are used and the tensile modulus of the resin in the surface portion of each is changed. [Figure 12] FIG. 12A shows the results of calculating the maximum contact pressure between the outer can and the gasket by using two types of base materials, PP and PPS, for the gasket of Structure 1 and changing the ratio of the tensile modulus of the resin of each surface to the tensile modulus of the base material, expressed as a relative ratio with respect to the case where the tensile modulus of the base material and the resin of the surface portion are equal. FIG. 12B shows the results of calculating the integrated value of the contact pressure between the outer can and the gasket by using two types of base materials, PP and PPS, for the gasket of Structure 1 and changing the ratio of the tensile modulus of the resin of each surface to the tensile modulus of the base material, expressed as a relative ratio with respect to the case where the tensile modulus of the base material and the resin of the surface portion are equal. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] An embodiment of a flat battery of the present application includes a battery container and a power generating element housed within the battery container, the battery container being composed of an outer can having a bottom portion and a peripheral wall portion, a sealing body, and an annular gasket arranged between the outer can and the sealing body, the outer peripheral side of the gasket being in contact with the inner surface of the peripheral wall portion of the outer can, the gasket being composed of a resin having a tensile modulus of elasticity of 1000 MPa or more as a base material, and the surface portion of the outer peripheral side of the gasket being composed of a resin having a tensile modulus of elasticity lower than that of the base material.

[0012] The flat battery of the present embodiment has the above-mentioned configuration, which improves the contact state between the outer can and the gasket, and provides excellent airtightness and leakage resistance, and improves sealing performance. The above-mentioned configuration was derived from the results of a structural analysis using the outer can and the gasket, which will be described later.

[0013] In the battery industry, flat batteries whose diameter is greater than their height are called coin batteries or button batteries, but there is no clear difference between coin batteries and button batteries, and the flat battery of this embodiment includes both coin batteries and button batteries.

[0014] Hereinafter, the flat battery of this embodiment will be described with reference to the drawings.

[0015] FIG. 1 is a schematic cross-sectional view of a flat battery of this embodiment, and FIG. 2 is an enlarged view of part A in FIG. 1. The flat battery 10 shown in FIG. 1 is configured by housing a power generating element formed by stacking a positive electrode 11, a separator 12, and a negative electrode 13 in a battery container formed of an outer can 14, a sealing body 15, and an annular gasket 16. The sealing body 15 is fitted to the opening of the outer can 14 via the gasket 16, and the opening end 14a of the outer can 14 is tightened inward by crimping, so that the gasket 16 abuts against the sealing body 15, sealing the opening of the outer can 14 and forming a sealed structure inside the battery. In addition, the crimping of the opening end 14a of the outer can 14 causes the bottom part of the gasket 16 to be compressed by the opening end 15a of the sealing body 15, realizing a strong sealed structure.

[0016] 2, in the flat battery of this embodiment, the outer periphery of gasket 16 contacts the inner surface of peripheral wall portion 14b of outer can 14, and the bottom side of gasket 16 contacts the inner surface of bottom portion 14c of outer can 14. Furthermore, gasket 16 is made of resin R1 having a tensile modulus of elasticity of 1000 MPa or more as a base material, and the surface portions of the outer periphery and bottom side of gasket 16 are both made of resin R2 having a tensile modulus of elasticity lower than that of the base material.

[0017] In this embodiment, an example is shown in which the surface portions of the outer periphery and bottom side of the gasket 16 are both made of resin R2 having a lower tensile modulus than the base material, but only the surface portion of the outer periphery of the gasket 16 may be made of resin R2 having a lower tensile modulus than the base material.

[0018] The thickness of the portion made of a resin having a lower tensile modulus than the base material of the gasket 16 is preferably 0.05 to 0.2 mm, and more preferably 0.1 to 0.15 mm. The tensile modulus of the resin having a lower tensile modulus than the base material of the gasket 16 is preferably 250 to 600 MPa. If the tensile modulus of the resin is lower than 250 MPa, the contact pressure between the outer can and the gasket decreases, and there is a possibility that the sealing performance may be impaired. Therefore, the tensile modulus of the resin is preferably 250 MPa or more. Furthermore, the tensile modulus of the resin having a lower tensile modulus than the base material of the gasket 16 is preferably 70% or less of the tensile modulus of the base material, and more preferably 50% or less.

[0019] The above-described preferable configuration of the flat battery of this embodiment was also derived from the results of a structural analysis using the outer can and the gasket.

[0020] A structural analysis using an exterior can and a gasket will be described below.

[0021] <Structural analysis software> In this structural analysis, the general-purpose structural analysis software "LS-DYNA" manufactured by Livermore Software Technology was used.

[0022] <Structural analysis structure> As the structures before crimping for the structural analysis, two types shown in FIG. 3 were used. However, FIG. 3 shows a partial cross-sectional view in which the above-mentioned FIG. 2 is turned upside down. In the structure 1 shown in FIG. 3A, only the outer peripheral surface portion 16b of the gasket 16 is made of a resin having a tensile modulus different from that of the base material 16a of the gasket 16 on the outer can 14. In the structure 2 shown in FIG. 3B, both the outer peripheral surface portion 16b and the bottom surface portion 16c of the gasket 16 are made of a resin having a tensile modulus different from that of the base material 16a of the gasket 16 on the outer can 14. In FIG. 3A and FIG. 3B, the entire thickness of the end portion T of the gasket 16 is set to 0.3 mm, and the thickness of the surface portion 16b of the end portion T is set to 0.1 mm.

[0023] <Effect of tensile modulus of surface resin 1> Fig. 4A is a diagram showing the results of calculating the contact pressure between the outer can and the gasket by changing the tensile modulus of elasticity of the resin in the surface portion of the above structure 1. Fig. 4B is a diagram showing the results of calculating the contact pressure between the outer can and the gasket by changing the tensile modulus of elasticity of the resin in the surface portion of the above structure 2.

[0024] In Fig. 4A and Fig. 4B, a gasket made of only resin with a tensile modulus of elasticity of 1372 MPa is used as a reference (ref), and cases in which a gasket made of a base material made of a resin with a tensile modulus of elasticity of 1372 MPa and a surface portion (thickness of 0.1 mm) made of a resin with a tensile modulus of elasticity of 300 MPa are used are shown as case 1-1 and case 2-1, and cases in which a gasket made of a base material made of a resin with a tensile modulus of elasticity of 1372 MPa and a surface portion (thickness of 0.1 mm) made of a resin with a tensile modulus of elasticity of 2000 MPa are shown as case 1-2 and case 2-2. In Fig. 4A, the horizontal axis indicates the length of the contact portion between the outer can and the gasket from point a to point b in Fig. 3A, and the vertical axis indicates the contact pressure between the outer can and the gasket. In Fig. 4B, the horizontal axis indicates the length of the contact portion between the outer can and the gasket from point a to point b in Fig. 3B, and the vertical axis indicates the contact pressure between the outer can and the gasket. The resin having a tensile modulus of elasticity of 1372 MPa is assumed to be polypropylene (PP).

[0025] Fig. 5A is a cross-sectional view of the above structure 1 in a crimped state of ref, and Fig. 5B is a cross-sectional view of the above structure 1 in a crimped state of case1-1. In Fig. 4A, peak 1 (P1) indicates the contact pressure near P1 in Fig. 5A and Fig. 5B, peak 2 (P2) indicates the contact pressure near P2 in Fig. 5A and Fig. 5B, and peak 3 (P3) indicates the contact pressure near P3 in Fig. 5A and Fig. 5B.

[0026] Fig. 6A is a cross-sectional view of the above-mentioned structure 2 in a crimped state of ref, and Fig. 6B is a cross-sectional view of the above-mentioned structure 2 in a crimped state of case2-1. In Fig. 4B, peak 1 (P1) indicates the contact pressure near P1 in Fig. 6A and Fig. 6B, peak 2 (P2) indicates the contact pressure near P2 in Fig. 6A and Fig. 6B, and peak 3 (P3) indicates the contact pressure near P3 in Fig. 6A and Fig. 6B.

[0027] 4A and 4B show that, compared to ref, case 1-1, in which the surface portion of the gasket on the outer periphery is made of a resin having a lower tensile modulus than the base material, and case 2-1, in which the surface portions of the gasket on the outer periphery and bottom sides are made of a resin having a lower tensile modulus than the base material, have improved contact pressure at P1 between the outer can and the gasket.

[0028] <Effect of tensile modulus of surface resin 2> Fig. 7A is a diagram showing the results of calculating the maximum contact pressure (P1 in Fig. 4A) between the outer can and the gasket by changing the tensile elastic modulus of the resin in the surface portion of the above structure 1. Fig. 7B is a diagram showing the results of calculating the maximum contact pressure (P1 in Fig. 4B) between the outer can and the gasket by changing the tensile elastic modulus of the resin in the surface portion of the above structure 2.

[0029] 7A shows that in the above structure 1, the contact pressure can be improved by about 50% compared to ref by setting the tensile modulus of the resin of the surface portion to 300 MPa. Also, FIG. 7B shows that the contact pressure can be improved compared to ref by setting the tensile modulus of the resin of the surface portion to about 500 MPa.

[0030] <Effect of tensile modulus of surface resin 3> Fig. 8A is a diagram showing the results of calculating the integral value of contact pressure (total area of ​​the graph in Fig. 4A) between the outer can and the gasket by changing the tensile modulus of the resin in the surface portion of the above structure 1. Fig. 8B is a diagram showing the results of calculating the integral value of contact pressure (total area of ​​the graph in Fig. 4B) between the outer can and the gasket by changing the tensile modulus of the resin in the surface portion of the above structure 2.

[0031] 8A and 8B show that the contact pressure integral value increases as the tensile modulus of the surface portion decreases.

[0032] <Relationship between tensile modulus of resin in surface area and thickness of surface area> 9A to 9D are diagrams in which the overall thickness of the end portion T of the above structure 1 is set to 0.3 mm, and the thickness of the surface portion of the end portion T is changed from 0.05 to 0.2 mm.

[0033] Fig. 10A is a diagram showing the relationship between the tensile modulus of elasticity of the resin in the surface portion of Structure 1 shown in Figs. 9A to 9D, the thickness of the surface portion, and the maximum contact pressure between the outer can and the gasket, expressed as a relative ratio based on the gasket in Reference. Also, Fig. 10B is a diagram showing the relationship between the tensile modulus of elasticity of the resin in the surface portion of Structure 1 shown in Figs. 9A to 9D, the thickness of the surface portion, and the integrated value of contact pressure between the outer can and the gasket, expressed as a relative ratio based on the gasket in Reference.

[0034] From Fig. 10A showing the maximum contact pressure, it can be seen that, when the total thickness of the gasket is 0.3 mm, the thickness of the surface portion of the above structure 1 is preferably 0.05 mm or more, more preferably 0.1 mm or more, preferably 0.2 mm or less, and more preferably 0.15 mm or less. Also, from Fig. 10B showing the integral value of the contact pressure, it seems that, when the total thickness of the gasket is 0.3 mm, the thickness of the surface portion of the above structure 1 is preferably 0.1 to 0.2 mm.

[0035] <Study of surface resin> 10A, when the overall thickness of the gasket is 0.3 mm, it is clear that the tensile modulus of the resin in the surface portion is preferably 250 to 600 MPa. Specific examples of resins having a tensile modulus in the range of 250 to 600 MPa include tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA, 310 to 350 MPa), tetrafluoroethylene-hexafluoropropylene copolymer (FEP, 350 MPa), polytetrafluoroethylene (PTFE, 410 MPa), etc.

[0036] As the resin-based material having a tensile modulus of elasticity of 250 to 600 MPa, a mixed material of resin and rubber can be used. Examples of the resin used in the mixed material include polyolefin-based resins such as polypropylene (PP) and polyethylene (PE); fluororesins such as PFA and tetrafluoroethylene-ethylene copolymer (ETFE); and polyphenylene sulfide (PPS). Examples of the rubber used in the mixed material include natural rubber (3 to 30 MPa), nitrile rubber (5 to 25 MPa), ethylene-propylene rubber (5 to 20 MPa), chloroprene rubber (5 to 25 MPa), silicone rubber (4 to 10 MPa), fluororubber (7 to 20 MPa), and ethylene-vinyl acetate rubber (7 to 20 MPa). The tensile modulus of elasticity of the mixed material can be adjusted by changing the mixing ratio of the resin and the rubber.

[0037] <Influence of base material 1> Fig. 11A is a diagram showing the results of calculating the maximum contact pressure between the outer can and the gasket by changing the tensile modulus of the resin of the surface portion of each of the two types of base materials of the gasket of the above structure 1, PP (tensile modulus: 1372 MPa) and PPS (tensile modulus: 3300 MPa). Fig. 11B is a diagram showing the results of calculating the integral value of the contact pressure between the outer can and the gasket by changing the tensile modulus of the resin of the surface portion of each of the two types of base materials of the gasket of the above structure 1, PP (tensile modulus: 1372 MPa) and PPS (tensile modulus: 3300 MPa). As described above, in the above structure 1, the entire thickness of the end T of the gasket is set to 0.3 mm, and the thickness of the surface portion of the end T is set to 0.1 mm.

[0038] 11A and 11B, it can be estimated that a resin having a tensile modulus of elasticity in the range of about 1000 to 3500 MPa can be used as the base resin. Examples of resins other than PP and PPS having a tensile modulus of elasticity in the range of about 1000 to 3500 MPa include methacrylic resin (PMMA, 3000 MPa), polycarbonate (PC, 2880 MPa), MC nylon (3500 MPa), nylon 66 (2900 MPa), polyacetal (3500 MPa), polyvinylidene fluoride (PVDF, 2140 MPa), etc.

[0039] The resin forming the base material may be made of two or more different materials. For example, the base material may have a core-shell structure, and a resin having a relatively high tensile modulus of elasticity may be used for the core portion, and a resin having a relatively low tensile modulus of elasticity may be used for the shell portion.

[0040] <Influence of base material 2> Fig. 12A is a diagram showing the results of calculating the maximum contact pressure between the outer can and the gasket by changing the ratio of the tensile modulus of the resin of each surface portion to the tensile modulus of the base material, using two types of base materials for the gasket of the above structure 1, PP (tensile modulus: 1372 MPa) and PPS (tensile modulus: 3300 MPa), and showing the results of calculating the maximum contact pressure between the outer can and the gasket by changing the ratio of the tensile modulus of the resin of each surface portion to the tensile modulus of the base material, as a relative ratio based on the case where the tensile modulus of the base material and the resin of the surface portion are equal. Fig. 12B is a diagram showing the results of calculating the integral value of the contact pressure between the outer can and the gasket by changing the ratio of the tensile modulus of the resin of each surface portion to the tensile modulus of the base material, using two types of base materials for the gasket of the above structure 1, PP (tensile modulus: 1372 MPa) and PPS (tensile modulus: 3300 MPa), and showing the results of calculating the integral value of the contact pressure between the outer can and the gasket by changing the ratio of the tensile modulus of the resin of each surface portion to the tensile modulus of the base material, as a relative ratio based on the case where the tensile modulus of the base material and the resin of the surface portion are equal. In the above structure 1, as described above, the entire thickness of the end T of the gasket was set to 0.3 mm, and the thickness of the surface portion of the end T was set to 0.1 mm.

[0041] From Figures 12A and 12B, it can be seen that in order to increase the contact pressure between the outer can and the gasket, the tensile modulus of the resin constituting the outer peripheral surface portion of the gasket is preferably set to 70% or less of the tensile modulus of the base material, and more preferably to 50% or less. [Explanation of symbols]

[0042] 10 Flat battery 11 Positive electrode 12 Separator 13 Negative electrode 14 Outer can 14a Open end 14b Peripheral wall part 14c Bottom part 15 Sealing body 15a Open end 16 Gasket 16a Base material 16b Surface portion of outer periphery of gasket 16c Bottom surface of gasket

Claims

1. A flat battery including a battery container and a power generating element housed in the battery container, the battery container is composed of an exterior can having a bottom portion and a peripheral wall portion, a sealing body, and an annular gasket disposed between the exterior can and the sealing body, an outer circumferential side of the gasket is in contact with an inner surface of a peripheral wall portion of the outer can; The gasket is made of a resin having a tensile modulus of elasticity of 1000 MPa or more as a base material, A flat battery in which the outer peripheral surface portion of the gasket is made of a resin having a lower tensile modulus than the base material.

2. 2. The flat battery according to claim 1, wherein the thickness of the portion made of the resin having a tensile modulus lower than that of the base material is 0.05 to 0.2 mm.

3. 3. The flat battery according to claim 1, wherein the resin having a lower tensile modulus than the base material has a tensile modulus of 250 to 600 MPa.

4. 4. The flat battery according to claim 1, wherein the resin having a lower tensile modulus than the base material has a tensile modulus of elasticity of 70% or less of the tensile modulus of elasticity of the base material.

5. a bottom side of the gasket contacts an inner surface of a bottom portion of the outer can, 5. The flat battery according to claim 1, wherein a surface portion on the bottom side of the gasket is also made of a resin having a lower tensile modulus than the base material.

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