Secondary battery

Abstract

To provide a secondary battery in which leakage of an electrolyte solution is further suppressed.SOLUTION: A secondary battery includes: an exterior body having an opening portion on one end side; a safety valve disposed in the opening portion; and a gasket interposed between the exterior body and the safety valve. The safety valve includes: a safety cover; and an external terminal stacked on the safety cover and located on the safety cover in a stacking direction. The gasket includes: a first gasket; and a second gasket in contact with an end surface of the first gasket and located on the first gasket in the stacking direction. A contact surface between the first gasket and the second gasket, which covers the end part of the safety valve and extends an upward from the end surface of the external terminal in a cross-sectional view, is located on a first virtual surface or outside of the first virtual surface, and is located on a second virtual surface or above the second virtual surface extending from a lower main surface of the safety cover in an extending direction of the lower main surface.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to secondary batteries. [Background technology]

[0002] Batteries can extract energy generated by chemical reactions as electrical energy. In particular, secondary batteries, which are so-called storage batteries, can be repeatedly charged and discharged and are used in a variety of applications. For example, batteries are used in mobile devices such as mobile phones, smartphones, and laptops.

[0003] Such a conventional secondary battery is disclosed, for example, in Patent Document 1. The secondary battery described in Patent Document 1 includes an electrode assembly including a positive electrode, a negative electrode, and an electrolyte, a cylindrical can that houses a battery element, a safety vent that has a predetermined notch formed therein so as to burst due to high-pressure gas in the battery, a protruding upper end cap that is connected along the outer periphery of the safety vent, and a gasket that is attached to the outer periphery of the upper end cap. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2024-517468 Summary of the Invention [Problem to be solved by the invention]

[0005] However, as a result of extensive research, the present inventors have found that the secondary battery described in Patent Document 1 still has room for improvement in terms of preventing leakage of the electrolyte.

[0006] The present inventors have made the present invention in view of the above-mentioned problems. That is, a main object of the present disclosure is to provide a secondary battery that further suppresses leakage of electrolyte. [Means for solving the problem]

[0007] The present inventors have attempted to solve the above problems by addressing them in a new direction rather than by simply extending the conventional technology. As a result, they have completed a battery according to the present disclosure in which the above-mentioned main object has been achieved. That is, the present disclosure includes the following embodiments.

[0008] A secondary battery according to an embodiment of the present disclosure includes: The safety valve includes an exterior body having an opening at one end thereof, a safety valve disposed in the opening, and a gasket disposed between the exterior body and the safety valve, the safety valve includes a safety cover and an external terminal stacked on the safety cover and positioned above the safety cover in a stacking direction; the gasket has a first gasket and a second gasket that contacts an end surface of the first gasket and is positioned on the first gasket in a stacking direction, and covers an end of the safety valve; The contact surface between the first gasket and the second gasket is located, in a cross-sectional view, on a first imaginary plane extending upward from the end face of the external terminal or outside the first imaginary plane, and is located on a second imaginary plane extending from the lower main surface of the safety cover in the extension direction of the lower main surface or above the second imaginary plane. [Effects of the Invention]

[0009] A secondary battery according to an embodiment of the present disclosure further suppresses leakage of electrolyte. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic perspective view showing the appearance of a secondary battery according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a schematic diagram showing the internal configuration of a secondary battery according to an embodiment of the present disclosure. [Figure 3] FIG. 3 is a cross-sectional view showing an upper portion of a secondary battery according to an embodiment of the present disclosure. [Figure 4]FIG. 4 is a schematic exploded perspective view showing components and related members of a safety valve of a secondary battery according to an embodiment of the present disclosure in an expanded state. [Figure 5] 5(a) and (b) are cross-sectional views showing a gasket in a secondary battery according to an embodiment of the present disclosure. [Figure 6] FIG. 6 is a schematic cross-sectional view showing a gasket in a conventional battery. [Figure 7] FIG. 7 is a schematic model diagram showing an ideal battery system in a secondary battery according to an embodiment of the present disclosure. [Figure 8] FIG. 8 is a schematic model diagram showing a conventional battery system. [Figure 9] FIG. 9 is a cross-sectional view showing the upper part of a secondary battery according to an embodiment of the present disclosure when the safety valve is operating. [Figure 10] FIG. 10 is a diagram for explaining a method for manufacturing a secondary battery according to an embodiment of the present disclosure. [Figure 11] 11(a) to 11(d) are cross-sectional views showing gaskets in a battery according to another embodiment of the present disclosure. [Figure 12] 12(a) to 12(d) are cross-sectional views showing gaskets of Comparative Examples 1 to 4. FIG. [Figure 13] FIG. 13 is a cross-sectional view showing a gasket in a battery according to another embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0011] The following describes specific embodiments of the present disclosure. The applicant provides the following description and examples to enable those skilled in the art to fully understand the present disclosure, and it should be noted that these are not intended to limit the subject matter described in the claims. In other words, the present disclosure is not particularly limited to the preferred embodiments described below, and can be implemented with appropriate modifications within the scope of its intended purpose. For convenience, the present invention may be described in terms of embodiments and examples, taking into account the ease of explanation or understanding of the key points. However, partial substitution and / or combination of the configurations shown in different embodiments is possible. In describing such embodiments, redundant description of substantially identical features may be omitted, and only differences may be described. In particular, similar effects resulting from similar configurations may not be mentioned in each embodiment.

[0012] Furthermore, references to directions or orientations in the description of this specification are merely for the convenience of explanation and are not intended to limit the scope of the present disclosure unless otherwise explicitly stated. For example, relative terms such as "outside (or outer, external, or outer periphery)" and "inside (or inner, internal, or inner periphery)," as well as their derivative terms, should be understood to refer to the directions as described or illustrated. Similarly, "on" an element includes not only contact with the top surface of the element but also non-contact with the top surface of the element. In other words, "on" an element includes not only a position above the element, i.e., a position above the element via another object or a position above the element with a gap, but also a position directly above the element. Furthermore, "on" does not necessarily mean above in the vertical direction. "On" merely indicates the relative position of an element. In other words, unless otherwise explicitly stated, the invention is not limited to a specific direction, orientation, or configuration. The same applies to terms such as "provided," "disposed," and "connected," as well as their derivative terms, and unless otherwise explicitly stated, they may not be limited to a direct form, but may also be forms in which other elements, such as intervening objects, are involved.

[0013] The various numerical ranges referred to in this specification are intended to include the lower and upper limit numerical values ​​themselves unless otherwise specified, such as "less than." In other words, for example, a numerical range such as 80% to 100% is interpreted as including the lower limit of 80% and the upper limit of 100%.

[0014] [Basic structure of secondary batteries] In this specification, a "secondary battery" is capable of repeated charging and discharging. Note that the term "secondary battery" is not limited to the name itself, and may also include, for example, "electricity storage devices."

[0015] A secondary battery according to one embodiment of the present disclosure will be described with reference to Figures 1 and 2. Figure 1 is a schematic perspective view showing the exterior of the secondary battery according to this embodiment. Figure 2 is a schematic view showing the internal configuration of the secondary battery according to this embodiment.

[0016] In Figures 1 and 2, the Z axis is parallel to the battery axis. In this specification, the battery axis corresponds to the central axis of the cylindrical exterior body. In this specification, the forward Z direction refers to a direction parallel to the battery axis and vertically upward. In this specification, the reverse Z direction refers to a direction parallel to the battery axis and vertically downward. In the vertical direction (Z direction), the forward Z direction is referred to as the upper side relatively, and the reverse Z direction is referred to as the lower side relatively. The R direction refers to a direction (radial direction) perpendicular to the Z direction and away from the battery axis in a plan view. In this specification, unless otherwise specified, the stacking direction refers to the direction in which the safety cover and the external terminals are stacked, and corresponds to the Z direction. In this specification, the cross-sectional view refers to the view of the cross section obtained by cutting the secondary battery in a plane that is parallel to the battery axis and includes the battery axis.

[0017] In this specification, the term "cylinder" refers to a cylindrical shape having a large aspect ratio (for example, an aspect ratio of 1 or more) of the height to the diameter of the equivalent circle diameter of the base. Here, the equivalent circle diameter of the base refers to the diameter of a circle having the same area as the area of ​​the base.

[0018] The secondary battery 1000 according to this embodiment is a cylindrical secondary battery (cylindrical secondary battery). The secondary battery 1000 is a cylindrical secondary battery, but is not limited to this. For example, the secondary battery may be a button-type or coin-type secondary battery. Here, the coin-type refers to a cylindrical shape in which the ratio of the height to the diameter of the equivalent circle diameter of the bottom surface (aspect ratio) is small (for example, an aspect ratio less than 1).

[0019] 1 and 2, a secondary battery 1000 according to this embodiment includes a battery assembly (battery element) 10, an electrolyte 30, an exterior body (battery can, housing member) 50 that houses the battery assembly 10 and has an opening (open end) 51 on one end side, a safety valve (sealing body) 100 disposed in the opening 51, and a gasket 20 interposed between the exterior body 50 and the safety valve 100. The safety valve 100 has a safety cover (sealing plate) 110 and an external terminal 170 that is stacked on the safety cover 110 and positioned above the safety cover 110 in the stacking direction. The secondary battery 1000 may also be a nonaqueous secondary battery in which the electrolyte is a nonaqueous electrolyte.

[0020] [Battery assembly] The battery assembly 10 is enclosed (housed) in an exterior case 50 together with an electrolyte (electrolytic solution, for example, a non-aqueous electrolyte). The battery assembly 10 includes a positive electrode 11, a negative electrode 12, and a separator 13 disposed between the positive electrode 11 and the negative electrode 12. In the secondary battery 1000 according to this embodiment, the battery assembly 10 is of a wound type (jelly roll type), but is not limited thereto. For example, the battery assembly 10 may be a stacked electrode assembly. A wound battery assembly has a wound structure (hereinafter also referred to as a "wound electrode assembly" or "wound structure") in which the separator 13 is disposed between the positive electrode 11 and the negative electrode 12 and wound into a roll. A stacked electrode assembly has a structure in which a plurality of electrode constituent layers, each including the positive electrode 11, the negative electrode 12, and the separator 13, are stacked.

[0021] (positive and negative electrodes) The positive electrode 11 has one or more positive electrode current collectors and one or more positive electrode material layers provided on at least one surface (that is, one surface or both surfaces) of the positive electrode current collectors. The negative electrode 12 has one or more negative electrode current collectors and one or more negative electrode material layers provided on at least one surface (that is, one surface or both surfaces) of the negative electrode current collectors.

[0022] -Electrode material layer- The positive electrode layer contains a positive electrode active material as an electrode active material, and may further contain a binder and / or a positive electrode conductive agent. The positive electrode layer may be a layer capable of absorbing and releasing carriers (e.g., alkali metal ions or alkaline earth metal ions, particularly lithium ions). The negative electrode material layer contains a negative electrode active material as an electrode active material, and may also contain a binder and / or a negative electrode conductive agent. Furthermore, the negative electrode material layer may contain a component resulting from a thickener component (e.g., carboxymethyl cellulose) used during battery production. The negative electrode material layer may be a layer capable of absorbing and releasing carriers (e.g., alkali metal ions or alkaline earth metal ions, particularly lithium ions).

[0023] =electrode active material= The electrode active materials (the positive electrode active material contained in the positive electrode 11 and the negative electrode active material contained in the negative electrode 12) are substances that are directly involved in the transfer of electrons in the secondary battery 1000, and are the main substances of the positive electrode 11 and the negative electrode 12 that are responsible for charging and discharging (i.e., the battery reaction). More specifically, ions are brought to the electrolyte due to the "positive electrode active material contained in the positive electrode material layer" and the "negative electrode active material contained in the negative electrode material layer", and these ions move between the positive electrode 11 and the negative electrode 12, transferring electrons and causing charging and discharging.

[0024] The secondary battery 1000 according to this embodiment may be a non-aqueous electrolyte secondary battery in which lithium ions move between the positive electrode 11 and the negative electrode 12 via a non-aqueous electrolyte to charge and discharge the secondary battery 1000. When lithium ions are involved in charging and discharging, the secondary battery 1000 according to this embodiment corresponds to a so-called "lithium ion battery" and has layers capable of absorbing and releasing lithium ions as the positive electrode 11 and the negative electrode 12.

[0025] When the secondary battery 1000 according to this embodiment is a lithium-ion battery, the positive electrode active material may be a material that contributes to the absorption and desorption of lithium ions. That is, the positive electrode layer may contain one or more positive electrode materials that can absorb and desorb lithium. From this perspective, the positive electrode active material may be, for example, a lithium-containing compound. The type of lithium-containing compound is not particularly limited, but examples include lithium-containing composite oxides and lithium-containing phosphate compounds. This is because a high energy density can be easily obtained.

[0026] In this specification, the term "lithium-containing composite oxide" refers to an oxide containing lithium and one or more other elements (elements other than lithium) as constituent elements, and may have, for example, a layered rock salt or spinel crystal structure. In this specification, the term "lithium-containing phosphate compound" refers to a phosphate compound containing lithium and one or more other elements as constituent elements, and may have, for example, an olivine crystal structure. The type of the other element is not particularly limited as long as it is one or more of any element. In particular, the other element is preferably one or more of elements belonging to Groups 2 to 15 of the long-form periodic table. More specifically, examples of the other element include nickel (Ni), cobalt (Co), manganese (Mn), and iron (Fe). This is because the addition of these other elements (additive elements) facilitates the production of a high voltage.

[0027] The lithium-containing composite oxide having a layered rock salt crystal structure may be, for example, a compound represented by each of the following formulas (1) to (3). Li a Mn (1-b-c) Ni b M11 c O (2-d) F e ···(1) (In formula (1), M11 is at least one of cobalt (Co), magnesium (Mg), aluminum (Al), boron (B), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), zinc (Zn), zirconium (Zr), molybdenum (Mo), tin (Sn), calcium (Ca), strontium (Sr), and tungsten (W). a to e satisfy 0.8 ≦ a ≦ 1.2, 0 < b < 0.5, 0 ≦ c ≦ 0.5, (b + c) < 1, -0.1 ≦ d ≦ 0.2, and 0 ≦ e ≦ 0.1. However, the composition of lithium varies depending on the charge-discharge state, and a is the value in the fully discharged state.) Li a Ni (1-b) M12 b O (2-c) F d ···(2) (In formula (2), M12 is at least one of cobalt (Co), manganese (Mn), magnesium (Mg), aluminum (Al), boron (B), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), zinc (Zn), molybdenum (Mo), tin (Sn), calcium (Ca), strontium (Sr), and tungsten (W). a to d satisfy 0.8 ≦ a ≦ 1.2, 0.005 ≦ b ≦ 0.5, -0.1 ≦ c ≦ 0.2, and 0 ≦ d ≦ 0.1. However, the composition of lithium varies depending on the charge-discharge state, and a is the value in the fully discharged state.) Li a Co (1-b) M13 b O (2-c) F d ···(3) (In formula (3), M13 is at least one of nickel (Ni), manganese (Mn), magnesium (Mg), aluminum (Al), boron (B), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), zinc (Zn), molybdenum (Mo), tin (Sn), calcium (Ca), strontium (Sr), and tungsten (W). a to d satisfy the following conditions: 0.8≦a≦1.2, 0≦b<0.5, −0.1≦c≦0.2, and 0≦d≦0.1. However, the lithium composition varies depending on the charge / discharge state, and a is the value in a fully discharged state.)

[0028] Specific examples of lithium-containing composite oxides having a layered rock salt crystal structure include LiNiO2, LiCoO2, and LiCo 0.98 Al 0.01 Mg 0.01 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.8 Co 0.15 Al 0.05 O2, LiNi 0.33 Co 0.33 Mn 0.33 O2, Li 1.2 Mn 0.52 Co 0.175 Ni 0.1 O2 and Li 1.15 (Mn 0.65 Ni 0.22 Co 0.13 )O2, etc. When the lithium-containing composite oxide having a layered rock-salt crystal structure contains nickel, cobalt, manganese, and aluminum as constituent elements, the atomic ratio of nickel is preferably 50 atomic % or more, because a high energy density is easily obtained.

[0029] The lithium-containing composite oxide having a spinel-type crystal structure may be, for example, a compound represented by the following formula (4). Li a Mn (2-b) M14 b O cF d ···(4) (In formula (4), M14 is at least one of cobalt (Co), nickel (Ni), magnesium (Mg), aluminum (Al), boron (B), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), zinc (Zn), molybdenum (Mo), tin (Sn), calcium (Ca), strontium (Sr), and tungsten (W). a to d satisfy the following conditions: 0.9≦a≦1.1, 0≦b≦0.6, 3.7≦c≦4.1, and 0≦d≦0.1. However, the lithium composition differs depending on the charge / discharge state, and a is the value in a fully discharged state.) A specific example of the lithium-containing composite oxide having a spinel-type crystal structure may be LiMn2O4.

[0030] The lithium-containing phosphate compound having an olivine-type crystal structure is, for example, a compound represented by the following formula (5). Li a M15PO4 (5) (In formula (5), M15 is at least one of cobalt (Co), manganese (Mn), iron (Fe), nickel (Ni), magnesium (Mg), aluminum (Al), boron (B), titanium (Ti), vanadium (V), niobium (Nb), copper (Cu), zinc (Zn), molybdenum (Mo), calcium (Ca), strontium (Sr), tungsten (W), and zirconium (Zr). a satisfies 0.9≦a≦1.1. However, the composition of lithium varies depending on the charge / discharge state, and a is the value in a fully discharged state.) Specific examples of lithium-containing phosphate compounds having an olivine-type crystal structure include LiFePO4, LiMnPO4, and LiFe 0.5 Mn 0.5 PO4 and LiFe 0.3 Mn 0.7 It may be PO4, etc.

[0031] The lithium-containing composite oxide may be a compound represented by the following formula (6). (Li2MnO3) x (LiMnO2) 1-x ···(6) (In formula (6), x satisfies 0≦x≦1. However, the lithium composition varies depending on the charge / discharge state, and x is the value in a fully discharged state.)

[0032] Alternatively, the positive electrode material may be one or more of oxides, disulfides, chalcogenides, and conductive polymers. Examples of oxides include titanium oxide, vanadium oxide, and manganese dioxide. Examples of disulfides include titanium disulfide and molybdenum sulfide. Examples of chalcogenides include niobium selenide. Examples of conductive polymers include sulfur, polyaniline, and polythiophene. However, the positive electrode material is not particularly limited and may be a material other than those listed above.

[0033] Similarly, the negative electrode active material of the negative electrode layer may be a material that contributes to the absorption and desorption of lithium ions. That is, the negative electrode layer may contain one or more negative electrode materials that can absorb and desorb lithium. From this perspective, the negative electrode active material may be, for example, various carbon materials, metal materials, and / or other materials.

[0034] When the negative electrode active material contains a carbon material, the change in the crystal structure during lithium absorption and desorption is very small, making it easy to stably obtain a high energy density. In addition, the carbon material also functions as a negative electrode conductive agent, making it easy to improve the conductivity of the negative electrode layer.

[0035] Specific examples of carbon materials include graphitizable carbon, non-graphitizable carbon, and / or graphite. More specifically, the carbon material may be, for example, pyrolytic carbon, cokes, glassy carbon fiber, organic polymer compound calcined bodies, activated carbon, and carbon blacks. Examples of cokes include pitch coke, needle coke, and petroleum coke. Examples of organic polymer compound calcined bodies are substances obtained by calcining (carbonizing) polymer compounds such as phenolic resins and furan resins at an appropriate temperature. Alternatively, the carbon material may be low-crystalline carbon heat-treated at a temperature of approximately 1000°C or less, or amorphous carbon. The shape of the carbon material is not particularly limited and may be at least one of fibrous, spherical, granular, and flaky.

[0036] The term "metal-based material" used as the negative electrode active material is a general term for materials containing one or more metal elements and metalloid elements as constituent elements. When a carbon material is used as the negative electrode active material, a high energy density is easily obtained. The metal-based material may be a simple substance, an alloy, a compound, or two or more of these, or may be a material containing at least one or more phases of these. However, alloys may include materials containing one or more metal elements and one or more metalloid elements in addition to materials consisting of two or more metal elements. The alloy may also contain nonmetallic elements. The structure of this metal-based material may be, for example, a solid solution, a eutectic (eutectic mixture), an intermetallic compound, or a mixture of two or more of these. Such metal elements and metalloid elements may be, for example, one or more metal elements and metalloid elements that can form an alloy with lithium. Examples of metal elements and metalloid elements include magnesium (Mg), boron (B), aluminum (Al), gallium (Ga), indium (In), silicon (Si), germanium (Ge), tin (Sn), lead (Pb), bismuth (Bi), cadmium (Cd), silver (Ag), zinc (Zn), hafnium (Hf), zirconium (Zr), yttrium (Y), palladium (Pd), and / or platinum (Pt). In a preferred embodiment, the metal elements are silicon and tin. This is because these metal elements have excellent lithium absorption and desorption capabilities, making it easier to obtain higher energy densities. The material containing silicon as a constituent element may be silicon itself, a silicon alloy, a silicon compound, or two or more of these, or may be a material that at least partially contains one or more of these phases. Similarly, a material containing tin as a constituent element may be tin alone, a tin alloy, a tin compound, two or more of these, or a material containing at least one or more of these phases. The term "simple element" used in this specification refers to a simple element in the general sense, and may contain trace amounts of impurities.That is, the purity of the single substance is not necessarily limited to 100%. The silicon alloy may contain, for example, any one or more of tin, nickel, copper, iron, cobalt, manganese, zinc, indium, silver, titanium, germanium, bismuth, antimony, and chromium as constituent elements other than silicon. The silicon compound may contain, for example, any one or more of carbon and oxygen as constituent elements other than silicon. Note that the silicon compound may contain any one or more of the series of elements described for the silicon alloy as constituent elements other than silicon. Specific examples of the silicon alloy and specific examples of the silicon compound include SiB4, SiB6, MgSi, Ni2Si, TiSi2, MoSi2, CoSi2, NiSi2, CaSi2, CrSi2, Cu5Si, FeSi2, MnSi2, NbSi2, TaSi2, VSi2, WSi2, ZnSi2, SiC, Si3N4, Si2N2O, SiO. v (0 < v ≤ 2), and / or LiSiO, etc. can be cited. Note that for SiO v the v in it may be 0.2 < v < 1.4. The tin alloy may contain, for example, any one or more of silicon, nickel, copper, iron, cobalt, manganese, zinc, indium, silver, titanium, germanium, bismuth, antimony, and chromium as constituent elements other than tin. The tin compound may contain, for example, any one or more of carbon and oxygen as constituent elements other than tin. Note that the tin compound may contain any one or more of the series of elements described for the tin alloy as constituent elements other than tin. Specific examples of the tin alloy and specific examples of the tin compound include SnO w(0 < w ≤ 2), SnSiO3, LiSnO, and / or Mg2Sn, etc. can be mentioned. In particular, a material containing tin as a constituent element may be, for example, a material (tin-containing material) containing a second constituent element and a third constituent element together with tin which is the first constituent element. The second constituent element may be, for example, any one or more of cobalt, iron, magnesium, titanium, vanadium, chromium, manganese, nickel, copper, zinc, gallium, zirconium, niobium, molybdenum, silver, indium, cesium (Ce), hafnium (Hf), tantalum, tungsten, bismuth, and silicon. The third constituent element may be, for example, any one or more of boron, carbon, aluminum, and phosphorus. This is because high battery capacity, excellent cycle characteristics, etc. are easily obtained by these elements. Among them, the tin-containing material may be a material (tin-cobalt-carbon-containing material) containing tin, cobalt, and carbon as constituent elements. This is because high energy density is easily obtained by these materials. In the tin-cobalt-carbon-containing material, at least a part of the carbon which is a constituent element may be bonded to a metal element or a metalloid element which is another constituent element. This is because aggregation of tin and crystallization of tin, etc. are easily suppressed. Such a tin-cobalt-carbon-containing material is not limited to a material (SnCoC) whose constituent elements are only tin, cobalt, and carbon. This tin-cobalt-carbon-containing material may contain, for example, in addition to tin, cobalt, and carbon, any one or more of silicon, iron, nickel, chromium, indium, niobium, germanium, titanium, molybdenum, aluminum, phosphorus, gallium, and bismuth as constituent elements. In addition to the tin-cobalt-carbon-containing material, a material (tin-cobalt-iron-carbon-containing material) containing tin, cobalt, iron, and carbon as constituent elements may also be used.

[0037] Alternatively, the negative electrode material may be one or more of metal oxides and polymer compounds. Examples of metal oxides include iron oxide, ruthenium oxide, and molybdenum oxide. Examples of polymer compounds include polyacetylene, polyaniline, and polypyrrole.

[0038] =Conductive agent= The cathode conductive agent that can be contained in the cathode material layer can facilitate the transfer of electrons that drive the battery reaction. Examples of the cathode conductive agent include carbon materials, metal materials, and conductive polymers. The carbon material may include at least one material selected from the group consisting of graphite, carbon black, acetylene black, and ketjen black.

[0039] The negative electrode conductive agent that can be contained in the negative electrode material layer facilitates the transfer of electrons that drive the battery reaction. Examples of the negative electrode conductive agent that can be contained in the negative electrode material layer include, but are not limited to, at least one selected from the group consisting of carbon black such as thermal black, furnace black, channel black, ketjen black, and acetylene black, graphite, carbon fibers such as carbon nanotubes and vapor-grown carbon fibers, metal powders such as copper, nickel, aluminum, and silver, and polyphenylene derivatives.

[0040] =Binder= The binder that can be contained in the positive electrode material layer may include, for example, one or more of synthetic rubbers and polymeric compounds. Examples of synthetic rubbers include styrene-butadiene rubbers, fluorine-containing rubbers, and ethylene-propylene-diene rubbers. Examples of polymeric compounds include polyvinylidene fluoride and polyimides.

[0041] The binder that can be contained in the negative electrode material layer is not particularly limited, but can include at least one selected from the group consisting of styrene butadiene rubber, polyacrylic acid, polyvinylidene fluoride, polyimide resins, and polyamideimide resins.

[0042] -Current collector- The current collectors (electrode current collectors, more specifically, the positive electrode current collector used in the positive electrode 11 and the negative electrode current collector used in the negative electrode 12) are members that contribute to collecting and supplying electrons generated in the electrode active material due to the battery reaction. Such electrode current collectors may be sheet-shaped metal members. The electrode current collectors may be single-layer or multi-layer. Furthermore, the electrode current collectors may be porous or perforated. For example, the current collectors may be metal foils, punched metals, mesh, expanded metals, or the like. The positive electrode current collector used in the positive electrode 11 may be made of, for example, a metal foil containing at least one selected from the group consisting of aluminum, nickel, stainless steel, and the like. On the other hand, the negative electrode current collector used in the negative electrode 12 may be made of, for example, a metal foil containing at least one selected from the group consisting of copper, aluminum, nickel, stainless steel, and the like.

[0043] (separator) The separator 13 used for the positive electrode 11 and the negative electrode 12 is a member provided from the viewpoint of preventing a short circuit due to contact between the positive electrode 11 and the negative electrode 12, retaining the electrolyte, etc. In other words, the separator 13 is a member that separates the positive electrode 11 and the negative electrode 12, and allows ions (e.g., lithium ions) to pass through while preventing a short circuit of current due to contact between the two electrodes. For example, the separator 13 may be a porous or microporous insulating member, and may have a membrane form due to its small thickness.

[0044] The separator 13 may be, for example, one or more types of porous membranes made of synthetic resins and / or ceramics, or may be a laminated membrane of two or more types of porous membranes. Examples of synthetic resins used for the separator 13 include polytetrafluoroethylene, polypropylene, and polyethylene. For example, the separator 13 may include a porous membrane (substrate layer) and a polymer compound layer provided on one or both sides of the substrate layer. This improves the adhesion of the separator to the positive electrode and the negative electrode, thereby making it easier to suppress distortion of the wound electrode assembly. The polymer compound layer may include, for example, one or more types of polymer compounds such as polyvinylidene fluoride. This improves physical strength and electrochemical stability. The polymer compound layer may also include, for example, one or more types of insulating particles such as inorganic particles. The inorganic particle species may be, for example, aluminum oxide and / or aluminum nitride. In the present invention, the separator should not be limited to a particular name, and may be a solid electrolyte, a gel electrolyte, and / or insulating inorganic particles, which have similar functions.

[0045] (Conductive material) The electrode assembly 10 may have a conductive member 15 as a connection terminal. The conductive member 15 is electrically connected to one of the positive electrode 11 and the negative electrode 12 of the electrode assembly 10 and contributes to the electrical connection between the electrode assembly 10 and the safety valve 100. The electrode assembly 10, such as a wound structure, is electrically connected to an external terminal 170 via the conductive member 15. In this specification, the conductive member 15 may be a member containing metal, preferably a metal member having an elongated shape. For example, the conductive member 15 may be formed from the electrode current collector of the electrode assembly 10, or may be a current collecting lead (i.e., a lead) provided on the electrode assembly (particularly its electrode). When the conductive member 15 is formed from the electrode current collector, the conductive member may be formed from a metal portion of the electrode current collector that is not provided with electrode material. When the conductive member 15 is formed from a current collecting lead, the conductive member may be formed from a metal member having a thin-walled and / or elongated shape. In this embodiment, the conductive member that electrically connects the electrode assembly 10 and the electrode terminal to each other may also be referred to as a “tab.” The conductive member 15 used in the secondary battery 1000 is preferably flexible and may be provided in a bent and / or curved form.

[0046] [Electrolytes] In the secondary battery 1000 according to this embodiment, a battery assembly 10 including a positive electrode 11, a negative electrode 12, and a separator 13 is enclosed in an exterior case 50 together with an electrolyte (electrolytic solution) 30. In one embodiment, the separator 13 is impregnated with the electrolytic solution, and the positive electrode 11 and / or the negative electrode 12 are also impregnated with the electrolytic solution. The electrolytic solution may be a so-called "nonaqueous" electrolytic solution (nonaqueous electrolyte solution).

[0047] The electrolytic solution contains a solvent and an electrolyte salt, and may further contain one or more of other materials such as additives.

[0048] (solvent) The solvent may contain one or more non-aqueous solvents such as organic solvents. An electrolyte containing a non-aqueous solvent can be a so-called non-aqueous electrolyte. The non-aqueous solvent may be, for example, a cyclic carbonate, a chain carbonate, a lactone, a chain carboxylic acid ester, and / or a nitrile (e.g., mononitrile). By including these non-aqueous solvents, it becomes easier to obtain better battery capacity, cycle characteristics, and / or storage characteristics. The cyclic carbonate may be, for example, ethylene carbonate, propylene carbonate, and / or butylene carbonate. The chain carbonate may be, for example, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and / or methyl propyl carbonate. The lactone may be, for example, γ-butyrolactone and / or γ-valerolactone. The chain carboxylic acid ester may be, for example, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, methyl butyrate, methyl isobutyrate, methyl trimethylacetate, and / or ethyl trimethylacetate. The nitrile may be, for example, acetonitrile, methoxyacetonitrile, and / or 3-methoxypropionitrile. Other examples of the nonaqueous solvent include 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 1,3-dioxane, 1,4-dioxane, N,N-dimethylformamide, N-methylpyrrolidinone, N-methyloxazolidinone, N,N'-dimethylimidazolidinone, nitromethane, nitroethane, sulfolane, trimethyl phosphate, and / or dimethyl sulfoxide. Among these, the nonaqueous solvent preferably contains one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. The inclusion of such a suitable nonaqueous solvent facilitates the achievement of higher battery capacity, better cycle characteristics, and / or better storage characteristics.

[0049] Furthermore, the nonaqueous solvent may be, for example, an unsaturated cyclic carbonate, a halogenated carbonate, a sulfonate, an acid anhydride, a dicyano compound (dinitrile compound), a diisocyanate compound, a phosphate ester, and / or a chain compound having a carbon-carbon triple bond. This facilitates improving the chemical stability of the electrolyte. The "unsaturated cyclic carbonate" referred to here is a cyclic carbonate having one or more unsaturated bonds (carbon-carbon double bonds or carbon-carbon triple bonds). Examples of such unsaturated cyclic carbonates include vinylene carbonate, vinylethylene carbonate, and / or methyleneethylene carbonate. The "halogenated carbonate" is a cyclic or chain carbonate containing one or more halogen elements as constituent elements. When the halogenated carbonate contains two or more halogen elements as constituent elements, the two or more halogen species may be one type or two or more types. Examples of cyclic halogenated carbonates include 4-fluoro-1,3-dioxolan-2-one and / or 4,5-difluoro-1,3-dioxolan-2-one. Chain halogenated carbonates may include, for example, fluoromethyl methyl carbonate, bis(fluoromethyl) carbonate, and / or difluoromethyl methyl carbonate. Sulfonate esters may include, for example, monosulfonate esters and / or disulfonate esters. Monosulfonate esters may be cyclic monosulfonate esters or chain monosulfonate esters. Cyclic monosulfonate esters may be sultones such as 1,3-propane sultone and / or 1,3-propene sultone. Chain monosulfonate esters are, for example, compounds in which a cyclic monosulfonate ester is cleaved midway. Disulfonate esters may be cyclic disulfonate esters or chain disulfonate esters. The acid anhydride may be, for example, a carboxylic acid anhydride, a disulfonic acid anhydride, and / or a carboxylic acid sulfonic acid anhydride, etc. The carboxylic acid anhydride may be, for example, a succinic acid anhydride, a glutaric acid anhydride, and / or a maleic acid anhydride, etc.The disulfonic acid anhydride may be, for example, ethanedisulfonic acid anhydride and / or propanedisulfonic acid anhydride. The carboxylic acid sulfonic acid anhydride may be, for example, sulfobenzoic acid anhydride, sulfopropionic acid anhydride, and / or sulfobutyric acid anhydride. The dinitrile compound may be, for example, a compound represented by NC-R-CN (R is either an alkylene group or an arylene group). The dinitrile compound may be, for example, succinonitrile (NC-C2H4-CN), glutaronitrile (NC-C3H6-CN), adiponitrile (NC-C4H8-CN), and phthalonitrile (NC-C6H4-CN). The diisocyanate compound may be, for example, OCN-R. 2 The diisocyanate compound is a compound represented by the formula -NCO (R2 is either an alkylene group or an arylene group). This diisocyanate compound is, for example, hexamethylene diisocyanate (OCN-CH 12 The phosphate ester may be, for example, trimethyl phosphate and triethyl phosphate. The chain compound having a carbon-carbon triple bond is a chain compound having one or more carbon-carbon triple bonds (-C≡C-). The chain compound having a carbon-carbon triple bond may be, for example, propargyl methyl carbonate (CH≡C-CH2-OC(=O)-O-CH3) and propargyl methylsulfonate (CH≡C-CH2-OS(=O)2-CH3).

[0050] (electrolyte salt) The electrolyte salt contained in the electrolyte solution may be an alkali metal salt or an alkaline earth metal salt. The alkali metal salt may include, for example, one or more salts such as a lithium salt. The electrolyte salt may include, for example, a salt other than a lithium salt. Such a salt other than lithium may be, for example, a salt of a light metal other than lithium. Examples of the lithium salt include lithium hexafluorophosphate (LiPF), lithium tetrafluoroborate (LiBF), lithium perchlorate (LiClO), lithium hexafluoroarsenate (LiAsF), lithium tetraphenylborate (LiB(CH)), lithium methanesulfonate (LiCHSO), lithium trifluoromethanesulfonate (LiCFSO), lithium tetrachloroaluminate (LiAlCl), dilithium hexafluorosilicate (LiSiF), lithium chloride (LiCl), and / or lithium bromide (LiBr). This is because it becomes easier to obtain better battery capacity, cycle characteristics and / or storage characteristics, etc. Among these, any one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate and lithium hexafluoroarsenate may be used.

[0051] [Exterior body] The exterior body 50 houses the battery assembly 10. The exterior body 50 has an opening (open end) 51 at one end. The exterior body 50 may have a hollow structure with the opening 51 at one end, or may have another opening at the other end. The exterior body 50 may be a cylindrical case, i.e., a cylindrical exterior body. A safety valve 100 is provided at the opening 51 of the exterior body 50. In this way, the exterior body 50 encloses the battery assembly 10 and protects it from the outside.

[0052] The exterior body 50 may have a beading portion (or a constricted portion or a narrowed portion) 57 that protrudes inward from the outer surface thereof. The beading portion 57 is formed in the circumferential direction of the exterior body 50.

[0053] [safety valve] The safety valve 100 is disposed in the opening 51 of the exterior body 50. The safety valve 100 has a safety cover 110 and an external terminal 170 that is stacked on the safety cover 110 and positioned on the safety cover in the stacking direction. The external terminal 170 is exposed on the surface of the secondary battery 1000 and can be electrically connected to other components.

[0054] In addition to the safety cover 110 and the external terminal 170, the safety valve 100 further includes a disc holder 120, a stripper disc 130, and a sub-disc 140. In this embodiment, the safety cover 110, the disc holder 120, the stripper disc 130, and the sub-disc 140 can constitute the safety valve.

[0055] (safety valve) The safety valve will be described with reference to Figures 3 and 4. Figure 3 is a cross-sectional view showing the upper part of the secondary battery according to this embodiment. Figure 4 is a schematic exploded perspective view showing the constituent members and related members of the safety valve of the secondary battery according to this embodiment in an expanded state. As shown in Figures 3 and 4, the safety valve has a configuration in which a safety cover 110 having a protruding portion 110T in the center (protruding relatively inwardly of the battery axis), a disc holder 120 having an opening in the center, a stripper disc 130 having an opening 130C in the center, and a sub-disc 140 that is connected to the protruding portion 110T extending through the opening of the disc holder and the opening of the stripper disc, are combined in order from the outside to the inside of the accommodating member (in the direction of the battery axis).

[0056] The safety valve does not operate during normal use, but operates in the event of an abnormality. Specifically, when an abnormality occurs (abnormality) in which an undesired high temperature occurs due to, for example, a short circuit, the safety valve can suppress and prevent the battery from smoking and / or catching fire. The operation of the safety valve will be described in detail later.

[0057] The safety valve has a configuration in which a safety cover 110, a disc holder 120, a stripper disc 130, and a sub-disc 140 are combined with one another in that order along the Z direction. When viewed along the axial direction of the cylindrical shape of the secondary battery 1000, the safety cover 110 is positioned relatively outside the battery (i.e., the side farther from the electrode assembly 10 such as a wound structure), while the sub-disc 140 is positioned relatively inside the battery (i.e., the side closer to the electrode assembly such as a wound structure). In other words, the disc holder 120 is positioned closer to the interior of the battery than the safety cover 110, the stripper disc 130 is positioned closer to the interior of the battery than the disc holder 120, and the sub-disc 140 is positioned closer to the interior of the battery than the stripper disc 130.

[0058] The safety valve also electrically connects the battery assembly 10 and the external terminal 170, and has a mechanism that can be displaced and broken due to excessive internal battery pressure (for example, the safety cover 110 and / or the sub-disk 140 can be displaced and broken), and has as its components the safety cover 110, the disk holder 120, the stripper disk 130, and the sub-disk 140. The safety valve can be provided in the opening 51 of the exterior body 50.

[0059] The safety cover 110 is disposed relatively outside the battery axis of the disc holder 120. The safety cover 110 closes the opening 51 of the exterior body 50 and is capable of deforming and / or displacing so as to be openable in response to an increase in the internal pressure of the exterior body 50. The internal pressure of the exterior body 50 may increase due to a side reaction such as a decomposition reaction of the electrolyte solution. When a side reaction such as a decomposition reaction of the electrolyte solution occurs, gases such as carbon dioxide are generated inside the exterior body 50, and an increase in the amount of gas generated can cause an undesirable increase in the internal pressure of the exterior body 50.

[0060] The disc holder 120 is interposed between the safety cover 110 and the stripper disc 130, and insulates the electrical connection between their outer peripheries 110X, 130X. This limits the electrical connection between the safety cover 110 and the stripper disc 130 in the safety valve to connection only via the joint, and enables the electrical connection to be cut off by displacing the joint in the event of an abnormality in the safety mechanism of the safety valve, which will be described later.

[0061] The disc holder 120 is also interposed between the safety cover 110 and the stripper disc 130 and can align the stripper disc 130 with respect to the safety cover 110 .

[0062] The stripper disc 130 is interposed between the disc holder 120 and the sub-disc 140, and contributes to the passage or release of gas generated inside the exterior body 50. In a plan view, the stripper disc 130 has a substantially circular central portion 130Y and an outer peripheral portion 130X that is disposed on the periphery of the central portion 130Y so as to surround the central portion 130Y.

[0063] The sub-disk 140 is a member that can be disposed between the stripper disk 130 and the electrode assembly 10 .

[0064] (Safety valve function (safety mechanism)) The operation of the safety valve will be described with reference to Fig. 9 in addition to Fig. 3. Fig. 9 is a cross-sectional view showing the upper part of the secondary battery according to an embodiment of the present disclosure when the safety valve is operating.

[0065] As mentioned above, if an abnormality such as a short circuit occurs inside the battery, it is possible that this may occur in conjunction with an abnormality such as an increase in internal pressure. That is, let us consider a case in which an increase in pressure inside the exterior body 50 due to a side reaction such as the decomposition reaction of the electrolyte 30 or other factors becomes excessive along with an undesired increase in temperature inside the secondary battery 1000. Figure 3 also shows a state in which the internal pressure of the secondary battery 1000 (i.e., the internal pressure of the exterior body 50) during normal use is within the normal range and the safety valve is not activated. As shown in Figure 3, the safety cover 110 has not yet been displaced, and the gas flow path or release path itself through the multiple openings 130K in the stripper disk 130 is not particularly functioning.

[0066] When gas is generated inside the exterior body 50 due to a side reaction, such as a decomposition reaction of the electrolyte 30, the gas accumulates inside the exterior body 50, causing an increase in the internal pressure of the exterior body 50. An increase in the internal pressure of the exterior body 50 can also be caused by an undesired excessive temperature rise inside the battery, such as a short circuit. When the internal pressure of the exterior body 50 exceeds a certain pressure, the sub-disk 140 is torn and separated, as shown in FIG. 9 . Although not particularly limited, for example, the sub-disk 140 may be torn or separated due to its thinness (small thickness), and the central portion 140Y of the sub-disk 140 is separated from the peripheral portion (i.e., the outer peripheral portion 140X). Then, due to the internal pressure of the exterior body 50, the safety cover 110 is displaced so as to be at least partially lifted, while the separated central portion 140Y of the sub-disk 140 remains connected to the protrusion 110T of the safety cover 110. In particular, the safety cover 110 is displaced so that the central portion 110Y of the safety cover 110 bends more outward (for example, bends in a bow shape), thereby reducing the pressure inside the battery. When a groove (for example, the portion designated by reference numeral "115" in the embodiment shown in FIG. 9) is provided in the safety cover 110, the groove can preferably act to deflect the safety cover 110. The groove 115 is provided on the surface of the safety cover 110 relatively outside the battery axis, near the peripheral portion 110Y' of the central portion.

[0067] The safety cover 110 and the outer peripheral portion 140X of the sub-disk 140 (particularly the outer peripheral portion 140X to which the conductive members 15 such as tabs and leads extending from the electrode assembly are still connected) are physically separated from each other. This cuts off the electrical connection between the external terminal 170 and the electrode assembly 10, and interrupts the path of current flowing between the electrode assembly 10 and the external terminal 170. By interrupting the current, gas generation inside the battery can be suppressed. During normal use, the safety cover 110 is electrically connected to the external terminal 170 that constitutes the external terminal of the secondary battery 1000.

[0068] As the internal pressure in the secondary battery 1000 increases further and the displacement of the safety cover 110 progresses, the safety cover 110 itself tears or breaks apart. The breaking point 115' of the safety cover 110 originates, for example, from the groove 115 of the safety cover 110. This allows communication between the inside and outside of the battery, opening the gas release path via the multiple openings 130K in the stripper disk 130. Gas accumulated inside the battery is released to the outside of the battery via the openings 130K. The internal pressure of the battery is further reduced.

[0069] First Embodiment The first embodiment of the present disclosure relates to a secondary battery 1000. The secondary battery 1000 will be described mainly with reference to Figs. 5 and 6 in addition to Figs. 1 to 4. Figs. 5(a) and 5(b) are cross-sectional views showing a gasket in the secondary battery according to the first embodiment. Fig. 6 is a schematic cross-sectional view showing a gasket in a conventional battery.

[0070] The gasket 20 is interposed between the exterior body 50 and the safety valve 100 and is disposed in the opening 51 of the exterior body 50. This prevents the electrolyte 30 from leaking out of the exterior body 50. More specifically, as shown in FIG. 5 , the gasket 20 fills the space between the inner surface of the exterior body 50 and the outer surface of the safety valve 100 so as to cover the ends of the safety valve 100 (the outer peripheral portion 110X of the safety cover 110 and the outer peripheral portion 170X of the external terminal 170). This isolates the interior of the secondary battery 1000 (the battery assembly 10 and the electrolyte 30) from the external environment. At the ends of the safety valve 100 (the outer peripheral portion 110X of the safety cover 110 and the outer peripheral portion 170X of the external terminal 170), the end face of the safety cover 110 (the outer peripheral portion 110X) and the end face of the external terminal 170 (the outer peripheral portion 1670X) are flush with each other.

[0071] The gasket 20 has a first gasket 21 and a second gasket 23. The gasket 20 is an integrated member in which two members (the first gasket 21 and the second gasket 23) form an interface (contact surface 25). In other words, the gasket 20 is a gasket composite having the first gasket 21 and the second gasket 23. The first gasket 21 and the second gasket 23 form the contact surface 25. The second gasket 23 contacts the end face of the second gasket 21 and is located above the first gasket 21 in the stacking direction. As shown in FIG. 5(b), the contact surface 25 between the first gasket 21 and the second gasket 23 is located on a first imaginary plane (indicated by a dashed line in FIG. 5(b)) extending upward from the end face of the external terminal 170 (the outer peripheral portion 170X) in a cross-sectional view, or is located outside the first imaginary plane, and on a second imaginary plane (indicated by a dashed line in FIG. 5(b)) extending from the lower main surface of the safety cover 110 (the outer peripheral portion 110X) in the direction of extension of the lower main surface, or is located above the second imaginary plane. Note that the contact surface is not limited to the contact surface 25 shown in FIG. 5(a) as long as it is located in the region defined by the first imaginary plane and the second imaginary plane (see FIG. 5(b)). For example, the contact surface may be contact surfaces 25a to 25d as shown in a second embodiment described later (see FIGS. 11(a) to 11(d)). Furthermore, in a cross-sectional view, contact surface 25 is located more inward than one end of exterior body 50. Furthermore, contact surface 25 has a linear shape parallel to the radial direction in a cross-sectional view.

[0072] In a cross-sectional view, the ratio of the first cross-sectional area of ​​the first gasket 21 to the second cross-sectional area of ​​the second gasket 23 (first cross-sectional area:second area) is, for example, 4:6 to 6:4. The ratio (first cross-sectional area:second area) is determined as follows: An image of a cross section of the secondary battery 1000 is captured using an optical microscope. The first cross-sectional area of ​​the first gasket 21 and the second cross-sectional area of ​​the second gasket 23 in the image of the cross section are obtained. The ratio (first cross-sectional area:second area) is calculated from the obtained first cross-sectional area and second cross-sectional area. The cross-sectional area is a surface formed by cutting the secondary battery 1000 along a plane that includes and is parallel to the central axis.

[0073] During storage and operation of the secondary battery 1000, the contact surface 25 between the exterior body 50 and the gasket 20 can become a leakage path 52 for the electrolyte. Here, if the gasket 20 is sufficiently filled in the spaces between the inner surface of the exterior body 50 and the outer surfaces (end faces and upper main surfaces) of the external terminal 170 and the outer surface (end faces and lower main surfaces) of the safety cover 110 (i.e., if the gasket 20 is filled at a high filling rate), as shown in FIG. 5(a), the electrolyte leakage path 52 corresponds to the inner surface of the exterior body 50 and is longer than the electrolyte leakage path 52z shown in FIG. 6 (described later). Therefore, the electrolyte 30 is less likely to leak to the outside of the secondary battery 1000 via the electrolyte leakage path 52. In other words, the occurrence of false leakage is suppressed. Note that the electrolyte leakage path 52 in FIG. 5(a) is exaggerated for ease of explanation. Specifically, it is depicted as an "arrow" indicating the direction of movement of the electrolyte 30. The same applies to the electrolyte leakage path 52z in FIG.

[0074] In contrast, as shown in FIG. 6 , in a conventional secondary battery, when the gasket 20 is not sufficiently filled in the space between the inner surface of the exterior body 50 and the outer surface of the external terminal 170 and the safety cover 110 (in other words, when the filling rate of the gasket 20 is not high), such as when a gap exists between the inner surface of the exterior body 50 and the gasket 20 and electrolyte 30 (isolated electrolyte 31) is present in the gap, electrolyte leakage path 52z is the interface between the isolated electrolyte 31 and the gasket 20z and is shorter than electrolyte leakage path 52. Therefore, when the filling rate of the gasket 20 is not high, isolated electrolyte 31 is likely to leak to the outside through electrolyte leakage path 52z.

[0075] In the manufacture of the secondary battery 1000 (described in detail below), the second gasket 23 is crimped, and the safety cover 110 and external terminal 170 are crimped to the opening 51 of the exterior body 50 via the gasket 20. During this process, the second gasket 23 deforms and interposes itself between the exterior body 50 and the external terminal 170 and safety cover 110, sealing them. If the contact surface 25 of the gasket 20 is within the above-described range shown in FIG. 5(b), stress applied as the gasket 20 deforms is unlikely to be applied to the contact surface 25, and the contact surface 25 is maintained even after crimping. For example, if the contact surface 25 is outside the above-described range (e.g., Comparative Examples 1 to 3 shown in FIGS. 12(a) to 12(c) below), the first gasket 21 and the second gasket 23 separate after crimping, and the contact surface 25 cannot be maintained, or only a small amount of contact surface remains. As a result, gaps are formed into which the electrolyte 30 can enter, and leakage of the electrolyte 30 cannot be sufficiently prevented.

[0076] If contact surface 25 is outside the above range, when external stress is applied to second gasket 23 to deform it during the manufacturing of secondary battery 1000, which will be described later, part of the external stress remains inside gasket 20, and this remaining stress (residual stress) is likely to act on contact surface 25 that is outside the above range. This makes it difficult to form contact surface 25 of gasket 20, making it difficult to sufficiently improve the filling rate of gasket 20, and causing voids.

[0077] 7 and 8, leakage due to isolated electrolyte 31 will be further described. Fig. 7 is a schematic model diagram showing an ideal battery system in secondary battery 1000 according to the first embodiment. Fig. 8 is a schematic model diagram showing a conventional battery system.

[0078] As shown in FIGS. 7 and 8 , a battery system such as a secondary battery 1000 or a (conventional) secondary battery 1000z is configured, for example, by electrically connecting an exterior body 50 to a battery assembly 10 via a conductive member 15. In such a battery system, when the exterior body 50 is configured with a metal substrate 53 and a plating layer 55 covering the surface thereof, the metal substrate 53 of the exterior body 50 may have an exposed portion 53b exposed to the electrolyte 30 (middle of the left side in FIGS. 7 and 8 ). Such an exposed portion may be generated, for example, when the exterior body 50 is deformed to form a crimping portion or a beading portion 57. Because the exposed portion 53b forms a battery system that is electrically connected to the battery assembly 10 and in contact with the same electrolyte 30, dissolution of the metal substrate 53 can be suppressed by adjusting the magnitude relationship of the ionization tendencies between the metals constituting the battery assembly 10 and the metal substrate 53, respectively.

[0079] In a conventional battery system, if there is a gap between the inner surface of the exterior body 50 and the outer surface of the gasket 20, where isolated electrolyte 31 exists, and the metal substrate 53 of the exterior body 50 has an exposed portion 53a exposed to the isolated electrolyte 31 (upper left side in Figure 8), the isolated electrolyte 31 is isolated from the electrolyte 30 by the gasket 20 and forms a separate system in contact with the metal substrate 53 and the plating layer 55. In this separate system, the metal substrate 53 may dissolve depending on the combination of metals constituting the metal substrate 53 and the plating layer 55 (the relationship between the magnitude of the ionization tendencies of these metals). If the metal substrate 53 dissolves, localized damage such as pinholes may occur, causing the electrolyte to leak from the exterior body 50 to the outside of the secondary battery 1000. Alternatively, the dissolution of the metal substrate 53 may reduce the thickness of the metal substrate 53, reducing the strength of the exterior body 50 and making the exterior body 50 more susceptible to damage due to the application of external stress.

[0080] In contrast, in the battery system of the first embodiment, as shown in FIG. 7, even if the metal substrate 53 of the exterior body 50 is exposed to the gasket 20, the filling rate of the gasket 20 in the space between the inner surface of the exterior body 50 and the outer surface of the external terminal 170 is high. Therefore, isolated electrolyte 31 is unlikely to exist, and the above-mentioned separate system is unlikely to form as in conventional battery systems. As a result, the strength of the exterior body 50 is unlikely to decrease, and breakage is unlikely to occur. In this way, in the secondary battery 1000 according to the first embodiment, leakage of electrolyte is sufficiently suppressed.

[0081] As described above, the battery system of the first embodiment sufficiently suppresses electrolyte leakage, allowing the use of materials that would have been difficult to adopt in conventional battery systems due to the reduction in strength of the exterior body 50 caused by elution from the exterior body 50. For example, the exterior body 50 may have a metal substrate 53 containing a first metal and a plating layer 55 formed on the inner surface of the metal substrate 53 and made of a second metal having a lower ionization tendency than the first metal. Here, for example, the first metal is Fe and the second metal is Ni. As such, the battery system of the first embodiment does not impose as strict restrictions on the material of the exterior body 50 as conventionally. Therefore, the secondary battery 1000 of the first embodiment offers greater design freedom in terms of the material of the exterior body 50.

[0082] The second gasket 23 includes a thermoplastic resin. Examples of such thermoplastic resins include polybutylene terephthalate (PBT). The first gasket 21 may also include a thermoplastic resin. In one embodiment, the first gasket 21 may include a thermosetting resin or may consist solely of a thermosetting resin. Examples of such thermosetting resins include thermosetting epoxy resins, and more preferably curable epoxy resins with a heat resistance temperature of 400°C or higher. When the first gasket 21 includes a thermosetting resin, it has high heat resistance even when internal stress is present, making it easy to maintain its shape. Additionally, when the first gasket 21 includes a thermosetting resin, it has high heat resistance and is therefore less likely to break even in an abnormal event where a large current flows through the first gasket 21 (i.e., gasket short-circuiting is less likely to occur). Thus, when the first gasket 21 includes a thermosetting resin, it can stably maintain its shape. The reason why first gasket 21 can contain thermosetting resin is that first gasket 21 does not need to be deformed in the manufacture of secondary battery 1000. In the manufacture of secondary battery 1000, second gasket 23 is deformed, and safety valve 100 and external terminal 170 are provided in opening portion 51 of exterior body 50 via gasket 20 by crimping.

[0083] In the secondary battery 1000 according to the first embodiment, the first gasket 21 contacts the lower main surface of the safety cover 110 but does not contact the upper main surface of the external terminal 170. The first gasket 21 contacts the end surfaces of the safety cover 110 and the external terminal 170, but does not have to contact the end surface of the external terminal 170. The second gasket 23 contacts the upper main surface of the external terminal 170 but does not contact the lower main surface of the safety cover 110. The first gasket 21 contacts the end surface of the external terminal 170 but does not contact the end surface of the safety cover 110, but may also contact the end surface of the safety cover 110.

[0084] (Secondary battery manufacturing method) An exemplary method for manufacturing the secondary battery 1000 will be described below. The secondary battery 1000 can be manufactured, for example, by the following procedure.

[0085] - Electrode fabrication - To fabricate the positive electrode 11, a positive electrode active material is mixed with, as needed, a positive electrode binder and a positive electrode conductor to obtain a positive electrode mixture. The positive electrode mixture is then dispersed in an organic solvent or the like to obtain a paste-like positive electrode mixture slurry. The positive electrode mixture slurry is then applied to one or both sides of a positive electrode current collector, and the positive electrode mixture slurry is dried to form a positive electrode active material layer. The positive electrode active material layer may then be compression-molded using a roll press or the like, as needed. In this case, the positive electrode active material layer may be heated, or the compression molding may be repeated multiple times. The negative electrode 12 can be fabricated in a similar manner. Specifically, a negative electrode active material is mixed with a negative electrode binder, a negative electrode conductor, and the like to obtain a negative electrode mixture, and the negative electrode mixture is then dispersed in an organic solvent or the like to obtain a paste-like negative electrode mixture slurry. Next, the negative electrode mixture slurry is applied to one or both surfaces of the negative electrode current collector, and the negative electrode mixture slurry is dried to form a negative electrode active material layer. Thereafter, if necessary, the negative electrode active material layer is compression-molded using a roll press or the like.

[0086] -assembly- When assembling the secondary battery 1000, a positive electrode lead is connected to a positive electrode current collector using a welding method or the like, and a negative electrode lead is connected to a negative electrode current collector using a welding method or the like. Next, the positive electrode 11 and the negative electrode 12 are stacked with a separator 13 interposed therebetween, and the positive electrode 11, the negative electrode 12, and the separator 13 are wound to form a wound electrode body as the electrode assembly 10. Next, a center pin is inserted into the winding space of the wound electrode body. Then, the wound electrode body is sandwiched between a pair of insulating plates and housed together with the pair of insulating plates inside the exterior housing 50. In this case, for example, one end of the positive electrode lead (conductive member 15) is connected to the safety valve 100 using a welding method or the like, and one end of the negative electrode lead is connected to the exterior housing 50 using a welding method or the like. Next, an electrolyte solution 30 is injected into the interior of the exterior housing 50, and the wound electrode body as the electrode assembly 10 is impregnated with the electrolyte solution 30.

[0087] The formation of the caulking will be further described with reference to Fig. 10. Fig. 10 is a view for explaining the method for manufacturing the secondary battery according to the first embodiment. After the wound electrode body is housed inside the exterior body 50, and before the safety valve 100 and external terminal 170 are placed, the first gasket 21 and the second gasket 23, before application of external stress, are placed near the opening 51 of the exterior body 50. At this stage, the gasket 20, which is composed of the placed first gasket 21 and second gasket 23, has a substantially L-shape in cross section. Next, the safety valve 100 and external terminal 170 are placed so as to be supported by the gasket 20. As shown in FIG. 10 , stress (e.g., stress in the direction indicated by the curved arrow in FIG. 10 ) is applied to the exterior body 50 and the second gasket 23 near the opening 51 of the exterior body 50 to form a crimped portion 59. In this way, a crimp is formed. At the same time, stress (e.g., stress in the direction indicated by the straight arrow in FIG. 10 ) is applied to form a beading portion 57. In this manner, the safety valve 100 (safety cover 110 and external terminal 170) is provided so as to be disposed in the opening at one end side of the exterior body 50, and the secondary battery 1000 is manufactured.

[0088] Second Embodiment The battery according to the second embodiment has a different contact surface (more specifically, a different position and / or shape) than the secondary battery 1000 according to the first embodiment. This different configuration will be mainly described below. In the second embodiment, the same reference numerals as those in the first embodiment have the same configuration as those in the first embodiment, and therefore, in principle, the description thereof will be omitted.

[0089] The contact surfaces in the second embodiment will be described below with reference to FIG. 11. The contact surfaces 25 of the secondary battery 1000 according to the first embodiment were linear and parallel to the radial direction. In contrast, the contact surfaces of the secondary battery according to the second embodiment may be linear, with the contact surfaces 25a and 25d forming a predetermined angle (greater than 0° and less than 180°: more specifically, approximately 20° or 90°) with the radial direction in a cross-sectional view, as shown in FIGS. 11(a) and 11(d). Furthermore, as shown in FIGS. 11(b) and 11(c), the contact surfaces 25b and 25c may have one or more bending points (more specifically, they may be V-shaped or zigzag-shaped) when viewed from the stacking direction. When contact surfaces 25b, 25c have one or more bending points, the area of ​​the contact surfaces increases compared to contact surface 25 in the first embodiment (because the length of the line indicating the contact surface increases in FIGS. 11(b) and 11(c)), making it difficult for electrolyte 30 to pass through the contact surfaces, thereby further suppressing leakage of electrolyte 30. Furthermore, when contact surfaces 25b, 25c have one or more bending points, contact surfaces 25b, 25c are less likely to shift even when unintended external stress is applied in the radial direction, thereby further suppressing leakage of electrolyte 30.

[0090] Third Embodiment The secondary battery according to the third embodiment differs from the secondary battery 1000 according to the first embodiment in the structure of the safety valve and the end of the external terminal. This different configuration will be mainly described below. In the second embodiment, the same reference numerals as those in the first embodiment have the same configuration as those in the first embodiment, and therefore, in principle, the description thereof will be omitted.

[0091] A secondary battery according to the third embodiment will be described with reference to Fig. 13. Fig. 13 shows the cross-sectional shape of a gasket in the secondary battery according to the third embodiment. As shown in Fig. 13, at the end of the safety valve 100, the lower main surface of (the outer peripheral portion 110iX of) the safety cover 110 that comes into contact with the gasket 20i extends to provide a curve and covers the end face and upper surface of (the outer peripheral portion 170X of) the external terminal 170. In other words, the gasket 20i covers the end of the safety valve 100 so as to have two curved portions in the vertical direction in cross-section (more specifically, so that the two curved portions form a U-shape).

[0092] In the third embodiment, leakage of the electrolyte solution 30 is further suppressed. The reason for this is presumed to be as follows, without being bound by any particular theory. The lower surface of the safety cover 110 (of the outer peripheral portion 110iX) extends to provide a curve and covers the end surface and upper surface of the external terminal 170 (of the outer peripheral portion 170X). In other words, the end of the safety cover 110i (i.e., the lower main surface of the outer peripheral portion 110iX of the safety cover 110) that contacts the inner peripheral surface of the gasket 20i is curved. Therefore, when applying external stress to the second gasket 23i to deform it during manufacturing of the secondary battery 1000i, the external stress is less likely to be applied locally to the second gasket 23i. Therefore, the second gasket 23i is more likely to deform along the shape of the end. As a result, gaps are less likely to occur between the inner peripheral surface of the second gasket 23i and the outer peripheral surface of the end of the safety valve 100 (the lower main surface of the outer peripheral portion 110iX of the safety cover 110). In this way, the filling rate of the gasket 20i can be improved. It is believed that this can further suppress leakage of the electrolyte 30.

[0093] In a more preferred embodiment, the radius of curvature of the safety cover 110i (of the lower main surface of the outer circumferential portion 110iX) is 80% to 120%, or 80% to 100%, of the radius of curvature of the outer surface of the gasket 20i that comes into contact with the inner surface of the outer casing 50 at the first curved portion that is located relatively higher of the two curved portions. If the radius of curvature of safety cover 110i is 80% to 100% of the radius of curvature of gasket 20i, then during the manufacture of secondary battery 1000i, external stress is less likely to be applied locally to second gasket 23i, and second gasket 23i is more likely to deform along the shape of the end of safety valve 100. As a result, a gap is less likely to occur between the inner circumferential surface of second gasket 23i and the outer circumferential surface of the end of safety valve 100 (the lower main surface of outer circumferential portion 110iX of safety cover 110).

[0094] Furthermore, when the second gasket 23i is deformed by applying an external stress during the manufacture of the secondary battery 1000i, the second gasket 23i can be deformed as a whole. This allows the second gasket 23i to easily deform along the inner circumferential surface of the exterior body 50. A gap is less likely to occur between the outer circumferential surface of the second gasket 23i and the inner circumferential surface of the exterior body 50.

[0095] In this way, second gasket 23i can deform overall to conform to the members that it contacts on its inner and outer circumferential surfaces, making it less likely for gaps to form between it and the members that it contacts, thereby improving the filling rate of gasket 20. Therefore, in this case, it is believed that leakage of electrolyte 30 can be further suppressed.

[0096] In the third embodiment, the first gasket 21i and the second gasket 23i are in contact with the outer surface of the safety cover 110i (i.e., the lower main surface of the outer periphery 110iX of the safety cover 110i), and are not in contact with the external terminal 170. Note that in the third embodiment, the lower main surface of (the outer periphery 110iX of) the safety cover 110i includes not only the lower main surface facing vertically downward, as shown in Fig. 13, but also the surface that extends to form a curve, and the surface near the end face of the safety cover 110i that faces vertically upward as a result of extending.

[0097] Although the embodiments of the present disclosure have been described above, they are merely typical examples. Therefore, it will be readily understood by those skilled in the art that the present invention is not limited to these and that various modifications are possible.

[0098] <Other embodiments> In the first to third embodiments, the shape of the contact surface between the first gasket and the second gasket is a shape formed by straight lines in a cross section parallel to the battery axis (specifically, a straight line, a V-shape, or a concave-convex (zigzag) shape), but is not limited thereto. The contact surface may be formed by curves only (more specifically, a U-shape) or by a combination of straight lines and curves.

[0099] In the first to third embodiments, the shape of the contact surface between the first gasket and the second gasket is uniform in the circumferential direction, but is not limited to this. For example, the contact surface may be continuous in the circumferential direction and may vary in the circumferential direction as long as it is located on a first imaginary plane extending upward from the end face of the external terminal 170 or on the outer side of the first imaginary plane in a cross-sectional view, and on a second imaginary plane extending from the lower main surface of the safety cover in the direction of extension of the lower main surface or above the second imaginary plane.

[0100] Moreover, the second embodiment and the third embodiment may be combined.

[0101] The battery of the present disclosure has the following features. <1> The safety valve includes an exterior body having an opening at one end thereof, a safety valve disposed at the opening, and a gasket disposed between the exterior body and the safety valve, the safety valve includes a safety cover and an external terminal stacked on the safety cover and positioned above the safety cover in a stacking direction; the gasket has a first gasket and a second gasket that contacts an end surface of the first gasket and is positioned on the first gasket in a stacking direction, and covers an end of the safety valve; a secondary battery in which the contact surface between the first gasket and the second gasket is located, in a cross-sectional view, on a first imaginary plane extending upward from an end face of the external terminal or outside the first imaginary plane, and is located on a second imaginary plane extending from a lower main surface of the safety cover in the extension direction of the lower main surface or above the second imaginary plane. <2> At the end of the safety valve, the end surface of the external terminal and the end surface of the safety cover are flush with each other. <1> The secondary battery according to claim 1. <3> In cross section, the contact surface has an inflection point. <1> or <2> The secondary battery according to claim 1. <4> At the end of the safety valve, the lower main surface of the safety cover that comes into contact with the gasket extends to have a curve and covers the end surface and the upper main surface of the external terminal. <1> ~ <3> 10. The secondary battery according to claim 9, wherein the second electrode is a conductor. <5> the gasket covers the end of the safety valve so as to have two curved portions in the up-down direction in a cross-sectional view, The radius of curvature of the safety cover is 80% to 100% of the radius of curvature of the outer surface of the gasket that comes into contact with the inner surface of the exterior body at a first curved portion that is located relatively higher of the two curved portions. <4> The secondary battery according to claim 1. <6> the second gasket contacts the upper main surface of the external terminal; <1> ~ <3> 10. The secondary battery according to claim 9, wherein the second electrode is a conductor. <7> The first gasket contacts the lower main surface of the safety cover. <1> ~ <6> 10. The secondary battery according to claim 9, wherein the second electrode is a conductor. <8> In a cross-sectional view, the contact surface is located inside the one end of the exterior body. <1> ~ <7> 10. The secondary battery according to claim 9, wherein the second electrode is a conductor. <9> The gasket is a gasket composite having the first gasket and the second gasket. <1> ~ <8> 10. The secondary battery according to claim 9, wherein the second electrode is a conductor. <10> In a cross-sectional view, the ratio of the first cross-sectional area of ​​the first gasket to the second cross-sectional area of ​​the second gasket (first cross-sectional area: second cross-sectional area) is 4:6 to 6:4. <1> ~ <9> 10. The secondary battery according to claim 9, wherein the second electrode is a conductor. <11> The first gasket includes a thermosetting resin. <1> ~ <10> 10. The secondary battery according to claim 9, wherein the second electrode is a conductor. <12> The exterior body has a base material including a first metal and a plating layer including a second metal having a lower ionization tendency than the first metal, the plating layer covering the inner surface of the base material. <1> ~ <11> 10. The secondary battery according to claim 9, wherein the second electrode is a conductor. <13> The exterior body has a beading portion protruding inward from its outer surface. <1> ~ <12> 10. The secondary battery according to claim 9, wherein the second electrode is a conductor. <14> A cylindrical, button, or coin type secondary battery. <1> ~ <13> 10. The secondary battery according to claim 9, wherein the second electrode is a conductor. [Example]

[0102] The present invention will be described in more detail below using examples, but the present disclosure is not limited to the following examples.

[0103] Example 1 [1. Preparation of test battery] A secondary battery having the following specifications was prepared. Table 1 summarizes the configuration of Example 1. Shape: Cylindrical (diameter: approx. 22 cm, axial length: approx. 70 mm) Positive and negative electrodes of the electrode assembly: Positive and negative electrodes capable of absorbing and releasing lithium ions ·Nominal capacity: approx. 4100mAh Nominal voltage: 3.6V Safety valve: Consists of a safety cover, disc holder, stripper disc and sub-disc

[0104] (Materials of each component) Safety cover: Made of metal (metal containing aluminum) Disc holder: Thermoplastic resin (polypropylene (PP)) Sub-disk: Made of metal (metal containing aluminum) Exterior: Metal (Fe) with a coating layer (Ni plating layer) on the inside First gasket: Made of thermosetting resin Second gasket: Thermoplastic resin

[0105] The battery element was housed in the exterior body, and a beading portion was formed. A first gasket was placed in the beading portion, and a safety valve and a top cover were placed on the first gasket. A second gasket was then placed on the first gasket. As shown in Figure 10, the safety valve and the outer periphery of the second gasket were crimped together. In this manner, a battery was fabricated.

[0106] As shown in FIG. 5(a), the contact surface between the first gasket and the second gasket of the battery of Example 1 was linear and parallel to the radial direction when viewed from the stacking direction.

[0107] [2. Judgment method] (2-1. Contact surface position) The fabricated battery was cut along the battery axis to form a cut surface of the gasket, and the cut surface of the obtained gasket was photographed using an optical microscope. The obtained images of the cut surfaces were visually observed. From the observation results, the position of the contact surface between the first gasket and the second gasket was judged based on the following criteria. The judgment results are summarized in Table 1. (Judgment criteria) A: The contact surface between the first gasket and the second gasket is located on a first imaginary plane extending upward from the end face or on the outer side of the first imaginary plane in a cross-sectional view, and is located on a second imaginary plane extending from the lower face of the safety cover in the extension direction of the main face or above the second imaginary plane. B: The contact surface between the first gasket and the second gasket does not satisfy at least one of the following conditions in cross section: on a first imaginary plane extending upward from the end face or located outside the first imaginary plane; and on a second imaginary plane extending from the bottom face of the safety cover in the extension direction of the main face or located above the second imaginary plane.

[0108] (2-2. Cross-sectional shape of contact surface) The shape of the contact surface was visually observed from the image of the cut surface obtained in the determination of (2-1. Position of the contact surface). The observation results are summarized in Table 1. It should be noted that the drawings in the annotations for Table 1 are diagrams showing the contact surfaces in the design drawings. Specifically, the contact surfaces in Examples 1 to 5 were almost identical to those in the design drawings, but as will be shown in the evaluation of (3-1. Sealing performance) described below, the contact surfaces in Comparative Examples 1 to 3 were significantly different from those in the design drawings, with the first gasket and second gasket separating and no contact surface being formed in either case.

[0109] [Table 1]

[0110] [3. Evaluation Method] (3-1.Sealability) An optical microscope was used to observe the image of the cut surface obtained in (2-1. Position of contact surface). From the observation results, the sealing ability of the gasket for the secondary battery was evaluated based on the following evaluation criteria. (Sealing performance evaluation criteria) Good: The first and second gaskets are in contact and there is a contact surface. × (bad): The first and second gaskets are separated, creating a gap and no contact surface.

[0111] (3-2. Assembly) In the battery manufacturing method, the ease of assembly of the battery was evaluated based on the following evaluation criteria to determine whether the work of placing the safety cover and top cover (external terminals) on the gaskets (first gasket and second gasket) before crimping could be carried out smoothly. (assembly evaluation criteria) Good: The gasket is L-shaped in cross section before crimping, and the safety cover and top cover can be placed on the gasket from the stacking direction. × (bad): The shape of the gasket before crimping is U-shaped in cross section, and the safety cover and top cover cannot be placed on the gasket from the stacking direction, and must be placed on the gasket from the radial direction.

[0112] (3-3. Gasket filling ability) An optical microscope was used to observe the image of the cut surface obtained in (2-1. Position of contact surface). From the observation results, the gasket filling property of the secondary battery using the gasket was evaluated based on the following evaluation criteria. (Gasket filling performance evaluation criteria) ◯ (Good): There is no gap between the gasket and the inner surface of the exterior body, or the gap is smaller than the gap observed on the cut surface of Comparative Example 4, and there are no cracks or fractures in the gasket. × (bad): A gap exists between the gasket and the inner surface of the exterior body, and the area of ​​the gap is equal to or larger than that of Comparative Example 4, or a crack or break exists in the gasket.

[0113] (3-4. Overall evaluation) The batteries were comprehensively evaluated for electrolyte leakage prevention based on the evaluation results of sealing property and gasket filling property, and the evaluation criteria are shown in Table 1. (Evaluation criteria for overall evaluation of electrolyte leakage prevention) 〇 (Good): The evaluation results for sealing and gasket filling were both 〇 (good). × (bad): At least one of the evaluation results for sealing and gasket filling was × (bad).

[0114] <Examples 2 to 5 and Comparative Examples 1 to 3> In Examples 2 to 5 and Comparative Examples 1 to 3, batteries were fabricated in the same manner as in Example 1, except that the battery configuration (shapes of the first gasket and second gasket) was changed. Specifically, the shapes of the first gasket and second gasket in Examples 2 to 5 were as shown in Figures 11(a) to 11(d), respectively. The shapes (design shapes) of the first gasket and second gasket in Comparative Examples 1 to 3 were as shown in Figures 12(a) to 12(c), respectively. The actual gasket shapes in Comparative Examples 1 to 3 did not allow for good contact surfaces.

[0115] <Comparative Example 4> In Comparative Example 4, except for changing the configuration of the battery (changing to a gasket in which the first gasket and the second gasket were integrated), a battery was fabricated in the same manner as in Example 1. The shape of the gasket in Comparative Example 4 was the shape shown in Fig. 12(d).

[0116] <Result> Examples 1 to 5 In the secondary batteries of Examples 1 to 5, the gasket was composed of a first gasket and a second gasket, and the contact surfaces of the first gasket and the second gasket were located on a first imaginary plane extending upward from the end face or outside the first imaginary plane in a cross-sectional view, and on a second imaginary plane extending from the lower face of the safety cover in the extension direction of the main face or above the second imaginary plane, as shown in Table 1. In other words, the secondary batteries of Examples 1 to 5 were secondary batteries encompassed within the scope of the invention according to claim 1 of the present application. Furthermore, as shown in Table 1, the secondary batteries of Examples 1 to 5 all received evaluations of sealing property and gasket filling property as ◯ (good), and the overall evaluation was ◯ (good).

[0117] (Comparative Examples 1 to 4) In the secondary batteries of Comparative Examples 1 to 3, as shown in Table 1, the contact surfaces of the first gasket and the second gasket were not located on a first imaginary plane extending upward from the end face or outside the first imaginary plane in a cross-sectional view, or on a second imaginary plane extending from the lower face of the safety cover in the extension direction of the main face or above the second imaginary plane. In the secondary battery of Comparative Example 4, as shown in Table 1, the gasket was composed of a single member and was not composed of a first gasket and a second gasket. In other words, the secondary batteries of Comparative Examples 1 to 4 were secondary batteries outside the scope of the invention according to claim 1 of the present application. In the secondary batteries of Comparative Examples 1 to 4, the evaluation results for either the sealing property or the gasket filling property were x (poor), and the overall evaluation was x (poor), as shown in Table 1. In the secondary battery of Comparative Example 4, a tear was present in the portion (shoulder) bent by the crimp of the second gasket.

[0118] From the above, it is clear that the batteries of Examples 1 to 5, which are included in the scope of the invention defined in claim 1, have better suppressed electrolyte leakage than the batteries of Comparative Examples 1 to 4, which are outside the scope of the invention defined in claim 1. [Industrial Applicability]

[0119] The battery according to the present disclosure can be used in applications that typically require the use of electrical energy. For example, the battery according to the present disclosure can be used in various fields where power storage is required. By way of example only, the battery according to the present disclosure can be used in the electrical, information, and communications fields where electrical and electronic devices are used (for example, the electrical and electronic devices or mobile device fields including mobile phones, smartphones, laptop computers and digital cameras, activity monitors, arm computers, electronic paper, wearable devices, and small electronic devices such as RFID tags, card-type electronic money, and smart watches), household and small industrial applications (for example, power tools, golf carts, and household, nursing care, and industrial robots), large industrial applications (for example, forklifts, elevators, and harbor cranes), transportation systems (for example, hybrid cars, electric cars, buses, trains, electrically assisted bicycles, and electric motorcycles), power system applications (for example, various power generation systems, road conditioners, smart grids, and general household installation-type power storage systems), medical applications (for medical devices such as earphone hearing aids), pharmaceutical applications (for example, medication management systems), as well as the IoT field and space and deep-sea applications (for example, space probes, submersible research vessels, and the like). [Explanation of symbols]

[0120] 10 Electrode assembly (battery element) 11 Positive electrode 12 Negative electrode 13 Separator 15 Conductive material 20, 20a~20d, 20i Gasket 21, 21a to 21d, 21i First gasket 23, 23a~23d, 23i Second gasket 25, 25a to 25d, 25i (contact surface between the first gasket and the second gasket) 30 Electrolyte 31 Isolated electrolyte 50 Exterior body (battery can, housing member) 51 Opening portion of exterior body (open end) 52 Electrolyte leakage path 53 Metal base material 53a (of the metal substrate exposed to the gasket) 53b (of the metal substrate exposed to the electrolyte) 55 plating layer 57 Beading section 59 Crimp section 100 Safety valve 110,110i safety cover 110T (Safety cover) protrusion 110X (Safety cover) outer periphery 110Y (Safety cover) center 110Y' (Safety cover) central edge 112 Z-fold part (of safety cover) 115 (Safety cover, especially its central part) groove 120 Disc Holder 120X (disc holder) outer periphery 120Y (disc holder) inner circumference 120Z (Disc holder) opening 130 Stripper disc 132 (Stripper disc) inner surface of center 140 subdisks 170 External terminal (battery cover, top cover, battery cover member) 1000 secondary battery

Claims

1. The safety valve includes an exterior body having an opening at one end thereof, a safety valve disposed at the opening, and a gasket disposed between the exterior body and the safety valve, the safety valve includes a safety cover and an external terminal stacked on the safety cover and positioned above the safety cover in a stacking direction; the gasket has a first gasket and a second gasket in contact with an end surface of the first gasket and positioned on the first gasket in a stacking direction, and covers an end of the safety valve; a secondary battery in which, in a cross-sectional view, a contact surface between the first gasket and the second gasket is located on a first imaginary plane extending upward from an end face of the external terminal or is located outside the first imaginary plane, and is located on a second imaginary plane extending from a lower main surface of the safety cover in the extension direction of the lower main surface or is located above the second imaginary plane.

2. The secondary battery according to claim 1 , wherein the end face of the external terminal and the end face of the safety cover are flush with each other at the end of the safety valve.

3. The secondary battery according to claim 1 , wherein the contact surface has a bending point in a cross-sectional view.

4. 2. The secondary battery according to claim 1, wherein the lower main surface of the safety cover that contacts the gasket at the end of the safety valve extends to provide a curve and cover the end face and upper main surface of the external terminal.

5. the gasket covers the end of the safety valve so as to have two curved portions in the up-down direction in a cross-sectional view, 5. The secondary battery according to claim 4, wherein the radius of curvature of the safety cover is 80% to 100% of the radius of curvature of the outer surface of the gasket that contacts the inner surface of the exterior body at a first curved portion that is located relatively higher of the two curved portions.

6. The secondary battery according to claim 1 , wherein the second gasket is in contact with an upper main surface of the external terminal.

7. The secondary battery according to claim 1 , wherein the first gasket is in contact with a lower main surface of the safety cover.

8. The secondary battery according to claim 1 , wherein the contact surface is located inside the one end of the exterior body in a cross-sectional view.

9. The secondary battery according to claim 1 , wherein the gasket is a gasket composite having the first gasket and the second gasket.

10. 3. The secondary battery according to claim 1, wherein, in a cross-sectional view, a ratio of a first cross-sectional area of ​​the first gasket to a second cross-sectional area of ​​the second gasket (first cross-sectional area:second area) is 4:6 to 6:

4.

11. The secondary battery according to claim 1 , wherein the first gasket includes a thermosetting resin.

12. 3. The secondary battery according to claim 1, wherein the exterior body has a base material containing a first metal and a plating layer containing a second metal having a lower ionization tendency than the first metal and covering an inner surface of the base material.

13. The secondary battery according to claim 1 or 2, wherein the exterior body has a beading portion that protrudes inward from an outer surface thereof.

14. 3. The secondary battery according to claim 1, which is a cylindrical, button, or coin type secondary battery.

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