Sealed battery

Abstract

The present disclosure provides a sealed battery in which both increased capacity and improved PTC element operability can be achieved while also having excellent sealing properties. A sealed battery according to the present disclosure comprises: a bottomed cylindrical battery case having an opening; an electrode body and an electrolyte solution accommodated in the battery case; and a sealing member that seals the opening of the battery case. In the sealing member, a terminal cap, a PTC element, and a bottom plate are arranged side by side in the above order, a peripheral edge part of the PTC element is located farther inward than a peripheral edge part of the terminal cap and a peripheral edge part of the bottom plate, the PTC element is in contact with the terminal cap and the bottom plate, the peripheral edge part of the terminal cap and the peripheral edge part of the bottom plate are laminated with an insulating layer interposed therebetween, and the open end of the battery case is formed by crimping the peripheral edge part of the terminal cap and the peripheral edge part of the bottom plate farther outward than the peripheral edge part of the PTC element, with a gasket interposed therebetween.

Description

Sealed battery

[0001] The present disclosure relates to a sealed battery.

[0002] Patent Document 1 proposes "a non-aqueous electrolyte battery comprising an outer can, an electrode body housed in the outer can and having a positive electrode, a separator, and a negative electrode wound in a spiral shape, a non-aqueous electrolyte housed in the outer can, and a sealing lid group having an explosion-proof function and terminals hermetically caulked by an insulating gasket at the upper end opening of the outer can, the sealing lid group including an inner lid body disposed opposite to the electrode body, a reinforcing plate disposed on the inner lid body via a valve film and sandwiched by an annular portion formed by bending the peripheral edge of the inner lid body inward, a PTC element disposed on the annular portion of the inner lid body, an outer lid body disposed with its peripheral portion abutting on the PTC element, and gas vent holes respectively opened in the inner lid body, the reinforcing plate, the PTC element, and the outer lid body, wherein each gas vent hole of the sealing lid group has an area of 0.15 to 1.2 cm per battery capacity (Ah). ２ The non-aqueous electrolyte battery is characterized in that it has an area of."

[0003] Patent Document 2 proposes "an organic electrolyte battery provided with a positive temperature coefficient resistance device forming a part of a conductive path between a power generation element and a terminal cap at a sealing portion of a battery case housing the power generation element, the positive temperature coefficient resistance device being sandwiched by two metal members having an outer diameter larger than that of the positive temperature coefficient resistance device, and a joint portion of the two metal members being adhesively fixed with an insulating adhesive having resistance to the organic electrolyte."

[0004] Japanese Patent Application Laid-Open No. 6-187957, Utility Model Laid-Open No. 2-32660

[0005] In recent years, in sealed batteries, an increasing demand for higher capacity has been growing. To increase the capacity, it is desirable to secure as much space as possible inside the battery case.

[0006] However, since the sealing members of conventional sealed batteries generally include a PTC element and an explosion-proof valve, the number of parts is large and the thickness is great. In that case, since the internal space of the battery case is limited, there is a limit to increasing the capacity.

[0007] Furthermore, as the capacity of sealed batteries increases, ensuring safety tends to become more difficult. Therefore, from the perspective of improving the safety of sealed batteries, it is also necessary to improve the operability of the PTC element.

[0008] However, if the sealing component has a large number of parts, the amount of heat conducted from the PTC element to the surroundings increases, requiring more heat to activate the PTC element. In other words, the more parts the sealing component has, the slower the PTC element will activate.

[0009] Furthermore, in conventional sealing components, the opening end of the battery case is crimped to the PTC element, and strong pressure is applied to the PTC element. PTC elements tend to have a delayed operation when pressurized. On the other hand, if the crimping pressure is reduced, the sealing performance of the battery case opening deteriorates.

[0010] One aspect of the present disclosure relates to a sealed battery comprising a bottomed cylindrical battery case having an opening, an electrode body and an electrolyte housed within the battery case, and a sealing member that seals the opening of the battery case, wherein a terminal cap, a PTC element, and a bottom plate are arranged in this order within the sealing member, the peripheral edge of the PTC element is positioned inward from the peripheral edge of the terminal cap and the peripheral edge of the bottom plate, the PTC element is in contact with the terminal cap and the bottom plate, the peripheral edge of the terminal cap and the peripheral edge of the bottom plate are laminated with an insulating layer in between, and the opening end of the battery case is crimped via a gasket so that the peripheral edge of the terminal cap and the peripheral edge of the bottom plate are outside the peripheral edge of the PTC element.

[0011] According to this disclosure, it is possible to provide a sealed battery that can achieve both high capacity and improved operability of the PTC element, while also having excellent sealing properties.

[0012] This is a cross-sectional view showing an example of a sealing member having a recess for housing a PTC element in the bottom plate. This is a cross-sectional view showing an example of a sealing member having a space for housing a PTC element in the terminal cap. This is a schematic cross-sectional view showing a lithium primary battery according to one embodiment of the present disclosure.

[0013] The embodiments of this disclosure will be described below with examples, but this disclosure is not limited to the examples described below. In the following description, specific numerical values ​​and materials may be given as examples, but other numerical values, materials, etc. may be applied as long as the effects of this disclosure are obtained. Notwithstanding, known components may be applied to components of parts that are characteristic of this disclosure. In this specification, when "the range of numerical values ​​A to numerical values ​​B" is used, that range includes numerical values ​​A and B.

[0014] In the following explanation, when examples are given of lower and upper limits for specific physical properties or conditions, any combination of either of the given lower limits and any of the given upper limits is permitted, as long as the lower limit does not exceed the upper limit. When multiple materials are given as examples, unless otherwise specified, one type may be selected and used alone, or two or more types may be used in combination.

[0015] This disclosure includes any combination of two or more claims that can be arbitrarily selected from the claims set forth in the attached claims. In other words, any combination of two or more claims that can be arbitrarily selected from the claims set forth in the attached claims is possible, as long as it does not result in a technical inconsistency.

[0016] [Sealed Battery] A sealed battery according to the embodiment of the present disclosure (hereinafter also referred to as "Sealed Battery (B)") comprises a bottomed cylindrical battery case having an opening, an electrode body (electrode group) and an electrolyte housed inside the battery case, and a sealing member that seals the opening of the battery case.

[0017] The sealing member comprises a terminal cap, a PTC (positive temperature coefficient) element, and a base plate. The outer diameter of the PTC element is smaller than the outer diameters of the terminal cap and the base plate, and the peripheral edge of the PTC element is positioned inward from the peripheral edges of the terminal cap and the base plate. The peripheral edges of the terminal cap and the base plate are laminated with an insulating layer in between.

[0018] The terminal cap, PTC element, and base plate are arranged in this order. The PTC element is sandwiched in the space between the terminal cap and the base plate and is in contact with both the terminal cap and the base plate. Specifically, one side of the PTC element is in contact with the area inside the periphery of the terminal cap, and the other side of the PTC element is in contact with the area inside the periphery of the base plate.

[0019] In the sealed battery (B), the open end of the battery case crimps the edges of the terminal cap and the bottom plate via a gasket, at a position outside the periphery of the PTC element. Therefore, no pressure is applied to the PTC element to seal the opening of the battery case. Even if the crimping pressure is sufficiently high, this does not cause a delay in the operation of the PTC element.

[0020] As described above, the sealing member of this disclosure has a simple structure without an explosion-proof valve. The sealing member consists of only four main components: a terminal cap, a PTC element, an insulating layer, and a bottom plate. Such a sealing member has a very small thickness, which allows for more space to be secured inside the battery case compared to a typical sealing member. Therefore, a large volume electrode body can be housed inside the battery case, making it possible to obtain a sufficiently high capacity.

[0021] On the other hand, in the sealing member of the sealed battery (B), the number of parts is small, the amount of heat conducted from the PTC element to the surroundings is limited, and no pressure is applied to the PTC element to seal the opening of the battery case, so the sensitivity of the PTC element to heat generation is increased. Therefore, if the temperature of the sealed battery (B) rises, the PTC element activates quickly to suppress any further rise in battery temperature. In other words, despite its high capacity, the sealed battery (B) is extremely safe.

[0022] In the sealing member of the sealed battery (B), a housing space for accommodating the PTC element is formed in the radial direction, in the area inside the peripheral edge of the terminal cap and the peripheral edge of the bottom plate, and a portion of the inner surface of this housing space is spaced apart from the PTC element. This configuration makes it possible to reduce the contact area between the PTC element housed in the housing space and the terminal cap or bottom plate. By reducing this contact area, it is possible to suppress the transfer of heat generated by the PTC element to the terminal cap or bottom plate when the PTC element generates heat, and the PTC element can be activated more quickly in the event of a malfunction.

[0023] A thin, explosion-proof section may be formed at the bottom of the battery case of the sealed battery (B). The thin, explosion-proof section is a thin section that functions as an explosion-proof mechanism (explosion-proof valve). The thin, explosion-proof section is configured to rupture when the internal pressure of the sealed battery (B) rises above a predetermined value. This thin, explosion-proof section ensures higher safety while maintaining the miniaturization of the sealing member compared to a sealed battery using a sealing member equipped with an explosion-proof section.

[0024] The PTC element of the sealed battery (B) may be annular (ring-shaped). An annular PTC element allows for a reduction in the contact area between the PTC element and the terminal cap and bottom plate. Therefore, the sensitivity of the PTC element to heat generation can be further increased.

[0025] The PTC element of the sealed battery (B) may be disc-shaped. In this case, the center of the bottom plate may be recessed toward the electrode body so that the center of the bottom plate becomes a non-contact portion with the PTC element. This reduces the contact area between the PTC element and the bottom plate, and further increases the sensitivity of the PTC element to heat generation. A part of the center of the terminal cap may be recessed toward the electrode body to form a non-contact portion with the PTC element.

[0026] The components of a sealed battery will be explained further below.

[0027] (Battery Case) The battery case is a bottomed cylindrical shape with an opening. The cross-sectional shape of the battery case is not particularly limited and may be elliptical or polygonal, but it is preferably circular.

[0028] The material of the battery case is not particularly limited and may include, for example, iron, iron alloys (including stainless steel), aluminum, aluminum alloys (such as alloys containing trace amounts of other metals such as manganese and copper).

[0029] Preferably, a thin, explosion-proof section is formed at the bottom of the battery case. In a sealed battery (B), the explosion-proof section can be formed in a predetermined shape on a part of the bottom of the battery case, extending from the outer surface to the inner surface. The explosion-proof section may be formed in a linear shape (such as a linear segment or arc) when the bottom of the battery case is viewed from the outer surface.

[0030] When a sealed battery (B) has a thin-walled explosion-proof section at the bottom of the battery case, the sealing member does not need to interpose a valve body that ruptures when the internal pressure of the sealed battery rises, or an annular spacer that supports the periphery of the valve body and restricts the rupture area to the center of the valve body, between the periphery of the terminal cap and the periphery of the bottom plate. Therefore, the thickness dimension of the sealing member can be reduced. This reduces the space occupied by the sealing member within the battery case and increases the space occupied by the electrode body. As a result, the battery capacity of the sealed battery (B) can be increased.

[0031] (Electrode Body) The electrode body is a wound type, constructed by winding a strip-shaped positive electrode and a strip-shaped negative electrode with a separator in between. The electrode body has a shape that corresponds to the shape of the battery case. If the battery case is cylindrical, the electrode body is usually cylindrical.

[0032] The positive electrode typically includes a positive electrode current collector and a positive electrode mixture attached to the positive electrode current collector. The positive electrode mixture contains a positive electrode active material. When the sealed battery is a lithium primary battery, manganese dioxide may be used as the positive electrode active material. As the positive electrode current collector, for example, expanded metal, net, or perforated metal made of stainless steel may be used.

[0033] The positive electrode mixture may contain optional components other than the positive electrode active material, such as a binder and a conductive agent. A resin material such as fluororesin may be used as the binder. A conductive material such as carbon material may be used as the conductive agent.

[0034] A negative electrode is made of metallic lithium (or a lithium alloy). For example, a strip-shaped sheet of metallic lithium or a lithium alloy can be used as the negative electrode. Examples of lithium alloys that can be used include Li-Al, Li-Mg, Li-Al-Mg, Li-Sn, Li-Ni-Si, and Li-Pb. Among these, Li-Al-Mg alloy is preferred.

[0035] When using a lithium alloy, the content of metal elements other than lithium in the lithium alloy is preferably 0.1% by mass or more and 5% by mass or less, from the viewpoint of ensuring sufficient discharge capacity and stabilizing internal resistance.

[0036] As a separator, for example, a microporous membrane or nonwoven fabric made of resin can be used. As a material for the separator, for example, polyolefin, polyamide, or polyamide-imide can be used. As a polyolefin, polyethylene (PE), polypropylene (PP), or laminates of PP and PE can be used.

[0037] (Electrolyte) When the sealed battery (B) is a lithium primary battery, a non-aqueous solvent in which a lithium salt is dissolved may be used as the electrolyte. Examples of non-aqueous solvents include propylene carbonate, ethylene carbonate, 1,2-dimethoxyethane, and γ-butyrolactone. Examples of lithium salts include lithium borofluoride, lithium hexafluoride phosphate, lithium trifluoromethanesulfonate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethylsulfonyl)imide.

[0038] (Sealing Member) As previously described, the sealing member comprises a terminal cap, a PTC element, an insulating layer, and a base plate. The terminal cap, for example, has a convex portion in the center and a flat peripheral portion extending from its outer edge. The base plate, for example, has a concave portion in the center and a peripheral portion extending from its outer edge. The peripheral portions of the terminal cap and the base plate are laminated with an insulating layer in between.

[0039] Preferably, the terminal cap, insulating layer, and bottom plate have shapes with generally matching outer diameters and are laminated so that their outer surfaces are flush. This improves the airtightness between the opening end of the battery case and the peripheral edge of the sealing member when the peripheral edge of the sealing member is crimped at the opening end of the battery case.

[0040] The material of the terminal cap and bottom plate is not particularly limited and includes, for example, iron, iron alloys (including stainless steel), aluminum, aluminum alloys, etc.

[0041] As the insulating layer, for example, an annular film or a sealant may be used. The annular film can be formed using, for example, an insulating resin. Examples of insulating resins include polypropylene resin, polyethylene resin, phenolic resin, and epoxy resin. Examples of sealants include rubber such as polybutadiene rubber and bronzed asphalt. The insulating layer may be formed as an annular layer by the sealant. When an annular film and a sealant are used in combination, the annular film may be attached to the peripheral edges of the terminal cap and the bottom plate, respectively, by the sealant.

[0042] In the sealed battery (B), the PTC element is housed in a space formed inside the peripheral edge of the terminal cap and the peripheral edge of the bottom plate. The PTC element is not disposed between the peripheral edge of the terminal cap and the peripheral edge of the bottom plate. The PTC element usually has a thickness several times larger than that of the insulating layer. Therefore, the sealed battery (B) can have a significantly smaller dimension in the thickness direction of the sealing member compared to a sealed battery in which the PTC element is disposed between the peripheral edge of the terminal cap and the peripheral edge of the bottom plate. As a result, in the battery case, the occupied space of the sealing member can be reduced, and the occupied space of the electrode body can be increased. Consequently, the battery capacity of the sealed battery can be increased.

[0043] In a conventional sealed battery, between the peripheral edge of the terminal cap and the peripheral edge of the bottom plate, in addition to the PTC element, there may be interposed a valve body that breaks when the internal pressure of the sealed battery rises, an annular spacer that supports the peripheral edge side of the valve body and restricts the breaking region to the central portion of the valve body, and the like. Further, by bending the outer edge side of the peripheral edge of the bottom plate inward, the valve body and the spacer may be held. In such a case, the sealing member becomes thick.

[0044] Between the peripheral edge of the terminal cap and the peripheral edge of the bottom plate, it is preferable that the insulating layer is in direct contact with the terminal cap and the bottom plate. In other words, it is preferable that only the insulating layer is interposed between the peripheral edge of the terminal cap and the peripheral edge of the bottom plate. In such a case, the dimension in the thickness direction of the sealing member can be further reduced.

[0045] (PTC element) The PTC element is also called a thermal resistance element and has the property that its electrical resistance increases as the temperature rises. For example, when an abnormal current flows through the sealed battery, the temperature of the PTC element rises due to heat generation, and accordingly, the resistance of the PTC element increases. Thereby, the current flowing through the sealed battery is decreased to suppress abnormal heat generation of the sealed battery. When the sealed battery (B) has an explosion-proof thin portion, abnormal heat generation of the sealed battery is suppressed before the explosion-proof thin portion cracks. The PTC element is preferably formed in a disk shape or an annular shape.

[0046] The PTC element may include a composite of a resin and conductive particles. The PTC element may have a structure in which such a composite layer is sandwiched between a pair of metal foils. As the resin, a polyethylene resin or the like can be used. As the metal foil, nickel, or a clad material of copper and nickel can be used. In such a PTC element, when the resin expands due to heat generation, the distance between the conductive particles dispersed in the resin increases, and the resistance of the composite (PTC element) increases.

[0047] The configuration of the PTC element is not particularly limited. For example, a ceramic-based PTC element may be used. For example, a PTC element mainly composed of barium titanate may be used.

[0048] Normally, in a sealed battery that is caulked and sealed at the opening end of the battery case together with a sealing member through a gasket, the PTC element is in a state of being pressed within the sealing member. Thus, when an abnormal current flows through the sealed battery in a state where the PTC element is pressed, the operation of the PTC element may be delayed due to the pressing from the gasket. Specifically, in the case of a PTC element including a composite of a resin and conductive particles, the resin becomes difficult to expand due to the pressing from the gasket, so the operation of the PTC element may be delayed. Also, in the case of a ceramic-based PTC element, due to the pressing from the gasket, a change such as a change in the crystal structure of barium titanate occurs, and the change from a ferromagnetic substance to a paramagnetic substance is suppressed, so the operation of the PTC element may be delayed.

[0049] On the other hand, in the sealed battery (B), the PTC element is disposed in a housing space formed inside the peripheral edge of the terminal cap caulked to the battery can and the peripheral edge of the bottom plate. Therefore, since the PTC element is sufficiently suppressed from being pressed by the gasket, the operability of the PTC element is not impaired.

[0050] The PTC element is in a state of being disposed in the above-described housing space, and a part of it is in contact with the terminal cap and the bottom plate. Thereby, when the sealed battery is normal, a conduction path between the terminal cap and the bottom plate can be ensured. On the other hand, when an abnormally large current flows through the sealed battery, the conduction path between the terminal cap and the bottom plate can be blocked.

[0051] In the sealed battery (B), the peripheral edges of the terminal cap and the base plate are laminated with an insulating layer in between. Therefore, the terminal cap and the base plate are electrically connected only by a conductive path via a PTC element. Consequently, by blocking the conductive path via the PTC element, the flow of current between the terminal cap and the base plate can be reliably suppressed.

[0052] The base plate is electrically connected to the terminal cap and one of the electrodes (positive or negative) of the electrode body. The base plate is connected, for example, to one of the electrodes of the electrode body via a lead member. In addition, the terminal cap and the base plate are electrically connected by a PTC element. In this way, one of the electrodes of the electrode body, the base plate, and the terminal cap are electrically connected.

[0053] Next, with reference to the drawings, the sealing member of the sealed battery according to the embodiment of this disclosure will be described.

[0054] In the sealed battery 100 shown in Figure 1, the terminal cap 21 of the sealing member 20 has a protrusion 21a in the center that functions as an external positive electrode terminal, and a flat peripheral portion 21b extending from its outer edge. The bottom plate 22 has a recess 22a in the center, and a peripheral portion 22b extending from its outer edge. Both the terminal cap 21 and the bottom plate 22 are circular in shape with the same outer diameter.

[0055] The recess 22a has a stepped portion 22c in the height direction (away from the terminal cap 21). The recess 22a is divided into a first region from the peripheral edge 22b of the bottom plate 22 to the stepped portion 22c and a second region. The first region forms a space for housing the PTC element 25, and the second region is spaced apart from the PTC element 25.

[0056] The first region forms a space for housing the PTC element 25, thereby preventing deformation of the PTC element 25 when the open end of the battery case 9 is crimped to the peripheral edge of the sealing member 20 via the gasket 26.

[0057] Because the second region is spaced apart from the PTC element 25, the contact area between the PTC element 25 and the bottom plate 22 can be reduced. Therefore, when an abnormal current flows inside the sealed battery 100 and heat is generated in the PTC element 25, excessive conduction of that heat to the bottom plate 22 can be suppressed. As a result, the operability of the PTC element 25 is further improved.

[0058] Furthermore, from the viewpoint of processability, weight, and cost, it is preferable that the recess in the bottom plate is formed by bending the plate material that will be used for the bottom plate. For this reason, the area of ​​the lower surface of the bottom plate 22 (the surface facing the electrode body) that overlaps with the recess 22a may be convex toward the electrode body.

[0059] The open end of the battery case 9 is crimped to the peripheral edge 21b of the terminal cap 21 and the peripheral edge 22b of the bottom plate 22 via a gasket 26. This seals the opening of the battery case 9.

[0060] The peripheral edge 21b of the terminal cap 21 and the peripheral edge 22b of the base plate 22 are laminated with an insulating layer 27 in between. The PTC element 25 is sandwiched between the peripheral edge 21b of the terminal cap 21 and the stepped portion 22c of the base plate 22. That is, the PTC element 25 is in contact with the terminal cap 21 and the base plate 22, and this contact forms a conductive path between the terminal cap 21 and the base plate 22.

[0061] The PTC element 25 is a flat, disc-shaped material whose electrical resistance increases with temperature. When an abnormally large current flows through the sealed battery 100, the temperature inside the PTC element 25 rises due to heat generation. Consequently, the electrical resistance of the PTC element 25 increases, and the current flowing through the sealed battery 100 decreases.

[0062] Figure 1 describes a sealing member having a recess in the bottom plate for housing the PTC element, but the terminal cap may also have a space for housing the PTC element.

[0063] In Figure 2, a stepped portion 21c is formed on the lower surface of the terminal cap 21 (the surface facing the electrode body) in a region near the center of the peripheral portion 21b, recessed in the direction away from the electrode body. In Figure 2, the convex portion 21a of the terminal cap 21 is formed inward from the stepped portion 21c. The PTC element 25 is sandwiched between the stepped portion 21c of the terminal cap 21 and the peripheral portion 22b of the bottom plate 22. It is preferable that the stepped portion 21c of the terminal cap is formed by bending the plate material that makes up the terminal cap; therefore, the region of the upper surface of the terminal cap that overlaps with the stepped portion 21c may be convex in the direction away from the electrode body.

[0064] As shown in Figures 1 and 2, in the sealing member 20, the peripheral edge 21b of the terminal cap 21 and the peripheral edge 22b of the bottom plate 22 are laminated with an insulating layer 27 in between. For example, an annular insulating layer can be used as the insulating layer. Therefore, the terminal cap 21 and the bottom plate 22 do not come into direct contact without the PTC element 25 in between.

[0065] Next, with reference to Figure 3, a specific configuration of a sealed battery according to one embodiment of the present disclosure will be described. In the following description, an example in which the sealed battery is a lithium primary battery will be described. Also, in Figure 3, the strip-shaped positive electrode, strip-shaped negative electrode, strip-shaped separator, and positive electrode current collector are omitted from the illustration.

[0066] As shown in Figure 3, the lithium primary battery 100 comprises a bottomed cylindrical battery case (battery can) 9 having an opening, a wound electrode body 10 housed in the battery case 9 together with an electrolyte (not shown), and a sealing member 20. In the lithium primary battery 100, the sealing member 20 is provided inside the opening of the battery case 9. The sealing member 20 comprises a terminal cap 21, a bottom plate 22, an insulating layer 27, and a PTC element 25. The configuration of the sealing member 20 is the same as in the example in Figure 1.

[0067] The electrode body 10 may be constructed by winding a strip-shaped positive electrode and a strip-shaped negative electrode via a strip-shaped separator. A positive electrode lead 4 is connected to the positive electrode. The positive electrode lead 4 is connected to the inner surface of the bottom plate 22 of the sealing member 20. Therefore, the terminal cap 21 is electrically connected to the positive electrode. A negative electrode lead 5 is connected to the negative electrode. The negative electrode lead 5 is connected to the inner surface of the bottom of the battery case. An upper insulating plate 6 is placed on the upper end face of the electrode body 10 to prevent internal short circuits, and a lower insulating plate 7 is placed on the lower end face of the electrode body 10 to prevent internal short circuits.

[0068] An arc-shaped groove is formed on the outer bottom surface of the battery case 9 as an explosion-proof thin-walled section 28.

[0069] (Note) The following technologies are disclosed as described above.

[0070] (Technical 1) A sealed battery comprising: a bottomed cylindrical battery case having an opening; an electrode body and an electrolyte housed in the battery case; and a sealing member that seals the opening of the battery case, wherein a terminal cap, a PTC element, and a bottom plate are arranged in this order in the sealing member; the peripheral edge of the PTC element is positioned inward from the peripheral edge of the terminal cap and the peripheral edge of the bottom plate; the PTC element is in contact with the terminal cap and the bottom plate; the peripheral edge of the terminal cap and the peripheral edge of the bottom plate are laminated with an insulating layer in between; and the open end of the battery case is crimped to the peripheral edge of the terminal cap and the peripheral edge of the bottom plate via a gasket, outside the peripheral edge of the PTC element.

[0071] (Technical 2) The sealed battery according to Technical 1, wherein a housing space for housing the PTC element is formed in the peripheral edge of the terminal cap and the inside of the bottom plate, and a part of the inner surface of the housing space is spaced apart from the PTC element.

[0072] (Technology 3) The sealed battery according to Technology 1 or 2, wherein a thin-walled explosion-proof portion is formed at the bottom of the battery case.

[0073] (Technology 4) The sealed battery according to Technology 1 or 2, wherein the PTC element is formed in the shape of a disc or annular ring.

[0074] Although the present invention has been described in relation to preferred embodiments at present, such disclosure should not be interpreted restrictively. Various modifications and alterations will undoubtedly become apparent to those skilled in the art in the field to which the invention pertains by reading the above disclosure. Accordingly, the appended claims should be interpreted as encompassing all modifications and alterations without departing from the true spirit and scope of the invention.

[0075] The present disclosure will be described in detail below based on examples and comparative examples, but the present disclosure is not limited to the following examples.

[0076] <Example 1> (1) Preparation of the positive electrode 100 parts by mass of electrolytic manganese dioxide and 5 parts by mass of Ketjenblack, a conductive agent, were mixed to obtain a powder mixture. Then, 5 parts by mass of polytetrafluoroethylene, a binder, and an appropriate amount of water were added to this powder mixture and kneaded to obtain a wet positive electrode mixture.

[0077] A positive electrode compound was pressed onto an expanded metal (positive electrode current collector) made of stainless steel using a roll. The positive electrode was then dried to obtain the positive electrode. The thickness of the positive electrode after rolling was 520 μm.

[0078] The positive electrode obtained as described above was cut into a strip with a width of 38 mm and a length of 192 mm. Then, a portion of the positive electrode mixture was peeled off from the strip of positive electrode to expose a portion of the positive electrode current collector, and a SUS positive electrode lead was resistance-welded to this exposed portion.

[0079] (2) Preparation of the negative electrode A sheet of Li-Al alloy (Al content 0.3 mass%) with a thickness of 200 μm was cut to a predetermined size to obtain a strip-shaped negative electrode. Nickel negative electrode leads were connected to predetermined locations on the negative electrode by pressure welding.

[0080] (3) Electrode preparation An electrode was obtained by spirally winding a positive electrode, a negative electrode, and a separator interposed between them. A microporous polyethylene membrane was used as the separator. The end of the separator at the winding end was fixed to the electrode with polypropylene tape.

[0081] (4) Preparation of the electrolyte A lithium salt, lithium trifluoromethanesulfonate, was dissolved at a concentration of 0.7 mol / L in a mixed non-aqueous solvent prepared by mixing propylene carbonate (PC) and 1,2-dimethoxyethane (DME) in a volume ratio of 4:6.

[0082] (5) Preparation of the battery case A bottomed cylindrical battery case made of nickel-plated steel sheet of a predetermined size was prepared. An arc-shaped groove was formed on the outer surface of the bottom of the battery case as a thin-walled section for explosion protection.

[0083] (6) Preparation of sealing member A sealing member as shown in Figure 1 was prepared.

[0084] The terminal cap is a stainless steel plate having a convex portion in the center and a flat, flange-shaped peripheral portion.

[0085] As the base plate, a SUS plate was prepared having a recess in the center and a peripheral edge extending from the outer edge of the recess. The recess has a stepped portion in the height direction. That is, the recess is divided into a first region that supports the peripheral edge of the PTC element and a second region that is spaced apart from the PTC element. The base plate 22 is circular with the same outer diameter as the terminal cap 21.

[0086] A polypropylene film with an annular shape was prepared as the insulating layer. The insulating layer is sized to be interposed between the periphery of the terminal cap and the periphery of the bottom plate.

[0087] The PTC element is a flat, disc-shaped component with a structure in which a layer of composite material consisting of resin (polyethylene resin) and conductive particles is sandwiched between a pair of metal foils. The PTC element is designed to activate earlier than the explosion-proof thin-wall section. The PTC element is sized to fit into the recess of the base plate.

[0088] After housing the PTC element in the recess of the base plate, the peripheral edges of the base plate and the peripheral edges of the terminal caps were laminated together with an insulating layer (polypropylene film) in between. This completed the sealing member.

[0089] (7) After placing an annular lower insulating plate on the bottom end face of the assembled electrode body of the sealed battery, the electrode body was housed inside the battery case. Then, the negative electrode lead was connected to the inner surface of the bottom of the battery case. A certain amount of electrolyte was poured into the inside of the battery case to impregnate the electrode body with the electrolyte. Next, upper insulating plates were placed on the upper multi-faceted surfaces of the electrode body. Next, the positive electrode lead was connected to the inner surface of the bottom plate of the sealing member.

[0090] Next, an annular step portion was formed near the open end of the battery case to support the sealing member, and the opening of the battery case was closed with the sealing member. Then, the open end was bent inward and crimped to the periphery of the sealing member via a gasket to seal the opening of the battery case. In this way, a lithium primary battery (battery E1) with an outer diameter of 17 mm and a height of 50 mm was completed.

[0091] <Comparative Example 1> (a) Preparation of sealing member A terminal cap, PTC element, valve body, spacer, and bottom plate were prepared. The terminal cap has the same configuration as in Example 1. The PTC element has the same configuration as in Example 1, except that it is annular. The valve body is aluminum foil with both sides covered with polyethylene film. The spacer is an annular SUS plate. The bottom plate has an opening in the center to facilitate the operation of the valve body, and the center is recessed toward the electrode body.

[0092] The base plate, valve body, and spacer were arranged in this order, and the periphery of the base plate was bent inward to crimp the spacer. The annular PTC element and terminal cap were then arranged on the bent periphery of the base plate in this order, and the periphery of the laminate was fixed with a gasket to complete the sealing member.

[0093] (b) Assembly of the sealed battery A sealed battery (battery R1) of Comparative Example 1, having the same dimensions as that of Example 1, was completed in the same manner as in Example 1, except that the electrode body and sealing member described above were used.

[0094] <Evaluation> [Trip Heat Quantity Q] For each example, the amount of heat Q (trip heat quantity) (in kJ) required for the PTC element to trip was calculated. Note that trip means that the PTC element is activated by heat. Trip heat quantity refers to the amount of heat generated in the sealing material when the PTC element is activated.

[0095] For each example, the trip heat quantity Q was calculated using the following formula (1). The heat quantity Q was calculated by determining the heat quantity for each component in contact with the PTC element and then summing these values.

[0096] Q = mCΔT .....(1) m: Mass of each component constituting the sealing member (unit: kg) C: Specific heat of each component constituting the sealing member (unit: kJ / (kg·K)) ΔT: Temperature difference between the temperature at the time of tripping and room temperature (25°C) (unit: K) [Trip time t] For each example, the trip time t (unit: seconds (s)) required for the PTC element to trip was determined. The trip time t was measured by cutting out a portion of the lithium primary battery in each example that was crimped at the open end of the battery case via a gasket (the portion not including the electrode body) and passing current from a power source through the test specimen. Specifically, the trip time was measured from the time when the current started to flow through the PTC element to the time until the battery value flowing through the PTC element decayed to 80% of its value. The test conditions of the power source when current was passed through the above test specimen were a voltage of 3.2V and a current of 12A. Furthermore, the temperature of the test chamber when current was passed through the test specimen was 25°C.

[0097] The evaluation results are shown in Table 1.

[0098]

[0099] Table 1 shows that in Example 1, where three components are stacked and the PTC element is positioned inside the peripheral edge of the terminal cap crimped to the opening edge of the battery case and the peripheral edge of the bottom plate, the amount of heat Q required for the sealing member to trip is 48 J. In contrast, in Comparative Example 1, where five components are stacked and the PTC element is crimped to the opening edge of the battery case together with the other components, the amount of heat Q is 62 J. In other words, in Example 1, the PTC element can operate even with a relatively small amount of heat Q.

[0100] Furthermore, as can be seen from Table 1, in Example 1, where three components are stacked and the PTC element is positioned inside the peripheral edge of the terminal cap crimped to the opening edge of the battery case and the peripheral edge of the bottom plate, the time t required for the sealing member to trip is 3.6 seconds, whereas in Comparative Example 1, where five components are stacked and the PTC element is crimped to the opening edge of the battery case together with the other components, the above time t is 5.2 seconds. From these results, it can be seen that the operability of the PTC element is improved in Example 1.

[0101] Furthermore, by comparing the configurations of each example with reference to Figures 1 and 2, it can be seen that the sealing member of Example 1 can be made much thinner than the sealing member of Comparative Example 1. From this, it can be seen that in Example 1, the space for housing the electrode body can be increased, and therefore the battery capacity can be increased.

[0102] The sealed battery described herein can be used in applications where it is required to achieve both high capacity and improved operability of the PTC element.

[0103] 4: Positive lead 5: Negative lead 6: Upper insulating plate 7: Lower insulating plate 9: Battery case 10: Electrode body 20: Sealing member 21: Terminal cap 22: Bottom plate 23: Valve body 24: Spacer 25: PTC element 26: Gasket 27: Insulating layer 28: Explosion-proof thin-walled section 100: Lithium primary battery (sealed battery)

Claims

1. A sealed battery comprising: a bottomed cylindrical battery case having an opening; an electrode body and electrolyte housed within the battery case; and a sealing member that seals the opening of the battery case, wherein a terminal cap, a PTC element, and a bottom plate are arranged in this order within the sealing member; the peripheral edge of the PTC element is positioned inward from the peripheral edge of the terminal cap and the peripheral edge of the bottom plate; the PTC element is in contact with the terminal cap and the bottom plate; the peripheral edge of the terminal cap and the peripheral edge of the bottom plate are laminated with an insulating layer in between; and the open end of the battery case is crimped to the peripheral edge of the terminal cap and the peripheral edge of the bottom plate via a gasket, outside the peripheral edge of the PTC element.

2. The sealed battery according to claim 1, wherein a housing space for housing the PTC element is formed in the peripheral edge of the terminal cap and the inside of the bottom plate, and a part of the inner surface of the housing space is spaced apart from the PTC element.

3. The sealed battery according to claim 1 or 2, wherein a thin-walled explosion-proof portion is formed at the bottom of the battery case.

4. The sealed battery according to claim 1 or 2, wherein the PTC element is formed in the shape of a disc or an annular ring.

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