Sealed battery

Abstract

The present disclosure provides a sealed battery with which both increased capacity and improved safety can be achieved. A sealed battery according to the present disclosure comprises: a bottomed cylindrical battery case having an opening; an electrode body and an electrolyte accommodated inside the battery case; and a sealing member for sealing the opening of the battery case. The sealing member comprises a terminal cap, a PTC element, and a bottom plate. The PTC element is in contact with the terminal cap and the bottom plate at least at a peripheral edge portion of the sealing member. The opening end portion of the battery case is tightly mated with the peripheral edge portion of the sealing member via a gasket. The electrode body is configured by spirally winding a band-shaped positive electrode, a band-shaped negative electrode, and a separator interposed therebetween. The negative electrode contains metallic lithium. The electrode on the outermost circumference of the electrode body is the positive electrode. The positive electrode and the inner circumferential surface of the battery case are insulated from each other. The battery case is electrically connected to the negative electrode.

Description

sealed battery

[0001] The present disclosure relates to sealed batteries.

[0002] Patent Document 1 describes a non-aqueous electrolyte battery comprising: an outer can; an electrode assembly housed in the outer can and formed by winding a positive electrode, a separator, and a negative electrode in a spiral; a non-aqueous electrolyte housed in the outer can; and a sealing lid group that is fixed airtightly to the upper opening of the outer can by crimping with an insulating gasket and serves both as an explosion-proof function and as a terminal, the sealing lid group comprising an inner lid body disposed opposite the electrode assembly; a reinforcing plate that is disposed on the inner lid body via a valve membrane and is sandwiched by an annular portion formed by bending the periphery of the inner lid body inward; a PTC element disposed on the annular portion of the inner lid body; an outer lid body that is disposed with its periphery abutting on the PTC element; and gas vent holes that are opened respectively in the inner lid body, the reinforcing plate, the PTC element, and the outer lid body. In this battery, the gas vent holes in the sealing lid group have a spacing of 0.15 to 1.2 cm per battery capacity (Ah). ２ The present inventors have proposed a non-aqueous electrolyte battery having an area of ​​1000 mm.

[0003] Patent Document 2 proposes a battery including "at least one electrochemical cell having an internal bore therethrough; a voltage converter module electrically coupled to the at least one electrochemical cell and disposed within a portion of the internal bore, the voltage converter module configured to convert a first voltage generated by the at least one electrochemical cell to a second, different voltage; a terminal pair electrically coupled to the voltage converter; and a bypass circuit coupled between one terminal of the terminal pair and the at least one electrochemical cell for conducting a charging current applied to the at least one electrochemical cell from an external power source."

[0004] Patent Document 3 proposes "a shield structure for a sealed battery, characterized in that it comprises an explosion-proof valve for releasing the internal pressure of the battery, which is elastic in a direction perpendicular to the surface of the valve body, a polyswitch plate for preventing overcurrent by cutting off the flow of overcurrent when it occurs, and a sealing cap that serves as the positive electrode terminal, which are stacked together, and these components are mounted in a packing container with an opening at the top made of an insulating synthetic resin material, and these components are clamped and pressed by a locking piece formed on the inner peripheral edge of the upper end of the packing container, which is mounted in a sealed state in the opening at the top of a battery case in which a non-aqueous electrolyte is loaded, and the opening at the top of the battery case is crimped."

[0005] Patent Document 4 proposes a battery comprising "a battery element having a positive electrode and a negative electrode, and a battery can that houses the battery element, wherein the battery element is housed and arranged within the battery can at a position where one of the positive electrode and the negative electrode can be in electrical contact with the battery can, and the battery can is electrically connected to the other of the positive electrode and the negative electrode, and an insulating member that prevents current flow between the battery element and one of the positive electrode and the negative electrode is arranged between the battery element and the battery can, and the insulating member is made of a material that shrinks or melts at a temperature lower than the reference temperature of the battery element."

[0006] JP-A-6-187957, Special Publication No. 2010-522963, JP-A 10-302745, JP-A 2007-80791

[0007] In recent years, there has been a demand for sealed batteries to have both higher capacity and safety. However, the higher the capacity of a sealed battery, the more difficult it tends to be to ensure safety.

[0008] To achieve high capacity, it is desirable to secure as much space as possible inside the battery case. However, the sealing material of conventional sealed batteries generally includes a PTC element and an explosion-proof valve, which means that the number of parts is large and the thickness is large. In this case, the internal space of the battery case is limited, which limits the capacity that can be increased.

[0009] Furthermore, in conventional sealed batteries, a negative electrode with the same polarity as the battery case is arranged at the outermost periphery of the electrode assembly to ensure safety. In this case, the outermost negative electrode tends to remain unreacted during discharge. This means that the utilization rate of the negative electrode is low, making it difficult to obtain a sufficiently high capacity.

[0010] Furthermore, the remaining negative electrode that has not fully reacted can cause heat generation in the battery. Specifically, if the overdischarge state continues, metal ions may leach out of the battery case and deposit as metal on the outer surface of the positive electrode, which may cause a short circuit between the battery case and the positive electrode. If highly reactive metallic lithium from the negative electrode remains on the outermost periphery, the battery temperature may rise rapidly when such a short circuit occurs.

[0011] One aspect of the present disclosure relates to a sealed battery including: a bottomed cylindrical battery case having an opening; an electrode assembly and an electrolyte housed in the battery case; and a sealing member that seals the opening of the battery case, the sealing member including a terminal cap, a PTC element, and a bottom plate, the PTC element being in contact with the terminal cap and the bottom plate at least at a peripheral portion of the sealing member; an open end of the battery case crimping the peripheral portion of the sealing member via a gasket; the electrode assembly being configured by spirally winding a strip-shaped positive electrode, a strip-shaped negative electrode, and a separator disposed therebetween; the negative electrode containing metallic lithium; the outermost electrode of the electrode assembly being the positive electrode; the positive electrode being insulated from an inner peripheral surface of the battery case; and the battery case being electrically connected to the negative electrode.

[0012] According to the present disclosure, it is possible to provide a sealed battery that has high capacity and is excellent in safety.

[0013] FIG. 1 is a cross-sectional view schematically illustrating a lithium primary battery according to an embodiment of the present disclosure.

[0014] Below, embodiments of the present disclosure will be described using examples, but the present disclosure is not limited to the examples described below. In the following description, specific numerical values ​​and materials may be exemplified, but other numerical values, materials, etc. may be applied as long as the effects of the present disclosure are obtained. Note that known components may be applied to components characteristic of the present disclosure. In this specification, when a "range from numerical value A to numerical value B" is mentioned, the range includes numerical value A and numerical value B.

[0015] In the following description, when lower and upper limits of numerical values ​​relating to specific physical properties, conditions, etc. are exemplified, any of the exemplified lower limits and any of the exemplified upper limits can be arbitrarily combined, as long as the lower limit is not equal to or greater than the upper limit. When multiple materials are exemplified, one of them can be selected and used alone, or two or more can be used in combination, unless otherwise specified.

[0016] The present disclosure encompasses any combination of two or more features arbitrarily selected from the appended claims, i.e., any combination of two or more features arbitrarily selected from the appended claims can be combined unless a technical contradiction arises.

[0017] [Sealed Battery] A sealed battery according to an embodiment of the present disclosure (hereinafter also referred to as "sealed battery (B)") includes a cylindrical battery case with an opening and a bottom, an electrode assembly (electrode group) and an electrolyte solution housed in the battery case, and a sealing member that seals the opening of the battery case. The open edge of the battery case is crimped to the periphery of the sealing member via a gasket, thereby sealing the interior of the battery.

[0018] The sealing member includes a terminal cap, a PTC (positive temperature coefficient) element, and a bottom plate. The PTC element is in contact with the terminal cap and the bottom plate at least along the periphery of the sealing member.

[0019] That is, the sealing member has a simple structure without an explosion-proof valve. The number of parts of the sealing member may be only three: a terminal cap, a PTC element, and a bottom plate. Such a sealing member has a very small thickness, allowing more space to be secured within the battery case than a typical sealing member. Therefore, a large-volume electrode assembly can be accommodated within the battery case, thereby enabling a sufficiently high capacity to be obtained.

[0020] A conventional sealing member generally includes a terminal cap, a PTC element, a valve body, a spacer, and a bottom plate. The peripheral edge of the bottom plate is crimped to the peripheral edges of the valve body and the spacer. Therefore, the thickness of the valve body, spacer, and bottom plate (crimped portion) is added to the sealing member of the sealed battery (B). In other words, the thicknesses of the valve body, spacer, and bottom plate (crimped portion) of the sealing member of the sealed battery (B) are reduced, and the dimension in the battery height direction is accordingly reduced.

[0021] On the other hand, the sealing material has a small number of components, and the amount of heat transferred from the PTC element to the surroundings is limited, so the sensitivity to heat generated by the PTC element is increased. Therefore, when the temperature of the sealed battery (B) rises, the PTC element quickly activates and suppresses further increases in the battery temperature. In other words, the sealed battery (B) is extremely safe despite its high capacity.

[0022] The electrode assembly is constructed by spirally winding a strip-shaped positive electrode, a strip-shaped negative electrode, and a separator disposed therebetween. That is, the sealed battery (B) has a wound electrode assembly.

[0023] The negative electrode contains metallic lithium. That is, the sealed battery (B) may be a battery generally referred to as a "metallic lithium battery," a "lithium battery," or a "lithium primary battery." The metallic lithium may be a lithium alloy.

[0024] The outermost electrode of the electrode assembly is a positive electrode. The positive electrode is insulated from the inner peripheral surface of the battery case (hereinafter, the outermost region of the positive electrode is also referred to as the "outermost positive electrode"). The positive electrode is electrically connected to, for example, the bottom plate of the sealing member. On the other hand, the battery case is electrically connected to the negative electrode.

[0025] The means or method for insulating the positive electrode from the inner peripheral surface of the battery case is not particularly limited. For example, the positive electrode may be insulated from the inner peripheral surface of the battery case by covering the outer surface of the outermost positive electrode with a separator. Specifically, the end of the separator on the winding end side may extend beyond the end of the outermost positive electrode, and the extended portion of the separator may cover the outer surface of the positive electrode. The end of the separator on the winding end side may be fixed to the electrode body with an insulating stop tape. The base sheet of the stop tape is made of a resin such as polypropylene. In this case, the separator and the stop tape insulate the positive electrode from the inner peripheral surface of the battery case.

[0026] The height of the battery is the longest for the separator, followed by the positive electrode, the stopper tape, and the negative electrode in that order.

[0027] When the outermost electrode of the electrode assembly is a positive electrode, naturally, no negative electrode exists between the inner peripheral surface of the battery case and the outermost positive electrode. Also, no negative electrode remains between the inner peripheral surface of the battery case and the outermost positive electrode. Therefore, the utilization rate of the negative electrode is increased, and it is possible to obtain even higher capacity.

[0028] The volumetric energy density of the sealed battery (B) can be, for example, 900 Wh / L or more, and even 950 Wh / L or more.

[0029] Furthermore, even if the sealed battery (B) were to be overdischarged, metal ions would leach out of the battery case and deposit as metal on the outer surface of the positive electrode, causing a short circuit between the battery case and the positive electrode, since there would be no highly reactive metallic lithium in the short circuit path, a rapid increase in battery temperature could be avoided. In other words, the safety of the sealed battery (B) is further improved.

[0030] The PTC element may be annular (ring-shaped) with a hollow portion formed therein. The annular PTC element allows the PTC element to expand into the hollow portion when activated. This expansion is less likely to impede the operation of the PTC element than a PTC element without a hollow portion that abuts against a flat bottom plate, and the PTC element's sensitivity to heat generation can be further increased.

[0031] The PTC element may be disk-shaped. In this case, the center of the bottom plate may be convex toward the end face of the electrode body so as to form a gap between the PTC element and the bottom plate. This gap allows the PTC element to expand toward the gap when the PTC element is activated. This expansion is less likely to impede the operation of the PTC element than a disk-shaped PTC element abutting against a flat bottom plate, and the PTC element's sensitivity to heat generation can be further increased.

[0032] The components of the sealed battery will be further described below.

[0033] (Battery Case) The battery case functions as a negative electrode terminal. The battery case and the negative electrode may be electrically connected via a negative electrode lead. The battery case is cylindrical with an opening and a bottom. The cross-sectional shape of the battery case is not particularly limited and may be elliptical or polygonal, but is preferably circular. The material of the battery case is not particularly limited and may be, for example, an iron alloy (including stainless steel), carbon steel, aluminum, or an aluminum alloy.

[0034] An explosion-proof thin-walled portion may be formed at the bottom of the battery case. The explosion-proof thin-walled portion functions as an explosion-proof mechanism (explosion-proof valve). The explosion-proof thin-walled portion ruptures when the internal pressure of the sealed battery (B) rises above a predetermined value. When the sealed battery (B) has an explosion-proof thin-walled portion, higher safety can be ensured.

[0035] The explosion-proof thin-walled portion may be formed, for example, as a groove of a predetermined shape on the bottom of the battery case. The explosion-proof thin-walled valve may be formed on the outer surface of the bottom of the battery case. The shape of the groove is not particularly limited, but may be, for example, a linear shape, an arc shape, or the like.

[0036] The explosion-proof thin-walled portion is not essential, and safety may be further enhanced by other methods.

[0037] (Electrode body) The electrode body is a wound type electrode body formed by winding a strip-shaped positive electrode and a strip-shaped negative electrode with a separator interposed therebetween. The electrode body is, for example, cylindrical in shape to correspond to the shape of the cylindrical battery case. The electrode body includes an outermost positive electrode, which is insulated from the inner peripheral surface of the battery case.

[0038] 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 includes 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. The positive electrode current collector may be, for example, a stainless steel expanded metal, net, or punched metal.

[0039] The positive electrode mixture may contain optional components such as a binder and a conductive agent in addition to the positive electrode active material. The binder may be a resin material such as a fluororesin. The conductive agent may be a conductive material such as a carbon material.

[0040] Metallic lithium (or a lithium alloy) is used for the negative electrode. 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. Of these, it is preferable to use a Li-Al-Mg alloy.

[0041] When a lithium alloy is used, the content of metal elements other than lithium contained in the lithium alloy is preferably 0.1% by mass or more and 5% by mass or less, from the viewpoint of ensuring a sufficient discharge capacity and stabilizing the internal resistance.

[0042] The separator may be, for example, a microporous resin film or nonwoven fabric. The separator may be made of, for example, polyolefin, polyamide, polyamideimide, or the like. Polyolefins that may be used include polyethylene (PE), polypropylene (PP), and the like.

[0043] If a negative electrode is disposed at the outermost periphery of the electrode assembly (hereinafter, the outermost region of the negative electrode is referred to as the "outermost negative electrode"), only one side of the outermost negative electrode faces the positive electrode. Therefore, the outermost negative electrode is likely to remain after the discharge reaction. In other words, the remaining outermost negative electrode does not sufficiently contribute to the discharge capacity. Furthermore, if a sealed battery enters an overdischarge state while the outermost negative electrode remains, lithium ions leach from the outermost negative electrode and deposit as metallic lithium on the surface of the opposing positive electrode. The deposition of metallic lithium on the positive electrode surface continues until all metallic lithium contained in the outermost negative electrode is consumed. If the overdischarge state continues, metallic ions leach from the battery case, which functions as the negative electrode terminal, and deposit on the surface of the positive electrode. Then, the battery case comes into contact with the metallic lithium deposited on the positive electrode surface, causing a short circuit between the battery case and the positive electrode. Because metallic lithium is extremely reactive, a short circuit causes a rapid rise in the temperature inside the battery case.

[0044] In contrast, the sealed battery (B) has an outermost positive electrode. That is, the outermost negative electrode of this electrode assembly is sandwiched between the outermost positive electrode and the innermost positive electrode. Therefore, the outermost negative electrode is fully consumed during discharge. This improves the discharge capacity. Furthermore, even if the sealed battery (B) is exposed to an overdischarge condition and metal ions are eluted from the battery case and precipitated on the surface of the outermost positive electrode, metallic lithium does not form a conductive path. Therefore, a sudden temperature rise in the sealed battery (B) is suppressed, improving safety.

[0045] The outermost positive electrode and the inner peripheral surface of the battery case are preferably insulated by a separator extending to the outermost periphery of the electrode assembly. The separator disposed on the outermost periphery of the electrode assembly is preferably fixed with tape. By combining the separator and tape in this manner, sufficient insulation between the outermost positive electrode and the inner peripheral surface of the battery case can be ensured. For example, a tape having a polypropylene substrate and an adhesive layer can be used as the tape.

[0046] In the height direction of the electrode assembly, the dimensions of the positive electrode, negative electrode, separator, and tape preferably increase in the order of negative electrode, tape, positive electrode, and separator. That is, it is preferable that the separator has the largest dimension in the height direction of the electrode assembly. This can prevent short-circuiting between the positive electrode and negative electrode near the end faces of the electrode assembly.

[0047] (Electrolyte) When the sealed battery (B) is a lithium primary battery, a non-aqueous solvent containing a lithium salt dissolved therein can be used as the electrolyte. Examples of the non-aqueous solvent include propylene carbonate, ethylene carbonate, 1,2-dimethoxyethane, and γ-butyrolactone. Examples of the lithium salt that can be used include lithium borofluoride, lithium hexafluorophosphate, lithium trifluoromethanesulfonate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethylsulfonyl)imide.

[0048] (Sealing member) As described above, the sealing member includes a terminal cap, a PTC element, and a bottom plate. The terminal cap has, for example, a convex shape facing outward and a flat flange portion on its periphery. The bottom plate may be configured as a flat plate, or may have a convex shape facing the end face of the electrode body and a flat flange portion on its periphery. The periphery of the PTC element is sandwiched between the periphery of the terminal cap and the periphery of the bottom plate.

[0049] When only the PTC element is disposed between the peripheral edge of the terminal cap and the peripheral edge of the bottom plate, the thickness of the peripheral edge of the sealing member can be reduced, thereby reducing the space occupied by the sealing member within the battery case and increasing the space occupied by the electrode assembly.

[0050] The bottom plate may be electrically connected to the positive electrode via a lead, and the bottom plate is electrically connected to the terminal cap via a PTC element.

[0051] The material of the terminal cap and the bottom plate is not particularly limited, and examples thereof include iron, iron alloys (including stainless steel), aluminum, and aluminum alloys.

[0052] (PTC element) A PTC element, also known as a thermosensitive resistor element, has the property that its electrical resistance increases with increasing temperature. For example, when an abnormal current flows through a sealed battery, the PTC element generates heat, causing the temperature to rise, and the resistance of the PTC element to increase. This reduces the current flowing through the sealed battery, suppressing abnormal heat generation in the sealed battery. If the sealed battery (B) has an explosion-proof thin-walled portion, abnormal heat generation in the sealed battery is suppressed before the explosion-proof thin-walled portion ruptures.

[0053] The PTC element may include a composite of resin and conductive particles. The PTC element may have a structure in which a layer of such a composite is sandwiched between a pair of metal foils. The resin may be polyethylene resin or the like. The metal foil may be nickel or a copper-nickel clad material or the like. 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.

[0054] The structure of the PTC element is not particularly limited, and a ceramic PTC element, for example, a PTC element containing barium titanate as a main component, may be used.

[0055] Next, the structure of a lithium primary battery 100, which is an example of a sealed battery (B), will be described with reference to FIG.

[0056] The lithium primary battery 100 includes a cylindrical battery case (battery can) 9 with an opening and a bottom, a wound electrode body 10 housed in the battery case 9 together with an electrolyte (not shown), and a sealing member 20. The opening of the battery case 9 is sealed with the sealing member 20. The sealing member 20 includes a terminal cap 21, a bottom plate 22, and a PTC element 25. The sealing member 20 consists of only these three parts.

[0057] The electrode assembly 10 is constructed by winding a positive electrode 1 and a negative electrode 2 with a separator 3 interposed therebetween. In the lithium primary battery 100, as shown in FIG. 1 , the positive electrode 1 is disposed as the outermost electrode of the electrode assembly 10. The positive electrode 1 includes a positive electrode current collector and a positive electrode mixture (positive electrode mixture layer) attached to the positive electrode current collector. A positive electrode lead 4 is connected to the positive electrode current collector. The positive electrode lead 4 is connected to the inner surface of the bottom plate 22 of the sealing member 20. Thus, the terminal cap 21 is electrically connected to the positive electrode 1.

[0058] A separator 3 and a tape 8 are disposed between the outermost positive electrode of the electrode assembly 10 and the inner peripheral surface of the battery case 9. The outermost positive electrode and the inner peripheral surface of the battery case 9 are insulated by the separator 3 and the tape 8. That is, the separator 3 extends to the outermost periphery of the electrode assembly 10, and the separator 3 disposed at the outermost periphery is fixed with the tape 8. A negative electrode lead 5 is connected to the negative electrode 2. The negative electrode lead 5 is connected to the inner bottom surface of the battery case 9.

[0059] An upper insulating plate 6 for electrical insulation is disposed on the upper end face of the electrode body 10, and a lower insulating plate 7 for electrical insulation is disposed on the lower end face of the electrode body 10.

[0060] The terminal cap 21 has a protrusion 21a in the center that functions as an external positive electrode terminal, and a flat flange 21b on its periphery. The bottom plate 22 is a flat disk. The terminal cap 21, the PTC element 25, and the bottom plate 22 all have the same circular shape with the same outer diameter.

[0061] A PTC element 25 is interposed between the flange portion 21b of the terminal cap 21 and the bottom plate 22. The terminal cap 21 and the bottom plate 22 are electrically connected by the PTC element 25.

[0062] The PTC element 25 has a flat, disk-like shape and contains a material whose electrical resistance increases with increasing temperature. When an abnormally large current flows through the lithium primary battery 100, the temperature inside the PTC element 25 increases due to heat generation. As a result, the electrical resistance of the PTC element 25 increases, and the current flowing through the lithium primary battery 100 decreases.

[0063] The flange portion 21b of the terminal cap 21 and the peripheral edge portion 22b of the bottom plate 22 are crimped to the open end of the battery case 9 via a gasket 26. This seals the opening of the battery case 9.

[0064] An arc-shaped groove is formed on the outer surface of the bottom of the battery case 9 as an explosion-proof thin-walled portion 28 .

[0065] (Additional Note) The above description discloses the following techniques.

[0066] (Technology 1) A sealed battery comprising: a bottomed cylindrical battery case having an opening; an electrode body and an electrolyte contained in the battery case; and a sealing member that seals the opening of the battery case, wherein the sealing member comprises a terminal cap, a PTC element, and a bottom plate; the PTC element is in contact with the terminal cap and the bottom plate at least at a peripheral portion of the sealing member; the open end of the battery case is crimped to the peripheral portion of the sealing member via a gasket; the electrode body is formed by spirally winding a strip-shaped positive electrode, a strip-shaped negative electrode, and a separator disposed therebetween; the negative electrode includes metallic lithium; the outermost electrode of the electrode body is the positive electrode; the positive electrode is insulated from an inner peripheral surface of the battery case; and the battery case is electrically connected to the negative electrode.

[0067] (Technology 2) The sealed battery according to Technology 1, wherein an explosion-proof thin-walled portion is formed at the bottom of the battery case.

[0068] (Technology 3) The sealed battery according to Technology 1 or 2, wherein the PTC element is annular.

[0069] (Technology 4) The sealed battery according to Technology 1 or 2, wherein the PTC element is disk-shaped, and the central portion of the bottom plate is a non-contact portion with the PTC element.

[0070] (Technology 5) The sealed battery according to any one of Technologies 1 to 3, wherein the separator covers an outer surface of the positive electrode at the outermost periphery of the electrode assembly, thereby insulating the positive electrode from an inner circumferential surface of the battery case.

[0071] While the present invention has been described in terms of presently preferred embodiments, such disclosure should not be interpreted as limiting. Various changes and modifications will no doubt become apparent to those skilled in the art to which the present invention pertains upon reading the above disclosure. It is therefore intended that the appended claims be interpreted to cover all changes and modifications that do not depart from the true spirit and scope of the invention.

[0072] Hereinafter, the present disclosure will be specifically described based on examples and comparative examples, but the present disclosure is not limited to the following examples.

[0073] Example 1 (1) Preparation of Positive Electrode 100 parts by mass of electrolytic manganese dioxide and 5 parts by mass of Ketjen black, which is a conductive agent, were mixed to obtain a powder mixture, and then 5 parts by mass of polytetrafluoroethylene, which is a binder, and an appropriate amount of water were added to this powder mixture and kneaded to obtain a wet positive electrode mixture.

[0074] The positive electrode mixture was pressed onto both sides of an expanded metal (positive electrode current collector) made of stainless steel using rolls, and then the positive electrode current collector with the pressed positive electrode mixture was dried to obtain a positive electrode.

[0075] The positive electrode was cut into a strip of a predetermined size, and a portion of the positive electrode mixture was peeled off from the strip of the positive electrode to expose a portion of the positive electrode current collector, and a positive electrode lead made of SUS was resistance-welded to the exposed portion.

[0076] (2) Preparation of negative electrode: A sheet of Li-Al alloy was cut to a predetermined size to obtain a strip-shaped negative electrode. A nickel negative electrode lead was connected to a predetermined position of the negative electrode by pressure welding.

[0077] (3) Preparation of Electrode Assembly: The electrode assembly was obtained by spirally winding a positive electrode, a negative electrode, and a separator interposed therebetween. The electrode assembly was configured so that the outermost electrode was the positive electrode, and the separator was disposed outside the positive electrode. A polyethylene microporous membrane was used as the separator. The end of the separator was fixed to the electrode assembly with polypropylene tape.

[0078] (4) Preparation of Electrolyte Solution An electrolyte solution was prepared by dissolving lithium trifluoromethanesulfonate, a lithium salt, at a concentration of 0.7 mol / L in a non-aqueous solvent mixture prepared by mixing propylene carbonate (PC), ethylene carbonate (EC), and 1,2-dimethoxyethane (DME) in a predetermined ratio.

[0079] (5) Preparation of Battery Case: A cylindrical battery case with a bottom 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 portion for explosion prevention.

[0080] (6) Preparation of Sealing Member A sealing member having three components (three-layer structure) as shown in FIG. 1 was prepared.

[0081] The terminal cap is a stainless steel plate having a convex portion in the center and a flat flange portion on the periphery.

[0082] The bottom plate is a flat, disk-shaped SUS plate.

[0083] The PTC element is a flat, disk-shaped device consisting of a layer of composite material made of resin (polyethylene resin) and conductive particles sandwiched between a pair of metal foils. The PTC element is designed to activate earlier than the thin-walled explosion-proof section.

[0084] The terminal cap 21, the PTC element 25 and the bottom plate 22 all have a circular shape with the same outer diameter.

[0085] (7) Assembly of a sealed battery: After placing a ring-shaped lower insulating plate on the bottom end surface of the electrode body, the electrode body was housed inside a battery case. Then, the negative electrode lead was connected to the inner bottom surface of the battery case. A certain amount of electrolyte was poured into the battery case, and the electrode body was impregnated with the electrolyte. Next, an upper insulating plate was placed on the upper end surface of the electrode body. Next, the positive electrode lead was connected to the inner surface of the bottom plate of the sealing member.

[0086] Next, an annular step for supporting the sealing member was formed near the open end of the battery case, and the opening of the battery case was closed with the sealing member. The open end was then bent inward and crimped to the periphery of the sealing member via a gasket, thereby sealing the opening of the battery case. In this way, a lithium primary battery of Example 1 having an outer diameter of 17 mm and a height of 50 mm was completed.

[0087] Comparative Example 1 (a) Preparation of Electrode Body An electrode body was prepared in the same manner as in Example 1, except that the outermost periphery was configured to be the negative electrode.

[0088] (b) Preparation of sealing material: A terminal cap, PTC element, valve body, spacer, and bottom plate were prepared. The terminal cap had the same configuration as in Example 1. The PTC element had the same configuration as in Example 1 except for being annular. The valve body was aluminum foil coated on both sides with polyethylene film. The spacer was an annular SUS plate. The bottom plate had an opening in the center to facilitate operation of the valve body, and the center was convex toward the electrode body.

[0089] The bottom plate, valve body, and spacer were stacked in this order, and the peripheral edge of the bottom plate was bent inward and crimped. The annular PTC element and terminal cap were stacked in this order on the peripheral edge of the bent bottom plate, and the peripheral edge of the stack was fixed with a gasket to complete a five-plate sealing member.

[0090] (c) Assembly of sealed battery A lithium primary battery of Comparative Example 1 having the same dimensions as Example 1 was completed in the same manner as Example 1, except that the electrode body and sealing member described above were used. However, since the sealing member of Comparative Example 1 had a greater number of components than the sealing member of Example 1, the external dimensions of Comparative Example 1 in the height direction were slightly larger than those of Example 1.

[0091] Comparative Example 2 The lithium primary battery of Comparative Example 2 uses a five-plate sealing member, as in Comparative Example 1, and has an outermost positive electrode in the electrode body, as in Example 1. In Comparative Example 2, the configuration other than the sealing member and the electrode body is the same as in Example 1. Comparative Example 2 is an example with almost the same dimensions as Example 1, but like Comparative Example 1, Comparative Example 2 also has slightly larger external dimensions in the height direction than Example 1.

[0092] Comparative Example 3 The lithium primary battery of Comparative Example 3 has an electrode body with an outermost negative electrode, as in Comparative Example 1, and a three-layer sealing member, as in Example 1. In Comparative Example 3, the configuration other than the electrode body is the same as in Example 1. Comparative Example 3 has the same dimensions as Example 1.

[0093] <Evaluation 1> [Discharge Capacity] The discharge capacity (unit: mAh) of each example was measured by discharging at an ambient temperature of 23±3° C. at a constant current of 3 mA until the voltage reached 2 V.

[0094] [Volumetric Energy Density] The volumetric energy density (unit: Wh / L) was calculated using the measured value of discharge capacity. The volumetric energy density was calculated by multiplying the discharge capacity by the rated voltage and dividing the result by the volume of the electrode body. The results of Evaluation 1 are shown in Table 1.

[0095]

[0096] From Table 1, it can be seen that the volumetric energy densities of Comparative Examples 1, 2, and 3 are 825 Wh / L, 893 Wh / L, and 884 Wh / L, respectively, while the volumetric energy density of Example 1 is 967 Wh / L. From this, it can be seen that Example 1 has a significantly improved volumetric energy density compared to Comparative Examples 1 to 3. This is because, in Example 1, the use of a sealing member with three components allowed the proportion of the space occupied by the electrode body in the space within the battery to be larger than in Comparative Examples 1 and 2, and because the use of an outermost positive electrode increased the utilization rate of the negative electrode compared to Comparative Example 3.

[0097] <Evaluation 2> [Trip heat quantity Q] For each example, the heat quantity Q (trip heat quantity) (unit: kJ) required for the PTC element to trip during the overdischarge test was calculated. Note that "trip" means that the PTC element is activated by heat. The trip heat quantity means the amount of heat generated in the sealing material when the PTC element is activated.

[0098] For each example, the trip heat quantity Q was calculated using the following formula (1): The heat quantity Q was calculated for each component in contact with the PTC element, and the total value of these was used.

[0099] 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 trip and room temperature (25°C) (unit: K) [Trip Time t] The trip time t (unit: seconds (sec)) of the PTC element in each example was determined. The trip time t was measured by cutting out a portion (a portion not including the electrode body) crimped by the open end of the battery case via the gasket and passing a current through the test piece. Specifically, the trip time was measured by measuring the time from when current began to flow through the PTC element until the battery value flowing through the PTC element attenuated to 80% of its original value. The results of Evaluation 2 are shown in Table 2.

[0100]

[0101] From Table 2, it can be seen that in Example 1 and Comparative Example 3, the trip heat quantity Q was 45 J and the trip time t was 3.8 seconds. In Comparative Examples 1 and 2, the trip heat quantity Q was 62 J and the trip time t was 5.2 seconds. From this, it can be seen that Example 1 and Comparative Example 3 have smaller trip heat quantities and shorter trip times than Comparative Examples 1 and 2, and the sensitivity of the PTC element is higher. This is thought to be because the number of parts in the sealing member is small, limiting the amount of heat conducted from the PTC element to the surroundings.

[0102] <Evaluation 3> [Over-discharge test] An over-discharge test was carried out for each example. During the over-discharge test and after the operation of the PTC element stopped, the maximum temperature at the center of the body in the height direction of each example was measured.

[0103] The overdischarge test was carried out by connecting two undischarged batteries in series to one battery (discharged to a depth of discharge of 75%) after measuring the discharge capacity in each example, and then short-circuiting the batteries via a resistor to forcibly discharge the batteries. The results of Evaluation 3 are shown in Table 3.

[0104]

[0105] From Table 3, it can be seen that in Example 1, despite the increased energy density, the maximum temperature of the body during overdischarge was the lowest, and no heat was observed after the PTC element stopped operating, significantly improving safety. In Comparative Example 1, the maximum temperature of the body during overdischarge was the highest, and heat was generated even after the PTC element stopped operating, with the maximum body temperature reaching 80°C. In Comparative Example 2, the maximum temperature of the body during overdischarge was almost the same as in Comparative Example 1, but no heat was generated after the PTC element stopped operating. In Comparative Example 3, the maximum temperature of the body during overdischarge was almost the same as in Example 1, but heat was generated after the PTC element stopped operating, and the maximum body temperature reached 77°C, close to that of Comparative Example 1.

[0106] From these results, it is presumed that Example 1 and Comparative Example 3, which contained less sealing material, had the effect of tripping earlier and suppressing the maximum temperature. Furthermore, when the outermost electrode was a negative electrode, lithium from the outermost negative electrode was deposited on the surface of the positive electrode facing this outermost negative electrode, initiating the elution of metal contained in the battery case, which functions as the negative terminal. This eluted metal then began to deposit on the surface of the positive electrode facing the inner circumferential surface of the battery case. As the metal eluted from the battery case continued to deposit on the surface of the positive electrode, a short circuit would occur between the lithium deposited on the surface of the positive electrode and the inner circumferential surface of the battery case via the metal that continued to deposit on the positive electrode. Because lithium is highly reactive, it is presumed that such a short circuit would result in a rapid rise in the temperature inside the battery case. Furthermore, in Comparative Example 3, the PTC element did not activate when the temperature began to rise again after the PTC element had stopped functioning. This is presumably because, unlike immediately after overdischarge, no large current was generated and the temperature rise was gradual, so the heat generated in the body was not enough to activate the PTC element.

[0107] As described above, Example 1 is a battery that, despite its high capacity, can quickly activate the PTC element and suppress the temperature rise of the battery, making it extremely safe. Furthermore, the above results also show that when the discharge capacity of the battery exceeds 3200 mAh, it exhibits particularly excellent safety.

[0108] The sealed battery according to the present disclosure can be used in applications that require both high capacity and improved safety.

[0109] 1: Positive electrode 1a: Positive electrode current collector 2: Negative electrode 3: Separator 4: Positive electrode lead 5: Negative electrode lead 6: Upper insulating plate 7: Lower insulating plate 8: Tape 9: Battery case 10: Electrode body 20: Sealing member 21: Terminal cap 22: Bottom plate 25: PTC element 26: Gasket 27: Insulating member 28: Explosion-proof thin-walled portion 100: Lithium primary battery

Claims

1. A sealed battery comprising: a cylindrical battery case having an opening and a bottom; an electrode body and an electrolyte contained in the battery case; and a sealing member that seals the opening of the battery case, wherein the sealing member comprises a terminal cap, a PTC element, and a bottom plate; the PTC element is in contact with the terminal cap and the bottom plate at least at the peripheral edge of the sealing member; the open end of the battery case is crimped to the peripheral edge of the sealing member via a gasket; the electrode body is formed by spirally winding a strip-shaped positive electrode, a strip-shaped negative electrode, and a separator disposed therebetween; the negative electrode contains metallic lithium; the outermost electrode of the electrode body is the positive electrode; the positive electrode is insulated from the inner peripheral surface of the battery case; and the battery case is electrically connected to the negative electrode.

2. The sealed battery according to claim 1, wherein the bottom of the battery case is formed with a thin-walled portion for explosion prevention.

3. The sealed battery according to claim 1 or 2, wherein the PTC element is annular.

4. A sealed battery according to claim 1 or 2, wherein the PTC element is disk-shaped, and the central portion of the bottom plate is not in contact with the PTC element.

5. A sealed battery according to claim 1 or 2, wherein the separator covers the outer surface of the positive electrode at the outermost periphery of the electrode assembly, thereby insulating the positive electrode from the inner surface of the battery case.

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