Secondary battery

Abstract

A secondary battery (10) is characterized by comprising a bottomed cylindrical outer can (14) that is open at the top, an electrode body (12) that is housed in the outer can (14) and is formed from a positive electrode and a negative electrode that are opposite with a separator therebetween, and a sealing body that seals the opening of the outer can (14), the sealing body having a top cap (16) that is a positive electrode terminal or a negative electrode terminal, a conductive member (20) that has a different polarity from the top cap (16), and an insulation member (18) that is interposed between the top cap (16) and the conductive member (20), the top cap (16) having a terminal body part (16a) and a flange part (16b) that is at the circumferential edge of the terminal body part (16a) and has a notch (16c) provided therein, the notch (16c) in the flange part (16b) being opposite the conductive member (20) with the insulation member (18) therebetween.

Description

secondary battery

[0001] The present disclosure relates to secondary batteries.

[0002] Secondary batteries such as lithium-ion secondary batteries are widely used as power sources for portable electronic devices such as mobile phones, smartphones, portable game consoles, laptop computers, etc. There is a trend toward ever-increasing capacity of secondary batteries, and at the same time, it is becoming increasingly important to ensure their safety and reliability through quality control.

[0003] Regarding the safety of secondary batteries, a technology has been proposed in which, for example, a groove acting as a safety valve is provided in the outer can or sealing body that serves as the battery case, and when gas is generated inside the battery due to heat generation from the battery and the internal pressure inside the battery reaches or exceeds a predetermined value, the groove is ruptured to release the gas, thereby preventing the battery from exploding (for example, Patent Document 1).

[0004] JP 10-261391

[0005] However, as the capacity of secondary batteries increases, the amount of heat generated by the battery increases when the internal pressure rises due to gas generation inside the battery, which has become a problem.

[0006] Therefore, an object of the present disclosure is to provide a secondary battery that can suppress the amount of heat generated by the battery when the internal pressure increases due to gas generation inside the secondary battery.

[0007] A secondary battery according to one aspect of the present disclosure comprises a cylindrical outer can with a bottom that is open at the top, an electrode assembly housed within the outer can and in which a positive electrode and a negative electrode are arranged opposite each other with a separator interposed therebetween, and a sealing body that seals the opening of the outer can, wherein the sealing body has a top cap that serves as a positive electrode terminal or a negative electrode terminal, a conductive member of a different polarity from that of the top cap, and an insulating member interposed between the top cap and the conductive member, and the top cap has a terminal main body portion and a flange portion located on the periphery of the terminal main body portion, and the flange portion has a bending point that can bend due to an increase in internal pressure caused by gas generation, and the bending point faces the conductive member via the insulating member.

[0008] According to one aspect of the present disclosure, it is possible to provide a secondary battery that can suppress the amount of heat generated by the battery when the internal pressure increases due to gas generation inside the secondary battery.

[0009] Fig. 1 is a partial schematic cross-sectional view showing an example of the configuration of a secondary battery according to an embodiment; Fig. 2 is a partial schematic cross-sectional view showing an example of the state of the secondary battery according to the embodiment in an abnormal state; Fig. 3 is a schematic perspective view of an electrode body; Fig. 4 is a schematic plan view of a top cap; Fig. 5 is a partial schematic cross-sectional view of a flange portion having a bending point;

[0010] Hereinafter, an embodiment of a secondary battery according to the present disclosure will be described.

[0011] 1 is a partial schematic cross-sectional view showing an example of the configuration of a secondary battery according to an embodiment. The secondary battery 10 shown in Fig. 1 is configured to include a cylindrical outer can 14 with a bottom and an open top, an electrode assembly 12 housed in the outer can 14, and a sealing body that seals the opening of the outer can 14.

[0012] FIG. 3 is a schematic perspective view of an electrode assembly. The electrode assembly 12 shown in FIG. 3 is a wound electrode assembly including a long positive electrode 34, a long negative electrode 36, and two long separators 38. The positive electrode 34 and the negative electrode 36 are wound with the separators 38 interposed therebetween. A positive electrode lead 40 is joined to the positive electrode 34, and a negative electrode lead 42 is joined to the negative electrode 36. While FIG. 3 shows three positive electrode leads 40 spaced apart at a predetermined interval and two negative electrode leads 42 at both ends of the negative electrode 36, the number and placement of the leads are not particularly limited. To suppress lithium deposition, the negative electrode 36 is preferably formed to be slightly larger than the positive electrode 34 and longer in both the longitudinal and width directions (short-side directions) than the positive electrode 34. The two separators 38 are preferably formed to be at least slightly larger than the positive electrode 34 and arranged to sandwich the positive electrode 34. The electrode body 12 is not limited to the wound electrode body described above, as long as it has a configuration in which a positive electrode and a negative electrode are arranged opposite each other with a separator interposed therebetween, and may also be a laminated electrode body in which positive electrodes and negative electrodes are alternately stacked with a separator interposed therebetween.

[0013] The sealing body includes a top cap 16 that serves as a positive electrode terminal or a negative electrode terminal, a conductive member 20 of a polarity different from that of the top cap 16, and an insulating member 18 interposed between the top cap 16 and the conductive member 20. The top cap 16 has a terminal main body portion 16a and a flange portion 16b located on the periphery of the terminal main body portion 16a. Details of the top cap 16, the conductive member 20, and the insulating member 18 will be described later.

[0014] The sealing body shown in FIG. 1 includes a current collector 24 and a metal plate 22. The current collector 24 and the metal plate 22 are, for example, annular metal plate members having a through-hole in the radial center. The current collector 24, the metal plate 22, and the top cap 16 are stacked in this order from the electrode body 12 side. As shown in FIG. 1, the current collector 24 has, for example, a recess recessed into the inside of the battery and a flange portion located around the recess, and the flange portion of the current collector 24 abuts against the flange portion 16b of the top cap 16. The flange portion of the current collector 24 is preferably joined to the flange portion 16b of the top cap 16 by welding such as resistance welding, ultrasonic welding, or laser welding.

[0015] As shown in FIG. 1 , one electrode lead 32, consisting of the aforementioned positive electrode lead 40 or negative electrode lead 42, extends toward the sealing body through a through hole in an insulating plate 28 arranged on the top of the electrode body 12, passes through a through hole in the current collector plate 24, and is bent to fit along the surface of the recess in the current collector plate 24. The tip of the one electrode lead 32 is sandwiched between the surface of the recess in the current collector plate 24 and the metal plate 22. The one electrode lead 32 and the metal plate 22, the one electrode lead 32 and the recess in the current collector plate 24, and the recess in the current collector plate 24 and the metal plate 22 are preferably joined by welding such as resistance welding, ultrasonic welding, or laser welding. In this way, the top cap 16 is electrically connected to the one electrode lead 32 via the current collector plate 24 and functions as an electrode terminal. If the one electrode lead 32 is a positive electrode lead 40 connected to a positive electrode 34, the top cap 16 serves as a positive electrode terminal. If the one electrode lead 32 is a negative electrode lead 42 connected to a negative electrode 36, the top cap 16 serves as a negative electrode terminal. The top cap 16 is preferably a positive terminal.

[0016] The outer can 14 shown in FIG. 1 is, for example, a cylindrical metal can with a bottom and an open top, which contains the electrode assembly 12, electrolyte, etc. The outer shape of the outer can 14 is not limited to a cylindrical shape with a bottom and may be, for example, a rectangular tubular shape with a bottom. The outer can 14 preferably has a grooved portion 30 in which a portion of the side surface is recessed inward. The grooved portion 30 is, for example, formed in an annular shape along the circumferential direction of the outer can 14. The top cap 16 and the current collector plate 24 are placed on the grooved portion 30 and are fixed to the opening of the outer can 14 by crimping via a gasket 26, thereby sealing the interior space of the outer can 14. The gasket 26 not only serves as a sealant to maintain airtightness inside the battery, but also as an insulating material to insulate the outer can 14 from the top cap 16 and the current collector plate 24.

[0017] Although not shown, the outer can 14 is joined to the other electrode lead, which is made up of the above-mentioned positive electrode lead 40 or negative electrode lead 42 and has a polarity different from that of the above-mentioned one electrode lead 32. Therefore, if the other electrode lead is the positive electrode lead 40 connected to the positive electrode 34, the outer can 14 serves as a positive electrode terminal, and if the other electrode lead is the negative electrode lead 42 connected to the negative electrode 36, the outer can 14 serves as a negative electrode terminal. It is preferable that the outer can 14 serves as a negative electrode terminal.

[0018] The top cap 16, conductive member 20, and insulating member 18 that constitute the sealing body will be described in detail below.

[0019] The top cap 16 is, for example, a metal disk, and as described above, has a terminal main body 16a and a flange 16b. The terminal main body 16a shown in FIG. 1 has a convex shape that protrudes toward the outside of the secondary battery 10. A notch 16c is formed on the surface of the flange 16b, and serves as a bending point that can bend when internal pressure increases due to gas generation inside the secondary battery 10. The notch 16c faces the conductive member 20 via the insulating member 18. The area where the notch 16c is formed is a thinner portion than the area where the notch 16c is not formed.

[0020] FIG. 4 is a schematic plan view of the top cap. The surface of the top cap 16 in FIG. 4 is the surface (external surface) facing the outside of the secondary battery 10. The shape of the cutout 16c in a plan view is not particularly limited, and may be a closed loop (e.g., a circular shape) as shown in FIG. 4 or a shape with a portion of the loop missing (e.g., a semicircular shape). Furthermore, the cutout 16c may be provided on the outer surface of the flange 16b as shown in FIGS. 1 and 4, or on the inner surface of the flange 16b (the surface opposite the outer surface and facing the inside of the secondary battery 10), or on both the outer and inner surfaces of the flange 16b.

[0021] The width of the notch 16c may be set appropriately so that the flange 16b can easily bend with an increase in internal pressure of the secondary battery 10, and may be, for example, 5 μm or more and 100 μm or less. The depth of the notch 16c may also be set appropriately so that the flange 16b can easily bend with an increase in internal pressure of the secondary battery 10, and may be, for example, 5% or more and 20% or less of the thickness of the flange 16b. The thickness of the flange 16b and the terminal main body 16a is, for example, 0.1 mm or more and 2.0 mm or less.

[0022] 5 is a partial schematic cross-sectional view of a flange portion having a bending point. The bending point that can bend due to an increase in internal pressure caused by gas generation inside the secondary battery 10 is not limited to the notch 16c described above, and may be, for example, a recess 16d as shown in FIG. 5. In any case, the bending point may be designed so that the flange portion 16b can bend due to an increase in internal pressure caused by gas generation inside the secondary battery 10.

[0023] The conductive member 20 shown in FIG. 1 abuts against the outer can 14 and has a polarity different from that of the top cap 16. The conductive member 20 is preferably a ring-shaped metal member with an opening in the center. The insulating member 18 is also preferably a ring-shaped insulating member with an opening in the center. For example, after the top cap 16 is fixed to the outer can 14 by crimping, the insulating member 18 is placed on the top cap 16, and the conductive member 20 is placed on the insulating member 18 so that the terminal main body portion 16 a of the top cap 16 is exposed from the openings of the insulating member 18 and the conductive member 20. The outer peripheral edge of the conductive member 20 is preferably fixed to the open edge or grooved portion 30 of the outer can 14 by crimping, or joined by welding such as resistance welding, ultrasonic welding, or laser welding.

[0024] The conductive member 20 preferably has a protrusion 20a that protrudes toward the flange portion 16b of the top cap 16 via the insulating member 18. The shape of the tip of the protrusion 20a is not particularly limited, and may be flat, curved, or acute-angled, as shown in Fig. 1. The protrusion 20a may be provided continuously or intermittently along the central opening of the conductive member 20, for example.

[0025] The protrusion 20a of the conductive member 20 may be disposed in a position facing the flange portion 16b with the insulating member 18 interposed therebetween. Preferably, the notch 16c (bending point) provided in the flange portion 16b is located closer to the outer periphery of the top cap 16 than the protrusion 20a of the conductive member 20. Furthermore, when the distance from the center of the top cap 16 to the outer periphery edge is 1, the distance from the center of the top cap 16 to the notch 16c (bending point) is preferably 0.8 or less. Furthermore, the insulating member 18 may be provided with a recess into which the protrusion 20a of the conductive member 20 is fitted.

[0026] When the secondary battery 10 is in a normal state, the insulating member 18 is interposed between the top cap 16 and the conductive member 20 to maintain insulation therebetween. However, the insulating member 18 is preferably made of a material that melts or softens due to heat generated by the secondary battery 10 when internal pressure increases due to gas generation inside the secondary battery 10. Specifically, the insulating material is preferably a resin-based or rubber-based material that has a melting point or glass transition point lower than the heat generation temperature of the secondary battery 10 when internal pressure increases due to gas generation inside the secondary battery 10. Note that the heat generation temperature of the secondary battery 10 when internal pressure increases due to gas generation inside the secondary battery 10 may be, for example, 200°C or higher.

[0027] Examples of resin-based materials include polytetrafluoroethylene, polyimide, polyamide, polystyrene, polypropylene, polyethylene, polyvinyl chloride, and nylon. Examples of rubber-based materials include natural rubber, ebonite, butyl rubber, chloroprene rubber, and silicone rubber. The glass transition point is defined as the inflection point of the baseline shift detected when a differential scanning calorimeter is used to raise the temperature from 0°C to a predetermined temperature (e.g., 340°C) at a rate of 20°C / min. The melting point is defined as the melting peak temperature detected when a differential scanning calorimeter is used to raise the temperature from 0°C to a predetermined temperature (e.g., 340°C) at a rate of 20°C / min, hold the temperature at 340°C for 1 minute, cool the temperature to 100°C at a rate of 20°C / min, hold the temperature at 100°C for 1 minute, and then raise the temperature again at 20°C / min to 340°C.

[0028] The operation of the secondary battery 10 according to this embodiment in normal and abnormal conditions will be described.

[0029] When the secondary battery 10 is in a normal state, as shown in FIG. 1, the top cap 16, which serves as the positive or negative terminal, and the conductive member 20, which has a polarity different from that of the top cap 16, are insulated from each other by the insulating member 18 interposed therebetween.

[0030] FIG. 2 is a partial schematic cross-sectional view showing an example of the state of the secondary battery of the embodiment during an abnormality. For example, when the secondary battery 10 generates heat due to overcharging or the like and its temperature rises, gas is generated due to decomposition of the electrolyte, etc., and the internal pressure of the secondary battery 10 increases. When the internal pressure of the secondary battery 10 increases, the top cap 16 bends from the notch 16c (bending point) provided in the flange portion 16b and is forced upward. As the top cap 16 is forced upward, the insulating member 18 breaks, bringing the top cap 16 and the conductive member 20 into contact, forcing the secondary battery 10 to short-circuit. As described above, by using a material for the insulating member 18 that melts or softens due to heat generated by the secondary battery 10 when the internal pressure increases due to gas generation inside the secondary battery 10, the insulating member 18 is more likely to break when the top cap 16 is forced upward, thereby more quickly shorting the secondary battery 10 due to contact between the top cap 16 and the conductive member 20. Furthermore, by providing the protrusion 20a on the conductive member 20, the insulating member 18 is more likely to break starting from the protrusion 20a when the top cap 16 is pushed up, which allows the secondary battery 10 to be short-circuited more quickly due to contact between the top cap 16 and the conductive member 20. Furthermore, by locating the notch 16c (bending point) closer to the outer periphery of the top cap 16 than the protrusion 20a of the conductive member 20, or by setting the distance from the center of the top cap 16 to the notch 16c within the above range, the secondary battery 10 can be short-circuited more quickly due to contact between the top cap 16 and the conductive member 20. By forcibly short-circuiting in this way and consuming thermal energy, it is possible to reduce the amount of heat generated by the battery when internal pressure increases due to gas generation inside the secondary battery 10.

[0031] The secondary battery 10 according to this embodiment is preferably applied to a lithium ion secondary battery, but is not limited to a lithium ion secondary battery and may be applied to other secondary batteries. The positive electrode, negative electrode, separator, and electrolyte used in the lithium ion secondary battery may be made of known materials, such as those listed below.

[0032] <Positive Electrode> The positive electrode includes a positive electrode current collector such as a metal foil and a positive electrode composite layer formed on the positive electrode current collector. The positive electrode current collector can be a foil of a metal such as aluminum that is stable in the potential range of the positive electrode, or a film with such a metal disposed on the surface layer. The positive electrode composite layer includes, for example, a positive electrode active material, a conductive material, and a binder.

[0033] Examples of the positive electrode active material include lithium transition metal composite oxides, and specifically, lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, lithium nickel manganese composite oxide, lithium nickel cobalt composite oxide, and the like can be used. These lithium transition metal composite oxides may also be doped with Al, Ti, Zr, Nb, B, W, Mg, Mo, and the like.

[0034] Examples of the conductive material include carbon powder such as carbon black, acetylene black, ketjen black, and graphite.

[0035] Examples of the binder include fluorine-based polymers, rubber-based polymers, etc. Examples of the fluorine-based polymers include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), and modified products thereof, and examples of the rubber-based polymers include ethylene-propylene-isoprene copolymers, ethylene-propylene-butadiene copolymers, styrene-butadiene copolymers, and carboxymethyl cellulose.

[0036] <Negative electrode> The negative electrode includes a negative electrode current collector such as a metal foil and a negative electrode composite layer formed on the negative electrode current collector. The negative electrode current collector can be a foil of a metal such as copper that is stable in the potential range of the negative electrode, or a film with such a metal disposed on the surface layer. The negative electrode composite layer includes, for example, a negative electrode active material and a binder.

[0037] The negative electrode active material can be a carbon material capable of absorbing and releasing lithium ions, such as graphite, non-graphitizable carbon, graphitizable carbon, fibrous carbon, coke, and carbon black. Furthermore, non-carbon materials can be silicon, tin, and alloys or oxides thereof. The binder can be the same as that used for the positive electrode.

[0038] <Electrolyte> The electrolyte has, for example, ion conductivity (for example, lithium ion conductivity). The electrolyte may be a liquid electrolyte (electrolytic solution) or a solid electrolyte.

[0039] The liquid electrolyte (electrolytic solution) contains, for example, a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of the non-aqueous solvent include esters, ethers, nitriles, amides, and mixed solvents of two or more of these. Examples of the non-aqueous solvent include ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and mixed solvents of these. The non-aqueous solvent may contain a halogen-substituted compound (e.g., fluoroethylene carbonate) in which at least a portion of the hydrogen atoms of these solvents are substituted with halogen atoms such as fluorine. Examples of the electrolyte salt include LiPF ６ Lithium salts such as

[0040] Furthermore, examples of the solid electrolyte that can be used include solid or gel-like polymer electrolytes, inorganic solid electrolytes, and the like. The polymer electrolyte includes, for example, a lithium salt and a matrix polymer, or a non-aqueous solvent, a lithium salt, and a matrix polymer. For example, a polymer material that absorbs a non-aqueous solvent and gels is used as the matrix polymer. Examples of the polymer material include fluororesin, acrylic resin, and polyether resin. For example, the inorganic solid electrolyte can be a material known in all-solid-state lithium ion secondary batteries (e.g., oxide-based solid electrolytes, sulfide-based solid electrolytes, halogen-based solid electrolytes, and the like). While the above-exemplified electrolytes are non-aqueous electrolytes, the electrolyte is not limited to non-aqueous electrolytes and may be an aqueous electrolyte.

[0041] <Separator> A porous sheet or the like having ion permeability and insulating properties is used as the separator. Specific examples of the porous sheet include a microporous thin film, a woven fabric, a nonwoven fabric, etc. Suitable materials for the separator include olefin-based resins such as polyethylene and polypropylene, and cellulose.

[0042] The present disclosure is further described by the following embodiments. Configuration 1: A secondary battery comprising: a cylindrical outer can with a bottom that is open at the top; an electrode assembly housed in the outer can, with a positive electrode and a negative electrode arranged opposite each other with a separator interposed therebetween; and a sealing body that seals the opening of the outer can, wherein the sealing body has a top cap that serves as a positive electrode terminal or a negative electrode terminal, a conductive member of a different polarity from the top cap, and an insulating member interposed between the top cap and the conductive member, and the top cap has a terminal main body and a flange portion located on the periphery of the terminal main body, and the flange portion has a bending point that can bend due to an increase in internal pressure caused by gas generation, and the bending point faces the conductive member via the insulating member. Configuration 2: The secondary battery according to Configuration 1, wherein the conductive member is ring-shaped with an opening in the center. Configuration 3: The secondary battery according to Configuration 1 or 2, wherein the conductive member has a protrusion that protrudes toward the flange portion via the insulating member. The secondary battery of any one of the preceding embodiments, wherein the bend point is located closer to the outer periphery of the top cap than the protrusion of the conductive member.

[0043] 10 Secondary battery, 12 Electrode body, 14 Outer can, 16 Top cap, 16a Terminal main body, 16b Flange portion, 16c Notch portion, 16d Recessed portion, 18 Insulating member, 20 Conductive member, 20a Protrusion portion, 22 Metal plate, 24 Current collector plate, 26 Gasket, 28 Insulating plate, 30 Grooved portion, 32 One electrode lead, 34 Positive electrode, 36 Negative electrode, 38 Separator, 40 Positive electrode lead, 42 Negative electrode lead.

Claims

1. A secondary battery comprising: a cylindrical outer can with a bottom that is open at the top; an electrode assembly contained within the outer can, with a positive electrode and a negative electrode arranged opposite each other with a separator between them; and a sealing body that seals the opening of the outer can, wherein the sealing body has a top cap that serves as a positive electrode terminal or a negative electrode terminal, a conductive member of a different polarity from that of the top cap, and an insulating member interposed between the top cap and the conductive member, the top cap having a terminal main body portion and a flange portion located on the periphery of the terminal main body portion, the flange portion having a bending point that can be bent due to an increase in internal pressure accompanying gas generation, and the bending point facing the conductive member via the insulating member.

2. The secondary battery according to claim 1, wherein the conductive member is ring-shaped with an opening in the center.

3. The secondary battery according to claim 1 or 2, wherein the conductive member has a protrusion that protrudes toward the flange portion via the insulating member.

4. The secondary battery according to claim 3, wherein the bending point is located closer to the outer periphery of the top cap than the protruding portion of the conductive member.

5. The secondary battery according to claim 3, wherein the tip of the protrusion of the conductive member is flat, curved or acute-angled.

Images