SEALED BATTERY

According to the present disclosure, a sealed battery comprises a cylindrical exterior can having a bottom, a sealing body closing one end of the exterior can, and an electrode assembly disposed in the exterior can. The sealing body includes a valve body. The valve body includes an annular or C-shaped first frangible portion, and an annular second frangible portion having an inside-portion area smaller than an inside-portion area of the first frangible portion. The valve body is configured such that a vent pressure when the second frangible portion is fractured is lower than a vent pressure when the first frangible portion is fractured.

TECHNICAL FIELD

The present disclosure relates to a sealed battery.

BACKGROUND ART

In recent years, there has been a need for a secondary battery to have a further increased capacity because applications have been expanding to a power source for electric vehicles, a power storage device for utilizing natural energy, and the like. In electric vehicle and power storage devices, a battery module is used, which is formed by connecting a number of secondary batteries in series or in parallel via an external lead. As the capacity of the secondary battery increases, higher safety is required for the secondary battery and the battery module. Traditionally, when a battery internal pressure is abnormally increased due to overcharge of the secondary battery, for example, a current path in the secondary battery is caused to be cut-off to prevent thermal runaway and rupture of the secondary battery in advance.

Patent Literature 1 describes a sealed battery in which a current shut-off mechanism is incorporated into a sealing member that seals one end of an exterior can to ensure safety. The current shut-off mechanism is configured by combining a vent member made of a metal, an insulating member, and a metal body having a ventilation hole. Respective central portions of the vent member and the metal body are connected to each other, and the insulating member is interposed between their respective outer peripheral portions. When a battery internal pressure increases, the metal body pulls a connection part with the vent member outward of the battery, and the connection part or a thin portion provided in the metal body is fractured so that a current path between the vent member and the metal body is cut-off. Further, when the battery internal pressure increases, the vent member is fractured with the thin portion of the vent member used as a starting point, whereby a gas in the battery is exhausted.

CITATION LIST

Patent Literature

PATENT LITERATURE 1: International Publication No. WO 2016/157748

SUMMARY

Technical Problem

In a configuration described in Patent Literature 1, the sealing member includes three components, i.e., the vent member, the insulating member, and the metal body to make the sealing member have a current cut-off function and a function of exhausting a gas in the battery. Since the components are required to reliably operate at the time of an abnormality in the battery, it is essential that each have a complicated and highly accurate processed shape. When the number of components constituting the sealing member is large, this places a large burden such as an increase in the number of man-hours in processing. Thus, it is desired to reduce the number of components constituting the sealing member. To make the sealing member have the current cut-off function, it is conceivable to form a small annular easy fracture part surrounding a portion, to which an external lead is connected, of the sealing member. However, in this case, when a gas is exhausted through a small hole formed by the easy fracture part being fractured over its entire circumference, the hole is more prone to being clogged with contents of the battery. Hence, there is room for improvement in terms of making the sealing member have a good current cut-off function and gas exhaust function.

It is an advantage of the present disclosure to provide a sealed battery capable of reducing the number of components constituting a sealing member by making a vent member have a good current cut-off function and gas exhaust function.

Solution to Problem

A sealed battery according to the present disclosure comprises an exterior can having a bottomed cylindrical shape, a sealing member that closes one end of the exterior can, and an electrode assembly arranged in the exterior can, in which the sealing member includes a vent member, the vent member includes an annular or C-shaped first easy fracture part and an annular second easy fracture part having an inner portion the area of which is smaller than the area of an inner portion of the first easy fracture part, and a vent pressure at which the second easy fracture part is fractured is lower than a vent pressure at which the first easy fracture part is fractured.

Advantageous Effect of Invention

The sealed battery according to present disclosure makes it possible to reduce the number of components constituting the sealing member by making the vent member have a good current cut-off function and gas exhaust function.

DESCRIPTION OF EMBODIMENTS

An embodiment of the present invention will be described in detail below with reference to the accompanying drawings. In the following description, specific shapes, materials, and directions, for example, are examples to facilitate understanding of the present disclosure, and can be appropriately changed to match uses, purposes, and specifications, for example, of a sealed battery. Although a case where the sealed battery is a non-aqueous electrolyte cylindrical secondary battery will be mainly described below, the sealed battery is not limited to this.

FIG.1is a sectional view of a sealed battery10according to the embodiment.FIG.2Ais a perspective view in a case where a sealing member11is cut into two halves. For example, a non-aqueous electrolyte secondary battery such as a lithium ion battery is used for the sealed battery10. The sealed battery10is configured by housing an electrode assembly20and a non-aqueous electrolyte (not illustrated) in a cylindrical exterior can100having a bottomed cylindrical shape. The sealing member11is fixed to an opening at one end (an upper end inFIG.1) of the exterior can100via a gasket18having electrical insulation. As a result, the opening at the one end of the exterior can100is closed by the sealing member11via the gasket18. The gasket18is an insulating member made of resin, and seals a space between the exterior can100and the sealing member11. The non-aqueous electrolyte contains a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. The non-aqueous electrolyte is not limited to a liquid electrolyte, and may be a solid electrolyte using a gel polymer or the like.

The electrode assembly20is of a wound type, includes a positive electrode plate21, a negative electrode plate22, and a separator23, and is obtained by winding the positive electrode plate21and the negative electrode plate22in a spiral shape with the separator23interposed therebetween. Hereinafter, one side in a winding axis direction of the electrode assembly20and the other side in the winding axis direction may be respectively referred to as “upper” and “lower”.

The sealing member11is composed of only a vent member12made of a metal. The vent member12has a function as a positive electrode terminal, a function as a current cut-off function for cutting-off a current path when a battery internal pressure increases, and a function of exhausting an internal gas when the battery internal pressure further increases. The sealing member11can also include other components such as a terminal cap disposed on the vent member12. The vent member12is entirely formed into a disk shape, and has a first thin portion13aon the outer side and a second thin portion13b,each having a groove shape concentrically formed on its inner surface (its lower side surface inFIG.1) on the inner side of the electrode assembly20. As a result, a first easy fracture part14composed of the annular first thin portion13ais formed in an outward portion in a radial direction of the vent member12, and a second easy fracture part15composed of the annular second thin portion13bis formed in an inward portion in the radial direction of the vent member12. The second easy fracture part15is provided radially inside the first easy fracture part14. In a planar view of the vent member12, the area of an inner portion S2of the second easy fracture part15is smaller than the area of an inner portion S1of the first easy fracture part14. The inner portion S1is a portion including the inner portion S2. The vent member12can be produced by aluminum or an aluminum alloy, for example. An external lead50to be electrically connected to another sealed battery in a battery module (not illustrated) or an external device (not illustrated) is welded to an outer surface (an upper side surface inFIG.1), radially inside the second easy fracture part15, of the vent member12. InFIG.1, only an end portion, on the connection side of the sealing member11, of the external lead50is illustrated.

An end portion of a positive electrode lead21ato be connected to the electrode assembly20is welded to the inner surface (the lower side surface inFIG.1) as a surface on the electrode assembly20side, radially outside the second easy fracture part15of the vent member12. The positive electrode lead21acorresponds to an electrode lead. Although a case where the end portion of the positive electrode lead21ais welded, radially outside the first easy fracture part14, to the inner surface of the vent member12is illustrated inFIG.1, the end portion of the positive electrode lead21amay be welded, between the second easy fracture part15and the first easy fracture part14, to the inner surface of the vent member12.

Further, the vent member12is configured such that a second vent pressure P2at which the second easy fracture part15is fractured is lower than a first vent pressure P1at which the first easy fracture part14is fractured (P2<P1). For example, the second vent pressure P2may be lower than the first vent pressure P1by making the thickness of the second easy fracture part15smaller than the thickness of the first easy fracture part14. Alternatively, the second vent pressure P2may be lower than the first vent pressure P1by making a cross-sectional shape of the second thin portion13bdifferent from a cross-sectional shape of the first thin portion13awhile the thickness of the second easy fracture part15is made smaller than the thickness of the first easy fracture part14or when the thickness of the second easy fracture part15is made the same as the thickness of the first easy fracture part14. For example, the cross-sectional shape of the first thin portion13ais set to a semi-circular shape or a semi-elliptical shape, and the cross-sectional shape of the second thin portion13bis set to a V shape, thereby making it easier to fracture the second easy fracture part15than the first easy fracture part14.

The gasket18is an annular member, and is disposed between an inner peripheral surface of the opening formed at one end (the upper end inFIG.1) of the exterior can100and an outer peripheral surface of the sealing member11and is caulked and fixed by the end portion of the exterior can100. In this state, an outer peripheral portion of the vent member12is caulked and fixed by the exterior can100via the gasket18. The gasket18and the sealing member11constitute a sealing structure at one end of the sealed battery10. A material, which enables electrical insulation to be ensured and does not affect a battery characteristic, can be used for the gasket18. Polymer resin is preferable as a material used for the gasket18, and examples thereof include polypropylene (PP) resin and polybutylene terephthalate (PBT) resin.

In the sealed battery10, when the battery internal pressure increases, the second easy fracture part15(FIG.1) is fractured in its entirety in its circumferential direction, and a disk portion of a central portion, to which the external lead50(FIG.1) is connected, of the vent member12is separated, as illustrated inFIG.2Bdescribed below, so that a current path between the external lead50and the positive electrode lead21a(FIG.1) is cut-off. In the vent member12, the disk portion of the central portion is separated, whereby an exhaust hole16is formed. The sealed battery10is configured such that when the battery internal pressure further increases, at least a portion in a circumferential direction of the first easy fracture part14is fractured, as illustrated inFIG.2Cdescribed below, whereby an internal gas is exhausted to the outside via a gap G caused by the fractured portion.

Then, the electrode assembly20will be described. The electrode assembly20is arranged in the exterior can100. The positive electrode plate21constituting the electrode assembly20includes a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector. For example, the positive electrode active material layer is formed on both surfaces of the positive electrode current collector. A metal foil made of aluminum or the like, or a film having a surface layer of the metal, for example, is used for the positive electrode current collector. A preferable positive electrode current collector is a metal foil made of aluminum or an aluminum alloy foil. The thickness of the positive electrode current collector is 10 μm to 30 μm, for example.

The positive electrode active material layer preferably contains a positive electrode active material, a conductive agent, and a binder. The positive electrode plate21is produced by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, a binder, and a dispersion medium such as N-methyl-2-pyrrolidon (NMP) onto both surfaces of the positive electrode current collector, followed by drying and rolling.

Examples of the positive electrode active material can include a lithium-containing transition metal composite oxide containing a transition metal element such as Co, Mn, or Ni. The lithium-containing transition metal composite oxide is not particularly limited, but may be preferably a composite oxide represented by a general formula: Li1+xMO2(in the formula, −0.2<x≤0.2, where M contains at least one of Ni, Co, Mn, and Al).

Examples of the above-described conductive agent include carbon materials such as carbon black (CB), acetylene black (AB), ketjen black, and graphite. Examples of the above-described binder include fluorine-based resin such as polytetrafluoroethylene (PTFE) or polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide (PI), acrylic-based resin, and polyolefin-based resin. The resins and carboxymethyl cellulose (CMC) or its salt, polyethylene oxide (PEO), or the like may be used in combination. These may be each used alone or in a combination of two or more thereof.

The positive electrode plate21is provided with a positive electrode current collector exposed part (not illustrated) where a surface of a metal composing a positive electrode current collector is exposed. The positive electrode current collector exposed part is a portion to which the positive electrode lead21ais connected and is a portion where a surface of the positive electrode current collector is not covered with a positive electrode active material layer. One end-side portion of the positive electrode lead21ais bonded to the positive electrode current collector exposed part by ultrasonic welding, for example. The other end-side portion of the positive electrode lead21ais guided upward through an opening formed in a disk-shaped first insulating plate30disposed on the upper side of the electrode assembly20and is connected to the inner surface on the electrode assembly20side of the vent member12. Examples of a material for the positive electrode lead21ainclude aluminum, an aluminum alloy, nickel, a nickel alloy, iron, and stainless steel.

The negative electrode plate22includes a negative electrode current collector and a negative electrode active material layer formed on the negative electrode current collector. For example, a negative electrode active material layer is formed on both surfaces of the negative electrode current collector. Further, the negative electrode plate22has a negative electrode current collector exposed part (not illustrated) provided in its winding-end-side end portion. The negative electrode current collector exposed part is a portion to which a negative electrode lead22ais connected and is a portion where a surface of the negative electrode current collector is not covered with the negative electrode active material layer. One end-side portion of the negative electrode lead22ais bonded to the negative electrode current collector exposed part by ultrasonic welding, for example. The other end-side portion of the negative electrode lead22ais connected to a bottom portion of the exterior can100through the outer peripheral side of a disk-shaped second insulating plate31disposed on the lower side of the electrode assembly20.

The negative electrode active material layer preferably contains a negative electrode active material and a binder. The negative electrode plate22is produced by applying a negative electrode mixture slurry containing a negative electrode active material, a binder, and water, for example, on both surfaces of the negative electrode current collector, followed by drying and rolling.

The negative electrode active material is not particularly limited as long as it can reversibly occlude and release lithium ions, and examples of the negative electrode active material to be used can include a carbon material such as natural graphite or artificial graphite, a metal to be alloyed with lithium, such as Si or Sn, an alloy containing these, and a composite oxide. As the binder contained in the negative electrode active material layer, resin similar to that in the positive electrode plate21, for example, is used. If the negative electrode mixture slurry is prepared with an aqueous solvent, styrene-butadiene rubber (SBR), CMC or its salt, a polyacrylic acid or its salt, polyvinyl alcohol, and the like can be used. These may be each used alone or in a combination of two or more thereof.

The negative electrode plate22is used by being wound with it being laminated on the positive electrode plate21via the separator23. With the use of the negative electrode lead22aor the negative electrode lead22abeing omitted, the negative electrode plate22may be electrically connected to the exterior can100by arranging a negative electrode current collector exposed part over the entire circumference of an outermost peripheral surface of the winding-end-side end portion of the negative electrode plate22and bringing the negative electrode current collector exposed part into contact with an inner peripheral surface of a cylindrical portion of the exterior can100. This makes it possible to ensure more preferable current collectability. At this time, the negative electrode lead22amay be bonded to a negative electrode current collector exposed part formed in a winding-start-side end portion of the negative electrode plate22.

A porous sheet having ion permeability and electrical insulation is used for the separator23. Specific examples of the porous sheet can include a microporous thin film, a woven fabric, and a non-woven fabric. As a material for the separator23, polyolefin-based resin such as polyethylene or polypropylene is preferable. The thickness of the separator23is 10 μm to 50 μm, for example. The separator23tends to be thinner as the battery increases in capacity and output power. The separator23has a melting point of approximately 130° C. to 180° C., for example.

The sealed battery10is assembled in the following manner, for example. For example, the electrode assembly20, together with the disk-shaped second insulating plate31on the lower side thereof, is inserted into the inside of the exterior can100having a bottomed cylindrical shape produced by drawing a steel plate, and the negative electrode lead22aconnected to the negative electrode plate22is connected to the bottom portion of the exterior can100by welding. Then, the disk-shaped first insulating plate30is inserted into the upper side of the electrode assembly20inside the exterior can100, and a groove portion101(FIG.1) having a U shape in cross section is formed by plastic working over its entire circumference in its circumferential direction on the side of the opening above the first insulating plate30in the exterior can100. Then, a predetermined amount of prepared non-aqueous electrolyte is injected into the exterior can100housing the electrode assembly20. The positive electrode lead21aconnected to the positive electrode plate21is connected to an inner side surface of the sealing member11by welding. The vent member12is housed via the gasket18on the groove portion101inside the exterior can100while the positive electrode lead21ais folded with the gasket18inserted into and disposed in the upper side of the groove portion101inside an opening end portion of the exterior can100, and the opening end portion of the exterior can100is caulked, thereby producing the sealed battery10.

The above-described sealed battery10exhibits a current cut-off function and a gas exhaust function in the following manner.FIG.2Bis a diagram corresponding toFIG.2Aand illustrating a state where the second easy fracture part15is fractured over its entire circumference due to an increase in battery internal pressure so that the inner portion is separated.FIG.2Cis a diagram corresponding toFIG.2Aand illustrating a state where a part of the first easy fracture part14is fractured due to a further increase in battery inner pressure from the state illustrated inFIG.2B.

Specifically, when the battery internal pressure increases, the second easy fracture part15(FIG.2A) is first fractured in its entirety in the circumferential direction, and the inner portion of the second easy fracture part15to which the external lead50(FIG.1andFIG.2A) is connected is completely separated from the vent member12, as illustrated inFIG.2B. As a result, a current path between the inner portion of the second easy fracture part15and the positive electrode lead21a(FIG.1) is cut-off. An exhaust hole16is formed in the central portion of the vent member12. If the speed of an exhaust from the exhaust hole16is insufficient, when the battery internal pressure further increases, at least a part in the circumferential direction of the first easy fracture part14is fractured, and the inner portion of the first easy fracture part14is deformed to the outside of the battery, as illustrated inFIG.2C. As a result, a gas in the battery is exhausted through the gap G. At this time, the second easy fracture part15is formed in an annular shape because it is necessary to cause the second easy fracture part15to be fractured entirely in the circumferential direction to cut-off the current path as described above. However, when the first easy fracture part14is to be fractured, it is sufficient that only a part of the first easy fracture part14in the circumferential direction is fractured. Hence, the first easy fracture part14is not limited to that to be formed in an annular shape in the vent member12, but may be formed in a C shape by a thin portion or the like in the vent member12. The first easy fracture part may be formed by forming a stepped portion the thickness of which changes in the radial direction of the vent member12.

The above-described sealed battery10makes it possible to make the vent member12have a good current cut-off function and gas exhaust function, thereby making it possible to reduce the number of components constituting the sealing member11. As a result, the number of components requiring a processing accuracy can be reduced, thereby leading to a reduction in manufacturing cost.

FIG.3is a diagram corresponding toFIG.2Aand illustrating a sealed battery in a first comparative example. In a vent member12aconstituting a sealing member11ain the sealed battery in the first comparative example, a second easy fracture part15(FIG.2A) is not formed, and only a first easy fracture part14is formed in an outward portion in a radial direction of the vent member12a,unlike in the vent member12illustrated inFIG.2A. In the first comparative example like this, if the first easy fracture part14can be fractured over its entire circumference with an increase in battery internal pressure, a current path between a portion radially outside the first easy fracture part14to which the positive electrode lead21a(FIG.1) is connected and a portion radially inside the first easy fracture part14in the vent member12acan be cut-off. However, in the first comparative example, the circumferential length of the first easy fracture part14is longer than the circumferential length of the second easy fracture part15in the embodiment illustrated inFIG.1toFIG.2C. In the first comparative example, this makes it difficult to stably fracture the first easy fracture part14over the entire circumference to cut-off the current path with an initial pressure at which the battery internal pressure has increased. Therefore, in the sealed battery in the first comparative example, it is difficult to make the vent member12ahave a good current cut-off function.

FIG.4is a diagram corresponding toFIG.2Aand illustrating a sealed battery in a second comparative example. In a vent member12bconstituting a sealing member11bin the sealed battery in the second comparative example, a first easy fracture part14(FIG.2A) is not formed, and only a second easy fracture part15is formed in an inward portion in a radial direction of the vent member12b,unlike in the vent member12illustrated inFIG.2A. In the second comparative example like this, the circumferential length of the second easy fracture part15is shorter than the circumferential length of the first easy fracture part14in the first comparative example illustrated inFIG.3. In fact, this makes it easy to stably fracture the second easy fracture part15over the entire circumference to cut-off a current path with an initial pressure at which a battery internal pressure has increased. However, it tends to reduce the diameter of an exhaust hole of a vent member formed after an inward portion of the second easy fracture part15is separated. As a result, the exhaust hole is more prone to be clogged with contents of the battery, decreasing the exhaust performance and abnormally increasing the battery internal pressure. This may causes damage to a portion, such as a side surface of the battery, where it is desirable to be kept undamaged. Therefore, in the sealed battery in the second comparative example, it is difficult to make the vent member12bhave a good gas exhaust function.

According to the embodiment illustrated inFIG.1toFIG.2C, when the second easy fracture part15having a small circumferential length is fractured over the entire circumference to separate the inner portion in the early stages of an increase in battery internal pressure due to occurrence of an abnormality in the battery, for example, the current path can be cut-off. When the battery internal pressure further increases, the first easy fracture part14larger than the second easy fracture part15is fractured, thereby making it possible to enhance an exhaust performance. As a result, in the present embodiment, problems occurring in the first comparative example and the second comparative example can be solved.

Although a case where the sealed battery10is set as a cylindrical secondary battery has been described in the embodiment illustrated inFIG.1toFIG.2C, the sealed battery according to the present disclosure is not limited to this, and instead may be a rectangular secondary battery whose exterior can has a rectangular parallelepiped shape, for example. The sealed battery according to the present disclosure is not limited to that in which the first easy fracture part and the second easy fracture part are concentrically formed in the sealing member, and instead a first easy fracture part and a second easy fracture part having different centers may be respectively formed at different positions of the sealing member. In this case, the area of an inward portion of the second easy fracture part is made smaller than the area of an inward portion of the first easy fracture part. Further, a vent member is configured such that a vent pressure at which the second easy fracture part is fractured is lower than a vent pressure at which the first easy fracture part is fractured. In this case, too, the number of components in the sealing member can be reduced in a configuration in which the vent member is made to have a good current cut-off function and gas exhaust function, like in the configuration illustrated inFIG.1toFIG.2C.

REFERENCE SIGNS LIST