Cap assembly and secondary battery including the same

A cap assembly and a secondary battery including the cap assembly including a cap-down, and at least a portion thereof is configured to open when pressure is applied to the cap-down, a vent portion, and at least a portion thereof is configured to open when pressure is applied to the vent portion, and a cap-up electrically connected to the vent portion.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean Patent Application No. 10-2014-0019690, filed on Feb. 20, 2014, in the Korean Intellectual Property Office, the entire content of which is incorporated herein by reference.

BACKGROUND

One or more embodiments of the present invention are directed to a cap assembly and a secondary battery including the same.

2. Description of the Related Art

A typical secondary battery includes an electrode assembly having a cylindrical shape, a can having a cylindrical shape and accommodating the electrode assembly, an electrolyte injected into the can and enabling the movement of lithium (Li) ions, and a cap assembly coupled to a side of the can and preventing leakage of the electrolyte and separation of the electrode assembly. Such secondary batteries generally have capacities of about 2000 to about 4000 mAH, and are mainly used in personal computers, digital cameras, camcorders, and electric vehicles that require large power capacity.

A plurality of secondary batteries may be connected in series or in parallel, assembled into a hard pack of a particular shape by including a protection circuit, and included in electronic devices to serve as a power supply. Methods of manufacturing secondary batteries include forming an electrode assembly by stacking together a negative electrode plate coated with a negative electrode active material, a separator, and a positive electrode plate coated with a positive electrode active material, and winding the negative electrode plate, the separator, and the positive electrode plate in an approximately cylindrical shape.

Next, the electrode assembly is inserted into a can having a cylindrical shape, an electrolyte is injected into the cylindrical can, and a cap assembly is coupled to an upper portion of the cylindrical can, thus manufacturing a lithium-ion battery having a cylindrical shape.

In order to prevent or reduce the possibility of explosion and/or ignition of the secondary battery, the battery may include a safety vent that changes its shape and interrupts the current if the internal pressure of the battery increases due to over-charging. The structure including the safety vent is usually referred to as a current interrupt device (CID), and is often a component of the cap assembly.

SUMMARY

One or more embodiments of the present invention include a cap assembly and a secondary battery including the same.

According to one or more embodiments of the present invention, a cap assembly includes a cap-down, at least a portion of the cap-down configured to open when pressure is applied to the cap-down; a vent portion, at least a portion of the vent portion is configured to open when pressure is applied to the vent portion; and a cap-up electrically connected to the vent portion.

The cap-down may include a dislocation portion configured to open when pressure is applied to the cap-down, and a second notch portion formed around the dislocation portion to define a region of the dislocation portion that opens when pressure is applied to the cap-down.

The cap-down may further include a support portion in the second notch portion and connecting the dislocation portion with another region of the cap-down.

A thickness of the second notch portion may be smaller than a thickness of the dislocation portion.

There may be at least one dislocation portion and at least one second notch portion; and when there is a plurality of dislocation portions and a plurality of second notch portions, the plurality of dislocation portions may be spaced from one another, and each of the plurality of second notch portions may be formed around each of the plurality of dislocation portions.

Each of the plurality of dislocation portions may form the same angle with a center of the cap-down.

Each of the plurality of dislocation portions may be the same distance away from a center of the cap-down.

The dislocation portion and the second notch portion may be circles.

At least a portion of the cap-down may include a dislocation portion configured to open when internal pressure of a can increases.

A thickness of the dislocation portion may be smaller than a thickness of the region of the cap-down not including the dislocation portion.

There may be a plurality of dislocation portions and the plurality of dislocation portions may be spaced from one another.

Each of the plurality of dislocation portions may form the same angle with a center of the cap-down.

Each of the plurality of dislocation portions may be the same distance away from a center of the cap-down.

The dislocation portion may be a circle.

An edge of the vent portion may extend beyond an edge of the cap-up and may be bent to cover at least a portion of an upper surface of the cap-up.

An opening may be formed in a center of the cap-down, and the cap assembly may further include a sub-disk covering the opening in the center of the cap-down.

The cap assembly may further include a sub-disk coupled to the cap-down.

The cap assembly may further include an insulator between the vent portion and the cap-down.

The insulator may cover an outside edge of at least one of the cap-down, the vent portion, and the cap-up.

The cap assembly may further include a cover plate covering the insulator and including a fluid hole.

An area of the fluid hole may be 10 mm2or less.

The cap-down may include a second lower plate; a second upper plate spaced from the second lower plate; and a plurality of second bridge portions connecting the second upper plate and the second lower plate, and spaces between adjacent second bridge portions include the insulator.

According to one or more embodiments of the present invention, a secondary battery includes: an electrode assembly; a can accommodating the electrode assembly and including an opening; and a cap assembly covering the opening, wherein the cap assembly includes: a cap-down, at least a portion of the cap-down configured to open when internal pressure of the can increases; a vent portion, at least a portion of the vent portion configured to open when internal pressure of the can increases; and a cap-up electrically connected to the vent portion.

The cap-down may include a dislocation portion configured to open when internal pressure of the can increases; and a second notch portion formed around the dislocation portion and defining a region of the dislocation portion that opens when internal pressure of the can increases.

The cap-down may further include a support portion in the second notch portion and connecting the dislocation portion with another region of the cap-down.

A thickness of the second notch portion may be smaller than a thickness of the dislocation portion.

There may be at least one dislocation portion and at least one second notch portion; and when there are a plurality of dislocation portions and a plurality of second notch portions, the plurality of dislocation portions may be spaced from one another, and each of the plurality of second notch portions may be formed around each of the plurality of dislocation portions.

Each of the plurality of dislocation portions may form the same angle with a center of the cap-down.

Each of the plurality of dislocation portions may be the same distance away from a center of the cap-down.

The dislocation portion and the second notch portion may be circles.

At least a portion of the cap-down may include a dislocation portion configured to open when internal pressure of the can increases.

A thickness of the dislocation portion may be smaller than a thickness of the region of the cap-down not including the dislocation portion.

There may be a plurality of dislocation portions and the plurality of dislocation portions may be spaced from one another.

Each of the plurality of dislocation portions may form the same angle with a center of the cap-down.

Each of the plurality of dislocation portions may the same distance away from a center of the cap-down.

The dislocation portion may be a circle.

An edge of the vent portion may extend beyond an edge of the cap-up and may be bent to cover at least a portion of an upper portion of the cap-up.

An opening may be formed in a center of the cap-down, and the secondary battery may further include a sub-disk covering the opening in the center of the cap-down.

The secondary battery may further include a sub-disk coupled to the cap-down.

The secondary battery may further include an insulator between the vent portion and the cap-down.

The insulator may cover an outside edge of at least one of the cap-down, the vent portion, and the cap-up.

The secondary battery may further include a cover plate covering the insulator and including a fluid hole.

An area of the fluid hole may be 10 mm2or less.

The cap-down may include a second lower plate, a second upper plate spaced from the second lower plate, and a plurality of second bridge portions connecting the second upper plate and the second lower plate, and spaces between adjacent second bridge portions may include the insulator.

DETAILED DESCRIPTION

Reference will now be made in detail to embodiments, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. However, the present embodiments may have different forms and should not be construed as being limited to the descriptions set forth herein. Accordingly, the embodiments are merely described below, by referring to the figures, to explain aspects of the present description. As used herein, the singular forms “a,” “an,” and “the,” are intended to include the plural forms as well, unless the context clearly displays otherwise. It will be further understood that the terms “comprises,” “comprising,” “includes,” and/or “including,” when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. It will be understood that although the terms “first”, “second”, etc. may be used herein to describe various components, these components should not be limited by these terms. These components are only used to distinguish one component from another. Expressions such as “at least one of,” when preceding a list of elements, modify the entire list of elements and do not modify the individual elements of the list. Further, the use of “may” when describing embodiments of the present invention refers to “one or more embodiments of the present invention.”

FIG. 1is a perspective view of a secondary battery100according to an embodiment of the present invention.FIG. 2is an exploded perspective view of the secondary battery100ofFIG. 1.FIG. 3is a cross-sectional view taken along line ofFIG. 1.

Referring toFIGS. 1 through 3, the secondary battery100may include an electrode assembly110, a can140accommodating the electrode assembly110, and a cap assembly170coupled to the can140.

The electrode assembly110may include a first electrode plate111, a second electrode plate112, and a separator113between the first electrode plate111and the second electrode plate112. In one embodiment, the electrode assembly110may be manufactured by sequentially stacking the first electrode plate111, the separator113, and the second electrode plate112, and winding the first electrode plate111, the separator113, and the second electrode plate112in a jelly-roll shape.

In one embodiment, the electrode assembly110may be formed to correspond to the shape of the can140. For example, when the can140has an oval shape, the electrode assembly110may have an oval jelly-roll shape. However, hereinafter, solely for convenience of explanation, circular can140and electrode assembly110will be described.

The first electrode plate111may be a positive electrode film or a negative electrode film. When the first electrode plate111is a positive electrode film, the second electrode plate112may be a negative electrode film, and when the first electrode plate111is a negative electrode film, the second electrode plate112may be a positive electrode film. In other words, the first electrode plate111and the second electrode plate112may have different electrical polarities, and are not limited to specific electrical polarities. However, hereinafter, solely for convenience of explanation, the first electrode plate111will be described as a positive electrode film, and the second electrode plate112as a negative electrode film.

The first electrode plate111may include a first active material portion coated with a first active material, and a first non-coated portion not coated with the first active material. In one embodiment, the first active material portion may be formed by coating a portion of at least one surface of an aluminum (Al) plate with the first active material, and the first non-coated portion may be formed by leaving the rest of the Al plate not coated with the first active material. The first active material may be a positive electrode active material, and may be, for example, a lithium (Li)-containing transition metal oxide, such as LiCoO2, LiNiO2, LiMnO2, and LiMnO4, or a Li chalcogenide compound.

The second electrode plate112may include a second active material portion coated with a second active material and a second non-coated portion not coated with the second active material. The second active material portion may be formed by coating a portion of at least one surface of a copper (Cu) plate with the second active material, and the second non-coated portion may be formed by leaving the rest of the Cu plate not coated with the second active material. The second active material may be a negative electrode active material, and may be, for example, a carbon material, such as crystalline carbon, amorphous carbon, a carbon compound, and a carbon fiber, a Li metal, or a Li alloy.

The separator113may be a porous polymer film, such as a polyethylene (PE) film or a polypropylene (PP) film. The separator113may further include ceramic particles and may be formed of a solid polyelectrolyte. The separator113may be formed as an independent film, or as a nonconductive porous layer on the first electrode plate111or the second electrode plate112.

In one embodiment, a first electrode tab114is electrically connected to the first electrode plate111, and a second electrode tab115is electrically connected to the second electrode plate112. One end of the first electrode tab114may be connected to the first non-coated portion by, for example, welding, and the other end of the first electrode tab114may be electrically connected to a current breaking portion150. In one embodiment, one end of the second electrode tab115may be connected to the second non-coated portion by, for example, welding, and the other end of the second electrode tab115may be welded to a bottom surface of the can140.

In one embodiment, one side of the can140includes an opening, and the electrode assembly110may be inserted into the can140through the opening. The can140may have, for example, a cylindrical shape, but is not limited thereto. The can140may be formed of a conductive material such as, for example, aluminum, and may protect the electrode assembly110from external shock, as well as function as a heat-insulating board that releases the heat generated by the charge and discharge operations of the electrode assembly110to the outside. In embodiments where the bottom surface of the can140is electrically connected to the second electrode tab115by welding, the can140may function as a second electrode.

A third notch portion146may be formed at the bottom of the can140. When internal pressure of the can140increases, the third notch portion146may change its shape or may break to emit the gas generated inside the can140to the outside.

A first insulating plate120and a second insulating plate130may be respectively positioned at the ends of the electrode assembly110, inside the can140. The first insulating plate120may be placed between an upper surface of the electrode assembly110and the cap assembly170, thereby insulating the electrode assembly110from the cap assembly170. The second insulating plate130may be placed between the electrode assembly110and the bottom surface of the can140, thereby insulating the electrode assembly110from the can140.

In one embodiment, the cap assembly170is coupled to the can140and seals the opening at the side of the can140. In one embodiment, a beading portion142is formed on the side of the can140and is dented toward the inside of the can140. The cap assembly170is inserted inside the can140through the beading portion142, and a top portion of the can140is then bent toward the inside of the can140to cover the edges of the cap assembly170, thus forming a crimping portion144. Accordingly, the cap assembly170may be combined with the can140. In one embodiment, the beading portion142and the crimping portion144firmly attach the cap assembly170to the can140, thereby preventing or reducing the possibility of dislocation of the cap assembly170and leakage of the electrolyte.

The cap assembly170may include a gasket141, the current breaking portion150, and a cap-up160.

In one embodiment, the gasket141is positioned at the top of the can140and has a ring-like shape. The current breaking portion150and the cap-up160are fixed to each other inside the gasket141, such that the gasket141, the current breaking portion150, and the cap-up160together correspond to the shape of the crimping portion144. In addition, the gasket141insulates the current breaking portion150and the cap-up160from the can140. As illustrated inFIG. 3, the cap-up160is positioned on the current breaking portion150, and the cap-up160and the current breaking portion150are fixed to each other inside the gasket141. However, embodiments of the present invention are not limited thereto. In another embodiment, the edge of the current breaking portion150may extend beyond the edge of the cap-up160and may be bent so as to cover the edge of the cap-up160, thus attaching the current breaking portion150to the cap-up160. Specifically, an edge of a vent portion154of the current breaking portion150may extend beyond the edge of the cap-up160and may be bent to cover the edge of the cap-up160, thus attaching the current breaking portion150to the cap-up160. Additionally, the current breaking portion150and the cap-up160may be further fixed together by the gasket141.

A first notch portion155of the current breaking portion150may break when the pressure inside the can140increases, thus interrupting the current and emitting the gas to the outside. In one embodiment, the current breaking portion150includes a dislocation portion153a(or253in another embodiment), which can open or rupture when internal pressure inside the can140increases, thus providing a passage through which the gas may be emitted toward the cap-up160. In one embodiment, the dislocation portion153a(or253) may allow the gas to evenly flow towards the top and bottom of the can140, such that the first notch portion155and the third notch portion146both rupture.

In embodiments where the current breaking portion150is electrically connected to the first electrode tab114, the cap-up160may be connected to the current breaking portion150and may function as the first electrode. In one embodiment, the cap-up160includes a plurality of through-holes164that aid in gas emission, and first bridge portions162formed between the plurality of through-holes164. The cap-up160may also include a first upper plate161and a first lower plate163, both connected to the first bridge portions162. In one embodiment, the first upper plate161and the first lower plate163may be spaced from each other. For example, the first upper plate161and the first lower plate163may be positioned one on top of the other.

Hereinafter, the current breaking portion150will be described.

FIG. 4is a plan view of the current breaking portion150illustrated inFIG. 3.FIG. 5is a cross-sectional view taken along line V-V ofFIG. 4.

Referring toFIGS. 4 and 5, the current breaking portion150may, for example, include a cap-down152, the vent portion154, an insulator156, and a sub-disk158.

In one embodiment, the cap-down152includes an opening in the center, and the vent portion154is positioned on the cap-down152. The insulator156is positioned on the outer edge between the cap-down152and the vent portion154, thereby insulating the cap-down152from the vent portion154. In addition, a gap may be formed between the cap-down152and the vent portion154by the insulator156.

The cap-down152may include a second upper plate152ahaving an opening in the center, a second lower plate152bplaced separate and spaced from the second upper plate152a, and a plurality of second bridge portions152cconnecting the second upper plate152aand the second lower plate152b. In one embodiment, the second lower plate152band the second upper plate152amay each be formed by molding, and one may be positioned on top of the other. In one embodiment, spaces between the adjacent second bridge portions152cmay be sealed by the insulator156.

The vent portion154may include the first notch portion155. The first notch portion155may have a groove shape and be relatively thin, and the first notch portion155may change its shape or break to emit gas from the can when the internal pressure of the can increases.

The cap-down152may include the dislocation portion153athat may open or rupture when the internal pressure of the can increases, and a second notch portion153bformed near the dislocation portion153a. The dislocation portion153aand the second notch portion153bmay be formed in at least one of the two surfaces of the cap-down152. In one embodiment, the dislocation portion153aand the second notch portion153bmay be formed in a first surface of the cap-down152, to which the sub-disk158is coupled. In another embodiment, the dislocation portion153aand the second notch portion153bmay be formed in a second surface of the cap-down152, which faces the vent portion154. In another embodiment, the dislocation portion153aand the second notch portion153bmay be respectively formed in the first and second surfaces of the cap-down152. However, hereinafter, solely for convenience of explanation, the dislocation portion153aand the second notch portion153bboth formed in the second surface of the cap-down152will be described.

The second notch portion153bmay be formed around the outer edge of the dislocation portion153aand may define the region where the dislocation portion153ais located.

In one embodiment, the cap-down152may include a support portion153cformed on the second notch portion153band supporting the dislocation portion153aby connecting the dislocation portion153awith another region of the cap-down152. In one embodiment, the support portion153csupports the dislocation portion153awhen the second notch portion153bis fractured, thus preventing or reducing the dislocation portion153afrom breaking away, being damaged, or colliding with other components.

The second notch portion153bmay have a different thickness from the dislocation portion153a. In one embodiment, the second notch portion153bmay have a groove shape and a relatively small thickness, compared to that of the dislocation portion153a. In one embodiment, the second notch portion153bmay rupture when the internal pressure of the can increases and may separate the dislocation portion153afrom the cap-down152.

The second notch portion153band the dislocation portion153amay have various shapes. For example, the dislocation portion153aand the second notch portion153bmay each be, without limitation, a circle, a quadrangle, a triangle, or a polygon. Hereinafter, solely for convenience of explanation, circular dislocation portion153aand second notch portion153bwill be described (i.e. the dislocation portion153ais a circle, and the second notch portion153bhas a circle-ring shape and is formed around the edge of the dislocation portion153aas described above).

A plurality of dislocation portions153aand a plurality of second notch portions153bmay be provided. In one embodiment, the plurality of dislocation portions153amay be spaced from one another. Each of the plurality of second notch portions153bmay be formed around the edge of each of the plurality of dislocation portions153aand may define the region where each of the plurality of dislocation portions153ais located.

Each of the plurality of dislocation portions153amay form the same angle with the center C of the cap-down152. For example, when there are two dislocation portions153a, the two dislocation portions153amay be positioned opposite each other with the center C of the cap-down152between the two dislocation portions153a. In embodiment where there are three dislocation portions153a, the three dislocation portions153amay be placed such that angles between the three adjacent dislocation portions are each 120°. While the number of dislocation portions153ais not limited thereto, hereinafter, solely for convenience of explanation, the cap-down including two dislocation portions153awill be described.

In one embodiment, the plurality of dislocation portions153amay be positioned in a radial form with respect to the center C of the cap-down152, such that the distance between each of the plurality of dislocation portions153aand the center C of the cap-down152may be the same. In one embodiment, a distance between the center of each of the dislocation portions153aand the center C of the cap-down152may be the same.

In one embodiment, the sub-disk158is attached to the first surface of the cap-down152to cover the opening in the cap-down152. One surface of the sub-disk158may be coupled to the first electrode tab114, and the other surface of the sub-disk158may be electrically connected to the vent portion154by, for example, ultrasonic welding, in the region where there is an opening of the cap-down152.

Hereinafter, method of operation of the current breaking portion150will be described.

A secondary battery may overheat due to external radiant heat, rapid heating, over-charging, etc. When the secondary battery overheats, electrolyte additives such as, for example, cyclohexylbenzene (CHB) and biphenyl (BP), may generate gas inside the secondary battery. As a result, the internal pressure inside the can containing the second battery may rapidly increase, and the secondary battery may explode.

In one embodiment of the present invention, when the gas is generated inside the can and the temperature of the gas rises to 600° C. or higher, the insulator156between the second bridge portions152c, as illustrated inFIG. 5, may be burned by the gas.

When the insulator156is burned, a space is formed between the end of the cap-down152and the end of the vent portion154, as well as between adjacent second bridge portions152c, and the gas may flow between the cap-down152and the vent portion154through the formed space. As the gas pressure in the gap between the cap-down152and the vent portion154continues to increase, the shape of the vent portion154may change, and a combining portion P1between the cap-down152and the sub-disk158may be dislocated, thus interrupting the current.

In addition, when the pressure in the gap between the cap-down152and the vent portion154further increases due to the continuous, flow of gas, the first notch portion155may rupture so that the gas inside the can may be released to the outside.

To prevent or reduce the possibility of explosion inside the can that may occur after the first notch portion155ruptures, the dislocation portion153amay rupture after than the first notch portion155, and the third notch portion146may rupture along with the dislocation portion153a.

If the third notch portion146or the dislocation portion153ado not rupture, a side of the can may rupture or break, thus transmitting heat to the neighboring cans or damaging external devices, and deteriorating the stability of the secondary battery.

In one embodiment, the cap assembly and the secondary battery may open the first notch portion155, the dislocation portion153a, and the third notch portion146, thus preventing or reducing a temperature increase inside the can.

Accordingly, the cap assembly and the secondary battery may smoothly release the combustion gas and materials generated inside the can due to overheating, and may improve the stability of the secondary battery.

FIG. 6is a plan view of the current breaking portion ofFIG. 3, according to another embodiment of the present invention.FIG. 7is a cross-sectional view taken along the line VII-VII ofFIG. 6.

Referring toFIGS. 6 and 7, a current breaking portion250may include a cap-down252, a vent portion254, an insulator256, and a sub-disk258. In one embodiment, the vent portion254, the insulator256, and the sub-disk258are substantially the same as the vent portion154, the insulator156, and the sub-disk158described above, respectively.

The cap-down252may include an opening in the center, and a dislocation portion253may be formed around the center of the cap-down252. In one embodiment, the cap-down252may include a second upper plate252a, a second lower plate252b, and a plurality of second bridge portions252c, similar to the second upper plate152a, the second lower plate152b, and the plurality of second bridge portions152cdescribed above, respectively. In one embodiment, the dislocation portion253may be formed in the second lower plate252b.

The dislocation portion253may be formed in at least one surface of the cap-down252. For example, the dislocation portion253may be formed only in a first surface of the cap-down252, to which the sub-disk258is attached, or the dislocation portion253may be formed only in a second surface of the cap-down252, which faces the vent portion254. In one embodiment, the dislocation portion253may be formed in both the first and second surfaces of the cap-down252. However, solely for convenience of explanation, the dislocation portion253formed in the first surface of the cap-down252will be described.

When the pressure is applied to the dislocation portion253, the dislocation portion253may rupture. In one embodiment, a thickness of the dislocation portion253may be different from a thickness of the portions of the cap-down252, in which the dislocation portion253is not formed. For example, the thickness of the dislocation portion253may be smaller than the thickness of the portions of the cap-down252, in which the dislocation portion253is not formed.

In embodiments where the thickness of the dislocation portion253is smaller than the thickness of the portions of the cap-down252, in which the dislocation portion253is not formed, the dislocation portion253may rupture and open when the internal pressure of the can increases. In one embodiment, the dislocation portion253may rupture after the first notch portion255is opened.

The dislocation portion253may have various shapes. For example, the dislocation portion253may be circular or quadrangular, but the shape of the dislocation portion253is not limited thereto. However, hereinafter, solely for convenience of explanation, the shape of the dislocation portion253will be described as circular.

There may be a plurality of dislocation portions253. In one embodiment, the plurality of dislocation portions253may be spaced from one another. Also, the dislocation portions253may be placed the same distance away from the center C of the cap-down252and may form identical angles with the center C of the cap-down252. The arrangement of the dislocation portions253may be substantially similar to the arrangement of the dislocation portions153adescribed above, and descriptions thereof will not be provided again. Hereinafter, solely for convenience of explanation, the cap-down having three dislocation portions253will be described.

In one embodiment, the gas generated inside the can may move toward the top and bottom portions of the can. In one embodiment, the gas moving toward the top of the can burns the insulator256positioned between the adjacent second bridge portions252c, and flows into the space formed between the end of the cap-down252and the end of the vent portion254, as well as between the adjacent second bridge portions252c.

The continuous flow of gas may increase the pressure in the gap between the cap-down252and the vent portion254and may separate the vent portion254from the sub-disk258by changing the shape of the vent portion254, thus interrupting the current.

In addition, when the flow of gas continues to increase the pressure in the gap between the cap-down252and the vent portion254, the first notch portion255may rupture and the gas inside the can may be released to the outside. In one embodiment, the dislocation portion253and a third notch portion should rupture along with the first notch portion255. If the dislocation portion253and the third notch portion do not rupture, a side surface of the can may be broken, as described above, and the stability of the secondary battery may deteriorate.

In one embodiment, the dislocation portion253may rupture after the first notch portion255. The third notch portion may rupture at the same time as the dislocation portion253.

In one embodiment, the first notch portion255, the dislocation portion253, and the third notch portion rupture so that the combustion gas and materials generated inside the can may be smoothly released to the outside.

In one embodiment, a cap assembly and the secondary battery described above may rapidly and smoothly release the heat and materials generated inside the can due to overheating, and may improve the stability of the secondary battery.

FIG. 8is a cross-sectional view of a portion of a secondary battery300according to another embodiment of the present invention.

Referring toFIG. 8, the secondary battery300may include an electrode assembly310, a can340containing the electrode assembly310, and a cap assembly370coupled to the can340. The secondary battery300may further include a first insulating plate320and a second insulating plate330, inserted into the can340. In one embodiment, the first insulating plate320and the second insulating plate330are substantially the same as the first insulating plate120and the second insulating plate130described above, respectively.

The can340may include a beading portion342and a crimping portion344. In one embodiment, the beading portion342and the crimping portion344are substantially the same as the beading portion142and the crimping portion144described above, respectively.

The electrode assembly310may include a first electrode plate311, a second electrode plate312, and a separator313. In one embodiment, the first electrode plate311, the second electrode plate312, and the separator313are substantially the same as the first electrode plate111, the second electrode plate112, and the separator113described above, respectively.

A first electrode tab314may be electrically connected to the first electrode plate311, and a second electrode tab315may be electrically connected to the second electrode plate312. In one embodiment, the second electrode tab315may be connected to the bottom surface of the can340.

The cap assembly370may include a gasket341, a current breaking portion350, and a cap-up360. In one embodiment, the gasket341and the cap-up360are substantially the same as the gasket141and the cap-up160described above, respectively.

The current breaking portion350may include a vent portion354including a first notch portion355, a cap-down352including a second upper plate352aand a second lower plate352bconnected by a bridge portion352c, a dislocation portion353, and a sub-disk358coupled to the first electrode tab314. The current breaking portion350may further include an insulator356between the vent portion354and the cap-down352. In one embodiment, the first notch portion355, the vent portion354, the dislocation portion353, the cap-down352, and the insulator356are substantially the same as the first notch portion155, the vent portion154, the dislocation portion153a, the cap-down152, and the insulator156described above, respectively.

The sub-disk358may be formed under the cap-down352. In one embodiment, the sub-disk358may be formed integrally with the cap-down352. Specifically, the sub-disk358may extend from the cap-down352to cover an open center portion of the cap-down352. In one embodiment, the first electrode tab314may be coupled to the sub-disk358.

In one embodiment, the current breaking portion350may operate as described above. For example, when the inside of the can340overheats or overcurrents are formed in the electrode assembly310, high temperature gas may be generated inside the can340, and the insulator356may be burned and destroyed by the gas.

The gas may then move through the spaces between the adjacent second bridge portions352cformed after the insulator356is destroyed, or the gas may move through the space between the end of a second upper plate352aof the cap-down352and the end of the vent portion354.

The gas moving as described above may increase the pressure in the gap between the cap-down352and the vent portion354, and may separate the vent portion354from the sub-disk358coupled to the cap-down352, thus interrupting the current and suspending the power supply. If the pressure in the gap between cap-down352and the vent portion354continues to increase, the gas may rupture the first notch portion355of the vent portion354and release the gas.

As the pressure inside the can340continues to increase further, the dislocation portion353may rupture and open (after the first notch portion355has ruptured), so that the gas and the heat generated inside the can340may be released to the outside. In one embodiment, a third notch portion346may rupture along with the dislocation portion353, to open the bottom of the can340and release the gas.

In one embodiment, when the internal pressure of the can340increases, the first notch portion355, the dislocation portion353, and the third notch portion346of the cap assembly370and the secondary battery300rupture and open to release the gas, heat, and electrolyte from inside the can340to the outside, thus improving the stability of the secondary battery300.

FIG. 9is a cross-sectional view of a portion of a secondary battery400according to another embodiment of the present invention.

Referring toFIG. 9, the secondary battery400may include an electrode assembly410, a can440accommodating the electrode assembly410, and a cap assembly470coupled to the can440. The secondary battery400may further include a first insulating plate420and a second insulating plate430inserted into the can440. In one embodiment, the first insulating plate420and the second insulating plate430are substantially the same as the first insulating plate120and the second insulating plate130described above, respectively.

The can440may include a beading portion442and a crimping portion444. In one embodiment, the beading portion442and the crimping portion444are substantially the same as the beading portion142and the crimping portion144described above, respectively.

The electrode assembly410may include a first electrode plate411, a second electrode plate412, and a separator413. In one embodiment, the first electrode plate411, the second electrode plate412, and the separator413are substantially the same as the first electrode plate111, the second electrode plate112, and the separator113described above, respectively.

A first electrode tab414may be electrically connected to the first electrode plate411, and a second electrode tab415may be electrically connected to the second electrode plate412. In one embodiment, the second electrode tab415may be attached to the bottom surface of the can440.

The cap assembly470may include a gasket441, a current breaking portion450, a cap-up460, and a cover plate480. In one embodiment, the gasket441and the cap-up460are substantially the same as the gasket141and the cap-up160described above, respectively.

The current breaking portion450may include a vent portion454including a first notch portion455. The current breaking portion450may further include a cap-down452including a second notch portion453band a dislocation portion453a, and an insulator456between the cap-down452and the vent portion454. The current breaking portion450may further include a sub-disk458connected to the cap-down452. In one embodiment, the dislocation portion453amay be connected to portion of the cap-down452by a support portion formed on the second notch portion453b. In one embodiment, the sub-disk458may be formed integrally with the cap-down452or may be formed separately from the cap-down452and may be attached to the cap-down452. Hereinafter, solely for convenience of explanation, the sub-disk458formed integrally with the cap-down452will be described.

The first notch portion455and the second notch portion453bmay each have a ring shape. In one embodiment, a diameter of the first notch portion455may be larger than a diameter of the second notch portion453b.

The cap-down452may include a first upper plate452a, a first lower plate452b, and first bridge portions452c. In one embodiment, the first bridge portions452cmay connect the first upper plate452aand the first lower plate452b, and space may be formed between the adjacent first bridge portions452c. In one embodiment, gas generated inside the can may flow through the spaces between the adjacent first bridge portions452c.

The insulator456may be positioned between the vent portion454and the cap-down452and may separate at least a portion of the cap-down452from the vent portion454. In one embodiment, the insulator456may wrap around and cover an outside edge of at least one of the vent portion454, the cap-down452, and the cap-up460. In one embodiment, the insulator456may completely seal the space between the vent portion454and the cap-down452. However, hereinafter, solely for convenience of explanation, the insulator456covering the outside edge of each of the vent portion454, the cap-down452, and the cap-up460will be described.

The cover plate480may cover the insulator456. In one embodiment, the cover plate480may include at least one fluid hole481. When the cover plate480includes at least one fluid hole481, the gas generated inside the can440may flow from the inside of the can440toward the cap-up460through the fluid hole481.

An area of the fluid hole481may be 10 mm2or less. When the area of the fluid hole481is larger than 10 mm2, the gas inside the can440may move too rapidly, or too much heat from the inside of the can440may be transmitted to the cap assembly470, and the cap assembly470may be damaged or separated from the can440.

When the temperature inside of the can440accommodating the secondary battery440increases, gas may be generated inside the can440. The generated gas may then pass through the fluid hole481and burn and destroy the insulator456, and may be injected into the space between the vent portion454and the cap-down452.

In one embodiment, the vent portion454and at least a portion of the cap-down452may first contact each other, and later may be separated from each other. Since the cover plate480and the cap-down452contact each other, when the vent portion454and at least a portion of the cap-down452are separated from each other, the first electrode tab414connected to the cover plate480may be short circuited.

If the internal pressure inside the can440continues to increase after the process described above takes place, the pressure between the vent portion454and the cap-down452may also increase. In one embodiment, when the pressure between the vent portion454and the cap-down452increases, the first notch portion455ruptures, such that at least a portion of the vent portion454may open.

Also, when the internal pressure of the can440continues to increase due explosion or the like, and the second notch portion453bhas already ruptured, the dislocation portion453amay also open.

In addition, the third notch portion446may also rupture, along with the second notch portion453b, and the gas, heat, and electrolyte from inside the can440may be released and may flow toward the top and bottom of the can440.

In one embodiment, the cap assembly470and the secondary battery400may release the gas and heat generated due to the heating or explosion inside the can440, towards the top and bottom of the can440. Accordingly, increase of the temperature inside the can440and damage to the side of the can440can be prevented or reduced.

In one embodiment, the cap assembly470and the secondary battery400smoothly release the gas, heat, and electrolyte from inside the can440to the outside, thus improving the stability of the secondary battery400.

It should be understood that the exemplary embodiments described therein should be considered in a descriptive sense only and not for purposes of limitation. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention as defined by the following claims and equivalents thereof.