Patent Description:
The present invention relates to a CID filter and a secondary battery comprising the CID filter, and more particularly, to a CID filter having improved safety under an abnormal high-temperature condition and a secondary battery comprising the CID filter.

Secondary batteries that are repetitively chargeable and dischargeable may be divided into cylindrical type secondary batteries, prismatic type secondary batteries, and pouch type secondary batteries according to their structures and manufacturing methods. In general, among them, the cylindrical type secondary battery has a structure in which an electrode assembly is accommodated in a cylindrical can with an upper portion opened, and a top cap is coupled to the upper portion of the cylindrical can.

In order to prevent explosion or fire that may occur when a temperature or pressure inside the cylindrical type secondary battery exceeds a certain value, generally, the cylindrical type secondary battery is provided with safety devices such as a safety vent and a CID filter. According to the related art, when the pressure inside the cylindrical type secondary battery exceeds a certain value, current is cut off by breaking the safety vent, and a gas inside the secondary battery is discharged to the outside.

One of the reasons for the abnormal increase in temperature or pressure inside the cylindrical type secondary battery is a short circuit phenomenon. When the short circuit occurs, heat is generated inside the cylindrical type secondary battery.

Particularly, a lot of heat is generated in a region in which an electrode tab protruding from an electrode assembly and the CID filter are bonded to each other. According to the related art, the heat generated in the region in which the electrode tab and the CID filter are bonded to each other passes through the CID filter and then is transferred to a CID gasket disposed around the CID filter, and thus, a temperature of the CID gasket increases to cause a problem in which the CID gasket is melted. In this case, even if the safety vent is broken, since the safety vent and the CID filter are reconnected to each other in the circumferential area of the CID filter to prevent the current of the cylindrical type secondary battery from being cut off, the cylindrical type secondary battery is impeded in safety. <CIT> and <CIT> disclose a secondary battery having a CID filter.

Therefore, the problem to be solved by the present invention is to solve a problem of melting a CID gasket by minimizing heat transferred to the CID gasket through a CID filter even if a short circuit occurs in a cylindrical type secondary battery.

According to one aspect of the present invention for achieving the above object, provided is a secondary battery as defined in the appended set of claims. The secondary battery of the present invention comprises: an electrode assembly having a structure in which electrodes and separators are alternately disposed; a battery can configured to accommodate the electrode assembly and having an opened upper portion; a top can coupled to the upper portion of the battery can; a CID filter provided below the top cap; a CID gasket provided in close contact with a side portion of the CID filter; and an electrode tab protruding from the electrode assembly, the electrode tab being electrically connected to the CID filter, wherein the CID filter comprises a body part defining a main body, the body part comprises: a plurality of main though-holes provided along a circumference of the body part and each of which has a first width (W1); and.

an auxiliary through-hole having a second width (W2) less than the first width (W1), an area (hereinafter, referred to as a `first connection area') of the CID filter, which is electrically connected to the electrode tab, leans toward one side with respect to a center of the CID filter, and the auxiliary through-hole is defined between the first connection area and the CID gasket.

The auxiliary through-hole is defined in a connection area (hereinafter, referred to as a 'second connection area') of the body part configured to connect the man through-holes to each other along a circumferential direction of the body part.

The auxiliary through-hole is defined in a circular arc of a virtual circle that is centered at a center of the CID filter while crossing the shortest distance between the first connection area and the CID gasket, and the second connection areas, in which the auxiliary through-hole is not defined, among the plurality of second connection areas is not disposed in the circular arc.

The second connection areas, in which the auxiliary through-hole is defined, among the plurality of second connection areas may be disposed adjacent to each other, and the second connection areas, in which the auxiliary through-hole is not defined, among the plurality of second connection areas may be disposed adjacent to each other.

A circumference of the body part may have a circular shape, and a middle point of the circular arc may be disposed in a semi-straight line extending outward from the center of the CID filter.

A central angle of the circular arc ranges of <NUM> degrees to <NUM> degrees.

The first connection area may be disposed at a center of the shortest distance between a center of the CID filter and the CID gasket.

The circular arc may cross a center of the shortest distance between the first connection area and the CID gasket.

According to the present disclosure for achieving the above object, provided is a CID filter comprising: a body part defining a main body, wherein the body part comprises: a plurality of main though-holes provided along a circumference of the body part and each of which has a first width (W1); and an auxiliary through-hole having a second width (W2) less than the first width (W1), a first point is defined at an area that leans toward one side with respect to a center of the body part, a second point is defined at a circumference of the body part, and the auxiliary through-hole is defined between the first point and the second point, wherein the auxiliary through-hole is defined in a connection area (hereinafter, referred to as a 'second connection area') of the body part configured to connect the main through-holes to each other along a circumferential direction of the body part.

The plurality of main through-holes may be provided at equal intervals along the circumferential direction of the body part.

The auxiliary through-hole may be connected to the two main through-holes defined in both sides of the second connection area in which the auxiliary through-hole is defined.

The auxiliary through-hole may be spaced apart from the two main through-holes defined in both sides of the second connection area in which the auxiliary through-hole is defined.

The auxiliary through-hole may be provided in plurality in the second connection area in which the auxiliary through-hole is defined.

Since total N main through-holes are defined in the body part, total N connection areas may be provided, and the number of second connection areas, in which the auxiliary through-holes are defined, among the total N second connection areas may be N/<NUM> or less (i) when N is an even number and is (N-<NUM>)/<NUM> or less (ii) when N is an odd number.

Total eight main through-holes may be defined, and the number of second connection areas in which the auxiliary through-holes are defined may range of one to four.

According to the present invention, even if the short circuit occurs in the cylindrical type secondary battery, the heat transferred to the CID gasket through the CID filter may be minimized to solve the problem of melting the CID gasket.

Hereinafter, a secondary battery and a structure of a CID filter according to the present invention will be described with reference to the drawings.

<FIG> is a side cross-sectional view illustrating a structure of a secondary battery according to the present invention.

As illustrated in <FIG>, a secondary battery <NUM> according to the present invention may comprise a battery can <NUM> having a structure with an upper portion opened. The battery can <NUM> may have a cylindrical shape in a horizontal cross-section. That is, the secondary battery according to the present invention may be a cylindrical type secondary battery.

A top cap <NUM> may be disposed on the upper portion of the battery can <NUM>. In more detail, as illustrated in <FIG>, a top cap <NUM> may be coupled to the upper portion of the battery can <NUM>.

A safety vent <NUM> may be provided below the top cap <NUM>. When a pressure inside the secondary battery <NUM> exceeds a certain value, the safety vent <NUM> may be configured to be broken to cut off the current of the secondary battery <NUM> and provide a path through which a gas inside the secondary battery <NUM> is discharged to the outside. As illustrated in <FIG>, a notch portion having a relatively thin thickness compared to other areas of the safety vent may be provided in the safety vent <NUM>.

A CID filter <NUM> may also be provided below the top cap <NUM>. In more detail, the CID filter <NUM> may be provided below the safety vent <NUM>. As illustrated in <FIG>, a central area of the CID filter <NUM> and a central area of the safety vent <NUM> may be bonded to each other. Thus, when a pressure inside the secondary battery <NUM> exceeds a certain value, and thus the safety vent is broken to move upward, the CID filter <NUM> may also move upward to cut off the current of the secondary battery <NUM>.

A gasket <NUM> may be provided in close contact with an inner surface of the battery can <NUM>. As illustrated in <FIG>, the gasket <NUM> may be provided in close contact with circumferential areas of the top cap <NUM> and the safety vent <NUM>. The gasket <NUM> may be configured to seal the inside the secondary battery <NUM>.

The secondary battery according to the present invention may further comprise a CID gasket <NUM> that is in close contact with a side portion of the CID filter <NUM>. The CID gasket <NUM> is provided to be separated from the above-described gasket <NUM> and may be configured to prevent the CID filter <NUM> and the safety vent <NUM> from directly contacting each other on the circumferential area of the CID filter <NUM>. Thus, as illustrated in <FIG>, the CID gasket <NUM> may be provided between the CID filter <NUM> and the safety vent <NUM> at the side portion of the CID filter <NUM>. Each of the gasket <NUM> and the CID gasket <NUM> may be made of a material having electrical insulation properties.

An electrode assembly <NUM> may be accommodated in the battery can <NUM>. The electrode assembly <NUM> may have a structure in which electrodes and separators are alternately disposed. For example, the electrode assembly <NUM> may be a jelly-roll type electrode assembly.

The electrode assembly <NUM> may comprise an electrode tab 700a. As illustrated in <FIG>, the electrode tab 700a may have a structure protruding from the electrode assembly <NUM>. Also, the electrode tab 700a may be electrically connected to the CID filter <NUM>. The electrode tab 700a and the CID filter <NUM> may be connected to each other, for example, through welding. In this specification, an area of the CID filter <NUM>, which is electrically connected to the electrode tab 700a will be referred to as a 'first connection area'. The first connection area C1 may lean toward one side with respect to a center of the CID filter <NUM>. <FIG> illustrates a state in which the first connection area C1 leans toward a left side with respect to the center of the CID filter <NUM>.

<FIG> is a plan view illustrating an example of the structure of the CID filter according to an embodiment of the present invention, and <FIG> is a plan view illustrating another example of the structure of the CID filter according to an embodiment of the present invention.

As illustrated in <FIG> and <FIG>, the CID filter <NUM> according to an embodiment of the present invention may comprise a body part 400a defining a main body. A circumference of the body part 400a may have a circular shape.

A plurality of main through-holes <NUM> provided along a circumference of the body part 400a may be defined in the body part 400a of the CID filter <NUM>. As illustrated in <FIG>, the main through-hole <NUM> may have a first width W1. The main through-hole <NUM> may have a circular shape. When the main through-hole <NUM> has the circular shape, the first width W1 may be a diameter of the main through-hole <NUM>. Also, the main through-hole <NUM> may be provided at equal intervals along the circumference of the body part 400a. <FIG> and <FIG> illustrate a case in which eight main through-holes <NUM> are provided at equal intervals along a circumferential direction of the body part 400a having the circular shape in the CID filter <NUM>.

The plurality of main through-holes <NUM> defined in the body part 400a of the CID filter <NUM> may be illustrated as being connected to each other by some areas of the body part 400a. In more detail, the plurality of main through-holes <NUM> may be connected to each other along the circumferential direction of the body part 400a by some areas of the body part 400a. In this specification, the area of the body part 400a of the CID filter, which connects the plurality of main through-holes <NUM> to each other along the circumferential direction of the body part 400a, will be referred to as a `second connection area'. <FIG> and <FIG> illustrate a case in which eight second connection areas C2 are provided between the main through-holes <NUM> to correspond to the eight main through-holes <NUM>.

An auxiliary through-hole <NUM> having a second width W2 may be defined in the body part 400a of the CID filter <NUM> according to the present invention. Here, the second width W2 may be less than the first width W1. That is, the auxiliary through-hole <NUM> may have a width less than that of the main through-hole <NUM>.

Subsequently, referring to <FIG>, in the CID filter <NUM> according to the present invention, the auxiliary through-hole <NUM> may be defined in the second connection area C2. According to the present invention, since the auxiliary through-hole <NUM> is defined in the second connection area C2 connecting the main through-holes <NUM> to each other, the heat transfer may be minimized due to heat conduction between the inside of the CID filter <NUM> in a central direction and the outside of the CID filter <NUM> in a circumferential direction.

Referring to <FIG> based on the above contents, in the secondary battery <NUM> according to the present invention, the auxiliary through-hole <NUM> (see <FIG>) of the CID filter <NUM> may be provided between the first connection area C1 and the CID gasket <NUM>. Thus, according to the present invention, transfer of heat transferred from the first connection area C1 (that is, the area on which the CID filter and the electrode tab are electrically connected to each other), which generate a lot of heat in the secondary battery <NUM>, to the CID gasket <NUM> may be minimized to prevent a problem of melting the CID gasket <NUM> from occurring.

The above feature of the present invention with respect to the auxiliary through-hole <NUM> may be understood as allowing the auxiliary through-hole <NUM> to block the shortest path of the heat transfer between a first point and a second point by providing the auxiliary through-hole <NUM> between the virtual first point disposed on an area that leans toward one side with respect to the center of the body part 400a and the virtual second point disposed around the body part 400a.

Subsequently, referring to <FIG>, the auxiliary through-hole <NUM> according to the present invention may be defined only in the second connection area C2 of a portion of the plurality of second connection areas C2. <FIG> illustrates a case in which the auxiliary through-hole <NUM> is defined in each of two second connection areas C2 of the eight second connection areas C2. However, as illustrated in <FIG>, the auxiliary through-hole <NUM> may be defined in each of four second connection areas C2 of the eight second connection areas C2. Alternatively, the auxiliary through-hole <NUM> may be defined in one or three second connection areas C2 of the eight second connection areas C2. That is, according to the present invention, when the eight main through-holes <NUM> are defined in the CID filter <NUM>, the number of second connection areas C2 in which the auxiliary through-holes <NUM> are defined may range of one to four.

As described above, the first connection area C1 may lean toward the one side with respect to the center of the CID filter <NUM>. Here, as illustrated in <FIG> and <FIG>, the auxiliary through-hole <NUM> may be defined in the second connection areas C2, which are disposed at a side to which the first connection area C1 leans, of the eight second connection areas C2.

The CID gasket <NUM> may be easily melted in the secondary battery <NUM>, particularly, on an area on which the first connection area C1, in which a lot of heat is generated, is relatively close to the CID gasket <NUM>. Thus, the structure in which the second connection areas C2 are disposed adjacent to the area, on which the first connection area C1 leans, of the plurality of second connection areas C2 provided on the CID filter <NUM>.

The number of second connection areas C2, in which the auxiliary through-holes <NUM> are defined, according to the number of main through-holes <NUM> will be described as follows by generalizing the foregoing contents.

When total N main through-holes <NUM> are defined in the body part 400a, total N second connection areas C2 connecting the plurality of main through-holes <NUM> to each other may also be provided. Here, the number of second connection areas C2, in which the auxiliary through-holes <NUM> are defined, among the total N second connection areas C2 is.

Also, as illustrated in <FIG> and <FIG>, according to the present invention, the second connection areas C2, in which the auxiliary through-holes <NUM> are defined, among the plurality of second connection areas C2 provided on the CID filter <NUM> may be disposed adjacent to each other, and the second connection areas C2, in which the auxiliary through-holes <NUM> are not defined, among the plurality of second connection areas C2 may also be disposed adjacent to each other. This may be understood as having a structure in which the second connection areas C2, in which the auxiliary through-holed <NUM> are defined, among the plurality of second connection areas C2 are continuously disposed along the circumferential direction of the body part 400a, and simultaneously, the second connection areas C2, in which the auxiliary through-holes <NUM> are not defined, among the plurality of second connection areas C2 are continuously disposed along the circumferential direction of the body part 400a.

In the CID filter <NUM> according to the present invention, the area in which the auxiliary through-hole <NUM> is defined is described by introducing the concept of a circular arc of a virtual circle.

That is, referring to <FIG>, the auxiliary through-hole <NUM> may be provided to cross the shortest distance between the first connection area C1 and the CID gasket <NUM>. For this, the auxiliary through-hole <NUM> may be defined in the circular arc A of the virtual circle that is centered at the center of the CID filter <NUM>. Also, the second connection areas C2, in which the auxiliary through-holes <NUM> are not defined, among the plurality of second connection areas C2 may not be provided on the circular arc A.

When the second connection areas C2, in which the auxiliary through-holes <NUM> is defined, among the plurality of second connection areas C2 provided on the CID filter <NUM> are disposed adjacent to each other, the virtual circular arc A is defined as a circular arc that is centered at the center of the body part 400a by using centers of the two main through-holes (for example, in <FIG>, the main through-holes respectively defined in left and right lower portions of the CID filter) defined in the outermost side among the main through holes <NUM> adjacent to the second connection areas C2, in which the auxiliary through-holes <NUM> are defined, as both ends.

As described above, since the circumference of the body part 400a has the circular shape, a middle point of the virtual circular arc A is disposed in a semi-straight line extending outward from the center of the CID filter <NUM>.

Also, a central angle of the virtual circular arc A ranges of <NUM> degrees to <NUM> degrees. <FIG> illustrates a case in which the central angle of the virtual circular arc A is <NUM> degrees, and <FIG> illustrates a case in which the central angle of the virtual circular arc A is <NUM> degrees. When the central angle of the virtual circular arc A exceeds <NUM> degrees, the shape of the CID filter may not be properly maintained because the auxiliary through-holes <NUM> are provided too much, and durability of the CID filter may be deteriorated. When the central angle of the virtual circular arc A is less than <NUM> degrees, the blocking of the heat transfer due to the auxiliary through-holes <NUM> may not effectively occur.

Subsequently, referring to <FIG>, the first connection area C1 is disposed at a center of the shortest distance between the center of the CID filter and the CID gasket <NUM>, and the virtual circular arc A crosses a center of the shortest distance between the first connection area C1 and the CID gasket <NUM>.

As illustrated in <FIG> and <FIG>, according to an embodiment of the present invention, the auxiliary through-hole <NUM> may be connected to two main through-holes <NUM> defined in both sides of the second connection area C2 in which the auxiliary through-hole <NUM> is defined. That is, according to an embodiment of the present invention, the auxiliary through-hole <NUM> and the main through-hole <NUM> adjacent to the auxiliary through-hole <NUM> may be connected to each other.

<FIG> is a plan view illustrating an example of a structure of a CID filter according to the present disclosure, and <FIG> is a plan view illustrating an example of the structure of the CID filter according to the present disclosure.

Within a range that does not contradict each other, the above descriptions of the structure of the CID filter according to an embodiment of the present invention may be equally applied to descriptions of a structure of a CID filter according to another embodiment of the present invention. Hereinafter, the structure of the CID filter according to another embodiment of the present invention will be described mainly based on differences from the structure of the CID filter according to an embodiment of the present invention.

Unlike the forgoing embodiment of the present invention, according to the present disclosure, an auxiliary through-hole <NUM>' may be spaced a predetermined distance from two main through-holes <NUM> defined in both sides of a second connection area C2 in which the auxiliary through-hole <NUM>' is defined. Also, according to the present disclosure, the auxiliary through-hole <NUM>' may be provided in plurality in the second connection area C2 in which the auxiliary through-hole <NUM>' is defined.

According to the present disclosure, the auxiliary through-hole <NUM>' may have a circular shape. When the auxiliary through-hole <NUM>' has the circular shape, a width of the auxiliary through-hole <NUM>' (that is, a second width) may be a diameter of the auxiliary through-hole <NUM>'.

<FIG> and <FIG> illustrate a case in which two auxiliary through-holes <NUM>', each of which has the circular shape, are defined in the second connection area C2 in which the auxiliary through-holes <NUM>' is defined.

Claim 1:
A cylindrical secondary battery comprising:
an electrode assembly having a structure in which electrodes and separators are alternately disposed;
a battery can (<NUM>) configured to accommodate the electrode assembly and having an opened upper portion;
a top cap (<NUM>) coupled to the upper portion of the battery can;
a CID filter (<NUM>) comprising:
a body part (400a) defining a main body,
wherein the body part (400a) comprises:
a plurality of main through-holes (<NUM>) provided along a circumference of the body part (400a) which has a circular shape and each of which has a first width (W1); and
an auxiliary through-hole (<NUM>) having a second width (W2) less than the first width (W1),
a first connection area (C1) of the CID filter (<NUM>) is disposed at a center of the shortest distance between the center of the CID filter and a circumference of the body part (400a), and leans toward one side with respect to a center of the CID filter (<NUM>),
a second connection area (C2) of the CID filter (<NUM>) is defined as an area configured to connect the main through-holes (<NUM>) to each other along a circumferential direction of the body part (400a),
characterized in that:
the auxiliary through-hole (<NUM>) is formed in the second connection area (C2) in a circular arc (A) of a virtual circle that is centered at the center of the CID filter and crosses a center of the shortest distance between the first connection area (C1) and the circumference of the body part (400a),
wherein said arc (A) is defined using centers of two main through-holes defined in the outermost side among the main through holes (<NUM>) adjacent to the second connection areas (C2), in which the auxiliary through-holes (<NUM>) are defined, as both ends,
and the central angle of the virtual circular arc (A) ranges from <NUM> degrees to <NUM> degrees, and
the second connection areas (C2), in which the auxiliary through-holes (<NUM>) are not defined, among the plurality of second connection areas (C2) are not provided on the circular arc A,
a CID gasket (<NUM>) provided in close contact with a side portion of the CID filter (<NUM>); and
an electrode tab protruding from the electrode assembly, the electrode tab (700a) being electrically connected to the first connection area (C1) of the CID filter (<NUM>).