Patent Description:
The present invention relates to a secondary battery.

Secondary batteries are rechargeable, unlike primarily batteries, and also they are very capable of compact size and high capacity. Thus, recently, many studies on secondary batteries have been carried out.

Secondary batteries are classified into coin type cells, cylindrical type cells, prismatic type cells, and pouch type cells according to a shape of a battery case. In such a secondary battery, an electrode assembly mounted in a battery case is a chargeable and dischargeable power generating device having a structure in which an electrode and a separator are stacked.

The electrode assembly may be generally classified into a jelly-roll type electrode assembly, a stacked type electrode assembly, and a stack-folding type electrode assembly. In a jelly-roll type electrode assembly, a separator is interposed between a positive electrode and a negative electrode, each of which is provided as the form of a sheet coated with an active material, and then, the positive electrode, the separator, and the negative electrode are wound. In a stacked type electrode assembly, a plurality of positive and negative electrodes with a separator therebetween are sequentially stacked. In a stack/folding type electrode assembly, stacked type unit cells are wound together with a separation film having a long length. Among them, the jelly-roll type electrode assembly is widely used because the jelly-roll type electrode assembly has advantages in ease of manufacturing and high energy density per weight. <CIT> discloses a rechargeable battery comprising a gasket between the first can and the second can.

One aspect of the present invention is to provide a secondary battery that can induce short circuit when high-temperature heat and high pressure occur, in order to improve stability of the battery.

A secondary battery according to an embodiment of the present invention is defined in the appended set of claims. The secondary battery comprises an electrode assembly in which a first electrode, a separator, and a second electrode are alternately stacked and wound together, a can having an accommodation part configured to accommodate the electrode assembly therein, the can comprising a first can and a second can each having a tubular shape with an opening in a direction facing one another, and an insulator configured to insulate an overlapping portion between the first can and the second can, wherein the first can is electrically connected to the first electrode, and the second can is electrically connected to the second electrode, the insulator includes a short-circuit induction through-part having the form of a through-hole or a cutoff line, and short circuit occurs between the first can and the second can through the short-circuit induction through-part that is deformed in shape as heat or a pressure is applied to contact or expand the insulator, and the first can has an inner circumferential surface larger than an outer circumferential surface of the second can so that the second can is inserted into the first can.

According to the present invention, the first electrode and the second electrode may be electrically connected to the first can and the second can, and the insulator in which the circuit-circuit induction through-part that insulates the first can and the second can from each other may be provided. As the high-temperature heat or the high pressure is applied to contract and expand the insulator, the insulator may be deformed in shape, and thus, the short circuit may occur between the first can and the second can through the short-circuit induction through-part. Therefore, the energy level of the battery may be reduced to prevent the battery from exploding.

The objectives, specific advantages, and novel features of the present invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings. It should be noted that the reference numerals are added to the components of the drawings in the present specification with consistent numerals as much as possible, even if they are illustrated in other drawings. Also, the present invention may be embodied in different forms and should not be construed as limited to the embodiments set forth herein.

<FIG> is a perspective view of a secondary battery according to an embodiment of the present invention, and <FIG> is a cross-sectional view of the secondary battery according to an embodiment of the present invention.

Referring to <FIG> and <FIG>, a secondary battery <NUM> according to an embodiment of the present invention comprises an electrode assembly <NUM> in which a first electrode <NUM>, a separator <NUM>, and a second electrode <NUM> are alternately stacked, a can <NUM> comprising a first can <NUM> and a second can <NUM>, which accommodate the electrode assembly <NUM> therein, and an insulator <NUM> insulating an overlapping portion between the first can <NUM> and the second can <NUM>.

<FIG> is an exploded perspective view of the secondary battery according to an embodiment of the present invention.

Hereinafter, the secondary battery according to an embodiment of the present invention will be described in more detail with reference to <FIG>.

Referring to <FIG> and <FIG>, the electrode assembly <NUM> may be a chargeable and dischargeable power generation element and have a structure in which an electrode <NUM> and the separator <NUM> are combined to be alternately stacked with each other. Here, the electrode assembly <NUM> may have a wound shape.

The electrode <NUM> may comprise the first electrode <NUM> and the second electrode <NUM>. Also, the separator <NUM> may separate the first electrode <NUM> from the second electrode <NUM> to insulate the first and second electrodes <NUM> and <NUM> from each other. Here, each of the first electrode <NUM> and the second electrode may be provided in the form of a sheet and then be wound together with the separator <NUM> so as to be formed in a jelly roll type. Here, the electrode assembly <NUM> may be wound, for example, in a cylindrical shape.

The first electrode <NUM> may comprise a first electrode collector 111a and a first electrode active material 111b applied on the first electrode collector 111a. Also, the first electrode <NUM> may comprise a first electrode non-coating portion 111c that is not coated with the first electrode active material 111b.

Here, the first electrode <NUM> may be provided as, for example, a negative electrode and comprise a negative electrode collector (not shown) and a negative electrode active material (not shown) applied on the negative electrode collector. Also, a negative electrode non-coating portion that is not coated with the negative electrode active material may be formed on the first electrode <NUM>.

For example, the negative electrode collector may be provided as foil made of a copper (Cu) or nickel (Ni) material. The negative electrode active material may comprise synthetic graphite, a lithium metal, a lithium alloy, carbon, petroleum coke, activated carbon, graphite, a silicon compound, a tin compound, a titanium compound, or an alloy thereof. Here, the negative electrode active material may further comprise, for example, non-graphite-based SiO (silica) or SiC (silicon carbide).

The second electrode <NUM> may comprise a second electrode collector 112a and a second electrode active material 112b applied on the second electrode collector 112a. Also, the second electrode <NUM> may comprises a second electrode non-coating portion 112c that is not coated with the second electrode active material 112b.

Here, the second electrode <NUM> may be provided as, for example, a positive electrode and comprise a positive electrode collector (not shown) and a positive electrode active material (not shown) applied on the positive electrode collector. Also, a positive electrode non-coating portion that is not coated with the positive electrode active material may be formed on the second electrode <NUM>.

For example, the positive electrode collector may be provided as foil made of an aluminum material, and the positive electrode active material may be made of lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide, lithium iron phosphate, or a compound or mixture thereof containing at least one or more of the above-described materials.

The separator <NUM> may be made of an insulating material, and the first electrode <NUM>, the separator <NUM>, and the second electrode <NUM> may be alternately stacked. Here, the separator <NUM> may be disposed between the first electrode <NUM> and the second electrode <NUM> on outer surfaces of the first electrode <NUM> and the second electrode <NUM>. Here, the separator <NUM> may be disposed at the outermost side in a width direction when the electrode assembly <NUM> is wound.

Also, the separator <NUM> may be made of a flexible material. Here, the separator <NUM> may be made of, for example, a polyolefin-based resin film such as polyethylene or polypropylene having micropores.

<FIG> is a front view of the secondary battery according to an embodiment of the present invention, and <FIG> is a perspective view illustrating a first example of the insulator in the secondary battery according to an embodiment of the present invention.

Referring to <FIG>, the can <NUM> may be provided with an accommodation part that accommodates the electrode assembly <NUM> therein, and the can <NUM> may comprise a first can <NUM> and a second can <NUM>, which have cylindrical shapes and are opened in a direction facing each other.

Here, the first can <NUM> may be electrically connected to the first electrode <NUM>, and the second can <NUM> may be electrically connected to the second electrode <NUM>.

Also, each of the first can <NUM> and the second can <NUM> may have a cylindrical shape. The first can <NUM> has an inner circumferential surface greater than an outer circumferential surface of the second can <NUM> so that the second can <NUM> is inserted into the first can <NUM>.

Furthermore, the first can <NUM> may have one side 121b in which a first opening (not shown) that is opened in one direction C1 is formed and the other side 121c at which a first connection part 121a that is closed in the other direction C2 is formed. The second can <NUM> may have the other side 122c in which a second opening 122d that is opened in the other direction C2 is formed and one side 122b at which a second connection part <NUM> that is closed in the one direction C1 is formed. At this time, the first electrode <NUM> may have one end connected to the first connection part 121a, and the second electrode <NUM> may have one end connected to the second connection part 122a.

Here, one end 123b of the insulator <NUM> may extend to be closer to the second connection part 122a than one end of the first can <NUM>. Also, the other end 123c of the insulator <NUM> may extend to be closer to the first connection part 121a than the other end of the second can <NUM>. However, as described below, when the insulator is formed to be applied on an outer circumferential surface of the second can, the other end 123c of the insulator <NUM> may match the other end of the second can <NUM>.

Here, a distance a between the one end of the first can <NUM> to the one end 123b of the insulator <NUM> may be greater than zero, and a distance b between the other end of the second can <NUM> to the other end 123c of the insulator <NUM> may be greater than zero.

The insulator <NUM> may comprise an insulation material to insulate the overlapping portion between the first can <NUM> and the second can <NUM>.

Also, referring to <FIG>, a short-circuit induction through-part 123a-<NUM> that is provided in the form of a through-hole or a cutoff line may be formed in the insulator <NUM>. Here, short circuit may occur between the first can <NUM> and the second can <NUM> through the short-circuit induction through-part 123a-<NUM> that is deformed in shape when the insulator <NUM> is contracted or expanded by high-temperature heat or a high pressure. Thus, an energy level of the secondary battery <NUM> may be lowered to prevent the secondary battery <NUM> from exploding. This is done because the insulator <NUM> is contracted or expanded when a predetermined temperature (or more) and a predetermined pressure (or more) are applied to the insulator <NUM>. When the can increases in temperature or is expanded under abnormal situations, the insulation may also be subjected to the high-temperature heat and the high pressure, and thus, the insulator may be contracted or expanded to be deformed in shape.

The insulator <NUM> may comprise a polymer material. Also, the polymer material may comprise, for example, any one of polyethylene (PE), polypropylene (PP), and polyethylene terephthalate (PET). Particularly, the polymer material may comprise a polyethylene (PE) or polypropylene (PP) material having a melting point at a temperature of <NUM> or less. More specifically, the polymer material may comprise, for example, low-medium density PE having a melting point of <NUM> or medium-high density PE having a melting point of <NUM> to <NUM>. Since the battery explodes at a temperature of about <NUM> degrees to <NUM> degrees, when the insulator made of the above-described material is used, the short circuit may occur between the first can <NUM> and the second can <NUM> so as to lower the energy level of the battery before the battery explodes.

Since resistance R corresponds to a value of the product of specific resistance and area per thickness, the resistance R of the cylindrical insulator <NUM> may satisfy following equation: R = material (p) * thickness (t)/A = material (p) * thickness (t)/(diameter (d) * height (L)).

If the resistance is high, there is an advantage that an amount of heat is suddenly reduced. However, if the resistance is too high, an amount of heat to be generated may be too small, and thus, the resistance may be adjusted to have the amount of heat within a proper range. In this case, the resistance of the insulator <NUM> may be adjusted by changing the material p and the shapes d, L, and t.

For example, the insulator <NUM> may be applied on an outer circumferential surface of the second can <NUM> to form a coating layer. Here, the insulator <NUM> may be formed by applying an insulation material on the outer circumferential surface of the second can <NUM>.

Furthermore, for another example, the insulator <NUM> may be attached to the outer circumferential surface of the second can <NUM> through any one of painting, printing, cladding, lamination, spraying, masking, dipping, and bonding. In more detail, the insulator <NUM> may be formed on the outer circumferential surface of the second can <NUM> through the painting of the insulation material on the outer circumferential surface of the second can <NUM>, the spraying of the insulation material on the outer circumferential surface of the second can <NUM>, the attaching of a masking agent on the outer circumferential surface of the second can <NUM> or attaching the insulation material to a portion except for a mask, putting the outer circumferential surface of the second can <NUM> into an insulation solution to form an insulation layer, allowing the insulator to adhere to the outer circumferential surface of the second can <NUM> by using an adhesive component, and laminating the insulator <NUM> on the outer circumferential surface of the second can <NUM>.

For example, the first can <NUM> disposed at the outside may comprise steel, and the second can <NUM> disposed at the inside may comprise aluminum. Here, since the second can <NUM> comprises the aluminum, the second can <NUM> may be expanded by the high-temperature heat. As a result, the insulator <NUM> attached to the outer circumferential surface of the second can <NUM> may be expanded, and thus, the short circuit may easily occur between the first can <NUM> and the second can <NUM> due to the high-temperature heat through the short-circuit induction through-part 123a-<NUM> formed in the insulator <NUM>.

Here, the first electrode <NUM> may be provided as the negative electrode, and the second electrode <NUM> may be provided as the positive electrode.

<FIG> is a perspective view illustrating a second example of the insulator in the secondary battery according to an embodiment of the present invention, <FIG> is a perspective view illustrating a third example of the insulator in the secondary battery according to an embodiment of the present invention, and <FIG> is a perspective view illustrating a fourth example of the insulator in the secondary battery according to an embodiment of the present invention.

Referring to <FIG>, as a first example, the short-circuit induction through-part 123a-<NUM> may be provided in plurality to form at least one column in the insulator <NUM>-<NUM>. Particularly, the short-circuit induction through-part 123a-<NUM> may be provided as through-holes to form the column along a longitudinal direction of the insulator <NUM>-<NUM>.

Referring to <FIG>, as a second example, a plurality of the short-circuit induction through-parts 123a-<NUM> may be provided to form at least one row in the insulator <NUM>-<NUM>. Particularly, the short-circuit induction through-part 123a-<NUM> may be provided as through-holes to form the row along a longitudinal direction of the insulator <NUM>-<NUM>.

Referring to <FIG>, as a third example, a plurality of the short-circuit induction through-parts 123a-<NUM> may be provided to form a lattice shape in the insulator <NUM>-<NUM>. Particularly, the short-circuit induction through-part 123a-<NUM> may be provided as through-holes.

Referring to <FIG>, as a fourth example, a plurality of the short-circuit induction through-parts 123a-<NUM> may be provided to form a cutoff line in the insulator <NUM>-<NUM>.

When the battery is in a normal state, the short-circuit induction through-part may have a size that is sufficient so that the first can and the second can do not contact each other. When the battery is in an abnormal state, the short-circuit induction through-part may be deformed in shape so that the first can and the second can contact each other.

<FIG> is a perspective view illustrating states before and after the insulator is deformed in the secondary battery according to an embodiment of the present invention. Here, <FIG> illustrates a state before the insulator is deformed, and <FIG> illustrates a state after the insulator is deformed.

Referring to <FIG>, it is seen that the short-circuit induction through-part may be provided as a plurality of through-holes so that a deformation amount of <NUM> occurs when an internal pressure is generated in the insulator having a lattice shape.

As a result, it is seen that as the insulator is subjected to high-temperature heat or a high pressure so as to be contracted or expanded to be deformed in shape, causing short circuit between the first can and the second can.

Hereinafter, a secondary battery according to another embodiment will be described.

<FIG> is a perspective view of a secondary battery according to another embodiment of the present invention, and <FIG> is an exploded perspective view of the secondary battery according to the embodiment of <FIG>.

Referring to <FIG> and <FIG>, a secondary battery <NUM> according to another embodiment of the present invention comprises an electrode assembly <NUM> in which a first electrode <NUM>, a separator <NUM>, and a second electrode <NUM> are alternately stacked, a can <NUM> comprising a first can <NUM> and a second can <NUM>, which accommodate the electrode assembly <NUM> therein, and an insulator <NUM> insulating an overlapping portion between the first can <NUM> and the second can <NUM>.

The secondary battery <NUM> according to the embodiment of <FIG> and <FIG> is different from the secondary battery according to the foregoing embodiment in the materials of the first can <NUM> and the second can <NUM> and the polarities of the first electrode <NUM> and the second electrode <NUM>. Thus, contents of this embodiment, which are duplicated with those according to the forgoing embodiment, will be briefly described, and also, differences therebetween will be mainly described.

In more detail, in the secondary battery <NUM> according to this embodiment of the present invention, the can <NUM> may be provided with an accommodation part that accommodates the electrode assembly <NUM> therein and comprises a first can <NUM> and a second can <NUM>, which have cylindrical shapes and are opened in a direction facing each other.

Furthermore, the first can <NUM> may have one side 221b in which a first opening (not shown) that is opened in one direction C1 is formed and the other side 221c at which a first connection part 221a that is closed in the other direction C2 is formed. The second can <NUM> may have the other side 222c in which a second opening 222d that is opened in the other direction C2 is formed and one side 222b at which a second connection part 222a that is closed in the one direction C1 is formed. At this time, the first electrode <NUM> may have one end connected to the first connection part 221a, and the second electrode <NUM> may have one end connected to the second connection part 222a.

Also, a short-circuit induction through-part 123a-<NUM> that is provided in the form of a through-hole or a cutoff line may be formed in the insulator <NUM>. Here, short circuit may occur between the first can <NUM> and the second can <NUM> through the short-circuit induction through-part 123a-<NUM> that is deformed in shape when the insulator <NUM> is contracted or expanded by heat or a pressure (see <FIG>).

Also, the first can <NUM> may comprise aluminum, and the second can <NUM> may comprise steel. Here, the second can <NUM> disposed at the inside may comprise the steel, and thus, the first can <NUM> and the second can <NUM> may be easily press-fitted with respect to each other due to physical properties of high rigidity (it is preferable that the first can and the second can according to the present invention are coupled to each other in the press-fitting manner). When external force occurs, it may be easy to protect an object to be accommodated such as the electrode assembly <NUM> accommodated into the can <NUM>. Also, in the can <NUM>, the first can <NUM> disposed at the outside may comprise aluminum having a high strain rate. Thus, when the first can <NUM> is deformed, the insulator may be deformed to easily cause short circuit between the first can <NUM> and the second can <NUM> through the short-circuit induction through-part 123a-<NUM>.

Here, the first electrode <NUM> may be provided as a positive electrode, and the second electrode <NUM> may be provided as a negative electrode.

Hereinafter, a secondary battery according to further another embodiment will be described.

<FIG> is a perspective view of a secondary battery according to further another embodiment of the present invention, and <FIG> is an exploded perspective view of the secondary battery according to further another embodiment of the present invention.

Referring to <FIG> and <FIG>, a secondary battery <NUM> according to the further embodiment of the present invention comprises an electrode assembly <NUM> in which a first electrode <NUM>, a separator <NUM>, and a second electrode <NUM> are alternately stacked, a can <NUM> comprising a first can <NUM> and a second can <NUM>, which accommodate the electrode assembly <NUM> therein, and an insulator <NUM> insulating an overlapping portion between the first can <NUM> and the second can <NUM>.

The secondary battery <NUM> according to this embodiment of the present invention is different from the secondary batteries according to the foregoing embodiments in a shape of the can <NUM>. Thus, contents of this embodiment, which are duplicated with those according to the forgoing embodiment, will be omitted or briefly described, and also, differences therebetween will be mainly described.

In more detail, in the secondary battery <NUM> according to this embodiment of the present invention, the can <NUM> may be provided with an accommodation part that accommodates the electrode assembly <NUM> therein, and the can <NUM> may comprise a first can <NUM> and a second can <NUM>, which have tubular shapes and are opened in a direction facing each other.

Also, the tubular shape of each of the first can <NUM> and the second can <NUM> may have a rectangular prism. The first can <NUM> has an inner width larger than an outer width of the second can <NUM> so that the second can is inserted into the first can <NUM>.

Furthermore, the first can <NUM> may have one side 321b in which a first opening (not shown) that is opened in one direction C1 is formed and the other side 321c at which a first connection part 321a that is closed in the other direction C2 is formed. The second can <NUM> may have the other side 322c in which a second opening 322d that is opened in the other direction C2 is formed and one side 322b at which a second connection part 322a that is closed in the one direction C1 is formed. At this time, the first electrode <NUM> may have one end connected to the first connection part 321a, and the second electrode <NUM> may have one end connected to the second connection part 322a.

Also, a short-circuit induction through-part 323a that is provided in the form of a through-hole or a cutoff line may be formed in the insulator <NUM>. Here, the short circuit occurs between the first can <NUM> and the second can <NUM> through the short-circuit induction through-part 323a that is deformed in shape when the insulator <NUM> is contracted or expanded by heat or a pressure.

In the secondary battery <NUM> according to this embodiment of the present invention, for example, the first can <NUM> may comprise steel, and the second can <NUM> may comprise aluminum.

Furthermore, for another example, the first can <NUM> may comprise aluminum, and the second can <NUM> may comprise steel.

In the secondary battery <NUM> according to this embodiment of the present invention, for example, the first electrode <NUM> may be provided as a negative electrode, and the second electrode <NUM> may be provided as a positive electrode.

Furthermore, for another example, the first electrode <NUM> may be provided as a positive electrode, and the second electrode <NUM> may be provided as a negative electrode.

<FIG> is a view illustrating a displacement of a can in a secondary battery according to Manufacturing Example <NUM>.

A secondary battery was manufactured comprising an electrode assembly, a can in which an accommodation part that accommodates the electrode assembly therein is formed and which comprises a first can and a second can, which have cylindrical shapes and are opened in a direction facing each other, and an insulator in which a short-circuit induction through-part that has a through-hole and insulates an overlapping portion between the first can and the second can is formed was manufactured.

Here, the outer can that is the first can disposed at the outside was made of steel, and the inner can that is the second can disposed at the inside was made of aluminum. Here, the outer can had a thickness of <NUM>. 1t (t=<NUM>), and the inner can had a thickness of <NUM>.

Also, the insulator was made of a polymer PP material and a thickness <NUM>. 1t (t=<NUM>).

The inner can had an outer diameter of <NUM>.

Here, the outer can that is the first can disposed at the outside was made of aluminum, and the inner can that is the second can disposed at the inside was made of steel. Here, the outer can has a thickness of <NUM>. 1t (t=<NUM>), and the inner can has a thickness of <NUM>.

Also, the insulator was made of a PP material and a thickness <NUM>. 1t (t=<NUM>).

<FIG> is a view illustrating a displacement of a can in a secondary battery according to Comparative Example <NUM>.

A secondary battery was manufactured comprising an electrode assembly, a can in which an accommodation part that accommodates the electrode assembly therein is formed and which comprises a first can and a second can, which have cylindrical shapes and are opened in a direction facing each other, and an insulator in which a short-circuit induction through-part that has a through-hole and insulates an overlapping portion between the first can and the second can is not formed was manufactured.

Here, the outer can that is the first can disposed at the outside was made of steel, and the inner can that is the second can disposed at the inside was made of aluminum. Here, the outer can has a thickness of <NUM>. 1t (t=<NUM>), and the inner can has a thickness of <NUM>.

A secondary battery was manufactured comprising an electrode assembly, a can in which an accommodation part that accommodates the electrode assembly therein is formed and which comprises a first can and a second can, which have cylindrical shapes and are opened in a direction facing each other, and an insulator in which a short-circuit induction through-part that insulates an overlapping portion between the first can and the second can is not formed was manufactured.

A displacement of an inner can due to a pressure acting to be expanded from the inside to the outside of the battery was displayed when an internal pressure acting on a can was <NUM> MPa, both inner and outer cans acted in an outward direction, and top and bottom surfaces of the can were subjected to the same restriction conditions.

As a result of the experiment, referring to <FIG>, it is seen that when the can made of aluminum (Al) according to Manufacturing Example <NUM> is located at the inside, a deformation amount of <NUM> occurs. Referring to <FIG>, it is seen that when the can made of steel according to Manufacturing Example <NUM> is located at the inside, a deformation amount of <NUM> occurs. That is, it is seen that when the can made of aluminum (Al) is located at the inside, the can expands more due to its lower elastic modulus lower than when the can made of steel is located at the inside. Also, it may be expected that even plastic deformation occurs to implement sufficient deformation. The large expansion under the same conditions may mean that the short-circuit induction through-part is more largely deformed under the same conditions. If the deformation of the short-circuit induction through-part is lager, the short circuit between the first can and the second can may occur more easily. However, when the can made of the steel material is located at the inside, a process (a press-fitting process) of fitting the inner can into the outer can may be easy due to physical properties of high rigidity of the steel.

Also, referring to <FIG>, it is seen that when the can made of aluminum (Al) according to Comparative Example <NUM> is located at the inside, a deformation amount of <NUM> occurs. Referring to <FIG>, it is seen that when the can made of steel according to Comparative Example <NUM> is located at the inside, a deformation amount of <NUM> occurs.

Therefore, as illustrated in <FIG>, when comparing to Comparative Examples <NUM> and <NUM> in which the insulator having no short-circuit induction through-part in the form of the through-hole is provided between the outer can and the inner can, it is seen that more expansion occurs than in the can according to Manufacturing Examples <NUM> and <NUM> in which the insulator comprising the short-circuit induction through-part formed in the form of the through-hole is provided between the outer can and the inner can.

As a result, the large expansion under the same conditions may mean that the insulator is more largely deformed under the same conditions. As a result, it is seen that the deformation of the short-circuit induction through-part largely occurs, and thus, the short circuit between the first can and the second can easily occurs.

Claim 1:
A secondary battery (<NUM>) comprising:
an electrode assembly (<NUM>) in which a first electrode (<NUM>), a separator (<NUM>), and a second electrode (<NUM>) are alternately stacked and wound together;
a can (<NUM>) having an accommodation part configured to accommodate the electrode assembly (<NUM>) therein, the can comprising a first can (<NUM>) and a second can (<NUM>) each having a tubular shape with an opening in a direction facing one another; and
an insulator (<NUM>) configured to insulate an overlapping portion between the first can (<NUM>) and the second can (<NUM>),
wherein the first can (<NUM>) is electrically connected to the first electrode (<NUM>), and the second can (<NUM>) is electrically connected to the second electrode (<NUM>),
the insulator (<NUM>) includes a short-circuit induction through-part (123a-<NUM>) having the form of a through-hole or a cutoff line, and
short circuit occurs between the first can (<NUM>) and the second can (<NUM>) through the short-circuit induction through-part (123a-<NUM>) that is deformed in shape as heat or a pressure is applied to contact or expand the insulator,
wherein each of the first can (<NUM>) and the second can (<NUM>) has a cylindrical shape, and
the first can (<NUM>) has an inner circumferential surface larger than an outer circumferential surface of the second can (<NUM>) so that the second can (<NUM>) is inserted into the first can (<NUM>); or
wherein each of the first can (<NUM>) and the second can (<NUM>) has a rectangular prism, and
the first can (<NUM>) has an inner width larger than an outer width of the second can (<NUM>) so that the second can (<NUM>) is inserted into the first can (<NUM>).