Patent Description:
The present invention relates to a secondary battery and a method for interrupting current of the secondary battery, and more particularly, to an apparatus and method for interrupting current in case of emergency such as short circuit in a secondary battery.

Secondary batteries are batteries capable of being repeatedly chargeable and dischargeable, and various kinds of secondary batteries are used according to electronic devices that require secondary batteries. Generally, such a secondary battery normally operates with charging or discharging according to a use thereof. However, when the secondary battery is short-circuited due to an external impact or the like, a gas is generated in the secondary battery to increase in pressure and temperature in the secondary battery. In this case, if the gas is not discharged to the outside, or the temperature in the secondary battery steadily increases, fire or explosion may occur. To prevent this phenomenon from occurring, a device for interrupting a flow of current of the secondary battery may be mounted in the secondary battery.

<FIG> is a cross-sectional view illustrating an example of a structure of a secondary battery according to the related art.

As illustrated in <FIG>, a secondary battery <NUM> may include a battery can <NUM> constituting a case of the secondary battery <NUM> and having an opened upper portion and a cap plate <NUM> disposed on the upper portion of the battery can <NUM> to seal the upper portion of the battery can <NUM>. A safety vent may be provided between the battery can <NUM> and the cap plate <NUM>. Also, a gasket <NUM> for further sealing the inside of the secondary battery from the outside may be disposed between an inner surface of the battery can <NUM> and the cap plate <NUM>. Also, a current interrupting device (CID) filter <NUM> may be attached to a lower portion of the safety vent <NUM> in a state of being welded to the safety vent <NUM>. The CID filter <NUM> may be a path through which current flows to allow current passing through the CID filter <NUM> from an electrode assembly to flow to the safety vent <NUM>.

According to the related art, when the pressure in the secondary battery <NUM> increases due to the short circuit or the like of the secondary battery <NUM>, the entire safety vent <NUM> or a central portion of the safety vent <NUM> may swell up. Thus, a portion or the whole of the safety vent <NUM> may be broken. When the safety vent <NUM> is broken, the safety vent <NUM> may be separated from the CID filter <NUM> to interrupt current and discharge the gas within the secondary battery <NUM>.

However, the current interrupting principle of the secondary battery according to the related art has a problem that current is not properly interrupted when an internal pressure of the secondary battery does not sufficiently increases due to a reason in which the secondary battery is not properly sealed because the current is interrupted after the internal pressure of the secondary battery increases. Also, there is a problem that fire already occurs before the current is interrupted when overcurrent flows to allow an internal temperature of the secondary battery to abnormally increase due to short circuit or the like before the internal pressure of the secondary batter reaches a predetermined pressure. <CIT> and <CIT> disclose current interruption means of the secondary battery.

Accordingly, an object of the present invention is to interrupt current when an internal temperature of a secondary battery reaches a predetermined temperature even before an internal pressure of the secondary battery reaches a predetermined pressure to effectively interrupt the current in case of emergency, thereby preventing the secondary battery from being exploded or fired.

According to an aspect of the present invention so as to achieve the abovementioned object, a secondary battery is provided as defined in the appended set of claims. The secondary battery includes: an electrode assembly; an electrode tab extending from the electrode assembly; a can member accommodating the electrode assembly and having an opened upper portion; a cap assembly coupled to the upper portion of the can member to cover the upper portion of the can member; and a bimetal coming into contact with the electrode tab and the cap assembly at a deformation temperature or less, wherein the bimetal is spaced apart from the cap assembly at the deformation temperature or more.

The cap assembly includes: a cap plate disposed on an outermost portion of the cap assembly; and a safety vent disposed between the cap plate and the electrode assembly and having a surface on which a notch is provided, the electrode tab includes a positive electrode tab; and a negative electrode tab, and the bimetal is disposed between the safety vent and the electrode assembly to come into contact with the safety vent and the positive electrode tab at the deformation temperature or less and to be spaced apart from the safety vent at the deformation temperature or more.

A material used for manufacturing the negative electrode tab has electric resistance less than that of nickel (Ni).

The material used for manufacturing the negative electrode tab includes nickel-clad (Ni-Clad).

The bimetal includes: an upper bimetal constituting an upper portion of the bimetal; and a lower bimetal constituting a lower portion of the bimetal, wherein the lower bimetal has a thermal expansion coefficient less than that of the upper bimetal.

The bimetal may include a shape memory alloy.

The deformation temperature may range from <NUM> to <NUM>.

According to another aspect of the present invention so as to achieve the abovementioned object, a method for interrupting current of a secondary battery as defined in the appended set of claims, the method includes: a short circuit step of allowing an electrode in the secondary battery to be short-circuited; a temperature increasing step in which the bimetal increases in temperature as abnormal current occurring in the short circuit step flows through the bimetal of which at least a portion comes into contact with an electrode tab connected to the electrode of the secondary battery and a cap assembly of the secondary battery; and an interrupting step in which the bimetal is warped through the temperature increasing step and spaced apart from the cap assembly to interrupt current flowing to the cap assembly when the bimetal has a deformation temperature or more.

The secondary battery includes: an electrode assembly; a can member accommodating the electrode assembly; and a cap assembly coupled to an upper portion of the can member, wherein the cap assembly includes: a cap plate disposed on an outermost portion of the cap assembly; and a safety vent disposed between the cap plate and the electrode assembly and having a surface on which a notch is provided, wherein the electrode tab extending from the electrode assembly includes: a positive electrode tab; and a negative electrode tab, in the temperature increasing step, the bimetal may come into contact with the safety vent and the positive electrode tab and increases in temperature by current flowing from the positive electrode tab, and in the interrupting step, the bimetal may be spaced apart from the safety vent to interrupt current flowing to the safety vent.

The negative electrode tab has electric resistance less than nickel (Ni).

A material for forming the negative electrode tab includes nickel-clad (Ni-Clad).

According to the present invention, an object of the present invention is to interrupt the current when the internal temperature of the secondary battery reaches the predetermined temperature even before the internal pressure of the secondary battery reaches the predetermined pressure to effectively interrupt the current in case of emergency, thereby preventing the secondary battery from being exploded or fired.

Hereinafter, a structure of a secondary battery according to an embodiment of the present invention will be described with reference to the accompanying drawings.

<FIG> is a cross-sectional view illustrating a structure of a secondary battery in ordinary times according to an embodiment of the present invention, and <FIG> is a cross-sectional view illustrating a structure of a secondary battery in case of emergency according to an embodiment of the present invention.

<FIG> illustrates a secondary battery <NUM> according to an embodiment of the present invention. The secondary battery <NUM> may have various shapes. For example, the secondary battery <NUM> may be a cylindrical secondary battery having a cylindrical shape.

The secondary battery <NUM> includes a can member <NUM> for accommodating internal components like an electrode assembly of the secondary battery <NUM>. The can member <NUM> may have a structure in which an upper portion is opened. When the secondary battery <NUM> has the cylindrical shape, the can member <NUM> may also have a cylindrical shape.

A cap plate <NUM> may be disposed on the upper portion of the can member <NUM>. The cap plate <NUM> may be a component for covering the upper portion of the can member <NUM>. That is, the cap plate <NUM> may be a component that seals the upper portion of the can member <NUM> to isolate an inner space of the can member <NUM> from the outside and also be a component that forms an electrode terminal (a positive electrode terminal of the present invention) of the secondary battery.

To improve sealability of the inside of the can member <NUM> (or the inside of the secondary battery <NUM>), a gasket <NUM> may be disposed between an inner surface of the can member <NUM> and the cap plate <NUM>.

Also, a safety vent <NUM> may be disposed on a lower portion of the cap plate <NUM>. The safety vent <NUM> is disposed between the cap plate <NUM> and the electrode assembly. One or more notches 140a may be provided on the safety vent <NUM>. When the notches 140a are provided on the safety vent <NUM>, if an internal pressure of the secondary battery increases, the safety vent may be broken through the notches to separate a portion of the safety vent from the other portion of the safety vent, thereby interrupting a flow of current. The cap plate <NUM>, the gasket <NUM>, and the safety vent <NUM>, which are described above, may be assembled with each other and then coupled to the upper portion of the can member <NUM> to constitute a cap assembly that covers the upper portion of the can member <NUM>.

The secondary battery according to an embodiment of the present invention includes a bimetal <NUM>.

The bimetal is a component manufactured by attaching different kinds of metals. The bimetal means that it is manufactured by generally attaching two different kinds of metals to each other in the meaning of 'bi' which is a prefix. However, the bimetal used in the present specification may be interpreted to include a component that is manufactured by attaching not only two kinds of metals but also three or more kinds of metals to each other.

As illustrated in <FIG>, the bimetal <NUM> comes into contact with the safety vent <NUM> in ordinary times at which the secondary battery normally operates. Also, although not shown, the bimetal <NUM> comes into contact with a positive electrode tab of the electrode assembly. Here, the meaning of 'contact' is interpreted not only as coming into direct contact, but also as coming into indirect contact through other components.

As described above, the bimetal <NUM> according to an embodiment of the present invention comes into contact with the safety vent <NUM> in ordinary times and be spaced apart from the safety vent <NUM> when an electrode of the secondary battery is short-circuited.

In more detail, as illustrated in <FIG>, in case of emergency such as the short circuit of the secondary battery, the bimetal <NUM> may be warped downward and thus spaced apart from the safety vent <NUM>. Thus, the flow of the current through the safety vent <NUM> may be interrupted to secure safety of the secondary battery.

Here, the warping of the bimetal <NUM> may be caused by an increase in temperature of the bimetal. That is, according to an embodiment of the present invention, since the bimetal <NUM> in which metals having different thermal expansion coefficients are attached to each other is applied to the secondary battery, the bimetal <NUM> may be changed in shape according to a temperature. Thus, when the bimetal <NUM> reaches a predetermined temperature or more, the bimetal <NUM> may be spaced apart from the safety vent <NUM>. Hereinafter, in the present specification and claims, a temperature at which the bimetal <NUM> begins to be spaced apart from the safety vent <NUM> or the cap assembly will be referred to as a 'deformation temperature'.

According to the present invention, the deformation temperature of the bimetal <NUM> may be about <NUM>. That is, according to an embodiment of the present invention, the bimetal <NUM> comes into contact with the safety vent <NUM> in ordinary times. Then, when the bimetal <NUM> has a temperature greater than about <NUM>, the bimetal <NUM> may be spaced apart from the safety vent <NUM> to interrupt a flow of current through the safety vent <NUM>. For example, according to an embodiment of the present invention, the bimetal <NUM> may have a deformation temperature ranging from <NUM> to <NUM>.

The bimetal <NUM> is manufactured by attaching two or more kinds of metals to each other. Thus, the bimetal <NUM> includes an upper bimetal <NUM> constituting an upper portion of the bimetal <NUM> and a lower bimetal <NUM> constituting a lower portion of the bimetal <NUM>. The upper bimetal <NUM> may come into contact with the safety vent <NUM> in ordinary times.

Since the bimetal according to an embodiment of the present invention has to be spaced apart from the safety vent at the deformation temperature or more, it is necessary to be warped at the deformation temperature or more. For this, the lower bimetal <NUM> has a thermal expansion coefficient less than that of the upper bimetal <NUM>. Also, the bimetal <NUM> may include a shape memory alloy.

When the shape memory alloy is applied to the bimetal <NUM>, since the bimetal <NUM> has a uniform shape according to a temperature thereof, the bimetal <NUM> coming into contact with the safety vent <NUM> and spaced apart from the safety vent <NUM> at the deformation temperature may be secured to improve the safety of the secondary battery when the short circuit occurs.

<FIG> is a plan view illustrating a structure of an electrode assembly that is capable of being applied to the secondary battery according to an embodiment of the present invention.

An electrode assembly <NUM> may be manufactured by alternately stacking an electrode and a separator. For example, the electrode assembly <NUM> may be manufactured through various manufacturing methods and have various shapes.

As illustrated in <FIG>, a positive electrode tab <NUM> and a negative electrode tab <NUM>, which extend from the electrode assembly <NUM>, may be disposed on ends of the electrode assembly <NUM>. Here, the positive electrode tab <NUM> may come into contact with the bimetal as described above.

The negative electrode tab <NUM> may be manufactured by using various materials. According to an embodiment of the present invention, a material used for manufacturing the negative electrode tab <NUM> has electric resistance less than that of nickel (Ni). Also, the material used for manufacturing the negative electrode tab <NUM> is nickel-clad (Ni-Clad).

According to an embodiment of the present invention, in case of emergency such as the short circuit of the electrode, the positive electrode tab coming into contact with the bimetal increases in temperature, and thus, the bimetal may also increase in temperature. Here, it is necessary to quickly rise the temperature of the positive electrode tab so that the bimetal is more quickly spaced apart from the safety vent in case of the emergency. Here, although the short circuit of the same electrode occurs, if the negative electrode tab has relatively large resistance, the current decreases in intensity. As a result, the positive electrode tab may relatively slowly increase in temperature, and thus, the bimetal may also relatively slowly increase in temperature. Therefore, when the negative electrode tab has relatively large resistance, since the bimetal relatively slowly increases in temperature, the current may not be quickly interrupted when the short circuit occurs.

Thus, according to an embodiment of the present invention, the material used for manufacturing the negative electrode tab <NUM> has electric resistance less than nickel (Ni) that is generally used for manufacturing the negative electrode tab according to the related art.

Particularly, the material used for manufacturing the negative electrode tab <NUM> is Ni-Clad formed by attaching nickel to a surface of a metal such as copper. Since the Ni-Clad has electric resistance less than that of nickel, if the Ni-Clad is used as the material for forming the negative electrode tab, the current may further increase in intensity when the electrode is short-circuited, and thus, the positive electrode tab may very quickly increase in temperature. As a result, since the bimetal coming into contact with the positive electrode tab quickly and sharply increases in temperature, the current may be effectively interrupted before an accident occurs in case of the short circuit of the electrode. The positive electrode tab <NUM> may be manufactured by using aluminum.

Hereinafter, a method for interrupting current of the secondary battery according to an embodiment of the present invention will be described.

<FIG> is a flowchart for explaining a method for interrupting current of the secondary battery according to an embodiment of the present invention.

As illustrated in <FIG>, a method for interrupting current of the secondary battery according to an embodiment of the present invention may include a short circuit step of allowing an electrode in the secondary battery to be short-circuited. When the short circuit step is performed, abnormal current occurring in the short circuit step may flow through a bimetal of which at least a portion comes into contact with an electrode tab (more particularly, a positive electrode tab) connected to the electrode of the secondary battery and a safety vent of the secondary battery. Thus, a temperature increasing step in which the bimetal increases in temperature may be performed. When the temperature increasing step is performed, the bimetal may be warped through the temperature increasing step. Thus, an interrupting step in which the bimetal is spaced apart from the safety vent to interrupt current flowing to the safety vent may be performed. A temperature of the bimetal when the bimetal is spaced apart from the safety vent is defined as a 'deformation temperature' in this specification as described above.

Claim 1:
A secondary battery (<NUM>) comprising:
an electrode assembly (<NUM>);
an electrode tab extending from the electrode assembly, and comprising a positive electrode tab (<NUM>) and a negative electrode tab (<NUM>) ;
a can member (<NUM>) accommodating the electrode assembly (<NUM>) and having an opened upper portion;
a cap assembly coupled to the upper portion of the can member to cover the upper portion of the can member, and comprising:
a cap plate (<NUM>) disposed on an outermost portion of the cap assembly, and
a safety vent (<NUM>) disposed between the cap plate (<NUM>) and the electrode assembly and having a surface on which a notch (140a) is provided ; and
a bimetal (<NUM>) being disposed between the safety vent (<NUM>) and the electrode assembly (<NUM>) to come into contact with the positive electrode tab (<NUM>) and the safety vent (<NUM>) below a deformation temperature and wherein the bimetal is spaced apart from the safety vent (<NUM>) of the cap assembly at the deformation temperature or more,
wherein a material used for manufacturing the negative electrode tab (<NUM>) is nickel-clad (Ni-Clad), and
wherein the bimetal (<NUM>) comes into direct contact with the positive electrode, and comprises:
an upper bimetal (<NUM>) constituting an upper portion of the bimetal; and
a lower bimetal (<NUM>) constituting a lower portion of the bimetal,
wherein the lower bimetal (<NUM>) has a thermal expansion coefficient less than that of the upper bimetal (<NUM>).