Patent Description:
In a case where a secondary battery is used in an abnormal state, like a shortcircuited or over-discharged state, an internal temperature of the battery may rise or internal gases may be generated, resulting in an increased pressure of the battery.

For example, a lithium secondary battery may be overcharged to release gases, such as carbon dioxide or carbon monoxide, during decomposition of electrolyte, so that the internal pressure of the battery may increase. In addition, when over-current flows in the battery due to over-discharge or short-circuiting, the internal temperature of the battery may rise to convert the electrolyte into gases. Accordingly, when the internal pressure and temperature of the battery are increased, a serious safety-related problem may be caused particularly due to a risk of ignition, resulting in the overall deterioration in view of performance and life characteristics of the battery. The <CIT> discloses a rechargeable battery and heat-resistant member between an upper portion of the gasket and an outer surface of the cap plate. Further secondary batteries are disclosed in <CIT> and <CIT>.

The present invention provides a secondary battery in which an insulation sheet is inserted between a cap-up and a case, thereby increasing safety.

In accordance with an aspect of the present invention, the above and other objects can be accomplished by providing a secondary battery including an electrode assembly, a case for receiving the electrode assembly, a cap assembly coupled to an upper part of the case, and a gasket interposed between the cap assembly and the case, wherein the cap assembly includes a cap-up, a safety vent installed at a lower part of the cap-up and extending to an upper part of the cap-up so as to surround a periphery of the cap-up, and an insulation sheet positioned at an upper part of the safety vent extending to the upper part of the cap-up.

In addition, the insulation sheet may be interposed between the safety vent upwardly extending from the cap-up and the gasket.

The insulation sheet is formed by anodizing an aluminum sheet.

In addition, the insulation sheet may be adhered to the safety vent using an adhesion member.

In addition, the insulation sheet may be adhered to the safety vent by welding.

In addition, the secondary battery may further include an upper insulation member interposed between the cap-up and the safety vent upwardly extending from the cap-up, wherein the insulation sheet is coupled to the upper insulation member.

Here, the upper insulation member may include a first region positioned between the cap-up and the safety vent, a second region positioned inside the first region and formed to be higher than the first region, and a third region positioned inside the second region and formed to be higher than the second region, and the insulation sheet is coupled to a stepped portion between the second region and the third region.

In addition, the insulation sheet may be formed to extend from an upper part of the safety vent to the upwardly protruding part of the cap-up.

Here, a plurality of cutting grooves may be formed in an inner peripheral edge of the insulation sheet.

In accordance with another aspect of the present invention, there is provided a secondary battery including an electrode assembly, a case for receiving the electrode assembly, a cap assembly coupled to an upper part of the case, and a gasket interposed between the cap assembly and the case, wherein the cap assembly comprises a cap-up, a safety vent installed at a lower part of the cap-up, and an insulation sheet positioned at an upper part of the cap-up and interposed between the cap-up and the gasket, and the insulation sheet is formed by anodizing an aluminum sheet.

As described above, in the secondary battery according to an embodiment of the present invention, an insulation sheet is formed between the cap-up and the case, thereby insulating the cap-up and the case from each other even when the gasket is burnt or melted by heat generated during an internal short-circuit. Accordingly, the secondary battery of the present invention can have improved safety.

Hereinafter, a preferred embodiment of the present invention will be described in detail.

<FIG> is a cross-sectional view of a secondary battery according to an embodiment of the present invention. <FIG> are enlarged cross-sectional views of a cap assembly shown in <FIG>.

Referring to <FIG>, the secondary battery <NUM> according to an embodiment of the present invention includes an electrode assembly <NUM>, a case <NUM> for receiving the electrode assembly <NUM>, a cap assembly <NUM> coupled to an upper part of the case <NUM>, and a gasket <NUM> interposed between the cap assembly <NUM> and the case <NUM>.

The electrode assembly <NUM> includes a first electrode <NUM>, a second electrode <NUM> and a separator <NUM> interposed between the first electrode <NUM> and the second electrode <NUM>. The electrode assembly <NUM> may be formed by winding a stack of the first electrode <NUM>, the separator <NUM> and the second electrode <NUM> in a jelly-roll configuration. Here, the first electrode <NUM> may operate as a cathode and the second electrode <NUM> may operate as an anode. The first electrode tab <NUM> is connected to the cap assembly <NUM> on the electrode assembly <NUM>, and the second electrode tab <NUM> is connected to a bottom surface of the case <NUM> under the electrode assembly <NUM>.

The first electrode <NUM> is formed by coating a first electrode active material, such as a transition metal oxide, on a first electrode current collector formed as a metal foil made of aluminum, etc. A first electrode non-coating portion without a first electrode active material coated thereon is formed on the first electrode <NUM>, and a first electrode tab <NUM> is attached to the first electrode non-coating portion. The first electrode tab <NUM> has one end electrically connected to the first electrode <NUM> and the other end upwardly protruding from the electrode assembly <NUM> and electrically connected to the cap assembly <NUM>.

The second electrode <NUM> is formed by coating a second electrode active material, such as graphite or carbon, on a second electrode current collector formed as a metal foil made of copper or nickel. A second electrode non-coating portion without a second electrode active material coated thereon is formed on the second electrode <NUM>, and a second electrode tab <NUM> is attached to the second electrode non-coating portion. The second electrode tab <NUM> has one end electrically connected to the second electrode <NUM> and the other end downwardly protruding from the electrode assembly <NUM> and electrically connected to the bottom surface of the case <NUM>.

The separator <NUM> positioned between the first electrode <NUM> and the second electrode <NUM> may prevent a short-circuit from occurring therebetween while allowing lithium ions to move. The separator <NUM> may be made of polyethylene, polypropylene, or a composite film of polyethylene and polypropylene.

The case <NUM> may include a side plate <NUM> that is shaped of a cylinder having a predetermined diameter to form a space for receiving the electrode assembly <NUM>, and a bottom plate <NUM> sealing a bottom portion of the side plate <NUM>. A top-end opening of the case <NUM> is opened to allow the electrode assembly <NUM> to be inserted into the case <NUM> therethrough to then be sealed. In addition, a beading part <NUM> for preventing the electrode assembly <NUM> from moving is formed at an upper portion of the case <NUM>. In addition, a crimping part <NUM> for fixing the cap assembly <NUM> and the gasket <NUM> is formed at the topmost part of the case <NUM>.

The cap assembly <NUM> includes a cap-up <NUM>, a safety vent <NUM>, an insulator <NUM>, a cap-down <NUM> and an insulation sheet <NUM>.

The cap-up <NUM> may have a top portion convexly formed to be electrically connected to an external circuit. In addition, the cap-up <NUM> may include a gas discharge hole <NUM> formed therein to provide a passageway for discharging internal gases generated in the case <NUM>. The cap-up <NUM> is electrically connected to the electrode assembly <NUM> and transfers electric current generated in the electrode assembly <NUM> to the external circuit.

The safety vent <NUM> is formed as a circular plate shaped to correspond to the cap-up <NUM>. A protrusion part <NUM> that protrudes downwardly is formed at the center of the safety vent <NUM>. The safety vent <NUM> is electrically connected to a sub-plate <NUM> fixed to a bottom surface of the cap-down <NUM> using the protrusion part <NUM> penetrating the throughhole <NUM> of the cap-down <NUM>. Here, the protrusion part <NUM> of the safety vent <NUM> and the sub-plate <NUM> may be welded to each other by, for example, laser welding, ultrasonic welding, resistance welding or equivalents thereof. In addition, a notch <NUM> for guiding rupture of the safety vent <NUM> is formed on an outer peripheral edge of the protrusion part <NUM>.

The outer peripheral edge of the safety vent <NUM> is brought into close contact with portions of the cap-up <NUM>, except for the upwardly protruding part of the cap-up <NUM>. That is to say, the outer peripheral edge of the safety vent <NUM> and an outer peripheral edge of the cap-up <NUM> come into contact with each other. In addition, the edge of the safety vent <NUM> is formed to upwardly extend from the cap-up <NUM> while surrounding the cap-up <NUM>. The safety vent <NUM> discharges the internal gases while cutting off the current when an abnormal internal pressure is generated in the case <NUM>. If the internal pressure of the case <NUM> exceeds an operation pressure of the safety vent <NUM>, the protrusion part <NUM> is upwardly moved by the gases discharged through a gas discharge hole <NUM> of the cap-down <NUM> to then be electrically separated from the sub-plate <NUM>. Here, the sub-plate <NUM> is electrically separated from the safety vent <NUM> such that the protrusion part <NUM> is torn at its welded portion. In addition, if the internal pressure of the case <NUM> exceeds a rupture pressure higher than the operation pressure of the safety vent <NUM>, the notch <NUM> of the safety vent <NUM> is ruptured, thereby preventing the secondary battery <NUM> from exploding.

The insulator <NUM> is interposed between the safety vent <NUM> and the cap-down <NUM> to insulate the safety vent <NUM> and the cap-down <NUM> from each other. In detail, the insulator <NUM> is interposed between the outer peripheral edge of the safety vent <NUM> and the outer peripheral edge of the cap-down <NUM>. The insulator <NUM> may be made of a resin material, such as polyethylene (PE), polypropylene (PP) or polyethylene terephthalate (PET).

The cap-down <NUM> is shaped of a circular plate. A throughhole <NUM> is formed at the center of the cap-down <NUM>, and the protrusion part <NUM> of the safety vent <NUM> penetrates the throughhole <NUM>. In addition, a gas discharge hole <NUM> is formed at one side of the cap-down <NUM>, and the sub-plate <NUM> is coupled to a lower part of the cap-down <NUM>. The gas discharge hole <NUM> functions to release internal gases when an excessive internal pressure is generated in the case <NUM>. Here, the protrusion part <NUM> of the safety vent <NUM> is elevated by the gases released through the gas discharge hole <NUM>, thereby separating the protrusion part <NUM> from the sub-plate <NUM>. The sub-plate <NUM> is welded between the protrusion part <NUM> of the safety vent <NUM> penetrating the throughhole <NUM> of the cap-down <NUM> and the first electrode tab <NUM>. Accordingly, the sub-plate <NUM> may electrically connect the first electrode tab <NUM> and the safety vent <NUM> to each other.

The insulation sheet <NUM> is formed as a ring-shaped plate and is mounted on the cap-up <NUM>. In detail, the insulation sheet <NUM> is mounted on the edge of the cap-up <NUM>. Therefore, the insulation sheet <NUM> is positioned on the safety vent <NUM> surrounding the edge of the cap-up <NUM>. That is to say, the insulation sheet <NUM> is positioned on the cap-up <NUM> and is interposed between the safety vent <NUM> and the gasket <NUM>. Here, the insulation sheet <NUM> may be fixed to the safety vent <NUM> positioned at the edge of the cap-up <NUM> through the adhesion member <NUM>. In addition, after being mounted on the safety vent <NUM> positioned at the edge of the cap-up <NUM>, the insulation sheet <NUM> may be fixed to the cap-up <NUM> by the gasket <NUM> and the crimping part <NUM> of the case <NUM> without using an adhesion member. In addition, the insulation sheet <NUM> may be fixed to the safety vent <NUM> positioned at the edge of the cap-up <NUM> by laser welding, ultrasonic welding, resistance welding or an equivalent thereof.

The insulation sheet <NUM> is formed by anodizing an aluminum sheet. Here, the anodizing is a process for forming an oxide layer by oxidizing a surface of a metal plate. In general, the most typically used material in anodizing is aluminum (Al), and other metals, including manganese (Mn), zinc (Zn), titanium (Ti), hafnium (Hf), niobium (Nb) and so on, may also be used. The thus formed oxide layer may have very high hardness and may be excellent in view of corrosion resistance and wear resistance. For example, the insulation sheet <NUM> may be completed such that an aluminum sheet is inserted into an electrolyte solution and electrodes are applied thereto, making a surface of the aluminum sheet react with oxygen to cause gradual oxidation to the surface of the aluminum sheet, and forming aluminum oxide (Al<NUM>O<NUM>) on the oxidized portion of the aluminum sheet, that is, forming an oxide layer. Here, the oxide layer may be formed on one surface of the aluminum sheet.

In general, when a short-circuit occurs to the secondary battery <NUM>, the internal pressure of the secondary battery <NUM> may increase, so that the internal gases are released through the gas discharge hole <NUM> of the cap-down <NUM>. Here, the protrusion part <NUM> of the safety vent <NUM> is elevated by the released gases, thereby cutting off electrical current by electrically disconnecting the protrusion part <NUM> of the safety vent <NUM> from the sub-plate <NUM>. However, the gasket <NUM> positioned between the cap-up <NUM> (and/or the safety vent <NUM>) and the case <NUM> may be burnt or melted down due to heat generated due to the short-circuit occurring to the secondary battery <NUM>, so that a short-circuit may be generated between the cap-up <NUM> (and/or the safety vent <NUM>) and the case <NUM>.

According to the present invention, the insulation sheet <NUM> is installed on the safety vent <NUM> positioned at the edge of the cap-up <NUM>, thereby insulating the cap-up <NUM> (and/or the safety vent <NUM>) and the case <NUM> from each other by the insulation sheet <NUM> even if the gasket <NUM> is burnt or melted down by the heat generated when a short-circuit occurs to the secondary battery <NUM>. Therefore, the secondary battery <NUM> according to the present invention can having improved safety by perfectly cutting off the electrical current flowing therein even during the short-circuit.

The gasket <NUM> is installed at the top-end opening of the case <NUM>. That is to say, the gasket <NUM> is assembled such that it is brought into close contact with the peripheral edges of the cap-up <NUM> and the safety vent <NUM>, and an inside of the case <NUM>. The gasket <NUM> may be made of a resin material, such as polyethylene (PE), polypropylene (PP) or polyethylene terephthalate (PET). The gasket <NUM> may prevent the cap assembly <NUM> from being separated from the case <NUM>.

<FIG> are partially cross-sectional views of a secondary battery according to another embodiment of the present invention. <FIG> is an exploded perspective view illustrating an insulation sheet and an upper insulator shown in <FIG>.

The secondary battery illustrated in <FIG> is substantially the same with the secondary battery illustrated in <FIG>, and the following description will focus on differences therebetween.

Referring to <FIG>, the insulation sheet <NUM> is formed as a ring-shaped plate and is mounted on a cap-up <NUM>. That is to say, the insulation sheet <NUM> is positioned on a safety vent <NUM> surrounding the edge of the cap-up <NUM>. The insulation sheet <NUM> may be formed by anodizing an aluminum sheet. In addition, an upper insulation member <NUM> may further be formed between the insulation sheet <NUM> and the cap-up <NUM>. The insulation sheet <NUM> is inserted into the upper insulation member <NUM> to then be fixed to the edge of the cap-up <NUM>. The upper insulation member <NUM> is formed as a substantially ring-shaped plate and may be made of a resin material, such as polyethylene (PE), polypropylene (PP) or polyethylene terephthalate (PET). In addition, the upper insulation member <NUM> includes a first region 285a positioned between the cap-up <NUM> and the safety vent <NUM>, a second region 285b positioned inside the first region 285a and formed to be higher than the first region 285a, and a third region 285c positioned inside the second region 285b and formed to be higher than the second region 285b. That is to say, the upper insulation member <NUM> is formed in a shape of a staircase having gradually decreasing heights away from the center. In addition, the insulation sheet <NUM> is inserted into a step s between the second region 285b and the third region 285c and is positioned on the second region 285b. Here, the height of the second region 285b is equal to that of the safety vent <NUM> positioned at the edge of the cap-up <NUM>. Therefore, the insulation sheet <NUM> is mounted along an area extending between the safety vent <NUM> and the second region 285b. Thereafter, the insulation sheet <NUM> may be brought into close contact with the cap-up <NUM> by the gasket <NUM> and the crimping part <NUM> of the case <NUM>.

<FIG> and <FIG> are partially cross-sectional views of a secondary battery according to still another embodiment of the present invention.

Referring to <FIG> and <FIG>, the insulation sheet <NUM> is mounted on a cap-up <NUM>. In detail, the insulation sheet <NUM> is mounted on the cap-up <NUM> and a safety vent <NUM> surrounding the edge of the cap-up <NUM>. Here, the safety vent <NUM> is configured to surround the edger of the cap-up <NUM> while not extending to an upper portion of the cap-up <NUM>. Therefore, the insulation sheet <NUM> may be mounted along an area extending between the cap-up <NUM> and the safety vent <NUM>. In addition, the insulation sheet <NUM> may be fixed to the cap-up <NUM> by, for example, laser welding, ultrasonic welding, resistance welding or equivalents thereof. Of course, the insulation sheet <NUM> may also be fixed to the cap-up <NUM> using an adhesion member. In addition, the insulation sheet <NUM> may be formed by anodizing an aluminum sheet.

<FIG> and <FIG> are partially cross-sectional views of a secondary battery according to still another embodiment of the present invention. <FIG> is a plan view illustrating a state in which an insulation sheet is coupled to a cap-up in <FIG>.

Claim 1:
A secondary battery comprising:
an electrode assembly (<NUM>);
a case (<NUM>) for receiving the electrode assembly (<NUM>);
a cap assembly (<NUM>) coupled to an upper part of the case (<NUM>); and
a gasket (<NUM>) interposed between the cap assembly (<NUM>) and the case (<NUM>),
wherein the cap assembly (<NUM>) comprises:
a cap-up (<NUM>);
a safety vent (<NUM>) installed at a lower part of the cap-up (<NUM>) and extending to an upper part of the cap-up (<NUM>) so as to surround a periphery of the cap-up (<NUM>); and
an insulation sheet (<NUM>) positioned at an upper part of the safety vent (<NUM>) extending to the upper part of the cap-up (<NUM>),
characterized in that
the insulation sheet (<NUM>) is formed by anodizing an aluminum sheet.