Patent Description:
In general, a cylindrical lithium ion secondary battery generally includes a cylindrical electrode assembly, a cylindrical case coupled to the electrode assembly, an electrolyte injected into the case to allow movement of lithium ions, and a cap assembly coupled to one side of the case to prevent leakage of the electrolyte and separation of the electrode assembly. In addition, a current interrupt device (CID) capable of interrupting the flow of current when abnormality occurs to the secondary battery is provided in the cap assembly.

For example, if the secondary battery is overcharged, decomposition of an electrolyte may occur due to discharge gases, such as carbon dioxide or carbon monoxide, and thus the internal pressure of the secondary battery may increase. In such a case, the CID of the cap assembly may operate to interrupt the flow of current, thereby preventing ignition or explosion of the secondary battery. However, although the current and component heat are rapidly generated due to an external short circuit, the internal pressure of battery may slowly increase, and thus the CID may not operate properly. In addition, sealing of the cap assembly may be cancelled due to a component damage, obstructing the proper operation of the CID.

The present invention provides a secondary battery enabling enhanced safety in case of an external short circuit.

According to an aspect of the present invention, provided is a secondary battery including: an electrode assembly; a case for accommodating the electrode assembly; and a cap assembly coupled to the top of the case, wherein the cap assembly comprises a cap-up, a safety vent provided below the cap-up, a cap-down provided below the safety vent and having a through hole and a gas discharge hole, an insulator provided between the safety vent and the cap-down, a sub-plate provided below the cap-down, and a solder member for electrically connecting the safety vent and the sub-plate, and the safety vent and the sub-plate are electrically connected by means of soldering.

The safety vent includes a fixing portion installed to make close contact with an edge portion of the cap-up, and a deforming portion positioned at an inner side of the fixing portion and downwardly protruding, and the deforming portion may include a first region extending from the fixing portion and having a notch formed therein, and a second region positioned at an inner side of the first region, having a coupling portion having a center hole formed therein, and downwardly protruding.

The sub-plate may include an accommodating groove located to correspond to the through hole of the cap-down, and the coupling portion and the solder member may be accommodated in the accommodating groove.

The accommodating groove may be configured to have a top-end diameter smaller than a bottom-end diameter.

A hook bent toward an outer side of the safety vent is provided at an end of the coupling portion.

The hook may have a diameter smaller than the top-end diameter of the accommodating groove.

A plurality of coupling holes may be provided in the second region, and the solder member may be injected into the coupling holes.

The solder member may have a melting point ranging from <NUM> to <NUM>.

When an external short circuit occurs to the secondary battery, the solder member may be melted and the safety vent may be upwardly convexly deformed, so that the safety vent is disconnected from the sub-plate.

When the internal pressure of the secondary battery is greater than or equal to an operating pressure of the safety vent, he internal temperature increases so that the solder member may be melted and the safety vent may be upwardly convexly deformed, so that the safety vent is disconnected from the sub-plate.

As described above, in the secondary battery according to an embodiment, the safety vent and the sub-plate are electrically connected by means of soldering, and the solder member is melted due to an external short circuit, so that the safety vent is disconnected from the sub-plate, thereby interrupting the current flowing through the secondary battery. Therefore, the secondary battery of the present invention may enable enhanced safety by preventing the electrode assembly from generating heat.

Hereinafter, example embodiments of the present invention will be described in detail.

Various embodiments of the present invention may be embodied in many different forms and should not be construed as being limited to the example embodiments set forth herein. Rather, these example embodiments of the invention are provided so that this invention will be thorough and complete.

In addition, in the accompanying drawings, sizes or thicknesses of various components are exaggerated for brevity and clarity.

As used herein, the singular forms are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprise or include" and/or "comprising or including," when used in this specification, specify the presence of stated features, numbers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, numbers, steps, operations, elements, components, and/or groups thereof.

<FIG> is a perspective view illustrating a secondary battery according to an embodiment. <FIG> is a cross-sectional view illustrating a cap assembly in the secondary battery according to an embodiment. <FIG> is a cross-sectional view illustrating another example safety vent.

Referring to <FIG> and <FIG>, the secondary battery <NUM> according to an embodiment of the present invention includes an electrode assembly <NUM>, a case <NUM>, a cap assembly <NUM>, and a gasket <NUM>.

The electrode assembly <NUM> includes a first electrode <NUM>, a second electrode <NUM>, and a separator <NUM> disposed between the first electrode <NUM> and the second electrode <NUM>. The electrode assembly <NUM> may be formed by winding a stacked structure of the first electrode <NUM>, the separator <NUM> and the second electrode <NUM> in a jelly-roll configuration. In some embodiments, the first electrode <NUM> may function as a positive electrode, and the second electrode <NUM> may function as a negative electrode. A first electrode tab <NUM> is connected to the cap assembly <NUM> at a top portion of the electrode assembly <NUM>, and a second electrode tab <NUM> is connected to a bottom surface plate <NUM> of the case <NUM> at a bottom portion of 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 of a metal foil, such as an aluminum foil. A first electrode uncoated portion without the 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 uncoated portion. One end of the first electrode tab <NUM> is electrically connected to the first electrode <NUM>, and the other end of the first electrode tab <NUM> upwardly protrudes from the electrode assembly <NUM> and is 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 of a metal foil, such as a copper or nickel foil. A second electrode uncoated portion without the 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 uncoated portion. One end of the second electrode tab <NUM> is electrically connected to the second electrode <NUM>, and the other end of the second electrode tab <NUM> downwardly protrudes from the electrode assembly <NUM> and is electrically connected to the bottom surface plate <NUM> of the case <NUM>.

The separator <NUM> is positioned between the first electrode <NUM> and the second electrode <NUM> to prevent a short circuit therebetween, and allows lithium ions to move. The separator <NUM> may include polyethylene, polypropylene, or a composite film of polyethylene and polypropylene.

The case <NUM> includes a side surface plate <NUM> having a cylindrically-shaped body having a predetermined diameter forming a space in which the electrode assembly <NUM> is accommodated, and the bottom surface plate <NUM> sealing a bottom portion of the side surface plate <NUM>. The top opening of the case <NUM> is opened to be sealed after the electrode assembly <NUM> is injected into the case <NUM>. In addition, a beading portion <NUM> is provided at an upper portion of the case <NUM> to prevent the electrode assembly <NUM> from moving. In addition, a crimping portion <NUM> is provided at a top end of the case <NUM> to fix the cap assembly <NUM>.

The cap assembly <NUM> includes a cap-up <NUM>, a safety vent <NUM>, a cap-down <NUM>, a sub-plate <NUM>, and a solder member <NUM>.

The cap-up <NUM> has an upwardly convex top portion to be electrically connected to an external circuit. In addition, the cap-up <NUM> has a gas discharge hole <NUM> providing a passage through which the gases generated inside the case <NUM> are discharged. The cap-up <NUM> is electrically connected to the electrode assembly <NUM> and transfers the current generated in the electrode assembly <NUM> to the external circuit.

The safety vent <NUM> is formed as a circular plate body shaped to conform with the cap-up <NUM> and is installed below the cap-up <NUM>. The safety vent <NUM> includes a fixing portion <NUM> positioned at its outer side thereof, and a deforming portion <NUM> positioned at an inner side of the fixing portion <NUM> and downwardly protruding. The fixing portion <NUM> is installed to make close contact with a portion of the cap-up <NUM>, except for an upwardly protruding portion of the cap-up <NUM>, that is, an edge portion of the cap-up <NUM>. In addition, an edge portion of the fixing portion <NUM> is formed to upwardly extend from the cap-up <NUM> while covering the edge portion of the cap-up <NUM>. Therefore, the safety vent <NUM> may be fixed to the cap-up <NUM> by the fixing portion <NUM>.

The deforming portion <NUM> includes a first region <NUM> positioned at its outer side and a second region <NUM> positioned at an inner side of the first region <NUM>. The deforming portion <NUM> may be electrically connected to the sub-plate <NUM> by means of soldering. The deforming portion <NUM> may be deformed when abnormality occurs to the secondary battery <NUM>, and thus the safety of the secondary battery <NUM> may be enhanced.

The first region <NUM> extends from the fixing portion <NUM> and downwardly protrudes from the inner side of the fixing portion <NUM>. The first region <NUM> is positioned between the fixing portion <NUM> and the second region <NUM>. In addition, a notch 153a guiding rupturing of safety vent <NUM> is provided in the first region <NUM>. In an example embodiment, when the internal pressure of the case <NUM> exceeds the operating pressure of the safety vent <NUM>, the deforming portion <NUM> upwardly moves by the gases discharged through the gas discharge hole <NUM> of the cap-down <NUM>, and thus the safety vent <NUM> is electrically disconnected from the sub-plate <NUM>. In addition, when the internal pressure of the case <NUM> exceeds a rupture pressure higher than the operating pressure of the safety vent <NUM>, the notch 153a is broken, thereby preventing the secondary battery <NUM> from exploding. The safety vent <NUM> may be made of aluminum (Al).

The second region <NUM> extends from the first region <NUM> and downwardly protrudes at the inner side of the first region <NUM>. A coupling portion <NUM> downwardly protruding from the second region <NUM> is provided at the center of the second region <NUM>, and a center hole 155a is provided at the center of the coupling portion <NUM>. That is, the coupling portion <NUM> is formed to have a hollow cylinder shape. In addition, the center hole 155a may provide a space in which the solder member <NUM> rises upward when the solder member <NUM> is melted. According to the invention, a hook 155b bent toward an outer side of the safety vent <NUM> is provided at an end of the coupling portion <NUM>. The hook 155b may function to increase a coupling force between the safety vent <NUM> and the sub-plate <NUM> to be described later. The coupling portion <NUM> may be electrically connected to the sub-plate <NUM> through the solder member <NUM>. As shown in <FIG>, a portion of the second region <NUM> is brought into contact with the sub-plate <NUM>, so that the safety vent <NUM> and the sub-plate <NUM> are electrically connected to each other. However, a current hardly flows through a contact portion between the second region <NUM> and the sub-plate <NUM> due to contact resistance, and the current actually flows between the safety vent <NUM> and the sub-plate <NUM> through the solder member <NUM>. In addition, as shown in <FIG>, a second region <NUM>' may not be brought into contact with the sub-plate <NUM>. Even if the second region <NUM>' is not brought into contact with the sub-plate <NUM>, the safety vent <NUM> may be electrically connected to the sub-plate <NUM> through the solder member <NUM>.

Additionally, when the coupling portion <NUM> is electrically connected to the sub-plate <NUM>, the coupling portion <NUM> may be coupled to the sub-plate <NUM> by soldering in a state in which the second region <NUM> is pressed. Therefore, when a large amount of current flows through the secondary battery <NUM> due to an external short circuit, the solder member <NUM> is melted by the heat generated in the secondary battery <NUM>, the second region <NUM> is upwardly inverted according to the elasticity restored to thus be electrically disconnected from the sub-plate <NUM>.

The cap-down <NUM> is formed as a circular plate body and is installed below the safety vent <NUM>. A through hole <NUM> is provided at the center of the cap-down <NUM>, and the second region <NUM> of the safety vent <NUM> penetrates the through hole <NUM>. In addition, a gas discharge hole <NUM> is provided at one side of the cap-down <NUM>. The gas discharge hole <NUM> may function to discharge internal gases when an excessive internal pressure is generated inside the case <NUM>. Here, the deforming portion <NUM> of the safety vent <NUM> may rise due to the gases discharged through the gas discharge hole <NUM>, and thus the safety vent <NUM> may be separated from the sub-plate <NUM>. In addition, an insulator <NUM> is provided between the cap-down <NUM> and the safety vent <NUM>. The insulator <NUM> insulates the cap-down <NUM> and the safety vent <NUM> from each other. The insulator <NUM> is installed under the fixing portion <NUM> of the safety vent <NUM> and is provided as a substantially ring-shaped configuration. The insulator <NUM> may be made of a resin material such as polyethylene (PE), polypropylene (PP), or polyethylene terephthalate (PET).

The sub-plate <NUM> is installed below the cap-down <NUM>. Specifically, the sub-plate <NUM> is coupled to a bottom portion of the cap-down <NUM> while covering the through hole <NUM> of the cap-down <NUM>. The sub-plate <NUM> includes a centrally positioned accommodating groove <NUM>. The coupling portion <NUM> of the safety vent <NUM> is accommodated in the accommodating groove <NUM>, and the solder member <NUM> fills the inside of the accommodating groove <NUM>. The accommodating groove <NUM> is configured to have a top-end diameter D1 smaller than a bottom-end diameter D2. In other words, the accommodating groove <NUM> is configured to have diameters gradually increasing away from its top end. In addition, the top-end diameter D1 of the accommodating groove <NUM> is larger than a diameter D3 of the hook 155b. This is for the purpose of separating the hook 155b of the safety vent <NUM> from the sub-plate <NUM> without being caught by the accommodating groove <NUM> when the solder member <NUM> filling the accommodating groove <NUM> is melted due to an external short circuit. The sub-plate <NUM> is electrically connected to the safety vent <NUM> through the solder member <NUM>. In addition, the first electrode tab <NUM> is electrically coupled to the bottom portion of the sub-plate <NUM>. That is, the sub-plate <NUM> may electrically connect the first electrode tab <NUM> and the safety vent <NUM> to each other.

The solder member <NUM> is accommodated in the accommodating groove <NUM> of the sub-plate <NUM>, and may electrically connect the coupling portion <NUM> of the safety vent <NUM> and the sub-plate <NUM> by means of soldering. Here, the soldering refers to coupling the safety vent <NUM> and the sub-plate <NUM> to each other by melting the solder member <NUM> by applying heat thereto, and injecting the molten solder member <NUM> into the accommodating groove <NUM>, followed by curing.

In addition, the solder member <NUM> is formed to surround the hook 155b of the coupling portion <NUM>, and the hook 155b may prevent the safety vent <NUM> from being easily separated from the solder member <NUM>. The safety vent <NUM> may be made of aluminum (Al) and the solder member <NUM> may include tin (Sn) as a main component, and thus a coupling force between the safety vent <NUM> and the solder member <NUM> is relatively weak. For example, if no hook is provided in a coupling portion, a safety vent may be separated from a solder member by a physical force even when the solder member is cured. In the present disclosure, however, since the hook 155b hooks to take hold of the solder member <NUM>, the safety vent <NUM> is not readily separated from the solder member <NUM>.

The solder member <NUM> may be made of one selected from the group consisting of Sn-Pb, Sn-Pb-Ag, Sn-Pb-Bi, Sn-Cu, Sn-Ag, Sn-Bi, Sn-Ag-Cu, Sn-Ag-Bi, Sn-Zn, and equivalents thereof. In addition, the solder member <NUM> may have a melting point ranging from <NUM> to <NUM>. As described above, the melting point of the solder member <NUM> is relatively low, and thus the solder member <NUM> may be easily melted due to an external short circuit or overcharging when heat is generated in the secondary battery <NUM>. Therefore, the safety vent <NUM> and the sub-plate <NUM> coupled to each other by means of soldering are easily separated from each other, thereby enhancing the safety of the secondary battery <NUM>.

The gasket <NUM> is installed at a top opening of the case <NUM>. That is, the gasket <NUM> is tightly assembled between each of the outer periphery of the cap-up <NUM> and the outer periphery of the safety vent <NUM> and the top opening of the case <NUM>. The gasket <NUM> may prevent the cap assembly <NUM> from being separated from the case <NUM>. The gasket <NUM> may be made of a resin material such as polyethylene (PE), polypropylene (PP), or polyethylene terephthalate (PET).

Next, a method of operating the safety vent in the secondary battery according to an embodiment will be described.

<FIG> is a cross-sectional view illustrating an example operation of the safety vent. <FIG> is a cross-sectional view illustrating another example operation of the safety vent.

First, referring to <FIG>, an operating state of the safety vent <NUM> in case of an external short circuit of the secondary battery <NUM> is illustrated. When the external short circuit occurs to the secondary battery <NUM>, a high current instantaneously flows in the secondary battery <NUM> and heat is generated. The solder member <NUM> is melted by the generated heat, and the second region <NUM> of the safety vent <NUM> is upwardly inverted, thereby electrically disconnecting the safety vent <NUM> from the sub-plate <NUM>. As described above, according to the present disclosure, the solder member <NUM> is melted in case of an external short circuit, and thus the safety vent <NUM> is disconnected from the sub-plate <NUM>, thereby interrupting the current from flowing in the secondary battery <NUM>. Therefore, the electrode assembly <NUM> can be prevented from generating heat, thereby enhancing the safety of the secondary battery <NUM>.

Next, referring to <FIG>, an operating state of the safety vent <NUM> in case of overcharging of the secondary battery <NUM> is illustrated. When the overcharging occurs to the secondary battery <NUM>, gases are generated in the secondary battery <NUM> to increase the internal pressure and the temperature slowly increases. The generated gases pass through the gas discharge hole <NUM> of the cap-down <NUM> to push the deforming portion <NUM>, specifically, the first region <NUM>, of the safety vent <NUM>. Here, since the solder member <NUM> is melted according to the increase in the internal temperature, the second region <NUM> of the safety vent <NUM> is also deformed to be upwardly inverted together with the first region <NUM>, thereby electrically disconnecting the safety vent <NUM> from the sub-plate <NUM>. As described above, according to the present disclosure, the solder member <NUM> is melted due to the heat and gases generated in case of overcharging, and thus the safety vent <NUM> is disconnected from the sub-plate <NUM>, thereby interrupting the current from flowing in the secondary battery <NUM>. Therefore, the electrode assembly <NUM> can be prevented from exploding due to the increase of the internal pressure, thereby enhancing the safety of the secondary battery <NUM>.

<FIG> is a cross-sectional view illustrating a safety vent according to another embodiment.

Referring to <FIG>, the safety vent <NUM> includes a fixing portion <NUM> positioned at its outer side, and a deforming portion <NUM> positioned at an inner side of the fixing portion <NUM> and downwardly protruding. The fixing portion <NUM> is installed to make close contact with a portion of the cap-up <NUM>, except for an upwardly protruding portion of the cap-up <NUM>, that is, an edge portion of the cap-up <NUM>. In addition, an edge portion of the fixing portion <NUM> is formed to upwardly extend from the cap-up <NUM> while covering the edge portion of the cap-up <NUM>. Therefore, the safety vent <NUM> may be fixed to the cap-up <NUM> by the fixing portion <NUM>.

The deforming portion <NUM> includes a first region <NUM> positioned at its outer side and a second region <NUM> positioned at an inner side of the first region <NUM>. The deforming portion <NUM> may be electrically connected to the sub-plate <NUM> by means of soldering. The deforming portion <NUM> may be deformed when abnormality occurs to the secondary battery <NUM>, and thus explosion of the secondary battery <NUM> may be prevented.

The first region <NUM> extends from the fixing portion <NUM> and downwardly protrudes from the inner side of the fixing portion <NUM>. The first region <NUM> is positioned between the fixing portion <NUM> and the second region <NUM>. In addition, a notch 253a guiding rupturing of the safety vent <NUM> is provided in the first region <NUM>. In an example embodiment, when the internal pressure of the case <NUM> exceeds the operating pressure of the safety vent <NUM>, the deforming portion <NUM> upwardly moves by the gases discharged through the gas discharge hole <NUM> of the cap-down <NUM>, and thus the safety vent <NUM> is electrically disconnected from the sub-plate <NUM>. In addition, when the internal pressure of the case <NUM> exceeds a rupture pressure higher than the operating pressure of the safety vent <NUM>, the notch 253a is broken, thereby preventing the secondary battery <NUM> from exploding. The safety vent <NUM> may be made of aluminum (Al).

The second region <NUM> extends from the first region <NUM> and downwardly protrudes at the inner side of the first region <NUM>. A coupling portion <NUM> downwardly protruding from the second region <NUM> is provided at the center of the second region <NUM>, and a center hole 255a is provided at the center of the coupling portion <NUM>. That is, the coupling portion <NUM> is formed to have a hollow cylinder shape. The coupling portion <NUM> may be electrically connected to the sub-plate <NUM> through the solder member <NUM>. Additionally, a plurality of coupling holes 255b are provided in the second region <NUM>. The coupling holes 255b may function to increase a coupling force between the safety vent <NUM> and the sub-plate <NUM>. Specifically, when the coupling portion <NUM> is coupled to the sub-plate <NUM> by means of soldering, the solder member <NUM> is injected into coupling holes 255b and then cured. Therefore, since the solder member <NUM> penetrating the coupling holes 255b takes hold of the second region <NUM>, the safety vent <NUM> is not readily separated from the solder member <NUM>.

Claim 1:
A secondary battery (<NUM>) comprising:
an electrode assembly (<NUM>);
a case (<NUM>) for accommodating the electrode assembly (<NUM>); and
a cap assembly (<NUM>) coupled to the top of the case (<NUM>),
wherein the cap assembly (<NUM>) comprises a cap-up (<NUM>), a safety vent (<NUM>, <NUM>) provided below the cap-up (<NUM>), a cap-down (<NUM>) provided below the safety vent (<NUM>, <NUM>) and having a through hole (<NUM>) and a gas discharge hole (<NUM>), an insulator (<NUM>) provided between the safety vent (<NUM>, <NUM>) and the cap-down (<NUM>), a sub-plate (<NUM>) provided below the cap-down (<NUM>), and a solder member (<NUM>) for electrically connecting the safety vent (<NUM>, <NUM>) and the sub-plate (<NUM>), and the safety vent (<NUM>, <NUM>) and the sub-plate (<NUM>) are electrically connected by means of soldering wherein the safety vent (<NUM>, <NUM>) includes a fixing portion (<NUM>, <NUM>) installed to make close contact with an edge portion of the cap-up (<NUM>), and a deforming portion (<NUM>, <NUM>) positioned at an inner side of the fixing portion (<NUM>, <NUM>) and downwardly protruding, and the deforming portion (<NUM>, <NUM>) includes a first region (<NUM>, <NUM>) extending from the fixing portion (<NUM>, <NUM>) and having a notch (153a, 253a) formed therein, and a second region (<NUM>, <NUM>) positioned at an inner side of the first region (<NUM>, <NUM>), having a coupling portion (<NUM>, <NUM>) having a center hole (155a, 255a) formed therein, and downwardly protruding, wherein a hook (155b) bent toward an outer side of the safety vent (<NUM>) is provided at an end of the coupling portion (<NUM>).