Cap assembly and secondary battery using the same

A cap assembly and a secondary battery using the cap assembly, the cap assembly including: a cap-up having a groove; a PTC thermistor disposed in the groove; and inner components disposed below the cap-up. The inner components can include a vent disposed under the cap-up; a cap-down disposed under the vent; a sub-plate disposed under the cap-down; and an insulating vent disposed between the vent and the cap-down The secondary battery includes: an electrode assembly; a can containing the electrode assembly, having an opening at one side; and the cap assembly to seal the opening of the can.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Korean Patent Application No. 2007-113805, filed Nov. 8, 2007, the disclosure of which is hereby incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Aspects of the present invention relate to a cap assembly, and a secondary battery using the cap assembly, to prevent an increase of internal resistance, and to increase the capacity of the secondary battery, per unit area.

2. Description of the Related Art

Recently, as portable electronic devices, such as, cellular phones, notebook computers camcorders, etc. have been widely distributed, the secondary battery has actively been developed for use as a power source of these electronic devices.

Secondary batteries can be classified as Nickel-Cadmium (Ni—Cd), Plumbum (Pb), Nickel-Hydrogen (N—H), Lithium ion, Lithium Polymer, and so on. Lithium secondary batteries have been widely used in electronic devices, because such batteries can be compact, and can have a large capacity, a high operating voltage, and a high energy density per unit weight.

Lithium secondary batteries can be divided into a can-type and a pouch-type, according to the shape of a casing containing an electrode assembly. The can-type batteries can be prismatic or cylindrical.

A cylindrical secondary battery comprises: an electrode assembly; a can to house the electrode assembly; and a cap assembly including an insulating gasket, to seal an opening of the can. The electrode assembly includes a positive electrode plate, a negative electrode plate, and a separator. An electrolyte is also contained within the can.

The cap assembly may be formed by sequentially stacking a cap-up, a current interrupt device, a positive temperature coefficient (PTC) thermistor, and an electrode terminal, in the opening of the can. The cap assembly may be formed by combining the cap-up, with other elements as a unit, and then sealing the opening of the can with the cap assembly.

Recently, an integrated configuration of the electrode assembly has been proposed, in order to simplify manufacturing, and to reduce any contact resistance of the components. Caulking and welding methods have been widely used to form the integrated configuration. With the welding method, however, it is very difficult to form an integrated configuration including a cap-up, since the PTC thermistor, whose characteristics are changeable by heat, is disposed between the cap-up and the current interrupt device.

SUMMARY OF THE INVENTION

Aspects of the present invention provide a cap assembly comprising a cap-up, a PTC thermistor, and inner components disposed below the cap-up. A groove is formed at one side of the cap-up, and the PTC thermistor is inserted into the groove.

Aspects of the present invention provide a secondary battery comprising an electrode assembly, a can containing the electrode assembly and having an opening, and a cap assembly to seal the can. The cap assembly comprises a cap-up having a groove at one side, a PTC thermistor, and inner components disposed under the cap-up. The PTC thermistor is inserted into the groove.

According to aspects of the present invention, the groove may be formed in a bottom surface of the cap-up. The PTC thermistor may be completely inserted into the groove. The PTC thermistor may also be partially inserted into the groove. The inner components may comprise a Current Interrupt Device (CID) disposed below the cap-up, and a vent disposed below the CID.

According to aspects of the present invention, the inner components may comprise a vent disposed below the cap-up, a cap-down disposed below the vent, a sub-plate disposed below the cap-down, and an insulating vent disposed between the vent and the cap-down.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Reference will now be made in detail to the exemplary embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The exemplary embodiments are described below, in order to explain the present invention by referring to the figures. The thickness and length of layers and regions may be exaggerated for convenience. As referred to herein, when a first element is said to be “disposed” on, or adjacent to, a second element, the first element can directly contact the second element, or can be separated from the second element by one or more other elements can be located therebetween.

FIG. 1is an exploded perspective view illustrating a configuration of a secondary battery, according to a first exemplary embodiment of the present invention.FIGS. 2A and 2Bare combined sectional views illustrating the secondary battery ofFIG. 1and a modified version thereof. Referring toFIGS. 1 through 2B, a jelly-roll type electrode assembly20may be formed, by winding two rectangular electrode plates21and23together.

Separators25may be disposed between the two electrode plates21and23. Accordingly, the separators25may be disposed to prevent a short circuit between the two electrode plates21and23.

The two electrode plates21and23may be formed by coating slurries of positive and negative electrode active materials, into a collector made of one of metal foil and a metal mesh of aluminum or copper, respectively. The slurries may be formed by combining a granular active material, an auxiliary conductor, a binder, and a plasticizer, with a solvent. The solvent is removed in a subsequent electrode-forming process.

Non-coating portions, in which slurries are not coated, may be formed at end portions of the collectors. Electrode tabs27and29may attached to the non-coating portions. The electrode tab27may upwardly protrude toward the opening portion of the can10. The electrode tab28may extend toward the bottom surface of the can10. A plurality of electrode tabs may be attached to an electrode plate.

The can10may be implemented in various shapes, including prismatic shapes, cylindrical shapes, and the like. The can10may be formed by a deep drawing method. The can10be formed of steel, an aluminum alloy, and the like.

If the can10is cylindrical, the can has a rounded side surface, a circular bottom surface, and an opening opposite to the bottom surface. The electrode assembly20may be inserted into the can10, through the opening. Before inserting the electrode assembly20, a inner insulating plate11be positioned to cover a bottom surface of the electrode assembly20, and the second electrode tab29may be bent, to be parallel with the bottom surface of the can10.

The electrode assembly20may be formed as a jelly-roll, and may be have a hollow center. A hole may be formed in the inner insulating plate11, which corresponds to the hollow center. A portion of the second electrode tab29may extend across the hole of the inner insulating plate11.

A welding rod may be inserted through the hollow center of the electrode assembly20, from above. Then, the second electrode tab29may be welded to the bottom surface of the can10. Accordingly, the can10may have the same polarity as the second electrode tab29, so that the can10may act as an electrode terminal.

According to exemplary embodiments of the present invention, the can10may comprise a center-pin13that is inserted in the hollow center of the electrode assembly20. The center-pin13may prevent a deformation of the electrode assembly20, provide a gas passage for the release of gas resulting from a malfunction of the electrode assembly20, and extend the life-time of the battery.

After welding the second electrode tab29, an upper insulating plate15may be disposed over the electrode assembly20. The first electrode tab27may protrude against the electrode assembly20, through holes of the upper insulating plate15. In the case that the upper insulating plate15has a hole in the center, the second electrode tab29may be welded after the installation of the upper insulating plate15. A bead17may be formed on an upper portion of the can10, by crimping a sidewall of the can10, to match a top level of the upper insulating plate. The bead17may provide highly reliable electrical connection, by preventing the electrode assembly from fluctuating in the can10.

An electrolyte may be injected into the can10, onto the electrode assembly. The injection of electrolyte may be carried out before forming the bead17. An insulating gasket30may be inserted into the opening of the can10, and a cap assembly40may be combined with the insulating gasket30, to seal the can10. The insulating gasket30may be an elastic material having good insulative properties. The insulating gasket30may completely wrap around an outer circumference of the cap assembly40, and may seal the can10, as well as insulate the cap assembly40from the can10.

The cap assembly40and the insulating gasket30may be installed on the can10, as a unit. Otherwise, the components may be stacked into the insulating gasket30, sequentially. The cap assembly40, according to a first exemplary embodiment of the present invention, may comprise a cap-up80, PTC thermistor70, and inner components disposed under the cap-up. The inner components may comprise a vent50electrically connected to the first electrode tab27, and a current interrupt device (CID)60to interrupt a current path, according to the operation of the vent50.

The cap assembly40may have a stacked configuration, with the CID60disposed below the cap-up80, which has a groove81on one side, and the vent50disposed below the CID60. The PTC thermistor70may be inserted into the groove81, which is formed opposite to the CID60, on the bottom surface of the cap-up80. The PTC thermistor70may be completely inserted into the groove, as illustrated inFIG. 2A.

Accordingly, it may be possible to integrate the cap-up80and the CID60through welding, since the cap-up80is in direct contact with the CID60, due to the PTC thermistor70into the cap-up80. Since the PTC thermistor70is inserted into the groove81of the cap-up80, an increase of internal resistance, due to contact among components, may be prevented. The contact among the components may result from the movement of the components. Further, aspects of the present embodiment may increase the capacity of a cell, by reducing a space that the PTC thermistor70occupies.

As illustrated inFIG. 2B, a portion of a PTC thermistor70′ may be inserted into a groove81′. This exemplary embodiment may have a small constraint in reducing space, due to an increased interval between a cap-up80′ and a CID60, as compared with the previous embodiment, in which the PTC thermistor70is completely inserted into the groove81. It may, however, have better characteristics in controlling current flow.

The exemplary embodiment may further comprise an insulating unit, having a thickness corresponding to a portion of the PTC thermistor70′ that is not inserted into the groove81′, between the CID60and the cap-up80′. The vent50may interrupt the current flow through the CID60, if an internal pressure exceeds a certain level, due to gas produced by the electrode assembly, and may exhaust the gas from the electrode assembly. A crimping process may be carried out, by pressing downward along an inner wall of the can10to form the bead17, after the cap assembly40is installed on the insulating gasket30.

FIGS. 3A and 3Bare sectional views illustrating a configuration of a secondary battery, according to another exemplary embodiment of the present invention. Referring toFIGS. 3A and 3B, a secondary battery may include: an electrode assembly120contained within a can110, an insulating gasket130inserted into an opening of the can110; and a cap assembly140combined with the insulating gasket130. Elements110through130, of the secondary battery illustrated inFIGS. 3A and 3B, are identical to elements10through30of the secondary battery illustrated inFIGS. 1 through 2B. Accordingly, a detailed description thereof will be omitted.

The cap assembly140may comprise: a cap-up141having a groove141aformed in one side; a PTC thermistor142inserted into the groove141a; and inner components disposed below the cap-up141. The inner components may comprise a vent143having a downward protruding portion143a, a cap-down144disposed below the vent143, and a sub-plate146disposed below the cap-down144.

According to some embodiments, the PTC thermistor142may be completely inserted into the groove141a, as illustrated inFIG. 3A. Accordingly, it may be possible to integrate the cap-up141and the vent143, through welding, since the cap-up141is in direct contact with the vent143, due to the insertion of the PTC thermistor142into the cap-up141.

The present embodiment may prevent an increase of internal resistance, due to contact among the components. The contact among the components may happen through the movement of the components. The present embodiment may increase the capacity of a cell, by reducing a space the PTC thermistor142occupies.

As illustrated inFIG. 3B, a portion of a PTC thermistor142′ may be inserted into a groove141b. This exemplary embodiment may have a small constraint in reducing space, due to an increased interval between a cap-up141′ and a vent143, as compared with the previous embodiment, in which the PTC thermistor142is completely inserted into the groove141a. It may, however, have better characteristics in controlling current flow.

The present embodiment may further comprise an insulating unit145, having a thickness corresponding to a portion of the PTC thermistor142′ that is not inserted into the groove141b, between the vent143and the cap-up141′. The insulating unit145may be interposed between the cap-down144and the vent143.

A sub-plate146may be disposed across a center hole formed in the cap-down144, below the cap-down144, and may be connected to a protruding portion143aof the vent143, which is exposed through the center hole. An electrode tab127protruding against the electrode assembly120may be connected to either the cap-down144, or the sub-plate146.

The bottom surface of the protruding portion143aof the vent143may be configured to cut off an electrical connection with the sub-plate146, by raising or lowering the protruding portion143a, in response to changes in the internal pressure of the battery. The cap-down144may be electrically connected to the sub-plate146, by laser welding. The protruding portion143aof the vent143may be electrically connected to the sub-plate146, by ultrasonic welding, etc. A crimping process may be carried out by pressing an inner wall of the can110to form a bead117, after the cap assembly140is combined with the opening portion of the can110.