Secondary battery

A secondary battery includes an electrode assembly comprising a first electrode plate, a second electrode plate and a separator interposed therebetween, and an electrolyte. A case accommodates the electrode assembly and an electrolyte. A finishing material is attached to an outer surface of the electrode assembly. In the secondary battery, the finishing material has an adhesive property on at least one surface.

RELATED APPLICATIONS

This application claims priority to and the benefit of Korean Patent Application No. 10-2010-0030908, filed on Apr. 5, 2010, in the Korean Intellectual Property Office, the entire content of which is incorporated herein by reference.

BACKGROUND

Embodiments of the present invention relate to a secondary battery, and more particularly, to a secondary battery capable of preventing the movement of an electrode assembly and the bending of an electrode tab in the interior of a case.

2. Description of the Related Technology

Recently, a variety of batteries has been used as power sources for small-sized electronic devices. Particularly, batteries such as lithium secondary batteries, which are small in size and large in capacity, are frequently used as power sources for mobile phones, notebook computers, camcorders and the like.

A lithium secondary battery is typically formed by accommodating an electrode assembly in the interior of a case. such as a pouch or a can, and injecting an electrolyte into the case. The electrode assembly may be divided into a wound-type electrode assembly and a stacked-type electrode assembly. The wound-type electrode assembly is typically formed by interposing a separator between positive and negative electrode plates and winding them in a jelly-roll shape. On the other hand, the stacked-type electrode assembly is typically formed by stacking a plurality of structures, each having positive and negative electrode plates, and a separator interposed therebetween.

In the wound-type electrode assembly, a finishing tape is typically attached on outer end surfaces of the electrode assembly so as to fix a portion to be finished. The electrode assembly having the finishing tape attached thereto is accommodated in a case, and an electrolyte is injected into the interior of the case. Then, the case is tightly sealed.

However, in the secondary battery described above, the electrode assembly is not adhered closely to the inner surface of the case. Hence, if an impact is applied to the secondary battery from the exterior of the case, the electrode assembly is moved in the interior of the case. Therefore, an electrode tab of the electrode assembly may become bent. Also, because the electrolyte typically serves as a lubricant, the electrode assembly may move inside the case. This occurrence may cause internal short circuits.

Particularly, in a pouch type case, the strength of the case is typically weak, and the safety of the case may be compromised. In case of a medium- or large-sized battery, a large amount of electrolyte can be distributed to a lower portion in a case, and thus unequally distributed in the case. Moreover, in a secondary battery using a pouch-type case, the appearance of the secondary battery may be unequal.

SUMMARY

In one embodiment, a secondary battery comprises a finishing material having an adhesive property on a surface of an electrode assembly, which can improve the adhesion between the case and the electrode assembly, and thus prevent the movement of the electrode assembly and the bending of an electrode tab in the interior of the case.

According to an aspect of the present invention, a secondary battery includes: an electrode assembly comprising a first electrode plate, a second electrode plate and a separator interposed therebetween; an electrolyte; a case for accommodating the electrode assembly and the electrolyte; and a finishing material attached to an outer surface of the electrode assembly, wherein the finishing material has an adhesive property on at least a surface.

The finishing material may include an oriented polystyrene (OPS) film.

The OPS film may have an adhesive strength of 6 to 15 kgf in the electrolyte.

The OPS film may not have the adhesive property when it is not immersed into the electrolyte.

The surface of the finishing material may be chemically changed by the electrolyte so that the finishing material has the adhesive property.

The finishing material may be attached to at least one major surface of the electrode assembly.

The finishing material may be attached to at least one major surface and another major surface opposite to the at least one major surface of the electrode assembly.

The finishing material may be attached to completely surround the outer surface of the electrode assembly.

An exterior tape may be further attached to a finishing portion of the electrode assembly.

As described above, according to embodiments of the present invention, the adhesion between the case and the electrode assembly is improved. Thus, it is possible to prevent the movement of the electrode assembly and the bending of the electrode tabs in the interior of the case. Also, the strength of the case is increased, and the inequality of the distribution of the electrolyte is minimized in a medium- or large-sized secondary battery. Thus, the uniformity of the external appearance of the secondary battery can be improved.

Accordingly, the alignment state of the electrode assembly is stably maintained, thereby preventing internal short circuits. Also, it is possible to prevent a low battery charge that can be caused by swelling of the electrode assembly.

Moreover, the reliability of the second battery can be enhanced in the long-term use of the secondary battery.

DETAILED DESCRIPTION

FIG. 1is a perspective view of a secondary battery using an electrode assembly according to an embodiment of the present invention.FIG. 2is a sectional view of the secondary battery ofFIG. 1.

Referring toFIGS. 1 and 2, a secondary battery according to an embodiment of the present invention includes an electrode assembly10and a case20in which the electrode assembly10and an electrolyte (not shown) are accommodated. The secondary battery can further include a finishing material15. The finishing material may be attached to a major surface of the electrode assembly10. The case20may be a pouch including an accommodating portion22and a cover portion24that seals the accommodating portion22. The electrode assembly10may be a wound-type electrode assembly formed by sequentially stacking a first electrode plate10a, a second electrode plate10band a separator10cinterposed therebetween, and then winding them in a jelly-roll shape.

When the electrode assembly10is a wounded-type electrode assembly as described in this embodiment, a finishing material15may be further included in the electrode assembly10. A material having adhesion with respective to the case20may be used as the finishing material15. The finishing material15may replace an exterior tape to prevent unwinding of the wound electrode assembly10. At this time, the finishing material15may be formed on a major surface of the electrode assembly10, at which a finishing portion14of the electrode assembly10is formed, or may also be formed on an opposite major surface of the electrode assembly10. Although not shown in these figures, the finishing material15may be used after the exterior tape is attached to the finishing portion14of the electrode assembly10.

The finishing material15may become chemically changed by the electrolyte. The surface of the finishing material15may have an adhesive property through the chemical change. The electrode assembly10having the finishing material15attached thereto can be accommodated in the pouch20, and the electrolyte can be injected into the pouch20. The electrolyte can allow the finishing material15to have an adhesive property. Thus, the electrolyte assembly10may be adhered closely to the pouch20, thereby reinforcing the adhesion between the electrode assembly10and the pouch20.

The finishing material15can include a material having a surface that is chemically changed to have an adhesive property when it is immersed into the electrolyte. For example, the finishing material15may include an oriented polystyrene (OPS) film and the like.

The OPS film may have no adhesive properties initially, but the surface of the OPS film can become chemically changed by an electrolyte including dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), propylene carbonate (PC) and/or the like. Therefore, the OPS film can have an adhesive property. The OPS film can be applied to the secondary battery advantageously because of its chemical and electrical safety.

More specifically, in the OPS film, bonding chains of its surface may become broken by the electrolyte as shown in the following Chemical Formula 1. Therefore, the OPS film can have an adhesive property.

That is, if the electrode assembly10having the finishing material15attached thereto is accommodated in the pouch20and then immersed into the electrolyte, the finishing material15can become chemically changed. Therefore, the finishing material15can have an adhesive property. The electrode assembly10can become adhered closely to the pouch20by the adhesive property of the finishing material15, thereby reinforcing the adhesion between the electrode assembly10and the pouch20.

The OPS film may have no adhesion initially (when the electrolyte is not immersed). However, if the OPS film comes in contact with the electrolyte, it has an adhesive property. The adhesive property may have an adhesive strength of 6 to 10 kgf. As described above, if the electrolyte is immersed into the OPS film, the adhesion between the pouch20and the electrode assembly10can improve. Thus, it is possible to prevent the movement of the electrode assembly10and the bending of an electrode tab in the interior of the pouch20.

The finishing material15may become attached to one surface of the electrode assembly10so as to increase the strength of the pouch20that forms an outer casing of the secondary battery. Thus, it is possible to protect the secondary battery from an external impact. Also, it is possible to prevent the electrode assembly10from swelling due to the initial charge/discharge of the secondary battery. Accordingly, a change in the outer dimension of the secondary battery can be reduced, so that the external appearance of the secondary battery becomes uniform. Also, the alignment state of the electrode assembly10can be stably maintained, thereby preventing internal short circuits and the like. Also, it is possible to prevent low battery charges due to the swelling of the electrode assembly10.

The electrode assembly10according to the embodiment of the present invention may be formed by winding the first electrode plate10a, the second electrode plate10band the separator10cinterposed therebetween. A first electrode tab12amay be connected to the first electrode plate10ato protrude upward from an upper end portion of the electrode assembly10, and a second electrode tab12bmay be connected to the second electrode plate10bto protrude upward from an upper end portion of the electrode assembly10. In the electrode assembly10, the first and second electrode tabs12aand12bmay be formed spaced apart from each other at a predetermined distance.

Portions of first and second electrode tabs12aand12bextracted from the electrode assembly10may be wound by lamination tapes11aand11b, respectively. The lamination tape11aor11bcan shield heat generated from the first or second electrode tabs12aor12b. The lamination tape11aor11bcan allow the electrode assembly10to not become compressed by an edge of the first or second electrode tab12aor12b.

An insulating tape13may become adhered to a surface22afor each of the first and second electrode tabs12aand12bthat come in contact with the pouch20. The insulating tape13may become partially protruded to the exterior of the pouch20. When the cover portion24of the pouch20is folded and sealed to the top of the accommodating portion22, the insulating tape13may be positioned at a region in which each of the first and second electrode tabs12aand12bis positioned between the cover portion24and the accommodating portion22.

The pouch20may be formed of aluminum with a thickness of 0.04 to 0.05 mm. Therefore, when an impact is applied from the exterior of the pouch20, the external appearance of the pouch20may be easily deformed. However, in this embodiment, the electrode assembly10can include a finishing material15having an adhesion on a surface of the electrode assembly10corresponding to the pouch20. Therefore, the electrode assembly10may become attached to the pouch20by the finishing material15. Accordingly, when an impact is applied from the exterior of the pouch20, it is possible to prevent the external appearance of the pouch20from becoming deformed. That is, the finishing material15can improve the strength of the pouch20and prevent the movement of the electrode assembly10in the interior of the pouch20.

Although a pouch-type secondary battery has been shown inFIGS. 1 and 2, the secondary battery of this embodiment may be applied to a can-type secondary battery. At this time, the finishing material15can function to prevent the electrode assembly10from moving in the interior of the secondary battery.

FIG. 3is a perspective view of an electrode assembly according to another embodiment of the present invention.

Referring toFIG. 3, finishing materials15may be attached to a major surface and the opposite major surface of the wound-type electrode assembly10. If the finishing materials15are immersed in an electrolyte, they are chemically changed. Therefore, the finishing materials15have an adhesive property.

Accordingly, the surfaces of the electrode assembly10having the finishing materials15attached thereto can be adhered closely to the inner surface of a pouch. Thus, it is possible to prevent the electrode assembly10from being moved in the interior of the pouch. As such, the electrode assembly10is not moved in the pouch, so that it is possible to prevent electrode tabs12aand12bfrom becoming bent in the pouch. Thus, it is possible to enhance the reliability of the secondary battery in the long-term use of the secondary battery.

FIG. 4is a perspective view of an electrode assembly according to another embodiment of the present invention.

Referring toFIG. 4, a finishing material15may become attached to surround the entire outer surface of the electrode assembly10. The finishing material15may replace an external tape so that a finishing portion of the wound electrode assembly10does not unwind. As described above, an OPS film may be used as the finishing material15. The surface of the OPS film may become chemically changed by an electrolyte, so that the OPS film has an adhesive property. Thus, the electrode assembly10and a pouch can be adhered closely to each other.

That is, if the electrolyte is immersed in the pouch, the finishing material15attached to surround the outer surface of the electrode assembly10can have an adhesive property. Thus, the outer surface of the electrode assembly10may become adhered closely to the inner surface of the pouch. As the adhesion between the electrode assembly10and the pouch is reinforced, the alignment state of the electrode assembly10can be stably maintained.

The secondary battery according to the embodiment of the present invention may be applied to a medium- or large-sized battery of which surface has a sectional area of 25 cm2or more. In this case, the inequality of the distribution of the electrolyte can be minimized. Thus, the uniformity of the external appearance of the secondary battery can improve.

Although the electrode assembly10formed by winding the first and second electrode plates10aand10band the separator10cinterposed therebetween has been described in the aforementioned embodiment, the present invention is not limited thereto. The electrode assembly10may be a stacked-type electrode assembly formed by stacking a plurality of structures each having the first and second electrode plates10aand10band the separator10cinterposed therebetween.

At this time, the finishing material may be attached to only one surface of the electrode assembly that comes in contact with the pouch or can-type case. Alternatively, the finishing material may be attached to opposite major surfaces of the electrode assembly. Alternatively, the finishing material may be attached to surround the entire outer surface of the electrode assembly.

Accordingly, the adhesion between the case and the electrode assembly can be improved. Thus, it is possible to prevent the movement of the electrode assembly and the bending of the electrode tabs in the interior of the case. Also, when the case is a pouch, it is possible to increase its strength. Also, in the medium- or large-sized pouch-type secondary battery, the inequality of the distribution of the electrolyte may become minimized, thereby improving the uniformity of the external appearance of the secondary battery. Also, the alignment state of the electrode assembly is stably maintained, thereby preventing internal short circuits. Thus, the reliability of the secondary battery can be enhanced in the long-term use of the secondary battery.

While the present invention has been described in connection with certain embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, and equivalents thereof.