1. Field of the invention
The present invention relates to a separator and a lithium rechargeable battery using the separator, and more particularly, to a separator in which a plurality of porous films having different strength from one another is disposed between a positive electrode plate and a negative electrode plate, thereby retaining an electrolyte due to a space formed among the porous films and improving stability by preventing an electrical short occurring between the two electrode plates of the electrode assembly, and a lithium rechargeable battery using the same.
2. Description of the Related Art
Recently, as demands for portable electronic apparatuses such as camcorders, portable computers, and mobile phones have increased, rechargeable batteries have been actively researched and developed. Examples of the rechargeable batteries include a nickel cadmium (Ni—Cd) battery, a nickel hydride (Ni-MH) battery, a nickel zinc (Ni—Zn) battery, and a lithium rechargeable battery. Particularly, the lithium rechargeable battery can be downsized and provide a big capacity. Further, the lithium rechargeable battery has a high operating voltage and a high energy density per unit weight. Therefore, the demands for the lithium rechargeable battery have rapidly increased.
The lithium rechargeable battery may be combined with a fuel cell to be used as one component of a hybrid battery. With the technical advances, more lithium rechargeable batteries are used for a high power battery. In this case, the lithium rechargeable battery requires a high output. Thus, a research for improving safety of the lithium rechargeable battery has been actively conducted. In a typical lithium rechargeable battery, one separator is disposed between a positive electrode plate and a negative electrode plate, and another separator is disposed at the outer side of the positive electrode plate. Thereafter, this is wound using a down coiler to form an electrode assembly. The separators have a thickness of 15˜30 μm. If an active material particle, which has a diameter larger than the above thickness, makes a hole in a separator, an internal electrical short may occur. If a thickness of the separator becomes extremely thick so as to avoid the above problem, not only an internal resistance increases, but also a volume of the separator becomes large. Thus, a thickness of an electrode plate needs to be reduced, which leads to deterioration of battery capability. The separator is made of a material that does not have good affinity to an electrolyte, such as polyethylene. Accordingly, in an electrode assembly including one film separator disposed between the positive electrode plate and the negative electrode plate and one film separator disposed at the outer side of the positive electrode plate, there is a drawback of the electrolyte between two electrodes, and thus lithium ion cannot easily move.