Electrolyte for lithium battery and lithium battery comprising same

#This application is based on Korean patent application No. 2002-18264 filed in the Korean Intellectual Property Office on Apr. 3, 2002, the disclosure of which is incorporated herein by reference.

#The present invention relates to an electrolyte for a lithium battery and a lithium battery comprising the same, and more particularly, to an electrolyte for a lithium battery to reduce overcharge and improve electrochemical characteristics of the battery, and a lithium battery comprising the same.

#The use of portable electronic instruments is increasing as electronic equipment gets smaller and lighter due to developments in high-tech electronic industries. Studies on lithium secondary batteries are actively being pursued in accordance with the increased need for a battery having high energy density for use as a power source in these portable electronic instruments. Such a lithium secondary battery, having an average discharge potential of 3.7 V (i.e., a battery having substantially a 4 V average discharge potential) is considered to be an essential element in the digital generation since it is an indispensable energy source for portable digital devices such as cellular telephones, notebook computers, camcorders, etc. (i.e., the “3C” devices).

#The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention, and together with the description, serve to explain the principles of the invention.

#FIG. 1 is a cross-sectional view of a lithium secondary battery cell;

#FIG. 2 is a graph illustrating cycle life characteristics of the battery cells according to Examples 1, 3, and 4 of the present invention, and Comparative Examples 2 and 3;

#In the following detailed description, the following embodiments of the invention have been shown and described, simply by way of illustration of the best mode contemplated by the inventors of carrying out the invention. As will be realized, the invention is capable of modification in various respects, all without departing from the invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not restrictive.

#A cross-sectional view of a general non-aqueous Li-ion cell is shown in FIG. 1. The Li-ion cell 1 is fabricated by inserting an electrode assembly 8 including a positive electrode 2, a negative electrode 4, and a separator 6 between the positive and negative electrodes into a battery case 10. An electrolyte 26 is injected into the battery case 10 and impregnated into the separator 6. The upper part of the case 10 is sealed with a cap plate 12 and a sealing gasket 14. The cap plate 12 has a safety vent 16 to release pressure. A positive electrode tab 18 and a negative electrode tab 20 are respectively attached on the positive electrode 2 and negative electrode 4. Insulators 22 and 24 are installed on the lower part and the side part of the electrode assembly 8 to prevent a short circuit occurrence in the battery.

#In a lithium battery, the temperature of the battery increases abruptly because of overcharge due to incorrect operation or break-down of the battery, or a short circuit occurrence due to a defect in battery design, so that thermal runaway takes place. During overcharge, an excessive amount of lithium ions are released from the positive electrode and deposited on the surface of the negative electrode to render the positive and negative electrodes unstable. As a result, exothermic reactions such as pyrolysis of an electrolyte, reactions between the electrolyte and lithium, an oxidation reaction of the electrolyte on the positive electrode, a reaction between the electrolyte and oxygen gas that is generated from the pyrolysis of the positive active material, etc., rapidly increase the temperature inside the battery to cause thermal runaway, and thus, the generation of fire and smoke.