Patent ID: 6730430
Filing Date: 2004-05-04
Classification: H01M,Y02E

Abstract:
An explosion-proof safety structure for a column shaped lithium battery, the structure comprising:a top cap comprising a first annular disk and a frusto-conical or substantially cylindrical first terminal extending from an inner edge of the first annular disk, the first terminal having a hole to vent gas produced internally within the battery to the atmosphere; an annular polyimide insulating sheet disposed in contact with a first surface of the first annular disk and circumscribing the first terminal; a safety valve comprising a second annular disk, a frusto-conical or substantially cylindrical second terminal extending from an inner edge of the second annular disk, a rim extending from an outer circumferential edge of the second annular disk, and first and second grooves circumferentially formed within the second annular disk on opposite surfaces and disposed closely together, the second terminal having a conductive tip at a distal end from the second annular disk; a washer-shaped resistivity board disposed between a second surface opposite the first surface of the first annular disk and a first surface of the second annular disk; a breaker sheet having a conductive stem connected to a positive electrode of the battery, the breaker sheet laser welded to the conductive tip of the safety valve and having a thinner cross section near the weld than a cross section far from the weld; and an insulating ring disposed between a second surface of the safety valve and a surface of the breaker sheet to provide electrical insulation between a surface area of the safety valve and a surface area of the breaker sheet, wherein: the rim of the safety valve is bent inward toward a radial axis of the safety valve to secure the polyimide insulating sheet against the top cap, secure the top cap against the resistivity board, and secure the resistivity board against the safety valve such that the polyimide insulating sheet, the top cap, the resistivity board, and the safety valve are fastened together, the thinner cross section of the breaker sheet breaks when a gas pressure within the battery exceeds a first pressure, and the break in the breaker sheet open circuits an electrical path between the first terminal and the positive electrode of the battery, and a break opens in the material of the safety valve separating the first and second grooves, when the gas pressure within the battery exceeds a second pressure, to provide a path for the gas pressure to vent to the atmosphere through the hole in the top cap.