Header Device for Electrochemical Cells

Electrochemical cells and particularly the lithium batteries contain highly reactive components. Packaging these materials properly is critical, since corrosion can readily destroy the most efficient battery through by-products and leakage. For that reason, stainless steel has become one of the most preferred packing materials for lithium batteries.

However, one other requirement in these high energy batteries is that the cells be hermetically sealed to prevent outside contamination of the cells and prevent leakage which can result in loss of performance and/or damage to the environment. Accordingly, efforts have been made to hermetically seal the battery, using stainless steel as mentioned above and glass which has been found to be an impervious insulator suitable for sealing the battery and preventing shorting of the cell between the anode and cathode.

Because of the differences in coefficient of expansion of stainless steel and glass and the relatively high temperatures required to fabricate glass to metal seals, glass to metal seals with a stainless steel pin have heretofore not been successfully fabricated. Normally, such seals between glass and metal require elevated fabrication temperatures of at least 1800.degree. Fahrenheit and preferable 2000.degree. Fahrenheit.

It has now been discovered that a new and improved useful header device for use with electrochemical cells requiring a hermetic seal can be manufactured according to the present invention. The header device permits a hermetic seal between the header, the terminal pin and the body of the cell. The device comprises a stainless steel header sized to hermetically fit the body and a glass annular ring bonded to the header. A terminal pin is bonded to the ring with the pin comprising a solid central core of a material selected from nickel and nickel alloys and further has a stainless steel sleeve on the core, the sleeve having a thickness of less than 0.01 inches. A nickel braze is employed to bond the sleeve to the core.

In a preferred embodiment, the sleeve covered core is bonded to the ring at a temperature of at least 1800.degree. Fahrenheit. In a preferred embodiment, the sleeve may range in thickness from about 0.001 inches to about 0.005 inches. To insure complete contact of cell with the terminal pin, the sleeve and core may be extended axially into the cell.

For a more complete understanding of the invention, reference is hereby made to the drawings, in which:

FIG. 1 is a schematic top view showing the preferred embodiment of the present invention; and

FIG. 2 is a schematic view in section of the device shown in FIG. 1.

The header device of the present invention is shown generally in the figures. The header device is admirally suited for forming a hermetic seal between the header, the terminal pin and the body of an electrical chemical cell, and particularly those cells with highly corrosive materials such as lithium-sulfur dioxide and lithium-thionyl chloride batteries. The stainless steel header 1 is sized to hermetically fit the body of a cell, whereby welding or other hermetically bonding can be accomplished in a conventional manner. Fitted inside the stainless steel header 1 is an annular glass ring 2 which is bonded to the stainless steel header. Fitted within the annular glass ring 2 is a terminal pin which consists of a central nickel core 3, and a stainless steel sleeve 4. High temperature nickel brazing 5 is applied to keep the thin outer shell 4 solidly bonded to the nickel core 3 under the high temperatures of fabrication, which may range from at least 1800.degree. F. to in excess of 2000.degree. F. The brazing 5 further prevents circumferential growth of the sleeve 4. The nickel braze 5 also provides a low resistance of electrical contact through the seal terminal pin. By making the sleeve 4 slightly longer than the nickel core 3, subsequent trimming of the sleeve and welding of the enclosures into the inside diameter of the sleeve can be accomplished. The glass 2 and the nickel core 3 have relatively closely matched coefficients of expansion, particularly when compared to the coefficient of expansion of the stainless steel.