Meaning
Differential volumetric change between the glass or ceramic insulator and the metallic pin or collar during temperature excursions threatens the seal of a battery cell. This feedthrough thermal mismatch occurs because each component of the terminal assembly possesses a distinct coefficient of thermal expansion. When the cell experiences rapid heating or cooling, the material boundaries expand and contract at different rates.
The resulting mechanical strain can create microcracks that break the hermetic seal.
Material Selection
Matching the coefficients of thermal expansion of the terminal pin and the insulating glass is the primary method to control this localized strain. Manufacturers select specific glass compositions that closely match the expansion rate of metals like stainless steel or specialized nickel alloys. This careful matching ensures that the glass remains under compression across the entire operating temperature range.
Compression seals are inherently more durable against thermal cycles than matched seals.
Hermetic Failure
Loss of the airtight seal allows moisture to enter the cell and react with the electrolyte to produce hydrofluoric acid. This reaction accelerates the degradation of the active materials and can cause internal short circuits. The feedthrough thermal mismatch thus directly affects both the performance and the safety of the stored energy system.
Experimental Evaluation
Thermal cycling tests between extreme temperature limits verify the durability of the terminal seal.
