This article presents a new technique for monitoring the health of lithium-ion cells. Whereas traditional methods use current, voltage, and temperature data to infer the overall health of the cell, the new method uses ultrasonic measurements to assess structural changes such as swelling, expansion, ruffling, and delamination. The article explains how and why these changes occur, how they are measured, and how they correlate with loss of battery capacity, safety, and failure. It also discusses the effect of charge and discharge cycles and the factors that contribute to gas generation.
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