Reversible and Irreversible Expansion of Lithium-Ion Batteries Under a Wide Range of Stress Factors

Lithium-ion batteries cell thickness changes as they degrade. These changes in thickness consist of a reversible intercalation-induced expansion and an irreversible expansion. In this work, we study the cell expansion evolution under variety of conditions such as temperature, charging rate, depth of discharge, and pressure. A specialized fixture was used to keep the cells at a constant pressure during cycling, while measuring the thickness change both within a cycle and the cumulative growth over many cycles. The changes in positive and negative electrode capacity and stoichiometric range can be diagnosed from the evolution of the reversible expansion. The changes in the reversible expansion if combined with the voltage, lead to a higher-confidence estimation of cell health parameters important for lifetime prediction and adaptive battery management such as asymmetric charge/discharge power limits. This study raises the importance of monitoring the expansion for enabling advanced and more-informed health diagnostics of lithium-ion batteries.