Operando Pressure Measurements Reveal Solid Electrolyte Interphase Growth to Rank Li-Ion Cell Performance

A non-destructive technique for physically detecting the growth of the solid electrolyte interphase (SEI) during cycling of Li-ion pouch cells is presented. Operando cell-stack pressure measurements performed on constrained pouch cells reveal a correlation between irreversible volume expansion and capacity loss caused by a continually thickening SEI. Several silicon-containing full-cell chemistries-LCO/graphite:Si-alloy, NCA/graphite:SiO, and NCA/Si:C-as well as a conventional NMC/graphite cell chemistry were investigated. The effect of FEC consumption on catastrophic failure was also investigated by comparing cells containing 10% FEC and 1% FEC. We show that once FEC is depleted, passivation failure occurs, resulting in massive, irreversible expansion indicating runaway SEI thickening and concomitant cell failure. This work demonstrates that irreversible volume expansion caused by SEI growth can be detected with operando pressure measurements, thus presenting a valuable tool for studying the degradation of Li-ion pouch cells and ranking the performance of different cell chemistries.