Insights into the swelling force in commercial LiFePO4 prismatic cell

Lithium-ion batteries undergo reversible and irreversible swelling force during cycling. The mechanical behavior and swelling force of lithium-ion batteries are important in practical applications. In this study, the variation and the aging mechanism of swelling force, and the growth pattern under different cycling conditions have been studied with commercial cells. The findings reveal distinct dynamic stress peaks corresponding to the state of charge (SOC) increase, indicative of notable lattice expansions in both cathode and anode. This expansion intensifies over cycles, with the most significant escalation observed at 30 % SOC, gradually assuming a pivotal role in battery expansion dynamics. Post-mortem analysis, coupled with stress-strain evaluations, attributes this phenomenon primarily to moduli variations across SOC during the aging process. Moreover, the trajectory of swelling force amplification varies across aging paths, with high-temperature cycling demonstrating accelerated growth. This accelerated growth stems from the broadened expansion of battery components beyond solid electrolyte interphase (SEI) formation induced by high-temperature aging.