Study on the deformation pattern of prismatic lithium-ion battery casings under different state-of-charge

To elucidate the deformation characteristics of prismatic lithium-ion battery casings under various charging conditions, this study designed a spring-clip-based deformation measurement fixture and conducted a series of measurements in conjunction with surface strain analysis. The results indicate that during standard charging and discharging cycles, the casing deformation of prismatic lithium batteries exhibits a certain correlation with the State of Charge (SOC). However, the maximum coefficient of determination reaches only approximately 0.8, rendering it unsuitable for precise SOC estimation, a finding that distinguishes prismatic batteries from their cylindrical counterparts. In overcharging experiments utilizing the spring-clip fixture, it was observed that in the early stages of overcharge, the casing deformation remained comparable to that observed during normal charging processes. Once a certain extent was exceeded, the battery casing deformation entered an accelerated phase, and the fixture strain can be more than ten times higher than that observed during a normal charging process. CT scanning and ultrasonic inspection subsequently confirmed that this accelerated expansion was attributable to internal gas generation. The experimental findings demonstrate that, for prismatic lithium batteries, the correlation between casing deformation and SOC is insufficient to support accurate SOC estimation; nevertheless, this method proves feasible for detecting abnormal casing deformation caused by factors such as gas generation, thereby offering a concise and effective reference solution for auxiliary state-of-health monitoring in lithium-ion batteries.