Strain-rate-dependent failure behavior of lithium-ion batteries: Role of liquid electrolyte in impact safety

The structural integrity of lithium-ion batteries (LIBs) under dynamic loading is critical to their safe deployment in electric transportation systems. While dry-state testing of battery components is common, the influence of liquid electrolyte on battery failure under dynamic loading remains largely unexplored. This study investigates the out-of-plane compressive behavior of lithium iron phosphate (LFP) pouch cells in both dry and electrolyte-saturated states across a wide range of strain rates (0.005/s to 2000/s), using quasi-static and Split Hopkinson Pressure Bar (SHPB) tests. High-speed imaging and transparent cell designs enabled real-time visualization of electrolyte migration and structural deformation. The results show that, although electrolyte presence has little effect under quasi-static loading, it significantly lowers peak stress, strain, and stiffness at elevated strain rates. Microscopy reveals that confined electrolyte flow induces internal pore pressure, accelerates microcrack initiation in separators and electrode coatings. A mechanistic framework is proposed to explain how fluid–solid interactions degrade structural integrity at high rates. The findings demonstrate that dry-state testing overestimates battery resilience under impact and highlight the need to account for electrolyte effects in crash safety assessments. This work provides new insights into battery failure mechanisms relevant to electric mobility and supports the development of impact-tolerant energy storage systems and more comprehensive testing protocols for crashworthiness analysis.