Role of High-Temperature Separator Stability on Safety and Thermal Signature of Li-Ion Pouch Cells

Abstract

Thermal safety hazards are a bottleneck problem that constrains the development of lithium-ion batteries with high energy density. Although the internal short circuit (ISC) caused by separator rupture has been identified as a primary driver of catastrophic failure, the effects of separator architecture and high-temperature robustness on thermal runaway behaviors still need fundamental understanding. This study investigates custom-built pouch cells assembled with a wide range of separators to understand the impact of separators on cell-level thermal stability and resistance to catastrophic ISC. Carefully designed thermal abuse tests reveal how the separator shrinkage, melting, and collapse correlate with micro and massive ISC to drive the unstoppable thermal runaway. Cells are subjected to extreme operating conditions to facilitate quantification of the role of separator characteristics on the thermal runaway signature. The implications of separator distinctions on modulating chemical crosstalk between anode and cathode are explored to determine the dominant mechanism that triggers the onset of thermal runaway, with mitigation strategies being proposed from a new perspective.