Rapid thermal runaway detection of lithium-ion battery via swelling-based state-of-charge monitoring using piezoresistive sponge sensor

The early detection of thermal runaway (TR) and the accurate monitoring of the state of lithium-ion batteries (LIBs) are exceptionally critical in large-capacity applications. However, achieving both practicality and effective sensing capability for module-level LIB state diagnosis remains a challenge. Herein, we developed a swelling-based module-applicable rapid TR detection system using sponge-type piezoresistive swelling sensor. The unique feature of the sensor with inter-layer contact under high compression facilitates practical swelling detection with its high sensitivity (3.90 kPa⁻¹), durability, outstanding stability, near-zero hysteresis, and a high sensing resolution (<10 μm) even under pre-compression. Based on its excellent scalability, pouch cell-level, prismatic cell-level, and module-level reversible swelling monitoring of LIBs in constrained structures were successfully validated under various operating conditions, with the swelling signal exhibiting a strong correlation with the state of charge (SOC). Finally, on the basis of reaction mechanism of TR and the swelling sensor signal, the module-level early TR detection occurs 1357 s before explosion. These results imply reliable LIB monitoring systems with substantial practicality using swelling sensors for enhanced TR detection of large-capacity LIB applications.