Early warning strategy for overheating-induced thermal runaway in lithium-ion batteries based on fast impedance measurement

Reliable early warning of lithium-ion batteries (LIBs) thermal runaway (TR) remains a pivotal yet unresolved challenge in battery safety research. Given the escalating risks of LIB fire hazards, developing timely and reliable early-stage TR detection methods holds significant practical importance. In this study, we conducted TR experiments triggered by overheating on pouch cells at varying states of charge (SOC). A rapid impedance testing platform was established to monitor real-time impedance at five characteristic frequency points during TR progression. Concurrently, parameters including temperature, voltage, and impedance were analyzed throughout the process. The TR event was divided into four distinct phases based on the evolution of impedance: heat conduction-dominated phase, gas generation-dominated phase, partial internal short circuit-dominated phase, and thermal runaway phase. Based on impedance characteristics at specified frequencies and their corresponding TR mechanisms, a two-level early warning strategy was developed. This method successfully achieved TR warning and demonstrated a 93.1 % alert time ahead of significant voltage drop or intense temperature rise in validation experiments using an NCA cell. These findings provide critical insights for enhancing the monitoring capabilities of battery management systems (BMS) and improving LIB safety.