Thermal safety boundary of lithium-ion battery at different state of charge

Thermal runaway (TR) is a critical issue hindering the large-scale application of lithium-ion batteries (LIBs). Understanding the thermal safety behavior of LIBs at the cell and module level under different state of charges (SOCs) has significant implications for reinforcing the thermal safety design of the lithium-ion battery module. This study first investigates the thermal safety boundary (TSB) correspondence at the cells and modules level under the guidance of a newly proposed concept, safe electric quantity boundary (SEQB). A reasonable thermal runaway propagation (TRP) judgment indicator, peak heat transfer power (PHTP), is proposed to predict whether TRP occurs. Moreover, a validated 3D model is used to quantitatively clarify the TSB at different SOCs from the perspective of PHTP, TR trigger temperature, SOC, and the full cycle life. Besides, three different TRP transfer modes are discovered. The inter-conversion relationship of three different TRP modes is investigated from the perspective of PHTP. This paper explores the TSB of LIBs under different SOCs at both cell and module levels for the first time, which has great significance in guiding the thermal safety design of battery systems.