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Numerous incidents have illustrated that lithium-ion batteries are flammable and thermally unstable when used improperly or at high temperature. Decomposition reactions further increase the possibility of fire and explosion. Polymer electrolytes have been partially applied to commercial lithium-ion polymer batteries (LIPBs) and determined to improve their thermal stability at high temperature. To determine the degree of thermal stability conferred by a polymer electrolyte and enable its future application to various battery types under different combination modes, this study conducted adiabatic thermal tests to simulate and analyse the thermal runaway curves of LIPBs under various states of charge (SOC) by conducting thermodynamic evaluations. Combining the simulation kinetic model, the pseudo-first-order model was fitted to the self-heating reaction of the polymer electrolyte. In a typical explosion, the LIPB had a TNT equivalent mass of 0.028 g in a nitrogen atmosphere and 0.023 g under ambient conditions. Moreover, under a limited overpressure (2068.4 Pa; 0.3 psig), the safety distance of the LIPBs was 1.66 m in a nitrogen atmosphere and 5.79 m in an air atmosphere. In addition, the value of pressure increased from 2.90 to 22,476.9 Pa within 0.2 m in the case of an SOC change from 30% to 100 % in a nitrogen atmosphere. In the same distance, the blast pressure of an LIPB in the nitrogen atmosphere was 43% higher than that in ambient air. Combined with the thermal analysis data and kinetic model, the thermal stability results for the various SOCs of the polymer electrolyte were confirmed in calculating the reaction kinetics and key safety parameters in nitrogen and air environments.

• Self-heating reaction of lithium ion battery is investigated by ARC. • SADT of different SOC cells are calculated under different cooling conditions. • The relationship between SOC and thermal-runaway criticality is analyzed. • Logarithmic relationship between SADT and heat dissipation condition is revealed. Thermal runaway of lithium ion batteries (LIBs) attracts more and more attentions. In this paper, the self-heating reaction of LIBs with different states of charge (SOCs) is investigated by the standard accelerating rate calorimeter (ARC). The onset temperature of self-heating and trigger temperature of thermal runaway are measured. The kinetics of self-heating reaction is obtained, and the self-accelerating decomposition temperatures (SADTs, i.e. the maximum safe storage temperature) are calculated based on thermal explosion model (Semenov model and Thomas model). The results show that the fully-charged LIB (18650-type, Li(Ni 0.5 Co 0.2 Mn 0.3)O 2 /graphite) self-ignites if the storage temperature exceeds 149.6 °C under the natural convection condition (the battery surface heat transfer coefficient is 10 W m−2 K−1). The logarithmic relationship between SADT and heat dissipation condition suggests that it is effective to reduce the fire risk of LIB by modifying the heat dissipation at low heat transfer coefficient (U), while it becomes inefficient when U is high. [ABSTRACT FROM AUTHOR]