Experimental study on heat and gas generation characteristics of commercial sodium-ion batteries during thermal runaway

Sodium-ion batteries have gradually been commercialized due to their wide range of material sources and low cost. However, there are few studies focusing on the commercial sodium-ion battery safety, especially the relationship between heat and gas generation is unclear. This work conducts the thermal runaway (TR) experiments of commercial 18650 sodium-ion batteries with different states of charge (SOCs) under adiabatic accelerated rate calorimetry and localized overheating. The results show that heat generation values of 50% and 100% SOC batteries during TR are 175.2 and 328.2 J g⁻¹, respectively. Whereas, 0% SOC batteries do not trigger TR. Moreover, the reaction sources and pathways of gas generation during TR are critically sorted out. Finally, two important conclusions are obtained. (i) During the five stages of TR, the heat generation from the safe venting to the triggering of TR stage is the highest in 50% SOC batteries, accounting for 62.5% of the total heat generation. However, for 100% SOC batteries, the heat generation from triggering TR to maximum temperature stage has the largest proportion during TR, at 57%. The 50% SOC batteries present characteristic of slow heat generation, while the 100% SOC batteries show characteristics of accelerated heat generation. (ii) Based on dimensionless analysis, the heat/gas generation ratios of 50% and 100% SOC batteries are 0.262 and 0.028, respectively. The gas generation behavior occur earlier than heat generation behavior during the whole process of TR of sodium-ion batteries. This study provides a direction for the development of high-safety sodium-ion batteries and thermal runaway suppression technology.