Uncovering Sodiated Hc Dominated Thermal Runaway Mechanism of Nfpp/Hc Pouch Battery

Abstract

Sodium-ion batteries (SIBs) are considered a promising technology for large-scale energy storage system (LSESS) because of rich resources and outstanding electrochemical performance. However, the safety of SIBs is rarely discussed, and the thermal stability is critical to the application of battery, especially for LSESS. In this study, the thermal runaway mechanism of Na3Fe2(PO4)(P2O7)||hard carbon (NFPP/HC) pouch battery dominated by heat generation from sodiated anode has been uncovered. To illustrate, the heat generation analysis based on batteries and materials level shows that the exothermic reaction between the HC and electrolyte begins to occur at 100 °C (The exothermic reaction between NFPP and electrolyte is near 230 °C). In addition, the reaction between the anode and electrolyte releases a large amount of heat at high temperatures, while NFPP materials exhibit less and milder exothermic behavior. Therefore, the exothermic reaction between the HC and electrolyte is not only the induction factor of thermal runaway but also the main heat source of thermal runaway. More seriously, when sodium plating on the HC, the self-heating temperature and thermal runaway triggering temperature of the battery will decrease 15.0 °C and 19.5 °C, respectively. For the characteristic of great heat generation in the early stage of thermal runaway of SIBs, the ceramic coated separators with higher thermal stability and higher wettability are applied to SIBs, which significantly improves battery safety. This study reveals the mechanism of thermal runaway in SIBs (NFPP/HC), which is expected to provide guidance for the research of safer SIBs.

Keywords: Sodium-ion Batteries, Thermal Runaway, Safety, Sodium Plating.