Self-purification and silicon-rich interphase achieves high-temperature (70°C) sodium-ion batteries with nonflammable electrolyte

Safety and stable cycling of sodium-ion batteries (SIBs) operating above 50 °C are huge challenges for applications in harsh environments, therefore in urgent need of the liquid electrolytes with high-temperature resistance. Herein, a two-pronged strategy in the non-flammable electrolyte is proposed to endow excellent thermal stability by bifunctional integration of acid-scavenging ability with synergistic film-forming mechanism. As a result, self-purification of the electrolyte and robust silicon-rich interphase formed ensure safe and stable operation of SIBs at high temperatures. The high-voltage Na3V2(PO4)2O2F (NVPF) cathode demonstrates exceptional cycling stability with 84 % capacity retention after 1,000 cycles at 60 °C and 86 % capacity retention after 100 cycles at 70 °C, far superior to known electrolytes. More importantly, for the first time, the assembled full cells with hard carbon and NVPF are successfully operated at 60 °C for more than 100 cycles, the highest temperature available to our knowledge. In short, the available electrolyte formula is proposed as an effective solution to lay the foundation for the development of SIBs at high temperatures.