Voltage and Temperature Limits of Advanced Electrolytes for Lithium-Metal Batteries

Several advanced electrolytes (mainly ether-based) have shown promising electrochemical performance in high-energy-density lithium-metal batteries. This work evaluates their thermal stability under abuse conditions to elucidate their safety limits compared to carbonate electrolytes typically used in Li-ion batteries. Electrolyte stability was assessed in conjunction with a LiNi_0.8Mn_0.1Co_0.1O₂ cathode and a Li-metal anode at ultra-high voltages (≤4.8 V) and temperatures (≤300 °C). The onset and extent of heat release were monitored via isothermal microcalorimetry and differential scanning calorimetry. Most ether-based electrolytes show improved thermal resilience over carbonate electrolytes. While extreme voltages severely destabilize the ether-based electrolytes, a phosphate-based localized high-concentration electrolyte exhibits improved stability over carbonate electrolytes, even at 60 °C. Although thermal analysis during the first charge process may be insufficient to conclude the long-term advantages of these electrolytes, a more stable electrolyte identified under extreme voltage and temperature conditions provides valuable guidance for the safety of future electrolyte designs.