SE985: Fluorinated ether electrolytes with additive synergy: Enabling high-voltage stable and long lifetime sodium-ion pouch cells

Sodium-ion batteries (SIBs) are a promising, low-cost alternative for grid-scale storage due to Earth-abundant elements, but conventional carbonate electrolytes suffer from parasitic reactions and interphase instability at high voltages (>4.0 V). This talk introduces fluorinated ether-based electrolytes for high-voltage Na0.97Ca0.03[Mn0.39Fe0.31Ni0.22Zn0.08]O2 (NCMFNZO)/hard carbon (HC) pouch cells. The use of 1,2-diethoxyethane to 1,2-bis(2,2-difluoroethoxy)ethane (F4DEE) enhances oxidative stability, reduces gas evolution and impedance, and improves cycling (~85% retention after 500 cycles at 25°C; ~80% at 40°C), with lower parasitic heat and transition metal dissolution. Further, ethylene sulfate (DTD) additive in F4DEE forms NaF/sulfur-rich SEI/CEI, yielding superior performance (~88% retention at 25°C; ~82% at 40°C after 500 cycles) and negligible gassing. Pouch bag studies show DTD suppresses cathode-anode cross-talk during high-temperature storage, stabilizing oxidation states and impedance. These solvent-additive synergies enable robust, high-voltage SIBs with enhanced lifespan and safety, offering a platform for interphase optimization and mechanistic insights toward practical deployment.