Search for: All records

Sodium-ion batteries (SIBs) with Earth-abundant elements are promising for global electrification, but electrolyte stability impacts electrochemical performance and safety. This study compares non-fluorinated 1,2-diethoxyethane (DEE) and fluorinated 1,2-bis(2,2-difluoroethoxy)ethane (F4DEE) as electrolyte solvents in Na_0.97Ca_0.03[Mn_0.39Fe_0.31Ni_0.22Zn_0.08]O₂(NCMFNZO)/hard carbon (HC) pouch cells up to 4.0 V. Fluorination slightly reduces ionic conductivity and increases viscosity but significantly enhances electrochemical stability and safety. Cells with F4DEE exhibit lower impedance, reduced gas evolution, and less voltage decay during high-voltage storage at 40 °C. Long-term cycling shows ∼85% capacity retention after 500 cycles at 25 °C and ∼80% at 40 °C with less transition metal dissolution, outperforming DEE-based cells. Isothermal microcalorimetry reveals lower parasitic heat generation with F4DEE, while soft X-ray absorption spectroscopy confirms stabilized Ni and Mn oxidation states, indicating suppressed electrolyte oxidation. Accelerating rate calorimetry reveals improved thermal stability with F4DEE. These findings highlight fluorinated ether solvents as a promising approach to enhance SIB lifespan and safety, with ongoing challenges requiring further solvent and additive optimization.