Enhancing SEI Stability of Hard Carbon Anodes with Low‐Solvating CPME Co‐Solvent for Wide‐Temperature Sodium‐Ion Batteries

The optimization of microstructure, surface area, defects, porosity, pore morphology, and interfacial engineering of the solid electrolyte interface (SEI) is critical in improving the battery metrics of hard carbon (HC) anodes for SIBs. Herein, cyclopentyl methyl ether (CPME), a weakly solvating and wide‐temperature‐range solvent, is employed as an alternative to ethylene carbonate (EC). In combination with HC, CPME‐PC‐based electrolytes demonstrate a high initial Coulombic efficiency (ICE) of up to 75% and superior cycling stability of 91% after 100 cycles, highlighting the potential of CPME as a co‐solvent. The reduction of CPME co‐solvent forms a more inorganic and thin SEI than EC‐generated SEI, boosting the ICE and cycling stability of the anode. The HC delivered the excellent reversible capacity of 356 mAh g −1 at the current density of 30 mA g −1 with a higher low potential plateau capacity (68%) using CPME‐PC‐based electrolyte. The low‐temperature battery metric for CPME‐PC‐based electrolytes showed ~30% added capacity and improved ICE value compared to EC‐PC‐based electrolytes. The CPME‐PC‐based electrolyte indicates close to 100% Coulombic efficiency at 10°C and 0°C, with excellent cycle stability for the HC anode. The work reports for the first time the use of greener, low‐solvating CPME in improving the reversible capacity and ICE for wide‐temperature applications of SIBs.