Electrolytes with competitive Na⁺-anion coordination for high-voltage sodium-ion batteries

The poor electrode/electrolyte interface compatibility and inferior electrolyte oxidative tolerance in commercial ethylene carbonate (EC)-based electrolytes have hindered the development of high-voltage sodium-ion batteries (SIBs). In this study, an anionic chemistry strategy is proposed to strengthen Na⁺-anion coordination in the solvation sheath, and subsequently reduce the coordination numbers of EC solvents with the addition of NaClO₄ into NaPF₆/EC/DEC electrolytes. Theoretical and experimental results confirm that the competitive coordination capabilities of Na⁺-ClO₄⁻, with high binding energy, induce a wide electrochemical window up to 4.8 V, highly reversible Na⁺ plating/stripping, and fast desolvation kinetics at the electrode/electrolyte interface, thereby hindering the continuous electrolyte decomposition. The optimized electrolyte PEDCF-0.20 demonstrates weakened Na⁺-EC coordination, increased interaction of Na⁺-anion in solvation, facilitating the formation of an inorganic-rich interface layer. Consequently, a 2.1 A h cylindrical full cell of hard carbon//NaNi_1/3Fe_1/3Mn_1/3O₂ delivers an impressive capacity retention of 93.7% after 300 cycles at an extended charging cutoff voltage of 4.1 V. This work provides a new insight into regulating the competitive coordination of anions to guarantee the remarkable cycling stability of high-voltage SIBs.