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 NaClO 4 into NaPF 6 /EC/DEC electrolytes. Theoretical and experimental results confirm that the competitive coordination capabilities of Na + -ClO 4 − , 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 Ah cylindrical full cell of hard carbon//NaNi 1/3 Fe 1/3 Mn 1/3 O 2 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.