Phosphate ester based nonaqueous electrolytes for sodium batteries

The scarcity and uneven distribution of lithium, with growing demand, accelerated the development of sodium batteries, wherein electrolyte compatibility decisively affects overall performance. Phosphate-based solvents attract interest for flame retardancy. However, their suboptimal lowest unoccupied molecular orbital (LUMO) energy levels cause poor stability against graphite anodes in lithium batteries, hindering stable solid electrolyte interphase (SEI) formation. Conversely, the higher reduction potential of sodium ions enhances the compatibility of phosphate esters, enabling stable interfacial layer formation. Combined with their wide electrochemical window and thermal stability, phosphate esters are ideal candidates for safe, high-voltage, long-life sodium batteries. This review summarizes advances in design strategies, interfacial mechanisms, and electrochemical performance of phosphate ester-based electrolytes for sodium batteries, offering future perspectives.