A Novel Sultone-Based Electrolyte Additive for Ultra-Long Cycle Life Sodium-Ion Batteries

For sodium-ion batteries, addressing the issue of limited cycle life is crucial for their widespread industrial application, and the electrolyte plays a pivotal role in this context. In this study, a practically viable electrolyte with industrial potential is proposed, introducing sulfone and borate as cooperative electrolyte additives to improve cycling stability. The optimized electrolyte formulation is composed of NaPF₆ (sodium hexafluorophosphate) dissolved in a mixed solvent of PC (propylene carbonate)/EMC (ethyl methyl carbonate), supplemented with PES (prop-1-ene-1,3-sultone) and NaODFB (sodium difluoro(oxalato)borate). In this system, the decomposition of PES generates S-O_x species, which modify the interfacial chemical environment and promote a more complete decomposition of ODFB^-. As a result, B- and S-containing organic intermediates are further transformed into oxygen-coordinated inorganic species (e.g., B-O_x and S-O_x), which subsequently reconstruct into a crosslinked inorganic interphase. This cooperative interfacial evolution leads to the formation of more uniform, compact, and chemically stable CEI/SEI layers, thereby enabling superior cycling stability. As a demonstration, the Na||NVP (sodium vanadium phosphate) half-cell retains a specific capacity of 109.8 mAh·g^-1 after 5000 cycles, corresponding to a capacity retention of 96.7%. This work offers valuable insights and experimental support for the large-scale industrialization of long-life sodium-ion battery electrolytes.