Siloxane Additive-Mediated Reconstruction of Solid Electrolyte Interphase for Fast-Charging Sodium-Ion Batteries

Ester-based electrolytes in sodium-ion batteries (SIBs) offer high oxidative stability but often suffer from poor stability of the solid electrolyte interphase (SEI) on hard carbon anodes, severely limiting fast-charging capabilities and cycling lifespan. To address this interfacial instability, this work introduces trimethoxysilane (HTOS) as an electrolyte additive into 1 M NaPF6 in EC:DMC electrolyte (denoted as ED). Compared with the rough and inorganic-rich interphase formed in the ED electrolyte, the HTOS additive induces the formation of a smoother, more uniform, and organic-rich SEI. This optimized interfacial structure effectively suppresses continuous interfacial degradation during cycling and significantly reduces the apparent activation energy for Na+ migration. Consequently, the HTOS-modified electrolyte demonstrates markedly superior electrochemical performance, delivering a reversible capacity of 198.76 mAh g−1 at 1C and maintaining 85% of the initial capacity after 200 cycles at 0.5 C. This study demonstrates that utilizing silicon-containing functional additives for SEI regulation is a highly effective strategy to enhance the fast-charging and long-term cycling stability of hard carbon anodes in SIBs.