Chemo-electrochemical Tandem Reduction Enables Eupolymer-Inorganic Solid-Electrolyte Interphases for Silicon-Based Anodes

Silicon-based anodes offer substantial potential for increasing batteries’ energy density but are limited by unstable solid-electrolyte interphases (SEIs). Here, we report a chemo-electrochemical tandem reduction strategy to construct an integrated eupolymer-inorganic SEI with both favorable mechanical robustness and fast Li+ transport. This strategy couples a selective ester–amine exchange reaction in the bulk electrolyte with a subsequent electrochemical reduction at the anode surface. The identified chemical intermediate exhibits facilitated de-fluorination kinetics, enriching the SEI with nanoscale inorganic species while triggering a free-radical polymerization of unsaturated additives. Benefiting from the integrated eupolymer-inorganic SEI, SiOx anodes demonstrate 80.1% capacity retention after 800 cycles and retain 551.9 mAh g–1 at 5 A g–1. Practical Ah-level Si/C∥NCM811 pouch cells operating under a cut-off voltage of 4.4 V achieve 90.9% capacity retention over 300 cycles, with an average Coulombic efficiency of 99.91%. This work provides profound insights into SEI tailoring, offering pathway toward long-life, fast-charging silicon-based batteries.