Reductively Passivated Ion-Conductive Interphase Enables High-Capacity Silicon Anodes for High-Energy-Density All-Solid-State Batteries

Silicon-based all-solid-state batteries (ASSBs) promise high energy density for next-generation energy storage systems. However, the poor solid−solid contact between silicon (Si) and the solid-state electrolyte (SSE), coupled with interfacial instability during cycling, leads to lithium trapping and parasitic reactions, resulting in a low initial coulombic efficiency (ICE). Herein, we report a solution-assisted in situ polymerization and prelithiation strategy to construct a highly ion-conductive interphase via reductive passivation for Si anodes. Lithium biphenyl replenishes active lithium while inducing the in situ formation of a highly stable hybrid interphase composed of polybiphenyl, lithium bis(trifluoromethanesulfonimide) (LiTFSI), and reductively passivated lithium fluoride. The electrochemically stable and ion-conductive interphase minimizes interfacial ion-transport resistance while suppressing SSE decomposition. The engineered anode delivers an ICE of 100.6% with a high electrode-level reversible capacity of 3215 mAh g−1 at the electrode level, enabling an ICE of 96.4% in LiCoO2 full cells (6.2 mAh cm−2) with 96.6% capacity retention after 300 cycles at 1 C. The all-solid-state pouch cell demonstrates a high energy density of 313 Wh kg−1 with 92.7% capacity retention after 100 cycles. This work underscores the critical role of stable ion-conductive interphase design at Si anodes and provides a viable strategy toward practical high-energy-density ASSBs.