Ion-Conductive Polyphosphasiloxane Networks: Constructing Robust Solid Electrolyte Interphase for SiO _x Anode

Silicon (Si) is famous for its high theoretical specific capacity, natural abundance, and low reduction potential. However, enormous volume change, fast capacity decay, and poor ionic conductivity hamper the practical utilization of Si-based anodes. Until now, strategies to improve cycling performance by tailoring solid electrolyte interphase (SEI) have remained less effective, especially in high-Si content anodes. In this work, the ion-conductive polyphosphasiloxane (PPS) network is constructed on the SiO_x anode via condensation of tetraethyl orthosilicate/tris(trimethylsilyl)phosphate (TEOS/TMSP) electrolyte additive to form a robust SEI. The PPS network with SiOP bonds exhibits a low Li⁺ transport barrier, high ionic conductivity, and decreased activation energy (E_a), enabling the regular (de)lithiation process. Moreover, the robust SEI mitigates the volume change of SiO_x anode due to the reinforcement effect from crosslinked PPS skeleton with strong SiOP linkages. As a result, SiO_x anode with TEOS/TMSP electrolyte additives exhibits superior cycling performance over 700 cycles with a high retention of 73.4% at 0.4 C and an average capacity decay rate of 0.038% per cycle in half cell. This work provides new insights into dual-additive electrolyte development and SEI design.