Electrolyte Design for Simultaneous Interfacial Stabilization in Si||NCM811 Full Cells

The combination of silicon anode and Ni‐rich cathode offers high energy density but suffers from severe interfacial instabilities during cycling. Silicon undergoes repeated volume changes that destabilize its solid electrolyte interphase (SEI), while NCM811 experiences surface degradation and transition‐metal dissolution, both of which are exacerbated by electrolyte‐derived side reactions. Here, a dual‐additive electrolyte design incorporating fluoroethylene carbonate (FEC), a commercially established SEI‐forming additive, and dimethoxydimethylsilane (DMDMS) is proposed to stabilize both electrode interfaces simultaneously. FEC promotes the formation of a LiF‐rich SEI on the silicon anode, whereas DMDMS suppresses acid‐driven degradation by scavenging HF and stabilizing PF 5 . This design effectively mitigates gas evolution, interfacial impedance growth, and electrode swelling. Benefiting from this synergistic electrolyte formulation, Si‐Fe alloy anode‐based Si||NCM811 full cells deliver an initial discharge capacity of 167.8 mAh g −1 and retain 65.5% of the capacity after 150 cycles, together with improved rate capability. These results highlight an effective electrolyte formulation strategy for enhancing the durability of high‐energy Si||NCM lithium‐ion batteries.