Molten Salt Electrolyte Enables Micro‐Sized Silicon Anode in Lithium‐Ion Batteries

Micro‐sized silicon (mSi) anodes offer high capacity for next‐generation lithium‐ion batteries but suffer from severe volume changes, causing unstable interphases and poor cycling. Traditional electrolytes derive unstable electrolyte/electrolyte interphases, and flammable solvents pose safety risks. Here, we introduce a non‐flammable molten salt electrolyte, which consists of lithium bis(fluorosulfonyl)imide, potassium bis(fluorosulfonyl)amide, and cesium bis(fluorosulfonyl)imide in a mole ratio of 0.3:0.35:0.35 (noted as Li 0.3 K 0.35 Cs 0.35 FSA), that forms an inorganic interphase on mSi, stabilizing the electrode/electrolyte interface. Computational and experimental insights elucidate the FSA − anion decomposition‐derived SEI predominantly of LiF, Li 3 N, Li 2 O, and Li 2 S, which exhibits mechanical resilience and low interfacial resistance, effectively accommodating the significant volume expansion of silicon during lithiation/delithiation. As a result, the Li||mSi half‐cell achieves 60.7% capacity retention after 100 cycles with 99.5% average Coulombic efficiency. Overall, the Li 0.3 K 0.35 Cs 0.35 FSA electrolyte eliminates flammability concerns while enabling robust cycling performance. This work demonstrates a safe, high‐energy battery system by coupling mSi anodes with stable molten salt electrolytes, addressing both interfacial instability and safety challenges in mSi‐based lithium‐ion batteries.