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_0.3K_0.35Cs_0.35FSA), 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, Li₃N, Li₂O, and Li₂S, 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_0.3K_0.35Cs_0.35FSA 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.

Mesoporous carbons have been widely utilized as the sulfur host for lithium-sulfur (Li-S) batteries. The ability to engineer the porosity, wall thickness, and graphitization degree of the carbon host is essential for addressing issues that hamper commercialization of Li-S batteries, such as fast capacity decay and poor high-rate performance. In this work, highly ordered, ultrathin mesoporous graphitic-carbon frameworks (MGFs) having unique cage-like mesoporosity, derived from self-assembled Fe₃O₄ nanoparticle superlattices, are demonstrated to be an excellent host for encapsulating sulfur. The resulting S@MGFs exhibit high specific capacity (1, 446 mAh·g^-1 at 0.15 C), good rate capability (430 mAh·g^-1 at 6 C), and exceptional cycling stability (~0.049% capacity decay per cycle at 1 C) when used as Li-S cathodes. The superior electrochemical performance of the S@MGFs is attributed to the many unique and advantageous structural features of MGFs. In addition to the interconnected, ultrathin graphitic-carbon framework that ensures rapid electron and lithium-ion transport, the microporous openings between adjacent mesopores efficiently suppress the diffusion of polysulfides, leading to improved capacity retention even at high current densities.