High-Performance All-Solid-State Silicon-Sulfur Batteries Enabled by Li₄(BH₄)₃I Hydride Electrolyte

Silicon anodes hold great potential for next-generation battery systems due to their significantly higher capacity compared with conventional graphite anodes. However, the low electrochemical potential of lithiated phases in lithium-silicon alloys drives spontaneous electrolyte reduction, resulting in interfacial instability. Herein, a high-performance silicon composite anode assembled with a Li₄(BH₄)₃I hydride electrolyte is developed. Prelithiation compensates for initial irreversible lithium consumption, while the combination of the Li₂₂Si₅ alloy and hydride electrolyte suppresses interfacial degradation, enabling an initial Coulombic efficiency of 99.6%. In silicon-sulfur full cells, the opposite volume changes of the Li₂₂Si₅ anode and sulfur cathode dynamically compensate for stress evolution during cycling and maintain intimate interfacial contact and structural integrity, enabling this configuration to deliver an ultra-high areal capacity of 23.88 mAh cm^-2 and retain 63.2% of its capacity after 1000 cycles, without observable cracking or structural degradation. These results provide an effective interfacial and structural design strategy for high-performance silicon-based anodes in all-solid-state batteries.