Surface halogenation engineering for reversible silicon-based solid-state batteries

Silicon-based solid-state batteries are promising next-generation high-energy-density technologies. However, poor (electro)chemical compatibility between silicon negative electrodes and solid electrolytes (e.g., Li₆PS₅Cl) plus sluggish interfacial kinetics severely limits their reversibility and Coulombic efficiency. Here, we propose a surface halogenation strategy that transforms the native amorphous SiO₂ passivation layer on silicon particles into a functional Al(Si)OCl composite surface via controlled reaction with AlCl₃. This artificial interphase reconciles interfacial incompatibility and enables fast ionic/electronic transport, suppressing irreversible lithium loss. The optimized negative electrode achieves a high initial Coulombic efficiency of 94.3% in half-cells and 85.6% initial Coulombic efficiency (86.6% with pre-lithiation) in full cells paired with LiNi_0.88Co_0.09Mn_0.03O₂. Enhanced reversibility further delivers long-term cyclability. The optimized negative electrode delivers 86% capacity retention and 99.998% average Coulombic efficiency over 200 cycles. Even at high-loading ( > 10 mAh cm^-2, and no adhesives/conductive carbon/electrolyte), it retains 72% capacity after 500 cycles. The full cells maintain 80% capacity after 200 cycles at 1 C, with an average Coulombic efficiency exceeding 99.95%. The versatility of this halogenation strategy underscores halide chemistry's broad potential in advancing high-performance, reversible silicon-based solid-state batteries.