Tailored medium-entropy Si alloy anodes with multi-element Fe-site substitution for high-performance Li-ion batteries

Silicon (Si) anodes offer a theoretical capacity nearly ten times higher than graphite, yet their practical use in lithium-ion batteries (LIBs) is impeded by severe volume expansion, particle pulverization, and low conductivity, resulting in rapid capacity decay. Considerable efforts have therefore focused on structural and compositional engineering to mitigate these drawbacks. In particular, alloying with transition metals (e.g., Fe Si systems) has demonstrated notable improvements in buffering volume changes and enhancing electronic conductivity, but the benefits of binary alloys are still limited. Here, we introduce a compositionally complex Si alloy (CCSA) approach to simultaneously achieve high capacity and durability. Medium-entropy CCSAs were synthesized via high-energy ball milling, incorporating multiple elements into Fe Si matrices. Structural analysis revealed lattice distortion and homogeneous elemental distribution, consistent with configurational entropy stabilization. Among them, Mg-containing CCSAs exhibited the best cycling stability and capacity retention. CCSAs are integrated with conductive carbon matrices, including reduced graphene oxide (rGO) and carbon nanotubes (CNTs), to enhance conductivity and structural stability. The resulting CCSA anode exhibits stable cycling performance with high reversible capacity. Building upon these results, practical Si/graphite blended composite anodes are fabricated, incorporating up to 30 wt% Si. These composite anodes deliver high reversible capacity, excellent rate capability, and superior capacity retention, thereby establishing Si-alloy-based materials as a scalable platform for next-generation high-energy-density LIB anodes.