Bi0.94Sb1.06S3 Nanorod Cluster Anodes for Sodium-Ion Batteries: Enhanced Reversibility by the Synergistic Effect of the Bi2S3–Sb2S3 Solid Solution

Bi0.94Sb1.06S3 solid solution anode with a nanorod cluster morphology has been synthesized by a hydrothermal reaction and investigated in sodium-ion batteries in comparison to the binary counterparts Bi2S3 and Sb2S3. The Bi0.94Sb1.06S3–graphite composite obtained by a mechanical milling of 80 wt % Bi0.94Sb1.06S3 and 20 wt % graphite exhibits much improved cycle stability with 79% capacity retention after 200 cycles in the full voltage window of 0.01–2.8 V compared to its Bi2S3–graphite (58% retention) and Sb2S3–graphite (10% retention) counterparts, demonstrating a synergistic effect. Cyclic voltammetry scans indicate that the polarization overpotential associated with the conversion reaction in Bi0.94Sb1.06S3 is lower than those in Sb2S3 and Bi2S3. Cycling under controlled voltage windows of 2.8–0.85 V corresponding to a conversion reaction and 0.85–0.01 V corresponding to an alloying reaction reveals both highly reversible conversion and alloying reactions in the Bi0.94Sb1.06S3 solid solution anode compared to that in the binary counterpart anodes.