Revealing Cu 4 SnS 4 Constructed by Composition Regulation Engineering With Enhanced Conversion Reversibility for Superior Zinc Storage Performance

ABSTRACT Conversion‐type anodes enable rocking‐chair zinc‐ion batteries (RCZIBs) to avoid Zn dendrites and corrosion. However, high‐capacity multi‐electron‐transfer anodes remain challenging. A composition‐regulation strategy is applied to copper tin sulfides via gelation‐assisted solvothermal synthesis. Orthorhombic Cu 4 SnS 4 with open ion channels and optimized electronic states is an ultra‐stable conversion‐type anode. In situ XRD reveals a phase‐conversion mechanism exclusive to Cu 4 SnS 4 , explaining its enhanced reversibility. In situ EIS coupled with distribution‐of‐relaxation‐times analysis tracks ion/electron transport and interfacial stability during cycling. The Cu 4 SnS 4 half‐cell delivers an initial capacity of 144.32 mAh g ‒1 at 0.2 A g ‒1 with 95.5% capacity retention after 300 cycles, and retains 60.26 mAh g ‒1 after 3000 ultralong cycles at 4 A g ‒1 . A rocking‐chair Cu 4 SnS 4 ||MnO 2 full cell achieves a capacity of 123.04 mAh g ‒1 at 0.2 A g ‒1 and 57.59 mAh g ‒1 at 1 A g ‒1 , together with excellent long‐cycle stability. DFT reveals that Cu 4 SnS 4 has higher Fermi‐level DOS and a lower Zn 2+ diffusion barrier (0.06 eV) than Cu 2 SnS 3 (0.36 eV) and Cu 3 SnS 4 (0.25 eV) due to open orthorhombic channels, enhancing conductivity and Zn 2+ transport and accelerating conversion. This work correlates composition, structure, and performance, offering a paradigm for durable multimetallic sulfide anodes in practical RCZIBs.