Fluorinated Interphase Enables Reversible Zn²⁺ Storage in Aqueous ZnSO₄ Electrolytes

Abstract

Aqueous zinc-ion batteries (AZIBs) using ZnSO4 aqueous electrolytes complement Li-ion batteries and offer high safety, low cost, and scalability. However, an inferior cycle life, attributed to the generation of basic layered double hydroxides (LDHs) on the cathode during cycling, hampers the development of AZIBs. Although Zn(CF3SO3)2 (Zn(OTf)2) electrolytes demonstrate exceptional performance, their higher cost in comparison to ZnSO4 offsets their electrochemical stability benefits. Toward this end, we propose a fluorinated interphase strategy to achieve a stable battery with ZnSO4 electrolytes by in situ pre-constructing the cathode–electrolyte interphase (CEI) of ZnOTf-LDH on the cathode surface. Unlike ZnSO4-LDH, which obstructs the diffusion channel of zinc ions, ZnOTf-LDH facilitates the desolvation of zinc ions, thereby enhancing the cycling stability (over 50 cycles at a low current density of 200 mA g–1). This work offers valuable insights into the degradation mechanism of AZIBs and provides an effective approach for developing stable and low-cost AZIBs.