A Synergistically Regulated Cathode/Electrolyte Interphase With High Stability and Rapid Zn²⁺ Migration Toward Advanced Flexible Zinc‐Ion Batteries

Na₃V₂(PO₄)₃(NVP), as a representative sodium superionic conductor with a stable polyanion framework, is considered a cathode candidate for aqueous zinc-ion batteries attributed to their high discharge platform and open 3D structure. Nevertheless, the structural stability of NVP and the cathode-electrolyte interphase (CEI) layer formed on NVP can be deteriorated by the aqueous electrolyte to a certain extent, which will result in slow Zn²⁺ migration. To solve these problems, doping Si elements to NVP and adding sodium acetate (NaAc) to the electrolyte are utilized as a synergistic regulation route to enable a highly stable CEI with rapid Zn²⁺ migration. In this regard, Ac^- competitively takes part in the solvation structure of Zn²⁺ in aqueous electrolyte, weakening the interaction between water and Zn²⁺, and meanwhile a highly stable CEI is formed to avoid structural damage and enable rapid Zn²⁺ migration. The NVPS/C@rGO electrode exhibits a notable capacity of 115.5 mAh g^-1 at a current density of 50 mA g^-1 in the mixed electrolyte (3 M ZnOTF₂+3 M NaAc). Eventually, a collapsible "sandwich" soft pack battery is designed and fabricated and can be used to power small fans and LEDs, which proves the practical application of aqueous zinc-ion batteries in flexible batteries.