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

Abstract 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.