Layered VOPO₄ as a Cathode Material for Rechargeable Zinc-Ion Battery: Effect of Polypyrrole Intercalation in the Host and Water Concentration in the Electrolyte

Rechargeable zinc-ion batteries (RZIB) present an interesting alternative to rechargeable Li-ion batteries. Among the active materials, layered vanadium-based oxides show a poor cell voltage but modifying this structure by attaching a phosphate group to the vanadium redox center can drastically enhance the cathode voltage. With this layered VOPO₄ material, we demonstrate that preintercalating polypyrrole between crystallographic layers and using electrolyte with controlled water amounts are two absolutely essential conditions for easy and reversible Zn²⁺ (de)intercalation, thus vastly improving battery outputs and long-term capacity retention. We establish that the rational design of open-layered structures hinges imperatively on factors like host structural integrity and electrode-electrolyte compatibility in delivering the performance of multivalent-ion batteries.