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.