Assisting Zn Storage in Layered Vanadyl Phosphate Cathode by Interactions with Oligoaniline Pillars for Rechargeable Aqueous Zinc Batteries

Abstract

Aqueous zinc batteries are promising energy storage devices owing to the high safety and low cost. The layered VOPO4·2H2O is a desired cathode material. However, it has not achieved satisfactory electrochemical performance. Herein, we report an in-situ intercalation-polymerization method to prepare the oligoaniline intercalated VOPO4 (OANI-VOPO4). Mechanism studies show that the oligoaniline pillars in the layers interact with inserted Zn2+ and reduce the binding by the lattice. The electron delocalization of oligoaniline further buffers the local charge change upon Zn2+ insertion. These factors promote the Zn storage behavior of OANI-VOPO4. In a medium concentration bi-salt electrolyte to suppress water induced side reactions, the OANI-VOPO4 cathode achieves 200 mAh g-1 capacity at 0.5 A g-1, superior to 135 mAh g-1 obtained with VOPO4·2H2O. OANI-VOPO4 also realizes 90% capacity retention after 2000 cycles, together with well-preserved charge/discharge voltage curves. The multi-electron redox reactions among VV/VIV/VIII are identified.

Keywords: aqueous zinc batteries, oligoaniline, Polyanion, pillars, multi-electron energy storage