Role of Conducting Polymer in Aqueous Zinc Ion Batteries

Abstract

Owing to high safety and low cost, aqueous rechargeable zinc-ion batteries (ZIBs) is currently a major research topic. In this study, we propose the microwave-assisted hydrothermal synthesis of polypyrrole (PPy)-coated Na1.1V3O7.9 (P-NVO) nanorods for the first time as a highenergy and high-power cathode material for ZIBs. The highly conductive PPy surface-coating layer is significant to enhance the electronic conductivity and Zn2+ diffusion kinetics, leading to utilize the V3+/V4+/V5+ multiple redox reactions of the NVO cathode in ZIBs. Compared to the NVO cathode, therefore, the P-NVO cathode offers higher discharge capacity, power capability and cycling stability; in particular, PPy coating triggers the full theoretical capacity of the NVO cathode (527 mAh g- 1 with ~ 3 mol Zn insertion per formula unit) and directly reflects a superior energy density of 408 Wh kg-1. Even at a high current density of 6000 mA g- 1, the P-NVO cathode sustains 1000 cycles with almost 100% capacity retention. Galvanostatic intermittent titration technique, cyclic voltammetry, in situ X-ray diffraction, and ex situ X-ray absorption near edge structure analyses are combined to verify the superior Zn2+ storage mechanism of the P-NVO cathode.