Fe-doped VO₂ as a high-rate and long-life cathode for aqueous zinc-ion batteries

Abstract

Rechargeable aqueous zinc ion batteries (AZIBs) have been recognized as an attractive choice for future large-scale energy storage systems because of their excellent theoretical capacities, high safety level, environmental sustainability, and inexpensive cost. Despite these advantages, most cathode material still suffers from a fundamental trade-off between fast charge-discharge kinetics and long-term electrochemical stability, which limits their rate capability and cyclic durability. As one among several choices, VO2 is highly valued because of the open tunnel-like structure of this compound which allows ions intercalation/ de-intercalation, coupled with its high reversible capacity. Unfortunately, their further use has become limited owing to the inherently poor conductivity of Zn2+ and sluggish diffusion dynamics of Zn2+. In this work, Fe ions are introduced into VO2 via simple one step hydrothermal method. Incorporating Fe ions into the structure lowers the diffusion barrier for Zn 2+ ions, making their insertion and extraction more efficient. The nanoroad morphology structure increases the available surface area, allowing more active sites for electrochemical reaction. DFT results indicate that dopant incorporation modifies the electronic structure by introducing states near the fermi level and reducing band gap. As a result, the Fe-VO2 electrode delivers strong electrochemical performance, with a high initial capacity of 380.11mAhg-1 at 0.1 Ag-1, good rate capability of 275.97mAhg-1 at 5Ag-1 and cyclic stability with 82.75% retention capacity after 500 cycles at 2Ag-1. These results show that using a cost-effective dopant can be a practical and efficient way for developing high performance VO2 cathodes towards AZIB.