Engineering a Multi-functional Interphase for Enhanced Performance of Vanadium Oxide Cathodes in Aqueous Zinc-ion Batteries

Abstract

Aqueous zinc-ion batteries (AZiBs) are promising next-generation secondary batteries for grid-scale energy storage systems (ESSs) owing to their low cost, high safety, and sustainability. Furthermore, AZiBs stand out for high energy densities, resulting from the low reduction potential (-0.76 V vs. SHE) and the high theoretical volumetric capacity (5854 mAh cm-3) of zinc metal anodes. However, the electrochemical performance of batteries is determined by the cathodes. Among the various cathode candidates for AZiBs, vanadium oxides with layered structures feature high specific capacities (~400 mAh g-1 in AZiBs). Nevertheless, vanadium oxides suffer from dissolution and subsequent phase transition to electrochemically inactive zinc pyrovanadates (Zn3V2O7(OH)2∙nH2O, ZVO) in aqueous electrolytes, disrupting the charge/discharge cycle and causing rapid capacity fading. To solve these problems, various strategies have been suggested, such as material engineering and electrolyte modulation to improve the material robustness or mitigate the water activity. Benefiting from these tremendous efforts, long-term cyclability at high current densities has been achieved. However, poor cycling stability at low current densities still occurs, which implies that the direct contact between vanadium oxide and water molecules has not been completely mitigated, limiting their practical applications. In this work, we propose a dual-engineering strategy that integrates structural engineering of lithium-intercalated vanadium oxide (LVO) with an in-situ formed multi-functional cathode electrolyte interphase (CEI). Pyrrole monomers are introduced as an electrolyte additive and electrochemically polymerized on the LVO electrode surface during the initial cycles, forming a uniform polypyrrole CEI. This interphase suppresses vanadium dissolution by blocking direct contact with water and simultaneously reinforces V–O bonding through electron donation. Moreover, the high electronic conductivity of the CEI facilitates rapid charge transfer and Zn2+ ion diffusion, leading to enhanced long-term cycling stability and high capacity even at a high current density of 10 A g-1.