Revealing the role of calcium ion intercalation of hydrated vanadium oxides for aqueous zinc-ion batteries

Exploring suitable high-capacity V2O5-based cathode materials is essential for the rapid advancement of aqueous zinc ion batteries (ZIBs). However, the typical problem of slow Zn2+ diffusion kinetics has severely limited the feasibility of such materials. In this work, unique hydrated vanadates (CaVO, BaVO) were obtained by intercalation of Ca2+ or Ba2+ into hydrated vanadium pentoxide. In the CaVO//Zn and BaVO//Zn batteries systems, the former delivered up to a 489.8 mAh g−1 discharge specific capacity at 0.1 A g−1. Moreover, the remarkable energy density of 370.07 Wh kg−1 and favorable cycling stability yard outperform BaVO, pure V2O5, and many reported cathodes of similar ionic intercalation compounds. In addition, pseudocapacitance analysis, GITT tests, and Trasatti analysis revealed the high capacitance contribution and Zn2+ diffusion coefficient of CaVO, while an in-depth investigation based on EIS elucidated the reasons for the better electrochemical performance of CaVO. Notably, ex-situ XRD, XPS, and TEM tests further demonstrated the Zn2+ insertion/extraction and Zn-storage mechanism that occurred during the cycle in the CaVO//Zn battery system. This work provides new insights into the intercalation of similar divalent cations in vanadium oxides and offers new solutions for designing cathodes for high-capacity aqueous ZIBs.