Effect of pre-inserted monovalent cations on vanadium-based cathode materials for rechargeable aqueous zinc-ion batteries

Understanding the effect of pre-inserted cations in vanadium-based from a comprehensive perspective plays a vital role in exploring novel cathode materials for Zn-ion storage. In this work, we provide a study of monovalent cations (i.e., Na ⁺, K ⁺, and NH ₄ ⁺) on the Zn ²⁺ storage behaviors of proton-substituted vanadates (i.e., NaVO, KVO, and NH ₄VO), revealing the intrinsic property (e.g., hydration capacity, bonding strength) of monovalent ions has a significant impact on the amount of pre-inserted cations and crystal water in stacked V–O layers, as well as the morphology of the obtained products, and the structural evolution during the activated process. Due to the enhancement of the ion-diffusion kinetics and stronger capacitance properties from the synergistic effect by pre-inserted Na ⁺ ions and crystal water, the NaVO cathode exhibits superior rate performance and better energy efficiency (60.87 % at 10 A g ⁻¹), delivers a high specific capacity of 427.0 mAh g ⁻¹ at 0.2 A g ⁻¹ and retains 74.3 % of capacity after 1900 cycles at 2 A g ⁻¹. Moreover, the correlation between the pre-inserted cations in the cathode and the issues (e.g., side-products and dendrites) of the Zn anode has been revealed, providing new insight into designing high-performance cathodes for Zn ion batteries.