Unveiling Intercalation Chemistry via Interference-Free Characterization Toward Advanced Aqueous Zinc/Vanadium Pentoxide Batteries.

Aqueous Zn/VO batteries are featured for high safety, low cost, and environmental compatibility. However, complex electrode components in real batteries impede the fundamental understanding of phase transition processes and intercalation chemistry. Here, model batteries based on VO film electrodes which show similar electrochemical behaviors as the real ones are built. Advanced surface science characterizations of the film electrodes allow to identify intercalation trajectories of Zn, HO, and H during VO phase transition processes. Protons serve as the vanguard of intercalated species, facilitating the subsequent intercalation of Zn and HO. The increase of capacity in the activation process is mainly due to the transition from VO to more active VO·nHO structure caused by the partial irreversible deintercalation of HO rather than the increase of active sites induced by the grain refinement of electrode materials. Eventually, accumulation of Zn species within the oxide electrode results in the formation of inactive (Zn(OH)VO·2HO) structure. The established intercalation chemistry helps to design high-performance electrode materials.