H⁺-empowered potassium vanadate cathode: An electron/ion/interface trifecta for high-performance zinc-ion batteries

Aqueous zinc-ion batteries are promising for large-scale storage due to low cost and great performance. Particularly, layered vanadium-based materials are appealing owing to their excellent capacity and diverse energy storage mechanisms. In here, potassium vanadate excluding/including H (K₂V₆O₁₆·1.57H₂O (KVO)/HKVO) are successfully synthesized to investigate the influence of H⁺ on its structural characteristics and electrochemical performance. DFT calculations indicate that HKVO achieves enhanced electrical conductivity and ion transport kinetics through the substitution of K with H atoms, which induces localized electronic and structural rearrangements, including narrowed band-gap, bond-length distortion and ion-channel expansion. Furthermore, the presence of H ions confers HKVO with a higher water molecule adsorption energy at the hydrogen sites and improved electrolyte wettability, which enhanced contact at the cathode/electrolyte interface and ion exchange and transport. Moreover, unlike KVO, release of structural H ions in HKVO activates the deintercalation from the host lattice, and intercalation from the electrolyte. This process drastically enhances ionic kinetics in the low-voltage region. Consequently, the HKVO shows a high capacity of 669.4 mAh g^-1 at a 0.1 A g^-1, retaining over 93.2 % capacity for 5000 cycles at 5 A g^-1, demonstrating the potential of H⁺ in regulating the cathode structure and performance of zinc-ion batteries.