Aqueous rechargeable zinc-ion batteries (ZIBs) have garnered considerable attention due to their safety, cost-effectiveness, and eco-friendliness. There is a growing interest in finding suitable cathode materials for ZIBs. Layered vanadium oxide has emerged as a promising option due to its ability to store zinc ions with high capacity. However, the advancement of high-performance ZIBs encounters obstacles such as sluggish diffusion of zinc ions resulting from the high energy barrier between V₂O₅ layers, degradation of electrode structure over time and consequently lower capacity than the theoretical value. In this study, we investigated the pre-doping of different cations (including ${\mathrm{N}\mathrm{a}}^{+}$, ${\mathrm{K}}^{+}$, and ${\mathrm{N}\mathrm{H}}_4^{+}$) into V₂O₅ to enhance the overall charge storage performance. Our findings indicate that the presence of V⁴⁺ enhances the charge storage performance, while the introduction of ${\mathrm{N}\mathrm{H}}_4^{+}$ into V₂O₅ (NH₄-V₂O₅) not only increases the interlayer distance (d₍₀₀₁₎ = 15.99 Å), but also significantly increases the V⁴⁺/V⁵⁺ redox couple (atomic concentration ratio increased from 0.14 to 1.08), resulting in the highest electrochemical performance. The NH₄-V₂O₅ cathode exhibited a high specific capacity (310.8 mAh·g^–1 at 100 mA·g^–1), improved cycling stability, and a significantly reduced charge transfer resistance (~ 17.9 Ω) compared to pristine V₂O₅ (112.5 mAh·g^–1 at 0.1 A·g^–1 and ~ 65.58 Ω charge transfer resistance). This study enhances our understanding and contributes to the development of high-capacity cathode materials, offering valuable insights for the design and optimization of cathode materials to enhance the electrochemical performance of ZIBs.

The non-noble metal (Fe, Co, Ni, etc.) catalysts possess promising potential to replace noble metals (e.g., Pt, Ru, Ir, etc.) as catalysts for oxygen electrocatalysis. Up to now, various mono- and dual-single-atom catalysts have been fabricated, though it is still challenging to synthesise ternary single-atom catalysts due to the difference of interaction forces between different metal ions (Fe, Co, Ni, etc.) and ligands. Here, we report a Fe-Co-Ni ternary single-atom catalyst (FeCoNi-N_x) derived from a zeolitic imidazolate frameworks (ZIF) precursor as an efficient oxygen electrocatalyst, and an optimised flexible casting-drying polyvinyl alcohol (CD-PVA) film as a quasi-solid electrolyte host, for high-efficiency solid-state Zn-air batteries. The aberration-corrected HAADF-STEM and EELS spectrum confirm the co-existence of Fe, Co and Ni single atoms in the FeCoNi-N_x catalyst, and the electrochemical, mechanical, and durability tests prove the superiority of the CD-PVA film. As a result, the FeCoNi-N_x-based rechargeable Zn-air battery delivers superior specific capacity (846.8 mAh·g_Zn^–1) and power density (135 mW·cm^–2) in aqueous electrolyte, as well as an over 60 mW·cm^–2 power density in quasi-solid electrolyte. As a result, the quasi-solid-state Zn-air battery with a small area of only 2 cm² is able to charge a mobile phone, which outperforms all the reported devices to date.