Rechargeable aqueous zinc-ion batteries (ZIBs) have gained extensive attention owing to the high safety, low cost, and high power/energy densities. But unfortunately the ZIBs universally suffer from the highly damaging series of side reactions, majorly including the insulating products formation, dendritic growth of zinc, and hydrogen evolution. To date there are few reports on the effective strategy that can solve the problems at the same time. Here we propose a novel hybrid electrolyte with Al³⁺ as additive to construct an aqueous ZIB composed of metallic zinc anode and K_0.51V₂O₅ (KVO) nanoplate cathode. The highly reversible multistep K⁺/Zn²⁺-ions co-insertion/extraction in the lamellar structure with large interlayer spacing is clearly evidenced by systematical characterizations. In the presence of Al³⁺, the insulating basic zinc salts on the cathode surface have been reduced greatly, and the electrochemical potential window has been significantly expanded from 3 to 4.35 V. More interestingly, the Al³⁺ acts as a dopant embedded into the lattice that strengthens the crystal structure. Benefits from the suppressed zinc dendrite growth, the symmetrical Zn/Zn battery exhibited a satisfactory cycling life over 1,500 h at a high rate of 3 mA·cm^–2 in the hybrid electrolyte. As a result, the Zn/KVO batteries delivered a high specific capacity of 210 mAh·g^–1 and retained high capacity retention of 91% after 1,600 h at a low current of 100 mA·g^–1.

How to effectively improve Zn²⁺-storage properties is now becoming an urgent issue in the development of high-energy-density aqueous zinc-ion batteries. Here, a new method is proposed to massively increase the electrochemical capacity of aqueous Zn/V₅O₁₂·6H₂O batteries. By adding a small amount of platinum (Pt, 1.5 wt.%) and keeping other factors constant, the V₅O₁₂·6H₂O-Pt electrodes deliver a much higher specific capacity (440 mAh g⁻¹ at 500 mA g⁻¹) than do V₅O₁₂·6H₂O electrodes (270 mAh g⁻¹ at 500 mA g⁻¹). The structural and morphological evolution of V₅O₁₂·6H₂O during cycling results in Zn²⁺ ion insertion/extraction and the formation/disappearance of the zinc hydroxyl complex (Zn₄SO₄(OH)₆∙5H₂O, ZHS), where the latter is closely related to the surface redox reaction, promoting Zn²⁺ ion stripping/plating on the Zn anode and consequently leading to extra electron transfer. Electrochemical tests in the absence of oxygen reveal that the Pt additive has no contribution and is even counterproductive to electric conductivity but favors remarkable enhancement of the pseudocapacitance. Accordingly, it is apparent that a strong causal relationship exists between Pt and the ZHS. In consideration of the catalytic application for oxygen reduction, Pt is expected to play a vital role in enhancing the electrochemical capacity through the pseudo-Zn-air reaction. This finding introduces a new strategy for achieving high-performance aqueous zinc-ion batteries.