Structural engineering of potassium vanadate cathode by pre-intercalated Mg²⁺ for high-performance and durable rechargeable aqueous zinc-ion batteries

Aqueous zinc (Zn)-ion batteries (AZIBs) have the potential to be used in massive energy storage owing to their low cost, eco-friendliness, safety, and good energy density. Significant research has been focused on enhancing the performance of AZIBs, but challenges persist. Vanadium-based oxides, known for their large interlayer spacing, are promising cathode materials. In this report, we synthesize Mg²⁺-intercalated potassium vanadate (KVO) (MgKVO) via a single-step hydrothermal method and achieve a 12.2 Å interlayer spacing. Mg²⁺ intercalation enhances the KVO performance, providing wide channels for Zn²⁺, which results in high capacity and ion diffusion. The combined action of K⁺ and Mg²⁺ intercalation enhances the electrical conductivity of MgKVO. This structural design endows MgKVO with excellent electrochemical performance. The AZIB with the MgKVO cathode delivers a high capacity of 457 mAh g^-1 at 0.5 A g^-1, excellent rate performance of 298 mAh g^-1 at 5 A g^-1, and outstanding cycling stability of 102% over 1300 cycles at 3 A g^-1. Additionally, pseudocapacitance analysis reveals the high capacitance contribution and Zn²⁺ diffusion coefficient of MgKVO. Notably, ex-situ X-ray diffraction, X-ray photoelectron spectroscopy, and Raman analyses further demonstrate the Zn²⁺ insertion/extraction and Zn-ion storage mechanisms that occurred during cycling in the battery system. This study provides new insights into the intercalation of dual cations in vanadium oxides and offers new solutions for designing cathodes for high-capacity AZIBs.