De-Ammonium Ba_0.18V₂O_4.95/NH₄V₄O₁₀ Film Electrodes as High-Performance Cathode Materials for Magnesium-Ion Batteries

Magnesium-ion batteries (MIBs) have been pushed into the research boom in the post-lithium-ion batteries era due to their low cost, no dendrite hazard, and high capacity. However, finding suitable cathode materials to improve the slow kinetics of Mg²⁺ is an ongoing challenge. In this work, Ba_0.18V₂O_4.95/NH₄V₄O₁₀ film electrodes were grown in one step on indium tin oxide (ITO) conductive glass using a low-temperature liquid-phase deposition method. Temperature was used as the probe condition, and it was concluded that the films annealed at 400 °C had suitable crystallinity and de-ammonium lattice space. At lower current density, with 0.5 M Mg(ClO₄)₂/PC as the electrolyte, it exhibited an initial discharge capacity of 130.99 mA h m^-2 at 210 mA m^-2 and 106.52% capacity retention after 100 cycles. In addition, it exhibited excellent electrochemical performance in long-term cycling (92.98% capacity retention after 300 cycles at 600 mA m^-2). According to the results of ex situ X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and high-resolution transmission electron microscopy (HRTEM), the removal of NH₄⁺ created more lattice space, assisting Ba_0.18V₂O_4.95 to increase the transfer channels of Mg²⁺, providing more active sites to promote diffusion kinetics (the average D_Mg²⁺ was 2.07 × 10^-12 cm² s^-1) and specific capacity. Therefore, these film electrodes for scalable Mg²⁺ storage are promising MIB cathode candidates that exhibit good performance advantages in storage applications.