A hydrothermal-assisted sol–gel method for microstructure manipulation of Mg–Mo co-doped V2O5 films toward enhanced electrochromic properties

Abstract

Mg–Mo co-doped V₂O₅ ion storage films were prepared via a hydrothermal-assisted sol–gel method. The effects of the Mg–Mo ratio and heat treatment temperature on their microstructure and electrochromic properties were investigated. When the total Mg–Mo co-doping amount was 10 mol%, the 2Mg8Mo–V₂O₅ film (2 mol% Mg and 8 mol% Mo) exhibited the optimal comprehensive performance. It achieved an ion storage capacity of 135.97 mC cm⁻², a coloring/bleaching response time of 5.4/5.0 s, a capacity decay rate of 13.79% after 2000 CV cycles, and an optical modulation range (ΔT) of 60.1%, all significantly outperforming those of pure V₂O₅ and single-doped 10Mg–V₂O₅/10Mo–V₂O₅ films. Mo⁶⁺ activated more active sites for Li⁺ insertion/extraction, while 2 mol% Mg²⁺ optimized the V₂O₅ lattice spacing, exerting a synergistic enhancement effect; excessive Mg²⁺ inhibited performance by occupying active sites or causing lattice distortion. Among heat treatment temperatures, 350 °C was optimal for 2Mg8Mo–V₂O₅ films. This temperature promoted high crystallinity, a regular layered structure, and uniform interlayer gaps, reducing defects and ion diffusion resistance. The film's Li⁺ oxidation/reduction diffusion coefficients (5.13 × 10⁻⁸/5.83 × 10⁻⁸ cm² s⁻¹) were significantly higher than those at 300 °C (insufficient crystallization) and 400 °C (excessive grain growth). The 2Mg8Mo–V₂O₅ film with optimal parameters (Mg : Mo = 2 : 8, 350 °C heat treatment) has excellent ion storage and optical properties, making it suitable as a high-performance ion storage layer for electrochromic glass.