Analysis of structural morphological changes from 3DOM V2O5 film to V2O5 nanorods film and its application in electrochromic device

Nanoscale V2O5 films possess excellent electrochemical properties and have great potential for application in electrochromic devices. Herein, we report a novel strategy for the transformation of three-dimensionally ordered macroporous(3DOM) V2O5 films into V2O5 nanorods film using a simple low-temperature annealing treatment, in which the heterogeneous nucleation sites provided by PS colloidal sphere surface, the anisotropic bonding of V2O5, atomic rearrangement, and Ostwald ripening are all important factors affecting the morphological transformation. According to this study, during the preparation of 3DOM V2O5 films, a small number of oxygen vacancies were introduced into the V2O5 lattice, and the annealing treatment (250–400 °C, 4–8 h) controlled the concentration of oxygen vacancies. Compared with the ion storage capacity of V2O5 films prepared by conventional sol-gel dip-coating method (17.79 mC cm−2 for unannealed V2O5 films and 13.90 mC cm−2 for V2O5 films after 6 h of annealing at 350 °C), the 350°C-6h films with nanorod structure had the highest ion-storage performance, the initial value raised to 98.77 mC cm−2. Further, the cycling stability was excellent, with only a 6.1% decrease after 5000 cycles. This was because of the special nanorod structure and the presence of a certain number of gradient oxygen vacancies in the 350°C-6h film. The 350°C-6h film also had good electrochromic properties, a wide range of transmittance modulation (73.6%), and a fast response time (3.2 s for coloring and 3.9 s for bleaching). In addition, electrochromic devices (ECDs) with 350°C-6h films as both ion-storage layers and electrochromic layers have been successfully assembled, which exhibit high performance.