High-performance self-doped V4+-V2O5 ion storage films grown in situ using a novel hydrothermal-assisted sol-gel composite method

Abstract

The advancement of efficient ion storage film is a formidable challenge. A kind of self-doped V4+-V2O5 ion storage nanofilm on ITO-coating glass substrate is prepared in situ by a novel hydrothermal-assisted sol-gel composite method, which is without seed layers of hydrothermal process and additives of traditional sol-gel method. There are two important factors for the growth of V2O5 nanofilm, that is, heterogeneous nucleation during hydrothermal method and the electrostatic attraction between V2O5 sol and ITO substrate. A small amount of oxygen vacancies are introduced into V2O5 lattice during the hydrothermal process, and the oxygen vacancy concentration is controlled by annealing treatment (200∼400 °C), which significantly improve the storage capacity and Li+ diffusion. The excellent cycling performance of 300 °C-V2O5 nanofilm is attributed to the synergistic effect of the gradient oxygen vacancies and the good bonding force between the film and the substrate. Comparing with the ion storage capacity of V2O5 film prepared by traditional sol-gel method with the same annealing treatment (17.88 mC cm−2) and V2O5 film without annealing treatment (17.79 mC cm−2), 300 °C-V2O5 film has the highest ion storage performance, whose initial value of ion storage is up to 112.25 mC cm−2 and cycling stability is excellent with only a 2.4% decrease after 2000 cycles. The electrochromic device (ECD) with 300 °C-V2O5 nanofilm as ion storage layer and WO3 as the electrochromic layer has been successfully assembled, which shows fascinating performance.