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

The advancement of efficient ion storage film is a formidable challenge. A kind of self-doped V 4+ -V 2 O 5 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 V 2 O 5 nanofilm, that is, heterogeneous nucleation during hydrothermal method and the electrostatic attraction between V 2 O 5 sol and ITO substrate. A small amount of oxygen vacancies are introduced into V 2 O 5 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-V 2 O 5 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 V 2 O 5 film prepared by traditional sol-gel method with the same annealing treatment (17.88 mC cm −2 ) and V 2 O 5 film without annealing treatment (17.79 mC cm −2 ), 300 °C-V 2 O 5 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-V 2 O 5 nanofilm as ion storage layer and WO 3 as the electrochromic layer has been successfully assembled, which shows fascinating performance.