Cation pre-inserted vanadium oxide nanobelts as multicolor electrochromic materials for adaptive camouflage

V₂O₅ is a promising electrochromic material for adaptive camouflage or electronic display. However, it is still challenging to enable fast response time, multicolor change and good cyclic stability. In this paper, we successfully synthesized different cation (NH₄⁺, K⁺ and Na⁺) pre-inserted vanadium oxide nanobelt films (NVO, KVO and NaVO) by stirring impregnation method. All nanobelts are composed of V₃O₈ layers with hydrated cations acting as pillars in the interlayer, exhibiting excellent electrochromic properties and remarkable multicolor changes. Among them, the NVO nanobelt films have the highest transmittance modulation (ΔT = 54 % at 510 nm and ΔT = 56 % at 950 nm), fastest response time (4.4 s for coloration time, 5.5 s for bleaching time at 422 nm and 6.8 s for coloration time and 7.7 s for bleaching time at 950 nm) and best stability (3000 cycles). Impressively, the NVO film is highly reversible between five colors: orange-red, orange, yellow, green and blue-grey, showing great breakthrough in adaptive camouflage application.