Designing V2O5/MXene van der Waals heterostructure for complementary electrochromic dual-ion capacitor

Developing highly efficient electrochromic energy storage device (EESD) is desirable for yielding ample color variation and large electrochemical capacity from the viewpoint of practical energy-saving. However, only a single type of cation or anion traveled back and forth between the cathode and anode in conventional electro-chromic devices (ECDs) results in low coloration efficiency and long switching time. Herein, for the first time, we designed a multicolor complementary electrochromic dual-ion capacitor (EDIC) based on ion insertion/extraction and doping/de-doping of the anodic and cathodic electrochromic materials, respectively, to realize the fast faradic reaction and rich color variation. Significantly, the prepared V2O5/MXene van der Waals heterostructure with improved conductivity and more "active" sites favors the charge transfer, effectively improving the switching speed and coloration efficiency. Since the excellent ion matching and synergy effect of Li+ insertion/ extraction in V2O5/MXene anode and ClO4- doping/de-doping at PANI/TiO2 cathode, the complementary EDIC exhibits significant color changes, large optical modulation (51%), short switching time (2.4/7.2 s) and high coloration efficiency (111 cm2 C-1), which is much superior to traditional V2O5-based ECDs. We believe that this work provides a general strategy for building a complementary EDIC with excellent electrochromic and energy storage performances.