Ultrafast, Stable Electrochromics Enabled by Hierarchical Assembly of V 2 O 5 @C Microrod Network.

Vanadium pentoxide (V 2 O 5 ) with multicolor transition is widely studied in the electrochromic (EC) field to enrich color species of transition-metal oxides; yet, it always suffers from slow switching speed caused by poor electron conductivity and slow ion diffusion, poor cycling stability induced by large volume change during the EC reaction process. Herein, hierarchical network assembly of V 2 O 5 @C microrods is introduced to develop an ultrafast, stable, multicolor EC film. Using a two-step pyrolysis that involves metal-organic framework templates, porous microrods with a well-preserved one-dimensional structure are prepared through the assembly of V 2 O 5 @C nanocrystals at nanoscale, providing more active sites for ionic insertion and accessible pathways for electron transport. After spray-coating the V 2 O 5 @C microrods on conductive substrates, interconnected networks composed of V 2 O 5 @C microrods at microscale ensures the infiltration of electrolyte and provide ion transport channels. In addition, the nanoscale porous structure and coated carbon layer can accommodate volumetric changes during ion insertion/extraction process, ensuring high electrochemical stability. As a result, EC electrode with V 2 O 5 @C microrods network performed rapid switching speed (1.1/1.0 s) and stable cycle ability (96% after 2000 cycles). At last, flexible large-scale devices and multicolor digital displays were assembled to demonstrate potential application in next-generation wearable electronics.