3D-printed film architecture via automatic micro 3D-printing system: Micro-intersection engineering of V2O5 thin/thick films for ultrafast electrochromic energy storage devices

Existing approaches to develop electrochromic (EC) energy storage devices typically focus on the modification of active materials toward a porous morphology, crystallinity, heteroatom-doping, and hybridization/composites with functional materials; however, these approaches may be unsuitable for the full commercialization of EC energy storage devices owing to their complex and expensive processes and incompatibility with large-scale and mass production. Herein, we fabricate 3D-printed film architectures for ultrafast EC energy storage devices, including micro-intersections of vanadium oxide (VO) thin/thick films, via an automatic micro 3D-printing system without active material modification. The micro-intersection originates from the one-pot 3D-printing of vertical lines, creating VO grid-micropatterns with nanoscale thin/thick films on fluorine-doped tin oxide (FTO)/glass. The micro-intersection density was engineered by adjusting the number of printed-lines per unit area and optimized micro-intersection density (OD-3DVO) allows enhanced behaviors of electrons and Li-ions as follows: (i) the thin film architecture alleviates rate-limiting processes that produce sluggish electron transfer and ionic diffusion kinetics by shortening transport channels between FTO and the electrolyte, thereby accelerating ultrafast charge transport. (ii) Micro-width/nano-depth 3D-wells induce capillary force pumping and deep electrolyte infiltration at the interface, thereby enhancing electrolyte wettability. (iii) grid-micropatterned film morphology provides extensive redox sites and high visible transmissivity; thus, the OD-3DVO active layers in EC energy storage devices featured simultaneously enhanced optical and energy storage performances, especially ultrafast switching speeds (0.7 and 0.9 s for coloration and bleaching) and record-high areal energy density at high areal power density (14.03 µWh/cm2 at 25 mW/cm2).