High performance NiOx nanoplatelet based films by a scrape-coating method for bifunctional electrochromic and energy storage devices

Abstract

Nickel oxide (NiO_x) is considered a promising candidate for constructing complementary electrochromic devices with tungsten oxide. However, the low electrochromic performance of NiO films has been a hindrance to its practical applications. In this study, crystal oriented NiO_x nanoplatelets with nickel vacancies were prepared using a facile chemical precipitation method and scrape-coated onto FTO substrates. The morphology and electrochromic properties of the obtained porous films can be controlled by adjusting the amount of polyethylene glycol in the slurry. The films exhibit an outstanding optical modulation range (63.09%), fast switching speed (1.7 s for colouring/1.5 s for bleaching) and high colouration efficiency (83.8 cm² C⁻¹) using propylene carbonate/LiClO₄ as an electrolyte. The films also present superior cycling stability, maintaining 95% of the original optical modulation after 1000 cycles, as well as high colouring efficiency (45.12 cm² C⁻¹) and good reversibility. The correlation between the Ni vacancy formation and crystal facets of the NiO_x was illuminated based on density functional theory (DFT) simulation. Furthermore, the electrochromic devices (ECDs) and flexible films of NiO_x were fabricated in addition, and electrochromic devices were prepared to demonstrate their electrochromic/energy storage bifunctionality and low temperature annealing properties, which can open up applications in wearable/energy storage devices and flexible displays. In addition, the ease and high efficiency of the scrape-coating technique makes it possible to commercially produce high performance electrochromic NiO_x nanoplatelet films.