Electrochromic properties of lithiated Co-oxide (LixCoO2) and Ni-oxide (LixNiO2) thin films prepared by the sol–gel route
Affiliation:
National Institute of Chemistry, SI-1000 Ljubljana, Hajdrihova 19, Slovenia
Abstract:
Layered LixCoO2 and LixNiO2 thin films (x1) were prepared by a peroxo wet chemistry route from Li(I), Co(II) and Ni(II) acetate precursors and the addition of H2O2. Structural changes during the processing of xerogel to final oxide were followed by X-ray diffraction and infrared spectroscopy. Electrochromic properties were determined with in-situ potentiodynamic, potentiostatic and galvanostatic spectroelectrochemical measurements. Single dipped films with composition Li0.99Co1.01O2 or Li0.94Ni1.06O2 exhibited stable voltammetric response in 1 M LiClO4/propylene carbonate electrolyte after about 60 cycles. The total charge exchanged in a reversible charging/discharging cycle was about ±30 mC cm?2 for Li0.99Co1.01O2 and ±20 mC cm?2 for Li0.94Ni1.06O2 oxide films. Galvanostatic measurements showed that about 1/2 (x0.5) and 2/3 (x0.3) of Li+ ions could be reversibly removed from the structure of Li0.99Co1.01O2 and Li0.94Ni1.06O2 films, respectively. Practical applicability of Li0.99Co1.01O2 and Li0.94Ni1.06O2 oxide films was studied in electrochromic devices with WO3(H+)Li+ormolyteLi0.99Co1.01O2 and WO3(H+)Li+ormolyteLi0.94Ni1.06O2 configuration. The monochromatic transmittance Ts (λ=633 nm) of dark blue coloured devices was extremely low (Ts3%), whereas in bleached state the value reached around Ts70%.