Electrochromic properties of lithiated co-oxide (LixCoO2) and Ni-oxide (LixNiO2) thin films prepared by the sol-gel route

Layered LixCoO2 and LixNiO2 thin films (x similar to 1) 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 xero gel to final oxide were followed by X-ray diffraction and infrared spectros copy. Electrochromic properties were determined with in-situ potentiodynami c, potentiostatic and galvanostatic spectroelectrochemical measurements. Si ngle dipped films with composition Li0.99Co1.01O2 or Li0.94Ni1.06O2 exhibit ed stable voltammetric response in 1 M LiClO4/propylene carbonate electroly te after about 60 cycles. The total charge exchanged in a reversible chargi ng/discharging cycle was about +/-30 mC cm(-2) for Li0.99Co1.01O2 and +/-20 mC cm(-2) for Li0.94N1.06O2 oxide films. Galvanostatic measurements showed that about 1/2 (x similar to 0.5) and 2/3 (x similar to 0.3) of Li ions co uld be reversibly removed from the structure of Li0.99Co1.01O2 and Li0.94Ni 1.06O2 films, respectively. Practical applicability of Li0.99Co1.01O2 and L i0.94Ni1.06O2 oxide films was studied in electrochrornic devices with WO(3) parallel to(H+)Li(+)ormolyte parallel to Li0.99Co1.01O2 and WO(3)parallel t o(H+)Li(+)ormolyte parallel to Li0.94Ni1.06O2 configuration. The monochroma tic transmittance T-s (lambda = 633 nm) of dark blue coloured devices was e xtremely low (T-s similar to 3%), whereas in bleached state the value reach ed around T-s similar to 70%. (C) 2000 Elsevier Science Ltd. All rights res erved.