Electrochromic effect in thin film electrode of lithium ion intercalation: material and crystallinity influences by W, Mo, V oxide and their binary mixtures

Full text: Currently, due to the phenomenon of global warming and the clear need for sustainability in the transformations created by human beings, there is a great demand for devices that generate clean power and minimize the negative environmental effects [1]. In this context, ion intercalation materials have great potential for use in technological devices such as high energy densities rechargeable batteries and micro batteries and in electrochromic devices to control and modulate inner solar radiation intensity. Results of electrochromic effect due to the intercalation of lithium ions into thin film electrodes of the V, W and Mo oxides as well in three of their binary mixtures (50/50), as-deposited and annealed in 200 and 500 deg C, are reported in this work. The oxide films were deposited by reactive magnetron sputtering. The electrochemical measurements were performed in a three electrodes electrochemical cell, whose work electrodes were the studied oxide films and wires of metallic lithium were used as reference and auxiliary electrodes. The electrolyte employed was a 1,0 mol.L^-1 solution of lithium perchlorate in propylene carbonate. The oxide crystalline structures were analyzed from x-ray diffraction measurements (Cu(Kα) radiation) and the opto-electrochemical characterization was performed by chronopotentiometry (CP) and chronoamperometry (CA) techniques with in situ transmittance measurements at 632.8 nm. These measurements supplied both the electrochromic efficiency and response time to lithium intercalation. X-ray diffraction measurements, identified the as-deposited as well the heat treated films at 200 deg C as amorphous and as polycrystalline the films treated at 500 deg C. The highest electrochromic efficiencies were obtained for W oxide and its mixtures treated at 500 deg C, with values around 30 cm² /C. Regarding the response time of the pure films showed low values, being optimized when treated at 500 deg C. Reference: [1] C.G. Granqvist et al. Thin Solid Films 518 (2010) 3046. (author)