Thick CeO_2-TiO_2 sol-gel coatings for Li-ion storage electrode in electrochromic devices

摘要

CeO_2-TiO_2 sol-gel coatings are well known as Li-ion storage electrode in electrochromic (EC) devices of the form glass/ TE/ WO_3/ electrolyte/ CeO_2-TiO_2/ TE/ glass (TE: transparent electrode, e.g. SnO_2:F, FTO). The charge capacity of the CeO_2-TiO_2 coating is a limiting factor to get a high coloration intensity of such devices. In order to improve the charge capacity of these electrodes, new routes for the preparation of thick porous CeO_2-TiO_2 sol-gel layers were tested. One route was the preparation of thick porous TiO_2 coatings on a conducting glass support (FTO) using a solution of colloidal TiO_2 particles. After heat treatment at temperatures up to 550℃ the coatings were soaked in a solution of a cerium-Ⅳ (Ce(NH_4)_2(NO_3)_6) or a cerium-Ⅲ salt (Ce(NO_3)_3 6H_2O) and heat treated again. Another route was the preparation of sols by mixing a solution of the cerium-Ⅳ or the cerium-Ⅲ salt or a colloidal CeO_2-sol with the colloidal solution of TiO_2. After dip coating on FTO-glass the coatings were also heat treated at temperatures up to 500℃. All these coatings were studied electrochemically in 1 M LiClO_4 in propylene carbonate electrolyte. Although thick porous single coatings could be obtained, typically 450 nm for TiO_2 and 600 nm for cerium-titanium oxide, the intercalated and deintercalated Li~+ charges remain small and lie in the range of 2 mC/cm~2 to 3 mC/cm~2. The reasons for such low charge capacity is discussed.