Thick CeO 2 -TiO 2 sol-gel coatings for Li-ion storage electrode in electrochromic devices

Abstract

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°C 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 2 O) and heat treated again. Another route was the preparation of sols by mixing a solution of the cerium-IV or 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°C. ALl these coatings were studied electrochemically in 1 M LiC1O 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 deintercalcated 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.