Electrochemistry of WO3 based smart windows: Beliefs and facts

WO₃ is believed to be the most stable electrochromic material, particularly in organic solvents. This paper deals with the effects of prolonged cycling around and below 2 V vs Li/Li⁺ in propylene carbonate/lithium triflate electrolyte. A dramatic loss of charge capacity was observed when the sample was cycled between 4.5 V and 1.6 V vs Li/Li⁺. This was not the case when the lower limit was set to 2.0 V vs Li/Li⁺. Spectrophotometric analysis showed that the charge capacity loss was not accompanied by presence of tungsten in the electrolyte or the counter electrode. SEM pictures show some electrode damage and precipitation at the electrode surface. A corrosion mechanism is suggested. Paper presented at the 4th Euroconference on Solid State Ionics, Renvyle, Galway, Ireland, Sept. 13–19, 1997.