Improving the durability of ion insertion materials in a liquid electrolyte

Abstract

Electrochromic (EC) devices fabricated with liquid or polymeric gel electrolyte are often less durable than those constructed with inorganic solid-state electrolyte. Long-term degradation of the ion insertion layer (with extensive cycling) by the liquid/gel electrolyte may contribute to this durability problem. In this respect, two V 2O 5 thin film electrodes were fabricated for extensive cyclic durability testing in a LiClO 4/propylene carbonate (PC) liquid electrolyte: One V 2O 5 film had no overlying coating while the other had a protective thin film of solid lithium ion-conducting LiAlF 4. The protected V 2O 5 exhibited improved durability in terms of constant capacity with repeated cycling up to 800 cycles, while the uncoated V 2O 5 electrode displayed significant capacity loss. Our results demonstrate that deposition of an inorganic solid electrolyte (LiAlF 4) on amorphous V 2O 5 films serves as a protective overlayer and enhances the long-term cycling efficiency and stability of the V 2O 5 in a liquid electrolyte.