Improving the durability of ion insertion materials in a liquid electrolyte

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 V2O5 thin film electrodes were fabricated for extensive cyclic durability testing in a LiClO4/propylene carbonate (PC) liquid electrolyte: One V2O5 film had no overlying coating while the other had a protective thin film of solid lithium ion-conducting LiAlF4. The protected V2O5 exhibited improved durability in terms of constant capacity with repeated cycling up to 800 cycles, while the uncoated V2O5 electrode displayed significant capacity loss. Our results demonstrate that deposition of an inorganic solid electrolyte (LiAlF4) on amorphous V2O5 films serves as a protective overlayer and enhances the long-term cycling efficiency and stability of the V2O5 in a liquid electrolyte.