Lithium insertion into TiO2 from aqueous solution – Facilitated by nanostructure

This work investigates the effect of mesoporosity of titanium dioxide on its electrochemical reactivity in water. Nanostructured titanium dioxide films formed by the surfactant template method, unlike films prepared without surfactant, have been found to be reduced when cathodically polarised in aqueous lithium hydroxide. The result is attributed to accelerated lithium ion diffusion within the porous nanostructure, allowing a rapidly reversible insertion of lithium ions forming LixTiO2 with x as high as 0.27, corresponding to a charge capacity of 127 mC cm−2 in a 1.3 μm thick film. Self-discharge is slower than expected, with half-life of a few minutes under oxygen-free conditions. An all-nanostructured supercapacitor constructed from LixTiO2 and NiOOH2−x electrodes showed an average cell potential of 1.6 V, which is close to the maximum possible potential range in an aqueous solution. A specific energy of 90 W h kg−1 is calculated, based on the combined mass of the charged electrodes.