Intercalation pseudocapacitance of amorphous titanium dioxide@nanoporous graphene for high-rate and large-capacity energy storage

In comparison to conventional supercapacitors that commonly fall short of energy densities, the intercalation pseudocapacitors have combined high charge-storage capacity and fast charge/discharge rates from their unique charge storage mechanism of fast kinetics without the limitation of diffusion. Nevertheless, only very limited crystalline materials have a structure that can fulfill the strict demands of fast ion transport pathways and insignificant structural variation upon ion insertion and extraction for the intercalation pseudocapacitance. Here we report that amorphous titanium dioxide, grown on highly conductive nanoporous graphene frameworks by atomic layer deposition, is capable of storing and delivering a large capacity at high rates by pseudocapacitive and bulk-form Li⁺ intercalation/de-intercalation reactions. Different from intercalation pseudocapacitive crystals, amorphous TiO₂ experiences local structure changes during Li⁺ insertion and extraction which essentially only lead to insignificant constraints on the overall kinetics as a result of loose packing and structure disorder of amorphous materials. This study paves a new way to develop high-energy capacitive materials in a wide spectrum of amorphous materials and may promote the practical implementation of high-rate and large-capacity energy storage.