Cation Intercalation and High Volumetric Capacitance of Two-Dimensional Titanium Carbide

The intercalation of ions into layered compounds has long been exploited in energy storage devices such as batteries and electrochemical capacitors. This chapter demonstrates the spontaneous intercalation of cations from aqueous salt solutions between two-dimensional (2D) Ti3C2 MXene layers. MXenes combine 2D conductive carbide layers with a hydrophilic, primarily hydroxyl-terminated surface. With the increased demand for portable and clean energy, electrochemical capacitors have been attracting attention because of their much greater power density and cyclability relative to Li batteries. Energy density enhancement of capacitors can be achieved by using hybrid devices, which combine a battery-like redox electrode and a porous carbon electrode. MXenes have shown promise as electrode materials for Li-ion batteries and Li-ion capacitors.