MXene-Derived Defect-Rich TiO₂@rGO as High-Rate Anodes for Full Na Ion Batteries and Capacitors

Sodium ion batteries and capacitors have demonstrated their potential applications for next-generation low-cost energy storage devices. These devices's rate ability is determined by the fast sodium ion storage behavior in electrode materials. Herein, a defective TiO₂@reduced graphene oxide (M-TiO₂@rGO) self-supporting foam electrode is constructed via a facile MXene decomposition and graphene oxide self-assembling process. The employment of the MXene parent phase exhibits distinctive advantages, enabling defect engineering, nanoengineering, and fluorine-doped metal oxides. As a result, the M-TiO₂@rGO electrode shows a pseudocapacitance-dominated hybrid sodium storage mechanism. The pseudocapacitance-dominated process leads to high capacity, remarkable rate ability, and superior cycling performance. Significantly, an M-TiO₂@rGO//Na₃V₂(PO₄)₃ sodium full cell and an M-TiO₂@rGO//HPAC sodium ion capacitor are fabricated to demonstrate the promising application of M-TiO₂@rGO. The sodium ion battery presents a capacity of 177.1 mAh g^-1 at 500 mA g^-1 and capacity retention of 74% after 200 cycles. The sodium ion capacitor delivers a maximum energy density of 101.2 Wh kg^-1 and a maximum power density of 10,103.7 W kg^-1. At 1.0 A g^-1, it displays an energy retention of 84.7% after 10,000 cycles.