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

Highlights: A freestanding MXene-derived defect-rich TiO₂@reduced graphene oxides (M-TiO₂@rGO) foam electrode was fabricated. M-TiO₂@rGO presents fast Na⁺ storage kinetics due to capacitive contribution. M-TiO₂@rGO foam electrode displays a capacity retention of 90.7% after 5000 cycles. 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. [ABSTRACT FROM AUTHOR]