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Porous carbon nanofibers (PCNFs), are widely used as free-standing anode materials for lithium-ion batteries (LIBs), due to their high specific surface area and excellent ion diffusion kinetics, but they also present problems of reduced rate performance and cycling performance, due to poor strength caused by porosity. Herein, a novel surface porous carbon nanofiber (SPCNFs) is prepared by coaxial electrospinning, followed by carbonization. All the pores are distributed in the shell of the fibers, with a dense amorphous carbon structure in the core, which would not only provide abundant lithium-ion embedding sites, and accelerate the penetration of electrolyte ions, but also alleviate the reduction of mechanical properties (with a ~ 30% improvement to PCNFs). Consequently, our LIBs assembled with this SPCNFs anode represent remarkable cycling stability (445.33 mAh g−1 at 100 mA g−1 after 100 cycles and 388.92 mAh g−1 at 1 A g−1 after 1000 cycles), and excellent rate capacity (317.55 mAh g−1 at 1 A g−1). [ABSTRACT FROM AUTHOR]

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]