Biomass-derived nitrogen-doped carbon fiber driven δ-MnO2 for aqueous zinc-ion batteries with high energy and power density

Aqueous zinc-ion batteries (AZIBs) are considered potential devices for energy storage because of their low cost and high level of safety. However, the efficiency of AZIBs is influenced by the cathode reaction kinetics. Herein, we propose the δ-MnO2 nanorods grow in situ on natural loofah sponge-derived nitrogen-doped hollow carbon fibers (HCF), which can significantly improve both ion/electron transfer rate and provide structural stabilization. The self-assembled δ-MnO2-HCF (HCM) electrodes exhibit excellent electrochemical performances, including an impressively specific capacity (341 mAh g−1 at 0.2 A g−1), exceptional long cycling stability (87% capacity retention after 3500 cycles at 2 A g−1), and superb energy density and power density (540 Wh kg−1 at 288 W kg−1 and 164 Wh kg−1 at 5485 W kg−1), all based on the mass of cathode. In addition, the inclusion of HCF leads to a notable enhancement in the electrical conductivity of HCM, and a reduction in the energy barriers for Zn ions to diffuse between the δ-MnO2 layers, according to density functional theory (DFT) calculations. It is promising that the HCM will serve as a design guide for developing cost-effective and high-performance cathode materials for AZIBs.