摘要
Direct growth of hierarchically interconnected Ni S nanofibers as binder-free electrodes for high-performance sodium (Na )-ion batteries was demonstrated by a facile one-step hydrothermal method on a nickel (Ni) foam. The hierarchically interconnected Ni S nanofibers can effectively relieve volume expansion of Ni S and shorten diffusion paths of Na ions that can enhance the high electronic conductivity during the electrochemical reaction, yielding high specific capacitance, excellent cycling stability, and outstanding rate capability. As a result, a high discharge specific capacity of 584.2 mAh g at a current density of 0.2 A g in the first sodiation process with a capacity retention of 91.9% after 100 cycles (retains 536.9 mAh g ) can be achieved. The asymmetric Na -ion capacitor based on the hierarchically interconnected Ni S nanofibers as binder-free anode materials and the activated carbon as a cathode material exhibits high energy and power density. Interestingly, the conversion reaction mechanism of Na -ion storage in the hierarchically interconnected Ni S nanofibers was also investigated by the ex situ X-ray diffraction studies, suggesting a promising material as the binder-free electrode for advanced Na -ion energy storage.