Synthesis of long hierarchical MoS nanofibers assembled from nanosheets with an expanded interlayer distance for achieving superb Na-ion storage performance.

MoS material is considered as a promising anode material candidate in Na-ion batteries (NIBs) due to its high theoretical capacity and layered structure. However, MoS nanosheets usually tend to restack or aggregate during the synthesis and cycling process, which makes the advantages of the separated nanosheets disappear. Here, we present a PVP-assisted synthesis for growing long hierarchical MoS nanofibers with a length up to 74.5 μm, which were further assembled from intercrossed curly nanosheets with expanded (002) interlayer spacings in the range of 0.62 nm to 1.14 nm. Such architectural design simultaneously combines multiple-scale structural features that are desired for Na-ion storage. On the one hand, the nanosheets can provide a large surface area which is in contact with the electrolyte, a short Na-ion diffusion pathway from the lateral side and facile Na-ion insertion and extraction through the expanded (002) interlayer; on the other hand, the hierarchical MoS nanofibers possess a one dimensional structure and a suitable amount of carbon, which can both serve as an electrical highway and prevent them from restacking, resulting in an enhanced electrochemical performance. When used as an anode in NIBs, they demonstrated excellent cycling performance (537 mA h g at 0.1 A g after 200 cycles, and 370 mA h g at 2 A g over 200 cycles) and outstanding rate capability (329 mA h g at 10 A g).