Amorphous, Crystalline and Crystalline/Amorphous Selenium Nanowires and Their Different (De)Lithiation Mechanisms

Selenium is applied as the cathode material of lithium/selenium (Li-Se) battery, which has high theoretical volumetric capacity density (3253 mA h.cm(-3)) and high output voltages. However, it has a low melting point (494 K) and a large sensitivity to thermal treatment, which often result in the phase transition between crystalline Se (trigonal phase) and amorphous Se during the charge/discharge cycles of Li-Se battery as reported in literatures. In order to clarify the different chemical (de)lithiation mechanisms between them in Li-Se battery, in this work large-area amorphous selenium (a-Se) nanowires (NWs) have been successfully prepared first through a facile high-energy ball-milling method. Subsequently the crystalline (c) and crystalline/amorphous (c/a) selenium NWs have also been prepared through annealing the above as-obtained amorphous products, respectively. The affirmative composition and morphology of the as-obtained Se nanostructures have been demonstrated by the XRD, SEM, TEM, HRTEM and Raman spectra measurements. And their specific surface area and pore size distribution have also been analyzed by BET measurements. Finally, it is proved that the as-obtained NWs used as the cathode material of Li-Se battery displayed different chemical reaction processes with Li+ and the related various storage capacities (a-Se: 755 mAh.g(-1); c/a-Se: 705 mAh.g(-1); c-Se: 250 mAh.g(-1)). This work has helped us to better understand and correlate the formation of intermediate phases with the electrochemical performance of Li-Se cells and shines new light on how to improve the cell performance by turning the phase of Se.