Electrodeposited Sulfur and Co_xS Electrocatalyst on Buckypaper as High-Performance Cathode for Li-S Batteries

Lithium-sulfur batteries (LSBs) are considered as the next generation of advanced rechargeable batteries because of their high energy density. In this study, sulfur and Co_xS electrocatalyst are deposited on carbon nanotube buckypaper (S/Co_xS/BP) by a facile electrodeposition method and are used as a binder-free high-performance cathode for LSBs. Elemental sulfur is deposited on buckypaper by electrooxidation of a polysulfide solution (~ S₆^2-). This approach substantially increased the current and time efficiency of sulfur electrochemical deposition on conductive material for LSBs. S/Co_xS/BP cathode could deliver an initial discharge capacity as high as 1650 mAh g^-1 at 0.1 C, which is close to the theoretical capacity of sulfur. At current rate of 0.5 C, the S/Co_xS/BP has a capacity of 1420 mAh g^-1 at the first cycle and 715 mAh g^-1 after 500 cycles with a fading rate of 0.099% per cycle. The high capacity of S/Co_xS/BP is attributed to both the homogeneous dispersion of nanosized sulfur within BP and the presence of Co_xS catalyst. The sodium dodecyl sulfate (SDS) pretreatment of BP renders it polarity to bind polysulfides and thus facilitates the good dispersibility of nanosized sulfur within BP. Co_xS catalyst accelerates the kinetics of polysulfide conversion and reduces the presence of polysulfide in the cathode, which suppresses the polysulfide diffusion to anode, i.e., the shuttle effect. The mitigation of the active material loss improves not only the capacity but also the cyclability of S/Co_xS/BP.