Sulfur encapsulated in thermally reduced graphite oxide as a cathode for Li-S batteries

摘要

Rechargeable Li-S batteries are receiving ever-increasing attention due to their high theoretical energy density and inexpensive raw sulfur materials. However, their practical applications have been hindered by short cycle life and limited power density owing to the poor electronic conductivity of sulfur species, diffusion of soluble polysulfide intermediates (Li2Sn, n = 4-8) and the large volume change of the S cathode during charge/discharge. Optimizing the carbon framework is considered as an effective approach for constructing high performance S/carbon cathodes because the microstructure of the carbon host plays an important role in stabilizing S and restricting the "shuttle reaction" of polysulfides in Li-S batteries. In this work, reduced graphite oxide (rGO) materials with different oxidation degree were investigated as the matrix to load the active material by an in situ thermally reducing graphite oxide (GO) and intercalation strategy under vacuum at 600 degrees C. It has been found that the loaded amount of S embedded in the rGO layer for the S/carbon cathode and its electrochemical performance strongly depended on the oxidation degree of GO. In particular, on undergoing CS2 treatment, the rGO-S cathode exhibits extraordinary performances in Li-S batteries. For instance, at a current density of 0.2 A g(-1), the optimized rGO-S cathode shows a columbic efficiency close to 100% and retains a capacity of around 750 mA h g(-1) with progressive cycling up to over 250 cycles.