Elaborate construction and electrochemical properties of lignin-derived macro-/micro-porous carbon-sulfur composites for rechargeable lithium-sulfur batteries: The effect of sulfur-loading time

In this paper, a framework of macro-/micro-porous carbon derived from commercial lignin is prepared by one-step carbonization/activation method and then utilized as sulfur-loading matrix to assay the effect of sulfur-loading time on the structural and electrochemical properties of carbon-sulfur composite (C-S-t, t defined as sulfur-loading time). As-prepared porous carbon possesses a high specific surface area of 1211.6 m2 g−1 and a pore volume of 0.59 cm3 g−1, acquires oxygen-containing functional groups on the surface of framework and functionalizes for the chemical adsorption of elemental sulfur. Under N2 atmosphere (flow rate ∼ 60 mL min−1) the longer is the sulfur-loading time, the lower value is the total sulfur content of carbon-sulfur composite and the higher percentage of sulfur embedded within the micropores. At a sulfur-loading time of ∼10 h, the resulting C-S-10 composites have a total sulfur content as low as 50.0 wt% (44.8% in micropores) but exhibit the better electrochemical performances than C-S-6 composites formed at 6 h (sulfur ∼ 58.8 wt%, 29.4% in micropores). Therefore, aside from the structural properties of porous carbon, an optimized sulfur-loading time, as well as the chemical binding between carbon host and sulfur, should be considered to develop high-performance cathode materials for liquid electrolyte lithium-sulfur (Li-S) batteries.