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The sulfonic acid group exhibits considerable ion affinity. The present work therefore synthesizes, a core-shell composite material having a sulfonated polyaniline shell, and a bamboo-derived porous carbon core loaded with sulfur. The thin, homogeneous shell has a thickness of approximately 20 nm. This composite is employed as a cathode material in Li-S batteries and the electrochemical properties of these devices are systematically investigated. This cathode (containing 64.0 wt% S) exhibits a higher initial discharge capacity (1484 mAh g−1 at 0.1 C), improved cycling stability (853 mAh g−1 after 100 cycles at 0.1 C), and remarkable rate performance (810.2, 682.7 and 353.0 mAh g−1 at 2, 3 and 5 C, respectively). These values are superior to those obtained using a polyaniline shell. Electrochemical impedance spectroscopy and density functional theory calculations are used to elucidate the internal mechanisms of the sulfonated polyaniline shell during cycling. The calculated results demonstrate that the shell possesses extremely high electron and Li ion conductivities, and so enhances the redox reaction kinetics during long-term cycling. It also physically confines and chemically anchors polysulfides, thus limiting the shuttle effect. This cathode design is expected to assist in the future commercialization of Li-S batteries.

Here, the hydroxyl content of reduced graphene oxide (rGO) is controlled by adjusting reduction time with l -ascorbic acid as reduction agent to study the effect on cathode performance of lithium sulfur batteries (LSBs). The results indicate that the hydroxyl content decreases from 35.8% to 17.9% with prolonging reduction time from 6 h to 48 h, and the C/O ratio increases. More importantly, it is demonstrated that the rGO with relatively low hydroxyl content within 36 h of reduction is more beneficial to enhance both the initial capacity and capacity retention as well as rate performance of LSBs, which is ascribed to the higher conductivity, stronger adsorption and relatively few reaction by-products with the decrease of hydroxyl content. However, when the reduction time is further prolonged to 48 h, the cathode performance deteriorates. As a result, rGO-36h/S electrode with the optimum hydroxyl content (19.2%) achieves an initial discharge capacity of 1340.9 mAh g−1, which still maintains 707.8 mAh g−1 over 100 cycles at 0.1C. This work may provide a guide for reducing GO when used as sulfur host material or matrix material of LSBs.