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.
An ultrathick lithium metal anode (LMA) is a prerequisite for developing practical lithium–sulfur (Li–S) batteries that simultaneously meet the requirements of high areal capacity, lean electrolyte, and limited excess Li. Inspired by the electrochemical process for an organosulfur cathode, herein, we reconfigure such a sulfur cathode by using an overlithiation strategy to enable the formation of a high performance LMA. Specifically, an applicable ultrathick LMA is successfully constructed by overlithiating a well-known organosulfur cathode material, sulfurized polyacrylonitrile (SPAN). SPAN contains a polymeric pyridine structure with an outstanding lithium-ion affinity, so that it can act as a lithiophilic matrix. More importantly, a Li2S-rich solid electrolyte interphase (SEI) can be generated on the surface of SPAN during the overlithiation process. The synergistic effect of the lithiophilic matrix and a robust SEI leads to a dense deposition of lithium, which enables one to form an ultrathick LMA (159 μm, 30 mAh cm–2) with high Coulombic efficiency (99.7%). Such an LMA paired with a sulfur cathode of high areal capacity (up to 16 mAh cm–2) shows stable cycling under practical conditions of a lean electrolyte (2.2 μL mgS–1) and a negative-to-positive capacity (N/P) ratio as low as 1.3. The applicability of the ultrathick LMA was further verified with Li–S pouch cells, indicating a highly prospective route toward realization of practical Li–S batteries.
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