A new graphitic carbon nitride-coated dual Core-Shell sulfur cathode for highly stable lithium-sulfur cells

Lithium-sulfur (Li-S) batteries have promise to deliver energy density two to three times higher than that of currently used lithium-ion batteries. The commercialization of Li-S batteries is primarily hindered due to the polysulfide shuttle (PSS) effect, which not only leads to the loss of active materials from the cathode, but also causes serious irreversible reactions between the polysulfide intermediates and the lithium metal anode, resulting in low coulombic efficiency, high self-discharge and short cycle life. In this paper, we report the design and synthesis of a new graphitic carbon nitride-coated dual core-shell structured sulfur cathode (S@HCS@g-C3N4) to address these issues, leading to superior capacity retention properties in Li-S cells. This structural design allows confinement of polysulfide intermediates within a dual-core electrically conductive structure consisting of a hollow mesoporous carbon sphere (HCS) core, and a peripheral graphitic carbon nitride (g-C3N4) layer, which is known to suppress the PSS effect by enhanced chemical interactions with polysulfide intermediates. Indeed, the S@HCS@g-C3N4 cathode displayed excellent electrochemical performance in terms of high initial specific capacity (1446 mA h g(-1) at 0.2C) and very good long-term cycling performance (capacity decay rate of 0.049% per cycle after 500 cycles at 1C).