Ultrathin Cobaltosic Oxide Nanosheets as an Effective Sulfur Encapsulation Matrix with Strong Affinity Toward Polysulfides

Two-dimensional ultrathin cobaltosic oxide nanosheets with numerous geometrical holes were synthesized by the hydrothermal method, and further used as an effective encapsulation matrix for sulfur and polysulfides in lithium-sulfur batteries. The cobaltosic oxide/sulfur nanosheet composite electrode exhibits high Coulombic efficiency (99%), a suppressed shuttle effect, and a reversible capacity of 656 mA h g^-1 at 0.2 C after 200 cycles, with small capacity fading of 0.219% per cycle, whereas its carbon-sulfur electrode counterpart only retains a capacity of 386 mA h g^-1 after 100 cycles. The improved performance is attributed to the strong chemical interaction between polysulfides and cobaltosic oxide, and its facile ionic transport and enhanced reaction kinetics, which can effectively control the diffusion of polysulfides and keep them within the cathode region, leading to good electrochemical stability.