Lithium-sulfur batteries have attracted worldwide interest due to their high theoretical capacity of 1672 mAh g and low cost. However, the practical applications are hampered by capacity decay, mainly attributed to the polysulfide shuttle. Here, the authors have fabricated a solid core-shell γ-MnO -coated sulfur nanocomposite through the redox reaction between KMnO and MnSO . The multifunctional MnO shell facilitates electron and Li transport as well as efficiently prevents polysulfide dissolution via physical confinement and chemical interaction. Moreover, the γ-MnO crystallographic form also provides one-dimensional (1D) tunnels for the Li incorporation to alleviate insoluble Li S /Li S deposition at high discharge rate. More importantly, the MnO phase transformation to Mn O occurs during the redox reaction between polysulfides and γ-MnO is first thoroughly investigated. The S@γ-MnO composite exhibits a good capacity retention of 82% after 300 cycles (0.5 C) and a fade rate of 0.07% per cycle over 600 cycles (1 C). The degradation mechanism can probably be elucidated that the decomposition of the surface Mn O phase is the cause of polysulfide dissolution. The recent work thus sheds new light on the hitherto unknown surface interaction mechanism and the degradation mechanism of Li-S cells.

Lithium-sulfur (Li-S) batteries have currently excited worldwide academic and industrial interest as a next-generation high-power energy storage system (EES) because of their high energy density and low cost of sulfur. However, the commercialization application is being hindered by capacity decay, mainly attributed to the polysulfide shuttle and poor conductivity of sulfur. Here, we have designed a novel dual core-shell nanostructure of S@C@MnO nanosphere hybrid as the sulfur host. The S@C@MnO nanosphere is successfully prepared using mesoporous carbon hollow spheres (MCHS) as the template and then in situ MnO growth on the surface of MCHS. In comparison with polar bare sulfur hosts materials, the as-prepared robust S@C@MnO composite cathode delivers significantly improved electrochemical performances in terms of high specific capacity (1345 mAh g at 0.1 C), remarkable rate capability (465 mA h g at 5.0 C) and excellent cycling stability (capacity decay rate of 0.052% per cycle after 1000 cycles at 3.0 C). Such a structure as cathode in Li-S batteries can not only store sulfur via inner mesoporous carbon layer and outer MnO shell, which physically/chemically confine the polysulfides shuttle effect, but also ensure overall good electrical conductivity. Therefore, these synergistic effects are achieved by unique structural characteristics of S@C@MnO nanospheres.

Lithium-sulfur (Li-S) batteries have recently attracted a large amount of attention as promising candidates for next-generation high-power energy storage devices because of their high theoretical capacity and energy density. However, the shuttle effect of polysulfides and poor conductivity of sulfur are still vital issues that constrain their specific capacity and cyclic stability. Here, we design coaxial MnO -graphitic carbon hollow nanofibers as sulfur hosts for high-performance lithium-sulfur batteries. The hollow C/MnO coaxial nanofibers are synthesized via electrospinning and carbonization of the carbon nanofibers (CNFs), followed by an in situ redox reaction to grow MnO nanosheets on the surface of CNFs. The inner graphitic carbon layer not only maintains intimate contact with sulfur and outer MnO shell to significantly increase the overall electrical conductivity but also acts as a protective layer to prevent dissolution of polysulfides. The outer MnO nanosheets restrain the shuttle effect greatly through chemisorption and redox reaction. Therefore, the robust S@C/MnO nanofiber cathode delivers an extraordinary rate capability and excellent cycling stability with a capacity decay rate of 0.044 and 0.051 % per cycle after 1000 cycles at 1.0 C and 2.0 C, respectively. Our present work brings forward a new facile and efficient strategy for the functionalization of inorganic metal oxide on graphitic carbons as sulfur hosts for high performance Li-S batteries.

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