Sulfur Immobilized in Hierarchically Porous Structured Carbon as Cathodes for Lithium-Sulfur Battery with Improved Electrochemical Performance

In order to overcome the main obstacles for lithium-sulfur batteries, such as poor conductivity of sulfur, polysulfide intermediate dissolution, and large volume change generated during the cycle process, a hard-template route is developed to synthesize large-surface area carbon with abundant micropores and mesopores to immobilize sulfur species. The microstructures of the C/S hybrids are investigated using field emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, nitrogen adsorption-desorption isotherms, and electrochemical impedance spectroscopy techniques. The large surface and porous structure can effectively alleviate large strain due to the lithiation/delithiation process. More importantly, the micropores can effectively confine small molecules of sulfur in the form of S2-4, avoiding loss of active S species and dissolution of high-order lithium polysulfides. The porous C/S hybrids show significantly enhanced electrochemical performance with good cycling stability, high specific capacity, and rate capability. The C/S-39 hybrid with an optimal content of 39 wt% S shows a reversible capacity of 780 mA h g(-1) after 100 cycles at the current density of 100 mA g(-1). Even at a current density of 5 A g(-1), the reversible capacity of C/S-39 can still maintain at 420 mA h g(-1) after 60 cycles. This strategy offers a new way for solving long-term reversibility obstacle and designing new cathode electrode architectures.