Entrapping polysulfides using mesoporous carbon hollow spheres with controlled internal SiO2 content for lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries, which are promising candidates for next-generation power sources, possess a high theoretical capacity of 1675 mAh g(-1) and a high energy density of 2600 Wh kg(-1). In addition, sulfur is an abundant, inexpensive, and environmentally friendly element suitable for large-scale production. However, Li-S batteries are still far from being used in practical applications because of known problems, including the insulating nature of sulfur, dissolution of polysulfide intermediates, and volume expansion of sulfur during the charge and discharge processes. To overcome these limitations, some efforts have been focused on the design of various structural matrices to encapsulate sulfur and develop new electrode active materials. In this study, a unique core-shell structure that mesoporous carbon hollow spheres with controllable SiO2 content as a sulfur host was designed. The hollow structure provides enough space to accommodate not only the active material, but also the volume changes during the charge and discharge processes. Moreover, the highly mesoporous structure can enhance the wettability and accessibility of the electrolyte, facilitating Li+ transfer, and confine the dissolved polysulfides in the pores. SiO2, a polar material, can effectively adsorb polysulfides and further enhance the electrochemical performance. An excellent reversible capacity of 694 mAh g(-1) after 100 cycles at 0.1 C-rate was obtained, which is attributed to the dual physical and chemical effects. Therefore, mesoporous carbon hollow spheres with moderate SiO2 contents are promising sulfur hosts for advanced high-performance lithium-sulfur batteries.