title: Janus Separator of Polypropylene-Supported Cellular Graphene Framework for Sulfur Cathodes with High Utilization in Lithium-Sulfur Batteries.
abstract: Owing to the conversion chemistry of the sulfur cathode, the lithium-sulfur (Li-S) batteries exhibit high theoretical energy density. However, the intrinsic mobile redox centers during the sulfur/Li2S-to-lithium polysulfides solid-to-liquid phase transition induce low sulfur utilization and poor cycling life. Herein, the Janus separator of mesoporous cellular graphene framework (CGF)/polypropylene membrane to promote the utilization of sulfur cathode is introduced. The porous polypropylene membrane serves as an insulating substrate in contact with lithium anode while CGFs that possess high electrical conductivity of 100 S cm-1, a large mesopore volume of 3.1 cm3g-1, and a huge surface area of 2120 m2g-1are adhered on cathode side to reactivate the shuttling-back polysulfides and to preserve the ion channels. Therefore, the Li-S cell with the "two-face" CGF Janus separator exhibit a high initial capacity of 1109 mAh g-1and superior capacity preserved upon 800 mAh g-1after 250 cycles at 0.2 C, which is 40% higher on sulfur utilization efficiency than the corresponding results with routine polypropylene separators. There are significant improvements on capacity as well as electrochemical kinetics. A very high areal capacity of 5.5 mAh cm-2combined with high sulfur content of 80% and areal loading amount of 5.3 mg cm-2is achieved for such advanced configuration. The negative impact of shuttle mechanism on lowering the utilization of sulfur and overall energy density of a Li-S battery is well eliminated by applying CGF separators. Consequently, employing carbonaceous materials as Janus face of separators enlightens new opportunities for improving the utilization of active materials and energy density of devices that involve complex phase evolution and conversion electrochemistry.
authors: Beijing Key Laboratory of Green Chemical Reaction Engineering and Technology Department of Chemical Engineering Tsinghua University Beijing 100084 P.R. China.
authors: Hong-Jie
authors: HJ
authors: Peng
authors: Beijing Key Laboratory of Green Chemical Reaction Engineering and Technology Department of Chemical Engineering Tsinghua University Beijing 100084 P.R. China.
authors: Dai-Wei
authors: DW
authors: Wang
authors: Beijing Key Laboratory of Green Chemical Reaction Engineering and Technology Department of Chemical Engineering Tsinghua University Beijing 100084 P.R. China.
authors: Jia-Qi
authors: JQ
authors: Huang
authors: Beijing Key Laboratory of Green Chemical Reaction Engineering and Technology Department of Chemical Engineering Tsinghua University Beijing 100084 P.R. China.
authors: Xin-Bing
authors: XB
authors: Cheng
authors: Beijing Key Laboratory of Green Chemical Reaction Engineering and Technology Department of Chemical Engineering Tsinghua University Beijing 100084 P.R. China.
authors: Zhe
authors: Z
authors: Yuan
authors: Beijing Key Laboratory of Green Chemical Reaction Engineering and Technology Department of Chemical Engineering Tsinghua University Beijing 100084 P.R. China.
authors: Fei
authors: F
authors: Wei
authors: Beijing Key Laboratory of Green Chemical Reaction Engineering and Technology Department of Chemical Engineering Tsinghua University Beijing 100084 P.R. China.
authors: Qiang
authors: Q
authors: Zhang
keywords: Janus structure; graphene; lithium–sulfur battery; mesoporous carbon; separator