Flexible Carbon Nanotube–Graphene/Sulfur Composite\nFilm: Free-Standing Cathode for High-Performance Lithium/Sulfur Batteries

Abstract

Flexible lithium\nbatteries with high energy density have recently\nreceived tremendous interest due to their potential applications in\nflexible electronic devices. Herein, we report a novel method to fabricate\nhighly flexible and robust carbon nanotube–graphene/sulfur\n(CNTs–RGO/S) composite film as free-standing cathode for flexible\nLi/S batteries with increased capacity and significantly improved\nrate capability. The free-standing CNTs–RGO/S cathode was able\nto deliver a peak capacity of 911.5 mAh g^–1_sulfur (∼483 mAh g^–1_electrode) and maintain 771.8 mAh g^–1_sulfur after\n100 charge–discharge cycles at 0.2C, indicating a capacity\nretention of 84.7%, which were both higher than the cathodes assembled\nwithout CNTs. Even after 100 cycles, the cathode showed a high tensile\nstrength of 62.3 MPa. More importantly, the rate capability was improved\nby introducing CNTs. The CNTs–RGO/S cathode exhibited impressive\ncapacities of 613.1 mAh g^–1_sulfur at\n1C with a capacity recuperability of ∼94% as the current returned\nto 0.2C. These results demonstrate that the well-designed nanocomposites\nare of great potential as the cathode for flexible lithium sulfur\n(Li/S) batteries. Such improved electrochemical properties could be\nattributed to the unique coaxial architecture of the nanocomposite,\nin which the evenly dispersed CNTs enable electrodes with improved\nelectrical conductivity and mechanical properties and better ability\nto avoid the aggregation and ensure the dispersive distribution of\nthe sulfur species during the charge/discharge process.