Graphene-Based Three-Dimensional Hierarchical Sandwich-type Architecture for High-Performance Li/S Batteries

A multiwalled cirbon nanotube/sulfur (MWCNT@S) composite with core-shellli structure was successfully embedded into the interlay galleries of graphene, sheets (GS) through a facile two-step assembly process. Scannirig and transmission electron microscopy images reveal a 3D hierarchial sandwich-type architecture of the composite GS-MWCNTOS. The thickness of the S layer on the MWCNTs is similar to 20 nm. Raman spectroscopy, X-ray diffraction, thermogravimetric analysis, and energy-dispersive X-ray analysis confirm that the sulfur in the composite is highly crystalline with a mass loading up to 70% of the composite. This composite is evaluated as a cathode material for Li/S batteries. The GS-MVVCNT@S composite exhibits a high initial capacity of 1396 mAh/g at a current density of 0.2C (1C = 1672 mA/g), corresponding to 83% usage of the sulfur active material. Much improved cycling stability and rate capability are achieved for the GS-MWCNT@S composite cathode compared with the composite lacking GS or MWCNT. The superior electrochemical performance of the GS-MWCNT@S composite is mainly attributed to the synergistic effects of GS and MWCNTs, which provide a 3D conductive network for electron transfer, open channels for ion diffusion, strong confinement of soluble polysulfides, and effective buffer for volume expansion of the S cathode during discharge.