Application Of CVD Graphene Materials In The Cathode Of Lithium Sulfur Battery

Lithium sulfur(Li-S)battery draws more and more attention of people,with ultrahigh energy density(2500 Wh·kg-1).It promises to realize widespread use in the fields of portable electronics,electric vehicle and energy storage equipment.However,the commercialization of this battery has been hindered by the low reversible capacity and bad cycle stability.Therefore,this article started out from the optimization of cathode materials and used graphene and graphene composites to enhance the stability of the cathode and improve the performance of Li/S battery.We prepared three kinds of graphene materials: nanomesh graphene(NMG),graphene/carbon nanotube hybrids(G-CNT)and graphene capsule(GC)using chemical vapor deposition(CVD)methode,and used them in the cathode of Li-S battery.NMG can be prepared using porous MgO layers with polygonal shapes as a template and methane as a carbon source.S powder was compounded with NMG into S/NMG.G-CNT hybrids can be prepared in the same condition using iron-bearing MgO.S powder was compounded with the G-CNT hybrids into S/G-CNT.The capacity of S/NMG decreased by 40.1% after 150 cycles at the current rate of 1C.However,the decrement of S/G-CNT was only 14.9% and the coulombic efficiency maintained over 98%.Meanwhile,the rate capability of S/G-CNT was superior to S/NMG.This was because in addition to the porous layer structure,G-CNT also had carbon nanotubes inserting in the NMG.This structure enhanced the interface bonding force when compounding with S powder,suppressing the shuttle effect.Therefore,the cycling stability and rate capability of S/G-CNT were better than S/NMG.At the same time,we explored the production of graphene capsule and used it in the cathode of Li-S battery in this work.GC can be prepared using sphere MgO as a template and methane or ethylene as carbon sources.S powder was compounded with GC into S/GCM(methane as a carbon source)and S/GCE(ethylene as a carbon source).The capacity of S/GCE decreased by 61.7% after 150 cycles at the current rate of 1C.However,the decrement of S/GCM was only 50.9% and the coulombic efficiency was close to 100% during cycle.Meanwhile,the rate capability of S/GCM was superior to S/GCE.This was mainly because the number of defects in GCM was more than GCE,which enhanced the interface bonding force between elemental sulfur and carbon materials,suppressing the shuttle effect.In addition,the utilization of elemental sulfur in S/GCM was higher than S/GCE because of the abundant reaction active sites.This work prepared carbon materials using different carbon sources and templates,and investigated the performances of these kinds of carbon materials in Li/S battery.The results indicated that the performance of G-CNT was better than NMG and the performance of GCM was better than GCE.