Carbon is an indispensible material for electrochemical energy storage applications. Graphene, with its high conductivity, high surface area, and high mechanical strength, has emerged as a magic material in the electrodes of the most advanced supercapacitors and lithium batteries. In this talk, I will demonstrate that graphene, with proper chemical functionalization, could play an important role in improving the lithium/sulfur cell’s active material utilization, specific capacity, as well as its cycle life. Using a nitrogen-functionalized graphene–sulfur electrode, we have achieved ultra-stable cycling exceeding 2000 cycles with a capacity decay rate as low as 0.028% per cycle. To understand the underlying mechanism of the electrochemical reaction processes, we developed various in-situ experimental tools so that we can conduct real time TEM and SEM Raman investigation during electrochemical measurements.  Based on these in-situ and other ex-situ characterization results, we develop a way to prevent lithium dendrite formation by using an optimized electrolyte and to minimize sulfur loss through the chemical interactions of the functional groups on graphene with the active electrode material, i.e. sulfur or lithium sulfide, as well as with the intermediate lithium polysulfide products.