Effect of thermally decomposable spacers on graphene microsphere structure and restacking of graphene sheets during electrode fabrication

Graphene has been proposed as a suitable material for electrodes in electrochemical double layer capacitors because of its excellent properties. However, a drawback is the irreversible restacking tendency of graphene during electrode preparation which, consequently, decreases the electrochemically accessible surface area. Therefore, to preserve the electrochemically accessible surface area of graphene, the development of controllable graphene structures with restacking-resistive property is highly desirable. In this work, spherical graphene with high restacking-resistive property during the re-dispersive process are synthesized using ionic liquid (IL), 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide as a decomposable spacer. During graphene assembly, the IL is not only used as a guide to obtain a spherical morphology, but also as a spacer that prevents restacking of graphene oxide (GO). Through our experiment, it was observed that, during the thermal treatment of spherical GO/IL to reduce GO to reduced graphene oxide (rGO), the IL could not only prevent restacking of GO sheets, but also protect its spherical morphology from the gas explosion generated by the reduction of GO. In particular, spherical rGO/IL has high surface area of 474 m² g⁻¹ and high restacking-resistive property such that it lost only 5% of its initial surface area after soaking in NMP, which exhibit high specific capacitance.