Edge-thionic acid-functionalized graphene nanoplatelets as anode materials for high-rate lithium ion batteries

Although lithium ion batteries (LIBs) hold great promise as a next generation power supply, the poor rate capability of the graphite that is mainly used as the battery anode limits high-performance LIBs. Compared to other reported carbon-based materials, however, its relatively low average working voltage still makes it attractive. Herein, we were able to introduce carbon disulfide (CS2) at the edges of graphene nanoplatelets (GnPs) with rich –C=S/-C-S bonds via ball-milling graphite in the presence of CS2. The resultant edge-thionic acid-functionalized GnPs (TAGnPs) exhibited a larger accessible surface area and smaller particle size than pristine graphite. Importantly, the TAGnPs retained a long-range-ordered layered structure similar to pristine graphite. When the TAGnPs were used as anode materials for LIBs, they displayed superior rate capability (e.g., high average reversible capacities of 228.3, 208.1, 141.0 and 80.6 mAh g−1 at 0.5, 1, 2 and 5 A g−1, respectively) compared to pristine graphite and the reference edge-hydrogenated GnPs (HGnPs), which mainly have -C-H bonds at their edges. Theoretical calculations also indicated that the presence of –C=S/-C-S bonds at the edges of TAGnPs enabled stronger Li+ adsorption capability.