Edge-NFx (x=1 or 2) Protected Graphitic Nanoplatelets as a Stable Lithium Storage Material

Abstract

Edge-NFx (x=1 or 2) protected graphitic nanoplatelets (NFGnPs) are synthesized for the first time as a stable anode material for lithium storage. The NFGnPs are prepared via mechanochemical reaction, by ball-milling graphite in the presence of nitrogen trifluoride (NF3) gas. The average grain size of the NFGnPs is dramatically reduced compared to the starting graphite. The ball-milling effectively unzips graphitic C-C bonds, generating active carbon species (C-.), which form edge C-NFx bonds and delaminate the graphite layers into a few layered NFGnPs. The resulting NFGnPs have a large specific surface area (671.0 m(2) g(-1)). The edge functionalities of the NFGnPs consist of major C(C)=NF1 and minor C-NF2 moieties. Because of their large specific surface area, the NFGnPs display high average reversible capacities of 850.5, 722.4, 576.4, 482.0, 369.1, 229.7, 127.5 mAh g(-1) at 0.2, 0.5, 1, 2, 5 and 10 C, respectively, with excellent rate capability. More importantly, due to the edge protection provided by the stable C(C)=NF1 bonds (pseudo-aromatic), the NFGnPs maintain a high reversible charge capacity of 421.6 mAh g(-1) at 2 C, with an initial capacity retention of 78.3 % after 200 cycles.