DOI: 10.1002/adma. 201402987 electrochemical performance.[9–11] Moreover, many reports have demonstrated that the electrochemical performance of graphene for LIBs was dramatically enhanced by doping with heteroatoms (eg, N, B, and P).[12] Recently, our group explored a simple, eco-friendly method by dry ball-milling graphite in the presence of different substances, leading to mass production of various heteroatom-doped graphene nanoplatelets (GnPs).[13, 14] By simply ball-milling graphite with chlorine (Cl 2), bromine (Br 2) or iodine (I 2), for instance, we have successfully prepared a series of edge-selectively halogenated graphene nanoplatelets (XGnPs, X= Cl, Br or I). These edge-functionalized GnPs (EFGnPs) were employed as promising metal-free electrocatalysts for oxygen reduction reaction (ORR) in fuel cells.[13] The XGnPs displayed excellent electrocatalytic activities with good cycle stability. Compared with other approaches for the production of graphene, including chemical vapor deposition (CVD),[15] arc-discharge,[16] Hummer’s methods,[17] and solvothermal synthesis,[18] this simple, eco-friendly ball-milling method is a low-cost and scalable approach for the production of XGnPs as anode materials to meet the ever-increasing demand of LIBs for our near-term needs, for example in a wide range of electric vehicles.

Here, we report the first study on the use of edge-selectively halogenated GnPs (XGnPs, X= Cl, Br, or I) prepared by the ball-milling method as anode materials for LIBs. For comparison, edge-hydrogenated GnP (HGnP) was also prepared by ball-milling graphite in the presence of hydrogen.[19] This method employed the repulsive interaction of edge-halogenated groups as the driving force to gradually exfoliate the graphite into XGnPs during the ball-milling process, and thus allowed for a low-cost and large-scale production of XGnPs. It was found that IGnP electrode delivered an initial charge capacity of 562.8 mAh g− 1 at 0.5 C in the voltage range of 0.02–3.0 V, which was higher than the reference HGnP with 511.3 mAh g− 1. Furthermore, after 500 cycles, the IGnP electrode was still able to deliver a higher charge capacity of 458.0 mAh g− 1 with a higher initial charge capacity retention of 81.4% than the HGnP with 208.5 mAh g− 1 and 40.8%, respectively. After 500 cycles and 1 month storage at ambient condition (25 C), the IGnP cell still maintained a reversible capacity of 464.1 mAh g− 1 at the end of additional 100 cycles, indicating a remarkably high stability. Such excellent electrochemical performance of the IGnP as anode for LIBs is attributable to the high electronegativity of I (χ= 2.66 higher than χ= 2.55 for carbon), high surface area of IGnP (736.8 m 2 g− 1), as well as the improved lithium-ion insertion/extraction at the edges (d I> d H) between graphitic layers,[13] which should lead to