Preparation Of Nitrogen And Fluorine Co-doped Graphene And Its Electrochemical Properties

Graphene,a two-dimensional mono-layer of sp2-hybridized carbon atoms,has attracted enormous attention owing to its fast electron transportation,high thermal conductivity,excellent mechanical flexibility,good biocompatibility,and large specific surface area.Recently,both theoretical and experimental studies have proved that the introduction of heteroatoms(B,N,F,S or P)into the graphene framework results in the change in the electronic structure and improves electrochemical activity significantly,which can be used in a more extensive field.In this paper,the nitrogen(N)and fluorine(F)co-doping graphene(NFG)with the N and F level as high as 3.24 at% and 10.8 at% was synthesized through one-step hydrothermal reaction of trimethylamine tri(hydrofluoride)[(C2H5)3N·3HF] and aqueous-dispersed graphene oxide(GO)as the anode material of lithium ion batteries(LIBs).The doping mechanism and reaction temperature were studied.The fluorine content experienced an increase in the first and then decreased process with the increase of temperature which may be related to the stability of C-F bond in aqueous solution.At the same time,the effect of temperature on the content of N and F and the properties of the materials were studied.NFG synthesized at 150? for 16 h exhibited the best electrochemical performances tested as anode of LIBs,including high coulombic efficiency about 56.7% in the first cycle,superior reversible specific discahrge capacity(765 mAh·g-1 at 100 mA·g-1),excellent rate capability(305 mAh·g-1 at 5 A·g-1),and outstanding cycling stability(capacity retention of ~95% at 5 A·g-1 after 2000 cycles).Excellent electrochemical performance was attributed to the synergetic effects of increased disorder and defects as well as expanded interlayer of graphene frameworks caused by the co-doping of N and F,the adequate amount of active site of pyridinc and pyrrolic N and electrical conductive graphitic N and semi-ionic C-F bonds,and the highly wrinkled nanostructures after the hydrothermal process.Therefore,the excellent electrochemical performances endowed the great potential of NFG being applied as anode materials of high power LIBs.