The fluorination of boron‐doped graphene for CF _x cathode with ultrahigh energy density

The enhancement of the fluorination degree of carbon fluorides（CF x ）compounds is the most effective method to improve the energy densities of Li/CF x batteries because the specific capacity of CF x is proportional to the molar ratio of F to C atoms（F/C）.In this study,B-doped graphene（BG） is prepared by using boric acid as the doping source and then the prepared BG is utilized as the starting material for the preparation of CF x .The B-doping enhances the F/C ratio of CF x without hindering the electrochemical activity of the C-F bond.During the fluorination process,B-containing functional groups are removed from the graphene lattice.This facilitates the formation of a defect-rich graphene matrix,which not only enhances the F/C ratio due to abundant perfluorinated groups at the defective edges but also serves as the active site for extra Li + storage.The prepared CF x exhibits the maximum specific capacity of 1204 mAh g -1 ,which is 39.2% higher than that of CF x obtained directly from graphene oxide（without B-doping）.An unprecedented energy density of 2974 Wh kg -1 is achieved for the asprepared CF x samples,which is significantly higher than the theoretically calculated energy density of commercially available fluorinated graphite(2180 Wh kg -1 ).Therefore,this study demonstrates a great potential of Bdoping to realize the ultrahigh energy density of CF x cathodes for practical applications.