The Fluorination of Boron‐Doped Graphene for CFx 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 as‐prepared 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 B‐doping to realize the ultrahigh energy density of CF x cathodes for practical applications.