Lithium-fluorinated carbon (Li-CF x) batteries have become one of the most widely applied power sources for high energy density applications because of the advantages provided by the CF x cathode. Moreover, the large gap between the practical and theoretical potentials alongside the stoichiometric limit of commercial graphite fluorides indicates the potential for further energy improvement. Herein, monolayer fluorinated graphene nanoribbons (F-GNRs) were fabricated by unzipping single-walled carbon nanotubes (SWCNTs) using pure F 2 gas at high temperature, which delivered an unprecedented energy density of 2738.45 W h kg −1 due to the combined effect of a high fluorination degree and discharge plateau, realized by the abundant edges and destroyed periodic structure, respectively. Furthermore, at a high fluorination temperature, the theoretical calculation confirmed a zigzag pathway of fluorine atoms that were adsorbed outside of the SWCNTs and hence initiated the spontaneous process of unzipping SWCNTs to form the monolayer F-GNRs. The controllable fluorination of SWCNTs provided a feasible approach for preparing CF x compounds for different applications, especially for ultrahigh-energy-density cathodes.
The enhancement of the fluorination degree of carbon fluorides (CFx) compounds is the most effective method to improve the energy densities of Li/CFx batteries because the specific capacity of CFx 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 CFx. The B‐doping enhances the F/C ratio of CFx 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 CFx exhibits the maximum specific capacity of 1204 mAh g−1, which is 39.2% higher than that of CFx obtained directly from graphene oxide (without B‐doping). An unprecedented energy density of 2974 Wh kg−1 is achieved for the as‐prepared CFx 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 CFx cathodes for practical applications.
F-doping hard carbon (F–HC) was synthesized through a mild fluorination at temperature at relative low temperature as the potential anode for sodium-ion batteries (SIBs). The F-doping treatment to HC expands interlayer distance and creates some defects in the graphitic framework, which has the ability to improve Na+ storage capability through the intercalation and pore-filling process a simultaneously. In addition, the electrically conductive semi-ionic C–F bond in F–HC that can be adjusted by the fluorination temperature facilitates electron transport throughout the electrode. Therefore, F–HC exhibits higher specific capability and better cycling stability than pristine HC. Particularly, F–HC fluorinated at 100 °C (F–HC100) delivers the reversible capability of 343 mAh/g at 50 mAh/g, with the Coulombic efficiency of 78.13%, and the capacity retention remains as 95.81% after 100 cycles. Moreover, the specific capacity of F–HC100 returns to 340 mAh/g after the rate capability test demonstrates its stability even at high current density. The enhanced specific capacity of F–HC, especially at low-voltage region, has the great potential as the anode of SIBs with high energy density.
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