Fluorine-Doped Hard Carbon as the Advanced Performance Anode Material of Sodium-Ion Batteries

Abstract

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.

Phosphorous/Fluorine Co‐doped Biomass‐derived Carbon for Enhanced Sodium‐ion and Lithium‐ion Storage

“…Phosphorous doping generates more defect sites compared to fluorine doping and the P/F co‐doped carbon exhibits highest proportion of defects among all the samples. The results are in accordance with that highlighted in earlier reports [10,14,16,19] . The surface area of the samples has been calculated from the N 2 adsorption isotherms by using BET method.…”

“…The corresponding plots are shown in Figure 1c. For CC, Type III isotherm with H3 hysteresis loop signifies the presence of mostly narrow slit shaped meso and macropores in the sample [19] . With fluorine doping, the CF sample exhibits a Type IV isotherm with H4 hysteresis loop which indicates the presence of minor proportion of micropores along with meso and macropores.…”

“…More detailed information about the valence state and bonding of these elements has been elucidated from the high resolution XPS spectra. The fitted C1s high resolution spectra of CF (Figure 4b) shows peaks at 284.8, 285.6, 285.9, 286.9, and 289.4 eV which correspond to carbon pertaining to sp 2 C, sp 3 C, C−O, C−F (semi ionic) and C−F (covalent) bonds, respectively [16,19] . The semi ionic C−F bond is associated with isolated fluorine atoms attached to the basal plane of the honeycomb carbon structure and helps in enhancing transport of electrons through the electrode material and also improve its rate capability [18,26,27] .…”

“…The semi ionic C−F bond is associated with isolated fluorine atoms attached to the basal plane of the honeycomb carbon structure and helps in enhancing transport of electrons through the electrode material and also improve its rate capability [18,26,27] . The deconvoluted F1s high resolution spectrum of CF (Figure 4c) shows a strong peak at 687.8 eV pertaining to semi ionic (C x F) n species and a weaker one at 688.3 eV which is ascribed to covalent (CF) n bonds [18,19,28] . For CP sample, the deconvoluted high resolution C1s spectrum (Figure 4d) shows three peaks at 284.9, 286.9 and 289.1 eV pertaining to carbon associated with C−C, C−P and C−O bonds [11] .…”

“…The presence of these bonds in CP is beneficial since it can provide more active sites for storage of Li + /Na + ions [9,11] . The high resolution C1s spectrum of CFP is shown in Figure 4f and peaks are seen at 284.8, 285.6, 286.9, and 289.1 eV which correspond to carbon pertaining to sp 2 C, sp 3 C, C−F (semi ionic) and C−F (covalent) bonds, respectively [16,19] . The peak corresponding to C−O bond is not distinctly visible in the spectrum and might be merged with the sp 3 C peak.…”