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.
Highlights
Lithium-ion batteries (LIBs) have become widely used electrochemical energy storage system because they have many advantages, such as high reversible capacity and excellent rate stability [1, 2]
The digital photographs of pristine hard carbon (HC) and F-doping hard carbon (F–HC) (Fig. S1) reveal that the color of HC becomes lighter after fluorination, indicating that F probably bonds with C and changes the color of materials [29]
Only diffraction rings exist in the SEAD patterns of F–HC, verifying that the ordered domains are disrupted by F 2 gas even at a relatively low temperature
Summary
Lithium-ion batteries (LIBs) have become widely used electrochemical energy storage system because they have many advantages, such as high reversible capacity and excellent rate stability [1, 2]. The resultant F–HC with a semiionic C–F bond, desirable F doping degree, and enlarged interlayer distance yielded a higher specific capacity and better cycling stability than pristine HC. After F doping, the FESEM images of F–HC (Fig. S2b–d) illustrate the preserved pristine morphological characteristics of HC without an obvious decrease in size and porous structure on the surface that differs from that of HC fluorinated at high temperatures [28].
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