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

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℃ (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.

Preparation,Characterization and Electronic Properties of Fluorine-doped Tin Oxide Films

Tin oxide（SnO2） and fluorine doped tin oxide（FTO） films were prepared on glass substrates by sol-gel spin-coating using SnCl4 and NH4F precursors.Fluorine doping concentration was fixed at 4 at%and 20 at%by controlling precursor sol composition.Films exhibited the tetragonal rutile-type crystal structure regardless of fluorine concentration.Uniform and highly transparent FTO films,with more than 85%of optical transmittance,were obtained by annealing at 600℃.Florine doping of films was verified by analyzing the valence band region obtained by XPS.It was found that the fluorine doping affects the shape of valence band of SnO2 films.In addition,it was observed that the band gap of SnO2 is reduced as well as the Fermi level is upward shifted by the effect of fluorine doping.

Hydrophobic, mechanical, and tribological properties of fluorine incorporated hydrogenated fullerene-like carbon films

Fluorine-incorporated hydrogenated fullerene-like nanostructure amorphous carbon films(F-FLC)were synthesized by employing the direct current plasma enhanced chemical vapor deposition(dc-PECVD)technique using a mixture of methane(CH4),tetra-fluoromethane(CF4),and hydrogen(H2)as the working gases.The effect of the fluorine content on the bonding structure,surface roughness,hydrophobic,mechanical,and tribological properties of the films was systematically investigated using Fourier transform infrared spectroscopy(FTIR),X-ray photoelectron spectroscopy(XPS),Raman analysis,atomic force microscope(AFM),contact angle goniometer,nano-indenter,and reciprocating ball-on-disc tester,respectively.The fluorine content in the films increased from 0 to 2.1 at.%as the CF4 gas flow ratio increased from 0 to 3 sccm,and incorporated fluorine atoms existed in the form of C-FX(X=1,2,3)bonds in the film.The fullerene nanostructure embedded in the hydrogenated amorphous carbon films was confirmed by Raman analysis.The water contact angle was significantly increased because of fluorine doping,which indicates that the hydrophobicity of the carbon films could be adjusted to some extent by the fluorine doping.The hardness and elastic modulus of the films remained relatively high(22 GPa)as the fluorine content increased.Furthermore,the friction coefficient of the carbon films was significantly reduced and the wear resistance was enhanced by fluorine doping.