Controllable Preparation Of Fluorinated Biomass Hard Carbons And Battery Applications

Lithium/fluorinated carbon f batteries have garnered considerable attention due to their high energy density,stable operating potential,low self-discharge,and long storage lifespan.However,fluorinated graphite,which is the most commonly used cathode material,suffers from drawbacks such as low discharge voltage and poor rate capability.Nanostructured fluorinated carbon materials,characterized by large specific surface area,small particle size,and porous structure,exhibit excellent electrochemical reactivity.Nonetheless,their commercialization is limited due to high cost and production instability.In comparison,hard carbon,with its wide availability,low cost,and moderate specific surface area,has become a promising alternative.In this study,we employed saccharides with different degrees of polymerization as carbon sources to investigate the influence of precursor structure on the electrochemical performance of fluorinated hard carbon.1.Firstly,saccharides with varying degrees of polymerization were directly pyrolyzed into hard carbon at the same temperature.Subsequently,a series of fluorinated hard carbon materials were prepared using high-temperature gas-phase fluorination,and their structures and electrochemical properties were examined.Characterization techniques such as SEM,XRD,Raman spectroscopy,N₂ adsorption-desorption,FTIR,and XPS were employed to analyze the properties of both hard carbon and fluorinated hard carbon.The experimental results revealed that an increase in the degree of saccharide polymerization led to higher specific surface area,enhanced pore structure,and increased defect level in the resulting hard carbon.Moreover,fluorination at the same temperature resulted in a decrease in the semi C-F bond and an increase in the content of non-electrochemically active groups（-CF₂ and-CF₃）,thereby compromising the electrochemical performance.The electrochemical performance was further evaluated using galvanostatic discharge tests,demonstrating that higher fluorination temperatures and degrees of polymerization resulted in increased maximum specific capacity but reduced rate capability.Notably,glucose-derived pyrolyzed carbon exhibited excellent electrochemical properties when subjected to heat treatment at a fluorination temperature of 500°C.It achieved a remarkable specific capacity of 876 m Ah g^-1,an energy density of 1872 W kg^-1,and a discharge power density of 3740 W kg^-1 at a discharge current density of 2 A g^-1.These findings provide valuable insights and references for scientists in selecting suitable hard carbon precursors to develop high-performance fluorinated carbon cathode materials.2.Furthermore,glucose,which was selected as the carbon source,was subjected to heat treatment in the range of 1000 to 1600°C to prepare hard carbon.A series of fluorinated glucose-derived carbons were then synthesized via high-temperature fluorination,and the effects of carbonization temperature on the structure and electrochemical performance of fluorinated hard carbon were investigated to achieve high-performance materials.Characterization techniques including SEM,TEM,XRD,Raman spectroscopy,N₂ adsorption-desorption,FTIR,and XPS were employed to analyze the properties of both hard carbon and fluorinated hard carbon.The results showed that an increase in carbonization temperature led to reduced interlayer spacing,decreased specific surface area,gradual crystalline ordering,and lowered oxygen content,thereby making hard carbon less susceptible to fluorination.Under the same fluorination conditions,the fluorine-to-carbon（F/C）ratio decreased,but the content of over-fluorinated groups decreased while the half-cell C-F bond content increased.The electrochemical performance was evaluated using galvanostatic discharge tests,revealing that both voltage plateau and specific capacity increased with increasing carbonization temperature.However,at a carbonization temperature of 1600°C,the fluorine content in the resulting fluorinated hard carbon was minimized,resulting in a decrease in specific capacity.Among them,the FHC-1400-500 exhibited excellent electrochemical performance,achieving a specific capacity of 959 m Ah g^-1 and an energy density of 2224.5 Wh kg^-1 at a discharge current density of 10 m A g^-1.It demonstrated stable discharge at a current density of 4000 m A g^-1 and achieved a power density of 7452 W kg^-1.These findings provide valuable insights and references for the preparation of high-performance fluorinated hard carbon materials.