Functionalization Of Fullerenes And Their Application In Sodium Batteries

Fullerene C₆₀ has attracted special attention in the field of energy storage owing to its unique structure and amazing physical&chemical properties.Various fullerene derivatives can be easily synthesized by introducting functional groups on the unsaturated bonds in fullerene cages.The abundant fullerene-based materials can not only be directly used as electrode materials,but also as modifiers to improve the electrochemical performance of other materials.This dissertation aims to expend the application of fullerene-based materials in sodium batteries.We have carried out the following work:（1）Fullerene-intercalated graphitic carbon nitride(C₆₀@CN)composities,in which fullerene as a bifunctional additive not only enhances the electronic conductivity but also enlarges interlayer spacing,are synthesized to improve the sodium storage performance of graphitic carbon nitride（g-CN）.As an anode material for sodium-ion batteries,C₆₀@CN displays high reversible capacity(430.5 m Ah g^-1),which is 3.8 times higher than that of pristine g-CN.Even at 5 A g^-1,C₆₀@CN exhibits high reversible capacity of101.2 m Ah g^-1 after 5000 cycles,showing excellent rate capability and ultra-long cycle life.Moreover,the high-loading C₆₀@CN electrode exhibits an areal capacity of1.35 m Ah cm^-2.Furthermore,a sodium-ion full cell combining C₆₀@CN anode and Na₃V₂（PO₄）₂F₃@r GO cathode displays exceptionally high energy density(359.8 Wh kg_anode^-1/105.1 W kg_anode^-1),promising great potential for future application.（2）Nitrofullerene(C₆₀（NO₂）₆)is designed and synthesized as an electrolyte-compatible additive to improve the electrochemical performance of sodium metal batteries.C₆₀（NO₂）₆ shows high solubility in both carbonate and ether electrolytes;and promotes the formation of desirable solid electrolyte interface（SEI）layer with sodium nitrides and fullerene,which induces the uniform Na deposition and suppresses the dendritic growth.Na||Na symmetrical cells show low voltage hysteresis,high rate capability and prolonged cycle life in both carbonate and ether electrolytes with C₆₀（NO₂）₆.Moreover,compared with the blank electrolytes,Na||Na₃V₂（PO₃）₄@C full cells exhibit significantly enhanced cycling stability in both ester and ether electrolytes with nitrofullerene.（3）Trifluormethylfullerene(C₆₀（CF₃）₆)is designed and synthesized as a new F-containing electrolyte additive to improve the rate capability of sodium metal batteries.C₆₀（CF₃）₆ not only enhances sodium-ion migration in electrolyte,but also assists the formation of a Na F-rich SEI layer.Moreover,Na||Cu cells with C₆₀（CF₃）₆ can be stably cycled at 2 m A cm^-2 over 250 cycles with an average Coulombic efficiency of 99.9%,and event at a capacity up to 10 m Ah cm^-2 over 180 cycles.Meanwhile,Na||Na symmetric cells with C₆₀（CF₃）₆ can be stably cycled at 10 m A cm^-2 over 600 cycles.Furthermore,Na||Na₃V₂（PO₃）₄@C full cell with C₆₀（CF₃）₆ displays a high capacity retention of 84%at20C(～3 m A cm^-2)after 2000 cycles.（4）Bromofullerene is designed and synthesized as an interface stabilizer to enhance the stability of sodium metal anodes based on the former two chapters.A Na Br-rich inorganic/organic hybrid interfacial protection layer is formed by the reaction of sodium with bromofullerene.This protection layer with high sodium-ion conductivity effectively inhibits the side reactions on the electrode/electrolyte interface and induces the the uniform Na deposition,thus the cycling performance of sodium metal anodes can achieve2.3 times speedup.Meanwhile,the full cell assembled with Na₃V₂（PO₄）₃@C cathode exhibits high Coulombic efficiency（～100%）,suggesting highly reversible Na plating/stripping.