Abstract
Porous graphite was prepared without the use of template by rapidly heating the carbonization products from mixtures of anthracene, fluorene, and pyrene with a CO2 laser. Rapid CO2 laser heating at a rate of 1.8 × 106 °C/s vaporizes out the fluorene-pyrene derived pitch while annealing the anthracene coke. The resulting structure is that of graphite with 100 nm spherical pores. The graphitizablity of the porous material is the same as pure anthracene coke. Transmission electron microscopy revealed that the interfaces between graphitic layers and the pore walls are unimpeded. Traditional furnace annealing does not result in the porous structure as the heating rates are too slow to vaporize out the pitch, thereby illustrating the advantage of fast thermal processing. The resultant porous graphite was prelithiated and used as an anode in lithium ion capacitors. The porous graphite when lithiated had a specific capacity of 200 mAh/g at 100 mA/g. The assembled lithium ion capacitor demonstrated an energy density as high as 75 Wh/kg when cycled between 2.2 V and 4.2 V.
Highlights
Carbonization is the first step in the production of synthetic graphite
The anthracene-biphenyl system produced a coke of in-homogeneous optical texture with regions that were similar to pure anthracene and pure biphenyl carbonization
Anthracene mesophase during carbonization as evidenced by the Anthracene goes goesthrough throughananextended extended mesophase during carbonization as evidenced byhigh the optical anisotropy shown in the polarized light micrograph, Figure
Summary
Carbonization is the first step in the production of synthetic graphite. A liquid crystalline state or mesophase formation during carbonization is a key process that determines the property of graphitizable carbon [1,2,3,4]. The nature of mesophase and the resulting carbon product is dependent upon the extent of planarity of intermediate compounds formed, rates of carbonization, fluidity and extent of fluidity, and possible effect of solids on mesophase formation and coalescence [6,7,13,14,15]. Walker and colleagues co-carbonized anthracene and phenanthrene with biphenyl to observe potential retardation of mesophase development and resulting graphitizability by its introduction [7,14,15]. The anthracene-biphenyl system produced a coke of in-homogeneous optical texture with regions that were similar to pure anthracene and pure biphenyl carbonization. The phenanthrene-biphenyl system exhibited a greater homogeneous texture and the observed optical texture of the anisotropic regions dropped sharply with increased additions of biphenyl. The in-homogeneous texture from anthracene-biphenyl and the homogenous texture from phenanthrene-biphenyl is due to the differences in carbonization reactivity between the compounds
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