Preparation And Electrochemical Performance Of Silicon Carbide Derived Carbon/Mesophase Pitch Carbon

In order to combine the advantages of Lithium-ion batteries with a high energydensity and supercapacitors with a high power density, the porous carbon that canstorage energy by double layer was combined with graphite-like carbon which caninsert/extract Li+to systhesize a composite in this article. Silicon carbide/mesophasepitch carbon precursors were prepared by mixing polycarbosilane and mesophase pitchwith different mass ratios at320oC and then pyrolysis, carbonization and graphitizationat different temperatures. The as-prepared precursors were etched by Cl2to obtainsilicon carbide derived carbon/mesophase pitch carbon composites with networkstructure. Polarizing microscope, X-ray diffraction, Raman spectrum, transmissionelectron microscope and nitrogen adsorption/disoportion were used to detect theinfluences of heat treatment temperature, PCS/MP mass ratio and etching temperatureon the micro-morphology, pore structure and distribution of the composites. Theprepared composites were used as anode and electrode of Li-ion batteries andsupercapacitors, respectively. Galvanostatic charge-discharge tests, cyclic voltammetryand electrochemical impedance were used to investigate the influences of pore structure,the distribution and proportion of two phase carbon of the composites on the propertiesof charge storage. The results show as follows:(1) By controlling the PCS/MP mass ratio and heat treatment temperature,well-distributed porous silicon carbide derived carbon and the different graphitizationdegrees of mesophase pitch carbon with network structure can be obtained. Mesophasepitch carbon presents small globular dispersing in the silicon carbide derived carbon at ahigher PCS/MP mass ratio. With the mass ratios decrease, the lamellar layer structure ofmesophase pitch carbon becomes more obvious, silicon carbide derived carbon isuniformly dispersed in the mesophase pitch carbon.(2) The preliminary heat treatment temperature, PCS/MP mass ratios and etching temperature have significant influences on the micro-morphology and specific surfacearea of the obtained SiC-CDCs/MPC. The specific surface area of the compositesdecreases with the increasing of heat treatment temperatures. When the heat treatmenttemperature keeps the same, SiC-CDCs/MPC prepared by a large mass ratio of PCS/MPhas a bigger specific surface area. Improving the etching temperature, the degree ofgraphitization of the carbide derived carbon is improved and becomes more ordered.The specific surface area reaches the maximum when the etching temperature is1000oC.(3) Heat treatment temperatures and PCS/MP mass ratios have marked impacts onthe performance of SiC-CDCs/MPC as the cathode material of Li-ion batteries. Byadjusting the PCS/MP mass ratio and heat treatment temperature, specific capacity andrate performance of SiC-CDCs/MPC can be significantly improved. The cycleperformance and the rate performance of SiC/MPC prepared at3000°C andSiC-CDCs/MPC followed by heat-treated at3000°C have been greatly improved.(4) SiC-CDCs/MPC composites also show higher specific capacitance as theelectrode of supercapacitor. With the increasing of heat treatment temperature, thespecific capacitance firstly increases and reaches a maximum at1800°C, and then drops.It exhibits a good capacitive performance under different current densities. Differentetching temperatures have a great influence on the specific capacitance. The specificcapacitance has a maximum value at1200°C.