Dissertation > Industrial Technology > Electrotechnical > Electrical > Capacitor

Preparation of Carbon-based Electrode Materials and Their Influence of Pore Structure on Capacitance Performance for Electrochemical Capacitors

Author WangYanSu
Tutor WangChengYang
School Tianjin University
Course Chemical processes
Keywords EDLC electrochemical properties porous carbons template pore structure electrolyte
Type PhD thesis
Year 2008
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Electrochemical double layer capacitors (EDLCs) are promising another new energy storage instrument after the lithium batteries, they will play an important role in national economy. The general carbon materials although have high surface area, the smaller pore size limits the diffusion of the electrolyte ions in the pores of the carbon. Though there is high theoretic specific capacitance, it will decrease when the working current increase, the power-energy performance gets worse. EDLCs need appropriate pore structure of the electrode materials to get higher power performance. Thus, tailoring the porous structures of carbon materials is a major goal of EDLC optimization. Based on the above depiction, in this paper, carbon materials with different pore structures were prepared, and their electrochemical performance were tested in different electrolyte in order to examine the suited electrolyte ion size and the pore structure, and expect to get new method for the electrode materials of EDLCs with higher power characteristic.First, one bought activated carbon with high surface area was used as the electrode material for the EDLCs, and tested its electrochemical performance in four electrolytes, in order to ascertain the optimal electrolyte with the best power-energy performance at fixed conditions. Results indicated that the best electrolyte was 1M LiClO4/PC in practical at the tested conditions.Then, activated carbons with different pore structures base on petroleum coke were prepared, and they were used as electrode materials of EDLCs. Their electrochemical performances were tested in 1M Et4NBF4/PC. By analyzing the pore characteristic of the electrode materials, testing their electrochemical performance and associating with the response time in the impedance spectrum, it could be confirmed qualitatively that the suited pore size range for the electrolyte ion was 1-3nm.And then, templated mesoporous carbons with high yield, high surface area, more mesopore and controllable pore structure were successfully prepared from thermoplastic precursor pitch, by the carbonization of a mixture with the MgO precursors (magnesium acetate and citrate), the difference of the prepared carbons is their different average pore size. After testing their electrochemical performance in 30wt%KOH, results indicated that the resultant mesoporous carbons could achieve perfect specific capacitance 220F/g at the current density 25A/g, and they could get good power characteristic and voltage maintenance. The capacitance maintainance of the prepared carbons could reach 90% at 25A/g, and the leakage current was lower than 0.05mA. The mesoporous carbons prepared from the mixture of magnesium acetate and the pitch got comparatively bigger pore size and obtained better power characteristic. But the mesoporous carbons prepared from the mixture of magnesium citrate and the pitch were ideal electrode materials if paying attention to the higher specific capacitance at lower current density.

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