Preparation And Capacitance Performance Of Carbon-based Electrode Materials For Electrochemical Capacitors

This paper was addressed on studying the carbon electrode materials for electrochemical capacitors with low cost, high specific energy and high power density. High performance carbon electrodes for capacitors were prepared using phenol-formaldehyde resin, petroleum coke and melamine resin as precursor. The preparation technology, structure, capacitance performance and the mechanism of energy storage for carbon electrode material were investigated deeply.The low cost carbon electrode was prepared by CO2 one-step activation of resole phenol-formaldehyde resin for the first time. The effect of activation temperature and activation time on the structure and capacitance performance of phenolic resin based micropore carbon was investigated systematically. The phenolic resin based micropore carbon prepared under optimum conditions had specific surface area over 2200m2/g and pore size of 1~2nm. The specific discharge capacitance was as high as 211.6F/g in the 30wt% KOH aqueous solution showing excellent power performance and cycle performance.The phenolic resin based porous carbon with different specific surface area and pore size distribution was prepared by KOH activation. The capacitance performance was investigated both in 30wt% KOH aqueous and in 1M Et4NBF4/PC electrolyte.The phenolic resin based porous carbon did not exist"ion sieving"in aqueous electrolyte since almost all the pores could form effective electric double layer, while it exhibited"ion sieving"in organic electrolyte because the pores of size smaller than 0.7nm could not form effective electric double layer. Micropore of 1~2nm was the optimum pore size for the formation of electric double layer, and suitable amount of mesopore was beneficial to the improvement of power capacitance for capacitors.The nanocrystallite carbon was prepared by KOH activation using petroleum coke as precursor. The effect of pre-carbonization temperature and activation temperature on the structure and capacitance performance of nanocrystallite carbon was investigated. The practical possibility and mechanism of novel energy storage were discussed. It was found that the combination of pre-carbonization and activation could realize the control of pore structure and nanocrystallite structure. And material with low specific surface area, large space interlayer and high electrode density could be obtained which displayed better capacitance performance than that of commercial activated carbon YP15. The essential of"electrochemical activation"was the process for the insertion of electrolyte ion into ordered or disordered crystallite interlayer which was confirmed by galvanostatic charge/discharge test and semi in-situ XRD analysis. For the first time the increase of interlayer space for ordered carbon crystallite and the formation of SEI-like layer on the surface of nanocrystallite carbon were observed by HRTEM. The mechanism of intercalation energy storage was shown by the combination of SEM, HRTEM observation and EDS spectra analysis.The nitrogen-enriched carbon material with low surface area was prepared using commercial melamine resin as precursors by carbonization for the first time. Results showed that the nitrogen-enriched carbon with low surface area had a high gravimetric capacitance of 205.5F/g, good power capacitance and cycle stability. The excellent power performance was associated with the pseudocapacitance provided by pyrrolic nitrogen or pyridine nitrogen on the surface of nitrogen-enriched carbon materials.