Preparation Of Activated Carbon From Petroluem Coke And The Research On Its Double-layer Capacitance Performance

In this paper, the high surface area activated carbon (HSAAC) was prepared from petroluem coke by the activation of KOH. The influences of the ratio of KOH to petroluem coke, the activating temperature and activating time on yield, pore structure and capacitance characteristic of HSAAC had been investigated. Based on these, the technologic methods and conditions of controlling structure and properties of HSAAC had been established. All activated carbon were adapted to electrode materials for electric double-layer capacitors (EDLCs), the electrochemical characterizations including charge- discharge performance, cyclic voltammetry and AC impedance were determined in 1mol/L LiPF6 electrolyte and 30wt% KOH electrolyte, and also the relations between the pore structure and the electrochemical properties of petroluem coke-based HSAAC were investigated.Experiment results show that the structure and performance of activated carbon are influenced mainly by the content of activating agents, activating temperature and activating time. The yield of HSAAC decreases with the increase of KOH, activating temperature and activating time while the BET specific surface area, total pore volume of HSAAC increase firstly and then decrease.The pore volume of pore size ranges from 2~5 nm increase obviously, and double-peaks exhibited in the pore size distributions with increasing the contents of KOH, activating temperature or activating time.The capacitance of petroluem coke–based HSSAC, when using 1mol/L LiPF6 as nonaqueous electrolyte, increase firstly and then decrease with the increase of KOH, activating temperature and activating time. The shape of cyclic voltammetry curve is similar to rectangle and obviously symmetrical without the peak of Faraday, which demonstrates that capacitance of HSSAC is mainly supplied through the electric double-layer formed at the the electrode / electrolyte interfaces. The half circular arcs,in high frequency of the AC impedance spectrum of EDLCs using HSSACs, is dissimilar, which indicates that the different transfer speed of electrolyte ions in different pore structues of HSSACs. It is advantageous to improve the transfer speed of electrolyte ions and reduce the resistance through the increase of mesopores in the petroluem coke–based HSSAC.The optima technologic conditions of preparing petroluem coke -based HSAAC by orthogonal test are ratio of KOH to petroluem coke 5, activating temperature 900 ℃and activating time 1 hours respectively. When at optima preparing conditions mentioned above, BET specific surface area and total pore volume of HSAAC reach 2646m2/g and 1.66cm3/g respectively. The electrode fabricated with the activated carbon exhibit high specific capacitance of 173.0 F/g in nonaqueous electrolyte (1mol /L LiPF6 solution) and 278.0F/g in aqueous electrolyte(30wt% KOH solution), which is much higher than the commercial activated carbon materials for EDLC. Moreover, the slight capacitance decay at high current density demonstrsates that the good rate performance of the activated carbon materials.The capacitance of petroluem coke-based HSAAC increases gradually with increasing the total surface area and total pore volume. The capacitance of HSAAC is supplied by microporous surface Cmicro and mesoporous surface Cmeso, However, The capacitance is mainly contributed to microporous surface Cmicro in aqueous electrolyte, and tied to mesoporous surface Cmeso in nonaqueous electrolyte.