Anthracite Based High Surface Area Activated Carbon Preparation And Its Application In The Electric Double Layer Capacitor Research

In this paper, the high surface area activated carbon (HSAAC) was prepared from low-ashed anthracite by the activation of KOH. The influences of the ratio of KOH to anthracite, the activating temperature and activating time on yield, adsorption properties, 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 have been established. The morphology of anthracite-based HSAAC was observed by scanning electron microscope; the structure of graphite microcrystalline in anthracite-based HSAAC was analyzed by X-ray diffraction analyzer; the specific surface area (BET) and pore structure of anthracite-based HSAAC were determined by adsorption method of low temperature nitrogen. The relations between specific capacitance of anthracite-based HSAAC and its specific surface area (BET) and pore structure were discussed. Using anthracite-based HSAAC as the electrode materials of electric double-layer capacitor (EDLC), its charge-discharge performance in 30wt%H2SO4 , 30wt%KOH and 1mol/L LiPFg electrolyte and the relations between the charge-discharge performance and specific surface area, pore structure of anthracite-based HSAAC were discussed.Experiment results show that the structure and performance of activated carbon (AC) are influenced mainly by amount of activating agent, activating temperature and activating time. The yield of AC decreases with the increase of KOH, activating temperature and activating time while at first the amount of iodine adsorption increases then decreases. The amount of iodine adsorption of AC reached maximum when the ratio of KOH to anthracite, activating temperature and activating time are 5, 750 C and 1.5 hours respectively. And the amount of iodine adsorption of AC is greatly influenced by its pore distribution, specific surface area and pore volume.Anthracite-based HSAAC prepared by activation with KOH, is mainly of micropores smaller than 2nm .We can increase the proportionality of its mesopores (> 2 nm) by increasing KOH, activating temperature and suitable activating time.The specific capacitance of anthracite-based HSAAC increases gradually with increase of the specific surface area, but the relationship between them is not lineardependence. It is because AC has more micropores and its surface is difficultly smeared by electrolyte.Anthracite-based HSAAC, used as the electrode materials of EDLC, has good performances in charge-discharge and cycling in 30 wt% H2SO4 , 30 wt% KOH and 1mol/L LiPFe electrolyte. It can discharge not only under the small current condition and long time, but also under the large current condition and short time. Its capacitance decreases under large discharge current, because anthracite-based HSAAC has too many micropores and low transport speed of solvated ions in electrolytes. The mass specific capacitance of anthracite-based HSAAC is smaller in organic electrolyte than that in aqueous electrolyte, because the diameter of solvated ions in the former is bigger and its electrical conductance smaller.The optima technologic conditions of preparing anthracite-based HSAAC by orthogonal test are ratio of KOH to anthracite 4, activating temperature 750 C and activating time 1.5 hours respectively.After the anthracite-based HSAAC is soaked in HC1, its charge-discharge performance becomes better while its specific capacitance decrease slightly.