The Preparation Of Coal-Based Activated Carbon And Investigation Of Electrochemical Performance

Compared to energy storage devices, such as batteries and conventional capacitors, supercapacitors perform as an environmental friendly energy system with high coulombic efficience and have been widely used in the military devices, electronic devices and new energy power generation. Due to the excellent properties of high specific surface area and well-developed porosity, activated carbons have played an important role in the carbon-based supercapacitors. Although coal resources are rich in Xinjiang, the coal chemical industry may develop slowly due to the shortage of water resource and also it can severely cause environmental problems. Besides, the Xinjiang non-caking coal have high carbon content and low ash content and it is suitable for preparing the coal-based activated carbons for supercapacitors.In this thesis, Xinjiang coal was used as a carbon precursor, potassium carbonate, zinc chloride and steam were used as activation agents. Coal-based activated carbons were prepared by chemical activation and physical activation. At the same time, boron and nitrogen atoms were successfully incorporated the carbon precursor. Boric, melamine and urea were used as boron and nitrogen source respectively. FTIR spectroscopy and XPS reveal the surface chemistry of as-prepared samples. Nitrogen sorption isotherms indicate the porosity of activated carbons. The electrochemical behavior was tested by cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy. Also, the surface chemistry and porosity of activated carbons are associated with the electrochemical behaviors. The main details are as following:1、By using the methods of potassium carbonate and zinc chloride activation, the specific surface area of as-prepared samples can reach about 1000 m2 g-1, which is much higher than non-activation samples and the yields can reach in the range of 80%-83%. Among which, KAC-1.5 and ZAC-2 with a higher specific surface area and suitable pore structure exhibit excellent specific capacitance of 175 and 190 at 0.5 A g-1 respectively.2、B,N co-doped activated carbons were fabricated by solid-state ball milling and steam activation. The content of B increases with the activation time. When activation time was set to 120 minutes, BNAC-120 exhibits a high specific surface area (1312 m2 g-1) and content of B and N (1.78 wt%,1.66 wt%) and highest specific capacitance of 176 F g-1, which is 64% higher than non-doped sample.3、When urea was used as nitrogen source, the content of N reduced to 1.05 wt %. And also, with the increase of boric resource, the content of B decreased. MBAC-3-3 under a low activation temperature (800 ℃) and high content of boric and melamine can reach the same specific surface area to the sample under the high activation temperature (850 ℃). Among them, MBAC-3-3 has a high specific surface area of 1104 m2 g-1 and the capacitance has no obviously loss after 20000 cycles.