Preparation, Characterization And Capacitive Properties Of Petroleum Based Activated Carbon

Supercapacitors were recognized as a new kind of electrochemical energy storage device with the advantages of high charge-discharge power density,long cycle life,no pollution,et al.They have been widely used in many fields such as electronic devices,information technology, electric vehicles and aviation & aerospace for the excellent properties.In this paper,a series of research have been carried out in order to obtain the activated carbon with high tap density and high specific capacitance. Activated carbon samples were prepared and the physical properties like yield,tap density,BET specific surface area and the pore structure of activated carbons were analyzed.On the other hand,the electrochemical properties of samples,such as constant-current charge-discharge measurement,cyclic voltammogram,and electrochemical impedance spectroscopy were investigated in non-aqueous electrolytes.The main results are as follows:(1) Taking petroleum cokes as raw material,activated carbons C_A and C_B have been prepared by chemical activation and physicalchemical activation,and the physical and electrochemical properties are studied.It can be found that C_A shows higher yield,tap density and BET specific surface area,which respectively are 61.28%,0.35 g/ml and 2760 m²/g,comparing to C_B.However,C_B has higher mesopore ratio of 24% and pore diameter of 2.3nm than CA.At the current density of 1 A/g,C_A attains the highest specific capacitance of 137.8 F/g.On the other hand, C_B shows good power discharge behavior with the capacitance loss of 4.7%at the current density of 20 A/g.(2) The effects of particle size of petroleum cokes on material and electrochemical properties of activated carbon were studied.Results indicate that the yield increases then decreases with the decreasing particle size of petroleum coke,and attain the biggist value at the particle size of 325～400 mesh.On the other hand,the activated carbon prepared by petroleum cokes of＜400 mesh shows the highest specific capacitance of 140.0 F/g.And activated carbon prepared by petroleum cokes of 325～400 mesh shows good power discharge behavior,the specific capacitance is 126.6 F/g at the current of 1 A/g and 116.2 F/g at the current of 20 A/g.(3) A,B,C and D were used in chemical activation process as activating agent respectively,and the effects of activating agent on properties of activated carbon were investigated.It can be found that the activated carbon prepared from A has the highest specific capacitance and the lowest tap density comparing with the samples made from other activating agents.Besides,the activated carbon prepared from B has the relatively higher tap density and lower specific capacitance,comparing with that made from A.Samples made from C and D has ultra-high tap density and inferior specific capacitance,with the unideal power discharge properties.It is obviously that the characteristic of activated carbon was improved when using mixed alkali metals hydroxide of different mass ratio as cooperation activating agent.The activated carbon with excellent characteristic can be obtained by controlling the mass ratio of A and B,and activated carbon C₂₁ shows good physical and electrochemical properties when the mass ratio was 2:1,with the tap density of 0.41 g/ml,specific capacitance of 114.0 F/g at the current density of 1 A/g.With the current density increasing from 1A/g to 20 A/g, the activated carbon shows ideal power discharge behavior and the specific capacitance was still kept at 93.4%.(4) The enlargement of activated carbon was carried out by the process optimized from previous experiments,with the prepared activated carbon C_BS as electrode material and the cylinder supercapacitor was prepared.Results indicate that C_BS has the familiar properties with the C₂₁ prepared in the pervious experiment,with the yield of 65%,tap density of 0.40 g/ml,BET specific surface of 1509 m²/g and mesopore ratio of 16.6%.The size of the supercapacitor isΦ12.5x28mm,and the capacitance is 14.7 F in the electrolyte of Et₄NF₄/AN,with the ESR is 45 mΩ.The mass specific capacitance of the supercapacitor is 135.9 F/g at the current density of 0.5 A/g.With the current density increasing to 10 A/g,the mass specific drops to 124.5 F/g.But it still shows ideal power discharge behavior.The current leakage is less than 2 mA after keeping stable voltage of 2.7V for 2h.After 2000 times cycles,the capacitance decay is only about 4%,compared with the capacitance of 500th cycle. The prepared supercapacitor shows ideal temperature properties,which can be operated at the temperature range of-40℃～70℃without obvious loss of capacitance.The ESR of the supercapacitor decreases firstly and then increase with the temperature raiseing.