Preparation Of Coconut Shell And Coconut Meat-based Porous Carbon And Application In Supercapacitor

The problem of energy and the environment is more and more serious in recent years,the development of new energy vehicles is expected to reduce gasoline consumption and pollutant emissions. Because of the high security, long cycle life, the low environmental pollution in the field of new energy, super capacitors are widely used in the new energy storage filed, especially the electro vehicle. In this paper, coconut shell-based activated carbon was prepared from coconut, and its application in supercapacitor was studied.The high surface area of the obtained activated carbon was up to 3512.83 m2 g-1, and its pore volume reached 2.11 cm3 g-1, which contained 39.3% mesoporous. In general, the presence of mesopore is benefit to the electrolyte ions diffusion, which improves the power density. The oxygen-containing functional groups on the carbon surface improve the infiltration of the electrolyte and enhanced accessibility of ions to more surface area, thus increasing the specific capacitances.The AC-4 electrode exhibits a high specific capacity of 325 F g-1 in the aqueous electrolyte and has an energy density of up to 11.28 Wh kg-1 with outstanding rate performance and excellent cycle life. In order to improve the energy density of the device,the wider voltage window with ion liquid was selected as the electrolyte, the specific capacitance of 198 F g-1 was obtained at 0.1 A g-1. When the power density was up to 74.2 kW kg-1, the high energy density of 46.6 Wh kg-1 still retained. These electrochemical tests show that coconut shell-based activated carbon prepared by low cost and simple methods has excellent capacitive properties, which is expected to be used in high power and renewable energy storage devices.In order to further improve the energy density of the supercapacitor, we used the prepared coconut meat-based porous carbon and Si/C to assembly a lithium ion hybrid supercapacitor (LIC). The effect of the pre-intercalation of lithium on the specific capacity,cycle stability and rate performance of LIC was studied. The optimum performance was obtianed when the degree of pre-intercalation was 100%. From the results of electrochemical test, the galvanostatic current charge-discharge test of LIC shows a high specific capacity of 70.7 mAh g-1 at current density of 0.1 A g-1 and still as high as 37 mAh g-1 at 50 A g-1, with ～52.3% capacity remained. LIC-100% exhibits a maximum energy density of 224 Wh kg-1 at 158.3 W kg-1, while remains of 102 Wh kg-1 with an elevated power density of 68.9 kW kg-1. Compared to the ionic liquid-based double-layer supercapacitor, the energy density of LIC increased by 2 times. These results show that the LIC will used in a wider range and has the potential to replace lithium batteries in some areas.