Preparation Of Biomass-based Porous Carbon/MnO₂ Composite Electrode Materials And Their Supercapacitor Performances

Supercapacitor is a new energy storage device.Compared with the traditional energe storage devices that consume petroleum and coal resources,supercapacitors have the characteristics of environmental protection,high power density and fast charge capability.As a core element of the supercapacitor,the electrode receives a great deal of attention,and a lot of research has been done on it.The biomass-based carbon electrode is cheap and widely available,and its natural porous structure can effectively improve its specific capacitance.Asymmetric supercapacitors are made of different electrode materials which can effectively increase the voltage window of the device and increase its energy density.In this thesis,pomelo peel was the carbon source,and the effect of different temperature on the performance of activated carbon electrode supercapacitor was explored.Meanwhile,based on this research result,asymmetric supercapacitors were prepared by complexing activated carbon electrodes with MnO₂.The main contents are as follow:?1?Taking pomelo peel as carbon precursor,activated carbon was prepared by KOH two-step activation,and the effect of different temperatures from 400? to700? on the performance of the supercapacitor was explored.In 1M H₂SO₄ electrolyte,the material at 600? has the best performance with an energy density of 7.3 Wh/kg,a mass specific capacitance of 208.7 F/g,and a volume specific capacitance of 219.3F/cm³ at a current density of 1 A/g.In the organic electrolyte1-ethyl-3-methylimidazolium tetrafluoroborate?EMIMBF₄?,the highest energy density can reach 21.6 Wh/kg at a current density of 1 A/g,and the capacitance retention was96.2%after 10,000 cycles at a current density of 5 A/g.?2?In order to ensure the porous structure and excellent performance of carbon electrodes,activated carbon was prepared by freeze-drying and activation at 600?.A composite electrode material of pomelo peel activated carbon and MnO₂ were prepared by method of vacuum thermal decomposition of KMnO₄,then used this composite material as the positive electrode,activated carbon as the negative electrode to produce asymmetric supercapacitors.This asymmetric supercapacitor had been tested to show excellent performance.The specific capacitance of the asymmetric supercapacitor was254.4 F/g when the voltage window was 0-1.8 V and the current density was 1A/g in1M Na₂SO₄ electrolyte.At the same time,a higher energy density of 28.3 Wh/kg was obtained,and its capacity retention exceeded 80%after 6000 cycles.