Study On The Capacitance Performance Of Electrode Materials In Molten Acetates

The energy is one of the basic resources to support the development of modern society,and has a profound impact on the development and progress of modern civilization.With the extensive use of fossil energy,a series of environmental problems appeared.For environmental protection,the sustainable use of energy supply is extremely urgent.Recent years,the developing of solar energy,nuclear energy and wind power has gradually by the attention of human beings.But the instability of wind energy and solar energy limit its application.Therefore,the development of energy storage conversion device with the development of new energy has been widely concerned.Electrochemical capacitor,a new promising energy storage conversion device,has attracted people's enormous attention because of their long cycle life,rapid charge-discharge,high power densities and green environment protection.Electrochemical capacitors have been used in consumer electronics,automotive,electric power and other fields.Electrochemical capacitor is composed of three parts:the material of electrode,electrolyte and separator.This thesis focuses on the research of electrolyte and puts forward to the molten acetates as electrolyte.The decomposition potential of molten salt was investigated by steady state polarization method;cyclic voltammetry,galvanostatic charge discharge and AC impedance method are used to study the electrochemical capacitance behavior in molten salt.In the first section,the decomposition voltage of three kinds of molten salt electrolyte was tested.The results showed that the decomposition voltage of sodium-potassium acetates molten system showed the best,up to 2.35V;the decomposition voltage of lithium-potassium acetates molten salt is slightly worse,can reach 2.14V at 523 K;473 K,the decomposition voltage of molten ternary acetate systemshave the worst performance,only reach 1.70V.In the molten salt,nickel foam is capable of carrying the active material better.In the experiment,nickel foam was used as current collector material for the preparation of activated carbon electrode.The specific capacitance of activated carbon electrode in the potential range of1.50V was 100F/g in the lithium-potassium acetates molten salt.In thesodium-potassium acetates molten system,the cyclic voltammograms of the activated carbon electrode tends to be more rectangular and the specific capacitance was 110F/g in potential range of 1.30V.In ternary acetates molten systems,the specific capacitance was 50F/g⁶0F/g.In the second section,at 523 K,in the lithium-potassium acetates molten salt,cyclic voltammograms of the activated carbon electrode at different scan rates showed that the specific capacitance of was 200F/g at 2mV/s and increased 10 times,only to maintain the 40%specific capacitance;the activated carbon electrode in molten salt hasa better specific capacitance in discharge current range of 50mA¹00mA.At 50mA,discharge specific capacitance reached 150F/g,and the current increases to 100mA,the electrode discharge specific capacitance was reached 100F/g.But the performance of cyclic test was poor.At the same temperature,in the sodium-potassium acetates molten salt,the electrode can achieve larger specific capacitance at low scan rate.With increasing scan rate,the specific capacitance remained relatively better.In addition,the activated carbon electrode has a better performance in different discharge current and maintained a higher specific capacitance.The AC impedance test indicated the electrode performance characteristics are the porous electrode impedance characteristic in molten salt.In the third section,manganese dioxide in lithium-potassium acetates molten salt showed the highest specific capacitance of the electrode at 523 K.Cyclic voltammograms of the activated carbon electrode at different scan rates showed that manganese dioxide electrode capacity can reach 100F/g at 2mV/s,and the capacitance has been maintained 30F/g at20mV/s.In the cycle test,the capacitance of the electrode in the first 50 cycle number attenuated rapidly,attenuation of 73.3%.Compared with the activated carbon electrode in molten salt,manganese dioxide electrode surface keep stability after testing,so we choose a certain proportion of the manganese dioxide and activated carbon to make electrodes and the results showed that theelectrodeof10%MnO₂+60%Cmaintained a stable electrode performance and thehighestspecific capacitance at the same scan rate.