Research And Application Of Novel Electrolytes For Carbon-based Electrochemical Supercapacitors

Compared with lithium-ion battery,electrochemical supercapacitors has a lower specific energy and a higher specific power,while maintaining a high specific power, it is essential to raise specific energy to resolve the issue.To improve the single supercapacitor's energy,ti is needed to raise the voltage at the same time,to increase the capacitance.Working voltage is related to decomposition voltage of the electrolyte.At present,the working electrolytes of supercapacitors mainly include: aqueous electrolyte,organic electrolyte,solid electrolyte and gel electrolyte.Aqueous electrolytes are generally the sulfuric acid solution or potassium hydroxide solution, which can provide high capacitance,low energy density and easily cause corrosion of equipments and the prepared single supercapacitor has a low working voltage(about 1V).Organic electrolyte for tetraethylammonium tetrafluoroborate salt electrolyte, the prepared single supercapacitor has a working voltage of more than 2.15 V;but organic solvents are volatile,their conductivity and operating voltage to increase difficultly,security trouble have impact on the environment to a certain extent.Solid polymer electrolyte in the supercapacitors have been limited,because most of the polymer electrolyte conductivity is low.The contact between electrode/electrolyte is very poor at room temperature,and solubility of electrolyte salts in the polymer matrix is relatively Low.Especially when the capacitors charge,the low solubility will lead to crystalization of electrolyte salt in the vicinity of polarization electrode. Therefore,it has become an urgent pursuit to look for novel electrolyte materials in this industry,which possesses high-conductivity,wide electrochemical window and low pressure.At present,a new material—room temperature molten salt(also known as room temperature ionic liquids,or ionic liquids) because it has many excellent properties, such as very low vapor pressure,no combustion,high electrochemical stability, chemical and physical stability Higher,so ionic liquid electrolyte in electrochemical supercapacitors,lithium secondary batteries,solar cells,and other electrochemical components and its impact on the performance of the battery electrolyte has become a hot point.In this paper,we study two new ionic liquids and an organic as electrolytes applied to electrochemical capacitor based on previous studies,respectively.This paper is divided into five chapters:ChapterⅠoutlines at home and abroad the research development of electrochemical capacitor and electrolytes for them,as well as the development of ionic liquids,the preparation and the properties.Finally,we present the general idea and research orientation of the paper;ChapterⅡoutlines application research and testing methods of ionic liquids as the electrolytes in the electrochemical supercapacitors;ChapterⅢpresents preparation and characterization of room temperature molten salt electrolyte LiBOB-2-oxazolidinone(OZO) and characterization of its application in electrochemical supercapacitors.We prepared with different molar ratio of 2-oxazolidinone(OZO) composite molten salt electrolytes,conductivity tests showed that the mole ratio of 1:7 for the complex system of higher conductivity,CV tests show that the system can reach potential window 3.9 V.With the best performance of the complex electrolyte assembled in electrochemical capacitors,activated carbon in the system has a good capacitance behavior.Experimental results show that the electrical conductivity of the electrolyte increase as the temperature increases,and the cycle performance of capacitors become better,and the specific capacitance also increased,an excellent electrolyte in line with request for electrochemical supercapacitors.ChapterⅣpresents preparation and characterization of room temperature molten salt electrolytes LiBOB-acetamide and characterization of its application in electrochemical supercapacitors.We prepared with different molar ratio of LiBOB-acetamide composite molten salt electrolyte,conductivity tests showed that the mole ratio of 1:7 for the complex system of higher conductivity,CV tests show that the system can reach potential window 2.7 V.With the best performance of the complex electrolyte assembled in electrochemical capacitors,activated carbon in the system has a good capacitance behavior.Experimental results show that the electrical conductivity of the electrolyte increase as the temperature increases,and the cycle performance of capacitors become better,and the specific capacitance also increased,an excellent electrolyte in line with request for electrochemical supercapacitors.ChapterⅤdescribes electrochemical properties of LiBOB-based aprotic solvent (1,3-dimethyl-2-imidazolinone,DMI) organic electrolyte and its applied research in an electrochemical capacitor.In our lab,We Prepared 0.7 M LiBOB/DMI.Tests show that the electrical conductivity of the system reaches 2.16 mS cm^-1 at room temperature;CV shows that the potential window reaches 3.0 V.As an electrolyte for activated carbon-based electrochemical supercapacitors.The results show that activated carbon in the system has a good capacitance behavior and an excellent cycle efficiency with cycle numbers in 2000,the capacity can be maintained at 28.2 Fg^-1.So we think it is a novel kind of liquid electrolyte for electrochemical supercapacitors.ChapterⅥpresents the conclusions and prospects in the future.