Design Of Super Capacitor Based On New Electrolyte And Study On Intercalation Characteristics

Supercapacitor with ultra high power density and long cycle life have great potential application in electric cars, new rail transit, solar energy, wind power, smart grids and other fields. Based on fundamental storage mechanisms of electric double-layer in porous carbon materials, this paper aims to study on preparation and electrochemical performance of organic electrolyte and electrode materials, which are the key parts of capacitors, and discusses on the relationship of electrolyte ions size and distance of microcrystalline carbon layer of electrode.This work demonstrats the superiority of the spiro-(1,1’)-bipyrrolidinium tetrafluoroborate (SBP-BF4) salt as EDLCs electrolyte salts. The SBP-BF4/PC electrolyte has high electrical conductivity and wide potential window. The SBP-BF4/PC based supercapacitors exhibit good cycle life and the energy density could reach to 43.0 kW/kg at 3.2 V. In order to further demonstrates excellent electrochemical performance of SBP-BF4 electrolyte salt at high working voltages, the mixture solvents compositions are adopted in to the experiment. The physical properties of the mixture solvent composition electrolytes can be tuned by solvent select on such as adding DMC with low viscosity to decrease the viscosity and adding EC with high dielectric constant to increase electrical conductivity. The maximum energy density of EDLCs using the ternary solvent system electrolyte is 47.2 Wh/kg. The EDLCs based on ternary solvent system electrolyte exhibits better cycle performance at the working voltage of 3.5 V. The binary system of PC+DMC exhibit excellent conductive behaviors at low temperature. When the temperature is down to-50℃, the specific capacitance of EDLCs based on binary solvents system electrolyte could reach 92 F/g, and the capacitance maintain ratio is 84.6%.The O-MCMB is prepared by low-temperature oxidation from MCMB graphite, followed by low-temperature oxidation-thermal reduction process to prepare layered micro-expansion carbon microbeads (H-MCMB) with distance of microcrystalline layer in the narrow range (0.3773 nm-0.5678 nm).The specific capacitances of the first cycle of the EDLCs based on SBP-BF4 and SBP-TFSI with the same cations increase from 31.4 F/g and 30.4 F/g to 117.8 F/g and 137.2 F/g, respectively, when the working voltage increases from 2.7 V to 3.5 V. The specific capacitances of the first cycle of the EDLCs based on SBP-BF4, Emim-BF4 and TEMA-BF4 with different cations increases from 31.4 F/g,50.5 F/g and 29.1 F/g to 117.8 F/g,151.9 F/g and 14.0 F/g, respectively, when the working voltage increases from 2.7 V to 3.5 V. When the voltage increases to 4.0 V, while the SBP-BF4 has good rate performance.The specific capacitances of the first cycle of the EDLCs based on H-MCMB with different distance of the macrocrystalline carbon layer are increased from 71.2 F/g,25.8 F/g and 31.4 F/g to 103.9 F/g、136.1 F/g and 153.1 F/g, respectively, when the working voltage increases from 2.7 V to 4.0 V.The micro-expansion carbon microspheres occur electrochemical activation process in the first charge-discharge performance, which is different from the conventional activated carbon charge discharge characteristics. At lower voltages, the amount of the electrolyte ions into the graphite layers is relatively small. With the voltage increasing, the more electrolyte ions can insert into the graphite sheet with less solvent layer and distorted solvent layer at higher driving force. These findings have an important role in improving capacity of the EDLCs and seeking high withstand voltage electrode materials, and have lay the foundation for the study for storage mechanism of microporous carbon material.