Research On Low Temperature Chloride Aqueous Electrolyte For Supercapacitors

Electrolytes are one of the main factors that affect the performance of supercapacitor, and aqueous electrolytes with the advantages of environment-friendly and wide application. At low temperature, the neutral electrolyte can freeze to be solid which results in directly supercapacitors cease to work. Therefore, it is very important to develop a low temperature neutral aqueous electrolyte with good electrochemical performance. In this paper, the mixed solutions of formamide(FA) and water(H2O) have the lowest freezing point, and the low temperature phase equilibrium relationship between the mixed solution of formamide and water and chloride salt in mixed formamide and water were further studied. Then, the low temperature performance of the supercapacitor was evaluted by using solutions of chloride salts in mixed solvent of formamide and water as the electrolyte and carbon nanotubes as the electrode. Specific contents are the following:1) The carbon nanotube suspensions were prepared by carbon nanotubes that were treated with mixed acid and surfactant(CTAB). Comparing the dispersion degree of carbon nanotube suspensions, and the corresponding electrode was prepared The specific capacitance was tested by cyclic voltammetry. The results show that multi-wall carbon nanotubes which were treated by the mixed acid have a high specific capacitance, and the suitable volume of the suspension for the preparation of the electrode is 15 ?L.2) Through freezing point testing experiment, the low temperature phase equilibrium relationship between the mixed solution of formamide-water mixture and the electrolyte bath solution chloride salt were studied, and the cooling curves and phase diagram were drawn. The results show that when FA:H2O=3:2(vol), the FA-H2 O system has the lowest freezing point(-47.4?); In the experimental conditions, the chloride salt solution in the volume ratio of FAH2 O mixed solvent have the lowest liquid-solid transition temperature: 0.5 mol·L-1 Ca Cl2/FA:H2O(3:2, vol) solution is-55?; 0.5 mol·L-1 Na Cl/FA:H2O(3:2, vol) solution is-52?; 1 mol·L-1 Na Cl/FA:H2O(3:2, vol) solution is-55.1?; 0.5 mol·L-1 KCl/FA:H2O(3:2, vol) solution is-47?; 1 mol·L-1 KCl/FA:H2O(3:2, vol) solution is-54.5?; 1.5 mol·L-1 KCl/FA:H2O(3:2, vol) solution is-55.8?; 2 mol·L-1 KCl/FA:H2O(3:2, vol) solution is-54?; 0.5 mol·L-1 Li Cl/FA:H2O(3:2, vol) solution is-48.9?; 1 mol·L-1 Li Cl/FA:H2O(3:2, vol) solution is-57.2?.3) The working electrode was prepared by acid treated multi-wall carbon nanotubes, and the electrode was prepared by the chloride salt solutions with the lowest liquid-solid transition temperature, the graphite rod was used as auxiliary electrolyte, the Ag/Ag Cl electrode was used as treference electrode, and the performance of supercapacitor was tested by cyclic voltammetry and constant current charge-discharge, the voltage range was-0.7~0.3 V and the scan rate was 100 m V/s. The results show that at-60?, the specific capacitance is the largest(45.54 F/g) when electrolyte is 2 mol·L-1 Ca Cl2/FA:H2O(2:3, vol), which has good low temperature performance.