Preparationand Properties Of Electrochemical Capacitors Based On Disulfonated Polyphenylene Sulfone/Poly (Ethylene Oxide) Composite Membranes

With the development of technology, it’s difficult for the traditional secondary battery and capacitor to meet the requirements of different fields for the new generation energy storage device. At this moment, electrochemical capacitors(ECs) appears in people’s field of vision as a new type of energy storage device. In comparison to conventional capacitors, the specific energy density of ECs is several orders of magnitude higher. What’s more, the ECs display faster power delivery or uptake performance than the batteries do. ECs are more and more popular with the advantages of long cycle life, simple preparation technology and environmentally friendly. The separator of ECs acts an important role in the operation of EC, which prevents forming a short circuit and separates the two electrodes. The separator of ECs needs to have the abilities of high ionic conduction, chemical stability, thermal stability and a certain mechanical strength. The research of new separator is essential for the development of ECs.Disulfonated Polyphenylene sulfone(SPPSU) shows good thermal stability and mechanical strength with the existence of aromatic structure. The existence of sulfone group makes the polymer amorphous, which also has a positive effect on ion of transmission. Ether bond in the polymer chain endows the molecular chain flexibility. Sulfonic acid in the chain makes the polymer have the ability of ionic conduction. But the conduction of SPPSU is not high enough for the neutral electrolyte ECs, however, the conduction of SPPSU can be improved by introducing polyethylene oxide(PEO) into SPPSU. With this perspective considering, a series of SPPSU/PEO composite membranes were prepared for the ECs and the influence of the PEO content and the molecular weight of PEO on ECs were investigated. Furthermore, we fabricated polymer electrolyte for the all solid state electrochemical capacitor and explored the relationship between the polymer electrolyte and all solid state electrochemical capacitor.Firstly, a series of SPPSU/PEO composite membranes were prepared by solution blending, which achieve the Li+ conducting in the neutral electrolyte EC. The EC cells were assembled by active carbon electrodes, the composite membranes as separator, 1mol L-1 Li2SO4 aqueous solution as electrolyte. The influence of the content of PEO and the molecular weight of PEO on ECs was investigated. When the content of PEO was 60%, the phase segregation of membrane appeared. The phase segregation degrades the mechanical properties of the membranes and the electrochemical performance of EC wasn’t promoted with increasing the content of PEO, so the suitable content of PEO was 50%. The molecular weight of PEO had a certain influence on EC, because the molecular chain distribution was different with the different molecular weight of PEO. The above result produced the different charge transfer resistance, which led to the change EC performance. After the electrochemical measurement, PEO of 100000 molecular weight was chosen. The EC was assembled by the composite membrane prepared by 50% PEO with Mw of 100000. The EC exhibited a specific capacitance of 134.9 F g-1 at a current density of 0.5 A g-1.The energy density and power density were 19.04 Wh kg-1 and 50.74 W kg-1, respectively. Electrochemical cycle performance of the fabricated EC indicated almost 100% cycling retention and near 99% coulombic efficiency over 5000 charge-discharge cycles at 0.5 A g-1.The SPPSU/PEO composite membrane prepared above brought out high energy density and power density for the neutral electrolyte(Li2SO4) ECs. However, the liquid electrolyte limited the further application of EC. We prepared composite membranes with the lithium perchlorate as modifier. The mechanical properties, thermal stability and electrochemical performance of the composite membranes with various contents of LiClO4 were investigated. All solid state EC was assembled by the membrane that had the best ability of ionic conduction, and the properties of the all solid state EC were conducted under the bending condition and unbending condition. The electrochemical performance of EC cells was investigated by using cyclic voltammetry(CV), galvanostatic charge and discharge(GCD), and electrochemical impedance spectroscopy(EIS) techniques. All the results showed that the all solid state EC kept a good performance under bending condition or unbending condition. Electrochemical cycle performance of the fabricated EC indicated almost 100% cycling retention and near 98% coulombic efficiency over 3000 charge-discharge cycles at 0.3 A g-1 under bending condition.This research aimed to obtain a wide voltage range EC through designing a new type of separator for neutral electrolyte EC. Further, we design polymer electrolyte for all solid state EC with a good performance. Our research provides a new way to study separator/ polymer electrolyte of electrochemical capacitor.