Study Of Active Polymer Electrolytes For Supercapacitors

Supercapacitor has been widely studied as one type of efficient, clean and sustainable candidate for the next generation energy conversion and storage, as the concern about global warming and the fossil fuel crisis grows. Supercapacitor can be used in some fields individually or combined with batteries for its higher energy density than that of traditional capacitors and higher power density and cycle life than that of batteries. The electrolyte is a basic and important part of the supercapacitor.Polymer gel electrolytes, as a kind of novel electrolyte, have higher ionic conductivity than solid electrolytes, and it also avoid the drawbacks of easy to leak and blast compared with liquid electrolytes. So it makes the development of supercapacitor tend to miniaturization and ultrathin possible. However, the application of polymer gel electrolytes is limited by some drawbacks of itself, like lower ionic conductivity which makes the charge-discharge performance of the fabricated supercapacitor worse.Therefore, in the recent decades some researchers improve the performance of polymer gel electrolytes by introducing redox active materials into gel electrolytes to enhance the electrochemical performance of supercapacitor.In order to improve the electrochemical performance of the gel polymer electrolytes based supercapacitors, we prepared two novel redox polymer gel electrolytes by doping redox active mediator into polyvinyl alcohol(PVA) matrix.Then study the electrochemical performance of the supercapacitor which is fabricated by using active carbon as electrode material and the prepared polymer gel as electrolyte and separator. The contents in detail are as follow:1. PVA-H2SO4-IC systemA high performance redox polymer gel electrolyte(PVA-H2SO4-IC) is prepared by a simple solution-mixing/casting method using indigo carmine(IC) as redox active mediator and PVA as a polymer matrix. The mechanical properties of polymer gel are measured and the results show that doping IC will not decrease stretching and bending properties. The electrochemical performance investigation shows that the ionic conductivity of PVA-H2SO4-IC gel electrolyte is increased by 188% up to 20.27 m S cm-1 compared with PVA-H2SO4 electrolyte system. The electrode specific capacitance of the fabricated supercapacitor with active carbon as electrodes and theprepared polymer as electrolyte and separator is 382 F g-1, increasing by 112.2%compared to supercapacitor with PVA-H2SO4 system. The energy density of the supercapacitor increases from 6.2 Wh kg-1 to 13.26 Wh kg-1. In addition, the supercapacitor exhibits excellent cycle-life stability after adding IC by cycle-life test.2. PVA-H3PO4-Py SH systemPVA-H3PO4-Py SH polymer gel electrolyte is prepared by solution-mixing/casting method using 2-mercapto pyridine(Py SH) as redox mediator. The properties measurements show that excellent stretching and bending properties of polymer gel are displayed, and the ionic conductivity is increased by 92% up to 22.57 m S cm-1. As a result of the redox reaction of Py SH in acid solution, high performance of PVA-H3PO4-Py SH gel electrolyte based supercapacitor, such as the electrode specific capacitance is 1128 F g-1 which is increased by 447% compared to supercapacitor with electrolyte without Py SH, are shown. The energy density of the supercapacitor increases from 10.42 Wh kg-1to 39.17 Wh kg-1. Besides, the supercapacitor also exhibits excellent cycle-life stability after adding Py SH by cycle-life test.