Studies On Polymer And Supramolecule-Based Electrolytes Applied For The Aqueous Supercapacitors

With the increasing demand for wearable electronic products,aqueous quasi-solid-state supercapacitors(QSSCs)have thus attracted extensive attention.Although aqueous QSSCs possess some merits including high safety and environment friendliness,they also face many challenges such as the low electrochemical window and strong electrode thickness dependency.To address these challenges,the polymer and supramolecule-based hydrogel electrolytes have been developed in this thesis to solve some problems of the aqueous QSSCs from the angle of electrolytes,including the thermal runaway,low electrochemical window,and strong electrode thickness dependency.The main results are as follows:(1)The specific ion effects on the thermosensitive behaviors of poly[2-(dimethylamino)ethyl methacrylate](PDMAEMA)in aqueous solutions have been investigated.The results demonstrate that obvious specific ion effects can be observed in the thermosensitive behaviors of PDMAEMA,and the specific ion effects are strongly dependent on the ion concentration and solution pH.The results also show that the observed specific ion effects on the thermosensitive behaviors arise from the specific ion-pairing and ionic dispersion interactions between ions and PDMAEMA.On the basis of the above studies,the influence of specific ion effects on the thermal self-protection behavior of PDMAEMA hydrogel-based QSSC have been further investigated.In comparison with Cl-,the stronger ion-specific interactions between ClO4-and PDMAEMA make the PDMAEMA hydrogel in the presence of ClO4-more effectively suppressing the ion transport at high temperatures,thereby giving rise to a better thermal self-protection performance of the PDMAEMA hydrogel-based QSSC.Therefore,the thermal self-protection performance of the PDMAEMA hydrogel-based QSSC can be tuned with specific ion effects.(2)A novel strategy to improve the performance of QSSCs by modulating the properties of electrolytes from bulk to interfaces has been developed.The utilization of polyzwitterion as the polymer matrix to prepare the gel polymer electrolyte is favorable for the ion transport and the suppression of both water decomposition and self-discharge.The employment of high concentration of lithium perchlorate and sodium perchlorate mixture to undertake the task of ionic conduction gives rise to the good flexibility and high reversibility of the gel polymer electrolyte as well as the strengthening suppression of water decomposition.The introduction of the interfacial propylene carbonate layer between electrolyte and electrode is advantageous for the suppression of water decomposition,the promotion of interfacial compatibility,and the weakening of electrode thickness dependency.The polymer matrix,salt mixture,and interfacial organic solvent layer not only play a respective role in,but also exhibit a cooperative effect on the improvement of the performance of the gel polymer electrolyte-based QSSC.This strategy will provide an effective method to improve the electrochemical performance of hydrogel electrolyte-based QSSCs.(3)The electrochemical performances of QSSCs based on polymer hydrogel electrolytes are strongly dependent on electrode thickness,which severely limits their applications.A low-molecular-weight 3-hydroxy-4-phenyl-3-cyclobutene-1,2-dione(HPCD)-based supramolecular gel electrolyte(SGE)has been successfully developed here to address this issue.HPCD can form a hydrogel through hydrogen bond interactions in a 1.0 M H2SO4 aqueous solution.The as-prepared HPCD hydrogel has an ionic conductivity as high as～421 mS cm-1,which gives rise to a rapid ion transport in the HPCD hydrogel.The combined advantages of small molecular size,low solution viscosity,and good wettability of the precursor solution of HPCD hydrogel endow the SGE with a capability to effectively infill the thick porous activated carbon electrodes through a sol-gel transition method.Therefore,the SGE-based QSSCs have a comparable dependence of electrochemical performances on electrode thickness to those based on the H2SO4 aqueous solution.Moreover,HPCD hydrogel can be prepared in the presence of different kinds of electrolytes,making the SGE suitable for fabricating different types of QSSCs.