Study On The Performance And Mechanism Of Organic Polar Additives Regulating The Electrolyte Of Supercapacitors

Carbon-based supercapacitors have the advantages of high power and long lifespan,but they have shortcomings such as low energy density and high cost.Electrolytes,as an essential component,are often seen as a potential research direction to address/improve the aforementioned shortcomings.Supercapacitor electrolytes mainly include aqueous,organic,ionic liquids,and ionic liquids analogues;compared to the low voltage window of water systems and the high cost of ionic liquids,organic/ionic liquids analogues have moderate voltage windows and lower costs,and ionic liquids analogues also have environmental advantages.However,the electrode system paired with typical activated carbon has issues such as lower specific capacitance（such as in organic systems lower than the corresponding water system）or lower voltage window（such as less than 2.0 V in ionic liquids analogues）compared to conventional levels.In response to these issues,this thesis addresses these issues by utilizing organic polar salts/small molecule additives to regulate the structure of ions/solvents/water molecules at the carbon electrode/electrolyte interface from the perspective of electrolyte functional additives.This approach does not involve redox reactions and can improve the comprehensive performance of typical carbon electrode/electrolyte systems while maintaining advantages of power and lifespan simultaneously,as follows:（1）From the perspective of designing non redox additive electrolyte,a highly polar organic ferroelectric salt diisopropylamine perchloric acid was developed as an additive.Compared to the traditional solid-state ferroelectric additive Ba Ti O₃,it has good compatibility with organic electrolytes.Adding 1 wt%diisopropylamine perchloric acid to commercial organic electrolytes and matching it with mesoporous carbon materials can achieve an increase of 27.5%in specific capacitance.In the case of nitrogen doping in the dielectric carbon material,the specific capacitance improvement reached 45.8%.The situation at the electrolyte/electrode interface was characterized through differential capacitance,in situ Raman spectroscopy,and molecular dynamics simulation,proving that the increase in capacitance does not come from the redox reaction,but from the reduction of the double layer thickness at the electrode interface,which enables the system to have high rate performance.（2）From the perspective of designing a green and low-cost new electrolyte system,an organic polar small molecule imidazole was developed as an additive.Environmentally friendly and low-cost ionic liquids were selected as the research object.The additive was interacted with other components in the ionic liquids,making the voltage window of the electrolyte increasing from 1.1 V to 2.2 V,overcoming the problem of voltage window reduction caused by ionic liquids analogues absorbing water in the air.And the optimal addition ratio of imidazole in the research system was determined to be 2 wt%.The combination of Raman spectroscopy and nuclear magnetic resonance spectroscopy revealed that the increase in voltage window comes from the strong hydrogen bonding between additives and ionic liquid analogues components.In situ Raman spectroscopy was used to characterize the situation at the electrolyte/electrode interface,and it was found that the solvent structure and charge distribution at the interface changed before and after addition,confirming that the voltage change comes from the changes in hydrogen bonding between components.