Application Of Ionic Liquids In Aluminum-ion Asymmetric Supercapacitor

Ionic liquids?IL?,sometimes called room-temperature molten salts,are typically organic salts consist of merely cations and anions.Due to their unique structure,ionic liquids possess the virtue of low vapor pressure,non-flammability,good ion conductivity,good chemical stability and wide electrochemical window.Ionic liquids can be applied in the fields of electrochemical,synthesis and so on.However,ionic liquids are usually hydroscopic and high-costing.To overcome these drawbacks,one can add siloxane chain,which has good flexibility and low-temperature properties,to the ionic liquid structure.In this paper phenyl silicone oil is sulfonated to achieve the goal of producing silicone ionic liquid with sulfo group.Acid-base titration and MS-GC method were used to investigate the influence of reaction time,temperature,complexing sulfonating agent and molecular weight to sulfonation.When 10g decomposed phenyl silicone oil dissolved in 90g CH2Cl2 and sulfonated by reacting with chlorosufonic acid for 12h under 40?,the sulfonation degree could reach 0.099mmol/g,yet still not enough for preparing ionic liquid.Since the result is not ideal,further investigations on improving sulfonation degree is necessary.Chloroaluminate ionic liquids are usually used as electrolytes for aluminum-ion asymmetric supercapacitor.However,chloroaluminate ionic liquids?such as AlCl₃/EMIMCl?,are often very sensitive to moisture.Here we searched the possibility of less water-sensitive ionic liquids,AlCl₃/EMIMTFSI and AlCl₃/BMPDCA,as alternative candidates for aluminum-ion asymmetric supercapacitor system.The behavior of mentioned candidates as electrolyte were tested with cyclic voltammetry tests and constant current charge-discharge tests.The results show that the capacitor using AlCl₃/EMIMTFSI electrolyte has a specific capacitance of 31.5F/g,which is close to the reported 55F/g of AlCl₃/EMIMCl,while AlCl3/BMPDCA behaves poorly.To improve water-and-air stability and wetting ability of AlCl₃/EMIMCl,we added two kinds of nonionic siloxane surfactants,OFX-3667 and OFX-5211,to AlCl₃/EMIMCl ionic liquid.Surfactant/chloroaluminate ionic liquid solutions with different concentrations were exposed in air for 24h,and it is found that the concentration of surfactant doesn't affect the water-sensitivity of AlCl₃/EMIMCl as expected.Surfactant/chloroaluminate ionic liquid solution with different concentration were used as electrolyte,mesoporous carbon were used as electrode to prepare supercapacitors,and the specific capacitances of different supercapacitors were calculated.The results show that 6wt%OFX-5211 solution has the best electrochemical properties.Then 6wt%OFX-5211/chloroaluminate ionic liquid solution were used as electrolyte,mesoporous carbon were used as cathode to prepare aluminum-ion asymmetric supercapacitor.The results indicate that mesoporous carbon is not proper for aluminum-ion asymmetric supercapacitor.It could be that the mesoporous carbon prepared is amorphous,and intercalation/de-intercalation progress destroyed the structure of mesoporous carbon structure.Thus amorphous mesoporous carbon should be further graphitized to improve its electrochemical stability.