Four Phosphonium-based Ionic Liquids.Synthesis,Characterization and Electrochemical Performance as Electrolytes for Silicon Anodes

摘要

Herein,we describe the synthesis,characterization and electrochemical performance of four phosphonium-based ionic liquids(ILs)as electrolytes,Physicochemical properties such as viscosity,density,ionic conductivity,and thermal stability of ILs and conventional organic solvent ethylene carbonate(EC)/diethyl carbonate(DEC)were experimentally determined at different temperatures.All ILs showed thermal stability greater than 300℃,surpassing the stability of the conventional organic solvent,whose flash points were 145 and 23℃ for EC and DEC,respectively.Nevertheless,at room temperature,all ILs are much more viscous than EC/DEC.The composite Si-[P2224][FSI](triethyl-n-butylphosphonium bis(fluoromethylsulfonyl)imide)and Si-EC/DEC anodes exhibit initial specific capacities at 0.15 A/g of 2409 and 2631 mAh/g,respectively.This demonstrates that despite the inferior transport properties of ILs,short alkyl-substituted phosphonium ILs like [P2224][FSI] are potentially competitive for the new generation of electrolytes for LIBs.NMR,DSC,TGA,and galvanostatic discharged/charged were used as characterization techniques.