The physical and electrochemical properties of the ionic liquids based on N-ethylpiperidinium cations and TFSI anion

A series of ionic liquids based on N-ethylpiperidinium cations and bis(trifluoromethylsulfonyl)imide (TFSI) anion were synthesized and their physical and electrochemical properties including melting point, glass transition temperature, density, viscosity, conductivity, heat capacity, thermal decomposition temperature and electrochemical window were investigated. These ionic liquids exhibited relatively high thermal stabilities, wide electrochemical windows and relatively high conductivities. Methoxy or methyl acetate group was introduced into the alkyl chain of the N-ethylpiperidinium cation, and the effect of such introduction on the properties of the corresponding ionic liquids was investigated. The results show that introducing methoxy group into the alkyl chain of N-ethylpiperidinium considerably increases the fluidity (decreases the viscosity and increases the conductivity) and slightly decreases the thermal and electrochemical stabilities of the corresponding dialkyl substituted ionic liquids. By comparison, replacing the n-butyl side group on the piperidinium cation with methyl acetate group significantly decreases the fluidity and slightly decreases the thermal and electrochemical stabilities of the ionic liquid.