Study On Electrical Conductivity Of Ternary Mixture Of Ionic Liquid And Organic Solvents

Ionic liquids?ILs?have the properties of high electrical conductivity,non-flammable,negligible vapor pressure,good thermal and electrochemical stability and wide electrochemical window,etc,so they are good potential electrolyte in electrochemical process,such as lithium batteries and super capacitors.The conductivity of ionic liquids is the basic data for its application in electrochemical systems.ILs can be mixed with organic solvents to reduce its viscosity and improve electrical conductivity.In this paper,the electrical conductivities of ionic liquid 1-butyl-3-methylimidazolium bis[?trifluoromethyl?sulfonyl]imide?[C₄mim][TFSI]?in mixed organic solvents of propylene carbonate?PC?+?-butyrolactone?GBL?and ethylene carbonate?EC?+dimethyl carbonate?DMC?were measured.The effects of mixed organic solvents with different ratios?1:0,2:1,1:1,1:2,0:1?on the electrical conductivity of ionic liquid were investigated.The organic solvents EC and DMC have synergistic effect for the electrical conductivity of[C₄mim][TFSI]-EC-DMC,and the optimal ratio of EC to DMC is 1:1,however,the organic solvents have no synergistic effect in[C₄mim][TFSI]-PC-GBL.The concentration dependence of the electrical conductivity of the solution can be well fitted by empirical Casteel-Amis equation.The effects of temperature on electrical conductivity can be described by Vogel-Tamman-Fulcher?VTF?equation and Arrhenius equation.The IL concentration dependence of activation energy E_a and pre-exponential factor A in Arrhenius equation was also investigated,and fitted by empirical equations.Based on VTF equation and Arrhenius equation,a quasi-Arrhenius equation was proposed to describe the effects of temperature and composition on the electrical conductivity simultaneously in binary systems and ternary systems,and the correlation results agree well with the experimental results.The molecular dynamics?MD?simulation of ionic liquid[C₄mim][TFSI]and ternary mixtures[C₄mim][TFSI]-PC-GBL,[C₄mim][TFSI]-EC-DMC were performed using COMPASS?force field in Materials Studio Software.The diffusion coefficients of ions in pure[C₄mim][TFSI]system calculated by Einstein equation almost increase linearly with the increase of temperature,and the self-diffusion coefficient of the cation?[C₄mim]⁺?is slightly higher than that of the anion?[TFSI]^-?.The self-diffusion coefficient of each particle in the ternary system[C₄mim][TFSI]-PC-GBL and[C₄mim][TFSI]-EC-DMC decreases monotonously with the increase of the ionic liquid concentration,and the diffusion coefficient of the organic solvent follows the order:DMC>GBL>EC>PC,which is contrary to the order of the viscosity.The electrical conductivities for the pure ionic liquid and the ternary systems were calculated by Nernst–Einstein equation,and the simulated conductivity is 0.5 to 0.9 times of that of experimental value.In addition,the simulation results can well reproduce the dependency of the electrical conductivity on composition and temperature.