A combined theoretical and experimental study of the influence of different anion ratios on lithium ion dynamics in ionic liquids

摘要

In this paper we have investigated via experimental and simulationstechniques the transport properties, in terms of total ionic conductivity andion diffusion coefficients, of ionic liquids and lithium salt mixtures composedof two anions, bis(fluorosulfonyl)imide (FSI) andbis(trifluoromethanesulfonyl)imide (TFSI), and two cations,N-ethyl-N-methylimidazolium (emim) and lithium. The comparison of theexperimental results with the simulations shows an exceptional agreement over awide temperature range. Of particular interest is the high agreement achievedat lower temperature, which is a result of the extended simulation length of,at least, a factor of 5 compared with previous work. The results show as theaddition of TFSI favor the formation of lithium dimers (Li+ - TFSI- - Li+). Acloser analysis of such dimers shows that involved lithium ions move nearly asfast as single lithium ions although they have a different coordination andmuch slower TFSI exchange rates.