  In this paper we have investigated via experimental and simulations
techniques the transport properties, in terms of total ionic conductivity and
ion diffusion coefficients, of ionic liquids and lithium salt mixtures composed
of two anions, bis(fluorosulfonyl)imide (FSI) and
bis(trifluoromethanesulfonyl)imide (TFSI), and two cations,
N-ethyl-N-methylimidazolium (emim) and lithium. The comparison of the
experimental results with the simulations shows an exceptional agreement over a
wide temperature range. Of particular interest is the high agreement achieved
at 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 the
addition of TFSI favor the formation of lithium dimers (Li+ - TFSI- - Li+). A
closer analysis of such dimers shows that involved lithium ions move nearly as
fast as single lithium ions although they have a different coordination and
much slower TFSI exchange rates.
