Akademska digitalna zbirka SLovenije - logo
E-viri
Celotno besedilo
Recenzirano
  • Computational and Experimen...
    Haskins, Justin B; Bennett, William R; Wu, James J; Hernández, Dionne M; Borodin, Oleg; Monk, Joshua D; Bauschlicher, Charles W; Lawson, John W

    The journal of physical chemistry. B, 09/2014, Letnik: 118, Številka: 38
    Journal Article

    We employ molecular dynamics (MD) simulation and experiment to investigate the structure, thermodynamics, and transport of N-methyl-N-butylpyrrolidinium bis(trifluoromethylsufonyl)imide (pyr14TFSI), N-methyl-N-propylpyrrolidinium bis(fluorosufonyl)imide (pyr13FSI), and 1-ethyl-3-methylimidazolium boron tetrafluoride (EMIMBF4), as a function of Li-salt mole fraction (0.05 ≤ x Li+ ≤ 0.33) and temperature (298 K ≤ T ≤ 393 K). Structurally, Li+ is shown to be solvated by three anion neighbors in pyr14TFSI and four anion neighbors in both pyr13FSI and EMIMBF4, and at all levels of x Li+ we find the presence of lithium aggregates. Pulsed field gradient spin-echo NMR measurements of diffusion and electrochemical impedance spectroscopy measurements of ionic conductivity are made for the neat ionic liquids as well as 0.5 molal solutions of Li-salt in the ionic liquids. Bulk ionic liquid properties (density, diffusion, viscosity, and ionic conductivity) are obtained with MD simulations and show excellent agreement with experiment. While the diffusion exhibits a systematic decrease with increasing x Li+ , the contribution of Li+ to ionic conductivity increases until reaching a saturation doping level of x Li+ = 0.10. Comparatively, the Li+ conductivity of pyr14TFSI is an order of magnitude lower than that of the other liquids, which range between 0.1 and 0.3 mS/cm. Our transport results also demonstrate the necessity of long MD simulation runs (∼200 ns) to converge transport properties at room temperature. The differences in Li+ transport are reflected in the residence times of Li+ with the anions (τLi/–), which are revealed to be much larger for pyr14TFSI (up to 100 ns at the highest doping levels) than in either EMIMBF4 or pyr13FSI. Finally, to comment on the relative kinetics of Li+ transport in each liquid, we find that while the net motion of Li+ with its solvation shell (vehicular) significantly contributes to net diffusion in all liquids, the importance of transport through anion exchange increases at high x Li+ and in liquids with large anions.