No abstract

Association between cations and anions plays an important role in the interfacial structure of room-temperature ionic liquids (ILs) and their electrochemical performance. Whereas great efforts have been devoted to investigating the association effect on the equilibrium properties of ILs, a molecular-level understanding of the charging dynamics is yet to be established. Here, we propose a theoretical procedure combining reaction kinetics and the modified Poisson-Nernst-Planck (MPNP) equations to study the influences of ionic association on the dynamics of electrical double layer (EDL) in response to an applied voltage. The ionic association introduces a new decay length λS and relaxation time scale τRC=λSL/D, where L is the system size and D is ion diffusivity, that are distinctively different those corresponding to non-associative systems. Analytical expressions have been obtained to reveal the quantitative relations between the dynamic timescales and the association strength.

High-purity lithium chloride is used in energy storage applications. A possible process to obtain it is through the separation of Li + and Mg 2+ ions from salt-lake brines with a high mass ratio of Mg 2+ /Li + . This separation can be achieved by nanofiltration and is not only important but also environmentally friendly. It requires a deep understanding of the competitive transport of Li + /Mg 2+ ions in the nanoscale. It is expected to be achieved by theoretical approaches since it remains a challenge for experimental observation. Here, a theoretical model combining the classical density functional theory (CDFT) with the Navier− Stokes (NS) equations was developed to study the selective separation of Li + /Mg 2+ ions in charged nanochannels. We found nanochannels have selectivity for the co-ions with a smaller radius and lower valence state, and the relationship between ion selectivity and surface potential is approximately exponential. Finally, we proposed an accurate empirical formula to characterize the influence of the pore structure, surface properties in the Li + /Mg 2+ separation performance, indicating that our work provides an effective approach to studying selective ionic transport.