Role of Multivalent Ion – Solvent Interaction on Restricted Mg2+ Diffusion in Dimethoxyethane (DME) Electrolytes

2D 1H-1H EXSY NMR and 1H PFG diffusion NMR are combined to obtain the self-diffusivities of Mg2+ clusters such as Mg(DME)32+ and [Mg(DME)1-2(TFSI)]+. The long-range charge-dipole interactions between Mg2+ and the solvent molecules may explain the significant restriction of divalent Mg2+ diffusion compared to Li+ and TFSI-.

Scientific Achievement

Comparison of the diffusion behaviors of Mg2+, TFSI-, DME, and Li+ reveals a relative restriction to Mg2+ diffusion that is caused by the long-range interaction between Mg2+ and solvent molecules, especially those with suppressed motions at high concentrations and low temperatures.

 Significance and Impact

In order to reduce this long-range effect of multivalent ions and to increase their diffusivities in electrolytes (and crucially at interfaces within working cells), adding anion ligands or using a cosolvent system must be considered.

Research Details

  • Exchange rates between “bound” DME (coordinating to Mg2+) and “free” DME (bulk) are obtained using 2D 1H-1H EXSY spectra.
  • Self-diffusivities of free DME and bound DME (which is equal to that of Mg2+) before the exchange occurs are calculated using PFG diffusion NMR measurements coupled with analytical formulas describing diffusion under the condition of two-site exchange.
  • The high activation enthalpy for exchange and the long lifetime of Mg-DME clusters can be explained by the structural change of bound DME as evidenced by its shorter C-H bond length manifested in 1H and 13C NMR.

Download this highlight

DOI: 10.1021/acs.jpcb.1c08729

Latest Updates

See All