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DOE OSTI · 2479913

Role of a Multivalent Ion–Solvent Interaction on Restricted Mg 2+ Diffusion in Dimethoxyethane Electrolytes

Chen, Ying·Atwi, Rasha·Han, Kee Sung·Ryu, Jaegeon·Washton, Nancy M.·Hu, Jian Zhi·Rajput, Nav Nidhi·Mueller, Karl T.·Murugesan, Vijayakumar
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Abstract

The diffusion behavior of Mg 2+ in electrolytes is not as readily accessible as that from Li + or Na + utilizing PFG NMR, due to the low sensitivity, poor resolution, and rapid relaxation encountered when attempting 25 Mg NMR. In MgTFSI 2 /DME solutions, “bound” DME (coordinating to Mg 2+ ) and “free” DME (bulk) are distinguishable from 1 H NMR. With the exchange rates between them obtained from 2D 1 H EXSY NMR, we can extract the self-diffusivities of free DME and bound DME (which are equal to that of Mg 2+ ) before the exchange occurs using PFG diffusion NMR measurements coupled with analytical formulas describing diffusion under two-site exchange. Further, the high activation enthalpy for exhange (65–70 kJ/mol) can be explained by the structural change of bound DME as evidenced by its reduced C–H bond length. Comparison of the diffusion behaviors of Mg 2+ , TFSI – , DME, and Li + reveals a relative restriction to Mg 2+ diffusion that is caused by the long-range interaction between Mg 2+ and solvent molecules, especially those with suppressed motions at high concentrations and low temperatures.

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37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRYDiffusionIonsMoleculesSolventsTransport properties

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Chen, Ying, Atwi, Rasha, Han, Kee Sung, Ryu, Jaegeon, Washton, Nancy M., Hu, Jian Zhi, Rajput, Nav Nidhi, Mueller, Karl T., Murugesan, Vijayakumar. 2021-11-08. Role of a Multivalent Ion–Solvent Interaction on Restricted Mg 2+ Diffusion in Dimethoxyethane Electrolytes. https://doi.org/10.1021/acs.jpcb.1c08729

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