Fully Characterizing an Electrolyte for Lithium - Ion Batteries Using Electrochemical Methods and Electrophoretic NMR

Improvements in current lithium - ion battery electrolytes are necessary to accomodate future energy storage needs. The electrolyte facilitates ion transport, and the transport properties of the electrolyte can be studied using Newman's concentrated solution theory. In this, the electrolyte is fully characterized by a thermodynamic factor and three transport parameters, conductivity, diffusion coefficient, and the transference number. The transference number is obtained by combining multiple electrochemical parameters, which can result in large error bars that obscure the transport behavior of the electrolyte. To reduce this error, we have used electrophoretic NMR (eNMR) to directly measure the electric-field-induced ion and solvent velocities to determine the transference number. This additionally enables the determination of the thermodynamic factor with greater certainty. The relevant transport and thermodynamic parameters have been studied in this work for a liquid electrolyte, lithium bis(trifluoromethanesulfonyl)imide dissolved in tetraethylene glycol dimethyl ether. Based on these results, it is evident that a combination of electrochemical methods and electrophoretic NMR can fully characterize liquid electrolytes for lithium-ion batteries with greater certainty.