Measurement of transference numbers for lithium ion electrolytes via four different methods, a comparative study

We report here on comparative measurements of cationic transference numbers of some lithium battery related electrolytes including lithium tetrafluoroborate in propylene carbonate, lithium hexafluorophosphate in blends of ethylene carbonate/diethyl carbonate and ethylene carbonate/propylene carbonate/dimethyl carbonate, as well as lithium difluoromono (oxalate) borate in an ethylene carbonate/diethyl carbonate blend via four different methods. Whereas three electrochemical methods yield transference numbers decreasing with concentration in accordance with electrostatic theories, valid for low to intermediate concentrations of the electrolyte, nuclear magnetic resonance spectroscopy measurements show increasing transference numbers with increasing concentration. The discrepancy is attributed to effects of ion–ion and ion–solvent interaction.

Research highlights
► Lithium ion transference numbers (t+) of lithium battery related electrolytes are studied.
► Four recently used methods for measuring t+ are compared.
► Electrochemical methods yield Li+ transference numbers decreasing with concentration and are in agreement with electrostatic theories.
► In contrast, NMR measurements show increasing Li+ transference numbers with increasing concentration.
► The discrepancy is attributed to effects of ion–ion and ion–solvent interaction.