Most liquid lithium-ion-battery
electrolytes incorporate
cosolvent
blends, but the dominant electrochemical transport models adopt a
single-solvent approximation, which assumes in part that nonuniform
cosolvent ratios do not affect cell voltage. For the popular electrolyte
formulation based on ethyl-methyl carbonate (EMC), ethylene carbonate
(EC), and LiPF6, we perform measurements with fixed-reference
concentration cells, finding appreciable liquid-junction potentials
when only the cosolvent ratio is polarized. A previously reported
junction-potential correlation for EMC:LiPF6is extended
to cover much of the ternary composition space. We propose a transport
model for EMC:EC:LiPF6solutions grounded in irreversible
thermodynamics. Thermodynamic factors and transference numbers are
entwined in liquid-junction potentials, but concentration-cell measurements
determine observable material properties we call junction coefficients,
which appear in the extended form of Ohm’s law that accounts
for how composition changes induce voltage drops. Junction coefficients
of EC and LiPF6are reported and illustrate the extent
to which ionic current induces solvent migration.