Stefan–Maxwell diffusivities of gas mixtures and liquid electrolytes.*

Stefan–Maxwell diffusivites describe drag created by relative motion of components in continuum multi-species transport models. They are key phenomenological parameters within the concentrated-solution theory of liquid electrolytes, which is important in battery modeling. In general, Stefan–Maxwell coefficients depend on composition, temperature and pressure. Those parameters can be measured experimentally, and we review some of the results and modelling challenges. It is desirable to develop robust microscopic methods that allow Stefan-Maxwell diffusivities to be computed from first principles, rather than relying on experimental data. A method that uses molecular dynamics and computes Stefan–Maxwell diffusivities by exploiting Onsager's regression hypothesis has been proposed. We investigate the method in the test case of gas mixtures where analytic results from kinetic theory, as well as experiments, are available. We discuss extension of the method to liquid electrolytes.