Abstract
A complete set of thermodynamic and mass-transport properties is determined for solutions of LiPF6 in propylene carbonate at 25°C, elucidating the composition dependences of six independent primary material parameters. Mass density is correlated with concentration to parameterize the partial molar volumes of electrolyte and solvent. Conductometry and Hittorf experiments yield correlations for equivalent conductance and cation transference number, respectively. A theoretical analysis connects the measured transference number to transport numbers measured by other standard approaches. Concentration-cell measurements yield the thermodynamic Darken factor; voltammetric restricted diffusion quantifies diffusivity. A Bruggeman factor is measured to relate true transport properties to the effective properties in polarization cells with glass-fiber separators. Taken together, the data reveal how the three Stefan–Maxwell diffusivities vary with composition, in terms of functions that interpolate between 0.2 M and 2 M. The property set is validated by simulations, which match voltage-relaxation experiments excluded from the parameterization.
Highlights
Lithium-ion cells dominate the commercial market for rechargeable batteries
Electrolyte, comprising a simple salt dissolved in a neutral solvent, three macroscopic transport coefficients d ionic conductivity, cation transference number, and thermodynamic diffusivity d characterize the species/species interactions
Solutions were made by dissolving LiPF6 salt (99.99%, battery grade, Sigma Aldrich) in propylene carbonate (PC) (99.9%, anhydrous, Sigma Aldrich); LiPF6 salts were used as received
Summary
Lithium-ion cells dominate the commercial market for rechargeable batteries. Accurate prediction of lithium-ion-battery behavior requires careful study of electrolyte thermodynamics and transport. Concentrated-solution theory, first developed in detail by Newman, Bennion, and Tobias [1], has been widely adopted to simulate mass transport in electrolytic solutions. For a binary electrolyte, comprising a simple salt dissolved in a neutral solvent, three macroscopic transport coefficients d ionic conductivity, cation transference number, and thermodynamic diffusivity d characterize the species/species interactions. Concentratedsolution theory includes thermodynamic parameters, which rigorously determine how concentration variation within an electrolyte affects the voltage drop across it. A binary electrolyte requires three equilibrium properties d the Darken thermodynamic factor, as well as partial molar volumes for salt and solvent d to specify how its thermodynamic state depends on composition
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