Electrochemical characterisation and modelling of the mass transport phenomena in LiPF₆–EC–EMC electrolyte

By Nyman, Andreas; Behm, Mà¥rten & Lindbergh, Göran
Published in Electrochimica Acta NULL 2008

Abstract

The conductivity, the salt diffusion coefficient, the lithium-ion transport number and the thermodynamic factor of the salt and the solvent were reported for LiPF₆ in EC:EMC (3:7) at 25 °C and for concentrations between 0.2 and 2.0 mol/dm³. The mass transport in the electrolyte was fully characterised by combining three types of electrochemical experiments; concentration cells, galvanostatic polarisation experiments and electrochemical impedance measurements with a mathematical description of the mass transport in the electrolyte. The apparent salt diffusion coefficient had a local maximum in the concentration range, while the viscosity-dependent salt diffusion coefficient decreased from 4.1 X 10⁻¹⁰ m²/s at 0.2 mol/dm³ to 4.4 X 10-11 m²/s at 2.0 mol/dm³. Both the thermodynamic factor and the conductivity varied strongly with the concentration. The conductivity had a maximum of 9.5 mS/cm at 1.0 mol/dm³. The lithium-ion transport number with respect to the room decreased with increasing salt concentration, with a maximum of 0.37 at 0.2 mol/dm³ in the concentration range. The Maxwell–Stefan diffusivities and the electrolyte potential drop in a lithium-ion battery at steady state were lastly calculated from the obtained transport properties. An analysis of the characterisation method was also done on the basis of the characterisation results.

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