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

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 IC and for concentrations between 0.2 and 2.0 mol/d M3. 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/d M3 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/dm 3. The lithium-ion transport numberwith respect to the room decreased with increasing salt concentration, with a maximum of 0.37 at 0.2 molldm 3 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. (c) 2008 Elsevier Ltd. All rights reserved.