The electrification of mobility has a strong potential to reduce fuel consumption and CO₂emissions. This alternative to combustion engines, however, is hampered by battery systems still insufficient in terms of energy, power and lifetime. Therefore it is important to investigate and understand the electrochemical processes and mechanisms that can maximize the power-to-energy ratio. The electrolyte plays an important role for the efficient operation of the battery. For example, electrolytes with low lithium-ion transport numbers and salt diffusion coefficients cause large concentration polarizations during operation of Li-ion batteries. This leads to poor high-rate performance, unwanted side reactions and ageing. It is therefore important to characterize and model the transport phenomena in electrolytes under battery operation conditions.

There are numerous experimental methods that can be used to characterize the thermodynamic and transport phenomena in electro-diffusion processes (e.g. NMR, Raman spectroscopy, etc.), but the electrochemical methods are more powerful, as they can mirror the relevant working processes occurring in a battery.

In the presented work, the electrolyte characteristics such as viscosity, conductivity, diffusion coefficients of lithium ions and transfer numbers are determined for various LiFP₆concentrations. Conductivity was measured by alternating current technique (PEIS and test cell with Pt-electrodes); the transfer numbers were obtained from the diffusion technique (concentration cell) and the diffusion coefficient was determined by the rotary disk electrode method and also calculated from conductivity measurements. Additionally, the temperature dependence of the studied properties was taken into account. The results were further used for the modelling of the mass transport processes in the real cell. The analysis of mass transport phenomena over a range of salt concentrations will be shown and discussed.

Acknowledgement

The authors would like to thank the Austrian Federal Ministry for Transport, Innovation and Technology (bmvit) and the Austrian Research Promotion Agency (FFG) for their financial support.