New Insights on Tortuosity Determination by EIS for Battery Electrodes: Effect of Electrolyte Concentration and Temperature

Abstract

Nowadays, lithium-ion battery design and manufacturing are supported more and more by modelling and simulation. In this context, tortuosity has become a critical parameter characterizing porous battery electrode, in particular for those phenomena involving microstructure-performance relationships. The modelling and simulation of such processes, including also performance characterization, requires an accurate and reliable estimation of tortuosity values to obtain meaningful results, but taking into account the experimental framework. In this work, we present our findings on the determination of tortuosity for a porous commercial-based NMC622 cathode using an intercalating electrolyte, LiPF6 in commonly used EC:EMC solvents, at different temperatures (−10 to 45 °C) and electrolyte concentrations (0.50 to 1.5 M), similar to those that can be found in a commercial lithium-ion battery. The approach followed, based on electrochemical impedance spectroscopy measurements in symmetric cells, reveals that it is possible to obtain reliable tortuosity values at practical operating experimental conditions found in commercial lithium-ion batteries, like different temperatures and electrolyte concentrations. In this sense, the use of modified ionic resistance vs conductivity logarithmic plots provides a way to consolidate the tortuosity measurement compared to single points (c, T), for which large point to point variations have been observed. Furthermore, the comparison of the tortuosity values obtained with those obtained using a non-intercalating electrolyte, TBAPF6 in EC:EMC, which are of the same order, attests for the validity of our approach.