Electroanalytical Quantification of Electrolyte Transport Resistance in Porous Electrodes

A generalized, noninvasive technique based on electrochemical impedance spectroscopy is proposed to quantify the electrolyte transport resistance of typical electrode microstructures for lithium ion batteries. The electrolyte transport resistance, representative of the pore network resistance, can be obtained via an impedance analytics approach, thus quantifying the tortuosity of porous electrode microstructures. A characteristic coefficient is defined and estimated for more electronically conductive graphite, lithium cobalt oxide (LCO), and nickel-manganese-cobalt oxide (NMC) electrodes, and for less electronically conductive lithium iron phosphate (LFP) and lithium titanate (LTO) electrodes. The fitting of the electrochemical impedance spectra by the general transmission line model yields unambiguous values by adding an independent determination of the electronic resistance. Such an independent determination of the electronic resistance can be easily done by sandwiching the composite electrode between two ion-blocking electrodes. This would be essential to verify the approach for electrodes with low electronic conductivity, such as LFP and LTO. This method is capable of adequately capturing the influence of particle size and morphology on the pore-scale tortuosity of electrode microstructures.