Demystifying Charge Transport Limitations in the Porous Electrodes of Lithium‐Ion Batteries

Abstract

A possible strategy to give a simultaneous boost to the energy and power attributes of the current generation of lithium-ion batteries is developing thick porous electrodes with high loading of active material alongside optimal percolation networks for the ions and electrons. However much the insertion capacity and kinetics of the single particle lithium-insertion materials, the energy and power density of the cell might be significantly capped by the ionic and electronic transport limitations in the porous electrode. In this work, a physical picture grounded in experiment and theory is proposed to spotlight and quantify the pivotal role of the micro-scale porosity and active-material loading in determining the tortuosity, effective transport properties, and performance limitations of a porous electrode. The outcome is a phenomenological picture coupled with a theoretical framework for the deconvolution of the relative shares of the electronic and ionic transport limitations over short and long ranges in the performance limitation of lithium-ion batteries. The porous electrodes' microstructure is well recognized to have a pivotal role in determining the energy and power capabilities and the life time of lithium ion batteries (LIBs). [1-2] This is due to the fact that the effective transport properties, namely ionic and electronic conductivities together with the ion diffusivity are strong functions of the microstructural details such as porosity and tortuosity of the electrodes. [3-5] Notwithstanding the high interest to quantify the rate limiting phenomena in the LIBs, the reports on the detailed juxtaposition of the electronic and ionic percolation limitations to the performance of LIBs are very scarce. [4] Although the current literature provides invaluable information about the methods for measuring the effective ionic [3,6-9] and electronic [9-11] conductivity in the lithium ion battery electrodes, but there are very limited comprehensive reports on the interplay between the electrode recipe, transport limitations, and the battery performance. [12-15] A variety of experimental and theoretical techniques have been proposed for the (in)direct measurement of the effective conductivities in the porous electrodes of LIBs. Several studies have investigated the ionic and electronic conduction in LIBs by reconstructing the three dimensional (3D) structure of the porous electrodes based on the cross sectional images obtained via X-ray tomography [6,16-19] or focused ion beam-scanning electron microscopy (FIB-SEM).