What Limits the Rate Capability of Ultrathick Composite Electrodes in Lithium-Ion Batteries? A Case Study on the Thickness-Dependent Impedance of LiCoO2 Cathodes

Abstract

Increasing the thickness of composite electrodes in lithium-ion batteries from about 80–100 μm in state-of-the-art commercial cells to several 100 μm would enhance the energy density, however at the expense of the power density. Despite this common knowledge, quantitative studies on the impedance and rate capability of composite electrode in dependence of the electrode thickness are scarce. Therefore, we have carried out a case study on LiCoO2 composite electrodes with thicknesses up to about 250 μm. We first demonstrate that conventional composite electrode preparation leads to ion transport tortuosities in the electrolyte-filled pores, which are virtually independent of the thickness. The thickness-dependent impedance of these electrodes decreases with increasing thickness and follows the predictions of a generalized transmission line (GTLM) model. We use the GTLM model for analyzing in what way cycling of ultrathick electrodes (250–300 μm) with a rate of 1 C should be achievable.