Understanding thickness and porosity effects on the electrochemical performance of LiNi0.6Co0.2Mn0.2O2-based cathodes for high energy Li-ion batteries

The targeted optimization of Li-ion batteries (LIBs) requires a fundamental understanding of the wide variety of interdependencies between electrode design and electrochemical performance. In the present study, the effects of thickness and porosity on the electrochemical performance and Li-ion insertion kinetics of LiNi0.6Co0.2Mn0.2O2-based (NCM-622) cathodes are investigated. Cathodes of different thickness and porosity are prepared and analyzed regarding their rate capability. The polarization behavior is investigated using electrochemical impedance spectroscopy. A simple mathematical model is employed to estimate the impact of Li-ion diffusion limitations in the electrolyte. The results are considered at both, the materials and the full-cell level. The design parameters are found to have distinct impact on the electrolyte, contact and charge transfer resistance as well as the Li-ion diffusion limitations in the electrolyte, significantly influencing the rate capability. The results attest an inherent tradeoff between energy and power density. The insights of this study can be used straightforward for the optimization of gravimetric and volumetric energy density of LIBs depending on the desired application.