Understanding energy-power trade-off in the structure of Li-Ion battery cathodes by localized operando XRD

Abstract

Power and energy density represent a trade-off in design of lithium-ion batteries at several scales. At the electrode scale this is because for high energy density, thick electrodes are required, and for high power density, thin electrodes are required. It is essentially a mass transport limitation. A strategy to break this trade-off is to develop structured - electrodes with regions of lower tortuosity (e.g. cracks or channels) that can alleviate the mass transport limitations of thick electrodes. However, to achieve a rational design of such electrodes a greater understanding of their inner workings is required. In this study we apply the multi-channel collimator X-ray diffraction technique, which obtains XRD patterns from a specific volume of space, to study a model system for a structured electrode - an NMC622 cathode with pronounced cracking - under operando conditions in a normal coin cell. Probing the local lithiation state near and far from a crack allows us to elucidate mass transport of lithium ions in the electrode and show how the mass transport problem cannot be separated from the electrochemical.