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

Power and energy density represent a trade-off in design of lithium-ion batteries. This is because for high energy density thick electrodes are required, and for high power density thin electrodes are required. A strategy to break this trade-off is to develop electrodes with regions of low 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 XRD technique, which obtains XRD patterns from a specific volume of space, to study 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 in the electrode and show how the mass transport problem cannot be separated from the electrochemical.