Calendering is an important step during the manufacturing process in order to improve the performance of lithium-ion batteries (LiBs) such as volumetric capacity and energy density. Moreover, calendering improves the cycle life of LiBs because it lowers growth of polarization resistance as well as ionic and electronic losses from the bulk during cycling.
This work focuses on effects of calendering on electrochemical performance and morphology of LiNi0.6Mn0.2Co0.2O2 (NMC622) cathodes. To achieve a better understanding of the impact of calendering, different characterization methods such as electrochemical impedance spectroscopy (EIS) as well as micro x-ray tomography (μCT) have been employed. By investigating the impedance spectra in a symmetrical cell configuration, we find that the interfacial resistance between current collector and cathode is high for uncalendered cathodes. From tomographic data obtained on the same cathodes, it can be seen that this large contact resistance is caused by low contact area at the interface between electrode material and current collector. Furthermore, EIS results show that contact resistance decreases by increasing the density of the electrode via calendering. Also, obtained results reveal that ionic resistance in porous cathodes change by variations of cathode density.
In summary, this study provides an overview of calendering impact on the microstructure and performance of Nickel-rich layered oxide cathodes. Highlight is the correlation between 3D-microstructural data obtained from x-ray tomography with results of electrochemical impedance spectroscopy at the current-collector/electrode interface.