Highly densified NCM-cathodes for high energy Li-ion batteries: Microstructural evolution during densification and its influence on the performance of the electrodes

For positive electrodes in Lithium ion batteries LiNi1/3Co1/3Mn1/3O2 (NCM) is widely used as an active material. The performance of the electrodes in different applications is mainly influenced through the electrode manufacturing process. This work aims to contribute to a better understanding of the relation between microstructure development caused by the densification of the electrodes and its influence on electrochemical behaviour as well as ageing. Therefore, NCM-based cathodes were compacted in several interstages down to a porosity of 18%. By detailed microscopic analyses and Hg porosimetry we provide important insights concerning the electrodes microstructure, its evolution during densification and the correlation to the electrochemical performance. In doing so it will become obvious that major microstructural changes take place when electrodes are compacted to porosities below 22-25% which goes along with a significant decline of the capacity and energy density at current rates of 2C and more. However, at current rates below 1C the highest energy density is observed for cathodes with even lower porosities. Additionally, the microscopic analyses provide important information about how this problem can be tackled.