A Study of Factors Responsible for Cracking during Drying of Thick Aqueous-Processed NMC811 Cathodes

Abstract

Replacing the widely used NMP solvent for processing of lithium-ion battery electrodes with water has both environmental and cost benefits. Compared to aqueous-processing of anodes, the aqueous-processing of cathodes is considerably more challenging. Issues such as damage of the NMC-type active material upon exposure to water, damage of the aluminum substrate due to highly basic aqueous-slurry, and cracking of the water-based cathode slurry coatings upon drying are known and are actively being researched. In this study, we focus on the cracking-issue which is more severe for relatively thick cathodes with loadings of >~11-12 mg/cm2. Our group has previously reported the role of high surface-tension of water compared to NMP on cracking and demonstrated that the addition of 20-30 wt% IPA as a co-solvent lead to crack-free thick (~25 mg/cm2) NMC532 cathodes. This finding was attributed to reduction of surface tension of water, which decreased the capillary forces during drying. Further investigations have resulted in identification of several other factors that are also responsible for the cracking-issue. These factors, which are not necessarily related to the surface tension, will be discussed.