Investigating the Structure and Performance Differences between the Electrodes Made by a Dry and a Wet Slurry Processes

Abstract

In the conventional wet slurry method for making lithium-ion battery (LIB) electrodes, unwanted N-Methyl-2-Pyrrolidone (NMP) solvent is used. The use of NMP increases the overall energy demand during electrode coating since NMP needs to be dried from the coated slurry and recovered. The improper use of NMP can also impose detrimental effects on health and the environment. Thus, solvent-free dry processes are gaining increased interest worldwide for electrode fabrication. Amongst different dry electrode manufacturing techniques, electrostatic spray deposition (ESD) is one of the most promising techniques. In this study, positive LiNi0.8Co0.1Mn0.1O2 (NMC811) electrodes were manufactured by the ESD process and wet slurry process. The differences between the electrodes made by these two processes were investigated by the peel strength test, electrochemical techniques (e.g., rate tests, electrochemical impedance spectroscopy, and constant voltage/constant current cycling), scanning electron microscopy with energy dispersive x-ray spectroscopy, and X-ray photoelectron spectroscopy. In the dry electrodes, most active material particles were densely covered by the binder and conductive agents. Whereas in wet slurry electrodes, binder and conductive agents were distributed more homogenously both on the active material surfaces and between the active material particles. The uniform distribution of the binder and conductive agents in the slurry electrodes results in a robust conductive network, leading to better performance at high C- rates (e.g., 2-5C). Interestingly, the dry electrodes had comparable performance to slurry electrodes at the initial stages of electrochemical testing with low current rates. Hence, it can be concluded that the distribution of the electrode materials affects active material usage and the conductive paths, and a homogenous distribution is needed to achieve faster discharge capacity at higher C rates. Future work will focus on the long-term cycling performance of the electrodes to further understand the degradation mechanisms and differences between the two types of electrodes.