Investigating the Influence of Different Aprotic Processing Solvents for the PVdF Binder on the Microstructure and Electrochemical Performance of High-Load Positive Electrodes for Lithium Ion Batteries

Abstract

State-of-the-art manufacturing of positive electrodes in lithium ion batteries is carried out in N-methyl-2-pyrrolidone (NMP), an aprotic organic solvent which stands out for good wetting properties, a high boiling point allowing controlled evaporation during electrode drying, and dissolving properties, for the conventionally used polymeric binder polyvinylidene difluoride. The replacement of NMP with nonhazardous, alternative solvents was proven to be difficult in terms of binder solubility. Furthermore, the inevitable energy-demanding recovery of NMP due to safety concerns and environmental impact amounts for noteworthy costs during electrode manufacturing. Here, the use of dimethyl sulfoxide (DMSO), γ-valerolactone (GVL), and dihydrolevoglucosenone (Cyrene) as possible alternative solvents to replace NMP in the production of positive electrodes based on LiNi 0.6 Mn 0.2 Co 0.2 O 2 with a high active material mass loading is presented. Homogeneous electrodes were produced and thoroughly examined regarding adhesion strength, electronic conductivity, microstructure, possible solvent residues after drying, and electrochemical performance. It was shown that DMSO and GVL are hopeful candidates to replace NMP with DMSO being the superior alternative with similar performance results compared to electrodes produced with NMP. The comparison of different aprotic solvents reveals that a replacement of NMP with DMSO could be a step toward a greener, more sustainable electrode production.