Experimental Analysis of Drying Kinetics and Quality Aspects of Convection-Dried Cathodes at Laboratory Scale

Abstract

The evaporation of N-Methyl-2-Pyrrolidone (NMP) solvent during the large-scale production of LiNixMn1−x−yCoyO2 (NMC) cathodes usually occurs in convection ovens. This paper aims to close the gap between the industrial convection drying method and the conventional vacuum oven typically used at the laboratory scale. Multiple studies focus on modeling convection dryers to reduce energy consumption, but few have studied their impact on the cathode quality experimentally and compared them to vacuum-dried cathodes. A convection oven designed for LIB electrode drying was developed to investigate the influence of drying kinetics on the formation of small electrode surface cracks (<1400 μm2) and binder migration. The drying kinetics were revealed through thermogravimetric analysis (TGA) at drying temperatures of 50 and 100 °C and hot air velocities of 0.5 and 1 m/s. Even at these relatively low drying rates, structural differences were detected when comparing the two drying methods, illustrating the importance of implementing drying conditions that represent the industry process in laboratories. Surface cracking increased with drying rates, and cathodes with multiple cracks after calendering obtained a higher discharge capacity at discharge currents >C/2. An alternative surface analysis with less sample preparation was sufficient for determining the relative change in binder migration.