Dry Extrusion Process for Manufacturing of High-Energy Cathodes for Lithium-Ion Batteries

Abstract

For a sustainable production of lithium ion batteries, more environmentally friendly, energy saving and faster strategies are required. For cathode production NCM/NCA layered oxides are commonly used as active materials. Nevertheless, application of the very toxic and teratogenic solvent N-methylpyrrolidone (NMP) is still common for the industrial production of these cathodes. Besides the high toxicity, the NMP recovery after coating is very energy-, time- and cost-intensive.As an alternative, to conventional NMP-based cathode production, we developed a dry extrusion process coupled with slot-die coating, to manufacture high-energy cathodes. The extrusion process offers continuous production, alongside a very good scalability to industrial demands and a significant reduction of mixing time. Since the process is NMP-free and the drying step is saved, it overcomes typical shortcomings of the wet coating as crack formation or binder migration occurring during solvent evaporation. In addition, producing high-energy electrodes leads to lower material costs and space savings, since less layers of Al/Cu foil and separator are required on cell level, compared to a battery of the same capacity and lower electrode mass loading.Herein, we present the development of a dry cathode manufacturing process, a suitable recipe for dry processing, consisting of NCM622, PVdF, carbon black and a superplasticizer, as well as the optimization of the formulation in terms of processability and active material content. We also discuss the influence of process parameters such as temperature or rotation speed on the viscosity of the cathode paste. As a proof of concept, we processed powder mixtures, corresponding to our optimized formulation with about 90 % of NCM, in a pilot scale twin-screw extruder. By melt extrusion through a slot die, we create a thin film from the cathode composite that we directly apply on an Al current collector. We show a schematic representation of the process in the attracted graphic. By repositioning of the electrode coil, we also produce double-sided coatings. After calendaring, we characterize the dry processed electrodes electrochemically in half-cells. The electrochemical performance data is comparable to state of the art cathodes and results are promising that even higher active material contents can be reached. Therefore, the solvent free extrusion of cathodes is highly relevant for industrial applications.AcknowledgementThe presented work was financially supported by BMBF within the project Tropex under the reference number 03XP0235C. Figure 1