Solvent free manufacture of ultra-thick high-energy cathodes for LIB

Summary:

Ultra-thick cathodes produced in a dry process, without the use of the toxic solvent NMP, can provide the solution for several problems limiting the competitiveness of LIB so far. In the electrode manufacturing, the very high costs for material, drying and recovery process and work safety can be saved. Furthermore, the production of solvent-free and therefore highly viscous electrode pastes enables the manufacture of ultra-thick cathodes, which provide enhanced energy density. In this respect, the limitation of the produceabele thickness, without cracks caused by the solvent, no longer applies [1] and the binder migration caused by the drying process and compromising the mechanical integrity can be avoided as well [2]. The very high areal capacity of thick electrodes offers the advantage of material savings, as fewer electrode layers are required for a battery of the same capacity. This meets the requirements especially for portable devices.

In this contribution, we present the elaboration of a suitable formulation and a process for the production of plasticizeable composits. Different formulations consisting of NMC 622, a binder, as well as conductive additives and a plasticizer have been investigated in a measuring kneader.
The influence of rotational speed on the viscosity and the temperature of the paste was examined.
It was possible to process solvent-free pastes in a twin screw extruder in pilot scale and in a single screw extruder in industrial scale. With the industrial scale extruder, it was also possible to pass the paste through a slot die and transfer it loosely roll-to-roll on an aluminium collector foil.
In further experiments with the measuring kneader the ratio between binder and plasticizer was optimized in order to increase the active material content of the pastes. We achieved an increase from 71 wt.-% to 83 wt.-% NMC under the condition of a smooth paste.
The possibilities for a roll-to-roll transfer process of the extruded cathode composites yielding good adhesion to the collector foil were evaluated by hot pressing and calendaring experiments. In order to investigate the suitability of cathode pastes as an electrode, conductivity measurements were performed. Whereas poor conductivity was measured in the extruded samples, pastes from the measuring kneader with > 80 wt.-% NMC showed promising values.

References
[1] Z. Du, et al., J. Power Sources, 354, 200 (2017).
[2] L. S. Kremer, et al., Energy Technol., 8, 1900167 (2020).