The all solid-state battery (ASSB) technology, where classical liquid electrolytes are replaced with ion-conducting solids, is becoming increasingly important today. Due to the interest in ASSBs, the transition from lab-scale production of ASSBs components to larger scale is attracting more attention. Expected to the wide range of process methods and its availability on the global market, polymer based solid electrolytes (SE) offer the prospect of facile upscaling. For example, extrusion provides the possibility of continuous dry thermal mixing of SE constituents to produce homogeneous polymer based SEs.
The processing of thermoplastic Poly(ethylene oxide) (PEO), that is capable of dissolving alkali salts like Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), is currently under investigation. Previous works from our research group show that the processability of PEO not only depends on the conductive salt, but also on the polymer’s molecular weight and applied process parameters. [1]
The aim of this work is to optimize the extrusion process using a co-rotating twin-screw extruder for the production of solid PEO/LiTFSI-electrolytes. We investigate the effects of several extruder set-ups and process parameters on the mixing behaviour of the constituents. Both, type of dosing and screw design are varied. For type of dosing, we compare the dry extrusion of a premixed PEO/LiTFSI (20:1) batch to the use of one feeding unit for each component. The screw designs are varied by conveying, kneading and mixing elements. During extrusion, the actual extruder torque and the pressure at the extruder die are continuously monitored to evaluate the process stability and flowability of the material. PEO/LiTFSI-electrolytes are produced with a constant process temperature of 90 °C and with screw speed of 5 – 15 rpm to avoid degradation. For product evaluation, we examine the homogeneity and quality of the extruded PEO/LiTFSI-electrolytes. Optical microscopy is used for macroscopic evaluation and the Li-salt distribution is checked with SEM/EDX. For the determination of lithium concentration and degradation processes, conductivity and rheology are examined, respectively. Electrochemical impedance spectroscopy (EIS) is performed to determine the ionic conductivity. With the characterisation of the extruded electrolytes, process parameters are optimised for the production of polymer based SEs.


References
[1] K. Platen, F. Langer, J. Schwenzel, M. Busse, Polym. Eng. Sci. (2022) (under Revision)