Rheology of Poly(ethylene oxide)-Based Slurries of Graphite Electrodes for All-Solid-State Polymer Batteries

All-solid-state batteries based on ion-conductive solid polymer electrolytes (SPEs) are regarded as future alternative energy storage devices because of their safety and processability. One of the major difficulties is the solid/solid contact between the electrode and the electrolyte, which is troublesome to efficiently construct during manufacturing. To overcome this problem, preliminary efforts have been made so far to incorporate SPEs as ion-conductive binders in electrodes, as reported in the literature. To further this concept, the present study examines in detail the rheological properties of aqueous graphite electrode slurries containing poly(ethylene oxide) (PEO)-based SPEs, which are critical for practical deployment but have not received much attention. The evaluations were conducted using flow curve, strain, and frequency sweep viscoelasticity, and step flow measurements. These evaluations demonstrate that the SPE-containing slurries exhibit practical feasibility with a shear-thinning and thixotropic nature. These properties resemble those of common battery slurries and are appropriate for manufacturing. The studies also suggest that viscosity and moduli can be controlled by optimizing the preparation procedure of the slurries as well as the SPE composition. Nevertheless, a slightly stronger tendency toward dilatancy and poor dispersion problems were identified, which may present challenges. The results demonstrate that the development of electrodes containing SPEs necessitates careful evaluation and optimization of the rheological properties of the slurries. The present study sheds significant light on the importance of specialized knowledge and techniques to obtain accurate and useful information on the non-Newtonian fluidity and viscoelasticity of battery electrode slurries containing SPE materials. We believe that the present feasibility study will contribute to advancing the concept of SPE-containing electrode slurries to the practical manufacturing level.