Thermally Robust and Highly Wettable Polyethylene Separators for Lithium-Metal Batteries Using Water-Based Processing of a Glass Platelet Coating

Commercial polyolefin separators for lithium-ion batteries (LIBs) exhibit only inadequate wettability and thermal stability. In large-scale production, high electrolyte uptake and wetting are essential to enable rapid electrolyte filling during battery assembly to reduce costs. In addition, it is imperative to develop separators with enhanced thermal stability for improved performance and safety. The focus of this study is the structure–property–performance relationship of separator coatings. Platelet-shaped glass particles are utilized as inorganic coating material for polyethylene (PE) separators. Styrene–butadiene rubber (SBR) was selected as binder due to its high thermal stability. Hybrid separators are prepared using a colloidal coating technology employing a water-based slurry. As the excessive use of binder in the coating can block pores, precise control of the binder content was essential to maintain battery performance. The resulting separators with an optimized binder content of 1 wt.% in the coating demonstrate high porosity, instantaneous wetting with electrolyte, and a 25 K increase in onset temperature for shrinkage. The utilization of glass platelets with an aspect ratio of 10 as coating material provided the best balance among processability, coating homogeneity, thermal stability, ionic conductivity, and cycling performance under the investigated processing conditions.