Investigation of Coating Stability in Alkaline Electrolytes of Commercial Porous Polyolefin Separators

Abstract Separators are essential components in battery technologies. Developed for Li-ion batteries, most commercial microporous separators are based on polyolefin and are generally used as reference materials rather than as primary research subjects. Today, batteries with aqueous electrolytes remain a vivid field of research and development, and the transfer of the separators characteristics and properties determined within the frame of Li-ion battery applications would be irrelevant. Thus, detailed investigations are needed to assess characteristics and properties of commercial separators in the presence of aqueous electrolytes, as well as to complete studies about their stability over time, which remain scarce in literature. Here, we present a simple, low-cost, method accessible to most laboratories to accelerate separator ageing using solid/liquid extractions with water and dichloromethane to simulate physical desorption of the hydrophilic coating on the polyolefin separator backbone and to assess mass loss. Relationships between separator properties (electrolyte uptakes, mass losses, contact angle, and ion diffusion coefficients) before and after extraction, and after long-term chemical ageing in strongly alkaline electrolyte are discussed to establish an initial accelerated degradation test. Finally, the proposed methodology allows the quick evaluation of any coatings developed for the surface modification of polyolefin separator.