Electrochemical and Mechanical Understanding of Extruded and Solvent‐Cast Solid Polymer Electrolytes

ABSTRACT Solid polymer electrolytes (SPEs) based on Poly(ethylene oxide)‐Lithium bis (trifluoromethanesulfonyl)imide (PEO–LiTFSI) are promising materials for solid‐state batteries. A comprehensive evaluation was conducted on their electrochemical and mechanical properties, with SPEs prepared via two processing methods: extrusion and solvent casting. The effects of Al 2 O 3 addition and membrane thickness on SPE performance and cyclability were investigated. Electrochemical characterization showed that extrusion enhanced SPE properties by shortening polymer chains, while the presence of Al 2 O 3 improved membrane stability. Thicker membranes exhibited larger polarization gradients, slower ion diffusion, and lower Sand times, leading to reduced electrochemical performance. Mechanical properties, including yield stress, storage modulus, and fracture toughness, were assessed using rheology and dynamic mechanical analysis. Extruded SPEs displayed higher stiffness and greater resistance to dendrite formation than solvent‐cast membranes. Monotonic crack growth tests indicated that the presence of Al 2 O 3 increased fracture toughness, enhancing crack resistance and potentially extending cycle life. Overall, membranes produced via extrusion, containing Al 2 O 3 , and optimized for reduced thickness, combined superior electrochemical properties, making them strong candidates for solid‐state battery applications, as demonstrated by their incorporation in multilayer cells.