Linking Local Ionic Conductivity, Microstructure, and Nanomechanical Properties to Bulk Performance for Enhanced Design of Solid Polymer Electrolytes

Poly(ethylene oxide) (PEO)-based solid polymer electrolytes (SPEs) incorporating LiTFSI and LiClO 4 are widely studied, yet the impact of salt type on Li + ion transport and morphology remains poorly understood. Here, we use current-sensing atomic force microscopy (CS-AFM) to probe the Li + migration and nanomechanical properties in SPEs with varying salt loadings. Topological and ionic current mapping over 80 × 80 μm 2 under 0.5 V bias reveals that LiClO 4 induces rapid spherulitic growth, expelling salt and causing spatial heterogeneity in conductivity. In contrast, LiTFSI yields more homogeneous structures and conduction. Elemental and nanomechanical mapping confirms these patterns, showing distinct moduli and hardness between crystalline and amorphous regions in LiClO 4 -based SPEs, while LiTFSI-based systems remain more uniform. These spatial variations adversely affect electrode contact and long-term stability. Our findings highlight the importance of understanding multiscale ionic transport and morphology to guide the design of next-generation SPEs for solid-state batteries.