Boosting cation mobility in sol-gel derived organic–inorganic hybrid solid electrolytes through physical conditioning

Organic-inorganic hybrid materials are explored for application as solid electrolytes for lithium-ion batteries. The material consists of a porous silica network, of which the pores are infiltrated by poly(ethylene oxide) and lithium perchlorate. The synthesis involves two steps: First, the inorganic backbone is created by the acid-catalyzed sol-gel synthesis of tetraethyl orthosilicate to ensure continuity of the backbone in three dimensions. In the second step, the polymer and salt are imbued into the porous backbone via solvent exchange. During drying, the cylindrical disk-shaped specimens shrink mainly in the radial direction, which results in spatially non-uniform structural developments. While this inhomogeneity is not discernible in the material's chemical compositional or thermal properties, it is manifest in its ionic conductivity and adiabatic elastic modulus. The ionic conductivity in the center of the specimens is projected to be between one and two orders of magnitude higher than the measured average across the sample diameter. The process that yields a structure with enhanced ionic mobility during post-synthesis physical conditioning is inferred from careful analysis and numerical interpretation of measurable quantities, and the implications for the design of nanostructured hybrid electrolytes with high ionic conductivity are discussed.