Orthogonal Solvent Mediation for Solid Composite Electrolyte Synthesis: Phase Integration via Particle Dispersion

Ceramic-rich solid-composite electrolytes exhibit ceramic-like ionic conductivity and enhanced mechanical property, making them promising candidates for market-relevant solid-state batteries. In-depth knowledge of the microstructure within the composite electrolytes for ideal performances and their correlation with the choice of materials and processing methods are not well-understood. Herein, we report a solution-cast, free-standing composite film comprised of well-integrated ceramic (Li3InCl¬6) and binder (Styrene-Ethylene-Butylene-Styrene, SEBS) phase, which simultaneously provides Li+ transport pathways and the required mechanical support. In the formation of this unique microstructure, we mark the mediator role of dibutyl ether – a low polarity solvent that forms a non-invasive polar-ionic interaction with the electronegative metal elements at the surface of Li3InCl¬6 particles to suspend and disperse Li3InCl6 particles in the dissolved SEBS matrix, facilitating phase integration. This weak interaction only occurs at chosen conditions; increased solvent-to-ceramic ratio and interaction time can induce Li3InCl6 decomposition. Our results correlate the electrochemical performance of a ceramic-rich Li3InCl6-SEBS composite electrolyte film with its microstructure; the latter was demonstrated to be potentially tunable by altering the molecular structure of the solvent and the parameters used in composite electrolyte synthesis procedures. This work provides materials structural-level insights that underpin the design principle of solution-cast solid composite electrolytes.