Inorganic-Organic Hybrid Sulfide Solid Electrolytes Based on the Tetraalkylammonium Iodide-LiI-Li₂S-P₂S₅ System

Abstract

A series of novel inorganic-organic hybrid sulfide solid electrolytes were synthesized by doping Li7P2S8I with a selection of tetraalkylammonium iodides, including tetramethylammonium iodide (TMAI), tetraethylammonium iodide (TEAI), tetrapropylammonium iodide (TPAI), and tetrabutylammonium iodide (TBAI). The electrolytes were prepared in varying compositions represented as (1-x) Li7P2S8I ⸱ x (TMAI, TEAI, TPAI, TBAI), where x values were adjusted to 0, 0.05, 0.1, and 0.2 (molar ratio) to assess their influence on the electrolyte properties. These hybrids exhibited predominantly amorphous structures. Tetraalkylammonium iodides with longer alkyl chain length of the dopants showed lower ionic conductivity. Mechanical characterization via indentation tests indicated that the incorporation of longer alkyl chain length tetraalkylammonium iodides contributes to a reduction in the elastic modulus of the composites. This work underscores a methodological approach to modulate the structural and mechanical properties of sulfide solid electrolytes through strategic organic doping.