A New Class of Lithium Hybrid Gel Electrolyte Systems

This report describes new materials prepared by using Li2PdCl4 [or (CH3)2SnCl2], Li3Fe(CN)6 and glycerol, as precursors. The nearly instantaneous sol --> gel process followed by complete dehydration under reduced pressure produced the [FexPdy(CN)zClv(C3H8O3)Lil] (I) and [FexSny(CH3)2y(CN)zClv(C3H8O3)Lil] (II) materials with the characteristics of a hybrid inorganic-organic gel (HGE), as confirmed by morphological studies. FIR, MIR, Raman laser, and UV-visible investigations together with detailed compositional data allowed us to propose a structural hypothesis and to describe the interactions between ions and glycerol in these materials. We concluded that the two HGEs consist of a hybrid backbone composed of a mixture of inorganic-organic clusters of Fe and Pd (or Sn) structural units with glycerol surrounded by nonbonded glycerol molecules. The materials I and II are thermally stable up to about 115 and 125 °C, respectively. DSC investigations revealed their Tg at -74 and -76 °C, respectively. Variable-temperature 1H and 7Li NMR line width, spin-lattice relaxation, and pulsed field gradient diffusion measurements were performed to investigate a possible correlation between glycerol mobility and lithium migration. Electrical spectroscopy measurements in the 10 mHz to 1 GHz range taken from -60 to +80 °C provided information regarding the systems' conductivity mechanism and structural relaxations. In addition, electrical spectra in the high frequency region revealed the presence of an beta relaxation event associated with glycerol molecules. This phenomenon suggests that the proposed HGEs exhibit the glycerol glass-forming behavior typical of supercooled materials. Finally, HGEs I and II exhibited room temperature conductivities of 5.0E-5 S/cm and 8.5E-5 S/cm, respectively, which classify these materials as good ion conductors.