A New Class of Lithium Hybrid Gel Electrolyte Systems

Abstract

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 ∼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 α 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 5.0 × 10-5 S·cm-1 and 8.5 × 10-5 S·cm-1, respectively, which classify these materials as good ion conductors.