Enhancement of Ion Mobility in Aluminosilicate-Polyphosphazene Nanocomposites

Abstract

Nanocomposites of poly(bis-(2(2-memoxyethoxy)ethoxy)phosphazene) (MEEP) or cryptand[2.2.2] with the aluminosilicate Na-montmorillonite (NaMont) were studied to develop new solid electrolytes with high conductivity and a unity cation transport number. An aluminosilicate was chosen because the low basicity of the Si-0-Al framework should minimize ion pairing. To further reduce ion pairing, solvating molecules or polymers such as cryptand[2.2.2] or MEEP were introduced into the aluminosilicate. When compared to pristine Na-montmorillonite, impedance spectroscopy indicates an increase in conductivity of up to 100 for MEEP-NaMont intercalates, and of 50 for cryptand[2.2.2]NaMont intercalates. The MEEPA NaMont intercalate exhibits high ionic conductivity anisotropy with respect to the montmorillonite layers (σ_para.σ^perp. = 100), which is consistent with increased tortuosity of the cation diffusion path perpendicular to the structure layers. The temperature dependance of the conductivity suggests that cation transport is coupled to segmental motion of the intercalated polymer, as observed previously for simple polymer-salt complexes. Nanocomposites of solvating polymers or molecules with aluminosilicates provide a promising new direction in solid-state electrolytes.