Solid Polymer Single-Ion Conductors:  Synthesis and Properties

Abstract

Optimal battery electrolyte materials provide for high transport of a single ionic species. Here we report solid single-ion conductors (SICs) based on composite polymer electrolytes consisting of poly(ethylene glycol) (PEG) and an organic−inorganic component (OIC) formed in situ. The resulting solid films showed transport properties with conductivity as high as 10-4 S/cm at room temperature and a cation transference number of 0.9. The materials were characterized using solid-state NMR, differential scanning calorimetry, X-ray diffraction, transmission electron microscopy (TEM), and impedance spectroscopy. The OIC was formed by sol−gel reaction of the three precursors: the sodium salt of 3-trihydroxysilylpropylmethylphosphonate (SPMP), (3-glycidylopropyl)trimethoxysilane (GLYMO), and tetramethoxysilane, resulting in a high degree of three-dimensional network character of OIC within SIC solid polymer electrolytes as indicated by solid-state NMR. TEM examination of calcined OIC shows that the silicate particles are fairly uniform and measure approximately 15 nm in diameter. Their uniformity and small size lead to the homogeneity of the composite material. The glycidyl group of GLYMO enhances the compatibility of OIC with PEG. The phosphonate group of SPMP furnishes immobile anions, while Na+ cations are the only source of conductivity.