Lithium conduction in inorganic gel monoliths containing LiNO3 or LiBr at low temperatures

Lithium conducting silica gels were prepared with LiNO3 and LiBr salts adde d at the beginning of the sol-gel process. The chemical compositions of the initial sols corresponded to the formula TMOS/H2O/HCl/LiX/MeOH = 1:n:5 x 1 0(-4):0.2:3 for n = 4 and n = 20, where LiX = LiNO3 or LiBr. The ionic cond uctivity of the gels and that of the relevant solutions was measured by imp edance spectroscopy in the temperature range 170-300 K. The temperature dep endence of the conductivity for gels with a large excess of water (n = 20) followed the Arrhenius formula sigma T= sigma(0) exp[-E/kT] at temperatures below ca. 210 K and above ca. 245 K with different values of sigma(0) and E in both ranges. The ionic conductivity of gels prepared from stoichiometr ic sols (n = 4) varied with temperature according to the Vogel-Tammann-Fulc her (VTF) equation sigma = A/root T exp[-B/(T - T-0)]. Results are discusse d on the basis of the properties of the ionically conducting liquid, fillin g the pores of the gels, and the influence of gel porosity (mainly pore siz e and interactions with the pore liquid) on the properties of the conductin g medium. (C) 1999 Elsevier Science B.V. All rights reserved.