EFFECTS OF LI2SO4 ADDITION, MOISTURE, AND LIOH ON THE IONIC-CONDUCTIVITY OF LI5ALO4

The ionic conductivity and thermal properties of 80Li5AlO4 + 20Li2SO4, 75Li2SO4 + 25LiOH, and 50Li2SO4 + 50LiOH composite polycrystalline samples have been determined in both wet and dry environments. A large increase in the ionic conductivity of 80Li5AlO4 + 20Li2SO4 in a wet environment above ∼350°C is due to the presence of LiOH. This same increase in conductivity is found for the two LiOH + Li2SO4 mixtures and is related to a eutectic reaction in the Li2SO4LiOH system. The phase diagram for the Li2SO4LiOH system was determined and supports this conclusion. The conductivity of 80Li5AlO4 + 20Li2SO4 in a dry environment is thermally activated [σ = σ0 exp( -E kT)] with E = 0.66 eV and σ0 = 450 (Ω-cm)-1. The addition of Li2SO4 to Li5AlO4 increases the total conductivity but decreases the electronic conductivity. Pressed pellets of Li5AlO4 and 80Li5AlO4 + 20Li2SO4 are stable in lithium up to at least 550 and 450°C, respectively. © 1979.