Li6Zr2O7 interstitial lithium-ion solid electrolyte

Li6Zr2O7 crystallizes in a framework structure with Li occupying 1D channels in three distinguishable square–pyramidal sites. Rao et al. have reported a factor 100 increase in Li+ conductivity at 300 °C by substitution of Ta(V) for Zr(IV). We demonstrate here that a similar enhancement in Li-ion conductivity can also be achieved by incorporation of interstitial Li in the formula unit Li6+xZr2−xMxO7 (M = Y or In). Insertion of x = 0.15 Li in the form of Li6+xZr2−xMxO7 can be obtained by simple solid state synthesis. In order to know the limit of Li insertion into Li6Zr2O7, we demonstrated electrochemical insertion into Li6+xZr1.5Ti0.5O7 of excess Li to at least x ≈ 0.17 at room temperature. The Lithium activation energy was 0.63 eV for Li6.15Zr1.85Y0.15O7.