New Li+ ion conductors in the system, Li4GeO4-Li3VO4

New Li+ ion conducting solid electrolytes have been found in the system Li4GeO4-Li3VO4. Of the compositions studied, Li3.6Ge0.6V0.4O4 has the highest conductivity with σ ∼ 4 × 10−5 ohm−1cm−1 at 18°C rising to ∼ 10−2 ohm−1 cm−1 at 190°C. The activation energy is ∼0.44 eV. These conductivity values are among the highest yet found for Li+ ion conductors; the room temperature value is much higher than in LISICON, Li3.5Zn0.25GeO4, or in Li3.4Si0.4P0.6O4 and is comparable to that in LiI/Al2O3 mixtures. These solid electrolytes are easy to synthesize, thermodynamically stable and insensitive to atmospheric attack. Structurally, they are solid solutions based on γII Li3VO4, a γ tetrahedral structure; high conductivity is due to the interstitial Li+ ions which are created during solid solution formation.