Low temperature synthesis of Li5La3Nb2O12 with cubic garnet-type structure by sol–gel process

A cubic Li5La3Nb2O12 phase with a garnet framework was synthesized by the sol–gel process, in which lithium hydroxide, niobium oxide and acetic lanthanum were used as starting materials, while water was used as solvent. Pure garnet-like Li5La3Nb2O12 powders were obtained after heating the gel precursor at 700 °C for 6 h with 10 % excess lithium salt. The calcination temperature is nearly 250 °C lower than that by the solid state reaction. The phase transforms from cubic to tetragonal symmetry with loss of lithium at 717 °C, but the garnet framework remains stable to above 900 °C. A pellet annealed at 900 °C for 6 h had a room-temperature Li+-ion conductivity σLi (22 °C) = 1.0 × 10−5 S cm−1, a little higher than that attained by solid-state synthesis. The Li5La3Nb2O12 compound was chemically stable against two commonly used cathode materials, LiMn2O4 and LiCoO2, up to 900 °C and against metallic lithium.