Optimising lithium lanthanum cerate garnet ceramic electrolytes for fast lithium-ion conduction

The garnet-type electrolytes are promising for solid-state lithium-metal batteries, while it is still challenging to realize fast lithium-ion conduction with moderate sintering process. To solve the problem, we proposed a novel cerium (Ce)-based cubic garnet electrolyte – Li 6.25 La 3 Ce 1.25 Ta 0.75 O 12 (LLCTO-0.75). The Ta 5+ doping of the tetragonal Li 7 La 3 Ce 2 O 12 (LLCO) results in a stable cubic phase at room temperature, whilst the presence of Ce 4+ is associated with enlarging lattice parameters to facilitate lithium-ion migration and promoting sintering. As a result, the LLCTO-0.75 achieves a dense ceramic microstructure with only 30 min sintering at 1150 °C, and an outstanding lithium-ion conductivity of 1.09 mS cm −1 at 30 °C. Benefiting from a small Li/LLCTO-0.75 interfacial resistance of 52.8 Ω cm 2 at 30 °C, the Li-Li symmetric cell cycles for over 700 h without short circuit, and the quasi-solid state LiFePO 4 /LLCTO 0.75/Li battery delivers a satisfying specific capacity of 127.0 mAh g −1 after 300 cycles. This work provides new insights into the development of practical solid-state oxide electrolytes for safe high-energy batteries. • A novel cerium based cubic garnet electrolyte – Li 6.25 La 3 Ce 1.25 Ta 0.75 O 12 . • Ta doping of the tetragonal Li 7 La 3 Ce 2 O 12 (LLCO) results in a stable cubic phase. • Dense Li 6.25 La 3 Ce 1.25 Ta 0.75 O 12 on 30 min sintering at 1150 °C. • Its lithium-ion conductivity is 1.09 mS cm −1 at 30 °C. • LiFePO 4 /LLCTO 0.75/Li delivers a specific capacity of 127.0 mAh g −1 on 300 cycles.