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_6.25La₃Ce_1.25Ta_0.75O₁₂ (LLCTO-0.75). The Ta⁵⁺ doping of the tetragonal Li₇La₃Ce₂O₁₂ (LLCO) results in a stable cubic phase at room temperature, whilst the presence of Ce⁴⁺ 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 cm² at 30 °C, the Li-Li symmetric cell cycles for over 700 h without short circuit, and the quasi-solid state LiFePO₄/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.