Fast Li-ion transport pathways via 3D continuous networks in homogeneous garnet-type electrolyte for solid-state lithium batteries

Solid-state lithium batteries (SSLBs) using solid-state electrolytes (SSEs) have attracted much attention due to their satisfying safety and high energy density. Towards further practical development, insufficient room temperature ionic conductivity in garnet-type Li_6.5La₃Zr_1.5Ta_0.5O₁₂ (LLZTO) SSEs (usually ˂1×10⁻³ S‧cm⁻¹) remains a significant challenge and calls for a giant leap. In this work, a novel solid-state sintering strategy is employed by introducing La₂O₃ nanoparticles to promote the homogenous distribution of the grains and construct 3D continuous Li-ion transport networks along the grain boundaries. The La₂O₃ nanoparticles are regarded as the second phase to inhibit the abnormal grain growth (AGG) of LLZTO grains and reduce the voids defect to improve the relative density. The LaLiO₂ Li-ion conductor is synthesized by combining the excess La₂O₃ nanoparticles and the gas Li₂O, providing continuous ionic pathways and enhancing the Li-ion conductivity. The Li-ion conductivity reaches 1.12×10⁻³ S•cm⁻¹ (64 % higher than the pure LLZTO electrolyte) with a relative density of 98.1 %. The results presented here show that SSLBs with LiFePO₄ cathode achieve a superior stable cycling performance with a high discharge capacity of 128.8 mA•h•g⁻¹ and a Coulombic efficiency over 99% after 600 long-term cycles (0.5 C) at room temperature. The work provides a feasible solid-state sintering approach to creating SSEs with high performances for future applications of SSLBs.