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

Abstract

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 Li6.5La3Zr1.5Ta0.5O12 (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.