Evolution of the Cell Structure, Ionic Conductivity, and Elastic Modulus of the γ-Irradiated LLZTO Electrolyte via Neutron Diffraction and Nanoindentation

Garnet-type lithium-lanthanum-zirconium-oxygen (LLZO) oxide solid-state electrolytes (SSEs) have become one of the most promising SSEs for future deep space exploration because of their excellent energy density and mechanical strength. However, the effects of high-energy irradiation on LLZO-type oxide SSEs in the space domain are still unknown. To this end, the Ta-doped lithium-lanthanum-zirconium-tantalum-oxygen (LLZTO) SSE with high ionic conductivity at room temperature was prepared by a solid-phase reaction method, and the gamma-irradiation effects on the cell structure and performance (ionic conductivity, hardness, and elastic modulus) of the LLZTO SSE were investigated in detail. The results show that the gamma-irradiated electrolyte did not produce other heterogeneous phases, but the lattice spacing was subsequently reduced, which would be detrimental to the ionic transport in the lattice. In addition, the neutron diffraction data also illustrate that irradiation does not change the cell structure of the LLZTO SSE, but the decrease in Li1 occupancy at the tetrahedral-24d site will have a detrimental causal effect on ion transport. The impedance test at room temperature further demonstrated that after gamma-irradiation, the total resistance of LLZTO becomes larger and the ionic conductivity of the corresponding irradiated samples tends to decrease. Fortunately, the ionic conductivity retention of irradiated samples at low temperatures was higher than that of unirradiated samples (48.45 > 29.9%). The test results of nanoindentation indicate that the irradiated samples have high mechanical properties at a low load (2 mN), which can effectively prevent lithium dendrite penetration, and this is supported by the low electronic conductivity of the irradiated samples at room temperature. The first use of gamma-irradiation to probe its effect on the cell structure and properties (electrochemical and mechanical) of the LLZTO oxide SSE has important research implications for the development of oxide SSEs for aerospace applications.