Elastic Modulus, Hardness, and Fracture Toughness of Li$_{6.4}$La$_{3}$Zr$_{1.4}$Ta$_{0.6}$O$_{12}$ Solid Electrolyte
Shan Hu1,2, Pengyu Xu3, Luize Scalco de Vasconcelos2, Lia Stanciu3, Hongwei Ni1*, and Kejie Zhao2*
1State Key Laboratory of Refractories and Metallurgy, Wuhan University of Science and Technology, Wuhan 430081, China 2School of Mechanical Engineering, Purdue University, West Lafayette, Indiana 47907, USA 3School of Materials Engineering, Purdue University, West Lafayette, Indiana 47907, USA
Abstract：Li$_{6.4}$La$_{3}$Zr$_{1.4}$Ta$_{0.6}$O$_{12}$ (LLZTO) is a promising inorganic solid electrolyte due to its high Li$^{+}$ conductivity and electrochemical stability for all-solid-state batteries. Mechanical characterization of LLZTO is limited by the synthesis of the condensed phase. Here we systematically measure the elastic modules, hardness, and fracture toughness of LLZTO polycrystalline pellets of different densities using the customized environmental nanoindentation. The LLZTO samples are sintered using the hot-pressing method with different amounts of Li$_{2}$CO$_{3}$ additives, resulting in the relative density of the pellets varying from 83% to 98% and the largest grain size of $13.21 \pm 5.22$ µm. The mechanical properties show a monotonic increase as the sintered sample densifies, elastic modulus and hardness reach $158.47 \pm 10.10$ GPa and $11.27 \pm 1.38$ GPa, respectively, for LLZTO of 98% density. Similarly, fracture toughness increases from 0.44 to 1.51 MPa$\cdot$m$^{1/2}$, showing a transition from the intergranular to transgranular fracture behavior as the pellet density increases. The ionic conductivity reaches $4.54 \times 10^{-4}$ S/cm in the condensed LLZTO which enables a stable Li plating/stripping in a symmetric solid-state cell for over 100 cycles. This study puts forward a quantitative study of the mechanical behavior of LLZTO of different microstructures that is relevant to the mechanical stability and electrochemical performance of all-solid-state batteries.
2021, Vol. 38 
