Mechanical behavior of inorganic lithium-conducting solid electrolytes

All-solid-state batteries using lithium-conducting solid electrolytes (SEs) require not only favorable electrochemical properties but also optimal mechanical properties. SEs need to exhibit high enough stiffness to resist lithium dendrite growth while also being compliant and ductile enough to accommodate volumetric expansions of the electrodes. Thus, understanding the chemo-mechanical behavior of SE materials is essential for their effective development and deployment. In this work, the temperature-dependent deformation behavior of a range of inorganic sulfide (LSPS, LPSCl) and oxide (LAGP, LLZTO) SEs has been systematically investigated for the first time. Quasi-static, viscoelastic, and viscoplastic nanoindentation experimentation was conducted on these materials over a range of temperatures (from −40 to 300 °C). The elastic modulus and hardness properties of the sulfide vs. oxide material categories largely grouped together, with the cold pressed and subsequently sintered LLZTO oxide showing favorably low hardness and high tendency to creep. While all the oxide and sulfide materials exhibited minimal viscoelastic damping, consistent viscoplastic creep behavior was observed and quantitatively analyzed. The temperature dependence of the creep stress exponent was key for identifying the dominant creep mechanism in the material systems.