Multi-Scale Mechanical Behavior of the Li₃PS₄ Solid-Phase Electrolyte

The need for smaller, lighter, and longer lasting rechargeable batteries is projected to increase rapidly in the coming years because of high demand for portable electronics and electric vehicles. While traditional Li-ion batteries use liquid-phase electrolytes, these suffer from safety risks and low energy density. Solid-phase electrolytes can avoid these issues by enabling a Li metal anode, but tend to fail during cycling due to Li metal dendrite growth between the electrodes. Because Li dendrite nucleation and growth can be viewed in terms of the mechanical behavior of the battery components, it is critical to understand the mechanical response of candidate electrolyte materials. In this work, we use nanoindentation and bulk acoustic techniques to characterize the mechanical properties of β-Li₃PS₄, a promising Li-ion conducting ceramic. We find that the bulk and shear moduli of an 80% dense bulk LPS sample are 10-12 GPa and 5-6 GPa, respectively. Although this value of shear modulus may be too low to prevent Li dendrite propagation, it is likely that there are many other mechanical properties that must be taken into account to fully understand Li dendrite nucleation and growth. Ultimately, this work represents a first step in understanding the relationship between Li₃PS₄ separator manufacture and its mechanical properties.