Investigation of the Mechanical Properties of Porous Argyrodite Sulfide Electrolytes for All-Solid-State Batteries

Argyrodite sulfide (Li 6 PS 5 Cl) has been recognized as a promising solid electrolyte material for all-solid-state high-energy-density lithium ion batteries. However, the issue of Li dendrite penetration through Li 6 PS 5 Cl continues to be a challenge that limits its performance and wider applications. To understand dendrite growth that is mediated by fracture, measurement of the relevant mechanical properties, i.e., the elastic modulus and the fracture toughness of Li 6 PS 5 Cl, is necessary to develop quantitative predictive models of dendrite initiation and propagation and help develop strategies to toughen Li 6 PS 5 Cl. Here, an investigation to measure the Young’s modulus and fracture toughness of porous Li 6 PS 5 Cl material is reported; it makes use of a custom-built experimental setup. An analysis of the experimental data in conjunction with finite element simulations shows the Young’s modulus of porous Li 6 PS 5 Cl to be 4.7 ± 1.1 GPa and the fracture toughness to be 0.17 ± 0.03 M P a m . These results characterize the bulk behavior of the material at a millimeter scale in contrast to the local surface properties at the micrometer scale through nanoindentation. Based on these values, for a pre-existing crack of size 1 μm, the corresponding critical overpotential and critical current density are estimated to be approximately 12 mV and 1 mA/cm 2 respectively. The measurements reported here contribute to the body of knowledge on Li 6 PS 5 Cl toward the larger goal of enhancing the ability to predict Li dendrite initiation and propagation in it.