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

Abstract

Argyrodite sulfide (Li₆PS₅Cl) 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 Li₆PS₅Cl 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 Li₆PS₅Cl, is necessary to develop quantitative predictive models of dendrite initiation and propagation and help develop strategies to toughen Li₆PS₅Cl. Here, an investigation to measure the Young’s modulus and fracture toughness of porous Li₆PS₅Cl 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 Li₆PS₅Cl to be 4.7 ± 1.1 GPa and the fracture toughness to be $0.17\pm 0.03MPa\sqrt{m}$. 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/cm² respectively. The measurements reported here contribute to the body of knowledge on Li₆PS₅Cl toward the larger goal of enhancing the ability to predict Li dendrite initiation and propagation in it.