Balancing the mechanical and electrochemical properties in glassy solid-state electrolytes (Invited)

Solid state electrolytes (SSEs) have the potential to overcome many of<br/>the problems associated with liquid electrolytes, including improve-<br/>ments of fire safety, energy density, and battery lifetime. However,<br/>SSEs introduce new problems, especially due to the brittle nature<br/>of most potential SSEs such as glasses. The constant cycling of ions<br/>leads to undesired stresses in the electrolyte, which may ultimately<br/>cause fracture of the SSE and device failure. Despite this, the fracture<br/>process and its relation to glass structure and electrochemical prop-<br/>erties are only vaguely understood. To address this, we here simulate<br/>a promising family of SSEs, namely alkali thiosilicate glasses, using<br/>classical molecular dynamics simulations based on a recently estab-<br/>lished force field. We probe the elasticity and fracture mechanics of<br/>the glasses as well as the ionic conductivity to establish correlations<br/>between electrolytic performance and mechanical stability of the<br/>SSEs. We also provide detailed analyses of the ion movement and<br/>dynamic heterogeneities in the glasses. Ultimately, our work high-<br/>lights the need to consider how the propensity for fracture generally<br/>increases simultaneously with the increase of conductivity. This calls<br/>for future optimizations of glassy SSEs to balance between mechan-<br/>ical stability and electrochemical properties.