Atomistic Modeling of the Mechanical Properties and Deformation Behavior of Lithium

Abstract We explore the mechanical properties of lithium metal and investigate how specimen size, crystallographic orientation, temperature and strain rate affect its deformation behavior. In single crystals, it is found that anisotropy plays an essential role both for elasticity and plasticity. We demonstrate that Li single crystal nanopillars plastically deform either by dislocation slip or by twinning, depending on orientation, loading mode (tension versus compression) and strain rate. In the cases of slip, deformation is predominantly mediated by dislocations with a Burgers vector of 1/2 ⟨111⟩, which are active on different planes. Conversely, twinning occurs singularly on {112} planes and displays a twinning/anti-twinning anisotropy, resulting in the strong dependence on orientation and loading mode observed. In terms of size dependence, specimens undergoing dislocation slip show a pronounced "smaller is stronger" trend in their yield strength. However, for specimens deforming exclusively by twinning, size effects are notably less significant. In polycrystalline nanostructures, opposed to the single crystal findings, the yield strength decreases with finer grain size in the spirit of an inverse Hall-Petch relationship, with grain boundaries being the central effect influencing their mechanical behavior.