A large deformation elastic-viscoplastic model for lithium

An essential ingredient in modeling the response of lithium in an all-solid-state lithium battery in which a lithium metal anode is paired with a non-flammable inorganic solid electrolyte (SE), is a constitutive model for the large deformation elastic-viscoplastic response of lithium. Wang and Cheng (2017) have recently published indentation load-versus-depth data from their microindentation experiments conducted in an argon-filled glove box to study the viscoplastic behavior of lithium at room temperature. In this paper we report on a large deformation isotropic elastic-viscoplastic theory for modeling the response of lithium. We have implemented the theory as a user-material-subroutine in a finite element program, and the material parameters for the theory have been calibrated using the data from the microindentation experiments of Wang and Cheng. To exhibit the utility of our finite element simulation capability, we show results from two representative numerical simulations of relevance to modeling the mechanical interaction between a lithium anode and a SE: (a) flattening of an asperity on the surface of lithium when it is mechanically impressed by a flat ceramic SE; and (b) intrusion of lithium into a cavity on the surface of SE, when the SE is mechanically impressed into lithium with a flat surface.