Solid-electrolyte fracture models driven by lithium metal plating require electrochemical mechanical couplings

A common failure mode for solid-state lithium-metal batteries is solid-electrolyte fracture during lithium plating, but fracture initiation is complicated to diagnose. Here, an electrochemically and mechanically coupled steady-state lithium-plating model is implemented numerically to study fracture initiation at the lithium/ solid-electrolyte interface. The solid electrolyte is treated as a linear elastic solid, while lithium is modeled as a Newtonian fluid. An electrochemical connection between the two phases is made via the stress-modified Butler-Volmer equation at the Gaussian-curved interface, where lithium protrudes into the solid electrolyte. The model simulations demonstrate that the couplings result in significantly different electrochemical and mechanical behaviors from those predicted by the model without the couplings. The J-integrals— an indicator of fracture—of the coupled and uncoupled models are six orders of magnitude apart. The coupled model supports a shear-traction-driven fracture concentrated at the asperity base instead of the commonly attributed pressure-driven fracture at the asperity tip. Finally, our sensitivity analysis reveals that lithium pseudo-viscosity and asperity geometry are important parameters determining fracture initiation.