Time- and Geometry-Driven Void Dynamics at the Lithium-Solid Electrolyte Interface Revealed by Phase-Field Modeling

Interfacial void formation at the lithium/solid electrolyte (Li/SE) interface is a primary degradation mechanism in solid-state lithium-metal batteries, leading to contact loss, current localization, and dendrite-induced failure. Here, a fully coupled electro-chemo-mechanical phase-field framework is employed to investigate void evolution under realistic cycling protocols, interfacial morphologies, and stack pressures. We demonstrate that void growth is fundamentally time-dominated, showing that fixed-time cycling protocols misrepresent degradation trends observed under fixed-capacity operation. Lower current densities promote severe void growth due to prolonged stripping durations, whereas higher current densities suppress void expansion while amplifying current localization. A critical void size is identified below which creep-mediated lithium flow enables void closure, with this threshold decreasing with increasing current density. We further show that void geometry, SE surface roughness, and defect positioning-not void area alone-govern interfacial stability and effective current density amplification. Stack pressure reduces void area but does not universally improve contact or interfacial stability, with outcomes strongly dependent on void morphology. These findings provide physics-based design guidelines for interface engineering, cycling strategies, and pressure management in solid-state lithium-metal batteries.