Void Evolution at the Li/LLZO Interface: Stack Pressure and Operating Temperature-Driven Creep Effect

All-solid-state lithium metal batteries hold promise for meeting the industrial demands for high energy density and safety. However, voids are formed at the lithium metal anode/solid-state electrolyte interface during stripping, deteriorating interface contact and reducing the cycle stability. Stack pressure and operating temperature are effective methods to activate creep deformation in lithium metal, promoting interfacial deformation and alleviating void-induced interface issues. Nevertheless, we lack a clear understanding of how stack pressure and operating temperature affect void evolution via the creep effect, as well as a theoretical basis for how to regulate pressure and temperature to achieve void healing and interface stability. Therefore, we develop a coupled electrochemical-diffusion-mechanical (creep)-phase field for void evolution (EDMP-VE) model, describing lithium stripping and deposition, bulk and surface diffusion, creep deformation, lattice distortion, and vacancy nucleation and annihilation. The model successfully captures void evolution at the interface during a stripping-plating cycle. We use normalized geometric parameters to quantitatively characterize the dynamic void evolution and describe the creep effect by the temporal and spatial evolution of hydrostatic stress, von Mises stress, and equivalent creep strain. It reveals the influence mechanism of stack pressure and operating temperature-driven lithium metal creep on void evolution. High stack pressure and operating temperature activate considerable creep deformation, suppress void expansion, accelerate void filling, achieve void annihilation, and improve interface contact. Considering the coupling effect of stack pressure and operating temperature, we construct a phase diagram of stack pressure-operating temperature-void healing rate, identify the void healing region, transition region, and void deterioration region, and determine the parameter window for achieving void healing. This work provides a theoretical foundation for understanding the impact mechanism of the creep effect on void evolution and supplies technical support for regulating stack pressure and operating temperature to implement void healing.