Enhancing Lithium Metal/Solid-State Electrolyte Interface Stability by Magnesium Alloying: Void Nucleation, Growth, and Interfacial Failure

The application of all-solid-state lithium metal batteries faces numerous challenges. The stripping-induced void nucleation and growth at the lithium metal/solid-state electrolyte interface can lead to poor interfacial contact, ultimately causing battery failure. In this study, we developed an electrochemical-diffusion-nucleation-phase field coupled interface evolution model (EDNP-IE) to investigate the interfacial void evolution and explore the regulatory mechanism of magnesium doping on interfacial stability. The nucleation and growth of interfacial voids are strongly correlated with the stripping current density. For the Li–metal anode, lower stripping current densities induce two-dimensional (2D) and three-dimensional (3D) growth of interfacial voids, leading to fewer but deeper voids and a thicker interfacial void layer. In contrast, higher stripping current densities primarily drive 2D void growth, resulting in more numerous but shallower voids and a thinner interfacial void layer. The interfacial failure mechanisms of lithium–magnesium (Li–Mg) alloy anodes vary significantly with magnesium content. For low-Mg-content Li–Mg alloy anodes, the primary cause of interface failure is a loss of physical contact due to the interfacial void layer formation. In high-Mg-content Li–Mg alloy anodes, interfacial failure is dominated by a loss of chemical contact due to hindered lithium diffusion within the electrode. The Li–Mg alloy anode effectively suppresses void nucleation and growth, enhances interfacial contact, and delays interfacial failure. However, as the Mg content increases, despite improved interfacial stability, the lithium diffusion capability decreases, leading to lower stripping capacity at high stripping current densities compared to pure lithium anodes. Therefore, to achieve higher stripping capacity, Li–Mg alloy anodes require being designed with a balance between interfacial stability and lithium diffusion capability. Furthermore, a relationship diagram of stripping current density, Mg content, and stripping capacity is constructed, revealing the complex interdependence between stripping current density and Mg content. This study provides theoretical guidance for optimizing interfacial stability and enhancing the stripping capacity of lithium–metal anodes in solid-state batteries.