Revealing the Competitive Reaction Mechanism Between Solid Electrolyte Interphase and Li Deposition Processes

Li dendrites are the main obstacle to the practical application of Li metal anodes. Although the solid electrolyte interphase (SEI) is essential for stabilizing Li metal anodes, its formation proceeds concurrently with Li deposition. Therefore, SEI evolution and Li growth are dynamically coupled, yet the underlying mechanism governing this interaction remains unclear. In this study, a competitive reaction mechanism between SEI formation and Li deposition is revealed. A phase-field model was employed at the mesoscopic level to elucidate the effects of Li deposition reaction rates and SEI microstructural integrity. At the macroscopic level, electrochemical impedance spectroscopy (EIS) demonstrated that rapid Li deposition outpaces SEI reconstruction at high current densities, causing severe interfacial rupture. Conversely, rapid SEI kinetics enable fast interfacial repair. Furthermore, the introduction of a competitive reaction mechanism framework (CRMF) advances this dynamic equilibrium from a qualitative concept to a computable metric. Molecular-level analysis then shows that optimizing the structure and kinetic behavior of Li⁺ solvation can promote anion reduction and lower the desolvation energy barrier. This encourages more anions and solvents to participate in interfacial reactions, accelerating the formation of a stable SEI film. These findings provide valuable insights into developing a stable electrolyte–anode interface in Li metal batteries.