Dynamic Evolution and Degradation of Silicon–Electrolyte Interfaces under Cycling via Chemical Potential–Controlled Molecular Dynamics

Silicon is a promising high-capacity anode material for next-generation lithium-ion batteries, but its large volume change and unstable solid-electrolyte interphase (SEI) cause rapid capacity fading. To uncover the atomistic origins of this degradation, we develop a chemical-potential-controlled reactive molecular dynamics framework that enables explicit multicycle lithiation-delithiation simulations of silicon anodes. By tuning the electronegativity of Si atoms, the chemical potential of lithium is modulated to drive spontaneous insertion and extraction, mimicking charging and discharging. The simulations capture the key electrochemical behaviors, including Li migration, anode expansion-contraction, and SEI evolution. Under fast charging, accelerated Li insertion induces severe Si dissolution, volume loss, and reduced lithium retention. Concurrently, ethylene carbonate (EC) decomposes at the Si surface through ring opening, releasing C₂H₄ and forming carbonate fragments that bond with Si. Repeated cycling promotes detachment of Si-C-O species into the electrolyte, linking interfacial decomposition with mechanical failure. This study provides a direct atomistic picture of coupled electrode-electrolyte degradation in Si-based batteries and introduces a transferable simulation approach for exploring charge-discharge processes in alloying and intercalation materials.