Understanding Electrochemical Reaction Mechanisms of All-Electrochem-Active Mg2Si Electrode in All-Solid-State Batteries

To better understand the electrochemical reaction mechanism of the Mg2Si electrode in all-solid-state batteries (ASSBs), a rational all-electrochem-active Mg2Si electrode is first designed to minimize the inactive component-related interfacial degradation. This is due to its unique mixed conductivity properties, including a high electronic conductivity of up to 8.9 × 10–2 S cm–1 and an ionic conductivity of 9.7 × 10–5 S cm–1, which allow for fast charges transport. In ASSBs, the Mg2Si electrode exhibits a higher initial Coulombic efficiency of 83.5% at 300 mA g–1 compared with the Si electrode (72.3%). X-ray diffraction and X-ray photoelectron spectroscopy results demonstrate that intermediate products (LixMg2Si, Li–Si alloy, and Li–Mg alloy) can form when the Mg2Si electrode discharges to 0.01 V, and partial Mg2Si still does not react with lithium. This work provides valuable insights into the reaction mechanisms and guides optimization strategies for developing next-generation Si-based ASSBs.