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 (Li_<i>x</i>Mg₂Si, 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.