Performance Degradation Mechanism of the Si@N, S‐Doped Carbon Anode in Sulfide‐Based All‐Solid‐State Batteries

Abstract Silicon (Si) anode is a promising anode material for all‐solid‐state lithium batteries with ultra‐high theoretical specific capacity and low lithium dendrite risk. However, the inevitable vast volume expansion of Si anode during charge/discharge is recognized as a major limitation preventing its commercial application. Herein, an N, S self‐doped amorphous carbon layer coated on porous micron‐sized Si (p‐mSi@C) is designed to construct an electron/ion conducting network while ensuring structural and interfacial stability. Uneven distribution of von mises stresses during p‐mSi lithiation leads to irregular volume expansion and even fragmentation. Meanwhile, the growth of by‐products at the interface between p‐mSi and electrolyte contact leads to a rapid capacity decay. Compared to p‐mSi anode, p‐mSi@C reduces the risk of fragmentation thanks to the stress‐absorbing effect of amorphous carbon, delivering excellent electrochemical performance (2679.65 mAh g −1 at 0.2 mA cm −2 with initial coulombic efficiency of 84%). More importantly, the chemical failure mechanisms of p‐mSi and p‐mSi@C composite anodes are revealed through structural characterization, chemical analysis, and simulation, which provides the necessary theoretical guidance for practicalization.