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

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.