Design of Microcrystalline Domains in Pitch‐Derived Carbon Phase for Si─C Interfacial Mechanical Adaptability in Si@C Anodes

ABSTRACT Severe volume expansion of silicon during lithiation and delithiation imposes substantial mechanical and electrochemical stress on the carbon coating and makes its microcrystalline structure a critical factor for interfacial stability and cycling adaptability. However, the microcrystalline domain characteristics required to achieve both interfacial adaptability and cycling stability remain unclear. To address this, a three‐dimensional structure–interface–performance mapping is proposed to correlate carbon microcrystalline domain characteristics with interfacial response and cycling stability. Different pitch‐derived carbon structures are employed to systematically clarify how carbon microstructure affects interfacial adaptability through structural, mechanical, electrochemical, and interfacial characterizations. The representative sample, Si@X‐OC, features locally disordered carbon microcrystalline domains and a stable carbon skeleton, with a d 002 of 3.47 Å and an sp 2 fraction of 50.94%. It also exhibits lower post‐cycling charge‐transfer resistance, a positive modulus evolution, and a capacity retention of 75.9%. These features are consistent with stronger interfacial stress buffering and improved preservation of interfacial stability during cycling. Molecular dynamics simulations support this mapping and reveal that a 50% sp 2 fraction corresponds to enhanced interfacial load‐bearing capacity and separation energy. These findings provide a rational design principle for regulating carbon microcrystalline structures in Si@C anodes.