Designing a Silicon/Iron Selenide Heterojunction as Liquid and All‐Solid‐State Lithium‐Ion Battery Anodes Displaying Excellent Performances

ABSTRACT Silicon (Si) anodes possess remarkable theoretical capacity in Li‐ion batteries; however, they are facing challenges including huge volume‐expansion leading to structural failure and performance decay. Conventional coatings commonly exhibit poor adhesion to Si, resulting in interfacial degradation and non‐ideal electron/ion transport. Here, a heterojunction‐induced Si@FeSe@C anode, composing of a robust Fe–Se–Si bonding at the heterointerface followed by an external carbon coating is developed. This design enables both structural stability and highly efficient ion and electron transport. The Si@FeSe@C anode delivers a high capacity of 1092.8 mAh g −1 after 100 cycles at 0.2 A g −1 , and maintains a Coulombic efficiency exceeding 99.6% over 500 cycles at 1.0 A g −1 . The electrochemical performance of full‐cell configurations assembled with both conventional liquid and all‐solid‐state electrolytes, also revealing remarkable cycling performances. In situ X‐ray diffraction and in situ Raman analysis confirm reversible phase‐ and species‐change, and density functional theory (DFT) calculations reveal that the heterojunction significantly reduces the energy barrier for Li + diffusion. These findings present a general design strategy that synergistically enhances electrochemical performance, which will find a broad set of applications in developing high‐performance secondary battery systems.