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

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.