Semi-Coherent Heterointerface Engineering via In Situ Phase Transition for Enhanced Sodium/Lithium-Ions Storage.

To improve ion transport kinetics and electronic conductivity between the different phases in sodium/lithium-ion battery (LIB/SIB) anodes, heterointerface engineering is considered as a promising strategy due to the strong built-in electric field. However, the lattice mismatch and defects in the interphase structure can lead to large grain boundary resistance, reducing the ion transport kinetics and electronic conductivity. Herein, monometallic selenide Fe 3 Se 4 -Fe 7 Se 8 semi-coherent heterointerface embedded in 3D connected Nitrogen-doped carbon yolk-shell matrix (Fe 3 Se 4 -Fe 7 Se 8 @NC) is obtained via an in situ phase transition process. Such semi-coherent heterointerface between Fe 3 Se 4 and Fe 7 Se 8 shows the matched interfacial lattice and strong built-in electric field, resulting in the low interface impedance and fast reaction kinetics. Moreover, the yolk-shell structure is designed to confine all monometallic selenide Fe 3 Se 4 -Fe 7 Se 8 semi-coherent heterointerface nanoparticles, improving the structural stability and inhibiting the volume expansion effect. In particular, the 3D carbon bridge between multi-yolks shell structure improves the electronic conductivity and shortens the ion transport path. Therefore, the efficient reversible pseudocapacitance and electrochemical conversion reaction are enabled by the Fe 3 Se 4 -Fe 7 Se 8 @NC, leading to the high specific capacity of 439 mAh g -1 for SIB and 1010 mAh g -1 for LIB. This work provides a new strategy for constructing heterointerface of the anode for secondary batteries.