Heterojunction interface between bimetallic (Co, Fe) selenides enhanced excellent electron/ion transport kinetics for sodium ion batteries

Abstract

Sodium-ion batteries (SIBs) represent a highly promising class of energy storage devices. Enhancing SIBs performance necessitates innovative anode material development to overcome persistent challenges associated with the large ionic radius of Na⁺, namely significant electrode volumetric expansion and sluggish reaction kinetics. Herein, a macroporous bimetallic (Co, Fe) selenide containing abundant heterojunction interfaces encapsulated into a carbon framework (M-CoSe₂/FeSe₂@C) is prepared by combining an in-situ crystallization strategy with carbonization-selenization treatment. The structural characterization reveals that the resulting M-CoSe₂/FeSe₂@C possesses a well-defined porous architecture with internal CoSe₂-FeSe₂ nanoparticles encapsulated by an external carbon matrix. This configuration not only enhances electrical conductivity but also stabilizes the composite structure throughout sodiation/desodiation cycling. Evaluated as an anode in SIBs, the M-CoSe₂/FeSe₂@C electrode delivers outstanding cycling stability (retaining 455.0 mA h g⁻¹ at 0.2 A g⁻¹ after 100 cycles) and exceptional rate capability (285.6 mA h g⁻¹ at 10 A g⁻¹). These superior properties are primarily attributed to the high density of interphase boundaries generated by the dual-phase configuration. Combined experimental and theoretical investigations demonstrate that these boundaries, particularly regions of high electron density on the FeSe₂ side, kinetically favor Na⁺ adsorption, thereby accelerating sodium storage kinetics. Furthermore, multi-step electrochemical reaction mechanisms within the composite were elucidated through in-situ and ex-situ characterization analyses.