FeSe2/MoSe2 heterostructures: interface engineering for enhanced high-rate sodium-ion storage

Abstract

The superior electrical conductivity and theoretical capacity of transition metal selenides have made them potential sodium-ion battery anode materials. However, the sluggish Na⁺ diffusion kinetics in bulk selenium render the rate performance unsatisfactory. In this study, ultrathin MoSe₂ nanosheets are vertically anchored onto FeSe₂ surfaces to form FeSe₂/MoSe₂ heterostructured microspheres to enhance the structural durability and rate performance of FeSe₂. In general, owing to the Fermi energy mismatch between FeSe₂ and MoSe₂, electrons around heterogeneous surfaces migrate across the phase boundary, thereby tuning the electronic structures of both building blocks and establishing a built-in electric field for Na⁺ diffusion, which effectively improves rate capability and specific capacity. In addition, strongly interacting heterointerfaces improve the structural integrity of FeSe₂/MoSe₂ microspheres, increasing their cycling lifespan. As expected, the reversible capacity (3000 mA g⁻¹, 391.6 mAh g⁻¹), rate performance, and cycling stability of the heterostructure electrodes improved compared with their building blocks. This study serves as a reference for optimizing electrode materials for the design of electrochemical energy storage systems.