Tannic acid etching construction of hollow heterogeneous CoSe2-FeSe2@nitrogen-doped carbon rhombic dodecahedron for high-performance sodium storage

Metal selenides are very promising anode materials for sodium ion batteries (SIBs) due to their rich redox behaviors, low cost, high theoretical capacity, and environmentally benign. However, the poor cycle performance and rate capability greatly hinder their widespread applications. In this paper, we have proposed a tannic acid etching zeolitic imidazolate framework-67 (ZIF-67)-derived selenide strategy to construct hollow heterogeneous CoSe₂-FeSe₂@N-doped carbon rhombic dodecahedron (CoSe₂-FeSe₂@NC) as anode for high-performance SIBs. The special microstructural characteristics with hollow rhombic dodecahedron can reduce the Na⁺/electron migration path and alleviate the volume variations during cycling. The NC can improve conductivity and reduce volume effects during cycling. What’s more, the built-in electric fields (BIEF) at the CoSe₂-FeSe₂ heterointerfaces can modulate the electronic structure and accelerate the kinetics of ionic diffusion, resulting in the improvement electrochemical properties. When applied as anodes for SIBs, the CoSe₂-FeSe₂@NC can deliver a remarkable electrochemical performance in terms of sodium storage capacity (648.5 mAh g⁻¹ at 0.2 A/g), initial coulombic efficiency (82.0 %), cycle performance (92.6 % capacity retention after 100 cycles), and rate capability of 450.6 mAh g⁻¹ after 1000 cycles at a high rate of 1 A/g. The kinetic analysis indicates that the discharging-charging process of CoSe₂-FeSe₂@NC is ascribed to both capacitive behavior and controlled diffusion.