Urchin-like hierarchical spheres of FeSe2 embedded in a TiN/C composite covered by CNTs as anodes for sodium-ion storage

Abstract

Transition-metal selenides are considered promising anode materials for sodium-ion batteries due to their high theoretical capacity based on multielectron conversion reactions. However, their low intrinsic electrical conductivity and severe volume variations result in poor cycling performance and rate capability. Herein, a composite material of urchin-like hierarchical spheres in which FeSe₂ embedded in TiN/C covered by in situ grown carbon nanotubes (denoted as FeSe₂@TiN/C@CNTs) was designed and fabricated using a facile sol–gel, carbonization, and selenization process. The carbon matrix can disperse FeSe₂ to prevent serious agglomeration, while TiN and CNTs could enhance the electrical conductivity of the composites. Additionally, TiN, carbon, and CNTs can buffer volume expansion during the charge/discharge process. Benefiting from the synergistic effects of FeSe₂, carbon, TiN, and CNTs, the hybrid urchin-like FeSe₂@TiN/C@CNTs spheres exhibit excellent cycling stability and ultrafast pseudocapacitive sodium-ion storage capability. The FeSe₂@TiN/C@CNTs electrode delivers reversible capacity of 343.5 mA h g⁻¹ at 200 mA g⁻¹ for 1000 cycles, and a rate capability of 262.5 mA h g⁻¹ at a high current density of 2 A g⁻¹. Supported by the detailed kinetic analysis, the superior sodium-ion storage performance is attributed to the fast charge transfer rate and pseudocapacitive sodium-ion storage mechanism. Therefore, this work is expected to provide valuable insights for the rational design of metal-based compounds towards advanced metal-ion storage materials.