Coupling hierarchical iron cobalt selenide arrays with N-doped carbon as advanced anodes for sodium ion storage

Abstract

Transition metal selenides have emerged as a class of promising anodes for sodium ion batteries (SIBs). However, the notorious issues of their low electrical conductivity and huge volume changes during sodium ion insertion/extraction lead to poor cycling stability and inferior rate capability. In this work, hierarchically core–branched iron cobalt selenide arrays coated with N-doped carbon shell (denoted as FeCo–Se@NC) were rationally designed and synthesized on carbon cloth through a combined strategy of hydrothermal, selenization and carbonization processes. Benefitting from the designed arrays with simultaneous Fe doping into the CoSe₂ matrix and N-doped carbon coating, the optimized FeCo–Se@NC electrode possesses greatly enhanced structural integrity and accelerated ion/electron transfer kinetics. When employed as a binder- and additive-free anode for SIBs, the FeCo–Se@NC electrode exhibits a high reversible capacity of 532.1 mA h g⁻¹ at 0.05 A g⁻¹, competitive rate capability (193.3 mA h g⁻¹ at 5 A g⁻¹), and good cycling stability (386.1 mA h g⁻¹ after 150 cycles at 0.5 A g⁻¹). Moreover, when coupled with Na₃V₂(PO₄)₃/C, the full cell delivers a high capacity of 350.6 mA h g⁻¹ at 0.1 A g⁻¹ and a high energy density of 276.7 W h kg⁻¹. This work is expected to provide a new avenue for the development of arrayed transition metal selenide-based materials for high-performance SIBs.