Direct synthesis of metal selenide hybrids as superior sodium storage anodes

Abstract

Transition metal selenides (TMSs) are widely used as anodes in sodium-ion batteries (SIBs) due to their good electrical conductivity and high energy density. Herein, we reported and prepared a class of hybrids (FeSe₂/CoSe₂ and FeSe₂/NiSe₂) composed of two metal selenides by a controlled two-step solvothermal method, and assessed their sodium storage characteristics for the first time. The results show that such hybrids exhibit excellent electrochemical properties in terms of capacity (380 mA h g⁻¹ after 9000 cycles at a current density of 2 A g⁻¹), rate capability (average specific capacities are 462, 441, 440, 424, 393 and 363 mA h g⁻¹ at 0.05, 0.1, 0.2, 0.5, 1 and 2 A g⁻¹) and cycle stability (a capacity ratio rate of 82% after 9000 cycles), which are superior to those of single phase (FeSe₂ and CoSe₂) or a mechanical mixture (FeSe₂ : CoSe₂ = 1 : 1). What is more significant is that the sodium-ion full cell constructed with FeSe₂/CoSe₂ as the anode and Na₃(VPO₄)₂F₃ as the cathode exhibits excellent long cycle durability. This work provides a way for the study of transition metal hybrids or composite anodes used in SIBs.