Effect of solvent on the crystal phase, morphology, and sodium storage performance of FeSe2

Abstract

Transition metal selenides (TMSes) are considered as promising anode materials for sodium-ion batteries (SIBs) due to their high electronic conductivity and satisfactory theoretical specific capacity. However, the rapid capacity fading has limited their practical application. In this work, an ethylene glycol solvent-induced synthesis strategy was applied to control the morphology and structure of FeSe₂, and we found that the ethylene glycol solvent can promote the growth of the (110) crystal face of FeSe₂, resulting in the formation of a unique three-dimensional (3D) flower structure. Density functional theory calculations clarify the lower adsorption energy and migration energy barrier of Na⁺ on the (110) crystal plane of FeSe₂. Meanwhile, reduced graphene oxide was added to the reaction system to limit the volume change of FeSe₂ and improve its cycle stability. FeSe₂/rGO-EG exhibits superior sodium storage performance, especially excellent cycling stability. At 1 A g⁻¹, the FeSe₂/rGO-EG electrode delivers a high capacity of 400 mA h g⁻¹ after 1000 cycles with a capacity retention of ∼100%. Furthermore, cyclic voltammetry, galvanostatic intermittent titration, and ex situ X-ray diffraction were employed to elucidate the reaction mechanism of FeSe₂. This work reveals the influence of the dominant crystal surface and morphology on the electrochemical performance of the FeSe₂ electrode and provides guidance for the follow-up research on TMSes as SIB anode materials.