High capacity/reversible Fe/Sn alloys for Na-storage anodes enabled by thermal reaction and then anchoring on exfoliated graphite

Abstract

Sn-based alloys have emerged as high-capacity, low-working voltage anodes for sodium-ion batteries (SIBs) in recent years, but the complex synthesis processes for highly reversible anodes have impeded their practical application. Herein, DFT calculations demonstrated that SnS₂ and Fe can undergo a series of reactions to form Fe–Sn alloys, along with high conductivity/reversible FeS_x sulfides. Guided by theoretical calculations, FeS/SnS, FeSn₂/FeS/SnS, and FeSn/FeSn₂/FeS/SnS heterostructure composites anchored on exfoliated graphite (namely FSS-1/G-15%, FSS-2/G-15%, and FSS-3/G-15%, respectively) were fabricated by annealing Fe and SnS₂ mixed powders, and subsequently, ball milling with 15 wt% graphite. Cyclic voltammetry tests, DFT calculations, and ex situ XRD analysis co-confirmed that FeSn and FeSn₂ are partially reversible, while FeS and SnS are reversible. FSS-3/G-15% exhibits the best overall Na⁺-storage performances, which delivered approximately 402, 351, 326, 302, 270, and 259 mA h g⁻¹ at 0.1, 1, 2, 4, 8, and 10 A g⁻¹, with an initial coulombic efficiency of 83.3% at 0.1 A g⁻¹, surpassing most of the recent-reported analogous alloy anodes. The universal material synthesis method only needs one step of thermal reaction, and then ball milling, which may hold great promise in future applications in various fields.