Thin solid electrolyte interface on chemically bonded Sb2Te3/CNT composite anodes for high performance sodium ion full cells

Abstract Nanostructured metal chalcogenides (MCs) and their composites are studied for high performance sodium-ion batteries (SIBs). Herein, we report the assembly of an emerging MC, Sb2Te3, with functionalized carbon nanotubes (CNTs) to form composite anodes. The role of oxygenated functional groups on CNTs in fostering the chemical interactions with Sb2Te3 for enhanced structural integrity of electrodes is elucidated by density functional theory combined with ab-initio molecular dynamics simulations and X-ray photoelectron spectroscopy analysis. Remarkably, cryogenic transmission electron microscopy (TEM) analysis reveals a uniform and thin solid electrolyte interface (SEI) layer of ∼19.1 nm on the Sb2Te3/CNT composite while the neat Sb2Te3 presents an irregular and ∼ 67.3 nm thick SEI. The ex-situ X-ray diffraction (XRD) and ex-situ/in-situ TEM analyses offer mechanistic explanations of phase transition and volume changes during sodiation. The Sb2Te3/CNT composite electrode with an optimal content of 10 wt.% CNTs delivers excellent reversible gravimetric and volumetric capacities of 422 mA h g-1 and 1232 mA h cm-3, respectively, at 100 mA g-1 with ∼97.5% capacity retention after 300 cycles. The excellent high-rate capability of 318 mA h g-1 at 6400 mA g-1 corroborates the structural robustness of the composite electrode. A sodium-ion full cell (SIFC) is assembled by pairing the above anode with a Na3V2(PO4)2F3 cathode, which exhibits remarkable energy density of ∼229 Wh kg-1 at 0.5 C and excellent cyclic stability of over 71% and 66% capacity retention at 5 C and 10 C, respectively, after 200 cycles. Even at 40 C, an ultrahigh power density of 5384 W kg-1 is delivered. Furthermore, the pouch SIFCs prove excellent flexibility with ∼85% capacity retention after 1000 bending cycles and satisfactory operation under temperatures ranging from 40 to -20˚C. The design strategy developed here can also be employed to other electrode materials to achieve better SEI stability and excellent Na storage performance.