Sb/Sb4O5Cl2/C composite as a stable anode for sodium-ion batteries

• We have developed a facile synthesis method of Sb/Sb4O5Cl2/C composite. • Composite anode materials may offer numerous advantages over single-phase materials. • Amorphous matrix alleviates the stress resulting from volume changes in antimony. • FEC addition to the electrolyte reduces electrode thickness changes during cycling. One of the most demanding goals in the field of Na-ion batteries is to find an appropriate anode material that delivers high capacities and can endure numerous cycles without structural degradation. Antimony stands out with a theoretical capacity of 660 mAh· g −1 and relatively high electrical conductivity. However, its challenges are pulverization and degradation of its microstructure due to volume changes. In this work, we used a solvothermal reaction to synthesize the composite material Sb/Sb 4 O 5 Cl 2 /C, which is made of Sb with branch-shaped morphology and Sb 4 O 5 Cl 2 with cuboids-shaped morphology. The mechanism of the (de)sodiation of the composite material was analyzed both through operando and ex-situ measurements: X-ray diffraction, Raman spectroscopy, X-ray absorption spectroscopy, scanning electron microscopy, dilatometry, and online electrochemical mass spectrometry. The results show great mechanical integrity of the electrode, ensured by a lot of space for volume changes in the branch-shaped microstructure, buffered expansion/contraction by the amorphous matrix (sodiated Sb 4 O 5 Cl 2 ), and high electronic conductivity, thanks to carbon. The microstructural features and the multistep (de)sodiation mechanism of the Sb/Sb 4 O 5 Cl 2 /C composite result in excellent cycling stabilities.