Owing to the abundance, low cost and similar electrochemistry of Na to Li, sodium ion batteries (SIBs) are considered an attractive, low-cost alternative to lithium ion batteries (LIBs) for large-scale energy storage ^[1]. Among various anode materials for SIBs, antimony trisulfide (Sb₂S₃) has drawn significant attention due its high theoretical capacity of 946 mAh g⁻¹. However, its underlying sodiation behavior is largely unexplored.

This work ^[2] reports the sodiation kinetics and the evolution of phase transformation in carbon-coated 1D van der Waals Sb₂S₃ nanorods based on the in-situ TEM, density functional theory (DFT) calculations and molecular dynamic (MD) simulations. Unique two-step reaction mechanisms of Sb₂S₃ nanorods are revealed, including Na⁺ ion intercalation and conversion/alloying reactions, during the first sodiation process. Na⁺ ions are inserted into the voids between the (Sb₄S₆)_n moieties at an ultrafast speed of 146 nm s⁻¹ upon the first sodiation, leading to amorphization of the crystalline Sb₂S₃ and negligible volume expansion of ~54 %. The in-situ SAED analysis verifies that the generated Na_xSb₂S₃ intermediate phases are transformed into Na₂S and Na₃Sb with a trace of Sb crystals during the consecutive conversion/alloying reactions. Upon subsequent desodiation, the Na⁺ ions extracted from the crystalline sodiated composites transform to amorphous desodiated products.

The DFT calculations attribute such anomalous reaction mechanisms to the unexpectedly low sodium diffusion barrier of Sb₂S₃ nanorods and the largely improved electronic conductivity arising from the amorphous Na_xSb₂S₃ intermediate phases. These findings on phase transformation routes, dynamics and kinetics occurring during the sodiation/desodiation processes in the Sb₂S₃ nanostructure will offer insights into better understanding of Na⁺ ion diffusion mechanisms in van der Waals force stacked materials.

References

[1] J. Cui, S. Yao, J.K. Kim, Recent progress in rational design of anode materials for high-performance Na-ion batteries. Energy Storage Mater., 7, 64–114 (2017).

[2] S. Yao, J. Cui, Z. Lu, Z.L. Xu, L. Qin, J. Huang, Z. Sadighi, F. Ciucci, J.K. Kim, Unveiling the unique phase transformation behavior and sodiation kinetics of 1D van der Waals Sb₂S₃ Anodes for sodium ion batteries, Adv. Energy Mater., 7, 1602149 (2017).