Unveiling the Unique Phase Transformation Behavior and Sodiation Kinetics of 1D van der Waals Sb2S3 Anodes for Sodium Ion Batteries

Carbon‐coated van der Waals stacked Sb 2 S 3 nanorods (SSNR/C) are synthesized by facile hydrothermal growth as anodes for sodium ion batteries (SIBs). The sodiation kinetics and phase evolution behavior of the SSNR/C anode during the first and subsequent cycles are unraveled by coupling in situ transmission electron microscopy analysis with first‐principles calculations. During the first sodiation process, Na + ions intercalate into the Sb 2 S 3 crystals with an ultrafast speed of 146 nm s −1 . The resulting amorphous Na x Sb 2 S 3 intermediate phases undergo sequential conversion and alloying reactions to form crystalline Na 2 S, Na 3 Sb, and minor metallic Sb. Upon desodiation, Na + ions extract from the nanocrystalline phases to leave behind the fully desodiated Sb 2 S 3 in an amorphous state. Such unique phase evolution behavior gives rise to superb electrochemical performance and leads to an unexpectedly small volume expansion of ≈54%. The first‐principles calculations reveal distinctive phase evolution arising from the synergy between the extremely low Na + ion diffusion barrier of 190 meV and the sharply increased electronic conductivity upon the formation of amorphous Na x Sb 2 S 3 intermediate phases. These findings highlight an anomalous Na + ion storage mechanism and shed new light on the development of high performance SIB anodes based on van der Waals crystals.