LAUSR

Carbon-coated van der Waals stacked Sb2S3 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 Sb2S3 crystals with an ultrafast speed of 146 nm s−1. The resulting amorphous NaxSb2S3 intermediate phases undergo sequential conversion and alloying reactions to form crystalline Na2S, Na3Sb, and minor metallic Sb. Upon desodiation, Na+ ions extract from the nanocrystalline phases to leave behind the fully desodiated Sb2S3 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 NaxSb2S3 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.