Novel layer-by-layer stacked VS2 nanosheets with intercalation pseudocapacitance for high-rate sodium ion charge storage

Highlights: • We firstly report a novel layer-by-layer stacked VS₂ nanosheets as the anode for sodium ion batteries (SIBs). The material is successfully synthesized through a facile one-step polyvinylpyrrolidone assisted assembly method, this method is simple and mass-produced. • The electrode exhibits high initial coulombic efficiency of 85%, superior rate capability (150 mA h g⁻¹ even at 20 A g⁻¹) and long-term cyclability, which stands out among the other layered intercalation SIBs. • A reversible intercalation-type electrochemical reaction during the Na⁺ insertion/extraction process of VS₂ is firstly proved by crystal structure analysis, electrochemical tests, in-situ XRD detections and ex-situ TEM. • The excellent electrochemical performance of the VS₂ materials can be attributed to stable framework for the volume swelling/shrink during Na ions insertion/extraction and intercalation pseudocapacitive mechanism, which facilitates the high-rate capability. Sodium ion batteries (SIBs) have been considered as a promising candidate for large scale energy storage systems due to their low cost and reasonable performance. However, developing desirable anode materials with high capacity, excellent cycling stability and high rate capability remains great challenges. Herein, novel layer-by-layer VS₂ stacked nanosheets (VS₂-SNSs) are synthesized using a facile one-step polyvinylpyrrolidone (PVP) assisted assembly method. With a highly stable orderly stacked layer structure, the VS₂ delivers excellent electrochemical performance in SIBs. A reversible discharge capacity of 250 mA h g⁻¹ is obtained at 0.2 A g⁻¹. A high specific capacity of 150 mA h g⁻¹ even at 20 A g⁻¹ is reached (discharged/charged in 27 s). Furthermore, the VS₂-SNSs deliver long cycling life with almost no capacity fading even after 600 cycles at 5 A g⁻¹. In-situ XRD and ex-situ TEM characterization reveal that VS₂ undertakes a reversible intercalation reaction mechanism. A detailed electrochemical kinetic analysis reveals that the sodium ion charge storage depends on intercalation pseudocapacitive behavior with a high capacitive contribution up to 69% for the total capacity at 1 mV s⁻¹. The impressive electrochemical performance reveals that the VS₂ has great potential for the next generation large scale energy storage.