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

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.