Polypyrrole modified hierarchical porous CoS 2 @RGO aerogel electrode for ultrafast sodium storage

CoS2 nanooctahedrons homogeneously encapsulated by hierarchical porous-reduced graphene oxide and polypyrrole thin film are constructed via a simple hydrothermal route, followed by vapor polymerization reaction. Owing to the porous conductive network and robust structural integrity characteristics, the optimal CoS2@RGO@PPy aerogel can not only facilitate electron and ion transfer but also shorten diffusion length and alleviate strain stress, ensuring superior sodium storage in terms of high capacity, excellent rate capability, and cycling stability. With a CoS2 content of 54.9%, CoS2@RGO@PPy electrode delivers a discharge capacity of 744 mAh g−1 at the current density of 0.1 A g−1. Moreover, it yields a reversible capacity of 554 mAh g−1 at 2.0 A g−1, higher than that of 495 mAh g−1 for CoS2@RGO electrode. The superior rate capability can be attributed to the favored surface capacitive behavior. And a combined contribution of diffusion-controlled and capacitive-induced process are derived. Furthermore, CoS2@RGO@PPy electrode maintains 348 mAh g−1 over a long period of 700 cycles at a high current density of 3 A g−1 and a capacity retention of 65.8%. The strategy can be extended to tailor the electrode structures for high-performance sodium-ion batteries.