Facile ion exchange to construct Ni-Fe-Co sulfides and hydroxides ultrathin nanosheets with rich interfaces for advanced all-solid-state asymmetric supercapacitors

Rationally designing self-supporting heterogeneous nanostructured electrode materials is an effective strategy to enhance electrochemical performance and mechanical strength for asymmetric supercapacitors. Herein, we report a facile synthesis of the self-supporting petal-like NiFeCo-S (Sulfides) @NiFeCo-TH (Ternary Hydroxides) heterogeneous ultrathin nanosheets on nickel iron foam (NIF) using an innovative electro-oxidation, sulfuration and controllable Co2+ exchange process. Petal-like NiFeCo-S@NiFeCo-TH ultrathin nanosheets with the thickness of only 1.8 nm consist of Ni2S3, FeS, CoNi2S4, FeCoS2 and NiFeCo hydroxides nanocrystallines to provide rich interfaces. The unique nanostructured NiFeCo-S@NiFeCo-TH lamellar hybrid delivers the high areal capacity (mass capacity) of 973 mu Ah cm(-2) (174 mAh g(-1)) at a current density of 10 mA cm(-2) and excellent rate capability of 68.3% at a high current density of 100 mA cm(-2). More importantly, the assembled NiFeCo-S@ NiFeCo-TH/NIF//AC all-solid-state ASC device exhibits a high energy density of 56.3 Wh kg(-1) at a power density of 543 W kg(-1) and the outstanding cycling stability of 90.1% capacity retention after 4000 chargedischarge cycles. This synthesis strategy exhibits wide application prospect in fabrication of the self-supporting transition metal nanostructured electrodes for energy storage and conversion.