Towards high-performance all-solid-state asymmetric supercapacitors: A hierarchical doughnut-like Ni3S2@PPy core-shell heterostructure on nickel foam electrode and density functional theory calculations

In this work, a hierarchical doughnut-like Ni3S2@polypyrrole (PPy) core-shell heterostructure has been successfully constructed on nickel foam (NF) (denoted as Ni3S2@PPy/NF) through a facile hydrothermal followed by electrodeposition method. The coating of highly conductive and electroactive PPy layer on the backbone of Ni3S2@NF can significantly boost the integrated electrochemical performance. More specifically, the resultant Ni3S2@PPy/NF electrode achieves an extremely high specific capacitance of 3148.0 mF cm(-2) at a current density of 2.0 mA cm(-2), and a desirable rate capability. Further, an asymmetric all-solid-state supercapacitor is assembled using Ni3S2@PPy/NF as the positive electrode and activated carbon (AC)/NF as the negative electrode. Remarkably, the obtained Ni3S2@PPy/NF//AC/NF device delivers a high energy density of 46.4 Wh kg(-1) at a corresponding power density of 166.7 W kg(-1), outmaneuvering most sulfide- and PPy-based materials or their hybrids reported recently. Moreover, density functional theory calculations disclose the formation of N-Ni and C-Ni bonds at the PPy/Ni3S2 heterostructure interface and the enhancement of the binding of Ni3S2 towards OH- after PPy coating. Such exceptional supercapacitive properties of Ni3S2@PPy/NF owe to its unique porous interpenetrating structure, the combined contribution of both electroactive PPy and Ni3S2 components, highly-conductive PPy as well as the optimized electropolymerization and dopant of PPy.

Automated summary

A hierarchical doughnut-like Ni3S2@polypyrrole (PPy) core-shell heterostructure has been successfully constructed on nickel foam (NF), exhibiting excellent electrochemical performance and high energy density. Density functional theory calculations reveal the formation of N-Ni and C-Ni bonds at the PPy/Ni3S2 heterostructure interface, contributing to the enhanced overall properties.