Flexible Solid-State Asymmetric Supercapacitors Based on Nitrogen-Doped Graphene Encapsulated Ternary Metal-Nitrides with Ultralong Cycle Life

To meet a fast-emerging demand, flexible energy storage applications have a great interest in the development of highly flexible hierarchical nanoarchitectures. Metal nitrides have recently been paid a significant interest as a promising electrode material for supercapacitors (SCs) owing to their high electrical conductivity, excellent redox properties, and outstanding mechanical strength. However, poor electrochemical stability seriously limits the commercialization possibilities. Herein, a novel strategy is presented for the synthesis of nitrogen-doped graphene encapsulated with ultrasmall nickel–cobalt nitride (NiCo₂N) and nickel–iron nitride (NiFeN) core–shell architectures that are explored as advanced electrodes for flexible solid-state SC. The flexible NiCo₂N@NG//NiFeN@NG asymmetric SC delivers an ultrahigh energy density of ≈94.93 Wh kg⁻¹ at 0.79 kW kg⁻¹, exceptional power density (≈74.67 Wh kg⁻¹ at 39.53 kW kg⁻¹), and ultralong cycle life (≈5.07% drop in initial capacity after 25 000 cycles). These results promote the core–shell hybrids that can be served as advanced supercapacitor materials for flexible energy storage applications.