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

Abstract 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 (NiCo 2 N) and nickel–iron nitride (NiFeN) core–shell architectures that are explored as advanced electrodes for flexible solid‐state SC. The flexible NiCo 2 N@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.