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 nickelcobalt 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.

All‐Solid‐State Fiber Supercapacitors with Ultrahigh Volumetric Energy Density and Outstanding Flexibility

“…The highest stack volumetric energy density of 61.2 mW h cm −3 can be achieved by our AFSC at a power density of 0.2 W cm −3 and it can remain at 42.1 mW h cm −3 even at a high power density of 10.1 W cm −3 . In addition, our AFSC also exhibits superior cycling stability with a high capacitance retention of 91.6% and unchanged EIS characteristic after 20 000 charge/discharge cycling at a current density of 0.5 A cm −3 , which is also comparable to those of recent reports [63][64][65] (Figure S25, Supporting Information). [12,13] The stack volumetric energy density is also much higher than those of other reports, including MnO 2 //PPy (2.98 mW h cm −3 at 0.08 W cm −3 ), [1,8,15,28,32,[60][61][62] MnO 2 @PEDOT:PSS//OMC (11.3 mW h cm −3 at 0.03 W cm −3 ), [28] RGO/SWCNT//RGO/SWCNT (6.3 mW h cm −3 at 0.05 W cm −3 ), [1] RGO+CNT@CMC//RGO+CNT@CMC (3.5 mW h cm −3 at 0.018 W cm −3 ), [8] and SWCNT@C//SWCNT@C (3.7 mW h cm −3 at 0.018 W cm −3 ).…”

Construction of CoO/Co‐Cu‐S Hierarchical Tubular Heterostructures for Hybrid Supercapacitors

“…[48] In the high-frequencyr egion, the intercept at the xaxis signifies the R s ,including the intrinsic resistance,electrolyte resistance and interfacial contact resistance.T he R ct is determined by estimating the diameter of the semicircle, which is related to the redox reaction kinetics. [2] According to the fitting results (Supporting Information, Table S2), the CoO/Co-Cu-S-2 HTHSs electrode presents the lowest R s of 0.56 W among different electrodes due to the higher electrical conductivity.A tt he same time,t he CoO/Co-Cu-S-2 HTHSs electrode also shows asmaller R ct of 0.68 W than those of the CoO/Co-Cu-S-1 HTHSs (0.78 W), CoO/Co-Cu-S-0.5 HTHSs (0.87 W), CoO/Co-Cu-S-2 NNDs (1.23 W), CoO/CoS x NFs (1.65 W)a nd Cu 1.81 SN Fs (1.89 W), indicating the fast charge transfer process.Inaddition, the straight line of the CoO/Co-Cu-S-2 HTHSs electrode is steeper than the others in the lowfrequency region, suggesting its small diffusion resistance.All these results are in accordance with the CV and GCD curves, which indicate the advantages of the hierarchical hollow architecture and synergistic effect between the components for the good electrochemical performance.T he cross-connected network of CoO/Co-Cu-S-2 HTHSs can also efficient-ly promote the transport of charges between the active materials and current collectors.Moreover, the CoO/Co-Cu-S-2 HTHSs possess the largest electrochemically active surface area (ECSA) among different samples,s uggesting that the multiple components and hollow structure can provide more electroactive sites to boost the reaction kinetics for the enhanced specific capacity (Supporting Information, Figure S12 and S13).…”

Recent Progress in Two‐Dimensional Layered Double Hydroxides and Their Derivatives for Supercapacitors

“…Metal nitride and phosphide based SC electrode materials have also generated tremendous research attention, owing to their high electrical conductivity (10 6 Ω −1 m −1 ), excellent corrosion resistance, mechanical stability, and faster charge/discharge ability . The incorporation of nitrogen and phosphorous atoms into the LDH parent materials can change the density of states in the d band of metal nitrides and phosphides, which can reduce the shortage of d‐band occupancy, leading to an enhancement in the electron‐donating ability of the metal nitrides and phosphides . A number of single‐metal nitrides and phosphides have been explored as SC electrodes.…”

“…[6] The incorporation of nitrogen and phosphorous atoms into the LDH parent materials can change the density of states in the db and of metal nitrides and phosphides, which can reduce the shortage of d-band occupancy, leading to an enhancement in the electron-donating ability of the metal nitrides and phosphides. [93] An umber of single-metal nitrides and phosphides have been explored as SC electrodes. The metals in these nitrides and phosphides typically include V, Mo, Ru, Cr,Co, Ni, Ga, Fe, and W. They not only serve as electrodes, but can also be combined with other active materials to construct composites with specific nanoarchitectures for SCs.…”