Hierarchical NiMoS and NiFeS Nanosheets with Ultrahigh Energy Density for Flexible All Solid‐State Supercapacitors

Abstract

Highly flexible supercapacitors (SCs) have great potential in modern electronics such as wearable and portable devices. However, ultralow specific capacity and low operating potential window limit their practical applications. Herein, a new strategy for the fabrication of free-standing NiMoS and NiFeS nanosheets (NSs) for high-performance flexible asymmetric SC (ASC) through hydrothermal and subsequent sulfurization technique is reported. The effect of Ni 2+ is optimized to attain hierarchical NiMoS and NiFeS NS architectures with high electrical conductivity, large surface area, and exclusive porous networks. Electrochemical properties of NiMoS and NiFeS NS electrodes exhibit that both have ultrahigh specific capacities (≈312 and 246 mAh g −1 at 1 mA cm −2 ), exceptional rate capabilities (78.85% and 78.46% capacity retention even at 50 mA cm −2 , respectively), and superior cycling stabilities. Most importantly, a flexible NiMoS NS//NiFeS NS ASC delivers a high volumetric capacity of ≈1.9 mAh cm −3 , excellent energy density of ≈82.13 Wh kg −1 at 0.561 kW kg −1 , exceptional power density (≈13.103 kW kg −1 at 61.51 Wh kg −1 ) and an outstanding cycling stability, retaining ≈95.86% of initial capacity after 10 000 cycles. This study emphasizes the potential importance of compositional tunability of the NS architecture as a novel strategy for enhancing the charge storage properties of active electrodes.

An Integrated Approach Toward Renewable Energy Storage Using Rechargeable Ag@Ni0.67Co0.33S‐Based Hybrid Supercapacitors

“…Moreover, the device even maintained good areal energy density of 0.26 mWh cm −2 at high power density 27.22 mW cm −2 . Impressively, the obtained energy and power density values of this HSC are comparable or even higher than the previously reported asymmetric SCs/HSCs, such as hierarchical Ni‐Co‐S NSs//graphene (0.118 mWh cm −2 at 10.4 mW cm −2 ), Ag@Ce 6 Mo 10 O 39 //AC (0.0183 mWh cm −2 at 0.739 mW cm −2 ), core–shell‐like NiCo 2 S 4 hierarchical structures//activated carbon (0.121 mWh cm −2 at 0.941 mW cm −2 ), Ni‐Co‐S nanoflakes//polypyrrole (0.112 mWh cm −2 at 1.5 mW cm −2 ), Ni 0.8 Cu 0.2 ‐S nanostructures//N‐doped graphene (0.138 mWh cm −2 at 6.4 mW cm −2 ), Ni‐Mo‐S//Ni‐Fe‐S (0.228 mWh cm −2 at 1.58 mW cm −2 ), Ni 3 S 2 @CdS//porous carbon (0.259 mWh cm −2 at 1.482 mW cm −2 ), Zn‐Ni‐P//Fe 2 O 3 @NG (0.346 mWh cm −2 at 2.37 mW cm −2 ), core–shell CoMoO 4 @Co(OH) 2 //porous carbon (0.167 mWh cm −2 at 1.5 mW cm −2 ), CoNi 2 S 4 /Ni 3 S 2 @Ni(OH) 2 //active carbon (0.432 mWh cm −2 at 1.646 mW cm −2 ), and MnCo 2 S 4 //rGO (0.25 mWh cm −2 at 6.4 mW cm −2 ), respectively. Moreover, the comparative results of our HSC with many other reports are also summarized in Table S2 (Supporting Information).…”

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

“…Hence, the NiCo 2 N@NG//NiFeN@NG based flexible ASC was constructed and studied. Although the mass loading of the positive and negative electrodes was adjusted, still the operating potential window has to be fine‐tuned to achieve high energy density without compromising power density and cycling life . Otherwise, degradation of the electrode materials and electrolyte triggers the unwanted side reaction at the interface and affects the cycling performance of the device.…”

“…In order to ensure and fix the potential window for NiCo 2 N@NG//NiFeN@NG ASC device, GCD studies were performed with different operating potential windows at a fixed current density of 3 A g −1 and are shown in Figure S33 (Supporting Information). Impressively, the higher value was attained from the complete Faradaic redox reaction process at a higher upper cut‐off potential of ≈1.6 V. Therefore, to adjust the optimal potential window, the Coulombic efficiency must be examined using the following equationwhere q c and q d are the total amount charge and discharge of the NiCo 2 N@NG//NiFeN@NG ASC device, respectively (achieved from the GCD). The Coulombic efficiency and average discharge capacity ( C sc ) of both electrodes (positive and negative electrodes) are validated with a function of the cell voltage in five duplicated flexible ASC devices.…”

Silver‐Quantum‐Dot‐Modified MoO3 and MnO2 Paper‐Like Freestanding Films for Flexible Solid‐State Asymmetric Supercapacitors

“…With the rapidly increasing interests in portable electronic devices, mobile electronics, electronic textiles, and skins, highly safe and flexible energy storage devices with high energy and power densities keep an ever‐growing demand. Supercapacitors, also known as electrochemical capacitors, bridging the gap between batteries and conventional capacitors, have been widely used in numerous areas due to their high power density, long lifetime, a wide range of working temperatures, and pollution‐free operations . However, the energy density is still the key challenge for supercapacitors to achieve wider applications.…”