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 Ni²⁺ 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. [ABSTRACT FROM AUTHOR]