Boosted Electrochemical Performance of Honeycomb-Like NiCu–LDH Nanosheets Anchoring on NiCo2S4 Nanotube Arrays for Flexible Solid-State Hybrid Supercapacitors

Nickel-based layered hydroxides (LDHs) have aroused much interest as promising battery-type electrodes for hybrid supercapacitors (HSCs) because of their high theoretical capacity, good safety, and abundant natural resources; however, the electrochemical performances are still notoriously limited owing to their intrinsically poor electrical conductivity and severe agglomeration features. Herein, an elaborate hierarchical NiCo2S4@NiCu–LDH nanotube/nanosheet hybrid electrode is designed and fabricated directly on carbon cloth by a facile multistep solution-based strategy. Through the rational engineering of nanostructures and atomic substitution of nickel by copper, the optimized NiCo2S4@NiCu–LDH hybrid electrode can yield a high areal capacity of 632.0 μAh/cm2 at a current density of 2 mA/cm2 and a good rate capability. Furthermore, the assembled flexible solid-state HSC device employing the NiCo2S4@NiCu–LDH exhibits a maximum volumetric energy density of 2.7 mWh/cm3 at a power density of 21.3 mW/cm3 with a robust long-term cycling stability over 2000 cycles and outstanding flexibility under repeated bending tests. Our work demonstrates the possibility of designing and fabricating nickel-based LDHs as superior battery-type electrodes towards highly durable and efficient flexible energy storage devices.