Study On Controllable Synthesis And Electrochemical Performance Of Nickel/cobalt-based Sulfides For Supercapacitors

Decentralized renewable energy production and its intermittency cause mismatch between energy supply and energy demand.Thus,the development of energy storage devices with high-energy and high-power density is essential to supply off-grid applications.Supercapacitors,also called electrochemical capacitors,are becoming the most promising energy storage solutions in virtue of fast charging/discharging,high power density,and excellent cycling stability.In this paper,we focus on the controllable synthesis,structure optimization,and performance improvement of nickel-cobalt sulfides electrode materials.Also,their structural features and electrochemical properties were investigated systematically.An effective and concise controllable hydrothermal approach was carried out for constructing a rational design of heterogeneous and low-crystalline architectures of MOF-derived bimetallic sulfides nanocomposite（denoted as Ni Co₂S₄/Co₃S₄）with abundant hetero-interfaces.Functional species of bimetallic active component（Ni and Co）are beneficial to providing numerous active sites for the redox reactions.Abundant interfaces can induce strong interfacial electron transfer properties.The resultant Ni Co₂S₄/Co₃S₄ electrode yields a high specific capacity of 1023 C g^-1 at a current density of 1 A g^-1,and an excellent cycling stability of 89.6%after 5000 cycles.Also,the proposed hybrid supercapacitor exhibits a superior energy density of 40.8 Wh kg^-1 and power density up to 8595.6 W kg^-1,and maintains about 88.3%of its initial capacitance after 10000 cycles.Core-shell-MOF-derived hollow nanocomposite consisting of amorphous metal sulfides anchoring on multi-component transition metal hydroxides（Ni Co Zn-LDH/M_xS_y）was fabricated through rational design and adjustment of composition.Numerous interfacial active sites originate from their complex chemical compositions involving different mixed valence states at the multi-metal centers and uniform distribution of amorphous metal sulfides.The resultant Ni Co Zn-LDH/M_xS_y electrode exhibits a high specific capacity of 1174.9 C g^-1 at a current density of 1 A g^-1,and an excellent cycling stability of 90.3%after 5000 cycles.Also,the proposed hybrid supercapacitor delivers a superior energy density of 36.3 Wh kg^-1 and power density up to 8799.7 W kg^-1,and maintains about 88.3%of its initial capacitance after10000 cycles.An in-situ strategy of successive hydrothermal process was designed for the facile synthesis of well-aligned hierarchical nickel-cobalt-zinc ternary chalcogenides supported on nickel foam（NF/Ni Co Zn S）.The ultrathin small ternary mixed metal sulfide nanosheets interleaved in the upper layer can provide sufficient active sites for fast reversible redox process,while the lower-layer nanoneedle array can provide good structural support.Moreover,the abundant point connections can create an unimpeded"super highway"for ions and electron transmission.The resultant NF/Ni Co Zn S electrode unveils a high specific capacity of 16.1 F cm^-2 at a current density of 3 m A cm^-2,and excellent cycling stability of 82.2%after 10000cycles.Along with high energy and power densities of 1.2 m Wh cm^-2 and 24.87 m W cm^-2,the fabricated prototype device retains excellent cyclability with a capacitance retention of 88.2%after 10000 cycles.