Preparation And Application Of NiCo₂S₄-based Nanomaterials In Supercapacitors

Supercapacitors（SCs）have been intensively studied in energy storage because of excellent power density,exceptional stability,long cycle lifetimes and eco-friendly properties.NiCo₂S₄has been widely studied as SCs electrode material owing to preeminent specific capacitance,tunable electronic structure and excellent cycling stability.However,the application of NiCo₂S₄is hampered by their inherent low conductivity and charge/discharge volume expansion.Tuning electronic structures of NiCo₂S₄ or building heterogeneous structures with other materials are effective approaches to address these issues.This study explored the preparation methods and electrochemical properties of NiCo₂S₄-based electrode materials and applied in supercapacitors.Firstly,we successfully synthesized NiCo₂S₄ electrode materials by one-step solvothermal method.Besides,we rational construction R-NiCo₂S₄@Cu Co₂S₄ and NCQDs@NiCo₂S₄electrode materials to enhance electrochemical performance of NiCo₂S₄.The specific researches are as follows:（1）We fabricated NiCo₂S₄ nanosheet by one-step solvothermal method on NF,the open network structure composed of nanosheet could provide more channels for ion diffusion,and the larger specific surface area may be shortened the charge transport channel and enhanced electrochemical performance.NiCo₂S₄ has metal properties and excellent conductivity by DFT calculation.NiCo₂S₄/NF electrode has more excellent specific capacitance(1002.5 F g^-1)than NiCo₂O₄/NF nanoneedle(477.5 F g^-1).In additional,we further assembled an aqueous ASC NiCo₂S₄//AC showed an outstanding energy density of 68.67 Wh kg^-1 at 400 W kg^-1.（2）We successfully constructed R-NiCo₂S₄@Cu Co₂S₄ composites on NF by solvothermal,electrochemical deposition and chemical reduction methods.Compatible with NiCo₂S₄/NF,Cu Co₂S₄/NF and NiCo₂S₄@Cu Co₂S₄ electrode,R-NiCo₂S₄@Cu Co₂S₄/NF exhibited an excellent capacity(2922.9 F g^-1 at 0.5 A g^-1),superior rate capability(2028.6 F g^-1 at 10 A g^-1)and extraordinary cycling stability（99.92%and 99.98%for capacitance retention and Coulomb efficiency after 10000 cycles）,which attributed to the core-shell heterostructure effectively enhanced the redox reaction process and improved the utilization of electrochemical surface area,and the introduction of sulfur vacancies exposes more active sites and reduces the Gibbs free energy of the surface reaction of active materials.（3）We successfully synthesized N-doped CQDs by solvothermal method,and then prepared NCQDs@NiCo₂S₄/NF electrode material on NF.NCQDs@NiCo₂S₄/NF shown excellent electrochemical performance as SCs electrode material.For instance,NCQDs@NiCo₂S₄/NF exhibited an excellent specific capacitance(2432.2 F g^-1 at 0.5 A g^-1)and outstanding retention rate(60.4%at 20 A g^-1)than NiCo₂S₄/NF(1283.3 F g^-1,31.2%).Besides,to study the practical application of NiCo₂S₄/NF electrode,we assembled an aqueous ASC NiCo₂S₄//AC showed an outstanding energy density of 104.44 Wh kg^-1 at 400 W kg^-1.