NiCo₂S₄ Base Preparation And Electrochemical Properties Of The Composite Materials Research

The advantages of supercapacitors,such as fast charge and discharge,high power density,and long cycle life,have attracted the attention of researchers.As an important component of supercapacitors electrode materials have become the focus of research.Bimetallic sulfides are widely used as electrode materials for supercapacitors because sulfur replaces oxygen to produce more flexible nanostructures.NiCo₂S₄combines the characteristics of nickel,cobalt and sulfur elements,not only has a high theoretical capacity(1055 C g^-1),but also has the characteristics of abundant reactive sites,high conductivity,and non-toxicity.However,during the long-term charge-discharge process of NiCo₂S₄as an electrode material for supercapacitors,due to the pseudocapacitive Faradaic reaction,the NiCo₂S₄nanostructure is prone to structural deformation,which affects its rate and cycle performance.Therefore,constructing rationally nanostructured NiCo₂S₄is the key to improving its electrochemical performance.In this paper,NiCo₂S₄and carbon materials are composite modified to synthesize high-performance NiCo₂S₄composite carbon material electrodes with thorn-like structure and hollow spherical shape to improve the electrochemical performance of composite materials.The main research contents and results of this paper are as follows:（1）Graphite paper growth NiCo₂S₄electrochemical performance studyVertically stacked thorn-like nanostructured NiCo₂S₄arrays are designed and in-situ grow on the electrochemical oxidized graphite paper by a two-step hydrothermal method where graphite papers act as heterogeneous nuclear sites to rationally construct the unique features of NiCo₂S₄.Bimetal synergistic effect and the presence of sulfur atoms can improve the ionic and electron conductivity of NiCo₂S₄.The unique structure of NiCo₂S₄fabricated in such way can allow more active sites exposed to reversible redox reactions,as well as provide relatively short ions/electrons transport pathways within the broken crystal structure and rich porous structure.As such,graphite paper supported NiCo₂S₄as a self-supported electrode（NiCo₂S₄@EGP）shows an extraordinarily high rate capability with the specific capacitance of 1276 F g^-1at 1 A g^-1,and even 1218 F g^-1at 20 A g^-1,as well as the excellent cycle stability with capacitance retention of 86%after 5000 cycles.When assembling into a flexible asymmetric all-solid-state supercapacitor device,this device reaches a high-power density of 55.3 Wh kg^-1at a power density of 747.6 W kg^-1,together with a superior high cycle stability（retained 95%in 5000 cycles）.（2）Electrochemical Properties of NiCo₂S₄@N-CNTNiCo₂S₄nanomaterials（NSC-X）with different contents of CNTs were synthesized by solvothermal method.Among them,NSC-5 has good electrochemical performance,and then NiCo₂S₄@N-CNT is synthesized on the surface of CNT by introducing nitrogen source through ammonia water and urea.N element can change the structure of adjacent carbon atoms,provide a large number of surface defects,and increase the wettability of the electrode,thereby improving the capacitive performance of the composite carbon material electrode.As a composite electrode,NiCo₂S₄@N-CNT has an extremely high specific capacity of 1789 F g^-1at a current density of 1 A g^-1and has 1595 F g^-1even when the current density is increased to 20A g^-1,while the capacitance retention rate is 89%after 5000 cycles.Furthermore,the asymmetric all-solid-state supercapacitor device assembled with NiCo₂S₄@N-CNT and activated carbon（AC）as anode and cathode achieves a high energy density of 59Wh kg^-1at a power density of 750 W kg^-1.Likewise,the device exhibits superior high cycle stability,maintaining a capacitance of 81%over 5000 cyclesThese results indicate that both NiCo₂S₄@EGP and NiCo₂S₄@N-CNT electrodes exhibit good electrochemical performance,and the assembled supercapacitors also exhibit excellent electrochemical performance and mechanical stability.It indicates that NiCo₂S₄composite carbon materials have broad application prospects in supercapacitors.