Preparation And Electrochemical Properties Of Ni/Co-S(Se) Porous Hollow Spheres

Supercapacitors have long been the research hot topic due to their high specific capacitance,energy density,and good cycle stability,and thus they have become the energy storage device with good application prospects.At present,Ni/Co-S?Se?compounds have been widely used as the electrode materials for supercapacitors.However,it is still a challenge that obtains the unique structures to improve their electrochemical characteristics and practical applications.Hollow porous structures with hetero-interfaces could endow electroactive materials with excellent properties,such as well-defined interior voids,low density,high pore volume,and surface permeability.Therefore,the Ni/Co-S?Se?hollow sphere material with a mixed composition is expected to be the desirable electrode material for supercapacitors.In this thesis,carbon spheres were first synthesized by the hydrothermal method.Then,using these carbon spheres as sacrificial templates,the hetero-structure Ni/Co-S?Se?hollow spheres compounds were synthesized by the sulfuration/selenization reactions and the removal of template by calcining in air.They were finally used as the supercapacitor materials to investigate the electrochemical properties.The specific research contents are as follows:1.The hetero-structure NiCo₂S₄/Co₉S₈ hollow spheres were synthesized by using the carbon spheres as the sacrificial template via the solvothermal method and anion exchange process.When evaluated as the electrode material for supercapacitors,the NiCo₂S₄/Co₉S₈electrode exhibited an excellent specific capacitance of 2180 F g^-1at the current density of1 A g^-1,a high capacity retention that the specific capacitance retained 1400 F g^-11 even at20 A g^-1,and a long stable cycling performance of retaining⁸5%after 10000 cycles.In addition,the asymmetric supercapacitors based on these hollow hetero-spheres exhibited a high energy density of 96.5 W h kg^-11 at a power density of 0.8 kW kg^-1.The energy density can achieve 51.7 W h kg^-11 even at a higher power density of 20 kW kg^-1.These results indicated that the NiCo₂S₄/Co₉S₈ hollow spheres could have good practical applications for energy storage.2.The carbon sphere templates with different sizes were first synthesized by the improved hydrothermal method.The precursors obtained by the oil bath were then removed by sulfuration reaction and calcination process.Finally,the hetero-structure NiS/NiS₂ hollow spheres were synthesized.Among the NiS/NiS₂ hollow sphere samples with different sizes,the 600 nm NiS/NiS₂ hollow spheres exhibited the optimal specific capacitance and cycle stability performance as supercapacitor materials.Specifically,when the current density is 1 A g^-1,the specific capacitance of the sample can reach an excellent capacitance value of 3520 F g^-1.After 10000 charge and discharge cycles at 5 A g^-1,the specific capacitance can still retain⁸1.5%of the original capacitance.In addition,the 600 nm NiS/NiS₂ hollow sphere as the anode material was assembled into an asymmetric supercapacitor,and it was found that it has good energy density and stability properties.The energy density is 53.13 W h kg^-11 at a power density of 0.75 kW kg^-1.The20000 charge/discharge cycles were carried out at the current density of 5 A g^-1and it showed that the energy density can retain⁵4%.Surprisingly,the NiS/NiS₂//AC asymmetric supercapacitor was used in the practical application test and it can illuminate LED lights for up to 30 min.Taken together,the prepared hetero-structure NiS/NiS₂hollow sphere material could be an energy storage material with practical application potentials.3.The Ni_0.85Se,NiCo₂Se₄ and NiCo₂S₄/Ni₃Se₂ hollow sphere samples were successfully synthesized by a hydrothermal method and anion exchange process using 600nm carbon spheres with uniform size as a sacrificial template.The mixed NiCo₂S₄/Ni₃Se₂hollow sphere samples have higher specific capacitance properties and excellent cycle stability.Specifically,at 1 A g^-1,the specific capacitance of the component-mixed NiCo₂S₄/Ni₃Se₂ hollow sphere electrode is 1806 F g^-1,and after cycling 5000 times at 5 A g^-1,the capacitance retention rate is still¹01.7%.In addition,we explored the electrochemical performance of NiCo₂S₄/Ni₃Se₂//AC asymmetric supercapacitor.The energy density is 97.8 W h kg^-11 at a power density of 0.8 kW kg^-1.After 10000 cycles,its energy density is still stored⁹1%.These results indicate that the NiCo₂S₄/Ni₃Se₂ hollow sphere electrode can be used as a potential energy storage material for practical applications.