Preparation And Supercapacitive Properties Of CoNi₂S₄/C Composites With High Specific Capacitance

As a supercapacitor electrode material,cobalt-nickel binary metal sulfide（CoNi₂S₄）has attracted much attention due to its high specific capacitance and easy preparation.However,bare CoNi₂S₄ exhibits poor electric conductivity,and is prone to agglomeration during charging and discharging,resulting in a decreased electrochemical performance.Preparing CoNi₂S₄/C nanocomposites that combined CoNi₂S₄ and carbon-based materials can improve the electrochemical performance of electrode materials effectively.In this paper,a variety of CoNi₂S₄/C composites with high specific capacitance have been prepared,and the energy storage mechanism of the electrode materials during charging and discharging has been also investigated.The CoNi₂S₄ material has been prepared by using a two-step hydrothermal method,and the specific capacitance of the CoNi₂S₄ electrode material is 1011 F g^-1 at4 A g^-1.T-CoNi₂S₄/CNFs-4 composite material has a high proportion of 1869.58 F g^-1,and after 5000 cycle charges,the capacitance retention ratio is as high as 85.09%.The energy density of the hybrid supercapacitor assembled with activated carbon is 44.99Wh kg^-1.Lignite has been utilized as the raw material to prepare porous carbon,N-doped porous carbon（NPC）,and K₂CO₃ activated porous carbon（KPC）,and three kinds of lignite-based carbon materials have been composited with CoNi₂S₄ materials.Among them,the specific capacitance of T-CoNi₂S₄/PC-6 composite prepared with porous carbon is 1318.24 F g^-1,and the retention rate is 80.9%after 5000 cycles.The energy density of the assembled hybrid supercapacitor is 39.99 Wh kg^-1.T-CoNi₂S₄/NPC-6 composite material reached a specific capacitance of 1534.24 F g^-1,the energy density of the hybrid supercapacitor is 48.58 Wh kg^-1,and the capacitance retention rate is 82.42%after 5000 cycles.The specific capacitance of T-CoNi₂S₄/KPC-4 composite material is 1462.92 F g^-1,and has a high capacitance retention rate of 87.2%after 5000 cycles of charging and discharging.The energy density of the hybrid supercapacitor is 45.59 Wh kg^-1.In order to further simplify the preparation process,a one-step hydrothermal method is used to prepare CoNi₂S₄（O-CoNi₂S₄）,The specific capacitance of O-CoNi₂S₄ material is 836.14 F g^-1 at a current density of 4 A g^-1.After combining with carbon nanofibers,the composite material has a specific capacitance of 1053.29F g^-1 at 4 A g^-1.The energy density of the assembled hybrid supercapacitor is 39.50Wh kg^-1.The specific capacitance of the composite material with 0.04 g of porous carbon is 1196.16 F g^-1,and the energy density of the hybrid supercapacitor is 39.12Wh kg^-1.The specific capacitance of O-CoNi₂S₄/NPC-4 composite material is1153.48 F g^-1,and the specific capacitance remains 104.63%of the initial capacity after 5000 cycles.The energy density of the hybrid capacitor is 39.61 Wh kg^-1.The specific capacitance of O-CoNi₂S₄/KPC-4 composite material is 1234.83 F g^-1,and the energy density of the hybrid supercapacitor is as high as 40.36 Wh kg^-1.This paper has 143 figures,12 tables and 128 references.