Synthesis And Electrochemical Properties Of Cobalt Sulfide/Nickel-Cobalt Layered Double Hydroxide Composites

In recent years,the layered double hydroxide?LDH?has been widely concerned as the electrode material of supercapacitors due to its unique two dimensional layered structure,high specific capacitance and other advantages.However,the poor electrical conductivity and structural instability restrict its application in the condition of high rate and multi-cycle.Compared with the metal hydroxide,metal sulfide has better electrical conductivity and structural stability.In this study,zeolitic imidazolate framework ZIF-67 is selected as precursors and templates for preparation of cobalt sulfide/nickel cobalt layered double hydroxide?CoS_x/Ni-Co LDH?composite,and the supercapacitor electrode materials with excellent electrochemical properties were obtained by controllable synthesis of material composition and structure,and full utilization of synergistic complementary effect between the two compounds.?1?Firstly,a simple chemical precipitation method was used to prepare the precursor and template ZIF-67,which was partially vulcanized with thioacetamide,and nickel nitrate was added to etch and precipitate the remaining ZIF-67.Finally,the CoS_x/Ni-Co LDH composites were prepared.For comparison,CoS_x and Ni-Co LDH nanomaterials with single component were prepared using ZIF-67 as precursors.The characterization results demonstrated that the CoS_x/Ni-Co LDH composites consisted of the hollow rhombic dodecahedral morphology with many nanosheets arrays on the shell.This distinctive multilevel structure enables the CoS_x/Ni-Co LDH composites to have higher specific surface area,larger porosity and more stable structure than the pure phase CoS_x and Ni-Co LDH nanomaterials.In addition,the effects of different preparation conditions on the morphology and properties of CoS_x/Ni-Co LDH composites were researched in detail,and the optimal preparation conditions we obtained were that adding amount of sulfur source and nickel source was 0.13 mmol and 0.86 mmol,respectively,the reaction temperature was 80?and the reaction time was 1 h in the process of sulfuration,and the optimal reaction solvent was ethanol.?2?The electrochemical properties of CoS_x/Ni-Co LDH composites were investigated.The results of electrochemical tests showed that the specific capacitance of CoS_x/Ni-Co LDH composite at the current density of 1 A g^-1 could reach 1562 F g^-1.Even at the current density of 20 A g^-1,it still had the specific capacitance of 1022 F g^-1,with better rate capability.In order to further identify the electrochemical properties of CoS_x/Ni-Co LDH composites for practical applications,an hybrid supercapacitor?HSC?was fabricated with CoSx/Ni-Co LDH composites as the positive electrode and active carbon?AC?as the negative electrode.The assembled HSC had a larger potential window?0-1.6 V?,a higher energy density(the energy density can reach 35.8 Wh kg^-1 at the power density of 800 W kg^-1,and the energy density can reach 11.13 Wh kg^-1 at the power density of 8014 W kg^-1)and excellent cycle stability(after 10000 cycles under of 5 A g^-1 current density,the retention rate was 94.56%).