The Fabrication Of MoS_x-based Composites And Their Electrochemical Performance

Supercapacitors have received attention for their advantages such as high power density,green and pollution-free,and fast charging,but the low energy density has limited their wide application.According to the energy formula of capacitor E=CU²,the main factors affecting E are the magnitude of operating voltage and capacitance of the capacitor,which are mainly determined by the electrode material.Therefore,this manuscript designs nanocomposites with good properties to improve the energy density and specific capacitance of supercapacitors.The main research is as follows:1.Preparation of NiCo₂S₄/MoS_x/NF nanosheets and their electrochemical properties:MoS_x was firstly deposited on porous nickel foam（NF）by electrodeposition,and then NiCo₂S₄ nanosheets were generated on the surface of MoS_x by secondary electrodeposition to obtain NiCo₂S₄/MoS_x/NF composite electrode materials.And aqueous symmetric supercapacitors were constructed in 1 mol/L Na₂SO₄ and 2 mol/L KOH electrolytes with maximum energy densities of 25.64 Wh/kg and 112.5 Wh/kg and maximum power densities of 4368 W/kg and 7500 W/kg,respectively,indicating that the alkaline electrolyte is more favorable for this electrode material.Furthermore,the maximum energy density of the solid-state symmetric supercapacitor constructed with PVA/KOH as the electrolyte was 32.54 Wh/kg at a maximum power density of2856.86 W/kg.2.Preparation of CoS₂/MoS_x/NF flower-like nanosheets and their electrochemical properties:CoS₂/MoS_x/NF flower-like nanosheet films were fabricated by a two-step electrochemical deposition method with MoS_x/NF as the substrate.Aqueous symmetric supercapacitors were assembled using 1 mol/L Na₂SO₄ and 2 mol/L KOH electrolytes,and the maximum specific capacitances were 927 F/g and 211 F/g,respectively.The obtained maximum energy densities were 82.40 Wh/kg and 57.44 Wh/kg and the maximum power densities were 5046 W/kg and 11216 W/kg,respectively.Furthermore,a maximum energy density of 47.64 Wh/kg at a power density of 535 W/kg was obtained for the solid-state symmetric supercapacitor assembled using CoS₂/MoS_x/NF flower-like nanosheet films.3.Preparation of Ni₃S₂/MoS_x/NF composite electrode materials and their electrochemical properties:Ni₃S₂/MoS_x/NF nanocomposites were fabricated by growing MoS_x and Ni₃S₂ on the surface of NF using a two-step electrochemical deposition method.The aqueous symmetric supercapacitors were assembled using it as positive and negative electrodes,and the highest specific capacitance values of the devices were 538 F/g and 944 F/g in 1 mol/L Na₂SO₄ and 2 mol/L KOH,respectively.The maximum energy densities calculated in the two electrolytes were 60.57 Wh/kg and 294.69 Wh/kg at a power density of 692 W/kg and 1153 W/kg,respectively,and their capacitance retention rates were still 92%and 84%,respectively,after 3000 cycles of stability testing.Moreover,the solid-state supercapacitor based on Ni₃S₂/MoS_x/NF composite electrode materials provided a maximum energy density of 134.73 Wh/kg at a power density of 541.93 W/kg,and its capacitance retention rate was 84%after 3000cycles of testing.