The Synthesis Of Nickel Selenide And Applications In Supercapacitors

Hybrid supercapacitor is composed of a battery-type electrode with high energy density and a capacitor-type electrode supplying ample power density and long life span.As a novel energy storage device,the hybrid supercapacitor can offer sufficient energy and power supply,which integrates the virtues of battery and supercapacitor,exhibiting excellent comprehensive performances.Among multitudinous available battery-type electrode materials,transition metal dichalcogenides have been extensively utilized as battery-type electrodes.Ni-based compounds exhibit promising electrochemical properties.Nickel selenides have rather high electronic and ionic conductivity than nickel oxides and nickel sulfides.As a sort of battery-type electrode,nickel selenides show wide-scale applications in energy storage devices,especially in all-solid-state devices and portable electronic devices.For these considerations,the main contents of this paper are the synthesis of NiSe2 materials and the characterization of their electrochemical properties.A one-step hydrothermal strategy has been developed to synthesize nickel selenide,which further simplified the preparation process and reduced the production cost.Moreover,the electrochemical performances have been studied.The main research contents are as follows:(1)NiSe2 structures have been synthesized by a one-step hydrothermal strategy,using Ni(NO3)2·6H2O as nickel source.The pyramid-like NiSe2 structures serving as electroactive materials,showing high specific area of the materials and short diffusion path of ions.The NiSe2 electrode exhibits superior electrochemical performances,including a high specific capacitance of 2168 F g-1 and a low internal resistance of 0.85 ?.The all-solid-state hybrid devices have been assembled with NiSe2 as the battery-type electrode and activated carbon as the capacitor-type electrode.The hybrid device exhibits a high energy density of 0.196 mW h cm-2 and a low internal resistance of 1.52 ?.Connecting two hybrid devices in series is able to drive a red LED for more than 3 min after charging for 9 s,exhibiting excellent energy storage ability and practical applications.(2)NiSe2-Ni2O3 structures have been synthesized by a short cycle and low cost hydrothermal strategy,using Ni foam as a nickel source.The grain-like NiSe2-Ni2O3 structures with high specific area increase the active sites in the electrochemical process.As battery-type electrode materials,NiSe2-Ni2O3 structures indicate superior electrochemical performance with a high specific capaciance of 2.87 F cm-2.Moreover,the hybrid supercapacitor has been fabricated with NiSe2-Ni2O3 materials as a battery-type electrode,which exhibits excellent performances,including a high energy density of 0.199 mW h cm-2,a high power density of 16 mW cm-2 and a low internal resistance of 0.91 ?.The relationship between the reaction time and the capacity ability of NiSe2-Ni2O3 structures is that with the reaction time extend,the specific capacitance increases first and then decreases.While the reaction time is 12 h,NiSe2-Ni2O3 structures show the highest capacitance value and the lowest internal resistance.Furthermore,the electrolyte system has great impacts on the capacity ability of hybrid devices.In NaOH electrolyte system,NiSe2-Ni2O3 electrode and its hybrid supercapacitor have the highest capacitance values;while the hybrid supercapacitors exhibit better rate performance and cycle stability in KOH electrolyte system.