| Supercapacitors,also known as electrochemical capacitors,have been research hotspots in the energy storage fields because of their high power density,long cycle life and friendly environmental.However,their practical applications have been restricted due to their lower energy density than Lithium ion battery.Thus,many strategies are suggested to improve the energy density of supercapacitors.The key to improve the energy density of supercapacitors is to explore new type hybrid materials.In this paper,transition metal compounds and transition metal cobalt or nickel sulfides composite are fabricated by a novel hydrothermal electrochemical deposition method.The effects of deposition current densities?10,15 and 20mA/cm2?and deposition temperatures?100,110,120 and 130??on the composition,morphology,structure and electrochemical performance were studied.Then,the optimal composite electrode materials was adopted to serve as the positive electrode and an asymmetric supercapacitor were assembled with activated carbon as the negative electrode.and the supercapacitive performance was evaluated.The results are shown as follows:?1?Micromorphology of as-synthesized samples prepared by hydrothermal electrochemical deposition method exhibited nanoflakes morphology.At the deposition current density of 10 mA/cm2 and 15 mA/cm2,the as-achieved phases were 4Ni?OH?2-NiOOH and Co9S8.With the current density increasing to 20 mA/cm2,the products are composed of4Ni?OH?2-NiOOH?Co3S4 and NiS.Moreover,their mass specific capacitance could reach a value as high as 1275.7 F/g at 10 mA/cm2.And its capacitance retention reached 74.4%of the initial value after 2000 cycles.The asymmetric pseudocapacitor device?4Ni?OH?2-NiOOH/Co9S8//AC?posed excellent capacitive performance.Its specific capacitances are 58.6,53.2,46.2,42.4,40.1 and 31.6 F/g at discharge current of 5,10,20,30,40 and 50 mA/cm2,respectively and its capacitance retention could be retained up to 90.6%of the initial specific capacitance after 10000 cycles at 10 mA/cm2,which indicates its outstanding cycle stability.?2?At the deposition temperature of 100?,the product were 4Ni?OH?2-NiOOH?Ni3-xS2and Ni3S2 composite phases.When the temperature inceased to 110?,the phases are4Ni?OH?2-NiOOH and Ni3S2.Further increased to 120?,the 4Ni?OH?2-NiOOH phase has disappeared,and a new phase of Ni7S6 is observed.the phases were found to be Ni3S2 and Ni7S6at 130??Among these composite phases,Ni3S2/Ni7S6 shows a specific capacitance of 1770F/g at discharge current density of 5 mA/cm2.However,its electrochemical cycling stability was very poor.After 1500 cycles,the capacitance retention is 42.7%at a current density of 10mA/cm2 in a voltage window of 0–0.4 V.Though 4Ni?OH?2-NiOOH/Ni3S2 composite phases was not superior in the specific capacitance,its cycle life is higher than that of the phases under other temperature.Besides,It could deliver specific capacitance of 903.4 F/g?i.e.4.83 F/cm2?when discharge current density was 5 mA/cm2.After 1500 cycles,its capacitance retention could be retained 113.6%of the initial value,which proves its prior cycling stability.Besides that,an asymmetric supercapacitor was assembled with 4Ni?OH?2-NiOOH/Ni3S2 composite electrode and active carbon,and its capacitance retention could be retained up to 109%of the initial value after 16000 cycles at 10 mA/cm2. |
PDF Full Text Request