| Because of the rapid expansion of human society,burning fossil fuels is insufficient for ever-growing energy demands.Thus,significant research efforts have been devoted to develop advanced electrochemistry devices for harvesting and storage of renewable energy resources.Supercapacitors,as the promising next-generation energy-storage devices,have attracted extensive attention owing to their high power density,excellent cycling stability,and rapid charge and discharge capacity.But,the unsatisfactory energy density of supercapacitors limits their applications,especially for the strict requirements in peak-power assistance devices.To solve this problem,optimizing the electrode materials are actively essential?Among the various energy storage materials,Transition-metal oxides(TMO)/hydroxides(TMH),have been explored intensively for supercapacitor owing to their redox reaction.Recently,bimetal hydroxides have attracted increasing popularity as battery-like electrodes,owing to their merits of better electrical conductivity and superior supercapacitance compared with their single-metal counterparts.Based on the Ni/Co hydroxides/sulfides,a series of functional nano/micro materials with hierarchicial hollow structure were fabricated.The performance of Ni/Co hydroxides/sulfides materials as electrodes were systematically evaluated,and the relationship between the structure,as well as the chemical composition and the properties were analyzed.meanwhile,the performance of assembled cell capacitor and flexible all-solid-state supercapacitors were objectively evaluated under real circumstance.The main research contents and results are as follows:(1)Based on Oswald effect,urchin-like hollow spheres of Ni2Co(CO3)2(OH)2 s have been designed for a high-performance cathode for asymmetric capacitors.owing to hollow structure and hierarchical pore system,Ni2Co(CO3)2(OH)2 shows The as-prepared electrode exhibits a high specific surface area(120 m2 g-1),large specific capacitance(890 C g-1 at 0.5 A g-1)and a remarkable rate retention(78.7%at 50 A g-1).The corresponding HCSs achieved a high energy density of 57.1 W h kg-1 at a power density of 400 W kg-1,outstanding specific capacitances(256.9 C g-1(160.5 F g-1)at 0.5 A g-1),and excellent electrochemical cycling stability(85.5%after 2000 cycles).The excellent electrochemical performance could be attributed to these aspects:he synergistic effects from nickel and cobalt ions that offer multiple oxidation states to achieve an excellent electrical conductivity,rich redox reactions,and a high electrochemical actVvity.The CO32-ions intercalation increase the interlayer spacing and wettability of the electrode.The urchin-like hollow structure provides a large accessible electroactive surface and high-speed pathways for electrons and electrolyte-ions.(2)Based on Ni2Co(CO3)2(OH)2 precursor,dual-hollow heterostructure of Ni2CoS4 sphere was fabricated by sulfidation for Flexible all-solid-state SupercapacitorsThe obtained Ni2CoS4HS-HT shows unique dual-hollow structure which is composed of inner hollow microsphere core and outer hollow nanotube shell.Benefiting from dual-hollow heterostructure,the obtained Ni2CoS4HS-HT electrode delivers an excellent specific capacity of 817.5 C g-1 at a current density of 1 A g-1 and remarkable rate retention of 75.3%at a high current density of 50 A g-1.Moreover,the flexible all-solid-state asymmetric supercapacitor(Ni2CoS4HS-HT-5//CAC)exhibits a high capacitance of 1511.5 mF cm-2 and 92.6 mWh cm-3(13.6 mWh cm-3)at 5 mA cm-2 within a wide voltage window of 1.8 V.Moreover,the flexible all-solid-state asymmetric supercapacitor displayed excellent mechanical stability with almost intact electrochemical performance under various bending angles.The superior electrochemical performances on Ni2CoS4HS-HT-5 should be ascribed to the elaborate nanostructure engineering and the following factors:(i)the bimetal sulfide compounds endow better conductivity than their single-metal sulfide and oxide counterparts;the dual-hollow structure richen electrochemical active sites between electrode and electrolyte and facilitate the ions transfer and electrode filtration;... |
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