Fabrication Of Flexible All-solid Transition Metal Sulfide-based Electrode Materials And Their Electrochemical Energy Storage Performance

At present,among various electrochemical energy storage devices that have developed,supercapacitors are attractive to researchers due to their excellent properties such as low toxicity,long cycle life,rapid charging speed,high power density,security and non-polluted.Nevertheless,the low energy density remains a key problem to be solved.Therefore,the design of reasonable heterogeneous interface structure,defect engineering of the introduction oxygen vacancies,or the combination of high energy battery type materials are feasible methods to solve the above problems.In this paper,due to effectively improve the energy density,flexible carbon cloth was selected as the substrate,two cathode electrode materials of Co₉S₈@NiMn bimetallic oxide with heterogeneous interface structure and Co₉S₈@MnO₂ nanoarray with defect engineering of oxygen vacancies(Co₉S₈@MnO₂-Vo),were designed for energy storage.The specific research content are as follows:1.Preparation and properties of Co₉S₈@NiMn bimetallic oxide cathode material with heterogeneous interface structureThe core-shell structure of Co₉S₈ nanotubes coupled with NiMn bimetallic oxide nanosheets was designed supported on flexible carbon cloth.Since the difference of Fermi energy levels with Co₉S₈ nanotubes and NiMn bimetal-oxide nanosheets,it is easy to form an internal electric field at the heterogeneous interface when they are combined,which is conducive to the adsorption of OH^-and the charge migration,so that they have excellent electrochemical energy storage performance.Under the light irradiation,the further improvement of capacitance directly proves the formation of heterogeneous interface.When the current density is 1 m A cm^-2,the specific capacitance of Co₉S₈@NiMn bimetallic oxide electrode material is up to 5.34 F cm^-2(741.7?Ah cm^-2).Importantly,the area capacitance increases from 3.485 to 4.07 F cm^-2(5 m A cm^-2)under light irradiation conditions,indicating that a properly designed heterogeneous interface could effectively promote charge transfer and accelerate the redox reaction kinetics.In addition,the assembled Co₉S₈@NiMn oxide//activated carbon(AC)flexible all-solid supercapacitor exhibits an energy density of 44.6 Wh kg^-1(power density of 242.53 W kg^-1).This unique heterogeneous interface has great application value in electrochemical energy storage.2.Co₉S₈@MnO₂ electrode material with defect engineering for supercapacitors and zinc ion hybrid supercapacitorsSupported on carbon cloth,Co₉S₈ nanotube arrays were directly grown as the frame by hydrothermal method,and a layer of MnO₂ nanosheets with high voltage window potential was coated.At the same time,oxygen vacancy defect engineering was introduced to improve the energy density of the electrode material for supercapacitor.Co₉S₈ nanotubes not only have good electrical conductivity and large specific surface area,but also can be used as the skeleton to grow MnO₂ nanosheets,which can improve the weak adhesion between MnO₂ nanosheets and substrate,overcome the shortcomings of easy to fall off.At the same time,the introduction of defects with oxygen vacancy can improve the electrical conductivity,the reaction kinetics in electrochemical reaction process and increase the active site.The optimized Co₉S₈@MnO₂-60displays a 1.1V ultra-high voltage window and a specific capacitance up to 3.7 F cm^-2,exhibits an initial capacitance of 91.4%after 5000 cycles,providing outstanding stability.The voltage window can be up to 2.4 V and the energy density can be up to 92.14 Wh kg^-1 in the Co₉S₈@MnO₂-60//AC flexible all-solid supercapacitor.More importantly,the zinc ion hybrid supercapacitor of Co₉S₈@MnO₂-60//Zn assembled with zinc foil as negative electrode can reach the energy density of 198.857 Wh kg^-1,which is twice of that supercapacitor assembled with AC negative electrode.