Construction Of Composite Electrode Materials Based On Transition Metal Sulfides/Phosphides And Their Applications In Energy Storage

With the increased development of new devices such as electric vehicles and portable electronic devices,the single advantage of traditional energy storage devices such as Li-ion batteries,Na-ion batteries,and supercapacitors is not enough to meet the needs of modern society.Hybrid supercapacitors show higher power density than Li-ion batteries and higher energy density than supercapacitors,which are potential next-generation energy storage devices.Designing the composition and structure of electrode materials reasonably is the key to improving the performance of hybrid supercapacitor.Transition metal sulfides/phosphides provide high theoretical specific capacity due to abundant redox reactions,which have huge application space as electrode materials for hybrid supercapacitors.However,transition metal compounds still face the problems of poor rate performance and cycling stability.Based on the background above,a variety of transition metal sulfides/phosphides-based composite electrode materials were designed and prepared in this paper.Their electrochemical properties,the multi-component synergistic effect of electrode materials,energy storage mechanism,and applications in the field of energy storage were further explored.The main research contents are as follows:(1)The Zn0.76Co0.24S/Co3S4 composite electrode materials with different morphologies were prepared on three-dimensional nickel foam by simple hydrothermal method and anion-exchange technology.The electrode materials with different morphologies were induced,with hexamethylenetetramine(HMT)serving as the alkaline source,ammonium fluoride(NH4F)or polyvinylpyrrolidone(PVP)as the surfactant.By adjusting the ratio of surfactant,the mechanism of surfactant on the morphology of electrode material was analyzed.Ammonium fluoride-induced flower Zn0.76Co0.24S/Co3S4 exhibited a high specific capacity of 1259.17 C g-1 at a current density of 5 mA cm-2,and still maintained 93.8%of the initial capacity after 7000 cycles.It was superior to the grass-like Zn0.76Co0.24S/Co3S4 induced by PVP.The assembled flower-like Zn0.76Co0.24S/Co3S4//RGO solid-state hybrid supercapacitor device has a maximum energy density of about 62.22Wh kg-1 and a maximum power density of 16 kW kg-1,and its capacity was still maintained at 86.3%after 8000 cycles.(2)A novel electrode material with Zn0.76Co0.24S nanoparticles embedded in a porous carbon shell was prepared using a metal-organic framework(MOF)as the precursor and a self-sacrificing template,with the introduction of dopamine as carbon and nitrogen sources.In the preparation process,the dissolution of MOF and the polymerization of dopamine were carried out at the same time,and the structure of Zn0.76Co0.24S nanoparticles embedded in the nitrogen-doped carbon layer was formed after annealing,which effectively improved the stability of the electrode material.When the current density was 1 A g-1,the specific capacity of the electrode material was 937 C g-1,and the capacity retention rate was 112%after 40000 cycles at the current density of 5 A g-1.The assembled hybrid supercapacitor has an energy density of 55.47 Wh kg-1 and a maximum power density of 16.55 kW kg-1.After 100000 cycles,the capacity can still maintain 108.9%,showing a very long cycle life.(3)The in-situ grown MOF precursors were prepared by the co-precipitation method.After the layered dihydroxide(LDH)transformation and annealing process,the cation and cation substitutions occurred.The ZnCo-S sulfide composite electrode material was constructed.Compared with single metal component sulfide Co-S,the composite electrode material shows high specific surface area,multi-channel structure and heterogeneous interface effect,which can provide abundant active sites and shorter electronic transmission path for electrochemical reaction,showing excellent electrochemical performance.At the current density of 2 A g-1,the specific capacity of ZnCo-S sulfide composite electrode material is as high as 1464.5 C g-1.The assembled solid-state hybrid supercapacitor shows an excellent energy density(64 Wh kg-1)and power density(16 kW kg-1),with a capacity retention rate of 92.7%after 10,000 cycles.(4)ZnNiP electrode materials based on Ni metal-organic framework were prepared by zinc doping optimization for high performance hybrid supercapacitors.The addition of zinc and phosphating treatment enhanced the synergistic effect and electronic conductivity of each component and enriched the electrochemical active cite.The structure of phosphide nanoparticles embedded in the carbon layer improves the stability of electrode materials.The ZnNiP-0.5 electrode material with the optimal doping amount was obtained by adjusting the doping ratio of zinc.The ZnNiP-0.5 electrode material exhibited both surface control and diffusion control behaviors and had the advantages of both capacitive and battery-type electrode materials.The assembled solid-state hybrid supercapacitors can provide an energy density of 67.4 Wh kg-1 and a power density of 15.9 kW kg-1.