| In recent years,with the development of human society and technology,electric vehicles and other equipment have gradually appeared in our daily lives.That also promotes the development of high-energy,high-power-density energy storage devices.Therefore,supercapacitors are popular due to their high power density and good cycle stability.The electrode of a supercapacitor is composed of an active material and a current collector.Generally,multiple steps are required from the selection and processing of the current collector to the integration of the electrode,and the preparation method is cumbersome.In addition,although the method of directly applying the active material on the surface of the current collector is simple,the active material easily fall off during the electrochemical reaction,thereby reducing the electrochemical performance of the electrode.Constructing an integrated electrode by designing a simple and reasonable preparation method is an effective way to solve the above problems.In this thesis,by using the hydrothermal reduction method to control the kinetic parameters in the liquid phase reaction,free-standing Ni@Ni(OH)2 core-shell net-like fiber active material with the current collector integrated electrode material successfully synthesize for the first time.We solve the problem of active material shedding and electrode deformation while reducing the contact resistance of the material.At the same time,a large number of defects in the Ni(OH)2 nanosheet shell layer enhance the charge transport performance,improve the conductivity of Ni(OH)2,and realize the excellent electrochemical performance of the Ni@Ni(OH)2 electrode material.It is well known that designing and optimizing the structure of materials is also an effective method to improve the electrochemical performance of the electrode material..Based on the successful synthesis of Ni nanofibers,this thesis also realize the design and preparation of Ni2P@Ni(PO3)2 core-shell structure fiber electrode material through high temperature phosphating method for the first time.Take advantage of the excellent conductivity of Ni2P and the high structural stability of phosphate,the high electrochemical performance of the material is improved.The main work content and research results are as follows:(1)The self-supporting sponge-like Ni@Ni(OH)2 core-shell fiber structure electrode material was successfully synthesized by the one-step hydrothermal reduction method.In the work,the kinetic conditions of the stepwise crystal growth process,such as reaction time,hydrazine hydrate addition,reaction temperature and nickel source,were studied.The growth process of the material,key experimental factors,and the formation mechanism of the core-shell structure were explored.The experimental results show that when the addition amount of hydrazine hydrate is 1 mL,the Ni@Ni(OH)2 core-shell network fiber structure material is obtained by hydrothermal treatment at 180℃ for 3 h.The material has good flexibility and excellent electrochemical performance and fabrication method is simple,easy operation and good repeatability.The contact resistanc of the integrated electrod is small and the large number of defects on the Ni(OH)2 nanosheets improve it’s low electrical conductivity,which lead to the enhancement of the electrical conductivity of the material.The specific capacity of Ni@Ni(OH)2 is 1640 F g-1 at 1 A g-1,and remains at 86.4%of the initial value at 20 A g-1 high current density,which is better than most of the work reported before.The maximum energy density of the asymmetric supercapacitor device assembled by Ni@Ni(OH)2 and activated carbon(AC)is 41.79 Wh kg-1 at 1499.98 W kg-1.(2)On the basis of work(1),Ni2P@Ni(PO3)2 core-shell structured electrode material was designed and prepared by using high temperature phosphating.Firstly,elemental nickel fibers were prepared successfully by adjusting the reaction conditions according to the results of above work(1).Phosphating of Ni fibers was carried out by annealing together with red phosphorus at different heating rates(1℃ min-1,5℃ min-1,and 10℃ min-1).The influence of the heating rate on the morphology and structure of the product was explored.It was found that Ni2P@Ni(PO3)2 core-shell structure(Ni2P@Ni(PO3)2-1)can be obtained at a heating rate of 1℃ min-1.Thanks to the slow heating rate to reduce the possibility of agglomeration and collapse of the material,the fiber Ni(PO3)2 shell is sheet-shaped and the front end of the fiber is partially hollow.The novol structure decreases the ion transmission path,and the specific surface area of the material is increased which increase the number of active sites.So NbP@Ni(PO3)2-1 has the best electrochemical performance.The specific capacity of Ni2P@Ni(PO3)2-1 is 847.9 F g-1 at the current density of 1 A g-1.When the current density was increased to 10 A g-1,the specific capacity of Ni2P@Ni(PO3)2-1 is 744 F g-1,and the capacity retention rate is 87.7%.The result indicate that the modified material has excellent rate performance.The maximum energy density of the device assembled by Ni2P@Ni(PO3)2-1 and activated carbon is 32.77 Wh kg-1,and the corresponding power density is 747.13 Wh kg-1.Ni2P@Ni(PO3)2-1//AC has a capacity retention rate of 86.5%after 3000 cycles. |
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