Preparations Of Nickel Based Nanomaterials/Nanocomposites And Their Supercapacitor Application

Supercapacitors,as a novel type of energy storage device between traditional capacitors and batteries,exhibit high specific power and specific energy,large current charge and discharge capacity,as well as long cycle stability,which have important applications in the transportation,energy storage and aerospace field.The electrode is considered to be a key component affecting the electrochemical performance of a supercapacitor.Ni O and Ni Co₂O₄ have drawn intensive research attention in supercapacitors due to the advantages of high theoretical capacitance and rich sources in recent years.However,the low electric conductivity and the poor practical capacitance limit their applications.It's widely accepted that the morphology,electronic conductivity and porosity of electrode materials play key roles in improving electrochemical performance of supercapacitors.To overcome the problem of low electric conductivity,fabricating nanostructured electrode materials with hierarchical/porous structure and composing them with other conductive materials to form composites are both feasible.Moreover,the morphology of the electrode materials can be easily controlled by adjusting the synthesis parameters,improving the electrochemical performance.Therefore,it is of great significance for the improvement of supercapacitor performance and other electrode material design to study the morphology control of electrode materials and its influence on electrochemical performance.We selected Ni O and Ni Co₂O₄ metal oxide electrode materials as the research object and improved their supercapacitor performance from the structure,composite and substrate three aspects,which also provides a reference for the rational design of electrode materials for energy storage applications.In addition,the morphology control of Ni Co₂O₄ and their corresponding electrochemical properties were also studied.The specific research contents and results are as follows:?1?An urchin-like porous NiO electrode material was synthesized via a simple hydrothermal method.The unique Ni O nanostructure was used as supercapacitor electrode material which exhibited excellent electrochemical performances with high specific capacity of 540.5 F g^-1 at 1 A g^-1 as well as an excellent capacitance retention of 80% after 1000 cycles(10 A g^-1).?2?Ag₂O-loaded Ni O ball-flowers were synthesized via a simple hydrothermal method.During the charge-discharge processes Ag₂O can convert to metallic Ag to enhance the conductivity of electrode materials.The unique hierarchical ball-flower architectures have a large specific surface area(165.4 m² g^-1),which can facilitate the completely contact between the electrolyte and the electrode materials.Electrochemical measurements reveal that electrode materials based on Ag₂O/Ni O nanocomposites exhibited high specific capacitance value(556 F g^-1)at a current density(1 A g^-1),as well as an excellent capacitance retention of 103% after 1000 cycles(5 A g^-1).?3?A novel Ni@Ni Co₂O₄ core/shells structure consisting of the Ni microspheres skeletons and nanosheet-like Ni Co₂O₄ skins was prepared by the solvothermal method and hydrothermal method.Due to the unique architecture with Ni microspheres as the highly conductive cores improving the electrical conductivity of electrode and external nanosheet-like Ni Co₂O₄ shells as the efficient electrochemical active materials which have a large specific surface area and active numerous sites,the as-prepared Ni@Ni Co₂O₄ exhibited excellent electrochemical performance with high specific capacity of 597 F g^-1(1 A g^-1),good rate capability(approximately 86.9% of the capacitance is still retained from 1 A g^-1 to 20 A g^-1),as well as remarkable capacitance retention of 96% after 3000 cycles(10 A g^-1).?4?Just by simply adjusting the kinds of alkali source?urea and HMTA?and the addition of NH4 F,four types of Ni Co₂O₄ electrode materials with different morphologies?tremella-like Ni Co₂O₄,flower-like Ni Co₂O₄,urchin-like Ni Co₂O₄ and pineneedle-like Ni Co₂O₄?were synthesized by a simple hydrothermal route.With the Ni foam as substrate,a series of hierarchical Ni Co₂O₄ arrays nanostructures with different morphologies?nanopetals,nanosheets,nanoneedles,nanorods arrays?were synthesized under the same conditions.The experimental results show that the alkali source and NH₄ F play the key roles in controlling the morphology of Ni Co₂O₄.Specially,urea can promote the formation of nanoneedle-like structure,HMTA can promote the formation of nanosheet-like structure,while NH4 F can stimulate the substrates to produce more active sites for nucleation and growth,and promote the growing of Ni Co₂O₄ arrays to a bigger size.When these Ni Co₂O₄ samples are evaluated as electrode materials for supercapacitors,the electrochemical properties of four nickel foam supported Ni Co₂O₄ arrays samples are generally better than that of the Ni Co₂O₄ powder samples.Ni Co₂O₄ nanoneedles electrode exhibits the optimal specific capacitances of 1584 F g^-1 under the current density of 1 Ag^-1 as well as an excellent stability.