Microstructure Regulation And Electrochemical Energy Storage Properties Of Ni-based Thin Film Electrode

Supercapacitor is an important energy storage device,however,the lower energy density limits its practicle application.In order to increase the energy density of supercapacitors,a new type of electrochemical energy storage device,which is also called hybrid supercapacitors?HSCs?have emerged.On the one hand,when compared to typical supercapacitors,the battery-type electrode often offers larger capacity than traditional electric double layer electrode,leading to the increased energy density.On the other hand,compared to batteries,capacitive electrode usually possesses a faster charge/discharge rate and longer life span than battery-type electrode.In this thesis,one-dimensional ultralong nickel nanowires were prepared by a simple one-step liquid-phase method.The synthesis method is simple and the reaction time is short.Self-supporting nickel nanowire film was obtained by vacuum filtration process,active materials were grown directly on the surface of nanowires.High-capacity electrode materials were prepared and their applications in hybrid supercapacitors were studied.The main work and conclusions are described as follows:1.An innovative electrochemical treatment of nickel nanowires for high-rate performance electrode materials is proposed.An important property of the as-synthesized Ni@Ni?OH?₂ membranes is that it can be directly utilized for electrochemical energy storage applications without the need for additional binders or conducting additives.The Ni@Ni?OH?₂ electrode demonstrates a high volumetric capacity?111.1 C/cm³ at 0.12 A/cm³?,significantly increased rate capability?83.1C/cm³ at 1.92 A/cm³?,and cycling stability at a high current density?78%capacity retention after 1500 cycles at 1.92 A/cm³?.2.A new nano-foaming process was invented to increase the volumetric capacity of electrode materials.The as-designed free-standing Ni@Ni?OH?₂ film electrodes display a significantly enhanced volumetric capacity?462 C/cm³ at 0.5 A/cm³?and excellent cycle stability.Moreover,the as-developed hybrid supercapacitor employed Ni@Ni?OH?₂ film as positive electrode and graphene-carbon nanotube film as negative electrode exhibits a high volumetric capacitance of 95 F/cm³?at 0.25 A/cm³?and excellent cycle performance?only 14%capacitance reduction for 4500 cycles?.Furthermore,the volumetric energy density can attain to 33.9 mWh/cm³,which is much higher than most thin film lithium batteries?1–10 mWh/cm³?.3.A cobalt doping process is proposed to effectively improve the electrochemical performance of Ni@Ni₃S₂ nanowire film electrode.Co ions are successfully and uniformly doped to Ni₃S₂ nanosheets by a facile ion exchange process.The electrochemical properties of film electrodes are greatly improved with ultrahigh volumetric capacity?increased from 105 to 730 C/cm³ at 0.25 A/cm³?and excellent rate capability after Co is doped to Ni@Ni₃S₂ core-sheath nanowires.A hybrid supercapacitor using Co-doped Ni@Ni₃S₂ as positive electrode is assembled,which exhibits an ultrahigh volumetric capacitance of 142 F/cm³?based on the total volume of both electrodes?at 0.5 A/cm³ and excellent cycle stability?only 3%capacitance decrease after 5000 cycles?.Moreover,the volumetric energy density can reach up to44.5 mWh/cm³ with a power density of 375 mW/cm³.4.One-step electrodeposition method was used to grow CoNi₂S₄ nanosheets on three-dimensional nickel nanowire films for high performance energy storage electrodes.The as-synthesized Ni@Ni–Co–S was directly employed as electrode for supercapacitor.Taking advantages of 3D conductive nanostructure for Ni substrate and mesoporous nanosheets nature for active material Ni–Co–S,the as-fabricated electrode exhibits a high capacity of 392.8 C/cm³ at 0.5 A/cm³ and excellent rate capability.A hybrid supercapacitor based on Ni@Ni–Co–S positive electrode and rGO-CNTs negative electrode was fabricated for practical supercapacitor application.Our device demonstrated an energy density reach up to 18.4 mWh/cm³?254.5 mW/cm³?and excellent long term cycle performance with 90.5%capacitance retention after 10000cycles.In summary,a simple chemical modification of one-dimensional nickel based nanostructrues were proposed to improve the electrochemical performance of the electrode material.It is a low-cost and stable method to improve the electrochemical performance of the material and can be used for other similar materials with one-dimensional nanostructures.