Structural Design And Electrochemical Performance Of Nickel-cobalt Based Nanomaterials For Hybrid Supercapacitor

Excessive consumption of traditional energy sources and the development of renewable energy sources have promoted the development of advanced electrochemical energy storage/conversion devices,such as batteries and supercapacitors.Nowadays,supercapacitors have been widely studied in the energy field due to their high power density,fast charge and discharge rate,long cyclic stability and good safety.In particular,the assembled hybrid supercapacitors by taking the battery-type materials as the positive electrode and the capacitor-type materials as the negative electrode can effectively combines the advantages of the secondary battery and the traditional capacitors,and fill the performance gap between the capacitors and battery.In order to further improve the energy density of hybrid supercapacitors,this dissertation focuses on the reserarches about new battery-type electrode materials with high efficiency,stability and high redox activity,constructing the different morphology of Ni Co-based phosphides,sulides and composite materials.Various characterization techniques were used to systematically investigate the phase structure,micro-nano structure,chemical composition,specific surface area and electrochemical properties of the prepared materials.The main contributions involved are as follows:1.Preparation of Ni Co P hollow nanocubes electrode materilas for hybrid supercapacitorTransitional Metal phosphides have been extensively studied for superior electrical conductivity,rich valences and high electrochemical activity,and the reasonably designed architecture of bimetals phosphides is considered to be very effective for adequately making full of its material advantages and breaking through its flaws of the low rate capability and bad cycle lifespan in applications.The Ni Co P hollow nanocubes were successfully prepared by combining template etching and one-step phosphating strategy.The phase structure,morphology and chemical composition of electrode materials were systematically studied.It is found that the unique hollow structure has large specific surface area,which can increase the contact area between electrode material and electrolyte,and improve the utilization rate of electrochemical active sites.In addition,the hollow cavity can also act as an"ion-buffering reservoirs",shortening the transport path for electrolyte ions.Through electrochemical tests,Ni Co P exihibited better charge storage capacity than Ni₂P and Co P due to the synergistic effect between metal ions,and showed good rate performance and cycle stability at high current density.Moreover,the assembled Ni Co P//AC hybrid supercapacitor device can achieved a ultra-high energy density of 41.3Wh kg^-1,and can still transmit 26.7 Wh kg^-1 even at a high power density of 7058.3 W kg^-1.Remarkably,the hybrid supercapacitor remained exceptional cycling stability of 90.8%at10 A g^-1 after 10000 cycles.2.Synthesis of flower-like Ni Co₂S₄ hollow nanospheres electrode materials for high-performance hybrid supercapacitorFlower-like Ni Co₂S₄ hollow nanospheres（F-NCS HNSs）were controllably designed and synthesized by integrating a surface self-reconstruction and sulfidation strategy.XRD,SEM,TEM,TG and FT-IR characterization techniques were used to investigate the formation mechanism of the morphology.In addition,BET analysis showed that the specific surface area of the F-NCS HNSs prepared by surface reconstruction strategy was twice that of the Ni Co₂S₄ hollow nanospheres,and it had abundant mesoporous structure that promoted the diffusion of electrolyte ions.Therefore,F-NCS HNSs electrode showed high specific capacitance(685.2 C g^-1 at 1 A g^-1),good rate performance(66.1%initial capacity retention rate at 30 A g^-1)and excellent cyclic stability(capacity retention rate of73.5%after 10000 cycles at 20 A g^-1).The hybrid supercapacitor device was constructed by F-NCS HNSs as the positive electrode and commercial activated carbon as the negative electrode,which achieved a high specific capacitance of 134.2 F g^-1 at 0.5 A g^-1 and stable cycling performance（92.2%capacity can be maintained after 10000 cycles）.Meanwhile,the device exibitied the maximum energy density of 47.7 Wh kg^-1 at 399.9 Wh kg^-1,and an ultrahigh power density of 7506.0 W kg^-1 at 29.4 Wh kg^-1.3.Preparation of Ni Co₂S₄@Ni Co-G-LDH core-shell structure electrode materials for hybrid supercapacitorThe core-shell Ni Co₂S₄@Ni Co-G-LDH electrode materials were successfully prepared by an in-situ growth of glucose-intercalated nickel-cobalt layered double hydroxides（Ni Co-G-LDH）on the surface of Ni Co₂S₄ hollow nanospheres by co-precipitation method.The glucose-intercalated LDHs showed an appropriate layer spacing of 8.9（?）,which minimized the diffusion path of electrolyte ions and accelerated the kinetics of redox reactions,further stimulating the energy storage capacity of LDH.Due to the excellent electrical conductivity of transition metal sulfides,the introduction of Ni Co₂S₄ can accelerate the electron transfer of Ni Co-G-LDH and effectively improve the rate performance.In addition,the preparation of Ni Co-G-LDH on the surface of Ni Co₂S₄hollow nanospheres by in-situ growth strategy could reduce the additional interface,thereby reducing the discontinuity of charge transfer and the influence of the built-in electric field.Examined as the supercapacitor electrode,the as-prepared Ni Co₂S₄@Ni Co-G-LDH material possesses an ultrahigh specific capacity of 986 C g^-1 at 1A g^-1 and a preeminent cyclic stability of 84.5%at 8 A g^-1.Furthermore,the fabricated hybrid supercapacitor device using Ni Co₂S₄@Ni Co-G-LDH as the positive electrode and commercial activated carbon as the negative electrode achieved 54.5 Wh kg^-1 and 32.7 Wh kg^-1 energy densities at 400.0 W kg^-1 and 8766.2 W kg^-1 power density,respectively.4.Synthesis of honeycomb-like Ni Co₂S₄/Mo S₂ heterostructure electrode materials for all-solid-state hybrid supercapacitorThe Mo₇O₂₄^6-ions intercalated Ni Co-LDH was firstly prepared by one-step hydrothermal method in this chapter,and then the Ni Co₂S₄/Mo S₂ heterostructure materials were further synthesized by a sulfidation strategy.The unique honeycomb-like nanostructre showed a large specific surface area of 86.19 m² g^-1 and abundant mesoporous structure.Due to the heterostructure between Ni Co₂S₄ and Mo S₂,the overall electron mobility of the material increased,further accelerating the redox reactions.Compared with the single-component of Ni Co₂S₄,the electrochemical properties of Ni Co₂S₄/Mo S₂ were significantly improved.Notably,by using Ni Co₂S₄/Mo S₂ as positive electrode and commercial activated carbon as the negative electrode,the Ni Co₂S₄/Mo S₂//AC all-solid-state hybrid supercapacitors was assembled,which exhibited high power density and energy density as well as excellent mechanical flexibility and stability.Two devices connected in series can lighted an LED for more than 5 min,which proved the considerable practicability.This chapter provides new insight into the design and synthesis of electrodes with complex components and outstanding structures for the flexible energy field.