High-performance Ni-based Compound Electrode Materials For Supercapacitor

Supercapacitors,as an important next generation energy storage device,have drawn extensive research interest because of their high power density,fast charging and discharging,long lifespan.A large number of research results indicate that the performance of supercapacitor is largely determined by electrode materials.But conventional electrode materials have far failed to meet the need of the rapid development of supercapacitor.Therefore,developing the electrode materials with high performance and low cost is still a hot topic in this field at present.Through unremiiting efforts for years,researcher found that Ni-based compound,including nickel hydroxide,nickel oxide and nickel cobaltite,have become an promising candidate as supercapacitor electrode due to their high theoretical specifical capacitance,abundant resources,environmental friendliness and low cost.In this thesis,the principle and feature of supercapacitor were elucidated straightforwardly,then the state-of-the-art,advantage and disadvantage of its electrode materials were reviewed systematically.In this regard,the synthesis and supercapacitive properties of Ni-based compound with different dismensional nanostructures were introduced in detail.Initially,hierarchical flower-like ?-Ni(OH)2 microspheres were prepared by combination conventional solvothermal route and a simple post-treatment by alkaline solution,only using sodium acetate(NaAc)and polyethylene glycol 600(PEG 600)as the additive,nickel nitrate hydrate as the nickel source,and ethylene glycol as the solvent.Through tuning the reaction time,reaction temperature and additive,a potential growth mechanism of flower-like precursor microspheres was proposed.Meanwhile,reaction condition to obtain the optimal morphology was determined,which is 190? for 8 h.The micro-morphology,crystal structure and texture feature were characterized using scaning electron microscopy(SEM),transmission electron microscope(TEM),X-ray diffraction(XRD)and Nitrogen adsorption-desorption measurements(BET),respectively.The as-obtained ?-Ni(OH)2 microspheres exhibit hierarchical porous loose structure,possessing a high surface area,larger porous volume and effective mesopore size distribution.The capacitance performances were systematically studied by cyclic voltammetry(CV),galvanostatic charge-discharge,and electrochemical impedance spectroscopy(EIS)measurements.The as-prepared ?-Ni(OH)2 microspheres can deliver an excellent capacitance of 1401.1 F/g at 1 A/g,and 720 F/g even at a higher current density of 20 A/g.Furthermore,at a higher current density of 20 A/g,the capacitance still remains 89%of its initial capacitance after cycling for 1000 times.Next,porous network-like ?-Ni(OH)2 films consisting of ultrathin nanoflakes were directly grown on the ITO/glass substrate via glucose-assisted mixed solvothermal method.After being calcined at 350? for 3 h,a novel 2D porous NiO film was obtained.The morphology,structure and crystalline type of the samples obtained before and after calcination were characterized using SEM,TEM and XRD,respectively.It is found that the annealing treatment not only retains porous network-like morphology,but also improves the crystallinity of nanoflakes and produes plenty of pores on the surface of nanoflakes.In addition,the capacitive behavior of porous NiO films were evaluated by CV,CP,cylcing charging and discharging,and EIS.Such porous NiO-based single electrode manifests a high pseudocapacitance of 1153 F/g at 1 A/g,and keeping 83.3%of initial value at 1 A/g even when at a very high current density of 20 A/g.More importantly,the capacitance loss is only 6.9%after 1000 charge/discharge cycles at a current density of 8 A/g.Finally,NiCo2O4 films were directly fabricated on the ITO/glass substrate by a two-step process involving conventional mixed solvothermal method and the following calcining treatment,using nickel nitrate hydrate and cobalt nitrate hydrate with certain moral ratio as the reaction source,and ethylene glycol and water as the solvent.The morphology,structure and crystalline type of the intermediate and production were characterized using SEM,TEM and XRD,respectively.The precursor film is composed of interconnected ultrathin nano flakes,showing honeycomb-like morphology.It might be preliminarily inferred that its main composition is Ni-Co-EG organic-inorganic hybrid.The final NiCo2O4 films not only retain original honeycomb-like morphology,but also appear plenty of pores on the surface of naoflake composing of film.The electrochemical performances of porous NiCo2O4 film annealed at different temperature were contrastively examined by using CV,galvanostatic charge-discharge and EIS.It is preliminarily determined that 300? is optimal calcining temperature to obtain the porous NiCo2O4 film with high capacitance and excellent rate performance.Meanwhile,supercapacitive properties of the as-prepared sample annealed at 300? were deeply investigated through using CV,charging-discharging,cycling charging-discharging and EIS curves.This film exhibits a high specific capacitance of 1350.8 F/g.Even when at a high current density of 40 A/g,the specific capacitance remains 952.3 F/g(about 70.5%of capacitance at 1 A/g).Especially,the specific capacitance retains approximately 83.1%of its maximum value after cycling for 3000 times at 16 A/g.