Preparation And Supercapacitr Performance Of Transition Metal(Double) Hydroxide-based Electrode Materials

In recent years, the haze phenomena is getting serious increasingly in some cities of China such as Beijing, Shijiazhuang, etc. A large number of automobile exhaust pollutant is one of the main culprit. In order to solve the increasingly serious energy and environmental problems, we must accelerate the development of the new environmentally friendly electric cars using clean energy storage devices. The supercapacitor, with many advantages of long cycle stability, low-cost, high power density and energy density that beyond other devices comparision, is a hotspot of current research as one of energy storage devices, which is currently a hot research. Developing electrode materials of excellent electrochemical performance become an important project around this pots. In this thesis, we combined the transition metal (double) hydroxides of high specific capacity with high conductivity substrate of graphene and carbon nanotubes by extensive literature research, building three dimension network structure with a larger specific surface area. The composite electrode materials that greatly improved the electrochemical properties since two energy storage mechanism of the electric doublelayer capacitance and redox pseudocapacitance, has good prospects for supercapacitor application.Firstly, a novel three-dimensional network structure electrode materials are prepared through directly electro-depositing porous Ni(OH)2nanoflakes on about five layers graphene films which is used as substrate. The3D Ni(OH)2/graphene/nickel foam electrode exhibits excellent rate capability with a specific capacitance of2161F/g at a current density of3A/g, and still remains a high capacitance of1520F/g at the current density up to60A/g, much higher than that of Ni(OH)2/nickel foam electrode. It is closely related to the presence of highly conductive graphene layer on nickel foam, which can remarkably boost the charge-transfer process at the electrolyte-electrode interface. The electrochemical cycling stability is significantly improved because of the strong adhesion between graphene film and electrodeposited Ni(OH)2nanoflakes.Secondly, three-dimensional Ni-doped Co(OH)2nanoflakes/graphene/nickel foam composites are synthesized succesfully continuning previous chapter structure. The effects on morphology and electrochemical behavior of obtained3D NixCo1-x-(OH)2/GE/NF composites are carefully investigated from the aspacts of diffrernt Ni content. The results show that an appropriate amount of Ni doping in Co(OH)2can improve the surface morphology due to synergistic effect of Ni(OH)2and Co(OH)2. At the same time, the specific capacitance and cycling performance are also increased sharply because of redox couple addition. The electrode materials demonstrate optimal electrochemical performances when the Ni content was34%. The as-prepared3D graphene/Nio.34Co0.66(OH)2electrode has a high capacitance of1714F/g at the current density of3A/g. The specific capacitance remains75%after1000cycles at the high current density of10A/g.Thirdly, a novel core-shell porous nanostructure are built for the first time on the preparation of nickel and cobalt double hydroxide/carbon nanotube/nickel foam(Ni-Co(OH)2/CNT/NF) via electrodeposition method.The effects on its electrochemical properties from activity material mass loading is discussed. Results show that the electrode materials also have high specific capacitance of1432F/g at current dengsity of3A/g a at the mass loading of8.5mg/cm2up to commercial level. The specific capacitance retention is still as high as85%after2000cycles at the alternative current density of3,5,10and3A/g, exhibiting excellent cycle stability.Finally, the asymmetric supercapacitor(ASC) is assembled and measured performances, which consist of Ni-Co(OH)2/CNT/NF with high mass loding as negative, activated carbon (AC) as positive and1mol/L KOH solution as electrolyte. The results showed that the potential window of Ni-Co(OH)2/CNT/NF//AC ASC is extended to1.6V, and remains specific capacity of107F/g at current density of17.1mA/cm2. It also preferably exhibits a large current discharge characteristics. In addition, An energy density of37.9Wh/kg was achieved corresponding to the power density of399.2W/kg. The ASC can drive a minifan and light the LED bulb served as power supply for a long time after fast charging of10seconds, showing good commercial value.