Preparation And Electrochemical Properties Of Graphene And Nickel-Iron Layered Double Hydroxide

ABSTRACT:With the development of hybrid electric vehicles and the huge demand for portable electronic devices, the requirement for the power source is increasing. Traditional battery has a high energy density, but the service life and power density can not meet all the requirements now. In this context, the demand for the new type of energy storage devices with low cost, environment friendliness and high performance is growing. Materials for supercapacitor and high rate battery have become a research hotspot in recent years. Graphene is a two-dimensional material with high surface area, chemical stability, conductivity, and mechanical strength and flexibility, making it as a promising electrode material for flexible supercapacitor applications. Layered double hydroxide, in which Faraday reaction can happens to provide a high energy density, is considered to be an excellent cathode material for high rate battery. The main researches carried out in this dissertation are presented as follows:(1) we demonstrate a simple and moderate electrochemical synthesis of FLG flakes, wherein, the highly expanded graphite at the cathode and the fully oxidized graphite at the anode were acquired in a protic ionic liquid (PIL)1-butyl-3-methyl imidazoliumbisulfate (BMIMHSO4) at a cell voltage of3.0V, then they were separately subjected to mechanical grinding in the said PIL to achieve CFLG (cathodic FLG) and AFLG (anodic FLG) flakes. Specifically, the graphene flakes detached from cathodic graphite receive a defect healing. From a durable point of view, the higher conductive but lower defective CFLG flakes are more efficient for electrochemical energy storage.(2) We illustrate a facile and economical strategy for the bulk production of aqueous graphene dispersions via a simple ball milling process assisted with non-ionic industrial surfactant——naphthol polyoxyethylene ether (NPE). Moreover, this surfactant is readily removed using ethanol to acquire high-quality graphene flakes. The fabricated flexible graphene electrode shows excellent high-rate charge -discharge performance suitable for supercapacitor applications. A high-rate specifc capacitance of96F·g-1is obtained at a current density of10A·g-1in1M H2SO4aqueous solution, and within10,000cycles the flexible graphene electrode can retain over98%of the initial capacitance.(3) Three dimensional flowerlike Nickel-Iron layered double hydroxide (Ni-Fe LDH)/Carbon Black (CB) composite was first synthesized by a facile one-step hydrothermal process. The pure Ni-Fe LDH has high specific capacity but short cycling life with30%deterioration after150cycles. The three-dimensional conducting network of the HT-LDH/CB composite resulted in a high specific capacity of86.11mA·h·g-1and excellent long cycle life with30%deterioration after700cycles at a current density of10A·g-1in6M KOH aqueous solution. The outstanding electrochemical capability of HT-LDH/CB composite holds great promise for cathode materials of high-rate nickel battery.