Preparations And Electrochemical Properties Of Graphene-supported Transiton Metal Sulfides By Layered Double Hydroxide Precursor

The use of lithium ion batteries in the expanding field of people and the rapid demand for portable electronic products, and promote the continuous development of high power density, high energy density, long service life, low cost and environmentally friendly lithium ion electrode material. In view of the problems of lower specific capacity and lower energy density of electrode materials, a feasible scheme for preparing electrode materials with excellent properties was proposed. Transition metal sulfides have wide range of sources and abundant active sites. They can be used as a variety of electrode materials,so they have attracted wide attention. Because of the transition metal sulfide have some shortcomings: the problem of poor conductivity and serious volume expansion, resulting in poor cycle performance. Therefore, the preparation of composite materials has become the trend of the times. The transition metal sulfide and carbon composite materials can both have the advantages of achieving significant improvement in material properties. In this paper, we using the intercalated anion properties and adjustable plate elements of LDH. Preparation of transition metal sulfide solid solution composite body supported on different carbon nano materials by the different methods. it is applied to the field of lithium ion battery, super capacitor / sodium ion battery.The essential relationship between structure and properties is discussed. The main research contents and innovations of this thesis are as follows:(1) The traditional methods to prepare SDS intercalated NiCoAl-LDH/G precursor, then after sulfuration, calcination with melamine, then acquire multistage structure (Ni,Co)9S8/N-CNTs/G, The lithium storage performance was also studied. XRD, HRTEM and XPS showed that the prepared material for solid solution structure. SEM/TEM proves that CNTs grows on the surface of graphene, and the active material particles (Ni, Co) 9S8 are wrapped by CNTs. Confinement effect of graphene layers hinder the growth of carbon nanotubes. Electrochemical test results show that the specific capacitance of(Ni,Co)9S8/N-CNTs/G can reach 797 mA·h·g-1 after 100 cycles at 100 mA·g-1.The capacity increase significantly when compared with graphene loaded(Ni,Co)9S8 (516 mA·h·g-1). And 739 mA·h g-1 after 400 cycle At 1A·g-1. The excellent lithium storage performance is attributed to the coating structure of CNTs and improves the cycle stability. Short CNTs is good for electron transport. In addition, the doping of N atoms in carbon nanotubes also increases the conductivity of carbon nanomaterials.(2) NiCo-LDH/3DGA was prepared by coprecipitation method, and the(Ni,Co)S2/3DGA solid solution composite was obtained by one-step calcination and sulfuration. We also obtain the solid solution of(Ni,Fe)S2/3DGA and (Co,Fe)S2/3DGA using the same method. Three kinds of electrode materials can exhibit excellent properties when used as the electrode material of supercapacitor and sodium ion battery. The electrochemical testing results showed that the (Ni,Co)S2/3DGA composites can deliver reversible capacity of 2264 F·g-1 at current density of 1A·g-1 as electrode materials for supercapacitors. And can deliver reversible capacity 750 F· g-1 at current density of 50 A·g-1. After 1000 cycles, the capacitance can still be retained 78%. At the same time, the three materials show good Sodium storage performance. The excellent electrochemical properties are attributed to the specific surface area and pore size distribution of graphene aerogel, providing more active sites and increasing the electron / ion transfer rates between the electrode and the electrolyte / electrolyte interface.