Preparation And Properties Of Binder-Free ZnO/Graphene Composites As Anodes For Lithium-ion Batteries

With increasing demand on high energy storage devices,lithium-ion batteries(LIBs)have universally attracted interest in recent years due to their high voltage,large energy density and excellent design flexibility.Used as LIBs anode,ZnO might be one of the most promising candidates due to its attractive properties such as low cost,abundant reserve and easy preparation.However,ZnO-based anodes still suffer from poor cycling stability and low reversible capacity due to the poor electronic conductivity and large volume change during charge/discharge process.To overcome the above-mentioned problems,in this paper,we try to prepare nanostructured ZnO materials in different ways,and use graphene to modify them to improve the electrochemical performance as anode materials for lithium ion batteries.It is mainly divided into the following three aspects:(1)ZnO/nickel foam composites(G-ZnO/Ni)were prepared via a facile solvothermal method with graphene as the morphology-controlling agent.Results showed that ZnO nanoparticles were uniformly distributed on nickel foam without overlap.Obvious clearance was found between ZnO nanoparticles,which help to accommodate the serious volume expansion during the charge/discharge process.In addition,ZnO nanoparticles were found to be attached on the nickel foam in monolayer providing enough adhesive force to stabilize the ZnO nanoparticles during charge/discharge process.The remarkably unique G-ZnO/Ni electrode shows high and stable specific capacity of 537 mAh g-1 at a current density of 600 mA g-1 after 1600 cycles when used as anode material for lithium ion batteries.(2)ZnO/graphene composite materials(Cu-ZnO/rGO)were prepared on the copper foil by electro-deposition method,and then directly used as binder-free anode materials for lithium ion batteries.Results showed that the graphene electrodeposited after ZnO can not only enhances the conductive properties of materials,but also reduce the interface impedance.At current density of 300 mA g-1,the initial discharge and charge capacities of sample Cu-ZnO/rGO are 1047.9 and 838.2 mAh g-1,respectively,with a corresponding coulombic efficiency of 80%,and the reversible capacity retains 284.5 mAh g-1 after 100 cycles.(3)By combining hydrothermal method with electrospining,ZnO and ZnO@graphene(ZnO@G)fibers were formed on the copper foil.The electrochemical characterization results showed that through electrospinning technique,material capacity and stability has been greatly improved.At current density of 150 mA g-1,the reversible capacity of ZnO fiber and ZnO@G fiber can retain at 578.3 mAh g-1 and 615.5 mAhg-1,respectively,and the reversible capacity of ZnO and ZnO@G powders can only maintain 144.7 mAh g-1 and 203.5 mAh g-1.