Preparation, Characterization And Electrochemical Properties Of ZnFe₂O₄and Graphene Composites As Anode Materials For Lithium Ion Batteries

Today, global energy use is growing dramatically due to steadily rising energy demand in developed nations and rapidly increasing demand in the emerging economies. Meeting this growing energy demand while avoiding resource depletion and long-term damage to the environment requires the development of high performance, low cost and environmentally benign energy systems. Secondary batteries are expressed to great expectations, especially the lithium-ion secondary battery.During the past few years, looking for new type anode materials with better safety performance, higher specific capacity and longer cycle life, becomes hotspot in the research for lithium ion batteries. Recently, much attention is paid to the Fe-based unitary and binary oxides (such as, Fe2O3, Fe3O4, ZnFe2O4, CoFe2O4and NiFe2O4) due to their advantages of low cost and non-pollution, which have been researched, to a certain extent, as important candidates of anode materials for lithium-ion batteries. The cubic spinel structure of ZnFe2O4stands out from others, because of its high theoretical capacity. As an oxide anode material, ZnFe2O4suffers from low electron conductivity and aggregation during charge/discharge cycle.In this thesis, based on the advantage of the nanotechnology and composite technology, we synthesized ZnFe2O4nanomaterials with different morphology and hybridezed ZnFe2O4with graphene nanosheets. The nano-composite technology enhances electrical conductivity of composite and improves aggregation of ZnFe2O4electrode during charge/discharge cycle.The main works of this paper are as follows:1. ZnFe2O4nanoparticles and ZnFe2O4nanospheres were synthesized by hydrothermal method and solvothermal method, respectively. This thesis primarily discussed the effects of annealing temperature on the crystalline structure, morphology and electrochemical perfonnance of the ZnFe2O4nanomaterials, and the effects of morphology on the electrochemical performance of the ZnFe2O4 nanomaterials. Test results show that the ZnFe2O4electrode has the best electrochemical performance after annealing at600℃, and the ZnFe2O4nanospheres electrode exhibits better in capacity and cycle stability in comparison to ZnFe2O4nanoparticles.2. ZnFe2O4/graphene composites were synthesized by one-step solvothermal method. The effects of the different content of graphene (5wt%,10wt%and15wt%) on the electrochemical performance of ZnFe2O4electrode materials were discussed. The electrochemical tests demonstrat that the ZnFe2O4/graphene composite exhibits higher specific capacity and more cycle stability when the amount of graphene is10wt%.