| As people were increasingly focus on energy and environment problem, a series of the development of clean energy storage devices have received considerable attention represented by lithium-ion batteries(LIBs) typically. Transition metal oxides(TMOs) have been considered as promising alternative anode materials owing to their high theoretical capacity, which is much higher compared to the traditional graphitic anode. Fe-based spinel binary TMOs anode materials have contendered to become the next generation of commercial anode materials due to their natural abundance, environmental benignity, and low cost.At the same time,graphene, as a new form of carbon-based materials, was widely used to fabricate various hybrid composites due to its superior electrical conductivity, ultrathin thickness, high specific area, and flexible structure.In graphene-ferrite composites,the incorporated graphene not only serves as a structural buffer to alleviate volume change and prevent aggregation of particles, but also provides a conductive network to facilitate transmission of electrons and diffusion of lithium ion. In this dissertation, the novel binary composites consisting of RGO and ferrite particles were fabricated by different methods and the lithium storage properties were discussed in detail. In addition, the formation mechanism of the binary composites were illustrated. Furthermore, the different contents of graphene effects to enhance the electrochemical performance were also explored. The main contents are as follows:(1)The graphene oxide was prepared by modified Hummers method using nature graphite powders as raw material and the reduction of graphene oxide was processed with the assistant of glycol. The results indicated that RGO wa s successfully prepared and the most oxygen-containing groups were removed. After reduction, the transparent RGO sheet appeared more wrinkles and the number of layers was increased.(2)The binary nanocomposites of RGO-hollow nanospheres Fe3O4 was synthesized by a facile route using polyvinylpyrrolidone as surfactants. The uniform Fe3O4 hollow nanospheres with the average size of 250-400 nm were grown on layers of RGO. The introduction of graphene greatly improved pure hollow ferroferric oxide as the electrochemical performance of lithium ion battery anode material.The results demonstrated that HFR anode exhibited a high initial discharge capacity of 1314.5 m Ah·g-1,the first reversible specific capacity of 1013.4 m Ah·g-1 which both higher than theoretical capacity of Fe3O4, and maintained a stable capacity of 885.2 m Ah·g-1 after 100 cycles at current densities of 100 m A·g-1.At the same time,HFR electrode showed an excellent rate capability.(3)The composites of RGO-Ni Fe2O4(NFR) were synthesized via solvothermal method and annealed at 600 ?for 2 h. The graphene nanosheets significantly suppressed the aggregation of Ni Fe2O4 nanoparticles as well as maintaining the good electrical conductivity of the overall samples. The effects of the different content of graphene on the electrochemical performance of Ni Fe2O4 electrode materials were discussed. The electrochemical tests demonstrat that the NFR composite exhibits higher specific capacity, more cycle stability and better rate capability when the amount of graphene is 20 wt%.(4)RGO-zinc ferrite(ZFR) nanocomposites were synthesized via hydrothermal method. The Zn Fe2O4 particles ranged from 10-20 nm uniformly dispersed on RGO nanosheets.The electrochemical results showed that the ZFR nanocomposite electrode had greatly improved charge-discharge specific capacity and cycling stability:high initial discharge capacity of 1475 m Ah·g-1,the first reversible specific capacity of 860 m Ah·g-1 , and maintained a stable capacity after 100 cycles at current densities of 100 m A·g-1. |
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