| Recent years,lithium-ion batteries are considered to be an ideal choice as energy storage devices for next generation of electric vehicles and renewable power station for its high energy density.To further improve the electrochemical performance of lithium-ion batteries and extend the cycle life,new electrode materials need to be further developed.In recent years,due to the high capacity and safety of lithium-ion battery anode materials,it has been widely studied.Due to the limited capacity of traditional negative electrode materials,the cycle capacity of new negative electrode materials decays faster.Therefore,based on the relationship between the structure and performance of materials,this paper focuses on how to design an ideal anode material for lithium ion batteries,to design and study different anode materials,and explore its various electrochemical properties.(1)A novel synthesis strategy has been developed to synthesize graphene nanosheets loaded Fe3O4 nanoparticles(GNSs/Fe3O4 NPs)via a freeze-drying of graphene and iron ion suspension and followed by a solvent thermal synthesis method,which is considered as a durable high-rate lithium ion battery anode material.The size of Fe3O4 loaded on the graphene nanosheets can be regulated from 20 nm to 100 nm by controlling the mass ratio of GNSs and Fe3O4.When the ratio of GNSs to Fe3O4 is 1:2,the obtaining Fe3O4 nanoparticles have?40 nm in diameter.Lithium ion battery anode made from GNSs/Fe3O4(1:2)without adding any other conductive agent can exhibit a high reversible capacity(?1145 mAh g-1 after 120 cycles at 100 mA g-1)and a remarkable rate capability(650 and 530 mAh g-1 at 0.5 and 1 A g-1,respectively).This excellent performance is caused by the unique morphology of graphene nanosheet loaded Fe3O4 nanoparticles,in which Fe3O4 nanoparticles can be steadily dispersed on the graphene surfaces and thus maintaining a large specific surface area and the structural integrity during the Li+insertion/extraction process.(2)Reduced graphene oxide/hollow Fe3O4 nanospheres/Carbon nanotubes(rGO/h-Fe3O4/CNTs)ternary heterostructure nanocomposites were constructed.The design of the ternary heterostructure consists of one-dimensional nanotubes,two-dimensional nanoflakes and three-dimensional hollow spheres.This obtained ternary heterostructure is considered to effectively alleviate volume changes in lithium-ion batteries cycling process;CNTs and rGO with excellent conductivity and large specific surface area benefits to electronic transmission;h-Fe3O4 spheres with hollow morphology are good for maintaining structural stability during charging and discharging and thus obtain enhance the properties of lithium-ion batteries.It is very unexpectedly,CNT concentration can effectively adjust the size of h-Fe3O4 spheres.In comparison with the rGO/h-Fe3O4 binary nanocomposite electrode,which shows a high reversible specific capacity of 913 mAh g-1 after 120 cycles at 100 mA g-1 and a remarkable rate capability(525 and 371 mAh g-1 at 0.5 and 1 A g-1,respectively),the rGO/h-Fe3O4/CNTs ternary heterostructure nanocomposite electrodes exhibit an excellent long cycle performance(-484 mAh g-1 after 500 cycles at 100 mA g-1)and fast charge-discharge efficiency(?4.09 h in one cycle).(3)We reported synthesis of rGO/PANI composite by in situ polymerization in the absence of conventional oxidants.This composite was obtained by careful polymerization of aniline in the presence of GO as a mild oxidant.The electrochemical performance of polyaniline-modified rGO as anode material for lithium ion batteries was thoroughly studied and the reaction mechanism of in-situ synthesis was discussed.The results show that low molecular weight polyaniline is firmly grafted on the surface of reduced graphene oxide through chemical bonds,and the microstructure is more stable.Compared with the unmodified rGO electrode,rGO/PANI composite electrode material exhibits a higher specific discharge capacity,more excellent long-cycle stability(?667 mAh g-1 after 300 cycles at 100 mA g-1)and better rate performance(444 and 359 mAh g-1 at 0.5 and 1 A g-1,respectively)and smaller charge-transfer resistance(Rct is 388.7 ?).More notably,the modified rGO/PANI composite electrode material greatly improved the first coulombic efficiency of the rGO electrode material(from 35.36%to 50.07%). |
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