| Li V3O8 with a layered structure has attracted significant interest as cathode material for Li-ion batteries because it is proposed to be a low cost material with large specific capacity and also has the potential of providing a long cycle life. It is also well known that the preparation methods and post-treatments have significant influence on the electrochemical properties of Li V3O8. So the preparation and improving methods of this material were studied in this dissertation. Electrochemical performance of the gained Li V3O8 cathode materials was also studied in this paper. With regards to the characters of several titanium oxides, the paper develops new strategies to prepare nanostructure electrode materials. XRD(X-ray diffraction), TG(Thermogravimetry analysis), SEM(Scanning Electron Microscopy), RTEM(Transmission Electron Microscopy), DC(Discharge and charge), EIS(Electrochemical impedance spectroscopy) measurements are performed to characterize the morphologies, structures and electrochemical pe rformance of the as-derived samples.Although there is an ongoing search for compositionally new electrode materials, the ability to fabricate nanoversions of known materials can also greatly enhance power performance by simply increasing the surface-to-volume ratio. This allows for an increase in electrode-electrolyte contact area and shortens the Li-ion insertion distances thus enhancing the power density compared to micrometer-sized particles. Unfortunately, for cathode materials, increasing the electrode surface area of course allows for significantly more unfavorable side reactions(e.g., dissolution of species within the active material). Therefore, in this work, an economical route based on hydrothermal and layer-by-layer self-assembly processes has been developed to synthesize unique Al2O3-modified Li V3O8 nanosheets, comprising a core of Li V3O8 nanosheets and a thin Al2O3 nanolayer. The thickness of the Al2O3 nanolayer can be tuned by altering the LBL cycles. When evaluated for their lithium-storage properties, the 1 LBL Al2O3-modified Li V3O8 nanosheets exhibit a high discharge capacity of 191 m A h g-1 at 300 m A g-1 over 200 cycles and excellent rate capability, demonstrating that enhanced physical and/or chemical properties can be achieved through proper surface modification.We developed a facile two-step hydrothermal procedure to prepare hybrid materials of Li V3O8 nanorods on graphene sheets. With a closer examination, the Li V3O8 nanorods were decorated on the surface of graphene with the sizes of 10-20 nm in diameter and 200-300 nm in length. The outstanding electrochemical performance of our Li V3O8-graphene hybrid material for lithium ion batteries was attributed to the intimate interactions between the nanorods and the underlying reduced graphene oxide sheets, and the small size and ideal nanorod morphology and crystallographic orientation of the Li V3O8 nano-crystals. It is obvious that this hybrid material have much better electrochemical performance than that of pure Li V3O8 nanorods. The reversible capacity of Li V3O8-graphene hybrid material is stable at 251 m A h g-1 after 10 cycles at a rate of 0.3 C. Upon increasing the discharge-charge rates to 1, 3, and 5 C, its reversible capacities are maintained at 215, 165, and 98 m A h g-1, respectively.Here, we report a novel and simple strategy, which is based on the idea of space confinement, for the synthesis of ultradispersed Li V3O8 nanoparticles(-10 nm) on graphene(denoted as LVO NPs-GNs) with an unprecedented degree of control based on the precise separation and manipulation of nanoparticles nucleated, grown, anchored, and crystallized of graphene oxide(GO) in a water-in-oil emulsion system over free growth in solution. The hybrid composites displayed high performance as an cathode material for lithium-ion battery, such as high reversible lithium storage capacity(237 m A h g-1 after 200 cycles), high coulombic efficiency(about 98%), excellent cycling stability and high rate capability(as high as 176 m A h g-1 at 0.9 A g-1, 128 m A h g-1 at 1.5 A g-1, 91 m A h g-1 at 3 A g-1 and 59 m A h g-1 at 6 A g-1, respectively). The remarkable electrochemical performance of LVO NPs-GNs composites was attributed to the effective combination of small nanoparticles(-10 nm), uniform distribution, and strong coupling with the graphene sheets.We have developed an directed self-assembly approach using electrostatic interactions for fabricating a novel multilayered Li V3O8 nanoparticle/graphene nanosheet hybrid electrode for potential use in high performance lithium ion batteries by using a porous Ni foam as a substrate. The reversible capacity of hybrid electrode stabilizes at 266 m A h g-1 after 20 cycles at current densities of 0.1 A g-1. Upon higher discharge-charge current densities at 0.3, 1, 3, 5 and 10 A g-1, its reversible capacities are maintained at 221, 180, 122, 90 and 57 m A h g-1, respectively. Cathode materials need to combine high lithium ion intercalation capacity, surface area, electrical as well as ionic conductivity, and mechanical toughness. In this paper, we report high surface area three-dimensional graphene composite from reduced graphene oxide loaded with Li V3O8 nanoparticles. Mechanical integrity of layer-by-layer self-assembly composites enabled unusually high cycling stability that enabled charge-discharge rate as high as 50 C with storage capacity of 67 m A h g-1 exceed all other LVO-based cathode materials. |
PDF Full Text Request