Doctor of Philosophy
Institute for Superconducting & Electronic Materials
Lu, Lin, Transition-metal oxides, sulphide and sulphur composites for lithium batteries, Doctor of Philosophy thesis, Institute for Superconducting & Electronic Materials, University of Wollongong, 2012. http://ro.uow.edu.au/theses/3872
Lithium batteries are important energy storage systems and can make energy storage and usage more efficient than with previous solutions. Moreover, among the lithium batteries, lithium-sulphur batteries are the next generation lithium battery that has the highest theoretical specific capacity (3860 mAh g-1) and the lowest gravimetric energy density. The applications of lithium-ion or lithium-sulphur batteries in electric vehicles, (plug-in) hybrid electric vehicles, or energy storage systems in smart grids require the battery to exhibit high rate capability, high power, and long cycle life. The key aspect for improving the performance of lithium-ion and lithium-sulphur batteries is to improve the performance of the active materials.
The use of nanostructured materials and conductive composite materials is designed to enhance both ion transport and electron transport by shortening the diffusion lengths of ions (such as, Li+, Na+, K+, H+, and OH-) and increasing the conductivity within the electrode materials, respectively. In this doctoral work, several nanostructured materials and conductive (carbon or conducting polymer) composites were examined and characterized for possible application as electrode materials for lithium-ion batteries or lithium-sulphur batteries. For the Li-ion battery, nanocrystalline Fe3O4/C as anode material, nanostructured CuFeO2 as anode material, transition metal oxide/carbon composite anode, and ionic liquid electrolyte were investigated. Furthermore, MoS2 − carbon nanotube (CNT) composite thin film made from layered MoS2 was investigated for a lithium-ion thin film battery. Meanwhile, conducting polymer coated sulphur-CNT composites and sulphur-graphene composite for lithium-sulphur batteries were studied.
Anode materials for lithium-ion battery:
Synthesis of nanocrystalline Fe3O4 by the sol-gel method with in situ carbon coating was conducted. Carbon coating on Fe3O4 nanoparticles can be formed in situ by solgel methods using suitable precursor materials and/or solvents. The physical and electrochemical characterizations were carried out on the synthesized Fe3O4/C composite and bare Fe3O4.
CuFeO2 has been synthesised in nanostructured form using a simple sol-gel method. This technique does not require any high cost precursors and produces powders with particle sizes of less than 1 μm. The cycle life and the high rate capability of nanostructured CuFeO2 have been studied in detail for the first time.
To study the compatibility of transition metal oxide/carbon composite anode and ionic liquid electrolyte for the lithium-ion battery, two types of room temperature ionic liquids (RTILs) were used as electrolyte for three types of transition metal oxide/carbon composites. The RTILs used were 1-ethyl-3-methyl-imidazolium bis(fluorosulfonlyl)imide (EMI-FSI) and 1-methyl-1 propylpyrrolidiniumbis (fluorosulfonyl) imide (Py13-FSI).
Rechargeable thin-film lithium batteries have attracted great attention recently due to their applications in areas of microelectronics such as smart cards, medical devices, and integrated circuits. Further progress will require the development of new electrode materials, for which a family of layered compound materials are potential candidates. A facile composite thin film preparation technique has been developed. Single-wall carbon nanotubes (SWCNTs) have been used as the carbon additive in order to generate thin films with 3D porous scaffolds, preventing the restacking of the MoS2 sheets in the composite.
Conducting composites for lithium-sulphur batteries:
Recently, great attention has been directed toward using the element sulphur for development of green, low-cost, and high-energy-density rechargeable batteries. In addition to the high capacity, utilization of sulphur as a cathode material has the advantages of natural abundance, low cost, and environmental friendliness. In this study, a conducting polypyrrole (PPy) coated sulphur-multiwalled carbon nanotube composite was prepared and investigated as a cathode material for Li/S batteries. The advantages of using the polypyrrole coating comparing with polyaniline (Pan) or poly(3,4-ethylenedioxythiophene) (PEDOT) is that the polypyrrole acts not only as a coating to improve the conductivity of the electrode and reduce polysulfide dissolution, but is also an active material, and it can contribute extra capacity to the sulphur cathode in the lithium battery. Moreover, the PPy nanoparticles coated onto the surface of the S-carbon composite can absorb polysulphide due to their porous surface morphology.
In recent years, graphene has attracted appreciable attention for use as an energy storage material, because of its superior electrical conductivity, high surface area of over 2600 m2g-1 per face, chemical tolerance, and broad electrochemical window. It has been reported that graphene can be used as a carbon matrix to improve the conductivity of electrode materials for lithium-ion batteries. Sulphur-coated graphene composite has been synthesized, and graphene nanosheet has been investigated for the first time as a carbon matrix to improve the performance of sulphur cathodes for rechargeable lithium sulphur batteries. Because of its good electrical conductivity, graphene in the composite acts as an electronic conductor.