Cathode Materials for Rechargeable Lithium-ion Batteries

Our research is focused on the structure-property correlation of cathode materials for rechargeable Lithium-ion batteries. We are currently interested in finding novel or improved cathode materials, such as LiCoMnNiO2, which have high capacity and stable long-term cycling performance; new materials based on spinel structure for high voltage cathode (up to 5 V); novel oxynitride materials for potential electrode and electrolytes applications. Projects involve systematic doping studies on established materials and explore potential novel materials using phase diagram studies. Rietveld refinement of X-ray diffraction (XRD) data will be used to solve structure of new phases. Impedance spectroscopy (IS) analysis will be used to evaluate their intrinsic levels of lithium-ion conductivity and electronic conductivity, electrochemical properties by constructing test cells using the new materials. Our battery research projects are in collaboration with Advanced Battery Lab, National University of Singapore, Singapore. Key projects;

• Layered rock salt-type materials for high energy density cathodes.

• Development of novel High voltage cathode materials.

• Synthesis and characterization of novel oxynitride materials

Keywords: Cathode materials, Lithium-ion batteries, Crystallography

Electronic and Magnetic Properties of Manganites

Chemical compounds called manganites have been studied for many years since the discovery of colossal magnetoresistance, a property that promises important applications in the fields of magnetic sensors, magnetic random access memories and spintronic devices. However, understanding -- and ultimately controlling -- this effect remains a challenge, because much about manganite physics is still not known. The pseudo-cubic perovskite series of oxides of type AMO3, where A is a divalent metal (or a rare earth) and M a transition metal, exhibit quite a wide range of magnetic and transport properties (depending on the elements A and M, as well as the doping). This, and their structural resemblance with the cuprates, has caused a revival of experimental and theoretical interest. Furthermore, many technical applications are appealing since thin films of these compounds can be grown relatively easily and there is much interest in using perovskite oxides for ferroelectric and superconducting applications. Almost all these compounds have a magnetically ordered ground state. However, the transition temperatures and the different types of order can vary considerably from one system to another. The peculiar transport properties, such as the colossal magnetoresistance (CMR) for the Mn based compounds are associated with a transition from a metallic ferromagnetic (FM) to an insulating anti-ferromagnetic (AF) or paramagnetic (PM) configuration. Sometimes this transition is accompanied by a structural distortion (as for Nd1-xSrxMnO3 or in La1-x Srx MnO3). In order to investigate the electronic and magnetic properties, we perform the first-principles calculations using the planewave self-consistent field (PWSCF) code based on density functional theory (DFT). Density functional theory is an approach for the description of ground state properties of metals, semiconductors, and insulators. The success of density functional theory (DFT) not only encompasses standard bulk materials, but also complex materials such as proteins and carbon nanotubes.

Keywords: Manganite, Density functional theory

The Study of Bioactivity Behavior of Co-Cr-Mo/bio Active Glass Composite Fabricated by

Powder Metallurgy Method for Biomedical Applications

 
Cobalt based alloys and stainless steels were the first metallic materials that successfully used during the twentieth century in orthopedic applications. However Co based alloy is bioinert and may not present bioactivity in human body, which needed behavior for biomedical applications. This research will focused on the fabrication and bioactivity behavior of novel Co-Cr-Mo alloy (ASTM F-75) filled with different amounts of bioglass which will be prepared by powder metallurgy method. In this study, Co-Cr-Mo alloy (F-75) powder will be mixed with 2-10 wt. % of bioglass, before cold compacted at 550 MPa using a uniaxial press machine. The composites will be sintered at 1100°C for 2 h. Bioactivity behavior of sintered F-75/bioglass composites will be evaluated in vitro by immersing the composites into simulated body fluids (SBF) for up to 18 days. The test after immersion will be carried out in term of XRD, SEM, FTIR and pH analysis in order to observe the presence of the apatite layer on the surface of F-75/bioglass composites. The expected results will be the formation of apatite layer on the surface of the prepared F-75/bioglass composite. This apatite layer formation is considered as the mark of bioactivity, which formed on the composite surfaces will bind the materials of various kinds to living bone. Furthermore, the apatite formed is very similar to the bone mineral in its composition and structure. In summary, Co-Cr-Mo alloy, which is bioinert will be expected can be successfully converted into bioactive composite by adding bioglass particles.

Keywords: Biomaterials, Co-Cr alloy, bioglass

The Study of Bioactivity Behavior of Co-Cr-Mo/bio Active Glass Composite Fabricated by

Powder Metallurgy Method for Biomedical Applications

 
Cobalt based alloys and stainless steels were the first metallic materials that successfully used during the twentieth century in orthopedic applications. However Co based alloy is bioinert and may not present bioactivity in human body, which needed behavior for biomedical applications. This research will focused on the fabrication and bioactivity behavior of novel Co-Cr-Mo alloy (ASTM F-75) filled with different amounts of bioglass which will be prepared by powder metallurgy method. In this study, Co-Cr-Mo alloy (F-75) powder will be mixed with 2-10 wt. % of bioglass, before cold compacted at 550 MPa using a uniaxial press machine. The composites will be sintered at 1100°C for 2 h. Bioactivity behavior of sintered F-75/bioglass composites will be evaluated in vitro by immersing the composites into simulated body fluids (SBF) for up to 18 days. The test after immersion will be carried out in term of XRD, SEM, FTIR and pH analysis in order to observe the presence of the apatite layer on the surface of F-75/bioglass composites. The expected results will be the formation of apatite layer on the surface of the prepared F-75/bioglass composite. This apatite layer formation is considered as the mark of bioactivity, which formed on the composite surfaces will bind the materials of various kinds to living bone. Furthermore, the apatite formed is very similar to the bone mineral in its composition and structure. In summary, Co-Cr-Mo alloy, which is bioinert will be expected can be successfully converted into bioactive composite by adding bioglass particles.

Keywords: Biomaterials, Co-Cr alloy, bioglass