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

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