Recent developments in cathode materials for lithium ion batteries

Band gap change in doped ZnO is an observed phenomenon that is very interesting from the fundamental point of view. This work is focused on the preparation of pure and single phase nanostructured ZnO and Cu as well as Mn-doped ZnO for the purpose of understanding the mechanisms of band gap narrowing in the materials. ZnO, Zn0.99Cu0.01O and Zn0.99Mn0.01O materials were prepared using a wet chemistry method, and X-ray diffraction (XRD) results showed that all samples were pure and single phase. UV-visible spectroscopy showed that materials in the nanostructured state exhibit band gap widening with respect to their micron state while for the doped compounds exhibited band gap narrowing both in the nano and micron states with respect to the pure ZnO materials. The degree of band gap change was dependent on the doped elements and crystallite size. X-ray photoelectron spectroscopy (XPS) revealed that there were shifts in the valence bands. From both UV-visible and XPS spectroscopy, it was found that the mechanism for band gap narrowing was due to the shifting of the valance band maximum and conduction band minimum of the materials. The mechanisms were different for different samples depending on the type of dopant and dimensional length scales of the crystallites.

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Band Gap Narrowing and Widening of ZnO Nanostructures and Doped Materials

Bioresource-based green synthesis of nanoparticles has gained significant interest as an emerging technology to reduce the toxicity of nanoparticles commonly associated with conventional chemical synthesis approaches. Studies on green synthesis of metal nanoparticles have been carried out with various biological materials including from bacteria, fungi, and plant extracts. Plant extracts in particular have been extensively used for the synthesis of metal and metal oxide nanoparticles, and this is due to the presence of essential phytochemicals in plant extracts especially from the leaves. Leaf extract contains various types of phytochemicals such as terpenoids, flavonoids, ketones, aldehydes, amides, and carboxylic acids, which play a major role in formulating and enhancing the bioactivity of the nanoparticles. This article discusses flavonoids as an essential phytochemical for the formation of metal and metal oxide nanoparticles and enhancement of their bio-functionality and compatibility. In addition, bioprocess developments for the synthesis of metal as well as metal oxide nanoparticles from various biological materials are discussed.

Biosynthesis of Metal and Metal Oxide Nanoparticles

A comprehensive review of up-conversion (UP) and down-conversion (DC) or down shifting of rare earth (RE) doped zinc oxide (ZnO) nanophosphors is presented. Research interest in the development of RE3+ doped ZnO for UP and DC nanophosphors has been encouraged by the potential application of these materials in light emitting diodes and different types of photovoltaic cells. A range of remarkable characteristics, which are organized into different sections describing the structure, optical, and luminescence properties of these materials, are discussed in detail. Undoped ZnO has two characteristic emissions in the ultraviolet and visible regions related, respectively, to excitonic recombination and intrinsic defects. X-ray photoelectron spectroscopy (XPS) data demonstrated a correlation between the visible emission and intrinsic defects. In the case of the DC or shifting process, there was simultaneous emissions related to f → f transitions of RE ions and defects in ZnO host. These emissions were dependent o...

Rare Earth Doped Zinc Oxide Nanophosphor Powder: A Future Material for Solid State Lighting and Solar Cells

Sodium-ion batteries (SIBs) are considered to be the most promising electrochemical energy storage devices for large-scale grid and electric vehicle applications due to the advantages of resource abundance and cost-effectiveness. The electrochemical performance of SIBs largely relies on the intrinsic chemical properties of the cathodic materials. Among the various cathodes, rhombohedral Na3V2(PO4)3 (NVP), a typical sodium super ionic conductor (NASICON) compound, is very popular owing to its high Na+ mobility and firm structural stability. However, the relatively low electronic conductivity makes the theoretical capacity of NVP cathodes unviable even at low rates, not to mention the high rate of charging/discharging. This is a major drawback of NVPs, limiting their future large-scale applications. Herein, a comprehensive review of the recent progresses made in NVP fabrication has been presented, mainly including the strategies of developing NVP/carbon hybrid materials and elemental doping to improve the electronic conductivity of NVP cathodes and designing 3D porous architectures to enhance Na-ion transportation. Moreover, the application of NVP cathodic materials in Na-ion full batteries is summarized, too. Finally, some remarks are made on the challenges and perspectives for the future development of NVP cathodes.

Na3V2(PO4)3: an advanced cathode for sodium-ion batteries

Preparation and band gap energies of ZnO nanotubes, nanorods and spherical nanostructures

In the preparation of nanostructured materials, it is important to optimize synthesis parameters in order to obtain the desired material. This work investigates the role of complexing agents, oxalic acid and tartaric acid, in the production of MgO nanocrystals. Results from simultaneous thermogravimetric analysis (STA) show that the two different synthesis routes yield precursors with different thermal profiles. It is found that the thermal profiles of the precursors can reveal the effects of crystal growth during thermal annealing. X-ray diffraction confirms that the final products are pure, single phase and of cubic shape. It is also found that complexing agents can affect the rate of crystal growth. The structures of the oxalic acid and tartaric acid as well as the complexation sites play very important roles in the formation of the nanocrystals. The complexing agents influence the rate of growth which affects the final crystallite size of the materials. Surprisingly, it is also found that oxalic acid and tartaric acid act as surfactants inhibiting crystal growth even at a high temperature of 950°C and a long annealing time of 36 h. The crystallite formation routes are proposed to be via linear and branched polymer networks due to the different structures of the complexing agents.

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Growth mechanisms of MgO nanocrystals via a sol-gel synthesis using different complexing agents.

Investigation of cell parameters, microstructures and electrochemical behaviour of LiMn2O4 normal and nano powders

In this work, the band gap energies of magnesium oxide (MgO) were investigated to see if calcination time affects the band gap energies of the MgO. MgO nanomaterials have been prepared by a sol-gel method. MgO precursors produced were calcined at a temperature of 600 °C for 24 hours and 48 hours. The structural characterization of samples is achieved using X-Ray Diffraction (XRD) and the morphology as well as particle size of MgO were examined by Field Emission Scanning Electron Microscopy (FESEM). UV-Vis NIR spectroscopy was used to determine the band gap energies of the materials. From the results, the band gap energy of the MgO with a longer heating time exhibited a higher value.

Band Gap Energies of Magnesium Oxide Nanomaterials Synthesized by the Sol-Gel Method

This paper discusses the issues concerning ethics, governance and regulatory systems of charitable organizations in Malaysia, highlights the key challenges in managing the organizations, and suggests a better approach that needs to be adopted by the charitable organizations in Malaysia to eradicate the bad practices that can lead to fraud and mismanagement.

http://ieeexplore.ieee.org/iel5/6416135/6422834/06422996.pdf

Norashikin Kamarudin

Papers

Preparation and band gap energies of ZnO nanotubes, nanorods and spherical nanostructures

Growth mechanisms of MgO nanocrystals via a sol-gel synthesis using different complexing agents.

Investigation of cell parameters, microstructures and electrochemical behaviour of LiMn2O4 normal and nano powders

Band Gap Energies of Magnesium Oxide Nanomaterials Synthesized by the Sol-Gel Method

Issues, challenges and the way forward for charitable organizations in Malaysia