The Role of Sintering Temperature and Dual Metal Substitutions (Al3+, Ti4+) in the Development of NASICON-Structured Electrolyte.

The aim of this study is to synthesize Li1+xAlxTixSn2-2x(PO4) sodium super ion conductor (NASICON) -based ceramic solid electrolyte and to study the effect of dual metal substitution on the electrical and structural properties of the electrolyte. The performance of the electrolyte is analyzed based on the sintering temperature (550 to 950 °C) as well as the composition. The trend of XRD results reveals the presence of impurities in the sample, and from Rietveld Refinement, the purest sample is achieved at a sintering temperature of 950 °C and when x = 0.6. The electrolytes obey Vegard's Law as the addition of Al3+ and Ti4+ provide linear relation with cell volume, which signifies a random distribution. The different composition has a different optimum sintering temperature at which the highest conductivity is achieved when the sample is sintered at 650 °C and x = 0.4. Field emission scanning electron microscope (FESEM) analysis showed that higher sintering temperature promotes the increment of grain boundaries and size. Based on energy dispersive X-ray spectroscopy (EDX) analysis, x = 0.4 produced the closest atomic percentage ratio to the theoretical value. Electrode polarization is found to be at maximum when x = 0.4, which is determined from dielectric analysis. The electrolytes follow non-Debye behavior as it shows a variety of relaxation times.

Effects of Al-dopant at Ni or Co sites in LiNi0.6Co0.3Ti0.1O2 on interlayer slabs (Li-O) and intralayer slabs (TM-O) and their influence on the electrochemical performance of cathode materials.

In order to satisfy the energy demands of the electromobility market, further improvements in cathode materials are receiving much attention, especially high energy density cathode materials for Li-ion batteries (LIBs). In this work, the self-propagating combustion (SPC) method is use to synthesise undoped LiNi0.6Co0.3Ti0.1O2 (LNCT), novel nano-sized Al-doped LiNi0.6Co0.3-x Al x Ti0.1O2 (LCA) and LiNi0.6-x Co0.3Al x Ti0.1O2 (LNA) (x = 0.01) cathode materials. LNCT, LCA and LNA were annealed at 700 °C for 24 h. Following the synthesis, the phase, chemical structure and purity of the materials were analysed using X-ray diffraction (XRD). Based on the XRD results, all materials exhibit a single-phase structure with rhombohedral layered structure. Based on the HRTEM and EDX results, all samples exhibit polyhedral-like shapes, while the Al-doped samples display smaller crystallite sizes compared to the undoped sample. As for the electrochemical performances, the initially discharged capacity of LCA (238.6 mA h g-1) is higher than that of LNA (214.7 mA h g-1) and LNCT (150.5 mA h g-1). However, LNA has a lower loss of capacity after the 50th cycle compared to the LCA sample, which makes it a more excellent candidate for electrochemical applications. The main reason for the excellent electrochemical behaviour of LNA is due to lower cation mixing. Furthermore, Rietveld refinements reveal that the LNA sample has a longer atomic distance of Li-O and shorter TM-O in the cathode structure, which makes Li+ ion diffusion more efficient, leading to excellent electrochemical performance. These findings further proved the potential of the novel nano cathode material of LiNi0.6-x Co0.3Al x Ti0.1O2 (LNA) to replace the existing commercialized cathode materials for rechargeable Li-ion batteries.

Band Gap Narrowing and Widening of ZnO Nanostructures and Doped Materials.

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.

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

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.