الفهرس 
IntroductionOnly 14 pages are availabe for public view
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Abstract
Everyday household items like flashlights, television remotes and power drills require batteries. Li-ion batteries are rechargeable batteries, which are the most important energy-storage device for many applications such as mobile phones, laptop computers, electric Vehicles (EVs) and Hybrid Electric Vehicles (HEVs) applications. Molybdenum trioxide (MoO3) has been recently attracting rapid interest due to its unique layered structure. MoO3 can be used in various types of applications, such as catalysts, photochromic, electrochromic devices, gas sensors, and batteries. The stable layered orthorhombic structure of α-MoO3 presents an open channels (2D) for fast Li-ions diffusion which provides high electrochemical activity versus Li/Li+.
The synthetic methods have an important effect on size, morphology and quality of the powders, so the sol-gel method was used here in this study using ammonium hepta molybdate tetra hydrate as a source of molybdenum and citric acid as a chelating agent. This method was used to prepare pristine and doped MoO3 by (Co, Ni, Mg and Mn) ions. Also coating process was carried out for the pristine MoO3 by zirconia.
This thesis aimed to study the physical and electrochemical properties of MoO3 during the intercalation and de-intercalation of lithium ions in molybdenum trioxide. Pristine, doped and coated MoO3 samples were prepared by sol-gel method and investigated by different techniques. In this thesis these techniques include X-Ray powder Diffraction (XRD), Thermal Gravimetric Analysis (TGA), Scanning Electron Microscope (SEM), Raman Spectroscopy (RS), Energy Dispersive Spectroscopy (EDS) and electrochemical performance.
The XRD and RS analyses reveal the presence of characteristic peaks and signals of the stable, orthorhombic α-MoO3 matched with JCPDS database number 05-0508 with the space group pbnm. Additional peaks and signals of metal molybdates were appeared in doped MoO3 due to presence of metal dopants beside the mean peaks and signals of orthorhombic α-MoO3. For the coated MoO3 and calcined in air (ZA-MoO3) almost the same peaks of pristine MoO3 with additional XRD peak at 2θ = 30.5 related to orthorhombic phase of ZrO2. For MoO3 coated with ZrO2 and calcined under reduced atmosphere (ZR-MoO3) additional peaks and signals related to nonstoichiometric molybdenum oxide Mo4O11 and coated ZrO2 were observed.
Thermal behavior of the precursors for the pristine and doped MoO3 shows stepwise decomposition with weight losses till the formation of stable parent MoO3. The large weight losses are attributed to the loss of water, ammonia, combustion of carboxylic acid and acetate ions xerogel (organic matter) from the hydrated precursor. At about 5000C the stable anhydrous α-MoO3 was formed without observation of other weight loss for pristine and doped samples until the melting point of MoO3 at about 7950C. TGA behavior of ZR-MoO3 has the same behavior as P-MoO3 and ZA-MoO3 until 5500C, then it shows pronounced increasing in the weight that is attributed to the oxidation process, which causes partial filling of the oxygen vacancies in the substoichiometric MoO3-x (here small fraction (24%) of Mo4O11 detected above from XRD and Raman spectra) into the stoichiometric MoO3.
The SEM of the samples reveal densely packed layers of well-developed regular particles of layered structure α-MoO3; the particles are basically straight forward and slab-sided. For the doped samples, slight white spots can be observed clearly on the surface of samples, these white spots may attribute to small amounts of dopants of transition elements (Co, Ni, Mg and Mn) or the appearance of small amounts of metal molybdate phases on the surface of MoO3. For the coated samples, no significant change in the shape was observed for P-MoO3 and ZA-MoO3. The particles seem to be clean and smooth layers like P-MoO3 with slight light spots may attribute to the presence of ZrO2 particles which did not deform the layer nature of the particles. For ZR-MoO3, the images show different shapes e.g. regular, irregular and rod light particles over the main layer particles of MoO3, light spot particles may attribute to ZrO2 and/or Mo4O11. Energy Dispersive Spectroscopy (EDS) for pristine P-MoO3 and doped samples reveal the existence of Mo and O atoms in P-MoO3 sample without any impurities or heterophase and existence of Co, Ni, Mn and Mg atoms in Co-MoO3, Ni-MoO3, and Mn-MoO3 and Mg-MoO3 samples, respectively.
The electrochemical behavior shows that the specific capacity and cycling stability of the doped samples compared to the parent are almost the same except for Mg-MoO3 which has the highest initial discharge capacity of 271 mAh/g and has the highest capacity retention about 71.6 %. Compared to the P-MoO3 and ZA-MoO3 electrode, ZR-MoO3 shows high specific capacity and good cycling stability with capacity retention of 46% compared to the capacity retention of P-MoO3 of 37%. The outstanding electrochemical performance of ZR-MoO3 electrode may attribute to the presence of Mo4O11 phase which increases the conductivity due to the effect of mixed transition metal oxidation states that created by the presence of Mo4O11. Mo4O11 has also multiple sites for lithium intercalation as appear in the cyclic voltammetry and discharge-charge profile. This improvement may attribute also to the presence of ZrO2, which provides electronic conduction channels and further facilitates the electrode reaction process.