Mehmet Oguz Guler

Cr- and V-Substituted LiMn2O4 Cathode Electrode Materials for High-Rate Battery Applications

Spinel Cr- and V-substituted LiMn2O4 cathode materials were prepared by facile sol–gel process, which used lithium carbonate and manganese carbonate as starting materials and citric acid as a chelating agent. In order to increase electronic conductivity and prevent the Mn ion dissolution into the electrolyte, surfaces of the as-synthesized powders were coated with Cu via electroless deposition technique. The structure and physicochemical properties of the obtained Cr- and V-substituted LiMn2O4 powders were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), galvanostatic charge discharge tests, and electrochemical impedance spectroscopy (EIS). The results have shown that the successful formation of Cr- and V-substituted LiMn2O4 product was highly dependent on its second-stage calcination temperature.

Freestanding graphene/MnO2 cathodes for Li-ion batteries

Different polymorphs of MnO2 (α-, β-, and γ-) were produced by microwave hydrothermal synthesis, and graphene oxide (GO) nanosheets were prepared by oxidation of graphite using a modified Hummers’ method. Freestanding graphene/MnO2 cathodes were manufactured through a vacuum filtration process. The structure of the graphene/MnO2 nanocomposites was characterized using X-ray diffraction (XRD) and Raman spectroscopy. The surface and cross-sectional morphologies of freestanding cathodes were investigated by scanning electron microcopy (SEM). The charge–discharge profile of the cathodes was tested between 1.5 V and 4.5 V at a constant current of 0.1 mA cm−2 using CR2016 coin cells. The initial specific capacity of graphene/α-, β-, and γ-MnO2 freestanding cathodes was found to be 321 mAhg−1, 198 mAhg−1, and 251 mAhg−1, respectively. Finally, the graphene/α-MnO2 cathode displayed the best cycling performance due to the low charge transfer resistance and higher electrochemical reaction behavior. Graphene/α-MnO2 freestanding cathodes exhibited a specific capacity of 229 mAhg−1 after 200 cycles with 72% capacity retention.

Nanocomposite Based on Li4Ti5O12 Structures for High-Rate Li-Ion Battery Applications

Lithium titanate is synthesized from titanium isopropoxide and lithium nitrate solution via sol–gel processes. The obtained nanocrystalline lithium titanates were then subjected to electroless deposition in order to obtain Cu/Li4Ti5O12 nanocomposite structures. The crystalline structure and morphological observation of the as-synthesized Li4Ti5O12 are characterized by X-ray diffraction (XRD) and scanning electron microscopy, respectively. It is demonstrated that the electrochemical performance is significantly improved by the copper deposition onto lithium titanate structure. The copper-coated lithium titanate exhibits a stable capacity of 170 mAh g−1 at 1 C. Besides, the reversible capacity at 80 C remains over half of that at 1 C. The superior C-rate performance is associated with the copper/lithium titanate nanocomposite structure, facilitating lithium transportation ability during cycling.

The Electrochemical Properties of Cu Coated LiCr_{0.2}V_{0.2}Mn_{0.6}O₂ Nanocomposites for High Rate Li-Ion Batteries

Several reported problems of commercial LiCoO2 electrode materials such as high cost, toxicity, limited rate capability and safety concerns are still remain to be problematic to develop the lithium ion consumer electronics such as mobile phones, tablets and notebook computers. In this study, an alternative nanocomposite electrode material based on LiCr0.2V0.2Mn0.6O2 and copper coated one were produced via a facile sol-gel method and electroless Cu deposition techniques. The resulting samples were characterized by X-ray di raction (Rigaku DMax 2200 di ractometer) using a monochromatized Cu-Kα source (λ =1.5406 Å) and 2θ scan range from 10◦ to 80◦ with a speed of 1◦min−1. The scanning electron microscope (SEM) was used in order to characterize the morphology of the active materials. The as-synthesized Cu/LiCr0.2V0.2Mn0.6O2 composite cathode exhibits a stable capacity on cycling and good rate capability after 50 cycles and total capacity retention of 93% is obtained. The unique 2D structure of the composite cathode material, its good electrochemical performances and its relatively low cost comparing to LiCoO2, make this material very promising for applications.

Oxidation Kinetics of Nano Crystalline Tin Oxide Conductive Thin Films

Tin oxide was the first transparent conductor to have achieved significant commercialization. SnO2 is an n-type semiconductor with an optical band gap of about 3.6 eV in poly crystalline form. One of the main reasons for the wide use is its rather desirable characteristic of having both, high optical transmittance and high electrical conductivity. Under optimum deposition conditions, tin oxide crystallizes in the tetragonal (rutile) structure. In this study, nano crystalline thin oxide conductive thin films has been manufactured by thermal evaporation techniques onto steel substrates using metallic tin targets and oxidation kinetics have been studied after D.C. plasma oxidation by using XRD (X-Ray Diffraction). The activation energy of SnO and SnO2 from Sn phase transformations has also been studied.Copyright