Porous ZnO thin films as anode electrodes for lithium ion batteries.

Zinc oxide (ZnO) nano structured thin films were prepared on Cr coated stainless substrates via a simple thermal chemical reactions vapor transport deposition method in air with a mixture of Zinc acetate anhydrate as reactants. The growth process was carried out at 200 degrees C, 300 degrees C and 400 degrees C in a stainless steel reactor with one side opened to the air. High purity oxygen gas was used as the carrier gas and kept at 1 L/min flow rate during the deposition process. There is no other metal catalyst and carrier gas in the process. The materials are characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM). Their electrochemical properties as anodes of lithium ion batteries are examined by galvanostatic discharge-charge tests. The results show that porous ZnO nano structured thin films exhibit higher reversible capacities and better cyclabilities than those of commercial ZnO powders. When cycled at 0.958 mA (1 C = 1 hour charge + 1 hour discharge) for the films deposited at 200 degrees C, these nano structured pyramid-like structures deliver initial discharge and charge capacities of 954, in addition, good rate capabilities have also obtained after 20 cycles. It is believed that the porous sheet nano structure plays an important role in the electrochemical performance.

Nano crystalline TiO2 thin films as negative electrodes for lithium ion batteries.

In this study, rutile (tetragonal, P42/mnm), anatase (tetragonal, I41/amd) polymorphs of titanium dioxide films were synthesized successfully magnetron sputtering of titanium films on stainless steel substrates followed by in situ direct current plasma oxidation. The as-prepared titanium dioxide thin films were oxidized at 75 W, 100 W and 125 W plasma powers in order to optimize the system with best electrochemical performance. The mean grain sizes of the deposited films were found to be in the range of 14.2-12.9 nm as revealed by the scanning electron microscopy and X-ray diffractometer studies. The electrochemical studies were performed with pure metallic lithium foil cathode with the best performing nano structured titanium dioxide as anode. The specific capacity of the nanocrystalline titanium dioxide films oxidized at 125 W direct current was 207 mA h g(-1) even after 20 cycles in the 0.02-2 V region, indicating excellent cycling stability and reversibility.