Sang Cheol Nam

Characterization of All-Solid-State Thin-Film Batteries with V 2 O 5 Thin-Film Cathodes Using Ex Situ and In Situ Processes

An all-solid-state thin-film battery with a full cell structure of Li/LiPON/V 2 O 5 /Pt has been fabricated. The structural and electrochemical properties of a thin-film battery fabricated by an in situ and an ex situ process were compared. In the in situ process, LiPON (lithium phosphorus oxynitride) electrolyte thin film was deposited on the V 2 O 5 thin film by radio frequency reactive sputtering at room temperature without breaking vacuum. After deposition of the amorphous LiPON, a thermal evaporator in a dry room grew Li metal film as an anode. According to the results of the ac impedance analysis after 500 discharge cycle tests, R i and R ct of a thin-film battery fabricated by the ex situ process are over ten times higher than those of the thin-film battery fabricated by the in situ process. The thin-film battery fabricated by the ex situ process showed high capacity reduction because of the high R i and R ct . This result indicated that the cyclability of the thin-film battery strongly depends on the interfacial stability between the solid electrolyte and the cathode during intercalation and deintercalation of Li ions. Therefore, the in situ process holds promise for the high performance of all-solid-state thin-film batteries.

Reduction of Irreversibility in the First Charge of Tin Oxide Thin Film Negative Electrodes

Sputter deposited 3000 A tin oxide thin films into which metallic lithium (6000 A) was reacted were studied to develop a new negative electrode for thin film rechargeable lithium batteries. The crystal structure and chemical composition of the lithium reacted tin oxide films were characterized by X-ray diffraction (XRD) analysis and Auger electron spectroscopy, respectively. The charge/discharge performances of these films exhibited capacities >400 mAh/g for >75 cycles. There was no irreversible plateau near 0.8 V vs. Li/Li due to reduction of SnO 2 to Sn and Li 2 O during the first charge half-cycle. XRD and scanning transmission electron microscopy results suggest that the lithium-reacted tin oxide thin film consists of metallic tin, lithium oxide, and reduced tin oxide, and the reacted thin films show reduced microcracks created by density fluctuations.

On the Origin of Electrodeposition Mechanism of ZnO on ITO Substrate

Zinc oxide (ZnO) was potentiostatically deposited on indium tin oxide (ITO) substrates. Comparing of the theoretical mass/charge ratio with experimental value measured byin-situ electrochemical quartz crystal microbalance, the origin of deposition mechanism of ZnO could be explained as follows: (i) surface pH enhancement due to the adsorption of hydroxide ion; (ii) the formation of intermediate species (i.e., zinc hydroxide (Zn(OH)+); (iii) ZnO deposition with production of water.Ex-situ morphological and structural analyses by scanning electron microscope and X-ray diffraction strongly supported the deposition mechanism of ZnO. This also showed that hexagonal shaped ZnO islands were first formed on ITO cathode and grew into compact ZnO films, and the formation behaviour of ZnO was clearly explainedvia analysis of the profile of measured current.

The effects of Cu-doping in V2O5 thin film cathode for microbattery

Copper-doped vanadium oxide (CuxV2O5) thin film cathode materials for a thin film microbattery have been prepared by DC reactive magnetron co-sputtering with O2/Ar ratio of 10/90 and compared with pure V2O5 thin film. The film structures have been characterized by x-ray diffraction analysis, transmission electron microscopy, Auger electron spectroscopy and X-ray photoelectron spectroscopy. X-ray diffraction and TEM studies show that the CuxV2O5 film was amorphous and phenomenal behavior of copper present in thin film with substrate has been explained by thermodynamical model. Copper doping helps to increase the thickness of the film more than 1 micrometer resulting increase of total capacity. Cycling behavior of the CuxV2O5/Lipon/Li configuration cell system was beyond 500 cycles with average capacity of 50 μAh/cm2-μm, which is higher than the pure V2O5 thin film system.

Influence of sputtering gas pressure on the LiCoO2 thin film cathode post-annealed at 400 °C

LiCoO2 thin film cathodes were prepared by RF magnetron sputtering and post-annealing. The surface morphological change of the LiCoO2 thin film wasin-situ measured by hot stage SEM with increasing temperature. The effects of sputtering gas pressure and post-annealing at low temperature (400 °C) were investigated by XRD, AFM, ICP-AES and RBS. The electrochemical characteristics of LiCoO2 thin films were changed with variation of sputtering gas pressure. A difference of micro-structural evolution after post-annealing was observed, which related to the thin film properties. The electrochemical analysis revealed that the optimal sputtering gas pressure with the low temperature annealing step increases cell capacity and rate capability.