The crystallinity of lithium cobalt oxide thin films deposited by the radio-frequency (rf) reactive magnetron sputtering method has been improved by the rf plasma irradiation method. Compared with conventional thermal annealing, reaction to form crystalline lithium cobalt oxide via rf plasma irradiation is fast and does not need any additional external heat supply. It is found that the nucleation and the growth reactions are determined during the film deposition and the rf irradiation, respectively. The film composition does not change significantly, and severe mechanical damages such as resputtering or etching phenomena do not appear after the irradiation. A model showing the process of the crystallization by rf plasma irradiation is suggested on the basis of phenomenological analyses using secondary electron microscopy, high-resolution transmission electron microscopy, etc.

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The electric vehicle (EV) and the hybrid-electric vehicle (HEV) have attracted significant interest in recent years, and the Ni/MH battery has been investigated as a highly promising power source for these advanced vehicles. However, the energy density of a Ni/MH battery must be improved in order to reach the target EV driving distance. The development of hydrogen storage electrodes with a high discharge capacity is one of the key requirements for improving the energy density of the Ni/MH battery.Recently, efforts have concentrated on Zr-based Laves phase alloys because they exhibit a larger hydrogen storage capacity than the AB 5 -type alloy as well as good cycle life durability. 1-3 However, Zr-based Laves phase alloys require many charge-discharge cycles to achieve activation because dense oxide layers on the surface inhibit the diffusion of hydrogen atoms into the bulk alloy. This slow activation can lead to overcharge of the Ni(OH) 2 electrode and the consequent formation of ␥-NiOOH, which degrades the electrode. In order to avoid overcharge of the Ni(OH) 2 electrode, it is necessary to fully activate the Zr-based alloy electrode within about five cycles.In order to improve the Zr-based alloy activation behavior, several pretreatments have been proposed. Lee et al. reported that Zrbased alloy activation was greatly improved by adding light rareearth elements, attributed to the formation of a porous La oxide film on the surface. 4-6 Beside the standard metallurgical methods, KBH 4 treatment, a pulse-charging and a hot-charging treatment have been suggested. 7-10 However, these proposed treatments are not satisfactory because they do not avoid overcharge of the Ni(OH) 2 electrode during the formation process.It was reported that immersion in a boiling 6 M KOH solution is very effective for improving the activation characteristics of Zrbased alloys. 11 After immersion, the Zr-oxide layer is eliminated and a Ni-rich region is formed at the alloy surface. However, it is difficult to apply this formation process, because the high immersion temperature could damage the separator or the Ni(OH) 2 electrode. To use an immersion treatment to form a Ni/MH cell, the temperature should be lowered.We recently found that the activation characteristics of Zr-based alloys depend on the applied current density. Charging at a low current density leads to more rapid activation, however, the reason for this improved activation is not yet clear.In this work, we introduce a new activation process by combining the hot-immersion treatment with a slow-charging method. It was reported in our previous work that the Zr 0.7 Ti 0.3 Cr 0.3 Mn 0.3 V 0.4 Ni 1.0 alloy (termed "alloy 1" throughout this paper) is one of the most promising materials for the MH electrode. 10 An alloy 1 electrode was treated through two steps as follows: the alloy electrodes were immersed at 80ЊC for 12 h in a KOH solution and then charged at a very low current density. The effects of this treatment on the alloy electrochemical and physicochemical properties are di...

As alternatives for the low temperature crystallization of LiCoO2 thin films prepared by radio frequency (rf) reactive magnetron sputtering, two different plasma treatments, microwave and rf plasma treatment, were introduced for the first time. The films deposited at 350°C showed (003) preferred orientation corresponding to a hexagonal layered structure. From X-ray diffraction patterns, it was found that the microwave plasma treatment was effective for enhancing the crystallinity of the as-deposited films. However, the microwave plasma treatment did not enhance electrochemical properties at all, which was associated with the deterioration of surface conditions by the bombardment of energetic particles from the plasma. In the case of rf plasma treatment, the crystallinity improved effectively without severe surface degradation. At the same time, the films treated with rf plasma exhibited relatively good electrochemical properties in comparison with those of bulk LiCoO2 or high temperature annealed LiCoO2 thin films. © 2001 The Electrochemical Society. All rights reserved.

For the purpose of developing a Zr-based Laves phase alloy with higher capacity and better performance for electrochemical application, extensive work has been carried out. After careful alloy design of ZrMn 2 -based hydrogen storage alloys through varying their stoichiometry by means of substituting or adding alloying elements, the Zr 0.9 Ti 0.1 (Mn 0.7 V 0.5 Ni 1.4 ) 0.92 with high capacity (392 mAh/g at the 0.25C) and improved performance (comparable to that of commercialized AB 5 type alloy) was developed. Another endeavor was made to improve the poor activation property and the low rate capability of the developed Zr-based Laves phase alloy for commercialization. The combination method of hot-immersion and slow-charging was introduced. It was found that electrode activation was greatly improved after hot immersion at 80 o C for 12 h followed by charging at 0.05C. The effects of this method are discussed in comparison with other activation methods. The combination method was successfully applied to the formation process of 80 Ah Ni/MH cells. A series of systematic investigations has been rendered to analyze the inner cell pressure characteristics of a sealed type Ni-MH battery. It was found that the increase of inner cell pressure in the sealed type Ni/MH battery of the above-mentioned Zr-Ti-Mn-V-Ni alloy was mainly due to the accumulation of oxygen gas during charge/discharge cycling. The fact identified that the surface catalytic activity was affected more dominantly by the oxygen recombination reaction than the reaction surface area was also identified. In order to improve the surface catalytic activity of a Zr¯Ti¯Mn¯V¯Ni alloy, which is closely related to the inner pressure behavior in a sealed cell, the electrode was fabricated by mixing the alloy with Cu powder and a filamentary type of Ni and replacing 75% of the carbon black with them; thus, the inner cell pressure rarely increases with cycles due to the active gas recombination reaction. Measurements of the surface area of the electrode and the surface catalytic activity showed that the surface catalytic activity for the oxygen recombination reaction was greatly improved by the addition of Cu powder and the filamentary type of Ni. Finally, we have collaborated with Hyundai Motors Company on fabrication of the 80Ah cells for Electric Vehicles and evaluated the cell performance.