1. Field of the Invention
The invention relates generally to the field of lithium cobalt oxide (LiCoO2) films. More particularly, the invention relates to fabrication of highly textured LiCoO2 films by rapid thermal annealing.
2. Discussion of the Related Art
Thin films of LiCoO2 are used as the cathode in thin film lithium and lithium ion batteries. The films are deposited by rf magnetron sputtering of LiCoO2. FIG. 1 shows an x-ray diffraction pattern of an LiCoO2 film annealed for two hours at 700xc2x0 C. according to the prior art. In order to crystallize the films and achieve the high degree of preferred orientation that optimizes battery performance, they are heated at 700xc2x0 C. in flowing O2 for 2 hours. In order to lower the cost of manufacturing, it is desirable to shorten the annealing time as much as possible without compromising battery performance.
Heretofore, the requirements of low cost manufacturing and short annealing times referred to above have not been fully met. What is needed is a solution that addresses each of these requirements independently or concurrently. The invention is directed to meeting these requirements, among others.
A goal of the invention is to reduce the costs associated with LiCoO2 thin films. Another goal is to reduce the annealing times associated with the manufacture of LiCoO2 thin films.
One embodiment of the invention is related to a method for manufacturing LiCoO2 films. The method includes depositing the LiCoO2 film, rapidly heating the LiCoO2 film to a target temperature and holding the temperature of the LiCoO2 film at the target temperature for a target annealing time.
The method can also include rapid cooling of the LiCoO2 film after holding the LiCoO2 film within the target temperature range for the target annealing time. The target temperature is preferably greater than approximately 700xc2x0 C., more preferably at least approximately 800xc2x0 C. and most preferably at least approximately 850xc2x0 C. Further, the target temperature range is preferably approximately 700-1000xc2x0 C., more preferably approximately 750-950xc2x0 C. and most preferably approximately 850-950xc2x0 C. The target annealing time is preferably at most approximately an hour, more preferably at most approximately 30 minutes and most preferably at most approximately 15 minutes. Further, the target annealing time is preferably approximately 5-60 minutes, more preferably approximately 10-20 minutes and most preferably about 12-17 minutes.
The invention includes cathodes made according to the above methods. The invention also includes batteries which include these cathodes.
These, and other, goals and embodiments of the invention will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following description, while indicating preferred embodiments of the invention and numerous specific details thereof, is given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the invention without departing from the spirit thereof, and the invention includes all such modifications.