Characterization and analysis of thin-film nickel oxide and hydroxide for use in high-power energy-storage devices

The goal of this dissertation is to understand the operation of electrochemical energy-storage devices that exhibit high-power characteristics and possess excellent cycle life. The theme is to develop structure-property correlations, which will help us understand the operation of these devices better and aid us in tailoring them to suit our needs. Shortages of oil, combined with environmental issues, have provided a huge impetus for both the improvement and development of alternatives to the presently used gasoline engine, for transportation purposes. Such modifications will benefit by the use of a high-power energy-storage device to sustain efficient operation during starting and acceleration. Two such high-power devices are electrochemical capacitors and thin-film batteries. This dissertation addresses three issues in both these devices. First, a mathematical model of an electrochemical capacitor is developed which is used as a tool to correlate design parameters to performance of capacitors. Second, an electrochemical precipitation technique is developed to fabricate low-cost thin porous metal-oxide films that are shown to be suitable for capacitor applications. The third issue addressed here is the use of nickel hydroxide in thin-film. Although the material has good high power characteristics, two problems plague the system, namely (i) poor cycle life; and (ii) a greater energy needed for charging the electrode than can be extracted in the discharge. Insight into the former problem was obtained by tracking the changes in the structure of the material during electrochemical cycling by considering the material to be extensively defective (containing Ni vacancies) with exchange of protons, potassium ions and waters taking place between the material and the solution during charge/discharge. The latter problem ( i.e., the charging inefficiency) was found to be the result of a hysteresis (a lag in the dependent variable when the direction of the independent variable is changed). Theories that have been proposed for other systems (adsorption, magnetism) were used to analyze the phenomenon. Although the dissertation does not provide remedies to these problems, considerable insight into the issues that are encountered during the development of high power systems are provided.