Nickel-Hydrogen Life Cycle Testing: Review and Analysis
LAWRENCE H. THALLER AND ALBERT H. ZIMMERMAN
The review and analyses reported here are the outcomes of a project carried out from 1998 to 2001 within the Energy Technology Department of The Aerospace Corporation to examine and interpret the results of different nickel-hydrogen life testing programs that had been or were being carried out for low Earth orbit (LEO) applications. The cycling programs, some of which are still in progress, were conducted under different sponsorships and carried out at different testing facilities.
The original intent of this project was to critically review the results of the cycling tests in light of the static and dynamic modeling capabilities within the Energy Technology Department. As the cells or cell components from these cycling programs became available, they were provided for posttest analytical studies in our Aerospace laboratory. The results of the posttest studies helped to form relationships between external voltage and pressure signatures available from testing programs and the subsequent findings related to the capacity loss mechanisms found from these studies. The ultimate goal of this project was to be able to suggest cell designs and recharge schemes that would be compatible with extended cycling durations at deeper DODs.
In addition to the department’s modeling capabilities, the staff’s in-depth understanding of the fundamental aspects of the nickel electrode provided valuable insight for our analyses. When results became available, the information was originally distributed to individuals who had an interest in reducing the weight of power systems for future LEO applications. The information was prepared as a newsletter approximately once a month over a 3-year period. In this book, these newsletters have been reviewed and updated in light of new developments and insights gained during the multiyear study.
It appears from the review to date of the different segments of the cycling programs made available to us that the potential usable energy density of nickel-hydrogen cells is being underestimated, and deeper depths of charge could be used, within certain limitations, for missions where battery weights are critical.
Besides the results of our DPA studies, techniques that have been found to be useful in the design, storage, and management of nickel-hydrogen cells and batteries are outlined for possible use by others. Studies carried out by researchers in other laboratories were helpful in our fuller understanding of the many subtle factors involved in the cycling of nickel-hydrogen cells, and they are included in the discussions and analyses. A brief overview of generic nickel-hydrogen individual pressure vessel cell designs is included to introduce the reader to some of the important aspects of this cell technology.
The authors have had more than twenty years of experience each in different areas of nickel-hydrogen technology. Their studies have included basic cell design, the chemistry and physics of nickel electrodes, life cycle modeling, cell performance modeling, electroanalytical studies, destructive physical analyses of the nickel hydrogen cells, and the interaction between cell operating parameters and cell degradation mechanisms. Well over a hundred reports, journal articles, conference presentations, user manuals, and handbooks have resulted from their efforts. Their writings have gained them both national and international recognition as experts in the area of nickel-hydrogen technology. Dr. Thaller, now retired, served as department manager in the area of energy storage at NASA GRC as well as at The Aerospace Corporation. Dr. Zimmerman serves as a distinguished staff scientist with a major emphasis on the fundamental understanding of the chemistry and electrochemistry of the nickel electrode as it relates to improved cell performance.