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  • 1
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    Impedance studies of nickel/cadmium and nickel/hydrogen cells using the cell case as a reference electrode (1990)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: Impedance measurements have been made on several Ni/Cd and Ni/H2 flight-weight cells using the case as a reference electrode. For these measurements, the voltage of the case with respect to the anode or cathode is unimportant provided that it remains stable during the measurement of the impedance. In the cells measured so far, the voltage of the cell cases with respect to the individual electrodes differ from cell to cell, even at the same overall cell voltage, but they remain stable with time. The measurements can thus be used to separate the cell impedance into the contributions of each electrode, allowing improved diagnosis of cell problems.
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: Journal of Power Sources (ISSN 0378-7753); 29; 467-476
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  • 2
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    Impedance studies of Ni/Cd and Ni/H2 cells using the cell case as a reference electrode (1989)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Impedance measurements have been made on several Ni/Cd and Ni/H2 flightweight cells using the case as a reference electrode. For these measurements the voltage of the case with respect to the anode or cathode is unimportant provided that it remains stable during the measurement of the impedance. In the cells measured so far, the voltages of the cell cases with respect to the individual electrodes differ from cell to cell even at the same overall cell voltage, but they remains stable with time. The measurements can thus be used to separate the cell impedance into the contributions of each electrode, allowing improved diagnosis of cell problems.
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: Space Electrochemical Research and Technology (SERT), 1989; p 197-209
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  • 3
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    Impedances of nickel electrodes cycled in various KOH concentrations (1991)
    In:  CASI
    Details
    Publication Date: 2013-08-29
    Description: Recent tests at Hughes have shown that Ni/H2 cells cycled in 26 percent KOH have much longer lives than those cycled in other concentrations. As part of an ongoing program to try to correlate the impedances of nickel electrodes with their life and performance, impedances were measured of a number of electrodes from these tests that had been cycled in concentrations from 21 to 36 percent KOH. These had ranged from about 1000 to 40,000 cycles. After cycling ten times to reduce possible changes due to storage, impedances were measured at five voltages corresponding to low states of charge. The results were analyzed using a standard circuit model including Warburg impedance term. Lower kinetic resistances and Warburg slopes were found for several electrodes which had been cycled in 26 percent KOH even though they had been cycled for a much longer time than the others. Interpretation of the data is complicated by the fact that the cycle lives, storage times, and failure mechanisms varied. Several other circuit models have also been examined, but the best correlations with life were found with parameters obtained from the simple model.
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: Space Electrochemical Research and Technology; p 89-100
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  • 4
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    Impedance measurements on a spiral-wound nickel/metal hydride cell cycled in a simulated Leo orbit (1993)
    In:  CASI
    Details
    Publication Date: 2016-05-14
    Description: A spiral-wound size C cell was cycled at 25 C in a low earth orbit (LEO) regime at 50 percent depth of discharge (DOD) with approximately five percent over-charge. The nominal capacity was 3.5 AH. The cell was cycled for 2000 cycles. Capacity checks and impedance measurements over the complete range of state of charge were made upon receipt and after 500, 1000, and 2000 cycles. The capacity of the cell was essentially unchanged until after the impedance measurements at 2000 cycles. Only small changes in the impedance parameters were observed, but there was somewhat more scatter in the data after 2000 cycles. When the cell was returned to LEO cycling after 2000 cycles, only 38 percent of the capacity could be obtained. It is believed that the cell failed because of an equipment failure at the end of the final impedance measurements which allowed an over-discharge.
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: Space Electrochemical Research and Technology; p 97-108
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  • 5
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    Raman spectral observation of a new phase observed in nickel electrodes cycled to failure (1991)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A new phase is reported in nickel electrodes from Ni/H2 boilerplate cells which were cycled to failure in electrolyte of variable KOH concentration (21 to 36 percent). Raman spectra clearly show the presence of this phase, and these spectra have been used to estimate the amounts present on these electrodes. Ten of 12 electrodes examined contain this new phase. The cycle life at higher KOH concentrations (31 and 36 percent) was greatly reduced, and nickel electrodes from these cells exhibited extensive amounts of this new phase. The presence of this new phase correlates with cell failure defined by low end of discharge voltages. It is proposed that the lowered capacity and failure of these electrodes was caused by loss of active mass and formation of a phase with reduced electrochemical activity. These results indicate that formation of the new phase is accelerated at higher KOH concentrations.
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: Space Electrochemical Research and Technology; p 81-87
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  • 6
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    Impedances of Li/SO2 cells retrieved from the Long Duration Exposure Facility (LDEF satellite) and comparison with cells stored terrestrially (1991)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Impedances were measured on several Li/SO2 cells retrieved from the Long Duration Exposure Facility (LDEF) satellite. These cells were used to power instruments and recorders and had all been partially or fully discharged. Impedances were also measured on several cells that were stored in cold storage since manufacture. Unfortunately, none of the cells stored terrestrially had undergone any discharge, whereas all of the cells on the satellite were at least partially discharged early in the mission and then remained on orbit for about 5 years further. It has been observed by others that storage of an Li/SO2 cell after partial discharge, increases the resistance and thickness of the passive film on the Li electrode, as indicated by an increase in the time for recovery of voltage when a load is applied (voltage lag), or in some cases by an inability of a cell to sustain a normal current after such storage. Since the cells stored terrestrially were not discharged in the same manner as the LDEF cells, a direct comparison cannot be made. Thus, the effects of the space environment cannot be separated from the effects of storage after partial discharge. It is believed that the increases in impedance in the LDEF cells are largely due to the storage upon partial discharge rather than the effects of the space environment.
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: NASA-TM-104526 , E-6400 , NAS 1.15:104526
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  • 7
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    Impedances of electrochemically impregnated nickel electrodes as functions of potential, KOH concentration, and impregnation method (1989)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Impedances of fifteen electrodes form each of the four U.S. manufactures were measured at 0.200 V vs. the Hg/HgO reference electrode. This corresponds to a voltage of 1.145 for a Ni/H2 cell. Measurements were also made of a representative sample of these at 0.44 V. At the higher voltage, the impedances were small and very similar, but at the lower voltage there were major differences between manufacturers. Electrodes from the same manufacturers showed only small differences. The impedances of electrodes from two manufacturers were considerably different in 26 percent KOH from those in 31 percent KOH. These preliminary results seen to correlate with the limited data from earlier life testing of cells from these manufacturers. The impedances of cells being tested for Space Station Freedom are being followed, and more impendance measurements of electrodes are being performed as functions of manufacturer, voltage, electrolyte concentration, and cycle history in hopes of finding better correlations of impedance with life.
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: NASA-TM-103283 , E-5738 , NAS 1.15:103283 , International Symposium on Electrochemical Impedance Spectroscopy; May 22, 1989 - May 26, 1989; Bombannes; France
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  • 8
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    Changes in impedance of Ni electrodes upon standing and cycling (1989)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Impedances of Ni electrodes vary with many factors including voltage, cycling, and manufacturer. However, results from Ni/H2 cells being tested for Space Station Freedom show that consistent results are obtained within a group of cells from the same manufacturer if the cells are cycled and stored in the same manner. Impedance changes with storage and cycling are being investigated. Impedances are low in the fully charged state but rise abruptly by several orders of magnitude at a voltage corresponding to a very low state-of-charge. After standing for several months, this increase occurred at a higher voltage, consistent with an increase in structural order during storage which hinders diffusion of protons and reduces high rate capacity. Early measurements on the effects of cycling on Ni/H2 cells being tested for Space Station Freedom show differences between cells from different manufacturers.
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: NASA-TM-102438 , E-5207 , NAS 1.15:102438 , 1989 Fall Meeting of the Electrochemical Society; Oct 15, 1989 - Oct 20, 1989; Hollywood, FL; United States
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  • 9
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    Changes in impedance of Ni/Cd cells with voltage and cycle life (1992)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Impedances of aerospace design Super Ni/Cd cells are being measured as functions of voltage and number of cycles. The cells have been cycled over 4400 cycles to date. Analysis of the impedance data has been made using a number of equivalent circuits. The model giving the best fit over the whole range of voltage has a parallel circuit of a kinetic resistance and a constant phase element in series with the ohmic resistance. The values for the circuit elements have been treated as empirical parameters, and no attempt has been made as yet to correlate them with physical and chemical changes in the electrode. No significant changes have been seen as yet with the exception of a decrease in kinetic resistance at low states of charge in the first 500 cycles.
    Keywords: ENERGY PRODUCTION AND CONVERSION
    Type: NASA-TM-106105 , E-7688 , NAS 1.15:106105 , International Symposium on Electrochemical Impedance Spectroscopy; Jul 12, 1992 - Jul 17, 1992; Santa Barbara, CA; United States
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