Impedances of nickel electrodes cycled in various KOH concentrations

✍ Scribed by Margaret A. Reid; Patricia L. Loyselle

• Publisher: Elsevier Science
• Year: 1991
• Tongue: English
• Weight: 796 KB
• Volume: 36
• Category: Article
• ISSN: 0378-7753
• DOI: 10.1016/0378-7753(91)87008-y

✦ Synopsis

Recent work has shown that NCHP cells cycled in 26% 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% KOH. These had been cycled under double-time LEO conditions at 80% DOD to failure. Cell life 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 a Warburg impedance term. Lower kinetic resistances and Warburg slopes were found for several electrodes which had been cycled in 26% 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.