Paterson, NJ 075 14, USA ABsTRAtrr Previous Intelec conferences have produced papers that have addressed the unique properties of this relatively new cell design. In this work we have attempted to review those previous articles critical to successful battery design, operation, testing, and performance. This paper's analysis starts with topics presented in the late eighties, i.e., the internal resistance-capacity relationship', and ends with the present day topic of noble metal catalysts'. The review spans approximately ten years and includes the following subjects:The relationship of internal resistance to capacity Temperature affects OR plate polarization Accelerated aging life tests Premature end of life * Field Failure Modes * Use of a catalyst "ALRE"CEThe intense interest in internal resistance (R) is based on the ability of this measurement to determine the capacity 0 ofthe W A cell. To accomplish this goal it is required that:The lass in cell capacity must be due to only increased cell inkma1 resistance Discharge curves (voltage versus time) must vary with age according to a predictable mathematical relationship For example, given a nonnaCIinear relationship between (R) and(C),the family of discharge curves associated with the aging cell process must be parallel, as shown in figure I. (Obviously the R-C relationship can be other than normal-linear, e.g., log-linear.) The accuracy at which (R) estimates capacity is then dependent an the degree of parallelism between the discharge curves.There are a number of variables that can impact on the ability and limits of the R-C calibration curve to estimate capacity. The cell resistancecapacity relationship studied in this paper is for a multi-cell module having only two terminal posts avallabfe for measurements. 8 j 1.86 l.?5 1.65 0 1 2 3 4 6 T I M E Figure 1Intelec conference papers and VRLA standards suggest a capacity test discharge be performed when the cell internal resistance increases by 20%3. For the multi-cell modulqwitbtwo terminalposts,thisUmltmayaeed to be drsmatically decreased to detect one errant cell in electrical series with cells of good internal resistance. However, at this lower limit, the sensitivity of the It-C may not be adequate to auomplish the desired accuracy.The change in resistance of the multi-cell module is obviously dependent on how uniform the aging is from cell to cell. The R-C relationship can be empioyed to determine the uniformity of cell aging in a multi-csll module. For example, when the resistance of onecell ofa six-call battery increases by 20%, the total battery resistance rise is only 3.3% (for this worst case scenario).The,sensitivity (slope) of the R-C curve may not be suficient to relate such small resistance changes to accurate estimates of capacity. The best case scenario is when all cells in the moduie age at a similar rate. In this case, the resistance of each cell in a 12-voIt module 0-7803-5924-01001$~0.00 Q2000 IEEE.-309
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