Reliability Evaluation of Primary Cells

Abstract

Evaluation of the reliability of a primary cell took place in three stages: 192 cells went through a slow-discharged test. A designed experiment was conducted on 144 cells; there were three factors in the experiment: Storage temperature (three levels), thermal shock (two levels) and date code (two levels). 16 cells experienced a cycled temperature and humidity environment. All tested cells showed acceptable performance. Results of the designed experiment showed the factor most affecting cell performance was the date code. A long- term capacity test on a sample of primary cells can provide information on their quality and reliability. The example shows a very tight capacity distribution. The cell employed a lithium anode. The capacity of many lithium-system is, by design, limited by the quantity of lithium in the anode. Controls on the quantity may permit the manufacturer to control, with considerable precision the capacity of the cells. From the designed experiment, we infer that the factor most affecting the performance of the cell is the time when it was made. Long term storage, perhaps up to 10 years, in a “normal” environment of 20°C will not appreciably affect it, nor will thermal shock or 2-way combinations of factors.