Comparative capacity performance and electrochemical impedance spectroscopy of commercial AA alkaline primary cells

Alkaline primary cells are a relatively inexpensive source of portable power and there is still a significant demand for them due to their lower retail costs, good shelf life and good energy densities. There is a range of imported and local brands available in South Africa that can differ in terms of their cost to the consumer and their performance. The study being reported here compared a range of seven different AA alkaline brands in terms of price and performance by discharging them using three different standard tests, namely at constant 250 mA current, motor/toy and photo-flash respectively. The study also used electrochemical impedance spectroscopy (EIS) to observe differences between the different cell brands at different stages of discharge during the different discharge test sequences. The results showed that all cell brands achieved similar discharge capacities for the low-power discharge test of around 1.7 Ah at a constant current of 250 mA with significant differences in their respective purchase prices. However, significantly better discharge capacities of around 1.4 Ah were achieved for the more expensive brands for the photo-flash test when compared to the cheaper brand, where only 0.4 Ah was achieved. Hence, one can get value for money by using cheaper brand cells for typical low-power applications such as digital clocks, while the more expensive brands are recommended for high-power applications. The results of the EIS analysis showed that the internal cell resistance of the cheaper branded cells was relatively higher when compared to the more expensive branded cells. The change in the cheaper cells’ internal resistance was also comparatively higher when measured during the various stages of the discharge tests, especially during the photo-flash test. The EIS analysis also showed that certain new cells displayed an unusually high electrode capacitance and resistance when compared to the other cell types. This phenomenon then disappeared once the cells were slightly discharged to 1% of their respective capacities.

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