Effects of Al- and Mn-contents in the negative MH alloy on the self-discharge and long-term storage properties of Ni/MH battery

Abstract

The charge retention and long-term storage properties of AB5-based Ni/MH batteries were studied by partial/complete replacements of Al- and Mn-contents by Ni in the AB5 alloys, separately. A high-temperature accelerated testing scheme (60°C and 60-days) was proven to be capable of predicting the status of batteries after long-term storages at room temperature (6-months and 293-days). Charge retention and impedance measured from the accelerated scheme can be correlated to the open-circuit voltage and impedance after long-term storage, respectively. While both Al and Mn were important to maintain good charge retention, Al, with its good oxidation resistance to slow down the oxidation/corrosion of the MH alloy, contributed to a lower internal impedance, Mn, on the other hand, slowed down the pulverization rate and reduced the irreversible capacity loss, however, contributed to a higher reversible capacity loss. The addition of Y2O3 in the positive electrode was found to raise the open-circuit voltage and reduce both reversible capacity loss and impedance increase during long period storage by slowing down the oxidation/corrosion of the MH alloy in the negative electrode.