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The potential of Mn2+/Mn3+ is approximately 1.5V, which is higher than the potential of Co2+/Co3+ approximately 1.82V). In this case, however, this potential exists on the lower side with respect to the actual potential (approximately 2V) at the time of occurrence of a side reaction on the positive electrode side such as generation of oxygen gas resulting from water decomposition or electrode oxidation as described above.
Co2+/Co3+: approximately 1.82V. Thus, this potential is higher than the potential of Mn2+/Mn3+.
When a divalent manganese ion (Mn2+) is contained, an oxidation reaction of Mn2+ is to first occur before occurrence of the side reaction on the positive electrode side such as generation of oxygen gas described.