Studies of Zn|ZnX2|polyaniline batteries. I. X.=Cl and Br

The cycling behaviour of polyaniline in chloride and bromide media is discussed. In both media some charge, equivalent to a charge storage capacity of 100Ahkg -1, may be stored in the first oxidation step of polyaniline. Further evidence is presented that the oxidation product is emeraldine rather than the fully oxidized imine. In chloride media, attempts to store more charge led to rapid irreversible changes in the polymer and degradation in battery characteristics. In bromide media, further charge may be stored via the Br-/Brf couple and, although the Br: attacks the polymer slowly, the polymer retains the ability to cycle charge efficiently and gives a stable open-circuit voltage. The nature of the changes caused by Br2 attack on the polyaniline is discussed. It is concluded that bromide is the better electrolyte, but self discharge by slow exchange of Br3 in the polymer with Br- in the surrounding electrolyte remains an unsolved problem.