• Alkaline batteries

First commercializerd in 1950, these are similar to the Leclanche-type cells but make use of an improved (more conductive) electrolyte - aqueous KOH. This is lowers the internal cell resistance, and therefore allows higher discharge rates and power densities to be achieved. Alkaline batteries also use a high-surface-area Zn powder anode and a high grade MnO2 cathode, which also improve performance at high rate discharge. The electrolyte is usually gelled by addition of a cellulose derivative.

Alkaline batteries have similar theroretical energy densities and cell voltages to Leclanche cells, but give higher experimental values, especially under high rate use. They are, however, more expensive. Other, related, alkaline batteries use HgO or Ag2O as the active cathode material. These are far more expensive but can provide even higher energy densities. There are serious environmental concerns about use of many heavy metals (and Hg and Ag are highly toxic), especially in disposable primary batteries.

The reaction at positive(cathode) electrode is

MnO2(s) + H2O(l) + e- ----> MnO·OH(s) + OH-(aq)

The reaction at negative(anode) electrode is

Zn(s) + 2OH-(aq) ----> ZnO(s) + H2O(l) + e-

The total reaction is

2Zn(s) + 2MnO2(s) + H2O(l) -----> 2MnO·OH(s) + 2ZnO(s)