Antipolar mass

Some manufacturers add a small (10—20% of the positive loading) amount of cadmium to positive plates as an antipolar mass to prevent some of the problems of reversal in sealed cells. This practice may, however, create as many problems as it solves in that positive capacity is reduced proportionally to the quantity of antipolar mass added. 

In sealed cells, which are the most important kind of Ni-Cd batteries, the gas (H2 and O2) evolution accompanying discharge should be minimized. This can be achieved by incorporation of antipolar mass - cadmium hydroxide in the positive electrode. In this case overdischarge results in reduction of Cd(OH)2 to Cd, instead of hydrogen evolution [348]. On the other hand, oxygen evolved on the positive electrode during overcharging can react with cadmium [348] ... 

Protection against overdischarge is achieved by the incorporation of a quantity of cadmium hydroxide - known as the antipolar mass - in the positive electrode. Overdischarge then results in the formation of cadmium by reduction of the antipolar mass, rather than the evolution of hydrogen. Any oxygen evolved at the exhausted cadmium electrode will diffuse to the... 

Antipolar mass — Upon -> deep discharge of a - NiCd-accumulator gas evolution might occur with associated problems of overpressure inside the cell. Because of production tolerances the actual capacity of cells might... 

Antipolar mass — Figure. Top Operation at overcharge bottom operation at deep discharge and polarity reversal, path of oxygen movement needed for pressure limitation indicated... 

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