EFFECT OF HYDROGEN AND OXYGEN ON STABILITY OF EXPANDERS AND PERFORMANCE OF LEAD-ACID-BATTERIES

Expanders are organic additives to the negative active mass that increase plate capacity, especially at low temperatures. They operate under constant hydrogen and oxygen attack at strongly negative potentials as a result of which they undergo degradation. This leads to changes in plate capacity, which may limit the life of the battery. The aims of the present work are: (i) to suggest a method for determining the effect of hydrogen, oxygen and the potential on the stability of expanders; (ii) to identify some of the structural groups in organic compounds that exert an efficient expander action. The influence of Velex, Mimosa, Quebraco, Syntan NK (SNK) and EZE-Skitan on the electrochemical characteristics and the life of negative battery plates has been investigated. It is established that structural groups of the pyrocatechin type (Quebraco and EZE-Skitan) have effective expander action. Quebraco increases the plate capacity during the first cycles. EZE-Skitan increases the capacity of the plates after 50 to 60 charge/discharge cycles, when disintegration of its structure, probably to pyrocatechin groups, proceeds. By applying a new method for determining the expander stability, it is found that expanders containing pyrocatechin structural groups are more easily oxidized than hydrogenated. It is concluded that the most effective expander should be a combination of several compounds with different stabilities to oxidation and reduction. Appropriate expanders should be selected for each type of battery.