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BATTERY THEORY - VRLA
The generation of gases in aqueous electrochemical cells is a fact of life that must be accommodated in their design. Overcharging of lead / acid cells gives rise to substantial amounts of gases from the electrolysis of water. Methods employed to reduce gassing have included the use of voltage-sensing over-charge limiting controls, catalytic recombination of hydrogen and oxygen, and now sealed operation is based on the chemical reaction of hydrogen and oxygen, which produces water. In a traditional flooded lead / acid battery, water is electrolysed on overcharge liberating oxygen at the positive plate and hydrogen at the negative plate. In order to prevent the battery from drying out, this water loss must be replaced on a regular maintenance schedule.
In a sealed immobilized electrolyte cell, the stoichiometry of active materials is arranged such that the positive plate becomes fully charged before the negative, and oxygen is liberated which diffuses to the negative plate where it reacts with lead to form lead oxide. The lead oxide then reacts with the sulphuric acid electrolyte to form lead sulphate and water, completely eliminating water loss.
Traditional Flooded Cell
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