Effects of electrolyte stratification on performances of flood lead-acid batteries

The electrolyte stratification in the charge/ discharge of lead- acid cells was monitored by a sensor of H2SO4 specific gravity and an in situ electrochemical scan technique was used to measure the current distribution directly on the plates in the rest state. A simulated cell was set up to study the electrochemical behavior of lead- acid batteries with electrolyte stratification. The active mass (AM) in the lower part is discharged in preference to that in the upper part. During recharging, however, the AM in the upper part is more easily charged. The more concentrated the H2SO4 solution, the finer the formed AM becomes. Two mechanisms of sulfation have been proposed. For the batteries often at rest or in the discharge state at very low current, the sulfation occurs in the lower part of the plates, but for the batteries in continual cycles at a high current, it often appears in the upper part. (c) 2006 The Electrochemical Society.