Abstract
A major cause of failure of a lead acid battery (LAB) is sulfation, i.e. accumulation of lead sulfate in the electrodes over repeated recharging cycles. Charging converts lead sulfate formed during discharge into active materials by reduction of Pb2+ ions. If this is controlled by mass transfer of the ions to the electrochemically active area, charging voltage can far exceed the OCV of a charged battery. Then, charge is partly consumed to electrolyse water, and for evolution of hydrogen and oxygen. It causes sulfation since regeneration of active materials will be incomplete. A mathematical model is developed incorporating resistance to mass transfer of Pb2+ ions into the rate of charge transfer reactions, changes in areas of active materials and sulfate particles, and dependence of electrodes’ resistance on content of lead sulfate. It was used to show that this mechanism of sulfation does lead to failure of flooded LABs because of increased resistance of electrodes, and to predict cycle life. Capacity fade, and increased cycle life when recharging protocol uses lower DoD are other features of degradation which the model predicts. The model also predicts the observed increase in cycle life when conducting additives are added to the negative electrode.
Highlights
As complete conversion of lead sulfate into active material is approached during the charging step, resistance to mass transfer of lead ions to active area becomes significant, and overpotential increases to such an extent that charge consuming hydrogen and oxygen evolution reactions due to water splitting begin to occur to a significant extent
This leads to incomplete conversion lead sulfate of to active materials, and its accumulation over repeated recharging cycles
When volume fraction of lead sulfate in any part of the electrode attains a critical level dictated by percolation theory, that portion of the electrode turns electronically insulating, and electrochemically inactive
Summary
Modeling of Sulfation in a Flooded Lead-Acid Battery and Prediction of its Cycle Life. Soc. 167 013538 View the article online for updates and enhancements. This content was downloaded from IP address 14.139.128.22 on 18/06/2020 at 07:13. This Paper is part of the JES Focus Issue on Mathematical Modeling of Electrochemical Systems at Multiple Scales in Honor of Richard Alkire. Subscripts indicate other areas per unit volume. Diffusivity of acid in water, cm[2] s−1. Subscripts indicate aqueous diffusivity for other species. Factor reflecting resistance to diffusion dc Critical volume fraction in percolation model. Applied current density in the cell, A cm−2 io Exchange current density of electrodes, A cm−2 Note they have different values in the positive and the negative.
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