The first batteries were vertical piles of metal discs, with material between them soaked in fluid electrolyte. That liquid soon dried away, and so another pioneer laid the piles horizontally in a leak-proof box filled with electrolyte. The first of the two basic lead-acid battery designs followed the same principles. It continues to be popular because it is the cheapest option available. However …
Flaws in Flooded Lead-Acid Batteries
The original lead battery design that is still on the market, has vertical plates standing in electrolyte. This flooded battery design is flawed though, because the water in the electrolyte evaporates. The user has to monitor this loss, and replace the evaporated water to maintain battery efficiency and avoid damage.
If the user does not perform this maintenance periodically, then the acid concentration in the electrolyte may become too intense. This can in turn gradually coat the plates, and shorten the operating life of the flooded lead-acid battery.
However, there are still more deficiencies in the design we would like to share. The battery case must remain vertical, to maintain the liquid electrolyte level, and provide space for vents to release hydrogen and oxygen gases. If the case leaks after physical damage, the electrolyte flows away condemning the battery.
The Second Type of Lead-Acid Batteries
The second of the two basic lead-acid battery types, is sealed inside a case within which the electrolyte is stabilized in one of two ways:
- The liquid electrolyte forms into gel after addition of porous silica particles.
- The electrolyte immobilizes inside a silica-fiber-based glass mat mesh.
This method prevents the water in the electrolyte evaporating, and the need for periodic inspection and maintenance. However, the issue of hydrogen and oxygen gassing remains, and this is potentially more important because this happens inside a sealed case.
To resolve this issue, the oxygen recombines at the negative electrode, while the water reduces at the positive electrode, forming hydrogen gas. The lead Pb at the negative electrode reacts with the absorbed oxygen, forming lead sulfate during the reaction, which subsequently reduces back to metallic lead.
The oxygen is freely able to travel between the plates, thanks to the electrolyte being either porous silica particles, or a non-woven silica fiber mat. The amount of hydrogen is relatively low. This releases naturally through vents in the valve-regulated battery.
More Information
Gel Lead-Acid Batteries And Solar Panels
Lead Battery Sulfation and How To Manage It
