You could be wondering what this means. Worry not because the definition is right down below.
A battery has cycles of charging and discharging. During these cycles sulfuric acid forms crystals with lead. These formed crystals do not mix well with water and they settle at the bottom of the battery. This is what we call battery stratification.
We have mentioned in our previous articles on this website that lead-acid batteries have an electrolyte that is made up of 65% water and 35% sulfuric acid. It is in this electrolyte that electrochemical reactions take place.
Battery acid has a density of around 1.8 g/cm3 while water has a density of 1gm/cm3. When you compare the two you find that acid is denser than water and therefore will settle at the bottom of the battery.
As time goes by, the concentrated sulfuric acid that settles at the bottom of the battery will start corroding the plates of the battery and therefore causing permanent battery damage.
Causes of Battery Stratification
The lead and lead dioxide electrodes react with sulfur in the electrolyte to form lead sulfate (PbSO4). This happens during discharge. The lead sulfate is broken down into lead and lead dioxide during charging.
The sulfur ions then recombine with water in the electrolyte to have the electrolyte formed. Some of the lead sulfates form crystal structures that are hard to break and even the introduction of charging current cannot have them broken.
These crystals will stick to the electrodes and lead to the formation of an insulating layer around the electrodes which in turn affects the capacity of the battery.
Some factors enhance the sulfation of the battery and they include:
- High acid concentrations
- High battery temperatures
- Deep discharging of the battery
- Storing of the battery when not charged to capacity
We can now look at some of the effects of battery stratification
Reduced Battery Capacity
The plate material and sulfur ions in the electrolyte are reduced when lead sulfide crystals form. This implies that there will be fewer active materials inside the battery to participate in the electrochemical reactions. This equally leads to a battery with reduced capacity to store charge.
Reduction in Battery Power
When the lead sulfate crystals form on the surface of the electrodes, they form an insulating layer that hinders the battery from providing the required power.
This means the cold cranking amps (CCA) of the battery will reduce way below the battery rating. This implies that the battery will not be able to provide sufficient power needed to have the engine cranked.
Sludge Formation
The lead sulfate crystals that are formed are soft and will probably not stick to the plates and electrodes for a long period. They will fall off from a sludge which will settle at the bottom of the battery. This sludge will damage the plates of the battery and eventually reduce the capacity of the battery.
How is Battery Stratification prevented?
Battery stratification can be prevented by doing routine battery maintenance regularly. Some of these maintenance practices are very easy and will not cost you any coin.
Let us have a look at them down below:
Avoid Storing a Discharged Battery
When the battery is not fully charged, the lead sulfate crystals form. More sulfur reacts with lead to form lead sulfate when the battery has a low charge.
As the battery stays discharged, the lead sulfate molecules combine to have complex crystals formed and these molecules will be hard to break. You can avoid this situation by making sure that the battery is fully charged before storage.
When the battery is in a fully charged state, it has only the lead and lead oxide electrodes and it will take long for lead to have a reaction with sulfur in the acid when we have no load connected to the battery.
When you are going to store a battery for a long without use, you can have a float charger connected.
Regulate Battery Temperature
Chemical reactions inside the battery are affected by temperature. When temperatures are high, the reactions also take place faster. The rate of self-discharge also increases when temperatures are high even when the battery is not discharged.
This means that more lead sulfites will be formed in the shortest period. Lead sulfates will be formed when the molecules combine.
Ensure the Concentration of Battery Acid is Right
There will be more free sulfur ions to react with lead to form lead sulfate when the battery acid is more concentrated than it is required. This implies that when the levels of free sulfur ions are high, the sulfation process is enhanced and the life of the battery will be shortened.
Use a Slow Charger
When the battery is charged slowly, there will be ample time to have the lead sulfate molecules broken down. Fast charging on the other hand will leave much of the sulfates unbroken and eventually crystals will be formed.
The battery should be charged for at least 10-12 hours. While at it, be very careful so that you don’t end up with an overcharged battery. Battery overcharging comes with its challenges.
You can also use a smart charger that is capable of regulating the charge current so that the battery is not overcharged.
Monitor the Electrolyte Levels
As we have mentioned previously, as the battery charges, water breaks down into oxygen and hydrogen gas which means a certain percentage of water is lost which means the electrolyte level drops. In this case, the electrolyte is left in a more concentrated state and that will trigger sulfation.
Always ensure that you maintain the right battery acid levels
When the electrolyte level drops and the lead plates are exposed, they will sulfate and oxidize easily because of the presence of air.
Attach Battery Tender or Float Charger to the Battery
A battery tender or float charger ensures that the battery is kept at full charge by providing it with a float charge. You can do this when you are going to store a battery for a long without use or when driving a car for short distances and switching it off.
When driving for short distances and switching off the engine, the alternator will not have the required time to have your battery fully recharged. In such a case a battery tender sorts you out to ensure the full charge is restored when the engine is off.
Conclusion
The leading cause of death in lead-acid batteries is sulfation. As batteries become old, they naturally suffer sulfation. However, with proper maintenance practices, the sulfation process can be delayed and the battery life will be extended.