Positive plate corrosion occurs mainly when the battery is being charged, especially towards the end of the charge cycle when the battery voltage is high. It is a slow but continuous process that takes place when a battery is floating. Oxidation increases the internal resistance and eventually causes the disintegration of the positive plate.
Lead corrosion
The high electrical potential of the positive electrode leads to irreversible corrosion of the lead, reducing the effective section of the conductive material and increasing the electrical resistance. To solve this problem, the use of thicker lead plates helps to reduce the effect of corrosion.
Sulfation
Sulphation occurs when lead sulphate crystals form on the lead plates, reducing the current within the electrolyte. When batteries are at rest without being charged, they begin to sulfate. The longer the battery is left unused, and if we add to this an increase in discharge, the worse the sulphation effect will be. In some cases, there will even be no turning back. To avoid this, pulse or slow charge chargers are often used. Sulphation could cause the active matter in the lead plates to break and fall to the bottom of the cells, which will cause a short circuit, resulting in battery failure.
Shedding
Shedding is a degrading phenomenon in which the active matter of the electrodes breaks off and eventually falls to the bottom of the battery. This is produced by the corrosion of the sulfuric acid stored inside the battery. This corrosion makes the battery increase its volume and makes the internal container swell and even break it, it also causes it to end up losing its water tightness due to the consequent sulphation of the connectors by the leakage of the acid.
A battery suffers the effects of the internal corrosion produced by the sulfuric acid (softening and shedding). This corrosion causes the battery to increase in volume internally, in some cases breaking the plastic container or swelling and losing its water tightness with the consequent sulphation of the connectors due to acid leakage.
Active material adhesion
When the battery is operating in low states of charge for long periods or is operating in very deep discharge cycles, the active matter loses adherence and is detached from the plates. In addition, very violent gassing can cause active matter to be released from the plates.
In all cases, the active matter released tends to settle at the bottom of the vessels, producing an irreversible loss of capacity. These deposits have a bright metallic color. In extreme cases the deposit at the bottom of the vessel can be so large that it produces a short circuit between plates causing the death of the battery.
Considering all the above, it is always essential to choose batteries for high quality solar panels, otherwise the profitability and durability of a photovoltaic project is condemned to failure.
Stratification of the electrolyte
The stratification of the electrolyte is due to the difference in density, the (heavier) acid tends to decant to the bottom of the battery, creating areas of concentrated acid. These zones create a point imbalance that accelerates the wear and corrosion of the battery. The deposited acid deposits leave areas of plate that are not covered by the electrolyte used for the reaction, reducing the capacity of the battery.