Effect of Overdischarge on German Solar Cells

Overdischarge refers to the discharge state of German sunlight battery when the deep discharge exceeds the termination voltage of the battery. The negative electrodes of sunlight batteries, which are often in this state of use, will sulphate and invalidate the batteries, whether they are liquid-rich or liquid-poor. In VRLA batteries, the probability of sulfation of negative electrodes is higher than that of ordinary lead-acid batteries.

In addition, VRLA batteries based on Pb-Ca alloy grid data and AGM separator and oxygen composite technology are liquid-poor design, and the amount of sulfuric acid electrolyte often plays a role in limiting capacity. In the overdischarge process, when H2SO4 in the electrolyte is depleted due to its participation in the discharge reaction, the solubility of PBSO4 as the discharge product increases greatly in the environment where the electrolyte is almost neutral or even weak alkaline. Data show that once H2SO4 is exhausted, when the electrolyte is neutral, the concentration of Pb2 + will rise by two orders of magnitude, and then the content of free Pb2 + in the electrolyte in the separator will increase by 100 times [2]. Usually in this situation, lead dendrite (plumb) short circuit is easily formed in the barrier and lead to battery failure. The mechanism is that the concentration of sulphuric acid will increase with the charging reaction, and lead SO4 will precipitate in the pore of the barrier, which will cause short-circuit immersion after being recovered to lead or oxidized to lead dioxide. It is worth mentioning that the positive grids of VRLA batteries placed in overdischarge for a long time may also exhibit abnormal corrosion. In a short time, the grids will be completely corroded.  On the other hand, overdischarge increases the internal resistance of the electrolyte, which makes the battery heated at the initial stage of overdischarge. In the process of over-discharge, the shrinkage of positive active material is obvious, and the irreversible "bulging" phenomenon will be formed when the battery is serious. The overdischarge of German solar cells is closely related to the way users use them.

In fact, overdischarge represents a tolerance ability of lead-acid batteries when they are abused. Because VRLA batteries are always used by overdischarge, it is necessary to improve and improve the overdischarge performance of VRLA batteries. Generally speaking, the over-discharge performance of lead-acid batteries includes two situations: (1) the durability of the battery to stop over-discharge repeatedly; (2) the rechargeable endurance ability of the battery after over-discharge placement. For a long time, there has been a lot of research on the effect of some additives in sulfuric acid electrolyte on the performance of lead-acid batteries at home and abroad. Because the use of electrolyte additives has the advantages of unchanged battery industry consumption process, low additional cost, good effect and easy implementation, the selection of appropriate electrolyte additives has become one of the main ways to improve the performance of lead-acid batteries. Some Japanese experts said that because of the reasonable electrolyte composition, even if VRLA batteries were repeatedly stopped for very deep overdischarge placement, the batteries were still stable, which could be said to have reached the level of no problem in practical application [5]. From the point of view of professional journals of power supply in China, there are few studies and reports on the over-discharge performance of VRLA batteries, which reflects that the over-discharge problem of German sunlight batteries has not attracted enough attention.