How to deal with lead - acid battery sulfation

Publish: 2017-06-29  Views: 110

Lead-acid batteries as a chemical power in the field of energy has been the first position continues to date, indicating that there are unparalleled advantages exist. But also has its worthy of attention, that is, most of the battery work can not meet the needs of today's advanced technology and equipment. According to common sense, lead-acid battery active material can be maintained for 8 - 10 years or longer, but in fact most cases can not reach the expected use of time. The actual life of the battery is 6 - 48 months, and can use 48 months of battery only 30%. Most of the battery is in advance capacity attenuation and failure. One of the main reasons for the life of lead-acid batteries is the accumulation of sulphates, which is sulfate, that is, the formation of white hard lead sulfate crystals on the plates, and it is very difficult to convert lead to the active substances, "Sulfate". Simply put, is the lead-acid battery plate is covered with lead sulfate crystals, resulting in decreased battery capacity or functional decline. The reason for the generation of this lead sulfate is the overdischarge or discharge after long-term placement, the lead sulfate particles dissolved in the electrolyte, was saturated, these lead sulfate in the low temperature when the re-crystallization, that is, lead sulfate precipitation. This time in the precipitation of lead sulfate particles again and again due to temperature changes and growth, development, so that the crystal grain increases. This lead sulfate conductivity is poor, resistance, solubility and dissolution rate is very small, difficult to recover when charging. Thus reducing the capacity and life shortening reasons.

From the molecular chemical structure analysis, crystallization generally refers to the formation of molecules and water into a new hydrated crystal, which molecules form molecules with water molecules. At this time, there must be extra energy, first break the molecular chain of molecules and water molecules, and then to allow this molecule and other molecules involved in chemical reactions. In addition the crystal has a common, is easy to adsorb the same molecules, the formation of more crystals. Lead-acid battery lead sulfate crystals are generally due to incomplete charging, we generally believe that the charging voltage to reach the battery voltage of 1.25 times, (12V battery to be 15V charge voltage), in order to make the negative plate active material recovery. If the charging voltage can not reach this standard, there will be some lead sulfate molecules are not converted, and thus gradually with the electrolyte in the water molecules to form crystals. With the passage of time, the formation of crystals will be more and more, eventually leading to battery decline. Therefore, we can say: First of all, the battery sulphate all the time to produce. Second, the battery produces sulfated, because of its irreversibility, must be the use of external energy to break down in order to restore the original state of the battery.

2 lead acid battery after the main performance of sulfate

Lead acid batteries after sulfite is the most obvious feature of the battery capacity decreased, increased internal resistance. Of course, these characteristics are also present if the battery is dehydrated and the positive plate is softened. To determine whether the battery because of the decline in capacity due to sulfation, often using a variety of repair methods for battery capacity recovery, if the capacity is significantly increased, that is, sulfation, if the battery capacity is not obvious changes in battery capacity may be caused by other reasons The

Lead-acid battery sulphation specific features are as follows:

① Charging bubbles appear earlier, the electrolyte density can not meet the required standards.

② charge the electrolyte temperature than the plate is not sulfated lead-acid batteries.

③ When the discharge is used or the battery capacity test is carried out, the terminal voltage drops faster. The electrolyte density drops below normal.

④ capacity significantly reduced.

⑤ plate color is not normal, the cathode was light brown (some white), the negative into gray, positive and negative plate surface hardened as sand.

3 reasons for the sulphation of lead acid batteries

It is generally believed that the irreversible sulphation of the lead-acid battery is due to the recrystallization of lead sulfate, which reduces the solubility after the formation of coarse crystals.

It is unavoidable to produce sulfation in the following cases:

① The battery has been shelved for a long time before installation. In fact, once the battery with sulfuric acid solution began after the chemical reaction and produce salt. Therefore, the new battery shelved for too long will be due to sulfate and failure.

② continuous over discharge or regular overdischarge or small current deep discharge, will be in the depths of the plate to generate more lead sulfate.

③ discharge, 24 hours without the timely replenishment of the charge.

④ can not be regularly overcharged or often lack of charge, in the active substance more or less part of the failure to restore the lead sulfate.

⑤ in the case of insufficient charge, the battery current work, will increase the battery sulphation.

⑥ ambient temperature is too high or too low on the battery performance have an impact. For example, when the temperature heats up, with the temperature increase of 10 degrees, salinization rate of 2 times the growth. During the charging period, if the outside temperature is high, when the temperature of the battery reaches 75 degrees, the internal resistance will increase, resulting in insufficient charge situation. In general, when the charge is 100%, the specific gravity of the electrolyte is about 1.27, when the solidification temperature of the electrolyte is minus 83 degrees Fahrenheit; when the specific gravity is about 1.2, the solidification temperature is minus 17 degrees Fahrenheit; if the specific gravity is 1.14 Also known as complete discharge), then only 8 degrees Fahrenheit.

⑦ lack of electrolyte. Due to excessive evaporation of water or electrolyte accidental leakage and no timely replenishment, resulting in the liquid level is too low, the upper part of the plate long exposed liquid, causing the upper plate sulphate plate.

4 battery sulphate hazards

The normal lead-acid battery is formed when the lead sulfate is discharged, and is easily converted to lead and lead oxide when charged. If the battery is used and poorly maintained, such as frequent overcharging or overdischarge, the negative electrode will gradually form a thick and hard lead sulfate. This lead sulfate is difficult to restore by conventional methods, requiring a high charging voltage, and a large amount of precipitated gas due to poor charging capacity during charging. This phenomenon usually occurs at the negative, known as irreversible sulfation. It causes the battery capacity to decline, and even become the reason for the termination of battery life. Slightly battery sulphate, will reduce the battery capacity, battery resistance increases, the serious failure of the electrode, charge into the power. Slightly battery sulphate, can still be used to restore it in some way, when the general use of the general charging method is not able to restore capacity.

Sulfate is an inevitable process of energy conversion process, but the formation of sulfate crystals is indeed a serious problem, the battery sulphide hazards are as follows:

① plate bending: the board somewhere there is a lack of crystallization of sulfate crystals to accept, causing the battery plate somewhere overcharge, and this overcharge so that the temperature here, so that the plate bent. Salinization causes the reactants on the grating of the plate to fall off, resulting in overcharging and plate bending.

② short circuit: due to salt to increase the internal resistance, plate bending, contact with another polar plate and short circuit or damage to the support plate of the frame.

③ off the active material: salt crystallization of the internal resistance increases, resulting in local overcharge, resulting in plate cracks and cracks off the material.

5 lead acid battery sulfite common application areas

Lead-acid battery application is very extensive, many applications. In general, the use of floating batteries used in the charging environment and conditions are more superior, the battery under normal circumstances, will not continue over discharge, long-term lack of charge in the state is rare, so the use of these conditions lead-acid batteries It is not easy to produce sulfation. The mobile use of the battery is very easy to produce sulfation, mainly due to the mobile use of the battery work, due to environmental conditions, in most cases can not get timely charging, and even often can not be filled, long-term loss, Discharge occurs, the passage of time, the crystallization of sulfate will produce, and continue to grow, so that the battery sulphate, therefore, mobile conditions used in the battery should pay more attention to prevent the occurrence and timely elimination of sulfation.

Treatment of Sulfate after Lead Acid Battery

Once the battery sulphate, if the timely treatment can still be restored. There are a variety of ways to eliminate the sulfation of the battery.

6.1 hydrotherapy

If the sulfate is not too serious, you can use the more dilute electrolyte, the density of 1.100g / cm3 below, that is, to the battery diluted with water to improve the solubility of lead sulfate. And the current below 20h rate, in the liquid temperature range of 30 ℃ ~ 40 ℃ for a long time charging, may be able to recover. If the electrolyte density is high, then only when the water decomposition, active material is difficult to restore.

6.2 Adjust the electrohydraulic charge activation method according to the degree of sulfation

Repair of the essence of sulphate is to make white hard lead sulfate crystals, softening and dissolving, enhance the internal resistance of the plate within the reversible chemical reaction ability to restore good performance.

6.2.1 Moderate, moderate sulphation can be repaired by the following methods:

① first lead-acid battery charging, followed by a 10 to 20 hours rate of current discharge, for the 6V battery into the 5.4V, for 12V to 10.8V.

② pour the electrolyte, replaced by the density of 1.04 ~ 1.06g / cm3 electrolyte, with 20h or less current charging more than 20 hours, until the electrolyte density is no longer so far.

③ with the standard electrolyte, according to the normal charge method to fully charge.

④ test the battery capacity, such as to achieve the nominal capacity of more than 80%, said the repair is successful; if not, then by severe sulphate repair treatment.

6.2.2 severe sulphate repair, generally available under the law:

① with 10% sodium sulfate aqueous solution or 0.1% ~ 0.5% potassium carbonate aqueous solution into the following 20h rate of small current continuous charging 70 ~ 80 hours.

② pour the aqueous solution, rinse with distilled water or pure water, then add the density of 1.40 g / cm3 electrolyte, and adjust to the standard density.

③ after a normal charge, discharge, capacity, if the return to the nominal capacity of about 90%, said the repair success.

6.2.3 Many heavy sulfated lead-acid battery electrolyte is almost dry, the use of the above method is difficult to "back to life." There are reports that special measures can be used to restore capacity. Now the method is as follows, the reader can try in the specific practice:

① in the deionized water, the appropriate addition of aluminum sulfate, magnesium sulfate, zinc sulfate, tartaric acid, ethylenediamine tetraacetic acid disodium (EDTA disodium), dubbed into aqueous solution.

② the original electrolyte solution, add the water solution, put it aside for 12 hours to 6A current charge 5 to 30 hours, then 5A current discharge 25 hours, drained the aqueous solution.

③ with a density of 1.40 g / cm3 of the electrolyte injection, transferred to the standard density, according to the normal method of adequate power.

④ test battery capacity, if the original capacity of about 90% of the nominal, said the repair success, or only scrapped.

The method applies to a variety of lead-acid batteries, including maintenance-free batteries and other storage batteries.

6.3 High current charge

If adsorption is considered to cause sulfation reasons, you can use high current density charge (up to 100mA / cm2). At such a current density, the negative electrode can reach a very negative potential value, altering the sign of the charged surface of the electrode, and the surface active substance will desorb, especially for the anionic surfactant, from which the deleterious surface active material After the surface of the electrode is desorbed, the charging can be carried out smoothly. At present, almost no domestic use this method to deal with irreversible sulfation, may be due to the following considerations: high current density polarization and ohmic pressure drop increase, this part of the energy into heat, so that the battery internal temperature, while A large number of gas precipitation, especially the large amount of gas precipitation gas, the erosion of the active material easy to fall off.