Sulfation and removal methods of lead-acid batteries

1. Overview

Lead-acid battery technology has remained largely unchanged for 100 years. Although there have been improvements in chemistry and structure, there is a common factor that causes battery failure. This failure is caused by sulfate accumulation on the plates, which leads to failure. The most effective way to solve these problems is to apply pulse technology.

Pulse technology helps to eliminate these battery faults. It can maintain a high active material reaction, make the battery internally balanced, and easily accept external charging. In this way, various related costs caused by replacing batteries are saved.

2. Technical Introduction

Experts predict that lead-acid batteries will continue to be the first in the field of battery power into the next century. However, the problem that deserves attention is that the working conditions of most batteries cannot meet the needs of today's technologically advanced transportation vehicles. In theory, the reaction materials of lead-acid batteries can last for 8 to 10 years or longer, but in fact it cannot. The average life of batteries now is 6 to 48 months. Only 30% of batteries can be used for 48 months. Most batteries age and fail prematurely. The reason for a series of problems that affect battery life is: the accumulation of sulfates, and the most effective way to solve these problems is pulse technology.

As early as 1989, the first patent was issued, which used pulse technology to improve the practicality of batteries and extend battery life. Its working principle is to keep the battery active material reaction at a high level, so that the battery is internally balanced and easy to accept charging. This technology can provide a large discharge capacity, accept charging quickly, and can be used for a long time. (In other words, it extends the working life of the battery)

Now let's understand how pulse technology benefits batteries and how it works. First, let's review how batteries work: According to the 11th edition of the International Battery Council Manual: "Batteries are designed according to electrochemical principles. The electrical energy generated by batteries is converted from stored chemical energy. Batteries are needed in vehicles and power machinery. Its three main functions are:

(1) Supply power to the ignition system to start the engine.

(2) Provide power to electrical equipment outside the engine.

(3) It stabilizes the voltage of the electrical system, making the output smooth and reducing the high voltage generated by the electrical system in an instant.

The battery is made of two different materials (lead and lead dioxide), which react in sulfuric acid to generate voltage. During the discharge process, the active material on the positive lead plate reacts with the sulfate in the electrolyte to generate PbSO4. At the same time, the active material on the negative plate also reacts with the sulfate in the electrolyte to generate PbSO4. Therefore, the result of discharge is that both the positive and negative plates are covered with lead sulfate (PbSO4). The battery is restored by charging it in the reverse direction.

During the charging process, the chemical reaction state is basically the reverse reaction of discharge. At this time, the lead sulfate (PbSO4) on the positive and negative plates decomposes into its original state, that is, lead and sulfate, and water decomposes into "H" and "O" atoms. When the separated sulfate combines with "H", it is reduced to sulfuric acid electrolyte.

From what has been mentioned above, the basic working principle of the battery is the energy generated by the chemical reaction process of ion exchange between sulfuric acid and lead. During the energy exchange process, the reaction product, lead sulfate, is "temporary" on the plate. But it is worth noting that during the charging and reduction process, the lead sulfate on the plate cannot be completely dissolved and piled up on the plate. This accumulation is the residue of the electrochemical reaction and occupies the position of the plate. In other words, the effective reaction material of the plate is constantly decreasing, which is the main cause of battery failure. (The phenomenon of battery failure due to lead sulfate is commonly known as plate saltization)

Plate salting problem: Most battery failures are attributed to the accumulation of lead sulfate. When the energy of lead sulfate molecules is greater than a minimum limit, they dissolve from the plates and return to a liquid state. Then, they can be recharged. But in fact, there is always a part of the sulfate that cannot return to the electrolyte, but is attached to the plates, eventually forming insoluble crystals. Sulfate crystals are formed in this way: the core energy of these individual sulfate molecules that cannot participate in the reaction is in an extremely low state, and it gradually absorbs other sulfate molecules with extremely low energy. When these molecules accumulate and combine tightly, a crystal is formed. This crystal cannot be effectively dissolved in the electrolyte. The existence of these crystals occupies the position of the plate, making the plate lose the ability to charge and discharge. Therefore, the point or part of the plate covered is equivalent to a dead point.

According to the BCI manual, page 58 says: "Batteries are essentially chemical devices, and their charging characteristics are often changed by chemical changes in the battery itself. For example, sulfate should be a normal product of chemical reactions, but under abnormal conditions, it becomes an excess substance and becomes the main problem affecting chemical reactions. These excess sulfates continue to accumulate on the plates and are ignored for a long time. In addition, if new batteries are stored for too long, this state will also occur. When the battery is severely salted, it cannot accept the generator's fast and full replenishment of its power. Similarly, it cannot be discharged satisfactorily. As the salting intensifies, the battery will eventually fail because it cannot accept charging and discharging." Page 56 says: "The charging voltage is affected by factors such as temperature and electrolyte concentration, the area of ​​electrolyte contacting the plates, the age of the battery, and the purity of the electrolyte. The salted crystals on the plates are very hard, which increases the internal resistance."

More than 80% of batteries fail due to the accumulation of these salt crystals. The speed, area and hardness of these crystals are closely related to time, battery charge status and energy reserve usage cycle. The accumulation of salt crystals on the battery is very troublesome. The following situations will inevitably cause salting:

1. The battery has been stored for a long time before installation. In fact, once sulfuric acid is added to the battery, a chemical reaction begins to produce salts. Therefore, the storage of new batteries will also cause salts, causing the new batteries installed in transportation vehicles to fail.

2. The vehicle is stationary and not working for a long time.

3. The battery is corroded, causing the internal resistance to increase during charging, resulting in insufficient charging.

4. Continuous over-discharge.

5. Temperature influence. For example, when the temperature gets hot, the salting rate doubles with every 10-degree increase in temperature. During charging, if the outside temperature is high, when the battery temperature reaches 75 degrees, the internal resistance will increase, resulting in insufficient charging. When the temperature gets colder, the lubricating oil of the vehicle becomes thicker, which requires more power to start the vehicle, that is, the battery discharge capacity needs to be greater. As a result, the accumulation of salts on the plates is accelerated. If you pay attention to the over-discharge of the battery, you will know that the battery electrolyte solidifies at this time, which greatly damages the plates. Under normal circumstances, when the charge reaches 100%, the specific gravity of the electrolyte is about 1.27, and the solidification temperature of the electrolyte at this time is -83 Fahrenheit; when the specific gravity is about 1.2, the solidification temperature is -17 Fahrenheit; if the specific gravity is 1.14 (also called full discharge), it will solidify at only 8 Fahrenheit.

6. In the case of insufficient charging, the battery cannot supply the maximum starting current, so frequently used vehicles often stall. According to the BIC manual, "When a vehicle uses an undercharged battery, it is possible that the engine speed is slow and idling and cannot start, consuming electricity. Conversely, the battery cannot be charged by the generator at the optimal rate. As a result, although the battery is charged 24 hours a day, it still cannot be fully charged. And if it is frequently undercharged, the battery salts more severely. This vicious cycle will eventually cause the battery to fail completely.

In summary, sulfate is an inevitable part of the energy conversion process, but sulfate crystals are a serious problem, not sulfate itself. More people need to understand the seriousness of this problem - sulfate crystals cause battery failure. The failure phenomena include:

1. Plate bending: Sulfate crystals somewhere on the plate weaken the acceptance of electrical energy, causing overcharging somewhere on the battery plate. This overcharge increases the temperature there, causing the plate here to bend.

2. Salinization causes the reactants on the grid mesh of the plate to fall off, which will lead to overcharging and bending of the plate.

3. Short circuit: Due to the increase of internal resistance caused by salinization, the plate bends and contacts the plate of the other polarity, causing a short circuit or destroying the frame supporting the plate.

4. Shedding of active substances: Salt crystals increase the internal resistance, causing local overcharge, leading to cracks in the plates and shedding of substances in the cracks.

Therefore, it is most appropriate to apply pulse technology to protect the plates, which also helps to reduce the damage to the battery plates caused by mechanical vibration. In the past, after the battery was salted, it was considered useless and discarded, or pulled to a distant place for repair. But now, pulse technology can solve this problem well.