Why does battery vulcanization occur and how to fix it

EVs are favored by people because of their affordable price, but they often damaged due to charging or improper use, and the most common damage is battery vulcanization. A layer of white hard crystals is attached to the surface of the anode plate inside the EV, and after charging, the surface of the anode plate cannot be peeled off and converted into lead sulfate of the active substance, which is battery vulcanization.

The battery vulcanization is like covering the anode plate with a thin film, causing the anode plate reaction area to drop significantly, resulting in battery failure. This article mainly introduces the phenomenon of battery vulcanization and how it can be repaired.

1. The basic and characteristics of lead-acid batteries

The main housing, cathode and anode plates, separators, and electrolytes are under the action of an electric field to convert electrical energy into chemical electric energy storage and chemical electric energy into DC electric energy, and they can repeatedly carry out several charge and discharge cycles of a device. Unlike lifepo4 battery, lead-acid batteries require maintenance in use.

The anode material is lead, the cathode material is lead sulfide, and the electrolyte solution mainly uses sulfuric acid. Lead-acid batteries are a complex electrochemical reaction system. Its performance life depends on the material used in the manufacture of cathode and anode plates, process environment, the composition of the active material purity combination, use environment and maintenance have a very important impact.

2. What is battery vulcanization

A layer of white hard crystals is attached to the surface of the plate inside the battery, and the lead sulfate that cannot be converted into active material on the surface of the plate after charging can still not be peeled off, which is sulfation, referred to battery vulcanization.

● The phenomenon of battery vulcanization

The internal resistance of the battery increases, and the charging voltage reaches the final charging voltage earlier than the voltage before battery vulcanization, and the larger the current, the more obvious it is. The acid density is below normal. The discharge capacity decreases, and the larger the discharge current, the more obvious the capacity decreases. When charging, bubbles are generated, and the charging temperature rises faster, which can lead to failure to charge in severe cases.

● Battery vulcanization formation

After each discharge of the battery, the different active substances of the cathode and anode plates are converted into lead sulfate, and each of them is restored to different active substances after charging. Operations that can easily lead to battery vulcanization include:

• Frequent overdischarge.
• Small current deep discharge.
• Low temperature and high current discharge.
• No timely replenishment of electricity .
• Insufficient charging.
• Too high acid density.
• Lack of water inside.
• Long shelved.

The lead sulfate on the surface of the plate accumulates in excess and dissolves in the electrolyte, and is recrystallized and precipitated on the surface of the plate. These are poorly soluble electrolytes that adhere to the plate surface and micropores hinder the normal operation of the battery. And the battery charge acceptance rate decreases, the battery heats up rapidly so that the charging can not continue, and then the active material is incomplete, thus becoming the cause of reduced capacity and shortened life.

3. Analysis of the causes of battery vulcanization

● Plate vulcanization

This crystal is difficult to eliminate during normal charging, and the degree of sulfurization formation has a lot to do with the capacity of lead-acid batteries. The more severe the battery vulcanization, the less capacitance until it is scrapped.

There are many factors in battery vulcanization. Mainly the storage time of lead-acid batteries is too long, because there is sulfuric acid on the surface of the active material during the formation treatment of the plates, resulting in the loss of ionization after the aging of the lead sulfate on the surface of the active material.

The lead-acid battery is discharged when it is shelved with electricity, and the battery is not charged in time after discharge, and the electrolyte density is too high or impure, which will make the surface of the active material in the cathode and anode plates form non-sulfurization. Therefore, battery vulcanization is the main reason for the failure and scrapping of the active material of the plate.

● Self-discharge

It means that the internal electricity of the lead-acid battery is consumed by itself, and if the discharge exceeds the self-discharge value, it will cause the capacity to decrease. The main reasons for self-discharge are: impure materials in manufacturing, and harmful impurities in the electrolyte. The pores of the cathode and anode plates are blocked after battery vulcanization, resulting in increased internal resistance consumption of lead-acid batteries, all of which cause self-discharge of lead-acid batteries.

● The plate active material falls off

Standard use of lead-acid batteries is not easy to fall off. The shedding of the active material of the cathode plate is mainly due to insufficient electricity or high current discharge at low temperatures, while the shedding of the active material of the anode plate is mainly due to overcharging or charging current. Use in a harsh environment can also accelerate the shedding of the active material. Therefore, lead-acid batteries are required to avoid overcharge and overdischarging in use.

● Failure of the battery

New lead-acid batteries fail and are scrapped before use because:

• The combination of active substances in the manufacturing materials of lead-acid batteries is unreasonable.
• The plates do not meet the charging and discharging standards during chemical treatment.
• The storage environment of the plates is poor or the storage time is too long.
• The seal is damaged and it is oxidized by the air for a long time, resulting in the aging of the active material of the plate.
• Improper maintenance during use, failure to maintain the battery in time.

In the use of lead-acid batteries, it is often not timely to add water to the battery in summer, and the high temperature evaporates quickly, resulting in insufficient or dry electrolyte, so that the plates are exposed to the electrolysis surface and are exposed to air and hydrogen oxide embrittlement leads to sulfide and necrosis of the plates. Therefore, the loss of lead-acid batteries is the summer period.

4. How to prevent battery vulcanization

Replenish electricity in time after each discharge and have sufficient power, especially after high-current discharge. Try to control the depth of discharge when the small current is discharged, the lead sulfate produced by the small current deep discharge is too dense, and the charge after discharge takes a small current for a long time.

For low-temperature and high-current discharge, 30% more charge should be taken to restore capacity. Battery that has been shelved for a long time should be fully charged before being shelved, and the power should be properly replenished every two months after the shelving. Because the battery is not used for a long time, there will be a serious power loss problem, which will lead to battery vulcanization. Let's take a look at ways to prevent battery vulcanization.

● Disconnect battery cable

Let's start with the most practical method:

• Open the base of the electric car first and find the battery pack.
• Use a screwdriver to disconnect the cable between two of the small batteries.

And in this way, if the electric car is placed for half a year, battery will not be damaged by any power loss. If you need to use the electric car again, the direct cable can be tightened and returned to normal.

● Turn off the leakage protector

Let's look at the simplest method again:

• Open the base and locate the leakage protector.
• Adjust it to the closed state.

It will also protect the battery to a certain extent and prevent battery vulcanization. However, this situation is generally only suitable for storage within 1 to 2 months. Because the leakage protector is turned off, the power lock is still in a power-on state, which will produce a small amount of self-discharge, so turning off the leakage protector can only prevent battery vulcanization in the short term.

● Charging is done once a week

Finally, let's look at a more effective method: If you do not use an electric car for half a year, or even for a long time. Then you can charge it once a week, and it is best to ensure a charge every 2 to 3 weeks. Only by doing so can the activity of the active substances of the batteries be guaranteed, effectively extend the service life of the EV battery, and reduce the risk of battery vulcanization.

5. How to repair the EV battery vulcanization

● Hydropathy

For vulcanized batteries, the batteries can be discharged first, the original electrolyte can be poured out and a dilute electrolyte can be injected, that is, water can be added to batteries to dilute the electrolyte to improve the solubility of lead sulfate.

A small current is charged for a long time to reduce the ohmic polarization and delay the early appearance of the water splitting voltage, and finally the battery vulcanization phenomenon is gradually reduced or eliminated in the dissolution and conversion into active substances.

The characteristics of this method are more suitable for water-added batteries, and can also be repeatedly treated for serious battery vulcanization phenomena. Repair itself without the need for equipment. The disadvantage is that the process is too cumbersome and not suitable for sealed batteries, and the requirements for safe operation are relatively high. You can ask battery stores nearby for help.

● Shallow cycle high-current charging method

For vulcanized batteries, a high current is used to charge battery to a slightly overcharged state. Control the liquid temperature not to exceed 40 degrees, and then discharge 30%, and so on several times to reduce and eliminate battery vulcanization phenomenon.

For slight battery vulcanization, it can be significantly repaired. However, it is not suitable for old batteries, because when the precipitated gas washes the sulfate, it also produces a strong erosion of the active substance of the cathode plate, making the active material soft or even fall off.

● Chemical remediation

For vulcanized batteries, pour out the original electrolyte, add pure water and mixed liquid, take normal charge and discharge several times, and then pour out pure water and add slightly high-density acid to adjust the acid in the battery to the concentration of standard solution, and the capacity can be considered successful if it is restored to more than 80%.

The addition of these sulfate coordination dopants can form coordination compounds with many metal ions, including sulfide salts. The repair efficiency and efficacy are higher than the previous two repair methods, and the disadvantages are too cumbersome.

● Pulse repair

For vulcanized batteries, some dedicated pulse repair instruments can be used to charge and discharge the battery several times to eliminate battery vulcanization. This method has characteristics, good effect and easy operation. However, it is necessary to have a dedicated pulse charger, which individual users do not have, and need to purchase. The pulse repair chargers on the market are uneven, unreasonable and cannot play a role in desulfurization.

6. Extend the normal service life of lead-acid batteries

The same battery, in different equipment conditions, different use conditions and different maintenance conditions, the service life varies greatly. This requires looking for differences in equipment conditions, usage conditions and maintenance conditions. The main phenomena of battery failure are:

• The cathode is softened.
• Cathode grid corrosion.
• Vulcanization of anode plates.
• Dehydration.
• A small number of batteries have thermal runaway (including bulging batteries).

In general, for users, we must pay attention to it; we must not wait for the battery to vulcanize and then think of a solution.

● Allow battery to cool down before charging it.

Short-term high temperature also has obvious adverse effects on the electrochemical performance of lead-acid batteries.

● Control charging time.

Charging time is too long will cause battery temperature to be too high and the sulfuric acid solution water to evaporate. The concentration of sulfuric acid increases, and battery conversion performance decreases, which affects battery life.

● Choose the right travel speed.

When an electric car rides too fast, the battery is overloaded, and the chemical reactions in it become more intense, causing the battery capacity to drop faster.

● Do not use fast charging freauently.

The driving distance is long, and battery is fully charged in advance before going out, reducing the use of fast charging, which also helps extend battery life.

● Match the charger model

We all know that the 12v battery of the EV is equipped with a corresponding charger, and only the best performance of the batteries can be achieved by using the matching charger. Of course, in daily life, it is also necessary to develop good battery maintenance habits, so that the battery life of EVs can be extended to the greatest extent.

7. Conclusion

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