Failure modes and repair methods of lead-acid batteries

At present, the battery is still mainly lead-acid battery according to its capacity. Lead acid battery has the advantage of large capacity, which can not be replaced by other batteries at present. In addition, its high current discharge characteristics also determine its advantages in starting battery. However, as a heavy metal, lead has certain toxicity in addition to its cost, which has different degrees of harm to the environment and human body. Therefore, prolonging the life of lead-acid batteries is not only to reduce the operating costs, but also to meet the needs of environmental protection. It is also an important issue to expand the application field of lead-acid batteries. Therefore, the research on repairing lead-acid battery and prolonging its service life will not only reduce the sales volume of lead-acid battery, but also increase the pollution to the environment.
In order to understand the repair of lead-acid battery, we must first understand the failure mode of lead-acid battery. Then, according to different failure modes, repair methods are discussed.
Failure mode of lead acid battery
Due to the differences in the types, manufacturing conditions and use methods of the plates, the final causes of battery failure are different. To sum up, the failure of lead-acid battery has the following conditions:
One
Corrosion deformation of positive plate
At present, there are three kinds of alloys used in production: traditional lead antimony alloy, antimony content is 4% - 7%, low antimony or ultra-low antimony alloy, antimony content is 2% or less than 1% mass fraction, containing tin, copper, cadmium, sulfur and other deformation agents; lead calcium series, actually lead calcium tin aluminum quaternary alloy, calcium content is 0.06% - 0.1% mass fraction. The positive grid made of the above-mentioned alloys will be oxidized into lead sulfate and lead dioxide during the charging process of the battery, which will eventually lead to the loss of the supporting active material and make the battery invalid; or the formation of the corrosion layer of lead dioxide will cause the lead alloy to produce stress and make the grid grow and deform. When the deformation exceeds 4%, the whole plate will be destroyed, and the active material and grid will be destroyed Poor contact and falling off, or short circuit at the bus bar.
Two
The active material of positive plate falls off and softens.
In addition to the active material shedding caused by the growth of the grid, the binding between PbO2 particles is also relaxed and softened with the repeated charging and discharging, and the particles fall off from the grid. A series of factors, such as grid manufacturing, assembly tightness and charge discharge conditions, have an impact on the softening and shedding of active materials in the positive plate.
Three
Irreversible sulfation
When the battery is over discharged and stored in the state of discharge for a long time, its negative electrode will form a kind of coarse lead sulfate crystal which is difficult to accept charging. This phenomenon is called irreversible sulfation. Some methods can be used to recover the slight irreversible sulfation. If it is serious, the electrode will be invalid and cannot be charged.
Four
Premature loss of capacity
When the low sb or Pb Ca alloy is grid alloy, the capacity of the battery will drop suddenly in the initial use period (about 20 cycles), which will lead to the failure of the battery.
Five
Heavy accumulation of antimony on active substances
Antimony on the positive grid is partially transferred to the surface of the active material of the negative plate along with the cycle. Since the overpotential of H + reduction on antimony is about 200mV lower than that on lead, the charging voltage decreases when antimony accumulates, most of the current is used for water decomposition, and the battery fails to charge normally.
The content of antimony in the negative active material of lead-acid battery was tested when the charging voltage was only 2.30v. It was found that the content of antimony in the surface layer of negative active material was 0.12% - 0.19%. For some batteries, such as submarine batteries, hydrogen evolution is limited. The content of antimony in the negative electrode of batteries with hydrogen evolution exceeding the standard was tested, and the average antimony content was 0.4%.
Six
Thermal failure
For the battery with less maintenance, the charging voltage should not exceed 2.4V per cell. In practical use, for example, in the automobile, the voltage regulator may be out of control, the charging voltage is too high, so the charging current is too large. The heat generated will increase the temperature of the battery electrolyte, resulting in the decrease of the internal resistance of the battery, which will strengthen the charging current. The excessive temperature rise and current of the battery strengthen each other, and eventually can not be controlled, resulting in the failure of the battery due to deformation and cracking. Although hotRunaway is not a common failure mode of lead-acid battery, but it is also common. Attention should be paid to the phenomenon of high charging voltage and battery heating when using.
Seven
Corrosion of negative bus bar
In general, there is no corrosion problem in the negative grid and bus bar, but in the valve regulated sealed battery, when the oxygen cycle is established, the upper space of the battery is basically filled with oxygen, and the bus bar is more or less the electrolyte in the diaphragm and climbs up to the bus bar along the electrode ear. The alloy of the bus bar will be oxidized and lead sulfate will be formed. If the electrode alloy of the bus bar is not selected properly, there will be slag inclusions and cracks in the bus bar, and the corrosion will deepen along these gaps, resulting in the separation of the electrode lug and the bus bar and the failure of the negative plate.
Eight
Short circuit caused by diaphragm perforation
Some kinds of separators, such as PP (polypropylene) diaphragm, have larger pore diameter, and the PP fuse will shift in the process of use, resulting in large pores. Active substances can pass through the large pores in the process of charging and discharging, resulting in micro short circuit and battery failure.
Factors affecting the life of lead acid battery
The failure of lead-acid battery is the result of many factors, which are determined by the internal factors of the plate, such as the composition of active substances. The crystal form, porosity, plate size, grid material and structure also depend on a series of external factors, such as discharge current density, electrolyte concentration and temperature, discharge depth, maintenance condition and storage time. Here are the main external factors.
One
Discharge depth
The discharge depth refers to the extent to which the discharge starts and stops in the process of use. 100% depth refers to the full discharge capacity. The life of lead-acid battery is greatly affected by the depth of discharge. The key point of design consideration is deep circulation, shallow circulation or floating charge. If the shallow cycle battery is used in the deep cycle, the lead-acid battery will fail quickly.
Because the positive active material lead dioxide itself is not firmly combined with each other, lead sulfate is generated during discharge, and then recovered to lead dioxide when charging. When the molar volume of lead sulfate is larger than that of lead oxide, the volume of active material expands during discharge. If one mole of lead oxide is converted into one mole of lead sulfate, the volume increases by 95%. In this way, repeated contraction and expansion will make the binding between PbO2 particles gradually relaxed and easy to fall off. If only 20% of the active material in one mole of PbO2 is discharged, the degree of shrinkage and expansion will be greatly reduced, and the destruction of binding force will be slower. Therefore, the deeper the discharge depth is, the shorter the cycle life will be.
Two
Overcharge level
When overcharge, a large amount of gas is precipitated, and the active material of the positive plate is impacted by the gas, which will promote the active material to fall off; in addition, the positive grid alloy is also subject to severe anodic oxidation and corrosion, so the battery life will be shortened when overcharged.
Three
Effect of temperatureThe life of lead-acid battery increases with the increase of temperature. In the range of 10 ℃～ 35 ℃, each increase of 1 ℃ will increase about 5-6 cycles, and between 35 ℃ and 45 ℃, the service life can be prolonged by more than 25 cycles; if the temperature is higher than 50 ℃, the service life will be reduced due to the loss of the capacity of the negative electrode.
The battery life increases with the increase of temperature in a certain temperature range, because the capacity increases with the increase of temperature. If the discharge capacity is constant, the discharge depth decreases and the solid life increases with the increase of temperature.
Four
Influence of sulfuric acid concentration
The increase of sulfuric acid density is beneficial to the capacity of positive plate, but the self discharge of battery increases, the corrosion of grid is accelerated, and the loose shedding of lead dioxide is also promoted. With the increase of sulfuric acid density in the battery, the cycle life decreases.
Five
Influence of discharge current density
With the increase of discharge current density, the life of the battery decreases, because under the condition of high current density and high acid concentration, the positive lead dioxide is loose and detached.
Another failure mode is water loss. For open battery, water loss is normal maintenance, for sealed battery, it should not appear under strict control. Therefore, water loss is not included in the failure mode. The problem of water loss of sealed batteries focuses on electric bicycles. Because the constant voltage of charging is too high.
Repair method of premature loss of capacity (PCL)
Characteristics of premature loss of capacity
When the low sb or Pb Ca alloy is grid alloy, the capacity of the battery will drop suddenly in the initial use period (about 20 cycles), which will lead to the failure of the battery. Almost every cycle of battery capacity will be reduced by 5%, the rate of capacity decline is faster and earlier.
In the past few years, lead calcium alloy series of batteries often inexplicably appear several battery capacity decline. Analysis of the positive plate did not soften, but the positive plate capacity is very low.
2. Find solutions to the causes of this phenomenon
 
One
The content of tin in the positive plate. For deep cycle batteries, the content of tin is 1.5% ~ 2%.
Two
Increase assembly pressure.
Three
The content of acid in electrolyte should not be too high.
3. Pay attention in use
One
Avoid continuous low initial charging current;
Two
Reduce deep discharge;
Three
Avoid overcharging too much;Four
Do not increase battery capacity by excessive utilization of active substances.
4 recovery of batteries with early capacity loss
One
Firstly, the initial charging current should be increased to 0.3C ~ 0.5c, and then small current should be used to make up the charging;
Two
Secondly, the fully charged battery should be stored at 40 ℃～ 60 ℃ and discharged to 0V with a small current less than 0.05c. When the battery voltage reaches half of the nominal voltage, the discharge will be slow. The capacity of the battery can be recovered after several times.
 
5 precautions
Be sure to identify whether the battery occurred in the first 20 cycles. If the capacity of the battery decreases in the middle and later period, this method can only destroy the positive plate of the battery and cause the positive plate to soften.
Lead calcium alloy series of batteries often inexplicably appear several battery capacity decline, the main reason is caused by battery imbalance, lead calcium alloy series battery sufficient voltage is high, generally 12 V battery charging voltage is greater than 16 v. When the voltage of charger is too low, it is easy to cause battery imbalance. This phenomenon occurs in this way. When a group of batteries are used together, the self discharge of each cell of the battery cannot be absolutely equal. The battery with a little larger self discharge can not be fully charged with constant voltage charger each time. The cell with insufficient power does not have gas evolution reaction, and the relative area of electrode plate contacting with the electrolyte is large, so the self discharge is large. The cell with small self discharge can be fully charged each time. When the cell is overcharged a little after sufficient power, the gas evolution reaction will occur and gas will be generated. The electrode plate contacts with the electrolytic liquid level and the self discharge will be reduced. At the same time, the charging voltage will increase and the charger will be turned off. Results the self discharge of cells with small self discharge and high voltage becomes smaller and smaller, and can be fully charged each time. However, the grid with large self discharge discharge is getting larger and larger, and it can not be fully charged every time. Moreover, the smaller the power consumption is, the vulcanization and failure will occur if the battery is not sufficient for a long time, If the constant voltage is too high, the battery will lose control of heat. The best way is to use multi-stage charger with multiple current and multi voltage. At the end of charging, a small current with high voltage and low current should be charged for a long time to balance the battery power
  
6 precautions
Overcharging often requires large current and high voltage, which will form a strong side reaction and damage the positive plate of the battery, as well as form the water loss of the battery. How to achieve overcharge repair? Now we have found a very effective method - pulse method. The basic principles are as follows:
High voltage and high current pulse is used to overcome the decline of battery acceptance caused by various reasons. Due to the pulse form, after the high current pulse disappears, the depolarization ability of the battery itself (or additional conditions) will not form serious side effects. With the birth of this method of pulse overcharge repair, no damage overcharge can be realized. This kind of charger has achieved excellent results. After several years of verification test, this method has greatly extended the cycle life of lead-acid battery.