The first reason: caused by the battery itself
Why do you say that? In the previous issue, we learned the working principle of lead-acid batteries. The process of charging and discharging lead-acid batteries is the process of electrochemical reaction. When charging, lead sulfate forms lead oxide, and lead oxide is reduced to lead sulfate during discharge. Lead sulphate is a substance that is very easy to crystallize. When the concentration of lead sulphate in the electrolytic solution in the battery is too high or the static idle time is too long, it will "carry" into a group and form small crystals. These small crystals will attract the surrounding area. The lead sulfate, like a snowball, forms a large inert crystal. When the lead sulfate is crystallized, it can not be reduced to lead oxide, but also precipitates on the electrode plate, causing the working area of the electrode plate to decrease. This phenomenon is called vulcanization. At this time, the battery capacity will gradually decrease until it is unusable. When the lead sulfate is piled up in a large amount, lead particles are attracted to form lead branches, and the lead bridge between the positive and negative plates causes a short circuit of the battery. If there is a gap in the surface of the plate or the sealed molded case, the lead sulfate crystals will accumulate in these gaps and cause expansion tension, which eventually causes the plate to break off or the outer casing to rupture, resulting in irreparable physical damage of the battery. Therefore, the main mechanism leading to failure and damage of lead-acid batteries is that the battery itself cannot avoid vulcanization.
The second reason: the reason for battery production
Various battery manufacturers have adopted various methods for the particularity of lead-acid batteries for electric bicycles. The most typical method is as follows:
1 Increase the number of plates. The original design of the single-frame 5-piece 6-piece system was changed to 6-piece 7-piece system, 7-piece 8-piece system, and even 8-piece 9-piece system. Increase the battery capacity by reducing the thickness of the plates and the spacers and increasing the number of plates.
2 increase the specific gravity of the battery sulfuric acid. The original sulfuric acid specific gravity of the floating battery is generally between 1.21 and 1.28, and the sulfuric acid specific gravity of the battery of the electric bicycle is generally around 1.36 to 1.38, which can provide a larger current and increase the initial capacity of the battery.
3 increase the amount and proportion of lead oxide active material active material. Increasing lead oxide increases the electrochemical reaction species involved in the discharge, which increases the discharge time and increases the battery capacity. Through these measures, the initial capacity of the battery satisfies the capacity requirements of the electric bicycle, and in particular, the characteristics of the large current discharge of the battery are improved. However, as the number of plates increases, the capacity of sulfuric acid decreases, and the battery heat causes a large amount of water loss. At the same time, the probability of micro-short circuit and lead-bridge bridging of the battery increases. Increasing the specific gravity of the sulfuric acid increases the initial capacity of the battery, but the vulcanization phenomenon is more serious. One of the most basic principles of sealed batteries is that after the oxygen is separated from the positive electrode plate, the oxygen is directly sent to the negative electrode plate and absorbed by the negative electrode plate to be reduced to water. The parameter of the technical index of the battery is called “sealing reaction efficiency”. This phenomenon is called “oxygen”. cycle". In this way, the battery has little water loss, achieving "maintenance-free", that is, no water is added. For this reason, it is required that the capacity of the negative electrode plate is made larger than that of the positive electrode plate, which is also called a negative electrode transition. Increasing the active material of the positive electrode plate inevitably reduces the transition of the negative electrode, the oxygen cycle becomes worse, the water loss increases, and the vulcanization is caused. Although these measures increase the initial capacity of the battery, they cause water loss and vulcanization, and water loss and vulcanization will contribute to each other, and the end result is to sacrifice the life of the battery.
4 There is also the problem of the virtual group loading of the welding. The place where the solder joint is easy to occur is the plate. Each cell has 15 plates, which are 15 solder joints. One battery has 6 cells, and there are 90 solder joints. One battery consists of 3 12V batteries, and there are 270 solder joints. . If there is a virtual solder joint in the solder joint, the capacity of the single cell decreases, and the cell forms a backward battery, causing the entire battery to lag behind, and the battery will form a serious imbalance, which causes the battery to fail prematurely. Even if the welding control is one in ten thousand, an average of one set of batteries in each of the 37 batteries will have a virtual weld, which is absolutely not allowed. The lead-calcium alloy grid cells will precipitate calcium during soldering to mask the problem of solder joints. As a result, many battery manufacturers prefer to use low-ruthenium alloy grids instead of lead-calcium alloys. The low-antimony alloy grid has a lower oxygen evolution and hydrogen evolution voltage, a larger battery output, a relatively serious water loss, and a battery that is more susceptible to vulcanization.
From the above we can see: Why the battery is good or bad, and some manufacturers grow the battery life will be longer under the same conditions of use.
The third reason: the cause of the use environment of the electric vehicle itself
As long as it is a lead-acid battery, it will be vulcanized during use, but lead-acid batteries in other fields have a longer life than lead-acid batteries used on electric bicycles. This is because lead-acid batteries for electric bicycles have a more easily vulcanized. Work environment.
1 deep discharge
The lead storage battery used in the car is only discharged in one direction during ignition. After ignition, the generator will automatically charge the battery without causing deep discharge of the battery. Electric bicycles are not likely to be charged when riding, and often exceed 60% of deep discharge. When deep discharge, the concentration of lead sulfate increases, and the vulcanization is quite serious.
2 large current discharge
The 20km cruise current of an electric vehicle is generally 4A, which is higher than the battery operating current in other fields, and the over-loaded electric vehicle has a larger operating current. Battery manufacturers have performed a cycle life test of 70% for 1C charging and 60% for 2C discharge. After such a life test, there are many batteries that can reach 350 cycles of charge and discharge cycles, but the actual use effect is far from the same. This is because the high current operation increases the depth of discharge by 50% and the battery accelerates vulcanization. Therefore, the battery life of the electric motorcycle is shorter, because the body of the electric motorcycle is too heavy, the motor power is large, and the working current reaches 8A or more during cruise. Some even reach 10A.
3 high charging and discharging frequency
The battery used in the backup power supply field will only discharge when the power is cut off. If it is stopped 8 times a year, it must reach 10 years of life, only 80 cycles of charging life, and the electric vehicle can charge and discharge 300 times a year. More than a few times are very common. Some people may charge it several times a day, and the charging time is short. It is used without being full.
4 short charge
Since the electric bicycle is a vehicle, the charging time is not much. It is necessary to complete the charging of 36 volts or 48 volts in 20 hours in 8 hours. This requires an increase in the charging voltage (usually a single section of 2.7 to 2.9 volts) when charging. When the voltage exceeds the oxygen evolution voltage (2.35 volts) or the hydrogen evolution voltage (2.42 volts) of a single cell, the battery will open and vent due to excessive oxygen evolution, causing water loss, increasing the electrolyte concentration, and aggravating the vulcanization of the battery. .
5 can not be charged in time after discharge
As a means of transportation, the charging and discharging of the electric bicycle are completely separated, and it is difficult to conditionally charge in time after discharging, and if a large amount of lead sulfate formed after the discharge is not charged and reduced to lead oxide for more than half an hour, the crystal will be vulcanized.
The fourth reason: the reasons for the production of electric bicycles
Most car controllers have a speed limit plug. Some car manufacturers simply remove the speed limiter from the factory, which can attract customers who value the speed and reduce the cost. Such a car will have a very high current at high speed and will be seriously shortened. Battery Life.
The minimum protection voltage of a 12V lead-acid battery is 10.5V. If it is a 36V battery pack, the minimum reserve voltage is 31.5V. At present, the undervoltage protection voltage of the controller used by most manufacturers is also 31.5V. On the surface, this is correct. However, when the 36V battery pack only has a voltage of 31.5V, due to the poor capacity of the battery, there will definitely be a battery voltage lower than 10.5V, and the battery is in an over-discharge state. At this time, the battery capacity of the overdischarge drops sharply, and the damage to the battery at this time is not only the single battery but the life of the entire battery. In fact, after the battery voltage is lower than 32V until 27V, the added capacity is less than 2 kilometers, and the damage to the battery is very large. As long as this happens 10 times, the battery capacity will be less than 70% of the nominal capacity. In addition, some users found that after the battery was under pressure for 10 minutes, the battery was not under pressure, and then the power was driven. This caused greater damage to the battery, and most of the car's instructions did not give the user a warning. At present, most controllers have adjustable potentiometers inside, and the vibration drift of this adjustable potentiometer is more serious. In the price competition, in the face of the user group that pays more attention to the appearance of the car, few products use precision multi-turn potentiometers that resist vibration. It is not surprising that such controllers drift after vibration.
The fifth reason: the reason for charging equipment
One word widely circulated in the industry is that the battery is not worn out, but is burnt. In order to meet the short-time high-capacity charging of the electric bicycle battery, in the three-stage constant voltage current limiting charging, it is necessary to increase the constant voltage value to 2.47V to 2.49V. Thus, the oxygen evolution voltage of the positive electrode plate of the battery and the hydrogen evolution voltage of the negative electrode plate are greatly exceeded. In order to reduce the charging time, some charger manufacturers' products have increased the current of the constant voltage to the floating charge, so that after the charging indication is fully charged, it is not fully charged, and it is compensated by increasing the floating charging voltage. Thus, the float voltage of many chargers exceeds the single cell voltage of 2.35V, so that a large amount of oxygen is also evolved during the floating charge phase. The oxygen circulation of the battery is not good, so that it is continuously exhausted during the floating charge phase. The constant voltage value is high, which guarantees the charging time, but the sacrifice is water loss and vulcanization. The constant voltage value is low, and the charging time and charging power are difficult to guarantee. On the basis of improving the battery grid alloy of the battery, improving the gassing potential, improving the oxygen cycle performance, and improving the efficiency of the sealing reaction, the maximum charging voltage for controlling charging is below 2.42V, that is, below the hydrogen evolution potential. This will inevitably lead to an increase in charging time. This requires the addition of a depolarized negative pulse in the state of high current charging (current limiting charging) to improve the charging acceptance of the battery and to charge more when charging at a high current. Some power, shorten the charging time. 70% of the 2C current is charged, when the battery is relatively large in charging capacity, the battery is charged with a large current, and the damage to the battery is relatively small. The battery is basically no higher than the severe hydrogen evolution voltage. Once above the hydrogen evolution voltage, the battery will quickly lose water. To use such a charger, continuous charging and discharging must be used. If the charging is stopped for a few days, the battery will be severely vulcanized and will fail prematurely. When the user uses the battery, there is no guarantee that it can be charged in time after each use. If the battery is not recharged several times within one year, the vulcanization of the battery will accumulate. Some charger manufacturers exaggerate certain features, and the finished product is not as good as its promotion.
Many batteries can get better results in the single test. However, for tandem battery packs, the difference is due to the difference in capacity, open circuit voltage, state of charge, and degree of vulcanization. The monomer that is enlarged and has a poor state affects the entire battery, and its life is significantly reduced.
From the charging of the battery on the production line to the use of the car after the user purchases the car, there are many links, and the interval may even last for several months. During this period, due to the lack of recharging of the battery, the self-discharge produces a large amount of lead sulfate. Stacking crystals, the new battery that the user just bought may be a battery that has been aging or even reported.
When the battery manufacturer performs the warranty, the battery is not completely eliminated. After the battery is returned, the battery manufacturer re-inspects the charge and discharge. In the inspection, it is often found that more than 60% of the single cells are batteries that do not meet the return conditions. The reason is that in the series battery pack, the individual batteries fall behind to form a whole group of batteries, and the whole group returns. Many battery manufacturers have re-supplied, hydrated, desulfurized, and packaged the returned battery to provide users with the opportunity to improve the effective service life of the battery, reduce the scrap rate, and reduce the loss of partial claims of the battery manufacturer. Therefore, many dealers have already felt that the battery provided by the manufacturer is obviously "a generation is not as good as the first generation", so you should polish your eyes when selecting the battery, and choose a battery with good quality and good reputation.