Cause of short service life of battery
Cause of short service life of battery
The first reason: the battery itself
Why do you say that! In the previous period, we know the working principle of the lead-acid battery. The process of charging and discharging lead acid battery is the process of electrochemical reaction. The lead sulfate forms lead oxide when charging, and lead oxide is reduced to lead sulfate when discharge. Lead sulfate is a very easy to crystallize substance. When the concentration of lead sulfate in the electrolysis solution is too high or the static idle time is too long, it will "hold" and form a small crystal. These small crystals attract the surrounding lead sulfate, like a snowball, forming a large inert crystal, when the crystalline lead sulfate is charged. Not only can it no longer be reduced to lead oxide, it will also precipitate on the electrode plate, resulting in a decrease in the working area of the electrode plate. This phenomenon is called vulcanization. The battery capacity will gradually decrease until it can not be used. When lead sulphate is accumulated in large quantities, it will also attract lead particles to form lead branches. The lead and branch bridge between positive and negative plates will lead to short circuit of batteries. If there is a gap in the surface of the plate or the sealed plastic shell, the crystallization of lead sulfate will accumulate in these crevice and produce expansion tension, which will eventually break off the fracture of the plate or rupture the shell, resulting in the non repairable physical damage of the battery. Therefore, the main mechanism leading to failure and damage of lead-acid batteries is that the battery itself can not avoid vulcanization.
Second reasons: the cause of battery production
In view of the particularity of lead-acid batteries for electric bicycles, various battery manufacturers have adopted various methods. The most typical methods are as follows:
(1) increase the number of plates. The original design of 5 tablets and 6 tablets was changed to 6 pieces of 7 tablets, 7 pieces of 8 tablets, and even 8 pieces of 9 pieces. The battery capacity can be increased by reducing the thickness of the electrode plate and the number of plates to increase the number of plates.
(2) increasing the proportion of sulphuric acid in the battery. The proportion of the sulfuric acid in the floating battery is usually between 1.21~1.28, and the proportion of the battery in the electric bicycle is about 1.36 to 1.38, which can provide a larger current and improve the initial capacity of the battery.
Increase the amount and proportion of lead oxide in positive plate. The addition of lead oxide increases the electrochemical reaction materials involved in the discharge, and also increases the discharge time and increases the capacity of the battery. Through these measures, the initial capacity of the battery meets the capacity requirements of the electric bicycle, especially the characteristics of the large current discharge of the battery. However, with the increase of the plate, the capacity of sulphuric acid is reduced, and the heating of the battery leads to a large amount of water loss. At the same time, the probability of the micro circuit and the bridge of the lead branch of the battery has increased. Increasing the proportion of sulfuric acid increases the initial capacity of the battery, but the sulphidation is even more serious. One of the most basic principles of sealed batteries is that after the positive plate is dissolved in oxygen, oxygen is directly absorbed to the negative plate and is reduced to water by the negative plate. The parameter of the battery is called the "sealing reaction efficiency", which is called the "oxygen cycle". In this way, the battery has very little water loss and has achieved "no maintenance", that is, no water is added. For this reason, negative plate capacity is required to be larger than positive plate capacity, also known as negative transition. Increasing the active material of the positive plate will make the negative transition decrease, the oxygen circulation becomes worse, and the loss of water will increase, which will lead to vulcanization. While these measures increase the initial capacity of the battery, it can cause water loss and vulcanization, and water loss and vulcanization will contribute to each other, and the final result is the life of the battery.
(4) the problem of assembling and welding of the polar groups. The place where the false welding is easily produced is the plate. Each cell has a single cell with 15 plates, 15 solder joints, one battery with 6 single cells, 90 solder joints, and a battery consisting of 3 12V batteries with 270 solder joints. If a solder joint exists in virtual welding, the single cell will decline, and the cell is backward, causing the whole battery to lag behind, and the battery will form a serious imbalance, making the battery failure in advance. Even if the solder joint is controlled at 1/10000, there will be a battery of solder joints on every 37 batteries, which is absolutely not allowed. And the lead calcium alloy grid battery, when welding, can precipitate calcium and mask the problem of virtual welding, so many battery manufacturers prefer to use low antimony alloy grid instead of lead calcium alloy. While the low antimony alloy has lower voltage of hydrogen evolution, larger discharge capacity and relatively serious loss of water.
From the above, we can see why the batteries are good and bad, and the batteries that some manufacturers grow will live longer under the same conditions.
The third reason: the cause of the environment of the electric vehicle itself.
As long as they are lead-acid batteries, they will be vulcanized in the process of use, but lead acid batteries in other fields have longer life than the lead-acid batteries used on electric bicycles, because the lead-acid batteries in electric bicycles have a more easily vulcanized working environment.
Deep discharge
The lead-acid batteries used on automobiles only discharge in one direction when they are ignited. The power generation after ignition can automatically charge the battery without causing deep discharge. While electric bicycles can not be charged when riding, they will often discharge more than 60%. When deep discharge, the concentration of lead sulphate will increase and sulfuration will be quite serious.
High current discharge
The 20 kilometre cruising current of an electric vehicle is generally 4A, which is already higher than the battery working current in other fields, and the electric current of the overspeed overloaded electric vehicle is greater. Battery manufacturers have carried out cycle life tests of 1C charging 70% and 2C discharge 60%. After this life test, the life cycle of charge and discharge can be reached 350 times.
But the actual effect is far from the same. This is because the large current will increase the discharge depth by 50%, and the battery will accelerate vulcanization. Therefore, the battery life of electric motorcycle is shorter, because the body of electric motorcycle is too heavy, the power of motor is large, and the current of the electric locomotive is more than 8A. Some have reached 10A.
High charge and discharge frequency
The battery used in the field of backup power supply will only be discharged when the power is stopped. If the battery is stopped 8 times a year, it will reach the life of 10 years. Only 80 cycles can be recharged, and the charging and discharging cycle of electric vehicles more than 300 times a year is very common. Some people may charge several times a day for a short time, but not enough to fill it.
Short time charging
Because the electric bicycle is a vehicle, the charging time is not much, to complete the 36 volt or 48 volt 20 AMV in 8 hours, it is necessary to increase the charge voltage (usually a single 2.7~2.9 volt), when the charging voltage exceeds the single cell's oxygen evolution voltage (2.35 volts) or the hydrogen evolution voltage (2.42 volts), the battery will be over The discharge of oxygen by opening the valve causes loss of water, increases the concentration of electrolyte, and aggravates the vulcanization of the battery.
Can not be charged in time after discharge
As a means of transportation, the charging and discharging of electric bicycles are completely separated. After discharge, it is difficult to be charged in time. And a large amount of lead sulfate formed after discharge is reduced to lead oxide for more than half an hour, and it will be vulcanized.
The fourth reason: the reasons for the production of electric bicycles
Most of the car's controllers have a speed limit plug, and some car factories simply remove the speed limiter out of the factory. It can not only attract the customers who see the speed, but also reduce the cost. The current is very high at high speed, which can seriously shorten the battery life.
The minimum protection voltage of 12V lead-acid battery is 10.5V. If it is a 36V battery, the minimum reserved voltage is 31.5V. At present, the under voltage protection voltage of the controller in most car factories is also 31.5V. On the surface, this is correct, but in fact, when the 36V battery pack has only a 31.5V voltage, because the battery has a poor capacity, it will certainly have a battery voltage below 10.5V and the battery is in a over discharge state. At this time, the capacity of the battery has dropped rapidly. The damage to the battery is not only the single battery, but also the whole battery life. In fact, after the battery voltage is less than 32V, it reaches to 27V. The added capacity of the battery is less than 2 km, and the damage to the battery is very large. As long as there is such a situation, the 10 time, the battery capacity will be lower than the nominal capacity of 70%. In addition, some users found that after the battery was under pressure, after 10 minutes, the battery was not under pressure, it took the electricity again, which was more damaging to the battery, and most of the car's instructions did not warn the user. At present, most controllers have adjustable potentiometers, and the vibration drift of this adjustable potentiometer is rather serious. In price competition, in the face of the user group that pays more attention to the appearance of the car, few products use the precision multi loop potentiometer with anti vibration, and it is not surprising that such a controller will drift after vibration.
Fifth reasons: the reasons for the charging equipment
The industry's widely circulated saying is that batteries are not damaged but are damaged. In order to meet the short time and high capacity charging of the electric bicycle battery, it is necessary to increase the constant voltage value to 2.47V ~ 2.49V in the three stage constant voltage current limiting charging. In this way, the oxygen evolution voltage and the hydrogen evolution voltage of the negative plate are greatly exceeded. In order to reduce the charging time, some charger manufacturers have increased the current of the constant voltage to the floating charge, and make the charging indicator full of electricity and make up for the floating charge voltage. In this way, the charging voltage of many chargers is more than 2.35V of single cell voltage, so there is a large amount of oxygen evolution in the floating charge stage. And the oxygen circulation of the battery is not good, so it is also constantly exhausting in the floating charge stage. The constant voltage is high, which ensures the charging time, but at the expense of water loss and sulfuration. The constant voltage value is low, and charging time and charging power are difficult to guarantee. On the basis of improving the battery grid alloy, improving the gas evolution potential, improving the oxygen cycle performance and improving the efficiency of the sealing reaction, the maximum charge voltage of the charge is under 2.42V, that is, below the hydrogen evolution potential. This will inevitably lead to the prolongation of the charging time. It is necessary to add the depolarized negative pulse in the state of high current charging (current limiting charging), improve the charging acceptance of the battery, and shorten the charging time when the large current is charged. 70% of the 2C current is charged. When the battery has a relatively high capacity to receive the charge, the battery is charged with high current and the damage to the battery is relatively small. The battery is basically not higher than the serious hydrogen evolution voltage. Once the voltage is higher than the hydrogen, the battery will lose water quickly. The use of such chargers must be continuous charging and discharging. If the battery is stopped for several days, the battery will produce more serious sulfidation and failure in advance. And users use batteries, it is impossible to ensure that every use, can be timely charged, a number of times within a year does not be timely charging, the battery will accumulate vulcanization. Some charger manufacturers exaggerate some functions, and the effectiveness of the finished products is not as good as advertised.
Other reasons
Many batteries can get better results in the monomer test. However, for the battery group, the difference in capacity, open circuit voltage, charge state and vulcanization degree will be expanded in the battery group. The single experience of state difference affects the whole battery, and the life of the battery is obviously reduced.
From battery charging on the production line, it takes many links to use this time after the user buys a car. The interval is even for a few months. During this period, a lot of lead sulfate produced by the battery is accumulated and crystallized as the battery is not supplemented. The new battery that the user has just bought may be already aged or even reported. Battery.
When the battery manufacturer is implementing quality assurance, the recovery battery is not completely eliminated. After the return of the battery, the battery manufacturer recharged the charge and discharge test. In the test, more than 60% of the single cell was found to be a battery that did not meet the return condition. The reason is that in the series of batteries, individual batteries are lagging behind and the whole battery function is reduced, which leads to the whole group retreating. Many battery manufacturers have retreated battery pack, replenishment, sulfur removal and packaging, and then re supply to users to improve battery life, reduce scrap rate, reduce the loss of battery manufacturer's partial claim, so many dealers have felt that the battery provided by the manufacturer is not as good as a generation. One generation, so you should shine your eyes when the battery is chosen