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.
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 such a life test, the battery can reach 350 times life cycle.
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