3 major cheats solve the inconsistency of charging lithium batteries

2022/04/08

  Author :Iflowpower – Portable Power Station Supplier

The inconsistency of the battery is formed in the production process, deepened during use. The battery in the same battery pack is weak, and the acceleration is weak. The degree of dispersion between the parameters between the monomer cells, increases with the degree of aging.

The power lithium-ion battery has stabilized the status of electric car power supply rivers and lakes. Long service life, high energy density, and great improvement. Security can be changed, energy density can continue to rise.

In the foreseeable time (legend about 2020), you can catch up with the battery life and cost performance, step into the first maturity stage of electric cars. However, lithium-ion batteries also have a lithium ion battery troubles. 1.

Why is the lithium-ion battery that is a lithium-ion battery, cylindrical battery, soft bag lithium battery, square battery, generally can't find a large piece of traditional lead-acid batteries, why not find the traditional lead-acid battery? ? High energy density, lithium-ion battery often does not dare to design a large capacity. The energy density of the lead-acid battery is about 40Wh / kg, while the lithium ion battery has exceeded 150Wh / kg. Energy concentration is improved, and the requirements for safety is high.

First, a lithium-ion battery that is too energy is too energy, encounter accidents, causes thermal out of control, and the internal response in the battery. In a short period of time, too much energy is everywhere, it is very dangerous. Especially in safety technology, the capacity of each battery should be restrained when there is still not enough development.

Secondly, the energy wrapped by the lithium-ion battery housing, once unexpected, firefighters, fire extinguishing agents can not touch, no power, can only isolate the site when there is an accident, the battery is self-reacting, energy burning. Of course, for safety reasons, current lithium-ion batteries have designed multiple safety means. Take a cylindrical battery as an example.

Safety valve, when the internal reaction is outside the normal range, the temperature rises, and accompanying the generation of the side reactive gas, the pressure reaches the design value, the safety valve is automatically opened, discharged from the pressure. The moment of the safety valve opens, the battery is completely invalid. Thermistor, the other battery is configured with a thermistor.

Once an overflow occurs, after a certain temperature reaches a certain temperature, the resistance has increased sharply, and the circuit current is lowered, and the temperature is further increased. The fuse, the battery is equipped with a fuse having an overflow-fuse function, once overcurrent risk, circuit is disconnected, preventing malignant accidents. 2.

Lithium-ion battery consistency problems The lithium-ion battery cannot be made, so I have to organize many small electric batteries. Everyone will make it, and they can fly with electric cars. At this time, we must face a problem, consistency.

Our daily related experience is that the two dry batteries, the positive and negative is connected, and the flashlight can illuminate, who can manage it. And the large-scale application of lithium-ion batteries, the situation is not so simple. The inconsistency of lithium-ion battery parameters is important means that capacity, internal resistance, and open circuit voltage are inconsistent.

The inconsistent battery string is used together, there will be the following questions. ❶ Capacity loss, battery cell monomer constitutes battery pack, capacity complies with "wooden bucket principle", the worst capacity of the battery determines the capacity of the entire battery pack. In order to prevent the battery overcharge, the logic of the battery management system is set this: When the lowest monomer voltage reaches the discharge cut voltage, the entire battery pack stops discharge; when charging, when the highest monomer voltage touches the shutoff voltage , Stop charging.

Take two batteries in series. One battery capacity is 1C, and another capacity is only 0.9c.

Series relationship, two batteries pass the same size. When charging, the battery with a small capacity will inevitably be full, reach the charging deadline, the system no longer continues to charge. When discharge is discharged, the battery is small, it will inevitably put all the available energy first, and the system will stop discharge.

In this way, the cells with small capacity are always full, and the capacity is large, but the part capacity has been used. The total capacity of the entire battery pack is in a part of the long-term life loss, and the life of a similar battery pack is determined by the lowest life. Very probably, the shortest battery, the battery is small.

Small capacity battery, every time it is full of full, excessive, greatly arrived at the heart of life. Continue to the end of the battery, a set of soldered batches, just fall in the end. The internal resistance increases, different internal resistance, flows through the same current, and the internal resistance of the battery is more compared.

The battery temperature is too high, causing deterioration speed, internal resistance will further increase. Internal resistance and temperature rise, form a pair of negative feedback, allowing high internal resistance to accelerate deterioration. The above three parameters are not completely independent, the degree of electrical core in the degree of aging is relatively large, and the capacity attenuation is more.

Separately explain, just want to express it clearly of their respective influence. 3. How to deal with inconsistency in the performance of inconsistency, it is formed during the production process, deepened during use.

The battery in the same battery pack is weak, and the acceleration is weak. The degree of dispersion between the parameters between the monomer cells, increases with the degree of aging. At present, the engineer should be inconsistent with the monomer battery, and it is important from three aspects.

Monomer battery sorting, formation of heat management, a small amount of inconsistency, battery management system supply equalization. 1 Some of the batches of different batches, theoretically do not put together. Even if the battery of the same batch is also screened, put the cells in the relatively concentrated cells in a battery pack, in the same battery pack.

The purpose of the sorting is to select the cells close to the parameters. The sorting method has been studied for many years, important division sorting and dynamic sorting two categories. Static sorting, screening for the open circuit voltage, internal resistance, capacity of the battery, selecting the target parameters, introducing the statistical algorithm, setting the filter criteria, and finally divide the same batch of battery cells into several groups.

Dynamic screening, is screening for the characteristics exhibited in the charging and discharge process, some chooses a constant current constant pressure charging process, and some choice of pulse impact charge and discharge process, some compare itself between charging and discharge curve relation. The dynamic combination is selected, and the preliminary grouping is made with a static screening. On this basis, the dynamic screening is performed, so that the group is more, the screening accuracy is higher, but the cost will also rise accordingly.

Here is the importance of a dynamic lithium-ion battery production scale. Large-scale shipments allow manufacturers to make more subtle sorting, getting performance closer battery packs. If the output is too small, there are too many groups, and a batch cannot be equipped with a battery pack, and a good method cannot be displayed.

2 thermal management is not consistent with the internal resistance, and the heat is not the same. The joining of the heat management system can adjust the temperature difference of the entire battery pack to keep it in a smaller range. Generate a large amount of heat, still high temperature rise, but will not pull the gap with other cells, and the level of deterioration will not have a significant gap.

3 Equilibrium The inconsistency of the core unit, some of the electrical end voltage, always in advance, the first arrival of the control threshold, resulting in small system capacity. In order to solve this problem, the battery management system BMS designs a balanced function. A certain core is the first to reach the charging cutoff voltage, and the rest of the electric core voltage is obviously hysteresis, the BMS starts charging equalization function, or the access resistance, the part of the high voltage cell, or the energy transfer, put it low Voltage battery.

Thus, the charging deadline is released, the charging process restarts, the battery pack is charged in more power. Until now, the inconsistency of the battery is still an important field of research in the industry. The energy density of the battery is high, encountering inconsistency to stir, battery pack capability will also be big discount.

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