Three tips for solving the inconsistency of lithium-ion batteries

Author: Iflowpower - Fornitur Portable Power Station

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 battery has steadily occupied 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 (around about 2020), you can catch up with the battery life and cost performance, step into the image of electric cars. However, lithium batteries also have the trouble of lithium battery. For all aspects of the lithium battery, the spectral electronic statistics have a technical problem that customers often ask.

We have answered for lithium batteries: 1: Why do the lithium batteries are lithium batteries, cylindrical batteries, soft Pack batteries, square batteries, generally long-term clear show, completely can't find large blocks like traditional lead-acid batteries, why? High energy density, lithium 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 battery has exceeded 150Wh / kg. Energy concentration is improved, and the requirements for safety is high.

First, a lithium battery having excellent energy is excessive, encountering accidents, triggering thermal out-of control, rapid response internally, in a short time, too much energy is now 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 up by the lithium battery housing, once unexpected, firefighters, fire extinguishing agents can not touch, no power, can only isolate the site during the accident, the battery is self-response, energy burning.

Of course, for safety reasons, current lithium 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 function, once overcurrent risk, circuit is disconnected, avoiding malignant accidents. Solving the three major cheats of lithium battery inconsistent harm 2: Lithium battery consistency problems can not be made into a big one, have to organize many small electric batteries, everyone will make, sincere cooperation, and electric cars Fly. At this time, you need to face a problem, consistency.

Our daily experience is that the two dry batteries, the positive and negative is connected, and the flashlight can shine, and whoever does not consistent. And the large-scale application of lithium batteries, the situation is not so simple. The inconsistencies of lithium battery parameters are mainly due to capacity, internal resistance, and open circuit voltage.

The inconsistent battery string is used together, there will be the following questions. The capacity loss, the battery cell composition is compliant with the "wooden bucket principle", and the capacity of the battery core of * poor 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 unit voltage is discharged, the entire battery pack stops discharge when the unit voltage reaches the discharge cutout voltage; when charging, when * monomer voltage touches the charging cutoff 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 capacity of the entire battery pack is in part in the idle state life loss, the life of a similar battery pack is determined by the battery end of life *. Very probably, the battery is short, the battery is small, the battery is small.

Small capacity battery, every time it is full of full, excessive, very likely * the key points of arrival 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 cell is relatively more.

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 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. At present, the engineer should be inconsistent with the monomer battery, mainly from three aspects. Monomer battery sorting, formation of heat management, a small amount of inconsistency, battery management system provides equalization.

Different batches of batches are selected, theoretically don't put together. Even with the same batch, it also needs to be screened, put the cells in the relatively concentrated parameters in a battery pack, in the same battery pack. The purpose of the sorting is to select the battery similar to the parameters.

The sorting method has been studied for many years, mainly divided by static sorting and dynamic sorting two categories. Static sorting, screening for the characteristic parameters such as the open circuit voltage, internal resistance, capacity of the battery, select the target parameters, introduced the statistical algorithm, set the filter criteria, * divide the same batch of battery cells into several groups. Dynamic screening is to screen for the characteristics exhibited during the charge and discharge process.

Some select the constant current constant pressure charger, and some choose the pulse impact charge and discharge process, some contrast the charge between the charge and the 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 a small reflection of the importance of a dynamic lithium battery production scale. Large-scale shipments allow manufacturers to make more subtle sorting, resulting in 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. Hot management is not consistent with the internal resistance, generating heat is not the same problem. 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 does not pull the gap with other cells, the level of deterioration does not have a significant gap. The inconsistency of equalization of the equalization of the core unit, some of the electrical end voltage, always in advance, * to 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. .