Analysis of Causes of Temperature Loss of Dynamic Lithium Battery

2022/04/08

  Author :Iflowpower – Portable Power Station Supplier

Dynamic lithium battery safety problem is summarized, it is called thermal out-of control, which is not controlled after reaching a certain temperature, and the temperature is rising, and then the explosion will be burned. Overheated, overcharge, short-circuit, collision, etc. are several key factors that cause thermal out-of control of dynamic lithium batteries.

(1) Overheating trigger heat loss causes the causes of dynamic lithium battery overheating from the selection of the battery and the unreasonable thermal design, or the temperature of the battery causes the temperature of the battery, and the cable connector is loose, and should be managed from battery design and battery management. Two aspects to solve. From the design angle of the battery material, it can be developed to prevent thermal out of control, block the reaction of thermal out-of control; from battery management perspectives, you can predict different temperature ranges to mean different security levels, thus grading alarm.

(2) Overcharge triggering heat loss This year, the reason why the pure electric bus fire event is that the thermal out of control of the charge trigger is the lack of the battery management system itself, which causes the battery's BMS that is out of control but still Charge. In response to this type of overcharge, the solution is first to find the failure of the charging machine, which can be solved by complete redundancy of the charging machine; secondly, it is unreasonable to see the battery management, such as no monitoring of each battery. It is worth noting that with the aging of the battery, the consistency between the various batteries will be getting worse, then the overcharging is more likely to occur.

This should be a balanced overall battery pack to keep the battery pack. For example, a series of battery packs of the most common battery pack combination method is used first, after solving the monomer consistency problem, the best case is the same as the same large capacity. After this consistency, the capacity rebounded, but also prevents overcharging.

In order to achieve consistency, there must be a method to make capacity estimates for each monomer. Ouyang Ming high suggests, the estimation of all battery pack status can be performed according to the similarity of the charging curve. That is to say, just understand the charging curve of one of the monomer batteries, other curves should be similar to it.

Through curve changes, they can be approximately complicated, and these differences in the middle of curve changes are easily calculated. Other monomers can be calculated according to a single body. With such a method, you can perform the balance of the consistency mentioned above.

Of course, this algorithm has time too long, simplified. (3) Internal short-circuit triggering heat loss of control Boeing 787 passenger aircraft once fired due to battery explosion. When finding the cause of the accident, it is found that there is a metal material on the electrode and the diaphragm.

Although experts can't confirm that thermal out of control is triggered by internal short circuit, it is the most likely reason, because other reasons are not found, and there is no way to short the short circuit. Battery manufacturing impurities, metal particles, charge and discharge, reflective, and lithium lithium, etc., it is possible to cause internal short circuits.

This intramine short circuit is slow, and the time is very long, and I don't know when it will have a thermal out of control. If you test, you cannot repeat the verification. At present, the world experts have not found the process of short-circuit caused by impurities, both in research.

To solve the internal short circuit problem, you must first find battery quality battery manufacturers, choose battery and battery monomer capacity; secondly short circuit safety prediction, you have to find a single single. This means that the characteristics of the monomer must be found, which can be started from the consistency. The battery is inconsistent, the internal resistance is inconsistent, as long as it finds a monomer having a variant in the middle, you can distinguish it.

Specifically, the equivalent circuit of the normal battery and the equivalent circuit of the micro-short circuit, the form of the equation is actually the same, but the normal monomer, the parameters of the micro-short single cells have changed. It can be studied for these parameters to see some of their characteristics in the short-circuit changes. One of the characteristics is the potential difference of the short-circuit monomer, which compares the difference between its internal resistance and other monomers.

Ouyang Minggao proposed that R & D personnel should use models to make monomers. After measuring the voltage and current of each monomer, the internal resistance of each monomer can be previvable by using these data. After all of the parameters of the monomer are all estimated, according to the change of the parameters, it can be determined whether the consistency has a significant change.

(4) Mechanical triggering heat loss collision is a way of typical mechanical triggering heat loss. Tesla repeatedly a fire accident is this reason. Ouyang Ming high revealed that Tsinghua University cooperates with MIT to analyze Tesla in the United States collision accident.

If a simulation collides in the laboratory, the closer is acupuncture. Solving the impact of the crash trigger is to do a good job in battery safety design. And this is to develop a person to first understand the process of thermal out-of control.

In general, after the thermal out of control, it will spread down. For example, there will be heat transfer after the first heat loss, start spread, and then the whole group is like a pen. In response to this transmission, a model can be established, including intermediate temperature rise, heat generation, heat transfer convection, etc.

The entire thermoelectric coupling model can be used to use the heat meter to do a related quantitative analysis. With the spread model, the R & D personnel can design how to block and suppress, this should be loaded. However, the addition of the heat-insulation layer is not simple, on the one hand, the volume is large, and the insulation layer is contradictory with the insulation layer and cooling.

These are the problems to solve. In summary, in terms of thermal out-of-control expansion and inhibition, R & D personnel should start from two aspects of safety protection design and battery management.

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