The safety of power battery safety is summarized as “heat out of control”, that is, after reaching a certain temperature, it is uncontrollable. The temperature rises straight and will then burn and explode. And overheating, overcoming, internal short circuit, collision, etc. are several key factors that cause power battery thermal control.
(1) Excessive trigger heat loss
The reason for the overheating of power batteries comes from the unreasonable selection and thermal design of the battery, or the temperature of the battery is increased and the connector of the cable is loose, etc., and the connection of the cable should be resolved from the two aspects of battery design and battery management.
From the perspective of battery material design, it can develop materials that prevent heat out of control and block the reaction of heat -outdooring; from the perspective of battery management, different temperature range can be predicted to define different safety levels, so as to conduct a hierarchical alarm.
(2) Over -charging trigger heat out of control
The reason for this year’s pure electric buses is “the heat -out -of -control triggers of overcharging”, which is specifically that the battery management system itself lacks the over -charging circuit safety function, which has caused the BMS of the battery to be out of control but is still charging.
For the reasons for this type of over -charging, the solution is first to find the failure of the charger, which can be solved by the fully redundant of the charger; the second is that the battery management is unreasonable, such as the voltage of each battery without monitoring.
It is worth noting that with the aging of the battery, the consistency between the batteries will become worse and worse, and it will be more likely to occur at this time. This requires the balance of the entire battery pack to maintain the consistency of the battery pack.
For example, a series of battery packs that use the most common battery group combination method of “first and back string”. After solving the consistency problem of the monomer, the best case is to have the same capacity as the minimum monomer. With this consistency, the capacity has risen, and it can also prevent overcoming.
In order to achieve consistency, there must be a way to estimate the capacity of each unit. Ouyang Minggao recommends that the status of the entire battery pack can be performed according to the similarity of the charging curve.
That is to say, as long as you know the charging curve of one of the single batteries, other curves should be similar to it. After curve changes, they can be approximately coincide, and these differences in the process of curve changes are easy to calculate. Other monomers can be calculated based on a single. With this method, the consistency of the consistency mentioned above can be performed. Of course, the time for this algorithm is too long and needs to be simplified.
(3) Internal short -circuit trigger heating out of control
The Boeing 787 passenger plane had fire due to the battery explosion. When looking for the cause of the accident, it was found that there were metal objects on the electrode and septum, which produced short circuit. Although experts cannot confirm that thermal out of control is triggered by short circuit, it is the most likely reason because it cannot find other reasons, and there is no way to “emerge” in the short circuit.
Battery manufacturing impurities, metal particles, shrinkage, and lithium analysis of the rechargement and discharge can cause short circuits. This internal short circuit occurs slowly, and it takes a long time, and I don’t know when it will occur. If the test is performed, the verification cannot be repeated. At present, experts around the world have not found internal short -circuit that can be repeatedly caused by impurities.
To solve the internal short -circuit problem, we must first find a battery manufacturer with good product quality and choose the capacity of the battery and battery monomer. Secondly, the internal short -circuit predicts the internal short circuit. Before the heat is out of control, you must find the internal short -circuit monologue.
This means that the characteristic parameters of the monomer must be found, and you can start with consistency first. The battery is inconsistent, and the internal resistance is inconsistent. As long as you find a monitoring single in the middle, you can distinguish it.
Specifically, the equivalent circuit of a normal battery and an equivalent circuit that occurs in micro -circuit. The form of the equation is actually the same, but the parameters of normal monomers and micro -circuit monomers have changed. You can study these parameters to see some characteristics in short circuit changes in internal.
One of the characteristics is the difference between the internal short -circuit monologue, comparing the difference between its internal resistance and other monomers. Ouyang Minggao proposed that R & D personnel should use models to identify single. After the voltage and current of each unit are measured, using these data and then combining the model can predict the internal resistance of each single. After all the parameters of the monomer are estimated, according to the changes in the parameters, you can determine whether its consistency has undergone significant changes.
(4) Mechanical trigger heating out of control
Crash is a typical method of mechanical trigger heating out of control. This is the reason for Tesla’s repeated fire. Ouyang Minggao revealed that Tsinghua University and MIT jointly analyzed Tesla’s collision in the United States. If a simulation of collision in the laboratory is the closest is acupuncture.
The solution to the collision trigger heating out of control is to do a good job in the safety protection design of the battery. And this requires research and development personnel to first understand the process of heat out of control.
Generally speaking, after the heat is out of control, it will spread down. For example, there will be heat transfer after the first section of heat is out of control, starting to spread, and then the whole group like a split cannon one by one. In response to this kind of communication, a model can be established, including the height of the middle temperature, the production heat production of chemical energy, and the heat transfer convection. The entire thermal coupling model can use the heat meter to do a related quantitative analysis.
With the communication model, R & D personnel can design how to block and suppress it, which requires the heating layer. However, the thermal insulation layer is not simple. On the one hand, the volume is large, and on the other hand, the thermal insulation layer is contradictory. These are issues that need to be solved.
In short, in terms of thermal output expansion and suppression, R & D personnel should start from two aspects: safety protection design and battery management.