Dynamic lithium battery thermal diffusion test standards and method introduction

　　Author ：Iflowpower – Portable Power Station Supplier

The fire of the power lithium battery is generally started by the thermal out of control of one or several batches, so we must study the thermal loss of the battery. Common thermal out-of-control causes include three major aspects, abuse, battery aging, and battery use. The third point is the defects in the manufacturing process.

At present, it is difficult to prevent it, although it is PPM level, but when we integrate battery cells into system, this ratio is also relatively high. In the first aspect, the internal short circuits caused by the abuse process, and then divided into mechanical abuse, electric abuse, heat abuse, abuse under the integrated use of multiple stress, which has been done in existing standard regulations. The corresponding requirements, but some structural damage or diameter growth in the aging process, and the inside short circuit caused by the manufacture of defects, the current regulations have no requirements, and the current technical means is more difficult to predict such a situation in advance.

So in this case, we proposed thermal out-of-control and thermal spread test projects. This situation SAEJ2464 and UL2580 have had corresponding requirements for thermal spread. At present, whether it is a single battery or a battery system, energy density is gradually improved, and according to the data and statistics of our test, it is found that the energy density of the battery is higher, the higher the energy density of the battery, and the thermal stability is relatively high.

It will be more likely to occur, which is more likely to occur. Based on this consideration, the new national standard introduces the thermal diffusion project. We have found that the new national standard and the national standard project that will be announced, in fact, the new national standard is in real weaken the requirements for the unit battery, while deleting the requirements for the module , But in the battery system, it has added thermal spread and overheating protection.

In fact, thermal spread is a comparative project, and I personally think that the thermal diffusion project can basically consider a safety comprehensive assessment project of power lithium batteries and battery systems, and even electric vehicles, which can be said to protect the person. A defense line. The second part briefly introduces some test standards and regulations of the current related thermal diffusion.

The first aspect is SAEJ2464, the test object requires modules and battery packs, and the test object is clear. When the single battery is thermal out of control, the system has The ability to prevent thermal out of control from spread to adjacent cells, and it is also recommended that manufacturers will test in battery modules. We are also such ideas in many companies in China, first test from module level.

The test method, compared to the national standard in which we have set it slightly, it is required to be 100% SOC, while testing at 55 degrees or the highest operating temperature in the battery, while the heating to 400 degrees or battery occurred in five minutes. Thermal out of control. Of course, it is also possible to supply its own method, as long as the method is described in detail, the standard is recommended, and the data to be recorded in the test includes temperature, voltage, etc.

, and photo video, and some Experimental phenomenon, including fire explosion and toxic substance leakage. This picture shows the five we can choose the trigger point recommended by the 2464, just a schematic, because the actual data is much more complicated than this, for us for reference only. The second standard is UL2580.

This standard directly references 2464 test methods. When testing, the battery sample cannot occur outside or explosion. EVS-GTR Electric Vehicle Safety Global Technical Regulations, the current phase of work results, form a document, used to indicate the inside short circuit, and in the appendix, the test procedure for my country and Japan joint research, as a reference.

The two-stage current work is studying, the important content includes the research of thermal out-of-control testing, we have to get high repeat triggers in the second stage. Research the impact of test equipment, as well as in the second-stage clear basic principles, what kind of test conditions or what kind of change can be accepted. Further research some potentially thermal disabled triggering methods, but also to achieve better experimental repeatability.

Finally, the reasonability of judging whether the thermal out of control is passed, and finally forming a judgment condition. This is our Chinese work plan, including four parts, including triggering methods research, and judgment conditions, as well as the same aspect, repeatability of experimental results, and different methods of experimental results, finally hot diffusion Research on project judgment conditions. First, you should study different trigger methods, clarify the parameters of different triggers, and obtain high repeatability experimental methods.

Taking heating as an example, there is a lot of conditions that affect our experimental results, where heating power and heating position is two key factors affecting the results, so we will take these two parameters to design experiments, say repetition Sex, only a language representation, there is no quantitative meaning, in order to better assess repetitability, a quantifier meanings, use heating time and thermal out-of control temperature, these two thermal out-of-control processes are more critical Difference coefficients can be repeatable as judging experimental methods. After we launched a large number of experiments, we can obtain experimental conditions with better repetitiveness by comparing the standard difference between heating time and thermal out-of control temperature, that is, the duplicity of repetitiveness, further we can pass through other constraints, such as heating Time, and how much energy is introduced in the system, reduce the target range, we want to finally obtain functional relationships between heating power and battery energy and battery weight, or between functional relationships. In order to give all the institutions in subsequent experiments, we have a relatively good experiment repeatability.

In order to carry out this work, we have made a test plan. Each battery has to do more than two hundred experiments, the workload is very good, this may also be the difficulty of our later work. At present, we are also in theory some analysis, and combined some simulation work, we want to reduce the experimental work.

Briefly introduces the work that has been carried out, this is a 18650 battery, the heating power of 80W, 100W, 120W is selected, and the heating trigger is extremely controlled. The most critical amount is the standard difference, you can see 80W heating conditions, the two standard differences are relatively low, repetitive is relatively better, of course, this experimental conditions are small, we want more experiments Get the best conditions. Place the three experimental temperature curves, we can see that the results are consistent, when 80W is heated, can repeatable intuitive look still.

This is our work now, and there are still many jobs to do. The third part is that I personally understand the thermal spread of national standards, this part may also be a point that many companies are more concerned now. Because hot diffusion is a new project, and is a semi-open project, there are many uncertain things, the basic requirements and the previous standards in the national standard are consistent, and the battery system has caused a single thermal out of control that leads to the prior five minutes beforehauling.

To issue a hot event alarm signal, understanding the danger of national standard is a fire explosion, there is no way to enter the crew as a danger (battery system as a test object), the company can use it as a request. Because this project is a semi-open project, we have to do with the company and test organizations, and the company has more instructions, as well as design and technical documents. Test institutions will carry out corresponding thermal diffusion experiments in accordance with the company's related design and demonstration.

This page shows some files to supply some files, relatively detailed requirements, is important to include alarm signals and technical documents to illustrate battery packages and system security. This technical document is much more covered, including our pair Risk analysis, as well as strategies to respond to risks, including structural design, functional design, and implementation of these functions, etc. This is a summary of our different situations we may encounter in the process of launching the thermal diffusion experiment.

There should be five possible situations, starting from the lower left corner of the battery, if the battery itself can pass different triggers and cannot trigger heat. If it is out of control, this project is my current understanding. The final standard is not announced, and the understanding of the comments, when the battery cannot trigger a heat loss, it can be considered directly, of course, this is also experimentally Verify; if the battery can trigger a thermal out-of control, it is divided into a few cases, the battery is detected by the thermal out-of-control, issuing alarm signal, only one battery is thermal out of control, but there is no spread, there is no harm, no fire and explosion This is through.

If the alarm signal is issued, the battery has a thermal spread, but the harm is also happened, and there is also the second and third cases. It has a heat spread, and there is a hazard. At this time, the condition is passed.

The time interval between the alarm signal and the hazard is not passed. T is more than 5 minutes. It is to give the passengers five minutes to the passengers in advance, remind passengers to escape.

There are several key concepts in this process, including thermal out-of control, thermal out-of control testing and alarm signals. We understand the improvasible heat reactions of thermal out-of-control meaning. In fact, it is difficult to implement, because it is a simple Description, we give a recommendation to judge the thermal out-of control conditions.

Why is it recommending, Tariir said that the different materials different systems have different design, which may have the difference in battery performance. Although the temperature is sharp, the temperature is sharp, if we quantitatively analyzed, this temperature will also have a relatively large difference, so it is not easy to give a very clear meaning at this stage. So, this standard has given an opening, this thermal out-of-control meaning can be meaningful by the company himself.

This page is an understanding of the alarm signal, because the alarm signal directly determines the time interval T, is it through, the alarm signal is a very critical point, the alarm signal will happen to when, the general company settings include four situations. In the figure, the alarm signal may be alarm signal in the process of thermal out-of control, or the thermal out-of-control occurrence process is allowed, or the alarm signal will issue alarm signal after the thermal out-of-control occurrence process. It is confirmed that the battery is completely out of control, but there are two cases before the alarm signal occurs actually in the actual occurrence of thermal out-control, and a case is that the alarm signal is issued.

There is no thermal out of control, which is not allowed, only when the battery After the thermal loss of control, the experiment will be normal acceptable. Incident, the issuance of the alarm signal does not have clear request, but the alarm signal is issued, and our trigger conditions should stop, but must ensure that the battery does not have thermal out-of control. Quaternary, several ways to short circuit, thermal out of control in batteries.

This page PPT is also useful in this report, briefly introduces, including the theoretical simulation short circuit, we manufacture some of the defects in the battery, whether it is introduced into some impurities, or how to make diaphragm defects, this is a method, However, this method should be a corresponding design and treatment in the production stage, so the difficulty of practice is still relatively high. Several methods, including acupuncture, heating, overtake, a lot of overcharges are invalid, it is difficult to trigger heat out of control, now the attention is in needling and heating. There are other methods, lasers, self-heating, etc.

Introduction to a self-heating, connecting a thermal resistor on the battery positive and negative, and heats the battery to heat the battery trigger. This method is now in the verification phase. You can verify that the fifth point of this method is the precautions for thermal diffusion test.

Before dividing, after the test and the test, everyone imagined, the smoke is very large, the fire is also very large, in the process of doing this test, in order to change the battery as small as possible before the test, some harness can be passed from the battery Some high and low pressure interfaces are connected. If we do heating experiments, if additionally punched or from sealing structural leads, it will destroy the battery sealing structure, because do not use the positive and negative of the battery in the test process, we are When doing transformation, it can actually use the powerful wire bundle to introduce the heating line, so that there is no test under the condition of the battery shell seal. It is very likely that there will be some sensors in the preparation process, and we will make some redundancy will better help us get data.

There will be a lot of toxic and flammable flue gas in the test process. It is necessary to consider exhaust and exhaust gas treatment. In addition, it is possible to fire and explode in the test process.

After the test, because the samples after the test may not completely occur thermal out-of control, there is a part of the battery may have some residual energy. We must first release the energy to do the follow-up processing. We are doing some project cooperation based on national key research programs based on national key research programs.

In the early stage, some gas types and contents of different batteries occurred in different batteries, which did have some toxic substances. When we did different capacity battery thermal out of control, we would find obvious New, but other gas content has no particular change, it may be that in this process, the production of carbon monoxide has a certain priority, which may be given to carbon monoxide. If the environment is open, the carbon monoxide may be further converted to carbon dioxide.

The last part is related to thermal out-of control prevention and testing, this piece is just simply. We think that the electrolyte leak detection can be made in the early days, and the electrical connection failure monitoring can be made by the change of the current voltage or the temperature information judgment circuit connection. There is also a monitoring of smoke and fire.

Wait, the creation of Li Pi should have a better way. In addition, it is internal short-circuit monitoring. We understand that short-circuit occurrence is a relatively relatively time process.

In general, short circuit is small range, and there will be no security issues, just in performance or There are some changes in the voltage. If we are better able to discover short circuit in the battery early, there is a more helpfulness of our prevention and judgment battery thermal out of control.