Research on the evaluation of 18650 battery lithium ion 2200mah safety performance

As we all know, whether it is the electric vehicle fire incident last year or this year, the first thing that comes to mind when an electric vehicle catches fire is the 18650 battery lithium ion 2200mah, at least the suspect is relatively large. In fact, if you really look at it, when an electric vehicle catches fire, the battery may be part of it. In fact, there are some other reasons, such as the charging system itself, or the interconnection between the entire system, or some corresponding related problems. Specifically for power batteries, there are some extreme abuses, and there may also be some system problems. For example, some problems that occur during the charging process may not only be problems with the 18650 battery lithium ion 2200mah itself, but also involve communication problems between the car and the charging system.

Let's go back to the discussion of electric vehicles. Various problems may occur during use, such as inability to drive, a significant decrease in driving range, insufficient power, etc., which may be caused by 18650 battery lithium ion 2200mah problems. For example, capacity decay may be due to the reduction of its effective lithium usage, the battery itself has insulation failure problems, leakage problems, etc. These problems are related to its past and present lives, in its material selection process, manufacturing process, and even in its actual application process.

How do we evaluate the safety of a battery? We should analyze it from several dimensions, microscopically and macroscopically. The microscopic aspect is analyzed from the material level, and the macroscopic aspect is analyzed from the system level, including the structure, functional safety, chemical safety and other related considerations of the entire electrical safety. In the process of 18650 battery lithium ion 2200mah evaluation and safety evaluation, it should be a closed-loop system, that is, from materials to the final product, whether it is a battery cell, module or system, and finally these performances are reflected in the application process, especially the safety performance that is the focus, which should be a closed-loop system. When we analyze, we should analyze it in combination with its past and present. As we all know, electric vehicles are required to be connected to the national monitoring platform, and power batteries should have a traceability system. The battery should be traced from material selection, manufacturing, testing, use, retirement and other related information.

The United States, the European Union and other countries have been studying the safety standards of electric vehicles and key components earlier. In recent years, the relevant standard system of electric vehicles and power batteries in my country has gradually improved. Internationally renowned 18650 battery lithium ion 2200mah research institutions, such as SAE, ISO, UL, etc., have formulated a system of standards, which cover battery cells, modules, systems, and test items include electrical performance, safety, reliability and other aspects.

Next, we will introduce some typical standards, such as UN38.3. Because power batteries are transported as dangerous goods, UN38.3 test reports must be issued before transportation, involving test contents from T1 to T9.

The standards that are used for reference include the US FreedomCarSand2005-3123, and the test contents include: mechanical abuse, thermal abuse, and electrical abuse tests. Thermal abuse is also a focus of our country. Specifically for thermal abuse, it includes relevant requirements such as thermal diffusion and thermal runaway expansion. At the same time, some corresponding test methods and test processes are also recommended. This process should be very meaningful for reference, and the number of test samples and the test sequence are reasonably arranged.

SAEJ2464 has made detailed introductions from the aspects of mechanical, thermal abuse, and electrical abuse.

Let's focus on the US UL2580 standard. In addition to the mechanical environment experiments we mentioned earlier, it is more distinctive in electrical testing. It mentions temperature rise experiments, including unbalanced charging, and even cooling system failure related experiments, because these experiments may be the problems we will face in our actual application process. Let's take a simple example, such as the thermal balance failure system. As you may know, in recent years, under the premise of higher and higher energy density requirements, some models have cancelled the thermal management system for cost and weight considerations. It may not have a big impact on new cars, but two years later or five years later, the battery life and safety performance will be a big question mark.

EU ECER100, power batteries have been mandatory since 2016, with 10 test items. The requirements of these standards are similar to those of our domestic standards.

Back to China, before 2015, the standards related to power batteries were relatively lacking. If you are familiar with this industry, the earliest battery announcement experiment in 2015 referred to the industry standard QC/T743 of the automotive industry, which was helpful in the early stage. If it is a comprehensive evaluation of a product, it is still lacking. However, with the release of our entire series of standards, including GB/T31467, 31484, 31485, 31486, and then to the recently released traceability system, the retired recycling system and other related standards, as well as the recently mentioned national standard for 18650 battery lithium ion 2200mah safety, these standards have played a good role in the front end of our products after they were successively issued. Specifically, 31485, the safety requirements experiment related to monomers and modules. 31467.3, the mandatory test requirements for battery systems, a total of 16 items.

Safety technical requirements for electric buses, the requirements for thermal runaway and thermal runaway extension of power batteries, mainly due to the hidden dangers of group deaths and injuries in buses. At present, relatively safe lithium iron phosphate batteries are mainly used, and ternary batteries cannot be used at present.

The focus is on the new GB power vehicle battery standard, because it is a GB mandatory standard. According to the current WTO notification, it is expected to be released in June or July this year. After the release, there will be a transition period of about one year, and it may be implemented after July 2020. This standard covers GB/T31485 and GB/T31467.3. At the same time, combined with the battery thermal runaway and thermal runaway extension related content in electric bus safety, the standard also defines the relevant test process.

Comparing domestic 18650 battery lithium ion 2200mah safety standards, at the cell and module level, from the perspective of the entire test items and requirements, my country's standards are relatively stricter. At the system level, you can see that our original 31467.3 standard largely draws on the ISO12405 standard.

Here we compare different standards for the puncture test. For example, the extrusion plate form of the 18650 battery lithium ion 2200mah we mentioned, including the new national standard, ECER100 standard, UL2580 standard, and SAEJ2464 standard, is different in terms of extrusion direction, extrusion degree, holding time, test object, SOC state before the test, and test requirements. Compared with international standards, the relevant standards in my country are more stringent.

In general, there are still many test standards for power batteries at home and abroad, and the test methods and acceptance standards are also different. After the development of the past few years, the current 18650 battery lithium ion 2200mah safety-related standards in our country are relatively comprehensive, basically covering some major international test items, including battery development trends and dynamic updates, such as thermal management-related test items, which will be further standardized and considered later. At the same time, the safety test of power batteries in my country needs to be further strengthened in terms of test resources, test equipment, and research objects.

Finally, I will briefly introduce some 18650 battery lithium ion 2200mah test case analysis we are doing. This is the requirement of electric vehicles. First of all, these requirements on the vehicle must be met, and the corresponding test requirements for the 18650 battery lithium ion 2200mah system, including its performance, safety, reliability, and even battery interface requirements. Among these requirements, the focus is on safety performance requirements. At present, when conducting relevant announcement experiments for customers or vehicle manufacturers, in fact, many companies' test requirements are far greater than the standard requirements. When companies conduct experiments, they require not only the relationship of Yes/No, but what requirements can be achieved. Many R&D experiments will be done here. This is a typical needle puncture test. Although there is no fire or explosion, which meets the standard requirements, the voltage changes and temperature conditions of the adjacent cells will be analyzed.

We also conduct needle puncture, overcharging and other abuse tests for different ternary battery cells, different types of batteries, such as soft packaging, square batteries, and different material systems.

At the same time, you can see that the thermal diffusion analysis of the lithium iron phosphate battery system triggers its thermal runaway through needle puncture, and we see the temperature of the surrounding cells, including the voltage. The analysis of related thermal performance is studied through overcharging and heating methods, and the characteristics of other related thermal performance are observed after the failure of some batteries.

The management of the surrounding environment after thermal diffusion, including the internal and external conditions after the partial failure of the battery pack. It includes three comprehensive experiments, combining vibration, environmental changes, charging and discharging working conditions, including mechanical impact experiments, and extreme extrusion experiments of battery packs. When doing the extrusion test, the extrusion direction is different, and the results may be different. For example, the position of the high-voltage interface and the wiring harness has an impact on the test results.

The standard requires a 2-minute fire test. In fact, many manufacturers may let you burn for 10 minutes or half an hour when doing the test. What is its state? There are also simulated collision tests, water immersion tests, drops, reliability, and protection function verification tests. In general, these verifications mainly control the front-end safety performance of new products. It is necessary to further strengthen safety supervision during and after the event.

At present, the safety of the entire 18650 battery lithium ion 2200mah should be further improved. There are many relevant standards at home and abroad. These standards are mainly used for the access or mandatory requirements of new products, but the supervision and relevant standards during and after the event need to be further studied and improved. This standard system can be used as a reference in the field of energy storage batteries.

In general, battery technology, whether it is lithium batteries or sodium batteries, these new battery technologies are constantly emerging. Whether they are used in power batteries or energy storage batteries, it should be said that the entire testing and evaluation methods and standards are constantly updated, which requires joint research and development in the industry.

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