UN38.3 Standard Requirements for Lithium Battery Production

 

UN38.3 Standard Testing Items & Procedures

The UN38.3 standard includes the following 8 detection items:

• T1 low pressure,
• T2 temperature cycle,
• T3 vibration,
• T4 shock,
• T5 external short circuit,
• T6 heavy object impact (lithium battery core),
• T7 overcharge (lithium battery or lithium battery )
• T8 forced discharge (lithium battery cells).

For lithium batteries or lithium battery packs, a total of 7 items of tests T1 → T5, T6, and T7 are required. However, for lithium battery cells, T1 → T5, T6 and T8 tests are required. Among them, T6, T7, and T8 tests need to use separate samples. And T1 → T5 test sequentially tests the same sample.

Comparison of UN38.3 & International Standards

Compared with other international lithium battery standards, the temperature cycling conditions specified in the UN38.3 standard are more demanding and longer. Other international standard test items generally use separate samples for testing. However, the T1 → T5 test in the UN3813 standard tests the same sample in sequence. The previous test may have a negative impact on the next test, resulting in failure to pass the test. If the lithium battery submitted for inspection is tested for T1 → T5 in the UN 38.3 standard, there will be one item unqualified. Enterprises need to re-test UN3813 standard after process improvement, which will greatly extend the testing cycle.

It can be known from Table 1 that compared with the international standard IEC62133, the high and low temperature exposure time of the temperature cycling item in the UN3813 standard is up to 6 hours, and the low temperature test temperature is -40 ± 2 ° C. The temperature cycle of the temperature cycle test is larger and the test cycle is longer. It is easier to cause the internal materials of the battery cell to decompose and generate gas. In the case of problems in the production process, when the gas generated during the temperature shock reaches a certain pressure, the gas is likely to leak from the weak point of the battery case or the internal seal, resulting in substandard phenomena such as gas leakage and liquid leakage.

Analysis of UN3813 Standard Test Results & Causes

First case

In the UN3813 standard, the lithium batteries tested in the temperature cycling project are fully charged (100% SOC). Therefore, when subjected to a long-term temperature shock, relatively serious side reactions may occur inside the battery, generating a large amount of gas. If there is a problem with the manufacturing process of the battery, when a certain amount of air pressure is accumulated, the gas and the electrolyte may leak from the gap in the case or the place where the solder is welded.

Problems in the manufacturing process may have the following conditions:

1. The welding of the battery case and the cap is not firm and not sealed;
2. There are missing welds, false welds and cracks, and welds have cracks, cracks, etc .;
3. When the steel ball is sealed, the size of the steel ball is improper, and the material of the steel ball is different from that of the cap;
4. The positive pole of the cap is not tightly riveted, and there is a gap;
5. The elasticity of the insulating gasket is not suitable, it is not resistant to corrosion, and it is easy to age.

Problems such as mass loss, leakage, and exhaust during the UN38.3 standard temperature cycle are mainly related to the manufacturing process. Anatomy of the leaked battery revealed that the battery was subjected to uneven force during assembly, which caused the internal insulation plate of the battery to deform, causing the battery to leak at the insulation plate.

Second Case

In addition, the test also found that some lithium batteries have no mass loss, no leakage, no exhaust, no disintegration, no cracking and no combustion after the temperature cycle test. However, due to the chemical reaction between the positive and negative electrode active materials and the electrolyte inside the battery during the temperature shock, a certain amount of gas was generated, which caused a bulging phenomenon during the test.

However, the swollen lithium battery is more difficult to pass the vibration test during the next high acceleration and long time vibration test. The battery is likely to produce gas leaks and leaks, resulting in excessive quality loss and ultimately failing the vibration test. This requires lithium battery manufacturers in the research and development stage, in addition to continuous improvement of electrical performance, but also must fully consider the adverse impact of temperature shock on lithium battery materials.

Starting with lithium battery materials, the stability of each chemical material at the test temperature specified in the temperature cycle of 75 ℃,-40 ℃, and the transition points between 75 ℃ and-40 ℃ was investigated. Find out which materials are liable to generate gas at the test temperature. Through a large number of experiments to improve the process of these materials, or to find other alternative materials, to seek a better balance between the electrical performance and safety performance of lithium batteries.

Third Case

In another case, the lithium cell that swelled during the temperature cycle passed the subsequent vibration and shock tests. However, the large amount of gas generated internally during the temperature cycle adversely affects the welding parts around the shell. The pressure shock of the gas directly causes the welding strength to weaken in some areas. In the external short-circuit test after the impact test, the lithium single-cell battery rapidly heated up, and a large amount of gas continued to be generated inside the case. When the internal pressure of the shell rises to a certain value, the gas is released from the area where the welding strength becomes weak, causing the shell to rupture. As a result, the external short-circuit test cannot be passed.

The following test chambers are used in the standard UN38.3:

• Servo Computer Battery Crush Tester

• Vibration Test System

• Shock Test System

• Battery Crush Nail Penetration Tester

• Altitude Simulation Test Chamber

• Heavy Impact Tester

• Temperature Control Battery Short Circuit Test Chamber

• Battery Crush Test Chamber

• Temperature Cycling Test Chamber