button battery cr1620

Analysis of thermal runaway phenomenon of ternary power button battery cr1620

With the continuous increase in the mileage of electric vehicles, ternary materials with higher energy density have gradually replaced lithium iron phosphate materials with better stability. Although ternary materials bring higher energy density to power lithium batteries, their thermal stability is low, especially high nickel materials begin to decompose at around 200°C and release O2, which also leads to the safety of ternary material lithium batteries being lower than that of lithium iron phosphate materials. Therefore, once electrical abuse, thermal abuse and mechanical abuse occur, it is easy to cause thermal runaway of the battery.

Recently, Xian Xuelei (first author) and Dong Haibin (corresponding author) of Tianjin Fire Research Institute of the Ministry of Emergency Management studied the thermal runaway behavior of ternary soft-pack lithium batteries under thermal triggering and overcharge triggering thermal runaway. The study showed that in the case of thermal triggering, the main thing is the high-temperature decomposition of the positive electrode material to produce O2 and the mixed gas produced after the electrolyte gasification, so the battery directly sprays flames, while the thermal runaway triggered by overcharge mainly comes from the large amount of alkane gas produced by the reaction of the negative electrode and the electrolyte, so the battery first sprays and then ignites.

The basic information of the soft-pack ternary button battery cr1620 used by the author in the experiment is shown in the figure below. The positive electrode material of the battery is NCM811, the negative electrode is graphite, and the battery capacity is 107Ah.

In order to observe the behavior of the above-mentioned soft-pack button battery cr1620 during thermal runaway, the author designed the observation system shown in the figure below, using a high-speed camera (4000 frames/s), a thermal imaging camera and an ordinary camera to record the entire thermal runaway process. In the experiment, the author used two methods to trigger thermal runaway. The first is heating. By adding a hot plate at the bottom of the battery, the fully charged battery is heated to trigger thermal runaway. The second method is to use charging and discharging equipment to continuously charge the battery and trigger battery thermal runaway by overcharging. Among them, the thermal trigger mainly includes the following steps:

Full charge

Heating until thermal runaway stops. Heating overcharge trigger includes the following steps:

Full charge

Continuously charge the battery with a current of 50A until thermal runaway stops. Charging and heating trigger. Thermal runaway thermal triggering process can be divided into five steps in total: 1. Heating, battery bulging; 2. Explosion at one end; 3. Explosion at the other end; 4. Quiet combustion; 5. End. Through test data, it was found that when the battery was heated to 215.7℃, the battery began to swell and the electrolyte exploded, and one end of the battery began to spit fire. About 7s later, the other end of the battery also began to spit fire, and the battery also began to crack and spit fire around it. This process lasted for 19s, with the highest temperature of 720.1℃. The battery then entered the process of quiet combustion, which lasted for 28s. During the entire heating process, the battery voltage basically did not change until the battery exploded, and the battery voltage suddenly dropped to 0V, which shows that we cannot warn of battery thermal runaway by detecting voltage abnormalities.

In order to verify the triggering temperature of battery thermal runaway, the author heated the battery to 100℃, 150℃ and 200℃ respectively. The test results show that the battery will not experience thermal runaway at 100℃ and 150℃, and thermal runaway will only be triggered when the heating temperature exceeds 200℃.

The figure below is a picture of the battery thermal runaway moment recorded by the author using a high-speed camera. It can be seen that the battery ruptures near the pole ear, and the battery explodes very quickly. In less than 0.5s, a large amount of flames spew out from the cracks in the aluminum-plastic film.

Overcharge triggers thermal runaway

Overcharge triggers thermal runaway can also be divided into 5 stages: 1. Battery bulging; 2. Explosion at one end; 3. Explosion at the other end; 4. Quiet combustion; 5. End.

The test found that when the battery overcharged to 126% SoC, the maximum temperature of the battery surface reached 98.7℃, and the maximum battery heating rate was 1.7℃/min. Then the battery expansion rate and heating rate also began to increase rapidly. The heating rate of the battery surface and the pole ear was not less than 5℃/min. Then one end of the battery exploded. About 2s after the explosion at one end, the other end also exploded. At the same time, the other two long sides of the battery also tore. The battery began to spray fire in multiple directions. The whole process lasted about 5s. Then the battery began to burn quietly. This process lasted about 43s. During the whole process, the battery voltage continued to rise until the battery exploded and the voltage suddenly dropped to 0V.

The figure below shows the battery explosion caused by overcharging recorded by a high-speed camera. From the figure, we can occasionally see that the pole ear at one end of the battery cracked, spraying mist and solid particles in a high-temperature molten state. During the explosion, sparks appeared at the opening of the battery, and the electrolyte was ignited, causing violent explosive combustion.

In the battery explosion caused by overcharging, the electrolyte sprayed out of the battery did not burn in the early stage. When these flammable gases and liquids and the oxygen in the air reach a certain concentration, the molten particles sprayed out of the battery will suddenly ignite them, causing explosive combustion (as shown in the figure below).

Xian Xuelei's research shows that there are certain differences in the behavior of batteries in thermal runaway triggered by heating and overcharging. When the battery shell ruptures during heating, the gas sprayed out is mixed with a considerable amount of O2, so the battery directly sprays flames. When overcharging triggers thermal runaway, the liquid and gas sprayed out by the battery first, as well as the mixture of molten particles, are ignited after mixing with oxygen in the air to a certain concentration, and then explosive combustion occurs, which is even more severe than thermal runaway triggered by heating.

This article refers to the following literature. The article is only used for the introduction and commentary of relevant scientific works, as well as classroom teaching and scientific research, and shall not be used for commercial purposes. If there are any copyright issues, please feel free to contact us.

Study on thermal runaway and fire characteristics of ternary lithium-ion power lithium batteries, Energy Storage Science and Technology, 2020.19(01):239-249, Xian Xuelei, Dong Haibin, Zhang Shaoyu, Li Yi, Liu Lianxi, Yu Dongxing, Sheng Yanfeng, Yi Chengyi, Han Guang

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