The BYD Blade cell is an overall design philosophy that enables high system level energy density with LFP chemistry.
This is enabled by assembling the cells all together at pack level, creating a Cell to Pack design.
The BYD blade cell to pack design is interesting as it has been designed by a company that understands vehicle design. Also, this pack design is used in production in a large number of their own vehicles.
The following image is from a BYD [1] and shows an image of the nail above the Blade cell and then on the right with the nail through the cell. The text that accompanies this image in the reference states:
“The nail penetration test is regarded as one of the most rigorous ways to test the thermal runaway of batteries. The purpose is to simulate an internal short circuit of the battery. This is usually caused by external sharp metal objects penetrating the battery in a severe traffic accident. The Blade Battery passed the nail penetration test, without emitting smoke or fire. The surface temperature only reached 30 to 60°C.”
However, the image on the right appears to show burning gases. This might be gas and the orange is due to a lighting flare. The cell has expanded significantly during the test and that is consistent with the cell materials reacting. Also, this is a very open environment and hence hot gases are being allowed to expand and cool rapidly.
Xiang Gao et al [2] describe the need for the nail test, but then discuss the variable reproducibility: The nail penetration test is designed to mimic a mechanical abusive scenario where a foreign object penetrates the cell, and now it is recommended as one of the safety standards a cell must pass before it is ready for the market, especially for the EV industry.
In a paper from Yuqing Chen et al [3] they have a table of test standards and this shows the variations in the nail test.
We know there is a lot of test to test variation and differences between standards. Hence showing an arbitrary nail test doesn’t really prove anything.
This variability in the testing is even shown in BYD’s own media posts on nail testing of the Blade cell.
The Blade cell in this test is very inert, no gas is released and the cell is not swelling as we see in the early test image.
Overall, we know that Lithium Iron Phosphate chemistry is far less reactive in this test compared to NMC or NCA. However, there is a lot of variability based on the cell conditions and the test conditions. This is even shown by BYD in their own promotional material.
If you have more data on the BYD Blade nail penetration test please do contact us.
This post has been built based on the support and sponsorship from: Eatron Technologies, About:Energy, AVANT Future Mobility, Quarto Technical Services, TAE Power Solutions and The Limiting Factor.
References
- BYD Song Plus DM-i, BYD
- Xiang Gao, Yikai Jia, Wenquan Lu, Qingliu Wu, Xinyu Huang, Jun Xu, Mechanistic understanding of reproducibility in nail penetration tests, Cell Reports Physical Science, Volume 4, Issue 9, 2023
- Yuqing Chen, Yuqiong Kang, Yun Zhao, Li Wang, Jilei Liu, Yanxi Li, Zheng Liang, Xiangming He, Xing Li, Naser Tavajohi, Baohua Li, A review of lithium-ion battery safety concerns: The issues, strategies, and testing standards, Journal of Energy Chemistry, Volume 59, 2021
- Nail Penetration Test on the BYD Blade Battery and NCM Battery, BYD Europe
- BYD’s revolutionary Blade Battery: all you need to know, BYD