JAKARTA - Independent testing of BYD's megawatt fast charging technology has sparked a debate on Chinese social media. This happened after a live charging session showed the surface temperature of the vehicle's battery penetrating more than 76 degrees Celsius during the ultra-fast charging process.
As reported by Carnewschina, Friday, May 8, Chinese automotive blogger James Yu or known as "Caishendao", tested the BYD FCB Tai 3 with charging from 8 percent to 97 percent. Based on the data published, the external temperature sensor placed in the lower center of the battery pack recorded the highest temperature of 76.42 degrees Celsius.
Meanwhile, vehicle diagnostic data is said to show the battery pole temperature in the range of 71 degrees Celsius. After a heated debate appeared on the internet, Caishendao provided additional clarification by confirming that the vehicle used in the test was officially purchased from a BYD 4S dealer and was still unregistered when the trial was conducted.
He also denied allegations that the battery pack had been drilled or modified. According to him, the five temperature sensors are only attached to the surface of the battery cell without changing the main structure.
In his statement, the vehicle's liquid cooling system continued to work during the test, and the charging process was said to be automatically stopped if the cooling system was disrupted.
The testing uses two measurement methods, namely through battery data read from the vehicle diagnostic interface and an independent temperature sensor placed at several points in the battery pack.
The test results show a temperature difference of about 6.5 degrees Celsius between the hottest and coldest sensor points during the charging process. In addition, the report said that external sensor readings began to show a greater difference than vehicle data when the battery capacity exceeded about 70 percent SOC.
Caishendao added that there is no final conclusion regarding the potential degradation of the battery or the safety impact of the test results. He said that further testing at the battery cell level would still be carried out and asked the public not to take the live broadcast quotes piecemeal or conclude the results of his team's testing.
The debate about the results of this trial has also spread across various Chinese social media platforms. A number of users questioned whether repeated high temperatures during ultra-fast charging could accelerate the decline in battery performance or increase the risk of safety in the long term.
In his discussion, Caishendao also mentioned the Chinese standard appendix GB/T 44500-2024 which contains the recommended threshold of the temperature of lithium iron phosphate batteries of 65 degrees Celsius, although the rule is not yet mandatory.
In addition, the report cites a number of academic studies related to the phenomenon of thermal runaway and the decomposition of the SEI layer in lithium-ion batteries. Based on the referenced papers, the process of decomposition and reconstruction of the SEI layer generally occurs at a temperature range of around 80 to 120 degrees Celsius, depending on the type of battery chemistry and the testing conditions.
However, the report emphasizes that the temperature measured is the surface temperature of the battery, not the internal core temperature of the cell. Until now, there has been no independent data that verifies the internal temperature of the battery cell of the tested vehicle, on the other hand BYD has also not announced any changes regarding the specifications of its fast charging system after the emergence of the debate.
Photo: BYD flash charging test. (Photo: Caishendao) Photo: BYD flash charging. (Photo: Denza)
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