ANSI/CAN/UL9540A:2019 test method, as a national standard recognized by Canada and the United States, has been widely recognized and adopted by the industry and organizations in evaluating the spread of thermal runaway fire in energy storage systems. The safety of the battery cell, and even the safety performance of the entire energy storage system, depends to a large extent on the quality and design of the battery cell itself. However, in the actual operation of cell testing, there are inevitably some problems worthy of further discussion. In response to these problems, Ankejie has combed out a series of common difficult points in the practice of cell-level testing, in order to provide clearer and more scientific guidance for the industry.
Q1: There are various ways to trigger battery thermal runaway, including overcharge, acupuncture, heating and other methods. So, in these ways, which one is more guaranteed to trigger the consistency of the battery thermal runaway?
A1: When considering the triggering method of battery thermal runaway, we need to consider a variety of factors, including the type of battery (such as lithium iron phosphate, ternary, etc.), shape (such as square, cylinder, soft bag, etc.), capacity size and objective conditions of the laboratory. Among the many triggering methods, the heating method is widely used because of its reliability and consistency. The heating mode can be realized by various forms, such as heating wire, heating sheet and heating plate. These methods have high feasibility and effectiveness in practical applications, which will help us to better study and understand the phenomenon of battery thermal runaway.
Q2: The standard indicates that the gas collection test can be carried out if the thermal runaway state of the sample is consistent for three consecutive times. If not, do you need to repeat the test? How many cells do you need to complete thermal runaway for gas testing?
A2: In order to verify the thermal runaway performance of the cell and its consistency, the standard regulates four cell samples. If they are inconsistent, you need to investigate the causes of the inconsistency, such as different trigger methods. In principle, it is necessary to ensure that four consecutive cell samples are triggered in the same way. The gas collection test generally uses a cell sample.
Q3: What are the key factors that affect the certification cycle during UL9540A testing?
A3: Generally, there is a large uncertainty in the battery core thermal runaway trigger, thermal runaway or not, thermal runaway consistency verification, gas collection, gas analysis and other links, which may lead to the suspension, delay, repetition or failure of the test process.
Q4: what is the impact of the results of the UL9540A cell test on the four levels of module, cabinet and installation?
A4: The idea of the standard specification is to divide it into four levels from the battery core to the module, the electrical cabinet and the installation level. In a sense, the test results of the battery core will directly affect or even determine the higher level of safety and judgment. If thermal runaway does not occur at the cell level and the gases released are verified to be non-flammable in air according to ASTM E918, no further consideration is required for thermal runaway testing at the module level.
Q5: What are the effects of the actual test results of the battery core, such as the trigger thermal runaway temperature of the battery core, the exhaust temperature of the battery core thermal runaway, the gas composition, the exhaust volume, the lower limit of the gas flammability, the gas combustion rate and the maximum explosion pressure of the gas on the test of the module, the electric cabinet and the installation level?
A5: As mentioned above, the basic idea of the four levels of the standard specification is that the test results of the lower level directly affect the test results of the higher level. When the thermal runaway is verified at the cell level and the above result parameters and characteristics are recorded, the heat release rate, combustible gas generation and composition data, smoke exhaust rate and total smoke exhaust volume, observation of spatter or explosive gas emission, observation of spark, arc or other electrical events, identification and positioning of the cell with thermal runaway in the module, the position of flame expansion and duration, etc. shall be considered during the module level verification, there are also many factors that are directly related or decisive to the inherent characteristics of the cell level.
Q6: how to determine the thermal runaway of the battery core? Will the thermal runaway of the battery core definitely catch fire?
Answer: Referring to the following standard original drawing, it can be seen that the heating rate of the battery core surface is required to be 4 to 7°C per minute. When the change rate of the battery core surface temperature exceeds the change rate of the external heat source, it is judged as thermal runaway. The thermal runaway of the battery core does not necessarily catch fire.
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