Interpretation of Lithium Battery Technology-Non-thermal runaway test-test naming for the whole package

by:CTECHi     2021-07-19

Lithium Grid News: EVS-GTR puts forward technical requirements closely around the safety performance of the whole vehicle and the power battery, and at the same time specifies the test methods for electric vehicles to meet the safety performance requirements. I personally think that if the battery level is high in resistance to abuse, many things are easy to say; if the battery level is not good, many things will be difficult to do. The simplest example is LEAF, this battery system, if the battery is The core becomes thermally out of control, and the result is like this, but apart from heating to a particularly high temperature, the AESC cell cannot be burned. This situation is also the case that the previous soft-packed cells such as Volt and LEAF can not burn more than 400,000. What is the root cause of a major accident. In the tests conducted in the United States and Canada, if the two soft package solutions really ignite, there is little hope, but a little bit has passed.

From the perspective of thermal runaway

The test methods and procedures are the most initial part. The solution here is the unity of testing and design.

Battery thermal runaway and expanded early warning mechanism, by adding newer sensors to capture this process more quickly for higher energy density batteries, Under SOC and different conditions, the hazards of the entire out-of-control process are separated by heat insulation to separate the problem areas, and heat conduction to reasonably discharge the heat and gas released by the cells that have been thermally out of control.

The conditions that caused thermal runaway were discussed repeatedly before. Here, the battery system of BMW I3 was selected, and 4 samples were selected for testing. The basic test conditions are as follows:

Selecting this cell mainly considers the position of the module and the position in the module. Module 5 is around 360° in the entire battery system. There are other batteries that may cause the heat to spread out of control on the whole.

After selecting the battery cell, it is necessary to determine the coordinate point of the insertion to ensure that the insertion of the steel needle can cause the internal short circuit of the inner core package.

In order to ensure the smooth progress of the experiment, it is necessary to drill holes in the plastic cover of the upper shell and the surface of the module to ensure that the steel needle can enter the battery in a smooth manner.< /p>

The test results are shown in the figure below. The repeatability of the whole process is still very high. All regional thermal runaways have formed, but heat transmission has not occurred. For thermally runaway cells and adjacent cells, there are temperature changes, and pressure changes appear in the entire battery system.

From the point of view of temperature and voltage, here are a few conclusions:

The drop of thermal runaway telecommunications is later than the rise of cell temperature, which is when the experimental problem occurs. , The voltage is maintained, and then there will be a sudden drop in voltage in the later stage

The speed of the temperature rise process of the battery cell is actually very different, but the final process is similar.

The following is the actual sample result graph, we can see the result caused by the thermal runaway of the cell. The thermal runaway cell itself fully releases the heat, but it does damage to the surroundings. Is different.

The results of a total of 4 reactions of the two left and right batteries are shown in the following two figures. In these 4 tests, one edge battery appeared Its own heat production reaction, the temperature is too high; the corresponding temperature of the other battery cell is too low, and the heat is not transferred.

This may be related to the opening of the pressure relief valve of the battery at that time, and the heat release has a certain bias.

The pressure change brought about by this injection can be clearly sensed

Summary: When the base of the battery changes At the time, the difficulty of the system's propagation control increased sharply, but then we need to carefully balance how to set the safety of the battery, and what can be done at the module and pack level. Not only energy density, but also low cost, but also to ensure that the volume and safety are not good. We are carefully looking at the battery cost from the previous stage to the next stage of the battery cost. There are a lot of things in it. Click to pick it out

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