LCD Display Inverter

Introduction: When the two B&Cs confronted the acupuncture experiment, the representatives from South Korea who participated in EVS-GTR in November last year shared some information, mainly about the thermal runaway experiment they did, especially the widely used 60Ah empirical experiment is still great value.

I personally feel the following two points:

1) It is easier to pick the battery out individually, it is easier to burn it

2) When evaluating the thermal runaway propagation experiment, the most important thing is to control the injected energy to a minimum, and do not make the whole reaction process particularly violent, so that the overall effect can be evaluated (the time caused by the short circuit in the cell is relatively long, The process is not drastic, but it will)

3) At present, from the point of view of soft package, there is no effective design isolation method between cells. The isolation method is the mainstream choice under certain module design, so it may be difficult to use the soft package to CTP for packaging.

01
Thermal runaway triggering method provided by KATRI

At present, the main consideration in the design of power battery systems in the world is to have a good solution in the heat transmission test. The purpose of this test is to evaluate the thermal runaway of the cells caused by short-circuit faults in the internal cells, then to evaluate the prevention of fire spread in the battery system, and finally to achieve the protection of the vehicle’s occupants. Therefore, in the test, it is necessary to simulate the startup method of internal short-circuit thermal runaway as much as possible, and the thermal runaway state caused by the adjacent cells should be as low as possible, and it should be repeatable and reproducible (currently, the fluctuation of thermal runaway propagation is really large, a will be up and down). Discussions on different methods will be given gradually in the follow-up. In fact, Europe and the United States also have their own views. The method proposed by South Korea’s KATRI is to make a heater made of nickel-chromium material (covered with high temperature resistant tape and refractory plate). The core is locally heated to 800°C

Figure 1 Construction of the micro heater

As shown in the figure below, from the perspective of a single belt, the thermal runaway of the cell occurs in the next 200 seconds from the start of heating, and the entire surface temperature of the cell rises sharply after 200 seconds. At this time, the cell also begins to violently The direction of thermal runaway of the cell is TC1 → TC2 → TC3 → TC4 → TC5 → TC6 → TC7, and there is a continuous flame after the soft pack is exhausted.

Figure 2 Thermal runaway caused by soft-packed 60Ah cells

02
The case of mods and packs

As a friend mentioned earlier, the thermal runaway of the battery is different from the state in the module. In the experiment of the module, after 600 seconds after the heating is started, there is a continuous flame after the exhaust.

Figure 3 2.6kWh module thermal runaway propagation

As shown in the figure below, we further expand to Pack. Due to cost saving considerations, three adjacent modules can be put together, and then the overall propagation situation is considered. Under a certain spacing and protection design, the thermal runaway of the module only occurs in the involved module, and does not burn the entire pack. Compared with the square shell, due to the non-directionality of the exhaust, it will not be as scary as the square shell. The super pressure + super flame like a flamethrower. After the exhaust of the cell and the burning of the flame, there is no global thermal runaway propagation after the dismantling of the overall pack.

Figure 4 Thermal runaway at the pack level

Summary: I think that if you want to make a long module, like a Tesla, with a width of 320mm and a length of 1.8-1.9 meters, you need to carefully design the interval between individual cells or take a thick insulation material every other section, and then test After thermal runaway, mandatory cooling measures are taken to assist heat dissipation. We can have some solutions at the system level under the condition of increasing a certain cost. If the LFP can be arranged in a whole row or in a double row, the ternary needs to work harder, especially the large-capacity cells with high discharge pressure are more difficult.