[background]

The thermal runaway fire process of the battery is complex and highly harmful, usually accompanied by a large amount of heat and toxic gas release. Therefore, it is very important to actively develop efficient fire-extinguishing materials to prevent the occurrence of battery thermal runaway accidents and reduce the loss. Existing studies show that aerogel has special advantages of low density, structural stability, easy distortion, poor thermal conductivity and good thermal stability. As a new type of fire extinguishing material, it has good prevention and control effect for solid and liquid fires, but its effectiveness in inhibiting battery fire has yet to be verified. Therefore, this paper aims to study the effect of aerogel foam fire extinguishing agent to inhibit the thermal runaway of lithium-ion batteries and the thermal runaway law of lithium-ion batteries, so as to lay a foundation for further exploring the rapid and effective suppression of the thermal runaway of lithium-ion batteries. The thermal runaway process state of lithium-ion battery can be judged by three characteristic parameters: measured battery shell temperature, flame temperature and extrusion stress caused by battery expansion. The experimental setup is shown in Figure Figure 11.

 Figure 1. The experimental setup

Through the characteristic parameters of the thermal runaway evolution process of 100 Ah lithium iron phosphate energy storage battery in the full charge state, three inflection points of disaster evolution characteristics are identified as the guiding nodes of fire extinguishing agent. Aerogel foam fire extinguishing agent and water mist with consistent fire extinguishing parameters were applied at the same node to carry out fire extinguishing comparison test. By comparing the temperature curve of lithium ion battery shell and battery flame after spraying with fine water mist and gasogel foam extinguishing agent at the guiding node, the advantages and principles of aerogel foam extinguishing agent compared with fine water mist in different thermal runaway stages are analyzed. The results show that the fire extinguishing agent before triggering the fire can effectively block the side reaction inside the battery, showing similar cooling efficiency; after the battery fire, the aerogel foam extinguishing agent shows a better fire suppression effect, and the dense foam formed on the battery surface can effectively block oxygen and realize rapid fire extinguishing, as shown in Figure 2.

Figure 2 surface bble surface of aerogel extinguishing agent

(1. Before thermal runaway; 2. after thermal runaway)

For the case where thermal runaway has been triggered, the aerogel fire extinguishing agent can significantly shorten the duration of the battery jet fire by virtue of the preheating coverage effect, which can greatly reduce the battery fire hazard.

 Figure 3 Flame temperature curve of the battery under the action of fire extinguishing agent

The analysis of the fire extinguishing phenomenon can be found that the fine water mist mainly depends on the confrontation between the fog field and the battery jet fire, and the battery fire shows drastic morphological changes, as shown in Figure 4. In contrast, under the action of aerogel fire extinguishing agent, the battery jet fire shows the coating fire extinguishing process, and the flame height gradually decreases until extinguished. The fire extinguishing process is fast and the flame fluctuation is not significant, which indicates the excellent fire control effect of aerogel fire extinguishing agent.

Fig. 4 Fire extinguishing process of fine water mist (top) and aerosols (bottom)

[conclusion]

1) Aerogel fire extinguishing agent has the ability to block the development of thermal runaway, and can effectively extinguish the battery open fire, which is reduced by about 70s compared with the fine water mist in the same working conditions.

2) After the thermal runaway trigger, the cooling and cooling effect is significantly weakened, but the duration of the battery jet fire is significantly shortened, and the fire risk is further reduced.

3) Under these experimental conditions, the aerogel fire extinguishing agent showed a more efficient open fire suppression efficiency, and the cover formed on the surface of the battery helps to asphyxiate the battery and prevent reignition.

This paper research build lithium ion battery thermal runaway experiment platform, creatively put forward fire extinguishing agent guidance node research ideas, fine water mist and aerogel foam extinguishing contrast experiment, to further analysis of aerogel extinguishing agent cooling, reignition and flame retardant principle, for lithium ion battery fire control provides a new way of thinking.

[Battery comprehensive performance test module]

Hefei stone instrument technology co., LTD., self-developed battery comprehensive performance experimental chamber can realize a variety of environmental elements (temperature, pressure, atmosphere, etc.) coupling, multiple battery test (acupuncture, extrusion, overcharge, discharge, short circuit, temperature cycle, ignition, fire), for batteries and small battery module comprehensive performance test.