Thermal runaway experiment of lithium titanate -Lithium - Ion Battery Equipment

Thermal runaway experiment of lithium titanate battery pack -Lithium - Ion Battery Equipment

Lithium batteries are widely used in portable devices such as mobile phones and computers due to their high energy density and good cycle performance. With the promotion of new energy, batteries are gradually applied to many large-scale equipment such as electric vehicles, energy storage power stations, and even the International Space Station. However, the battery itself is unstable in a high temperature environment. Once the thermal runaway occurs in the battery, it may cause a chain thermal runaway of the surrounding batteries, resulting in huge economic losses.

research content

Wang Qingsong's research group from the State Key Laboratory of Fire Science comprehensively considered the two arrangements in practical applications of batteries, and conducted experimental studies on their thermal runaway transfer behaviors. By heating the bottom middle battery to cause thermal runaway of the battery, the temperature characteristics and combustion behavior of the surrounding batteries under the influence of the runaway battery are obtained.

The experimental study has drawn some important conclusions as follows:

(1) The flame scouring of the surrounding battery by the flame of the runaway battery plays an important role in the thermal runaway transfer of the battery, but the thermal runaway of the surrounding battery does not have general regularity. When the parallel-arranged batteries are heated at the bottom, the surface temperature of the batteries reaches the range of 120~140℃, and fire will occur. However, for the rhombus-arranged cells, the surface temperatures at which the 3# and 4# cells ignited appeared at 185°C and 78.5°C under only the bottom thermal runaway cell flame application.(Lithium - Ion Battery Equipment)

(2) The battery washed by the flame still has a certain explosion hazard even if the flame is extinguished. 20 minutes after the flames of all batteries were extinguished, the temperature of 1# battery and 4# battery stabilized in the range of 120 to 130 ℃ and rose steadily in the "smoldering" stage, and then 4# battery and 1# battery suddenly exploded in succession.

In order to explain the "smoldering" stage of the battery and the thermal runaway transfer behavior of the battery, the C80 was used to measure the heat flow of the battery electrode material and it was calculated using two traditional thermal explosion models (the Semenov model and the Frank-Kamenetskii model).

The thermophysical parameters of the reaction of the electrode material can be obtained from each reaction heat flow curve. The self-accelerating decomposition temperatures of the respective models were obtained from the thermophysical parameters of the total reaction: SADTsem=126.1℃ and SADTF-K=139.2℃. The surface temperature of the battery where thermal explosion occurred in the experiment is just in the temperature range under the two limit model conditions. According to the analysis of the author's previous article, the thermal decomposition of the cathode material is an important reason for the thermal runaway of the battery. Therefore, the self-accelerating decomposition temperature of the positive electrode material leading to thermal runaway of the battery was calculated by the two-limit model, which were obtained as 160.1 °C (Simenov) and 196.6 °C (Frank-Kamenetskii), respectively. It means that when the battery temperature reaches these two temperature ranges, the battery is not cooled in time, and the battery will inevitably suffer from thermal runaway.



Aiming at the thermal runaway transfer behavior of the battery pack, the team found through experiments the irregular runaway caused by the flame flushing to the surrounding batteries and the hidden danger of explosion caused by the flame flushing and its previous "smoldering" stage; In the "burning" stage, the team analyzed the thermophysical parameters of the electrode materials inside the battery, and used two extreme thermal runaway models to calculate them. The calculated results were in line with the temperature characteristics of the "smoldering" stage before the thermal explosion of the battery. This paper provides a reference for the large-scale application of batteries and the design of safety plans. However, due to the limitations of the model itself, the critical state of thermal runaway of the battery cannot be accurately obtained. At present, the team has revised the model and obtained the critical criterion and calculation model for battery thermal runaway for the first time. The results will be announced in the near future, so stay tuned!



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