Why would a lithium battery get out of control?

80 % of accidents in lithium-ion batteries are caused by short circuits. After short circuits, batteries are caught in flames and explosions are frequently reported. The safety of lithium batteries is once again pushed to the point of public opinion. The reason why short circuits cause more serious consequences is related to the phenomenon of "heat out of control."

Thermal stability of battery materials has always been an important factor in the safety of powered lithium batteries. Compared with negative electrode materials, the thermal reaction between positive materials and electrolytes with low energy density and low power density is also considered to be the main cause of thermal runaway development of batteries.. Therefore, the search for positive materials with better thermal stability has become the key to power lithium batteries.

In essence, "thermal runaway" is an energy positive feedback cycle: higher temperatures cause the system to heat up, and the system to heat up, which in turn makes the system hotter. Thermal runaway is a common phenomenon. From concrete maintenance to stellar explosions, thermal runaway may occur.

There are several reasons for the thermal runaway of lithium ion batteries:

1, often overcharge.

2, unauthorized modification of the shell.

3, the ambient temperature exceeds 60 °C.

4, the separation of lithium ion battery negative and positive membrane tears will lead to short circuit, and short circuit will often cause thermal collapse.

The "thermal runaway" reaction involves cobalt oxide chemicals in lithium batteries. Heating this chemical to a certain temperature, it starts to heat itself up and then develops into a fire and explosion. In some cases, the release pressure of this organic electrolyte can cause the battery to rupture. If it is exposed to high temperatures, or if it encounters sparks, it may also burn.

The probability of thermal runaway is related to the lithium battery base. The output of lithium batteries in China, Japan and the ROK is increasing year by year. Especially in the field of mobile hands/notebook computers with wider applications, battery accidents seem to occur more. From 2006 to 2011, a number of large-scale electronic companies have had related incidents. Since 2012, there have been fewer small electronic products, but large-scale applications, such as accidents on aircraft, are commonly reported, which shows the following. phenomenon.

Thermal runaway and its strength are related to the size, configuration and number of cell units of lithium batteries. Lithium batteries have only a few lithium cells, so the chances of heat runaway spreading from problematic cells to other cells are relatively low. The Boeing 787's huge battery pack is another thing: they are packed in sealed metal boxes and can not emit excess heat. When one cell is hot enough to ignite the electrolyte, the rest of the cell will quickly follow suit.

When the battery is charged, the surface deposition of metallic lithium is very easy to aggregate into branching lithium branching crystals, thus piercing the diaphragm and causing a direct short-circuit of the positive and negative poles. Moreover, metallic lithium is very active and can react with the electrolyte directly. Its melting point is very low. Even if the surface lithium crystal does not pierce the diaphragm, as long as the temperature is slightly higher, the metallic lithium will dissolve, causing a short circuit. The higher the temperature of the Redox heat reaction of the material, the weaker the oxidation ability of the material, the stronger the oxidation ability of the positive electrode material, the more intense the reaction occurs, and the more likely it is to cause a safety accident.

Lithium-ion batteries, regardless of size, require regular maintenance to extend their life, and all lithium-ion batteries should normally be replaced every 36 months or so. And whenever the battery drops to 20, you should charge it. Excessive discharge can damage lithium batteries, increasing the likelihood of "thermal runaway" and other accidents.

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