First of all, we must analyze the situation of the lithium battery. If it is not for the negative electrode lithium (lithium ions are incompletely combined with carbon to produce lithium crystals), the lithium ions are in a stable state and will not react due to lithium and air. Even if lithium is precipitated, it is not the main cause of combustion. The reason for spontaneous combustion is that after the battery is destroyed,
1. The metal weapon caused a short circuit in the battery;
2. The external force damages the diaphragm and causes the battery to short circuit.
The explosion of the battery mainly occurs in the charged battery, most of the reasons are as follows:
1. Overheating caused by high current (external short circuit, internal short circuit).
2. The rupture may also expose the unstable negative electrode (with lithium deposits) to the air and cause a large amount of heat to be released after charging.
3. Overcharge can also cause explosion.
When a DC short-circuit occurs, the heat is huge, causing the battery to run out of thermal control, and the temperature will rise to more than 300 degrees Celsius in milliseconds when the battery is out of control. The most important flammable substance in lithium batteries is actually electrolyte. In the absence of flame retardants (basically all products have flame retardants), the ignition point of the electrolyte is about 130 degrees Celsius. For example, the fire accidents of electric vehicles that we have seen on the news are, in the final analysis, caused by the destruction of the battery and the outflow and burning of the electrolyte. However, it is also divided into technical systems. We all know that lithium-ion batteries are roughly divided into cobalt-lithium, manganese-lithium, ternary, iron-lithium batteries, etc. The thermal runaway temperature of cobalt-lithium and ternary is lower than 300 degrees Celsius, and manganese-lithium is about 400 In degrees Celsius, the iron-lithium battery is higher than 700 degrees Celsius, and there are also iron-manganese-lithium binary battery products. Depending on the doped raw materials, the thermal runaway is critical at 400-600 degrees Celsius. It can be seen that there is a big difference, which is one of the reasons why iron-lithium is safe. Therefore, in the iron-lithium national standard, the metal needle test is a must-do safety test, such as the metal needle test of 18650 lithium batteries. That is to say, for iron-lithium batteries that meet the requirements of international standards, during the battery testing process, the supervisory agency will ask the unplaning battery to check whether there is an internal structure. The standard is whether there is only one battery in the unified electrolyte structure. All iron-lithium battery products that meet the national standards, due to their chemical characteristics and the protection after adding flame retardants, should not be spontaneously ignited after being pierced. Other products cannot be guaranteed.
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