Chemical reaction of 18650 lithium battery in flame

In a test experiment, what happened when an 18650 cylindrical lithium-ion battery was subjected to flames. In the experiment, when the lithium ion was heated to a high temperature of 600 degrees or more by the flame, the flammable battery internal materials such as the electrolyte were ejected from the safety valve and caught fire.

When a lithium-ion battery is subjected to extreme high temperature (such as near the ignition point), its pressure relief valve will open, possibly discharging combustible gas, and then it will rapidly self-heat and eject materials such as pole pieces inside the cell. The former usually refers to safety valve activation, while the latter usually refers to thermal runaway.

The thermal failure of the battery is initiated by an electrical heating device, while the internal energy release of the battery is measured by the temperature rise of the battery case and the loss of battery mass. In order to simultaneously measure the heat generated by the combustion flame ejected from the safety valve, the experiment needs to be placed in a standard cone calorimeter, while the gas analysis system is used to monitor the oxygen consumption during the combustion process. Converted to heat release.

The positive electrode of the lithium-ion battery is a compound containing metallic lithium, generally lithium iron phosphate (such as lithium iron phosphate LiFePO4, lithium cobalt phosphate LiCoO2, etc.), and the negative electrode is graphite or carbon (generally, graphite is used), and organic organic matter is used between the positive and negative electrodes. Solvent acts as electrolyte.

When the battery is charged, the positive electrode is decomposed to generate lithium ions, and the lithium ions enter the negative electrode of the battery through the electrolyte and are embedded in the micropores of the carbon layer of the negative electrode. During the use of the battery (equivalent to discharge), the lithium ions embedded in the micropores of the negative electrode move back to the positive electrode.

The more lithium ions that return to the positive electrode, the higher the discharge capacity. The battery capacity we usually refer to is the discharge capacity. In this way, during the charging and discharging process of the battery, lithium ions continuously run back and forth between the positive and negative electrodes, so the lithium ion battery is also called a rocking chair battery.