lithium 18650 li ion battery

　　Methods to ensure the safety technology of 18650 lithium-ion batteries

　　The 18650 lithium battery cell has two protections in the internal hardware design, which are CID (CurrentInterruptDevice) pressure relief valve and PTG (PositiveTemperatureCoefficient) thermal resistance.

　　The 18650 lithium-ion battery cell has two protections in the internal hardware design, which are CID (CurrentInterruptDevice) pressure relief valve and PTG (PositiveTemperatureCoefficient) thermal resistance. Among them, the safety valve is the standard configuration of each 18650 battery, and it is also the most important explosion-proof barrier.

　　The working principle of ClD and PTC: When the internal temperature of the battery is abnormal, a large amount of gas appears due to overcharging, short circuit and other reasons, and when the air pressure rises to 1.0-1.2Mpa, the unified aluminum sheet on the safety net will bounce upwards, which is the same as the following If the pressure continues to rise, the safety valve will rupture and open to remove the internal gas to release the internal pressure and prevent the explosion caused by excessive pressure. For Prismatic square soft-coated cells, when the internal air pressure rises, the most common phenomenon is "pregnancy" swelling. Secondly, the PTC thermal resistance, when the input and output current of the battery is too high, the PTG will heat up, and when the temperature reaches the preset value, the PTC resistance will suddenly increase, cutting off the external current input into the cell or preventing the current output in the cell , let the cell stop working. In addition to the above two, the battery also has an unknown third line of defense - the diaphragm. When the temperature of the battery rises above 160 degrees Celsius, the micropores in the diaphragm will close, so that the positive and negative electrodes are physically isolated, and the battery will naturally no longer output current.

　　Since the 18650 battery itself is so safe, why is it not uncommon for mobile power supply fire accidents? The mystery lies in the mobile power itself. Components such as external charging of mobile power supplies are often made of plastic. Plastic itself is flammable and can spontaneously ignite when exposed to high temperatures. The USB output of the qualified mobile power supply has short-circuit protection, so when the output is short-circuited, no large current will flow. However, there are also connections such as chips or wires from the 18650 to the circuit board inside the mobile power supply. If this is all unfortunately short-circuited, then the output short-circuit protection is completely powerless. The PTC of the 18650 battery itself can only cut the current of the new battery before the battery itself overheats. Because the heat capacity of the battery is considerable, the temperature rise is not so fast. Maybe the battery has not yet heated up when the wires and chips are red. Cut new output. In this way, when the red-hot missing piece is in contact with the plastic of the outer filling, a fire is inevitable.

　　A qualified mobile power supply often performs multiple insulations on the conductors from 18650 to the circuit board, and the insulating body used is a high-temperature polyimide tape (mylar sheet) that can withstand a high temperature of 300 degrees and a flame-retardant green paper. At the same time, this section of conductor has an appropriate fixed design to prevent the conductor from moving or deforming under mechanical impact. Thereby ensuring that short circuits will not occur to the greatest extent.