From the perspective of battery safety protection, 18650 battery cells are designed with safety valves, which not only release excessive internal pressure, but also physically disconnect the battery from the external circuit, equivalent to physically isolating the battery cell to ensure the safety of other battery cells in the battery pack. In addition, lithium-ion battery packs are usually equipped with BMS protection boards, which can accurately control the state of each cell in the battery pack, directly solving the problem of overcharging and discharging at the root.
The lithium-ion battery BMS Battery management system can provide full protection for the battery, including: charging/discharging high and low temperature protection; Single section overcharge/overvoltage protection; Charge/discharge overcurrent protection; Cell equalization; Short circuit protection; Charging reminder, etc.
The electrolyte of the lithium-ion battery pack is a mixed solution of lithium salt and organic solvent, of which the commercial lithium salt is Lithium hexafluorophosphate. This material is prone to thermal decomposition at high temperatures, and Thermochemistry reactions are carried out with trace water and organic solvents to reduce the thermal stability of the electrolyte.
The power lithium ion battery is important to use Lithium iron phosphate. The P-O bond in Lithium iron phosphate crystal is stable and difficult to decompose. Even at high temperature or overcharge, it will not collapse and heat or form strong oxidizing substances like lithium cobalt oxide, so it has good safety. There are reports indicating that a small number of samples were found to have combustion phenomena during acupuncture or short-circuit experiments in actual operations, but no explosion event occurred. The safety of lithium-ion battery packs has greatly improved compared to this.
On the contrary, lead-acid batteries lack BMS system protection. Lead-acid batteries seem to lack safety protection beyond safety valves. BMS protection is almost non-existent, and many low-quality chargers cannot even fully charge and power off, which is far from lithium-ion batteries in terms of safety protection. Coupled with a low-quality charger, you have a good character if nothing goes wrong.
Spontaneous combustion and explosion often occur in electric vehicles, most of which are caused by battery charging and discharging. Some experts explained that the charging time of Lead–acid battery is too long. When the charging reaches the end, after the two poles are converted into effective substances, if the charging continues, a large number of hydrogen and oxygen gases will appear. When the concentration of this mixed gas accounts for 4% in the air and there is no time to escape, if the exhaust hole is blocked or there is too much gas, an explosion will occur when encountering an open flame, ranging from damage to the battery, to injury or damage to objects. That is to say, once a lead-acid battery is overcharged, it will increase the probability of explosion. At present, lead-acid batteries on the market do not have any overcharging protection, which makes charging, especially in the late stage, extremely dangerous.