Lithium-ion batteries may be overcharged for too long. Li-ion batteries or chargers will automatically stop charging when the batteries are fully charged, and nickel battery chargers will not provide so-called "spot" charging that lasts more than 10 hours. In other words, if the lithium battery is fully charged, it is futile on the charger. And there is no guarantee that the characteristics of the battery's charge and discharge protection circuit will never change and the quality is safe, so the battery will be on the verge of danger for a long time.
For example, the battery design and manufacturing process simulated by UN38.3 T1-T4 is poor or affected by the external environment. The battery may leak. Test the battery to ensure that it does not leak during transportation. Even if there is a leak, it must be packed to ensure safe transportation.
External short circuit: ExternalShortCircuit
The occurrence of external short circuit is also very dangerous, the temperature will rise very high, and even fire and explosion may occur. In UN38.3, T5 simulates the external short circuit of the battery. After the harsh environment that may be encountered during the transportation of T1-T4, the external short circuit test of the lithium battery can be considered as the worst case. Under these conditions, Li-ion batteries can meet safety requirements. In addition, protecting the battery during transportation can eliminate such risks.
The important thing is that the battery diaphragm is not good or the battery has small conductive particles entering and piercing the diaphragm during the production process. Lithium metal has phenomena such as overcharging in the use of ternary lithium batteries. The internal short circuit is an important cause of fire and explosion of cylindrical lithium batteries, so we should change the design through experiments to reduce the risk of ternary lithium batteries.
The T6 crash test in UN38.3 is to simulate a battery short circuit. Of course, the existing T6 collision is not a real short-circuit simulation cell. Many institutions and experts are studying more suitable experimental methods, but recently UN38.3 drafted a new extrusion experiment, and most of the liion battery requirements and extrusion experiments, The squeeze experiment can not make a lot of forms of internal short-circuit batteries, and the safe traffic is very bad. We also put forward his opinions and submit the official documents
Lithium metal batteries are usually not rechargeable, so they cannot be overcharged.
During the charging process of lithium ion batteries, due to the failure of the voltage limit circuit or the deviation of the limited voltage value, the battery will be charged, and the lithium metal will be overcharged in the Li-ion battery. There will be unstable substances and the electrolyte will decompose. When the lithium battery explodes, fires, and the lithium ion battery is usually overcharged to protect it.
The T7 test is to verify the overcharge protection and overcharge safety of liion batteries. The main danger is used batteries
Explosive materials will appear when lithium metal batteries are over-discharged, and they will explode at a certain temperature. They should be protected by design in case of fire.
When a lithium ion battery is over-discharged, negative electrode materials such as copper will precipitate.
The T8 test is to test the safety of the battery during discharge.
For large lithium batteries, large power supplies usually consist of multiple battery cells in series or in parallel:
Because of the series connection, only the terminal voltage is controlled during charging. How to make the voltage of each battery cell equal is very important. Imbalance will cause the battery to overcharge, which is dangerous.
Due to the parallel connection, in each group of parallel batteries, due to internal short circuits and other reasons, the voltage drop of one battery will generate a large current in this group of batteries, which may cause the battery to explode and catch fire. We should also conduct appropriate experiments to prevent this risk from happening.
In addition, the high voltage of large-capacity lithium batteries will cause high voltage breakdown, and withstand voltage and insulation resistance tests are also very necessary.
So do you understand the dangers of lithium batteries?