A serious problem with Li-ion batteries is the danger of explosion in critical situations. In this regard, it is interesting to understand why this happens and what effects are accompanied by. It is also important to understand what needs to be done to reduce the risk of fire for a device equipped with such a battery (photo below).
The essence of the problem
It will be easier to understand why a fire has occurred if the battery design is known. Let's start with the fact that Li-ion batteries contain an anode and a cathode with a porous separator baffle. Metals from the transition group with embedded lithium ions are usually used as the cathode. The function of the anode is performed by graphite.
Electrolytes for batteries of this class are made on the basis of lithium salts in solution. When a battery is first charged during production, a free ion layer (SEI) is formed on the anode. The chemical barrier they form protects the battery electrodes from dangerous contact with electrolyte.
In most known situations, spontaneous combustion occurs due to an accidental short circuit in the battery cell.
The reason for its appearance may be:
- Mechanical deformation possible after dropping the phone to the floor or hitting a hard surface.
- Manufacturing defects.
- Growth of dendrites.
The latter phenomenon is associated with fast discharge or charging processes, due to which lithium ions simply do not have time to integrate into the crystals of the graphite anode. As a result, they grow to a size that leads to the failure of the separator.
Features of spontaneous combustion
A short circuit inside the battery leads to the heating of its components, and upon reaching 70-90 degrees, the ion barrier is destroyed in the anode region. Because of this, lithium integrated into it begins to come into contact with the electrolyte, which causes the release of gases from the group of hydrocarbons (methane and the like). In the presence of an explosive mixture, it remains for the main component necessary for ignition - oxygen.
The resulting mixture begins to boil inside a tightly closed housing, which inevitably leads to a jump in temperature and pressure in it. When the composition reaches a critical state (plus 180-200 degrees), the cathode particles begin to support the reaction with abundant oxygen evolution. It was then that an explosion occurs, accompanied by a sudden rise in temperature (up to 300-600 degrees) and abundant heat release.
How to protect yourself from an explosive process
Battery manufacturers provide several levels of protection against an unpleasant effect according to the principle: the more powerful the model, the more these levels are. One of them includes a separator, which creates an insurmountable barrier to developing dendrites in the battery section at a sharp temperature jump. But if an avalanche-like process occurs, then the separator does not have time to "work"; it melts instantly.
They also have special valves and fuses to protect the batteries. The user will be able to avoid the described unpleasant effects if he handles his device with care (do not drop it and charge it correctly).