Why and how to blow up the lithium-ion batteries

Probably everyone remembers about the sensational story with self-ignition and even explosion of batteries in Note 7 phones from Samsung. So, this is not just a problem specifically with this particular phone model and it is more or less true of all lithium-ion batteries.

After all, on the Internet here and there you can find a movie like giroskuter, elektrosamokat or phone on the charging suddenly puffed and burst into flames.

In this article I want to tell you why this is happening and what to do to minimize the risks of spontaneous combustion is your gadget with this battery type.

What is the problem

So, in order to understand the cause of the fire, let's say a few words about the structure of such batteries.

Li-ion batteries are made of a pair of anode and cathode, which are separated by a porous polymer separator. In most cases, the active cathode material is a transition metal oxides with imbedded in the crystal structure of lithium ions. A use as anode graphite.

The electrolyte in the battery is generally made of solutions of lithium salts. So at the initial charge in the factory in the integration process on the electrodes in lithium anode (in substantially ion-conducting protective layer is formed at the anode) (SEI), formed from decomposed electrolyte. Formed barrier protects electrodes from harmful reactions with the electrolyte.

In most cases, the cause of self-ignition of the battery is a banal short circuit in the cell itself. The reason for forming electrical contact between the electrodes can be:

1. Mechanical damage element. Let's say you drop your phone or battery on the floor, and thus damage the internal structure of the battery.
2. Manufacturing defects. Even in an age of robotic production no one is immune from the banal to manufacturing defects, such as insufficient exactly electrodes were cut or got metal portion between the cathode and the anode, resulting in damage to separator.
3. Germination of lithium metal (dendrites). This phenomenon occurs at too rapid discharging or charging, when lithium ions just do not have time to be integrated into anode crystal and bringing it (the anode) crystal growth process begins, which leads to damage separator.

So one of the above reasons have caused a short circuit. Let's see what happens next.

development of spontaneous combustion

Short circuit occurred in the element, this fact battery starts when the heating process and temperature reaches 70-90gradusov Celsius, ion-conducting barrier begins to deteriorate anode.

Thereafter, lithium, integrated in the anode, the reaction starts with the electrolyte, as a result of this process, the release of volatile gases, ethane, methane, ethylene, etc...

So, there is an explosive mixture, but there is a main ingredient for fire - oxygen.

All of this chemical cocktail starts to boil in a closed sealed enclosure, as well as an exothermic reaction, it inevitably leads to increase in temperature and pressure.

Upon reaching 180-200 degrees Celsius cathode material included in the reaction and the resulting oxygen evolution occurs. Here at this very moment, and there is a "puff" and an abrupt increase in temperature. Parallel to this, decomposition of the electrolyte continues (300 degrees Celsius), which also generates heat.

And the final step of this process with the electrolyte residues reacts graphite, which further It raises the temperature to about 600 degrees centigrade, resulting in melting of aluminum susceptor.

How to protect batteries

Of course, manufacturers are aware of the problem and have provided several degrees of protection against possible self-ignition and then working principle, the more powerful battery, the greater the degree of protection in it.

One of the degrees of protection is a separator, which temperature is raised at a point becomes impermeable and thus prevents the dendrites grow in the battery section. But if the process is developing rapidly, the separator is melted banal.

In addition batteries are manufactured with integrated valves and fuses. Thus, when the pressure is increased and the temperature electrodes are simply disconnected from the network, and go through the valve formed gases. Of course, in this case in contact with oxygen gas burns.

Additionally lithium-ion batteries are equipped with controllers, sensors, and so charge balancers. D.

As you probably already realized the most dangerous element in the construction of a lithium-ion battery is the electrolyte, which is just broken down into these well burning and exploding gases. To date, the whole team of scientists are actively searching for a viable alternative, but so far that is not present.

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