Lithium-ion batteries are used to power just about any electronic device you can think of but sometimes they go faulty and can even explode.

They are suspected to have caused the loss of three cargo planes in recent years when their loads of lithium-ion batteries have caught fire and the plane’s fire suppression systems were overwhelmed by the intensity of the subsequent intense fires.

Lithium-ion batteries are used in personal electronic devices ranging from mobile phones and even earphones through to laptops and, when ignited, the battery emits dense, highly irritating smoke.

According to a major feature on the subject in Aviation Weekly it is the ability to concentrate a relatively large amount of energy into a small and lightweight package that makes rechargeable lithium-ion batteries so useful and attractive to the manufacturers of digital electronic devices and other applications.

Their “power density” allows high performance and long duration — up to eight or nine hours for laptop computers and several days for mobile phones, depending on how much they are used.

But there are also drawbacks.

Lithium batteries work when lithium ions flow from the negative electrode (or anode) through an electrolyte to a positive electrode (or cathode) during discharge.

When charging, the process is reversed and the ions flow back to the negative electrode. 'Intercalation' is the process by which ions are sent from the anode to the cathode. Generally, the negative electrode is carbon-based (usually graphite), while the positive electrode is a metal oxide (generally, cobalt). The electrolyte, meanwhile, is a lithium salt in an organic solvent. Pure lithium is highly reactive, responding violently with water to form lithium hydroxide and hydrogen gas. Consequently, a non-aqueous electrolyte is employed in lithium batteries, sequestered in a sealed container that protects the battery pack from moisture.

Problems happen when the electrolyte is compromised, as a short circuit can occur, and due to the power density of the battery the concentrated energy discharges very quickly. This causes the cell or battery to overheat, possibly catching fire and burning at temperatures in excess of 1,100°F. In batteries made up of multiple cells, adjacent ones can, in turn, overheat and fail, causing the entire battery to rupture and ignite. This is what is known as thermal runaway results. In rare cases, the power of the energy released can cause the battery to explode.

During the discharge process, either normal or runaway, the positive electrode produces oxygen which can feed ignition during a rupture. Furthermore, the liquid electrolyte used in li-ion batteries is both flammable and highly toxic to human skin when released, causing burns.

So, although it did get somewhat technical, now you know why lithium-ion batteries can explode.

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* Lithium-ion battery fires can be particularly dangerous on aircraft which is why more than 50 airline companies across the world – including some of the biggest and best-known - now carry AvSax fire containment bags to deal with fires in personal electronic devices caused by lithium-ion batteries that power them.

The bag – which won the Queen’s Award for Enterprise this year - has been used 27 times to deal with emergencies since the start of 2017.