A jeep fire caused by a Samsung Galaxy Note 7 (Image Source: BGR)
You plug your brand new phone into the charger and sink into dreamland. The next thing you know, you are choking on thick smoke, your bedroom engulfed in flames.
What happened? The answer is simple: your phone is a Samsung Galaxy Note 7, one of more than 100 that have burst into flames this year.
Samsung stopped sales of this dangerous smartphone, and worked with government agencies and cellular carriers around the world to provide replacements; however, the supposedly safe version of the Galaxy Note 7 still caught fire. On October 13, Samsung officially recalled every single Note 7, including replacement units, telling users not to turn them on or charge the phones.
The batteries used in the phones were lithium-ion batteries.
How Lithium-ion Batteries Work
There are many variations, but all batteries contain these core parts:
- Cathode: the positive side, made of conductive material.
- Anode: the negative side, often made of graphite.
- Electrolyte: a very flammable liquid, often made of lithium salt and an organic solvent.
- Separator: a thin piece of material, usually plastic, that separates the positive side from the negative.
If the battery short-circuits, by puncturing the super thin separator, the puncture point becomes the path of least resistance for electricity to flow. This heats up the flammable electrolyte at that spot. If the liquid heats up quickly enough, the battery can explode.
However, no brand or model is necessarily safe – the Galaxy Note 7 is not the only phone to catch on fire. iPhones have caught on fire, and Nokia recalled 46 million phone batteries in 2009.
Why the Galaxy Note 7?
According to an unpublished preliminary report sent to Korea’s Agency for Technology and Standards (obtained by Bloomberg), Samsung had a manufacturing error that caused the separator to get punctured, creating a huge fire hazard.
Samsung’s phones are prone to overheating, causing a fire or explosion (Image Source: Extreme Tech)
MIT materials chemistry Professor Don Sadoway explains that today’s smartphone batteries cramming in as much battery capacity as possible, but still having a small battery.
Sadoway has two theories: the company could have put so much pressure in the battery that the positive and negative terminals poked through the separator and touched. The sponge-like separator could also have gotten squished. Normally, the separator allows electrolyte to pass through pores connecting the negative and positive sides of the battery, while keeping the two terminals separate. If there is too much pressure, the pores are constricted, the resistance goes up and more heat is generated.
Dendrites – Another Interesting Theory
The battery may have been partly squeezed, causing it not to know when the phone is at 100 percent battery. When lithium-ion batteries are continually trickle charged, lithium ions can start to cover the surface of the negative contact in a coating of lithium metal through a process called plating. In extreme conditions, that lithium metal can form tiny spikes called dendrites that can poke through the separator, creating a short circuit.
Lithium-ion Batteries – Good or Bad?
This does not mean that lithium-ion batteries are necessarily bad. These batteries are safely used in all types of devices around the world. Even though production rates have greatly increased, the failure rate has stayed fairly low. All lithium-ion batteries pose a small risk, but they are much smaller, lighter, and more efficient than other batteries.