On a recent flight to Vancouver, the flight attendant warned us that Galaxy Note 7 or any other Samsung smartphone are no longer allowed on domestic flights. Anyone with such a phone was required to leave it behind.
Lithium-based batteries have been the subject of many stories of late. These energy storage devices are increasingly popular due to their high energy density - the amount of electrical energy they can store in a given volume for a given weight.
But they have been thrust into the safety spotlight as a result of laptops overheating, "hoverboards" bursting into flames, and airplane electronics smoldering and even catching fire.
I worked on lithium metal batteries for Ballard Research in the early 1980s and saw firsthand the safety precautions necessary for working with the element.
Modern batteries do not employ lithium metal in its massive form. They are not reactive in the same way throwing a chunk of sodium in water would be. But lithium does react with water to give lithium hydroxide, which is a problem in battery design.
Simply put, when designing a lithium-based battery, you can't have a water-based electrolyte. Lead acid batteries and dry cells (Energizer, Duracell, etc.) are built around water-based reactions. In the case of a lead acid battery, the solution is concentrated sulphuric acid, which is very corrosive.
For a dry cell - which you would expect to be "dry" - water hydrates the powdered ingredients. The electrolytes are not liquids but they do contain water as part of their structure.
In a lithium battery, the electrolyte is based on organic solvents, such as ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate. Organic solvents do not react with lithium in the same way as water.
Under normal circumstances they do not represent a hazard.
However, they are organic compounds and are flammable. Under the right circumstances they can catch fire or the lithium battery can explode.
To understand this a bit better, we need to consider the basics of a battery. First of all, a battery doesn't create electricity.
Batteries have two sets of reactions within them. One is an oxidation reaction which gives up electrons and the other is a reduction reaction which takes in electrons.
The difference in the chemical potential between these two reactions gives us the voltage for the cell.
When a battery is discharged, electrons move between these reactions. The electrons are already there.
All a battery does is hold them in place until an external circuit causes the electrons to flow. In the case of a disposable battery, the chemical reactions are a one way trip.
Once all of the chemicals are used up, the battery is dead.
For a rechargeable battery, the reactions are reversible. Apply an external voltage greater than the voltage of the battery and the electrons can be forced to move backwards. Electrons can be added to the oxidation reaction compounds and removed from the reduction reaction compounds.
A reversible battery is designed to store up electrons.
For a battery to work, it has to be part of a circuit. When a lithium battery is being charged, the lithium ions in the electrolyte move to the positive electrode and recreate a compound such as lithium cobalt oxide.
When the battery is discharging, the lithium ions are released into the electrolyte while the electrons flow through the external circuit powering our phones or computers or hover boards.
It is the flow of external electrons and lithium ions into the organic electrolyte which form the basis of a battery.
However, there is a porous separator keeping the two halves of the battery apart.
It separates the positive and negative electrodes. Charging a battery for a long time or physically damaging the battery can impact this separator. This causes the battery to discharge too rapidly generating a lot of heat. Heat and a flammable organic electrolyte are not a good combination.
Further, when overcharged, lithium cobalt oxide releases oxygen. If you recall the fire triangle, you need a source of heat, a fuel and oxygen to have a fire. The heat arises from the short circuiting through the separator, the fuel is the organic electrolyte, and the electrode provides the oxygen.
The result is a fire.
Finally, the electrolytes used can decompose to give carbon dioxide without causing a fire. The pressure generated by the gas can cause a pressure explosion.
This exposes potentially flammable components to the surroundings and could possibly lead to a fire.
Needless to say, a great deal of research is being conducted on improving lithium batteries to get away from flammable liquid electrolytes. Lithium ion batteries are ideal for storing energy but they do need to be treated with respect. With any luck, the next generation of batteries will likely be solid state, so they shouldn't suffer from a flammability problem.
