INTERNATIONAL - Lithium-ion batteries have become a part of the digital revolution, but not without a serious setback - sometimes, they spontaneously explode.
There's a few different reasons why this happens: overcharging, overheating, physical damage or faulty manufacturing can all result in an electrical short - and this is what happened to Samsung's Galaxy 7.
But as researchers develop new kinds of battery technologies, including one with a solid-glass electrolyte, exploding batteries may soon become an event of the past. A new video by the American Chemical Society and PBS Digital Studios explains why batteries explode and how science can address this. According to the video, electricity is generated by the flow of electrons through a conductive material, and a battery is a way of storing and controlling this flow.
The four basic parts of a battery include a cathode, anode, electrolyte and circuit. The electrons flow from the negative anode around to the positively charged cathode, and the electrolyte is usually a fluid between the two. Lithium metal is the current standard for cathodes - it allows for the easy transfer of electrons and it's lightweight, making for a more portable battery pack.
Lithium batteries usually have a lithium cobalt oxide as a cathode, graphite as an anode and a lithium salt bathed in a mixture of one or more alkyl carbonates as the electrolyte. However, these materials come with problems.
For example, lithium is an alkali metal which means it's highly reactive, and organic electrolytes like dimethly carbonate are very combustible.
Commonly used liquid electrolytes can be flammable, and they're also prone to forming dendrites - thin, finger-like protrusions of metal that build up from one electrode and, if they reach all the way across to the other electrode, can create a short-circuit that can damage the battery.
The lithium and electrolyte form what's called 'thermal runaway.'
Thermal runaway is what happens when a battery cell spontaneously explodes, and there are different reasons why this can happen, including overcharging of a battery, overheating, physical damage, or faulty manufacturing, leading to an electrical short.
'To keep it simple, anything that can lead to a rapid increase in heat can cause a problem,' the narrator of the video said.
When multiple chemical reactions cause super-heating, the lithium cobalt oxide begins to release oxygen which can react with the alkyl carbonate electrolyte and even the leftover cobalt oxide.
And during overcharging, the alkyl carbonate electrolyte can break down, creating carbon dioxide gas that will expand outward and burst the electrolyte open, exposing its flammable contents.
According to the video, in laboratory studies, two flammable gases, hydrogen and methane, have also been detected as well as temperatures a high as 850°C (1562°F)
This kind of heat is dangerous - for example, Dale Holzworth from Massachusetts filed a class action lawsuit that claimed the Galaxy S7 Edge he had purchased last year burst into flames while it sat charging in his son's bedroom.
The fire allegedly spread to the bed and the melting parts of the phone burnt holes in the carpet.
The issue has become serious enough that the Federal Aviation Administration has recently banned certain smartphone models fro planes, and the National Transportation Safety Board has even issued alerts regarding lithium batteries as cargo, based on investigations of a plane crash in 2011.
However, the future of lithium batteries may change at the hands of one of its co-inventors, Dr John Goodeneough. The new battery technology could be used for mobile devices, electric cars and stationary energy storage. It was developed with Dr Maria Helena Braga, a senior research fellow at the Cockrell School of Engineering at The University of Texas at Austin.
The battery is low-cost, all-solid state and noncombustible. It has a long cycle life (battery life) and charges and discharges rapidly. The new battery has glass electrolytes inside it instead of flammable liquid ones like alkyl carbonate. It’s better at storing energy, would charge and discharge faster and could be physically shaped into more options.