In January, Boeing’s new, lightweight 787 Dreamliners were grounded due to issues with two of their Lithium-ion batteries overheating, leading to potential fire risks. These were the latest well-publicised yet rare, incidents involving lithium-ion batteries – which abound in our modern lives, powering devices such as mobile phones and laptops.
Though relatively new and packing some advanced features, lithium-ion batteries operate according to the basic principles of all batteries, with chemical reactions producing electrical power.
The first known batteries may date from 250 BC-640 AD. Archaeological discoveries from modern day Iran include the “Parthian jar”, which features an iron rod surrounded by a copper cylinder. When filled with an electrolyte such as vinegar it produces a small voltage. Maybe this was used for electroplating.
While the purpose of the jar is debated, the invention of the battery is credited to Alessandro Volta (1745-1827). In 1800, he demonstrated a voltaic cell: a stack of alternating copper and zinc discs in an acidic solution, which produced an electric current. His name lives on in the unit of measure for electrical potential, voltage.
Various forms of batteries have since been developed, using metals including lead, zinc, cadmium, nickel and lithium. Lithium batteries have proven especially attractive as they produce high power relatively to their size. This is chiefly because lithium atoms are tiny – with just three protons, they are larger only than hydrogen and helium – and a high electrical potential, meaning they readily lose an electron to become ions.
In a charged lithium-ion battery, there are lithium atoms within an anode material, which is usually carbon. There’s an electrolyte containing lithium ions, and a cathode with a chemical that can accept lithium ions, to result in overall chemistry that is more stable. When an electrical circuit links the anode and cathode, electrons flow from the lithium in the anode, and lithium ions move from the carbon to the cathode.
Recharging – using outside electrical power – reverses this process.
Though the basic concept of lithium ions seems simple, development of lithium-ion batteries proved challenging. Work on lithium batteries began in 1912, yet it wasn’t until the 1970s that lithium batteries became commercially available. Sony Corporation was first to commercialise rechargeable lithium-ion batteries in 1991.
While Volta just stacked metal discs along with electrolyte, lithium-ion batteries cannot be as simple. You surely know from using a mobile phone or laptop that these batteries can become warm or hot during use. If discharge rates become too high, they can overheat, perhaps exploding or setting fire to the electrolyte. So the batteries have safety features, including voltage-limiting devices, thermal interrupts, and vents to release any excess pressure.
Even with such features, the Dreamliner batteries experienced problems. And as each weighed 63 pounds, any internal fire could prove catastrophic on an airliner. Now, a redesigned version supposedly ensures prevents fires. “Everyone feels very comfortable with what we are doing,” Ray Conner, Boeing’s CEO of commercial aircraft, said this month. “I plan to fly on the very first flight.”
Research is underway on chemistry to enhance lithium-ion batteries. A version using a combination of lithium and sulphur shows promise, as it packs more electrical power for a given volume. A version in which lithium reacts with oxygen from the air may prove more revolutionary, and is the focus of an IBM project. Yet while the concept is appealing, the science and technology director at IBM Research, USA, told Bloomberg: “We picked the path with the biggest risks and the biggest rewards. This is a moonshot.”