In January, Boeing's new, 787 Dreamliners were grounded due to overheating problems with their lithium-ion batteries, leading to potential fire risks. These were 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 250BC to AD640. In Iran, artefacts found such as the "Parthian jar" 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 jar's purpose 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, producing an electric current. His name lives on in the unit of measure, voltage.
Various forms of battery have since been developed, using metals including lead, zinc, cadmium, nickel and lithium. Lithium batteries have proven especially attractive as they produce high power relative to their size.
This is mainly 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 is an electrolyte containing lithium ions, and a cathode with a chemical that can accept lithium ions. The result is a stable chemical reaction.
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 external electrical power - reverses this process.
Though the basic concept of lithium ions seems simple, development of such batteries proved challenging. Work began in 1912, yet it was not until the 1970s that lithium batteries became commercially available. Sony was first to commercialise rechargeable lithium-ion batteries in 1991.
While Volta stacked metal discs along with electrolyte, lithium-ion batteries cannot be as simple. Using a mobile phone or laptop shows these batteries can become warm or hot during use. If discharge rates become too high, they can overheat, perhaps exploding, so the batteries have safety features, including voltage-limiting devices and vents to release excess pressure.
Even with such features, the Dreamliner batteries had problems. And as each weighed 28.6kg, an internal fire could prove catastrophic. Now, a redesigned version supposedly prevents fires. "Everyone feels very comfortable with what we are doing," Ray Conner, Boeing's chief executive of commercial aircraft, said this month. "I plan to fly on the very first flight."
Research is under way to improve 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, said: "We picked the path with the biggest risks and the biggest rewards."
Martin Williams is a Hong Kong-based photographer and writer specialising in conservation and the environment. He holds a PhD in physical chemistry from Cambridge University.