The Quiet Revolution of the Lithium-Ion Battery

The mobile telephone in a pocket, the laptop on a desk and the electric car on the road all share a hidden ingredient that makes them possible: a small, rechargeable store of electricity known as the lithium-ion battery. Quietly, over the past few decades, this device has transformed daily life, freeing our machines from the wall socket and allowing them to be carried anywhere. Its rise has been so gradual and so complete that most people give it no thought at all, yet without it the portable, wireless world we now take for granted could not exist.

A battery is, in essence, a device for storing energy in chemical form and releasing it as electricity when it is needed. Inside a lithium-ion battery there are two electrodes, a positive one and a negative one, separated by a liquid called the electrolyte through which tiny charged particles, known as ions, are able to move. When the battery is charged, the lithium ions are driven across to one electrode and held there; when it is used, they move back again to the other electrode, and it is this steady movement of ions inside the battery that pushes a matching stream of electrons out through the wires of the circuit to do useful work.

The heart of the design is the element lithium, and it was chosen for good reasons. Lithium is the lightest of all the metals, so a battery made with it can store a great deal of energy without being heavy, an advantage that matters enormously in a device meant to be carried about. Just as importantly, the battery is rechargeable: unlike the old batteries that had to be thrown away once they were flat, a lithium-ion cell can be recharged and used again hundreds of times, its ions shuttling back and forth with each cycle of charging and use.

These qualities explain why the lithium-ion battery has spread into almost every corner of modern life. It powers the mobile phones and laptops that have become part of daily existence, and, on a much larger scale, it drives the growing fleet of electric cars that are beginning to replace those burning petrol. Because it can store plentiful energy in a light and reliable package, it has become the natural choice wherever electricity must be carried rather than drawn from a wire, from the smallest earphone to the largest vehicle.

For all its success, the lithium-ion battery is far from perfect, and its drawbacks are the subject of much research. One difficulty is that it does not last for ever: with every charge and discharge the battery ages a little, and after a few years it loses some of its capacity and can hold less energy than when it was new, as anyone whose old phone runs flat too quickly will know. There are safety concerns too, for if such a battery is damaged, overcharged or badly made it can overheat and, in rare cases, catch fire, which is why they must be built and handled with care.

Further problems arise at the two ends of the battery's life. Making these batteries requires the mining of certain materials, including lithium itself and several other metals, and obtaining them can be costly and can harm the environment where they are dug from the ground. At the other end, a worn-out battery is difficult to deal with, for its tightly packed chemical parts are not easily taken apart, and improving how batteries are recycled so that their valuable materials can be recovered and used again has become an urgent goal. Solving these problems is now one of the great tasks of engineering, for the batteries on which so much of modern life depends must be made not only powerful but also safe, affordable and clean.