Technology

A Nobel prize battery

 By Luca Longo

We probably have no alternative but surrender. The evidence of electricity’s omnipresence is overwhelming; we live in a world of gadgets that are totally reliant on it…

Looking around at most of the appliances in a house, they all seem rather straightforward. They have a cable with a plug, connected to a socket in the wall that feeds them the electric current they need to work. But other electric things, like smart phones, tablets, scooters and cars, rely on batteries, and we live in constant fear that they will run out. It is therefore becoming ever more important to find batteries that are as light and small as possible, that can store electricity and provide as much of it as we need even when there is no socket at hand with which to recharge them. We should then be thanking John B. Goodenough, M. Stanley Whittingham and Akira Yoshino for having improved our lives by taking some of the misery out of our constant hunt for a plug. The Royal Swedish Academy of Sciences clearly thought so, at any rate, when they awarded these men the Nobel Prize in Chemistry 2019.

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Sketches of the Nobel Prize winners for chemistry 2019, from left: John B. Goodenough, M. Stanley Whittingham and Akira Yoshino (Ill. Niklas Elmehed, Nobel Media)

All three of them have made a great contribution to the development of lithium batteries. Although they were invented 40 years ago, they are still the most efficient type, and you can find them inside everything, from smart phones to electric cars. Traditional batteries were made of lead and sulphuric acid, nickel and cadmium, or nickel and nickel-metal hydride. The first studies into more efficient, reliable models were in the 1970s, and were prompted by the first petrol crisis. A search for alternative sources and carriers of energy threw up lithium as a potential candidate for the batteries of the future. Lithium happens to have the smallest atoms of any element in the periodic table after hydrogen and helium, and is the lightest of any in a solid state. It can also lose one of its three electrons easily, to become a positive ion. That is not all. This tiny positive ion can be placed within materials used as electrodes in batteries, and carry a positive charge from one electrode to another.
Let us pause here to remind ourselves how batteries work. They are highly precious objects that can collect, store and release electric energy when needed. They are made of two electrodes – an anode connected to the negative pole and a cathode connected to the positive – divided by a semi-permeable barrier which lets through the odd ion here and there, holding back all the other elements of the battery. To charge a battery, you connect the two poles to an electric plug, through a transformer which lifts the alternating current of 220 V to the direct current with the right voltage. Electrons are pushed along the electrical wire to the negative pole and gather on the anode. At the same time, an equivalent amount of electrons are sucked to the positive pole and end up on the cathode. When instead you want to get energy out of the battery, you need to extract all the electrons collected on the anode and use them to produce an electric current, which goes into the device, makes it work and comes back to the positive pole of the battery. Here, they are “eagerly” swept up by the positive ions in the cathode, each one bonds with an electron and turn itself back into a neutral atom. It does not have to be the same electron they lost before; any will do. All are equal in this sense. At this point, we go back to the charging and emptying cycle… as soon as we find a plug.

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Diagram of a battery with polymer separator (Tkarcher, Wikimedia)

The electrons taken from the anode when lithium batteries are charged come from lithium atoms that have lost an electron and become positive ions. These ions move about inside the battery and pass through the membrane, arriving at the cathode and wait to receive their orders. When the battery is employed, the electrons that have powered the device go to the cathode. At this point, the lithium ions, pair off with electrons and return to the anode, ready for another go.

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A representation of the lithium battery

Lithium by chance

Exxon took on M. Stanley Whittingham to work on batteries in the petrol crisis, and it was his idea to use lithium for its electrons. In fact, he himself admitted to having stumbled on it while studying new materials for superconductors based on tantalum disulphide. From 1972 to 1976, Whittingham invented a battery with a negative pole made of lithium metal and a positive pole made of titanium disulphide, a compound that is very light and, above all, cheap, but whose crystal structure can easily accommodate lithium ions, like tantalum disulphide.

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The Whittingham Battery Scheme (Royal Academy of Swedish Sciences)

After this, the story of lithium batteries comes to a standstill for two reasons: the first is the end of the petrol crisis, the second is more technical. During the charge cycles, lithium atoms returning to the anode after finding themselves an electron from the cathode have no motive for going back to the exact same point from which they left the anode. They merely have to land somewhere on its outer surface. The atoms that follow them are even lazier; they do not even make it to the anode, but land on top of the others. The next land on them and so on, forming metal filaments known as cat’s whiskers to researchers. The whiskers get longer and longer until they reach the cathode, making the battery short-circuit and the lithium metal explode.

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Image of metal filaments known as "cat’s wiskers" to researchers (Royal Academy of Swedish Sciences)

Whittingham’s research was interrupted when his local firemen, after being called out to his laboratory dozens of times, threatened to start charging him for the special extinguishers they needed to douse lithium metal. This is where John B. Goodenough appears on the scene. As a boy he had trouble learning to read, which is why he decided to concentrate on numbers. From there it was a short step to becoming professor of chemistry at Oxford.

Good things come to those who wait

With his research group, Goodenough picked up where Whittingham’s studies had left off. In 1980 he replaced titanium disulphide with cobalt oxide on the cathode. With this it was possible to build empty batteries, then charge them (whereas the Exxon model had to be built already charged). More than anything, this increased the difference in potential between the two poles, doubling the figure of 2 volts for Whittingham’s battery up to 4 volts.

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Representation of the replacement of titanium disulphide with cobalt oxide on the cathode (Accademia reale delle scienze svedese)

Meanwhile, an electronic revolution was under way in the Far East. Japanese companies were flooding the world market with new transistor devices like laptops, video cameras, cordless phones and walkmans. They needed light, powerful batteries. Now was Akira’s turn to start working on batteries. At the Asah Kasei Corporation, he began changing the negative pole Whittingham and Goodenough had used, replacing the lithium metal in the anode. He first chose graphite, but it got damaged after a few cycles of charging and emptying. In 1986 he settled on carbon coke, a by-product of oil with three advantages: it prevented short-circuiting by cutting the cat’s whiskers, stabilised the anode to stop it exploding as with lithium metal and, in a pioneering example of the circular economy, by re-using petrol by-product that is hard to sell.

READ MORE: Lithium batteries, a real green solution? by Amanda Saint

about the author
Luca Longo