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36 | New Scientist | 23 January 2021

that was more powerful than any other

at the time. Together with Akira Yoshino

and Stanley Whittingham, he won a Nobel

prize for the work in 2019.

Lithium batteries soon came to dominate

the market and they have remained peerless

for reasons of inescapable chemistry. In the

periodic table, lithium appears at the top of

the group 1 metals, a set of elements whose

atoms tend to bear a charge of +1. Lithium is

the smallest and lightest of the bunch and so

has the highest charge density, meaning that

a lithium battery can pack in more ions and

so hold more power than a battery of the

same weight made from another group 1

metal. It is easy to see why that is attractive

for smartphone users and electric car makers.

But lithium batteries come with serious

environmental drawbacks. While lithium

isn’t the rarest of metals, sizeable production

happens in two places: mines in Australia and

salt flats in the “lithium triangle” around the

borders of Chile, Bolivia and Argentina. In

South America, lithium brines are sequentially

dissolved and allowed to evaporate to remove

impurities. This requires about 1.9 million

litres of water per tonne of lithium, a

prodigious amount that leaves local farms

and communities parched. With lithium

found in so few countries, there is also a risk

of geopolitical ructions between producers

and big consumers, such as China, if – as is

predicted – the supply becomes more scarce.

There are efforts to get around these

difficulties (see “Fresh lithium”, right).

But our best batteries have another grave

problem: cobalt. Goodenough’s design,

still in use today, uses a cathode made of

lithium cobalt oxide. Cobalt is rare stuff

indeed. Around two-thirds of mined cobalt

comes from one country, the Democratic

Republic of the Congo. Much of the metal

is dug up by miners, including children,

who often work without safety equipment

in awful conditions and earn $3 a day

or less. Another type of lithium battery

uses a cathode made of manganese

and nickel, which are both also rare. GT

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Salar de Uyuni in Bolivia is

the world’s largest salt flat and

a hub for lithium extraction

Sodium’s potential as a replacement

for lithium is suggested by a glance at the

periodic table. It sits in the square below

lithium, also in group 1, but weightier.

While having almost the same chemistry

as lithium, it has none of the environmental

baggage or geographical limitations.

“Sodium is so democratic,” says battery

researcher Maria Helena Braga at the

University of Porto in Portugal. The

US Geological Survey doesn’t even

attempt to put a number on the size of

Earth’s salt reserves, simply saying: “World

continental resources of salt are vast.”

Sodium isn’t an automatic solution though.

Largely, that is because it is quite a bit heavier,

with a relative mass of 23 to lithium’s 7. This

is reflected in the standard potentials of the

“ Purifying

a tonne of

lithium brine

can require

1.9 million litres

of water”