23 January 2021 | New Scientist | 37how much charcoal expands and contracts
as sodium ions move in and out – too much
of this and the battery will lose performance
and possibly short circuit. Tapia-Ruiz says
she and others are trying different alloys
and forms of carbon to find the best option.
Third is the most challenging component,
the electrolyte. The trouble is that in metal-
ion batteries of all kinds the electrolyte can
react with the anode and cathode, forming
a layer on them that depletes performance.
This happens in lithium-ion batteries, but
it isn’t a problem because the layer remains
stable after the first charging cycle. In sodium
battery prototypes, however, the solid layer
tends to build up. Getting a working sodium
battery, then, involves redesigning each
of the three components and getting them
to work together seamlessly.two metals, an indication of the maximum
amount of work that a battery made from
them can do. Lithium, at -3.03 volts, has the
best value of any metal, with sodium trailing
behind at -2.71 volts. “Sodium is heavier, it
has a lower voltage,” says Nuria Tapia-Ruiz,
a battery researcher at Lancaster University,
UK. “To make it comparable to a lithium-ion
battery, we need much more material, and
so we are going to make heavier batteries.”
This is why sodium batteries tend to conjure
up images of electric vehicles with all the
dynamism of a milk float.Big, but not bad
But a bulky battery isn’t always bad. “If you
want to store energy from solar panels or
a wind farm, what you want is a very big
battery. You don’t necessarily worry about
energy density or how heavy it is,” says
Robert Armstrong at the University of St
Andrews, UK. Spurred by this thought,
research into sodium cells – and all sorts of
other battery designs – has been going on
for ages (see “Bizarre batteries”, page 38).
It isn’t possible to simply use sodium
ions in existing lithium batteries. Instead,
each of the three battery components must
be redesigned. But in doing so, we have
learned that sodium batteries have benefits
that go beyond the environment.
First, the cathode, which in lithium-ion
batteries requires metals such as cobalt.
The good news is that we have already
learned to make sodium battery cathodes
from layers of more sustainable metal oxides,
such as magnesium, iron and copper. “We’re
always trying to avoid cobalt and nickel,”
says Tapia-Ruiz. These cathodes have made
it into working batteries, including those
made by HiNa Battery Technology in China.
Second is the anode. This is made of
graphite in lithium-ion batteries, but the
pores of this material are too small for
sodium. The best alternative found so far is
an engineered form of charcoal, which has
bigger pores. Not enough is yet known aboutSE
BA
ST
IANM
EY
ER
/GETTY^ IMAGES>Fresh
lithium
The vast majority of the
world’s lithium comes from
just two places: Australia and
South America. In both cases,
its extraction is damaging
to the environment. But there
are plans afoot to get lithium
from other areas using
gentler methods.
Some of the action is
happening in Cornwall, an area
of the UK best known for its
beautiful beaches. A company
called Cornish Lithium has
discovered that beneath the
peninsula’s granite bedrock are
pools of lithium-rich hot brines.
The firm wants to
get at it in a relatively
environmentally friendly way,
drilling 1-kilometre-deep
boreholes and pumping the brine
to the surface. The liquid will
then be fed though a column
of beads that lithium ions cling
to, with the remaining water
then washed back underground.
If it works, it could provide
a much needed raw material
for battery makers in the UK.
“The world is hurtling down
this lithium route,” says Cornish
Lithium’s CEO Jeremy Wrathall.
“Either we have to find a
way of mining lithium in an
environmentally benign way or
we go to another technology.”
A young miner ties up bags
of cobalt near Kolwezi, in the
Democratic Republic of the Congo