Former UChicago Pritzker School of
Molecular Engineering graduate student Grant Hill, PhD’24, and UChicago PME
Assoc. Prof. Chong Liu are behind a new paper in Nature Communications
exploring a new, promising way to extract the battery material lithium from
water. Credit: John Zich
The supply of lithium—the battery
material that keeps digital devices humming, EVs racing and renewable energy on
the grid—will not meet even half the expected demand by 2040.
Ramping up production using old
methods will create new problems, including environmental damage, pollution,
cost and water scarcity. Unconventional ways must be found to fill this lithium
gap.
One promising solution is
electrochemical intercalation. Common in the world of batteries and
supercapacitors, it's when researchers apply electricity to insert ions between
the layers of a different material.
Using this technique to extract
materials from water creates force-fed filters, using electrical currents to
pull charged lithium ions through microscopic pathways. But the pathways that
let lithium ions through will also admit other ions, including the vastly more
common sodium.
In new research published in Nature Communications, a team
from the University of Chicago Pritzker School of Molecular Engineering
(UChicago PME) was able to crack this problem. They used electrochemical
intercalation to extract 99% pure lithium from a solution where the ratio of
sodium to lithium was 1,000 to 1.
"Our goal is to develop
materials that can selectively separate lithium from other salts," said
the paper's first author, former UChicago PME graduate student Grant Hill,
Ph.D."24. "For this class of materials, the main competitor is sodium,
because they're just so chemically similar in charge and size."
The work reveals that the ion
pathways that let lithium through layered material—in this particular research,
cobalt oxide—are governed by the push and pull between two forces. This
represents both an advance in pure science and a way forward for developing
new, real-world extraction techniques.
"We know there are two
parallel reactions that will always occur at the same time," said UChicago
PME Associate Professor Chong Liu, corresponding author of the new work.
"One is driven by the charge, when we put current in the material. The
other one is that naturally, the materials will find equilibrium."
'The parking lot is full'
Batteries are the workhorses of the
global transition off fossil fuels, but the methods used to harvest the common
battery material lithium are far from eco-friendly. They require huge
quantities of acid to melt roasted spodumene ore or massive brine pits to pull
millions of gallons (liters) of salt water from deep under the earth and let it
dry in the sun.
Battery researchers across UChicago
PME are exploring ways around this problem. For the Liu Group, this means
advanced materials and methods for extracting lithium directly from water.
The challenge is making sure they
only extract lithium. Before they could apply electrochemical intercalation to
this problem, they had to discover how materials respond when multiple ions are
inserted at the same time. This co-intercalation is the real-world situation faced when
extracting lithium from salty water—and a major blind spot in pre-existing
research.
Liu's team first explored this
class of material in a 2021 Matter paper and a 2024 Nature Materials paper.
"People might not realize the
interactions could be that complicated, and that there is a phase equilibrium
that's governing the ion exchange behavior," Liu said.
One major problem is lithium's
downstairs neighbor on the periodic table—sodium.
Sodium ions are also a third larger
than lithium ions, similar enough in size and charge to be pulled by the
electric field along with lithium, but large enough to cause problems. The Liu
Group's new research found sodium ions pushed the smaller lithium ions to the
side of the pathway, toward lithium-friendly open sites in the material.
Hill describes the ion pathways as
a highway surrounded by parking lots.
"Every lithium ion when it's
starting has a lot of open sites next to it, and when the sodium is getting put
in, it ends up squeezing all the lithium sites next to each other," Hill
said. "For the lithium-friendly areas of the material, that parking lot's
all full."
Speed limits
Overcoming this challenge required
both optimizing the particle size of the lithium ions and finding a balance
between two competing reactions.
The first of the two reactions is
the intercalation itself, caused by the researchers using current to add ions
between the layers. That's the traffic down the highway. The second is the ion
exchange. As the competing sodium and lithium ions find equilibrium, the rate
ions pull into the metaphorical parking lot.
Equilibrium occurs at its own rate,
but the researchers can determine how quickly they pump ions in. This means
they can set the "speed" of the first reaction to one of three
options: faster, slower or the same as the speed of the second reaction.
"We discovered that the three
regimes behave very differently, and it's only when you allow enough time to
let the ion exchange catch up with the intercalation that we can have this very
reversible material response," Liu said.
Slowly inserting the ions and
finding the ideal particle size allowed this reversibility.
"Reversibility means that the
material can repeatedly take up and release lithium without getting stuck in an
undesirable state," Hill said. "By designing smaller particles that
can quickly adapt to their environment, we ensure the material can reliably
return to its preferred state each cycle. This reversibility allows us to keep
extracting lithium efficiently over many cycles, improving both selectivity and
total recovery."
Hill said the lithium cobalt oxide
material the team studied is near-ideal for this kind of work. But cobalt is
comparatively costly and difficult to source, with most of the world's reserves
found in the Democratic Republic of Congo.
"Expanding this research to
more abundant and economically friendly transition metals, especially the
manganese-rich ones, would really make this breakthrough an attractive
opportunity for future applications," Hill said.
Provided by University of Chicago
Source: Electrochemical research takes major strides towards harvesting a vital battery material
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