April 2022, ScientificAmerican.com 212
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C H E M I S T R YPower Up
New technique puts crumbling batteries
back togetherFor electric cars to run as long as possible between charges,
their batteries need to pack a punch. One option would be lith-
ium-metal batteries, which have a key component made of this
lightweight element. This gives them greater storage capacity
than widely used lithium-ion batteries, with the same compo-
nent made from graphite. Although lithium-metal batteries
can store more energy than lithium-ion batteries of the same
size, they also degrade faster, limiting how many times they
can charge and discharge. But researchers have found a new
charging technique that can actually restore the damaged
material, significantly extending the battery’s lifetime.
As a rechargeable lithium-based battery charges and dis-
charges, lithium ions move back and forth between the positively
charged cathode and the negatively charged anode. But over
time, small pieces of the reactive material fail to latch onto the
anode’s body. Within the battery, the lost chunks form tiny lith-
ium “islands” that most researchers had considered inactive—
until now. Stanford University researchers found that these iso-
lated bits could still respond electrically, physically moving back
and forth as the battery charged and discharged. Their discovery
was published in Nature.
The scientists found that the islands could wiggle around
enough to reestablish an electrical connection between the
isolated lithium and the anode. They realized they could coax
the material back together by immediately discharging a small
amount of electricity after the battery had been charged to
capacity. “That’s how we promote [the lost lithium’s] growth
toward the anode to reestablish the electrical connection,” says
the study’s lead author and Stanford materials scientist Fang
Liu. When a lithium-metal test battery was charged using this
protocol, it could perform more charging cycles, lasting 29 per-
cent longer than a battery that underwent standard charging.
Kelsey Hatzell, a Princeton University electrochemical and
materials scientist who was not involved in the study, says the
finding contributes to the fundamental understanding of lith-
ium-metal batteries. “Observing... the dynamics of isolated
lithium metal is very challenging,” she says, adding that the
researchers “have designed a lot of very intriguing experiments
to start to deconvolute the mechanisms.” She notes, however,
that practical applications may be far off; these batteries still
fall short of the thousands of charging cycles that rechargeable
batteries must endure.
The Stanford researchers hope to further develop their
charging method to maximize lithium-metal battery lifetime.
They are also working on a charging protocol that would extend
lithium-ion batteries’ usability. “I will consider [this study] as a
major discovery for the battery field—lithium-ion, lithium-metal,”
says senior author and Stanford materials scientist Yi Cui. “It can
be generalized, I think, to the whole battery field.”
— Sophie Bushwick