Tue, 04/25/2017 - 2:29pm
by Argonne National Laboratory
Like you, me and everyone we know, batteries have a finite lifespan.
When a battery enters “old age,” scientists refer to its diminished
performance as “capacity fade,” in which the amount of charge a battery
can supply decreases with repeated use. Capacity fade is the reason why
a cell phone battery that used to last a whole day will, after a couple
of years, last perhaps only a few hours.
But what if scientists could reduce this capacity fade, allowing
batteries to age more gracefully?
“Now that we know the mechanisms behind the trapping of lithium ions and
the capacity fade, we can find methods to solve the problem.”
Researchers at the U.S. Department of Energy’s (DOE) Argonne National
Laboratory identified one of the major culprits in capacity fade of
high-energy lithium-ion batteries in a paper published in The Journal of
the Electrochemical Society.
For a lithium-ion battery – the kind that we use in laptops,
smartphones, and plug-in hybrid electric vehicles – the capacity of the
battery is tied directly to the amount of lithium ions that can be
shuttled back and forth between the two terminals of the battery as it
is charged and discharged.
This shuttling is enabled by certain transition metal ions, which change
oxidation states as lithium ions move in and out of the cathode.
However, as the battery is cycled, some of these ions – most notably
manganese – get stripped out of the cathode material and end up at the
Once near the anode, these metal ions interact with a region of the
battery called the solid-electrolyte interphase, which forms because of
reactions between the highly reactive anode and the liquid electrolyte
that carries the lithium ions back and forth. For every electrolyte
molecule that reacts and becomes decomposed in a process called
reduction, a lithium ion becomes trapped in the interphase. As more and
more lithium gets trapped, the capacity of the battery diminishes.
Some molecules in this interphase are incompletely reduced, meaning that
they can accept more electrons and tie up even more lithium ions. These
molecules are like tinder, awaiting a spark.
When the manganese ions become deposited into this interphase they act
like a spark igniting the tinder: these ions are efficient at catalyzing
reactions with the incompletely reduced molecules, trapping more lithium
ions in the process.
“There’s a strict correlation between the amount of manganese that makes
its way to the anode and the amount of lithium that gets trapped,” said
study coauthor and Argonne scientist Daniel Abraham. “Now that we know
the mechanisms behind the trapping of lithium ions and the capacity
fade, we can find methods to solve the problem.”
The study, “Transition Metal Dissolution, Ion Migration,
Electrocatalytic Reduction and Capacity Loss in Lithium-Ion Full Cells,”
appeared in the online edition of The Journal of the Electrochemical
Society on January 5. The other two authors were James Gilbert and Ilya
Shkrob, both with Argonne.
The research was funded by DOE’s Vehicle Technologies Office.
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