Researchers uncover new avenue for overcoming the performance decline that occurs with repeated charge-discharge cycling in the cathodes of next generation batteries.
From: U.S. Department of Energy’s (DOE) Argonne
National Laboratory
By Joseph E. Harmon
March 23, 2022 -- Battery-powered
vehicles have made a significant dent in the transportation market. But that
market still needs lower cost batteries that can power vehicles for greater
ranges. Also desirable are low-cost batteries able to store on the grid the
intermittent clean energy from solar and wind technologies and power hundreds
of thousands of homes.
To meet those needs,
researchers around the world are racing to develop batteries beyond the current
standard of lithium-ion materials. One of the more promising candidates is the
sodium-ion battery. It is particularly attractive because of the greater
abundance and lower cost of sodium compared with lithium. What’s more, when
cycled at high voltage (4.5 volts), a sodium-ion battery can greatly increase
the amount of energy that can be stored in a given weight or volume. However,
its fairly rapid performance decline with charge-discharge cycling has stymied
commercialization.
Researchers at the U.S.
Department of Energy’s (DOE) Argonne National Laboratory have discovered a key
reason for the performance degradation: the occurrence of defects in the atomic
structure that form during the steps involved in preparing the cathode
material. These defects eventually lead to a structural earthquake in the
cathode, resulting in catastrophic performance decline during battery cycling.
Armed with this knowledge, battery developers will now be able to adjust synthesis
conditions to fabricate far superior sodium-ion cathodes.
Key to making this
discovery was the team’s reliance on the world-class scientific capabilities
available at Argonne’s Center for Nanoscale Materials (CNM) and Advanced Photon
Source (APS), both of which are DOE Office of Science user
facilities.
“These capabilities
allowed us to track changes in the atomic structure of the cathode material in
real time while it is being synthesized,” said Guiliang Xu, assistant chemist
in Argonne’s Chemical Sciences and Engineering division.
During cathode
synthesis, material fabricators slowly heat the cathode mixture to a very high
temperature in air, hold it there for a set amount of time, then rapidly drop
the temperature to room temperature.
“Seeing is believing,”
said Yuzi Liu, a CNM nanoscientist. “With Argonne’s world-class
scientific facilities, we do not have to guess what is happening during the
synthesis.” To that end, the team called upon the transmission electron
microscope in CNM and synchrotron X-ray beams at the APS (at
beamlines 11-ID-C and 20-BM).
Their data revealed
that, upon rapidly dropping the temperature during material synthesis, the
cathode particle surface had become less smooth and exhibited large areas
indicating strain. The data also showed that a push-pull effect in these areas
happens during cathode cycling, causing cracking of the cathode particles and
performance decline.
Upon further study, the
team found that this degradation intensified when cycling cathodes at high
temperature (130 degrees Fahrenheit) or with fast charging (one hour instead of
10 hours).
“Our insights are
extremely important for the large-scale manufacturing of improved sodium-ion
cathodes,” noted Khalil Amine, an Argonne Distinguished Fellow. “Because
of the large amount of material involved, say, 1000 kilograms, there will be a
large temperature variation, which will lead to many defects forming unless
appropriate steps are taken.”
Earlier research by
team members had resulted in a greatly improved anode. “Now, we should be able to match our improved
cathode with the anode to attain a 20% - 40% increase in performance,” said
Xu. “Also important, such batteries will maintain that performance with
long-term cycling at high voltage.”
The impact could result
in a longer driving range in more affordable electric vehicles and lower cost
for energy storage on the electric grid.
The team published
their research in Nature Communications in an article entitled, “Native lattice
strain induced structural earthquake in sodium layered oxide cathodes.” In
addition to Xu, Liu and Amine, authors include Xiang Liu, Xinwei Zhou, Chen
Zhao, Inhui Hwang, Amine Daali, Zhenzhen Yang, Yang Ren, Cheng-Jun Sun and Zonghai
Chen. Zhou and Liu performed the analyses at CNM while Ren and Sun
did the analyses at APS.
This research was
supported by DOE’s Vehicle Technologies Office.
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