Researchers are discovering a new way to overcome the drop in performance that occurs with repeated charge-discharge cycles in the cathodes of next-generation batteries.
Battery-powered vehicles have made a major breakthrough in the transport market. But this market still needs lower cost batteries that can power vehicles for longer range. Also desirable are low cost Battery capable of storing intermittent clean energy from solar and wind technologies on the grid and powering hundreds of thousands of homes.
To meet these needs, researchers around the world are rushing to develop batteries beyond the current standard of lithium-ion materials. One of the most promising candidates is the sodium-ion battery. It is particularly attractive due to the greater abundance and lower cost of sodium compared to lithium. Additionally, when cycled at high voltage (4.5 volts), a sodium-ion battery can dramatically increase the amount of energy that can be stored in a given weight or volume. However, its fairly rapid decline in performance with charge-discharge cycles hampered commercialization.
Researchers from the US Department of Energy (DOE) Argonne National Laboratory discovered a key reason for performance degradation: the occurrence of defects in the atomic structure that form during the cathode material preparation steps. These faults ultimately lead to a structural earthquake in the cathode, causing a catastrophic drop in performance during the battery cycle. Armed with this knowledge, battery developers will now be able to adjust synthesis conditions to fabricate far superior sodium-ion cathodes.
Key to this discovery was the team’s confidence in the world-class scientific capabilities available at the Argonne 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 during its synthesis in real time,” said Guiliang Xu, assistant chemist in Argonne’s Chemical Sciences and Engineering Division.
During cathode synthesis, material manufacturers slowly heat the cathode mixture to a very high temperature in air, hold it there for a set amount of time, and then quickly lower the temperature to room temperature.
“Seeing is believing,” said Yuzi Liu, a CNM nanoscience.“With Argonne’s world-class scientific facilities, we don’t have to guess what happens during synthesis. For this, the team used the transmission electron microscope in CNM and synchrotron X-ray beams to APS (to the lines of light 11-ID-C and 20-BM).
Their data revealed that as the temperature rapidly dropped during material synthesis, the surface of the cathode particles became less smooth and exhibited large areas indicative of strain. The data also showed that a push-pull effect in these areas occurs during cathode cycling, causing cathode particles to crack and performance to drop.
Upon further study, the team found that this degradation intensified when cycling the cathodes at high temperatures (130 degrees Fahrenheit) or with rapid charging (one hour instead of 10 hours).
“Our knowledge is extremely important for the large-scale fabrication of improved sodium-ion cathodes,” said Khalil Amine, an Argonne Fellow Emeritus.“Due to the large amount of material involved, say 1000 kilograms, there will be a large variation in temperature which will lead to the formation of many defects unless proper measures are taken.
Previous research by members of the team had resulted in a greatly improved anode.“Now we should be able to match our upgraded cathode with the anode to achieve a 20-40% increase in performance,” Xu said.“It is also important that these batteries maintain this performance with a long term cycle at high voltage.
The impact could mean longer range in more affordable electric vehicles and reduced costs for storing energy on the electric grid.
The team published their research in Nature Communications in an article titled,“Structural earthquake induced by native lattice strain in layered sodium 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 analyzes at CNM while Ren and Sun did the analyzes at APS.
This research was supported by DOE Vehicle Technology Office.
About the Argonne Center for Nanoscale Materials: The Center for Nanoscale Materials is one of five DOE Nanoscale Science Research Centers, the primary national user facilities for interdisciplinary nanoscale research supported by the DOE Science Office. Together, the NSRCs comprise a suite of complementary facilities that provide researchers with state-of-the-art capabilities to fabricate, process, characterize and model materials at the nanoscale, and constitute the largest infrastructure investment of the National Initiative on nanotechnology. The NSRCs are located at DOEArgonne, Brookhaven, Lawrence Berkeley, Oak Ridge, Sandia, and Los Alamos National Laboratories. For more information on the DOE NSRC, please visit https://science.osti.gov/User-Facilities/U ser-Facilitis-at-a-Glance.
Article courtesy of Argonne National Laboratory. By Joseph E. Harmon
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