Researchers at the U.S. Department of Energy’s (DOE) Argonne National Laboratory have discovered a key reason for the performance degradation in sodium-ion batteries.
The team found that defects in the atomic structure formed during the preparation of the cathode material causes performance declines when cycling the battery.
The scientists tracked changes in the atomic structure of the cathode material in real time while it was being synthesised using a transmission electron microscope in Argonne’s Center for Nanoscale Materials (CNM) and synchrotron X-ray beams at the Advanced Photon Source (APS) (at beamlines 11-ID-C and 20-BM).
The impact could result in a longer driving range in more affordable electric vehicles and lower cost for energy storage on the electric grid.
An article outlining the research entitled “Native lattice strain induced structural earthquake in sodium layered oxide cathodes” was published in the peer reviewed journal Nature Communications.
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.
The 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 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 this degradation intensified when cycling cathodes at high temperature (130 degrees Fahrenheit) or with fast charging (one hour instead of 10 hours).
The team hope the data will allow battery developers to adjust synthesis conditions to fabricate superior sodium-ion cathodes.
Khalil Amine, an Argonne Distinguished Fellow, said: “Our insights are extremely important for the large-scale manufacturing of improved sodium-ion cathodes.
“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.”
Guiliang Xu, assistant chemist in Argonne’s Chemical Sciences and Engineering division, said: “Now, we should be able to match our improved cathode with the anode to attain a 20% – 40% increase in performance.
“Also important, such batteries will maintain that performance with long-term cycling at high voltage.”