Researchers have solved a key problem with sodium-ion batteries for electric vehicles and grid energy storage

Artistic rendering of the important discovery that lowering the heating rate during the fabrication of cathodes in sodium-ion batteries eliminates the problem of distortion and cracking in core-shell particles with concentration gradients. Credit: Argonne National Laboratory.
Lithium-ion batteries have long dominated the market as the go-to power source for electric vehicles. Consideration is also underway to store renewable energy for use in the power grid. However, due to the rapid expansion of this market, lithium supply shortages are predicted within the next 5 to 10 years.
“Sodium-ion batteries are emerging as an attractive alternative to lithium-ion batteries due to their abundance of sodium and low cost,” said Gui-Liang Xu, a chemist at the U.S. Department of Energy’s (DOE) Argonne National Laboratory. said.
To date, there have been significant obstacles to the commercialization of such batteries. In particular, the performance of cathodes containing sodium deteriorates rapidly after repeated discharging and charging.
A team at Argonne University has made significant progress in solving this problem with a new design of a sodium ion oxide cathode. It is closely based on the earlier Argonne design of a lithium-ion oxide cathode with proven high energy storage capacity and long lifetime. The research is published in the journal Nature Nanotechnology.
A key feature of both designs is that the fine cathode particles contain a mixture of transition metals such as nickel, cobalt, iron, and manganese. Importantly, these metals are not uniformly distributed in individual cathode particles. As an example, nickel appears in the core. Surrounding this core are cobalt and manganese, forming a shell.
These elements serve different purposes. The manganese-rich surface provides structural stability to the particles during charge-discharge cycles. The nickel-rich core provides large capacity for energy storage.
However, when testing this design, the energy storage capacity of the cathode steadily decreased during cycling. The cause of this problem was found to be due to cracks forming in the particles during cycling. These cracks are formed by the strain that occurs between the shell and core of the particle. The team sought to eliminate that burden before cycling by tweaking the way the cathode was prepared.
The precursor material used to start the synthesis process is hydroxide. In addition to oxygen and hydrogen, it contains three metals: nickel, cobalt, and manganese. The research team created two versions of this hydroxide. One with a gradient metal distribution from the core to the shell, and one with an even distribution of three metals throughout each particle for comparison.
To form the final product, the team heated a mixture of precursor materials and sodium hydroxide to 600°C, maintained that temperature for a selected period of time, and then cooled it to room temperature. They also tried different heating rates.
Throughout this process, the team monitored structural changes in particle properties. This analysis involved two DOE Office of Science user facilities: the Advanced Photon Source at Argonne (beamlines 17-BM and 11-ID) and the National Synchrotron Light Source II at DOE Brookhaven National Laboratory (beamline 18-ID). included the use of.
“The X-ray beams at these facilities allow us to determine changes in particle composition and structure in real time under realistic synthesis conditions,” said Argonne beamline scientist Wenqian Xu.
The research team also used Argonne’s Center for Nanoscale Materials (CNM) for additional analysis to characterize the particles and used the Polaris supercomputer at the Argonne Leadership Computing Facility (ALCF) to analyze the X-ray data. was reconstructed into a detailed 3D image. CNM and ALCF are also DOE Office of Science user facilities.
Initial results showed no cracks in the uniform particles, but cracks were found to form in the gradient particles at temperatures as low as 250°C. These cracks occurred at the core and core-shell boundaries and then migrated to the surface. Apparently, the gradient of the metal created large strains that caused these cracks.
“We know that gradient particles can produce cathodes with high energy storage capacity, so we wanted to find heat treatment conditions that would eliminate cracks in gradient particles,” said Wenhua Zuo, a postdoctoral fellow at Argonne University. ” he said.
The heating rate was found to be a key factor. Cracks formed at a heating rate of 5 degrees per minute, but not at a slower rate of 1 degree per minute. Tests in small cells using cathode particles prepared at low speeds maintained high performance over 400 cycles.
“Preventing cracks during cathode synthesis has significant benefits when subsequently charging and discharging the cathode,” said Gui-Liang Xu. “Sodium-ion batteries do not yet have enough energy density to power vehicles over long distances, but they are ideal for driving in urban areas.”
The research team is currently working on eliminating nickel from the cathode, which would further reduce costs and make it more sustainable.
“The prospects for future sodium-ion batteries look very good, with energy densities comparable to those of the lithium iron phosphate cathodes currently used in many lithium-ion batteries, as well as low cost and long life. ,” said Argonne Honoree Khalil Amin. fellow. “This will lead to longer range and more sustainable electric vehicles.”
Further information: Wenhua Zuo et al, Microstrain screening towards defect-free layered transition metal oxide cathodes, Nature Nanotechnology (2024). DOI: 10.1038/s41565-024-01734-x
Provided by Argonne National Laboratory
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