Argonne National Lab scientists discover method to prevent cracks in sodium-ion battery cathodes, increasing lifespan.

A breakthrough from Argonne National Laboratory may have paved the way for a new era of affordable, sustainable sodium-ion batteries.

As the global push for clean energy accelerates, batteries have become essential for powering electric vehicles and storing renewable energy. While lithium-ion batteries remain the standard due to their high energy density and more matured development, a need to diversify supply chains has intensified the search for alternatives – technologies like solid-state, zinc-air, and vanadium flow batteries offer different solutions, each catering to specific energy storage needs.

Among these competitors, sodium-ion batteries stand out not only for sodium's abundance and lower cost but also for its potential to alleviate supply chain constraints that lithium faces, particularly as demand continues to rise.

"Sodium-ion batteries are emerging as a compelling alternative to lithium-ion batteries due to the greater abundance and lower cost of sodium," said Gui-Liang Xu, a chemist at the U.S. Department of Energy's Argonne National Laboratory.

Beyond its abundance, sodium-ion technology offers several additional benefits. These batteries sidestep the significant mining concerns associated with lithium and cobalt, making them more environmentally friendly. They also perform better in colder climates, where lithium-ion batteries often struggle, making them ideal for certain grid storage applications.

Finally, and perhaps most significantly, sodium-ion batteries are less prone to thermal runaway events, meaning they carry a reduced risk of overheating or catching fire compared to lithium-based cells.

Despite these advantages, sodium-ion batteries have faced significant barriers to wider adoption.

One of the most notable issues is their lower energy density, which, though improving, still lags behind lithium-ion batteries, limiting their use in EVs. Additionally, the cycle life and long-term stability of sodium-ion batteries have been problematic, as they tend to degrade more rapidly over repeated charge and discharge cycles.

These challenges have kept sodium-ion technology from competing directly with lithium-ion in key sectors – at least until now.

Salty breakthrough

By focusing on the structural integrity of the sodium-ion cathode, a team of researchers from Argonne National Lab has developed a method to prevent the formation of cracks in the cathode particles during the synthesis process – a long-standing issue that has plagued sodium-ion batteries.

This breakthrough could significantly enhance the durability and performance of these batteries, positioning them as a viable alternative for large-scale energy storage and even electric vehicles.

The team's innovation lies in a new design for the sodium-ion oxide cathode, drawing inspiration from earlier work on lithium-ion cathodes. Like its lithium counterpart, the sodium-ion cathode is constructed using a mix of transition metals, including nickel, cobalt, manganese, and iron.

These metals are distributed in a unique core-shell configuration, where each metal performs a specific role – the nickel-rich core provides energy storage capacity, while the manganese-rich outer shell enhances the structural stability during repeated charging and discharging cycles.

Despite this advanced design, the team found that the gradient distribution of metals within the cathode particles led to strain, which caused the particles to crack during use. To address this, the researchers fine-tuned the heat treatment process, discovering that slowing the rate at which the cathode particles are heated eliminated the strain, significantly improving the cathode's ability to maintain performance over hundreds of charge cycles.

Science breakdown

Argonne National Laboratory

This artistic rendering illustrates that lowering the heat-up rate during cathode preparation for sodium-ion batteries eliminates the strain and cracking problem in core-shell particles.

The key to this breakthrough was in optimizing the synthesis process. The researchers heated a mixture of precursor materials, including nickel, cobalt, manganese, and sodium hydroxide, to as high as 600 degrees Celsius (1,112 degrees Fahrenheit).

During this process, they monitored the structural changes in the particles in real time using advanced X-ray techniques at the Advanced Photon Source at Argonne and the National Synchrotron Light Source II at Brookhaven National Laboratory. These facilities allowed the team to observe how the metals were distributed throughout the cathode particles and how their structure evolved during heating.

"With the X-ray beams at these facilities, we could determine real-time changes in the particle composition and structure under realistic synthesis conditions," said Argonne beamline scientist Wenqian Xu.

By closely analyzing these changes, the researchers discovered that the formation of cracks was linked to the rate at which the materials were heated.

When the particles were heated too quickly, significant strain developed between the nickel-rich core and the manganese-rich shell, leading to cracks.

Slowing the heat-up rate to just one degree Celsius (1.8 degrees Fahrenheit) per minute allowed the particles to maintain their structural integrity, eliminating the cracks and extending the lifespan of the battery.

"Preventing cracks during cathode synthesis pays big dividends when the cathode is later charged and discharged," said Gui-Liang Xu. "And while sodium-ion batteries do not yet have sufficient energy density to power vehicles over long distances, they are ideal for urban driving."

The results from this fine-tuned process were impressive. In tests, sodium-ion cells using these optimized cathode particles retained their high performance for more than 400 charge-discharge cycles, a significant improvement over previous designs.

While sodium-ion batteries may not yet offer the energy density required for long-distance EVs, this advancement positions them as a strong candidate for urban driving and stationary energy storage applications.

Future sights

Argonne's researchers are now looking to take this breakthrough a step further by eliminating the use of nickel from the cathode, which could lower costs and make the batteries more sustainable.

Nickel, while important for energy storage in many battery chemistries, is expensive and presents its own environmental and supply chain challenges. By removing nickel from the equation, the team hopes to create sodium-ion batteries that are not only cost-effective but also easier to scale for mass production.

"The prospects seem very good for future sodium-ion batteries with not only low cost and long life but also energy density comparable to that of the lithium iron phosphate cathode now in many lithium-ion batteries," said Khalil Amine, an Argonne Distinguished Fellow.

The team's efforts are supported by funding from several DOE programs, including the Vehicle Technologies Office, the Office of Energy Efficiency and Renewable Energy, and the Advanced Scientific Computing Research Program.

The findings from this research were published in Nature Nanotechnology and detail the team's progress toward improving sodium-ion battery performance for both electric vehicles and grid energy storage.