Scientists at the US Department of Energy’s Argonne National Laboratory have achieved an important advancement in making sodium-ion batteries more effective.
They have developed a new way to solve a major problem that has stopped these batteries from being used widely – the issue of declining performance due to cracking in the cathode during charge-discharge cycles.
This new development could help sodium-ion batteries become a practical substitute for the commonly used lithium-ion batteries.
This change is crucial as the world faces increasing issues with the limited supply and rising costs of lithium needed for lithium-ion batteries.
“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 Argonne National Laboratory.
Innovative cathode design
The Argonne researchers have worked on improving the cathode, which is a vital part of the battery. They crafted a cathode using a sodium-ion oxide material with a unique metal composition, including nickel, cobalt, and manganese.
“Importantly, these metals are not uniformly distributed in individual cathode particles. As an example, nickel appears at the core; surrounding this core are cobalt and manganese, which form a shell,” explained the researchers.
“These elements serve different purposes. The manganese-rich surface gives the particle its structural stability during charge-discharge cycling. The nickel-rich core provides high capacity for energy storage.”
They structured it with a manganese-rich surface and a nickel-rich core to improve stability and energy output.
However, initial tests revealed cracks forming at the core-shell boundary and within the core itself, even at temperatures as low as 250 degrees Celsius.
“These cracks appeared at the core and the core-shell boundary and then moved to the surface. Clearly, the metal gradient caused significant strain leading to these cracks,” emphasized the scientists.
X-ray analysis to uncover the cause
To understand why these cracks developed, the researchers used advanced X-ray techniques to study the cathode’s structure during its creation.
They heated a mix of precursor material and sodium hydroxide, reaching temperatures up to 600 degrees Celsius, to monitor how cracks formed.
The research team discovered that the speed at which they heated the cathode during its creation was critical.
“Cracks formed at a heat-up rate of five degrees per minute, but not at a slower rate of one degree per minute,” they highlighted.
By slowing down this heating process, they could prevent cracks from forming. This simple change significantly improved the cathode’s performance, allowing it to maintain high energy capacity for more than 400 charge-discharge cycles .
Potential impact and future research
This breakthrough paves the way for sodium-ion batteries with not only low cost and long life but also potentially high energy density comparable to lithium-ion batteries.
“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.
While further research is underway to optimize the cathode composition and eliminate the use of nickel, the prospects for sodium-ion batteries look brighter than ever.
This development could have far-reaching implications, from more sustainable and affordable electric vehicles to efficient grid-scale energy storage.
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