Lithium-ion batteries power nearly everything in our modern lives—from smartphones to electric vehicles—but lithium is both scarce and unevenly distributed around the world.
As demand rises, scientists have been searching for alternatives that are cheaper, more sustainable, and easier to source.
One promising candidate is the sodium-ion battery (SIB), which uses sodium—a plentiful element found in seawater—instead of lithium.
Sodium-ion batteries have clear advantages: they are safer, more affordable, and ideal for storing renewable energy on a large scale.
But they also come with a significant challenge. The materials used in their cathodes, which are crucial for storing and releasing charge, tend to degrade when exposed to air or moisture.
This instability reduces battery performance and shortens lifespan, posing a major obstacle to commercialization.
Now, a team of researchers from the Tokyo University of Science (TUS), led by Professor Shinichi Komaba along with Assistant Professors Zachary T. Gossage and Changhee Lee, has found a surprisingly simple solution—adding a touch of calcium.
Their study, published in Journal of Materials Chemistry A, shows that incorporating tiny amounts of calcium into a promising sodium-based cathode material dramatically improves its stability and performance.
The researchers focused on a compound called Na₂/₃[Fe₁/₂Mn₁/₂]O₂ (NFM), a leading candidate for sodium battery cathodes.
By replacing less than 2% of its sodium ions with calcium—a process known as doping—the team found that the material not only maintained high energy output but also resisted degradation from air and water.
After two days of exposure to air, regular NFM lost about 35% of its discharge capacity, while the calcium-doped version showed no loss at all.
Further investigation revealed why. When exposed to air, the calcium atoms naturally migrated toward the surface of the material, forming a thin, protective layer.
This calcium-enriched coating acted like a shield, preventing damaging reactions such as sodium loss and unwanted chemical exchanges with moisture.
“This newly explored mechanism appears to be quite effective in suppressing surface degradation,” said Professor Komaba.
In addition to improving stability, calcium doping enhanced the material’s crystal structure and slightly increased the spacing between atomic layers, allowing sodium ions to move more smoothly—boosting battery performance even further.
Because calcium is cheap and abundant, this discovery could significantly reduce the cost of sodium-ion batteries while making them more durable and easier to manufacture.
That could pave the way for large-scale energy storage systems powered by renewable sources like solar and wind, reducing dependence on expensive lithium-based technology.
“This study shows how a small change can make a big difference,” said Prof. Komaba. “Calcium’s simple addition could be the key to unlocking the future of stable, sustainable sodium batteries.”
