As the world moves toward cleaner energy and electric technologies, better batteries are becoming more important than ever.
Batteries power everything from phones and laptops to electric vehicles and renewable energy storage systems.
Today, lithium-ion batteries dominate the market, but lithium is relatively scarce and expensive. Scientists are therefore searching for alternatives that are cheaper, more abundant, and just as powerful.
One promising option is the sodium-ion battery. Sodium is widely available and inexpensive, making it attractive for large-scale energy storage.
Until recently, however, it was unclear whether sodium-ion batteries could match—or even exceed—the performance of lithium-ion batteries, especially when it comes to fast charging.
A new study from researchers at the Tokyo University of Science suggests they can. The team found that sodium-ion batteries using a special carbon material can charge faster than comparable lithium-ion batteries.
Their findings were published in the journal Chemical Science.
The key material behind this performance is called hard carbon. Hard carbon is a form of carbon with a porous, disordered structure.
These tiny pores can store large numbers of sodium ions, allowing sodium-ion batteries to reach energy levels similar to today’s lithium-ion batteries. Scientists have long suspected that hard carbon allows fast charging, but proving it has been difficult.
The challenge lies in how batteries are usually tested. In real batteries, electrodes are dense mixtures of active materials and other components.
During fast charging, ions can get stuck in these crowded structures, creating what researchers describe as “ion traffic jams.” This slows the reaction and hides the true speed of the material itself.
To overcome this problem, the research team used a clever technique called the diluted electrode method. They mixed hard carbon particles with an inactive material so that each carbon particle had plenty of space and access to ions.
This removed the usual bottlenecks and allowed the researchers to measure how fast sodium and lithium ions could truly move into the hard carbon.
The results were striking. Sodium ions entered the hard carbon faster than lithium ions under the same conditions.
In fact, the charging speed of sodium-ion batteries using hard carbon matched or exceeded that of lithium-ion batteries using graphite, the standard lithium battery material. Measurements showed that sodium ions moved more quickly through the carbon structure, confirming their advantage.
The researchers also identified the main factor limiting charging speed. Inside hard carbon, ions first attach to the surface and then move into tiny pores, where they gather into clusters. This pore-filling step turned out to be the slowest part of charging.
Importantly, sodium ions need less energy than lithium ions to complete this step, which helps explain why sodium-ion batteries can charge faster.
According to lead researcher Professor Shinichi Komaba, this study provides clear evidence that sodium-ion batteries are not just cheaper alternatives but can offer real performance benefits.
Faster charging, combined with abundant materials and stable operation, makes sodium-ion batteries especially attractive for high-power applications and large-scale energy storage.
As scientists continue improving hard carbon materials, sodium-ion batteries could play a major role in building a more sustainable and reliable energy future.
