Scientists have uncovered an important secret about how lithium ions travel through a promising new type of battery material, a discovery that could help create safer, longer-lasting, and more powerful batteries in the future.
The study shows that lithium ions can suddenly speed up by as much as 10,000 times when tiny molecular “cages” surrounding them briefly open, giving the ions a clear path to move.
The research was led by Professor Bong June Sung from Sogang University in South Korea and Professor Shinji Saito from the Institute for Molecular Science in Japan.
Their findings were published in the Journal of the American Chemical Society.
Lithium-ion batteries power many of the devices people use every day, including smartphones, laptops, and electric vehicles. Most of these batteries rely on liquid electrolytes, which allow lithium ions to move between the battery’s two electrodes during charging and discharging.
Although liquid electrolytes work well, they have one major drawback.
They are flammable and can catch fire or even explode if the battery is damaged, overheats, or develops a fault. Because of this, researchers around the world are searching for safer alternatives.
One of the most promising options is a group of materials called organic ionic plastic crystals, or OIPCs.
These materials are solid, making them much safer than liquids. At the same time, they behave differently from most solids because the molecules and ions inside them can still rotate and move while remaining in place. Scientists often describe them as “soft solids” because they combine the safety of a solid with some of the flexibility normally found in liquids.
For many years, researchers believed that lithium ions moved through these materials using what is known as the paddlewheel mechanism. According to this idea, the rotating molecules inside the crystal act like the blades of a paddlewheel, pushing lithium ions from one location to the next.
However, no one had been able to watch exactly how individual lithium ions actually moved inside these complex materials.
To solve this mystery, the research team used powerful supercomputer simulations together with a technique called hop-function analysis. This method allowed them to track the movement of individual lithium ions instead of only measuring their average behavior. It gave the scientists a much clearer picture of what happens at the molecular level.
The results surprised the researchers. They found that although the larger molecules and ions inside the material do rotate as expected, this motion is not what directly drives lithium ions forward. Instead, the key factor is a tiny cage formed by nearby negatively charged ions, known as anions.
Normally, each lithium ion sits inside one of these cages, surrounded by several anions that hold it in place. The researchers discovered that the anions sometimes work together to rearrange themselves. During this brief moment, the cage partially opens before a new cage forms nearby.
As the old cage opens and the new one appears, the lithium ion is able to escape and jump into its new position. This temporary opening creates a much easier pathway for movement.
The team found something even more remarkable. When the cage becomes especially open and only a few anions remain around the lithium ion, the ion’s movement speeds up dramatically. In these moments, lithium ions can travel up to 10,000 times faster than they normally do.
This discovery challenges the long-standing paddlewheel theory by showing that the most important step is not simply the rotation of nearby molecules. Instead, the opening and closing of the ion cages creates the opportunity for lithium ions to move quickly through the material.
The findings could have a major impact on the design of future battery materials. Rather than focusing only on making molecules rotate more easily, scientists may now be able to design materials whose ion cages open and close more efficiently. This could allow lithium ions to move faster while maintaining the safety advantages of solid electrolytes.
The research team also believes that the analytical method used in this study can be applied to many other solid electrolyte materials.
By understanding exactly how ions move at the molecular level, scientists may be able to develop new batteries based on scientific design principles instead of trial and error.
As the demand for electric vehicles, renewable energy storage, and portable electronics continues to grow, discoveries like this could help pave the way for the next generation of safer, faster-charging, and higher-performance lithium-ion batteries.
