Scientists in South Korea have discovered an important design rule that could help future electric vehicle batteries last much longer and perform more safely.
Their research focuses on solid-state batteries, a next-generation battery technology widely seen as a possible replacement for today’s lithium-ion batteries.
The study was published in Energy Storage Materials by researchers led by Tae Joo Park from Hanyang University.
Unlike conventional lithium-ion batteries, which use liquid electrolytes, solid-state batteries use solid materials to move lithium ions between the battery’s electrodes.
This design could improve safety because solid electrolytes are less likely to catch fire.
Solid-state batteries may also store more energy, potentially allowing electric vehicles to travel farther on a single charge.
However, one major problem has slowed their development. The solid electrolyte can react chemically with the cathode material inside the battery. Over time, these harmful reactions damage the battery and reduce its lifespan.
To solve this issue, scientists have been experimenting with extremely thin protective coatings placed on the cathode surface.
These coatings act like a barrier, preventing direct contact between the cathode and the electrolyte while still allowing lithium ions to move through.
Previous studies suggested that these coatings must be thinner than 5 nanometers to work properly. A nanometer is one-billionth of a meter. But researchers still did not know the minimum thickness needed to effectively protect the battery.
The South Korean team decided to investigate this question in detail.
The researchers used a protective material called lithium niobium oxide, or LNO, and applied it to a common cathode material known as NCM811. Using a highly precise manufacturing method called atomic layer deposition, they created coatings with thicknesses of 1.0 nanometer, 2.5 nanometers, and 5.0 nanometers.
The results revealed a clear trade-off between battery performance and long-term durability.
The thinnest coating, measuring 1 nanometer, delivered the highest initial battery capacity. In simple terms, it allowed the battery to store and release slightly more energy at first.
However, the thicker coatings performed much better over time. Batteries using 2.5-nanometer and 5-nanometer coatings lasted about 28% longer than batteries using the 1-nanometer coating.
The researchers also found that the 1-nanometer coating created much higher resistance for lithium-ion movement inside the battery. Meanwhile, batteries without any protective coating performed far worse, showing much shorter lifespans and far greater internal resistance.
Detailed microscopic and chemical analyses showed that harmful side reactions were effectively blocked only when the coating reached at least 2.5 nanometers thick.
According to the researchers, this finding provides a practical guideline for designing future solid-state batteries. Knowing the minimum effective coating thickness could help companies build more durable batteries for electric vehicles and other technologies.
The team believes the coating process could eventually be scaled up for large-scale battery manufacturing, helping speed up the commercialization of longer-lasting solid-state batteries.
