"Charge Faster, Drive Farther"... Birth of a Nano "Armor" That Extends EV Battery Life [Unboxing the Lab]

[The Financial News] A team led by Professor Yang Hyeon-woo and Professor Kim Sun-jae at the Department of Nanotechnology and Advanced Materials Engineering of Sejong University has developed a silicon anode technology that dramatically increases the capacity of electric vehicle batteries while effectively solving the performance degradation that occurs during fast charging. They evenly coated silicon on the surface of carbon fibers thinner than a human hair, structurally overcoming the chronic problem in which the silicon swelled during charging and destroyed the electrode.

The results of this study are expected to accelerate the commercialization of the silicon anode, a key material for next-generation lithium-ion batteries. The biggest challenge in today’s electric vehicle market is to extend driving range while shortening charging time. Silicon can store more than 10 times as much energy as graphite, which is currently used. However, in real applications it has been limited because its volume swells to more than three times its original size during repeated charging and discharging, causing the electrode to break apart.
The technology developed by the team solves the volume expansion problem of the battery while at the same time dramatically improving fast-charging performance. Once commercialized, it could greatly extend the fully charged driving range of electric vehicles. Drivers would no longer need to wait for long periods in parking lots; just a few minutes of rapid charging would be enough to travel a substantial distance. It is also expected to significantly help extend the operating time of power-hungry IT devices such as smartphones and drones.

To tackle silicon’s chronic expansion problem, the team led by Professor Yang Hyeon-woo and Professor Kim Sun-jae focused on a "freestanding" structure that can maintain its shape without any separate supporting frame. Conventional battery anodes are made by coating electrode material onto a copper foil, so when the material swells it easily peels off. The researchers instead created a carbon nanofiber support that serves as a robust framework for the electrode without the need for copper foil.
The core of the research process was the chemical design of the carbon nanofiber surface. The team drew out a special fiber into an extremely fine thickness and then engineered its surface so that specific chemical reactions would occur. This induced the silicon material to attach uniformly to the fiber surface. After heat treatment, they formed a very thin yet robust silicon protective layer, only about 40–50 nanometers thick—thousands of times thinner than a human hair—on the carbon nanofiber framework.

The team’s design demonstrated outstanding performance in actual experiments. The thin, uniform silicon layer formed on the carbon fiber surface absorbed lithium ions and swelled, but the empty spaces between the carbon fibers buffered this expansion. As a result, it fundamentally prevented the electrode from tearing apart or suffering a sharp drop in performance.
Performance evaluations showed that it far surpassed the limits of existing technologies. The anode developed by the team achieved a capacity of 727 mAh/g, storing about twice as much energy as conventional graphite anodes. The long-term lifetime data are particularly notable. Even after 2,000 cycles of very fast charging and discharging, the new electrode maintained about 80% of its initial performance. Compared with conventional silicon electrodes, which often fail after only a few dozen charge cycles, this is a remarkable leap forward.
Under conditions similar to those in real batteries, it also retained more than 90% of its performance even after 300 charge cycles, demonstrating high stability. This indicates that the technology is not just at a laboratory concept stage but has the level of maturity needed for direct application in commercial products. The study was published in "Advanced Fiber Materials," one of the world’s leading journals in materials science, underscoring the innovative nature of the technology.

monarch@fnnews.com Kim Man-gi Reporter