KAIST researchers crack key barrier to fast-charging EV batteries

(Clockwise from bottom left) Lee Kang-taek, a professor of mechanical engineering; Cho Eun-ae, a professor of materials science and engineering; and Kang Ye-jin, a doctoral candidate in mechanical engineering. [KAIST]

Researchers at KAIST say they have found a way to address one of the most persistent problems in electric vehicle technology: battery degradation during fast charging.

KAIST announced Monday that a joint research team led by Lee Kang-taek, a professor of mechanical engineering, and Cho Eun-ae, a professor of materials science and engineering, built a three-dimensional digital twin of the graphite anode used in commercial lithium-ion batteries and used it to quantitatively identify the causes of performance loss during rapid charging.

A battery electrode consists of graphite particles that store lithium, a binder that holds them together, and pores through which lithium ions travel. During charging, lithium ions move into the graphite particles in the anode and are stored there. But when charging happens too quickly, some lithium ions cannot enter the graphite fast enough and instead accumulate on the surface as metallic lithium — a phenomenon known as lithium plating. If this continues, it degrades both battery performance and lifespan.

The challenge is that these processes occur simultaneously inside an extremely small battery, making it difficult to pinpoint through experiments alone where and how problems arise.

The research team created a virtual replica of an actual commercial graphite anode, reconstructing in three dimensions the graphite particles, the binder that holds them together, and the pores through which lithium ions move.

Using this virtual electrode, the team varied the electrode thickness, the amount of pore space, and the placement of the binder, then analyzed how lithium ions moved under fast-charging conditions. They also examined where lithium accumulated, how the protective film formed, and which parts of the electrode experienced the greatest mechanical stress.

As a result, the team found that even when total charge capacity appeared similar, the extent of battery damage varied significantly depending on how the binder and pores were arranged inside the electrode.

In a 50-micrometer-thick electrode, the difference in total charge capacity based on binder placement was within 4 percent — meaning there was little visible difference in charging performance. Inside the electrode, however, the locations where lithium was stored and where performance-degrading reactions occurred differed markedly.

The back cover of InfoMat, the international academic journal in which the study was published. [KAIST]

When the binder was concentrated on one side of the electrode, the available pore space for lithium ions shrank, impeding their movement — much like traffic congestion caused by a narrowing road. In such cases, lithium plating near the current collector, where electrical current converges, increased by more than 10 percent compared with electrodes where the binder was evenly distributed.

Conversely, when the binder was spread relatively evenly across the electrode, lithium ions moved more smoothly and the protective film formed more uniformly.

These differences grew more pronounced as the electrode became thicker. In an 83-micrometer-thick electrode, the gap in charge capacity based on binder placement widened to about 18 percent. The finding suggests that designing thicker electrodes to store more energy requires careful attention not only to the amount of material used but also to how it is arranged internally.

"By optimally arranging the binder and pore space within the electrode, we expect this research will help design batteries that can store large amounts of energy, charge quickly, and last longer," Lee said.

The study was selected as the back-cover paper of InfoMat in its July 7 issue.

nbgkoo@heraldcorp.com