A Clue from Jeju's Stone Walls... Battery Storage Capacity 2.5 Times Higher

UNIST-KIST-Korea University Joint Research Team Reports Achievement

Develops Composite Material to Address Silicon Expansion

Retains 85% Capacity After 200 Charge-Discharge Cycles

Jeju's stone walls are built by fitting large and small stones together. They leave gaps for the wind to pass through, yet do not easily collapse. What if silicon in a battery were arranged in the same way?

A team of Korean researchers has developed an anode material that combines materials of different sizes to store more electricity while reducing the volume expansion that occurs during repeated charging and discharging. Its storage capacity was about 2.5 times that of conventional graphite anodes.

A joint research team led by Professor Kang Seokju of the Department of Energy and Chemical Engineering at UNIST, Dr. An Seokhun of the Korea Institute of Science and Technology (KIST), and Professor Kwak Sanggyu of Korea University announced on October 19 that it had developed a composite anode containing graphite, an organic material, and silicon particles arranged according to size.

In lithium-ion batteries, the anode stores electricity by receiving lithium ions during charging. Graphite, which is widely used in current commercial batteries, is stable but has a limited capacity for storing electricity.

Silicon can hold far more electricity than the same weight of graphite. However, as it swells during charging and contracts during discharging, it can cause cracks in the electrode. In other words, adding more silicon to increase capacity can shorten a battery's lifespan.

Research on battery anodes that boost durability by combining particles of different sizes, like Jeju's stone walls.

The team focused not only on the types of materials but also on particle size and arrangement. It used the largest graphite particles to form a framework for conducting electricity, then filled the gaps with cHBC, an organic material made up of medium-sized particles, to support the structure. Smaller silicon particles were placed in between to store electricity. This structure provides room for the silicon to expand, reducing stress on the electrode.

Just as a stone wall gains stability by fitting large and small stones together, the different-sized particles were designed to fill gaps while accommodating changes in the silicon's volume.

Tests also showed a difference in performance. The developed anode had a storage capacity of about 890 mAh per gram at a current density of 0.1 A/g. Under the same conditions, a graphite anode measured about 350 mAh. This means the silicon composite anode stored about 2.5 times as much electricity per unit weight of anode active material.

Improvements were also confirmed over repeated charge-discharge cycles. A battery paired with a high-capacity NCM811 cathode retained about 85% of its initial capacity after 200 cycles at a rate of 2C, which completes one charge-discharge cycle in about 30 minutes. A comparison group with the same silicon content but no organic material retained only about 55% of its capacity.

In pouch cells, which more closely resemble the form of actual batteries, capacity retention remained above 85% after 185 charge-discharge cycles at a rate of 1C. The results show that appropriately arranging the materials can make use of silicon's high storage capacity while also improving durability.

Computer simulations also showed that the size and distribution of silicon particle clusters affect performance. The researchers explained that silicon must be evenly distributed in appropriately sized particles, rather than simply added in large quantities, to store enough lithium while reducing the stress caused by volume expansion.

Research also explores composite anodes that control silicon distribution using three materials of different sizes.

Professor Kang Seokju said, "This research shows that battery performance depends not only on how much high-capacity material is added, but also on how it is arranged." He added, "It could help improve the performance of batteries for electric vehicles and energy storage systems (ESS) and, in the long term, reduce replacement costs."

The research was supported by the National Research Foundation of Korea (NRF), UNIST, the Ministry of Science and ICT (InnoCORE), and the Commercialization Promotion Agency for R&D Outcomes (COMPA).

The findings were published online on September 2 in the international materials science journal Advanced Functional Materials. They were selected for the journal's back cover and will be formally published.

UNIST Professor Kang Seokju (left) and researcher Joo Jeongmi.

This content was produced with the assistance of AI translation services.