ULSAN — A South Korean research team has developed a technology that combines three materials of differing particle sizes to curb the volume expansion that has long plagued silicon anodes, while raising battery capacity to 2.5 times the previous level.
A joint team led by Professor Kang Seok-ju of the Department of Energy and Chemical Engineering at Ulsan National Institute of Science and Technology (UNIST), Dr. Ahn Seok-hoon of the Korea Institute of Science and Technology (KIST) and Professor Kwak Sang-kyu of Korea University said on Oct. 19 that it had developed a ternary composite anode that improves both storage capacity and durability by controlling the position and distribution of silicon particles. The findings were published in Advanced Functional Materials, an international materials science journal, and were selected for the back cover.
The graphite anodes used in commercial lithium-ion batteries today are structurally stable, but their theoretical storage capacity is limited to 372 mAh per gram of material, capping further gains. Silicon, a next-generation material, has a theoretical capacity roughly 10 times that of graphite, but it repeatedly expands and contracts during charging and discharging. When silicon particles clump together in one spot, stress concentrates in that area, cracking the electrode and sharply shortening battery life.
The team solved the problem with a spatial control method that mixes graphite, a small-molecule organic material known as cHBC, and silicon nanoparticles, each of a different particle size. The largest graphite particles form a conductive framework, the mid-sized organic material fills the spaces between them to support the structure and assist lithium-ion movement, and the smallest silicon particles settle evenly into the remaining gaps to raise electrical storage capacity. The structure prevents silicon particles from clumping and leaves room to accommodate expansion, limiting electrode damage during charging and discharging.
In performance testing, a composite anode containing 15% silicon by weight recorded a reversible capacity of about 890 mAh/g at a current density of 0.1 A/g. That is roughly 2.5 times the storage capacity of a conventional graphite anode under the same conditions, at about 350 mAh/g. It also retained about 250 mAh/g after 1,000 charge-discharge cycles at 1 A/g.
Durability was confirmed in battery demonstrations paired with commercial cathode materials. A battery combined with a high-capacity cathode material, SC-NCM811, retained about 85% of its initial capacity after 200 cycles under fast-charging conditions (2C) that complete a charge and discharge in 30 minutes. By contrast, a control cell mixing only graphite and silicon, without the organic material, retained just 55% under the same conditions. A pouch-type battery also showed a capacity retention rate of more than 85% after 185 cycles under one-hour charge-discharge conditions (1C).
Using real-time optical observation, cross-sectional analysis and multiscale computer simulations, the team established that when silicon clusters are distributed evenly at an appropriate size, lithium storage capability is maintained while structural damage from expansion is reduced.
"This study demonstrates that battery performance hinges not only on the content of high-capacity materials but also on how the particles are arranged," the UNIST professor said. "It will help improve the performance and lifespan of batteries for electric vehicles and energy storage systems, and over the long term contribute to reducing replacement costs."
The research was supported by the Ministry of Science and ICT, the National Research Foundation of Korea (NRF), the Korea Institute of Science and Technology Commercialization Promotion Agency (COMPA) and UNIST.