The development of a technology that can implement stable, high-energy-density lithium-ion batteries even for rapid charging of electric vehicles is expected to contribute to the expansion of electric vehicle distribution.

The team led by Dr. Jeong-hee Choi of the Electric Materials Process Research Center at the Korea Electrotechnology Research Institute (KERI), together with the teams led by Professor Jong-won Lee of Hanyang University and Professor Min-sik Park of Kyunghee University, developed a core technology that can secure charge/discharge stability and realize long-life of lithium-ion batteries even under rapid charging conditions.

The most critical issues to be resolved for expanding the use of electric vehicles include technical issues such as increasing driving range and ensuring safety, and fast charging speeds are also required for user convenience.

On the other hand, in order to design a high-energy density lithium-ion battery, the electrode thickness must be high, but in this case, problems such as deterioration of the battery performance occurred during continuous rapid charging.

The method discovered by KERI was to partially coat the surface of the lithium-ion battery's negative electrode (-) plate with very small 'aluminum oxide (Al2O3)' particles of less than 1 micrometer (㎛).

Meanwhile, many researchers at home and abroad have been introducing functional nanotechnology to cathode materials (graphite, etc.). While the focus was mainly on the active material inside the electrode, Dr. Choi Jeong-hee's team solved the problem with a simple processing technology of coating aluminum oxide on the electrode surface.

Aluminum oxide is a material widely used in various ceramic fields because it is inexpensive and has excellent electrical insulation, heat resistance, chemical stability, and mechanical properties.

The KERI research team confirmed that aluminum oxide particles effectively control the interface between the lithium-ion battery negative electrode and electrolyte and induce rapid movement of lithium ions.

Through this, lithium deposition (irreversible lithium that cannot be charged or discharged) can be prevented even during rapid charging, and a stable charge/discharge lifespan of lithium-ion batteries can be secured.

Another advantage of the technology is that it can promote high energy density of lithium-ion batteries.

In order to improve the performance and stability of lithium-ion batteries, if other functional materials are introduced into the internal electrode materials, the synthesis process becomes complicated, and the disadvantage is that the amount of reversible lithium (initial efficiency) decreases.

In addition, the electrode thickness increases, and performance is bound to decrease under rapid charging conditions.

On the other hand, since KERI technology processes the surface of the graphite cathode rather than the interior, stable performance can be achieved even when rapid charging is applied to high-energy-density thick-film electrodes without reversible lithium quantity reduction.

Through various verifications, the research team confirmed that the high-energy-density cathode electrode (4.4 mAh/cm2) coated with aluminum oxide has world-class excellence, such as maintaining a performance (residual capacity ratio) of more than 83.4% even after 500 rapid charges.

Currently, the effectiveness has been verified up to 500 mAh pouch cells, and the plan is to develop the technology so that it can be applied to large-area, medium-to-large-capacity batteries through scale-up in the future.

Dr. Choi Jeong-hee said, “Convenient rapid charging and the energy density of lithium-ion batteries are perceived as a trade-off, which is one of the reasons preventing the popularization of electric vehicles.” She added, “We expect that our achievement will allow us to implement a high-energy density lithium-ion battery that is stable even with rapid charging, and we expect that this will greatly contribute to expanding the supply of electric vehicles and realizing carbon neutrality nationwide.”

The results of this study were recognized for their excellence and were patented in Korea and the United States, and a paper was recently published in 'Advanced Functional Materials', a renowned international academic journal in the field of materials engineering (JCR Impact Factor 19, top 3.7%).

Meanwhile, KERI is a government-funded research institute under the National Research Council of Science and Technology of the Ministry of Science and ICT. This research was conducted as part of the Samsung Future Technology Promotion Project and the Ministry of Trade, Industry and Energy’s Industrial Technology Innovation Project (Development of Electric Vehicle High-Output Battery and Charging System Technology).