A technology has been developed to quickly and easily manufacture sodium ion battery cathode materials using the microwave oven principle, and the commercialization of next-generation batteries with less risk of fire is expected in the future.

The Korea Electrotechnology Research Institute (KERI) Nano Convergence Research Center's Dr. Dae-ho Kim and Dr. Jong-hwan Park's team announced on the 7th that they have developed a groundbreaking process technology to rapidly manufacture a hard carbon cathode for a sodium ion battery in just 30 seconds using microwave induction heating technology, which is the principle of microwave ovens.

The sodium-ion battery, one of the next-generation secondary batteries, replaces the currently most widely used lithium (Li) with sodium (Na). Sodium, the main component of salt, has reserves that are more than 1,000 times greater than lithium, and is easy to mine and refine. In addition, sodium has a lower reactivity than lithium, so it has high electrochemical stability inside the battery, is advantageous for high-speed charging and discharging, and has the advantage of maintaining performance well even at low temperatures.

On the other hand, sodium-ion batteries have a very complicated manufacturing process, so they have the disadvantages of lower energy density and shorter lifespan than lithium-ion batteries. Since sodium ions have larger particles than lithium ions, hard carbon with a larger interlayer distance than graphite, a conventional negative electrode material, is used.

Hard carbon does not exist in nature, so it must be artificially created, and the process is very difficult. To create hard carbon, hydrocarbon materials, which are the main components of plants and polymers, must be burned in an airless space at a high temperature of over 1,000 degrees Celsius for a long time. The so-called 'carbonization process' is required, which is economically and environmentally burdensome, and this was one of the reasons that prevented the commercialization of sodium-ion batteries.

While many research teams are working hard on this, Dr. Kim Dae-ho and Dr. Park Jong-hwan's team suggested a method of rapid heating using 'microwaves', the principle of microwave ovens. First, a small amount of carbon nanotubes, a new material that conducts electricity well, is mixed with polymer raw materials to create a film. Then, when a microwave magnetic field is applied to this, an induced current is generated in the carbon nanotubes, and only the film material is selectively heated to over 1,400℃ in 30 seconds.

Already, KERI possesses the technology to uniformly heat-treat thin films made of conductive materials such as metals using microwave magnetic fields through years of research, and has received much attention in industrial processes such as displays and semiconductors. In addition, the research institute’s Nano Convergence Research Center has the best technology in Korea in the field of carbon nanomaterials. Using this capability, the team of Dr. Dae-ho Kim and Dr. Jong-hwan Park took on the challenge of a new field called sodium-ion battery cathode materials, and achieved good results.

The core technique is ‘Multiphysics Simulation’ developed by the research team. Through this, we were able to fundamentally understand the complex process that occurs when an electromagnetic field in the microwave band is applied to nanomaterials, and create a new concept process for manufacturing sodium ion battery cathode materials. The related research results were highly evaluated and were recently published in a paper in the 'Chemical Engineering Journal (IF: 13.3, JCR top 3%)', a world-renowned academic journal in the field of chemical engineering. Student researchers Ryu Kyung-beom and Shin Ji-won, who completed the academic-research cooperation course at KERI, participated as co-first authors in the paper.

Dr. Jong-Hwan Park of KERI said, “Sodium-ion batteries, which are safe and operate well even in the cold winter, have been in the spotlight due to electric vehicle fire incidents, but the carbonization process for making cathode materials has been very poor in terms of energy efficiency and cost.”

Dr. Kim Dae-ho said, “Our microwave induction heating technology can quickly and easily manufacture hard carbon, which will greatly contribute to the commercialization of sodium-ion batteries.”

In the future, the research team will continue to work on improving the performance of the cathode material, and also aims to develop technology that can continuously mass-produce large-area hard carbon films. In addition, the research team plans to expand the scope of the technology’s application, judging that microwave induction heating can be used in fields such as all-solid-state batteries that require a high-temperature sintering process.

KERI, which has completed domestic patent application, expects that this technology will receive a lot of attention from companies related to energy storage materials, and plans to discover companies in demand and promote technology transfer.

Meanwhile, KERI is a government-funded research institute under the National Research Council of Science and Technology of the Ministry of Science and ICT.