A quick and easy way to produce anode materials for sodium-ion batteries using microwaves

The research team led by Dr. Daeho Kim and Dr. Jong Hwan Park at the Nano Hybrid Technology Research Center of the Korea Electrotechnology Research Institute (KERI) has developed a groundbreaking process technology that enables for ultrafast, 30-second preparation of hard carbon anodes for sodium-ion batteries using microwave induction heating.

One of the next-generation secondary batteries, the sodium-ion battery uses sodium (Na) in lieu of the current mainstay, lithium (Li). Sodium, the main component of salt, is more than a thousand times more abundant than lithium and is easier to extract and refine. Furthermore, its lower reactivity compared to lithium means greater electrochemical stability when used for batteries, making it more favorable for fast charging and discharging, while maintaining performance even at low temperatures.

Despite these advantages, sodium-ion batteries face significant challenges, including lower energy density and shorter lifespan compared to lithium-ion batteries due to the complexity of the manufacturing process. The larger size of sodium ions compared to lithium necessitates the use of hard carbon, which has a larger interlayer spacing than graphite, the current mainstay of anode materials.

Hard carbon is not found in nature and therefore must be synthesized. The preparation process is highly intricate, requiring hydrocarbon materials—main components of plants and polymers—to be heated in an oxygen-free environment at temperatures exceeding 1,000°C for extended periods. This “carbonization” process is both economically and environmentally burdensome, which has been a key obstacle to the commercialization of sodium-ion batteries.

Among the many teams trying to address this challenge, the team led by Dr. Kim and Dr. Park proposed a rapid heating method using microwave technology, which we can easily find from a microwave oven in the kitchen. They first created films by mixing polymers with a small amount of highly conductive carbon nanotubes^*. They then applied a microwave magnetic field to the films to induce currents in the carbon nanotubes, selectively heating the films to over 1,400°C in just 30 seconds.
^{* Carbon Nanotubes: Carbon nanomaterials are conductive materials at the nanoscale, composed of carbon arranged in hexagonal honeycomb patterns. These materials include graphene, which has a two-dimensional planar structure, and carbon nanotubes, which are helical cylinder forms of graphene. Carbon nanotubes exhibit electrical and thermal conductivity comparable to copper, and their strength is approximately 100 times that of steel, making them a highly promising material for next-generation applications.}

Through years of research, KERI has developed a technology to uniformly heat-treat conductive thin films, such as metals, using microwave magnetic fields. This technology has attracted considerable attention in industrial processes such as displays and semiconductors. KERI's Nano Hybrid Technology Research Center is recognized as the nation's leading center for carbon nanomaterials technology. Dr. Kim and Dr. Park leveraged the center's capabilities to venture into sodium-ion battery anode materials and achieved promising results.

The key to their success lies in the team's own "multiphysics simulation" technique. It allowed them to have a profound understanding of the complex processes occurring when an electromagnetic field in the microwave bandwidth is applied to nanomaterials, leading to the creation of a novel process for preparing sodium-ion battery anode materials. The significance of the team’s findings has been demonstrated by the recent publication of their results in the prestigious Chemical Engineering Journal (IF: 13.3, ranked in the top 3% by JCR). The paper was co-first-authored by Geongbeom Ryoo and Jiwon Shin, student researchers who participated in KERI’s academia-research collaborative research program.

“Due to recent electric vehicle fires, there has been growing interest in sodium-ion batteries that are safer and function well in colder conditions. However, the carbonization process for anodes has been a significant disadvantage in terms of energy efficiency and cost,” said Dr. Jong Hwan Park. Dr. Daeho Kim added: “Our microwave induction heating technology enables fast and easy preparation of hard carbon, which I believe will contribute to the commercialization of sodium-ion batteries.”

Moving forward, the team plans to continue working to improve the performance of their anode materials and develop technology for the continuous mass production of large-area hard carbon films. They also see the potential of their microwave induction heating technology applicable to other fields, such as all-solid-state batteries that require high-temperature sintering, which warrants further research.

KERI, having already completed a domestic patent application, expects this technology to attract significant interest from companies involved in energy storage materials and anticipates technology transfer deals with potential industry partners.

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