The KERI 's research on anode materials for solid-state batteries (SSBs), conducted in collaboration with Kumoh National Institute of Technology and Inha University, has been selected as the cover article of a world-leading journal in the energy field.
The SSBs have replaced the combustible liquid electrolyte that transfers ions between the anode and cathode with a solid electrolyte, significantly reducing the risk of fire or explosion. However, SSBs, due to their 'solid' nature, require much advanced technology, such as ensuring electro-chemo-mechanical stability during the charging and discharging processes. In particular, since the anode has a significant impact1) on the charging rate and lifespan of the battery, the choice of material is extremely important.
1) Anode: In secondary batteries, the anode functions to store and release lithium ions that migrate from the cathode (+).
Currently, 'Li-metal' is the most extensively researched anode material for SSBs. However, in the case of Li-metal, repeated charging and discharging lead to 'dendrite growth,' where lithium grows in tree-like structures on the surface. This phenomenon can result in internal short circuits, threatening the battery's lifespan and stability. Besides Li-metal, silicon anode materials are also available; however, they face several challenges, including low electronic and ionic conductivity, as well as cracks caused by volumetric expansion.
The anode materials proposed by KERI and the university team this time are tin(Sn)-based2) alloy materials, specifically 'FeSn2.' The research team identified through detailed mechanical property analysis that FeSn2 exhibits a characteristic of particle size reduction due to recombination reactions during repeated charging and discharging. This confirms that in SSBs, the contact between the internal solid particles is maintained for a long period of time, resulting in a dense and uniform electrode. Even in environments with external stimuli, FeSn2 exhibits high elasticity and deformation energy, ensuring good electrochemical stability without cracking.
2) Tin: A metallic element with the symbol Sn, atomic number 50, group 14, period 5 of the periodic table. Due to its low melting point, high workability, and stability, it has been one of the longest-used metals in human history. Today, more than 50% of tin is used as solder in the manufacture of electronic circuits, and other uses include storage containers, utensils, and PVC stabilizers..
The research team developed a test 'SSB full cell3)' to validate the technology, utilizing ▲FeSn2 anode ▲NCM622 (nickel 6, cobalt 2, manganese 2 combination) cathode ▲sulfide solid electrolytes (Li6PS5C1). As a result, an areal capacity of 15.54 mAh/cm² was achieved, which is five times higher than that of conventional lithium-ion batteries. Additionally, high-rate charging and discharging were conducted for over 1,000 cycles under 3-minute (20C current density) and 6-minute (10C current density) conditions, achieving a capacity retention of over 70-80%.
3) Full cell : There are two types of test cells that are created to evaluate electrochemical properties: full cells and half cells. A full cell is a complete cell that includes both anode and cathode, allowing for the measurement of the overall battery performance. A half cell, on the other hand, uses only one electrode as the working electrode while employing a reference electrode for the other, enabling detailed analysis of the electrochemical properties of a specific electrode.
In addition, the research team evaluated the performance of the FeSn2 anode in SSBs by applying it to a prototype 'pouch cell' format. A high energy density of over 255 Wh/kg4) was recorded, demonstrating its commercial potential.
4) Commercial Li-ion batteries typically have an energy density in the range of 200 to 300 Wh/kg.
Yoon-Cheol Ha, Director of the Next Generation Battery Research Center at KERI, stated, "Our achievement is significant as it breaks away from the conventional focus on Li-metal and silicon in the research of anode materials for SSBs, demonstrating the great potential of tin-based alloy anode materials." Additionally, Professor Cheol-Min Park of Kumoh National Institute of Technology expressed his ambition, stating, "Through the development of stable high-performance anode materials that surpass existing limitations, we aim to contribute to the commercialization of non-flammable SSBs."
This research result has been recognized for its excellence and published as a cover article in the October issue of Joule, an international journal ranked in the top 1% of journal citation indicators (JCR). The Joule is a leading journal in the energy field and a sister journal to Cell, which is considered one of the top three journals in the scientific field, alongside Nature and Science. It is a world-class journal with an impact factor (IF) of 38.6.
The corresponding authors of the paper are Yoon-Cheol Ha, Director of the Next Generation Battery Research Center at KERI, Professor Cheol-Min Park from the Department of Materials Science and Engineering at Kumoh National Institute of Technology, and Professor Ki-Joon Jeon from the Department of Environmental Engineering at Inha University. Additionally, the first author is Young-Han Lee, a doctoral student in the Department of Materials Science and Engineering at Kumoh National Institute of Technology. The co-authors of the paper include Jeong-Hee Choi, Director of the Battery and Materials Processing Research Center at KERI, Professor In-Chul Choi from the Department of Materials Science and Engineering at Kumoh National Institute of Technology, as well as researchers Do-Hyeon Kim (doctoral student) and Jeong-Myeong Yoon (doctoral student).
