Guidelines for Developing Ultrahigh-Capacity Hard Carbon Materials in Sodium-Ion Batteries
Professor Yun Young-soo’s group in the KU-KIST Graduate School of Converging Science and Technology identified the core thermodynamic and kinetic parameters that determine the sodium plateau capacities of hard carbon anode materials and presented an equation representing their relationship.
Based on the established relationship formula, the research group designed hard carbon from waste plastics and developed ultrahigh-capacity hard carbon featuring the world’s highest reversible capacity (~507 mAhg-1), thereby proving the validity of the first hard carbon design guideline relationship and, at the same time, achieving an original patent for ultrahigh-capacity hard carbon anode design.
The results obtained from this study were published online in Energy & Environmental Science on March 26.
Sodium ion batteries have garnered much attention as the next-generation energy storage system, since they are based on the sodium resources abundant on the earth’s crust and the chemistries are compatible with commercialized lithium-ion batteries. However, their inferior energy density has been a significant barrier to penetrating the predominant lithium-ion battery markets.
Potential candidates for feasible anode materials have been extensively explored in the last decade. Nevertheless, a competitive sodium-ion battery anode material able to comprehensively correspond to the electrochemical performances of lithium–graphite intercalation compounds (Li+–GIC) in lithium-ion battery systems has not been unrealized. Of the various anode material candidates, the material known as hard carbon has long been considered as an anode material for sodium ion batteries due to its inexpensive and simple manufacturing process. However, the microstructures of hard carbon, which consist of intricate and entangled graphite lattices, are difficult to understand completely, and, as a result of the unclear information on the material design, plateau capacity varies across a wide range from about 100 to 250 mAhg-1.
In this study, the researchers investigated the major kinetic parameters of hard carbon that affect its coefficient of plateau capacity utilization. Through a systematic study, they revealed a close relationship between the I2D/IG band intensity ratio in the Raman spectrum and the internal kinetic barrier for sodium-ion transfer. Based on the thermodynamic and kinetic parameters, they developed the sodium plateau capacity (SPC) factor, which is a structural indicator for characterizing the coefficient of capacity utilization of the plateau capacity. The SPC factor explained the optimal hard carbon anode having a high pore volume ratio, and a low I2D/IG value. In addition, they achieved the highest SPC of about 400 mAhg-1 through advanced microstructural tuning, demonstrating the feasibility of the proposed design guidelines for a high-performance hard carbon anode for sodium-ion batteries.
This study was conducted by Hyun Jong-chan, a doctoral student in the KU-KIST Graduate School of Converging Science and Technology under the guidance of Professor Yoon with assistance from Professor Hin Hyeong-min’s group of Chungnam National University and Professor Jin Hyong-joon’s group of Inha University.