报告题目：Innovating layered cathode materials through the mechanistic understanding of its disorders

报告人：Yong-Mook Kang （教授，高丽大学）

报告时间：2025年1月9日（星期四）9:00

报告地点：大学城B5栋副楼3楼会议室

主办单位：材料科学与工程学院

报告人简介：

Yong-Mook Kang教授分别于1999年、2001年和2004年在韩国科学技术院获得学士、硕士和博士学位。他曾任职于三星有限公司，担任高级研究员。现任韩国高丽大学材料科学与工程学院教授，并在高丽大学KU-KIST融合科学技术研究生院担任教授。Kang教授的研究领域主要涉及可充电电池的电极或催化剂材料。2015年，他被英国皇家化学学会授予会员资格，并任韩国代表；2020年，他被选为韩国青年科学技术院的成员。

报告摘要:

Irreversible phase transformations of layered oxide cathodes during charging have been detrimental for most of them. Even if a lot of efforts have been made to relieve this highly irreversible phase transformation, there have been just a few successful results, which definitely limit the amount of extracted alkali ions and thereby the available capacities of the layered oxides. So, this presentation will suggest couple of strategies to get over the saturated cathode technology.  

As an inverse conceptual strategy, we first observed the possibility to make this irreversible phase transformation extremely reversible by utilizing crystal water as a pillar. Although we found a few cyrstal structures working with this reversible phase transition, the works using Na-birnessite (NaxMnO2•yH2O; Na-bir) or Li-birnessite (Li-bir) as basic structural units will be highlighted here. The crystal water in the structure contributes to generating metastable spinel-like phase, which is the key factor for making this unusual reversibility happen. The reversible structural rearrangement between layered and spinel-like phases during electrochemical reaction can activate new cation sites and enhance ion diffusion with higher structural stability. This unprecedented reversible phase transformation between spinel and layered structure is affected by the steric coordination or amount of crystal water in the lattice as well as the low crystallinity of pristine layered materials. Hence, this research may be correlated with the mechanism behind DRX(disordered rocksalt) cathodes. Pseudo Jahn-Teller effect (Pseudo JTE) will be also stressed out as a fundamental reason behind lattice distortion of layered oxide cathodes. Even though Jahn-Teller effect (JTE) has been regarded as one of the most important determinators of how much stress layered cathode materials undergo during charge and discharge, there have been many reports that traces of superstructure exist in pristine layered materials and irreversible phase transitions occur even after eliminating the JTE. A careful consideration of the energy of cationic distortion using a Taylor expansion indicated that second-order JTE (Pseudo JTE) is more widespread than the aforementioned JTE because of the various bonding states that occur between bonding and anti-bonding molecular orbitals in transition metal octahedra. As a model case, some of layered oxide cathodes will be dealt with in this presentation. In order to manipulate more Li from layered cathodes, oxygen redox should be stabilized because the capacity from cationic redox has been already saturated. Herein, by investigating more fundamental reasons for oxygen redox which can be valid for not only Li-rich layered cathodes but also conventional ones with rhombohedral symmetry, we will suggest the realistic solution to stabilize oxygen redox toward higher energy density and safety.

The aforementioned strategies will provide deep insight into novel class of intercalating materials, and thus it can break up some typical prejudices which we have about the layered cathodes for alkali ion (Li or Na) secondary batteries.