Recently, the research group of Professor Huang Jiaqi from the Advanced Research Institute for Multidisciplinary Science of Beijing Institute of Technology has made important progress in understanding the co-solvent regulation solvation structure and the formation mechanism of the lithium metal interface. The research results were published online in the top international journal Angew. Chem. Int. Ed. with the title "Non-Solvating and Low-Dielectricity Cosolvent for Anion-Derived Solid Electrolyte Interphases in Lithium Metal Batteries" ", impact factor 12.959. The corresponding author of this article is Professor Huang Jiaqi from Advanced Research Institute for Multidisciplinary Science of Beijing Institute of Technology, and the co-first authors are Ding Junfan, a postgraduate student, and Xu Rui, a doctoral student, from School of Materials Science & Engineering/ Advanced Research Institute for Multidisciplinary Science of Beijing Institute of Technology.

Lithium metal has a very high theoretical specific capacity (3860mAh g−1) and the most negative electrochemical potential (−3.040 V vs. the standard hydrogen electrode). It is one of the most promising anode materials for the next generation of high energy density rechargeable batteries. However, the unstable metal lithium electrode/electrolyte interface (SEI) is a serious problem that hinders the practical application of high specific energy lithium metal batteries. A deep understanding of the internal relationship between the solvation structure of the inner layer of lithium ion (Li⁺) and the properties of SEI can lay the foundation for the further rational design of the electrode/electrolyte interface.

In the latest research, Professor Huang Jiaqi’s team clarified the important influence of co-solvent characteristics on the Li⁺solvation structure and the formation of SEI on the surface of lithium metal. In this work, the author clarified through model studies that the introduction of a non-solvated and low dielectric (NL) co-solvent can essentially enhance the strength of the association between anions and Li⁺by providing a specific low-dielectric environment. It is conducive to the production of a large number of anion-cation clusters (AGGs, one anion is coordinated with two or more Li⁺).

Figure 1. NL co-solvent changes the solvation structure and regulates the SEI generation process

The systematic research results show that the NL co-solvent itself does not participate in the solvation structure and provides a low-dielectric environment. Its introduction makes the positively charged anion-cation clusters dominate, so that the anion can be close to the same negatively charged lithium metal electrode surface, thereby accelerating the decomposition of anions and producing a component-rich SEI dominated by anion decomposition.

Figure 2. NL co-solvent strengthens the binding strength of anions and Li+, and promotes the generation of a large number of anion-cation clusters

The author further clarified the boundary conditions of the ideal NL co-solvent by constructing a solvent diagram based on the relative binding energy and dielectric constant. The L co-solvent needs to have a large relative binding energy difference (E_{base solvent}−E_cosolvent). The weak coordination ability of the main solvent indicates that it is less involved in the Li⁺inner solvation structure; at the same time, it must have low dielectric properties. The resulting low-dielectric environment can effectively enhance the internal interaction between anions and cations, which is conducive to more anions entering the Li⁺solvation sheath to form a large number of AGGs, thereby promoting the decomposition of anions near the lithium metal surface.

Figure 3. Solvent diagram based on the relative binding energy and dielectric constant with Li+

Compared with the main solvent (ethylene glycol dimethyl ether, DME in this article), a solvent with a lower dielectric constant and a larger relative binding energy (cyan region) can be used as an NL co-solvent to promote anion-cation association.

This work clarifies the importance of basic physical and chemical principles in electrolyte design, and provides new ideas for the development of new non-solvated, low-dielectric, and high-compatibility co-solvents for next-generation lithium metal batteries.

About the author:

Huang Jiaqi is a professor from the Advanced Research Institute for Multidisciplinary Science, Beijing Institute of Technology, a doctoral supervisor, and a member of the Jiu San Society. He mainly carries out research on energy interface chemistry. He has published more than 100 research papers in journals such as Angew Chem Int Ed, J Am Chem Soc, Adv Mater, Adv Funct Mater, Sci Bull, etc., with an h factor of 80, and more than 60 papers are ESI highly cited papers. He was selected into the First Technology Young Talents Support Program (2015) by China Association for Science, and was awarded the Hou Debang Chemical Technology Youth Award of the Chinese Society of Chemical Industry, Young Particle Science Award of the Chinese Society of Particulates, the 2018 National Ten Thousand Talents Program Young Top Talent, 2018-2020 Clarivate Analytics Cited Scientist, , the 2020 Beijing Natural Science Foundation Outstanding Youth Project, etc.

About the article:

Non-Solvating and Low-Dielectricity Cosolvent for Anion-Derived Solid Electrolyte Interphases in Lithium Metal Batteries

Jun-Fan Ding+,Rui Xu+,Nan Yao,Xiang Chen,Ye Xiao,Yu-Xing Yao,Chong Yan,Jin Xie,Jia-Qi Huang*

Angewandte Chemie International Edition ，doi：10.1002/anie.202101627

Link to the article: https://onlinelibrary.wiley.com/doi/10.1002/anie.202101627