Prabhakaran Venkateshkumar, Agarwal Garvit, Howard Jason D, Wi Sungun, Shutthanandan Vaithiyalingam, Nguyen Dan-Thien, Soule Luke, Johnson Grant E, Liu Yi-Sheng, Yang Feipeng, Feng Xuefei, Guo Jinghua, Hankins Kie, Curtiss Larry A, Mueller Karl T, Assary Rajeev S, Murugesan Vijayakumar
Joint Center for Energy Storage Research, Argonne National Laboratory, Lemont, Illinois, 60439, United States.
Pacific Northwest National Laboratory, Richland, Washington 99352, United States.
ACS Appl Mater Interfaces. 2023 Feb 8;15(5):7518-7528. doi: 10.1021/acsami.2c18477. Epub 2023 Jan 30.
Charge transfer across the electrode-electrolyte interface is a highly complex and convoluted process involving diverse solvated species with varying structures and compositions. Despite recent advances in in situ and operando interfacial analysis, molecular specific reactivity of solvated species is inaccessible due to a lack of precise control over the interfacial constituents and/or an unclear understanding of their spectroscopic fingerprints. However, such molecular-specific understanding is critical to the rational design of energy-efficient solid-electrolyte interphase layers. We have employed ion soft landing, a versatile and highly controlled method, to prepare well-defined interfaces assembled with selected ions, either as solvated species or as bare ions, with distinguishing molecular precision. Equipped with precise control over interfacial composition, we employed in situ multimodal spectroscopic characterization to unravel the molecular specific reactivity of Mg solvated species comprising (i.e., bis(trifluoromethanesulfonyl)imide, TFSI) anions and solvent molecules (i.e., dimethoxyethane, DME/G1) on a Mg metal surface relevant to multivalent Mg batteries. In situ multimodal spectroscopic characterization revealed higher reactivity of the undercoordinated solvated species [Mg-TFSI-G1] compared to the fully coordinated [Mg-TFSI-(G1)] species or even the bare TFSI. These results were corroborated by the computed reaction pathways and energy barriers for decomposition of the TFSI within Mg solvated species relative to bare TFSI. Finally, we evaluated the TFSI reactivity under electrochemical conditions using Mg(TFSI)-DME-based phase-separated electrolytes representing different solvated constituents. Based on our multimodal study, we report a detailed understanding of TFSI decomposition processes as part of coordinated solvated species at a Mg-metal anode that will aid the rational design of improved sustainable electrochemical energy technologies.
电荷在电极 - 电解质界面间的转移是一个高度复杂且曲折的过程，涉及具有不同结构和组成的多种溶剂化物种。尽管原位和操作中的界面分析近来取得了进展，但由于缺乏对界面成分的精确控制和/或对其光谱指纹的理解不够清晰，溶剂化物种的分子特异性反应性仍难以捉摸。然而，这种分子特异性的理解对于合理设计节能型固体电解质界面层至关重要。我们采用了离子软着陆这一通用且高度可控的方法，以制备由选定离子组装而成的明确界面，这些离子既可以是溶剂化物种，也可以是裸离子，具有独特的分子精度。通过对界面组成的精确控制，我们利用原位多模态光谱表征来揭示镁溶剂化物种（即双（三氟甲磺酰）亚胺，TFSI）阴离子和溶剂分子（即二甲氧基乙烷，DME/G1）在与多价镁电池相关的镁金属表面上的分子特异性反应性。原位多模态光谱表征显示，与完全配位的[Mg - TFSI - (G1)]物种甚至裸TFSI相比，配位不足的溶剂化物种[Mg - TFSI - G1]具有更高的反应性。相对于裸TFSI，镁溶剂化物种中TFSI分解的计算反应途径和能垒证实了这些结果。最后，我们使用代表不同溶剂化成分的基于Mg(TFSI)-DME的相分离电解质，评估了电化学条件下TFSI的反应性。基于我们的多模态研究，我们详细阐述了TFSI在镁金属阳极处作为配位溶剂化物种一部分的分解过程，这将有助于合理设计改进的可持续电化学能源技术。
