PNNL

Abstract

Charge transfer across the electrode-electrolyte interface is a highly complex and convoluted process involving diverse solvated species with varying structure and compositions. Despite recent advances in in situ and operando interfacial analysis, molecular specific reactivity of solvated species is inaccessible due to lack of precise control over the interfacial constituents and/or an un-clear understanding of their spectroscopic fingerprints. However, such molecular specific understanding is critical to the rational design of energy efficient electrode-electrolyte interfaces (EEIs). 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 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 comprised of (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 undercoor-dinated solvate species (Mg-TFSI-G1+) compared to the fully coordinated (Mg-TFSI-[G1]¬2+) 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 solv-ate species relative to bare TFSI-. We report a detailed understanding of TFSI- decomposition processes as part of solvate species at a Mg-metal anode that will aid the rational design of improved sustainable electrochemical energy technologies.