Structure and chemical composition of the Mg electrode during cycling in a simple glyme electrolyte

Dimogiannis, Konstantinos; Sankowski, Andrzej; Holc, Conrad; Parmenter, Christopher D.J.; Newton, Graham N.; Walsh, Darren A.; O'Shea, James; Khlobystov, Andrei N.; Johnson, Lee R.

Abstract

The volumetric energy density of magnesium exceeds that of lithium, making magnesium batteries particularly promising for next-generation energy storage. However, electrochemical cycling of magnesium electrodes in common battery electrolytes is coulombically inefficient and significant charging and discharging overpotentials are observed. Several additives and electrolyte formulations based on Mg(TFSI)2-glyme electrolytes have been proposed as solutions to these problems. However, the impact and value of these advances is often hard to discern due to a lack of knowledge of the composition and performance of the Mg electrode in the underlying Mg(TFSI)2-glyme electrolyte. In this paper, the chemical and structural changes that occur during electrochemical cycling of Mg in Mg(TFSI)2-glyme electrolyte solutions are described for the first time. Using focused ion beam-scanning electron microscopy, we show that the Mg deposited during cycling consists of a shell of degradation products, which in turn surrounds an active Mg core. These structures undergo expansion and contraction during cycling due to incorporation of Mg into the core, resulting in structural deformation and degradation of the deposits. Using this structural model, we discuss the complexities observed during electrochemical cycling of Mg electrodes and elucidate the origins of the overpotentials observed during charging. The new understanding and methodology presented here will allow the impact of electrolyte additives on the performance of the Mg electrode to be resolved.

• Journal Article Type: Article
• Acceptance Date: Feb 18, 2024
• Online Publication Date: Mar 7, 2024
• Publication Date: 2024-03
• Deposit Date: Mar 28, 2024
• Publicly Available Date: Mar 28, 2024
• Journal: Energy Storage Materials
• Print ISSN: 2405-8297
• Electronic ISSN: 2405-8297
• Publisher: Elsevier
• Peer Reviewed: Peer Reviewed
• Volume: 67
• Article Number: 103280
• DOI: https://doi.org/10.1016/j.ensm.2024.103280
• Public URL: https://nottingham-repository.worktribe.com/output/32450213
• Publisher URL: https://www.sciencedirect.com/science/article/pii/S2405829724001077