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Activating Magnesium Electrolytes through Chemical Generation of Free Chloride and Removal of Trace Water

Kim, Seong Shik and See, Kimberly A. (2021) Activating Magnesium Electrolytes through Chemical Generation of Free Chloride and Removal of Trace Water. ACS Applied Materials & Interfaces, 13 (1). pp. 671-680. ISSN 1944-8244. doi:10.1021/acsami.0c19053.

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Mg batteries are attractive next-generation energy storage systems due to their high natural abundance, inexpensive cost, and high theoretical capacity compared to conventional Li-ion based systems. The high energy density is achieved by electrodeposition and stripping of a Mg metal anode and requires the development of effective electrolytes enabled by a mechanistic understanding of the charge-transfer mechanism. The magnesium aluminum chloride complex (MACC) electrolyte is a good model system to study the mechanism as the solution phase speciation is known. Previously, we reported that minor addition of Mg(HMDS)₂ to the MACC electrolyte causes significant improvement in the Mg deposition and stripping voltammetry resulting in good Coulombic efficiency on cycle one and, therefore, negating the need for electrochemical conditioning. To determine the cause of the improved electrochemistry, here we probe the speciation of the electrolyte after Mg(HMDS)₂ addition using Raman spectroscopy, ²⁷Al nuclear magnetic resonance spectroscopy, and ¹H–²⁹Si heteronuclear multiple bond correlation spectroscopy on MACC + Mg(HMDS)₂ at various Mg(HMDS)₂ concentrations. Mg(HMDS)₂ scavenges trace H₂O, but it also reacts with MACC complexes, namely, AlCl₄⁻, to form free Cl⁻. We suggest that although both the removal of H₂O and the formation of free Cl⁻ improve electrochemistry by altering the speciation at the interface, the latter has a profound effect on electrodeposition and stripping of Mg.

Item Type:Article
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Kim, Seong Shik0000-0003-2604-6392
See, Kimberly A.0000-0002-0133-9693
Additional Information:© 2020 American Chemical Society. Received: October 23, 2020; Accepted: December 8, 2020; Published: December 24, 2020. The authors thank Dr. David Vander Velde at the Liquids NMR facility for his assistance with parameter optimization of the NMR spectrometers. This work was supported by funding from Caltech. The authors declare no competing financial interest.
Funding AgencyGrant Number
Subject Keywords:magnesium electrolyte; magnesium deposition; electrolyte speciation; conditioning-free electrolyte; water scavenger; free chloride formation; ¹H–²⁹Si HMBC NMR
Issue or Number:1
Record Number:CaltechAUTHORS:20201224-134416302
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Official Citation:Activating Magnesium Electrolytes through Chemical Generation of Free Chloride and Removal of Trace Water. Seong Shik Kim and Kimberly A. See. ACS Applied Materials & Interfaces 2021 13 (1), 671-680; DOI: 10.1021/acsami.0c19053
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:107291
Deposited By: George Porter
Deposited On:04 Jan 2021 16:49
Last Modified:16 Nov 2021 19:01

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