Understanding the Initial Stages of Reversible Mg Deposition and Stripping in Inorganic Nonaqueous Electrolytes

Abstract

Multi-valent (MV) battery architectures based on pairing a Mg metal anode with a high-voltage (∼ 3 V) intercalation cathode offer a realistic design pathway toward significantly surpassing the energy storage performance of traditional Li-ion based batteries, but there are currently only few electrolyte systems that support reversible Mg deposition. Using both static first-principles calculations and ab initio molecular dynamics, we perform a comprehensive adsorption study of several salt and solvent species at the interface of Mg metal with an electrolyte of Mg 2+ and Cl − dissolved in liquid tetrahydrofuran (THF). Our findings not only provide a picture of the stable species at the interface, but also explain how this system can support reversible Mg deposition and as such we provide insights in how to design other electrolytes for Mg plating and stripping. The active depositing species are identified to be (MgCl) + monomers coordinated by THF, which exhibit preferential adsorption on Mg compared to possible passivating species (such as THF solvent or neutral MgCl2 complexes). Upon deposition, the energy to desolvate these adsorbed complexes and facilitate charge-transfer is shown to be small (∼ 61 -46.2 kJ mol −1 to remove 3 THF from the strongest adsorbing complex), and the stable orientations of the adsorbed but desolvated (MgCl) + complexes appear favorable for charge-transfer. Finally, observations of Mg-Cl dissociation at the Mg surface at very low THF coordinations (0 and 1) suggest that deleterious Cl incorporation in the anode may occur upon plating. In the stripping process, this is beneficial by further facilitating the Mg removal reaction.

Solution Structure and Magnesium Deposition Electrochemistry of Mixing Alkylmagnesium Halide with Magnesium Sulfonyl Amide/Glyme Solution

“…A magnesium deposition-dissolution mechanism has been proposed, whereby some cationic magnesium halide complexes have mediated interface charge-transfer probes, preventing the formation of a passivation layer on the deposited magnesium. 13,18 The change in the overpotential by the content of EtMgBr appears to correspond with such previous reports. The existence of EtMgBr reduces the overpotential, even for content as low as 17%.…”

“…They aid the charge transfer of magnesium by changing ligands. 11,[13][14][15][16][17][18] Despite these advantages, the high reactivity of alkylmagnesium halides and anodic instability of ether solvent (typically tetrahydrofuran THF) prevents this ideal system from use in practical batteries.…”

Sponge-Like Porous Manganese(II,III) Oxide as a Highly Efficient Cathode Material for Rechargeable Magnesium Ion Batteries

“…al. 16 Recently, Aurbach et al revealed that the activity and composition of the MACC electrolyte (the magnesium aluminum chloride complex electrolyte, similar composition with APC electrolyte) varies with cycling. 57 Furthermore, the work done by Gewirth et al showed that the coordinated THF molecules (which with RMg + species formed at the surface of electrode) are more easily oxidized to GBL (γ-butyrolactone) due to the presence of Lewis acidity of RMg + , compared with the uncoordinated THF molecules.…”

Magnesiumbatterien – ein Aufruf an Synthesechemiker: Elektrolyte und Kathoden dringend gesucht

“…Lithiumionen-Batterien sind die fortgeschrittensten kommerziell erhältlichen Energiespeicher.D emgegenüber hat der Wunsch nach einer wesentlich grçßeren Energiedichte für ein starkes Interesse an mçglichen Nachfolgetechniken wie Lithium-Luft-und Lithium-Schwefel-Batterien, multivalenten Batterien und Feststoffbatterien gesorgt. [14][15][16][17][18][19][20] Die Verwendung von Magnesium-anstelle von Lithiummetall als Anodenmaterial hat viele Vorteile,wie die Verdoppelung der volumenspezifischen Kapazität, nichtdendritisches Verhalten und geringere Kosten. Ein großer Vorteil der neuen Te chniken besteht im Ersatz der lithiierten Graphitanode,d ie sich auf einem Stromabnehmer aus Kupfer als Träger befindet, durch eine Metallanode.L ithiummetall gilt als aussichtsreicher Kandidat fürd as Anodenmaterial von Lithium-Luft-und Lithium-Schwefel-Batterien, mit dem sich Eigengewicht, das keinen Beitrag zur Kapazitätd er Anode leistet, vermeiden lässt.…”