On the Mechanisms of Reversible Magnesium Deposition Processes

Abstract

Magnesium deposition processes from ethereal solutions of Grignard salts of the RMgX type ͑R ϭ alkyl, aryl groups and X ϭ halide; Cl, Br͒, and complexes of the Mg͑AX 4Ϫn R n Ј R n Љ Ј ) 2 type ͑A ϭ Al, B, X ϭ halide; R,RЈ ϭ alkyl or aryl groups and nЈ ϩ nЉ ϭ n͒ were investigated. These complexes can be considered as interaction products between RЈRMg bases and AX 3Ϫn R n Ј R n Љ Ј Lewis acids. The use of such complexes in ether solvents enables solutions of high anodic stability to be obtained, which can be suitable for rechargeable Mg battery systems. In situ scanning tunneling microscopy, scanning electron microscopy in conjunction with element analysis by dispersive X-ray, electrochemical quartz crystal microbalance, and impedance spectroscopy were used. Mg deposition in all the solutions studied initially form a porous deposit that becomes compact and crystalline as the process continues. It was found that the morphology of Mg deposition is strongly dependent on the solution's composition. This is because these processes are accompanied by adsorption processes. The specific adsorbed species in each solution probably influence the nucleation processes and thus affect the final morphology of Mg deposition in each solution. There is a clear correlation between the morphology of these processes and the cycling efficiency of Mg anodes measured in each solution. The results thus obtained are important for R&D of rechargeable Mg battery systems.

Electrochemical Behavior of Magnesium in Mixed Solutions Consisting of Ionic Liquid and Alkylmagnesiumbromides with Different Alkyl-Chains

“…In the case of CH 3 MgBr/THF with DEMETFSI solution, the redox current response was higher than that observed in the other systems. In addition, the overpotential between Mg deposition and dissolution was smaller in the CH 3 MgBr/THF/ DEMETFSI system than that in the other systems. The coulombic efficiency for Mg deposition and dissolution calculated from the electricity passed in CV is summarized in Table 1.…”

“…Figure 3 shows the charge and discharge profiles of Mg on the Ni substrate in the mixed electrolyte consisting of CH 3 Electrochemistry, 80(10), 774776 (2012) for discharge in the 1st cycle. The potential difference between charge and discharge tended to increase with the repeated cycles.…”

“…Variations in the coulombic efficiency with the repeated cycle in the CH 3 MgBr/THF/DEMETFSI and n-C 8 H 17 MgBr/THF/DEMETFSI systems are compared in Fig. 4.…”

“…However, not like lithium (Li) metal whose surface is covered with a Li + -conducting film, the surface of Mg metal in organic electrolyte solutions generally consists of compact passivation films that are produced by reactions with solvent molecules and/or electrolyte anion. 3 Thus, it has generally accepted that reversible Mg deposition and dissolution do not occur in usual organic electrolyte solutions dissolving conventional Mg salts. As the possibility of Mg anode (negative electrode) for rechargeable batteries, Liebenow 4 first reported the reversible deposition and dissolution of Mg in ether solutions of so-called Grignard reagents.…”

Electrochemical reversibility of magnesium deposition-dissolution on aluminum substrates in Grignard reagent/THF solutions

“…The magnesium deposits on Au and Ag substrates have smooth and compact morphologies. Aurbach et al [10][11][12][13][14] studied the electrochemical deposition-dissolution mechanisms of magnesium on Au substrates in different ethereal solutions of complexes of the Mg(AX 4n R n′ R′ n″ ) 2 type (A=Al, B; X=Cl, Br; R, R′= alkyl or aryl groups; and n′+n″=n) by using various analytical techniques. They found that the electrolyte was a key factor on morphologies of the magnesium deposits.…”