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

Abstract

The electrochemical behavior of magnesium deposition-dissolution on scratched aluminum foils in Grignard reagent/tetrahydrofuran (THF) solutions (1 mol L 1 EtMgBr/THF), which is regarded as a potential electrolyte of rechargeable magnesium batteries, was studied by using various methods such as cyclic voltammetry (CV), scanning electron microscopy (SEM), X-ray diffraction (XRD) and charge-discharge (deposition-dissolution) tests. The results present that the obtained magnesium deposits do not exhibit the morphology of dendrite and the Mg-Al alloy is not found on the surface of aluminum foils. The magnesium deposited on the aluminum substrates have excellent electrochemical cyclic performance in 1 mol L 1 EtMgBr/THF solution. The aluminum can be used as a candidate material of the negative current collector for rechargeable magnesium batteries. Electrochemical energy storage devices are key components for innovative power train systems such as plug-in hybrid vehicle (PHV), fuel cell hybrid vehicle (FCHV), and electric vehicle (EV) [1,2]. Currently, Li-ion batteries have been widely used in the fields of hybrid electric vehicles (HEV) and EV due to their high energy densities. However, there are some shortcomings which have not been resolved in Li-ion batteries, such as poor safety performance and high cost [3,4]. Magnesium as an electrode has the advantages of high Faradic capacity, environmental acceptability, good reliability, high safety and low cost. Therefore, the rechargeable magnesium battery is considered as an ideal substitution for the Li-ion battery in the future [5,6], which is becoming an attractive power battery and developed by many international companies and research institutes [7,8]. Liebenow [9] has investigated that the reversibility of electrochemical magnesium deposition on Au and Ag substrates in Grignard reagent/ether 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. Nuli et al. [15,16] reported that electrochemical deposition-dissolution processes of magnesium in both ionic liquid electrolytic solutions of BMIMBF 4 and PP13TFSI with 1 mol L 1 Mg(CF 3 SO 3 ) 2 are highly reversible. Wang et al. [17] have studied the electrochemical magnesium deposition-dissolution behavior in a mixed ionic liquid of BMIMBF 4 and PP13TFSI with the volume ratios of 2 : 1, 3 : 1, and 4 : 1 in the presence of 0.3 mol L 1 Mg(CF 3 SO 3 ), respectively. They found that those mixed electrolyte systems were well compatible with the deposition-dissolution of magnesium

On the Road to Stable Electrochemical Metal Deposition in Multivalent Batteries

“…43,46,48 Furthermore, the difference in the morphology between dendritic Mg and dendritic Li results from the low diffusion energy and high adsorption energy of the Mg atom, as shown by the DFT calculation results. [41][42][43]45 Our group observed by operando X-ray imaging (Figure 4a) that spherical deposits are formed at 2 mA/cm 2 , but branched dendritic Mg are formed at 10 mA/cm 2 in PhMgCl in THF electrolyte. 45 Interestingly, unlike dendritic Li, the dead Mg formation during the stripping process is not mentioned.…”

“…The polyhedral Mg deposits are also reported in the presence of Grignard reagent electrolyte, which consist of crystalline Mg (Figure 3b). 43 Similarly, in Mg(TFSI) 2 electrolytes, small 3D crystalline structured Mg is formed during deposition. 37 In Mg(TFSI) 2 in glyme/diglyme 1:1 volume ratio electrolyte, the scanning electron microscopy (SEM) image (Figure 3c) shows agglomerated Mg particles consisting of 50 nm hemispherical crystals at high current density (3.25 mA/cm 2 ).…”

“…25,26 The morphology of Mg deposits shows hemispherical or grape-like structure, which is distinct from that of the needle-like Li dendrites, and this set the ground for Mg as nondendritic metal anodes. 43,44 A strong, insoluble native oxide layer of Al requires unique ionic liquid electrolytes for the Al metal anode, which makes the reaction mechanism different from those of other metal anodes, as AlCl 4 − is the main charge transfer agent. 55 The pebble-like morphology of dendritic Al results from the Al 2 O 3 layer and sluggish AlCl 4 − reaction.…”

Homoleptic octahedral coordination of CH3CN to Mg2+ in the Mg[N(SO2CF3)2]2–CH3CN system

“…Ethereal solutions of RMgX, Mg(AlCl 3 R) 2 , and Mg(AlCl 2 RR′) 2 (R and R′ = alkyl or allyl groups) are widely used because they enable a stable Mg metal deposition/dissolution behavior. 2,5,7 In addition, magnesium-aluminum chloride complexes provide a wide electrochemical window within the anodic limit of Mg deposition-dissolution. 8 The Mg source Mg[TFSA] 2 (TFSA = bis(trifluoromethylsulfonyl)amide) readily dissolves in polar solvents and its Mg 2+ ions have a high affinity to σ-donor ligands.…”

Efficient Magnesium Plating and Stripping in DOL/DME-Mg(HMDS)2-Based Electrolytes and Application in Mg/S Batteries

“…This was the first demonstration of a family of Mg-electrolytes. The Aurbach group proposed a series of organometallic electrolytes by combining a Lewis acid and a Lewis base, with close to 100% Coulombic efficiency. − They demonstrated reversible Mg-intercalation in the Chevrel phase cathode, Mo 6 S 8 . Another prominent organohaloaluminate-based electrolyte is the all-phenyl complex or APC, formed by the reaction of PhMgCl with AlCl 3 in tetrahydrofuran (THF) .…”