Solvent Molecule Design Enables Excellent Charge Transfer Kinetics for a Magnesium Metal Anode

Abstract

Lacking of suitable electrolytes is a fatal obstacle for the development of rechargeable magnesium batteries (RMBs). Herein, according to the design of a series of solvent molecules, we find 3methoxypropylamine possesses a middle coordination ability that can be used as an effective solvent and realize a reversible Mg anode with traditional Mg salts. Mechanism study indicates, attributed to its unique solvated structure, energy barriers in both the charge transfer process and desolvation process are extremely low, thus leading to the fast charge transfer kinetics. The relationship between solvated structures and performances is precisely revealed for the first time in RMBs. Additionally, electrolytes with amine solvents possess outstanding water-resistant properties owing to strong hydrogen bonds between amine groups and water. This work proposes a universal design principle of solvent molecules for RMBs, inspiring a new thinking of developing advanced electrolytes in the view of solvents.

Effect of long range interactions on the reduction of divalent ions inN,O-chelating solvents

“…31 Such a simulation is performed for three molecules and one magnesium ion in accordance with theoretical and experimental data on Mg 2+ coordination in chelating solvents. 6,7 Molecules are brought in contact with the ion using a harmonic potential applied between the nitrogen/oxygen atoms of the solvent molecules and magnesium ion. After the formation of the solvation shell, the harmonic restraint is removed and energy is minimized.…”

“…It is confirmed by visual inspection that the solvated magnesium configurations are the same as presented in ref. 6 and 7.…”

“…We demonstrate that, for electrolytes based on divalent ions with novel (M4, 6 S2 7 ) solvents, the effect of molecules and materials outside the solvation shell is of significant importance for a reduction process. This effect is described as a dependence of reduction potential on the dielectric permittivity of the continuum around the shell.…”

“…New molecules were suggested as an additive for dimethoxyethane (DME) 6 solvent and as stand-alone solvents. 7 The main strategy in the development of new solvents is to design a magnesium solvation shell that supports effective electrodeposition of ions. A two-step mechanism was suggested for electrodeposition of magnesium.…”

“…It is especially important for novel (M4, 6 S2 7 ) N , O -chelating solvents that have low dielectric permittivity and strong ion–solvent interaction due to nitrogen atoms. 7 As a result, additives such as DME do not displace M4 solvent molecules from a solvation shell as demonstrated by DFT simulation and NMR experiments. 6 Thus, such additives stay outside the solvation shell.…”