An efficient Hauser-base electrolyte for rechargeable magnesium batteries

Abstract

Rechargeable magnesium batteries (RMBs) are considered the promising candidates for post lithium-ion batteries due to the abundant storage, high capacity, and dendrite-rare characteristic of Mg anode. However, the lack of practical electrolytes impedes the development and application of RMBs. Here, through a one-step reaction of LiCl congenital-containing Knochel–Hauser base TMPL (2,2,6,6-tetramethylpiperidinylmagnesium chloride lithium chloride complex) with Lewis acid AlCl3, we successfully synthesized an efficient amino-magnesium halide TMPLA electrolyte. Raman and mass spectroscopy identified that the electrolyte comprises the typical di-nuclear copolymer [Mg2Cl3·6THF]+ cation group and [(TMP)2AlCl2]− anion group, further supported by the results of density functional theory calculations (DFT) and the Molecular dynamics (MD) simulations. The TMPLA electrolyte exhibits promising electrochemical performance, including available anodic stability (>2.65 V vs. SS), high ionic conductivity (6.05 mS cm−1), and low overpotential (<0.1 V) as well as appropriate Coulombic efficiency (97.3%) for Mg plating/stripping. Both the insertion Mo6S8 cathode and conversion CuS cathode delivered a desirable electrochemical performance with high capacity and good cycling stability based on the TMPLA electrolyte. In particular, when compatible with low cost and easily synthesized CuS, the CuS||Mg cell displayed an extremely high discharge capacity of 458.8 mAh g−1 for the first cycle and stabilized at 170.2 mAh g−1 with high Coulombic efficiency (99.1%) after 50 cycles at 0.05 C. Our work proposes an efficient electrolyte with impressive compatibility with Mg anode and insertion/conversion cathode for practical RMBs and provides a more profound knowledge of the Lewis acid–base reaction mechanisms.