Deeping insight of Mg(CF3SO3)2 and comprehensive modified electrolyte with ionic liquid enabling high-performance magnesium batteries

Research and development of appropriate electrolytes have been deemed as the key for the commercial utilization of rechargeable magnesium batteries (RMBs) with high energy densities, especially for the storage systems containing high capacity cathode materials. In this study, the cost-competitive magnesium salt Mg(CF3SO3)2, which is structurally similar to Mg(TFSI)2, has been proved to possess stronger hydrophobic property, weaker reducibility and reactivity with Mg anodes by experimental comparison and calculation analysis, whereas limited self-generated oxidation resistance of the anion and inferior ionic conductivity in aprotic solvents restrain its practical application. Herein a small amount of PP14TFSI ionic liquid (IL) as multifunctional additive in Mg(CF3SO3)2-based electrolytes has been demonstrated comprehensive improvements in performance, including broadened electrochemical window, ameliorated ionic conductivity (∼6 mS cm−1), homogenization and optimization in interfacial flux and composition, and stable cycling reversibility with low polarization (0.11 V), etc. The IL tailored electrolytes also exhibit desirable compatibility with Mo6S8 (66.9 mAh g−1 after 100 cycles at 0.1 C) and Cu3Se2 (131.7 mAh g−1 after 100 cycles at 200 mAh g−1). Meanwhile, the nucleophilicity of CF3SO3- has been initially discussed on the basis of the cycling results of S@MC||Mg (sulfur@microporous carbon||Mg) and CuS||Mg full batteries. This work has deepened the understanding of Mg(CF3SO3)2 and IL in RMB electrolytes, and provided a new insight for the exploration of electrolyte systems based on simple magnesium salts.