Abstract
Benefiting from the appealing Mg metal anodes, magnesium batteries (MBs) present attractive potential as sustainable batteries of tomorrow. However, the Mg metal anode-compatible electrolytes generally contain large-size and strongly bonded Mg-clusters ( i.e., Mg x Cl y 2x-y ), resulting in the inefficient cathode chemistries associated with the sluggish Mg-species insertion. Here, using the iconic TiS 2 cathode, we demonstrate the pronounced effect of ionic liquid on regulating Mg x Cl y 2x-y clusters in the MB electrolyte and promoting the high-kinetics multi-Mg-species insertion into TiS 2 . Specifically, the addition of 1-butyl-1-methylpiperidinium bis(trifluoromethylsulfonyl)imide (PP14TFSI) ionic liquid into the conventional Mg bis(hexamethyldisilazide)/4MgCl 2 electrolyte induces a nontrivial two-plateau charge/discharge profile of the TiS 2 electrode, in which Mg 2+ insertion is mainly disclosed at the high-potential plateau and MgCl + insertion dominates the low-potential plateau. Molecular dynamic simulations indicate that the PP14TFSI additive can dissociate large Mg x Cl y 2x-y clusters to produce MgCl + , which can be effectively stabilized by PP14 + and TFSI – . Meanwhile, PP14TFSI catalyzes the Mg-Cl dissociation, thus creating the desirable Mg 2+ species. These electrolyte-regulation effects consequently enable the TiS 2 cathode with a decent specific capacity (81 mAh g –1 at 10 mA g –1 ), high rate capability (63 mAh g –1 at 200 mA g –1 ), and long-term durability (86% capacity retention after 500 cycles).
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