Anion-Incorporated Mg-Ion Solvation Modulation Enables Fast Magnesium Storage Kinetics of Conversion-Type Cathode Materials.

Rechargeable magnesium batteries (RMB) have emerged as one of the most promising alternatives to lithium-ion batteries due to the prominent advantages of magnesium metal anodes. Nevertheless, their application is hindered by sluggish Mg-ion storage kinetics in cathodes, although various structural modifications of cathode materials have been performed. Herein, an electrolyte design using an anion-incorporated Mg-ion solvation structure is developed to promote the Mg-ion storage reactions of conversion-type cathode materials. The addition of the trifluoromethanesulfonate anion (OTf - ) in the ether-based Mg-ion electrolyte modulates the solvation structure of Mg 2+ from [Mg(DME) 3 ] 2+ to [Mg(DME) 2.5 OTf] + (DME = dimethoxy ethane), which facilitates Mg-ion desolvation and thus significantly expedites the charge transfer of the cathode material. As a result, the as-prepared CuSe cathode material on copper current collector exhibits a considerable increase in magnesium storage capacity from 61% (228 mAh g -1 ) to 95% (357 mAh g -1 ) of the theoretical capacity at 0.1 A g -1 and a more than twofold capacity increase at a high current density of 1.0 A g -1 . This work provides an efficient strategy via electrolyte modulation to achieve high-rate conversion-type cathode materials for RMBs. This article is protected by copyright. All rights reserved.