Unexplored Class of Eutectic Electrolytes for Rechargeable Magnesium Batteries

Lithium-ion batteries have had huge success in the last three decades. Although their chemistry has matured along with commercial acceptance, there is a strong incentive to design battery materials from abundant resources; yet they can deliver high energy and power density with enhanced safety parameters competitively. Magnesium-metal rechargeable batteries remain as one of the potential candidates offering similar chemistry, which might provide an affordable solution. Nevertheless, there are quite a few challenges that restrict their adaptation. One of the major issues is the choice of solvent-based electrolytes that hampers the thermal and electrochemical stability apart from the safety limitations imposed by the volatile and flammable solvents. Herein, we report an unexplored class of electrolytes composed of 1-ethyl-3-methylimidazolium chloride (EMIC) with Mg(ClO4)2 or Mg(CF3SO3)2 based on the class of deep eutectic solvents (DESs) for application in rechargeable magnesium batteries. The optimized molar ratio 1:0.16 and 1:0.14 identified for EMIC-Mg(ClO4)2 and EMIC-Mg(CF3SO3)2 offers appreciably high conductivity, σ25°C of 2.8 and 2.4 mS cm–1, respectively. The anodic stability recorded with graphite as a working electrode was ∼3.0 V vs Mg/Mg2+, and the Graphite|DES|Mg cells were found to deliver ∼40 mAh g–1 over 50 cycles with remarkable stability. Albeit preliminary, the study opens up prospects for designing an alternate class of safe and stable eutectic electrolytes for rechargeable magnesium battery application.