Advanced Electrolyte for Rechargeable Magnesium Batteries

Abstract

Recently, rechargeable magnesium batteries gains more and more attention as a commercially-viable future energy storage system for mid-/large-scale applications such as ESS and electric vehicles (EV).[1-4] Magnesium is attractive as an anode material, since it is not only naturally abundant, but delivers a high gravimetric and volumetric capacity of 2,205 mAh/g and 3,833 mAh/cm3 at relatively low reduction potential of -2.372 V vs. standard hydrogen electrode. Therefore, batteries based on magnesium metal negative electrode can be potentially manufactured at very low cost and possess a market competitiveness in their energy density. However, the most intriguing problems of these systems are slow development of electrolyte systems having a reversible Mg plating/stripping character on the anode without a dendrite formation and at the same time exhibiting a wide electrochemical window, which would hire a cathode material having a high electrode potential for the high energy density of the system. It is well-known that the conventional Grignard solution (RMgX, R = alkyl or aryl, X = Cl, Br) which has a good reversibility on Mg plating/stripping reaction, functions as strong nucleophile and its anodic stability is poor so that it cannot be applied to common cathode materials. In this work, we will present a new electrolyte system which can be prepared by a simple process and can be directly applied to magnesium electrode with a high coulombic efficiency more than 99.9 % and stability up to 4.0 V vs. magnesium electrode. We will characterize this electrolyte system through many analysis tools including NMR, single-crystal XRD and other spectroscopic methods. We will also show that full cells employing Mo6S8 Chevrel phase cathode and this new electrolyte can be run for hundreds of cycles without a noticeable capacity fading.