Hybrid MgCl₂/AlCl₃/Mg(TFSI)₂ Electrolytes in DME Enabling High-Rate Rechargeable Mg Batteries

Abstract

Rechargeable magnesium batteries (RMBs) are considered as one of the most promising next-generation secondary batteries due to their low cost, safety, dendrite-free nature, as well as high volumetric energy density. However, the lack of suitable cathode material and electrolyte is the greatest challenge facing practical RMBs. Herein, a hybrid electrolyte MgCl2/AlCl3/Mg­(TFSI)2 (MACT) in dimethyl ether (DME) is developed and exhibits excellent electrochemical performance. The high ionic conductivity (6.82 mS cm–1) and unique solvation structure of [Mg2(μ-Cl)2(DME)4]2+ promote the fast Mg kinetics and favorable thermodynamics in hybrid Mg salts and DME electrolyte, accelerating mass transport and the charge transfer process. Therefore, the great rate capability can be realized both in symmetric Mg/Mg cell and in CuS/Mg full cell.

Organic Electrolyte Design for Rechargeable Batteries: From Lithium to Magnesium

“…[119a] The beneficial characteristics of chloride anions in enhancing the electrochemical performance of Mg(TFSI) 2based RMBs are shown in Figure 7d. Firstly, the higher Lewis basicity of chloride anions could relieve the strong solvation of Mg 2 + cations by the DME molecules, allowing the formation of active Mg-containing species [e.g., Mg x Cl y , [120] [Mg 2 (μ-Cl) 2 (DME) 4 ] 2 + , [48,121] [Mg 2 (μ-Cl) 3 -(THF) 6 ] + , [122] etc.]. Secondly, the chloride anions tend to form Cl-containing complexes in close vicinity to the anode surface, which possibly act as an effective absorption layer that could prevent the reduction of TFSI À anion at the Mg 0 anode.…”

A Simple Cl–-Free Electrolyte Based on Magnesium Nitrate for Magnesium–Sulfur Battery Applications

“…Figure b shows the fitting curves of logarithmic conductivity against the inverse of the temperature of the HFE, PLI|HFE, and PLI electrolytes. From the linear fit curve slope, the calculated activation energies are 0.1, 0.45, and 0.13 eV, respectively, indicating a lower energy barrier for Mg 2+ migration in the liquid and the dual electrolyte . The relaxation time is estimated from the relation − , where v , u, and h = 2α/π are the distance between an experimental point and ( O , R b ), the distance between the experimental point and (0, 0), and the depressed angle from the Z ′-axis, respectively, and ω is the angular frequency.…”

“…From the linear fit curve slope, the calculated activation energies are 0.1, 0.45, and 0.13 eV, respectively, indicating a lower energy barrier for Mg 2+ migration in the liquid and the dual electrolyte. 28 The relaxation time is estimated from the relation…”

A Passivation-Free Solid Electrolyte Interface Regulated by Magnesium Bromide Additive for Highly Reversible Magnesium Batteries

“…The increasing usage of electrochemical energy storage technologies in daily life drives the development of new battery systems to succeed existing Li-ion batteries. − Among these, rechargeable magnesium batteries (RMBs) using a bivalent Mg 2+ charge carrier display great potential in meeting future battery needs, due to high earth abundance (1.94% for Mg vs 0.002% for Li), high volumetric capacity (3833 mAh cm –3 for Mg vs 2062 mAh cm –3 for Li), low reduction potential (−2.4 V vs standard hydrogen electrode), low possibility of dendrite growth, and low cost. − Unlike in Li battery systems, conventional Mg battery electrolytes readily passivate on the Mg anode surface due to the spontaneous reduction of electrolyte components, resulting in low Mg-ion diffusion and high overpotential. − Constructing solid electrolyte interfaces (SEI) with high Mg conductivity and reversibility is a logical step to prevent passivation, either extrinsically − or intrinsically. − The most widely implemented strategy is the addition of inorganic chlorides (such as MgCl 2 ) in high concentrations with traditional salts. − The addition of Cl – ions forms electroactive species with Mg cations, while modifying the Mg anode surface with adsorbed chloride ions that regulate Mg diffusion. Even though this strategy is accepted as a working paradigm in Mg batteries, it is still limited by high corrosion behavior, low anodic stability, and low salt solubility in the electrolyte.…”