Stripping and Plating a Magnesium Metal Anode in Bromide‐Based Non‐Nucleophilic Electrolytes

Abstract

A non‐nucleophilic Hauser base hexamethyldisilazide (HMDS) magnesium electrolyte possesses inherent properties required for a magnesium–sulfur battery. However, the development of full cell batteries using HMDSCl‐based electrolytes is still hampered by a low coulombic efficiency. A new electrolyte formulation of non‐nucleophilic HMDS magnesium containing bromide as a halide instead of chloride was obtained through a simple and straightforward synthesis route. The electrochemistry of magnesium was investigated through plating and stripping in three different HMDSBr‐based electrolytes: Mg(HMDS)Br, Mg(HMDS)Br‐BEt3, and Mg(HMDS)Br‐AlEt3 dissolved in tetrahydrofuran. The different magnesium species present in the electrolytes were determined using NMR. Weak electron‐withdrawing Lewis acids, BEt3 and AlEt3 were used intentionally and their impact was investigated. Contrary to expectation, the substitution of chloride by bromide does not drastically narrow the electrochemical stability window. HMDSBr‐based electrolytes demonstrated long‐term (1000 cycles) stable reversibility and highly efficient (≈99 %) magnesium plating/tripping without a high ratio of bromide compared with the MgHMDSCl‐based electrolytes. The aprotic electrolyte shows comparatively high anodic stability (≈2.4 V vs. Mg/Mg2+) and high ionic conductivity of 1.16 mS cm−1 at room temperature. Plating of magnesium with low overpotential (<188 mV) revealed a morphology dependence on the electrolyte type with a shiny metallic homogenous layer, suggesting a rational balance between the nucleation and growth process in HMDSBr‐based electrolytes.

Activating Magnesium Electrolytes through Chemical Generation of Free Chloride and Removal of Trace Water

“…Peak A is therefore ascribed to HMDS coordinated to Mg 2+ . The 29 Si chemical shifts of Mg­(HMDS) 2 and H(HMDS) also align with previously reported values . Although the exact stoichiometry of the complexes in the solutions is unknown, we will simply refer to them as Mg­(HMDS) 2 and H­(HMDS) hereafter.…”

“…The 29 Si chemical shifts of Mg(HMDS) 2 and H(HMDS) also align with previously reported values. 59 Although the exact stoichiometry of the complexes in the solutions is unknown, we will simply refer to them as Mg(HMDS) 2 and H(HMDS) hereafter. 39 Yamane et al also proposed that H(HMDS) reacts with H 2 O and forms (CH 3 ) 3 SiOSi(CH 3 ) 3 and NH 3 .…”

Recent Advances of Emerging 2D MXene for Stable and Dendrite‐Free Metal Anodes

“…Alkali-metal and Zn-metal anodes have been extensively studied in the past few years for alkali-metal and Zn-metal batteries, respectively. In addition to alkali-metal and Znmetal anodes, Ca-metal, Mg-metal, Al-metal, and Fe-metal anodes have also been probed recently for Ca-metal, [36,140] Mgmetal, [35,[141][142][143][144][145] Al-metal, [37] and Fe-metal batteries, [38] respectively. However, their investigation is limited.…”

Suitability of Carbazolyl Hauser and Turbo‐Hauser Bases as Magnesium‐Based Electrolytes

“…[8] Besides the widely used application of Hauser and turbo-Hauser bases as selective metalation reagents, we are interested in magnesium batteries. [9] Not only the nature of the electrodes [10] plays an important role, but also the electrolyte causes challenges that have to be addressed beyond aqueous systems. [11] The realization of zero-emission is one of the greatest challenges of our generation.…”