Efficient Magnesium Plating and Stripping in DOL/DME-Mg(HMDS)₂-Based Electrolytes and Application in Mg/S Batteries

Abstract

We discuss here various combinations of magnesium bis (hexamethyldisilazide) (Mg(HMDS) 2 ) with aluminum chloride (AlCl 3 ) or magnesium chloride (MgCl 2 ) in a solvent mixture of 1,3-dioxalane (DOL) and 1,2-dimethoxyethane (DME) (DOL/DME) as alternative electrolytes for practical rechargeable Mg−sulfur batteries. This design strategy is contrary to the usage of the solvents tetraglyme and tetrahydrofuran (THF) commonly used with Mg(HMDS) 2 to generate electrolyte formulations for Mg/S batteries. Cyclic voltammetry measurements reveal a higher current response for DOL/DME compared to tetraglyme and THF solvent-based electrolytes. Exemplary plating/stripping efficiency is obtained at room temperature and is observed to be strongly dependent on the salt concentrations. The remarkable stripping/plating reversibility (at a current density of 0.1 mA cm −2 ) in a Mg|| Mg symmetric cell indicates the extraordinary compatibility of the electrolyte with the Mg anode. The plating of Mg on the gold working electrode is ascertained using X-ray diffraction and scanning electron microscopy. The versatility of the Mg(HMDS) 2 -based electrolyte in the DOL/DME solvent is further utilized in a Mg/S cell with a simple carbon nanotube−sulfur composite as the cathode and Mg-metal as the anode. The DOL/DME-Mg(HMDS) 2 electrolyte-based Mg/S cell exhibited stable electrochemical performance over widely varying current densities ranging from 0.05 to 0.5 C.

Synchrotron Radiation Spectroscopic Studies of Mg2+ Storage Mechanisms in High‐Performance Rechargeable Magnesium Batteries with Co‐Doped FeS2 Cathodes

“…[ 12 ] Later, a myriad of electrolytes were prepared and reported to improve MSB performance, [ 6a,13 ] focusing on non‐nucleophilic properties and the compatibility between Mg anodes, S cathodes, and electrolytes. These electrolytes are always prepared using Mg(HMDS) 2 , [ 14 ] Mg(CB 11 H 12 ) 2 , [ 15 ] Mg(TFSI) 2 , [ 16 ] Mg(CF 3 SO 3 ) 2 , [ 17 ] Mg[B(hfip) 4 ] 2 salts, [ 18 ] rendering synthesis costs quite high, which is far from practical application. In addition, MSBs still suffer from the shuttling of magnesium polysulfides, low actual specific capacity, and short cycle life.…”

Efficient and Stable Magnesium Plating/Stripping in High-Capacity Novel Mg//Ni0.6Co0.4Se2 Batteries Enabled by Interfacial Chemistry Modulation

“…(d) Discharge–charge curves at different current densities and (e) long-term cycle curves at 0.1 mA cm –2 of the Mg∥Mg symmetric cells using Mg­(HMDS) 2 -AlCl 3 - 50 mmol/L I 2 -G2 electrolyte. (f) Comparison of electrochemical performance for this work and other Mg­(HMDS) 2 -based electrolytes. − …”

A bifunctional electrolyte for activating Mg–Li hybrid batteries

“…17,18 Perhaps even more troublesome is that as the cathode and anode challenges were generally considered separately in most early reports, the compatibility of the electrolyte with varied functional composition across a full Mg battery is still debated. 19,20 Therefore, in addition to electrode design, we are constantly looking for new techniques to pair the electrolyte design of the cathode and anode into a full Mg battery for practical use.…”