A Chlorine-Free Electrolyte Based on Non-nucleophilic Magnesium Bis(diisopropyl)amide and Ionic Liquid for Rechargeable Magnesium Batteries

Abstract

The electrolyte based on magnesium bis­(diisopropyl)­amide (MBA), a low-cost and non-nucleophilic organic magnesium salt, is proposed to be an admirable alternative for rechargeable magnesium batteries but suffers from limited ionic conductivity and an inferior electrochemical window in the commonly used ether solvents. In this work, the 1-butyl-1-methylpiperidinium bis­(trifluoromethyl sulfonyl)­imide (PP14TFSI) ionic liquid as the cosolvent of tetrahydrofuran (THF) in chlorine-free MBA-based electrolytes has been first demonstrated to remarkably improve the ionic conductivity and broaden the oxidative stable potential (2.2 V vs Mg/Mg2+) on stainless steel. Reversible Mg electrochemical plating/stripping with a low overpotential below 200 mV and ca. 90% Coulombic efficiency are obtained. The current density of Mg plating/stripping is increased 238 times after the addition of PP14TFSI, where the mechanism of competitive coordination of TFSI– making an easier Mg plating/stripping is proposed theoretically. The MBA-2AlF3 electrolyte with a ratio-optimized THF/PP14TFSI cosolvent exhibits good compatibility with the Mo6S8 cathode. Furthermore, the Se@pPAN|Mg full cell exhibits an initial capacity of 447.8 mAh g–1 and as low as ∼0.66% capacity decay per cycle for more than 70 cycles at 0.2 C with the synergy of LiTFSI additives. The facile modification strategy of ionic liquid in the MBA-based electrolyte sheds inspiring light on exploring non-nucleophilic and chlorine-free electrolytes for practical rechargeable magnesium batteries.

An Efficient Bulky Mg[B(Otfe)4]2 Electrolyte and Its Derivatively General Design Strategy for Rechargeable Magnesium Batteries

“…As shown in Figure 5a, the Mg stripping current density is qualitatively improved to 1.38 mA cm −2 after the in situ reaction with B(Otfe) 3 borate, compared with the single MBA/THF solution with only a 30 μA cm −2 Mg stripping response current density. 20 Nevertheless, its oxidation stability in Figure 5b is about 2.8 V even on the SS, which is inferior to the electrolyte prepared by route 1. This defect is due to the inherently easy-oxidation weakness of organic MBA salt (∼1.2 V in single THF).…”

“…Attractively, the optical color of the brown MBA solution became light-yellowish after the addition of B­(Otfe) 3 (Figure S1). As shown in Figure a, the Mg stripping current density is qualitatively improved to 1.38 mA cm –2 after the in situ reaction with B­(Otfe) 3 borate, compared with the single MBA/THF solution with only a 30 μA cm –2 Mg stripping response current density . Nevertheless, its oxidation stability in Figure b is about 2.8 V even on the SS, which is inferior to the electrolyte prepared by route 1.…”

Rational Design Strategy of Novel Energy Storage Systems: Toward High‐Performance Rechargeable Magnesium Batteries

“…Therefore, non-nucleophilic electrolytes compatible with sulfur cathode have been intensely investigated due to the strong reversibility of sulfur conversion with enhanced performances. [19,63,112,[114][115][116][117][118] For instance, in 2014, Fichtner's group [116] reported a modified non-nucleophilic electrolyte Mg(HMDS) 2 -2AlCl 3 -MgCl 2 /tetraglyme with moderate oxidation stability (≈3 V versus Mg/Mg 2+ ) and ionic conductivity (≈11 mS cm −1 ), and the MgS battery delivered ≈250 mAh g −1 at 20 mA g −1 for 20 cycles. However, the existence of Cl − would cause severe corrosion and affect the cycling stability.…”

“…However, the existence of Cl − would cause severe corrosion and affect the cycling stability. [ 118 ] Thereafter, the same group further synthesized a chlorine‐free electrolyte, namely magnesium tetrakis(hexafluoroisopropyloxy) borate (Mg‐[B(hfip) 4 ] 2 (hfip = OC(H)(CF 3 ) 2 )) in THF. [ 62 ] The electrolyte processes a series of advantages, including high oxidative stability (>4.3 V versus Mg/Mg 2+ ) ( Figure a), high ionic conductivity (≈11 mS cm −1 ), and low polarization potential (<0.1 V at 0.4 mA cm −2 ).…”

Ether–Water Hybrid Electrolyte Contributing to Excellent Mg Ion Storage in Layered Sodium Vanadate

“…On the other hand, common electrolytes for MIBs mainly include organic and aqueous electrolytes. , Some judiciously tailored organic electrolytes allow the plating/stripping of metallic Mg, which enables the use of Mg metal as an anode to achieve high voltage and energy density . However, during the plating/stripping process, metallic Mg anodes have a tendency to form an insulated and passivated surface layer in some current organic electrolyte systems .…”