A Stable, Non‐Corrosive Perfluorinated Pinacolatoborate Mg Electrolyte for Rechargeable Mg Batteries

Abstract

Mg batteries are a promising energy storage system because of physicochemical merits of Mg metal as an anode material. However, the lack of electrochemically and chemically stable magnesium electrolytes impedes the development of Mg batteries. In this study, a newly designed chloride-free magnesium fluorinated pinacolatoborate, Mg[B((CF3)4C2O2)2]2 (abbreviated as Mg-FPB), was synthesized by convenient methods from commercially available reagents and fully characterized. The Mg-FPB electrolyte delivered outstanding electrochemical performance, specifically, 95% coulombic efficiency and 197 mV overpotential for reversible Mg deposition, and anodic stability up to 4.0 V vs Mg. The Mg-FPB electrolyte was applied to demonstrate a high voltage rechargeable Mg/MnO2 battery with a discharge capacity of 150 mAh/g.

A Stable Solid Electrolyte Interphase for Magnesium Metal Anode Evolved from a Bulky Anion Lithium Salt

“…Tetrakis(hexafluoroisopropyloxy)borate anion (denoted as B(hfip) 4 − ) based Mg electrolytes have been reported almost simultaneously by our group and Zhao's group, which exhibits superior electrochemical performance, especially in Mg‐S battery system 4e,h,11. However, in this contribution, we have observed that the Mg/Cu asymmetric cell (with Mg[B(hfip) 4 ] 2 based electrolyte, 0.5 m Mg[B(hfip) 4 ] 2 dissolved in dimethoxyethane (DME), abbreviated as MBhfip/DME) cannot sustain the stability in the long cycle charge–discharge process, as shown in Figure S1 (Supporting Information).…”

“…However, this system is generally known to possess unsatisfactory energy density owing to the low operating voltage (≈1.1 V) and the low specific capacity (80 mAh g −1 ) of Mo 6 S 8 cathode. Since then, tremendous endeavors have been devoted to improving the energy density of rechargeable Mg metal batteries, aimed at exploiting the high‐voltage Mg cathode and developing the high‐performance Mg electrolytes …”

“…The current prevailing view is that such surface film generally blocks the reversible Mg plating/stripping and passivates the Mg anode due to the difficult transport of Mg 2+ in this surface interphase. Hence, many previous investigations on Mg electrolytes mainly focused on synthesizing new Mg salts based on carbanion (such as Grignard reagents) and hydride anions (such as boron‐cluster hydrides) that are stable to Mg metal and soluble in ethereal solvent (the only feasible organic solvents currently inert to Mg metal) 4a,e,h,j,6. Those reported Mg electrolyte components, which are strongly reduction‐resistant but generally vulnerable oxidation or corrosive, intrinsically limit the possibility of a high‐voltage Mg battery operating above 3.0 V .…”

Computational Insights into Mg‐Cl Complex Electrolytes for Rechargeable Magnesium Batteries

“…Simple Mg salts including Mg(TFSI) 2 and Mg (PF 6 ) 2 were confirmed as not working for reversible Mg deposition due to the instability of anions with Mg metal. [46,48] Magnesium carborane, [49][50][51] Magnesium hexafluoroisopropylaluminate, [52] Magnesium hexafluoroisopropylborate, [53][54][55] and Magnesium perfluorinated pinacolatoborate [56] salts were reported as rare examples of Cl-free non-corrosive electrolytes for reversible Mg deposition.…”

Bor in energiebezogenen Prozessen und Anwendungen

“…So sind für Lithiumionenbatterien geeignete Boratanionen nicht notwendigerweise auch für andere Batterieklassen die beste Wahl. Erst kürzlich konnte beispielsweise Mg[B{O 2 C 2 (CF 3 ) 4 } 2 ] 2 als vielversprechendes, chlorfreies Elektrolyt in Magnesiumbatterien ausgemacht werden ( FPB , Abbildung ) …”