Toward Highly Reversible Magnesium–Sulfur Batteries with Efficient and Practical Mg[B(hfip)₄]₂ Electrolyte

Abstract

The rechargeable magnesium (Mg) battery has been considered a promising candidate for future battery generations due to unique advantages of the Mg metal anode. The combination of Mg with a sulfur cathode is one of the attractive electrochemical energy storage systems that use safe, low-cost, and sustainable materials and could potentially provide a high energy density. To develop a suitable electrolyte remains the key challenge for realization of a magnesium sulfur (Mg–S) battery. Herein, we demonstrate that magnesium tetrakis­(hexafluoroisopropyloxy) borate Mg­[B­(hfip)4]2 (hfip = OC­(H)­(CF3)2) satisfies a multitude of requirements for an efficient and practical electrolyte, including high anodic stability (>4.5 V), high ionic conductivity (∼11 mS cm–1), and excellent long-term Mg cycling stability with a low polarization. Insightful mechanistic studies verify the reversible redox processes of Mg–S chemistry by utilizing Mg­[B­(hfip)4]2 electroylte and also unveil the origin of the voltage hysteresis in Mg–S batteries.

Halide‐Based Materials and Chemistry for Rechargeable Batteries

“…The as‐prepared Mg[B(hfip) 4 ] 2 /DME electrolyte delivers high anodic stability (>4.5 V, Figure b,c), high ionic conductivity (ca. 11 mS cm −1 ), and excellent long‐term Mg cycling stability with low polarization . It is impressive that the as‐prepared Mg[B(hfip) 4 ] 2 ⋅DME salt is air‐ and water‐insensitive.…”

“…Recently, chlorine‐free and noncorrosive electrolytes based on Mg salts such as Mg(BH 4 ) 2 , Mg(CB 11 H 12 ) 2 (MMC), Mg[Al(hfip) 4 ] 2 , and borate‐based Mg salts for RMBs have also been developed . Inspired by the lithium electrolyte of LiAl(hfip) 4 with its high conductivity and electrochemical stability, Herb et al.…”

Mg Cathode Materials and Electrolytes for Rechargeable Mg Batteries: A Review

“…In comparison to pure DME, the formation of such solvates (i. e., [Mg(DME) n ][B(Hfip) 4 ]) additionally increase their thermal stability. Recently the same group thoroughly investigated the use of borate salt Mg[B(HFIP) 4 ] 2 in a full Mg/S cell (See Table ).…”

Halogenid‐basierte Materialien und Chemie für wiederaufladbare Batterien

“…Kürzlich wurden auch chlorfreie und nichtkorrosive Elektrolyte auf Basis von Mg‐basierten Salzen wie Mg(BH 4 ) 2 , Mg(CB 11 H 12 ) 2 (MMC), Mg[Al(hfip) 4 ] 2 und Borat‐basierten Mg‐Salzen für RMBs entwickelt . Inspiriert vom Lithium‐Elektrolyten von LiAl(hfip) 4 mit hoher Leitfähigkeit und elektrochemischer Stabilität, entwickelten Herb et al.…”

“…Sie präsentierten im Weiteren eine Reihe fluorierter Borat‐basierter Mg‐Salze wie Mg[B(hfip) 4 ] 2 (Abbildung a) und Mg[B(pfpina) 2 ] 2 (pfpina=OC(CF 3 ) 2 C(CF 3 ) 2 O)). Der präparierte Mg[B(hfip) 4 ] 2 /DME‐Elektrolyt liefert eine hohe anodische Stabilität (>4.5 V, Abbildung b,c), hohe Ionenleitfähigkeit (≈11 mS cm −1 ) und hervorragende langfristige Mg‐Zyklenstabilität mit niedriger Polarisation . Es ist beeindruckend, dass das präparierte Mg[B(hfip) 4 ] 2 ⋅DME luft‐ und wasserunempfindlich ist.…”