Application of a Sulfur Cathode in Nucleophilic Electrolytes for Magnesium/Sulfur Batteries

Abstract

We report the potential feasibility of a high-capacity and low-cost sulfur cathode that is compatible with nucleophilic electrolytes for Mg/S batteries. The electrochemical performance of sulfur in an easily prepared (PhMgCl) 2 -AlCl 3 /THF nucleophilic electrolyte depends on cathode current collectors. A sulfur cathode that uses Cu as a current collector, which is electrochemically stable in the range of operating voltage, exhibits an initial discharge capacity approximately corresponding to 659 mAh g −1 , and maintains a reversible capacity of 113 mAh g −1 after 20 cycles at a current density of 10 mA g −1 . It is different from the sulfur cathode with few capacities that uses stainless-steel as a current collector. Copper sulfides formed when sulfur is coated on a Cu current collector at 50 • C provide a strong chemical interaction between Cu and sulfur, which protects sulfur and increases its compatibility with the electrolyte. A metal-stabilized sulfur cathode provides an effective approach to improve the electrochemical performance of Mg/S batteries in nucleophilic electrolytes. There is a constant increase in the demand for low-cost, highenergy-density rechargeable batteries that utilize environmentally friendly elements for applications, such as market-competitive electric vehicles and large-scale power storage systems due to fossil energy shortage and environmental issues. Following the rapid development of electric vehicles with space available to mount battery packs, it is now necessary for batteries to possess good safety characteristics 1 and high volumetric energy density, which is more important than gravimetric energy density.2 Rechargeable magnesium batteries with magnesium as the anode may correspond to superior candidates compatible with post Li-ion batteries that contain a lithium metal anode, which provides a volumetric capacity (2062 mAh cm −3 ) exceeding that of a current graphite anode (777 mAh cm −3 ), 2 due to a relatively lower price ($2700 and $64800/ton for Mg and Li, respectively), 2,3 a higher theoretical volumetric capacity (3832 mAh cm −3 ), 2 and higher expected safety (the dendritic morphologies for magnesium deposits are lower than that for lithium). 4 Muldoon et al. first suggested an electrophilic sulfur cathode candidate with a high theoretical capacity (1671 mAh g −1 or 3459 mAh cm −3 ) corresponding to a conversion class as opposed to an insertion class. It is chemically incompatible with nucleophilic magnesium organohaloaluminate electrolytes and compatible with a non-nucleophilic electrolyte based on a recrystallized Mg complex [Mg 2 (μ-Cl) 3 (THF) 6 ][HMDSAlCl 3 ] formed from a reaction between hexamethyldisilazide magnesium chloride (HMDSMgCl) and AlCl 3 (3:1 molar ratio) in tetrahydrofuran (THF).2,4 The magnesium/sulfur (Mg/S) batteries yield a theoretical volumetric energy density exceeding 4000 Wh L −1 as compared to 2800 Wh L −1 for lithium/sulfur (Li/S) batteries.5 However, on cycling, Mg/S batteries also suffer from capacity fading, which results from low active...

A Multifunctional Separator Enables Safe and Durable Lithium/Magnesium–Sulfur Batteries under Elevated Temperature

“…[27] Besides, the high temperature performance in this work outperforms most other batteries that utilize delicately designed sulfur-carbon composites, indicating the superiority of the CuNWs-GN/PI/LLZO separator ( Table 1). [37] These promising results indeed prove the critical role of the CuNWs-GN/PI/LLZO separator in improving the efficient sulfur utilization by the in situ chemical/electrochemical reaction between copper and polysulfides. [37][38][39][40] Especially, even at an elevated temperature of 50 °C and high sulfur loading conditions, the as-designed Mg-S cells show almost 7.6-fold capacity increasement compared to that utilizing typical polyolefin separators.…”

“…Promisingly, our as constructed Li-S cell demonstrates several folds improvement in respect of both the cycling stability and the specific capacity (≈3.3 times improvement) at 80 °C, as compared to the similar puresulfur work in literature. [37][38][39][40] Especially, even at an elevated temperature of 50 °C and high sulfur loading conditions, the as-designed Mg-S cells show almost 7.6-fold capacity increasement compared to that utilizing typical polyolefin separators. [7,[26][27][28][29][30] In addition, the as-designed Mg-S cells display dramatically improved capacities and cycling performances.…”

Rechargeable Magnesium–Sulfur Battery Technology: State of the Art and Key Challenges

“…Apart from high conductivity, the major benefit of a Cu current collector is that it allows for the formation of copper sulfides via reaction with the free sulfur that exists outside the carbonaceous matrix during the cathode drying process at 50 °C. The strong interaction between Cu and S protects the sulfur from reacting with the nucleophilic electrolyte: This increases cycle stability and suppresses the dissolution of polysulfides . This novel concept for the stabilization of the cathode material by copper has also been used by Zeng et al In a similar approach, Cui et al filed a patent about the cathode based on sulfur, a metal sulfide and a ternary copper composite.…”

“…The strong interaction between Cu and S protects the sulfur from reacting with the nucleophilic electrolyte: This increases cycle stability and suppresses the dissolution of polysulfides . This novel concept for the stabilization of the cathode material by copper has also been used by Zeng et al In a similar approach, Cui et al filed a patent about the cathode based on sulfur, a metal sulfide and a ternary copper composite. The metal sulfides comprised FeS 2 , SnS 2 , MoS 2 , Co 3 S 4 , and Ni 2 S 3 .…”

“…In Mg–S batteries, the choice of the current collector has also a great impact on the electrochemical behavior particularly in the case of halogen‐containing corrosive electrolytes, the nature of the electroactive cathode materials and the dissolution of polysulfides during cycling . The currently reported commercial metal‐based current collectors include aluminum foil, stainless‐steel (SS) foil, carbon‐coated aluminum foil, copper, and the anticorrosion alloy Inconel 625 . While Cu is generally considered unstable against chloride‐containing electrolytes, Zeng et al recently reported that a sulfur cathode is compatible with the traditional APC electrolyte using copper as current collector below 1.7 V versus Mg/Mg 2+ .…”