Enhancing the Reversibility of Mg/S Battery Chemistry through Li⁺ Mediation

Abstract

Mg metal is a promising anode material for next generation rechargeable battery due to its dendrite-free deposition and high capacity. However, the best cathode for rechargeable Mg battery was based on high molecular weight MgxMo3S4, thus rendering full cell energetically uncompetitive. To increase energy density, high capacity cathode material like sulfur is proposed. However, to date, only limited work has been reported on Mg/S system, all plagued by poor reversibility attributed to the formation of electrochemically inactive MgSx species. Here, we report a new strategy, based on the effect of Li(+) in activating MgSx species, to conjugate a dendrite-free Mg anode with a reversible polysulfide cathode and present a truly reversible Mg/S battery with capacity up to 1000 mAh/gs for more than 30 cycles. Mechanistic insights supported by spectroscopic and microscopic characterization strongly suggest that the reversibility arises from chemical reactivation of MgSx by Li(+).

Magnesium-sulfur battery: its beginning and recent progress

“…10(a)]. Interestingly, the overcharging behavior is much less significant compared with the previous [29,32] 3.9 ∼2 ∼100 Yes 260@20/20 [32] 1000@71/30 [33] 236@20/50 [34] 800@167/20 [ [47,53] 3.1 [47] , 2.5 [53] 2 [47] , 8.5 [53] 99 Yes 70@17/20 [53] Mg(TFSI) 2 Prospective Article reports and an overpotential during charge and discharge was <0.4 V. The Mg-S cells were cycled for 30 times with capacity retention >86% [ Fig. 10(b)].…”

“…This is the obvious reason for the superior electrochemical performance when compared with the electrolyte generated from HMDSMgCl-AlCl 3 containing several anionic species in form HMDS n AlCl 4−n − (n = 1-3). [28] Owing to the favorable electrochemical and chemical properties and its simplicity in preparation, this type of electrolyte has been employed in different Mg battery systems with both intercalation and conversion cathodes, including Mo 6 S 8 , [29] vanadium oxychloride (VOCl), [31] S, [32][33][34][35] Se, [36] and iodine. [37] Fluorinated alkoxide-based electrolytes…”

“…[33] The authors assumed that Li + either undergoes an ion exchange reaction with MgS and MgS 2 , transforming them to rechargeable Li 2 S and Li 2 S 2 , or reacts with MgS and MgS 2 to form the long-chain polysulfide MgLi-PS, thereby decreasing the kinetic barrier for re-oxidation of MgS and MgS 2 (Fig. 8).…”

Self‐Established Rapid Magnesiation/De‐Magnesiation Pathways in Binary Selenium–Copper Mixtures with Significantly Enhanced Mg‐Ion Storage Reversibility

“…[4] It delivers a limited specific capacity ≈100 mAh g −1 and a relatively low operation voltage of ≈1.1 V versus Mg, making this Mg battery system energetically uncompetitive. [2,5] The conversion-type sulfur (S) and selenium (Se) cathodes, with theoretical volumetric capacity of 3467 mAh cm −3 for S and 3268 mAh cm −3 for Se, fulfill the criteria of high energy density, high safety, materials sustainability, and cost-effective features. [6][7][8] Nevertheless, researches on rechargeable Mg/S and Mg/Se battery systems are still in the nascent stage.…”

“…[5,9,10] These two aspects result in the overcharge behavior and low electrode utility, respectively. The large kinetic barriers during the recharge process of MgS also cause irreversibility and low Coulombic efficiency in all Mg/S cells, which is believed to be the major culprit for fast capacity fade.…”