Low cost and safety qualify magnesium (Mg) metal batteries as one of the utmost post-lithium batteries. Nonetheless, most Mg electrolytes suffer from conditionality and incompatibility with most ...useable cathodes, hindering realising applicable Mg batteries. Herein, we study the effect of the stoichiometric ratio of Mg(CF
3
SO
3
)
2
/AlCl
3
on the physical, electrical and electrochemical performance of an electrolyte system based on Mg(CF
3
SO
3
)
2
in acetonitrile (ACN) and tetraethylene glycol dimethyl ether (G4). The physicochemical analyses include Fourier-transform infrared spectroscopy (FTIR), UV-Vis irradiation, electrochemical impedance spectroscopy (EIS) and Mg plating/stripping of electrolytes exhibit the optimum stoichiometric ratio is
0.28M
AlCl
3
/
0.17M
Mg(CF
3
SO
3
)
2
. The present study offers new approaches for designing promising efficient electrolytes for Mg batteries. The work extends to using an unconventional electrode based on sulphur, silicon carbide, and barium titanate to demonstrate the performance of the full cell. This optimised electrolyte coupled with the unconventional cathode allows a high initial specific discharge capacity, ~ 241 mAhg
−1
. However, the dissolution of polysulphides issue still exists and leads to irreversible cycling.
•An artificial interphase composed of Zn/MgZn2/MgCl2 was pre-constructed by replacement reaction of ZnCl2 and Mg.•The Mg plating/stripping overpotential of the modified Mg electrode can be reduced ...0.2 V at 0.1 mA/cm2.•The reversibility of cathode can be improved by serving Cu powders as additive in cathode.•The change of redox couple from S/S2− to Cu2S/Cu0 is completed during the cycle.
The Mg-S battery has great development potential benefiting from its high volume energy density and high-safety. However, it also confronts with two key issues especially when using the Mg(TFSI)2-based electrolyte. One is the poor compatibility between electrolyte and Mg anode, and the other is the poor reversibility of cathode. In this work, an artificial interphase including Zn/ZnCl2/MgZn2/MgCl2 was firstly pre-constructed by replacement reaction of ZnCl2 and Mg, which can reduce Mg plating/stripping overpotential to 0.2 V at 0.1 mA/cm2. Meanwhile, the reversibility of cathode can be improved by using copper powders as additive in sulfur/carbon composite cathode, and the improvement effect is directly related to the addition amount and particle size of copper powders. In addition, it is also revealed that the chemical reaction can occur between copper and intermediates MgS8 at the initial stage of discharge process. The reaction product of Cu2S continues to participate in the electrochemical reduction reaction to regenerate copper, which can be reoxidized to Cu2S during the charging process. The conversion of redox couple from S/S2− to Cu2S/Cu0 in cathode improves the cycling stability of the battery in comparison with the conversional Mg-S battery.
The Mg/S battery is attractive because of its high theoretical energy density and the abundance of Mg and S on the earth. However, its development is hindered by the lack of understanding to the ...underlying electrochemical reaction mechanism of its charge–discharge processes. Here, using a unique in situ X-ray absorption spectroscopic tool, we systematically study the reaction pathways of the Mg/S cells in Mg(HMDS)2–AlCl3 electrolyte. We find that the capacity degradation is mainly due to the formation of irreversible discharge products, such as MgS and Mg3S8, through a direct electrochemical deposition or a chemical disproportionation of intermediate polysulfide. In light of the fundamental understanding, we propose to use TiS2 as a catalyst to activate the irreversible reaction of low-order MgS x and MgS, which results in an increased discharging capacity up to 900 mAh·g–1 and a longer cycling life.
Mg–S batteries are a promising next-generation system for beyond conventional Li-ion chemistry. The Mg–S architecture pairs a Mg metal anode with an inexpensive, high-capacity S8 cathode. However, ...S8-based cathodes exhibit the “polysulfide shuttle” effect, wherein soluble partially reduced S x 2– species generated at the cathode diffuse to and react with the anode. While dissolved polysulfides may undergo reactions to form Li+-permeable layers in Li–S systems, the interfaces on Mg anodes are passivating. In this work, we probe the reactivity of various Mg polysulfide solutions at the Mg anode interface. Mg polysulfide solutions are prepared without any chelating agents to closely mimic conditions in a Mg–S cell. The polysulfides are synthesized by reacting Mg metal and S8 in electrolyte, and the speciation is controlled by varying the Mg:S precursor ratio. S-poor precursor ratios produce magnesium polysulfide solutions with a higher proportion of short-chain polysulfides that react at the Mg anode faster than the longer-chain analogues. Anode passivation can be slowed by shifting the polysulfide equilibria toward longer-chain polysulfides through addition of S8.
As Li-ion battery optimization approaches theoretical limits, interest has grown in designing next-generation batteries from low-cost earth-abundant materials. Mg–S batteries are promising ...candidates, exhibiting widespread abundance of elemental precursors and a relatively large theoretical energy density albeit at lower cell voltage. However, Mg–S batteries exhibit poor reversibility, in part due to interactions between dissolved polysulfides and the Mg anode. Herein, we employ electrochemical experiments using Ag2S quasi-reference electrodes to probe the interactions between Mg anodes and dissolved polysulfides. We show that Mg2+ reduction (charging) is impeded in the presence of polysulfides, while Mg metal oxidation (discharging) remains facile. Large reduction overpotentials arise due to the formation of a passivation layer on the anode surface, likely composed primarily of MgS. The passivation layer is removed under oxidative conditions but quickly reforms during reduction. We discover that dissolved S8 influences the rate of MgS formation by shifting the polysulfide disproportionation equilibria. Shorter-chain polysulfides react more readily than longer-chain polysulfides at the Mg electrode, and thus, film formation is mediated by the electrochemical generation of shorter-chain polysulfide species.
Magnesium sulfur (MgS) batteries are considered one of the most promising next-generation technologies for energy storage, expecting high energy density and low cost. The challenges of practical ...applications of reliable MgS batteries are finding non-nuclefilic electrolytes compatible with the electrophilic nature of sulfur cathodes and magnesium anodes, tailoring the interface and microstructure in the sulfur scaffold to effectively mitigate the soluble magnesium polysulfide shuttle and enhance the reaction kinetics. We add succinonitrile (SN) as a functional additive to halogen free electrolyte (HFE) in concentration range (0–4 wt%). The optimum ratio 2 wt% of SN improves the Mg stripping/plating stability, enhances the diffusion coefficient DMg2+ from 1.19 × 10−16 cm2s−1 to 4.06 × 10−14 cm2s−1 and increases the ionic conductivity with a transference number of 0.81. Herein, we synthesize the nano cathode material using low cost and superfast microwave-assisted methods, then assemble full cell by using a polymer interface, HFE electrolyte, and coated fiber separator by carbonized barium titanate as a promising technique raising battery cycling life and the capacity value up to ≈ 200 mAhg−1 after the twenty-second cycle, comparing with pristine HFE electrolyte of capacity value of ≈ 110 mAhg−1 after the fifth cycle. The Fourier transform infrared (FTIR) and UV–Vis spectroscopy supported the HFE_SN electrochemical performance. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM) and energy dispersive X-ray (EDS) confirmed Mg insertion within the S cathode throughout the conversion reaction.
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•Establishing magnesium‑sulfur ion battery with a cathode of sulfur, barium titanate and carbon with specific proportions•Microwave-assisted superfast preparation method verifying good results of mixed cathode components•Succinonitrile (SN) with specific ratio within halogen free electrolyte was satisfying for low potential barrier.•Barium titanate coating separator improved the cycling of the battery remarkably.
Nowadays, rechargeable batteries utilizing an S cathode together with an Mg anode are under substantial interest and development. The review is made from the point of view of materials engaged during ...the development of the Mg–S batteries, their sulfur cathodes, magnesium anodes, electrolyte systems, current collectors, and separators. Simultaneously, various hazards related to the use of such materials are discussed. It was found that the most numerous groups of hazards are posed by the material groups of cathodes and electrolytes. Such hazards vary widely in type and degree of danger and are related to human bodies, aquatic life, flammability of materials, or the release of flammable or toxic gases by the latter.
We discuss here various combinations of magnesium bis (hexamethyldisilazide) (Mg(HMDS)2) with aluminum chloride (AlCl3) or magnesium chloride (MgCl2) in a solvent mixture of 1,3-dioxalane (DOL) and ...1,2-dimethoxyethane (DME) (DOL/DME) as alternative electrolytes for practical rechargeable Mg–sulfur batteries. This design strategy is contrary to the usage of the solvents tetraglyme and tetrahydrofuran (THF) commonly used with Mg(HMDS)2 to generate electrolyte formulations for Mg/S batteries. Cyclic voltammetry measurements reveal a higher current response for DOL/DME compared to tetraglyme and THF solvent-based electrolytes. Exemplary plating/stripping efficiency is obtained at room temperature and is observed to be strongly dependent on the salt concentrations. The remarkable stripping/plating reversibility (at a current density of 0.1 mA cm–2) in a Mg||Mg symmetric cell indicates the extraordinary compatibility of the electrolyte with the Mg anode. The plating of Mg on the gold working electrode is ascertained using X-ray diffraction and scanning electron microscopy. The versatility of the Mg(HMDS)2-based electrolyte in the DOL/DME solvent is further utilized in a Mg/S cell with a simple carbon nanotube–sulfur composite as the cathode and Mg-metal as the anode. The DOL/DME-Mg(HMDS)2 electrolyte-based Mg/S cell exhibited stable electrochemical performance over widely varying current densities ranging from 0.05 to 0.5 C.
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