Structure of Magnesium Chloride Complexes in Ethereal Systems: Computational Comparison of THF and Glymes as Solvents for Magnesium Battery Electrolytes

Jankowski, Piotr; Lastra, Juan Maria García; Vegge, Tejs

doi:10.1002/batt.202000168

Cited by 18 publications

(18 citation statements)

References 68 publications

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“…, with coordination numbers of six, as found before to be the most stable, [20] and then the number of oxygen atoms in the first coordination shell was gradually decreased by one each time. At least four different starting geometries were created at each of the steps, and re-optimized.…”

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confidence: 60%

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Modeling of Electron‐Transfer Kinetics in Magnesium Electrolytes: Influence of the Solvent on the Battery Performance

et al. 2021

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The performance of rechargeable magnesium batteries is strongly dependent on the choice of electrolyte. The desolvation of multivalent cations usually goes along with high energy barriers, which can have a crucial impact on the plating reaction. This can lead to significantly higher overpotentials for magnesium deposition compared to magnesium dissolution. In this work we combine experimental measurements with DFT calculations and continuum modelling to analyze Mg deposition in various solvents. Jointly, these methods provide a better understanding of the electrode reactions and especially the magnesium deposition mechanism. Thereby, a kinetic model for electrochemical reactions at metal electrodes is developed, which explicitly couples desolvation to electron transfer and, furthermore, qualitatively takes into account effects of the electrochemical double layer. The influence of different solvents on the battery performance is studied for the state-of-the-art magnesium tetrakis(hexafluoroisopropyloxy)borate electrolyte salt. It becomes apparent that not necessarily a whole solvent molecule must be stripped from the solvated magnesium cation before the first reduction step can take place. For Mg reduction it seems to be sufficient to have one coordination site available, so that the magnesium cation is able to get closer to the electrode surface. Thereby, the initial desolvation of the magnesium cation determines the deposition reaction for mono-, tri-and tetraglyme, whereas the influence of the desolvation on the plating reaction is minor for diglyme and tetrahydrofuran. Overall, we can give a clear recommendation for diglyme to be applied as solvent in magnesium electrolytes.

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confidence: 60%

“…The determined rate constant for the oxidation reaction can be applied for all solvents, whereas the corresponding desolvation rate constant has to be adjusted for the different solvents following Eq. ( 17) and (20). The final set of parameters is listed in Table 2.…”

Section: Rate Constants Of the Desolvation And Oxidation Reactionsmentioning

confidence: 99%

Modeling of Electron‐Transfer Kinetics in Magnesium Electrolytes: Influence of the Solvent on the Battery Performance

et al. 2021

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“…Finally, DFT calculations comparing the different abilities to coordinate cations in chloride‐containing Mg complexes in monoglyme‐, diglyme‐, triglyme‐ and tetraglyme‐based electrolytes indicated that the longer and more flexible glymes were increasingly able to adjust their conformation and thus enhance the interaction between Mg and solvent. This was proposed to allow for the formation of larger Mg 2+ ‐, Cl − ‐ and solvent‐containing aggregates, which, in turn, improves the reversibility of Mg deposition/dissolution, though at higher overpotentials [60] …”

Section: Resultsmentioning

confidence: 99%

“…This was proposed to allow for the formation of larger Mg 2 + -, Cl À -and solvent-containing aggregates, which, in turn, improves the reversibility of Mg deposition/dissolution, though at higher overpotentials. [60] Focusing on BH 4…”

Section: Electrochemical Characterizationmentioning

confidence: 99%

Influence of Complexing Additives on the Reversible Deposition/Dissolution of Magnesium in an Ionic Liquid

et al. 2021

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Aiming at a fundamental understanding of the synergistic effects of different additives on the electrochemical Mg deposition/dissolution in an ionic liquid, we have systematically investigated these processes in a combined electrochemical and theoretical study, using 1-butyl-1-methylpyrrolidinium bis (trifluoromethylsulfonyl) imide (BMP-TFSI) as the solvent and a cyclic ether (18-crown-6) and magnesium borohydride as additives. Both crown ether and BH 4 À improve Mg deposition, its reversibility, and cycling stability. The combined presence of both additives and their concentration relative to that of Mg 2 + are decisive for more facile and reversible Mg deposition/ dissolution. These results and those of quantum chemical calculations indicate that 18-crown-6 can partly displace TFSI À from its direct coordination to Mg 2 +. Furthermore, the interaction between Mg 2 + and directly coordinated TFSI À is weakened by coordination with 18-crown-6, preventing its Mg +-induced decomposition. Finally, Mg deposition is improved by the weaker overall coordination upon Mg 2 + reduction to Mg + .

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“…All these structures are in agreement with previous calculations and experimental structures. 14,16,39,[47][48][49]…”

Section: Theoretical Approachmentioning

confidence: 99%

Building Ab Initio Interface Pourbaix diagrams to Investigate Electrolyte Stability in the Electrochemical Double Layer: Application to Magnesium Batteries

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Bitenc

Dominko

et al. 2021

ACS Appl. Mater. Interfaces

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Insights into the electrochemical processes occurring at the electrode-electrolyte interface are a crucial step in most electrochemistry domains and in particular in the optimization of the battery technology.However, studying potential dependent processes at the interface is one of the biggest challenges, both for theoreticians and experimentalists. The challenge is pushed further when stable species also depend on the concentration of specific ligands in the electrolyte, such as chlorides. Herein we present a general theoretical ab initio methodology to compute Pourbaix-like diagram of complex electrolytes as a function of electrode potential and anion's chemical potential, i.e. concentration. This approach is not only developed for the bulk properties of the electrolytes, but also for electrode-electrolyte interfaces.In the case of chlorinated magnesium complexes in dimethyl ether, we show that the stability domains of the different species are strongly shifted at the interface compared to the bulk of the electrolyte due to the strong local electric fields and charges occurring in the double layer. Thus, as the interfacial stability domains are strongly modified, this approach is necessary to investigate all interface properties that often govern reaction's kinetics, such as solvent degradation at the electrode. Interface Pourbaix diagram is used to give some insight into the improved stability at the Mg anode induced by the addition of chloride. Due to its far-reaching insights, transferability and wide applicability, the methodology presented herein should serve as a valuable tool not only for the battery community but also for the wider electrochemical one.

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Structure of Magnesium Chloride Complexes in Ethereal Systems: Computational Comparison of THF and Glymes as Solvents for Magnesium Battery Electrolytes

Cited by 18 publications

References 68 publications

Modeling of Electron‐Transfer Kinetics in Magnesium Electrolytes: Influence of the Solvent on the Battery Performance

Modeling of Electron‐Transfer Kinetics in Magnesium Electrolytes: Influence of the Solvent on the Battery Performance

Influence of Complexing Additives on the Reversible Deposition/Dissolution of Magnesium in an Ionic Liquid

Building Ab Initio Interface Pourbaix diagrams to Investigate Electrolyte Stability in the Electrochemical Double Layer: Application to Magnesium Batteries

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