Effect of Interaction among Magnesium Ions, Anion, and Solvent on Kinetics of the Magnesium Deposition Process

Tuerxun, Feilure; Yamamoto, Kentaro; Mandai, Toshihiko; Tateyama, Yoshitaka; Nakanishi, Koji; Uchiyama, Tomoki; Watanabe, Toshiki; Tamenori, Y.; Kanamura, Kiyoshi; Uchimoto, Yoshiharu

doi:10.1021/acs.jpcc.0c08268

Cited by 23 publications

(38 citation statements)

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“…Also the formation of bigger clusters due to entropic effects, which can happen at high concentrations close to the solubility limit, is neglectable for electrolyte concentrations smaller than 0.35 M. [48] The simulations will focus on 0.2 M electrolytes, in which the Mg[B(hfip) 4 ] 2 salt is highly dissociated and the fully solvated magnesium cations are the main electrochemically active specie. [ 18 , 26 , 49 , 50 ] Consequently, only one specie has to be considered in the kinetic model ( j =1) and Equation (1) simplifies to Equation 2 :

…”

Section: Methodsmentioning

confidence: 99%

“…[ 2 , 10 , 11 , 12 , 13 , 14 ] At the same time the desolvation of magnesium ions close to the electrode surface plays an important role during the deposition or intercalation process. [ 1 , 9 , 15 , 16 , 17 , 18 ] Since a sluggish desolvation can kinetically hinder the charge transfer reaction, the solvation of the magnesium cation should only be as good as necessary. Consequently, the choice of both – solvent and anion – is crucial for the performance of magnesium batteries.…”

Section: Introductionmentioning

confidence: 99%

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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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…”

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

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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“…Experimental evidence for the influence of ion-pair formation on TFSI stability has only been reported rather recently, [94,95] accomplished by combining XPS and operando soft X-ray absorption spectroscopy (SXAS) measurements on Mg(TFSI) 2 in different solvents, effectively tailoring the speciation of Mg-TFSI complexes. Decomposition of TFSI was observed when a high proportion of CIPs is present, changing the solvent from 2-MeTHF to a more effective G4 decreased the CIP population and led to less pronounced anion decomposition.…”

Section: Formulations Containing Tfsimentioning

confidence: 99%

Interfaces and Interphases in Ca and Mg Batteries

Forero-Saboya

Tchitchekova

Johansson

et al. 2021

Adv Materials Inter

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The development of high energy density battery technologies based on divalent metals as the negative electrode is very appealing. Ca and Mg are especially interesting choices due to their combination of low standard reduction potential and natural abundance. One particular problem stalling the technological development of these batteries is the low efficiency of plating/stripping at the negative electrode, which relates to several factors that have not yet been looked at systematically; the nature/concentration of the electrolyte, which determines the mass transport of electro‐active species (cation complexes) toward the electrode; the possible presence of passivation layers, which may hinder ionic transport and hence limit electrodeposition; and the mechanisms behind the charge transfer leading to nucleation/growth of the metal. Different electrolytes are investigated for Mg and Ca, with the presence/absence of chlorides in the formulation playing a crucial role in the cation desolvation. From a R&D point‐of‐view, proper characterization alongside modeling is crucial to understand the phenomena determining the mechanisms of the plating/stripping processes. The state‐of‐the‐art is here presented together with a short perspective on the influence of the cation solvation also on the positive electrode and finally an attempt to define guidelines for future research in the field.

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“…Also the formation of bigger clusters due to entropic effects, which can happen at high concentrations close to the solubility limit, is neglectable for electrolyte concentrations smaller than 0.35 M. [48] The simulations will focus on 0.2 M electrolytes, in which the Mg[B(hfip) 4 ] 2 salt is highly dissociated and the fully solvated magnesium cations are the main electrochemically active specie. [18,26,49,50] Consequently, only one specie has to be considered in the kinetic model (j = 1) and Equation (1) simplifies to Equation (2):…”

Section: Kinetic Modelmentioning

confidence: 99%

“…[2,[10][11][12][13][14] At the same time the desolvation of magnesium ions close to the electrode surface plays an important role during the deposition or intercalation process. [1,9,[15][16][17][18] Since a sluggish desolvation can kinetically hinder the charge transfer reaction, the solvation of the magnesium cation should only be as good as necessary. Consequently, the choice of both -solvent and anion -is crucial for the performance of magnesium batteries.…”

Section: Introductionmentioning

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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The possibility to store electricity from renewable sources is a key component of a sustainable energy supply system. Thereby, batteries based on metal anodes possess a considerably higher theoretical energy density than state-of-the-art Li-ion-technology. Taking into account additional requirements for economic, sustainable and safe applications, it becomes apparent, that magnesium-metal based next-generation batteries are of great interest.However, the processes in the electrolyte and at the magnesium metal surface are not yet properly understood. The bivalency of the magnesium cations leads to strong coulomb interactions with the anion as well as with the solvent. It was found that magnesium salts are prone to form ion pairs and bigger clusters – especially at high concentrations, which may adversely affect the transport in the electrolyte and the plating behaviour at the electrode.[1] Consequently, a good solvation is important for the dissociation of the magnesium salts, which is in turn crucial for a high ionic conductivity of the electrolyte. At the same time, the desolvation of double charged magnesium cations usually goes along with high energetic barriers, which can have a crucial impact on the deposition process. This can lead to significantly higher overpotentials for magnesium deposition compared to magnesium dissolution.In our contribution we will present a newly developed kinetic model for electrochemical reactions at metal electrodes, which explicitly couples desolvation to electron transfer and, furthermore, qualitatively considers effects of the electrochemical double layer. By including this kinetics into our general transport model [2] the impact of five different solvents on the battery performance is studied for the state-of-the-art, chloride-free Mg[B(hfip)4]2 electrolyte salt [3]. The parametrization of the model is mainly based on DFT calculations [4] and the simulation results are validated and supported by experimental data. It becomes apparent that the desolvation of one coordination site of the solvated cation is limiting the overall magnesium deposition. Consequently, the thermodynamics of this initial desolvation, which are determined by the solvent, play a crucial role for the battery performance. However, the impact of the electrochemical double layer is equally important to reproduce the non-intuitive qualitative trends observed in the experiments with different solvents.All in all, the combination of different modelling techniques with experimental measurements provides extensive insights into the deposition mechanism of magnesium and enables to identify the general properties, which are relevant for fast kinetics and consequently small overpotentials. These fundamental insights on the operation of magnesium batteries are key to further optimize their performance. Acknowledgements This project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 824066 (E-MAGIC). Furthermore, this work contributes to the researc...

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Effect of Interaction among Magnesium Ions, Anion, and Solvent on Kinetics of the Magnesium Deposition Process

Cited by 23 publications

References 50 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

Interfaces and Interphases in Ca and Mg Batteries

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

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