Elsevier

Journal of Power Sources

Volume 195, Issue 7, 2 April 2010, Pages 2096-2098
Journal of Power Sources

Short communication
Mixed electrolyte consisting of ethylmagnesiumbromide with ionic liquid for rechargeable magnesium electrode

https://doi.org/10.1016/j.jpowsour.2009.10.073Get rights and content

Abstract

A novel electrolyte system for a rechargeable magnesium battery has been developed. The electrolyte consists of ethylmagnesiumbromide in tetrahydrofuran (EtMgBr/THF) with an ionic liquid (IL) of quaternary ammonium salt. The ionic conductivity of the electrolyte with the composition of EtMgBr/THF:IL being 3:1 in volume was 7.44 mS cm−1 at 25 °C. A reversible processes of cathodic deposition and anodic dissolution of magnesium has been successfully achieved in the mixed electrolyte system of EtMgBr/THF + IL at room temperature.

Introduction

Magnesium (Mg) is an attractive candidate for the anode (negative electrode) material of high energy density batteries. However, it is generally difficult to establish a reversible process of electrochemical reduction and oxidation for Mg, not only in aqueous but also in organic electrolyte solutions, because Mg is easily oxidized by water and other protic solvents to form passivation films [1], [2], [3]. As to the possibility of Mg anode for rechargeable Mg batteries, Conner et al. [4] reported the cathodic deposition of Mg in ethereal solutions dissolving MgBr2. Liebenow [5] demonstrated the possibility of reversible deposition and dissolution of Mg in ethereal solutions of Grignard reagents (RMgX, where R = alkyl, aryl groups; X = Cl, Br). Aurbach et al. [6], [7], [8], [9] also reported the reversible process of Mg in electrolyte solutions based on organo-haloaluminate salts: Mg(AlCl3R)2 or Mg(AlCl2RR′)2, where R and R′ are alkyl groups, in THF or polyethers of glyme family. It is considered that, in these solutions, no compact passivating film covers the surface of Mg, for which reversible deposition/dissolution of Mg can occur with low overvoltage. Thus, Gregory et al. [3] and Aurbach's group [8] have separately presented rechargeable Mg battery systems using intercalation compound cathodes (positive electrode) with nonaqueous ether-based electrolytes. In general, however, as ether solvents have high vapor pressure and strong flammability, the proposed battery systems still have practical problems of safety and reliability.

Ionic liquids (ILs), also known as room temperature molten salts, possess many advantages such as high ionic conductivity, wide electrochemical window, good thermal and chemical stability, non-flammability, and non-volatility. Therefore, ILs are expected as the promising components of novel electrolyte systems for rechargeable batteries, especially for lithium-ion batteries. The present authors previously reported that Mg can be co-deposited with Li in quaternary ammonium salt based ionic liquid, N,N-diethyl-N-methyl-N-(2-methoxyethyl) ammonium-bis(trifluoromethanesulfonyl)imide (DEMETFSI) dissolving LiTFSI and Mg(TFSI)2 [10]. The salts of DEME+ cation have wide electrochemical window (ca. 6.0 V) and good stability for cathodic reduction [11]. Cheek et al. [12] have investigated the electrodeposition of Mg in imidazolium-based ionic liquids containing a Grignard reagent, and reported reversible deposition and dissolution of Mg in the system consisting of 1:2 mixture of the Grignard reagent and the ionic liquids at 150 °C.

In the present work, we have developed a novel electrolyte system consisting of Grignard reagent (ethylmagnesiumbromide in THF, EtMgBr/THF) and an IL of quaternary ammonium salt (DEMETFSI) for rechargeable magnesium batteries working at ambient temperature. Reversibility of Mg deposition and dissolution has been investigated in such a mixed electrolyte system. Then, the applicability of the present electrolyte system to rechargeable Mg batteries is briefly demonstrated.

Section snippets

Experimental

The ionic liquid used in this work was DEMETFSI (purchased from Kanto Chemical). A Grignard reagent, 1.0 mol dm−3 (M) EtMgBr/THF (purchased from Kanto Chemical) was used as an Mg source. These reagents were used as received, but stored in a grove box filled with dry Ar before use. Proper volume ratios of DEMETFSI and EtMgBr/THF were mixed to obtain the electrolyte solution.

The ionic conductivity of the electrolytes was measured by an ac impedance technique (Solartron 1260 coupled with

Results and discussion

The ionic conductivity of the mixed electrolyte consisting of 3:1 (by volume) mixture of Grignard reagent (EtMgBr/THF) and DEMETFSI was measured at 25 °C. The result is shown in Table 1, compared with those of EtMgBr/THF and neat DEMETFSI. The mixed electrolyte containing EtMgBr/THF and DEMETFSI showed higher ionic conductivity, 7.44 mS cm−1 at 25 °C, than that of neat EtMgBr/THF or DEMETFSI. The viscosity of the mixed electrolyte consisting of EtMgBr/THF with DEMETFSI is higher than that of the

Conclusions

Rechargeability of metal Mg electrode was investigated in a novel electrolyte system of Grignard reagent (EtMgBr/THF) mixed with ionic liquid (DEMETFSI). High ionic conductivity of 7.44 mS cm−1 (at 25 °C) was obtained in the 3:1 mixture (by volume) of EtMgBr/THF and DEMETFSI. The ionic liquid DEMETFSI works as not only the solvent but also the supporting electrolyte in the present electrolyte system. A reversible process of cathodic deposition and anodic dissolution of Mg has been successfully

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Cited by (62)

  • Progress in development of electrolytes for magnesium batteries

    2019, Energy Storage Materials
    Citation Excerpt :

    Following this report, Morita et al. published a series of articles on using Grignard reagents as the Mg source [62–64]. In their first report, the authors developed an electrolyte mixture with ethylmagnesiumbromide in THF (EtMgBr/THF) and an IL of quaternary ammonium salt, N,N-diethyl-N-methyl-N-(2-methoxyethyl) ammonium-bis(trifluoromethanesulfonyl)imide (DEMETFSI) [62]. Herein, the authors evaluated the conductivity of this mixture to be 7.4 mS cm−1 at room temperature, and noted that the solution was capable of Mg deposition/dissolution on a silver substrate.

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