JP2018073615A - Electrolyte solution and magnesium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrolyte solution which is superior in heat resistance and in which magnesium metal can be electrochemically precipitated and dissolved.SOLUTION: An electrolyte solution comprises magnesium cations, a compound represented by the formula 1, and an ionic liquid. In the electrolyte solution, a mole concentration Amol/L of the magnesium cations to a total quantity of the electrolyte solution, and a mole concentration Bmol/L of the compound represented by the formula 1 to the total quantity of the electrolyte solution satisfy a relation given by 0.1≤B/A≤1. A magnesium secondary battery comprises the electrolyte solution.SELECTED DRAWING: None

Description

  The present disclosure relates to an electrolytic solution and a magnesium secondary battery.

Lithium-ion rechargeable batteries occupy a major position as a power source for small devices such as mobile phones and smartphones to large devices such as hybrid vehicles and electric vehicles because of their high energy density (product of operating voltage and storage capacity) ing.
On the other hand, however, the lithium ion battery has many problems such as heat generation and ignition risk depending on use conditions, energy density approaching the theoretical value, and the cost of the transition metal used for the lithium source and electrode is high.
Therefore, a magnesium secondary battery using magnesium instead of lithium has been proposed.
Magnesium metal is an electrode material having a low standard electrode potential, a divalent ion, a large capacity, and a high energy density. Further, since magnesium resources are abundant near the surface of the earth, secondary batteries using magnesium metal are expected to have a higher energy density than lithium ion secondary batteries and become inexpensive secondary batteries.
As an electrolytic solution used for a secondary battery using a conventional magnesium metal, for example, Patent Document 1 discloses a solution containing a magnesium cation, a monovalent anion, and a polyether compound represented by the formula (I). An electrolyte solution is described.
^{_{R 1 -O (CH 2 CH 2}} O) n-R 2 (I)
(In the formula, R ¹ and R ² are each independently a hydrocarbon group having 1 to 12 carbon atoms which may have a substituent, and n represents an integer of 1 to 8)
Non-Patent Document 1 describes an electrolytic solution containing a glyme compound (a symmetric glycol diether compound), an ionic liquid, and a magnesium cation.

JP 2014-186940 A

Kitada, et.al. “Room Temperature Magnesium Electrodeposition from Glyme-Coordinated Ammonium Amide Electrolytes” Journal of The Electrochemical Society 162 (8) D389-D396 (2015)

As a result of intensive studies, the present inventors have found that the reaction of the magnesium secondary battery, that is, the dissolution and precipitation of magnesium metal in the negative electrode, and the retention and release of magnesium ions in the positive electrode are two-electron reactions. We thought it was essentially slower than the reaction of some lithium ion batteries.
Therefore, the present inventors examined increasing the use temperature in order to rapidly advance the charge / discharge reaction. That is, it was considered that the magnesium secondary battery is preferably operable not only at room temperature but also in a high temperature environment of 100 ° C. to 300 ° C.
In addition, the present inventors have made it difficult to cause expansion and rupture of the battery case even in a high temperature environment of 100 ° C. to 300 ° C. due to diversification of battery use environments and applications. I thought it was important to use
Conventionally, it has been proposed to use an ether solvent such as tetrahydrofuran (THF) or a glyme compound as an electrolyte for a magnesium secondary battery (for example, Patent Document 1 and Non-Patent Document 1). It has also been found that a glyme compound having a short chain length has a boiling point of 100 ° C. or lower and is not suitable for high temperature operation.
Further, the present inventors have disclosed that triglyme (bp: 216 ° C.) and tetraglyme (bp: 276 ° C.), which are glyme compounds having a long chain length, disclosed in Patent Literature 1 and Non-Patent Literature 1 are relatively high. Although it has a boiling point, it has been found that there is a possibility of heat generation and ignition of the battery because it is flammable.
Furthermore, the present inventors have examined the use as a solvent of an ionic liquid electrolytic solution that is known to have high heat resistance. In an electrolytic solution in which a magnesium salt is dissolved in an ionic liquid, It was found that precipitation was difficult.

  Therefore, the present inventors include a magnesium cation, a compound represented by the following formula 1, and an ionic liquid, the molar concentration Amol / L of the magnesium cation with respect to the total amount of the electrolytic solution, and the formula 1 According to the electrolytic solution satisfying the relationship of 0.1 ≦ B / A ≦ 1, the molar concentration Bmol / L of the represented compound with respect to the total amount of the electrolytic solution is excellent in heat resistance and magnesium metal electrochemical It was found that precipitation and dissolution are possible.

In formula 1, each R independently represents an alkylene group having 2 to 4 carbon atoms or an arylene group having 6 to 10 carbon atoms, and X independently represents —O—, —S—, or —NR ^a. - represents, when X contains an -S-, at least two X are -S-, X is -NR ^a - if it contains, at least two X are -NR ^a - a, ^{R a} is hydrogen An atom or an alkyl group having 1 to 4 carbon atoms is represented, and n represents an integer of 6 to 8 inclusive.

Although the detailed mechanism by which the above effect is obtained is unknown, it is presumed as follows.
The compound represented by Formula 1 has a strong coordination property with magnesium ions, and by preparing the molar concentration A and the molar concentration B so as to satisfy the relationship of 0.1 ≦ B / A ≦ 1, the electrolytic solution It is considered that almost the entire amount of the compound represented by Formula 1 contained therein is coordinated with magnesium ions.
The compound represented by Formula 1 has a chemically more stable structure by coordinating with magnesium ions, hardly volatilizes or decomposes even in a high temperature environment (100 ° C. to 300 ° C.), and is considered to increase heat resistance. .
In addition, the electrolytic solution according to the present disclosure is considered to further improve the heat resistance as the electrolytic solution by including an ionic liquid having high heat resistance.
As described above, in general, when an ionic liquid is used alone as a solvent, it is difficult to electrochemically deposit magnesium metal.
However, in the electrolytic solution according to the present disclosure, magnesium ions are present in a coordinated state with the compound described in Formula 1. Therefore, it is considered that magnesium ions themselves are in an environment close to the case where they are present in the compound described in Formula 1, and that electrochemical deposition of magnesium metal is possible.

The problem to be solved by an embodiment of the present invention is to provide an electrolytic solution that is excellent in heat resistance and capable of electrochemical deposition and dissolution of magnesium metal.
Another problem to be solved by another embodiment of the present invention is to provide a magnesium secondary battery having excellent heat resistance and capable of electrochemical deposition and dissolution of magnesium metal.

Means for solving the above problems include the following aspects.
<1>
Magnesium cation,
A compound represented by Formula 1 below:
An ionic liquid,
The relationship of 0.1 ≦ B / A ≦ 1 between the molar concentration Amol / L of the magnesium cation with respect to the total amount of the electrolytic solution and the molar concentration Bmol / L with respect to the total amount of the electrolytic solution of the compound represented by the formula 1 Satisfying electrolyte.

In formula 1, each R independently represents an alkylene group having 2 to 4 carbon atoms or an arylene group having 6 to 10 carbon atoms, and X independently represents —O—, —S—, or —NR ^a. - represents, when X contains an -S-, at least two X are -S-, X is -NR ^a - if it contains, at least two X are -NR ^a - a, ^{R a} is hydrogen An atom or an alkyl group having 1 to 4 carbon atoms is represented, and n represents an integer of 6 to 8 inclusive.
<2>
The electrolytic solution according to <1>, wherein in formula 1, R is an alkylene group having 2 carbon atoms.
<3>
The electrolyte solution according to <1> or <2>, wherein in formula 1, X is all -O-.
<4>
In Formula 1, n is 6, The electrolyte solution in any one of <1>-<3>.
<5>
The electrolyte solution according to any one of <1> to <4>, wherein the ionic liquid is a sulfonium amide salt.
<6>
The electrolyte solution according to any one of <1> to <5>, further including a sulfonium amide anion represented by the following formula SA-1.

In Formula SA-1, are each R ^N independently represents a halogen atom, having 1 to 8 halogenated alkyl group carbon atoms or, 2 to 8 halogenated alkenyl group carbon atoms.
<7>
<1>-<6> The magnesium secondary battery containing the electrolyte solution as described in any one of <6>.

According to one embodiment of the present invention, an electrolytic solution having excellent heat resistance and capable of electrochemical deposition and dissolution of magnesium metal could be provided.
Moreover, according to another embodiment of the present invention, a magnesium secondary battery having excellent heat resistance and capable of electrochemical deposition and dissolution of magnesium metal can be provided.

It is the schematic which shows the electrochemical cell used in the Example. It is the result of the thermogravimetry (TG) and the differential thermal analysis (DTA) of the electrolyte solutions 1-3. It is the result of the thermogravimetry (TG) of the electrolyte solutions 1, 7, and 8. It is the confirmation result of the electrochemical deposition and melt | dissolution with respect to the electrolyte solutions 1-3 by the cyclic voltammetry. It is the confirmation result of the electrochemical deposition and melt | dissolution with respect to the electrolyte solutions 7-9 by cyclic voltammetry. It is a confirmation result of electrochemical deposition and dissolution by cyclic voltammetry for electrolyte solutions 10-11. It is the confirmation result of the electrochemical deposition and melt | dissolution by the electrolytic voltammetry with respect to the electrolyte solutions 12-14. In the confirmation of electrochemical deposition and dissolution by cyclic voltammetry when the electrolytic solution 2 is used, a photograph of a test electrode on which magnesium is deposited, an electron microscope image of the deposit, and an X-ray diffraction pattern of the deposit. It is a photograph of the test electrode on which magnesium was deposited when the electrolytic solution 13 or 14 was used.

Hereinafter, the present disclosure will be described in detail.
In addition, in this specification, description of "xx-yy" represents the numerical range containing xx and yy.
In the present disclosure, “mass%” and “wt%” are synonymous, and “part by mass” and “part by weight” are synonymous.
In the present disclosure, a combination of two or more preferred embodiments is a more preferred embodiment.
In the present specification, regarding the notation of the group in the compound represented by the formula, when there is no substitution or no substitution, the above group can further have a substituent unless otherwise specified. In addition to an unsubstituted group, a group having a substituent is also included. For example, in the formula, when “R represents an alkyl group” is described, it means “R represents an unsubstituted alkyl group or an alkyl group having a substituent”.
In this specification, the term “process” is not only an independent process, but is included in this term if the intended purpose of the process is achieved even when it cannot be clearly distinguished from other processes.
Hereinafter, the present disclosure will be described in detail.

(Electrolyte)
The electrolytic solution according to the present disclosure includes a magnesium cation, a compound represented by the above formula 1, and
The molar concentration Amol / L of the magnesium cation with respect to the total amount of the electrolytic solution, and the molar concentration Bmol / L with respect to the total amount of the electrolytic solution of the compound represented by the formula 1 are 0.1 ≦ Satisfies the relationship of B / A ≦ 1.

<Magnesium cation>
〔Content〕
From the viewpoint of electrochemical deposition and dissolution of magnesium metal in the electrolytic solution, the molar concentration Amol / L of the magnesium cation in the electrolytic solution according to the present disclosure with respect to the total amount of the electrolytic solution is 0.1 mol / L to 2.0 mol / L. It is preferable that it is 0.5 mol / L to 1.0 mol / L.
The molar concentration Amol / L of the magnesium cation with respect to the total amount of the electrolyte is measured by density measurement and the mass of magnesium hydroxide precipitated in an aqueous sodium hydroxide solution.

[Magnesium salt]
The magnesium cation is added to the electrolytic solution by adding, for example, a magnesium salt compound to a mixed solution of the compound represented by Formula 1 and an ionic liquid, or an ionic liquid.
The magnesium salt is not particularly limited and may be an inorganic salt or an organic salt, but is preferably an organic salt from the viewpoint of electrochemical precipitation and dissolution of magnesium.
Examples of the inorganic salt include MgCl ₂ , Mg (PF ₆ ) ₂ , Mg (BF ₄ ) ₂ , Mg (ClO ₄ ) ₂ , Mg (AsF ₆ ) _{2 and the} like.
Examples of the organic salt include magnesium citrate, magnesium oxalate, and a salt with an anion represented by the following formula SA-1, and are represented by the following formula SA-1 from the viewpoint of dissociation and oxidation resistance. Salts with sulfonium amide anions are preferred.
By using a salt with a sulfonium amide anion represented by the following formula SA-1, ion conductivity (for example, 10 ⁻³ S / cm or more at room temperature) is excellent, and oxidation resistance (for example, 3.5 V) An electrolytic solution excellent in degree) is obtained.
That is, the electrolytic solution according to the present disclosure preferably further includes a sulfonium amide anion represented by the following formula SA-1.

In Formula SA-1, are each R ^N independently represents a halogen atom, having 1 to 8 halogenated alkyl group carbon atoms or, 2 to 8 halogenated alkenyl group carbon atoms.

Examples of the halogen atom in the R ^N, is not particularly limited, a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom. Among these halogen atoms, a fluorine atom is preferable from the viewpoint of securing an appropriate electronegativity.

The number of carbon atoms of the halogenated alkyl group having 1 to 8 carbon atoms in the R ^N is 1 or more, easy to handle solubility, in order to ensure the viscosity and melting point, is 8 or less.
The halogenated alkyl group having 1 to 8 carbon atoms is not particularly limited. For example, a perfluoromethyl group, a perfluoroethyl group, a perfluoropropyl group, a perfluorobutyl group, a perfluoropentyl group, a perfluoroheptyl group, C1-C8 fluoroalkyl group such as perfluorooctyl group; perchloromethyl group, perchloroethyl group, perchloropropyl group, perchlorobutyl group, perchloropentyl group, perchloroheptyl group, perchlorooctyl group A C1-C8 chloroalkyl group such as
A bromoalkyl group having 1 to 8 carbon atoms such as perbromomethyl group, perbromoethyl group, perbromopropyl group, perbromobutyl group, perbromopentyl group, perbromoheptyl group, perbromooctyl group; And an iodoalkyl group having 1 to 8 carbon atoms such as a periodoethyl group, a periodopropyl group, a periodobutyl group, a periodopentyl group, a periodate heptyl group, and a periodooctyl group.
Among these halogenated alkyl groups having 1 to 8 carbon atoms, perfluoroalkyl groups having 1 to 8 carbon atoms are preferable, and perfluoromethyl groups are more preferable from the viewpoint of ensuring solubility, viscosity, and melting point that are easy to handle. preferable.

The number of carbon atoms of the halogenated alkenyl group having 2 to 8 carbon atoms in the R ^N is 2 or more, easy to handle solubility, in order to ensure the viscosity and melting point, is 8 or less.
Although it does not specifically limit as a C2-C8 halogenated alkenyl group, For example, C2-C8 fluoro alkenyl, such as a perfluoro vinyl group, a perfluoro allyl group, a perfluoro butenyl group, a perfluoro pentenyl group, etc. Group and the like.
Among these alkenyl halides having 2 to 8 carbon atoms, a fluoroalkenyl group having 2 to 8 carbon atoms is preferable, and a fluoroallyl group is more preferable from the viewpoint of ensuring solubility, viscosity, and melting point that are easy to handle.

Specific examples of the sulfonylamide anion represented by the formula SA-1 include bis (trifluoromethylsulfonyl) amide anion, fluorosulfonyl (trifluoromethylsulfonyl) amide anion, bis (fluorosulfonyl) amide anion, and the like. The present invention is not limited to such examples.
Among these sulfonylamide anions represented by the formula SA-1, bis (trifluoromethylsulfonyl) amide anion and bis (fluorosulfonyl) amide anion are preferable from the viewpoint of securing solubility that is easy to handle.

<Compound represented by Formula 1>
The electrolytic solution according to the present embodiment contains a compound represented by the following formula 1.

In formula 1, each R independently represents an alkylene group having 2 to 4 carbon atoms or an arylene group having 6 to 10 carbon atoms, and X independently represents —O—, —S—, or —NR ^a. - represents, when X contains an -S-, at least two X are -S-, X is -NR ^a - if it contains, at least two X are -NR ^a - a, ^{R a} is hydrogen An atom or an alkyl group having 1 to 4 carbon atoms is represented, and n represents an integer of 6 to 8 inclusive.

In formula 1, each R independently represents an alkylene group having 2 or more and 4 or less carbon atoms or an arylene group having 6 or more and 10 or less carbon atoms, each from 2 to 3 carbon atoms. It is preferably an alkylene group, more preferably an alkylene group having 2 carbon atoms.
As the arylene group having 6 to 10 carbon atoms, a phenylene group is preferable.
In Formula 1, each X independently represents —O—, —S—, or —NR ^a —, R ^a represents ^a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and each represents —O—. Preferably there is.
In Formula 1, when X contains -S-, it is preferable from a viewpoint of the coordination property of magnesium that at least 2 X is -S- and all X are -S-.
In Formula 1, X is -NR ^a - if it contains, in terms of coordinating magnesium, at least two X are -NR ^a - a, all X are -NR ^a - is preferably.
In Formula 1, R ^a represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and is preferably a hydrogen atom or a methyl group, more preferably a hydrogen atom from the viewpoint of magnesium coordination. .
In formula 1, from the viewpoint of magnesium coordination, n represents an integer of 6 to 8, and is preferably 6.
In Formula 1, a carbon atom contained in one R and a carbon atom contained in another R may be bonded to each other through a linking group to form a ring containing X, but it is preferable that no ring be formed.
Examples of the ring formed include a furan ring, a thiophene ring, and a pyrrole ring.

〔Content〕
From the viewpoint of improving electrochemical deposition and dissolution of metallic magnesium in the electrolytic solution, the molar concentration Bmol / L of the compound represented by Formula 1 in the electrolytic solution according to the present disclosure with respect to the total amount of the electrolytic solution is 0.1 mol / L. It is preferable that it is L-2.0 mol / L, and it is more preferable that it is 0.5 mol / L-1.0 mol / L.
The molar concentration Bmol / L is calculated from the density measurement of the electrolytic solution and the result of the magnesium content described above.
The molar concentration Amol / L of the magnesium cation with respect to the total amount of the electrolytic solution and the molar concentration Bmol / L with respect to the total amount of the electrolytic solution of the compound represented by the formula 1 are likely to cause electrochemical precipitation and dissolution. From this point of view, it is preferable that the relationship 0.1 ≦ B / A ≦ 1 is satisfied, the relationship 0.2 ≦ B / A ≦ 1 is satisfied, and the relationship 0.5 ≦ B / A ≦ 1 is satisfied. More preferred.

〔Concrete example〕
Specific examples of the compound represented by Formula 1 include the following compounds, but are not limited thereto.

<Ionic liquid>
The electrolytic solution according to the present disclosure contains an ionic liquid.
In the present disclosure, the ionic liquid refers to a salt that is liquid at 100 ° C., and is preferably a salt that is liquid at 25 ° C.
An ionic liquid generally has properties such as flame retardancy and non-volatility.
Although it does not specifically limit as an ionic liquid used for this indication, For example, the salt etc. of a quaternary ammonium cation and a sulfonylamide anion are mentioned.
Examples of the quaternary ammonium cation include a piperidinium cation (eg, 1-methyl-3-propylpiperidinium ion (PP ₁₃ ⁺ ion)), an ammonium cation (tetraethylammonium ion (TEA ⁺ ion), N, N-diethyl-N-methyl-N- (2-methoxyethyl) ammonium ion (DEME ⁺ ion) and the like).
Examples of the sulfonylamide anion include bis (trifluoromethylsulfonyl) amine anion (TFSA ^- ion), bis (fluorosulfonyl) amide anion (FSA ^- ion), and the like.

〔Content〕
The content of the ionic liquid with respect to the total mass of the electrolytic solution according to the present disclosure is the molar ratio of the ionic liquid to the content of the compound represented by the formula 1 from the viewpoint of the heat resistance of the electrolytic solution. The compound represented is preferably 1: 1 to 20: 1, more preferably 1: 1 to 10: 1, and still more preferably 1: 1 to 5: 1.
The content of the ionic liquid is measured by ion chromatography.

<Other ingredients>
The electrolytic solution according to the present disclosure may contain an organic solvent or the like as other components.
Examples of the organic solvent include sulfolane, 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 3-methyl-1,3-dioxolane, dimethylsulfone, diethylsulfone, and ethylmethylsulfone. Is mentioned.

<Applications of electrolyte>
The electrolytic solution according to the present disclosure is not particularly limited, but is preferably for a magnesium secondary battery, for the production of metal magnesium, or for the production of a metal magnesium film by electrolytic plating or the like, and for a magnesium secondary battery. It is more preferable.

(Magnesium secondary battery)
The magnesium secondary battery according to the present disclosure includes the electrolytic solution according to the present disclosure.
As described above, the electrolytic solution according to the present disclosure is suitable as an electrolytic solution for a magnesium secondary battery because of excellent heat resistance and capable of electrochemical deposition and dissolution of magnesium metal.

  The magnesium secondary battery according to the present disclosure is not particularly limited and can have the same configuration as that of a known magnesium secondary battery except that the electrolytic solution according to the present disclosure is included. It is preferable to include a positive electrode that holds and discharges (electrochemical deposition and dissolution), a negative electrode that is disposed to face the positive electrode with a separator interposed therebetween, and an electrolytic solution according to the present disclosure.

<Positive electrode>
The positive electrode is an electrode in which a current collector is loaded with a positive electrode material containing a positive electrode active material that reversibly holds and releases magnesium cations.
The positive electrode material preferably contains a positive electrode active material and further contains a conductive additive and a binder.

[Current collector]
The current collector may be a current collector made of a material that is electrochemically stable during the reaction via the magnesium cation at the positive electrode. Examples of the material constituting the current collector include aluminum and nickel, but are not particularly limited.

[Positive electrode active material]
The positive electrode active material only needs to be a substance capable of reversibly holding and releasing magnesium. For example, a sulfide capable of reversibly holding and releasing magnesium cations, and reversibly holding and releasing magnesium cations. Examples include, but are not limited to, oxides that can be released and organic compounds that can reversibly hold and release magnesium cations.
Specific examples of the positive electrode active material are not particularly limited, and examples thereof include molybdenum sulfide and manganese oxide.

[Conductive aid]
Although it does not specifically limit as said conductive support agent, For example, the powder of carbon materials, such as acetylene black, graphite, and carbon black, etc. are mentioned.
Since the content of the conductive auxiliary in the positive electrode material varies depending on the type of the positive electrode active material, the type of conductive auxiliary, and the like, it can be appropriately determined according to the type of positive electrode active material, the type of conductive auxiliary, and the like. preferable.

[Binder]
The binder is not particularly limited, and examples thereof include fluorine resins such as polytetrafluoroethylene and polyvinylidene fluoride; polyolefin resins such as polyethylene and polypropylene.
Since the binder content in the positive electrode material varies depending on the type of the positive electrode active material, the type of the binder, and the like, it is preferable to appropriately determine the content depending on the type of the positive electrode active material, the type of the binder, and the like.

<Negative electrode>
The negative electrode is preferably an electrode containing metal magnesium or a magnesium alloy as a negative electrode active material.
Although it does not specifically limit as a magnesium alloy, For example, the alloy of magnesium and aluminum, the alloy of magnesium and zinc, the alloy of magnesium and manganese, etc. are mentioned.
The negative electrode may be an electrode in which metallic magnesium or a magnesium alloy is supported on a current collector, and is an electrode obtained by forming metallic magnesium or a magnesium alloy into a shape (for example, a plate shape) suitable for the electrode. There may be.

<Separator>
The separator may be any separator that can separate the positive electrode and the negative electrode and hold the electrolytic solution. The material constituting the separator is not particularly limited, and examples thereof include fluorine resins such as polytetrafluoroethylene, polyolefin resins such as polyethylene and polypropylene, glass, and ceramics.

  Hereinafter, the present disclosure will be described in detail by way of examples, but the present disclosure is not limited thereto.

(Examples and Comparative Examples)
<Preparation of electrolyte>
An electrolyte solution having the following composition was prepared in a glove box maintained in an argon atmosphere with a dew point of −70 ° C. or less. Since TEATFSA is a solid at room temperature, a solution was prepared by heating and melting at 90 ° C. Each ratio indicates a molar ratio.
Electrolytic solution 1: Mg (TFSA) ₂ : PP ₁₃ TFSA = 1: 5
Electrolytic solution 2: Mg (TFSA) ₂ : 18C6: PP ₁₃ TFSA = 1: 1: 5
Electrolytic solution 3: Mg (TFSA) ₂ : 18C6: PP ₁₃ TFSA = 1: 5: 5
Electrolyte solution 4: Mg (TFSA) ₂ : TEATFSA = 1: 5
Electrolyte 5: Mg (TFSA) ₂ : 18C6: TEATFSA = 1: 1: 5
Electrolyte 6: Mg (TFSA) ₂ : 18C6: TEATFSA = 1: 5: 5
Electrolyte 7: Mg (TFSA) ₂ : Diglyme: PP ₁₃ TFSA = 1: 1: 5
Electrolytic solution 8: Mg (TFSA) ₂ : Diglyme: PP ₁₃ TFSA = 1: 2: 5
Electrolyte 9: Mg (TFSA) ₂ : Diglyme: PP ₁₃ TFSA = 1: 5: 5
Electrolytic solution 10: Mg (TFSA) ₂ : Monoglyme: PP ₁₃ TFSA = 1: 1: 5
Electrolyte 11: Mg (TFSA) ₂ : triglyme: PP ₁₃ TFSA = 1: 1: 5
Electrolytic solution 12: Mg (TFSA) ₂ : 1-N-18C6: TEATFSA = 1: 1: 5
Electrolytic solution 13: Mg (TFSA) ₂ : 18C6: TEATFSA = 1: 0.5: 5
Electrolytic solution 14: Mg (TFSA) ₂ : 18C6: TEATFSA = 1: 0.25: 5

Abbreviations in the above composition are as follows.
Mg (TFSA) ₂ : Mg [N (SO ₂ CF ₃ ) ₂ ] ₂
PP ₁₃ TFSA: 1-methyl-3-propylpiperidinium bis (trifluoromethanesulfonyl) amide 18C6: 1,4,7,10,13,16-hexaoxacyclooctadecane (18-crown-6 ether)
TEATFSA: tetraethylammonium bis (trifluoromethanesulfonyl) amide 1-N-18C6: 1,4,7,10,13-pentaoxa-16-azacyclooctadecane (1-aza-18-crown-6 ether)

<Thermogravimetry, differential thermal analysis>
Thermogravimetry (TG) was performed on the electrolyte solutions 1 to 14 using TG / DTA6200 manufactured by Seiko Instruments Inc. Furthermore, in the electrolyte solutions 1-6, the differential thermal analysis (DTA) was also performed simultaneously. During the measurement, argon gas was flowed, and the rate of temperature increase was 10 ° C./min.

<Confirmation of electrochemical deposition and dissolution>
[Construction of electrochemical cell]
The electrochemical cell shown in FIG. 1 was constructed. The cell was constructed in a glove box maintained in an argon atmosphere with a dew point of −70 ° C. or lower.
FIG. 1 is a schematic view of an electrochemical cell 10 used in the embodiment, in which an electrolytic solution 16 is filled between a working electrode 12 and a counter electrode 14, and a reference electrode 20 is disposed in the electrolytic solution 16.
The reference electrode 20 has a silver wire 18 immersed in a solution in a glass tube.
Details of each component used in this example are as follows.
Working electrode: mirror-polished platinum plate Counter electrode: polished magnesium plate Reference electrode: Triglyme solution containing 0.01 mol · dm ^-3 silver nitrate and 0.1 mol · dm ^-3 Mg (TFSA) ₂ Silver wire soaked in. In order to avoid the solution of the reference electrode from being mixed with the electrolyte, a glass tube having a porous glass at the tip was used.
Electrolyte: The above electrolyte 1 to electrolyte 14

[Electrochemical measurement]
As an electrochemical measurement device, HSV-110 manufactured by Hokuto Denko Co., Ltd. was used, and cyclic voltammetry was performed from the reduction direction in a scanning range of −4 V to 0 V (relative to the reference electrode). The scanning speed was 1 mV / s.
The measurement was performed using a sealed container filled with an argon atmosphere, and was performed at a measurement temperature of 80 ° C.

[Confirmation of precipitates]
After cyclic voltammetry, the potential was maintained at −4 V (relative to the reference electrode) for 3 hours, and the presence or absence of deposits was visually confirmed on the working electrode.
When deposits were observed, they were identified by X-ray diffraction measurement and scanning electron microscope observation.
X-ray diffraction measurement was performed in the atmosphere using an X-ray diffractometer, Ultimate IV, manufactured by Rigaku Corporation. The sample was measured together with the working electrode (Pt) plate.
Scanning electron microscope observation was performed using a scanning electron microscope apparatus JCM-6000 manufactured by JEOL Ltd.

<Evaluation results>
[Thermogravimetry]
FIG. 2 shows the results of thermogravimetry (TG) and differential thermal analysis (DTA) of the electrolytic solutions 1 to 3.
From the results shown in FIG. 2, PP ₁₃ TFSA (electrolytic solution 1) containing Mg (TFSA) ₂ does not show a large weight change even under a high temperature environment of 300 ° C., and is excellent in thermal stability. Recognize.
Further, from the results shown in FIG. 2, in the electrolytic solution 2 in which the molar ratio of Mg (TFSA) ₂ and 18C6 is 1: 1, no significant weight change is observed even under a high temperature environment of 300 ° C. It turns out that it is excellent in stability.
Furthermore, from the results shown in FIG. 2, in the electrolytic solution 3 in which the molar ratio of Mg (TFSA) ₂ and 18C6 is 1: 5, a large weight change was observed at 200 ° C. to 300 ° C., and the high temperature of 300 ° C. It can be seen that the thermal stability at is poor.
This is considered to be because 18C6 which is not coordinated with the magnesium cation in the electrolytic solution decomposes at 200 ° C to 300 ° C.
Further, in the results of thermogravimetry, the results of the electrolytic solutions 4, 13 and 14 are the results of the electrolytic solution 1, the results of the electrolytic solution 5 are the results of the electrolytic solution 2, and the results of the electrolytic solution 6 are the results of the electrolytic solution 3. And similar results.
From the above results, the molar concentration Amol / L of the magnesium cation with respect to the total amount of the electrolytic solution and the molar concentration Bmol / L with respect to the total amount of the electrolytic solution of the compound represented by Formula 1 are 0.1 ≦ B / A. When ≦ 1, it is understood that the heat resistance of the electrolytic solution is excellent.

FIG. 3 shows the results of thermogravimetry (TG) of the electrolytic solutions 1, 7 and 8.
From the results shown in FIG. 3, it can be seen that the electrolyte solution 7 is excellent in thermal stability with no significant weight change even at 300 ° C.
Moreover, in the electrolyte solution 8, there exists a weight change from about 100 degreeC, and it turns out that it is inferior to thermal stability. This is thought to be because diglyme not coordinated with the magnesium cation volatilizes in the electrolyte.

[Confirmation of electrochemical deposition and dissolution]
FIG. 4 shows the results of confirming electrochemical deposition and dissolution for the electrolytic solutions 1 to 3 by cyclic voltammetry.
From the results shown in FIG. 4, it can be seen that no precipitation of magnesium is confirmed in PP ₁₃ TFSA (electrolytic solution 1) containing Mg (TFSA) ₂ .
Further, from the results shown in FIG. 4, it can be seen that in the electrolytic solution 2 in which the molar ratio of Mg (TFSA) ₂ and 18C6 is 1: 1, precipitation and dissolution of magnesium are repeated.
Furthermore, it can be seen from the results shown in FIG. 4 that the deposition and dissolution of magnesium are repeated also in the electrolytic solution 3 in which the molar ratio of Mg (TFSA) ₂ and 18C6 is 1: 5.
In addition, in the result of confirming the electrochemical deposition and dissolution by cyclic voltammetry, the result of the electrolytic solution 4 is the result of the electrolytic solution 1, the result of the electrolytic solution 5 is the result of the electrolytic solution 2, and the result of the electrolytic solution 6 is electrolytic. The results were the same as the results for Liquid 3.
From the above results, it can be seen that magnesium does not precipitate in an electrolytic solution containing only a magnesium salt and an ionic liquid, and magnesium precipitates when the electrolytic solution contains the compound described in Formula 1.

FIG. 5 shows the results of confirming electrochemical deposition and dissolution of the electrolytes 7 to 9 by cyclic voltammetry.
From the results shown in FIG. 5, it can be seen that neither the electrolytic solution 7 nor the electrolytic solution 8 confirms the precipitation of magnesium.
Further, from the results shown in FIG. 5, it is understood that when the electrolytic solution 9 is used, precipitation and dissolution of magnesium are repeated.
From the above results, when the amount of diglyme is an excess amount of about 5 times the amount of magnesium cation, magnesium can be precipitated, but the amount of diglyme is twice the amount of magnesium cation. When it is below, it turns out that magnesium does not precipitate.

FIG. 6 shows the results of confirming electrochemical deposition and dissolution by cyclic voltammetry for the electrolyte solutions 10-11.
From the results shown in FIG. 6, it can be seen that neither the electrolytic solution 10 nor the electrolytic solution 11 confirms the precipitation of magnesium.
From the above results, it is understood that magnesium does not precipitate when the amount of monoglyme or triglyme is one time the amount of magnesium cation.

FIG. 7 shows the results of confirming electrochemical deposition and dissolution by cyclic voltammetry for the electrolyte solutions 12-14.
From the results shown in FIG. 7, it can be seen that magnesium deposition is not confirmed in the electrolytic solution 12.
Moreover, it can be seen from the results shown in FIG. 7 that in the electrolytic solutions 13 and 14, precipitation and dissolution of magnesium are repeated.
These results, in Formula 1, X only one is -NR a ^- it can be seen that no magnesium precipitation when it is.
Moreover, it turns out that magnesium precipitates also when the above-mentioned B / A is 0.5 or 0.25.

FIG. 8 shows a photograph of a test electrode on which magnesium was deposited, an electron microscopic image of the precipitate, and an X-ray diffraction of the precipitate in the confirmation of electrochemical precipitation and dissolution by cyclic voltammetry when the electrolytic solution 2 was used. The pattern is shown.
It can be seen from the photograph of the test electrode that a black deposit is deposited on the test electrode. Further, it can be seen from the X-ray diffraction turn that the precipitate contains metallic magnesium.
In addition, in the electrolytic solutions 2, 3, 5, 6, 9, 13, and 14 in which precipitation was similarly observed, the appearance of the precipitate and the result of the X-ray diffraction pattern were the same.
FIG. 9 shows a photograph of the test electrode on which magnesium was deposited when the electrolytic solution 13 or 14 was used.

The results of each example or comparative example are summarized in Table 1 below.
In Table 1, the description in the column of B / A is that the molar concentration of magnesium cation with respect to the total amount of the electrolytic solution is Amol / L, and the molar concentration of the compound represented by Formula 1 with respect to the total amount of the electrolytic solution is Bmol / L. In this case, the value of B / A is shown.
In Table 1, the description in the column of thermogravimetry is as follows.
A: The amount of decrease in mass at 300 ° C. in the result of thermogravimetry described above is less than 90%. B: The amount of decrease in mass at 300 ° C. in the result of thermogravimetry described above is 90% or more. .
Moreover, the description of the column of electrochemical precipitation and melt | dissolution in Table 1 is as follows.
A: In the above-described confirmation of electrochemical precipitation and dissolution, it was confirmed that precipitation and dissolution of magnesium were repeated.
B: In the above-described confirmation of electrochemical precipitation and dissolution, it was not confirmed that magnesium precipitation and dissolution were repeated.

  Moreover, 18C6 in the electrolytic solution 2 was changed to 1,4,7,10,13,16-hexaazacyclooctadecane or 1,4,7,10,13,16-hexathiacyclooctadecane. As in Example 1, thermogravimetry and electrochemical precipitation and dissolution were confirmed, and the same results as in Example 1 were obtained.

  The cyclic voltammetry measurement in the above examples is performed in an environment of 80 ° C. From the results of thermogravimetry, the electrolytic solution according to the present disclosure is magnesium metal even in a high temperature environment of 100 ° C. to 300 ° C. It is thought that the electrochemical deposition and dissolution of can be performed.

10 Electrochemical Cell 12 Working Electrode 14 Counter Electrode 16 Electrolyte 18 Silver Wire 20 Reference Electrode

Claims (7)

Magnesium cation,
A compound represented by Formula 1 below:
An ionic liquid,
The relationship of 0.1 ≦ B / A ≦ 1 between the molar concentration Amol / L of the magnesium cation with respect to the total amount of the electrolytic solution and the molar concentration Bmol / L with respect to the total amount of the electrolytic solution of the compound represented by the formula 1 Satisfying electrolyte.

In formula 1, each R independently represents an alkylene group having 2 to 4 carbon atoms or an arylene group having 6 to 10 carbon atoms, and X independently represents —O—, —S—, or —NR ^a. - represents, when X contains an -S-, at least two X are -S-, X is -NR ^a - if it contains, at least two X are -NR ^a - a, ^{R a} is hydrogen An atom or an alkyl group having 1 to 4 carbon atoms is represented, and n represents an integer of 6 to 8 inclusive.   The electrolytic solution according to claim 1, wherein in Formula 1, R is an alkylene group having 2 carbon atoms.   The electrolyte solution of Claim 1 or Claim 2 whose all are -O- in Formula 1.   The electrolytic solution according to any one of claims 1 to 3, wherein n in formula 1 is 6.   The electrolyte solution according to claim 1, wherein the ionic liquid is a sulfonium amide salt. The electrolyte solution according to any one of claims 1 to 5, further comprising a sulfonium amide anion represented by the following formula SA-1.

In Formula SA-1, are each R ^N independently represents a halogen atom, having 1 to 8 halogenated alkyl group carbon atoms or, 2 to 8 halogenated alkenyl group carbon atoms. The magnesium secondary battery containing the electrolyte solution of any one of Claims 1-6.