JP2014192128A - Molten salt, electrolyte for batteries, and polyvalent ion battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrolyte which can electrochemically precipitate and dissolve a polyvalent metal, and to provide a polyvalent ion battery arranged by use thereof.SOLUTION: A molten salt of the present invention comprises: an amide anion expressed by the formula (1) below; an alkali-earth metal cation; and an alkali metal cation.

Description

  The present invention relates to a molten salt. More specifically, the present invention relates to a molten salt suitable as an electrolyte for a multivalent ion battery.

  Various types of chemical batteries that convert energy of chemical reaction into electric energy are known. In particular, lithium ion batteries are widely used as power sources for mobile devices such as mobile phones. In recent years, due to increasing social interest in global environmental problems, electric vehicles with a low environmental load have attracted attention, and electric vehicles equipped with lithium ion batteries have begun to be put into practical use.

  The lithium used in lithium ion batteries is a metal with a relatively high abundance of elements in the earth's crust (also called the Clark number), but the production area is unevenly distributed, so if the electric vehicle market expands in the future Concerns have been pointed out, such as the realization of procurement risks and rising material costs.

  Further, batteries for electric vehicles are required to be large and have high safety. Lithium-ion batteries include lithium, which is a metal with a low melting point, and organic solvents that are volatile and flammable as the main elements, so it is expected that there will be certain limits to achieving both large size and safety. Yes.

  Furthermore, development of an innovative next-generation battery having a high energy density exceeding that of a lithium ion battery is awaited in every application, not limited to automobile applications.

  As one of the technologies for such next-generation batteries, International Publication No. 2006/101141 (Patent Document 1) and Japanese Patent Application Laid-Open No. 2009-67644 (Patent Document 2) include molten salts that can be used as battery electrolytes. (Also referred to as ionic liquid).

International Publication No. 2006/101141 JP 2009-67644 A

As a next-generation battery that replaces the lithium ion battery, a polyvalent ion battery is expected. “Polyvalent ion battery” means, for example, a cation having a valence of 2 or more (hereinafter also referred to as a cation) such as magnesium ion (Mg ²⁺ ) or aluminum ion (Al ³⁺ ) It is a battery responsible for electrical conduction. That is, in the multivalent ion battery, a plurality of electrons corresponding to the valence of the cation can be taken out from one atom and used as electric energy. Accordingly, a higher energy density can be expected as compared with a lithium ion battery in which lithium ions that are monovalent cations are responsible for electrical conduction. Hereinafter, a metal that is ionized to become a polyvalent ion is also referred to as a “multivalent metal”.

  Magnesium, aluminum, calcium, zinc, and the like have been studied as metals used in multivalent ion batteries. Of these, magnesium is a metal with a low oxidation-reduction potential, a large number of Clarkes, and a high melting point, and is therefore the most powerful next-generation battery material that is highly compatible with high energy density, low cost, and high safety. Promising.

  However, since there has not been an electrolyte with a wide potential window that enables electrochemical deposition and dissolution of magnesium, a multivalent ion battery utilizing such a magnesium potential, that is, a magnesium ion battery, It has not yet been realized.

  For example, examples in which precipitation and dissolution of magnesium were confirmed by using an organic solvent containing Grignard reagent (organomagnesium halide) or magnesium bromide as an electrolyte have been reported. Since it is chemically unstable and the potential window on the positive electrode side (oxidation side) is narrow, only a battery with a small electromotive force can inevitably be constructed. Further, considering the reactivity, volatility, flammability, etc. of these electrolytes, it is not preferable from the viewpoint of safety. In addition, attempts have been made to use room temperature ionic liquids containing organic cations characterized by non-volatility and non-flammability, but precipitation and dissolution of magnesium are unlikely to occur, conductivity is low, organic cations are expensive, etc. There are many problems, and the present situation is that a viable battery system has not been constructed.

  The present invention has been made in view of the above situation, and an object of the present invention is an electrolyte capable of electrochemically depositing and dissolving a polyvalent metal and a polyvalent ion using the same To provide a battery.

  The inventors of the present invention have so far studied a molten salt composed of an alkali metal cation and a specific amide anion used as an electrolyte of a lithium ion battery or a sodium ion battery. In this process, it may be possible to obtain a battery electrolyte having a wide potential window by combining an alkali metal cation that has a very low reduction potential as a cation and does not decompose even at a noble potential and a specific amide anion. As a result of further research based on such knowledge, it is surprising that when a suitable amount of an alkaline earth metal cation is contained in a molten salt composed of an alkali metal cation and a specific amide anion, the molten salt The inventors have found that polyvalent metals such as magnesium can be electrochemically deposited and dissolved, and have completed the present invention.

  That is, the molten salt of the present invention includes an amide anion represented by the following formula (1), an alkaline earth metal cation and an alkali metal cation.

  In the above formula (1), X1 and X2 each independently represent a fluorine atom, a fluoromethyl group or a fluoroethyl group.

  Here, the alkaline earth metal cation is preferably at least one of magnesium ion and calcium ion.

  The alkali metal cation is preferably one or more metal ions selected from the group consisting of lithium ions, sodium ions, potassium ions, rubidium ions, cesium ions, and francium ions.

  In the total cation contained in the molten salt, the proportion of the alkaline earth metal cation is preferably 0.01 or more and 0.50 or less in terms of molar ratio.

  The molten salt further includes one or more halide ions selected from the group consisting of fluoride ions, chloride ions, bromide ions, and iodide ions, and in all the anions contained in the molten salt, The ratio of the halide ions is preferably 0.001 or more and 0.10 or less in terms of molar ratio.

  The present invention also relates to a battery electrolyte, wherein the battery electrolyte contains the molten salt.

  Furthermore, the present invention relates to a polyvalent ion battery using the battery electrolyte, and the polyvalent ion battery includes a positive electrode, a negative electrode, and an electrolyte containing the molten salt, and a discharge reaction is performed on the positive electrode. And a reduction reaction involving a polyvalent metal cation and an oxidation reaction involving a polyvalent metal cation in the negative electrode.

  The multivalent ion battery of the present invention can also be an air battery, and the air battery includes a positive electrode, a negative electrode, and an electrolyte containing the molten salt, and the discharge reaction reduces oxygen at the positive electrode. The reaction is accompanied by an oxidation reaction involving a polyvalent metal cation in the negative electrode.

  Here, the multivalent ion battery or the air battery is preferably a secondary battery that can be charged and discharged in a temperature range of 60 ° C. or higher and 300 ° C. or lower.

  The polyvalent metal cation is preferably magnesium ion.

  In the molten salt of the present invention, electrochemical precipitation and dissolution of polyvalent metals are possible. And a polyvalent ion battery is realizable by using the molten salt of this invention as an electrolyte for batteries.

It is a figure which shows an example of the measurement result of the thermal decomposition temperature of Mg (TFSA) _2- Cs (TFSA) binary system molten salt which concerns on the Example of this invention. 1 is a phase diagram of a Mg (TFSA) ₂ —Cs (TFSA) binary molten salt according to an example of the present invention. It is a figure which shows an example of the measurement result of the viscosity of the Mg (TFSA) _2- Cs (TFSA) binary molten salt which concerns on the Example of this invention. It is a figure which shows typically the experimental instrument used for electrical conductivity measurement. It is a figure which shows an example of the measurement result of the electrical conductivity of Mg (TFSA) _2- Cs (TFSA) binary system molten salt which concerns on the Example of this invention. It is a figure which shows typically the experimental instrument used for the electrochemical measurement. It is a figure which shows an example of the cyclic voltammogram of Mg (TFSA) _2- Cs (TFSA) binary system molten salt which concerns on the Example of this invention. It is a figure which shows an example of the cyclic voltammogram of Mg (TFSA) _2- Cs (TFSA) binary system molten salt which concerns on the Example of this invention. It is a figure which shows an example of the cyclic voltammogram of Mg (TFSA) _2- Cs (TFSA) binary system molten salt which concerns on the Example of this invention. It is a figure which shows an example of the cyclic voltammogram of Mg (TFSA) _2- Li (TFSA) -Cs (TFSA) ternary molten salt which concerns on the Example of this invention. It is a figure which shows an example of the measurement result of the X-ray diffraction of the electrode after a constant potential electrolysis test. It is a figure which shows an example of the measurement result of the thermal decomposition temperature of Mg (TFSA) _2- Rb (TFSA) binary molten salt which concerns on the Example of this invention. 1 is a phase diagram of a binary molten salt of Mg (TFSA) ₂ —Rb (TFSA) according to an example of the present invention. It is a figure which shows an example of the measurement result of the viscosity of the Mg (TFSA) _2- Rb (TFSA) binary molten salt which concerns on the Example of this invention. It is a figure which shows an example of the measurement result of the viscosity of the Mg (TFSA) _2- Rb (TFSA) binary molten salt which concerns on the Example of this invention. It is a figure which shows an example of the cyclic voltammogram of Mg (TFSA) _2- Rb (TFSA) binary system molten salt which concerns on the Example of this invention. It is a figure which shows an example of the cyclic voltammogram of Mg (TFSA) _2- Rb (TFSA) binary system molten salt which concerns on the Example of this invention. It is a figure which shows an example of the cyclic voltammogram of Mg (TFSA) _2- Rb (TFSA) binary system molten salt which concerns on the Example of this invention. It is a figure which shows the dependence to the mixing molar ratio of melting | fusing point of Mg (TFSA) _2- K (FSA) binary molten salt which concerns on the Example of this invention. It is a figure which shows an example of the cyclic voltammogram on Ni electrode in the Mg (TFSA) _2- K (FSA) binary system molten salt which concerns on the Example of this invention. It is a figure which shows an example of the cyclic voltammogram on the glassy carbon (GC) electrode in the Mg (TFSA) _2- K (FSA) binary system molten salt which concerns on the Example of this invention. It is a figure which shows an example of the cyclic voltammogram on the Mg electrode in the Mg (TFSA) _2- K (FSA) binary molten salt which concerns on the Example of this invention.

  Hereinafter, although the embodiment concerning the present invention is described in detail, the present invention is not limited to these.

<Embodiment 1: Molten salt>
The molten salt of the present embodiment includes at least an amide anion having sulfonylamide as a basic skeleton and an alkaline earth metal cation and an alkali metal cation as counter cations of the amide anion. As long as such a molten salt contains these components, it can contain any other components, and even if other components are contained, the effects of the present invention are shown.

  The molten salt of the present embodiment containing the anion and cation as described above typically comprises a first molten salt comprising an amide anion and an alkaline earth metal cation, and an amide anion and an alkali metal cation. It can be obtained by mixing with the second molten salt. It can also be obtained, for example, by synthesizing a complex salt composed of an amide anion, an alkaline earth metal cation and an alkali metal cation.

  Since the molten salt of the present embodiment including the above components has a wide liquid phase range of 60 ° C. to 300 ° C., a battery system having a wide operating temperature can be constructed. Conventionally, in a room temperature molten salt battery using an organic cation or the like, the problem is that the electrode reaction rate and the ion diffusion rate are slow. On the other hand, in the molten salt of the present embodiment, the battery operating temperature can be set to 60 ° C. to 300 ° C., so that the electrode reaction rate and the ion diffusion rate can be dramatically improved. That is, it is possible to realize a battery that can cope with large current charge / discharge.

  Moreover, the molten salt of this Embodiment can be manufactured cheaply compared with the molten salt using an organic cation, and has high economical efficiency.

  Moreover, the molten salt of this Embodiment has a wide electric potential window of 3.0V-5.5V. Therefore, a battery configuration having a large electromotive force is possible, and a battery having a high energy density can be realized.

  Furthermore, the molten salt of the present embodiment is nonflammable, unlike the electrolytic solution conventionally used for lithium ion batteries. Therefore, it is possible to realize a high level of safety that could not be realized with a conventional battery system.

  And in the molten salt of this Embodiment, the electrochemical precipitation and melt | dissolution of a polyvalent metal are possible. Thereby, an innovative battery system called a polyvalent ion battery in which the polyvalent metal cation is responsible for charge / discharge electrical conduction can be provided. Since the polyvalent ion battery is charged and discharged by a multi-electron reaction, the energy density of the battery can be dramatically increased.

Hereinafter, each component of the molten salt of this Embodiment is demonstrated.
<Amide anion>
The molten salt of the present embodiment contains an amide anion represented by the above formula (1). This amide anion has a feature of showing a remarkably low melting point by using an alkaline earth metal cation and an alkali metal cation as a counter cation. Therefore, the molten salt of the present embodiment can have a wide liquid phase range (temperature range in a liquid state). In addition, since this amide anion is extremely stable electrochemically and thermally, it greatly contributes to the expansion of the potential window of the molten salt and the liquid phase range.

Here, in the above formula (1), X1 and X2 each independently represent a fluorine atom (F), a fluoromethyl group or a fluoroethyl group. Examples of the fluoromethyl group or fluoroethyl group include a trifluoromethyl group (CF ₃ ), a difluoromethyl group (CHF ₂ ), a monofluoromethyl group (CH ₂ F), a pentafluoroethyl group (CF ₂ CF ₃ ), 1,2,2,2-tetrafluoroethyl group (CHFCF ₃ ), 1,1,2,2-tetrafluoroethyl group (CF ₂ CHF ₂ ), 2,2,2-trifluoroethyl group (CH ₂ CF ₃ ), 1,2,2-trifluoroethyl group (CHFCHF ₂ ), 1,1,2-trifluoroethyl group (CF ₂ CHF), 2,2-difluoroethyl group (CH ₂ CHF ₂ ), 1, 2-difluoroethyl group (CHFCH ₂ F), 1,1- difluoroethyl group (CF ₂ CH _3), 2- monofluoroethyl group _{(CH 2 CH 2 F),} 1- monofluoroethyl group CHFCH _3), and the like. In the present embodiment, among these, a trifluoromethyl group (CF ₃ ) and a pentafluoroethyl group (CF ₂ CF ₃ ) are preferable.

In the present specification, an amide anion in which X1 and X2 each represent a fluorine atom, that is, a bisfluorosulfonylamide ion is also referred to as “FSA anion or FSA ⁻ ”.

Further, an amide anion in which X1 and X2 each represent a trifluoromethyl group, that is, a bistrifluoromethylsulfonylamide ion is also referred to as “TFSA anion or TFSA ⁻ ”.

Furthermore, an amide anion in which X1 and X2 each represent a pentafluoroethyl group, that is, a bispentafluoroethylsulfonylamide ion is also referred to as “BETA anion or BETA ⁻ ”.

For example, a compound composed of a TFSA anion and a magnesium ion (Mg ²⁺ ) may be described as Mg (TFSA) ₂ .

The molten salt of the present embodiment may contain two or more amide anions as described above. For example, TFSA ⁻ and FSA ⁻ may coexist as amide anions in the molten salt.

<Alkali metal cation>
The alkali metal cation in this embodiment refers to an ion of a metal element belonging to Group 1 of the periodic table. As the alkali metal cation of the present embodiment, lithium ion (Li ⁺ ), sodium ion (Na ⁺ ), potassium ion (K ⁺ ), rubidium ion (Rb ⁺ ), cesium ion (Cs ⁺ ), and francium ion (Fr) It is preferable to use at least one selected from ⁺ ). Since such an alkali metal cation has a very low reduction potential and does not decompose even at a noble potential, the potential window of the molten salt can be expanded, whereby the molten salt of the present embodiment can be expanded. Can be used as an electrolyte even in a battery system having a large electromotive force.

<Alkaline earth metal cations>
The alkaline earth metal cation of the present embodiment refers to ions of metal elements belonging to Group 2 of the periodic table. Specifically, beryllium ions (Be ²⁺ ), magnesium ions (Mg ²⁺ ), calcium ions (Ca ²⁺ ), strontium ion (Sr ²⁺ ), barium ion (Ba ²⁺ ), radium ion (Ra ²⁺ ) can be mentioned.

  The alkaline earth metal cation of the present embodiment can be an ion responsible for electrical conduction when the molten salt of the present embodiment is used as an electrolyte of a multivalent ion battery. Here, since the alkaline earth metal cation is involved in the reaction at the positive and negative electrodes of the battery, the alkaline earth metal cation having a small atomic number is required to increase the capacity density of the positive and negative electrodes. It is preferable. Furthermore, considering that beryllium has high toxicity, the alkaline earth metal cation of the present embodiment is preferably at least one of magnesium ion and calcium ion.

  In the total cation contained in the molten salt of the present embodiment, the proportion of the alkaline earth metal cation is preferably 0.01 or more and 0.50 or less in terms of molar ratio. When the alkaline earth metal cation is present in such a molar ratio, the liquid phase range of the molten salt tends to be widened. Moreover, it also exists in the tendency which shows suitable viscosity and electrical conductivity as an electrolyte for batteries.

  Here, in the total cation contained in the molten salt, the proportion of the alkaline earth metal cation is, for example, 0.50, the first molten salt composed of an amide anion and an alkaline earth metal cation The second molten salt composed of an amide anion and an alkali metal cation may be mixed at a molar ratio of 50:50. For example, in order to set the ratio of the alkaline earth metal cation to 0.01, the first molten salt and the second molten salt described above may be mixed at a molar ratio of 1:99. That is, the ratio of the alkaline earth metal cation in the total cation contained in the molten salt is 0.01 or more and 0.50 or less in terms of molar ratio means that the first molten salt and the second molten salt described above are used. It is equivalent to the salt being mixed at a molar ratio of 1:99 to 50:50.

The first molten salt and the second molten salt described above preferably form a eutectic when mixed in a molar ratio of 1:99 to 50:50. By adopting such a combination, the liquid phase range of the molten salt can be further expanded. Here, when the molten salt obtained by mixing Mg (TFSA) ₂ and Cs (TFSA) is referred to as “Mg (TFSA) ₂ -Cs (TFSA)”, the eutectic is in the above molar ratio range. As a combination that can form, for example, Mg (TFSA) ₂ -Cs (TFSA), Mg (TFSA) ₂ -Rb (TFSA), Mg (TFSA) ₂ -K (TFSA), Mg (TFSA) ₂ -Na (TFSA), Mg (TFSA) ₂ -Li (TFSA), Mg (TFSA) ₂ -Cs (FSA), Mg (TFSA) ₂ -Rb (FSA), Mg (TFSA) ₂ -K (FSA), Mg ( TFSA) ₂ -Na (FSA), Mg (TFSA) ₂ -Li (FSA), Mg (FSA) ₂ -Cs (FSA), Mg (FSA) ₂ -Rb (FSA), Mg (FSA) ₂ -K ( FSA), _{g (FSA) 2 -Na (FSA} ), Mg (FSA) 2 -Li (FSA), Ca (TFSA) 2 -Cs (TFSA), Ca (TFSA) 2 -Rb (TFSA), Ca (TFSA) 2 - K (TFSA), Ca (TFSA) ₂ -Na (TFSA), Ca (TFSA) ₂ -Li (TFSA), Ca (TFSA) ₂ -Cs (FSA), Ca (TFSA) ₂ -Rb (FSA), Ca (TFSA) _2- K (FSA), Ca (TFSA) _2- Na (FSA), Ca (TFSA) _2- Li (FSA), Ca (FSA) _2- Cs (FSA), Ca (FSA) _2- Rb (FSA), Ca (FSA) _2- K (FSA), Ca (FSA) _2- Na (FSA), Ca (FSA) _2- Li (FSA), and the like can be given.

  In the total cation contained in the molten salt of the present embodiment, the proportion of the alkaline earth metal cation is more preferably 0.05 or more and 0.40 or less, and particularly preferably 0.10 in molar ratio. It is 0.30 or less. By including the alkaline earth metal cation in such a range, the liquid phase range of the molten salt can be further expanded, and a viscosity and conductivity more suitable as a battery electrolyte can be exhibited.

<Halide ion>
The molten salt of the present embodiment can further contain halide ions. The inclusion of halide ions is preferred when the molten salt is used as an electrolyte for batteries because it tends to cause precipitation and dissolution of multivalent ions in the negative electrode. Here, as the halide ions, at least one selected from the group consisting of fluoride ions (F ⁻ ), chloride ions (Cl ⁻ ), bromide ions (Br ⁻ ), and iodide ions (I ⁻ ). It is preferable to use ions.

Examples of the method of including halide ions in the molten salt of the present embodiment include a method of adding to the molten salt as a salt with an alkaline earth metal or an alkali metal. For example, it can be added to the molten salt as a salt such as magnesium fluoride (MgF ₂ ), magnesium chloride (MgCl ₂ ), magnesium bromide (MgBr ₂ ), or magnesium iodide (MgI ₂ ).

  Here, the proportion of halide ions in all the anions contained in the molten salt is preferably 0.001 or more and 0.10 or less in terms of molar ratio.

<Organic cation>
The molten salt of the present embodiment can further contain an organic cation. The inclusion of the organic cation is preferable because the conductivity of the electrolyte is increased and the melting point is lowered, that is, the liquid phase range tends to be widened. Here, as the organic cation, for example, alkyl imidazolium cation such as 1-ethyl-3-methylimidazolium cation, alkyl pyrrolidinium cation such as N-ethyl-N-methylpyrrolidinium cation, 1- Alkylpyridinium cations such as methyl-pyridinium cation, quaternary ammonium cations such as trimethylhexylammonium cation, quaternary phosphonium cations such as triethylpentylphosphonium cation, tertiary sulfonium cations such as triethylsulfonium cation, etc. it can.

<Embodiment 2: Multivalent ion battery>
Hereinafter, the multivalent ion battery according to the second embodiment of the present invention will be described.

  The multivalent ion battery of the present embodiment includes a positive electrode, a negative electrode, and an electrolyte, and the electrolyte includes an amide anion represented by the above formula (1), an alkaline earth metal cation, and an alkali metal cation. The discharge reaction is a multivalent ion battery with a reduction reaction involving the polyvalent metal cation in the positive electrode and an oxidation reaction involving the polyvalent metal cation in the negative electrode. That is, the multivalent ion battery of the present embodiment is a battery provided with the molten salt of the first embodiment as an electrolyte.

  As a typical configuration of the multivalent ion battery of the present embodiment, the electrolyte is provided between the positive electrode and the negative electrode. In addition to the above configuration, a separator that separates the positive electrode and the negative electrode, an exterior body that stores them, and a housing can be provided. The internal structure of the battery other than the above is not particularly limited, and any conventionally known structure can be adopted. For example, a revolving electrode group may be formed by rotating a sheet-like positive electrode, a separator, and a negative electrode, or a positive electrode, a separator, and a negative electrode may be sequentially stacked to form a stacked electrode group. Further, the outer shape of the battery is not particularly limited, and any shape such as a cylindrical shape, a square shape, a coin shape, and a sheet shape can be adopted. Such a polyvalent ion battery may be a primary battery that only discharges, or a secondary battery that can be charged and discharged.

In the polyvalent ion battery of the present embodiment, the polyvalent metal cation is preferably magnesium ion (Mg ²⁺ ), calcium ion (Ca ²⁺ ), or aluminum ion (Al ³⁺ ). Of these, magnesium ions are particularly preferred. Since magnesium has a base reduction potential, a battery having a large electromotive force can be formed by combining with the molten salt according to Embodiment 1 having a wide potential window. Moreover, since magnesium is abundant in resources, it is preferable from the viewpoint of battery manufacturing cost. Further, magnesium has a remarkably high melting point compared to lithium, sodium, and the like, and therefore is a preferable material from the viewpoint of battery safety.

  The operating temperature of the multivalent ion battery of the present embodiment is preferably 60 ° C. or higher and 300 ° C. or lower. In such a temperature range, by making a battery that performs charging and discharging, the electrode reaction rate accompanying charging and discharging can be dramatically increased, and the high conductivity of the molten salt according to Embodiment 1 is maximized. Can be used.

<Positive electrode>
In the positive electrode of the present embodiment, when the battery is discharged, a reduction reaction involving a polyvalent metal cation occurs. When the polyvalent metal cation is magnesium ion, for example, MgFeSiO ₄ , MgNiSiO ₄ or the like can be used as the positive electrode active material. In addition, for example, a composite metal oxide containing magnesium and a transition metal, a composite metal sulfide containing magnesium and a transition metal, or the like having a site capable of inserting and releasing magnesium ions in the crystal may be employed. it can. As described above, if the positive electrode active material is a material capable of inserting and releasing polyvalent metal cations, the polyvalent ion battery of this embodiment can be used as a secondary battery.

  The positive electrode of the present embodiment can typically include a conductive additive and a binder in addition to the positive electrode active material. And a positive electrode active material and a conductive support agent are adhere | attached with a binder, and an electrode can be comprised. Further, for example, these may be fixed to a current collector core made of a metal such as aluminum to form an electrode.

  The conductive auxiliary agent only needs to be conductive, and a conventionally known conductive auxiliary agent can be used without any particular limitation. For example, acetylene black, ketjen black, vapor-grown carbon fiber (VGCF), natural graphite, or the like can be used. Moreover, the content rate of the conductive support agent in a positive electrode can be made into about 1 mass%-about 30 mass%, for example, Preferably it can be 1 mass% or more and 20 mass% or less, More preferably, it is 1 mass. % To 10% by mass.

  Any binder can be used as long as it can fix the positive electrode active material and the conductive additive, and any conventionally known binder can be used without any particular limitation. For example, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), polyamide resin, polyimide resin, or the like can be used. The content of the binder in the positive electrode can be, for example, about 1% by mass to 20% by mass, preferably 1% by mass to 10% by mass, and more preferably 1% by mass. % Or more and 5% by mass or less.

  As the current collector core, for example, a sheet-like metal foil, a punching metal, a metal foam, or the like made of a metal material that can withstand the positive electrode potential can be used without any particular limitation.

<Negative electrode>
In the negative electrode of the present embodiment, when the battery is discharged, an oxidation reaction involving polyvalent metal cations, that is, ionization of the polyvalent metal occurs. Moreover, when the multivalent ion battery of this Embodiment is a secondary battery, precipitation of a polyvalent metal cation occurs at the time of charge. This is realized by including the molten salt according to Embodiment 1 in which the multivalent ion battery of the present embodiment enables the precipitation and dissolution of the multivalent metal.

The negative electrode of the present embodiment is composed of a negative electrode active material. As the negative electrode active material, a polyvalent metal, an alloy composed of a polyvalent metal and another metal, or the like can be used. When the polyvalent metal cation is magnesium ion, for example, magnesium (Mg), magnesium lead alloy (Mg ₂ Pb), magnesium zinc alloy (MgZn), magnesium tin alloy (Mg ₂ Sn), magnesium aluminum alloy (Mg) ₁₇ Al ₁₂ ), magnesium bismuth alloy (Mg ₃ Bi ₂ ), magnesium gallium alloy (Mg ₅ Ga ₂ ), magnesium antimony alloy (Mg ₃ Sb ₂ ), magnesium silicon alloy (Mg ₂ Si), etc. can be adopted. . The electrode shape is not particularly limited, and may be a plate shape, a sheet shape, or the like. The electrode can also be a porous body.

<Embodiment 3: Air battery>
Hereinafter, an air battery according to Embodiment 3 of the present invention will be described.

  The air battery according to the present embodiment includes a positive electrode, a negative electrode, and an electrolyte. The electrolyte includes a molten salt containing an amide anion represented by the above formula (1), an alkaline earth metal cation, and an alkali metal cation. The reaction is a polyvalent ion battery involving an oxygen reduction reaction at the positive electrode and an oxidation reaction involving the polyvalent metal cation at the negative electrode. That is, it differs from the multivalent ion battery according to Embodiment 2 in that the positive electrode is an air electrode and the positive electrode active material is oxygen. In addition, as an electrolyte and a negative electrode, the structure similar to what was demonstrated in the multivalent ion battery of Embodiment 2 is employable.

  Since the air battery of the present embodiment includes the electrolyte containing the molten salt according to the first embodiment, the operating temperature can be set to 60 ° C to 300 ° C. Thereby, the influence of the moisture in the air which was a problem in the conventional air battery can be removed, and the reaction efficiency can be dramatically increased. The operating temperature is more preferably 80 ° C. or higher and 300 ° C. or lower, and particularly preferably 100 ° C. or higher and 300 ° C. or lower.

<Positive electrode (air electrode)>
The positive electrode of the present embodiment is a reaction field where a reduction reaction of oxygen, which is a positive electrode active material, is performed when the battery is discharged, and is also called an air electrode. The air electrode is typically a conductive material,
Provided with catalyst material, current collector core material, etc. Furthermore, a material capable of storing a polyvalent metal cation may be employed. By adopting such a material, it is possible to suppress a decrease in reaction efficiency due to accumulation of reaction products of polyvalent metal cations at the air electrode, which was a problem in conventional air batteries.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, this invention is not limited to these.

<Production of molten salt>
(1) Preparation of reagents As molten salt, Mg (TFSA) ₂ (purity 99.9% or more, manufactured by Kishida Chemical), Li (TFSA) (purity 99.0% or more, manufactured by Morita Chemical Co., Ltd.), K (FSA) (Purity 99% or more, manufactured by Mitsubishi Materials Electronic Chemicals) was prepared. In addition, Mg (TFSA) ₂ and Li (TFSA) were used after being vacuum-dried at 120 ° C. for 12 hours and K (FSA) for 48 hours at 80 ° C. after opening.

Other reagents necessary for the synthesis of the molten salt include Rb ₂ CO ₃ (purity 99.0% or more, Sigma-Aldrich), Cs ₂ CO ₃ (purity 99.9% or more, Sigma-Aldrich) ), H (TFSA) (purity 99.0% or more, manufactured by Morita Chemical Industries), respectively. And according to the following procedures, M (TFSA) molten salt was obtained. M represents Rb or Cs.

M ₂ CO ₃ and H (TFSA) are weighed in a glove box under an argon atmosphere, and then dissolved in an ethanol solvent in a fume hood, and the reaction according to the following chemical reaction formula (2) is carried out in the solvent. Made progress. At this time, the pH of the solution was sequentially confirmed using a pH test paper so that one of them would not become excessive, and an operation for appropriately maintaining neutralization was performed. In addition, commercially available ethanol (purity 99%) was used.

M ₂ CO ₃ + 2H (TFSA) → 2M (TFSA) + CO ₂ + H ₂ O (2)
Thereafter, the solvent was removed by an evaporator to obtain white coarse crystal powder. The crude crystal powder was vacuum-dried at 90 ° C. The crude crystal powder thus obtained was dissolved again in ethanol to obtain a saturated solution, and trifluorobenzene was added to the solution to reprecipitate crystals. Subsequently, suction filtration was performed using an evaporator to obtain a white crystalline powder.

  Thereafter, the crystal powder was vacuum-dried at room temperature for 12 hours, and then vacuum-dried at 90 ° C. for 12 hours. Next, the crystal powder was pulverized, the particle size was adjusted, and vacuum dried again at 90 ° C. for 12 hours to obtain high-purity M (TFSA).

Mg (TFSA) ₂ obtained as described above, Li (TFSA), K (FSA), Rb (TFSA) and Cs (TFSA) are mixed at a predetermined molar ratio, and the above formula (1) A molten salt containing an amide anion represented by the following formula, an alkaline earth metal cation and an alkali metal cation was prepared.

<Experimental example 1: Mg (TFSA) _2- Cs (TFSA)>
First, various characteristics required as a battery electrolyte were evaluated for each molten salt obtained by mixing Mg (TFSA) ₂ and Cs (TFSA) at a predetermined molar ratio. In the following description, such a molten salt is also referred to as “Mg (TFSA) ₂ —Cs (TFSA) binary molten salt” or the like.

(1) Measurement of thermal decomposition temperature The thermal decomposition temperature of Mg (TFSA) ₂ -Cs (TFSA) binary molten salt obtained by mixing Mg (TFSA) ₂ and Cs (TFSA) at 50:50 (molar ratio). , And was measured using a thermal analyzer (product name “DTG-60H”, manufactured by Shimadzu Corporation). The measurement was performed in an argon (Ar) atmosphere, and the scanning speed was 5 K / min. Further, as a reference test, the same measurement was performed for each molten salt of Mg (TFSA) ₂ and Cs (TFSA). The results are shown in Table 1 and FIG.

As shown in Table 1 and FIG. 1, Mg (TFSA) ₂ -Cs (TFSA) binary molten salt mixed at Mg (TFSA) ₂ : Cs (TFSA) = 50: 50 (molar ratio) is 601K ( 328 ° C.).

(2) Preparation of phase diagram Mg (TFSA) ₂ -Cs (TFSA) binary molten salt in which Mg (TFSA) ₂ and Cs (TFSA) are mixed in a molar ratio of 10:90 to 80:20. Were respectively measured, and differential scanning calorimetry was performed using a differential scanning calorimeter (product name “DSC60”, manufactured by Shimadzu Corporation). From the results, Mg (TFSA) ₂ -Cs (TFSA) binary molten salt A state diagram was created. FIG. 2 shows a phase diagram of the Mg (TFSA) ₂ —Cs (TFSA) binary molten salt. Table 2 shows the relationship between the mixing molar ratio and the melting point.

As shown in Table 2 and FIG. 2, this binary molten salt has a wide liquidus range in the region where Mg (TFSA) ₂ : Cs (TFSA) = 0: 100 to 50:50 (molar ratio). It was confirmed that That is, a molten salt containing an alkaline earth metal cation and an alkali metal cation at a molar ratio within this range is suitable for a wide range of applications as an electrolyte for batteries. Further, it was confirmed that the molten salt forms a eutectic near the composition where Mg (TFSA) ₂ : Cs (TFSA) = 10: 90, and shows a particularly wide liquid phase range around this composition. . Therefore, from the viewpoint of the liquid phase range, the Mg (TFSA) ₂ —Cs (TFSA) binary molten salt is Mg (TFSA) ₂ : Cs (TFSA) = 1: 99 to 30:70 (molar ratio). Preferably there is.

(3) Measurement of Viscosity Mg (TFSA) ₂ and Cs (TFSA) mixed at a molar ratio of Mg (TFSA) ₂ : Cs (TFSA) = 10: 90, 20:80, 0: 100 TFSA) ₂ -Cs (TFSA) binary molten salt was prepared, and the viscosity was measured using a viscometer (product name “DV-II + PRO”, manufactured by Brookfield Engineering laboratories). The results are shown in Table 3 and FIG. The viscosity was measured in air.

As shown in Table 3 and FIG. 3, it was confirmed that as the mixing ratio (molar ratio) of Cs (TFSA) increases and the temperature rises, the viscosity decreases. Moreover, Mg (TFSA) ₂ and Cs (TFSA) and a, Mg in a molar ratio _{(TFSA) 2: Cs (TFSA} ) = 10: 90,20: mixed Mg as _{80 (TFSA) 2 -Cs (TFSA} ) two It was confirmed that any of the original molten salts had a sufficiently low viscosity as a battery electrolyte in the measured temperature range.

(4) Measurement of electrical conductivity The resistance value of the same molten salt as the three types of molten salt for which the viscosity was measured was measured by the AC impedance method, and the electrical conductivity of the molten salt was calculated by the following mathematical formula (3). . Here, an electrochemical measurement system (product name “HZ-3000”, manufactured by Hokuto Denko) was used for measuring the resistance value. In FIG. 4, the schematic diagram of the glass cell used for the measurement of resistance value is shown. This glass cell was made of Pyrex (registered trademark) glass, and the cell constant was 10.211 cm ⁻¹ . This cell constant is a value obtained using a KCl solution whose resistivity is known. The measurement results of conductivity are shown in Table 4 and FIG.

K = χ / R (3)
In Equation (3), K represents conductivity (S / cm), χ represents cell constant (cm ⁻¹ ), and R represents resistance (Ω).

As shown in Table 4 and FIG. 5, it was confirmed that the conductivity increased as the mixing ratio (molar ratio) of Cs (TFSA) increased and the temperature increased. Moreover, Mg (TFSA) and ₂ and Cs (TFSA), in a molar ratio of 10: 90, 20: mixed Mg as _{80 (TFSA) 2 -Cs (TFSA} ) binary molten salt was measured temperature In the range, it was confirmed that all had sufficiently high conductivity as the electrolyte for batteries.

(5) the measurement of the potential window Mg (TFSA) ₂ and Cs (TFSA), Mg in a molar ratio _{(TFSA) 2: Cs (TFSA} ) = 10: Mg mixed as 90 (TFSA) ₂ -Cs (TFSA) The potential window of this molten salt was determined by measuring the cyclic voltammetry of the binary molten salt. A schematic diagram of the electrolytic cell used for the measurement is shown in FIG. In this measurement, the working electrode (WE) in FIG. 6 is a nickel wire (reduction side) or glassy carbon (sometimes referred to as “GC”) (oxidation side), and the counter electrode (CE). And the reference electrode (RE) is a magnesium ribbon. For the measurement, an electrochemical measurement system (product name “HZ-3000”, manufactured by Hokuto Denko) was used, the scanning speed was 10 mV / s, and the measurement temperature was 473 K (200 ° C.). The measurement results are shown in FIGS.

7 and FIG. 8, Mg (TFSA) ₂ and Cs (TFSA) and a, Mg in a molar ratio _{(TFSA) 2: Cs (TFSA} ) = 10: Mg mixed as 90 (TFSA) ₂ -Cs The (TFSA) binary molten salt has a reduction limit of -1.83 V (vs. RE) and an oxidation limit of 3.18 V (vs. RE). That is, it was confirmed that it has a very wide potential window of 5.01V. Therefore, it is possible to construct a battery system having a large electromotive force by using this molten salt as a battery electrolyte.

(6) Constant potential electrolysis test I
Regarding Mg (TFSA) ₂ -Cs (TFSA) binary molten salt in which Mg (TFSA) ₂ and Cs (TFSA) are mixed at a molar ratio of Mg (TFSA) ₂ : Cs (TFSA) = 10: 90, Whether or not magnesium could be precipitated and dissolved at a potential nobler than the reduction limit of -1.83 V (vs. RE) was confirmed by a constant potential electrolysis test. As in the above, the electrolytic cell used was a nickel wire for the working electrode and a magnesium ribbon for the counter electrode and the reference electrode. The measurement temperature was 473 K (200 ° C.), and a constant potential of −1.75 V (vs. RE) was maintained for 1.5 hours. After 1.5 hours, the working electrode was collected, and the electrode surface was analyzed by energy dispersive X-ray spectroscopy (EDX). The analysis results are shown in Table 5. For the analysis, an EDX apparatus (product name “EDAX Genesis APEX2”, manufactured by AMETEK) was used.

  As shown in Table 5, it was confirmed that the atomic concentration of magnesium on the electrode surface after constant potential electrolysis was higher than that of cesium. In the molten salt, magnesium ion: cesium ion = 10: 90, and considering that magnesium ion is far less than cesium ion, it is suggested that magnesium may be precipitated and dissolved on the electrode surface. Is done. That is, it is considered that the molten salt can be used as an electrolyte of a magnesium ion battery (multivalent ion battery).

(7) Electrochemical measurement Except for changing the working electrode (WE) to lead (Pb), Mg (TFSA) ₂ and Cs (TFSA) were converted in the same manner as in the above-mentioned “(5) Measurement of potential window”. Cyclic voltammetry (reduction side only) of Mg (TFSA) ₂ -Cs (TFSA) binary molten salt mixed at a molar ratio of Mg (TFSA) ₂ : Cs (TFSA) = 10: 90 was measured. The result is shown in FIG. As shown in FIG. 9, a peak derived from precipitation and dissolution of metal was observed in the vicinity of −1.1 V (vs. RE).

Here, the reason for using lead is that although lead forms an alloy with magnesium but does not form an alloy with cesium, Mg (TFSA) ₂ -Cs (TFSA) binary molten salt is used as an electrolyte. This is because an alloy of magnesium and lead (for example, Mg ₂ Pb) is promising as a negative electrode active material.

(8) Constant potential electrolysis test II
In order to confirm whether or not the peak in the vicinity of −1.1 V is derived from the precipitation and dissolution of magnesium, a constant potential electrolysis test was performed. Similarly to the above, a cell having lead as a working electrode was used as an electrolytic cell, and a constant potential of −1.1 V (vs. RE) was maintained at 473 K (200 ° C.) for 15 hours. After 15 hours, the working electrode was collected and the surface of the electrode was analyzed by the EDX method. The results are shown in Table 6.

  As shown in Table 6, it was confirmed that the atomic concentration of magnesium on the electrode surface after constant potential electrolysis was higher than that of cesium. Therefore, it was suggested that the peak in the vicinity of −1.1 V (vs. RE) in the cyclic voltammetry measurement described above was derived from precipitation and dissolution of magnesium.

(9) Summary As described above, from the result of “Experimental Example 1”, Mg (TFSA) ₂ —Cs, which is a molten salt containing the amide anion represented by the above formula (1), the alkaline earth metal cation and the alkali metal cation. It was confirmed that the (TFSA) binary molten salt has the following characteristics.
(I) It has a wide liquid phase range of 395 K (122 ° C.) to 601 K (328 ° C.).
(Ii) It has a viscosity and conductivity suitable as an electrolyte for a battery.
(Iii) It has a very wide potential window of 5.01V.
(Iv) Magnesium, which is a polyvalent metal, can be precipitated and dissolved.

<Experimental example 2: Mg (TFSA) _2- Li (TFSA) -Cs (TFSA)>
Mg (TFSA) ₂ and Li a (TFSA) and the Cs (TFSA), in a molar ratio of 10: 1: 89,10: 5: 85,10: 10: mixed Mg as 80 (TFSA) ₂ -Li (TFSA ) -Cs (TFSA) ternary molten salts were prepared and subjected to electrochemical measurements.

(1) Electrochemical measurement The electrolytic cell used for the measurement here is represented by the schematic diagram of FIG. 6 in the same manner as described above. The working electrode (WE) is a nickel wire, the counter electrode (CE), and the reference. The electrode (RE) was a lithium ribbon. For the measurement, an electrochemical measurement system (product name “HZ-3000”, manufactured by Hokuto Denko) was used, the scanning speed was 10 mV / s, and the measurement temperature was 443 K (170 ° C.). The measurement results are shown in FIG.

  As shown in FIG. 10, a peak considered to be derived from precipitation and dissolution of magnesium was observed at 0.03 V (vs. RE). Further, it was confirmed that as the mixing ratio (molar ratio) of Li (TFSA) increases, the current density increases and the overvoltage of magnesium precipitation and dissolution decreases. That is, it is suggested that Li (TFSA) contributes to precipitation and dissolution of magnesium.

(2) Constant-potential electrolysis test Next, a constant-potential electrolysis test was performed using the above-mentioned Mg (TFSA) ₂ -Li (TFSA) -Cs (TFSA) ternary molten salt, and 0.03 V (vs. RE). It was confirmed whether or not the peak observed in Fig. 1 was derived from the precipitation and dissolution of magnesium. The electrolytic cell used for the measurement is represented by the schematic diagram of FIG. 6 as described above, and the working electrode (WE) is a nickel wire, and the counter electrode (CE) and the reference electrode (RE) are lithium ribbons. . Then, a constant potential of 0.03 V (vs. RE) was maintained at 443 K (170 ° C.) for 3 hours. After 3 hours, the working electrode was collected and analyzed by X-ray diffraction (XRD) method to identify elements on the electrode surface. The results are shown in FIG. For the analysis, an XRD apparatus (product name “Ultima IV”, manufactured by Rigaku) was used.

  As shown in FIG. 11, the peak derived from magnesium is observed from the electrode after the test, and the intensity of the peak derived from magnesium increases as the mixing ratio (molar ratio) of Li (TFSA) increases. It was confirmed. From this result, it is preferable that the molten salt containing the amide anion represented by the above formula (1), the alkaline earth metal cation and the alkali metal cation contains lithium ions.

<Experimental example 3: Mg (TFSA) _2- Rb (TFSA)>
Various characteristics required as a battery electrolyte for Mg (TFSA) ₂ -Rb (TFSA) binary molten salt molten salt obtained by mixing Mg (TFSA) ₂ and Rb (TFSA) at a predetermined molar ratio Was evaluated.

(1) the thermal decomposition temperature of the measurement Mg (TFSA) ₂ and Rb (TFSA) and a 50:50 Mg mixed (molar ratio) (TFSA) ₂ -Rb (TFSA) binary molten salt thermal decomposition temperature The measurement was performed in the same manner as “(1) Measurement of thermal decomposition temperature” in “Experimental Example 1”. The results are shown in Table 7 and FIG.

As shown in Table 7 and FIG. _{12, Mg (TFSA) 2:} Rb (TFSA) = 50: 50 Mg mixed (molar _{ratio) (TFSA) 2 -Rb (TFSA} ) binary molten salt, 587K ( 314 ° C.).

(2) Preparation of phase diagram Mg (TFSA) ₂ -Rb (TFSA) binary molten salt in which Mg (TFSA) _{2 and} Rb (TFSA) are mixed in a molar ratio of 100: 0 to 0: 100. Were prepared in the same manner as in “(2) Creation of phase diagram” in “Experimental example 1”, and a phase diagram of Mg (TFSA) ₂ -Rb (TFSA) binary molten salt was created. FIG. 13 shows a phase diagram of the binary molten salt of Mg (TFSA) ₂ —Rb (TFSA). Table 8 shows the relationship between the mixing molar ratio and the melting point.

As shown in Table 8 and FIG. 13, this binary molten salt has a wide liquidus range in a region where Mg (TFSA) ₂ : Rb (TFSA) = 0: 100 to 50:50 (molar ratio). It was confirmed that That is, a molten salt containing an alkaline earth metal cation and an alkali metal cation at a molar ratio within this range is suitable for a wide range of applications as an electrolyte for batteries. Further, it was confirmed that the molten salt formed a eutectic near the composition of Mg (TFSA) ₂ : Rb (TFSA) = 30: 70 and showed a particularly wide liquid phase range centering on this composition. Therefore, from the viewpoint of the liquid phase range, the Mg (TFSA) ₂ -Rb (TFSA) binary molten salt is Mg (TFSA) ₂ : Rb (TFSA) = 1: 99 to 30:70 (molar ratio). Preferably there is.

(3) Viscosity Measurement Mg (TFSA) ₂ and Rb (TFSA) mixed in a molar ratio of Mg (TFSA) ₂ : Rb (TFSA) = 10: 90, 20:80, 0: 100 TFSA) ₂ -Rb (TFSA) binary molten salts were respectively prepared, and the viscosity was measured in the same manner as “(3) Measurement of viscosity” in “Experimental example 1”. The results are shown in FIG. FIG. 14 is an Arrhenius plot of the viscosity that shows the relationship between the common logarithm of the viscosity and the inverse of the temperature.

As shown in FIG. 14, it was confirmed that the viscosity decreases as the mixing ratio (molar ratio) of Rb (TFSA) increases and the temperature increases. Moreover, Mg (TFSA) ₂ and Rb (TFSA) and a, Mg in a molar ratio _{(TFSA) 2: Rb (TFSA} ) = 10: 90,20: mixed Mg as _{80 (TFSA) 2 -Rb (TFSA} ) two It was confirmed that any of the original molten salts had a sufficiently low viscosity as a battery electrolyte in the measured temperature range.

(4) Measurement of electrical conductivity The electrical conductivity was measured in the same manner as in “(4) Measurement of electrical conductivity” in “Experimental example 1” for the three types of molten salts for which the viscosity was measured. The results are shown in FIG. FIG. 15 is an Arrhenius plot of conductivity showing the relationship between the common logarithm of conductivity and the inverse of temperature.

As shown in FIG. 15, it was confirmed that the conductivity increased as the mixing ratio (molar ratio) of Rb (TFSA) increased and the temperature increased. Further, Mg (TFSA) ₂ -Rb (TFSA) binary molten salt in which Mg (TFSA) _{2 and} Rb (TFSA) are mixed at a molar ratio of 10:90 and 20:80 is measured at the temperature measured. In the range, it was confirmed that all had sufficiently high conductivity as the electrolyte for batteries.

(5) the measurement of the potential window Mg (TFSA) ₂ and Rb (TFSA), Mg in a molar ratio _{(TFSA) 2: Rb (TFSA} ) = 10: Mg mixed as 90 (TFSA) ₂ -Rb (TFSA) The potential window of this molten salt was determined by measuring the cyclic voltammetry of the binary molten salt. Measurement conditions are the same as “(5) Measurement of potential window” in “Experiment 1”. The results are shown in FIG. 16 and FIG.

As shown in FIG. 16 and FIG. 17, Mg (TFSA) ₂ and Rb (TFSA) are mixed at a molar ratio of Mg (TFSA) ₂ : Rb (TFSA) = 10: 90, Mg (TFSA) ₂ -Rb The (TFSA) binary molten salt has a reduction limit of -1.60 V (vs. RE) and an oxidation limit of 3.20 V (vs. RE). That is, it was confirmed that it has a very wide potential window of 4.80V. Therefore, it is possible to construct a battery system having a large electromotive force by using this molten salt as a battery electrolyte.

(6) Electrochemical measurement Except for changing the working electrode (WE) to magnesium (Mg), Mg (TFSA) ₂ and Rb (TFSA) were converted in the same manner as in the above-mentioned “(5) Measurement of potential window”. Cyclic voltammetry of Mg (TFSA) ₂ -Rb (TFSA) binary molten salt mixed at a molar ratio of Mg (TFSA) ₂ : Rb (TFSA) = 10: 90 was measured. The results are shown in FIG.

As shown in FIG. 18, a reduction current was observed in the vicinity of −1.2 V (vs. RE). That is, it is suggested that magnesium is precipitated around −1.2 V (vs. RE). Therefore, it is considered that this Mg (TFSA) ₂ -Rb (TFSA) binary molten salt can be used as an electrolyte of a magnesium ion battery (multivalent ion battery).

(7) Summary As described above, from the result of “Experimental Example 3”, Mg (TFSA) ₂ -Rb, which is a molten salt containing the amide anion represented by the above formula (1), the alkaline earth metal cation and the alkali metal cation. It was confirmed that the (TFSA) binary molten salt has the following characteristics.
(I) It has a wide liquid phase range of 420 K (147 ° C.) to 587 K (314 ° C.).
(Ii) It has a viscosity and conductivity suitable as an electrolyte for a battery.
(Iii) It has a very wide potential window of 4.80V.
(Iv) Magnesium, which is a polyvalent metal, can be precipitated and dissolved.

<Experimental Example 4: Mg (TFSA) _2- K (FSA)>
Evaluation of various characteristics required for battery electrolytes for Mg (TFSA) ₂ -K (FSA) binary molten salt obtained by mixing Mg (TFSA) ₂ and K (FSA) at a predetermined molar ratio Was done.

(1) Measurement of melting point The melting point of Mg (TFSA) ₂ -K (FSA) binary molten salt in which Mg (TFSA) ₂ and K (FSA) are mixed at respective molar ratios is expressed as “Experimental Example 1”. Measurement was performed in the same manner as (2) Creation of phase diagram. The result is shown in FIG.

As shown in FIG. 19, it is confirmed that the Mg (TFSA) ₂ -K (FSA) binary molten salt mixed in each composition has a melting point of 361 K (88 ° C.) regardless of the composition (mixing molar ratio). It was done.

(2) the measurement of the potential window Mg (TFSA) ₂ and K (FSA), in a molar ratio _{Mg (TFSA) 2: K (} FSA) = 10: Mg mixed as 90 (TFSA) ₂ -K (FSA) The potential window of this molten salt was determined by measuring the cyclic voltammetry of the binary molten salt. The measurement conditions are the same as “(5) Measurement of potential window” in “Experiment 1” except that the measurement temperature is 383 K (110 ° C.). The results are shown in FIG. 20 and FIG.

20 and FIG. 21, Mg (TFSA) ₂ and K (FSA) and a, Mg in a molar ratio _{(TFSA) 2: K (FSA} ) = 10: Mg mixed as 90 (TFSA) ₂ -K The (FSA) binary molten salt has a reduction limit of -2.00 V (vs. RE) and an oxidation limit of 3.50 V (vs. RE). That is, it was confirmed that it has a very wide potential window of 5.50V. Therefore, it is possible to construct a battery system having a large electromotive force by using this molten salt as a battery electrolyte.

(3) Electrochemical measurement Except for changing the working electrode (WE) to magnesium (Mg), Mg (TFSA) ₂ and K (FSA) are changed in the same manner as in the above-mentioned “(2) Measurement of potential window”. Cyclic voltammetry of Mg (TFSA) ₂ -K (FSA) binary molten salt mixed at a molar ratio of Mg (TFSA) ₂ : K (FSA) = 10: 90 was measured. The results are shown in FIG.

As shown in FIG. 22, a reduction current was observed around −0.8 V (vs. RE). That is, it is suggested that magnesium is precipitated around −0.8 V (vs. RE). Therefore, it is considered that this Mg (TFSA) ₂ -K (FSA) binary molten salt can be used as an electrolyte of a magnesium ion battery (multivalent ion battery).

(4) Summary As described above, from the result of “Experimental Example 4”, Mg (TFSA) ₂ -K, which is a molten salt containing the amide anion represented by the above formula (1), the alkaline earth metal cation and the alkali metal cation. The (FSA) binary molten salt was confirmed to have the following characteristics.
(I) The melting point is 361 K (88 ° C.) regardless of the composition.
(Ii) It has a very wide potential window of 5.50V.
(Iii) Magnesium, which is a polyvalent metal, can be precipitated and dissolved.

  Although the embodiments and examples of the present invention have been described as described above, it is also planned from the beginning to appropriately combine the configurations of the above-described embodiments and examples.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  INDUSTRIAL APPLICABILITY The present invention can be used for batteries for all purposes, and is particularly suitable for large-sized batteries, automobile batteries, power storage devices for power leveling, power storage facilities associated with solar power generation and wind power generation, and the like. .

  1 electrolysis cell, 2 molten salt, 3 working electrode, 4 counter electrode, 5 reference electrode, 6 thermocouple, 7 heater, 8 exhaust port.

Claims (10)

A molten salt comprising an amide anion represented by the following formula (1), an alkaline earth metal cation and an alkali metal cation.

(In formula (1), X1 and X2 each independently represent a fluorine atom, a fluoromethyl group or a fluoroethyl group.)   The molten salt according to claim 1, wherein the alkaline earth metal cation is at least one of magnesium ion and calcium ion.   The molten salt according to claim 1 or 2, wherein the alkali metal cation is one or more metal ions selected from the group consisting of lithium ions, sodium ions, potassium ions, rubidium ions, cesium ions, and francium ions.   The molten salt according to any one of claims 1 to 3, wherein a ratio of the alkaline earth metal cation in the total cation contained in the molten salt is 0.01 or more and 0.50 or less in terms of molar ratio. The molten salt further includes one or more halide ions selected from the group consisting of fluoride ions, chloride ions, bromide ions, and iodide ions,
The molten salt according to any one of claims 1 to 4, wherein a proportion of the halide ions in the total anion contained in the molten salt is 0.001 or more and 0.10 or less in terms of molar ratio.   The electrolyte for batteries containing the molten salt in any one of Claims 1-5. A positive electrode, a negative electrode, and the electrolyte according to claim 6,
The discharge reaction is a multivalent ion battery involving a reduction reaction involving a polyvalent metal cation in the positive electrode and an oxidation reaction involving a polyvalent metal cation in the negative electrode. A positive electrode, a negative electrode, and the electrolyte according to claim 6,
The discharge reaction is a polyvalent ion battery, which is an air battery with an oxygen reduction reaction at the positive electrode and an oxidation reaction involving a polyvalent metal cation at the negative electrode.   The multivalent ion battery according to claim 7 or 8, which is a secondary battery that can be charged and discharged in a temperature range of 60 ° C or higher and 300 ° C or lower.   The multivalent ion battery according to claim 7, wherein the polyvalent metal cation is magnesium ion.

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