Boron-based magnesium salt, electrolyte, and secondary battery

Abstract

To provide a boron-based magnesium salt that offers excellent electrochemical activity when used for an electrolyte solution of a magnesium secondary battery, an electrolyte solution, and a secondary battery.SOLUTION: The present invention provides a boron-based magnesium salt represented by the formula 9: Mg[B(OR9)4]2. (In the formula 9, R9 independently represent a monovalent hydrocarbon group having an alkyl group optionally substituted with a halogen atom, and two or more of R9 may be linked to each other, forming a ring. Provided that all of four R9 groups within the molecule should not be identical).SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a boron-based magnesium salt, an electrolyte, and a secondary battery.

Background Art

[0002] The use of a boron-based magnesium salt (Magnesium organo-borate) is expected as an electrolyte for magnesium secondary batteries. As a method for producing a boron-based magnesium salt, Non-Patent Document 1 describes a method (Formula A) of reacting a magnesium borohydride salt with 8 equivalents or more of an alcohol using the magnesium borohydride salt as a substrate. In Formula A, R represents a fluoroalkyl group. Formula A: Mg(BH 4 ) + 8ROH → Mg[B(OR) 4 2

Prior Art Documents

Non-Patent Documents

[0003]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The present inventors have found that when a boron-based magnesium salt produced by the method described in Non-Patent Document 1 is used as an electrolyte for a magnesium secondary battery, the desired electrochemical activity may not be obtained.

[0005] Therefore, an object of the present invention is to provide a boron-based magnesium salt, an electrolyte, and a secondary battery that exhibit excellent electrochemical activity when used as an electrolyte for a magnesium secondary battery.

Means for Solving the Problems

[0006] As a result of intensive studies to achieve the above problems, the present inventor has found that the above problems can be achieved by the following configuration.

[0007] [1] A boron-based magnesium salt represented by the following formula 9: Mg[B(OR 9 ) 4 2 . [2] The boron-based magnesium salt according to [1], wherein the carbon number of the group represented by the above R 9 is 1 to 6. [3] The boron-based magnesium salt according to [1], wherein at least one of the groups represented by the above R 9 is a group represented by the following formula 1R: *-L-C(R 0 ) n (CX 3 ) 3-n . [4] An electrolytic solution containing the boron-based magnesium salt according to any one of [1] to [3] and a solvent. [5] The electrolytic solution according to [4], wherein the solvent contains a compound represented by the following formula 11: R 11 (OC 2 H 4 ) p OR 12 . [6] A secondary battery including the electrolytic solution according to [4] or [5]. [Advantages of the Invention]

[0008] According to the present invention, it is possible to provide a boron-based magnesium salt, an electrolytic solution, and a secondary battery that exhibit excellent electrochemical activity when used in the electrolytic solution of a magnesium secondary battery. [Brief Description of the Drawings]

[0009]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0010] Hereinafter, the present invention will be described in detail. The description of the constituent elements described below may be made based on typical embodiments of the present invention, but the present invention is not limited to such embodiments. In this specification, a numerical range represented by "~" means a range including the numerical values described before and after "~" as the lower limit value and the upper limit value.

[0011] The present inventors have earnestly studied the reason why when a boron-based magnesium salt produced by the method described in Non-Patent Document 1 is applied to the electrolyte of a magnesium secondary battery, the desired electrochemical activity may not be obtained. Specifically, the inventors have repeatedly and painstakingly conducted elaborate experiments in which the boron-based magnesium salt is synthesized multiple times by the reaction represented by Formula A, and the electrochemical activity of each of the obtained products is evaluated.

[0012] As a result, it has been found that even though the electrochemical activity is evaluated by the same method using the products synthesized by the same method, there are variations in the results, and in some cases, the desired electrochemical activity cannot be obtained at all.

[0013] The present inventors analyzed the obtained products from various viewpoints in order to study the above-mentioned cause. As a result, it has been found that the reaction products obtained by the reaction represented by Formula A may contain impurities other than the boron-based magnesium salt. From this, the present inventors speculated that the variation in electrochemical activity is caused by the impurities contained in the reaction products.

[0014] The inventor further investigated the origin of the above impurities that may affect the electrochemical activity. As a result, it was found that the above impurities are likely to originate from the manufacturing process of magnesium borohydride used as a substrate in the reaction of formula A.

[0015] Based on the above findings, the inventor conceived that if a boron-based magnesium salt is synthesized by a synthetic route that does not rely on magnesium borohydride (without using magnesium borohydride), when it is used in an electrolyte, better electrochemical activity can be obtained.

[0016] As a result of investigations based on this idea, according to the method of reacting a magnesium source compound represented by formula 1 described below with a boron source compound represented by formula 2 described below to obtain a boron-based magnesium salt represented by formula 3, the inventor found that excellent electrochemical activity can be obtained when the resulting reaction product is used in an electrolyte, and thus completed the present invention.

[0017] [Method for producing boron-based magnesium salt] Hereinafter, the method for producing a boron-based magnesium salt according to an embodiment of the present invention (hereinafter, also referred to as "the present production method") will be described in detail. The present production method includes the following step 1, and preferably further includes step 2 and / or step 3 described below.

[0018] (Step 1) The method for producing a boron-based magnesium salt according to an embodiment of the present invention involves reacting a magnesium source compound represented by formula 1: Mg(OR 1 ) 2 with a boron source compound represented by formula 2: B(OR 2 ) 3 to obtain a reaction product containing a boron-based magnesium salt represented by formula 3: Mg[B(OR 1 )(OR 2 ) 3 2 (hereinafter, also referred to as "step 1").

[0019] [Chemical formula] ​

[0020] Here, in Formula 1 and Formula 3, R 1 is a monovalent hydrocarbon group having an alkyl group which may be substituted with a halogen atom, and a plurality of Rs in the molecule 1 may be the same or different. In Formula 2 and Formula 3, R 2 is a hydrocarbon group having an alkyl group which may be substituted with a halogen atom, and a plurality of Rs in the molecule 2 may be the same or different, and any two or more Rs 2 may be bonded to each other to form a ring.

[0021] Here, the "monovalent hydrocarbon group having an alkyl group which may be substituted with a halogen atom" includes, for example, a group having an alkyl group which may be substituted with a halogen atom as a partial structure of the monovalent hydrocarbon group. In that case, as a whole, it is a monovalent hydrocarbon group, and means a group having, as a partial structure, an alkyl group which may be substituted with a halogen atom in a part thereof, and this includes an alkyl group substituted with a halogen atom itself (for example, a perfluoroalkyl group, etc.).

[0022] The reaction of Step 1 can typically be represented by the following Formula S1. Formula S1: Mg(OR 1 ) 2 + 2B(OR 2 ) 3 → Mg[B(OR 1 )(OR 2 ) 3 ) 2

[0023]

Chemical formula

[0024] It is presumed that a boron-based magnesium salt is obtained by the reaction represented by the above Formula S1 because boron (B(III)) has a stronger Lewis acidity (higher positive charge density) than magnesium (Mg(II)). When ions with different Lewis acidities coexist in the same system, the ion species with stronger Lewis acidity attracts the negative charge more strongly. Therefore, boron with stronger Lewis acidity attracts the anion species more strongly, and the anion species interacting with magnesium is pulled to the boron compound side. As a result, it is presumed that the target boron-based magnesium salt is obtained.

[0025] As the reaction conditions for the reaction represented by Formula S1, in an inert gas atmosphere (an argon atmosphere is preferred), the magnesium source compound and the boron source compound are dissolved in a solvent to prepare a solution, and the prepared solution may be held at 10 to 40 °C for 30 minutes to 48 hours. At this time, the solvent to be used is not particularly limited as long as it does not contain water. Generally, chain ethers, cyclic ethers, etc. are preferred.

[0026] Examples of the cyclic ether include 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, propylene oxide, 1,2-butylene oxide, 1,4-dioxane, 1,3,5-trioxane, furan, 2-methylfuran, 1,8-cineole, crown ether, and derivatives thereof. Tetrahydrofuran is preferred.

[0027] Examples of the chain ether include 1,2-dimethoxyethane, diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, dihexyl ether, ethyl vinyl ether, butyl vinyl ether, methyl phenyl ether, ethyl phenyl ether, butyl phenyl ether, pentyl phenyl ether, methoxytoluene, benzyl ethyl ether, diphenyl ether, dibenzyl ether, o-dimethoxybenzene, 1,2-diethoxyethane, 1,2-dibutoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, 1,1-dimethoxymethane, 1,1-diethoxyethane, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl, and derivatives thereof. As the chain ether, a specific ether compound described later or the like is preferable, and among them, 1,2-dimethoxyethane (DME) is preferable.

[0028] In Step 1, the charging amounts of the magnesium source compound and the boron source compound are not particularly limited. However, in terms of the yield of the boron-based magnesium salt being more likely to increase, the molar ratio (boron source compound / magnesium source compound) of the amount (charging amount) of the boron source compound to the amount (charging amount) of the magnesium source compound in the system is preferably 1.80 to 2.80, and more preferably 2.01 to 2.60.

[0029] When the amount of the boron source compound is in excess relative to the magnesium source compound, after the reaction, by removing the excess boron source compound from the reaction product by solvent washing, it is preferable in that the boron-based magnesium salt can be more easily purified to a high purity.

[0030] Typically, since the boron-based magnesium salt decomposes when it comes into contact with water, it has been difficult to purify it to a high purity by recrystallization. Recrystallization requires operations such as heating, cooling, and adding a solvent, and there is a possibility that water may be mixed into the system during these operations. Also, in the conventional synthesis method using magnesium hydride as a substrate, since many of the impurities are salts of magnesium hydride or the like, it has been very difficult to separate them from the boron-based magnesium salt. As described above, this production method is also excellent in that the boron-based magnesium salt can be purified to a high purity only by washing the reaction product with a solvent.

[0031] In Formula 1 and Formula 3, R 1 is a monovalent hydrocarbon group having an alkyl group which may be substituted with a halogen atom. The halogen atom is not particularly limited, and examples thereof include a fluorine atom (F), a chlorine atom (Cl), and an iodine atom (I). In terms of obtaining a more excellent effect of the present invention, a fluorine atom is preferable.

[0032] R 1Although there is no particular limitation on the total number of carbon atoms of the hydrocarbon group, generally, 1 or more and 20 or less are preferable, 10 or less are more preferable, 8 or less are still more preferable, 6 or less are particularly preferable, and 4 or less are most preferable.

[0033] Also, R 1 The hydrocarbon group of may be linear, branched, or cyclic, but linear or branched is preferable in terms of obtaining a boron-based magnesium salt having a more excellent effect of the present invention, and a linear or branched alkyl group is more preferable.

[0034] R 1 The hydrocarbon group of preferably has a linear or branched alkyl group having 1 to 10 carbon atoms in total and at least one or more hydrogen atoms substituted with a halogen atom (preferably a fluorine atom); more preferably has a linear or branched alkyl group having 1 to 8 carbon atoms in total and at least one or more hydrogen atoms substituted with a halogen atom (preferably a fluorine atom); still more preferably has a linear or branched alkyl group having 1 to 5 carbon atoms in total and at least one or more hydrogen atoms substituted with a halogen atom (preferably a fluorine atom); particularly preferably is an alkyl group itself having 1 to 4 carbon atoms in total and being linear or branched and substituted with a halogen atom (preferably a fluorine atom). R 1 When the hydrocarbon group of has 1 to 5 carbon atoms, it is preferable in terms of making the size of the anion of the boron-based magnesium salt smaller and improving the mobility of the cation.

[0035] R 1 When the hydrocarbon group of has an alkyl group substituted with a halogen atom (halogenated alkyl group), due to the electron-withdrawing property of the halogen atom, the electrons in the anion of the boron-based magnesium salt are more delocalized, and the oxidation resistance is further improved. R 1The number of alkyl halide groups in the hydrocarbon group is not particularly limited, and one or more are preferred. More preferably, all hydrogen atoms bonded to carbon atoms are substituted with alkyl halide groups.

[0036] Examples of the linear or branched alkyl group having 1 to 10 carbon atoms include the following groups. A methyl group having 1 carbon atom; An ethyl group having 2 carbon atoms; A propyl group having 3 carbon atoms, an isopropyl group; A butyl group having 4 carbon atoms, an isobutyl group, a tert-butyl group, a sec-butyl group; A pentyl group having 5 carbon atoms, a 1-methylbutyl group, a 2-methylbutyl group, a 3-methylbutyl group, a 1,1-dimethylpropyl group, a 2,2-dimethylpropyl group, a 1-ethylpropyl group; A hexyl group having 6 carbon atoms, a 1-methylpentyl group, a 2-methylpentyl group, a 3-methylpentyl group, a 4-methylpentyl group, a 1,1-dimethylbutyl group, a 1,2-dimethylbutyl group, a 1,3-dimethylbutyl group, a 1,4-dimethylbutyl group, a 2,3-dimethylbutyl group, a 2,2-dimethylbutyl group, a 3,3-dimethylbutyl group, a 1-ethylbutyl group, a 2-ethylbutyl group, a 1-ethyl-2-methyl-propyl group, a 1,1,2-trimethylpropyl group; A heptyl group having 7 carbon atoms, a 1-methylhexyl group, a 2-methylhexyl group, a 3-methylhexyl group, a 4-methylhexyl group, a 5-methylhexyl group, a 1,1-dimethylpentyl group, a 2,2-dimethylpentyl group, a 3,3-dimethylpentyl group, a 4,4-dimethylpentyl group, a 1,2-dimethylpentyl group, a 1,3-dimethylpentyl group, a 1,4-dimethylpentyl group, a 2,3-dimethylpentyl group, a 2,4-dimethylpentyl group, a 3,4-dimethylpentyl group, a 1-ethylpentyl group, a 2-ethylpentyl group, a 3-ethylpentyl group, a 1,2,2-trimethylbutyl group, a 1,1,2-trimethylbutyl group, a 1,3,3-trimethylbutyl group, a 1,1,3-trimethylbutyl group, a 2,2,3-trimethylbutyl group, a 2,3,3-trimethylbutyl group; Octyl groups with 8 carbon atoms, 1-methylheptyl groups, 2-methylheptyl groups, 3-methylheptyl groups, 4-methylheptyl groups, 5-methylheptyl groups, 6-methylheptyl groups, 1-ethylhexyl groups, 2-ethylhexyl groups, 3-ethylhexyl groups, 4-ethylhexyl groups, 1-propylpentyl groups, 2-propylpentyl groups, 1,1-dimethylhexyl groups, 2,2-dimethylhexyl groups, 3,3-dimethylhexyl groups, 4,4-dimethylhexyl groups, 5,5-dimethylhexyl groups, 3-ethyl-3-methylpentyl groups, 1,1-diethylbutyl groups, 2,2-diethylbutyl groups, 1,1,2,2-tetramethylbutyl groups, 1,1,3,3-tetramethylbutyl groups, 2,2,3,3-tetramethylbutyl groups, 1,1-dimethyl-2-ethylbutyl groups; Nonyl groups with 9 carbon atoms, 2-methyloctyl groups, 3-methyloctyl groups, 4-methyloctyl groups, 2,2-dimethylheptyl groups, 2,3-dimethylheptyl groups, 2,4 dimethylheptyl groups, 2,6 dimethylheptyl groups, 3,3 dimethylheptyl groups, 3,4 dimethylheptyl groups, 3,5 dimethylheptyl groups, 4,4 dimethylheptyl groups, 3-ethylheptyl groups, 4-ethylheptyl groups, 2,2,3-trimethylhexyl groups, 2,2,4-trimethylhexyl groups, 2,2,5-trimethylhexyl groups, 2,3,3-trimethylhexyl groups, 2,3,4-trimethylhexyl groups, 2,3,5-trimethylhexyl groups, 2,4,4-trimethylhexyl groups, 3,3,4-trimethylhexyl groups, 2 methyl-3-ethylhexyl groups, 3-methyl-3-ethylhexyl groups, 3-ethyl-4-methylhexyl groups, 3-ethyl-5-methylhexyl groups, 2,2,3,3-tetramethylpentyl groups, 2,2,3,4-tetramethylpentyl groups, 2,2,4,4-tetramethylpentyl groups, 2,3,3,4-tetramethylpentyl groups, 2,2-dimethyl-3-ethylpentyl groups, 2,3-dimethyl-3-ethylpentyl groups, 2,4-dimethyl-3-ethylpentyl groups, 3,3-diethylpentyl groups; Decyl groups with 10 carbon atoms, isodecyl groups; etc. can be mentioned.

[0037] R 1Examples of the alkyl group substituted with a halogen atom that may be present include groups in which at least one or more of the hydrogen atoms of the above alkyl group are substituted with a halogen atom (preferably a fluorine atom). Among them, a perfluoroalkyl group is preferred, a perfluoroalkyl group having 1 to 4 carbon atoms is more preferred, and a trifluoromethyl group is even more preferred.

[0038] R 1 Examples of the monovalent hydrocarbon group represented by formula 1R: *-L-C(R O ) n (CX 3 ) 3-n are preferred.

[0039]

Chemical formula

[0040] In formula 1R, L represents a single bond or a divalent hydrocarbon group (preferably an alkylene group having 1 to 4 carbon atoms), R O represents a hydrogen atom or a monovalent hydrocarbon group, X represents a halogen atom (preferably a fluorine atom), and n represents an integer from 0 to 3. Note that * represents the bonding position, and the same applies hereinafter in this specification.

[0041] In formula 1R, L is preferably a single bond. In formula 1R, examples of the monovalent hydrocarbon group of R 0 include an alkyl group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, an aryl group having 3 to 10 carbon atoms, and an aralkyl group having 7 to 10 carbon atoms, etc. Preferably, none of them are substituted with a halogen atom.

[0042] R O Examples of the alkyl group having 1 to 10 carbon atoms of R 1 include the linear or branched alkyl groups exemplified in the description of R Also, R Omay be a cyclic alkyl group, for example, a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, a bicyclo[2.2.1]heptyl group, a bicyclo[2.2.2]octyl group, a bicyclo[3.2.1]octyl group, a bicyclo[3.3.1]nonyl group, a bicyclo[3.2.2]nonyl group, an adamantyl group, etc.

[0043] R O Examples of the alkenyl group having 1 to 10 carbon atoms for

[0044] R O Examples of the aryl group having 3 to 10 carbon atoms for R O Examples of the aralkyl group having 7 to 10 carbon atoms for

[0045] The method for obtaining the magnesium source compound represented by Formula 1 is not particularly limited, and a commercially available product may be purchased, or it may be synthesized using a known method. Examples of known methods include the method described in Chemistry of Materials, (USA), 2010, vol. 22, No. 4, p. 1376-1385, etc.

[0046] Among them, in terms of more easily obtaining the magnesium source compound, a method of reacting dialkylmagnesium represented by Formula 4 described below, or dialkoxymagnesium represented by Formula 5 described below, with an alcohol represented by Formula 6 described below to obtain the magnesium source compound is preferable. This production method preferably includes the above step (hereinafter, also referred to as "Step 2").

[0047] (Step 2) This production method preferably includes Step 2. Step 2 is a step (process) of reacting a compound represented by Formula 4: Mg(R 4 ) 2 or a compound represented by Formula 5: Mg(OR 4 ) 2 with a compound represented by Formula 6: R 1 OH to obtain a magnesium source compound.

[0048]

Chemical formula

[0049] In Formulas 4 and 5, R 4 represents an alkyl group (preferably an alkyl group having 1 to 10 carbon atoms), and a plurality of R 4 may be the same or different. In Formula 6, R 1 represents the same group as R 1 in Formula 1.

[0050] The above reaction can typically be represented by the following Formula S2-1 using the compound represented by Formula 4 as a substrate, or the following Formula S2-2 using the compound represented by Formula 5 as a substrate, respectively.

[0051] Formula S2-1: Mg(R 4 ) 2 +2R 1 OH → Mg(OR 1 ) 2 +2HR 4 Formula S2-2: Mg(OR 4 ) 2 +2R 1 OH → Mg(OR 1 ) 2 +2HOR 4

[0052]

Chem.

[0053] Among them, the method represented by Formula S2-1 is preferred in that the purification of the magnesium source compound is easier. Note that the above reaction proceeds, for example, by dropping an alcohol represented by Formula 6 while stirring a solution of a compound represented by Formula 4 or Formula 5 in an inert gas atmosphere. The reaction temperature at this time is not particularly limited, but it is preferably maintained at 0 to 40 °C after dropping the alcohol represented by Formula 6. In terms of further suppressing the volatilization of the alcohol represented by Formula 6, it is more preferable to maintain the temperature at 0 to 10 °C during dropping and then raise the temperature and maintain it at 10 to 40 °C.

[0054] Also, the reaction solvent is not particularly limited as long as it does not contain water. Among them, chain ethers, cyclic ethers, etc. are preferred.

[0055] Cyclic ethers include, for example, 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, propylene oxide, 1,2-butylene oxide, 1,4-dioxane, 1,3,5-trioxane, furan, 2-methylfuran, 1,8-cineole, crown ether, and derivatives thereof. Tetrahydrofuran is preferred.

[0056] Chain ethers include, for example, 1,2-dimethoxyethane, diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, dihexyl ether, ethyl vinyl ether, butyl vinyl ether, methyl phenyl ether, ethyl phenyl ether, butyl phenyl ether, pentyl phenyl ether, methoxytoluene, benzyl ethyl ether, diphenyl ether, dibenzyl ether, o-dimethoxybenzene, 1,2-diethoxyethane, 1,2-dibutoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, 1,1-dimethoxymethane, 1,1-diethoxyethane, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl, and derivatives thereof. As the chain ether, specific ether compounds described later and the like are preferable, and among them, 1,2-dimethoxyethane (DME) is preferable.

[0057] When this production method includes Step 2, after Step 2, Step 1 may be carried out, or Step 2 and Step 1 may be carried out continuously or simultaneously. Further, when this production method further includes Step 3 described later, the order of Steps 1 to 3 is not particularly limited, but it is preferable to carry out Step 1 after carrying out Steps 2 and 3. Further, after carrying out Step 2, Steps 1 and 3 may be carried out together.

[0058] In Formula 4, R 4 represents an alkyl group, and the compound represented by HR 4 tends to have a higher vapor pressure, and as a result, separation from the generated magnesium source compound tends to be easier. In this regard, a linear or branched alkyl group having 10 or fewer carbon atoms is preferable, a linear or branched alkyl group having 8 or fewer carbon atoms is more preferable, a linear or branched alkyl group having 6 or fewer carbon atoms is still more preferable, a linear or branched alkyl group having 5 or fewer carbon atoms is particularly preferable, and a linear or branched alkyl group having 4 or fewer carbon atoms is most preferable. Note that the number of carbon atoms may be 1 or more. In addition, the linear and branched alkyl groups having 1 to 10 carbon atoms are R 1 as exemplified in the description of.

[0059] Furthermore, HR 4 which is a by-product in formula S2-1, is a gas at normal temperature and pressure, and thus it is easier to separate from the magnesium source compound which is typically a solid. Therefore, R 4 is preferably a linear or branched alkyl group having 4 or fewer carbon atoms. Note that 4 the lower limit of the number of carbon atoms of the alkyl group of R is 1 or more in the linear case, and 3 or more in the branched and cyclic cases.

[0060] When the production method includes step 2, a higher purity magnesium source compound can be easily obtained. As a result, when an electrolyte containing a boron-based magnesium salt obtained by the production method is applied to a magnesium secondary battery, it is preferable in that more excellent electrochemical activity can be obtained.

[0061] Returning to the description of the reaction of formula S1 (step 1), next, the boron source compound represented by formula 2: B(OR 2 ) 3 used in this reaction will be described in detail.

[0062] In formula 2, R 2 is a monovalent hydrocarbon group having an alkyl group which may be substituted with a halogen atom, and a plurality of Rs 2 in the molecule may be the same or different, and any two or more Rs 2 may be bonded to each other to form a ring.

[0063] As the hydrocarbon group of R 2 , groups similar to the monovalent hydrocarbon group of R 1 in formula 1 can be mentioned, and the preferred forms are the same. The group represented by R 2 is contained 3 in the molecule of the boron source compound, and each of them may be the same or different, and 1 to 3 of them may be the same group as the group represented by R 1 in formula 1.

[0064] R 2 The group represented by (corresponding to the group represented by R in Formula 3 described later). Three of them, and the R in Formula 1 2 corresponding to the group represented by. When all of them are the same group, the anion of the boron-based magnesium salt obtained [B(OR 1 (corresponding to the group represented by R in Formula 3 described later). 1 corresponding to the group represented by. When all of them are the same group, the anion of the boron-based magnesium salt obtained [B(OR 1 )(OR 2 ) 3 - will have a symmetric structure. On the other hand, when any one or more of the groups represented by R 2 are different from the group represented by R in Formula 1, and when two or more of the groups represented by R 1 are different from each other, the anion of the boron-based magnesium salt [B(OR 2 )(OR 1 )(OR 2 ) 3 - will have an asymmetric structure.

[0065] According to this production method, by adjusting the group represented by OR 1 of the magnesium source compound and the group represented by OR 2 of the boron source compound respectively, the symmetry of the anion of the obtained boron-based magnesium salt can be easily controlled. In the conventional production method using magnesium borohydride as a substrate, it was very difficult to obtain a boron-based magnesium salt containing an asymmetric anion. That is, the structure control of the asymmetric anion could not be achieved.

[0066] Here, the method for obtaining the boron source compound is not particularly limited, and a commercially available product may be purchased, or it may be synthesized using a known method. Examples of known synthesis methods include the method described in Journal of the Electrochemical Society, (USA), 1998, vol. 145, No. 8, 2813 - 2817, etc.

[0067] ​​Among them, a method of obtaining a boron source compound by reacting a borane complex with a compound represented by Formula 7 described below or a compound represented by Formula 8 described below is preferable in that the boron source compound can be obtained more simply. This production method preferably includes the above step (hereinafter also referred to as "Step 3").

[0068] (Step 3) This production method preferably includes Step 3. Step 3 is to react a borane complex with a compound represented by Formula 7: R 2 represented by OH, or a compound represented by Formula 8: R 8 (OH) m to obtain a boron source compound.

[0069] [Chemical formula]

[0070] In Formula 7, R 2 represents the same group as R 2 in Formula 2, and the preferred forms are the same. In Formula 8, R 8 represents an m-valent hydrocarbon group which may be substituted with a halogen atom, and m represents 2 or 3.

[0071] R 8 The m-valent hydrocarbon group of may consist only of an aliphatic hydrocarbon group or an aromatic hydrocarbon group, or may be a group formed by bonding an aliphatic hydrocarbon group and an aromatic hydrocarbon group, or may be a repetition of these groups.

[0072] Examples of the divalent aliphatic hydrocarbon group include chain aliphatic hydrocarbon groups such as a methylene group, an ethylene group, a trimethylene group, a tetramethylene group, a pentamethylene group, a hexamethylene group, a heptamethylene group, an octamethylene group, a nonamethylene group, and a decamethylene group; alicyclic aliphatic hydrocarbon groups such as a cyclopropylene group, a cyclotetramethylene group, a cyclopentamethylene group, a cyclohexamethylene group, a cycloheptamethylene group, a cyclooctamethylene group, a cyclononamethylene group, and a cyclodecamethylene group; and aromatic hydrocarbon groups such as a phenylene group and a naphthalene-diyl group.

[0073] R 8 Examples of the trivalent hydrocarbon group of R include chain aliphatic hydrocarbon groups such as a propane-1,2,3-triyl group, a butane-1,2,3-triyl group, a 2-methylpropane-1,2,3-triyl group, a butane-1,2,4-triyl group, a pentane-1,2,3-triyl group, a pentane-1,3,5-triyl group, and a hexane-1,2,5-triyl group; alicyclic aliphatic hydrocarbon groups such as a cyclopentane-1,2,3-triyl group, a cyclopentane-1,2,4-triyl group, a cyclohexane-1,2,3-triyl group, a cyclohexane-1,2,4-triyl group, a cyclohexane-1,2,5-triyl group, and a cyclohexane-1,3,5-triyl group; and aromatic hydrocarbon groups such as a benzene-1,2,3-triyl group, a benzene-1,2,4-triyl group, a benzene-1,2,5-triyl group, and a benzene-1,3,5-triyl group.

[0074] R 8 One or more hydrogen atoms of the m-valent hydrocarbon group of R may be substituted with a halogen atom (preferably a fluorine atom). When R 8 has a fluorine atom, it is preferable that R 8 has a halogenated alkyl group (preferably a perfluoroalkyl group). R 8The number of carbon atoms is not particularly limited, but from the viewpoint of obtaining more excellent effects of the present invention, 1 to 20 are preferable, 2 to 15 are more preferable, 3 to 10 are still more preferable, and 4 to 8 are particularly preferable.

[0075] In addition, for the above reaction, for example, in an inert gas atmosphere, a borane complex and a compound represented by Formula 7 or Formula 8 may be dissolved in a solvent to prepare a solution. The reaction may be carried out while holding the solution. The reaction temperature at this time is not particularly limited, but 0 to 40°C is preferable, and 0 to 20°C is more preferable from the viewpoint of further suppressing the volatilization of the compound represented by Formula 7 or Formula 8. The reaction time is preferably 5 minutes to 48 hours.

[0076] Step 3 may be carried out separately from Step 1 before Step 1, but when the present production method includes Step 3, Step 1 and Step 3 may be carried out simultaneously. Here, carrying out Step 1 and Step 3 simultaneously typically means proceeding with the reaction according to the procedure shown in the following Formula S3.

[0077] Formula S3: Mg(OR 1 ) 2 +2BH 3 -L+6R 2 OH→Mg[B(OR 1 )(OR 2 ) 3 2 +3H 2

[0078]

Chemical formula

[0079] In the above Formula S3, 2BH 3 -L represents a borane complex, and the compound represented by Mg[B(OR 1 )(OR 2 ) 3 2 is the compound represented by Formula 3. At this time, R 1 is the same group as R 1 in Formula 1, and R 2 is R in Formula 2.​​2 is the same group as

[0080] The reaction of Formula S3 typically involves mixing a solution of Mg(OR 1 ) 2 with a borane complex solution in an inert gas atmosphere, stirring at 10 - 40 °C for 5 minutes to 48 hours, and then adding 6R 2 OH and holding at 10 - 40 °C for 30 minutes to 48 hours to proceed. The reaction solvent for the above reaction is not particularly limited as long as it does not contain water, but a specific ether compound described later is more preferable.

[0081] The borane complex is one in which unstable monoborane (BH 3 ) is stabilized by a Lewis base or the like. For example, commercially available ones as solutions can be used. For example, ether complexes such as borane - tetrahydrofuran complex and borane - 2 - methyltetrahydrofuran complex; sulfide complexes such as borane - dimethyl sulfide complex and borane - 1,2 - bis(tert - butylthio)ethane complex; phosphine complexes such as borane - di(tert - butyl)phosphine complex; amine complexes such as borane - tert - butylamine complex, borane - dimethylamine complex, borane - triethylamine complex, borane - trimethylamine complex, borane - N,N - diisopropylethylamine complex, borane - aniline complex, borane - N,N - dimethylaniline complex, borane - pyridine complex, borane - 2 - methylpyridine complex, borane - morpholine complex, and borane - 4 - methylmorpholine complex; can be mentioned.

[0082] Among them, in terms of better handleability, ether complexes, sulfide complexes, and amine complexes are preferable, and sulfide complexes and ether complexes are more preferable. For example, ether complexes, etc. are commercially available as solutions and can be used in the available form.

[0083] The charged amounts of the magnesium source compound, the borane complex, and the compound represented by Formula 7 are not particularly limited. However, in terms of the ease of further increasing the yield of the boron-based magnesium salt, the molar ratio (borane complex / magnesium source compound) of the amount (charged amount) of the borane complex to the amount (charged amount) of the magnesium source compound in the system is preferably from 1.80 to 2.80, more preferably from 2.01 to 2.60. In addition, the amount of the compound represented by Formula 7 relative to the amount of the borane complex is not particularly limited, and a molar ratio of 2.9 to 3.1 (compound represented by Formula 7 / borane complex) is preferred.

[0084] By making the amount of the borane complex (boron source compound produced by the reaction) excessive relative to the magnesium source compound, after the reaction, the reaction product is washed with a solvent to remove the excessive boron source compound, and the boron-based magnesium salt can be more easily purified to a high purity.

[0085] (Step 4) In addition to the above, this method may further include a step of washing the obtained reaction product with a solvent. At this time, the solvent to be used is not particularly limited, but an aprotic solvent is preferred in terms of lower reactivity with the boron source compound and the fluorine source compound that may be contained in the reaction product.

[0086] The aprotic solvent is not particularly limited, and examples thereof include hydrocarbons such as pentane, hexane, heptane, cyclohexane, methylcyclohexane, and decalin; ketones / aldehydes such as acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone, butanone, pentanone, cyclohexanone, and benzaldehyde; aromatic compounds such as benzene, toluene, trifluorotoluene, xylene, anisole, chlorobenzene, aniline, N,N-dimethylaniline, and benzonitrile; ethers such as dimethoxyethane, dimethyl ether, diethyl ether, diisopropyl ether, methyl t-butyl ether (MTBE), tetrahydrofuran, 1,4-dioxane, glyme, diglyme, polyethylene glycol (PEG), PEG ester, PEG sorbitan, PEG ether, PEG ester, and polypropylene glycol (PPG); esters / amides such as methyl acetate, ethyl acetate, propyl acetate, butyl acetate, amyl acetate, ethyl benzoate, benzyl benzoate, dimethyl phthalate, dibutyl phthalate, dimethylacetamide, and dimethylformamide (DMF); nitriles such as acetonitrile; carbonates such as dimethyl carbonate, diethyl carbonate, propylene carbonate, and ethylene carbonate; halogenated compounds such as carbon tetrachloride, chloroform, dichloromethane, dichloroethane, and trichloroethane; sulfur / phosphorus-containing compounds such as dimethyl sulfoxide (DMSO), carbon disulfide, sulfolane, and hexamethylphosphoric triamide; and pyridine, triethylamine, and N-methylpyrrolidinone (NMP).

[0087] Among these, aprotic solvents having a boiling point of 150 °C or lower are preferred in that removal by drying is easier. Examples of such solvents include acetonitrile (82 °C), acetone (56 °C), ethyl acetate (77 °C), tetrahydrofuran (66 °C), dichloromethane (40 °C), diethyl ether (35 °C), chloroform (61 °C), 1,4-dioxane (101 °C), toluene (111 °C), benzene (80 °C), hexane (69 °C), ethyl methyl ketone (80 °C), carbon tetrachloride (77 °C), 1,2-dichloroethane (84 °C), xylene (144 °C), cyclohexane (81 °C), pentane (36 °C), heptane (98 °C), and pyridine (115 °C). In this paragraph, the values in parentheses are the boiling points.

[0088] The cleaning solvent is preferably a solvent that more easily dissolves the magnesium source compound, borane complex, boron source compound, the compound represented by Formula 7, and the compound represented by Formula 8, which are starting materials of the reaction, and less easily dissolves the obtained boron-based magnesium salt. Among such cleaning solvents, those with a high donor property are preferred from the viewpoint of more easily dissolving impurities in the reaction product. The donor number of the cleaning solvent is preferably 0.1 or more, more preferably 1.0 or more, still more preferably 5.0 or more, and particularly preferably 10.0 or more. The upper limit of the donor number is not particularly limited, but generally 50.0 or less is preferred, 31.0 or less is more preferred, and 17.0 or less is still more preferred.

[0089] Examples of aprotic solvents having a donor number within the above numerical range include benzene (0.1), toluene (0.1), dichloromethane (1.0), chloroform (4.0), anisole (9.0), acetonitrile (14.1), 1,4-dioxane (14.8), ethyl acetate (17.1), N,N-dimethylformamide (26.6), dimethyl sulfoxide (29.8), and pyridine (33.1). In this paragraph, the values in parentheses represent the donor number.

[0090] Here, the donor number means the value specific to each solvent defined on page 19 of Viktor Gutmann, “The Donor-Acceptor Approach to Molecular Interactions”, Springer, 1978 (ISBN-13: 978-0306310645). This value is the molar enthalpy value (kcal·mol 5 when a donor molecule is reacted in 1,2-dichloromethane at 10 -3 M with SbCl -1 ) as the reference acceptor. In addition to the table on page 20 of the above literature, the donor number is also described in Table 2 on page 95 of EUROPEAN CHEMICAL BULLETIN, 2015, vol.4, No.2, 92-97, etc.

[0091] Note that as the cleaning solvent, one kind can be used alone or two or more kinds can be used in combination. As the cleaning solvent, it is preferable to contain at least one solvent selected from the group consisting of toluene, dichloromethane, chloroform, and 1,4-dioxane in that the solubility of the boron-based magnesium salt is lower and the solubility of impurities (for example, the reaction product of a borane complex and an alcohol compound) is higher. It is more preferable to contain 1,4-dioxane, and it is even more preferable to consist of 1,4-dioxane.

[0092] The cleaning method is not particularly limited. For example, a method of dispersing a reaction product containing a boron-based magnesium salt in a cleaning solvent at a temperature of 0 to 50°C under an inert gas atmosphere and performing solid-liquid separation can be mentioned.

[0093] According to this production method, since a boron-based magnesium salt can be obtained without using a magnesium borohydride salt, it is presumed that it is less likely to be affected by impurities mixed in the production process of the magnesium borohydride salt. As a result, a reaction product with excellent electrochemical activity can be provided when used in an electrolyte. In other words, a boron-based magnesium salt with higher purity can be provided.

[0094] Next, the boron-based magnesium salt represented by Formula 3: Mg[B(OR 1 )(OR 2 ) 3 2 obtained by the present production method will be described. Here, in Formula 3, R 1 represents the same group as R 1 in Formula 1, and R 2 represents the same group as R 2 in Formula 2, and the preferred forms are the same.

[0095] According to the present production method, as already described, by selecting the group represented by R 1 of the magnesium source compound and the group represented by R 2 of the boron source compound, respectively, the symmetry of the anion of the obtained boron-based magnesium salt can be easily controlled.

[0096] Among the boron-based magnesium salts that can be produced by the present production method, a boron-based magnesium salt containing an anion having an asymmetric structure is shown in Formula 9. Formula 9: Mg[B(OR 9 ) 4 2

[0097]

Chemical formula

[0098] In Formula 9, each R 9 independently represents a monovalent hydrocarbon group having an alkyl group which may be substituted with a halogen atom, and any two or more of R 9 may be linked to each other to form a ring. However, all four R 9 in the molecule being the same group is excluded.

[0099] R 9 Examples of the hydrocarbon group of R 1 include the hydrocarbon groups of R R 9 ​​The ring formed by the connection is preferably an aliphatic ring, which may be either saturated or unsaturated. Further, the number of carbon atoms contained in the ring skeleton is preferably 2 to 6. R 9 Examples of the ring formed by the connection include those represented by the following formulae.

[0100]

Chemical formula

[0101]

Chemical formula

[0102] In the above formulae, at least one or more hydrogen atoms may be substituted with a halogenated alkyl group. As the halogen atom, a fluorine atom is preferred. As the alkyl group, the alkyl groups exemplified in the description of R 1 are mentioned. In particular, an alkyl group having 1 to 6 carbon atoms is preferred, a perfluoroalkyl group having 1 to 6 carbon atoms is more preferred, and a trifluoromethyl group is even more preferred.

[0103] The compound represented by Formula 9 is not particularly limited, but examples include the compound represented by the following Formula 10.

[0104]

Chemical formula

[0105] The boron-based magnesium salt containing an anion having an asymmetric structure is likely to have a lower melting point, and thus has excellent electrochemical activity as an electrolyte for a magnesium secondary battery by forming a molten complex.

[0106] According to this production method, a boron-based magnesium salt having excellent electrochemical activity can be produced when used in the electrolyte of a magnesium secondary battery. Further, the group represented by OR 1 of the magnesium source compound, and OR of the boron source compound2 By adjusting the group represented by the formula, it is possible to synthesize a boron-based magnesium salt containing an anion having an asymmetric structure, which has been difficult to achieve conventionally. In addition, the raw materials used are less expensive compared to the conventional method using magnesium hydride as a substrate, and this tendency is more prominent when the present manufacturing method includes Step 2 and / or Step 3.

[0107] The structure of the boron-based magnesium salt is determined by NMR (Nuclear Magnetic Resonance) measurement.

[0108] [Electrolyte solution] The electrolyte solution according to the embodiment of the present invention contains the boron-based magnesium salt and the solvent described above. The content of the boron-based magnesium salt in the electrolyte solution is not particularly limited, but generally, 0.05 to 1 mol / L is preferable. This electrolyte solution can be produced by mixing a boron-based magnesium salt, a solvent, and, if necessary, other components, typically in an inert gas atmosphere. When this electrolyte solution is used as the electrolyte solution of a magnesium secondary battery, excellent electrochemical activity can be obtained.

[0109] The solvent contained in this electrolyte solution is not particularly limited as long as it does not contain water. For example, it preferably contains at least one compound selected from the group consisting of cyclic ethers, chain ethers, cyclic carbonates, chain carbonates, cyclic carboxylic acid esters, chain carboxylic acid esters, pyrocarbonates, phosphoric acid esters, boric acid esters, sulfuric acid esters, sulfites, cyclic sulfones, chain sulfones, nitriles, amides, and sultones.

[0110] Examples of the cyclic ether include 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, propylene oxide, 1,2-butylene oxide, 1,4-dioxane, 1,3,5-trioxane, furan, 2-methylfuran, 1,8-cineole, crown ether, and derivatives thereof.

[0111] Chain ethers include, for example, 1,2-dimethoxyethane, diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, dihexyl ether, ethyl vinyl ether, butyl vinyl ether, methyl phenyl ether, ethyl phenyl ether, butyl phenyl ether, pentyl phenyl ether, methoxytoluene, benzyl ethyl ether, diphenyl ether, dibenzyl ether, o-dimethoxybenzene, 1,2-diethoxyethane, 1,2-dibutoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, 1,1-dimethoxymethane, 1,1-diethoxyethane, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl, and derivatives thereof.

[0112] Cyclic carbonates include, for example, ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, fluoroethylene carbonate, 4,5-difluoroethylene carbonate, 4,4,4-trifluoroethylene carbonate, fluoromethyl ethylene carbonate, trifluoromethyl ethylene carbonate, 4-fluoropropylene carbonate, 5-fluoropropylene carbonate, and derivatives thereof.

[0113] Chain carbonates include, for example, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl isopropyl carbonate, and derivatives thereof.

[0114] Cyclic carboxylic acid esters include, for example, γ-butyrolactone, γ-valerolactone, γ-caprolactone, ε-caprolactone, α-acetolactone, and derivatives thereof.

[0115] Chain carboxylic acid esters include, for example, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, and derivatives thereof.

[0116] Pyrocarbonic acid esters include, for example, diethyl pyrocarbonate, dimethyl pyrocarbonate, di-tert-butyl dicarbonate, and derivatives thereof.

[0117] Phosphoric acid esters include, for example, trimethyl phosphate, triethyl phosphate, hexamethyl phosphoramide, and derivatives thereof. Boric acid esters include, for example, trimethyl borate, triethyl borate, and derivatives thereof. Sulfuric acid esters include, for example, trimethyl sulfate, triethyl sulfate, and derivatives thereof. Sulfurous acid esters include, for example, ethylene sulfite and derivatives thereof.

[0118] Cyclic sulfones include, for example, sulfolane and derivatives thereof. Chain sulfones include, for example, alkyl sulfones and derivatives thereof. Nitriles include, for example, acetonitrile, valeronitrile, propionitrile, trimethylacetonitrile, cyclopentanecarbonitrile, adiponitrile, pimelonitrile, and derivatives thereof. Amides include, for example, dimethylformamide and derivatives thereof. Sulfones include, for example, 1,3-propanesulfone and derivatives thereof. Note that as the solvent, one of the above compounds may be used alone, or two or more thereof may be used in combination.

[0119] In terms of easily obtaining an electrolyte solution having more excellent effects of the present invention, it is preferable that this electrolyte solution contains a specific ether compound represented by the following formula 11. Formula 11: R 11 (OC 2 H 4 ) p OR 12

[0120] In Formula 11, R 11 and R 12 each independently represents a hydrocarbon group having 1 to 14 carbon atoms, and p represents an integer of 1 to 8.

[0121] In Formula 11, R 11 and R 12 are each independently preferably a hydrocarbon group having 1 to 8 carbon atoms.

[0122] Examples of the hydrocarbon group having 1 to 14 carbon atoms include an alkyl group having 1 to 14 carbon atoms, an alkenyl group having 2 to 14 carbon atoms, an aryl group having 6 to 14 carbon atoms, and an aralkyl group having 7 to 14 carbon atoms.

[0123] More specifically, the alkyl group having 1 to 14 carbon atoms includes linear or branched alkyl groups such as methyl group, ethyl group, propyl group, isopropyl group, butyl group, isobutyl group, tert-butyl group, pentyl group, hexyl group, heptyl group, octyl group, nonyl group, decyl group, undecyl group, and dodecyl group; alicyclic alkyl groups such as cyclopentyl group, cyclohexyl group, cycloheptyl group, cyclooctyl group, norbornyl group, and adamantyl group. Among them, a methyl group or an ethyl group is preferable, and a methyl group is more preferable in terms of easily obtaining an electrolyte solution having more excellent effects of the present invention.

[0124] Examples of the alkenyl group having 2 to 14 carbon atoms include vinyl group, allyl group, butenyl group, pentenyl group, and hexenyl group.

[0125] Examples of the aryl group having 6 to 14 carbon atoms include phenyl group and naphthyl group.

[0126] Examples of the aralkyl group having 7 to 14 carbon atoms include a benzyl group, a phenylethyl group, a methylbenzyl group, a naphthylmethyl group, and the like.

[0127] As the compound represented by Formula 11, a symmetric glycol diether is preferable in that the precipitation and dissolution reaction of magnesium is more likely to be improved. In Formula 11, p is preferably an integer of 2 to 4, and more preferably 2 or 3.

[0128] More specifically, the compound represented by Formula 11 is more preferably at least one selected from the group consisting of 1,2-dimethoxyethane (DME, glyme), diethylene glycol dimethyl ether (diglyme), triethylene glycol dimethyl ether (triglyme), and tetraethylene glycol dimethyl ether (tetraglyme). When the electrolytic solution contains the above solvent, handling in a high-temperature environment becomes easier, or the efficiency of the charge-discharge reaction is more improved, and the voltage loss is more suppressed.

[0129] This electrolyte may contain, if necessary, a boron-based magnesium salt and components other than the solvent. Examples of such other compounds include biphenyl, alkyl biphenyl, terphenyl, terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, dibenzofuran, 2-fluorobiphenyl, o-cyclohexylfluorobenzene, p-cyclohexylfluorobenzene, 2,4-difluoroanisole, 2,5-difluoroanisole, 2,6-difluoroanisole, 3,5-difluoroanisole, ethylene sulfite, propylene sulfite, dimethyl sulfite, propane sultone, propene sultone, butane sultone, methyl methanesulfonate, busulfan, methyl toluenesulfonate, dimethyl sulfate, ethylene sulfate, sulfolane, dimethyl sulfone, diethyl sulfone, dimethyl sulfoxide, diethyl sulfoxide, tetramethylene sulfoxide, diphenyl sulfide, thioanisole, diphenyl disulfide, and dipyridinium disulfide, etc.

[0130] The content of the above components in the electrolyte is not particularly limited, but in terms of obtaining better effects of the present invention, when the total mass of the electrolyte is 100% by mass, 0.01 to 5% by mass is preferable. In addition, the above components may be used alone or in combination of two or more. When two or more of the above components are used in combination, it is preferable that the total content is within the above range.

[0131] [Secondary battery] FIG. 1 is a schematic diagram showing the configuration of a secondary battery according to an embodiment of the present invention. As shown in FIG. 1, the secondary battery 1 includes a positive electrode 11, a negative electrode 12, an electrolyte 13, and a container 14. This secondary battery has excellent electrochemical activity.

[0132] The positive electrode 11, although not shown, is composed of a positive electrode current collector and a positive electrode active material held on the positive electrode current collector. The positive electrode current collector has a function of donating electrons to the positive electrode active material during discharge. The material used as the positive electrode current collector is not particularly limited, but nickel, iron, stainless steel, titanium, aluminum, etc. are preferred in terms of excellent corrosion resistance and lower cost. The material used as the positive electrode active material is not particularly limited, but typically, those capable of inserting and extracting magnesium ions are preferred, such as MgFeSiO 4 、MgMn 2 O 4 、and V 2 O 5 and the like. As a specific configuration of the positive electrode 11, for example, a laminate in which a layer of V 2 O 5 is disposed on stainless steel can be mentioned. On the other hand, magnesium and magnesium alloys are preferred for the negative electrode 12.

[0133] Next, a method for manufacturing the secondary battery 1 will be described. First, the electrolytic solution 13 is prepared. The method for preparing the electrolytic solution 13 is as already described. Next, the positive electrode active material is brought into contact with the positive electrode current collector to produce the positive electrode 11. The secondary battery 1 can be produced using the thus obtained electrolytic solution 13, positive electrode 11, and negative electrode 12.

[0134] Note that the secondary battery may further have a separator located between the positive electrode and the negative electrode. The material of the separator is not particularly limited, and examples include fluororesins such as polytetrafluoroethylene; polyolefin resins such as polyethylene and polypropylene; glass; ceramics, and the like.

Examples

[0135] The present invention will be described in more detail based on the following examples. The materials, amounts used, ratios, treatment contents, treatment procedures, etc. shown in the following examples can be appropriately changed without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the following examples.

[0136] (Materials) The materials used in the examples are as follows.

[0137] Di-n-butylmagnesium solution 1.0 M in heptane (Di-n-butylmagnesium heptane solution) Product number: 345113-800ML, manufactured by Sigma-Aldrich

[0138] Tetrahydrofuran-Borane Tetrahydrofuran Solution (Tetrahydrofuran solution of tetrahydrofuran-borane complex) Product number: 201-14865, manufactured by Fujifilm Wako Pure Chemical Corporation Product number: T2346, manufactured by Tokyo Chemical Industry Co., Ltd. Product number: 176192-800ML, manufactured by Sigma-Aldrich

[0139] Dimethyl Sulfide Borane (Dimethyl sulfide borane) Product number: D1843, manufactured by Tokyo Chemical Industry Co., Ltd.

[0140] Borane dimethyl sulfide complex solution 2.0M in THF (Borane dimethyl sulfide complex solution) Product number: 192120-800ML, manufactured by Sigma-Aldrich

[0141] 1,1,1,3,3,3-Hexafluoro-2-propanol (1,1,1,3,3,3-Hexafluoro-2-propanol) Product number: 084-10315, manufactured by Fujifilm Wako Pure Chemical Corporation Product number: H0424, manufactured by Tokyo Chemical Industry Co., Ltd.

[0142] 2,2,2-Trifluoroethanol (2,2,2-Trifluoroethanol) Product number: T0435, manufactured by Tokyo Chemical Industry Co., Ltd.

[0143] Hexafluoro-2,3-bis(trifluoromethyl)-2,3-butanediol (Hexafluoro-2,3-bis(trifluoromethyl)-2,3-butanediol) Manufactured by Tokyo Chemical Industry Co., Ltd. Product number: H1279

[0144] Ethylene glycol dimethyl ether (Ethylene glycol dimethyl ether) Manufactured by Kanto Chemical Co., Inc. For electrochemical use. Product number: 14121-08

[0145] 1,4-Dioxane anhydrous (1,4-Dioxane (anhydrous)) Manufactured by Kanto Chemical Co., Inc. Dehydrating solvent for organic synthesis. Product number: 11337-05

[0146] (Abbreviations) The abbreviations used are as follows. HFIP: hexafluoroisopropoxy group TFE: 2,2,2-tetrafluoroethoxy group FP: fluorinated pinacolate group / Hexafluoro-2,3-bis(trifluoromethyl)-2,3-butanedialkoxide

[0147] (Example 1: Synthesis of Mg[B(HFIP) 4 2 ) Using the following reagents and following the following procedure, Mg[B(HFIP) 4 2 was synthesized.

[0148] ·Reagents used Di-n-butylmagnesium solution 1.0 M in heptane (Sigma-Aldrich, 345113-800ML) ​​Tetrahydrofuran-Borane Tetrahydrofuran Solution (Fujifilm Wako, 201-14865) 1,1,1,3,3,3-Hexafluoro-2-propanol (Fujifilm-Wako, 084-10315) Ethylene glycol dimethyl ether 1,4-Dioxane anhydrous

[0149] In a glove box under an Ar (argon) atmosphere, a magnetic stir bar with a length of 2 cm was placed at the bottom of a 200 mL eggplant flask, and 5 mL (5 mmol) of Di-n-butylmagnesium solution 1.0 M in heptane was added using a syringe. Then, 1.04 mL (10.0 mmol) of 1,1,1,3,3,3-Hexafluoro-2-propanol was added dropwise over 10 minutes, and the solution was continuously stirred at 25 °C during that time.

[0150] Butane gas was generated immediately after the addition dropwise, and when the total amount of 1,1,1,3,3,3-Hexafluoro-2-propanol was added dropwise, a white solid was obtained. The obtained white solid was dissolved in 20 mL of Ethylene glycol dimethyl ether to prepare a homogeneous solution. 12.2 mL (11.0 mmol) of Tetrahydrofuran-Borane Tetrahydrofuran Solution was added to the prepared solution, and the mixture was stirred at 25 °C for 30 minutes.

[0151] Then, 3.42 mL (33.0 mmol) of 1,1,1,3,3,3-Hexafluoro-2-propanol was added dropwise over 30 minutes, and the solution was continuously stirred at 25 °C during that time. After the total amount of 1,1,1,3,3,3-Hexafluoro-2-propanol was added dropwise, the solution was further stirred at 25 °C for 12 hours.

[0152] Next, a three-way cock was attached to the eggplant flask containing the reaction solution, and the flask was taken out of the glove box while maintaining an Ar atmosphere inside the flask. The eggplant flask was evacuated using an oil rotary vacuum pump and dried at 50 °C for 8 hours to remove the solvent. By the drying treatment, Mg[B(HFIP) 4 2 and excess B(HFIP) 3 as a white solid containing were obtained.

[0153] Next, the eggplant flask containing the white solid was introduced into the glove box again, the three-way cock was removed, and the white solid was washed three times with 30 mL of 1,4-dioxane (a total of 90 mL of 1,4-dioxane was used). The three-way cock was attached to the flask again, and the flask was taken out of the glove box while maintaining an Ar atmosphere inside the flask. By evacuating using an oil rotary vacuum pump and drying at 50 °C for 24 hours, the target compound Mg[B(HFIP) 4 2 containing the reaction product was obtained. Note that the structure of Mg[B(HFIP) 4 2 was confirmed by nuclear magnetic resonance spectrum. The structure of Mg[B(HFIP) 4 2 is shown below.

[0154]

Chemical formula

[0155] (Example 2: Synthesis of Mg[B(HFIP) 3 (TFE)] 2 ) In a glove box under an Ar atmosphere, a magnetic stir bar with a length of 2 cm was placed at the bottom of a 200 mL eggplant flask, and 5 mL (5 mmol) of a 1.0 M Di-n-butylmagnesium solution in heptane was added using a syringe. ​​​​To this, 0.72 mL (10.0 mmol) of 2,2,2-trifluoroethanol was added dropwise over 10 minutes, and the solution was continuously stirred at 25 °C during that time.

[0156] Butane gas was generated immediately after the addition dropwise, and when the total amount of 2,2,2-trifluoroethanol was added dropwise, a white solid was obtained. The obtained white solid was dissolved in 20 mL of ethylene glycol dimethyl ether to prepare a homogeneous solution. To the prepared solution, 12.2 mL (11.0 mmol) of tetrahydrofuran-borane tetrahydrofuran solution was added, and the mixture was stirred at 25 °C for 30 minutes.

[0157] To this, 3.42 mL (33.0 mmol) of 1,1,1,3,3,3-hexafluoro-2-propanol was added dropwise over 30 minutes, and the solution was continuously stirred at 25 °C during that time. After the total amount of 1,1,1,3,3,3-hexafluoro-2-propanol was added dropwise, the solution was further stirred at 25 °C for 12 hours.

[0158] Next, a three-way cock was attached to the eggplant flask containing the reaction solution, and the flask was taken out of the glove box while keeping the inside of the eggplant flask under an Ar atmosphere. The eggplant flask was depressurized using an oil rotary vacuum pump and dried at 50 °C for 8 hours to remove the solvent. By the drying treatment, a white solid containing Mg[B(HFIP) 3 (TFE)] 2 and excess B(HFIP) 3 was obtained.

[0159] Next, the eggplant flask containing the white solid was introduced into the glove box again, the three-way cock was removed, and the white solid was washed three times with 30 mL of 1,4-dioxane (a total of 90 mL of 1,4-dioxane was used). The three-way cock was attached to the flask again, and the flask was taken out of the glove box while keeping the inside of the flask under an Ar atmosphere. By depressurizing using an oil rotary vacuum pump and drying at 50 °C for 24 hours, the target compound Mg[B(HFIP) 3(TFE)] 2 A reaction product containing 3 (TFE)] 2 was confirmed by nuclear magnetic resonance spectrum. The structure of Mg[B(HFIP) 3 (TFE)] 2 is shown below.

[0160] [Chemical formula]

[0161] (Example 3: Synthesis of Mg[B(FP)(HFIP) 2 2 ) In a glove box under an Ar atmosphere, a magnetic stir bar with a length of 2 cm was placed at the bottom of a 200 mL eggplant flask, and 5 mL (5 mmol) of Di-n-butylmagnesium solution 1.0 M in heptane was added using a syringe. 1.04 mL (10.0 mmol) of 1,1,1,3,3,3-Hexafluoro-2-propanol was added dropwise thereto over 10 minutes, and the solution was continuously stirred at 25 °C during that time.

[0162] Butane gas was generated immediately after the dropwise addition, and when the total amount of 1,1,1,3,3,3-Hexafluoro-2-propanol was added dropwise, a white solid was obtained. The obtained white solid was dissolved in 20 mL of Ethylene glycol dimethyl ether to prepare a homogeneous solution. 12.2 mL (11.0 mmol) of Tetrahydrofuran-Borane Tetrahydrofuran Solution was added to the prepared solution, and the mixture was stirred at 25 °C for 30 minutes.

[0163] ​To this, 3.67 g (11.0 mmol) of hexafluoro-2,3-bis(trifluoromethyl)-2,3-butanediol was added over 30 minutes, and the solution was continuously stirred at 25 °C during that time. After the entire amount of hexafluoro-2,3-bis(trifluoromethyl)-2,3-butanediol was added, the solution was further stirred at 25 °C for 3 hours.

[0164] To this, 2.38 mL (23.0 mmol) of 1,1,1,3,3,3-hexafluoro-2-propanol was added over 30 minutes, and the solution was continuously stirred at 25 °C during that time. After the entire amount of 1,1,1,3,3,3-hexafluoro-2-propanol was added, the solution was further stirred at 25 °C for 12 hours.

[0165] Next, a three-way cock was attached to the eggplant flask containing the reaction solution, and it was taken out of the glove box while keeping the inside of the eggplant flask under an Ar atmosphere. The eggplant flask was depressurized using an oil rotary vacuum pump and dried at 50 °C for 8 hours to remove the solvent. By the drying treatment, Mg[B(FP)(HFIP) 2 2 and an excess of B(FP)(HFIP) 2 were obtained as a white solid containing

[0166] Next, the eggplant flask containing the white solid was introduced into the glove box again, the three-way cock was removed, and the white solid was washed three times with 30 mL of 1,4-dioxane (a total of 90 mL of 1,4-dioxane was used). The three-way cock was attached to the eggplant flask again, and it was taken out of the glove box while keeping the inside of the eggplant flask under an Ar atmosphere. By depressurizing using an oil rotary vacuum pump and drying at 50 °C for 24 hours, the reaction product containing the target compound Mg[B(FP)(HFIP) 2 2 was obtained. The structure of Mg[B(FP)(HFIP) 2 2 was confirmed by nuclear magnetic resonance spectrum. The structure of Mg[B(FP)(HFIP) 2 2 is shown below.​​​​

[0167]

Chem.

[0168] (Comparative Example) According to the method described in Non-Patent Document 1, Mg[B(HFIP) 4 2 was synthesized. Magnesium borohydride was dissolved in dimethoxyethane, and 8.5 times the molar amount of hexafluoroisopropanol with respect to magnesium was added. The solution was maintained at room temperature and stirred for 24 hours, and then dried under reduced pressure to obtain a reaction product containing Mg[B(HFIP) 4 2 .

[0169] [Evaluation] The electrochemical activities of the reaction products of Example 1 and the comparative example were evaluated when used as the electrolyte of a magnesium secondary battery. All operations such as the preparation of the electrolyte, the assembly of the three-electrode cell and the battery were carried out in a glove box under an argon atmosphere.

[0170] By the method of Example 1, two kinds of products (Lot 1, Lot 2) manufactured on different days using different lots of raw materials were each blended with triethylene glycol dimethyl ether (0.3 mol / L) to prepare an electrolyte. Using platinum as the working electrode, 0.6 mL of the electrolyte was placed, Mg as the counter electrode, and silver as the reference electrode, a three-electrode cell was assembled. In a glove box under an argon atmosphere, a cyclic voltammetry test was performed at a scan rate of 50 mV / s. The results of the cyclic voltammetry test are shown in Figure 2.

[0171] In Figure 2, the horizontal axis represents the potential (vs Mg 2+ / Mg), and the vertical axis represents the current (mAcm -2 ). Also, in Figure 2, "cycle number" indicates the number of cycles, and in Figure 2, "1st": the first time and "10th": the tenth time are shown. ​​The potential was changed in the order shown by the numbers (1) to (6) and the arrows in Fig. 2. The redox currents observed near 0 V vs. Mg 2+ / Mg in Fig. 2 correspond to the dissolution and deposition of magnesium, respectively.

[0172] Next, using raw materials from different lots, two types of products (Lot C1, Lot C2) manufactured on different days were blended with triethylene glycol dimethyl ether (0.3 mol / L) according to the method of the comparative example to prepare electrolytes. Cycle voltage-current tests were performed on these electrolytes in the same manner as above. The results are shown in Fig. 3. In Fig. 3, the redox currents observed near 0 V vs. Mg 2+ / Mg correspond to the dissolution and deposition of magnesium, respectively. The legends etc. are the same as in Fig. 2.

[0173] According to Fig. 2, it can be seen that in Lot 1 and Lot 2, a large deposition / dissolution current flowed from the initial cycle (1st). According to Fig. 3, in Lot C1 and Lot C2, the current values are smaller compared to Lot 1 and Lot 2, and the response in the initial cycle (1st) is poor. Also, the peak shape on the dissolution side is distorted (the current flows stepwise). This suggests that there are impurities in the electrolyte. The results of Fig. 2 and Fig. 3 are summarized in Table 1.

[0174]

Table 1

[0175] Table 1 shows the overvoltage (deposition overvoltage / dissolution overvoltage) and current values (deposition current value / dissolution current value) for each lot. For example, the deposition overvoltage in the first cycle of Lot 1 is -0.48 V, the dissolution overvoltage is +0.05 V, the deposition current value is -0.6 mAcm -2 and the dissolution current value is +2.97 mAcm -2 respectively.

[0176] When an electrolyte containing a boron-based magnesium salt is applied to a magnesium secondary battery, its electrochemical activity can be evaluated by the overvoltage and current value in a cycle test. The smaller the absolute value of the overvoltage and / or the larger the absolute value of the current value, the higher the electrochemical activity.

[0177] Comparing Lot 1 and 2 with Lot C1 and C2, it can be seen that in Lot 1 and 2, the deposition overvoltage was halved and the dissolution overvoltage was reduced to about 1 / 10. Also, the corresponding current values were improved by about 3 to 20 times. From this result, it was found that Lot 1 and 2 have excellent electrochemical activity compared to Lot C1 and C2.

Explanation of Symbols

[0178] 1 Secondary battery 11 Positive electrode 12 Negative electrode 13 Electrolyte 14 Container

Claims

1. A boron-based magnesium salt consisting of any one of Mg[B(HFIP) 4 ] 2 represented by the following formula 12, Mg[B(HFIP) 3 (TFE)] 2 represented by the following formula 13, and Mg[B(FP)(HFIP) 2 ] 2 represented by the following formula 14. 【Chemistry 1】 【Chemistry 2】 【Chemistry 3】

2. An electrolyte solution comprising the boron-based magnesium salt according to claim 1 and a solvent.

3. The solvent has formula 11: R １１ (OC ２ H ４ ) ｐ OR １２ The electrolyte solution according to claim 2, comprising a compound represented by the formula: (In formula 11, R １１ and R １２ each independently represents a monovalent hydrocarbon group having 1 to 14 carbon atoms, and p represents an integer of 1 to 8.

4. The electrolyte solution of claim 3, wherein the compound represented by formula 11 is a symmetric glycol diether.

5. The electrolyte solution according to claim 4, wherein the compound represented by formula 11 is at least one selected from the group consisting of 1,2-dimethoxyethane (DME, glyme), diethylene glycol dimethyl ether (diglyme), triethylene glycol dimethyl ether (triglyme), and tetraethylene glycol dimethyl ether (tetraglyme).

6. A secondary battery comprising the electrolyte solution according to any one of claims 2 to 5.

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