JP2019186207A - Electrolyte solution for rocking chair type secondary battery, which is high in charge and discharge characteristics and low in aluminum collector corrosion, and rocking chair type secondary battery - Google Patents

Abstract

To provide: a dense electrolyte solution for a rocking chair type secondary battery, which eliminates the need for using an expensive additive agent, which has good ion conductivity and electric charge transfer resistance characteristic, which is superior in oxidation stability and thermal stability and/or which can suppress the corrosion of an Al current collector under a high positive electrode electric potential environment; and a rocking chair type secondary battery that uses the electrolyte solution.SOLUTION: An electrolyte solution for a rocking chair type secondary battery comprises: an alkali metal salt; an oxygen-containing solvent; and a metal ester compound represented by the following general formula (1): M[-O-(A-O)-R](1). In the electrolyte solution, the content of the alkali metal salt is 4-88 mass%. Otherwise, the oxygen-containing solvent of such a quantity that the oxygen-containing solvent/the alkali metal salt(mole ratio) is 0.7 or more and 4.0 or less is present in the electrolyte solution.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an electrolyte for a rocking chair type secondary battery and a rocking chair type secondary battery having high charge / discharge characteristics and low Al current collector corrosivity.

  2. Description of the Related Art Conventionally, so-called rocking chair type secondary batteries that charge and discharge by reciprocating ions in an electrolyte solution disposed between electrodes have been developed. In recent years, electrolytes having excellent oxidation stability and thermal stability have been demanded for next-generation rocking chair type secondary batteries. In addition, the current collector for the positive electrode of the rocking chair type secondary battery uses a metal (for example, Al (aluminum) or Al alloy) that forms a stable passive film on the surface in order to withstand corrosion by the electrolyte. However, in a next-generation rocking chair type secondary battery, a higher positive electrode potential (for example, around 4.0 V or higher) is assumed. However, in an environment with a high positive electrode potential (for example, exceeding 3.5 V), even a current collector having a passive film formed on the surface gradually undergoes corrosion, and Al is removed from the current collector. There is a concern that the battery performance may be degraded due to elution. Therefore, there is a demand for an electrolytic solution that hardly corrodes the positive electrode current collector even in a high positive electrode potential environment.

  Regarding the improvement of oxidation stability and thermal stability of the electrolyte, for example, by increasing the concentration of the alkali metal salt as the electrolyte to improve the charge / discharge performance, and by solvating the alkali metal salt and the solvent. An electrolyte solution having a high alkali metal salt concentration (that is, a concentrated electrolyte solution), which focuses on improving oxidation stability and thermal stability, has attracted attention. For example, Patent Document 1 relates to providing a lithium ion secondary battery excellent in safety and various battery characteristics. The carbon-based electrode is a negative electrode, various metal oxides are positive electrodes, and the electrolyte is a low molecular ether solvent as a solvent. A lithium ion secondary battery using a complex electrolyte in which a lithium salt having a concentration is dissolved is described.

  Concentrated electrolytes have the advantage of improved charge / discharge performance due to high alkali metal salt concentrations, but generally tend to be highly viscous. Since the movement of alkali metal ions derived from alkali metal salts is limited in high-viscosity electrolytes, reforming by adding additives such as viscosity modifiers to concentrated electrolytes has been widely performed. Patent Document 2 describes a nonaqueous electrolytic solution containing a chain ether compound having a specific structure, a lithium salt, and an ionic liquid. Patent Document 3 discloses a sulfur-based electrode active material including a negative electrode having carbon as a negative electrode active material and at least one selected from the group consisting of elemental sulfur, metal sulfide, metal polysulfide, and organic sulfur compound. A positive electrode as a positive electrode active material, a separator disposed between the negative electrode and the positive electrode, a lithium metal salt and four or five glymes of ether oxygen [O] in the molecule form a complex. A solvated ionic liquid, and a hydrofluoroether having a donor number of less than 10 that is miscible with the solvated ionic liquid and does not chemically react with lithium (ether oxygen [O] / lithium metal salt in glyme molecule) ) Having a molar ratio of less than 6 and an ionic conductivity (30 ° C.) of 1 mS / cm or more, and a viscosity (30 ° C.) of the electrolyte of 10 mPa · s or less, Describe secondary battery characterized by comprising.

Non-Patent Document 1 maintains a solvated structure by diluting a LiBF ₄ -based concentrated electrolyte with tris (2,2,2-trifluoroethyl phosphate) (TFEP), which is a fluorinated phosphate. In addition, the viscosity of the electrolyte can be reduced without impairing the oxidation resistance, and the high voltage operation LiNi _0.5 Mn _1.5 O ₄ (LNMO) / graphite (Gr) based lithium ion battery to which this is applied has the discharge characteristics and charge / discharge cycle characteristics. In addition, the TFEP diluted electrolyte is further diluted with bis (2,2,2-trifluoroethyl) carbonate (FDEC), which is a fluorinated chain carbonate, as a second diluent solvent. by applying the voltage differential _{LiNi 0.5 Co 0.2 Mn 0.3 O 2} (NCM523) / Gr -based lithium-ion battery, Wei the oxidation resistance of LiBF ₄ system dense electrolyte While the describes that can improve further the battery characteristics.

  On the other hand, as a method of suppressing corrosion of the current collector, a method of selecting the type of electrolyte salt (for example, lithium salt in a lithium ion battery) and solvent in the electrolyte solution, decomposition on the current collector surface to form a protective film A method of adding such a compound as an additive in an electrolytic solution, alloying of a current collector, various processes (such as coating of an inorganic layer or an organic layer), and the like are known.

  Patent Document 4 discloses a non-aqueous electrolyte used for an electricity storage device including a current collector containing aluminum or an aluminum alloy, and a polyethylene oxide derivative having a specific structure. And a nonaqueous electrolytic solution for an electricity storage device, wherein lithium bis (trifluoromethanesulfonyl) amide is dissolved as a supporting electrolyte in a nonaqueous solvent containing an aprotic organic solvent.

Patent Document 5 is a lithium ion secondary battery provided with a positive electrode, a negative electrode, and a non-aqueous electrolyte, and the non-aqueous electrolyte includes LiPF ₆ and an imide salt having a specific structure. The body is an aluminum foil having a purity of 97.0% or more and 99.0% or less.

  Patent Document 6 is a nonaqueous electrolyte secondary battery having a positive electrode, a negative electrode, and an electrolytic solution, wherein the positive electrode has a positive electrode current collector made of aluminum or an aluminum alloy, and the electrolytic solution is: A salt having alkali metal, alkaline earth metal or aluminum as a cation, and an organic solvent having a hetero element, and the peak intensity derived from the organic solvent in the vibrational spectrum of the electrolyte solution is a peak of the original peak of the organic solvent. A nonaqueous electrolyte secondary battery characterized in that Is> Io, where Io is the intensity and Is is the intensity of the peak shifted from the peak, is described.

  Patent Document 7 describes an electrolyte solution containing an electrolyte salt and an electrolyte solvent, wherein the electrolyte solvent contains a specific ratio of fluorinated acyclic dialkyl carbonate with respect to 100% by weight of the total amount of the electrolyte solvent. .

JP 2012-104268 A JP-A-2006-91926 JP 2014-112526 A JP 2014-157672 A JP 2017-84739 A Japanese Patent Laid-Open No. 2006-189340 Japanese Translation of PCT National Publication No. 2006-532237

Takahashi et al., “Application of LiBF4 Concentrated Electrolyte with Diluting Solvent to High Voltage Operated Lithium Ion Batteries”, 58th Battery Conference (2017) Abstract, 1E04

  However, for example, the fluorine-based compound contributes to the improvement of charge / discharge performance by reducing the viscosity of the concentrated electrolyte solution, but is expensive and has room for improvement in terms of cost. Of the fluorine-based compounds, hydrofluoroether (HFE) and hydrofluorocarbon (HFC) are generally highly volatile and have a boiling point of 100 ° C. or less. It is considered that the battery characteristics are adversely affected by the generation of bubbles in the battery. In particular, in recent years, electrolytes have been required to have good oxidation stability that is difficult to decompose even in combination with electrodes of a wide range of materials and good thermal stability suitable for use under high temperature conditions. However, a technique for obtaining an electrolytic solution exhibiting such good oxidation stability and thermal stability and excellent charge / discharge performance has not yet been established. One embodiment of the present invention is a rocking chair that solves the above-described problems, does not require the use of an expensive additive, has good ionic conductivity and charge transfer resistance characteristics, and is excellent in oxidation stability and thermal stability. It is an object to provide an electrolytic solution for a type secondary battery and a rocking chair type secondary battery using the same.

In addition, as described above, as a measure for suppressing corrosion of a current collector containing Al or an Al alloy (also referred to as “Al current collector” in the present disclosure), the molecular structure of the solvent or electrolyte salt is specified. In this case, on the surface of the Al current collector, a passive film (for example, Al ₂ O ₃ , and LiF, AlF ₃ or the like when the electrolyte salt is a fluoride, for example) is provided. Can be formed. However, the conventional technology has not yet sufficiently obtained the corrosion-inhibiting effect of the current collector even in an environment with a high positive electrode potential (for example, 4.0 V or more) as expected in the next-generation rocking chair type secondary battery. . An object of one embodiment of the present invention is to avoid corrosion of an Al current collector even when a rocking chair type secondary battery is used in an environment having a high positive electrode potential (for example, 4.0 V or more).

The present invention includes the following aspects.
[1] An electrolyte for a rocking chair type secondary battery,
The electrolytic solution is an alkali metal salt, an oxygen-containing solvent, and the following general formula (1):
M [—O— (A ¹ —O) _m —R ¹ ] ₃ (1)
(In the formula, M represents a trivalent element selected from the group consisting of boron and aluminum, A ¹ represents each independently an alkylene group having 2 to 4 carbon atoms in the formula, and m represents each independently in the formula. is an integer of 0 to 50, and R ¹ represents an aliphatic hydrocarbon group having a carbon number of 1 to 13 independently in formula.)
And a metal ester compound represented by
The electrolyte solution whose content of the alkali metal salt in the electrolyte solution is 4 to 88% by mass.
[2] An electrolyte for a rocking chair type secondary battery,
The electrolytic solution is an alkali metal salt, an oxygen-containing solvent, and the following general formula (1):
M [—O— (A ¹ —O) _m —R ¹ ] ₃ (1)
(In the formula, M represents a trivalent element selected from the group consisting of boron and aluminum, A ¹ represents each independently an alkylene group having 2 to 4 carbon atoms in the formula, and m represents each independently in the formula. is an integer of 0 to 50, and R ¹ represents an aliphatic hydrocarbon group having a carbon number of 1 to 13 independently in formula.)
And a metal ester compound represented by
The oxygen-containing solvent is an electrolyte solution in which the oxygen-containing solvent / alkali metal salt (molar ratio) is present in the electrolyte solution in an amount of 0.7 or more and 4.0 or less.
[3] In the above aspect 1 or 2, the oxygen-containing solvent is present in the electrolytic solution in an amount such that the oxygen-containing solvent / the alkali metal salt (molar ratio) is 0.9 or more and 1.1 or less. Electrolyte of description.
[4] In any one of the above aspects 1 to 3, wherein in the general formula (1), M is aluminum, A ¹ is an ethylene group, m is 3 to 9, and R ¹ is a methyl group. Electrolyte of description.
[5] The electrolyte solution according to any one of the above aspects 1 to 4, wherein the oxygen-containing solvent is selected from the group consisting of an ether compound and a carbonyl compound.
[6] The oxygen-containing solvent is represented by the following general formula (2):
R ² O— (A ² —O) _n —R ² (2)
(In the formula, A ² each independently represents an alkylene group having 2 to 4 carbon atoms, n is an integer of 0 to 10, and R ² is independently an integer of 1 to 13 carbon atoms in the formula. Represents a hydrocarbon group.)
The electrolyte solution according to the aspect 5, which is an alkylene glycol dialkyl ether compound represented by the formula:
[7] The electrolytic solution according to the above aspect 6, in which, in the general formula (2), A ² is an ethylene group, n is 3, and R ² is a methyl group.
[8] The lithium salt contains lithium bis (trifluoromethanesulfonyl) imide (LiTFSI), lithium bis (fluorosulfonyl) imide (LiFSI), lithium tetrafluoroborate (LiBF ₄ ), and lithium hexafluorophosphate (LiPF _6). The electrolyte solution in any one of the said aspects 1-7 selected from the group which consists of.
[9] The electrolyte solution according to any one of the above aspects 1 to 8, comprising a complex of an alkali metal derived from the alkali metal salt and the oxygen-containing solvent.
[10] A rocking chair type secondary battery including the positive electrode, the negative electrode, and the electrolyte solution according to any one of the above aspects 1 to 9.

  According to one embodiment of the present invention, it is not necessary to use an expensive additive, the ion conductivity and the charge transfer resistance characteristics are good, and the rocking chair type secondary battery is excellent in oxidation resistance and thermal stability. And a rocking chair type secondary battery using the same. Further, according to one embodiment of the present invention, even when a rocking chair type secondary battery including an Al current collector is used in an environment having a high positive electrode potential (eg, 4.0 V or more), the Al current collector is hardly corroded. An electrolyte for a rocking chair type secondary battery and a rocking chair type secondary battery using the same are provided.

FIG. 1 is a diagram illustrating a measurement result of charge transfer resistance. FIG. 2 is a diagram showing the measurement result of the oxidation side potential window. FIG. 3 is a diagram showing the results of a charge / discharge test (LFP / LTO electrode). FIG. 4 is a diagram showing the results of a charge / discharge test (LFP / LTO electrode). FIG. 5 is a diagram showing the results of a charge / discharge test (LCO / LTO electrode). FIG. 6 is a diagram showing the results of a charge / discharge test (NMC / LTO electrode).

  Hereinafter, exemplary embodiments of the present invention will be described, but the present invention is not limited to the following embodiments.

<Electrolytic solution for rocking chair type secondary battery>
One embodiment of the present invention provides an electrolyte solution for a rocking chair type secondary battery, which includes an alkali metal salt, an oxygen-containing solvent, and a metal ester compound having a specific structure.

  In one aspect | mode, content of the alkali metal salt in electrolyte solution is 4-88 mass%. In one embodiment, the oxygen-containing solvent is present in the electrolytic solution in an amount such that the oxygen-containing solvent / alkali metal salt (molar ratio) is 0.7 or more and 4.0 or less. An electrolytic solution having such a content of alkali metal salt and / or a content ratio (molar ratio) between the oxygen-containing solvent and the alkali metal salt is one of typical embodiments of the concentrated electrolytic solution.

  In one embodiment, at least a part, preferably substantially all of the alkali metal derived from the alkali metal salt forms a complex with the oxygen-containing solvent in the electrolytic solution. An electrolytic solution in which substantially all of the alkali metal forms a complex with the oxygen-containing solvent is one of the typical embodiments of the concentrated electrolytic solution. The content of the alkali metal salt and each of the oxygen-containing solvent / alkali metal salt (molar ratio) are advantageous from the viewpoint of ease of forming a complex of the alkali metal and the oxygen-containing solvent. The formation of the complex is advantageous in terms of oxidation stability and thermal stability of the electrolytic solution, and corrosion inhibition of the Al current collector when an Al current collector is used as the current collector. The presence of the complex can be confirmed by thermogravimetry.

  The content of the alkali metal salt in the electrolytic solution is 4% by mass or more, preferably 20% by mass or more, more preferably 50% by mass or more, in one embodiment, from the viewpoint of favorable formation of the concentrated electrolytic solution. In addition, from the viewpoint of allowing an oxygen-containing solvent and a metal ester compound to be present in an appropriate amount as desired in an electrolytic solution, in one embodiment, it is 88% by mass or less, preferably 80% by mass or less, more preferably 70% by mass or less. is there.

  In one embodiment, the oxygen-containing solvent / alkali metal salt (molar ratio) is 0.7 or more, preferably 0.8 or more, more preferably 0, from the viewpoint of ease of movement of alkali metal ions in the electrolytic solution. From the viewpoint of obtaining good oxidative stability as a concentrated electrolyte, it is 4.0 or less, preferably 2.0 or less, more preferably 1.1 or less.

[Metal ester compounds]
In one embodiment, the metal ester compound has the following general formula (1):
M [—O— (A ¹ —O) _m —R ¹ ] ₃ (1)
(In the formula, M represents a trivalent element selected from the group consisting of boron and aluminum, A ¹ represents each independently an alkylene group having 2 to 4 carbon atoms in the formula, and m represents each independently in the formula. is an integer of 0 to 50, and R ¹ represents an aliphatic hydrocarbon group having a carbon number of 1 to 13 independently in formula.)
It is represented by

  Although not wishing to be bound by theory, the Lewis acidity of boron or aluminum of the metal ester compound is the oxygen derived from the solvent (for example, ether oxygen or carbonyl oxygen) in a complex composed of an alkali metal and an oxygen-containing solvent. By reducing the activation energy of alkali metal desolvation, it is possible to maintain good oxidation stability and thermal stability due to complex formation between the alkali metal and the oxygen-containing solvent while maintaining the desired degree of alkalinity. It is considered that high ion conductivity and low charge transfer resistance can be realized by good mobility of metal ions in the electrolyte. In particular, a metal ester compound having an alkylene oxide chain may have a more remarkable effect of reducing charge transfer resistance compared to a metal ester compound having no alkylene oxide chain. Ether oxygen in the alkylene oxide chain is thought to reduce the charge transfer resistance near the electrode-electrolyte interface by entraining the desolvated alkali metal ions and bridging them to the electrode.

  Further, the metal ester compound represented by the general formula (1) contributes particularly to the corrosion inhibition of the Al current collector. Without being bound by theory, the corrosion of the current collector is caused by the solvent molecules and electrolyte components in the electrolyte solution. It is effective to suppress direct contact with the body. The metal ester compound represented by the general formula (1) is arranged on the surface of the current collector due to the high affinity with the Al current collector by the group 13 element (that is, boron or aluminum). It is considered that a protective layer is formed thereon. Thereby, it is thought that the solvent molecule | numerator and electrolyte component in electrolyte solution become difficult to approach the surface of Al collector, and the corrosion inhibitory effect is acquired. The electrolytic solution of the present disclosure contributes to high performance of the next-generation battery in order to satisfactorily suppress the corrosion of the current collector even in a secondary battery used in a high positive electrode potential environment of, for example, 4.0 V or higher. . In particular, since the electrolytic solution of the present disclosure can suppress corrosion of the current collector without requiring processing of the current collector, the battery manufacturing process can be simplified and the cost can be reduced accordingly.

  In general formula (1), M is a trivalent element selected from the group consisting of boron and aluminum from the viewpoint of promoting desolvation of alkali metal due to the contribution of Lewis acidity. M is preferably aluminum from the viewpoint of a good function as Lewis acidity and a good affinity with an Al current collector.

In the general formula (1), A ¹ is each independently in the formula (that is, they may be the same or different from each other in the case where there are a plurality of formulas), from the viewpoint of obtaining a good effect of reducing the charge transfer resistance. It is an alkylene group having 2 to 4, preferably an ethylene group.

  In the general formula (1), m is an integer of 0 to 50 in the formula independently of each other (that is, they may be the same or different when there are a plurality of formulas). m is preferably 3 or more from the viewpoint of obtaining a good effect of reducing the charge transfer resistance. On the other hand, if the value of m is too large, (1) the periphery of the metal portion of the metal ester compound becomes bulky, and it becomes difficult to interact with oxygen in the oxygen-containing solvent. (2) alkylene oxide of the metal ester compound If the chain is too long, it becomes difficult to transport the desolvated alkali metal ion (that is, there is an optimal ethylene oxide chain length for transporting the alkali metal ion well) and / or (3) the alkylene of the metal ester compound If the oxide chain is too long, it is conceivable that the oxidative stability decreases due to the oxidative decomposition of the alkylene oxide chain. From the above viewpoint, m is 50 or less, preferably 20 or less, more preferably 9 or less. m is preferably 3 from the viewpoint of a good corrosion inhibitory effect of the Al current collector.

In general formula (1), each R ¹ is independently in the formula (ie, when there are a plurality of formulas, they may be the same or different from each other), the effect of reducing charge transfer resistance, and the inhibition of corrosion of the Al current collector From the viewpoint of obtaining good effects, it is an aliphatic hydrocarbon group having 1 to 13 carbon atoms. An aliphatic hydrocarbon group can be linear, branched, or alicyclic, and can be saturated or unsaturated. Examples of R ¹ include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a t-butyl group, a pentyl group, an isopentyl group, a hexyl group, a 2-ethylhexyl group, a lauryl group, and a tridecyl group. And is preferably a methyl group, an ethyl group, or a propyl group, and particularly preferably a methyl group. Examples of the alkenyl group having 3 to 6 carbon atoms of R ¹ include allyl group, 2-methylallyl group, 3,3-dimethylallyl group, 2,3,3-trimethylallyl group, and preferably allyl group. 2-methylallyl group, particularly preferably an allyl group. As the acryloyl group or methacryloyl group for R ¹ , a methacryloyl group is particularly preferred.

The total carbon number of a plurality of R ¹ in the formula is the viewpoint of good affinity with oxygen in the oxygen-containing solvent and the desolvated alkali metal ion, and the viewpoint of the good corrosion inhibitory effect of the Al current collector. Therefore, it is preferably 9 or less, more preferably 5 or less. R ¹ may have a structure having a substituent, and the carbon number of R ¹ in this case is a number including the substituent. Substituents include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, t-butyl, pentyl, isopentyl, hexyl, 2-ethylhexyl, lauryl, tridecyl, carbon number Examples include 1-5 alkoxy groups, fluoro groups, chloro groups, bromo groups, cyano groups, nitro groups, hydroxyl groups, aldehyde groups, carboxyl groups, and the like. In one embodiment, R ¹ has no substituent. R ¹ is preferably a methyl group, an ethyl group, or a propyl group, and more preferably a methyl group.

In a particularly preferred embodiment, in the general formula (1), M is aluminum, A ¹ is an ethylene group, m is 3 to 9, and R ¹ is a methyl group.

  Although the manufacturing method of the metal ester compound represented by General formula (1) is not specifically limited, For example, it can manufacture with the following method. In a typical embodiment, the metal ester compound represented by the general formula (1) can be obtained by a transesterification reaction between a trialkyl metal ester and a polyalkylene glycol derivative.

  The metal in a trialkyl metal ester is a metal corresponding to the metal (namely, boron or aluminum) which the target metal ester compound has. As the alkyl group of the trialkyl metal ester, a linear or branched lower alkyl group having 1 to 8 carbon atoms such as a methyl group, an ethyl group, a propyl group, an isopropyl group, an isobutyl group, a t-butyl group, and sec-butyl group, pentyl group, isopentyl group, hexyl group, and 2-ethylhexyl group, preferably methyl group, ethyl group, propyl group, isopropyl group, butyl group, isobutyl group, t-butyl group, A sec-butyl group is exemplified, and an isopropyl group and a sec-butyl group are particularly preferable.

As a polyalkylene glycol derivative, the following general formula (1a):
_{^{HO- (A 1 -O) m -R}} 1 (1a)
(In the formula, A ¹ , m and R ¹ are the same as defined in the general formula (1).)
And a compound having A ¹ , m, and R ¹ corresponding to A ¹ , m, and R ¹ of the target metal ester compound can be used.

  The transesterification reaction is usually carried out under heating. Since the transesterification reaction is an equilibrium reaction, it is preferable to carry out the reaction while removing alcohol generated as a result of the reaction from the reaction system in order to advance the reaction quickly. A known method is used as the removal method, and examples thereof include a method of removing by distillation, a method of removing by adsorbing to an adsorbent such as molecular sieve, and the like. The reaction temperature and distillation pressure vary depending on the raw material polyalkylene glycol derivative and trialkyl metal ester, but the reaction temperature is usually room temperature to 250 ° C, preferably 50 to 200 ° C, particularly preferably. 50 to 150 ° C. The distillation pressure is normal pressure to 0.5 mmHg, preferably normal pressure to 5 mmHg, and particularly preferably normal pressure to 10 mmHg.

  There is no need to use a reaction solvent, but when it is used, there is no particular limitation as long as it does not react with the resulting metal ester compound, and aromatic hydrocarbons such as toluene, xylene, benzene, hexane, heptane, octane. Aliphatic hydrocarbons such as cyclohexane and cycloheptane, cyclic ethers such as dioxane and tetrahydrofuran, ethers such as diethyl ether and isopropyl ether, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, and triethylene glycol Examples include glymes such as dimethyl ether, esters such as ethyl acetate and methyl acetate, preferably aromatic hydrocarbons such as toluene, xylene and benzene, aliphatic hydrocarbons such as hexane, heptane and octane, cyclohexane Particularly preferred are cycloaliphatic hydrocarbons such as cycloheptane, cyclic ethers such as dioxane and tetrahydrofuran, ethers such as diethyl ether and isopropyl ether, and glymes such as ethylene glycol dimethyl ether, diethylene glycol dimethyl ether and triethylene glycol dimethyl ether. Are aromatic hydrocarbons such as toluene, xylene and benzene, aliphatic hydrocarbons such as hexane, heptane and octane, and alicyclic hydrocarbons such as cyclohexane and cycloheptane.

  A polymerization inhibitor may be added to the polymerization system in order to prevent polymerization of the metal ester compound that is a reaction product. Polymerization inhibitors include the group of hydroquinone compounds, sterically hindered phenols, sterically hindered amines and hydroxyamine derivatives. Examples of hydroquinone compounds include hydroquinone and hydroquinone monomethyl ether. Examples of sterically hindered phenols include 4-methyl 2,6-di-t-butylphenol and 2,4-dimethyl-6-t-butylphenol. Examples of hydroxyamine derivatives such as 2,2,6,6-tetramethylpiperidine-N-oxyl and 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl include N, N -Diethylhydroxylamine etc. can be mentioned, You may use combining 2 or more types of polymerization inhibitors.

  While the reaction time varies depending on the reaction temperature and the raw material compound, the reaction time is usually 1 to 30 hours, preferably 2 to 20 hours, particularly preferably 2 to 10 hours.

  For the isolation of the produced metal ester compound represented by the general formula (1), a known method is used. For example, when the reaction yield is high and it is not particularly necessary to perform a purification operation or a decolorization operation, it is only necessary to perform filtration. It is enough. When a solvent is used, it can be isolated by distilling off the solvent after filtration. Moreover, purification operation and decoloring operation can also be performed as needed. As the purification operation, a known method is used, and column chromatography and the like can be mentioned. As the decoloring operation, a known method is used, and examples thereof include adsorbent treatment such as activated carbon treatment, silica treatment, and Kyodo word treatment.

[Alkali metal salt]
The alkali metal salt can be various alkali metal salts understood by those skilled in the art to be useful as an electrolyte for a rocking chair type secondary battery. The alkali metal can be selected from lithium, sodium, potassium, rubidium, and cesium, but is preferably lithium, sodium, or potassium from the viewpoint of availability or production, and is easily complexed with an oxygen-containing solvent. From the viewpoint of safety, lithium is more preferable. That is, in a preferred embodiment, the electrolytic solution is a lithium ion battery electrolytic solution.

Counter anions constituting the alkali metal salt include Cl, Br, I, BF ₄ , PF ₆ , CF ₃ SO ₃ , SCN, ClO ₄ , CF ₃ CO ₂ , AsF ₆ , SbF ₆ , AlCl ₄ , N (CF ₃ SO ₂ ) ₂ , N (CF ₃ CF ₂ SO ₂ ) ₂ , PF ₃ (C ₂ F ₅ ) ₃ , N (FSO ₂ ) ₂ , N (FSO ₂ ) (CF ₃ SO ₂ ), N (CF ₃ CF ₂ SO ₂ ) ₂ , N (C ₂ F ₅ SO ₂ ) ₂ , N (C ₂ F ₄ S ₂ O ₄ ), N (C ₃ F ₆ S ₂ O ₄ ), N (CN) ₂ , N ( Examples thereof include CF ₃ SO ₂ ) (CF ₃ CO), C (CF ₃ SO ₂ ) _{3 and the} like.

As a lithium salt which is a suitable example of an alkali metal salt, various lithium salts that are understood by those skilled in the art to be useful as an electrolyte for a rocking chair type secondary battery, for example, LiTFSI (lithium bis (trifluoromethanesulfonyl) Imide), LiFSI (lithium bis (fluorosulfonyl) imide), LiBF ₄ , LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , Li (C ₂ F ₅ SO ₂ ) ₂ N, Li (CF ₃ SO ₂ ) ₃ C, LiI, LiSCN, etc. can be used, but the lithium salt is preferably LiTFSI (lithium bis (trifluoromethanesulfonyl) imide), LiFSI (lithium bis (fluorosulfonyl) imide), LiBF ₄ (tetrafluoroboric acid). Lithium) and LiPF ₆ (hexafluorophosphate) Selected from the group consisting of:

When the alkali metal salt is LiPF ₆ , LiPF ₆ can form a passive film of a fluorine compound (LiF, AlF _3, etc.) on the Al current collector. For example, when the alkali metal salt is an imide lithium salt or the like Compared with, the corrosion effect of the Al current collector is better and preferable.

[Oxygen-containing solvent]
The oxygen-containing solvent can be selected from various compounds that can be understood by those skilled in the art to be a compound capable of forming a complex with an alkali metal derived from an alkali metal salt. From the viewpoint of ease of complex formation, ether oxygen and / or carbonyl It is preferable to have oxygen. That is, the oxygen-containing solvent is preferably selected from the group consisting of ether compounds and carbonyl compounds.

The oxygen-containing solvent is preferably an ether compound in that it has a good complex forming ability with an alkali metal, and more preferably the following general formula (2):
R ² O— (A ² —O) _n —R ² (2)
(In the formula, A ² each independently represents an alkylene group having 2 to 4 carbon atoms, n is an integer of 0 to 10, and R ² is independently an integer of 1 to 13 carbon atoms in the formula. Represents a hydrocarbon group.)
It is an alkylene glycol dialkyl ether compound represented by these.

In the general formula (2), each A ² is independently carbon in the formula (that is, they may be the same or different from each other in the case where a plurality of formulas are present), from the viewpoint of ease of forming a complex with an alkali metal. It is an alkylene group of 2 to 4, preferably an ethylene group or a propylene group, and more preferably an ethylene group.

  In general formula (2), n is an integer of 0-10. n is preferably 2 or more from the viewpoint of ease of forming a complex with an alkali metal, and is 10 or less, preferably 7 or less, more preferably 5 or less from the viewpoint of ease of forming a complex with an alkali metal. is there. n is most preferably 3.

In the general formula (2), R ^{2 s} are each independently in the formula (that is, they may be the same or different when there are a plurality of formulas), from the viewpoint of ease of forming a complex with an alkali metal. It is a hydrocarbon group of formula 1-13. The hydrocarbon group can be aliphatic (ie, linear, branched, or alicyclic) or aromatic, and can be saturated or unsaturated. Examples of R ² include methyl group, ethyl group, propyl group, isopropyl group, butyl group, isobutyl group, t-butyl group, pentyl group, isopentyl group, hexyl group, 2-ethylhexyl group, lauryl group, and tridecyl group. Preferred are a methyl group, an ethyl group, and a propyl group, and particularly preferred is a methyl group. The total number of carbon atoms of the plurality of R ² in the formula is preferably 9 or less, more preferably 5 or less, from the viewpoint of obtaining a good ionic conductivity by making the electrolytic solution relatively low in viscosity. R ² may have a structure having a substituent, and the carbon number of R ² in this case is a number including the substituent. As the substituent, methyl group, ethyl group, propyl group, isopropyl group, butyl group, isobutyl group, t-butyl group, pentyl group, isopentyl group, hexyl group, 2-ethylhexyl group, lauryl group, tridecyl group, carbon number Examples include 1-5 alkoxy groups, fluoro groups, chloro groups, bromo groups, cyano groups, nitro groups, hydroxyl groups, aldehyde groups, carboxyl groups, and the like. In one embodiment, R ² has no substituent. R ² is preferably a methyl group, an ethyl group, or a propyl group, and more preferably a methyl group.

In a particularly preferred embodiment, in general formula (2), A ² is an ethylene group, n is 3, and R ² is a methyl group (that is, triethylene glycol dimethyl ether).

  Examples of the carbonyl compound include dimethyl carbonate, ethylene carbonate, diethyl carbonate, propylene carbonate, butylene carbonate, methyl ethyl carbonate, vinylene carbonate, methyl vinylene carbonate, ethyl vinylene carbonate, phenyl ethylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, tri Carbonates such as fluoroethylene carbonate; aliphatic carboxylic acid esters such as methyl formate, methyl acetate, methyl propionate, ethyl propionate, ethyl acetate, propyl acetate, butyl acetate, aluminum acetate; γ-butyllactone, γ-valero Lactones such as lactones; trimethyl phosphate, ethyl dimethyl phosphate, diethyl methyl phosphate, triethyl phosphate Phosphoric esters such as N; amides such as N-methylformamide, N-ethylformamide, N, N-dimethylformamide, N, N-dimethylacetamide, N-methylpyrrolidinone, N-vinylpyrrolidone; dimethylsulfone, ethyl And sulfur compounds such as methylsulfone, diethylsulfone, sulfolane, 3-methylsulfolane, and 2,4-dimethylsulfolane.

[Other ingredients]
In addition to the above components, the electrolyte solution contains additives such as viscosity modifiers, antioxidants, film forming agents, preservatives, surfactants, stabilizers, ultraviolet absorbers, inorganic or organic fillers, flame retardants, etc. Further, it may be included. For example, the electrolytic solution may contain hydrofluoroether in an amount of preferably 30 to 70% by mass, more preferably 50 to 70% by mass.

  The electrolytic solution can be produced by mixing an oxygen-containing solvent, an alkali metal salt, a metal ester compound, and other optional components in a dry room.

  In a rocking chair type secondary battery, stability against an electrode potential (that is, a potential window) is important. The potential (oxidation or reductive decomposition potential) at which the decomposition current (obtained as a function of the potential) when the oxidation and reductive decomposition of the electrolytic solution are tested with an electrode with a controlled potential is obtained as a potential window. It becomes an index of the oxidation stability of the liquid. The potential window of the electrolytic solution is preferably 3 V or higher, more preferably 4 V or higher, and still more preferably 5 V or higher. The potential window is a value measured by a linear sweep voltammetry method.

  The current value measured for the Al / Li electrode by the linear sweep voltammetry method can be an indicator of the corrosion of the Al current collector by the electrolytic solution. In particular, in the measurement by the linear sweep voltammetry method, the current value does not increase remarkably even at a high potential of, for example, 4.0 V or higher. This is a rocking chair type secondary using an Al current collector at a high positive electrode potential of, for example, 4.0 V. In a battery, it represents that corrosion of the Al current collector is satisfactorily suppressed by the electrolytic solution. In the linear sweep voltammetry method, in a preferred embodiment, the current value measured under the conditions described in or equivalent to [Example] of the present specification is the current value at a potential of 4.0 V, the current value at a potential of 3.5 V, and In a more preferred embodiment, the difference between the current value at a potential of 4.5 V and a potential of 3.5 V is 16.0 μA or less.

<Rocking chair type secondary battery>
One embodiment of the present invention provides a rocking chair type secondary battery including a positive electrode, a negative electrode, and the electrolytic solution of the present disclosure. In a preferred embodiment, the rocking chair type secondary battery is a lithium ion battery. Active materials for positive electrodes include lithium cobalt oxide, lithium manganate, lithium iron phosphate, nickel manganese lithium cobalt oxide (NMC), nickel cobalt lithium aluminate (NCA), etc., sulfur alone, lithium polysulfide (Li2Sx (0 <x ≦ 8)), sulfur-based metal polysulfides (MSx (M = Ni, Cu, Fe, 0 <x ≦ 2)), organic disulfide compounds, sulfur compounds such as carbon sulfide compounds, negative electrodes Active materials include carbon-based materials such as graphite, hard carbon, and soft carbon, crystalline or amorphous silicon alone, silicon-containing compounds such as silicon oxide, silicone resin, and silicon-containing polymer compounds, lithium titanate LiC, LiSi, LiGr, Li metal, etc. can be used, but the configuration of the electrodes is not limited. In one embodiment, the rocking chair type secondary battery includes a separator disposed between the positive electrode and the negative electrode. As the separator, various sheet-like materials that can hold an electrolytic solution, for example, porous films formed from materials such as polyolefin, polyimide, cellulose, and glass, nonwoven fabrics, and the like can be used.

  EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, the scope of the present invention is not limited to the following Example.

<Metal ester compound 1>
Aluminum-tri sec butoxide (“Aluminum sec-butoxide A-0244” manufactured by Tokyo Chemical Industry Co., Ltd.) was used.

<Metal ester compound 2>
Using the metal ester compound 1 as a raw material, the metal ester compound 2 was synthesized by the following procedure.
In a dry room having a dew point temperature of −40 ° C. or lower, 20.20 g (0.082 mol) of aluminum-trisec butoxide (manufactured by Tokyo Chemical Industry Co., Ltd.) and triethylene glycol monomethyl ether (molecular weight 164.19: Japanese emulsifier) MTG) (40.39 g, 0.246 mol) was mixed to form a transesterification reaction system. The reaction system was heated to 60 to 65 ° C. with a water bath while stirring under nitrogen bubbling. After dissolving aluminum-trisec butoxide, the transesterification reaction was allowed to proceed while maintaining 60 to 65 ° C. for about 2 hours. Thereafter, the by-product free isobutyl alcohol was removed while the pressure of the reaction system was gradually reduced to 10 mmHg (1.3 kPa) over about 3 hours. Thereafter, the reaction system was cooled to room temperature and then filtered to obtain 42.3 g (yield 99.9%) of metal ester compound 2 (Al [O (CH ₂ CH ₂ O) ₃ CH ₃ ] ₃ ). It was.

<Metal ester compound 3>
Using the metal ester compound 1 as a raw material, the metal ester compound 3 was synthesized by the following procedure.
In a dry room having a dew point temperature of −40 ° C. or lower, 20.20 g (0.082 mol) of aluminum-trisec butoxide (manufactured by Tokyo Chemical Industry Co., Ltd.) and polyethylene glycol monomethyl ether (molecular weight 427.83: Japanese emulsifier ( MPG-130) (105.2 g) (0.246 mol) was mixed to form a transesterification reaction system. The reaction system was heated to 60 to 65 ° C. with a water bath while stirring under nitrogen bubbling. After dissolving aluminum-trisec butoxide, the transesterification reaction was allowed to proceed while maintaining 60 to 65 ° C. for about 2 hours. Thereafter, the by-product free isobutyl alcohol was removed while the pressure of the reaction system was gradually reduced to 10 mmHg (1.3 kPa) over about 3 hours. Thereafter, the reaction system is cooled to room temperature and then filtered to obtain 106.7 g (yield 99.5%) of metal ester compound 3 (Al [O (CH ₂ CH ₂ O) ₉ CH ₃ ] ₃ ). It was.

<Metal ester compound 4>
Tributyl borate (Tokyo Chemical Industry Co., Ltd. tributyl borate B-0518) was used.

<Metal ester compound 5>
The metal ester compound 5 was prepared in the same manner as the synthesis of the metal ester compound 2 except that 18.87 g (0.082 mol) of the metal ester compound 4 was used instead of 20.20 g (0.082 mol) of the metal ester compound 1. 40.98 g (yield 99.9%) of (B [O (CH ₂ CH ₂ O) ₃ CH ₃ ] ₃ ) was obtained.

<Metal ester compound 6>
Metal ester compound 6 In the same manner as the synthesis of metal ester compound 3 except that 18.87 g (0.082 mol) of metal ester compound 4 was used instead of 20.20 g (0.082 mol) of metal ester compound 1, metal ester compound 6 (B [O (CH ₂ CH ₂ O) ₉ CH ₃ ] ₃ ) 105.6 g (yield 99.7%) was obtained.

<Preparation of mixture 1 containing lithium / solvent complex>
Triethylene glycol dimethyl ether (“DMTG” manufactured by Nippon Emulsifier Co., Ltd.) and LiTFSI (lithium bis (trifluoromethanesulfonyl) imide) dried dehydrated product (“Bis (trifluoromethanesulfonyl) imide lithium” manufactured by Tokyo Chemical Industry Co., Ltd.) And equimolar with a stirrer at room temperature overnight to give mixture 1. When the mixture 1 was examined by a thermogravimetric method (TG-DTA 2000S MacScience), it was confirmed that lithium and the solvent formed a complex.

<Preparation of mixture 2 containing lithium / solvent complex>
In a mixed solvent of ethylene carbonate (EC manufactured by Toa Gosei Co., Ltd.): Ethyl methyl carbonate (EMC manufactured by Ube Industries, Ltd.) = 3: 7 (volume ratio) at a concentration of 1 mol / L, LiPF ₆ (hexafluoro Lithium phosphate) (Mixed hexafluorophosphate manufactured by Kanto Denka Kogyo Co., Ltd.) (mixed solvent / LiPF ₆ molar ratio = 10.8 / 1) was mixed overnight at room temperature with a stirrer, Obtained.

<Preparation of Electrolytic Solutions 1-16 and Comparative Electrolytic Solution A>
With respect to the mixture 1 obtained above, each of the metal ester compounds 1 to 6 was added so as to have a mol% shown in Tables 1 and 2 (extra percentage with respect to 100 mol% of the alkali metal salt), and a room temperature was obtained with a stirrer. Were mixed overnight to obtain electrolytes 1-16. Moreover, the mixture 1 obtained above was used as a comparative electrolytic solution A.

<Preparation of Electrolytic Solutions 17 and 18 and Comparative Electrolytic Solution B>
To the mixture 2 obtained above, each of the metal ester compounds 3 and 4 is added so as to be 1.8 mol% (extra percentage with respect to 100 mol% of the alkali metal salt), and mixed overnight at room temperature with a stirrer. Thus, electrolytic solutions 17 and 18 were obtained. Moreover, the mixture 2 obtained above was used as a comparative electrolytic solution B.

<Preparation of mixture 3 containing lithium / solvent complex>
A mixture 3 was obtained in the same procedure as the mixture 1 except that the molar ratio of triethylene glycol dimethyl ether to LiTFSI was 0.7 / 1.0.

<Preparation of Electrolytic Solution 19 and Comparative Electrolytic Solution C>
To the mixture 3 obtained above, the metal ester compound 3 is added so as to be 1.8 mol% (extra percentage with respect to 100 mol% of the alkali metal salt), and the mixture is mixed overnight at room temperature with a stirrer. Liquid 19 was obtained. Moreover, the mixture 3 obtained above was used as a comparative electrolytic solution C.

<Preparation of mixture 4 containing lithium / solvent complex>
A mixture 4 was obtained in the same procedure as the mixture 1 except that the molar ratio of triethylene glycol dimethyl ether to LiTFSI was 4/1.

<Preparation of Electrolytic Solutions 20 and 21 and Comparative Electrolytic Solution D>
To the mixture 4 obtained above, each of the metal ester compounds 3 and 6 was added so as to be 1.8 mol% (extra percentage with respect to 100 mol% of the alkali metal salt), and mixed overnight at room temperature with a stirrer. Thus, electrolytic solutions 20 and 21 were obtained. The mixture 4 obtained above was used as a comparative electrolyte D.

<Preparation of mixture 5 containing lithium / solvent complex>
Triethylene glycol dimethyl ether (“DMTG” manufactured by Nippon Emulsifier Co., Ltd.) and LiPF ₆ (lithium hexafluorophosphate) (lithium hexafluorophosphate manufactured by Kanto Denka Kogyo Co., Ltd.) at a molar ratio of 3/1. At room temperature overnight to give mixture 5.

<Preparation of Electrolytic Solutions 22 and 23 and Comparative Electrolytic Solution E>
To the mixture 5 obtained above, each of the metal ester compounds 3 and 6 is added so as to be 1.8 mol% (extra percentage with respect to 100 mol% of the alkali metal salt), and mixed overnight at room temperature with a stirrer. Thus, electrolytic solutions 22 and 23 were obtained. Moreover, the mixture 5 obtained above was used as a comparative electrolytic solution E.

<Preparation of mixture 6 containing lithium / solvent complex>
LiTFSI (lithium bis (trifluoromethanesulfonyl) imide) dry dehydrated product (Tokyo Chemical Industry Co., Ltd. “bis (trifluoromethanesulfonyl) imide) at the concentration of 1 mol / L in the same mixed solvent used in the mixture 2 Lithium ”) (molar ratio of mixed solvent / LiTFSI = 10.8 / 1) was mixed overnight at room temperature with a stirrer to obtain mixture 6.

<Preparation of Electrolytic Solution 24 and Comparative Electrolytic Solution F>
The metal ester compound 3 is added to the mixture 6 obtained above so as to be 1.8 mol% (extra percentage with respect to 100 mol% of the alkali metal salt), and the mixture is mixed overnight at room temperature with a stirrer. A liquid 24 was obtained. The mixture 6 obtained above was used as a comparative electrolyte F.

<Examples 1-24 and Comparative Examples 1-6>
The following evaluation was performed using each of the electrolytic solutions 1 to 24 and A to F prepared above as shown in Tables 1 to 4.

<Performance evaluation>
[Ionic conductivity]
Each prepared electrolytic solution was impregnated into cellulose (thickness 25 μm) and incorporated into a UFO type two-electrode cell (electrode: SUS-SUS).
Impedance was measured at 30 ° C. using a VSP potentiogalvanostat (manufactured by BioLogic).
The results are shown in Tables 1-3.

[Charge transfer resistance]
Each prepared electrolytic solution was impregnated in cellulose (thickness 25 μm) and incorporated in a UFO type two-electrode cell (electrode: LTO-Li). The configuration of the cell is as follows.
Cell: HS Flat Cell Hosen Co., Ltd.
Cellulose separator: Model No. TF 44-25 Nippon Kogyo Co., Ltd.
Electrode diameter: 15.0mm in diameter
Charging / discharging was performed at 30 ° C. using a VSP potentiogalvanostat (manufactured by BioLogic), and stopped at a charging depth (SOC) of 50%, and impedance was measured.
The results are shown in Tables 1 and 2 and FIG.

[Oxidation-side potential window] (oxidation stability)
Each prepared electrolytic solution was impregnated into cellulose (thickness 25 μm) and incorporated into a UFO type two-electrode cell (electrode: SUS-Li).
When LSV (linear sweep voltammetry) is performed at 25 ° C. with a VSP potentiogalvanostat (manufactured by BioLogic) and the current of 3.0 V is 0, a current value of 1.0 × 10 ⁻² mA / cm ² flows. Was obtained as the value of the oxidation-side potential window.
The results are shown in Tables 1 and 2 and FIG.

[Aluminum corrosion evaluation]
Current values at the potentials of 4.0 V and 4.5 V (first cycle) were measured by the linear sweep voltammetry (LSV) method under the following conditions. An increase in the current value at the Al / Li electrode is an indicator of aluminum corrosion by the electrolyte.
Measurement cell: Bipolar PP electrochemical measurement cell Test temperature: 30 ° C
Potential sweep rate: 20 mV / sec Counter electrode / reference electrode: Li metal working electrode: Al foil The results are shown in Tables 1-4.

[Charge / discharge test]
Each of the prepared electrolytes was impregnated with cellulose (thickness 25 μm) and incorporated in a coin battery (diameter 20 mm, thickness 3.2 mm).
Using a charge / discharge test apparatus (HJD1010mSM8 manufactured by Hokuto Denko Co., Ltd.), the following three types of electrodes were subjected to a charge / discharge test at 30 ° C. under the following charge / discharge conditions.
LFP (positive electrode) / LTO (negative electrode):
0.5C (0.1C every 20 cycles) or 1.0C (0.1C every 20 cycles) or 2.0C (0.1C every 20 cycles)
LCO (positive electrode) / LTO (negative electrode):
0.3C (0.05C every 50 cycles) or 1.0C (0.05C every 50 cycles)
NMC333 (positive electrode) / LTO (negative electrode):
0.3C (0.05C every 50 cycles)
(Explanation of abbreviations)
LFP: lithium iron phosphate LTO: lithium titanate NMC333: nickel manganese lithium cobaltate LCO: lithium cobaltate The results are shown in Tables 1 to 4 and FIGS.

[Shear viscosity]
Each prepared electrolytic solution was set in a viscoelasticity measuring apparatus MCR101 (manufactured by Anton paar), and the shear viscosity was measured at 25 ° C. and a shear rate of 10 sec ⁻¹ .
The results are shown in Tables 1-3.
The shear viscosity of the metal ester compound 3 alone was 278 mPa · s.

  Examples 1 to 10 are examples using triethylene glycol dimethyl ether as a solvent and an aluminum ester having a specific structure as a metal ester compound. From the results shown in Table 1 and FIGS. 1 to 6, in the examples containing the metal ester compound having a specific structure, the charge transfer resistance was reduced and the discharge capacity was improved as compared with the comparative examples not containing this, The capacity improvement effect was obtained even when the positive electrode type was changed. The viscosity of the metal ester compound was comparable to that of the alkali metal salt / solvent complex, and the above performance improvement was not considered to be an effect of viscosity reduction. It can be seen that the discharge capacity improves as the amount of the metal ester compound increases. Examples 3, 7 and 9 are examples in which the molar ratio of the metal ester compound to 100 mol% of the oxygen-containing solvent was 1.8 mol%, and the metal ester compound species were changed. It was relatively small. On the other hand, Examples 6, 8 and 10 are examples in which the molar ratio of the metal ester compound to 100 mol% of the oxygen-containing solvent was 10.7 mol%, and the metal ester compound species was changed. The longer the chain length, the better the discharge capacity (see also FIG. 4). Further, from the results shown in Table 1, in the electrolytic solution containing an aluminum ester having a specific structure as a metal ester compound, aluminum corrosion was observed even in a high positive electrode potential environment of 4.0 V or higher compared to the electrolytic solution not containing the metal ester compound. It can be seen that it can be suppressed.

  Examples 11 to 16 are examples using triethylene glycol dimethyl ether as a solvent and a boron ester having a specific structure as a metal ester compound. From the results shown in Table 2, even in an electrolytic solution containing a boron ester as a metal ester compound, the discharge capacity is improved and / or in a high positive electrode potential environment of 4.0 V or higher compared to an electrolytic solution not containing a metal ester compound. It can be seen that aluminum corrosion can be suppressed.

  Examples 17-24 are the examples which changed variously the kind of solvent and alkali metal salt, and the molar ratio of solvent / alkali metal salt. From the results shown in Tables 3 and 4, the metal ester compound having a specific structure can improve the discharge capacity and / or suppress the corrosion of aluminum in a high positive electrode potential environment of 4.0 V or more over various electrolyte compositions. It turns out that it is. In particular, in Examples 17, 18, and 24 using a mixed solvent of ethylene carbonate / ethyl methyl carbonate, which is an example of a solvent generally used in a rocking chair type secondary battery, the discharge capacity is improved and / or 4.0 V or higher. It is unexpected that aluminum corrosion can be suppressed in a high positive electrode potential environment.

  The electrolyte solution according to the present invention is suitably applied to various rocking chair type secondary batteries, particularly lithium ion secondary batteries.

Claims (10)

An electrolyte for a rocking chair type secondary battery,
The electrolytic solution is an alkali metal salt, an oxygen-containing solvent, and the following general formula (1):
M [—O— (A ¹ —O) _m —R ¹ ] ₃ (1)
(In the formula, M represents a trivalent element selected from the group consisting of boron and aluminum, A ¹ represents each independently an alkylene group having 2 to 4 carbon atoms in the formula, and m represents each independently in the formula. is an integer of 0 to 50, and R ¹ represents an aliphatic hydrocarbon group having a carbon number of 1 to 13 independently in formula.)
And a metal ester compound represented by
The electrolyte solution whose content of the alkali metal salt in the electrolyte solution is 4 to 88% by mass. An electrolyte for a rocking chair type secondary battery,
The electrolytic solution is an alkali metal salt, an oxygen-containing solvent, and the following general formula (1):
M [—O— (A ¹ —O) _m —R ¹ ] ₃ (1)
(In the formula, M represents a trivalent element selected from the group consisting of boron and aluminum, A ¹ represents each independently an alkylene group having 2 to 4 carbon atoms in the formula, and m represents each independently in the formula. an integer of 0 to 50, and R ¹ represents an aliphatic hydrocarbon group having a carbon number of 1 to 13 independently in formula.)
And a metal ester compound represented by
The oxygen-containing solvent is an electrolyte solution in which the oxygen-containing solvent / alkali metal salt (molar ratio) is present in the electrolyte solution in an amount of 0.7 or more and 4.0 or less.   3. The electrolysis according to claim 1, wherein the oxygen-containing solvent is present in the electrolytic solution in an amount such that the oxygen-containing solvent / the alkali metal salt (molar ratio) is 0.9 or more and 1.1 or less. liquid. 4. The general formula (1), wherein M is aluminum, A ¹ is an ethylene group, m is 3 to 9, and R ¹ is a methyl group. Electrolyte.   The electrolytic solution according to claim 1, wherein the oxygen-containing solvent is selected from the group consisting of an ether compound and a carbonyl compound. The oxygen-containing solvent is represented by the following general formula (2):
R ² O— (A ² —O) _n —R ² (2)
(In the formula, A ² each independently represents an alkylene group having 2 to 4 carbon atoms, n is an integer of 0 to 10, and R ² is independently an integer of 1 to 13 carbon atoms in the formula. Represents a hydrocarbon group.)
The electrolyte solution of Claim 5 which is an alkylene glycol dialkyl ether compound represented by these. The electrolytic solution according to claim 6, wherein in the general formula (2), A ² is an ethylene group, n is 3, and R ² is a methyl group. The lithium salt comprises lithium bis (trifluoromethanesulfonyl) imide (LiTFSI), lithium bis (fluorosulfonyl) imide (LiFSI), lithium tetrafluoroborate (LiBF ₄ ), and lithium hexafluorophosphate (LiPF ₆ ). The electrolyte solution according to any one of claims 1 to 7, which is selected from the group.   The electrolyte solution according to any one of claims 1 to 8, comprising a complex of an alkali metal derived from the alkali metal salt and the oxygen-containing solvent.   A rocking chair type secondary battery comprising the positive electrode, the negative electrode, and the electrolyte solution according to claim 1.

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