JP6650701B2 - Method for improving electrochemical stability of aqueous electrolyte, electrolyte with improved electrochemical stability, aqueous sodium ion battery and aqueous lithium ion battery using the same - Google Patents

Description

  The present invention relates to a method for improving the electrochemical stability of an aqueous electrolyte, an aqueous electrolyte with improved electrochemical stability, an aqueous sodium ion battery operating using the electrolyte, and an aqueous lithium. It relates to an ion battery.

  Non-aqueous lithium-ion batteries are widely used as high energy density secondary batteries. A non-aqueous lithium ion battery normally operates in a battery voltage range of 3 V to 4 V because the positive electrode active material takes in and out of lithium at a potential of +3 V to +4 V with respect to a metal lithium negative electrode or a carbon negative electrode. On the other hand, a non-aqueous sodium ion battery using sodium, which is more abundant in resources than lithium, as an electrolyte has been proposed (for example, see Patent Document 1).

These batteries use a non-aqueous electrolyte which is flammable but hardly electrolyzed for the purpose of increasing the energy density.
For such a non-aqueous battery, an aqueous sodium ion battery using an aqueous solution as an electrolyte (for example, see Patent Documents 2 and 3) or an aqueous lithium ion battery is known (Patent Documents 4 to 4). 6).

This aqueous solution-based battery has the advantages of not only being nonflammable and easy to handle because the electrolytic solution is an aqueous solution, but also having lower conductivity due to being more conductive than non-aqueous-based electrolyte. is there.
However, the voltage of a battery using an aqueous electrolytic solution cannot be raised in principle to a voltage higher than the electrolysis voltage of water, and there is a limit to increasing the energy density of the battery (for example, see Non-Patent Document 1). ).

  On the other hand, in non-aqueous lithium-ion secondary batteries, non-aqueous lithium-ion batteries using lithium salts of alkyl sulfonic acids as electrode coatings and fillers for separators have been proposed for the purpose of improving cycle characteristics at high temperatures and high voltages. (For example, see Patent Documents 7 and 8).

International Publication No. WO 2010/109889 JP 2011-086402 A JP 2012-054208 A JP-A-2005-095431 JP 2009-259473 A JP 2009-094034 A JP 2009-187940 A JP 2014-11476A

Noboru Sato and Akira Yoshino, "High-safety technologies and materials for lithium-ion batteries", CMC Publishing Co., Ltd., first print, February 13, 2009, pp. 105-115 Takashi Yoshida, "High Performance Storage Batteries-From Basic Design Research to Development and Evaluation-", NTT, Inc., published September 11, 2009, pp. 337-343

The decomposition voltage of water (that is, the potential window) is expressed as 1.23-0.059 pH> E (equilibrium potential)> − 0.059 pH from the following Nernst equation, and “1.23-0.059 pH” Is based on O ₂ + 4H ⁺ + 4e ⁻ = 2H ₂ O, and “−0.059 pH” is based on 2H ⁺ + 2e ⁻ = H ₂ . At a potential higher than this, there is a problem that water is electrolyzed.

(Where E ⁰ : is the standard electrode potential, R is the gas constant, T is the absolute temperature (K), z is the number of mobile electrons, a is the activity (reducing side (a _Red ) and oxidizing side (a _Ox )) , F represents the Faraday constant = 96485 C (coulomb) / mol)
Takashi Yoshida, "High-performance storage batteries-From basic design research to development and evaluation-", published by NTT Co., Ltd., September 11, 2009, pages 337-343 (Non-Patent Document 2) In order to operate the lithium-ion secondary battery stably, water surrounded by the Nernst equation exists stably so that the aqueous electrolyte solution is electrolyzed and oxygen and hydrogen are not generated at both the positive and negative electrodes. It states that the charge / discharge potentials of the positive and negative electrodes must fall within a potential window of 1.23 V (volt) width.

Japanese Patent Application Laid-Open No. 2012-054208 (Patent Document 3) proposes an electrolytic solution containing a buffer substance that exhibits a buffer action against a pH change for the purpose of suppressing corrosion and the like of an electrode. In this document, a 6 mol / L NaNO ₃ aqueous solution is used, but the upper limit voltage is 1.5 V, the lower limit voltage is 0.9 V, and charge / discharge is performed only within the potential window of the aqueous solution. There is no description about charging and discharging in a voltage range exceeding this.

As described above, it is difficult to generate a high electromotive force higher than the electrolysis voltage of water with the conventional aqueous electrolyte solution, and the combination of electrodes falling within the range of this potential window is also limited. Improvement of the electrochemical stability (potential window) of the liquid has been required.
The present invention has been made in view of these problems. That is, an object of the present invention is to provide a method for improving the electrochemical stability (potential window) of an aqueous electrolyte solution, an aqueous electrolyte solution having improved electrochemical stability, and a high energy density containing the same. It is an object of the present invention to provide an aqueous battery.

  The present inventors have conducted intensive studies in order to solve the above problems, and as a result, suppressed the electrolysis of water by using an alkali metal salt such as a sodium salt of an alkylsulfonic acid compound having a specific structure as an electrolyte salt. The inventors have found that the present invention is stabilized over a wide voltage range, and have completed the present invention. That is, the present invention relates to the following gist.

1. The method for improving the electrochemical stability of the aqueous electrolyte solution of the present invention is represented by the following general formula (1)
The following general formula (1)

(In the formula (1), M is one or more elements selected from the group consisting of Li, Na, K, Rb and Cs, and X is a linear or branched hydrocarbon having 1 to 10 carbon atoms. An aqueous metal-based electrolyte solution comprising adding an alkali metal salt of an alkylsulfonic acid compound represented by the formula (1) to water: This is a method for improving the electrochemical stability of the polymer.

  2. The method for improving the electrochemical stability of the electrolytic solution of the present invention preferably comprises the following general formula (2)

(In the formula (2), X is a linear or branched hydrocarbon having 1 to 10 carbon atoms, and may have a 5- to 8-membered cyclic structure, and n represents an integer of 1 to 3) ), Wherein the sodium salt of the alkyl sulfonic acid compound represented by the formula (1) is added to water to improve the electrochemical stability of the aqueous electrolyte solution.

  3. The method for improving the electrochemical stability of the aqueous electrolyte solution of the present invention is preferably a method represented by the following general formula (3):

(In the formula (3), X is a linear or branched hydrocarbon having 1 to 10 carbon atoms and may have a 5- to 8-membered cyclic structure, and n represents an integer of 1 to 3) ), Wherein the lithium salt of the alkylsulfonic acid compound represented by the formula (1) is added to water, and the electrochemical stability of the aqueous electrolyte solution is improved.
Techniques for adding a specific lithium alkylsulfonate to electrodes of nonaqueous batteries, fillers of separators, and the like have been proposed (JP-A-2009-187940 (Patent Document 7), JP-A-2014-2014). No. 114768 (Patent Document 8)). In these patent documents, it is described that the lithium sulfonate salt described in the present invention can improve cycle characteristics at high temperature and high voltage as a coating of an active material or a filler of a separator, but all of these prior arts are described. It is a technique applied to non-aqueous secondary batteries, which has the effect of expanding the potential window of the aqueous electrolyte solution as in the present invention, and further mentions that it can be used for aqueous electrolyte secondary batteries. Absent.

  4. In the method of the present invention, in the alkyldisulfonic acid compound in which n in any one of the general formulas (1) to (3) is 2, the electrochemical stability is specifically improved.

  5. The aqueous electrolyte solution of the present invention contains an alkali metal salt such as a sodium salt or a lithium salt of an alkylsulfonic acid compound represented by any of the general formulas (1) to (3) as an electrolyte salt, and is dissolved in water. Aqueous electrolyte solution. In particular, in order to obtain good ion conductivity as an electrolytic solution, 0.05 mol / L (liter) of an alkali metal salt of an alkylsulfonic acid compound represented by any of the general formulas (1) to (3) is used. It is preferable to dissolve at the above concentration. Moreover, it is preferable that the hydrocarbon in any of the general formulas (1) to (3) has 1 to 3 carbon atoms.

  6. In the aqueous electrolyte solution of the present invention, the alkali metal salt of the alkylsulfonic acid compound represented by any one of the general formulas (1) to (3) is selected from the group consisting of disodium methanedisulfonate, disodium ethanedisulfonate, and propanedisulfonic acid. Preference is given to disodium, dilithium methanedisulfonate, dilithium ethanedisulfonate and dilithium propanedisulfonate.

  7. The aqueous sodium ion battery of the present invention is an aqueous sodium ion battery comprising: a positive electrode including a positive electrode active material capable of storing and releasing sodium; a negative electrode including a negative electrode active material capable of storing and releasing sodium; and the aqueous solution electrolyte described above. It is a sodium ion battery.

  8. The aqueous lithium-ion battery of the present invention is an aqueous lithium-ion battery comprising: a positive electrode containing a positive electrode active material capable of inserting and extracting lithium; a negative electrode containing a negative electrode active material capable of inserting and extracting lithium; and the above aqueous electrolyte. It is a lithium ion battery.

According to the present invention, by dissolving an alkali metal salt of a specific alkyl sulfonic acid compound in an aqueous solution, the electrochemical stability is improved, and an electrode that can not be used until now and that can be charged and discharged in a wide voltage range is used. Thus, a battery having a high energy density, which has been a problem of the aqueous electrolyte solution, can be constructed.
As described above, an aqueous solution in which a specific alkyl sulfonate is dissolved is stabilized over a wide voltage range by suppressing the electrolysis of water, and the effect of improving the potential window (electrochemical stability) is the same as the conventional one. This is a surprising effect that is not known at all in an aqueous solution in which the electrolyte salt is dissolved.

It is sectional drawing of the triode type cell used in Examples 1-12 and Comparative Examples 1-3. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view of a coin cell type battery showing an example of an embodiment of the present invention and schematically showing a structure of an aqueous sodium battery or an aqueous lithium ion battery containing an aqueous electrolyte.

  In the method for improving the electrochemical stability of the aqueous electrolyte solution according to the present invention, an alkali metal salt of an alkylsulfonic acid compound represented by the general formula (1) is added to water. At this time, an alkali metal salt such as a sodium salt of an alkyl sulfonic acid compound may be added to predetermined water, or an alkyl sulfonic acid compound dissolved in water, sodium hydroxide, sodium carbonate, lithium hydroxide or lithium carbonate may be added. And the like. Alternatively, both formulations can be used in combination.

Here, the predetermined water refers to distilled water, ion-exchanged water, or the like, and refers to water whose dissolved ion concentration is limited to a certain amount or less. The temperature of the dissolving water is not particularly limited as long as it is a temperature at which an alkali metal salt such as a sodium salt of an alkylsulfonic acid compound dissolves.
The mechanism by which the electrochemical stability is improved is not clear, but the higher the concentration of an alkali metal salt such as a sodium salt of an alkylsulfonic acid compound, the higher the stability is, so that, for example, solvation is performed. It is considered that electrochemical stability is improved by a mechanism such as improvement in stability of water molecules.

  The alkali metal salt such as a sodium salt of an alkyl sulfonic acid compound used in the present invention is a dialkali metal alkyl disulfonate such as a disodium alkyl disulfonate, or a trialkali alkyl trisulfonate such as a trisodium alkyl trisulfonic acid. The use of a metal salt is preferred because the electrochemical stability of the electrolytic solution is further improved. Although this mechanism is not clear, the alkanols of the alkyldisulfonic acid and the alkali metal of the alkyltrisulfonic acid have an increased ionic strength as compared with the alkali metal salts of the alkylmonosulfonic acid such as the sodium salt of the alkylmonosulfonic acid. It is considered that the decomposition of water is suppressed by a mechanism that suppresses electrolysis by solvation with water.

  The effect of improving the electrochemical stability of the aqueous electrolyte solution due to the coexistence of the specific electrolyte as described above has not been found so far and is a surprising effect.

  The aqueous electrolyte solution of the present invention is an aqueous solution in which an alkali metal salt such as a sodium salt of an alkylsulfonic acid compound represented by the general formula (1) is dissolved in water. The alkali metal salt is not particularly limited, but among the alkali metal salts, sodium salt and lithium salt are particularly preferable because of high saturation solubility.

  In the aqueous electrolyte solution of the present invention, the concentration of an alkali metal salt such as a sodium salt of an alkylsulfonic acid compound is preferably 0.05 mol / L or more and a saturation concentration or less, more preferably 0.5 mol / L or more. It is more preferable that the concentration is not more than the saturation concentration. When the concentration of the alkali metal salt of the alkylsulfonic acid compound is less than 0.05 mol / L, the effect of electrochemical stabilization may not be sufficient. Since the electrochemical stability of water is improved in accordance with the concentration of the alkali metal salt of the alkylsulfonic acid compound, the most preferred form is an aqueous solution in which the alkali metal salt of the alkylsulfonic acid is dissolved at a saturated concentration.

  In the method of the present invention, for the purpose of improving the conductivity of the electrolyte, metal ions of Group 1 of the periodic table other than sodium, such as potassium, have a larger ion size than sodium and lower surface charge density. Thereby, improvement in ionic conductivity and faster charging and discharging can be expected. Further, since lithium is an element lighter than sodium, there is a possibility that the energy density per unit weight can be improved. Further, a metal ion of Group 2 of the periodic table other than the alkali metal may be allowed to coexist. For example, since magnesium and calcium can dissociate into divalent ions, more charges can be transferred, and an improvement in energy density can be expected.

  In an alkali metal salt such as a sodium salt of an alkylsulfonic acid compound represented by the general formula (1) used in the aqueous electrolyte solution of the present invention, X represents a linear or branched hydrocarbon group having 1 to 10 carbon atoms. And may have a 5- to 8-membered ring structure. Examples of the linear or branched hydrocarbon group having 1 to 10 carbon atoms include methyl, ethyl, propyl, butyl, methylene, ethylene, trimethylene, tetramethylene, pentamethylene, cyclopentyl, and hexahexyl. Methylene, cyclohexyl, heptamethylene, cycloheptyl, octamethylene, cyclooctyl, nonamethylene, decamethylene, 2-methylethylene, 2-methyltrimethylene, 3-methyltrimethylene, Methyltetramethylene group, 3-methyltetramethylene group, 2-methylpentamethylene group, 3-methylpentamethylene group, 4-methylpentamethylene group, 2-ethyltrimethylene group, 3-ethyltrimethylene group, 2-ethyl Tetramethylene group, 3-ethyltetramethylene group, etc. It can be.

  Examples of the sodium salt of such an alkylsulfonic acid compound include sodium methanesulfonate, sodium ethanesulfonate, sodium 1-propanesulfonate, sodium 2-propanesulfonate, sodium 1-butanesulfonate, and 2-butanesulfonic acid. Sodium, sodium 1-pentane sulfonate, sodium 2-pentane sulfonate, sodium 3-pentane sulfonate, sodium 1-hexane sulfonate, sodium 2-hexane sulfonate, sodium 3-hexane sulfonate, sodium 1-heptane sulfonate Sodium 2-heptanesulfonate, sodium 3-heptanesulfonate, sodium 4-heptanesulfonate, sodium 1-octanesulfonate, sodium 2-octanesulfonate, 3-octane Sodium sulfonate, sodium 4-octane sulfonate, sodium 1-nonane sulfonate, sodium 2-nonane sulfonate, sodium 3-nonane sulfonate, sodium 4-nonane sulfonate, sodium 5-nonane sulfonate, 1-decane sulfone And sodium 2-decanesulfonate, sodium 3-decanesulfonate, sodium 4-decanesulfonate and sodium 5-decanesulfonate.

  Examples of such lithium salts of alkylsulfonic acid compounds include lithium methanesulfonate, lithium ethanesulfonate, lithium 1-propanesulfonate, lithium 2-propanesulfonate, lithium 1-butanesulfonate, and 2-butane. Lithium sulfonate, lithium 1-pentane sulfonate, lithium 2-pentane sulfonate, lithium 3-pentane sulfonate, lithium 1-hexane sulfonate, lithium 2-hexane sulfonate, lithium 3-hexane sulfonate, 1-heptane sulfone Lithium acid, lithium 2-heptanesulfonate, lithium 3-heptanesulfonate, lithium 4-heptanesulfonate, lithium 1-octanesulfonate, lithium 2-octanesulfonate, lithium 3-octanesulfonate, 4-octane Lithium sulfonate, lithium 1-nonane sulfonate, lithium 2-nonane sulfonate, lithium 3-nonane sulfonate, lithium 4-nonane sulfonate, lithium 5-nonane sulfonate, lithium 1-decane sulfonate, 2-decane sulfone Lithium acid, lithium 3-decanesulfonate, lithium 4-decanesulfonate, lithium 5-decanesulfonate, and the like can be given.

  Specific examples of the disodium salt of the alkyl disulfonate include, for example, disodium methanedisulfonate, disodium 1,2-ethanedisulfonate, disodium 1,1-ethanedisulfonate, disodium 1,1-propanedisulfonate Disodium 1,2-propanedisulfonate, disodium 1,3-propanedisulfonate, disodium 1,4-butanedisulfonate, disodium pentanedisulfonate, disodium hexanedisulfonate, disodium 2-methylethanedisulfonate Sodium, disodium 2-methylpropanedisulfonate, disodium 3-methylpropanedisulfonate, disodium 2-methylbutanedisulfonate, disodium 3-methylbutanedisulfonate, disodium 2-methylpentanedisulfonate, - methylpentanoic disulfonic acid disodium, 4-methyl-pentanoic disulfonic acid disodium, 2-ethyl-propane disulfonic acid disodium can be mentioned 3-ethyl-propanedisulfonic acid disodium or the like.

  Further, specific examples of the trisodium salt of an alkyltrisulfonic acid compound include, for example, trisodium 1,2,3-propanetrisulfonate, trisodium 1,3,5-pentanetrisulfonate, and the like.

  Specific examples of the dilithium salt of the alkyl disulfonic acid compound include, for example, dilithium methanedisulfonic acid, dilithium 1,2-ethanedisulfonic acid, dilithium 1,1-ethanedisulfonic acid, dilithium 1,1-propanedisulfonic acid, Dilithium 2-propanedisulfonic acid, dilithium 1,3-propanedisulfonic acid, dilithium 1,4-butanedisulfonic acid, dilithium pentanedisulfonic acid, dilithium hexanedisulfonic acid, dilithium 2-methylethanedisulfonic acid, dilithium 2-methylpropanedisulfonic acid Dilithium 3-methylpropanedisulfonate, dilithium 2-methylbutanedisulfonate, dilithium 3-methylbutanedisulfonate, dilithium 2-methylpentanedisulfonate, 3-methylpentanedisulfoate Acid dilithium, 4-methyl-pentanoic disulfonic acid dilithium, 2-ethyl-propane disulfonic acid dilithium, mention may be made of 3-ethyl-propane disulfonic acid dilithium like.

  Furthermore, specific examples of the trilithium salt of the alkyl trisulfonic acid compound include, for example, trilithium 1,2,3-propanetrisulfonate and trilithium 1,3,5-pentanetrisulfonate.

  Of these alkali metal salts of alkylsulfonic acid compounds such as sodium, disodium alkyldisulfonate and dilithium alkylsulfonate are preferable, and among them, disodium methanedisulfonate, dilithium methanedisulfonate and 1,2-ethanedisulfonic acid Sodium, dilithium 1,2-ethanedisulfonate, disodium 2-methyl-1,2-ethanedisulfonate, dilithium 2-methyl-1,2-ethanedisulfonate, disodium 1,3-propanedisulfonate, Dilithium 3-propanedisulfonate is particularly preferred in that it can further improve electrochemical stability.

  The aqueous sodium ion battery of the present invention comprises a positive electrode containing a positive electrode active material capable of inserting and extracting sodium, a negative electrode, and a separator in which sodium salt of the alkylsulfonic acid compound of the general formula (1) is added in water at 0.05 mol / L. It consists of an aqueous solution dissolved at the above concentrations.

As the positive electrode of the aqueous sodium ion battery of the present invention, for example, a positive electrode material obtained by mixing a positive electrode active material capable of inserting and extracting sodium, a conductive agent, and a binder, and pressing the positive electrode material onto the surface of the current collector Alternatively, a paste obtained by adding an appropriate solvent to the positive electrode material may be applied and dried on the surface of the current collector, and may be compressed as necessary to increase the electrode density. In the aqueous sodium ion battery of the present invention, the positive electrode active material can be used without any particular limitation as long as it can store and release sodium in the aqueous solution. Examples of such a positive electrode active material include manganese oxides such as NaMnO ₂ , olivine-type composite oxides such as NaFePO ₄ and NaFe _n Mn _1-n PO _4, and NASICONs such as Na ₃ V ₂ (PO ₄ ) _3. complex oxide having a Na Super Ionic Conductor) structure, layered oxides such NaCoO _2, can be mentioned spinel oxide, etc., such as NaMn ₂ O _4.

As the negative electrode of the aqueous sodium ion battery of the present invention, for example, a negative electrode material is prepared by mixing a negative electrode active material capable of inserting and extracting sodium, a conductive agent, and a binder, and then pressed against the surface of the current collector. Alternatively, a paste obtained by adding an appropriate solvent to the negative electrode material may be applied and dried on the surface of the current collector, and may be formed by compression if necessary to increase the electrode density. In the aqueous sodium ion battery of the present invention, the negative electrode active material can be used without any particular limitation as long as it can store and release sodium in the aqueous solution. Examples of such a negative electrode active material include oxides and hydroxides containing transition metals such as iron, titanium, manganese, and vanadium, and composite oxides of these metals and sodium. For example, FeOOH, TiP ₂ O ₇ , NaTi ₂ (PO ₄ ) _{3 and the} like can be mentioned.

  The separator is not particularly limited as long as it can withstand the voltage range of the sodium ion battery, but it is preferable to use a microporous membrane or the like that has been subjected to a hydrophilic treatment so that the aqueous electrolyte solution can easily penetrate. For example, a microporous film of a polyolefin resin such as polyethylene or polypropylene, or a polymer nonwoven fabric such as a polyolefin nonwoven fabric such as polypropylene can be used.

  The shape and form of the aqueous sodium ion battery of the present invention are not particularly limited, and examples thereof include a cylindrical type, a laminated type, a square type, a coin type, a card type, and a laminated type.

  The aqueous lithium ion battery of the present invention comprises a positive electrode containing a positive electrode active material capable of inserting and extracting lithium, a negative electrode, and a lithium salt of the alkylsulfonic acid compound of the general formula (1) in water at 0.05 mol / L. It consists of an aqueous solution dissolved at the above concentrations.

As the positive electrode of the aqueous lithium ion battery of the present invention, for example, a positive electrode material is prepared by mixing a positive electrode active material capable of inserting and extracting lithium, a conductive agent and a binder, and then pressed against the surface of the current collector. Alternatively, a paste obtained by adding an appropriate solvent to the positive electrode material may be applied and dried on the surface of the current collector, and may be compressed as necessary to increase the electrode density. In the aqueous lithium ion battery of the present invention, the positive electrode active material can be used without any particular limitation as long as it can store and release lithium in the aqueous solution. As such positive electrode active material, for example, manganese oxides such as LiMn ₂ O _4, olivine-type composite oxide such as LiFePO ₄ and _{LiFe n Mn 1-n PO 4} , such as _{Li 3 V 2 (PO 4)} 3 Examples thereof include a composite oxide having a LISON (Li Super Ionic Conductor) type structure and a layered oxide such as LiCoO ₂ .

As the negative electrode of the aqueous lithium ion battery of the present invention, for example, a negative electrode material is prepared by mixing a negative electrode active material capable of inserting and extracting lithium, a conductive agent, and a binder, and then pressed against the surface of the current collector. Alternatively, a paste obtained by adding an appropriate solvent to the negative electrode material may be applied and dried on the surface of the current collector, and may be formed by compression if necessary to increase the electrode density. In the aqueous lithium ion battery of the present invention, the negative electrode active material can be used without any particular limitation as long as it can store and release lithium in the aqueous solution. Examples of such a negative electrode active material include oxides and hydroxides containing transition metals such as iron, titanium, manganese, and vanadium, and composite oxides of these metals and lithium. For example, FeOOH, TiP ₂ O ₇ , LiTi ₂ (PO ₄ ) _{3 and the} like can be mentioned.

  The separator is not particularly limited as long as it can withstand the voltage range of the lithium ion battery, but it is preferable to use a microporous membrane or the like that has been subjected to a hydrophilic treatment so that the aqueous electrolyte solution can easily penetrate. For example, a microporous film of a polyolefin resin such as polyethylene or polypropylene, or a polymer nonwoven fabric such as a polyolefin nonwoven fabric such as polypropylene can be used.

  The shape and form of the aqueous lithium ion battery of the present invention are not particularly limited, and examples thereof include a cylindrical type, a laminated type, a square type, a coin type, a card type, and a laminated type.

  FIG. 2 is a cross-sectional view of a coin cell type battery showing an example of the embodiment of the present invention and schematically showing a structure of an aqueous solution type sodium ion battery or an aqueous solution type lithium ion battery. In this battery, a positive electrode in which a positive electrode material 6 is fixed on a current collector 7 with a separator 13 interposed therebetween and a negative electrode in which a negative electrode material 9 is fixed on a current collector 10 are opposed to each other. The leaf spring 12 was installed, and the laminate including the negative electrode, the separator, and the positive electrode was accommodated in a coin-type cell. After the electrolyte solution of the present invention is injected into the laminate, the gasket 14 is arranged, the positive electrode stainless steel cap 8 is covered, and the coin cell case is crimped.

Hereinafter, the present invention will be described with reference to Examples, but the present invention is not limited thereto.
[Example 1]
63 g of disodium 1,3-propanedisulfonate (hereinafter abbreviated as PDSS) was dissolved in pure water to prepare a 100 ml aqueous solution. The sodium ion concentration in this aqueous solution was 5 mol / L.
Cyclic voltammetry (CV) of the PDSS aqueous solution was performed in a three-electrode cell using a platinum plate electrode as a working electrode, an Ag / AgCl electrode as a reference electrode, and a platinum mesh electrode as a counter electrode.

  As a result of CV measurement using the aqueous solution of PDSS, the decomposition voltage on the oxidation side was 1.75 V on the basis of the hydrogen electrode. On the other hand, the decomposition voltage at which hydrogen is generated on the reduction side is -0.77 V based on the hydrogen electrode, and the electrochemical stability of oxidation-reduction of the PDSS aqueous solution, that is, the potential window is 1.75 V-(- 0.77V) = 2.52V.

[Example 2]
59 g of disodium 1,2-ethanedisulfonate (hereinafter abbreviated as EDSS) was dissolved in pure water to prepare a 100 ml aqueous solution. The sodium ion concentration of this aqueous solution was 5 mol / L.

  Using this EDSS aqueous solution, CV measurement was performed in the same manner as in Example 1. As a result, the decomposition voltage on the oxidation side was 1.70 V based on the hydrogen electrode. On the other hand, the decomposition voltage at which hydrogen is generated on the reduction side is -0.75 V based on the hydrogen electrode, and the electrochemical stability of oxidation-reduction of the EDSS aqueous solution, that is, the potential window is 1.70 V-(- 0.75V) = 2.45V.

[Example 3]
33 g of disodium methanedisulfonate (hereinafter abbreviated as MDSS) was dissolved in pure water to prepare a 100 ml aqueous solution. The sodium ion concentration of this aqueous solution was 3 mol / L.
Using this aqueous solution of MDSS, CV measurement was performed in the same manner as in Example 1. As a result, the decomposition voltage on the oxidation side was 1.66 V on the basis of the hydrogen electrode. On the other hand, the decomposition voltage at which hydrogen is generated on the reduction side is -0.74 V on the basis of the hydrogen electrode, and the electrochemical stability of oxidation-reduction of the MDSS aqueous solution, that is, the potential window is 1.66 V-(- 0.74V) = 2.40V.

[Comparative Example 1]
CV measurement was carried out in the same manner as in Example 1, except that 100 g of a 48% by weight aqueous sodium hydroxide solution was used. As a result, the decomposition voltage on the oxidation side was 0.24 V based on the hydrogen electrode. On the other hand, the decomposition voltage at which hydrogen is generated on the reduction side is -0.99 V on the basis of the hydrogen electrode, and the potential window of the aqueous solution of sodium hydroxide is 0.24 V-(-0.99 V) = 1.23 V. there were.

[Example 4]
12.4 g of PDSS was dissolved in pure water to make 100 ml of an aqueous solution. The sodium ion concentration in this aqueous solution was 1 mol / L.
Using this aqueous solution of PDSS, CV measurement was performed in the same manner as in Example 1. As a result, the decomposition voltage on the oxidation side was 1.57 V on the basis of the hydrogen electrode. On the other hand, the decomposition voltage at which hydrogen is generated on the reduction side is -0.73 V based on the hydrogen electrode, and the electrochemical stability of oxidation-reduction of the PDSS aqueous solution, that is, the potential window is 1.57 V-(- 0.73V) = 2.30V.

[Example 5]
1.24 g of PDSS was dissolved in pure water to prepare a 100 ml aqueous solution. The sodium ion concentration in this aqueous solution was 0.1 mol / L.
Using this aqueous solution of PDSS, CV measurement was performed in the same manner as in Example 1. As a result, the decomposition voltage on the oxidation side was 0.91 V based on the hydrogen electrode. On the other hand, the decomposition voltage at which hydrogen is generated on the reduction side is -0.70 V based on the hydrogen electrode, and the electrochemical stability of oxidation-reduction of the PDSS aqueous solution, that is, the potential window is 0.91 V-(- (0.70V) = 1.61V.

[Example 6]
Sodium methanesulfonate (11.2 g) was dissolved in pure water to prepare a 100 ml aqueous solution. The sodium ion concentration in this aqueous solution was 1 mol / L.
Using this aqueous solution of sodium methanesulfonate, CV measurement was performed in the same manner as in Example 1. As a result, the decomposition voltage on the oxidation side was 1.46 V on the basis of the hydrogen electrode. On the other hand, the decomposition voltage at which hydrogen is generated on the reduction side is -0.77 V based on the hydrogen electrode, and the electrochemical stability of oxidation-reduction of the aqueous solution of sodium methanesulfonate, that is, the potential window is 1.46 V − (− 0.77 V) = 2.23 V was calculated.

[Example 7]
Sodium ethanesulfonate (13.2 g) was dissolved in pure water to prepare a 100 ml aqueous solution. The sodium ion concentration in this aqueous solution was 1 mol / L.
Using this aqueous solution of sodium methanesulfonate, CV measurement was performed in the same manner as in Example 1. As a result, the decomposition voltage on the oxidation side was 1.48 V based on the hydrogen electrode. On the other hand, the decomposition voltage at which hydrogen is generated on the reduction side is -0.78 V based on the hydrogen electrode, and the electrochemical stability of oxidation-reduction of the aqueous solution of sodium ethanesulfonate, that is, the potential window is 1.48 V − (− 0.78 V) = 2.26 V was calculated.

Example 8
Sodium cyclohexylsulfonate (18.6 g) was dissolved in pure water to prepare a 100 ml aqueous solution. The sodium ion concentration in this aqueous solution was 1 mol / L.
Using this aqueous solution of sodium cyclohexylsulfonate, CV measurement was performed in the same manner as in Example 1. As a result, the decomposition voltage on the oxidation side was 1.39 V on the basis of the hydrogen electrode. On the other hand, the decomposition voltage at which hydrogen is generated on the reduction side is -0.80 V based on the hydrogen electrode, and the electrochemical stability of the oxidation-reduction of the aqueous solution of sodium cyclohexylsulfonate, that is, the potential window is 1.39 V − (− 0.80 V) = 2.19 V was calculated.

[Example 9]
Trisodium 1,2,3-propanetrisulfonate (11.7 g) was dissolved in pure water to prepare a 100 ml aqueous solution. The sodium ion concentration in this aqueous solution was 1 mol / L.
Using this aqueous solution of 1,2,3-propanetrisulfonic acid trisodium salt, CV measurement was performed in the same manner as in Example 1. As a result, the decomposition voltage on the oxidation side was 1.45 V on the basis of the hydrogen electrode. On the other hand, the decomposition voltage at which hydrogen is generated on the reduction side is -0.81 V on the basis of the hydrogen electrode, and the electrochemical stability of oxidation-reduction of an aqueous solution of trisodium 1,2,3-propanetrisulfonate, that is, , And the potential window was calculated as 1.45 V − (− 0.81 V) = 2.26 V.

[Example 10]
In pure water, 11.7 g of trisodium 1,3,5-pentanetrisulfonate was dissolved to prepare a 100 ml aqueous solution. The sodium ion concentration in this aqueous solution was 1 mol / L.
Using this aqueous solution of 1,3,5-pentanetrisulfonic acid trisodium salt, CV measurement was performed in the same manner as in Example 1. As a result, the decomposition voltage on the oxidation side was 1.60 V based on the hydrogen electrode. On the other hand, the decomposition voltage at which hydrogen is generated on the reduction side shows -0.75 V on the basis of the hydrogen electrode, and the electrochemical stability of oxidation-reduction of the aqueous solution of 1,3,5-pentanetrisulfonic acid trisodium salt, that is, , And the potential window was calculated as 1.60 V − (− 0.75 V) = 2.35 V.

(Experimental result)
Table 1 shows composition examples and results of Examples 1, 2, and 3 and Comparative Example 1. The aqueous solution of PDSS, EDSS and MDSS, which are the sodium salts of alkylsulfonic acid of the present invention, showed a potential window almost twice as large as that of the aqueous sodium hydroxide solution. Although the mechanism of this stabilization is not clear, for example, water molecules are only electrochemically unstable when hydrated to sodium ions, but are protected electrochemically by alkylsulfonic acid ions around them. Improved.
Alternatively, it is considered that the alkyl sulfonate ion was dissolved at a high concentration, thereby forming a stable protective film on the electrode surface and suppressing the electrolysis of water.
From the results of Example 1 and Examples 4 and 5, the higher the concentration of PDSS, the higher the oxidative decomposition voltage. Therefore, the higher the concentration of this alkyl sulfonic acid ion, the more the effect of suppressing the oxidative decomposition. It is considered excellent.

  Examples 6 to 10 are examples using sodium monosulfonate and trisodium trisulfonate. It was confirmed that the stability was improved electrochemically even when these sodium salts of alkylsulfonic acids were allowed to coexist. From these facts, the use of the method of the present invention makes it possible to improve the electrochemical stability of the aqueous electrolyte solution, which has not been considered conventionally.

[Example 11]
Dilithium 1,3-propanedisulfonate (hereinafter, abbreviated as PDSL) was dissolved in pure water under a condition of 25 ° C. until the solution became saturated to obtain a saturated aqueous solution. The Li concentration in this aqueous solution was 5.8 mol / L.
The CV of this saturated PDSL aqueous solution was measured using the same method as in Example 1. As a result, the decomposition voltage on the oxidation side was 1.70 V on the basis of the hydrogen electrode. On the other hand, the decomposition voltage at which hydrogen is generated on the reduction side is -0.89 V based on the hydrogen electrode, and the electrochemical stability of oxidation-reduction of the PDSL aqueous solution, that is, the potential window is 1.70 V-(- 0.89V) = 2.59V.

[Comparative Example 2]
Under a condition of 25 ° C., lithium hydroxide monohydrate was dissolved in pure water until saturated, to prepare a saturated solution of lithium hydroxide. When this saturated solution was quantified, 12.4 wt% (5.3 mol / L) of lithium hydroxide in terms of lithium hydroxide was dissolved. This solution was subjected to CV measurement in the same manner as in Example 1. As a result, the decomposition voltage on the oxidation side was 1.01 V based on the hydrogen electrode, and the decomposition voltage at which hydrogen was generated on the reduction side was -0.67 V based on the hydrogen electrode. The electrochemical stability of the oxidation-reduction of the PDSL aqueous solution, that is, the potential window was calculated as 1.01 V − (− 0.67 V) = 1.67 V.

[Example 12]
Under a condition of 25 ° C., 2.2 g of PDSL was dissolved in pure water to obtain a 20 ml aqueous solution. The Li concentration in this aqueous solution was 1 mol / L.
The CV of this 1 mol / L PDSL aqueous solution was measured in the same manner as in Example 1. As a result, the decomposition voltage on the oxidation side was 1.39 V based on the hydrogen electrode, and the decomposition voltage at which hydrogen was generated on the reduction side was -0.75 V based on the hydrogen electrode. The potential window for oxidation-reduction of the 1 mol / L PDSL aqueous solution was calculated as 1.39 V-(− 0.75 V) = 2.21 V.

[Comparative Example 3]
Under a condition of 25 ° C., 0.84 g of lithium hydroxide monohydrate was dissolved in pure water to obtain 20 ml of an aqueous solution. The Li concentration in this aqueous solution was 1 mol / L.
This solution was subjected to CV measurement in the same manner as in Example 1. As a result, the decomposition voltage on the oxidation side was 0.96 V based on the hydrogen electrode, and the decomposition voltage at which hydrogen was generated on the reduction side was -0.75 V based on the hydrogen electrode. The electrochemical stability of the oxidation-reduction of the PDSL aqueous solution, that is, the potential window was calculated as 0.96 V − (− 0.75 V) = 1.71 V.

(Experimental result)
Table 2 shows the experimental results of Examples 11 and 12 and Comparative Examples 2 and 3. It was confirmed that the potential window (electrochemical stability) was improved even in the aqueous solution in which the sodium salt described in Example 1 was replaced with the lithium salt. As compared with the results of Comparative Examples 2 and 3, this stabilizing effect revealed that alkylsulfonate ions were involved in improving the potential window. Although the mechanism of this stabilization is not clear, water molecules are electrochemically unstable only by dissolving lithium ions, but electrochemical stability is caused by the involvement of alkyl sulfonate ions. It is considered that the water molecule was hardly approached to the electrode surface due to the improvement or the dissolution of the alkyl sulfonate ion at a high concentration, and as a result, it was considered that the electrolysis of water was suppressed.

  According to the present invention, since it is possible to charge and discharge even at a high voltage where charging and discharging were difficult due to the limited electrochemical stability of the aqueous solution, a safe and high energy density sodium ion battery or lithium ion A battery can be built.

1 Working electrode (platinum plate electrode)
2 Counter electrode (platinum mesh electrode)
3. Reference electrode (Ag / AgCl electrode)
4 O-ring made of Viton 5 Electrolyte solution 6 Positive electrode material 7 Positive electrode collector 8 Positive electrode stainless steel cap 9 Negative electrode stainless steel cap 10 Negative electrode material 11 Negative electrode current collector 12 Stainless steel leaf spring 13 Inorganic filler-containing polyolefin porous separator 14 Gasket

Claims (9)

The following general formula (2)

(In the formula (2), X is a linear or branched hydrocarbon having 1 to 10 carbon atoms, and may have a 5- to 8-membered cyclic structure, and n represents an integer of 1 to 3) A method for improving the electrochemical stability of an aqueous electrolyte solution by adding a sodium salt of an alkylsulfonic acid compound represented by the formula) to water. The following general formula (3)

(In the formula (3), X is a linear or branched hydrocarbon having 1 to 10 carbon atoms and may have a 5- to 8-membered cyclic structure, and n represents an integer of 1 to 3) A method for improving the electrochemical stability of an aqueous electrolyte solution by adding a lithium salt of an alkylsulfonic acid compound represented by the formula) to water. The method for improving the electrochemical stability of an electrolytic solution according to claim 1 or 2, wherein n in any of formulas (2) to (3) is 2. The following general formula (2)

(In the formula (2), X is a linear or branched hydrocarbon having 1 to 10 carbon atoms, and may have a 5- to 8-membered cyclic structure, and n represents an integer of 1 to 3) An aqueous electrolyte solution having improved electrochemical stability, comprising, as an electrolyte salt, a sodium salt of an alkylsulfonic acid compound represented by the formula (1). The following general formula (3)

(In the formula (3), X is a linear or branched hydrocarbon having 1 to 10 carbon atoms and may have a 5- to 8-membered cyclic structure, and n represents an integer of 1 to 3) An aqueous electrolyte solution having improved electrochemical stability, comprising, as an electrolyte salt, a lithium salt of an alkylsulfonic acid compound represented by the formula (1). The electrochemical method according to claim 4 , wherein the alkali metal salt of the alkylsulfonic acid compound represented by any of the general formulas (2) to (3) is contained in an amount of 0.05 mol / L or more as an electrolyte salt. Aqueous electrolyte with improved stability. The electrolytic solution with improved electrochemical stability according to any one of claims 4 to 6 , wherein the hydrocarbon in any of formulas (2) to (3) has 1 to 3 carbon atoms. An aqueous sodium ion battery including a positive electrode including a positive electrode active material capable of inserting and extracting sodium, a negative electrode including a negative electrode active material capable of inserting and extracting sodium, and an aqueous electrolytic solution, wherein the aqueous electrolytic solution is An aqueous sodium ion battery, which is an aqueous solution containing an alkali metal salt of an alkylsulfonic acid compound represented by the general formula (2) according to claim 4 . An aqueous lithium ion battery including a positive electrode including a positive electrode active material capable of inserting and extracting lithium, a negative electrode including a negative electrode active material capable of inserting and extracting lithium, and an aqueous electrolytic solution, wherein the aqueous electrolytic solution is An aqueous lithium-ion battery, which is an aqueous solution containing an alkali metal salt of an alkylsulfonic acid compound represented by the general formula (3) according to claim 5 .

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