JP7599322B2 - Electrolyte, surface treatment agent for electrochemical element electrodes, surface treatment method for electrochemical element electrodes, and manufacturing method for electrochemical element electrodes - Google Patents

Description

The present invention relates to an electrolyte, a surface treatment agent for electrochemical element electrodes, a surface treatment method for electrochemical element electrodes, and a manufacturing method for electrochemical element electrodes.

Graphite substrates and electrodes, such as electrodes for electrochemical elements, have been attracting attention as electronic components. Conventionally, a technique for electroplating has been known to create a metal layer on the surface of an electrochemical element electrode, such as a graphite substrate (see, for example, Patent Document 1).

JP 2011-46998 A

In the process of concentrating metals on electrodes by electrochemical methods, an electrolyte solution obtained by dissolving an electrolyte and a metal raw material in a solvent is usually used. By inserting a positive electrode and a negative electrode into this electrolyte and applying a potential, an electrochemical reaction proceeds on the electrodes, and metals and/or metal ions are concentrated on the electrodes. At this time, depending on the form of the metal raw material, the following two problems may occur:
(1) When a metal salt that does not have a ligand and is composed only of a metal ion and an anion is used as a metal source, the solubility in the electrolyte is low, and the target amount of the metal source cannot be used for the reaction. In addition, the anion, which is the counter ion of the metal salt, itself undergoes an electrochemical oxidative or reductive decomposition reaction, and the by-product acts on the electrode surface, making it impossible to form a suitable electrode surface.
(2) When a metal complex consisting of a ligand for a metal ion and an anion is used as the metal raw material, the solubility in the electrolyte is improved compared to (1), but the ligand or anion of the metal complex itself undergoes an electrochemical oxidative or reductive decomposition reaction, resulting in a loss of electrical capacity that would otherwise be used for electrode surface treatment, and therefore a decrease in the efficiency of the electrochemical reaction on the electrode. In addition, by-products from the reaction of the ligand or counter ion act on the electrode surface, making it impossible to form a suitable electrode surface.
In view of the above, an object of the present invention is to suppress loss of electrical capacitance due to side reactions in a metal ion concentration treatment process on an electrode surface and to concentrate metals and/or metal ions on the electrode surface efficiently in an electrochemical reaction.

In view of the above-mentioned circumstances, the present inventors have conducted intensive research and have found that by disposing a polar solvent and an electrolyte in an electrolytic solution and containing a metal raw material whose ligand consists of the polar solvent and whose counter ion of the metal ion is the same as the anion of the electrolyte, it is possible to suppress loss of capacitance due to side reactions in the metal ion concentration treatment step on the electrode surface and to concentrate metal and/or metal ions on the electrode surface efficiently through electrochemical reaction, thereby completing the present invention.
That is, the gist of the present invention lies in the following.
[1] An electrolytic solution comprising a metal complex compound represented by the following general formula (1), a polar solvent, and an electrolyte comprising an anion having at least one bond selected from the group consisting of a B-F bond, an S-F bond, and a P-F bond:
[(M ⁿ⁺ ) S _x ] (A ^m- ) _m/n (1)
(In formula (1), M ⁿ⁺ is an n-valent metal ion, n is an integer from 1 to 6; S is the same compound as the polar solvent, x is an integer from 1 to 6; A ^m- is the same as the anion contained in the electrolyte, is an m-valent anion having at least one bond selected from the group consisting of a B-F bond, an S-F bond, and a P-F bond, and m is an integer from 1 to 4.)
[2] The electrolyte solution according to [1], wherein the polar solvent contains at least one selected from the group consisting of cyclic carbonates, chain carbonates, nitrile compounds, and carboxylic acid esters.
[3] A surface treatment agent for an electrochemical element electrode, comprising the electrolytic solution according to [1] or [2].
[4] A step of arranging a first electrochemical element electrode and a second electrochemical element electrode so as to be in contact with the surface treatment agent for electrochemical element electrodes according to [3], and a step of applying a voltage to the surface treatment agent for electrochemical element electrodes using the first electrochemical element electrode and the second electrochemical element electrode;
The surface treatment method of an electrochemical element electrode comprises the steps of:
[5] A step of arranging a first electrochemical element electrode and a second electrochemical element electrode so as to be in contact with the surface treatment agent for electrochemical element electrodes according to [3], and a step of applying a voltage to the surface treatment agent for electrochemical element electrodes using the first electrochemical element electrode and the second electrochemical element electrode;
4. A method for producing an electrochemical element electrode, comprising:

According to the electrolyte of the present invention, in the step of concentrating metal ions on the electrode surface, the loss of capacitance due to side reactions can be reduced, and metal ions can be concentrated on the electrode surface efficiently in the electrochemical reaction.
The action and principle by which the use of the electrolyte of the present invention can reduce the loss of electrical capacity in the metal ion concentration treatment step and efficiently concentrate metal ions on the electrode surface is not clear, but is thought to be as follows, however, the present invention is not limited to the action and principle described below.

The metal complex compound represented by the general formula (1) (hereinafter also referred to as "compound represented by formula (1)") has a polar solvent, which is a component of the electrolyte, as a ligand. Since the ligand is the same compound as the component of the electrolyte, electrochemical side reactions are suppressed to the same extent as when the electrolyte does not contain the compound represented by formula (1), and loss of capacitance can be suppressed. Even if the ligand reacts electrochemically, it gives a by-product similar to the reaction of the electrolyte, so that the effect on the electrode surface caused by adding the compound represented by formula (1) to the electrolyte can be suppressed.
In addition, the compound represented by formula (1) has the same anion as the electrolyte in the electrolytic solution. Therefore, the electrochemical side reaction is suppressed to the same extent as when the electrolytic solution does not contain the compound represented by formula (1), and the loss of electric capacity can be suppressed. Even if this anion reacts electrochemically, it gives a by-product similar to the reaction of the electrolytic solution, so that the effect on the electrode surface caused by adding the compound represented by formula (1) to the electrolytic solution can be suppressed.

Therefore, by using the compound represented by formula (1) as the metal raw material, it is possible to reduce the loss of capacitance associated with the electrochemical reaction and efficiently concentrate metal ions on the electrode surface while suppressing the effects on the electrode surface.

The following describes in detail the form for carrying out the present invention. However, the description given below is one example (representative example) of the embodiment of the present invention, and the present invention is not limited to these contents as long as it does not exceed the gist of the claims.

[1. Electrolyte]
The electrical liquid according to the present invention contains a metal complex compound represented by formula (1).
[(M ⁿ⁺ ) S _x ] (A ^m- ) _n/m (1)
(In formula (1), M ⁿ⁺ is an n-valent metal ion, n is an integer from 1 to 6; S is the same compound as the polar solvent, x is an integer from 1 to 6; A ^m- is the same anion as the anion contained in the electrolyte, and is an m-valent anion having at least one bond selected from the group consisting of a B-F bond, an S-F bond, and a P-F bond, and m is an integer from 1 to 4.)

<Metal complex compound represented by formula (1)>
(Metal ions)
In formula (1), M ⁿ⁺ is not particularly limited as long as it is a metal ion having a valence of n (wherein n is an integer of 1 to 6). As the metal ion, nickel ion, palladium ion, platinum ion, cobalt ion, copper ion, silver ion, gold ion, manganese ion, titanium ion, zirconium ion, molybdenum ion, tungsten ion and aluminum ion are preferred, nickel ion, palladium ion, cobalt ion, copper ion, silver ion, manganese ion, titanium ion, molybdenum ion, tungsten ion and aluminum ion are more preferred, and nickel ion, cobalt ion, manganese ion, copper ion, molybdenum ion, tungsten ion and aluminum ion are even more preferred. When the metal ion is one of these ions, the metal complex compound represented by the general formula (1) can be obtained inexpensively and easily, and in the metal ion concentration treatment step on the electrode surface, the loss of electrical capacity due to side reactions is reduced, and the effect of the present application of concentrating metal ions on the electrode surface efficiently in the electrochemical reaction is easily obtained, which is preferable.

In formula (1), n represents the valence of the metal ion M ⁿ⁺ , and is an integer corresponding to the valence that the metal ion M ⁿ⁺ can take, and is usually an integer of 1 to 6. n is preferably an integer of 2 to 6, and more preferably 2, 4 or 6. If the valence of the metal ion M ⁿ⁺ is divalent, tetravalent or hexavalent, the compound of formula (1) is particularly stable, so it can be easily handled, and the capacity required for the electrochemical reaction is reduced, so that in the metal ion concentration treatment step on the electrode surface, the metal ion can be concentrated on the electrode surface while reducing the loss of electrical capacity, which is preferable. The metal ion may be one type, or may contain two or more types in any ratio. That is, the electrolyte according to this embodiment may contain two or more types of metal ions of the same metal species but different valences, or may contain two or more types of metal ions of different types.

(Polar Solvent S)
In formula (1), S is not particularly limited as long as it is the same compound as the polar solvent contained in the electrolyte used in the electrochemical element, and examples thereof include cyclic carbonates, chain carbonates, nitrile compounds, carboxylates, ether compounds, and sulfone compounds. Among these, cyclic carbonates, chain carbonates, nitrile compounds, and carboxylates are preferred, cyclic carbonates, chain carbonates, and nitrile compounds are more preferred, and cyclic carbonates or nitrile compounds are particularly preferred. These solvents are strongly coordinated to metal ions and form stable coordinate bonds with metals, making it easy to obtain the metal complex compound represented by general formula (1), and are therefore preferred.
In addition, in formula (1), x indicates the coordination number of the polar solvent S with respect to the metal ion M ⁿ⁺ , and is an integer corresponding to the coordination number determined by M ⁿ⁺ and S. x is usually an integer of 1 to 6. Hereinafter, the cyclic carbonates, chain carbonates, nitrile compounds, and carboxylate esters will be described.

Cyclic carbonates The cyclic carbonates are not particularly limited as long as they can be coordinated to the metal ion Mn ⁺ in formula (1), and examples thereof include ethylene carbonate, propylene carbonate, butylene carbonate, etc. Among these, from the viewpoint of the chemical stability and electrochemical stability of the cyclic carbonate compound, ethylene carbonate or propylene carbonate is preferred, and ethylene carbonate is more preferred. The cyclic carbonate may be used alone or in any ratio of two or more.

Chain carbonates The chain carbonate is not particularly limited as long as it can coordinate to the metal ion Mn ⁺ in formula (1), and examples thereof include dimethyl carbonate, diethyl carbonate, di-n-propyl carbonate, diisopropyl carbonate, n-propyl isopropyl carbonate, ethyl methyl carbonate, and methyl-n-propyl carbonate. Among these, from the viewpoint of production, dimethyl carbonate, diethyl carbonate, or ethyl methyl carbonate is preferred. The chain carbonate may be used alone or in any ratio of two or more.

Nitrile Compounds The nitrile compounds are not particularly limited as long as they can be coordinated to the metal ion M ⁿ⁺ in formula (1), and examples thereof include acetonitrile, propionitrile, butyronitrile, pentanenitrile, hexanenitrile, heptanenitrile, octanenitrile, benzonitrile, etc. Among these, from the viewpoints of the chemical stability and electrochemical stability of the nitrile compounds and the coordination to the anion A ^m- in formula (1), acetonitrile, propionitrile, butyronitrile, pentanenitrile, benzonitrile, etc. are preferred, acetonitrile, propionitrile, and butyronitrile are more preferred, and acetonitrile and propionitrile are even more preferred. These nitrile compounds may be used alone or in any ratio of two or more.

Carboxylic acid esters are not particularly limited as long as they can be coordinated to the metal ion Mn ⁺ in formula (1), and examples thereof include methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, and butyl propionate. Among these, from the viewpoints of chemical stability, electrochemical stability, and coordination to A in formula (1), methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and propyl propionate are preferred, and methyl acetate, ethyl acetate, methyl propionate, and ethyl propionate are more preferred, and methyl acetate, ethyl acetate, and methyl propionate are even more preferred. These carboxylates may be used alone or in any ratio of two or more.

Polar solvent S may be used alone or in any combination of two or more kinds in any ratio. Thus, cyclic carbonates, chain carbonates, nitrile compounds, and carboxylic acid esters may be used alone or in any combination of two or more kinds in any ratio.

(anion)
In formula (1), A ^m- is the same compound as the anion of the electrolyte, and is not particularly limited as long as it is an anion having at least one bond selected from the group consisting of a B-F bond, an S-F bond, and a P-F bond, and examples thereof include BF ₄ ^- , [BF ₂ (C ₂ O ₂ )] ^- , (FSO ₂ ) ₂ N ^- , (FSO ₂ ) ₃ C ^- , FSO ₃ ^- , PF ₄ (CF ₃ ) ₂ ^- , [PF ₂ (C ₂ O ₂ ) ₂ ] ^- , and PF ₆ ^- . Among these, BF ₄ ^- , (FSO ₂ ) ₂ N ^- , FSO ₃ ^- , and PF ₆ ^- are preferred from the viewpoint of production.
In formula (1), m represents the valence of the counter anion A ^m- , is an integer corresponding to the possible valence of the anion A ^m- , and is usually an integer of 1 to 4. m is preferably an integer of 1 to 3, more preferably 1 or 2. If the valence of the counter anion A is monovalent or divalent, the capacity required for the electrochemical reaction can be reduced, and therefore, in the metal ion concentration treatment step on the electrode surface, metal ions can be concentrated on the electrode surface while further suppressing loss of electrical capacity, which is preferable.
In formula (1), the number of anions n/m is determined relative to [(M ⁿ⁺ )S _x ] so that the entire compound of formula (1) is electrochemically neutral, and is usually an integer of 1 to 6. n/m is preferably 2, 4, or 6. Designing the compound of formula (1) so that n/m is in such a range makes it possible to reduce the loss of capacitance due to the side reaction of A, which is preferable because it makes it easier to obtain the effect of the present application of concentrating metal ions on the electrode surface efficiently in the electrochemical reaction.

The metal complex compound represented by formula (1) can be synthesized and used. The synthesis method is not particularly limited, but for example, a method of suspending a metal compound serving as a metal ion source in a solvent and adding a compound serving as a counter anion source thereto to obtain a metal complex compound consisting of a cation and an anion in which the solvent is coordinated to the metal ion can be exemplified. The solvent coordinated to the metal ion can be exchanged with another polar solvent to obtain the desired metal complex compound.
The metal ion source is not particularly limited, and examples of the nickel ion source include nickel halides such as Ni( _CH3COO ) ₂ , Ni(OH) ₂ , NiO, _NiCO3 , _NiSO4 , and nickel chloride. Examples of the cobalt ion source include Co( _CH3COO ) ₂ , Co(HCOO) ₂ , Co(OH) ₂ , cobalt oxides such as CoO and _Co3O4 , _CoLiO2 , _CoCO3 , _CoSO4 , Co( _NO3 ) _{2 ,} and cobalt halides such as cobalt(II) fluoride, cobalt(III) fluoride, cobalt(II) bromide, and cobalt(II) chloride. Examples of copper ion sources include Cu( _CH3COO ) ₂ ; Cu(HCOO) ₂ ; Cu(OH) ₂ ; copper oxides such as CuO and _Cu2O ; _CuCO3 ; _CuSO4 and Cu( _NO3 ) ₂ ; and copper halides such as copper(I) chloride and copper(II) chloride. _Examples of manganese ion sources include manganese acetate hydrates such as Mn( _CH3COO ) _2.2H2O , Mn( _CH3COO ) _2.4H2O , and Mn( _CH3COO ) _3.2H2O ; manganese oxides such as Mn(OH) ₂ , _{MnO2 , and Mn3O4 ;} manganese halides such as _{MnCO3 , MnSO4 , KMnO4} , _MnB4O7.8H2O , and manganese(II) _chloride . Examples of titanium ion sources include tetraalkyl titanates such as Ti(CH ₃ COO) ₄ , Ni(OH) ₄ , TiO ₂ , and Ti(OCH ₂ CH ₃ ) ₄ , metal complexes such as bis(2,4-pentanedionato)titanium(IV) oxide, and titanium halides such as titanium tetrachloride. Examples of zirconium ion sources include metal complexes such as Zr(CH ₃ COO) ₄ , Zr(OH) ₄ , and tetrakis(2,4-pentanedionato)zirconium(IV), and zirconium halides such as zirconium chloride(IV). Examples of molybdenum ion sources include metal complexes such as molybdenum dioxide(VI) dichloride and bis(2,4-pentanedionato)dioxomolybdenum(VI), and molybdenum halides such as molybdenum chloride(III) and molybdenum chloride(V). Examples of the tungsten ion include tungsten halides such as tungsten chloride (II) and tungsten chloride (VI). Examples of the aluminum ion source include aluminum salts such as Al( _FSO3 ) ₃ , Al( _CH3COO ) ₃ , Al( _CF3COO ) ₃ , Al( _CF3SO3 ) ₃ , aluminum alkoxides such as tris(2,4- _{pentanedionato} )aluminum, aluminum ethoxide, aluminum isopropoxide, and aluminum-n-butoxide, alkyl aluminums such as trimethylaluminum, and aluminum halides such as aluminum chloride.

In the case where the compound represented by formula (1) is a compound that cannot be isolated, the compound represented by formula (1) contained as a metal complex compound in the same polar solvent as S in formula (1) can also be used as a metal raw material for the electrolyte solution of an electrochemical element. In this case, the ratio (S (mol)/M ^{n +} (mol)) of the amount of substance (S mol) of the polar solvent to the amount of substance (M n+ (mol)) of the metal ion contained in the metal raw material is 200 or less, preferably 150 or less, and more preferably 100 or less. This range is preferable because it is easy to adjust the concentration of the metal ion when preparing an electrolyte solution using a metal raw material containing the compound represented by formula (1).

The content of metal ions in the electrolyte prepared using the metal complex compound represented by formula (1) (including a solution containing the metal complex compound represented by formula (1)) is usually 1 mass ppm or more, preferably 5 mass ppm or more, more preferably 10 mass ppm or more, and even more preferably 25 mass ppm or more. On the other hand, it is usually 1000 mass ppm or less, preferably 700 mass ppm or less, and even more preferably 500 mass ppm or less. This range is preferable because it is possible to reduce the loss of electric capacity due to the electrochemical reaction of excess metal ions, and therefore it is easy to obtain the effect of the present application of concentrating metal ions on the electrode surface efficiently in the electrochemical reaction. When the amount of metal ions in the electrolyte is measured, a member containing the electrolyte is taken out from the electrochemical element, and the electrolyte is extracted and measured. For example, the electrolyte can be extracted by a centrifuge, or it can be extracted using an organic solvent. The extracted electrolyte is used to perform inductively coupled plasma atomic emission spectrometry (ICP-AES, for example, Thermo Fischer
The metal element, i.e., metal ion, is quantified by Li and acid concentration matching calibration curve method using a meter (iCAP 7600duo, Scientific). The electrolyte according to one embodiment of the present invention may contain one type of metal complex compound represented by formula (1), or may contain two or more types.

<Polar Solvent>
The electrolytic solution of the present embodiment contains a polar solvent. The polar solvent is not particularly limited as long as it contains the polar solvent S contained in the metal complex compound represented by formula (1), and a known polar solvent can be used, but from the viewpoint of easy dissolving the electrolyte, organic polar solvents such as cyclic carbonates, chain carbonates, nitrile compounds, carboxylates, ether compounds, or sulfone compounds are preferred. Among these, cyclic carbonates, chain carbonates, nitrile compounds, and carboxylates are preferred from the viewpoint of handling of the compounds. These can be used alone or in combination of two or more. As a combination of two or more polar solvents, a combination of two or more selected from the group consisting of saturated cyclic carbonates, chain carbonates, and carboxylates is preferred, and a combination of saturated cyclic carbonates or chain carbonates is more preferred.

<Electrolytes>
The electrolytic solution of the present embodiment includes an electrolyte. The electrolyte used in the electrolytic solution of the present embodiment is not particularly limited as long as it includes a salt containing an anion having at least one bond selected from the group consisting of a BF bond, a SF bond, and a PF bond, and any known electrolyte can be used. Specific examples of the electrolyte will be described in detail below.

(Lithium salt)
Lithium salts can be used as the electrolyte in the electrolytic solution of this embodiment. The lithium salt is not particularly limited as long as it is known to be used in electrolytic solutions, and any one or more can be used. Specific examples of lithium salts include fluoroborate lithium salts such as _LiBF4 ; fluorophosphate lithium salts such as _LiPF6 and _LiPO2F2 ; sulfonate lithium salts such as _FSO3Li ; lithium imide salts such as LiN( _FSO2 ) ₂ ; lithium methide salts such as LiC( _FSO2 ) ₃ ; lithium oxalate salts such as Li[ _BF2 ( _C2O2 )] and Li[ _PF2 ( _{C2O2 ) 2} ]; and fluorine-containing organic lithium _salts such as _LiPF4 ( _CF3 ) _{2 .}

The electrochemically stable salt is preferably selected from lithium fluoroborates, lithium fluorophosphates, lithium sulfonates, lithium imide salts, and lithium oxalates, from the viewpoints of occurrence of few side reactions and suppression of loss of capacitance, and more preferably selected from lithium fluoroborates, lithium fluorophosphates, and lithium sulfonates.
The total concentration of the electrolyte in the electrolytic solution is not particularly limited, but is usually 8% by mass or more, preferably 8.5% by mass or more, more preferably 9% by mass or more, based on the total amount of the electrolytic solution. The upper limit is usually 18% by mass or less, preferably 17% by mass or less, more preferably 16% by mass or less. When the total concentration of the electrolyte is within the above range, the electrical conductivity is appropriate for the electrochemical reaction, so that the metal and/or metal ions can be efficiently concentrated on the electrode surface.

<Method of manufacturing electrolytic solution>
The method for producing the electrolyte solution according to the present embodiment is not particularly limited as long as it is possible to prepare an electrolyte solution containing a metal complex compound represented by general formula (1), a polar solvent, and an electrolyte containing an anion having at least one bond selected from the group consisting of a BF bond, an SF bond, and a PF bond.
Specifically, for example, as in the examples described later, a solution containing a reaction product obtained by synthesizing a metal complex compound represented by formula (1) can be diluted with a polar solvent, and an electrolyte can be added to obtain an electrolytic solution.

[2. Surface treatment agent for electrochemical element electrodes]
A surface treatment agent for an electrochemical element electrode according to one embodiment of the present invention contains the above-described electrolyte solution.
The electrolytic solution according to one embodiment of the present invention can be used as a surface treatment agent for an electrochemical element electrode in the metal ion concentration treatment step, or a polar solvent or the like can be further added to the electrolytic solution and used as a surface treatment agent for an electrochemical element electrode in the metal ion concentration treatment step. Specific examples of the polar solvent include those described in the section [1. Electrolytic solution].

[3. Surface treatment method for electrochemical element electrodes]
A surface treatment method for an electrochemical element electrode according to one embodiment of the present invention is not particularly limited as long as it is a method of using the above-mentioned surface treatment agent for electrochemical element electrodes, and includes a step of applying a voltage to the surface treatment agent for electrochemical element electrodes using a plurality of electrodes in a state in which the plurality of electrodes are in contact with the surface treatment agent for electrochemical element electrodes.
For example, a method including a step of placing a first electrochemical element electrode and a second electrochemical element electrode in contact with an electrolyte solution containing a surface treatment agent for electrochemical element electrodes, and a step of applying a voltage to the surface treatment agent for electrochemical element electrodes using the first electrochemical element electrode and the second electrochemical element electrode. The conditions of the concentration treatment, such as the applied voltage and time, depend on the electrochemical element. For example, when the electrochemical element is a lithium ion secondary battery, a method of performing the concentration treatment by performing CC-CV charging to 4.2 V after initial conditioning, leaving it for several hours, and then discharging it to 2.5 V can be exemplified. In addition, a method of performing the concentration treatment by leaving the electrochemical element in a charged state at an appropriate temperature of room temperature to 85 ° C. for several days in order to further increase the concentration treatment speed can be exemplified.

<Electrochemical element electrodes>
The surface treatment agent for electrochemical element electrodes according to one embodiment of the present invention can be applied to the metal ion concentration treatment of known electrochemical element electrodes. The electrochemical element electrode is preferably one having a substance capable of electrochemically absorbing and releasing metal ions on a part of the collector surface. Examples of the substance capable of electrochemically absorbing and releasing metal ions include carbon-based materials, materials containing a metal capable of alloying with Li, lithium-containing metal composite oxide materials, and mixtures thereof. Among these, it is preferable to use a carbon-based material, a material containing a metal capable of alloying with Li, or a mixture of a material containing a metal capable of alloying with Li and graphite particles, in terms of good cycle characteristics and safety, and excellent continuous charging characteristics. These may be used alone or in any combination of two or more.

[4. Manufacturing method of electrochemical element electrodes]
A method for producing an electrochemical element electrode having a surface in which metals and/or metal ions are concentrated using the above-mentioned surface treatment agent for electrochemical element electrodes is also one aspect of the present invention. The method for producing an electrochemical element electrode having a surface in which metals and/or metal ions are concentrated is not particularly limited as long as it includes a step of applying a voltage between a plurality of electrodes in a state in which the electrodes are in contact with the surface treatment agent for electrochemical element electrodes.
For example, an electrochemical element electrode in which metal and/or metal ions are concentrated on the surface of the first electrode can be produced by a process of placing a first electrochemical element electrode and a second electrochemical element electrode so as to be in contact with the above-mentioned surface treatment agent for electrochemical element electrodes, and a process of applying a voltage between the first electrochemical element and the second electrochemical element electrode.
For the first electrochemical element electrode and the second electrochemical element electrode, a known electrochemical element electrode can be used, and a preferred embodiment of the known electrochemical element electrode is as described in [3. Surface treatment method of electrochemical element electrode]. In addition, the conditions of the concentration treatment, such as the applied voltage and time, depend on the electrochemical element, but the description in [3. Surface treatment method of electrochemical element electrode] is applied. For example, when the electrochemical element is a lithium ion secondary battery, after initial conditioning, a method of performing the concentration treatment by performing CC-CV charging to 4.2 V, leaving it for several hours, and then discharging it to 2.5 V can be mentioned. In order to increase the concentration treatment speed, a preferred embodiment is also to leave the electrochemical element in a charged state at an appropriate temperature of room temperature to 85 ° C. for several days.

[Preparation of a solution containing a metal complex compound represented by formula (1)]
1. Nickel complex-containing solution In an argon glove box, 0.5 g (3.9 mmol) of NiCl ₂ was weighed into a 50 mL beaker and suspended in acetonitrile (AN). While stirring, 1.95 g (7.7 mmol) of AgPF ₆ was added slowly in small portions, and then stirred at room temperature for 3 hours. As the reaction proceeded, a white solid of AgCl was generated. After leaving it as it was overnight, AgCl was filtered off, and the obtained filtrate was concentrated under reduced pressure using a rotary evaporator to obtain a blue solid of [Ni ²⁺ (AN) _x' ] (PF ₆ ^- ) ₂ (x' = 0 to 6). To this was added 5.0 g (56.8 mmol) of ethylene carbonate (EC) melted at 45° C. to dissolve the solid, and the mixture was evacuated at 35° C. for 6 hours to remove AN, which was the coordination solvent, and a nickel complex-containing solution was obtained as an EC solution containing [Ni ²⁺ (EC) _x ](PF ₆ ⁻ ) ₂ (x=1 to 6).

2. Manganese complex-containing solution In an argon glove box, 0.10 g (0.8 mmol) of MnCl ₂ was weighed into a 50 mL beaker and suspended in acetonitrile (AN). While stirring, 0.402 g (1.6 mmol) of AgPF ₆ was added slowly in small portions, and then stirred at room temperature for 3 hours. As the reaction proceeded, a white solid of AgCl was generated. After leaving it overnight, AgCl was filtered off, and the obtained filtrate was concentrated under reduced pressure using a rotary evaporator to obtain a white solid of [Mn ²⁺ (AN) _x' ] (PF ₆ ^- ) ₂ (x' = 0 to 6). To this was added 5.0 g (56.8 mmol) of ethylene carbonate (EC) melted at 45° C. to dissolve the solid, and the mixture was evacuated at 35° C. for 6 hours to remove the AN, which was the coordination solvent, and a manganese complex-containing solution was obtained as an EC solution containing [Mn ²⁺ (EC) _x ](PF ₆ ⁻ ) ₂ (x=1 to 6).

3. Copper complex-containing solution In an argon glove box, 0.50 g (3.7 mmol) of CuCl ₂ was weighed into a 50 mL beaker and suspended in acetonitrile (AN). While stirring, 1.88 g (7.4 mmol) of AgPF ₆ was added slowly in small portions, and then stirred at room temperature for 3 hours. As the reaction proceeded, a white solid of AgCl was generated. After leaving it overnight, AgCl was filtered off, and the obtained filtrate was concentrated under reduced pressure using a rotary evaporator to obtain a blue solid of [Cu ²⁺ (AN) _x' ] (PF ₆ ^- ) ₂ (x' = 0 to 6). To this was added 5.0 g (56.8 mmol) of ethylene carbonate (EC) melted at 45° C. to dissolve the solid, and the mixture was evacuated at 35° C. for 6 hours to remove AN, which was the coordinating solvent, and a copper complex-containing solution was obtained as an EC solution containing [Cu ²⁺ (EC) _x ](PF ₆ ⁻ ) ₂ (x=1 to 6).

Example 1
[Preparation of positive electrode]
85 parts by mass of Li(Ni _1/3 Mn _1/3 Co _1/3 )O ₂ as a positive electrode active material, 10 parts by mass of acetylene black as a conductive material, and 5 parts by mass of polyvinylidene fluoride (PVdF) as a binder were mixed in N-methylpyrrolidone solvent with a disperser to form a slurry, which was uniformly applied to one side of an aluminum foil with a thickness of 15 μm, dried, and pressed to form a positive electrode.

[Preparation of negative electrode]
To 98 parts by mass of natural graphite, 1 part by mass of an aqueous dispersion of sodium carboxymethylcellulose (concentration of sodium carboxymethylcellulose: 1% by mass) and 1 part by mass of an aqueous dispersion of styrene-butadiene rubber (concentration of styrene-butadiene rubber: 50% by mass) were added as a thickener and binder, and mixed in a disperser to form a slurry. The obtained slurry was applied to one side of a copper foil having a thickness of 10 μm, dried, and then pressed to form a negative electrode (also referred to as a "negative electrode plate").

[Preparation of electrolyte]
Under a dry argon atmosphere, an EC solution containing [Ni ²⁺ (EC) _x ](PF ₆ ⁻ ) ₂ (x=1 to 6) was diluted with EC, EMC, and DMC so that the nickel ion concentration in the mixed solvent was as shown in Table 1, and the solvent composition was a mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 3:4:3, and LiPF ₆ that had been thoroughly dried was dissolved at 1 mol/L (as the concentration in the electrolyte). The electrolyte that does not contain a nickel complex-containing solution is called the reference electrolyte. In the table, the content of nickel element (nickel ion) is a value obtained based on the measurement results of inductively coupled plasma atomic emission spectrometry (ICP-AES) described later. In the table, the "content (mass%)" and "content (mass ppm)" are the contents when the reference electrolyte is taken as 100 mass%.

<Measurement of nickel content in electrolyte>
100 μL (about 130 mg) of the electrolyte was taken out. The taken electrolyte was weighed into a PTFE beaker, and an appropriate amount of concentrated nitric acid was added and wet decomposed on a hot plate, and the volume was adjusted to 50 mL. The content of Li and nickel elements was measured by an inductively coupled plasma atomic emission spectrometry (ICP-AES, Thermo Fischer Scientific, iCAP 7600duo) using an acid concentration matching calibration curve method.

[Manufacturing electrochemical cells for electrode treatment]
The above positive electrode, negative electrode, and polyethylene separator were laminated in the order of negative electrode, separator, and positive electrode to prepare an electrochemical cell element. This electrochemical cell element was inserted into a bag made of a laminate film of aluminum (thickness 40 μm) coated on both sides with a resin layer so that the positive and negative terminals were protruding, and the above prepared electrolytic solution was then poured into the bag and vacuum sealed to prepare a laminated electrochemical cell.

<Evaluation of electrochemical cells>
[Initial conditioning]
In a thermostatic bath at 25 ° C., the electrochemical cell was charged at a constant current and constant voltage (hereinafter referred to as CC-CV charging) to 4.2 V at a current equivalent to 1/6 C (1 C refers to a current value that takes 1 hour to charge or discharge. The same applies below.) and then discharged to 2.5 V at 1/6 C to perform the initial charge and discharge. CC-CV charging was performed to 4.1 V at 1/6 C. Then, aging was performed under conditions of 60 ° C. and 24 hours. Then, the electrochemical cell was discharged to 2.5 V at 1/6 C to stabilize the electrochemical cell. Furthermore, CC-CV charging was performed to 4.2 V at 1/6 C, and then discharged to 2.5 V at 1/6 C to perform initial conditioning. The initial capacity loss was calculated from the difference between the charge capacity and discharge capacity at the time of the initial charge and discharge (charge capacity - discharge capacity). The aging capacity loss was calculated from the difference between the charge capacity and discharge capacity at the time of aging (charge capacity - discharge capacity). The sum of the initial capacity loss and the aging capacity (initial capacity loss + aging capacity) was defined as the capacitance loss. Table 1 below shows the relative values (%) when the capacitance loss in Comparative Example 1 is set to 100.

[Metal ion concentration treatment process on electrode surface]
The electrochemical cell after the initial conditioning was again subjected to CC-CV charging at 1/6C to 4.2V, and then stored at high temperature under conditions of 60 ° C. and 168 hours. After high-temperature storage, the electrochemical cell was cooled, and then the electrochemical cell was discharged at 1/6C to 2.5V at 25 ° C., and the electrochemical cell was disassembled in an argon glove box to remove the negative electrode plate, washed with DMC, thoroughly dried, and the amount of nickel element on the negative electrode was measured by the method described below. At this time, the value of the amount of nickel element on the negative electrode (μg / cm ² ) relative to the initial concentration of nickel element in the electrolyte (μg / g) was taken as the concentration rate of metal ions on the negative electrode. Table 1 below shows the relative values when the concentration rate of Comparative Example 1 is set to 100.

[Measurement of nickel element content on electrode]
The negative electrode plate was cut in half and extracted with water, and the entire extract except for the copper foil was subjected to wet Kjeldahl decomposition and measured by ICP-AES. Note that for negative electrodes with a separator attached, the separator was also subjected to wet decomposition.

<Comparative Example 1>
The same procedure as in _Example ¹ was carried out except that the electrolytic solution was prepared using commercially available bis(2,4-pentanedionato)nickel(II) (Ni-acac, Aldrich) instead of the EC solution containing [Ni ²⁺ ( _EC ) _x ](PF 6 − ) 2 (x=1 to 6). The concentration rates obtained are set to 100 and are shown in the table below.

Example 2
The same _method as in Example 1 was used to prepare the electrolyte, except that an EC solution containing [Mn ²⁺ (EC) _x ] (PF ₆ ⁻ ) ₂ (x = 1 to 6) was used instead of the EC solution containing [Ni ²⁺ (EC) x ] (PF ₆ ⁻ ) ₂ (x = 1 to 6). The analysis of the electrolyte and metal elements on the negative electrode was performed using manganese element instead of nickel element as the analysis target. The obtained concentration ratios are shown in Table 1 below as relative values when the concentration ratio of Comparative Example 2 is set to 100.

<Comparative Example 2>
The electrolyte was prepared in the same manner as in _{Example 2} , except that commercially available manganese(II) bis(trifluoromethanesulfonate) (Mn-OTf, Aldrich) was used instead of the EC solution containing [Mn ²⁺ (EC) _x ]( ^PF 6 − ) 2 (x=1 to 6). The concentration rates obtained are set to 100 and are shown in the table below.

Example 3
The _{same method} as in Example 1 was used to prepare the electrolyte, except that an EC solution containing [Cu ²⁺ (EC) _x ] (PF ₆ ⁻ ) ₂ (x = 1 to 6) was used instead of the EC solution containing [Ni ²⁺ (EC) x ] (PF ₆ ⁻ ) ₂ (x = 1 to 6). The analysis of the electrolyte and metal elements on the negative electrode was performed using copper element instead of nickel element as the analysis target. The obtained concentration ratios are shown in Table 1 below as relative values when the concentration ratio of Comparative Example 3 is set to 100.

<Comparative Example 3>
The same procedure as in Example 3 was carried out, except that the electrolyte was prepared using commercially available _copper (II) trifluoromethanesulfonate (Cu-OTf, Aldrich) instead of the EC solution containing [Cu ²⁺ (EC) _x ](PF ₆ ⁻ ) 2 (x=1 to 6). The concentration rates obtained are set to 100 and are shown in the table below.

Comparison between the Examples and Comparative Examples for each metal type showed that the metal complex compound represented by formula (1) contained less capacitance loss due to side reactions during the metal ion concentration treatment process on the electrode surface, and was able to concentrate the metal and/or metal ions on the electrode surface with efficient electrochemical reactions.

The present invention is useful in that it is possible to suppress the loss of electrical capacity due to side reactions in the metal ion concentration treatment process on the electrode surface and to concentrate metals and/or metal ions on the electrode surface efficiently through electrochemical reactions.

Claims (5)

An electrolytic solution comprising an electrolyte containing a metal complex compound represented by the following general formula (1), a polar solvent (excluding acetonitrile) , and an anion having at least one bond selected from the group consisting of a B-F bond, an S-F bond, and a P-F bond :
[(M ⁿ⁺ ) S _x ] (A ^m- ) _n/m (1)
(In formula (1), M ⁿ⁺ represents an n-valent metal ion (including an alkali metal ion and an alkali
ions of metal-earth metals are excluded) , n is an integer from 1 to 6; S is the same compound as the polar solvent, x is an integer from 1 to 6; A ^m- is the same as the anion contained in the electrolyte and is an m-valent anion having at least one bond selected from the group consisting of a B-F bond, an S-F bond, and a P-F bond, and m is an integer from 1 to 4 . 2. The electrolyte solution according to claim 1, wherein the polar solvent comprises at least one selected from the group consisting of cyclic carbonates, chain carbonates, nitrile compounds (excluding acetonitrile) , and carboxylates. A surface treatment agent for electrochemical element electrodes, comprising the electrolyte solution according to claim 1 or 2. A step of disposing a first electrochemical element electrode and a second electrochemical element electrode so as to be in contact with the surface treatment agent for electrochemical element electrodes according to claim 3; and a step of applying a voltage to the surface treatment agent for electrochemical element electrodes by using the first electrochemical element electrode and the second electrochemical element electrode.
The surface treatment method of an electrochemical element electrode comprises the steps of: A step of disposing a first electrochemical element electrode and a second electrochemical element electrode so as to be in contact with the surface treatment agent for electrochemical element electrodes according to claim 3; and a step of applying a voltage to the surface treatment agent for electrochemical element electrodes by using the first electrochemical element electrode and the second electrochemical element electrode.
4. A method for producing an electrochemical element electrode, comprising: