JP2023004087A - Storage method of non-aqueous electrolyte - Google Patents

Abstract

To provide a storage method suitable for a low-acid non-aqueous electrolyte.SOLUTION: A non-aqueous electrolyte that contains an acidity of less than 1 meq/kg, preferably a water content of less than 10 ppm by mass, and 0.5 to 1.5 mol/L of LiPF6 is obtained by manufactured by bringing a lithium salt electrolyte in which LiPF6 is dispersed in a carbonate ester into contact with a weakly basic anion exchange resin is stored at 20°C or less in a sealed container.SELECTED DRAWING: None

Description

The present invention relates to a method for storing a non-aqueous electrolyte having a low acidity, particularly an acidity of less than 1 meq/kg.

In a lithium ion battery, a non-aqueous electrolyte obtained by dissolving a lithium-based electrolyte such as lithium hexafluorophosphate (LiPF ₆ ) in an organic non-aqueous solvent is used as the non-aqueous electrolyte.
However, a small amount of water remains in the solvent and the lithium _- based electrolyte that constitute the electrolytic solution. Hydrogen fluoride (HF) and the like are generated as shown in (3).
(1) LiPF ₆ ⇔ LiF + PF ₅
( ₂ ) _PF5 + _H2O⇒POF3 +2HF
(3) POF ₃ +H ₂ O ⇒ POF ₂ (OH) + HF

When acidic impurities such as hydrogen fluoride (hydrofluoric acid) are present in the non-aqueous electrolyte, the battery capacity and charge-discharge cycle characteristics of the lithium-ion battery are likely to decrease, and corrosion inside the battery tends to occur. (See Patent Document 1, etc.).
Therefore, the nonaqueous electrolyte is generally stored in a sealed container in order to prevent contamination with water.
For example, Non-Patent Document 1 discloses that a non-aqueous electrolyte can be kept in a sealed container made of stainless steel or aluminum to maintain stable quality at 40° C. for about 4 to 12 weeks.

Japanese Unexamined Patent Application Publication No. 2011-71111

Journal of Power Sources 81-82 (1999) 119-122

However, the non-aqueous electrolyte investigated in Non-Patent Document 1 has a high acidity of about 2 to 4 meq/kg, and has a low acidity, especially a low acidity of less than 1 meq/kg. No consideration has been given to closed storage of the non-aqueous electrolyte.
According to the studies of the present inventors, when a high-quality non-aqueous electrolyte with low acidity is sealed and stored by a general method such as that studied in Non-Patent Document 1, the acidity is reduced even if water is not mixed. It was found to increase over time.
Accordingly, an object of the present invention is to provide a storage method suitable for a low-acid non-aqueous electrolyte.

In view of the above problems, as a result of intensive studies by the present inventors, it was found that the quality of the non-aqueous electrolyte can be maintained by storing the non-aqueous electrolyte with low acidity at a certain temperature or less. The present invention has been completed.
That is, the present invention relates to the following [1] to [6].
[1] A method for storing a non-aqueous electrolyte, which comprises storing a non-aqueous electrolyte having an acidity of less than 1 meq/kg in a sealed container at 20° C. or lower.
[2] The method for storing a non-aqueous electrolyte according to [1], wherein the water content of the non-aqueous electrolyte is less than 10 ppm by mass.
[3] The method for storing a non-aqueous electrolyte according to [1] or [2], wherein the non-aqueous electrolyte contains 0.5 to 1.5 mol/L of LiPF ₆ .
[4] The non-aqueous electrolyte is a non-aqueous electrolyte produced by contacting a weakly basic anion exchange resin with a lithium salt electrolyte-containing liquid in which LiPF6 is dispersed in a carbonate ester. The method for storing the non-aqueous electrolyte according to any one of [1] to [3] above.
[5] The method for storing a non-aqueous electrolyte according to any one of [1] to [4], wherein the non-aqueous electrolyte contains 0.1 to 50% by mass of an organic fluorine compound.
[6] The method for storing a nonaqueous electrolyte according to any one of [1] to [5], wherein the nonaqueous electrolyte contains 0.1 to 10% by mass of an organic sulfur compound.

ADVANTAGE OF THE INVENTION According to this invention, the storage method of the non-aqueous electrolyte which can maintain the acidity of a non-aqueous electrolyte low can be provided.

It is a figure which shows the form example of the storage method of the non-aqueous electrolyte which concerns on this invention. It is a figure which shows the form of the manufacturing apparatus of the non-aqueous electrolyte in the manufacturing example of this invention.

Hereinafter, the present invention will be described in detail based on preferred embodiments.
The present inventors have studied a method for removing acidic impurities such as hydrogen fluoride from a non-aqueous electrolyte. We have realized the provision of a low-acidity non-aqueous electrolyte.
In the present invention, when such a low-acidity non-aqueous electrolyte whose acidity is lowered to the limit is stored in a closed container, even if moisture does not enter the container, the low-acidity non-aqueous electrolyte can be stored. The present invention solves the new problem that the acidity increases over time when stored at room temperature (25°C), which did not exist when conventional highly acidic non-aqueous electrolytes were stored in closed containers.
Therefore, the storage method of the non-aqueous electrolyte of the present invention is intended for a non-aqueous electrolyte having a low acidity of less than 1 meq/kg.
In the present invention, a non-aqueous electrolytic solution having an acidity of less than 1 meq/kg is stored at 20° C. or lower to suppress an increase in acidity over time. On the other hand, when the temperature exceeds 20°C, especially when the temperature exceeds room temperature (25°C), the acidity of the non-aqueous electrolyte increases with time, and the effects of the present invention cannot be obtained. Although the lower limit of the storage temperature is not particularly limited, it is usually preferably 0° C. or higher from the viewpoint of preventing solidification of the electrolytic solution and deposition of the electrolyte.
In addition, the storage method of the present invention is a method effective only for non-aqueous electrolytes with an acidity of less than 1 meq/kg. Even if the liquid is stored at room temperature (25° C.) or about 40° C. from 20° C. or lower to over 20° C., the acidity does not increase over time unlike the low acidity non-aqueous electrolyte. , the effect of setting the temperature below 20° C. is not obtained.

In the storage method of the present invention, the non-aqueous electrolyte is stored by, for example, preparing a sealed container as shown in FIG. After replacement, the low-acidity non-aqueous electrolyte is placed in the container, and then the container is sealed and stored at 20° C. or less. The upper limit of the storage period is preferably 100 days or less, preferably 50 days or less.

As the closed container to be used, as long as it is a closed container that can prevent contamination of moisture in the outside air, it can have a wide range of forms and functions without requiring a special structure or constituent materials. For example, storage tanks, which are fixed storage containers, and pressure-resistant containers such as canisters used for transportation can be used. Moreover, as a constituent material of the sealed container, for example, carbon steel, manganese steel, chromium molybdenum steel and other low alloy steels, stainless steel, aluminum alloy, and the like can be used.

The non-aqueous electrolyte to which the storage method of the present invention is applied is not particularly limited except that the acidity is less than 1 meq/kg. A non-aqueous electrolytic solution produced by preparing a salt electrolyte-containing solution and bringing this alkali metal salt electrolyte-containing solution into contact with a weakly basic anion exchange resin can be preferably used. In the following paragraphs of this specification, the non-aqueous electrolyte before treatment with the weakly basic anion exchange resin is referred to as an alkali metal salt electrolyte-containing solution or a highly acidic non-aqueous electrolyte. The non-aqueous electrolyte after treatment with the ion exchange resin is referred to as a low-acidity non-aqueous electrolyte or simply as a non-aqueous electrolyte.

As the carbonate ester, one or more selected from cyclic carbonate esters and chain carbonate esters can be used.
Examples of the cyclic carbonate include one or more selected from ethylene carbonate (ethylene carbonate), propylene carbonate (propylene carbonate), and the like. Examples of the chain carbonate include dimethyl carbonate (dimethyl carbonate), diethyl carbonate (diethyl carbonate ), ethyl methyl carbonate (ethyl methyl carbonate), and the like.

Examples of alkali metal salt electrolytes include lithium-based electrolytes. Lithium-based electrolytes include one or more selected from LiPF ₆ , LiClO ₄ , LiBF ₄ , LiAsF ₆ , LiSbF ₆ , LiAlCl ₄ , LiCF ₃ SO ₃ and the like. LiPF ₆ is preferable when battery performance is considered.

The content of an alkali metal salt such as LiPF ₆ in the nonaqueous electrolyte is preferably 0.5 to 1.5 mol/L, more preferably 0.5 to 1.2 mol/L, and more preferably 0.8 to 1.5 mol/L. 2 mol/L is more preferred.

The non-aqueous electrolytic solution preferably contains an organic fluorine compound from the viewpoint of improving cycle characteristics. Examples of organic fluorine compounds include fluoroethylene carbonate (FEC), 4-(fluoromethyl)-1,3-dioxolan-2-one, fluoromethyl methyl carbonate and the like.
The content of the organic fluorine compound in the non-aqueous electrolyte is preferably 0.1 to 50% by mass, more preferably 0.5 to 25% by mass, even more preferably 1 to 10% by mass.

Furthermore, the non-aqueous electrolyte preferably contains an organic sulfur compound from the viewpoint of improving cycle characteristics. Organic sulfur compounds include 1,3-propanesultone (PS), sulfolane, ethylmethylsulfone, 1-ethanesulfonyl-2-methoxy-ethane, and the like.
The content of the organic sulfur compound in the nonaqueous electrolyte is preferably 0.1 to 10% by mass, more preferably 0.5 to 5% by mass.

In the non-aqueous electrolytic solution according to the present invention, the water content is preferably as low as possible, but from the viewpoint of increasing the acidity, it is preferably less than 10 ppm by mass. The water content of the non-aqueous electrolyte can be measured by the method described in Examples.

The method for preparing the alkali metal salt electrolyte-containing liquid is not particularly limited, but for example, it can be prepared by adding and dissolving an alkali metal salt electrolyte and, if necessary, an organic fluorine compound and/or an organic sulfur compound in carbonate ester. can.

A low acidity non-aqueous electrolyte can be obtained by bringing the alkali metal salt electrolyte-containing liquid prepared by the above method into contact with a weakly basic anion exchange resin to lower the acidity to less than 1 meq/kg.
The contact between the alkali metal salt electrolyte-containing liquid and the weakly basic anion exchange resin is performed using, for example, an apparatus as shown in FIG. The apparatus shown in FIG. 2 has an ion exchange section containing a weakly basic anion exchange resin, and the alkali metal salt electrolyte-containing liquid is passed through the ion exchange section to generate a weak base. contact with a volatile anion exchange resin occurs.

The weakly basic anion exchange resin used in the ion exchange section has a styrene resin as a base.

A styrene-based resin means a resin obtained by homopolymerizing or copolymerizing styrene or a styrene derivative and containing 50% by mass or more of constitutional units derived from styrene or a styrene derivative.

Examples of the styrene derivative include one or more selected from α-methylstyrene, vinyltoluene, chlorostyrene, ethylstyrene, i-propylstyrene, dimethylstyrene, bromostyrene and the like.

The styrene-based resin may be a copolymer with other copolymerizable vinyl monomers, as long as the main component is a homopolymer or a copolymer of styrene or a styrene derivative. Examples include divinylbenzenes such as o-divinylbenzene, m-divinylbenzene and p-divinylbenzene; alkylene glycol di(meth)acrylates such as ethylene glycol di(meth)acrylate and polyethylene glycol di(meth)acrylate; One or more selected from polyfunctional monomers, (meth)acrylonitrile, methyl (meth)acrylate, and the like can be used.

As the other copolymerizable vinyl monomer, ethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate having an ethylene polymerization number of 4 to 16, divinylbenzene are more preferable, and divinylbenzene, ethylene glycol di(meth) ) acrylates are more preferred, and divinylbenzene is even more preferred.

The weakly basic anion exchange resin used in the ion exchange section has tertiary amino groups as weakly basic anion exchange groups.

（ただし、Ｒ¹基およびＲ²基は炭素数１～３の炭化水素基であって互いに同一であっても異なっていてもよく、＊は基体または基体へ結合するための結合基との結合部位を示す。）
で表されるものを挙げることができる。 As the tertiary amino group, the following general formula (I)

(where R ¹ and R ² are hydrocarbon groups having 1 to 3 carbon atoms and may be the same or different; indicate the part.)
can be mentioned.

In the weakly basic anion exchange group represented by general formula (I), R ¹ and R ² are hydrocarbon groups having 1 to 3 carbon atoms.
As the R ¹ group or R ² group, one or more selected from alkyl groups and alkenyl groups can be mentioned, and alkyl groups are preferred.
As the R ¹ group or R ² group, specifically, one or more selected from methyl group, ethyl group, propyl group and propylene group can be mentioned, and methyl group is preferable.
In the weakly basic anion exchange group represented by the general formula (I), the R ¹ group and the R ² group may be the same or different.

Examples of the weakly basic anion exchange group represented by the general formula (I) include a dimethylamino group, a diethylamino group, and a dipropylamino group, with the dimethylamino group being preferred.

In the above general formula (I), * indicates a binding site between the weakly basic anion exchange group represented by the above general formula (I) and the substrate or the binding group for binding to the substrate.

（ただし、Ｒ^１基およびＲ^２基は炭素数１～３の炭化水素基であって互いに同一であっても異なっていてもよく、Ｒ^３基は炭素数１～３の炭化水素基であり、＊は基体との結合部位を示す。） The weakly basic anion-exchange group represented by the above general formula (I) is attached to a substrate made of a styrene-based resin, as shown in the following general formula (II), via the R ³ group, which is an appropriate bonding group. Bonding is preferred.

(where R ¹ and R ² are hydrocarbon groups having 1 to 3 carbon atoms and may be the same or different, and R ³ is a hydrocarbon group having 1 to 3 carbon atoms. , * indicates the binding site to the substrate.)

Examples of the R ¹ group and R ² group include the same groups as those described above.
The R ³ group is a hydrocarbon group having 1 to 3 carbon atoms, and examples of the R ³ group include one or more selected from an alkylene group and an alkenylene group, preferably an alkylene group.
Specific examples of the R ³ group include one or more selected from a methylene group (--CH ₂ --), an ethylene group (--CH ₂ CH ₂ --), a propylene group (--CH ₂ CH ₂ CH ₂ --), and the like. and methylene groups are preferred.

The weakly basic anion exchange group represented by the general formula (I) can be introduced into the styrene resin by introducing it into styrene or a styrene derivative as a substituent.

The weakly basic anion exchange resin accommodated in the ion exchange part may have any structure of a gel type structure, a macroporous (MP) type structure, and a porous type structure, and has a macroporous type structure. things are preferred.

The size of the weakly basic anion exchange resin is not particularly limited, but the harmonic mean diameter is preferably 300 to 1000 μm, more preferably 400 to 800 μm, even more preferably 500 to 700 μm.

Such a weakly basic anion exchange resin may be a commercially available product, and examples thereof include one or more selected from Diaion WA30 manufactured by Mitsubishi Chemical Corporation and ORLITE DS-6 manufactured by Organo Corporation. be able to.

The accommodation form of the weakly basic anion exchange resin accommodated in the ion exchange section is not particularly limited as long as the alkali metal salt electrolyte-containing liquid and the weakly basic anion exchange resin can come into contact with each other.
For example, the ion exchange section may be a column or tank filled with a weakly basic anion exchange resin through which the alkali metal salt electrolyte-containing liquid can flow.
Further, the ion exchange section may be provided with a pump for passing the alkali metal salt electrolyte-containing liquid.

The flow rate (liquid hourly space velocity) for passing the alkali metal salt electrolyte-containing liquid through the weakly basic anion exchange device in the ion exchange unit is appropriately selected from the rate at which acidic impurities in the alkali metal salt electrolyte-containing liquid can be removed. do it.

In the contact treatment with the weakly basic anion exchange resin, for example, first, the weakly basic anion exchange resin is washed in advance with a carbonate solvent that constitutes the alkali metal salt electrolyte-containing liquid to be treated, and then about 40 to 40 minutes. It is dried at 80° C. under reduced pressure, then the weakly basic anion exchange resin is swollen with a carbonate solvent constituting the alkali metal salt electrolyte-containing liquid to be treated again, and then packed into a column.
After that, after performing backwashing, extrusion, etc. according to a conventional method, the electrolytic solution to be treated is preferably SV (flow rate/ion exchange resin volume ratio) 1 to 100 hr ^-1 , more preferably SV 2 to 50 hr ^-1 . , and more preferably at SV 5 to 20 hr ^-1 .

(Production example 1)
<Production of high acidity non-aqueous electrolyte 1>
Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a volume ratio of 1:3, LiPF ₆ was dissolved to a concentration of 1 mol/L, and fluoroethylene carbonate (FEC) was added to a concentration of 5% by mass. to prepare an alkali metal salt electrolyte-containing liquid (hereinafter referred to as "high acidity non-aqueous electrolyte 1"). The acidity and water content of the high-acidity non-aqueous electrolytic solution immediately after preparation were measured by the methods described below, and the acidity was 1.9 meq/kg and the water content was less than 10 ppm.

(Production example 2)
<Production of low-acid non-aqueous electrolyte 1>
As an ion exchange unit constituting the production apparatus shown in FIG. 2, a column filled with a weakly basic anion exchange resin having styrene-divinylbenzene as a base and having dimethylamino groups as weakly basic anion exchange groups was prepared.
Next, the highly acidic non-aqueous electrolyte 1 produced in Production Example 1 is passed through the column at a space velocity (SV) of 10 (L / L-resin) / hr using a pump P, and A low acidity non-aqueous electrolyte 1 having an acidity of less than 1 meq/kg was prepared by contacting with a weakly basic anion exchange resin.

(Example 1)
Prepare a sealed container (material: stainless steel, volume: 1 L) shown in FIG. bottom.

(Example 2)
The low-acidity non-aqueous electrolyte 1 was stored at 15° C. in the same manner as in Example 1.
(Comparative example 1)
The low-acidity non-aqueous electrolyte 1 was stored at 25° C. in the same manner as in Example 1.
(Comparative example 2)
The highly acidic non-aqueous electrolyte 1 was stored at 5° C. in the same manner as in Example 1.
(Comparative Example 3)
The highly acidic non-aqueous electrolyte 1 was stored at 15° C. in the same manner as in Example 1.
(Comparative Example 4)
The highly acidic non-aqueous electrolyte 1 was stored at 25° C. in the same manner as in Example 1.

(Production example 3)
<Preparation of highly acidic non-aqueous electrolyte 2>
Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a volume ratio of 1:3, LiPF ₆ was dissolved to a concentration of 1 mol/L, and 1,3-propanesultone (PS) was added to 1 mass. % to prepare an alkali metal salt electrolyte-containing liquid (hereinafter referred to as "high acidity non-aqueous electrolyte 2").

(Production example 4)
<Preparation of low-acid non-aqueous electrolyte 2>
As an ion exchange unit constituting the production apparatus shown in FIG. 2, a column filled with a weakly basic anion exchange resin having styrene-divinylbenzene as a base and having dimethylamino groups as weakly basic anion exchange groups was prepared.
Next, the highly acidic non-aqueous electrolyte 2 produced in Production Example 3 is passed through the column at a space velocity (SV) of 10 (L / L-resin) / hr using a pump P, and A low-acidity non-aqueous electrolyte 2 having an acidity of less than 1 meq/kg was prepared by contacting with a weakly basic anion exchange resin.

(Example 3)
The low-acidity non-aqueous electrolyte 2 was stored at 5° C. in the same manner as in Example 1.
(Example 4)
The low-acidity non-aqueous electrolyte 2 was stored at 15° C. in the same manner as in Example 1.
(Comparative Example 5)
The low-acidity non-aqueous electrolyte 2 was stored at 25° C. in the same manner as in Example 1.
(Comparative Example 6)
The highly acidic non-aqueous electrolyte 2 was stored at 5° C. in the same manner as in Example 1.
(Comparative Example 7)
The highly acidic non-aqueous electrolyte 2 was stored at 15° C. in the same manner as in Example 1.
(Comparative Example 8)
The highly acidic non-aqueous electrolyte 2 was stored at 25° C. in the same manner as in Example 1.

Tables 1 and 2 show the results of measuring changes in acidity and water content over time after storing each non-aqueous electrolyte under each condition. The acidity and water content were measured by the following methods.

<Method for measuring acidity>
The sample is dissolved in ice water, and the acid content (meq) in the sample is quantified by neutralization titration with a 0.01 N sodium hydroxide aqueous solution while stirring, and the acidity (meq) is divided by the sample amount (kg). / kg).

<Method for measuring moisture content>
The sample was introduced into a trace moisture measuring device AQ-2200AF manufactured by Hiranuma Sangyo Co., Ltd., and the moisture content (mass ppm) in the sample was measured by the Karl Fischer titration method.

From the results in Table 1, in Examples 1 and 2, the acidity could be maintained at less than 0.1 meq/kg even after 8 weeks. On the other hand, in Comparative Example 1, the acidity increased to 1.0 meq/kg after 8 weeks. These results demonstrate the effect of the present invention that the quality of the non-aqueous electrolyte can be maintained by storing the non-aqueous electrolyte at 20° C. or lower. In addition, in Comparative Examples 2 to 4, the acidity is stable at 1.8 to 1.9 meq/kg regardless of the storage temperature, so the present invention is effective only for non-aqueous electrolytes with an acidity of less than 1 meq/kg. shown.
The results in Table 2 show the same tendency as in Table 1, thus demonstrating that the effects of the present invention can be obtained regardless of the composition of the electrolytic solution.

1 non-aqueous electrolyte
2 Closed container 3 Non-aqueous electrolyte manufacturing device 4 Ion exchange unit (accommodating weakly basic anion exchange resin)
S High acidity non-aqueous electrolyte (liquid containing alkali metal salt electrolyte)
T Low-acid non-aqueous electrolyte P Pump

Claims (6)

A method for storing a non-aqueous electrolyte, comprising storing the non-aqueous electrolyte having an acidity of less than 1 meq/kg in a sealed container at 20° C. or lower. 2. The method for storing a non-aqueous electrolyte according to claim 1, wherein the water content of said non-aqueous electrolyte is less than 10 mass ppm. 3. The method for storing a non-aqueous electrolyte according to claim 1, wherein the non-aqueous electrolyte contains 0.5 to 1.5 mol/L of LiPF ₆ . The non-aqueous electrolyte is a non-aqueous electrolyte produced by contacting a weakly basic anion exchange resin with a lithium salt electrolyte-containing liquid in which LiPF ₆ is dispersed in a carbonate ester. , The storage method of the non-aqueous electrolyte according to any one of claims 1 to 3. 5. The method for storing a nonaqueous electrolyte according to claim 1, wherein the nonaqueous electrolyte contains 0.1 to 50% by mass of an organic fluorine compound. The method for storing a nonaqueous electrolyte according to any one of claims 1 to 5, wherein the nonaqueous electrolyte contains 0.1 to 10% by mass of an organic sulfur compound.

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