JP2011154783A - Method of manufacturing electrolyte for electrochemical device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing an electrolyte for an electrochemical device, having a wide potential window, resulting in the electrolyte being hard to deposit and having higher specific conductivity. <P>SOLUTION: The electrolyte for the electrochemical device contains an organic solvent and lithium salt or sodium salt dissolved therein, the organic solvent containing at least one nitrile compound from among a chain saturated hydrocarbon dinitrile compound having nitrile groups bonded to both terminals of a chain saturated hydrocarbon compound; a chain cyanoether compound having nitrile groups, bonded to at least one terminal of a chain ether compound; and a cyanoacetic acid ester, and at least one of cyclic carbonate, cyclic ester and chain carbonate, The method for manufacturing the electrolyte for the electrochemical device includes a mixing step of mixing the organic solvent, having water content of 100 ppm or lower and the lithium salt or the sodium salt having water content of 100 ppm or lower and form a uniform solution. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for producing an electrolytic solution for an electrochemical device that has a wide potential window and can maintain an electrolyte in a stable dissolved state, and relates to an electrolytic solution for a secondary battery using a positive electrode active material having a high charging voltage, and withstand voltage. It can be suitably used for an electrolytic solution of a capacitor having a high value.

A conventional lithium ion battery uses lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), a solid solution thereof, lithium manganate (LiMn ₂ O ₄ ) or the like as a positive electrode, and consists of carbon such as graphite as a negative electrode. A negative electrode material is used. An electrolytic solution in which a liquid organic compound such as ethylene carbonate or propylene carbonate is dissolved in a solvent and a lithium salt as a solute is used.

In order to further increase the energy density of such a lithium ion battery, a search for a new positive electrode active material is underway. For example, _Li 2 NiPO ₄ F in Patent Documents 1 and _2, LiNiPO _4, LiCoPO 4 and _Li 2 CoPO ₄ F has been proposed as a high positive electrode active material energy density. If these positive electrode active materials having a large energy density are used in a lithium ion battery, theoretically, a lithium ion battery having a large charge capacity should be obtained.

  However, since the charging reaction of such a positive electrode active material occurs at an extremely high potential, the conventional lithium ion battery electrolyte using an organic solvent such as cyclic carbonate or chain carbonate is used after the solvent is oxidized and decomposed. There was a problem that it was impossible. For this reason, there is a problem that the capacity that can be actually taken out is less than half of the theoretical capacity (Non-Patent Document 1).

  On the other hand, in the field of electrolytic solutions for capacitors, an electrolytic solution having a wide potential window has been demanded in order to improve the withstand voltage.

Under these circumstances, the present inventors have found that an organic solvent having a nitrile group is difficult to decompose even at a high positive potential and has a wide potential window, and the nitrile compound is contained in an amount of 90% by weight or more based on the weight of the organic solvent. A lithium-ion battery electrolyte solution has been developed (Patent Document 3). According to this electrolyte solution for lithium ion batteries, because it has a wide potential window, particularly at high positive _{potential, Li 2 CoPO 4 F, Li} 2 NiPO 4 F, a high positive electrode material having the redox potential such LiCoPO 4, LiNiPO ₄ Can be used. For this reason, it can be set as a battery with a large electromotive force.

Patent No. 3624205 Patent No. 3631202 JP 2009-158240 A

Journal of Power Sources 146 (2005) 565-569

Furthermore, since the electrolyte solution for lithium ion batteries described in Patent Document 3 uses a nitrile compound having a high viscosity as a main solvent component, the specific conductivity is small and it is difficult to extract a large current. In view of this, not only a wide potential window, but also a low-viscosity and high specific conductivity lithium-ion battery electrolyte, a cyclic carbonate, a cyclic ester, and a chain carbonate were further added. An electrolyte for lithium ion batteries has been developed and a patent application has already been filed (Japanese Patent Application No. 2009-046955).
That is,
An electrolyte for a lithium ion battery in which a lithium salt is dissolved in an organic solvent,
The organic solvent includes a chain saturated hydrocarbon dinitrile compound having a nitrile group bonded to both ends of the chain saturated hydrocarbon compound, and a chain cyano ether compound having a nitrile group bonded to at least one terminal of the chain ether compound. And at least one nitrile compound of cyanoacetic acid ester and at least one of cyclic carbonate, cyclic ester, and chain carbonate.

As for a sodium ion battery, an electrolyte solution having not only a wide potential window but also a low viscosity and a large specific conductivity has been developed and a patent application has already been filed (Japanese Patent Application No. 2009-285997).
That is,
An electrolyte solution for a sodium ion battery in which a sodium salt is dissolved in an organic solvent, wherein the organic solvent includes a chain saturated hydrocarbon dinitrile compound having a nitrile group bonded to both ends of the chain saturated hydrocarbon compound, a chain Included are at least one nitrile compound of a chain cyanoether compound and a cyanoacetate ester having a nitrile group bonded to at least one terminal of the formula ether compound, and at least one of a cyclic carbonate, a cyclic ester and a chain carbonate It is the electrolyte solution for sodium ion batteries characterized by the above-mentioned.

  However, in these lithium ion batteries and sodium ion batteries, the electrolyte may be difficult to dissolve in the organic solvent during the preparation, or the dissolved electrolyte may be deposited. For this reason, there has been a problem that the specific conductivity of the electrolytic solution is lowered and the internal resistance and overvoltage of the battery are increased.

  The present invention has been made in view of the above-described conventional situation, and should solve the problem of providing a method for producing an electrolytic solution for an electrochemical device that has a wide potential window and can maintain an electrolyte in a stable dissolved state. It is an issue.

  The inventor has intensively studied the cause of the electrolyte deposition phenomenon. As a result, the difficulty of dissolving the electrolyte in the organic solvent and the phenomenon of precipitation from the electrolyte are closely related to the moisture content in the electrolyte, and these problems can be solved by reducing the moisture content. The headline and the present invention were completed.

That is, in the method for producing an electrolytic solution for an electrochemical device of the present invention, a lithium salt or a sodium salt is dissolved in an organic solvent,
The organic solvent includes
Of chain saturated hydrocarbon dinitrile compounds having nitrile groups bonded to both ends of the chain saturated hydrocarbon compound, chain cyano ether compounds having nitrile groups bonded to at least one terminal of the chain ether compound, and cyanoacetate At least one nitrile compound;
At least one of cyclic carbonate, cyclic ester and chain carbonate;
A method for producing an electrolytic solution for an electrochemical device, comprising:
It has a mixing step of mixing the organic solvent having a water content of 100 ppm or less and a lithium salt or sodium salt having a water content of 100 ppm or less to obtain a uniform solution.

In the method for producing an electrolytic solution for an electrochemical device of the present invention, an organic solvent having a moisture content of 100 ppm or less and a lithium salt or a sodium salt having a moisture content of 100 ppm or less are mixed in the mixing step to obtain a uniform solution. Therefore, the obtained solution also has a water content of 100 ppm or less. For this reason, the electrolyte is easily dissolved, the precipitation is prevented, the specific conductivity is increased, and as a result, the electrolyte is low in specific resistance and overvoltage.
More preferably, the water content of the organic solvent is 50 ppm or less, the water content of the lithium salt or sodium salt is 50 ppm or less, and most preferably, the water content of the organic solvent is 30 ppm or less, and the water content of the lithium salt or sodium salt. The content is 30 ppm or less.

The electrolytic solution for electrochemical devices obtained by the production method of the present invention comprises at least the chain saturated hydrocarbon dinitrile compound having a nitrile group bonded to both ends of the chain saturated hydrocarbon compound as an organic solvent, and at least the terminal of the chain ether compound. It includes at least one nitrile compound among a chain ether nitrile compound to which a nitrile group is bonded and a cyanoacetate. This nitrile compound widens the potential window.
Furthermore, since the nitrile compound is mixed with at least one of a cyclic carbonate, a cyclic ester, and a chain carbonate, the viscosity is lowered and the specific conductivity is also increased.

Although the electrolytic solution for an electrochemical device obtained by the production method of the present invention contains at least one of a cyclic carbonate, a cyclic ester, and a chain carbonate, which does not have a wide potential window, it has a wide potential window. Although it is not necessarily clear about the reason for having, it thinks as follows. That is, among the organic solvents contained in the electrolytic solution, the nitrile compound serves to widen the potential window. In addition, chain carbonate is presumed to play a role of increasing specific conductivity in order to lower the viscosity. Cyclic carbonates and cyclic esters dissolve many lithium salts and sodium salts, and form a protective film called SEI on the carbon negative electrode, thereby improving the reduction resistance and reducing Li ions and Na ions. The characteristic which can be passed can be provided. Therefore, it is considered that the effect can be exerted on the enlargement of the potential window on the negative side and the positive side.
For the above reasons, it is preferable to use a chain carbonate and a cyclic carbonate and / or a cyclic ester in combination. More preferably, it is a combined use of a chain carbonate and a cyclic carbonate. Specifically, dimethyl carbonate and ethylene carbonate are used in combination. The blending ratio of both is not particularly limited, but the same amount is preferable.

Examples of the chain saturated hydrocarbon dinitrile compound in which nitrile groups are bonded to both ends of the chain saturated hydrocarbon compound include succinonitrile NC (CH ₂ ) ₂ CN, glutaronitrile NC (CH ₂ ) ₃ CN, adiponitrile In addition to linear dinitrile compounds such as NC (CH ₂ ) ₄ CN, sebaconitrile NC (CH ₂ ) ₈ CN, dodecanedinitrile NC (CH ₂ ) ₁₀ CN, etc., 2-methylglutaronitrile NCCH (CH ₃ ) _CH 2 _CH 2 CN may have a branched as such. These chain saturated hydrocarbon dinitrile compounds are not particularly limited in carbon number, but are preferably 7 to 20. More preferably, it is 10-12.

Examples of the chain ether nitrile compound in which a nitrile group is bonded to at least one end of the chain ether compound include oxydipropionitrile NCCH ₂ CH ₂ —O—CH ₂ CH ₂ CN and 3-methoxypropionitrile. _{CH 3 -O-CH 2 CH 2} CN , and the like. These chain ether nitrile compounds are not particularly limited in carbon number, but are preferably 20 or less.

  Furthermore, examples of the cyanoacetate include methyl cyanoacetate, ethyl cyanoacetate, propyl cyanoacetate, and butyl cyanoacetate. These cyanoacetic acid esters are not particularly limited in carbon number, but are preferably 20 or less.

Examples of the lithium salt added in the method for producing an electrolytic solution for an electrochemical device of the present invention include LiPF ₆ (lithium hexafluorophosphate), LiBF ₄ (lithium tetrafluoroborate), LiTFSI (lithium bis (trifluoromethane). (Sulfonyl) imide), LiTFS (lithium trifluoromethanesulfonate), LiBETI (lithium bis (pentafluoroethanesulfonyl) imide), and the like can be used. These lithium salts dissolve in the nitrile organic solvent used in the electrolyte for lithium ion batteries of the present invention and have a sufficient potential window that does not decompose even at high potentials. Among these, it is preferable that at least one of LiPF ₆ (lithium hexafluorophosphate), LiBF ₄ (lithium tetrafluoroborate) and LiTFSI (lithium bis (trifluoromethanesulfonyl) imide) is contained. LiPF ₆ (lithium hexafluorophosphate) and LiBF ₄ (lithium tetrafluoroborate) are less corrosive to aluminum, which is often used as an electrode substrate for a positive electrode of a lithium ion battery. Furthermore, they are also more effective in expanding the potential window than LiTFS (lithium trifluoromethanesulfonate) and LiBETI (lithium bis (pentafluoroethanesulfonyl) imide). LiTFSI (lithium bis (trifluoromethanesulfonyl) imide) has a particularly high decomposition temperature, improved heat resistance, high solubility, and high specific conductivity.

As the sodium salt added in the production method of the liquid electrolyte for electrochemical device of the present _{invention, NaPF 6, NaBF 4, (} CF 3 SO 2) 2 NNa and _{(C 2 F 5 SO 2)} 2 NNa, NaClO ₄ , NaCF ₃ SO ₃ , NaN (FSO ₂ ) ₂ , NaC (CF ₃ SO ₂ ) _3, or the like can be used. These sodium salts may be used alone or in combination of two or more kinds. Particularly preferred is NaPF _6.

  The concentration of the lithium salt or sodium salt is preferably 0.01 mol / L or more, and is preferably lower than the saturated state. When the concentration of the lithium salt or sodium salt is less than 0.01 mol / L, since the number of dissociated Li ions is small, the Li ion conductivity becomes extremely small, and Li ion conduction cannot be secured. Therefore, there is a possibility that the overvoltage is increased and the potential of the original electrolyte is greatly shifted. On the other hand, when the concentration of the lithium salt is saturated, there is a possibility that the dissolved lithium salt precipitates due to a change in temperature and deforms the electrode or the like.

  In the method for producing an electrolytic solution for an electrochemical device of the present invention, the mixing step is preferably performed in an area where the humidity is controlled so that the dew point is −76 ° C. or lower. In the mixing step, an organic solvent having a moisture content of 100 ppm or less is mixed with a lithium salt or a sodium salt having a moisture content of 100 ppm or less, but water vapor present in the surrounding atmosphere is absorbed by the electrolyte in the mixing step. And the moisture content may be increased. If the mixing process is performed in an area where the humidity is controlled so that the dew point is −76 ° C. or less, the water vapor pressure existing in the surrounding atmosphere is small, and the water absorbed in the electrolyte is very small. An electrolytic solution for an electrochemical device having a low water content is obtained, the easily soluble electrolyte and the precipitation preventing property, which are the effects of the present invention, are enhanced, and the specific conductivity is increased. For this reason, it becomes an electrolyte solution with low specific resistance and overvoltage.

  In order to control the humidity so that the dew point is −76 ° C. or lower, the glove box is used, the inside is depressurized, and then the dried gas (argon, nitrogen, etc.) is supplied to dry the inside of the glove box. Holding.

  It is also preferable to dry the organic solvent with zeolite before the mixing step. By providing such a drying step, the water in the organic solvent is adsorbed by the zeolite, the water content in the organic solvent is further reduced, and as a result, an electrolyte for an electrochemical device with a low water content can be produced. Here, the zeolite may be put in a mixed organic solvent in a state where the organic solvent to be used is mixed, or may be put in each organic solvent before mixing.

  The nitrile compound is preferably purified by distillation before the mixing. By performing such a predistillation step, the water content of the nitrile compound can be further reduced.

Furthermore, the mixing step is a first mixing step in which the lithium salt or sodium salt is mixed with at least one of the cyclic carbonate, cyclic ester, and chain carbonate to form a uniform solution;
The solution obtained in the first mixing step may be carried out in two stages: a second mixing step in which a nitrile compound is mixed to obtain a uniform electrolyte. When the lithium salt or sodium salt is dissolved in an organic solvent in this order, the dissolution is less than in the other order or when all the organic solvents to be used are mixed and finally the lithium salt or sodium salt is dissolved. It becomes easy and a uniform electrolyte can be produced in a short time.

  Moreover, it is also preferable to perform a mixing process in the glass container with a sliding cover. If it is like this, the penetration | invasion of the water | moisture content to the electrolyte solution for electrochemical devices from external atmosphere can be prevented effectively.

When the electrolytic solution for an electrochemical device obtained by the production method of the present invention is used for an electrolytic solution of a lithium ion battery or a sodium ion battery, the potential for charging exceeds 5.2 V (vs. Li / Li ⁺ ). A high potential redox positive electrode active material such as that present in FIG. For this reason, it can be set as a battery with a large electromotive force and high energy density.

2 is a potential-current curve of Example 1 and Comparative Example 1. FIG. It is the electric potential-current curve of Examples 2-9 and Comparative Example 1. 6 is a potential-current curve of Comparative Example 1. It is an electric potential-current curve of Examples 10-14 and Comparative Examples 1-4. 10 is a potential-current curve of lithium occlusion / release of various positive electrode active materials for lithium ion batteries in the electrolyte solution for lithium ion batteries of Example 11. FIG. It is an electric potential-current curve of Examples 15-19 and Comparative Example 10. 6 is a potential-current curve of Example 20 and Comparative Example 10. 6 is a potential-current curve of Examples 21 and 22 and Comparative Example 10.

Hereinafter, embodiments embodying the present invention will be described.
<Drying process>
First, as a drying process, an organic solvent necessary for producing an electrolytic solution for an electrochemical device is prepared. These organic solvents preferably have a purity of 99.5% by mass or more, and preferably have a water content of 50 ppm or less. More preferably, the organic solvent has a purity of 99.5% by mass or more and a water content of 50 ppm or less.
Then, these organic solvents are rubbed into a glass container (for example, Schlenk tube) with a glass stopper, dried zeolite (for example, molecular sieves 3A, 4A, 5A, etc.) is placed, the lid is closed, and a sealing tape is attached. Roll, store in desiccator and let dry for more than a week. In order to obtain a dried zeolite, the adsorbed water is removed by heating to 300 ° C. to 350 ° C. in a stream of 10 ⁻¹ to 10 ⁻³ mmHg and / or dry nitrogen immediately before use. A microwave oven may be used for heating. It is also preferable to repeat heating and decompression a plurality of times.
In addition, as an organic solvent required for manufacture of the electrolyte solution for electrochemical devices, when the thing dehydrated to 100 ppm or less is marketed, the said drying process may be abbreviate | omitted using it. However, even if the organic solvent is dehydrated to 100 ppm or less, if it is stored until use, it is placed in a glass container (for example, a Schlenk tube) with a rubbed glass stopper, and dried zeolite ( For example, it is preferable to store molecular sieves 3A, 4A, 5A, etc.), then close the lid, wind a sealing tape, and store in a desiccator. For long-term storage, it is preferable to store in a glove box with a sufficiently low dew point (for example, −76 ° C. or lower), and further, in a glove box with a sufficiently low dew point, put in a bag made of an aluminum laminate film. It is particularly preferable to store it in an enclosed state.

  The organic solvent necessary for the production of the electrolytic solution for electrochemical devices is a chain saturated hydrocarbon dinitrile compound, a chain cyanoether compound in which a nitrile group is bonded to at least one end of the chain ether compound, and a cyanoacetate ester. It is at least one of at least one nitrile compound and cyclic carbonate, cyclic ester, and chain carbonate.

The chain saturated hydrocarbon dinitrile compound, for example, succinonitrile NC _{(CH 2) 2} CN, glutaronitrile NC _{(CH 2)} 3 CN, adiponitrile NC _{(CH 2)} 4 CN, sebaconitrile NC _{(CH 2) 8} In addition to linear dinitrile compounds such as CN and dodecandinitrile NC (CH ₂ ) ₁₀ CN, it has branches such as 2-methylglutaronitrile NCCH (CH ₃ ) CH ₂ CH ₂ CN May be. These chain saturated hydrocarbon dinitrile compounds are not particularly limited in carbon number, but are preferably 20 or less. More preferably, it is 7-12.

Examples of the chain ether nitrile compound in which a nitrile group is bonded to at least one end of the chain ether compound include oxydipropionitrile NCCH ₂ CH ₂ —O—CH ₂ CH ₂ CN and 3-methoxypropionitrile. _{CH 3 -O-CH 2 CH 2} CN , and the like. These chain ether nitrile compounds are not particularly limited in carbon number, but are preferably 20 or less.

  Furthermore, examples of the cyanoacetate include methyl cyanoacetate, ethyl cyanoacetate, propyl cyanoacetate, and butyl cyanoacetate. These cyanoacetic acid esters are not particularly limited in carbon number, but are preferably 20 or less.

The organic solvent thus prepared, and lithium salt (for example, LiPF ₆ (lithium hexafluorophosphate), LiBF ₄ (lithium tetrafluoroborate), LiTFSI (lithium bis (trifluoromethane), which are put in a moisture-proof bag made of aluminum laminate, are prepared. Sulfonyl) imide), LiTFS (lithium trifluoromethanesulfonate), LiBETI (lithium bis (pentafluoroethanesulfonyl) imide) and the like, and sodium salts (eg, NaClO ₄ , NaPF ₆ , NaBF ₄ , NaCF ₃ SO ₃ , NaN ( CF ₃ SO ₂ ) ₂ , NaN (FSO ₂ ) ₂ , NaN (C ₂ F ₅ SO ₂ ) ₂ , NaC (CF ₃ SO ₂ ) _3, etc.) are placed in the glove box.
In addition, all materials necessary for the production of electrolytes for electrochemical devices (electronic balances, glass containers with sliding lids, distillation equipment, desiccants such as silica gel and molecular sieves, spatels, pipettes, magnetic stirrers, stirrers, etc.) Insert. The glove box is connected to an argon cylinder through a dehydration tube containing dry zeolite (for example, molecular sieves 3A, 4A, 5A, etc.) and a dehydration tube containing dry silica gel. Argon was introduced from the argon cylinder and dried in the glove box. Argon gas is sent and left for one day or more while keeping the dry state. Thereby, the dew point in a glove box can be made into -76 degrees C or less. A method using a gas circulation type purified glove box is also effective. In the case of using a gas circulation type purification apparatus in which a dried molecular sieve is prepared in advance, it is preferable to previously remove moisture in the argon gas in the cylinder or the pipe. By carrying out like this, the dew point in a glove box can be made into -76 degrees C or less.

<Predistillation process>
And the lid | cover of the glass container containing the nitrile compound in a glove box is opened, a nitrile compound is put into a distillation apparatus, and distillation is performed. The distilled nitrile compound thus obtained has a purity of 99.9% by weight or more and a water content of 20 ppm or less.

<First mixing step>
On the other hand, a predetermined amount of the organic solvent to be used is taken out of the cyclic carbonate, cyclic ester and chain carbonate contained in the glass container with a rubbing glass stopper in the glove box together with the dry zeolite, and these are mixed. Further, a predetermined amount of lithium salt (or sodium salt) contained in an aluminum laminate bag in the glove box is weighed, added to the mixed solution, and stirred with a magnetic stirrer to obtain a uniform solution.

<Second mixing step>
A predetermined amount of the distilled nitrile compound obtained in the pre-distillation step is weighed, added to the solution obtained in the first mixing step, and stirred with a magnetic stirrer, whereby the electrolyte for the lithium (sodium) ion battery of the embodiment Get.

  The electrolyte solution for lithium (sodium) ion batteries of the above embodiment has a moisture content of about 10 to 50 ppm, and it is difficult for the electrolyte to dissolve in an organic solvent at the time of preparation, or the dissolved electrolyte does not precipitate. Therefore, there is no problem that the specific conductivity of the electrolytic solution is lowered and the internal resistance and overvoltage of the battery are increased.

  In addition, this electrolytic solution for electrochemical devices has a chain saturated hydrocarbon dinitrile compound in which a nitrile group is bonded to both ends of the chain saturated hydrocarbon compound, and a nitrile group bonded to at least one of the ends of the chain ether compound. Since it contains at least one nitrile compound of a chain cyanoether compound and a cyanoacetate ester, it has a wide potential window.

  Furthermore, since it contains at least one of cyclic carbonate, cyclic ester, and chain carbonate, the viscosity is lower than when only the nitrile compound is used as the organic solvent, and the specific conductivity is increased. As a result, it can be set as a battery with small internal resistance and overvoltage.

By using the electrolytic solution for an electrochemical device of the embodiment, a high potential redox positive electrode active material that exists in a region where the potential for charging exceeds 5 V (vs. Li / Li ⁺ ) is used as the positive electrode active material. Therefore, the electromotive force and energy density of the battery can be extremely increased. Such high potential redox positive electrode active material, for _{example, Li 2 CoPO 4 F, Li} 2 NiPO 4 F, LiCoPO 4, LiNiPO 4 , and the like. These positive electrode active materials have high energy density and can be a lithium ion battery having a large capacity. For example, Li ₂ CoPO ₄ F is predicted to have a theoretical energy density that is at least twice that of LiCoO ₂ as a positive electrode active material. If the potential density can be sufficiently exhibited, a lithium-ion battery having a large capacity can be produced. be able to. In addition, since the potential at which Li ₂ CoPO ₄ F is oxidized extends to a high potential region, a battery with high electromotive force can be obtained. Further, Li ₂ CoPO ₄ F is excellent in thermal stability, and it is known from the thermal analysis results that even when the temperature is as high as 400 ° C., it can be understood that the rise in battery temperature can be prevented.
On the other hand, NaMPO ₄ and NaMPO ₄ F (M = Ni, Co, Mn) are conceivable as high-potential redox positive electrode active materials for sodium ion batteries. These positive electrode active materials and electrolysis for sodium ion batteries of the present invention are considered. By combining with the liquid, a sodium ion battery having a high energy density and a large capacity can be obtained.

Hereinafter, examples that further embody the present invention will be described in detail.
<Electrolyte for lithium ion battery>
Example 1
In Example 1, a solvent in which adiponitrile, ethylene carbonate (EC), and dimethyl carbonate (DMC) were mixed at a volume ratio of 50:25:25 was used as the organic solvent, and LiPF ₆ ( Lithium hexafluorophosphate) was dissolved at 0.05 mol / L to obtain an electrolyte for a lithium ion battery.
Ethylene carbonate (EC) and dimethyl carbonate (DMC) having a purity of 99.5% by mass or more and having a water content of 50 ppm or less are used in a glove box dried so that the dew point is -76 ° C. or less. The one stored with molecular sieves was used.
Moreover, about adiponitrile, the water content was made 50 ppm or less by the purity of 99.5 mass% or more by distilling a commercial item.
Furthermore, LiPF ₆ is opened in a glove box that has been dried so that the dew point is −76 ° C. or less, in a bag with an aluminum laminate bag having a purity of 99.5% by mass or more and a water content of 50 ppm or less. And used it on the spot.
As a dissolution procedure, first, EC and DMC were mixed by 25 volume parts with a magnetic stirrer, LiPF ₆ was dissolved therein, and finally 50 volumes of adiponitrile was added to obtain an electrolytic solution for a lithium ion battery.

(Comparative Example 1)
In Comparative Example 1, a mixed solvent of 50% by volume of ethylene carbonate and 50% by volume of dimethyl carbonate was used as the organic solvent, and LiPF ₆ as a lithium salt was dissolved to 1 mol / L to obtain an electrolyte solution for a lithium ion battery. did. About the purity of a solvent, water content, and the preparation method of electrolyte solution, it is the same as that of Example 1, and description is abbreviate | omitted.

(Examples 2-9)
In Examples 2 to 9, the solvent was various nitrile: ethylene carbonate: dimethyl carbonate = 50: 25: 25 (volume ratio), and the electrolyte was LiPF ₆ (lithium hexafluorophosphate) at 1 mol / L in this mixed solvent. The so-dissolved solution was used as an electrolyte solution for a lithium ion battery (however, in Example 6 in which the nitrile compound was oxydipropionitrile, LiPF ₆ was 0.5 mol / L). About the purity of a solvent, water content, and the preparation method of electrolyte solution, it is the same as that of Example 1, and description is abbreviate | omitted.
The types of nitriles used in each example are as follows.
Example 1 Adiponitrile NC (CH ₂ ) ₄ CN
Example 2 Succinonitrile NC (CH ₂ ) ₂ CN
Example 3 Sevacononitrile NC (CH ₂ ) ₈ CN
Example 4 Dodecanedinitrile NC (CH ₂ ) ₁₀ CN
Example 5 2-Methylglutaronitrile NCCH (CH ₃ ) CH ₂ CH ₂ CN
Example 6-oxy dipropionate nitrile _{NCCH 2 CH 2 -O-CH 2} CH 2 CN
EXAMPLE 7 3-methoxy propionitrile _{CH 3 -O-CH 2 CH 2} CN
Example 8 Methyl cyanoacetate NCCH ₂ COOCH ₃
Example 9 cyanoacetate butyl _{NCCH 2 COO (CH 2) 3} CH 3

-Evaluation-
(Measurement of moisture content)
The water content of the electrolyte solutions for lithium ion batteries of Examples 1 to 9 prepared as described above was measured by the Karl Fischer method (coulometric titration). As a result, it was confirmed that all were 50 ppm or less.

(Electrolytic deposition test)
The lithium ion battery electrolytes of Examples 1 to 9 prepared as described above were put into a eggplant flask with a lid and wrapped with a sealing tape, and humidity conditions under which the dew point was −76 ° C. or lower in the glove box And stored for 1 week. As a result, no electrolyte deposition was observed.

(Measurement of potential-current curve)
With respect to the electrolyte solutions for lithium ion batteries of Examples 1 to 9 and Comparative Example 1 prepared as described above, potential-current curves were measured. A potentiogalvanostat was used for measurement, glassy carbon was used for the working electrode, and a platinum wire was used for the counter electrode. As the reference electrode, (Ag / Ag ⁺ ) or (Li / Li ⁺ ) was used. In the measurement, the positive side and the negative side were scanned several times, and then the potential was swept from the natural potential in the positive direction or the negative direction at a rate of 5 mV / sec, and the potential-current curve was measured. The results are shown in FIGS.

As a result, as shown in FIG. 1, the potential window of the electrolyte solution of Example 1 was 6.9 V with respect to the Li potential (Li / Li ⁺ ) (the judgment criterion of the potential window was 50 μA / cm ^2, and so on). It became. On the other hand, the potential window of Comparative Example 1 using a mixed solvent of ethylene carbonate and dimethyl carbonate is 5.2 V as shown in FIG. 3, and the potential window of the electrolytic solution of Example 1 is Comparative Example 1. Compared to the electrolyte solution of, it was found that it spreads greatly on the positive side. From this result, when the electrolytic solution of Example 1 is used, a high potential redox positive electrode active material that exists in a region where the potential for charging exceeds 5.2 V can be used as the positive electrode active material of the lithium ion battery. Thus, a lithium ion battery having high electromotive force and energy density and large capacity can be obtained. For example, in the electrolytic solution of Comparative Example 1, the organic solvent undergoes electrolysis even at the redox potential of Li ₂ CoPO ₄ F or Li ₂ NiPO ₄ F, and these positive electrode oxidizing substances cannot be used. If the electrolytic solution of Example 1 is used, not only Li ₂ CoPO ₄ F or Li ₂ NiPO ₄ F can be used as the positive electrode active material, but also LiCoPO ₄ , LiNiPO _4, etc. can be used.

Moreover, as shown in FIG. 2, also in the electrolyte solution of Examples 2-9, it turned out that an electric potential window spreads in the positive direction as compared with the electrolyte solution of Comparative Example 1 similarly to Example 1. . From these results, the chain saturated hydrocarbon dinitrile compound (Examples 1 to 5) in which nitrile groups were bonded to both ends of the chain saturated hydrocarbon compound, ethylene carbonate and dimethyl carbonate, the end of the chain ether compound By adding a chain ether nitrile compound (Examples 6 and 7) having at least one nitrile group bonded thereto and at least one nitrile compound (Examples 8 and 9) among cyanoacetic acid esters, the solvent is decomposed to a high potential. It was found that it can exist stably without doing. In particular, the potential window greatly widened in Examples 1 to 5 using a chain saturated hydrocarbon dinitrile compound in which a nitrile group was bonded to both ends of a chain saturated hydrocarbon compound as a nitrile compound, which has branches. Also in Example 5, it was found that the potential window greatly spreads in the positive direction. Also, in Example 6 using oxydipropionitrile NCCH ₂ CH ₂ —O—CH ₂ CH ₂ CN, it was found that the potential window greatly expanded in the positive direction.

(Examples 10 to 14)
In Examples 10 to 14, the solvent was sebacononitrile (adiponitrile in Example 12): ethylene carbonate: dimethyl carbonate = 50: 25: 25 (volume ratio), and various electrolytes were dissolved in this mixed solvent so as to be 1 mol / L. This was used as an electrolyte for lithium ion batteries. About the purity of a solvent, water content, and the preparation method of electrolyte solution, it is the same as that of Example 1, and description is abbreviate | omitted.
The types of electrolyte used in each example are as follows.
Example 10 LiPF ₆
Example 11 LiTFSI
Example 12 LiTFSI
Example 13 LiBF ₄
Example 14 LiBETI

(Comparative Examples 2 to 4)
In Comparative Examples 2 to 4, various lithium salts were added instead of LiPF ₆ which is the lithium salt in Comparative Example 1. That is, various lithium salts (LiTFSI in Comparative Example 2, LiBF ₄ in Comparative Example 3, LiBETI in Comparative Example 4) at 1 mol / L as an organic solvent, ethylene carbonate: dimethyl carbonate = 50: 50 (volume ratio). It was made to melt | dissolve and it was set as the electrolyte solution for lithium ion batteries.

-Evaluation-
(Measurement of potential-current curve)
About the electrolyte solution of Examples 10-14 and Comparative Examples 1-4, the electric potential-current curve was measured like the above-mentioned method. The results are shown in FIG. In addition, Table 1 shows the value of the potential obtained from this figure when the current density is 50 μA / cm ² .
From this FIG. 4 and Table 1, in addition to the nitrile compound as a solvent, in the electrolyte solutions of Examples 10 to 14 where ethylene carbonate as a cyclic carbonate and dimethyl carbonate as a chain carbonate were added as solvents, regardless of the type of the electrolyte It was found that the potential window greatly expanded in the positive direction as compared with the electrolytic solutions of Comparative Examples 1 to 4 in which no nitrile compound was added.

Similarly, the lithium salt and LiPF _6, the electrolyte of the other examples and comparative examples, the potential - was determined from current curve, shown in Table 2 an electrode potential when a predetermined current density. From this table, a chain saturated hydrocarbon dinitrile compound having a nitrile group bonded to both ends of the chain saturated hydrocarbon compound, a chain ether nitrile compound having a nitrile group bonded to at least one of the ends of the chain ether compound, and cyano It can be seen that the potential window widens in the positive direction when at least one nitrile compound of acetic acid ester and at least one of cyclic carbonate, cyclic ester and chain carbonate are contained.

<Measurement of battery characteristics>
Using the electrolytic solution of the above experimental example, Li _1-x CoO ₂ , Li _1-x NiO ₂ , Li _1-x Mn ₂ O _4, 2-1-3 lithium manganate, and composites thereof as the positive electrode active material And Li _1−x FePO ₄ , Li _1−x MnPO ₄ , Li _2−y FePO ₄ F, Li _2−y MnPO ₄ F (wherein x is a number from 0 to 1 and y is 0) A lithium ion battery according to the present invention by using the above-mentioned number of 2 or less, including those in which a part of Co, Ni, Mn and Fe is doped with other metal atoms including Li) Is configured. Examples of the metal atom to be doped include one or more of Mg, Al, Ti, V, Cu, Zn, Zr, Nb, and Mo.
As a specific example, for the positive electrode on which LiCoO ₂ is supported as the positive electrode active material, the electrolyte solution for lithium ion battery of Example 11 (that is, EC: DMC: sebacononitrile in a volume ratio = 25: 25: 50, lithium salt) LiTFSI (1.0 mol / L of lithium bis (trifluoromethanesulfonyl) imide) was used to measure the potential-current curve. The potential-current curve was also measured for the cathode for a lithium ion battery supporting Li ₄ Ti ₅ O ₁₂ and the cathode for a lithium ion battery supporting LiCoPO ₄ which is an olivine phosphate-based positive electrode active material. A potentiogalvanostat was used for the measurement. Further, (Ag / Ag ⁺ ) was used as the reference electrode. In the measurement, after scanning several times on the positive side and the negative side, the potential was swept from the natural potential in the positive direction or in the negative direction at a speed of 0.5 mV / sec, and the potential-current curve was measured.

As a result, as shown in FIG. 5, Li ₄ Ti ₅ O ₁₂ as the negative electrode for the lithium battery and LiCoO ₂ and LiCoPO ₄ as the positive electrode for the lithium battery had both lithium (0) and lithium ions. A nearly reversible current associated with redox was observed. From this result, it was found that by using the lithium ion battery electrolyte of Example 11, smooth charge / discharge between lithium (0) and lithium ions was possible.

<Sodium ion battery electrolyte>
Hereinafter, Examples 15 to 22 and Comparative Example 10 in which the method for producing an electrolytic solution for an electrochemical device of the present invention is embodied in an electrolytic solution for a sodium ion battery will be described.

  Examples 15 to 19 are examples including a chain saturated hydrocarbon dinitrile compound in which both ends of a chain saturated hydrocarbon compound are substituted with a nitrile group as an organic solvent. Further, Example 20 is an example including a chain cyano ether compound in which both ends of the chain ether compound are substituted with nitrile groups as an organic solvent. Further, Examples 21 and 22 are examples containing cyanoacetate as an organic solvent. Table 1 shows the compositions of the electrolyte solutions of the examples and comparative examples.

(Example 15)
In Example 15, a solvent in which succinonitrile, ethylene carbonate (EC), and dimethyl carbonate (DMC) were mixed at a volume ratio of 50:25:25 was used as the organic solvent. Sodium fluorophosphate (NaPF ₆ ) was dissolved to a concentration of 0.5 mol / L to obtain a sodium ion battery electrolyte. About the purity of a solvent, water content, and the preparation method of electrolyte solution, it is the same as that of Example 1, and description is abbreviate | omitted.

(Example 16)
In Example 16, a solvent in which glutaronitrile, ethylene carbonate (EC), and dimethyl carbonate (DMC) were mixed at a volume ratio of 50:25:25 was used as the organic solvent. The purity of the solvent, the water content, and the method for preparing the electrolytic solution are the same as in Example 15 and will not be described.

(Example 17)
In Example 17, a solvent in which adiponitrile, ethylene carbonate (EC), and dimethyl carbonate (DMC) were mixed at a volume ratio of 50:25:25 was used as the organic solvent. The purity of the solvent, the water content, and the method for preparing the electrolytic solution are the same as in Example 15 and will not be described.

(Example 18)
In Example 18, a solvent in which sebacononitrile, ethylene carbonate (EC), and dimethyl carbonate (DMC) were mixed at a volume ratio of 50:25:25 was used as the organic solvent. The purity of the solvent, the water content, and the method for preparing the electrolytic solution are the same as in Example 15 and will not be described.

(Example 19)
In Example 19, a solvent in which dodecandinitrile, ethylene carbonate (EC), and dimethyl carbonate (DMC) were mixed at a volume ratio of 50:25:25 was used as the organic solvent. The purity of the solvent, the water content, and the method for preparing the electrolytic solution are the same as in Example 15 and will not be described.

(Example 20)
In Example 20, a solvent in which oxypropionitrile, ethylene carbonate (EC), and dimethyl carbonate (DMC) were mixed at a volume ratio of 50:25:25 was used as the organic solvent. The purity of the solvent, the water content, and the method for preparing the electrolytic solution are the same as in Example 15 and will not be described.

(Example 21)
In Example 21, a solvent in which methyl cyanoacetate, ethylene carbonate (EC), and dimethyl carbonate (DMC) were mixed at a volume ratio of 50:25:25 was used as the organic solvent. The purity of the solvent, the water content, and the method for preparing the electrolytic solution are the same as in Example 15 and will not be described.

(Example 22)
In Example 22, a solvent in which butyl cyanoacetate, ethylene carbonate (EC), and dimethyl carbonate (DMC) were mixed at a volume ratio of 50:25:25 was used as the organic solvent. The purity of the solvent, the water content, and the method for preparing the electrolytic solution are the same as in Example 15 and will not be described.

(Comparative Example 10)
In Comparative Example 1, a solvent in which ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed at a volume ratio of 50:50 was used as the organic solvent, and no nitrile compound was added. The concentration of sodium hexafluorophosphate (NaPF ₆ ) was 1.0 mol / L. The purity of the solvent, the water content, and the method for preparing the electrolytic solution are the same as in Example 15 and will not be described.

-Evaluation-
(Measurement of potential-current curve)
With respect to the electrolyte solutions for sodium ion batteries of Examples 15 to 22 and Comparative Example 10 prepared as described above, potential-current curves were measured. A potentiogalvanostat was used for measurement, glassy carbon was used for the working electrode, and a platinum net was used for the counter electrode. Further, metallic lithium was used for the reference electrode. The potential was swept at a rate of 5 mV / sec, and a potential-current curve was measured. The results are shown in FIGS.

As shown in FIG. 6, the organic solvent is composed of ethylene dicarbonate and dimethyl carbonate, and in Comparative Example 10 not containing a nitrile compound, it is 50 μA / cm ² at 5.8 V, and it rises greatly at higher voltages. On the other hand, in Examples 15 to 19 using various chain saturated hydrocarbon dinitrile compounds, 50 μA / cm ² is not exceeded unless a higher potential is reached (the current value at 50 μA / cm ² is 6. 5V, 7.0 V in Example 16, 7.5 V in Example 17, 7.2 V in Example 18, and 7.2 V in Example 19.

Further, as shown in FIG. 7, in the electrolytic solution of Example 20, the organic solvent contains a chain cyanoether compound in which both ends of the chain ether compound are substituted with nitrile groups, and further contains ethylene dicarbonate and dimethyl carbonate. The voltage at which the current was 50 μA / cm ² was 6.8 V, and it was found that the electrolyte was stable up to a high voltage.

  Further, as shown in FIG. 8, in the electrolyte solutions of Examples 21 and 22 in which the organic solvent contains cyanoacetate and further contains ethylene dicarbonate and dimethyl carbonate, the organic solvent is composed of ethylene dicarbonate and dimethyl carbonate. Compared with Comparative Example 10, the current value at a voltage of 6.2 V or higher was small, and it was found that the electrolytic solution was excellent in resistance to decomposition at a high voltage.

  From the above results, when the electrolytes of Examples 15 to 22 are used, the high potential redox positive electrode active material that exists in the region where the voltage for charging exceeds 6 V is used as the positive electrode active material of the sodium ion battery. As a result, it was found that the battery voltage and energy density are high, and a sodium ion battery having a large capacity can be obtained.

  The present invention is not limited to the description of the embodiment of the invention. Various modifications may be included in the present invention as long as those skilled in the art can easily conceive without departing from the description of the scope of claims.

Claims (7)

Lithium salt or sodium salt is dissolved in the organic solvent,
The organic solvent includes
Of chain saturated hydrocarbon dinitrile compounds having nitrile groups bonded to both ends of the chain saturated hydrocarbon compound, chain cyano ether compounds having nitrile groups bonded to at least one terminal of the chain ether compound, and cyanoacetate At least one nitrile compound;
At least one of cyclic carbonate, cyclic ester and chain carbonate;
A method for producing an electrolytic solution for an electrochemical device, comprising:
For an electrochemical device, comprising a mixing step of mixing the organic solvent having a water content of 100 ppm or less with the lithium salt or the sodium salt having a water content of 100 ppm or less to obtain a uniform solution. Manufacturing method of electrolyte solution.   The method for producing an electrolytic solution for an electrochemical device according to claim 1, wherein the mixing step is performed in an area where the humidity is controlled so that the dew point is -76 ° C or lower.   The method for producing an electrolytic solution for an electrochemical device according to claim 1, further comprising a drying step in which the organic solvent is dried with zeolite before the mixing step.   The method for producing an electrolytic solution for an electrochemical device according to any one of claims 1 to 3, wherein the nitrile compound has a pre-distillation step in which the nitrile compound is purified by distillation before the mixing step. The mixing step includes a first mixing step of mixing the lithium salt or sodium salt with at least one of the cyclic carbonate, cyclic ester, and chain carbonate to form a uniform solution;
5. A second mixing step in which a nitrile compound is mixed with the solution obtained in the first mixing step to obtain a uniform electrolytic solution. 5. Electrochemistry according to claim 1, A method for producing an electrolytic solution for a device.   The method for producing an electrolytic solution for an electrochemical device according to any one of claims 1 to 5, wherein the mixing step is performed in a glass container with a rubbed glass stopper.   The lithium salt and the sodium salt have a purity of 99.5% by mass or more, and the organic solvent used in the electrolyte for an electrochemical device has a purity of 99.5% by mass or more. The manufacturing method of the electrolyte solution for electrochemical devices described in any one of these.

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