JP2015079629A - Solvent and electrolyte arranged by use thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solvent containing a particular carbonate compound which enables particularly the improvement in the permeability of an electrolytic solution of a lithium ion secondary battery.SOLUTION: A solvent comprises a chain carbonate compound expressed by the following general formula (1). [Chem. Formula(1)] (In the formula, Rrepresents a hydrogen atom or RO-; Rrepresents a saturated hydrocarbon group having 1-4 carbon atoms; and Rrepresents a saturated hydrocarbon group having 1-4 carbon atoms.)

Description

  The present invention relates to a solvent containing a specific carbonate compound. The solvent of the present invention is particularly useful for an electrolytic solution of a lithium ion secondary battery.

  In recent years, mobile devices such as smartphones, tablets, and notebook computers, or electric vehicles and power storage power sources can be rapidly charged, and both volume energy density and weight energy density are high. Lithium ion secondary batteries are widely used as possible batteries.

A lithium ion secondary battery mainly includes a positive electrode plate and a negative electrode plate containing a material capable of occluding and releasing lithium, an electrolytic solution containing a lithium salt and a nonaqueous solvent, and a separator that partitions the positive electrode plate and the negative electrode plate.
For the positive electrode plate, a lithium metal oxide such as LiCoO ₂ , LiMnO ₂ , LiNiO ₂ , or LiFePO ₄ is used as a positive electrode active material. In addition, for the negative electrode plate, metallic lithium as a negative electrode active material, metal compounds capable of occluding and releasing lithium (metal simple substance, oxide, lithium alloy, etc.) and graphite-based carbon materials are known. Coke, artificial graphite, and natural graphite that can be stored and released are used.
As an electrolytic solution, a mixed solvent of a carbonate compound such as ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, LiPF ₆ , LiBF ₄ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ CF ₂ CF ₃ ) ₂ A solution in which a Li electrolyte is mixed is used as a non-aqueous electrolyte.

  As the application field of such lithium ion secondary batteries is expanding year by year, higher capacity is demanded, and the density and thickness of the active material are increased. However, coupled with the increase in tightness of the positive electrode plate, the negative electrode plate, and the separator, it is difficult for the electrolyte to penetrate, the charge / discharge characteristics are not improved, or the penetration time is prolonged and the productivity of the battery is lowered. Has occurred.

To solve these problems, a method of reducing the pressure inside the battery case before injecting the electrolyte solution and replacing it with carbon dioxide, then injecting the electrolyte solution again after reducing the pressure again, and further pressurizing (Patent Document 1) And a method of increasing the permeability of the electrolytic solution by making the porosity of the layer near the current collector of the active material-containing layer in the electrode higher than that of the layer away from the current collector (see Patent Document 2) ) Etc. are known.
In addition, a method of adding dodecane nitrile (lauronitrile) as an additive for improving permeability (see Patent Document 3) or a method of adding a pivalate ester such as butyl pivalate or dodecyl pivalate (see Patent Document 4). ) Etc. are also known.

JP2013-77404A JP2013-62226A JP 2011-3364 A Patent 5104848

  However, despite the fact that various methods for improving the electrolyte permeability have been disclosed, there is a high market demand for improved battery performance and cost reduction, so that it is still cheap, simple and efficient. Therefore, a method for improving the permeability of an electrolyte is desired.

  As a result of intensive studies, the present inventors have found that the above-mentioned problems can be solved by applying a solvent containing a specific carbonate compound as an electrolytic solution of a lithium ion secondary battery, and the present invention has been completed.

That is, the present invention provides the following [1] to [4].
[1] A solvent containing a chain carbonate compound represented by the following general formula (1).

(Wherein, .R ³ .R ^{2 R 1} is representative of the O- hydrogen atom or ^R 3 representing a saturated hydrocarbon group having 1 to 4 carbon atoms represents a saturated hydrocarbon group having 1 to 4 carbon atoms.)
[2] The solvent according to [1], wherein R ² and R ³ are a methyl group or an ethyl group.
[3] An electrolytic solution containing the solvent of [1] or [2].
[4] The electrolyte solution according to [3], which is for a lithium ion secondary battery or a lithium ion capacitor.

  If the solvent containing the specific carbonate compound of this invention is applied to electrolyte solution, the penetration time of electrolyte solution can be shortened and the productivity of a lithium ion secondary battery can be improved.

  Hereinafter, the present invention will be described in detail.

  The solvent of the present invention is a chain carbonate compound represented by the formula (1) [hereinafter referred to as carbonate (1). ] As an active ingredient. Carbonate (1) is an asymmetric chain carbonate compound, and it is essential to have an alkyl group having a branched chain structure at the 3-position.

In the formula, R ¹ represents a hydrogen atom or R ³ O—. R ² represents a saturated hydrocarbon group having 1 to 4 carbon atoms. R ³ represents a saturated hydrocarbon group having 1 to 4 carbon atoms. The saturated hydrocarbon group having 1 to 4 carbon atoms in R ² and R ^3, preferably a linear or branched alkyl group having 1 to 4 carbon atoms, such as methyl group, ethyl group, n- propyl group, isopropyl Group, n-butyl group, isobutyl group, s-butyl group and t-butyl group.

Although the specific example of carbonate (1) is shown below, it is not limited to these in particular.

  There is no restriction | limiting in particular in the acquisition method of carbonate (1), You may obtain commercially and may manufacture from the raw material suitable for the objective. Although there is no restriction | limiting in particular in the manufacturing method of carbonate (1), For example, it can also manufacture by the method shown in following Reaction formula (1).

（反応式（１）におけるＲ^１およびＲ^２は前記定義のとおりである。）

(R ¹ and R ² in the reaction formula (1) are as defined above.)

  That is, as a typical method, alcohol (2) and carbonate (3) are preferably reacted in the presence of a base. For example, isoamyl alcohol (196 mmol), dimethyl carbonate (392 mmol) and 1.7 g of potassium carbonate are placed in a reactor and stirred at 90 ° C. under reflux conditions for 2 hours. It was found that isoamyl methyl carbonate was obtained in a yield of 52% by distillation. R. Chimie 14 (2011) 636-646.

  If necessary, the carbonate (1) obtained by the above method can be further purified by a method generally used for separation and purification of organic compounds, that is, distillation, silica gel column chromatography, recrystallization, etc. It can also be purified. In addition, it is possible to reduce coloring and moisture by appropriately contacting with activated carbon or molecular sieve. (Registered trademark) "(trade name, manufactured by Sumitomo 3M Co., Ltd.), Protego (trade name, manufactured by Nihon Entegris Co., Ltd.) and Ion Clean (trade name, manufactured by Nihon Pall Co., Ltd.) It is also possible to reduce the metal content of the carbonate (1).

  In the solvent of the present invention containing carbonate (1), the content of carbonate (1) is usually preferably 60% by mass, more preferably 85% by mass or more, and 95% by mass or more. It is more preferable that the solvent is composed of only carbonate (1). In the solvent of the present invention, the carbonate (1) may be used alone or in combination of two or more.

The solvent of the present invention can be used as a solvent or an extraction solvent in various organic synthesis reactions. Also, it can be suitably used for various solvent applications such as paint solvents, coating agent solvents, agricultural chemical solvents, etc .; various cleaning agent applications; and lithium ion secondary battery electrolyte applications.
In particular, when the solvent of the present invention is applied to an electrolyte solution of a lithium ion secondary battery, the surface tension is smaller than that of an electrolyte solution that does not contain carbonate (1), so that the permeability to electrode active materials and separators is improved. As a result, the permeation time of the electrolytic solution can be shortened, and the productivity of the lithium ion secondary battery can be improved.
When applying the solvent of this invention to the electrolyte solution of a lithium ion secondary battery, content of the carbonate (1) in electrolyte solution is 0.1 mass%-80 mass% with respect to electrolyte solution total mass. Is preferable, it is more preferable that it is 0.5 mass%-75 mass%, and it is further more preferable that it is the range of 1 mass%-70 mass%. If the amount is less than the above range, the effect of improving the permeability is small. If the amount is more than the above range, the resistance is increased, and the expected battery performance may not be sufficiently obtained.

  When applying the solvent of this invention to the electrolyte solution of a lithium ion secondary battery, electrolyte solution may contain arbitrarily the well-known component used as a lithium ion secondary battery other than carbonate (1). The electrolytic solution generally contains an electrolyte and a nonaqueous solvent.

Examples of the nonaqueous solvent include a cyclic or chain aprotic solvent.
Examples of the cyclic aprotic solvent include cyclic carbonates, cyclic carboxylic acid esters, cyclic sulfones, and cyclic ethers. These may be used singly or in combination of two or more. Good.
Specific examples of the cyclic carbonate include ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, 2,3-pentylene carbonate and the like. Among these, ethylene carbonate and / or propylene carbonate are preferable from the viewpoint of the dielectric constant. In the case of a battery using graphite as the negative electrode material, ethylene carbonate is more preferable. These cyclic carbonates may be used as a mixture of two or more.
Specific examples of the cyclic carboxylic acid ester include γ-butyrolactone, δ-valerolactone, methyl γ-butyrolactone, ethyl γ-butyrolactone, methyl δ-valerolactone, and ethyl δ-valerolactone.
Specific examples of the cyclic sulfone include sulfolane, 2-methylsulfolane, and 3-methylsulfolane.
Examples of the cyclic ether include tetrahydrofuran, tetrahydropyran, 2-methyltetrahydrofuran, 1,3-dioxolane, 1,4-dioxane and the like.

Examples of the chain aprotic solvent include chain carbonates other than carbonate (1), chain carboxylic acid esters, chain ethers, chain sulfones, and chain phosphate esters.
Specific examples of chain carbonates other than carbonate (1) include dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl-n-propyl carbonate, methyl isopropyl carbonate, ethyl n-propyl carbonate, di-n-propyl carbonate, methyl -N-butyl carbonate, ethyl-n-butyl carbonate, di-n-butyl carbonate and the like.
Specific examples of the chain carboxylic acid ester include methyl acetate, ethyl acetate, propyl acetate, methyl propionate, and methyl pivalate.
Specific examples of the chain ether include dimethoxymethane, 1,2-dimethoxyethane, bis (2-methoxyethyl) ether, 1,2-bis (2-methoxyethoxy) ethane and the like.
Specific examples of the chain sulfone include dimethyl sulfone, diethyl sulfone, dipropyl sulfone, methyl ethyl sulfone, methylpropyl sulfone and the like.
Specific examples of the chain phosphate ester include trimethyl phosphate, triethyl phosphate, ethyl dimethyl phosphate, diethyl methyl phosphate, tripropyl phosphate, tributyl phosphate, tri (trifluoromethyl) phosphate, and the like. .

  Other nonaqueous solvents other than the above include, for example, amides such as dimethylformamide and dimethylacetamide; cyclic amides such as N-methylpyrrolidone and N-ethylpyrrolidone; boron compounds such as trimethyl borate, triethyl borate and tributyl borate; acetonitrile Examples thereof include nitriles such as: chain carbamates such as methyl-N, N-dimethylcarbamate; cyclic ureas such as N, N-dimethylimidazolidinone; and fluorine-containing ethers.

  When the cyclic aprotic solvent and the chain aprotic solvent are used as components of the electrolytic solution in combination with the solvent of the present invention, only one cyclic or chain aprotic solvent is used. Alternatively, two or more kinds may be used, and a cyclic aprotic solvent and a chain aprotic solvent may be mixed and used. When improving the load characteristics and low temperature characteristics of the battery, it is preferable to use a mixture of a cyclic aprotic solvent and a chain aprotic solvent as the nonaqueous solvent. From the electrochemical stability of the electrolytic solution, it is preferable to use a cyclic carbonate as the cyclic aprotic solvent and a chain carbonate other than the carbonate (1) as the chain aprotic solvent. In addition, the ionic conductivity of the electrolyte solution related to the charge / discharge characteristics of the battery can also be increased by a combination of a cyclic carboxylic acid ester and a cyclic carbonate other than cyclic carbonate and / or carbonate (1).

From the viewpoint of forming the surface film of the negative electrode, a vinylene carbonate compound may be contained as another additive to the electrolytic solution. Specific examples of the vinylene carbonate compound include vinylene carbonate, methyl vinylene carbonate, ethyl vinylene carbonate, propyl vinylene carbonate, dimethyl vinylene carbonate, and the like. Of these, vinylene carbonate is most preferred. These may be used alone or in combination of two or more.
When the vinylene carbonate compound is contained, the amount thereof (the total content in the case of two or more) is usually preferably 0.001% by mass to 10% by mass, and 0.05% by mass to More preferably, it is 5 mass%.

From the viewpoint of forming the surface film of the negative electrode, a halogenated cyclic carbonate may also be contained as another additive to the electrolytic solution. Specific examples of the halogenated cyclic carbonate include 4-fluoroethylene carbonate, 4,4-difluoroethylene carbonate, 4,5-difluoroethylene carbonate, 4,4,5-trifluoroethylene carbonate, 4,4,5,5. -Tetrafluoroethylene carbonate etc. are mentioned. Among these, 4,5-difluoroethylene carbonate and 4-fluoroethylene carbonate are most preferable. These may be used alone or in combination of two or more.
When the halogenated cyclic carbonate is contained, the amount thereof (in the case of two or more types, the total content) is usually preferably 0.001% by mass to 10% by mass, and 0.05% by mass with respect to the total mass of the electrolytic solution. More preferably, it is -5 mass%.

From the viewpoint of forming the surface film of the negative electrode, an S═O bond-bearing compound may also be contained as another additive to the electrolytic solution. Specific examples of the compound having an S═O bond include 1,3-propane sultone, 1,4-butanediol dimethane sulfonate, divinyl sulfone, 2-propynyl methane sulfonate, trifluoromethane sulfonate, ethylene sulfite, and vinyl ethylene sulfite. Vinylene sulfite, methyl 2-propynyl sulfite, ethyl 2-propynyl sulfite, dipropynyl sulfite, cyclohexyl sulfite, ethylene sulfate and the like. These may be used alone or in combination of two or more.
When the S═O bond-bearing compound is contained, the amount (the total content in the case of two or more) is usually preferably 0.001% by mass to 10% by mass with respect to the total mass of the non-aqueous electrolyte. It is more preferable that it is 0.05 mass%-5 mass%.

The electrolyte can be used without any particular limitation those generally used as an electrolyte of a lithium ion secondary battery, lithium salts of inorganic acids _{[LiPF 6,} etc. LiBF _4, LiSbF 6, LiAsF _6, and LiClO _4]; [LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ and LiC (CF ₃ SO ₂ ) ₃ etc.]. Among these, LiPF ₆ is preferable from the viewpoint of battery output and cycle characteristics. The concentration of the electrolyte is preferably 0.01 mol / L to 3 mol / L, more preferably 0.05 mol / L to 1.5 mol / L from the viewpoint of battery output and cycle characteristics.

  There is no restriction | limiting in particular about the preparation method of electrolyte solution, It can prepare by mixing and dissolving an electrolyte, the solvent of this invention, a nonaqueous solvent, and another additive as needed. In preparing the electrolytic solution, it is preferable to dehydrate each raw material in advance so that the amount of water in the electrolytic solution is 50 ppm or less.

  The solvent of the present invention can be used as an electrolytic solution for a lithium ion secondary battery or a lithium ion capacitor, and is particularly useful as an electrolytic solution for a lithium ion secondary battery.

EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited by these. The abbreviations of the carbonates used are shown below.

Reference Example 1 Synthesis of IAMC In a 500 mL three-necked flask equipped with a distillation head and a thermometer, 100.0 g (1.11 mol) of isoamyl alcohol, 204.4 g (2.27 mol) of DMC, 9.84 g of K ₂ CO ₃ ( 71 mmol) was added, stirring was started, and the bath temperature was heated to 90 ° C. When the internal liquid was quantitatively analyzed when no more methanol was observed, the yield of IAMC was 66% (based on isoamyl alcohol). Next, instead of the distillation head, Helipac No. Distillation under reduced pressure was carried out using a distillation column packed with 3 in a height of 50 cm. 90.8 g of IAMC having a purity of 99.9% (distillation recovery rate 83%) was obtained as a distillate at a pressure of 3 kPa at 68.7 to 69.8 ° C.

(Reference Example 2) Synthesis of MMBMC 3-methoxy-3-methyl-1-butanol 150.0 g (1.27 mol), DMC 228.7 g (2.54 mol) in a 500 mL three-necked flask equipped with a distillation head and a thermometer , 11.0 g (80 mmol) of K ₂ CO ₃ was added, stirring was started, and the bath temperature was heated to 90 ° C. When the internal liquid was quantitatively analyzed at the point where no distillation of methanol was observed, the yield of MMBMC was 66% (based on 3-methoxy-3-methyl-1-butanol). Next, instead of the distillation head, Helipac No. Distillation under reduced pressure was carried out using a distillation column packed with 3 in a height of 50 cm. As a distillate at a pressure of 1 kPa at 85.8 to 86.2 ° C., 119.3 g of MMBMC having a purity of 99.9% (distillation recovery rate: 86%) was obtained.

Comparative Example 1
A 1/1 (w / w) mixture of EC and DEC was prepared. The surface tension of this mixed solution was measured at a temperature of 21 ° C. by a ring method according to JIS K 3362 using a Dunui surface tension measuring instrument. The average of 5 measurements was 31.3 (mN / m).

Example 1
IAMC was added to a 1/1 (w / w) mixture of EC and DEC at 1.0%, 2.0%, and 5.0% by mass with respect to the total mass. The surface tension was measured in the same manner as in Comparative Example 1. The results are shown in Table 1.

Example 2
MMBMC was added to a 1/1 (w / w) mixture of EC and DEC so as to be 1.0 mass%, 2.0 mass%, and 5.0 mass% with respect to the total mass. The surface tension was measured in the same manner as in Comparative Example 1. The results are shown in Table 1.

From Table 1, as the addition amount of the solvent containing the carbonate (1) of the present invention (corresponding to the carbonate (1) content of 100% in the above example) is increased, 1 / EC of EC and DEC. It can be seen that the surface tension of the 1 (w / w) mixture decreases.
Therefore, when the solvent containing carbonate (1) of the present invention is applied to the electrolyte solution of a lithium ion secondary battery, the surface tension of the electrolyte solution is lowered, and as a result, an electrolyte solution with improved permeability is obtained. I can expect that.

  The solvent containing carbonate (1) of the present invention is useful as an electrolyte for a lithium ion secondary battery, and such an electrolyte is excellent in the permeability of an electrode plate when a lithium ion secondary battery is produced.

Claims (4)

A solvent containing a chain carbonate compound represented by the following general formula (1).

(Wherein, .R ³ .R ^{2 R 1} is representative of the O- hydrogen atom or ^R 3 representing a saturated hydrocarbon group having 1 to 4 carbon atoms represents a saturated hydrocarbon group having 1 to 4 carbon atoms.) The solvent according to claim 1, wherein R ² and R ³ are a methyl group or an ethyl group.   An electrolytic solution containing the solvent according to claim 1.   The electrolytic solution according to claim 3, which is used for a lithium ion secondary battery or a lithium ion capacitor.