JP5739728B2 - Electrolyte and lithium ion secondary battery - Google Patents

Description

The present invention relates to a lithium ion secondary battery obtained using the electrolyte及beauty the electrolytic solution using an electrolyte.

 Lithium ion secondary batteries are characterized by high energy density and electromotive force compared to lead-acid batteries and nickel metal hydride batteries, so they are widely used as power sources for mobile phones and laptop computers that require small size and light weight. ing.

 A lithium ion secondary battery is generally composed of a negative electrode, a positive electrode, and a separator that prevents short-circuiting of both electrodes, and holds an electrolytic solution in which a lithium salt is dissolved in a nonaqueous solvent.

In a lithium ion secondary battery, metallic lithium, a lithium alloy, a carbon-based material that can occlude and release lithium, a metal oxide, or the like is usually used as a negative electrode. In addition, transition metal oxides such as lithium cobaltate, lithium nickelate, lithium manganate, and olivine-type lithium iron phosphate are used as the positive electrode.
Many of the current lithium ion secondary batteries are used as an electrolyte solution in various nonaqueous solvents such as ethylene carbonate, propylene carbonate, gamma butyrolactone, methyl carbonate, ethyl methyl carbonate, ethyl carbonate, and lithium hexafluorophosphate (LiPF). ₆ ), lithium boron tetrafluoride (LiBF ₄ ), lithium bis (trifluoromethylsulfonyl) imide (LiN (SO ₂ CF ₃ ) ₂ ), lithium perchlorate (LiClO ₄ ), lithium trifluoromethanesulfonate ( LiCF ₃ SO _3), lithium hexafluoro antimonate (LiSbF _6), hexafluoroarsenate arsenate periodate lithium (LiAsF _6), lithium tetraphenylborate _{(LiB (C 6} H ₅₎ by dissolving a lithium salt such as ₄₎ Using non-aqueous electrolyte (example) If, refer to Patent Document 1, Patent Document 2).

Japanese Patent No. 3369583 Japanese Patent No. 4407205

During initial charging of a lithium ion secondary battery, for example, cyclic carbonates such as ethylene carbonate are reduced on the negative electrode surface and are made of a solid electrolyte-like interfacial film made of Li ₂ CO ₃ , Li ₂ O, LiOH, or the like. (Hereinafter referred to as SEI). This SEI film has a role of preventing the breakdown of the negative electrode structure by preventing the solvent molecules solvated with lithium ions from being inserted into the negative electrode during charging and discharging.

 However, when charging and discharging are repeated, the SEI gradually collapses due to factors such as repeated expansion and contraction of the negative electrode and partial overvoltage. Since the carbonate solvent is further decomposed on the negative electrode surface exposed by the collapse of SEI, there is a problem that battery characteristics such as cycle characteristics and storage characteristics are deteriorated.

 Therefore, the present inventor has sought various additives to solve the problems of the prior art as described above, and as a result, the lithium salt of organic acid and a boron compound are added to the non-aqueous electrolyte described above. As a result, it was found that deterioration of cycle characteristics can be reduced, and the present invention has been completed. That is, the present invention relates to an electrolyte solution or gel electrolyte for a lithium ion secondary battery and a lithium ion secondary battery including the same, which prevents capacity deterioration due to repeated charge and discharge, that is, lithium ion secondary battery having excellent cycle life characteristics. It is an object to provide a secondary battery.

To solve the above problem,
In the electrolytic solution in which the first lithium salt is dissolved in a non-aqueous solvent, the present invention further comprises (A) a lithium salt of an organic acid and (B) a boron compound as a second lithium salt. A) The lithium salt of the organic acid is a lithium salt of a carboxylic acid, the first lithium salt is a lithium salt other than the lithium salt of the carboxylic acid, and the (B) boron compound is boron trifluoride. Boron trifluoride dimethyl ether complex, Boron trifluoride diethyl ether complex, Boron trifluoride di n-butyl ether complex, Boron trifluoride di tert-butyl ether complex, Boron trifluoride tert-butyl methyl ether complex, Trifluoride Boron tetrahydrofuran complex, boron trifluoride methanol complex, boron trifluoride propanol complex and boron trifluoride To provide an electrolytic solution, characterized in that at least one member selected from the group consisting Lumpur complex.

In the electrolytic solution of the present invention, the first lithium salt is lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroboron (LiBF ₄ ), lithium bis (trifluoromethylsulfonyl) imide lithium (LiN (SO ₂ CF _{3) 2),} lithium perchlorate (LiClO _4), trifluoromethane sulfonic lithium _(LiCF 3 _SO 3), lithium hexafluoro antimonate (LiSbF _6), hexafluoroarsenate arsenate periodate lithium (LiAsF ₆ And at least one selected from the group consisting of lithium tetraphenylborate (LiB (C ₆ H ₅ ) ₄ ) .
In the electrolytic solution of the present invention, the lithium salt of the carboxylic acid is lithium formate, lithium acetate, lithium propionate, lithium butyrate, lithium isobutyrate, lithium oxalate, lithium lactate, lithium tartrate, lithium maleate, lithium fumarate It is preferably at least one selected from the group consisting of lithium malonate, lithium succinate, lithium malate, lithium citrate, lithium glutarate, lithium adipate, lithium phthalate and lithium benzoate.
In the electrolytic solution of the present invention, the amount of pre-Symbol first lithium salt: (A) the amount of the lithium salt of an organic acid is 99.5: 0.5 to 50: from 50 (molar ratio) Is preferred.

In the electrolytic solution of the present invention, (A) a lithium salt of an organic acid and (B) a boron compound are further added as a second lithium salt, and the lithium salt of the (A) organic acid is lithium carboxylic acid. The first lithium salt is a lithium salt other than the lithium salt of the carboxylic acid, and the (B) boron compound is boron trifluoride, boron trifluoride dimethyl ether complex, boron trifluoride diethyl Ether complex, boron trifluoride di n-butyl ether complex, boron trifluoride di tert-butyl ether complex, boron trifluoride tert-butyl methyl ether complex, boron trifluoride tetrahydrofuran complex, boron trifluoride methanol complex, trifluoride One selected from the group consisting of boron bromide propanol complex and boron trifluoride phenol complex A top, the non-aqueous solvent, cyclic carbonate, chain carbonate, ethers, carboxylic acid esters, nitriles, that Do one or more is blended is selected from the group consisting of amides and sulfones It is preferable.

The present invention also provides a lithium ion secondary battery obtained by using the electrolytic solution or gel electrolyte of the present invention.

 The lithium ion secondary battery to which the electrolytic solution or the gel electrolyte according to the present invention is applied prevents a capacity deterioration due to repeated charge and discharge by generating a stable SEI film at the time of initial charge, that is, has a cycle life characteristic. An excellent lithium ion secondary battery can be provided.

Embodiments of the electrolytic solution, gel electrolyte, and lithium ion secondary battery of the present invention will be described.
Note that this embodiment is specifically described in order to better understand the gist of the invention, and does not limit the present invention unless otherwise specified.

<Electrolyte>
The electrolytic solution of the present invention is an electrolytic solution in which a first lithium salt is dissolved in a non-aqueous solvent, and (A) a lithium salt of an organic acid and (B) a boron compound are further blended as a second lithium salt. It is characterized by becoming.
By adding (A) a lithium salt of an organic acid and (B) a boron compound to an electrolytic solution in which the first lithium salt is dissolved in a non-aqueous solvent, the electrolytic solution of the present invention has a stable SEI upon initial charging. By forming a film, the cycle life characteristics are excellent, and it is suitable for application to a lithium ion secondary battery.

(First lithium salt)
The first lithium salt is not particularly limited as long as it dissolves in a non-aqueous solvent, and preferable ones include lithium hexafluorophosphate (LiPF ₆ ) and lithium tetrafluoroboron (LiBF ₄ ). , lithium perchlorate (LiClO _4), lithium hexafluoro antimonate (LiSbF _6), hexafluoroarsenate arsenate periodate lithium (LiAsF _6), lithium hexafluoro tantalate (LiTaF _6), lithium hexafluoro niobate ( LiNbF ₆ ), lithium tetraphenylborate (LiB (C ₆ H ₅ ) ₄ ), bis (fluorosulfonyl) imide lithium (LiN (FSO ₂ ) ₂ ), bis (trifluoromethylsulfonyl) imide lithium (LiN (SO ₂₎ CF _{3) 2),} bis (pentafluoroethyl sulfonyl) imide (LiN ( _{O 2 C 3 F 5) 2} ), trifluoromethane sulfonic lithium _(LiCF 3 _SO 3), can be mentioned lithium salt and the like.

The said 1st lithium salt may be used individually by 1 type, and may use 2 or more types together. When two or more kinds are used in combination, the combination and ratio may be appropriately selected according to the purpose.
The compounding quantity of said 1st lithium salt is not specifically limited, For example, what is necessary is just to adjust suitably according to the kind of said 1st lithium salt and solvent. Usually, it is preferable that the molar concentration of [the above-mentioned blending amount (number of moles) of the first lithium salt] / [total weight of blended substances] is 0.2 or more, and 0.5 or more. It is more preferable. By setting it as such a range, the ionic conductivity of electrolyte solution improves further. The upper limit of the molar concentration is not particularly limited as long as the effect of the present invention is not hindered, but is preferably 3.0, more preferably 2.0.

 The non-aqueous solvent includes cyclic carbonates such as ethylene carbonate, propylene carbonate and butylene carbonate, lactones such as gamma butyrolactone and bunvalerolactone, chain carbonates such as dimethyl carbonate, methyl ethyl carbonate and diethyl carbonate, tetrahydrofuran 1,2-dimethoxyethane, 2-methyltetrahydrofuran, 1,3-dioxolane, ethers such as 4-methyl-1,3-dioxolane, methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, propyl acetate , Carboxylic acid esters such as methyl propionate, ethyl propionate and methyl butyrate, nitriles such as acetonitrile, glutaronitrile, adiponitrile, methoxyacetonitrile, 3-methoxypropionitrile S, N, N-dimethylformamide, N, N-amides such as dimethylacetamide and sulfolane, sulfones such as dimethyl sulfoxide can be exemplified.

 The said non-aqueous solvent may be used individually by 1 type, and may use 2 or more types together. When two or more kinds are used in combination, the combination and ratio may be appropriately selected according to the purpose.

((A) lithium salt of organic acid)
The lithium salt of (A) organic acid is preferably a lithium salt of carboxylic acid. In the lithium salt of (A) organic acid, the number of acid groups constituting the lithium salt is not particularly limited.

 The lithium salt of the carboxylic acid may be any lithium salt of aliphatic carboxylic acid, alicyclic carboxylic acid and aromatic carboxylic acid, and may be any lithium salt of monovalent carboxylic acid and polyvalent carboxylic acid. Preferred lithium salts of the carboxylic acid include lithium formate, lithium acetate, lithium propionate, lithium butyrate, lithium isobutyrate, lithium oxalate, lithium lactate, lithium tartrate, lithium maleate, lithium fumarate, lithium malonate, and succinate. Examples include lithium acid, lithium malate, lithium citrate, lithium glutarate, lithium adipate, lithium phthalate, and lithium benzoate. More preferable examples of the lithium salt of carboxylic acid include lithium formate, lithium oxalate, lithium malonate, and lithium succinate.

 (A) The lithium salt of organic acid may be used individually by 1 type, and may use 2 or more types together. When two or more kinds are used in combination, the combination and ratio may be appropriately selected according to the purpose. The compounding quantity of said 1st lithium salt is not specifically limited, For example, what is necessary is just to adjust suitably according to the kind of said 1st lithium salt and solvent. Usually, the blending amount of the first lithium salt: The blending amount of the lithium salt of the organic acid is preferably 99.5: 0.5 to 50:50 (molar ratio), and 99: 1 to 70. : 30 (molar ratio) is more preferable. By setting it as such a range, better SEI is formed and the lithium ion secondary battery excellent in cycle life characteristics is obtained.

((B) Boron compound)
Although the (B) boron compound is not particularly limited, specifically, preferred are boron halides such as boron trifluoride (BF ₃ ); boron trifluoride dimethyl ether complex (BF ₃ O (CH ₃ ) ₂ ) Boron trifluoride diethyl ether complex (BF ₃ O (C ₂ H ₅ ) ₂ ), boron trifluoride di n-butyl ether complex (BF ₃ O (C ₄ H ₉ ) ₂ ), boron trifluoride di tert- Butyl ether complex (BF ₃ O ((CH ₃ ) ₃ C) ₂ ), boron trifluoride tert-butyl methyl ether complex (BF ₃ O ((CH ₃ ) ₃ C) (CH ₃ )), boron trifluoride tetrahydrofuran complex boron halides alkyl ether complexes _(BF 3 _OC 4 _{H 8)} or the like; boron trifluoride methanol complex _{(BF 3} HOCH 3), trifluoroethylene C iodine propanol complex _{(BF 3 HOC 3 H 7)} , boron trifluoride phenol complex _(BF 3 _HOC 6 _{H 5)} boron halide alcohol complexes such as; boron trifluoride piperidinium complexes, such as boron trifluoride ethylamine complex Boron halide amine complex; 2,4,6-trialkoxyboroxine such as 2,4,6-trimethoxyboroxine; trimethyl borate, triethyl borate, tri-n-propyl borate, tri-n borate -Trialkyl borate such as butyl, tri-n-pentyl borate, tri-n-hexyl borate, tri-n-heptyl borate, tri-n-octyl borate, triisopropyl borate, trioctadecyl borate Triaryl borate such as triphenyl borate; tris (trial) such as tris (trimethylsilyl) borate Illustrative is (kylsilyl) borate. More preferred are boron halides such as BF ₃ ; BF ₃ O (CH ₃ ) ₂ , BF ₃ O (C ₂ H ₅ ) ₂ , BF ₃ O (C ₄ H ₉ ) ₂ , BF ₃ O (( Boron halide alkyl ether complexes such as CH ₃ ) ₃ C) ₂ , BF ₃ O ((CH ₃ ) ₃ C) (CH ₃ ), BF ₃ OC ₄ H ₈ ; BF ₃ HOCH ₃ , BF ₃ HOC ₃ H ₇ And boron halide alcohol complexes such as BF ₃ HOC ₆ H ₅ .
(B) The boron compound (A) in the lithium salt of an organic acid is presumed to have a function of promoting dissociation from the anion portion of lithium ions and improving the solubility in a non-aqueous solvent.

 (B) A boron compound may be used individually by 1 type, and may use 2 or more types together. When two or more kinds are used in combination, the combination and ratio may be appropriately selected according to the purpose.

 (B) The compounding quantity of a boron compound is not specifically limited, What is necessary is just to adjust suitably according to the kind of (B) boron compound and the lithium salt of (A) organic acid in the range by which the effect of this invention is not lost. Usually, the molar ratio of [(B) Boron compound content (mole number)] / [Mixed (A) mole number of lithium atoms in lithium salt of organic acid] is 0.7 or more. Preferably, it is 0.8 or more, more preferably 0.9 or more. By setting it as such a range, the solubility of the lithium salt of (A) organic acid with respect to various non-aqueous solvents further improves. The upper limit of the molar ratio is not particularly limited as long as the effect of the present invention is not hindered, but is preferably 1.5, more preferably 1.3, and further preferably 1.2. .

(Other ingredients)
In the electrolyte of the present invention, in addition to the lithium salt of the organic acid (A) and the boron compound (B), other components may be blended within a range not impeding the effects of the present invention.

(Method for producing electrolyte)
The electrolytic solution of the present invention can be produced by appropriately blending the first lithium salt, the non-aqueous solvent, (A) a lithium salt of an organic acid, (B) a boron compound, and other components as necessary. Each condition such as the order of addition, temperature, time and the like at the time of blending each component can be arbitrarily adjusted according to the type of the blended component.

<Gel electrolyte>
The gel electrolyte of the present invention is characterized in that a matrix polymer is further blended with the electrolytic solution of the present invention. The electrolytic solution is held in a matrix polymer. The gel electrolyte is preferably one that does not exhibit fluidity in an environment of 40 ° C. or lower where a lithium ion secondary battery is normally used.

(Matrix polymer)
The matrix polymer is not particularly limited, and those known in the gel electrolyte field can be used as appropriate.
Specific examples of preferred matrix polymers include polyether polymers such as polyethylene oxide and polypropylene oxide; polyvinyl fluoride, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyvinylidene fluoride-hexafluoride. Fluoropolymers such as acetone copolymers and polytetrafluoroethylene; polyacrylic polymers such as poly (meth) acrylate methyl, poly (meth) ethyl acrylate, polyacrylamide, polyacrylates containing ethylene oxide units; polyacrylonitrile; Polyphosphazene; polysiloxane can be exemplified.

The matrix polymer may be used alone or in combination of two or more. When two or more kinds are used in combination, the combination and ratio may be appropriately selected according to the purpose.
The blending amount of the matrix polymer is not particularly limited. For example, the blending amount of the matrix polymer in the total amount of the blending components may be appropriately adjusted according to the type of the solvent constituting the electrolytic solution. It is preferable that it is 50 mass%. By setting the lower limit value or more, the strength of the gel electrolyte is further improved, and by setting the lower limit value or less, the lithium ion secondary battery shows more excellent battery performance.

(Gel electrolyte production method)
The gel electrolyte of the present invention can be produced by appropriately blending the electrolytic solution of the present invention, the matrix polymer, and other components as necessary. Each condition such as the order of addition, temperature, time and the like at the time of blending each component can be arbitrarily adjusted according to the type of the blended component.

<Lithium ion secondary battery>
The lithium ion secondary battery of the present invention is obtained using the electrolytic solution of the present invention or the gel electrolyte of the present invention.
The lithium ion secondary battery of the present invention can have the same configuration as the conventional lithium ion secondary battery except that the electrolytic solution of the present invention or the gel electrolyte of the present invention is used. For example, a negative electrode, a positive electrode, A separator and the electrolytic solution are provided.

The material of the negative electrode is not particularly limited, but may be exemplified by metal lithium, lithium alloy, carbon-based material capable of inserting and extracting lithium, metal oxide, etc., and may be one or more selected from the group consisting of these materials. preferable.
The material of the positive electrode is not particularly limited, and examples thereof include transition metal oxides such as lithium cobaltate, lithium nickelate, lithium manganate, olivine type lithium iron phosphate, and lithium cobalt / nickel / manganese composite oxide. It is preferable that it is 1 or more types selected from the group which consists of.

 Although the material of the separator is not particularly limited, it can be exemplified by a microporous polymer film, a nonwoven fabric, glass fiber, and the like, and is preferably at least one selected from the group consisting of these materials.

 The shape of the lithium ion secondary battery of the present invention is not particularly limited, and can be adjusted to various shapes such as a cylindrical shape, a square shape, a coin shape, a sheet shape, and a laminate shape.

 What is necessary is just to manufacture the lithium ion secondary battery of this invention using the said electrolyte solution and an electrode according to a well-known method, for example in a glove box or dry air atmosphere.

 Hereinafter, the present invention will be described in more detail with reference to specific examples. However, the present invention is not limited to the following examples.

(1) Chemical substances used The chemical substances used in this example are shown below.
Lithium hexafluorophosphate (LiPF ₆ ) (Kishida Chemical Co., Ltd.)
-(A) Organic acid lithium salt raw material Formic acid (manufactured by Aldrich)
Oxalic acid (Aldrich)
Malonic acid (manufactured by Aldrich)
Succinic acid (Aldrich)
Lithium hydroxide monohydrate (LiOH.H ₂ O) (Aldrich)
(B) Boron compound Boron trifluoride diethyl ether complex (BF ₃ O (C ₂ H ₅ ) ₂ ) (manufactured by Aldrich)
Boron trifluoride di n-butyl ether complex (BF ₃ O (C ₄ H ₉ ) ₂ ) (Aldrich)
Boron trifluoride tetrahydrofuran complex (BF ₃ OC ₄ H ₈ ) (manufactured by Aldrich)
(D) Nonaqueous solvent Ethylene carbonate (hereinafter abbreviated as EC) (Kishida Chemical Co., Ltd.)
Dimethyl carbonate (hereinafter abbreviated as DMC) (Kishida Chemical Co., Ltd.)
Ethyl methyl carbonate (hereinafter abbreviated as EMC) (manufactured by Kishida Chemical Co., Ltd.)

(2) (A) Preparation of lithium salt of organic acid (2-1) Preparation of lithium formate Formic acid (20.0 g, 434.5 mmol) was weighed into a round bottom flask and dissolved in 50 mL of distilled water. . A solution obtained by dissolving LiOH.H ₂ O (17.87 g, 426.0 mmol) in 100 ml of distilled water was slowly added dropwise thereto. After stirring for 24 hours at room temperature, the solution was concentrated using a rotary evaporator. The concentrated solution was slowly added dropwise to 200 mL of acetonitrile, and the precipitated solid was washed again with acetonitrile and then dried to obtain white powder of lithium formate.

(2-2) Preparation of lithium oxalate Oxalic acid (10.0 g, 111 mmol) was weighed into a round bottom flask and dissolved in 100 mL of distilled water. A solution prepared by dissolving LiOH.H ₂ O (9.23 g, 220 mmol) in 100 ml of distilled water was slowly added dropwise thereto. After stirring for 24 hours at room temperature, the solution was concentrated using a rotary evaporator. The concentrated solution was slowly added dropwise to 200 mL of acetonitrile, and the precipitated solid was washed again with acetonitrile and then dried to obtain white powder of lithium oxalate.

(2-3) Preparation of lithium malonate Malonic acid (20.0 g, 192.2 mmol) was weighed into a round bottom flask and dissolved in 100 mL of distilled water. A solution obtained by dissolving LiOH · H ₂ O (16.13 g, 384.4 mmol) in 100 ml of distilled water was slowly added dropwise thereto. After stirring for 24 hours at room temperature, the solution was concentrated using a rotary evaporator. The concentrated solution was slowly added dropwise to 200 mL of acetonitrile, and the precipitated solid was washed again with acetonitrile and then dried to obtain white powder of lithium malonate.

(2-4) Preparation of lithium succinate Succinic acid (10.0 g, 84.7 mmol) was weighed into a round bottom flask and dissolved in 50 mL of distilled water. A solution obtained by dissolving LiOH.H ₂ O (7.27 g, 169.8 mmol) in 100 ml of distilled water was slowly added dropwise thereto. After stirring for 24 hours at room temperature, the solution was concentrated using a rotary evaporator. The concentrated solution was slowly added dropwise to 200 mL of acetonitrile, and the precipitated solid was washed again with acetonitrile and then dried to obtain white powder of lithium succinate.

(3) Manufacture of electrolyte solution and cell All the operations in Examples and Comparative Examples shown below were performed in a dry box.

[Example 1]
<Manufacture of electrolyte>
A mixed solvent of EC and DMC (EC: DMC = 30: 70 (volume ratio)) as a nonaqueous solvent was weighed into LiPF ₆ (0.807 g, 5.31 mmol) in a sample bottle, and the concentration of lithium atoms was 1. The electrolyte solution (1) was obtained by mixing so that it might become 0 mol / kg. In addition, the non-aqueous solvent was added to the lithium oxalate (0.284 g, 2.79 mmol) and BF ₃ O (C ₂ H ₅ ) ₂ (0.792 g, 5.58 mmol) obtained in (2-2) above. As a mixed solvent of EC and DMC (EC: DMC = 30: 70 (volume ratio)) is weighed into a sample bottle and mixed so that the concentration of lithium atoms is 1.0 mol / kg. )
The electrolytic solution used in this example was obtained by adding 10 parts by weight of the electrolytic solution (2) to 90 parts by weight of the electrolytic solution (1) obtained above.

<Manufacture of coin cell>
A negative electrode (manufactured by Hosen Co., Ltd.) and a positive electrode (manufactured by Hosen Co., Ltd.) were punched into a disk shape having a diameter of 16 mm. Further, a glass fiber was punched into a disk shape having a diameter of 17 mm as a separator. The obtained positive electrode, separator and negative electrode were laminated in this order in a battery container made of SUS (CR2032), the separator, the negative electrode and the positive electrode were impregnated with the electrolytic solution obtained above, and a SUS plate was placed on the negative electrode. A coin-type cell was manufactured by placing (covering a thickness of 1.2 mm, a diameter of 16 mm) and capping.

[Example 2]
The same as Example 1 except that the electrolyte solution (1) and the electrolyte solution (2) were produced by using a mixed solvent of EC and EMC (EC: EMC = 30: 70 (volume ratio)) as the nonaqueous solvent. The electrolytic solution and the coin-type cell were manufactured by the method described above.

[Example 3]
Example 1 is the same as Example 1 except that 1 part by weight of the electrolytic solution (2) obtained in Example 1 was added to 99 parts by weight of the electrolytic solution (1) obtained in Example 1. In the same manner, an electrolytic solution and a coin-type cell were manufactured.

[Example 4]
Example 1 is the same as Example 1 except that 5 parts by weight of the electrolytic solution (2) obtained in Example 1 was added to 95 parts by weight of the electrolytic solution (1) obtained in Example 1. In the same manner, an electrolytic solution and a coin-type cell were manufactured.

[Example 5]
Example 1 is the same as Example 1 except that 20 parts by weight of the electrolytic solution (2) obtained in Example 1 was added to 80 parts by weight of the electrolytic solution (1) obtained in Example 1. In the same manner, an electrolytic solution and a coin-type cell were manufactured.

[Example 6]
Example 1 is the same as Example 1 except that 50 parts by weight of the electrolytic solution (2) obtained in Example 1 was added to 50 parts by weight of the electrolytic solution (1) obtained in Example 1. In the same manner, an electrolytic solution and a coin-type cell were manufactured.

[Example 7]
<Manufacture of electrolyte>
A mixed solvent of EC and EMC (EC: EMC = 30: 70 (volume ratio)) as a nonaqueous solvent was weighed into LiPF ₆ (0.807 g, 5.31 mmol) in a sample bottle, and the concentration of lithium atoms was 1. The electrolyte solution (1) was obtained by mixing so that it might become 0 mol / kg. In addition, lithium oxalate (0.183 g, 1.80 mmol) and BF ₃ O (C ₄ H ₉ ) ₂ (0.712 g, 3.60 mmol) obtained in (2-2) above were used as a non-aqueous solvent. A mixed solvent of EC and EMC (EMC: EMC = 30: 70 (volume ratio)) is weighed into a sample bottle and mixed so that the concentration of lithium atoms is 1.0 mol / kg. Got.
The electrolytic solution used in this example was obtained by adding 10 parts by weight of the electrolytic solution (2) to 90 parts by weight of the electrolytic solution (1) obtained above.

<Manufacture of coin cell>
A negative electrode (manufactured by Hosen Co., Ltd.) and a positive electrode (manufactured by Hosen Co., Ltd.) were punched into a disk shape having a diameter of 16 mm. Further, a glass fiber was punched into a disk shape having a diameter of 17 mm as a separator. The obtained positive electrode, separator and negative electrode were laminated in this order in a battery container made of SUS (CR2032), the separator, the negative electrode and the positive electrode were impregnated with the electrolytic solution obtained above, and a SUS plate was placed on the negative electrode. A coin-type cell was manufactured by placing (covering a thickness of 1.2 mm, a diameter of 16 mm) and capping.

[Example 8]
<Manufacture of electrolyte>
A mixed solvent of EC and EMC (EC: EMC = 30: 70 (volume ratio)) as a nonaqueous solvent was weighed into LiPF ₆ (0.807 g, 5.31 mmol) in a sample bottle, and the concentration of lithium atoms was 1. The electrolyte solution (1) was obtained by mixing so that it might become 0 mol / kg. In addition, the lithium oxalate (0.170 g, 1.67 mmol) and BF ₃ OC ₄ H ₈ (0.467 g, 3.34 mmol) obtained in (2-2) above were added to EC and EMC as non-aqueous solvents. A mixed solvent (EC: EMC = 30: 70 (volume ratio)) was weighed into a sample bottle and mixed so that the concentration of lithium atoms was 1.0 mol / kg to obtain an electrolytic solution (2).
The electrolytic solution used in this example was obtained by adding 10 parts by weight of the electrolytic solution (2) to 90 parts by weight of the electrolytic solution (1) obtained above.

<Manufacture of coin cell>
A negative electrode (manufactured by Hosen Co., Ltd.) and a positive electrode (manufactured by Hosen Co., Ltd.) were punched into a disk shape having a diameter of 16 mm. Further, a glass fiber was punched into a disk shape having a diameter of 17 mm as a separator. The obtained positive electrode, separator and negative electrode were laminated in this order in a battery container made of SUS (CR2032), the separator, the negative electrode and the positive electrode were impregnated with the electrolytic solution obtained above, and a SUS plate was placed on the negative electrode. A coin-type cell was manufactured by placing (covering a thickness of 1.2 mm, a diameter of 16 mm) and capping.

[Example 9]
<Manufacture of electrolyte>
A mixed solvent of EC and EMC (EC: EMC = 30: 70 (volume ratio)) as a nonaqueous solvent was weighed into LiPF ₆ (0.807 g, 5.31 mmol) in a sample bottle, and the concentration of lithium atoms was 1. The electrolyte solution (1) was obtained by mixing so that it might become 0 mol / kg. In addition, the lithium formate (0.174 g, 3.35 mmol) and BF ₃ O (C ₂ H ₅ ) ₂ (0.475 g, 3.35 mmol) obtained in (2-1) above were added to EC as a nonaqueous solvent. And an EMC mixed solvent (EC: EMC = 30: 70 (volume ratio)) are weighed into a sample bottle and mixed so that the concentration of lithium atoms is 1.0 mol / kg. Obtained.
The electrolytic solution used in this example was obtained by adding 10 parts by weight of the electrolytic solution (2) to 90 parts by weight of the electrolytic solution (1) obtained above.

<Manufacture of coin cell>
A negative electrode (manufactured by Hosen Co., Ltd.) and a positive electrode (manufactured by Hosen Co., Ltd.) were punched into a disk shape having a diameter of 16 mm. Further, a glass fiber was punched into a disk shape having a diameter of 17 mm as a separator. The obtained positive electrode, separator and negative electrode were laminated in this order in a battery container made of SUS (CR2032), the separator, the negative electrode and the positive electrode were impregnated with the electrolytic solution obtained above, and a SUS plate was placed on the negative electrode. A coin-type cell was manufactured by placing (covering a thickness of 1.2 mm, a diameter of 16 mm) and capping.

[Example 10]
<Manufacture of electrolyte>
A mixed solvent of EC and EMC (EC: EMC = 30: 70 (volume ratio)) as a nonaqueous solvent was weighed into LiPF ₆ (0.807 g, 5.31 mmol) in a sample bottle, and the concentration of lithium atoms was 1. The electrolyte solution (1) was obtained by mixing so that it might become 0 mol / kg. In addition, lithium malonate (0.196 g, 1.69 mmol) and BF ₃ O (C ₂ H ₅ ) ₂ (0.479 g, 3.38 mmol) obtained in (2-3) above were used as a non-aqueous solvent. A mixed solvent of EC and EMC (EC: EMC = 30: 70 (volume ratio)) is weighed into a sample bottle and mixed so that the concentration of lithium atoms is 1.0 mol / kg. Got.
The electrolytic solution used in this example was obtained by adding 10 parts by weight of the electrolytic solution (2) to 90 parts by weight of the electrolytic solution (1) obtained above.

<Manufacture of coin cell>
A negative electrode (manufactured by Hosen Co., Ltd.) and a positive electrode (manufactured by Hosen Co., Ltd.) were punched into a disk shape having a diameter of 16 mm. Further, a glass fiber was punched into a disk shape having a diameter of 17 mm as a separator. The obtained positive electrode, separator and negative electrode were laminated in this order in a battery container made of SUS (CR2032), the separator, the negative electrode and the positive electrode were impregnated with the electrolytic solution obtained above, and a SUS plate was placed on the negative electrode. A coin-type cell was manufactured by placing (covering a thickness of 1.2 mm, a diameter of 16 mm) and capping.

[Example 11]
<Manufacture of electrolyte>
A mixed solvent of EC and EMC (EC: EMC = 30: 70 (volume ratio)) as a nonaqueous solvent was weighed into LiPF ₆ (0.807 g, 5.31 mmol) in a sample bottle, and the concentration of lithium atoms was 1. The electrolyte solution (1) was obtained by mixing so that it might become 0 mol / kg. In addition, lithium succinate (0.221 g, 1.70 mmol) and BF ₃ O (C ₂ H ₅ ) ₂ (0.483 g, 3.41 mmol) obtained in (2-4) above were used as a non-aqueous solvent. A mixed solvent of EC and EMC (EC: EMC = 30: 70 (volume ratio)) is weighed into a sample bottle and mixed so that the concentration of lithium atoms is 1.0 mol / kg. Got.
The electrolytic solution used in this example was obtained by adding 10 parts by weight of the electrolytic solution (2) to 90 parts by weight of the electrolytic solution (1) obtained above.

<Manufacture of coin cell>
A negative electrode (manufactured by Hosen Co., Ltd.) and a positive electrode (manufactured by Hosen Co., Ltd.) were punched into a disk shape having a diameter of 16 mm. Further, a glass fiber was punched into a disk shape having a diameter of 17 mm as a separator. The obtained positive electrode, separator and negative electrode were laminated in this order in a battery container made of SUS (CR2032), the separator, the negative electrode and the positive electrode were impregnated with the electrolytic solution obtained above, and a SUS plate was placed on the negative electrode. A coin-type cell was manufactured by placing (covering a thickness of 1.2 mm, a diameter of 16 mm) and capping.

[Comparative Example 1]
Except that only the electrolytic solution (1) obtained in Example 1 was used, an electrolytic solution and a coin-type cell were manufactured in the same manner as in Example 1.

[Comparative Example 2]
Except that only the electrolytic solution (1) obtained in Example 2 was used, an electrolytic solution and a coin-type cell were manufactured in the same manner as in Example 1.

(4) Evaluation of battery performance For the coin-type cells of Examples 1 to 11 and Comparative Examples 1 and 2, a constant current and constant voltage charge of 0.2 C at 25 ° C. was set to an upper limit voltage of 4.2 V, and a current value of 0.1 C Then, 0.2C constant current discharge was performed up to 2.7V. Thereafter, the charge / discharge current was set to 1 C and the charge / discharge cycle was repeated several times to several tens of times in the same manner to stabilize the state of the battery. Thereafter, the charge / discharge cycle was repeated in the same manner at a charge / discharge current of 1C, and the capacity retention rate at 100 cycles (discharge capacity at the 100th cycle (mAh) / discharge capacity at the 1st cycle (mAh)) × 100 Was calculated.

As is clear from the results of Examples 1 to ₃ , by adding lithium oxalate and BF ₃ O (C ₂ H ₅ ) ₃ in combination in an electrolytic solution using LiPF ₆ as the first lithium salt. As in Comparative Examples 1 and ₂ , the capacity retention rate was improved and sufficient charge / discharge characteristics were exhibited as compared with the system in which lithium oxalate and BF ₃ O (C ₂ H ₅ ) ₃ were not added.
Further, as is clear from the results of Examples 4 to 7, even when the addition amounts of lithium oxalate and BF ₃ O (C ₂ H ₅ ) ₃ were variously changed, the same results as in Examples 1 to 3 were obtained. Obtained.
Further, as is clear from the results of Examples 8 to 9, even when boron compounds having different structures were blended, the same results as in Examples 1 to 7 were obtained.
Further, as is clear from the results of Examples 10 to 12, the same results as in Examples 1 to 9 were obtained even when organic acid lithiums having different structures were blended.

The present invention can be used in the field of lithium ion secondary batteries.

Claims (6)

In the electrolytic solution in which the first lithium salt is dissolved in a nonaqueous solvent, (A) a lithium salt of an organic acid and (B) a boron compound are further blended as the second lithium salt,
(A) The lithium salt of the organic acid is a lithium salt of a carboxylic acid, and the first lithium salt is a lithium salt other than the lithium salt of the carboxylic acid,
The boron compound (B) is boron trifluoride, boron trifluoride dimethyl ether complex, boron trifluoride diethyl ether complex, boron trifluoride di n-butyl ether complex, boron trifluoride di tert-butyl ether complex, trifluoride. It is at least one selected from the group consisting of boron tert-butyl methyl ether complex, boron trifluoride tetrahydrofuran complex, boron trifluoride methanol complex, boron trifluoride propanol complex and boron trifluoride phenol complex. Electrolytic solution. The first lithium salt is lithium hexafluorophosphate (LiPF ₆ ), lithium boron tetrafluoride (LiBF ₄ ), lithium bis (trifluoromethylsulfonyl) imide (LiN (SO ₂ CF ₃ ) ₂ ), lithium chlorate (LiClO _4), trifluoromethane sulfonic lithium _(LiCF 3 _SO 3), lithium hexafluoro antimonate (LiSbF _6), hexafluoroarsenate arsenate periodate lithium (LiAsF ₆₎ and lithium tetraphenylborate ( The electrolytic solution according to claim 1, wherein the electrolytic solution is one or more selected from the group consisting of LiB (C ₆ H ₅ ) ₄ ).   The lithium salt of carboxylic acid is lithium formate, lithium acetate, lithium propionate, lithium butyrate, lithium isobutyrate, lithium oxalate, lithium lactate, lithium tartrate, lithium maleate, lithium fumarate, lithium malonate, lithium succinate The electrolyte solution according to claim 1, wherein the electrolyte solution is at least one selected from the group consisting of lithium malate, lithium citrate, lithium glutarate, lithium adipate, lithium phthalate, and lithium benzoate. .   The blending amount of the first lithium salt: The blending amount of the lithium salt of the organic acid (A) is 99.5: 0.5 to 50:50 (molar ratio). Electrolyte as described in any one of these. The non-aqueous solvent is a mixture of one or more selected from the group consisting of cyclic carbonates, chain carbonates, ethers, carboxylic esters, nitriles, amides and sulfones. The electrolyte solution as described in any one of Claims 1-4 . A lithium ion secondary battery obtained by using the electrolytic solution according to any one of claims 1 to 5 .