JP3409852B2 - New lithium organic borate compound, non-aqueous electrolyte using organic borate compound and lithium secondary battery - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a novel organic boric acid.
Lithium compounds, it relates to non-aqueous electrolyte solution using an organic borate compound and a lithium secondary batteries using the same, in particular,
Oxidation highly novel organic lithium borate compound, relates to lithium secondary batteries with improved cycle life using improved non-aqueous electrolyte solution and this oxidation resistance by using an organic borate.

[0002]

2. Description of the Related Art A lithium secondary battery composed of a positive electrode and a negative electrode capable of inserting and extracting lithium and a non-aqueous electrolyte has a high energy density per weight and volume and a high voltage, so that it is a small portable power source or an electric vehicle. Is expected to be used as a source of energy. Since the lithium secondary battery has a high driving voltage of 3 V or more, a non-aqueous electrolyte solution having a wide withstand voltage range is used. There are problems that the non-aqueous electrolyte has a low electric conductivity when compared with the aqueous electrolyte, and that many organic solvents suitable for the non-aqueous electrolyte have high flammability (or low flash point).

Therefore, a study to improve the conductivity and improve the load characteristics of the battery (eg, 40th battery discussion meeting, Proceedings, P.4)
53, 455, (1999)), using non-flammable or low-flammable organic solvents for non-aqueous electrolytes (e.g., 40th Battery Symposium, Proceedings, P.459 (1999)). Has been done. In order to improve the conductivity, it is necessary to select an organic solvent that can improve the dissociation property of the supporting electrolyte or can increase the dissociation of the supporting electrolyte. Regarding the electrolyte, an organic lithium salt has been proposed as a lithium salt having a higher dissociation property than lithium hexafluorophosphate (LiPF ₆ ) and lithium tetrafluoroborate (LiBF ₄ ) which are mainly used at present.

Among them, bis (trifluoromethanesulfonyl) imide lithium (LiN [S0 ₂ CF ₃ ] ₂ ) disclosed in JP-A-5-326018 is more suitable for a non-aqueous electrolyte solvent than an inorganic electrolyte. It is known as a promising material with high solubility. However, it has been pointed out that lithium bis (trifluoromethanesulfonyl) imide corrodes aluminum used as a positive electrode current collector of a lithium secondary battery.

Further, Japanese Patent Laid-Open No. 7-65843 discloses an organolithium salt having boron as a central ion and disalicylate as a ligand, and Japanese Patent Laid-Open No. 7-65843 discloses a ligand having boron as a central ion. Discloses an organolithium salt having a benzenediolate derivative. However, since these compounds have a benzene ring in the molecule, their solubility is poor and their electrical conductivity and oxidation resistance are not satisfactory.

Further, as a solvent for making the material incombustible or flame-retardant, an example of using a fluorinated solvent as shown in JP-A-9-97627, JP-A-10-12272, etc. is effective. However, there has been a problem that the fluorinated solvent has a high electron-withdrawing property of fluorine, so that the electron donating property of the functional group is lowered and the solubility and dissociation property of the lithium salt are lowered. The organic lithium salt has better solubility than the inorganic lithium salt and is an effective material. For these reasons, improvements in organic lithium salts have been earnestly desired as promising materials for improving the safety and performance of lithium secondary batteries.

[0007]

An object of the present invention is to provide a organic lithium borate reduction that can realize a high conductivity non-aqueous electrolyte solution
Compound, also, non-aqueous electrolyte can improve the characteristics of the I Ri electric chemical capacitor to be used non-flammable fluorinated solvent having no property deterioration even in mixed nonaqueous electrolyte organic borate compounds and this and to provide a good lithium secondary batteries of the life performance using the non-aqueous electrolyte.

[0008]

The conductivity is determined by the number of lithium ions and their mobility. Also, the solubility is considered to depend on the radius of the ions surrounded by the solvent. Therefore, the present inventors can suppress the local aggregation of the solvent by increasing the anion of the organolithium salt and delocalize the charge of the ion, and increase the affinity between the anion and the solvent. By introducing into the anion a functional group capable of increasing the electron withdrawing property of the element, it is considered that a lithium salt having high dissociation and good solubility can be obtained, and as a result of diligent studies on such a compound, the present invention Has been completed.

That is, the present invention has the general formula (1)

[Chemical 2] [However, X is any of lithium, quaternary ammonium and quaternary phosphonium, and R ¹ , R ² , R ³ and R ⁴ each independently represent a halogen atom-substituted alkyl group having 1 to 4 carbon atoms] organic borate Li said X tHAT represented is lithium
Tium compound or X is lithium or quaternary ammonium
And quaternary phosphonium borates
A non-aqueous electrolyte solution containing a compound and a solvent .

The organic borate represented by the general formula (1) is a novel compound, has excellent solubility in a non-aqueous solvent, and an electrolytic solution using this compound as an electrolyte has high conductivity. That is, by introducing a halogen-substituted acyloxy group, which has a high electron-withdrawing property and is capable of delocalizing the charge in the carbonyl group, into the boron, which is the central element of the anion, the ionic radius of the anion is increased and the charge of the anion is non-localized. It could be localized and the solubility could be increased. Therefore, the electrolytic solution using this supporting electrolyte has a small dipole moment and a low dielectric constant,
A nonflammable fluorinated solvent or the like can also be used. Also,
Unlike the imide-based organic salt, this compound does not corrode the aluminum current collector because the central ion is surrounded by the ligand.

In the embodiment of the present invention, the organic borate compound has a chemical structure represented by the general formula (1), and in the general formula (1), X is lithium or a quaternary anion.
Represents either monium or quaternary phosphonium ,
R ¹ , R ² , R ³ , and R ⁴ are each independently a halogen atom-substituted alkyl group having 1 to 4 carbon atoms. From the viewpoint of molecular weight and oxidation resistance, R ¹ , R ² , R ³ and R ⁴ are trifluoromethyl groups,
Alternatively, a pentafluoroethyl group is preferable.

The organic borate of the present invention is soluble in cyclic carbonates such as ethylene carbonate and propylene carbonate, chain carbonates such as dimethyl carbonate and ethyl methyl carbonate, or insoluble materials such as dimethoxyethane. Is extremely high, and it is possible to obtain a non-aqueous electrolytic solution using these solvents alone or in combination. Further, in the general formula (1), R ¹ ,
A compound in which R ² , R ³ and R ⁴ are fluorinated alkyl groups or partially fluorinated alkyl groups is nonafluorobutyl methyl ether which is a non-flammable fluorinated solvent in addition to the above non-aqueous solvent. 1.8mo even for a solution containing a low dielectric constant solvent such as (trademark: HFE7100) in the range of 5 to 90% by volume.
A non-aqueous electrolyte solution having a high conductivity with a solubility of 1 · dm ⁻³ or more can be obtained. Furthermore, the electrolytic solution of the present invention in which the organic lithium borate is dissolved does not corrode aluminum, and the oxidative decomposition potential is about 5 V (vs. Li metal) or more, and the potential application range is wide.

Specific compounds in the organic borate of the present invention include, for example, lithium tetrakis (trifluoroacetate) borate, lithium tetrakis (difluoroacetate) borate, lithium tetrakis (fluoroacetate) borate, lithium tetrakis (chlorodifluoroacetate). Borate, lithium tetrakis (trichloroacetate) borate, lithium tetrakis (dichloroacetate) borate, lithium tetrakis (pentafluoropropanoate) borate, lithium tetrakis
(3-Chlorotetrafluoropropanoate) borate, lithium tetrakis (heptafluorobutanoate) borate, lithium tetrakis (2, 21-bistrifluoromethylpropanoate) borate, tetraethylammonium tetrakis (trifluoroacetate) borate, lithium Tetrakis (difluoroacetate) borate, tetraethylammonium tetrakis (fluoroacetate)
Borate, tetraethylammonium tetrakis (chlorodifluoroacetate) borate, tetraethylammonium tetrakis (trichloroacetate) borate,
Tetraethylammonium tetrakis (dichloroacetate) borate, tetraethylammonium tetrakis
(Pentafluoropropanoate) borate, tetraethylammonium tetrakis (31-chlorotetrafluoropropanoate) borate, tetraethylammonium tetrakis (heptafluorobutanoate) borate, tetraethylammonium tetrakis (2,21-bistrifluoromethylpropanoate) ) Borate, triethylmethylammonium tetrakis (trifluoroacetate) borate, tetraethylphosnium tetrakis (trifluoroacetate) borate, triethylmethylphosnium tetrakis (trifluoroacetate) borate and the like can be mentioned.

The organic lithium borate of the present invention is, for example,

[Chemical 3] It can be synthesized through the following processes.

That is, the organic lithium borate of the present invention can be easily synthesized by reacting boric acid with 3 equivalents of an acid anhydride and lithium carboxylate. However, the above process is an example for synthesizing the organic lithium borate of the present invention, and the synthesizing process is not limited to the above process. Further, by using a carboxylic acid quaternary ammonium salt or a carboxylic acid quaternary phosphonium salt instead of lithium carboxylic acid, the organic boric acid ammonium salt or organic boric acid phosphonium salt of the present invention can be obtained.

Solvents for the non-aqueous electrolyte include chain carbonates such as dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, dipropyl carbonate and methyl propyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, trifluoropropylene carbonate and chloro carbonate. Cyclic carbonates such as ethylene carbonate, vinylene carbonate and dimethylvinylene carbonate, cyclic esters such as γ-butyrolactone and valerolactone, 1,3-dioxolane,
Cyclic materials such as tetrahydrofuran can be used alone or in combination.

In the non-aqueous electrolyte, the tetrahaloacetate borate of the present invention can be used as a main supporting salt,
LiPF ₆ , LiBF ₄ , LiN (S0 ₂ CF ₂ CF ₃ ) ₂ , as supporting salts,
LiN (S0 ₂ CF ₃ ) ₂ or the like can be used as a main supporting salt, and the tetrahaloacetate borate of the present invention can be used as an additive.

A lithium composite oxide of a transition metal such as cobalt, nickel or manganese capable of occluding / releasing lithium can be used for the positive electrode of the lithium secondary battery, and a lithium metal, graphite or a non-lithium capable of occluding / releasing lithium can be used for the negative electrode. Quality carbon materials, oxides of silicon and tin, and composites of these with carbon can be used.

For the separator, polyethylene, polypropylene, or a microporous membrane having a structure in which these are laminated can be used.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited to these Examples.

Example 1 Synthesis and identification of lithium tetrakis (trifluoroacetate) borate (hereinafter referred to as LB1). Boric acid (4.9 g), lithium trifluoroacetate (9.5 g) and dimethyl carbonate (100 ml) were added to a 300 m1 three-neck flask, and trifluoroacetic anhydride (50 g) was added dropwise with stirring under ice cooling. After the dropping, the mixture was stirred at 80 ° C. for about 7 hours. The solvent was removed from the reaction solution, and the obtained solid was recrystallized from tetrahydrofuran.
The obtained crystals were dried under reduced pressure to obtain lithium tetrakis (trifluoroacetate) borate in a yield of 67%. The infrared absorption spectrum of the obtained compound is shown in FIG.

Infrared absorption: 1770 cm ^-1 (C = 0), 1230 cm ^-1 (C-
^{F), 1180cm -1 (C-} F), 1040cm -1 (C-0). ¹¹ B-NMR spectrum (CD ₃ OD / trimethyl borate standard): δ-18.3 ppm.
Elemental analysis (theoretical values in parentheses): Li = 1.5 (1.5)%, B = 2.2 (2.3)
%, C = 20.5 (20.4)%, melting point: 163 ° C. (decomposition).

Example 2 Synthesis and Identification of Lithium Tetrakis (pentafluoropropanoate) borate (hereinafter referred to as LB2) 8.8 g of boric acid, 24.2 g of lithium pentafluoropropionate and carbonic acid were placed in a 1000 ml three-fold flask. 265 ml of dimethyl was added, and 132.2 g of pentafluoropropionic anhydride was added dropwise with stirring under ice cooling. After dropping, the mixture was stirred at 90 ° C. for about 17 hours. The solvent was removed from the reaction solution, and the obtained solid was recrystallized from tetrahydrofuran. The obtained crystals are dried under reduced pressure,
Lithium tetrakis (pentafluoropropanoate) borate was obtained with a yield of 38%. The infrared absorption spectrum of the obtained compound is shown in FIG.

Infrared absorption: 1770 cm ^-1 (C = 0), 1230 cm ^-1 (C
^{-F), 1180cm -1 (CF)} ,! 040cm -1 (C-0). ¹¹ B-NMR spectrum (CD ₃₀ D / trimethyl borate standard): δ-18.6 ppm.
Elemental analysis (theoretical values in parentheses): Li = 1.O (1.0)%, B = 1.3 (1.61)
%, C = 21.8 (21.5)%, melting point: 198 ° C. (decomposition).

(Example 3) Lithium tetrakis (trichloroacetate) borate
(Hereinafter, referred to as LB3.) Synthesis and Identification 6.7 g of boric acid, 18.3 g of lithium trichloroacetate and 130 ml of dimethyl carbonate were added to a 300 ml three-fold flask, and 100 g of trichloroacetic anhydride was added dropwise with stirring under ice cooling. After the dropping, the mixture was stirred at 110 ° C. for about 10 hours. The solvent was removed from the reaction solution to obtain a solid. The obtained solid was heated under reduced pressure, and the contained trichloroacetic acid was sublimated and removed.
Subsequently, the crystals were recrystallized from tetrahydrofuran, and the obtained crystals were dried under reduced pressure to obtain lithium tetrakis (trichloroacetate) borate in a yield of 24%. The infrared absorption spectrum of the obtained compound is shown in FIG.

Infrared absorption: 1770 cm ^-1 (C = O), 1040 cm ^-1
(CO). ¹¹ B-NMR spectrum (CD ₃₀ D / trimethyl borate standard): δ-19.1 ppm. Elemental analysis (theoretical values in parentheses): Li = 1.0 (1.
0)%, B = 1.5 (1.6)%, C = 14.7 (14.4)%, melting point: 281 ° C.

(Example 4) Synthesis and identification of lithium tetrakis (acetate) borate (hereinafter referred to as LB4) 5
22.Og boric acid and 23.
5 g and 327.Og of acetic anhydride were added, and the mixture was stirred at 150 ° C for about 17 hours. The reaction solution was filtered to remove insoluble matter, and 760 ml of isopropyl alcohol was added to the filtrate to precipitate crystals. The obtained crystals were recrystallized from tetrahydrofuran to obtain lithium tetrakis (acetate) borate in a yield of 11%. The infrared absorption spectrum of the obtained compound is shown in FIG. Infrared absorption: 1700 cm ⁻¹ (C = O), 1040 cm ⁻¹ (CO). ¹¹ BN
MR spectrum (CD ₃ OD / trimethyl borate standard): δ-17.5
ppm. Elemental analysis (theoretical values in parentheses): Li = 2.8 (2.7)%, B = 4.2
(4.4)%, C = 40.1 (37.8)%, H = 4.9 (4.8)%, melting point: 140 ° C.

Example 5 Synthesis and Identification of Lithium Tetrakis (chlorodifluoroacetate) borate (hereinafter referred to as LB5) 6.5 g of boric acid, 14 g of lithium chlorodifluoroacetate, and 100 ml of dimethyl carbonate were added to a 200 ml three flask. While stirring under ice-cooling, 77 g of chlorodifluoroacetic acid anhydride was added dropwise. After the dropping, the mixture was stirred at 80 ° C for about 14 hours. The solvent was removed from the reaction solution, and the obtained solid was recrystallized from tetrahydrofuran. The obtained crystals were dried under reduced pressure to obtain lithium tetrakis (chlorodifluoroacetate) borate (yield 4
Five%). ¹¹ B-NMR spectrum (CD ₃₀ D / trimethyl borate standard): δ-18.0 ppm. Elemental analysis (theoretical values in parentheses): Li = 1.3
(1.3)%, B = 1.8 (2.0)%, C = 18.1 (17.9)%, melting point: 150 ° C. (decomposition).

Example 6 Synthesis and Identification of Tetraethylammonium Tetrakis (trifluoroacetate) borate (hereinafter referred to as AB1) 31000 g of boric acid, 150 g of tetraethylammonium trifluoroacetate and dimethyl carbonate were placed in a 1000 ml three-fold flask. 50
0 ml was added, and 427 g of trifluoroacetic anhydride was added dropwise with stirring under ice cooling. After dropping, the mixture was stirred at 80 ° C for about 3 hours.
The solvent was removed from the reaction solution, and the obtained solid was recrystallized from tetrahydrofuran. The obtained crystals were dried under reduced pressure to obtain tetraethylammonium tetrakis (trifluoroacetate) borate (yield 90%).

¹¹ B-NMR spectrum (CD ₃ OD / trimethyl borate standard): δ-18.3 ppm. ¹ H-NMR spectrum (CD ₃ OD / TMS
Standard): δ1.28ppm (tt, CH ₃ , 12H), 3.28ppm (q, CH ₂ , 8
H). Elemental analysis (theoretical values in parentheses): B = 1.9 (1.8)%, C = 32.5 (3
2.4)%, H = 3.4 (3.4)%, N = 2.4 (2.4)%, melting point: 124 ° C.

(Comparative Example 1, Examples 7 to 11) Propylene carbonate (hereinafter referred to as PC) as a solvent for evaluating solubility and conductivity.
And dimethyl carbonate (hereinafter, referred to as DMC) were mixed at a volume ratio of 1: 2 (hereinafter, referred to as solvent A), and lithium bis salicylate borate was dissolved as Comparative Example 1. did. As a result, lithium bis-salicylate borate 0.1 mol ^-3 (hereinafter, moldm ^{- 3} the referred to M.) Did not dissolve only up. The conductivity of this non-aqueous electrolyte at this concentration was O.43 mS / cm as evaluated by a CM-60S conductivity meter manufactured by Toa Denpa Kogyo KK using a CGT-511B cell.

As Example 7, lithium salt LB1 was dissolved in solvent A. As a result, LB1 dissolves better than 1.2M and 0.8M
Gave a maximum conductivity of 7.8 mS / cm. As described above, it was found that the lithium salt LB1 of the present invention improves the solubility 12 times or more and the conductivity 18 times.

As Example 8, lithium salt LB2 was used as PC / DMC (1:
It was dissolved in the solvent A of 2). As a result, LB2 also dissolved well above 1.2M and gave a maximum conductivity of 5.8 mS / cm at 0.6M. Thus, it was found that the lithium salt LB2 of the present invention improved the protein solubility 12 times or more, and the conductivity also 13.4 times.

As Example 9, lithium salt LB3 was used as PC / DMC (1:
It was dissolved in the solvent A of 2). As a result, LB2 also dissolved well above 1.2 M and gave a maximum conductivity of 4.3 mS / cm at 0.5 M. As described above, it was found that the lithium salt LB2 of the present invention improved the solubility 12 times or more and the conductivity up to 10 times.

As Example 10, lithium salt LB4 was used as PC / DMC.
It was dissolved in solvent A of (1: 2). As a result, LB4 was dissolved up to O.1M and gave a conductivity of O.02mS / cm.

In Example 11, lithium salt LB5 was used as PC / DMC.
It was dissolved in solvent A of (1: 2). As a result, LB5 dissolved well above 1.2M and gave a maximum conductivity of 6.2mS / cm at 0.8M. As described above, it was found that the lithium salt LB5 of the present invention improved the solubility 12 times or more and the conductivity up to 14.4 times.

As described above, by forming a single bond with oxygen as a bond with the boron ion, the lithium salt of the present invention could achieve high solubility and conductivity.

(Comparative Examples 2-5, Examples 12-14) Solubility in Fluorine-Based Solvents and Conductivity Nonflammable Solvent Nonafluorobutyl Methyl Ether
(Trademark: HFE7100) and dimethyl carbonate are mixed in a mixed solvent (hereinafter, referred to as solvent B) mixed at a volume ratio of 80 (HFE7100): 20 (DMC), which is a composition with no flash point, and lithium is used as Comparative Example 2. As bissalicylate borate, lithium bisbenzenediolate was dissolved in solvent B as Comparative Example 3. As a result, in both Comparative Examples 2 and 3, O.05M was not dissolved, and the electrical conductivity could not be measured.

Further, as Comparative Example 4, LiBF ₄ was used, and Comparative Example 5
As a solution, LiN (S0 ₂ CF ₃ ) ₂ was dissolved in the solvent B. as a result,
In Comparative Example 4, the solvent was phase-separated into two layers when LiBF ₄ was dissolved in O.1M, and the conductivity could not be measured. Comparative Example 5 dissolved well above 1M and gave a maximum conductivity of 0.69 mS / cm at a concentration of 1M.

Next, LB1 as Example 12 and Example 1
LB2 as 3 and LB5 as Example 14 were dissolved in the solvent B. As a result, in Example 12, LB1 was dissolved well at 1.2 M or more, and the maximum conductivity was 1.55 mS / cm at 0.8 M. That is, by using LB1, the conductivity is changed to LiN (S0 ₂ CF ₃ ) ₂
It was possible to improve 2.2 times compared with the case of using (Comparative Example 5). The LB2 of Example 13 also dissolved well above 1.2 M and gave a maximum conductivity of 1.7 mS / cm at 0.6 M. By using LB2, the conductivity in the case of using LiN (S0 ₂ CF ₃ ) ₂ (Comparative Example 5) was 2.
It could be improved by 4 times. LB5 of Example 14 also dissolved well at 1.2 M or more and gave a maximum conductivity of 1.8 mS / cm at 0.6 M. In LB5, it was possible to improve the conductivity by 2.6 times as compared with Comparative Example 5 when LiN (S0 ₂ CF ₃ ) _{2 was} used.

As described above, the organic lithium borate compound of the present invention has a small dipole moment, is well dissolved in a mixed solvent containing a large amount of a fluorinated solvent having a low dielectric constant, and is well known in the prior art. It was found that higher conductivity can be obtained at a lower concentration as compared with the known organic lithium salt. That is, if the organic lithium borate of the present invention is used, the cost can be reduced by reducing the amount of the lithium salt used,
In addition, it is possible to obtain an electrolytic solution having high characteristics.

Comparative Example 6, Examples 15 to 18 Measurement of Aluminum Anodizing Current As Comparative Example 6, a nonaqueous electrolytic solution was prepared by dissolving LiN (S0 ₂ CF ₃ ) ₂ in solvent A at 0.7 M. As Example 15, LB1 was added to solvent A
The non-aqueous electrolyte solution containing O.7M was added to solvent A as Example 16
A non-aqueous electrolyte solution containing B2 as an O.7M solvent was used as a solvent in Example 17.
A non-aqueous electrolyte solution in which LB3 was dissolved in 0.7 M in A was prepared, and a non-aqueous electrolyte solution in which LB5 was dissolved in Solvent A in 0.7 M was prepared as Example 18. The following evaluations were performed in order to evaluate the corrosiveness of aluminum with anions using these electrolytic solutions.
A cell was fabricated using aluminum for the working electrode and lithium metal for the counter electrode and the reference electrode, and aluminum was used for 4.OV (vs. Li).
The current value after 10 minutes when the potential was kept at (metal) was evaluated.

As a result, in Comparative Example 6, a high current of 18 mA / cm ₂ was observed. Furthermore, the surface of the aluminum turned black after continuing this test for 1 h. In contrast, the oxidation current value in Example 15 to 10 .mu.A / cm _2, to 5 .mu.A / cm ² in Example 16, in 5 .mu.A / cm ₂ in Example 17, in 5 .mu.A / cm ₂ in Example 18, respectively Fell. In addition, no change in the appearance of the aluminum surface was observed in any of the samples after continuing this test for 1 hour.

As described above, by using the organic lithium borate of the present invention, the anodic oxidation of aluminum even at a high potential of 4 V was compared with that of LiN (S0 ₂ CF ₃ ) ₂ of Comparative Example. It was found that the value was reduced to 1/1800 in Example 15 and to 1/3600 in Examples 16, 17 and 18. Thus, the organic lithium borate of the present invention can be used to provide an electrolytic solution having high solubility, good conductivity, and suppressed corrosion of an aluminum current collector.

Comparative Example 7, Examples 19 to 22 Evaluation of Oxidative Decomposition Potential As a comparative example 7, PC which is a solvent having high oxidation resistance was used.
LiN (S0 ₂ CF ₃ ) ₂ 1 M dissolved non-aqueous electrolyte, Example 19
As a non-aqueous electrolytic solution in which 1 M of LB1 is dissolved, as Example 20 L
Non-aqueous electrolyte solution in which B2 is dissolved by 1M, and LB3 is prepared by 1M as Example 21
A non-aqueous electrolyte solution was prepared. As Example 22, a non-aqueous electrolyte solution was prepared by dissolving 1 M of LB5. The oxidative decomposition potentials of these non-aqueous electrolyte solutions were compared by the following method.
Using an electrochemical cell using platinum as the working electrode and lithium as the counter electrode and the reference electrode, the potential sweep rate was set to 10 mV / sec, and the oxidation current with respect to the potential was measured. The measurement result is shown in FIG.
For LiN (S0 ₂ CF ₃ ) _{2 of} Comparative Example 7, a large change in oxidation current was observed from 5.8V. In contrast, in Example 19,
6.7V for LB1 and 6.5V for LB2 of Example 20
No large oxidation current was observed up to 6.4 V in LB3 and 6.8 V in LB5 of Example 22. That is, LB1 is 0.9V, and LB2 is
O.7V, LB3, O.6V, and LB5, 1V, improved oxidation resistance by 1V.

As described above, the acetate-substituted lithium salt having boron as the anion center element of the present invention has good solubility, high conductivity, does not corrode aluminum, and has an oxidation potential. It has been found that the material has high characteristics and is suitable as a supporting electrolyte for a high capacity, high operating voltage lithium secondary battery.

(Comparative Example 8, Example 23) Withstand voltage characteristics of ammonium salt As Comparative Example 8, tetraethylammonium tetra was added to PC.
Fluoroborate ((CH_ThreeCH_Two)_FourNBF_Four) 1M dissolved non-water
An electrolytic solution was prepared. As Example 23, tetraethyl was added to the PC.
Lumonium tetrakis (trifluoroacetate)
Rate ((CH_ThreeCH _Two)_FourNB (0C0-CF_Three)_Four) 1M dissolved non-water
An electrolytic solution was prepared. Using these electrolytes, the working electrode
Using an electrochemical cell using Li for Pt, counter electrode and reference electrode
For cyclic voltammetry under the condition of sweep speed 10 mV / sec
The potential window was evaluated more. As a result, in Comparative Example 8, 1V to 5.
While it was 5 V, in Example 23 it was 1 V to 6 V,
The O.5V potential window became higher on the oxidation side.

Thus, even in the case of ammonium salt, the performance of the non-aqueous electrolyte can be improved by adopting the anion structure of the present invention. Since the capacity of the electric double layer capacitor is determined in proportion to the square of the withstand voltage characteristic V1 of the electrolytic solution, it is about 1.2 by using the ammonium salt of the present invention.
Doubled capacity can be expected.

Comparative Example 9 High Temperature Storage Characteristics of Lithium Secondary Battery In order to compare and evaluate the storage characteristics at high temperature, a cylindrical lithium secondary battery having a structure shown in FIG. 6 was produced by the method described below. Artificial graphite is used as the negative electrode active material, PVDF is used as the binder, and these are mixed at a ratio of 91: 9 by weight to be a solvent.
It was dissolved in N-methylpyrrolidone (hereinafter referred to as NMP) and kneaded to obtain a paste of negative electrode material. This is applied to both sides of the copper foil used as the negative electrode current collector 1, dried, heated and pressed, and then vacuum dried to form the negative electrode layer 2 on both sides of the negative electrode current collector 1 to obtain a negative electrode. It was

Lithium cobalt oxide was used as the positive electrode active material, graphite carbon was used as the conductive agent, and PVDF was used as the binder, and these were mixed at a ratio of 85: 7: 8 by weight to form NMP as a solvent. It was melted and kneaded to obtain a paste of positive electrode material.
This is applied to both sides of the aluminum foil used as the positive electrode current collector 3, dried, heated and pressed, and then vacuum dried to form a positive electrode current collector.
A positive electrode layer 4 was formed on both surfaces of 3 to obtain a positive electrode.

After attaching the negative electrode lead 5 and the positive electrode lead 6 made of nickel foil to the uncoated portions of the negative electrode and the positive electrode by electric welding, respectively, these electrodes are sandwiched by the separators 7 and wound, and the outermost separator is taped. It was fixed with and the electrode group was formed. This electrode group is inserted into a stainless steel outer can 10 through a polypropylene insulator 8 for insulation with the negative electrode lead 5 as the can bottom, and the outer can 10 and the negative electrode lead 5 are electrically welded at a low can to form a negative electrode circuit. Was formed. Positive lead 6
Was electrically welded to the positive electrode cap 12 through the positive electrode insulator 9. As electrolyte, ethylene carbonate (EC)
A solution was prepared by dissolving LiN (S0 ₂ CF ₃ ) ₂ at a concentration of 1M (mol / dm ⁻³ ) in a solvent prepared by mixing 1: 1 and dimethyl carbonate (DMC) in a volume ratio of 1: 2 (hereinafter, the electrolytic solution composition is 1 MLiN. (S0 ₂ CF ₃ ) ₂ E
It is shown as C / DMC (1/2 volume ratio). ). About 4 m1 of this electrolytic solution was injected from the opening of the negative electrode outer can 10 of the battery prepared earlier, and then the positive electrode cap 12 provided with the gasket 11 and the negative electrode outer can 10 were mechanically caulked and used for Comparative Example 1. A cylindrical lithium secondary battery (cobalt type battery) was produced.

This battery has a constant current value of 1 A and a constant voltage of 4.2 V.
Then, the battery was charged at a constant current and a constant voltage with a charge end condition of 20 mA, and discharged at a current value of 1 A with a discharge end voltage of 3 V.
The discharge capacity at this time (hereinafter referred to as "initial capacity") is 1510.
It was mAh. Next, set this battery at a constant current value of 1 A and a constant voltage of 4.2 V, and set the constant charge constant voltage to 20 for the charge termination condition.
Charged as mA. This battery was left in a charged state in an environment of 60 ° C. for 20 days. After that, remove this battery from the test tank, leave it at room temperature for 1 day, discharge it once with a constant current of 1 A to 3 V, and then with a constant current of 1 A and a final current of 20 mA, a 4.2 V condition.
The discharge capacity when the battery is charged with a constant voltage at 3 V and discharged at a constant current of 1 A up to 3 V is an index of storage characteristics (hereinafter referred to as "recovery capacity").
Evaluated as. The recovery capacity of the battery of Comparative Example 9 is 1020 mAh
Met. Therefore, the capacity maintenance ratio for the initial capacity of 1510 mAh was 67%.

(Example 24) 1 M LBl EC / DM in a non-aqueous electrolyte
Example 2 was performed in the same manner as Comparative Example 9 using C (1/2 volume ratio).
4 was produced. The initial capacity of this battery evaluated in the same manner as in Comparative Example 9 was 1610 mAh. In addition, the recovery capacity of this battery was 1420 mAh, which was 400 mAh higher than that of Comparative Example 9 even after the high temperature storage. Furthermore, the capacity retention rate of this battery was 87%, which was 20% higher than that of Comparative Example 9.

(Example 25) 1 M LB2 EC / DM in a non-aqueous electrolyte
Example 2 was performed in the same manner as Comparative Example 9 using C (1/2 volume ratio).
5 was produced. The initial capacity of this battery evaluated in the same manner as in Comparative Example 9 was 1590 mAh. The recovery capacity of this battery was 1380 mAh, which was higher than that of Comparative Example 9 by 360 mAh, which was higher than the recoverable capacity after high-temperature storage. Further, the capacity maintenance ratio of this battery was 86%, which was improved by 19% as compared with Comparative Example 9.

(Example 26) 1 M LB5 EC / DM in a non-aqueous electrolyte
Example 2 was performed in the same manner as Comparative Example 9 using C (1/2 volume ratio).
6 was produced. The initial capacity of this battery evaluated in the same manner as in Comparative Example 9 was 1620 mAh. The recovery capacity of this battery was 1390 mAh, which was higher than that of Comparative Example 9 by 370 mAh, which was higher than the recoverable capacity after high temperature storage. Further, the capacity retention rate of this battery was 85%, which was 18% higher than that of Comparative Example 9.

(Comparative Example 10) 1M LiPF ₆ EC / as an electrolyte
Comparative Example 1 using DMC (1/2 volume ratio) in the same manner as Comparative Example 9
0 batteries were made. The initial capacity of this battery was 1650 mAh. The recovery capacity of this battery was 1390 mAh and the capacity retention rate was 85%.

(Example 27) 2% by weight of LB1 was further dissolved in 1M LiPF ₆ EC / DMC (1/2 volume ratio) to prepare an electrolytic solution of Example 27. A battery of Example 27 was produced using this electrolytic solution. The initial capacity of this battery was 1640 mAh. Also,
The recovery capacity of this battery is 1430 mAh, which is 40 m compared to Comparative Example 10.
Ah also had a higher recoverable capacity after high temperature storage. Furthermore,
The capacity retention rate of this battery was 87%, which was 2% higher than that of Comparative Example 10.

Example 28 An electrolyte solution of Example 28 was prepared by further dissolving 2% by weight of LB2 in 1M LiPF ₆ EC / DMC (1/2 volume ratio). A battery of Example 28 was produced using this electrolytic solution. The initial capacity of this battery was 1630 mAh. Also,
The recovery capacity of this battery is 1410 mAh, which is 20 m compared to Comparative Example 10.
Ah also had a higher recoverable capacity after high temperature storage. Furthermore,
The capacity retention rate of this battery was 86%, which was an improvement of 1% as compared with Comparative Example 10.

(Example 29) 2% by weight of LB5 was further dissolved in 1M LiPF ₆ EC / DMC (1/2 volume ratio) to prepare an electrolytic solution of Example 29. A battery of Example 29 was produced using this electrolytic solution. The initial capacity of this battery was 1660 mAh. Also,
The recovery capacity of this battery is 1450 mAh, which is 60 m compared to Comparative Example 10.
Ah also had a higher recoverable capacity after high temperature storage. Furthermore,
The capacity retention rate of this battery was 87%, which was 2% higher than that of Comparative Example 10.

Example 30 An electrolyte solution of Example 30 was prepared by further dissolving 2% by weight of LB1 and 2% by weight of vinylene carbonate in 1M LiPF ₆ EC / DMC (1/2 volume ratio). A battery of Example 30 was produced using this electrolytic solution. The initial capacity of this battery was 1640 mAh. Also, the recovery capacity of this battery is 1
At 460 mAh, the recoverable capacity after high temperature storage was 70 mAh higher than that of Comparative Example 10. Further, the capacity maintenance ratio of this battery was 89%, which was 4% higher than that of Comparative Example 10.

COMPARATIVE EXAMPLE 11 1M LiN (S0 ₂ C
A battery of Comparative Example 11 was produced in the same manner as in Comparative Example 9 using F ₃ ) ₂ HFE7100 / DMC (8/2 capacity ratio). The initial capacity of this battery was 1570 mAh. Also, the recovery capacity of this battery is 1
The capacity retention rate was 110 mAh and 70%.

(Example 31) 1 M LB1 HFE71 as electrolyte
A battery of Example 31 was made in the same manner as Comparative Example 9 using 00 / DMC (8/2 capacity ratio). The initial capacity of this battery is 1610mA
It was h. The recovery capacity of this battery was 1330 mAh, and the capacity retention rate was 82%.
12% improvement in mAh and capacity retention rate.

(Example 32) 1 M LB2 HFE71 as an electrolyte
A battery of Example 32 was made in the same manner as Comparative Example 9 using 00 / DMC (8/2 capacity ratio). The initial capacity of this battery is 1620mA
It was h. The recovery capacity of this battery was 1350 mAh, and the capacity retention rate was 83%.
mAh and capacity retention rate improved by 13%.

(Example 33) 1M LB5 HFE71 as electrolyte
A battery of Example 33 was made in the same manner as in Comparative Example 9 using 00 / DMC (8/2 capacity ratio). The initial capacity of this battery is 1630mA
It was h. The recovery capacity of this battery was 1350 mAh, and the capacity retention rate was 82%.
12% improvement in mAh and capacity retention rate. As described above, by using the organic lithium borate of the present invention as the supporting electrolyte, the reliability for high temperature storage in a charged state is dramatically improved. It is considered that this is because the oxidation resistance was improved, and thus the acceleration of the decomposition reaction of the anion at a high potential due to temperature was suppressed.

(Embodiment 34) FIG. 7 is a diagram showing a drive system configuration of an electric vehicle using the lithium secondary battery described in Embodiments 24 to 33.

When the key switch is turned on and the accelerator is depressed, the torque or rotation of the electric motor is controlled in accordance with the accelerator depression angle, as in a normal gasoline vehicle. When the accelerator is released, the regenerative brake equivalent to the engine brake is operated, and when the brake is depressed, the regenerative braking force is further increased. The shift lever signal is used to switch the vehicle between forward and reverse, and the gear ratio is always constant. As the control method, the IGBT vector control inverter method using an induction motor is adopted, and the power supply voltage is set to 336V from the IGBT withstand voltage. In this embodiment, the output is the maximum from the power performance (acceleration / hill climbing performance) of the vehicle. The output was 45 kW, the maximum torque was 176 N · m, and the rated output was 30 kW from the maximum speed specifications. As the main control items, in addition to forward and reverse control of the vehicle, regenerative control,
Fail-safe control is performed.

Since heat density increases as the electric motor becomes smaller and lighter, it is important to have an efficient cooling structure. Since the temperature rise of the electric motor is high in the general air-cooled type, we used the water-cooled type like the general engine. The cooling water passage was provided in an aluminum frame that covers the main body of the electric motor, and the shape was optimized by a temperature rise simulation. The cooling water flows in from the water supply port of the water passage of the frame, absorbs the heat of the electric motor body, is then discharged, and is cooled by the radiator in the circulation path. By adopting such a water cooling structure, the cooling performance could be improved about three times as much as the air cooling.

In the inverter, an IGBT is used as a power element, and the maximum output is about several kilowatts of heat. In addition to this, heat is also generated from surge absorption resistors, filter capacitors, etc., and it is necessary to keep these parts below the allowable temperature and to cool them efficiently. In particular, the cooling of the IGBT is a problem, and the cooling method may be air cooling, water cooling, oil cooling, or the like. Here, the forced water cooling system is used because it is easy to handle and allows efficient cooling.

The protection circuit shown in the figure is formed in a lithium secondary battery as a power source in Examples 31 to 33. The protection circuit protects the battery from overcharging and overdischarging. The protection circuit is composed of a balance compensation circuit for adjusting the cell voltage of each battery as shown in FIG. 8, and is provided for each battery. This balance compensation circuit is controlled by a microcomputer. In a conventional lithium secondary battery, since the electrolyte has flammability, a thermistor is provided in each battery to detect temperature or pressure,
Although it was monitored by this, in Examples 31 to 33, since the flame does not have a flash point that does not transfer to the liquid even if the fire point is brought close to the electrolyte, it is a non-combustible one, so that the special temperature or It does not require pressure monitoring. As a result, the safety mechanism can be reduced as a protection circuit. As shown in FIG. 7, the power supply can be opened and closed automatically when over-discharge is detected.

Although this embodiment shows an example using an induction motor, the same applies to an electric vehicle using a permanent magnet type synchronous motor and a DC shunt winding motor as shown in FIG. It can be used. INV (In
verter: Inverter), IM (Induction Motor: Induction motor), E (Encoder: Encoder), SM (Synchron)
us Motor: Synchronous motor, PS (Position Sensor: Position detector), PWM (Pulse Width Modulation: pulse width modulation), DCM (DC Motor: DC motor), CH (Chop
per: chopper), N ^* : speed command, T ^* : torque command. In the figure, each paragraph shows the control method, system configuration, and main control parameters.

(Embodiment 35) FIG. 10 shows Embodiments 31 to 33.
FIG. 3 is a configuration diagram showing a power storage system for nighttime power using the lithium secondary battery described in FIG. This example of the power storage system is an example in which the battery capacity is 2000 kW × 4 h, the cell capacity is 1000 Wh, and 360 batteries are connected in series and 24 columns are connected in parallel. Also in this embodiment, it is necessary to protect the battery from overcharge and overdischarge as in the case of the 33rd embodiment, and the protection circuit shown in FIG. 8 has a monitoring / balance compensating circuit.
In this embodiment as well, the battery is protected as described above.

Although this embodiment is intended to store a large amount of electric power, it is also effective for a home air conditioner, an electric water heater, and the like.

[0073]

As described above in detail, in the organic lithium borate of the present invention, tetravalent boron is used as the anion center, and further the electron withdrawing property and the molecular size of the functional group bonded to this are devised. Thus, a low dipole moment like a non-flammable fluorinated solvent, the solubility in a solvent having a low dielectric constant can be improved, and the conductivity of this solution can be improved,
It was possible to provide an effective non-aqueous electrolyte solution for lithium secondary batteries and electrochemical capacitors. Further, the problems of corrosiveness and oxidation resistance of aluminum, which have been problems with conventional organic lithium salts, can be solved by using the organic lithium borate of the present invention as a supporting electrolyte. In addition, since the oxidation resistance is improved, the storage characteristics of the lithium secondary battery at high temperature can be improved.

Particularly, a mixed solvent containing a large amount of a fluorinated solvent
Also, the concentration is 0.8 mol · dm ^-3Can dissolve more than
0.4 mol · dm^-3Conductivity at low concentration
It is possible to obtain the non-aqueous electrolytic solution exhibiting the highest value.

Furthermore, according to the present invention, a lithium secondary battery for consumer use can be essentially made non-flammable to a large capacity lithium secondary battery for power storage use or electric vehicle use, and reliability is drastically improved. It is possible to provide a lithium secondary battery according to various highly versatile applications. Furthermore, in order to secure the safety of this battery conventionally, further weight reduction and size reduction can be expected. It is possible to achieve a remarkable effect in which the protection mechanism inside the battery and the protection circuit provided outside are not reduced or the battery that does not have the battery is provided. In addition, since the electrolyte is non-flammable, the restrictions on the amount of electrolyte that can be stored at the manufacturing site are relaxed, so a larger amount of electrolyte can be stocked for manufacturing than at present, and manufacturing adjustments can be made. There is also a merit that it will spread to inventory adjustments.

[Brief description of drawings]

FIG. 1 is an infrared absorption spectrum of an example of the present invention.

FIG. 2 is an infrared absorption spectrum of an example of the present invention.

FIG. 3 is an infrared absorption spectrum of an example of the present invention.

FIG. 4 is an infrared absorption spectrum of an example of the present invention.

FIG. 5 is a cathode polarization curve.

FIG. 6 is a cross-sectional view of a cylindrical lithium secondary battery showing an embodiment of the present invention.

FIG. 7 is a configuration diagram of a drive system of an electric vehicle according to the present invention.

FIG. 8 is a protection circuit diagram according to the present invention.

FIG. 9 is a control system diagram of the electric vehicle according to the present invention.

FIG. 10 is a diagram of an electric power storage system according to the present invention.

[Explanation of symbols]

1 ... Negative electrode current collector, 2 ... Negative electrode layer, 3 ... Positive electrode current collector, 4 ... Positive electrode layer, 5 ... Negative electrode lead, 6 ... Positive electrode lead, 7 ... Separator,
8, 9 ... Insulator, 10 ... Exterior can, 11 ... Gasket,
12 ... Positive electrode cap.

─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Mitsuru Kobayashi 7-1-1 Omika-cho, Hitachi-shi, Ibaraki Hitachi Research Laboratory, Hitachi Ltd. (72) Inventor Hiroyuki Yamaguchi 1-7-1 Inari, Soka-shi, Saitama No. Kanto Chemical Co., Ltd. Central Research Laboratory (72) Inventor Hideki Takahashi 1-7-1 Inari, Soka City, Saitama Prefecture Kanto Chemical Co., Ltd. Central Research Laboratory (72) Inventor Katsushi Kato 1-7-1 Inari, Soka City, Saitama Prefecture No. Kanto Chemical Co., Ltd. Central Research Laboratory (56) Reference JP-A-8-196911 (JP, A) JP-A-10-45873 (JP, A) JP-A-8-295721 (JP, A) JP-A-9 -176283 (JP, A) JP-A-3-129717 (JP, A) JP-A 2001-181282 (JP, A) JP-A 2002-167390 (JP, A) JP-A 2002-138092 (JP, A) JP-A 2002-13 8091 (JP, A) JP 2001-261684 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C07F 5/00 H01G 9/00 H01M 10/00 CA (STN) REGISTRY ( STN)

Claims (11)

(57) [Claims] 1. A general formula (1): [However, X is ^{lithium, R 1, R 2, R} 3, R 4 each independently represents a halogen atom-substituted alkyl group having 1 to 4 carbon atoms and] organic characterized by being represented by Lithium borate
Compound-free. 2. The method according to claim 1, wherein the R ¹ , R ² , R ³ and
R ⁴ is a trifluoromethyl group or a pentafluoroethyl group, a lithium organic borate compound characterized by the above-mentioned. 3. A general formula (1): [However, X is any of lithium, quaternary ammonium and quaternary phosphonium, and R ¹ , R ² , R ³ and R ⁴ each independently represent a halogen atom-substituted alkyl group having 1 to 4 carbon atoms] A non-aqueous electrolytic solution comprising an organic borate compound represented by and a solvent. 4. The method according to claim 3, wherein the R ¹ , R ² , R ³ and
A non-aqueous electrolytic solution in which R ⁴ is a trifluoromethyl group or a pentafluoroethyl group. 5. The non-aqueous electrolyte solution according to claim 3, wherein the solvent comprises at least one of cyclic carbonate, chain carbonate and ether. 6. The non-aqueous electrolytic solution according to claim 3, wherein the solvent is at least one selected from ethylene carbonate, propylene carbonate, dimethyl carbonate, ethylmethyl carbonate and dimethoxyethane. 7. The non-aqueous electrolytic solution according to claim 3, which contains a fluorinated solvent. 8. The non-aqueous electrolyte solution according to claim 7, wherein the fluorine solvent is at least one of perfluorobutyl methyl ether, perfluorobutyl ethyl ether and methyl perfluoroalkyl ether. 9. A non-aqueous electrolyte solution according to claim 3, which contains an inorganic lithium salt. 10. The inorganic lithium salt according to claim 9, wherein LiPF ₆ , LiBF ₄ , LiCl, LiF and Li.
A non-aqueous electrolytic solution comprising one or more of Br and LiI. 11. A lithium secondary battery comprising a negative electrode capable of occluding / releasing lithium, a positive electrode capable of occluding / releasing lithium, a separator and a non-aqueous electrolytic solution, wherein the non-aqueous electrolytic solution comprises 10. A lithium secondary battery comprising the non-aqueous electrolyte solution according to any one of 10.