JP2002193973A - New organic borate compound, and nonaqueous electrolyte and lithium secondary battery using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an organic borate compound which has high solubility in a solvent with low permittivity and realizes high conductivity, a nonaqueous electrolyte in which the organic borate compound is dissolved, a lithium secondary battery having an improved stability at high temperature, electrical equipment in which a protection circuit may be omitted and other uses. SOLUTION: The organic borate compound is represented by formula (1) [wherein, X is Li, a quaternary ammonium group, or a quaternary phosphonium group; R1, R2, R3 and R4 are each independently a 1-4C halogenated alkyl group, a trifluoromethyl group, or a pentafluoroethyl group.]. The lithium secondary battery using the organic borate compound shows low decrease in recovery capacity at high temperature, and can be used in protection-circuit-free electrical equipment and for other uses.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel organic borate compound, a non-aqueous electrolyte using the same, a lithium secondary battery using the same, and electric equipment. The present invention relates to a novel organic borate, a non-aqueous electrolyte having improved oxidation resistance by using the same, a lithium secondary battery and an electric device having improved cycle life using the same, and various uses.

[0002]

2. Description of the Related Art A lithium secondary battery comprising a positive electrode and a negative electrode capable of occluding and releasing lithium and a non-aqueous electrolyte has a high energy density per weight and volume and a high voltage. It is expected to be used as a source of power. Since a lithium secondary battery has a high driving voltage of 3 V or more, a nonaqueous electrolyte having a wide withstand voltage range is used. As compared with the aqueous electrolyte, the non-aqueous electrolyte has problems of low electric conductivity and many organic solvents suitable for the non-aqueous electrolyte have high flammability (or low flash point).

[0003] Therefore, a study of improving the load characteristics of a battery by improving the conductivity (eg, the 40th Battery Symposium, Proceedings, p.4)
53, 455, (1999)), Research on using nonflammable or low flammable organic solvents for non-aqueous electrolytes (e.g., The 40th Battery Symposium, Proceedings, P.459 (1999)) Is being done. In order to improve the conductivity, it is necessary to improve the dissociation of the supporting electrolyte or to select an organic solvent capable of increasing the dissociation of the supporting electrolyte. As for 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.

[0004] Among them, bis shown in JP-A-5-326018 (trifluoromethanesulfonyl) imide lithium _{(LiN [S0 2 CF 3]} 2) , to the non-aqueous electrolyte solvent as compared with an inorganic electrolyte It is known as a promising material having 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.

JP-A-7-65843 discloses an organic lithium salt having boron as a central ion and disalicylate as a ligand. JP-A-7-65843 discloses a ligand having boron as a central ion and a ligand as a ligand. Discloses an organic lithium salt having a benzenediolate derivative. However, since these compounds have a benzene ring in the molecule, they have poor solubility, and their electrical conductivity and oxidation resistance are not satisfactory.

[0006] As a solvent for making a substance nonflammable or flame retardant, an example using a fluorinated solvent as disclosed in JP-A-9-97627 and JP-A-10-12272 is effective. However, the fluorinated solvent has a problem that the electron donating property of the functional group is reduced due to the high electron withdrawing property of fluorine, and the solubility and dissociation of the lithium salt are reduced. Organic lithium salts have better solubility than inorganic lithium salts and are effective materials. For these reasons, improvement of organic lithium salts as a promising material for improving the safety and performance of lithium secondary batteries has been desired.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an organic boric acid which can realize a non-aqueous electrolyte having a high electric conductivity and which does not deteriorate even in a non-aqueous electrolyte mixed with a nonflammable fluorinated solvent. A non-aqueous electrolyte that can improve the characteristics of a lithium secondary battery or an electrochemical capacitor by using a salt compound and a lithium secondary battery with good life performance using this non-aqueous electrolyte, an electric device, and various uses. To provide.

[0008]

SUMMARY OF THE INVENTION The conductivity is determined by the number of lithium ions and their mobility. Further, it is considered that the solubility depends on the radius of the ions surrounding the solvent. Thus, the present inventors have made it possible to suppress local aggregation of the solvent by increasing the anion of the organic lithium salt and delocalizing the charge of the ion, and also increase the affinity between the anion and the solvent. By introducing a functional group capable of increasing the electron-withdrawing property of an element into an anion, it is thought that a lithium salt having high dissociation and good solubility can be obtained. Was completed.

That is, the present invention provides a compound represented by the general formula (1):

Embedded image [Where X is any one 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] An organic borate compound represented by the formula:

The organic borate represented by the general formula (1) is a novel compound, has excellent solubility in non-aqueous solvents, 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 can delocalize the electric charge to the carbonyl group, to boron, which is the central element of the anion, the ionic radius of the anion is increased and the anion charge is delocalized And increased the solubility. Therefore, the electrolyte using this supporting electrolyte has a small dipole moment, a low dielectric constant,
Nonflammable fluorinated solvents and the like can also be used. Also,
Unlike imide-based organic salts, this compound does not corrode the aluminum current collector because the central ion is surrounded by ligands.

In an embodiment of the present invention, an organic boric acid
The salt compound has a chemical structure represented by the general formula (1)
Therefore, in the general formula (1), X is lithium or tet
Represents laethylammonium;¹, R^Two, R^Three, R^FourIs each
Each independently a halogen-substituted alkyl group having 1 to 4 carbon atoms
It is. From the viewpoint of molecular weight and oxidation resistance, R¹, R^Two,
R ^Three, R^FourIs a trifluoromethyl group or pentaflu
Oroethyl groups are preferred.

The organic borate of the present invention is soluble in a cyclic carbonate such as ethylene carbonate or propylene carbonate, a chain carbonate such as dimethyl carbonate or ethyl methyl carbonate, or a polyester such as dimethoxyethane. And a non-aqueous electrolyte using these solvents alone or as a mixture can be obtained. Further, in the general formula (1), R ^1,
Compounds in which R ² , R ³ , and R ⁴ are fluorinated alkyl groups or partially fluorinated alkyl groups are nonaqueous solvents and nonflammable fluorinated solvents such as nonafluorobutyl methyl ether 1.8 mol 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 having a solubility of 1 · dm ⁻³ or more and high conductivity can be obtained. Furthermore, the electrolytic solution prepared by dissolving the lithium organic borate of the present invention does not corrode aluminum, and has an oxidative decomposition potential of about 5 V (vs. Li metal) or more, and has a wide potential use range.

Specific examples of the organic borate of the present invention include, for example, lithium tetrakis (trifluoroacetate) borate, lithium tetrakis (difluoroacetate) borate, lithium tetrakis (fluoroacetate) borate, and 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 (2,2-bistrifluoromethylpropanoate) borate, tetraethylammonium tetrakis (trifluoroacetate) borate, lithium Tetrakis (difluoroacetate) borate, tetraethylammoniumtetrakis (fluoroacetate)
Borate, tetraethylammonium tetrakis (chlorodifluoroacetate) borate, tetraethylammonium tetrakis (trichloroacetate) borate,
Tetraethylammonium tetrakis (dichloroacetate) borate, tetraethylammonium tetrakis
(Pentafluoropropanoate) borate, tetraethylammonium tetrakis (3-chlorotetrafluoropropanoate) borate, tetraethylammonium tetrakis (heptafluorobutanoate) borate, tetraethylammonium tetrakis (2,2-bistrifluoromethylpropanoate) ) Borate, triethylmethylammonium tetrakis (trifluoroacetate) borate, tetraethylphosphoniumtetrakis (trifluoroacetate) borate, triethylmethylphosphoniumtetrakis (trifluoroacetate) borate and the like.

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

Embedded image Can be synthesized through the following process.

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 in the case of synthesizing the organic lithium borate of the present invention, and the synthesis process is not limited to the above process. Further, by using a quaternary ammonium carboxylate or a quaternary phosphonium carboxylate in place of lithium carboxylate, the organic ammonium borate or phosphonium borate 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, methyl propyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, trifluoropropylene carbonate, and chlorocarbon. Ethylene carbonate, vinylene carbonate, cyclic carbonates such as dimethylvinylene carbonate, γ-butyrolactone, cyclic esters such as valerolactone, 1,3-dioxolane,
A cyclic ester such as tetrahydrofuran can be used alone or as a mixture.

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 a supporting salt,
LiN the (S0 ₂ CF _{3) 2} or the like as a main supporting salt, it is possible to use tetra haloacetate borate of the invention as an additive.

For the positive electrode of a lithium secondary battery, a lithium composite oxide of a transition metal such as cobalt, nickel or manganese capable of inserting and extracting lithium can be used. For the negative electrode, lithium metal, graphite and non-metal which can insert and extract lithium can be used. High quality carbon materials, oxides of silicon and tin, and composites of these with carbon can be used.

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

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to embodiments, but the present invention is not limited to the embodiments.

Example 1 Synthesis and identification of lithium tetrakis (trifluoroacetate) borate (hereinafter referred to as LB1). To a 300 ml three flask, 4.9 g of boric acid, 9.5 g of lithium trifluoroacetate and 100 ml of dimethyl carbonate were added, and 50 g of trifluoroacetic anhydride was added dropwise with stirring under ice cooling. After the dropwise addition, 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 at a yield of 67%. FIG. 1 shows the infrared absorption spectrum of the obtained compound.

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) In a 1000 ml three-necked flask, 8.8 g of boric acid, 24.2 g of lithium pentafluoropropionate, and carbonic acid were placed. 265 ml of dimethyl was added, and 132.2 g of pentafluoropropionic anhydride was added dropwise while stirring under ice cooling. After the dropwise addition, 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 were dried under reduced pressure,
Lithium tetrakis (pentafluoropropanoate) borate was obtained with a yield of 38%. FIG. 2 shows the infrared absorption spectrum of the obtained compound.

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
Synthesis and identification of LB3 (hereinafter referred to as LB3) 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-necked flask, and 100 g of trichloroacetic anhydride was added dropwise while stirring under ice-cooling. After the dropwise addition, 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 to remove the contained trichloroacetic acid by sublimation.
Subsequently, the crystals were recrystallized from tetrahydrofuran, and the obtained crystals were dried under reduced pressure to obtain lithium tetrakis (trichloroacetate) borate at a yield of 24%. FIG. 3 shows the infrared absorption spectrum of the obtained compound.

Infrared absorption: 1770 cm ^-1 (C = O), 1040 cm ^-1
(CO). ¹¹ B-NMR spectrum (CD ₃ 0D / trimethylborate reference): δ-19.1ppm. 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
In a 00 ml three-neck flask, 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 insolubles, 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 at a yield of 11%. FIG. 4 shows the infrared absorption spectrum of the obtained compound. 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) To a 200 ml three-necked flask, 6.5 g of boric acid, 14 g of lithium chlorodifluoroacetate, and 100 ml of dimethyl carbonate were added. While stirring under ice-cooling, 77 g of chlorodifluoroacetic anhydride was added dropwise. After the addition, 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 ₃ 0D / trimethylborate reference): δ-18.0ppm. 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) 38.1 g of boric acid, 150 g of tetraethylammonium trifluoroacetate and dimethyl carbonate were placed in a 1000 ml three-necked flask. 50
After adding 0 ml, 427 g of trifluoroacetic anhydride was added dropwise while stirring under ice cooling. After the dropwise addition, 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
(Reference): δ 1.28 ppm (tt, CH ₃ , 12H), 3.28 ppm (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) Evaluation of solubility and conductivity Propylene carbonate (hereinafter referred to as PC) as a solvent.
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 bissalicylate 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 the nonaqueous electrolyte at this concentration was 0.43 mS / cm as evaluated by a CM-60S conductivity meter manufactured by Toa Denpa Kogyo Co., Ltd. using a CGT-511B cell.

In Example 7, a lithium salt LB1 was dissolved in a solvent A. As a result, LB1 dissolved better than 1.2M and 0.8M
Gave a maximum conductivity of 7.8 mS / cm. Thus, according to the lithium salt LB1 of the present invention, it was found that the solubility was improved by 12 times or more and the electric conductivity was also improved by 18 times.

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

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

In Example 10, lithium salt LB4 was converted to PC / DMC
It was dissolved in (1: 2) solvent A. As a result, LB4 dissolved up to 0.1M, and gave conductivity of 0.02mS / cm.

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

As described above, the lithium salt of the present invention was able to achieve high solubility and conductivity by making the bond with the boron ion a single bond with oxygen.

(Comparative Examples 2 to 5, Examples 12 to 14) Solubility and Conductivity in Fluorinated Solvent Nonafluorobutyl methyl ether which is a nonflammable solvent
As a comparative example 2, lithium was added to a mixed solvent (hereinafter, referred to as solvent B) in which dimethyl carbonate (trademark: HFE7100) and dimethyl carbonate were mixed at a volume ratio of 80 (HFE7100): 20 (DMC), which is a composition having no flash point. Bis salicylate borate and lithium bisbenzenediolate as Comparative Example 3 were dissolved in solvent B. As a result, in both Comparative Examples 2 and 3, 0.05M was not dissolved, and the electrical conductivity could not be measured.

As Comparative Example 4, LiBF ₄ was used.
LiN the (S0 ₂ CF _{3) 2} were dissolved in a solvent B as. as a result,
In Comparative Example 4, when LiBF ₄ was dissolved in 0.1 M, the solvent was phase-separated into two layers, and the conductivity could not be measured. Comparative Example 5 dissolved well at 1 M or more, and gave a maximum conductivity of 0.69 mS / cm at a concentration of 1 M.

Next, LB1 is used as the twelfth embodiment,
LB2 was dissolved in solvent B as Example 3, and LB5 as Example 14. As a result, in Example 12, LB1 dissolved well at 1.2 M or more, and gave a maximum conductivity of 1.55 mS / cm at 0.8 M. That is, by using LB1, the conductivity is changed to LiN (S0 ₂ CF ₃ ) ₂
Was improved to 2.2 times that in the case of using (Comparative Example 5). LB2 of Example 13 also dissolved well by 1.2 M or more, and gave a maximum conductivity of 1.7 mS / cm at 0.6 M. By using LB2, if the conductivity using LiN (S0 ₂ CF _{3) 2} (Comparative Example 5) 2.
It was able to improve four times. LB5 of Example 14 also dissolved well by 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 2.6 Baishirube conductivity relative to Comparative Example 5 in the case of using _{LiN (S0 2 CF 3) 2} .

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

[0042] (Comparative Example 6, Example 15 to 18) were prepared aluminum anode measured Comparative Example 6 as LiN in solvent A oxidation current (S0 ₂ CF _{3) 2} nonaqueous electrolyte prepared by dissolving O.7M a. Example 15: LB1 in solvent A
A non-aqueous electrolyte solution containing an O.7M solvent was added to solvent A in Example 16 as L.
A non-aqueous electrolyte in which B2 was a 0.7M solvent was used as a solvent in Example 17
A non-aqueous electrolyte prepared by dissolving 0.7 M of LB3 in A was prepared, and a non-aqueous electrolyte prepared by dissolving 0.7 M of LB5 in solvent A as Example 18 was prepared. In order to evaluate the corrosiveness due to aluminum anions using these electrolytic solutions, the following evaluation was performed.
A cell was prepared using aluminum as the working electrode and lithium metal as the counter and reference electrodes, and the aluminum was converted to 4.OV (vs. Li
The current value after 10 minutes when the potential was maintained 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 1 h of this test. 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 Dropped. In addition, no change in the appearance of the aluminum surface was observed in any of the samples after the test was continued for 1 hour.

As described above, by using the lithium organic borate of the present invention, even at a potential as high as 4 V, the anodic oxidation of aluminum is smaller than that of LiN (SO ₂ CF ₃ ) ₂ of the comparative example. 15, it was found to be reduced to 1/1800, and in Examples 16, 17 and 18 to 1/3600. As described above, it is possible to provide an electrolytic solution using the organic lithium borate of the present invention, which has high solubility, good electric conductivity, and suppressed corrosion of the aluminum current collector.

(Comparative Example 7, Examples 19 to 22) Evaluation of Oxidation Decomposition Potential Using PC which is a solvent having high oxidation resistance, Comparative Example 7 was used.
LiN (S0 ₂ CF ₃₎ non-aqueous _{electrolyte 2} was dissolved 1M, Example 19
As a non-aqueous electrolyte in which LB1 was dissolved at 1 M, as Example 20 L
Non-aqueous electrolyte in which B2 was dissolved at 1 M, LB3 was 1 M as Example 21
A dissolved non-aqueous electrolyte, that is, a non-aqueous electrolyte in which 1 M of LB5 was dissolved as Example 22 was prepared. Using these non-aqueous electrolytes, the respective oxidative decomposition potentials were compared by the following method.
Using an electrochemical cell using platinum as the working electrode and lithium as the counter and reference electrodes, the potential sweep rate was 10 mV / sec, and the oxidation current with respect to the potential was measured. FIG. 5 shows the measurement results.
In LiN (S0 ₂ CF _{3) 2} in Comparative Example 7, a large change in oxidation current from 5.8V was observed. On the other hand, in Example 19
LB1 is 6.7 V, LB2 of Example 20 is 6.5 V, and
No large oxidation current was observed up to 6.4 V in LB3 and 6.8 V in LB5 of Example 22. That is, O.9V for LB1, LB2
O.7V and LB3 showed improvement in oxidation resistance of 0.6V and LB5 showed 1V oxidation resistance.

As described above, the acetate-substituted lithium salt containing boron as the anion central 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 lithium secondary battery having a high capacity and a high operating voltage.

(Comparative Example 8, Example 23) Withstand voltage characteristics of ammonium salt
Fluoroborate ((CH₃CH₂)₄NBF₄) In 1M
An electrolyte was prepared. In Example 23, tetraethyl was added to PC.
Luammonium tetrakis (trifluoroacetate)
Rate ((CH₃CH ₂)₄NB (0C0-CF₃)₄) In 1M
An electrolyte was prepared. Using these electrolytes, the working electrode
Using an electrochemical cell with Li for Pt, counter electrode and reference electrode
For cyclic voltammetry at a sweep speed of 10 mV / sec
The potential window was evaluated more. As a result, in Comparative Example 8, 1V to 5.
In contrast to 5 V, in Example 23, it was 1 V to 6 V,
The O.5V potential window was higher on the oxidation side.

As described above, also in the case of the ammonium salt, the performance of the non-aqueous electrolyte can be improved by using the anion structure of the present invention. Incidentally, 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, about 1.2% by using the ammonium salt of the present invention.
Double the capacity can be expected.

Comparative Example 9 High-Temperature Storage Characteristics of Lithium Secondary Battery For comparative evaluation of high-temperature storage characteristics, a cylindrical lithium secondary battery having a structure shown in FIG. 6 was manufactured by the following method. Using artificial graphite as the negative electrode active material, using PVDF as a binder, mixing these in a ratio of 91: 9 by weight, it is a solvent
It was dissolved in N-methylpyrrolidone (hereinafter, referred to as NMP) and kneaded to obtain a paste of a negative electrode material. This was applied to both surfaces 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 layers 2 on both surfaces of the negative electrode current collector 1 to obtain a negative electrode. Was.

Using lithium cobalt oxide as a positive electrode active material, graphite carbon as a conductive agent, and PVDF as a binder, these were mixed at a ratio of 85: 7: 8 by weight, and mixed with NMP as a solvent. The mixture was dissolved and kneaded to obtain a paste of a 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 dried in vacuum to form a positive electrode current collector.
A positive electrode layer 4 was formed on both surfaces of No. 3 to obtain a positive electrode.

After the negative electrode lead 5 and the positive electrode lead 6 made of nickel foil were attached to the uncoated portions of the negative electrode and the positive electrode, respectively, by electric welding, these electrodes were sandwiched between separators 7 and wound, and the outermost separator was taped. To form an electrode group. 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 bottom of the can, 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 electrode lead 6
Was electrically welded to the positive electrode cap 12 via the positive electrode insulator 9. Ethylene carbonate (EC) as electrolyte
And the dimethyl carbonate (DMC) 1: 2 of the mixed solvent at a volume ratio LiN (S0 ₂ CF _{3) 2} was prepared 1M (mol / dm ^-3) dissolved solution (hereinafter, the electrolyte composition 1MLiN (S0 ₂ CF ₃ ) ₂ E
Shown as C / DMC (1/2 volume ratio). ). After about 4 m1 of this electrolyte was injected from the opening of the negative electrode outer can 10 of the battery prepared earlier, the positive electrode cap 12 having the gasket 11 and the negative electrode outer can 10 were mechanically caulked and provided for Comparative Example 1. A cylindrical lithium secondary battery (cobalt-based battery) was produced.

The battery was operated at a constant current of 1 A and a constant voltage of 4.2 V.
The battery was charged at a constant current and a constant voltage at a charge termination condition of 20 mA, and discharged at a current value of 1 A with a discharge termination voltage of 3 V.
The discharge capacity at this time (hereinafter, referred to as “initial capacity”) is 1510
mAh. Next, this battery was set at a constant current value of 1 A, the constant voltage was set to 4.2 V, and the charging termination condition was set to 20 at a constant current constant voltage.
Charged as mA. The battery was left in a charged state at 60 ° C. for 20 days. Thereafter, the battery was taken out of the test tank, left at room temperature for one day, and then discharged once at a constant current of 1 A to 3 V, and further at a constant current of 1 A and a final current of 20 mA at a current of 4.2 V.
The discharge capacity when the battery is charged at a constant voltage and discharged at a constant current of 1 A to 3 V is an index of storage characteristics (hereinafter referred to as “recovery capacity”).
Was evaluated. The recovery capacity of the battery of Comparative Example 9 was 1020 mAh
Met. Therefore, the maintenance ratio of the capacity to the initial capacity of 1510 mAh was 67%.

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

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

Example 26 1M LB5 EC / DM was added to a non-aqueous electrolyte.
Example 2 using C (1/2 capacity ratio) in the same manner as in Comparative Example 9.
No. 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, and the recovery capacity after high-temperature storage was 370 mAh higher than that of Comparative Example 9. 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 /
Comparative Example 1 using DMC (1/2 volume ratio) in the same manner as Comparative Example 9.
No. 0 was prepared. 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 An electrolytic solution of Example 27 was prepared by further dissolving 2% by weight of LB1 in 1M LiPF ₆ EC / DMC (1/2 volume ratio). Using this electrolyte solution, a battery of Example 27 was produced. 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 higher recoverable capacity after high temperature storage. Furthermore,
The capacity retention 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). Using this electrolyte solution, a battery of Example 28 was produced. 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 higher recoverable capacity after high temperature storage. Furthermore,
The capacity retention of this battery was 86%, which was 1% higher than Comparative Example 10.

Example 29 An electrolyte of Example 29 was prepared by further dissolving 2% by weight of LB5 in 1M LiPF ₆ EC / DMC (1/2 volume ratio). Using this electrolyte solution, a battery of Example 29 was produced. 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 higher recoverable capacity after high temperature storage. Furthermore,
The capacity retention of this battery was 87%, which was 2% higher than that of Comparative Example 10.

Example 30 An electrolyte 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). Using this electrolyte, a battery of Example 30 was produced. 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 retention rate of this battery was 89%, which was 4% higher than that of Comparative Example 10.

[0061] (Comparative Example 11) 1M LiN as an electrolytic solution (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
110 mAh, capacity retention was 70%.

(Example 31) 1 M LB1 HFE71 as an electrolytic solution
A battery of Example 31 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 1610mA
h. The recovery capacity of this battery was 1330 mAh and the capacity retention rate was 82%.
mAh, capacity maintenance rate improved by 12%.

(Example 32) 1M LB2 HFE71 as electrolyte
A battery of Example 32 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 1620mA
h. The recovery capacity of this battery was 1350 mAh and the capacity retention rate was 83%.
13% improvement in mAh and capacity retention.

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
h. The recovery capacity of this battery was 1350 mAh and the capacity retention rate was 82%.
mAh, capacity maintenance rate improved by 12%. As described above, by using the lithium organic borate of the present invention as a supporting electrolyte, the reliability for high-temperature storage in a charged state is dramatically improved. This is considered to be due to the fact that the oxidation resistance was improved, thereby suppressing the acceleration of the decomposition reaction of the anion at a high potential depending on the temperature.

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

When a key switch is turned on and the accelerator pedal is depressed in the same manner as in a normal gasoline-powered vehicle, the torque or rotation of the motor is controlled in accordance with the accelerator pedal depression angle. When the accelerator is released, the regenerative brake corresponding to the engine brake is operated, and when the brake is depressed, the regenerative braking force is further increased. The shift lever signal switches the vehicle forward or backward, and the gear ratio is always constant. As the control system, an IGBT vector control inverter system using an induction motor is adopted, and the power supply voltage is set to 336 V from the IGBT withstand voltage. The output was 45 kW, the maximum torque was 176 Nm, and the rated output was 30 kW from the maximum speed specification. The main control items are forward / reverse control of the car, regenerative control,
The failsafe control is performed.

Since the heat density is increased by reducing the size and weight of the motor, it is important to provide an efficient cooling structure. Since the temperature rise of the electric motor is high in a general air-cooled type, the water-cooled type is used like a general engine. The cooling water channel was provided in an aluminum frame that covered the motor body, and the shape was optimized by temperature rise simulation. The cooling water flows in from a water supply port of a water channel of the frame, is discharged after absorbing heat of the motor body, and is cooled by a radiator in a circulation path. With such a water cooling structure, the cooling performance could be improved about three times as compared with the air cooling.

The inverter uses an IGBT as a power element, and generates a maximum of several kilowatts at the maximum output. In addition, heat is also generated from surge absorbing resistors, filter capacitors, and the like, and it is necessary to keep these components below the allowable temperature and cool them efficiently. Particularly, the cooling of the IGBT is a problem, and the cooling method may be air cooling, water cooling, oil cooling, or the like. Here, a forced water cooling system that can be easily handled and efficiently cooled was used.

The protection circuit shown in the figure is formed in the lithium secondary battery as the power source in Examples 31 to 33. The protection circuit protects the battery from overcharge and overdischarge. The protection circuit comprises 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 conventional lithium secondary batteries, since the electrolyte has flammability, a thermistor is provided for each battery to detect the temperature or pressure,
Although monitoring was performed by this, in Examples 31 to 33, even when the flash point was brought close to the electrolytic solution, the flame was nonflammable and did not have a flash point that did not burn into the liquid. It does not require pressure monitoring. Thereby, the number of safety mechanisms can be reduced as a protection circuit. As shown in FIG. 7, when overdischarge is detected, the power supply can be automatically opened and closed.

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 motor as shown in FIG. It can be used. In the figure, INV (In
verter: Inverter), IM (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 indicates a control method, a system configuration, and main control parameters.

(Embodiment 35) FIG. 10 shows Embodiments 31 to 33.
1 is a configuration diagram illustrating a power storage system for nighttime power using a lithium secondary battery described in FIG. This example of the power storage system is an example of 2000 kW × 4 h, cell capacity of 1000 Wh, 360 batteries connected in series, and 24 columns connected in parallel. Also in the present embodiment, it is necessary to protect the battery from overcharging and overdischarging as in Embodiment 33, and the protection circuit shown in FIG. 8 has a monitoring / balance compensation circuit.
Also in this embodiment, the battery is protected in the same manner as described above.

The present embodiment is intended for large-capacity power storage, but is also effective for home air conditioners, electric water heaters and the like.

[0073]

As described in detail above, the lithium organic borate of the present invention uses tetravalent boron at the center of the anion, and further devises the electron-withdrawing property and molecular size of the functional group bonded thereto. Thereby, a low dipole moment such as a nonflammable fluorinated solvent, the solubility in a solvent having a low dielectric constant can be improved, and the conductivity of the solution can be improved.
A non-aqueous electrolyte effective for lithium secondary batteries and electrochemical capacitors could be provided. In addition, the problems of corrosiveness and oxidation resistance of aluminum, which were problems with conventional organic lithium salts, can be solved by using the organic lithium borate of the present invention as a supporting electrolyte. Further, by improving the oxidation resistance, the storage characteristics of the lithium secondary battery at high temperatures can be improved.

Particularly, a mixed solvent containing a large amount of a fluorinated solvent
0.8mol ・ dm ^-3Can be dissolved
0.4mol ・ dm^-3Conductivity at low concentrations
A non-aqueous electrolyte exhibiting the highest value can be obtained.

Further, according to the present invention, a large-capacity lithium secondary battery for power storage and electric vehicles can be essentially made non-flammable from a lithium secondary battery for consumer use, and the reliability is drastically improved. It is possible to provide a lithium secondary battery suitable for various uses having high performance. Furthermore, it can be expected that the battery is conventionally safer and further lighter and smaller. A remarkable effect that a protection mechanism in a battery provided, an external protection circuit, and the like are not reduced or none is obtained can be achieved. In addition, since the electrolyte is non-flammable, regulations on the amount of electrolyte that can be stored at the manufacturing site are eased, so that a larger amount of electrolyte can be stocked for production than at present, and production adjustments can be made. It also has the advantage of spreading to inventory and inventory adjustments.

[Brief description of the drawings]

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

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

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

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

FIG. 5 is a cathode polarization curve.

FIG. 6 is a sectional view of a cylindrical lithium secondary battery showing one 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 power storage system diagram 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… Outer can, 11… Gasket,
12 ... Positive electrode cap.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hideaki Katayama 7-1-1, Omikacho, Hitachi City, Ibaraki Prefecture Inside Hitachi Research Laboratory, Hitachi, Ltd. (72) Inventor Mitsuru Kobayashi 7-1 Omikamachi, Hitachi City, Ibaraki Prefecture No. 1 Inside Hitachi Research Laboratory, Hitachi, Ltd. (72) Inventor Hiroyuki Yamaguchi 1-7-1, Inari, Soka City, Saitama Prefecture Inside Central Research Institute, Kanto Chemical Co., Ltd. (72) Inventor Hideki Takahashi Inari One, Soka City, Saitama Prefecture 7-1-1, Kanto Kagaku Co., Ltd. Central Research Laboratory (72) Inventor Masaru Kato 1-7-1, Inari, Soka-shi, Saitama F-term (reference) 4K048 AA01 AB91 VA75 VB10 5H029 AJ01 AJ04 AJ05 AJ07 AJ12 AJ13 AK03 AL02 AL06 AL07 AL11 AL12 AM02 AM03 AM04 AM05 AM07 BJ02 BJ14 BJ27 HJ02 5H030 AA03 AA04 AA06 AA10 AS01 AS08 BB09 BB10 FF42 FF43 FF44

Claims (14)

[Claims] 1. A compound of the general formula (1) [Where X is any one 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] An organic borate compound represented by the formula: 2. The method according to claim 1, wherein said R ¹ , R ² , R ³ ,
An organic borate compound, wherein R ⁴ is a trifluoromethyl group or a pentafluoroethyl group. 3. A non-aqueous electrolyte comprising the organic borate compound according to claim 1 and a solvent. 4. The non-aqueous electrolyte according to claim 3, wherein the solvent comprises at least one of a cyclic carbonate, a chain carbonate, and an ether. 5. The non-aqueous electrolyte according to claim 3, wherein the solvent comprises at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and dimethoxyethane. 6. A non-aqueous electrolytic solution according to claim 3, further comprising a fluorinated solvent. 7. The non-aqueous electrolyte according to claim 6, wherein said fluorine solvent is at least one of perfluorobutyl methyl ether, perfluorobutyl ethyl ether and methyl perfluoroalkyl ether. 8. A non-aqueous electrolytic solution according to claim 3, further comprising an inorganic lithium salt. 9. The method according to claim 8, wherein said inorganic lithium salt is LiPF ₆ , LiBF ₄ , LiCl, LiF, LiF
A non-aqueous electrolyte characterized by being at least one of Br and LiI. 10. A lithium secondary battery comprising a negative electrode capable of occluding and releasing lithium, a positive electrode capable of occluding and releasing lithium, a separator, and a non-aqueous electrolyte, wherein the non-aqueous electrolyte is A lithium secondary battery comprising the non-aqueous electrolyte according to any one of claims 9 to 10. 11. An electric device using the lithium secondary battery according to claim 10 as a power supply. 12. The protection means according to claim 11, wherein said protection means against overcharge and overdischarge of said secondary battery comprises voltage or current detection means for said battery and control means for opening and closing said power supply based on said detection value. An electric device, wherein temperature and pressure detection of the battery are free. 13. An electric vehicle comprising the electric device according to claim 11. 14. An electric power storage device comprising the electric device according to claim 11.