JP2001210332A - Electrolytic solution for electrochemical device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrolytic solution of improved safety, which is utilized as an electrochemical device such as lithium battery, lithium-ion battery, electric double layer capacitor or the like. SOLUTION: This is the electrolytic solution for an electrochemical device using fluorine-containing organic solvent, and containing a compound composed of chemical structural formula as shown in equation (1).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrolyte having improved safety and used for electrochemical devices such as lithium batteries, lithium ion batteries, and electric double layer capacitors.

[0002]

2. Description of the Related Art With the development of portable devices in recent years, electrochemical devices using electrochemical phenomena such as batteries and capacitors as power sources thereof have been actively developed. Became. Further, as an electrochemical device other than the power supply, an electrochromic display (ECD) in which a color changes due to an electrochemical reaction is given.

[0003] These electrochemical devices generally comprise a pair of electrodes and an electrolyte filling between them. This is the electrolyte solution and cations (A ⁺⁾ called solvent and an electrolyte anion (B ^-) obtained by dissolving a made of salts (AB) is used. As this solvent, organic solvents such as propylene carbonate, dimethyl carbonate, and dimethoxyethane are often used. However, since these solvents have a low flash point and there is a risk of inflammation, recently, due to the problem of safety against fire, etc. The use of such a flammable electrolyte has become an undesirable situation.

On the other hand, fluorine-containing organic solvents having a fluorine atom in the molecule, such as chlorofluorocarbons, are nonflammable or flame-retardant, so they are excellent in terms of safety, but generally have a dielectric constant. Because of its low content, salts (eg, LiPF ₆ , LiBF ₄ , LiCF ₃ SO
₃ , LiN (CF ₃ SO ₂ ) ₂ , LiSbF ₆ and LiC
For lO _4, etc.) not capable of completely dissolving, for use as an electrolyte has been difficult.

[0005]

[Specific means for solving the problem]
As a result of intensive studies in view of the problems of the prior art, a flame-retardant electrolyte having excellent device performance was found by combining an electrolyte having a novel chemical structural characteristic and a fluorine-containing organic solvent, and reached the present invention. It was done.

That is, according to the present invention, in an electrochemical device using an organic electrolyte, a fluorine-containing organic solvent is used as a main solvent of the organic electrolyte, and the electrolyte has a general formula (1).
Including a compound having a chemical structural formula represented by

[0007]

Embedded image

In the formula, A ^{q +} is a metal ion or onium ion, M is a transition metal, group III of the periodic table, IV
Group or group V element, a is 0 or 1, b is 0 to
8, c is 0 to 8, d is 0 to 8, n is 1 to 3, q
Is 1 to 3, p is n / q, Z is O, S, NR ⁶ or NR ⁶ R ^7,, X is halogen, R ¹ is alkylene of ^{_{C 1 ~C 10, R 2,}} R ³ and R ⁴ are each independently H, halogen, C _{1 to} C ₁₀ alkyl, C _{1 to} C ₁₀ halogenated alkyl, C _{4 to} C ₂₀ aryl, or C _{4 to} C ₂₀ halogenated aryl. , R ⁵ are C ₁ -C ₁₀ alkyl, C ₁
Alkyl halides -C _10, C ₁ -C ₁₀ alkoxy, halogenated alkoxy C ₁ -C _10, aryl of C ₄ ~C _20, C ₄ ~C ₂₀ aryl halide, the C ₄ -C ₂₀ Aryloxy or C _{4 to} C ₂₀ halogenated aryloxy, R ⁶ and R ⁷ each represent H or alkyl of C _{1 to} C ₁₀ , and further, the fluorinated organic solvent as the main solvent contains fluorine. Carbonates, esters,
Ethers, lactones, nitriles, amides, or sulfones, and
It is an object of the present invention to provide an electrolytic solution for an electrochemical device, which contains an organic compound containing a hetero element having a dielectric constant of 1 or more as an electrolyte dissociation promoter.

The alkyl, alkyl halide, aryl and aryl halide used in the present invention include those having another functional group such as a branch, a hydroxyl group and an ether bond.

Hereinafter, the present invention will be described in more detail.

The present invention is realized by combining an electrolyte having a novel chemical structural characteristic and a fluorine-containing organic solvent. Here, specific examples of the compound represented by the general formula (1) used as the electrolyte are as follows. An example is shown below.

[0012]

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Here, lithium ion is mentioned as A ^{q +} , but cations other than lithium ion include, for example, sodium ion, potassium ion, magnesium ion, calcium ion, barium ion, cesium ion, silver ion, zinc ion, copper ion. Ion, cobalt ion, iron ion, nickel ion, manganese ion, titanium ion, lead ion, chromium ion, vanadium ion, ruthenium ion, yttrium ion, lanthanoid ion, actinoid ion, tetrabutylammonium ion, tetraethylammonium ion, tetramethylammonium Ion, triethylmethylammonium ion, triethylammonium ion, pyridinium ion, imidazolium ion, proton, tetraethylphosphonic ion Ion, tetramethyl phosphonium ion, tetraphenylphosphonium ion, triphenylsulfonium ion, triethylsulfonium ion, etc. is also used.

In consideration of applications such as electrochemical devices, lithium ions, tetraalkylammonium ions and protons are preferred. Valence q of the cation of A ^{q +}
Is preferably 1 to 3. If it is larger than 3, the crystal lattice energy becomes large, so that there is a problem that it becomes difficult to dissolve in a solvent. Therefore, when solubility is required, 1 is more preferable. Similarly, the valence n of the anion
Similarly, 1 to 3 are preferable, and 1 is more preferable.
The constant p representing the ratio between the cation and the anion is inevitably determined by the ratio n / q of the valences of the two.

The electrolyte of the present invention has an ionic metal complex structure, and M as the center thereof is selected from transition metals, Group III, Group IV, and Group V elements of the periodic table. Preferably, Al, B, V, Ti, Si, Zr, Ge, Sn,
Cu, Y, Zn, Ga, Nb, Ta, Bi, P, As,
It is any of Sc, Hf, or Sb, and is more preferably Al, B, or P. Although it is possible to use various elements as the central M, Al, B,
V, Ti, Si, Zr, Ge, Sn, Cu, Y, Zn,
In the case of Ga, Nb, Ta, Bi, P, As, Sc, Hf, or Sb, synthesis is relatively easy, and further, Al,
B or P has excellent properties in all aspects such as low toxicity, stability and cost, in addition to easy synthesis.

Next, a description will be given of a ligand part which is a feature of the electrolyte (ionic metal complex) of the present invention. Hereinafter, the organic or inorganic portion bonded to M is referred to as a ligand.

In the general formula (1), Z is O, S, NR ⁶ ,
Or NR ⁶ R ⁷ , and through these heteroatoms, M
To join. Here, bonding other than O, S, and N is not impossible but very complicated in synthesis.

The constant a in the ligand is 0 or 1. X is a halogen, preferably fluorine, and R ¹ is C ₁
-C ₁₀ alkylene, R ² , R ³ and R ⁴ are each independently H, halogen, C ₁ -C ₁₀ alkyl, C ₁ -C ₁₀ halogenated alkyl, C ₄ -C ₂₀ aryl, Or C ₄
Aryl halides -C _20, R ⁵ is, C ₁ -C alkyl _10, halogenated alkyl C ₁ ~C _10, C ₁ ~C ₁₀ alkoxy, C ₁ -C _{1 0} halogenated alkoxy, C _{4 to} C
₂₀ aryl, aryl halide of C ₄ ~C _20, C ₄ ~
C ₂₀ aryloxy or C ₄ -C ₂₀ halogenated aryloxy, R ⁶ and R ⁷ each represent H or C ₁ -C ₁₀ alkyl, but preferably at least one of R ² , R ³ and R ⁴ One is fluorinated alkyl. The presence of electron-withdrawing fluorine or fluorinated alkyl in R ² , R ^3, and R ⁴ disperses the negative charge of the central M and increases the electrical stability of the anion. As a result, solubility in a solvent, ionic conductivity, catalytic activity, and the like increase. Further, other heat resistance, chemical stability and hydrolysis resistance are also improved. Further, since the structure is similar to the fluorine-containing organic solvent described later, the solubility is further increased by the effect. The constants b, c, and d related to the number of ligands described above are determined by the type of the center M. However, b is 0 to 8, c
Is preferably 0 to 8 and d is preferably 0 to 8. The above electrolyte has a very high solubility in a fluorine-containing organic solvent in which the conventional electrolyte hardly dissolves due to the characteristics derived from its structure. By taking advantage of this,
It is possible to construct a flame-retardant electrolytic solution that has not been possible before.

Next, the fluorine-containing organic solvent used in the present invention may have a flash point of 100 ° C. or higher, and is preferably a carbonate, ester, ether, lactone or nitrile containing fluorine. , Amides,
Or sulfones, more preferably those having a fluorine content of 50% or more, and more preferably those having a portion common to the ligand of the electrolyte used. In order to safely use the electrochemical device which is the object of the present invention, the flash point of the fluorinated organic solvent is 100 ° C.
Or more, and carbonates,
Those containing a hetero element such as esters, ethers, lactones, nitriles, amides, or sulfones have higher dissolving power, and those having a common part with the ligand of the electrolyte. It is preferable because the dissolving power is higher.

Specifically, CH ₃ OCOOCH ₂ CF ₃ ,
CH ₃ OCOOCH ₂ CF ₂ CF ₃ , CH ₃ OCOOCH
(CF ₃ ) ₂ , C ₂ H ₅ OCOOCH ₂ CF ₃ , C ₂ H ₅ OCO
OCH ₂ CF ₂ CF ₃ , C ₂ H ₅ OCOOCH (CF ₃ ) ₂ ,
(CF ₃ ) ₂ CHOCOOOCH (CF ₃ ) ₂ , CF ₃ CH ₂ O
A chain fluorinated carbonate such as COOCH ₂ CF ₃ ,

[0021]

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Cyclic fluorine-containing carbonates such as (CF
_Three)_TwoCHOCH_Three , C_FourF₉OCH_Three, CF_ThreeCFHCF_Two
OCH_Three , CF_ThreeCF_TwoCH_TwoOCF_TwoCF_TwoH, HCF_TwoC
F_TwoOCH_Three, HCF_TwoCF_TwoOC_TwoH_Five , CF _ThreeCH_TwoOC
H_TwoCF_Three, C_ThreeF₇OCHFCF_Three , (CF_Three)_TwoCHOC
H_TwoF, CF_ThreeCH_TwoOC_TwoH_FourOCH_TwoCF_ThreeChain containing
Fluorine ether,

[0023]

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Cyclic fluorinated ethers such as CF ₃ CO
Fluorinated esters such as OC ₂ H ₅ , C ₄ F ₉ COOCH ₃ , C ₃ F ₇ COOCH ₃ ,

[0025]

Embedded image

Fluorinated lactones such as CF ₃ CONHC
_{H 2 CH 2 CF 3, C} 3 F 7 CON (CH 3) fluorinated amide of ₂ such _{as, CH 2 FCN, CF 3 CHFCN} , (CF 2)
Fluorine-containing nitriles such as ₄ (CN) ₂ can be used.

The electrolyte of the present invention has a very high solubility in these fluorine-containing organic solvents, but a fluorine-containing organic solvent having a high fluorine content generally has a low dielectric constant and a low donor property. The inhibition causes a problem that the ionic conductivity required for the electrochemical device is reduced. Therefore, by adopting a method of adding an organic compound containing a hetero element having a dielectric constant of 1 or more as an electrolyte dissociation accelerator to the electrolytic solution of the present invention, the conductivity can be improved. As the dissociation accelerator, an aprotic organic compound is preferable. For example, carbonates, esters, ethers, lactones, nitriles, amides, sulfones and the like can be used. In addition, not only a single compound but also a mixture of two or more kinds may be used. Specific examples include propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, dimethoxyethane, acetonitrile, propionitrile, tetrahydrofuran, 2-methyltetrahydrofuran, dioxane, nitromethane, N, N-dimethylformamide, dimethylsulfoxide. , Sulfolane, γ-butyrolactone, polymers having polyethylene oxide in the main chain or side chain, methacrylic acid ester polymers, polyacrylonitrile, and the like. However, since these dissociation accelerators are flammable substances, the amount of addition is preferably 50 vol% or less in the electrolytic solution. When these dissociation accelerators having a high dielectric constant are added, Li is generally used.
PF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃
Although electrolytes such as SO ₂ ) ₂ , LiSbF ₆ , or LiClO ₄ also appear to dissolve in the fluorinated organic solvent,
Even if mixing is possible without these electrolytes, the addition of these electrolytes causes phase separation between the fluorinated organic solvent and the dissociation promoter, and therefore cannot be used as an electrolyte.

The concentration of the electrolyte in the electrolyte is 0.1 mol
/ Dm ³ or more and a saturation concentration or less, more preferably 0.5 to 1.5 mol / dm ³ . 0.1mo
If the concentration is lower than 1 / dm ³ , the ionic conductivity is low, which is not preferable.

When an electrochemical device is constructed using the electrolytic solution of the present invention, its basic components include an electrolytic solution, a negative electrode, a positive electrode, a current collector, a separator, a container, and the like.

The material of the negative electrode is not particularly limited.
In the case of a lithium battery, lithium metal or an alloy of lithium and another metal is used. In the case of a lithium ion battery, a material utilizing a phenomenon called intercalation, such as carbon, natural graphite, or a metal oxide obtained by firing a polymer, an organic substance, pitch, or the like, is used. In the case of an electric double layer capacitor, activated carbon, porous metal oxide, porous metal, conductive polymer and the like are used.

The cathode material is not particularly limited, but
For lithium batteries and lithium ion batteries, for example,
LiCoO_Two , LiNiO_Two , LiMnO_Two , LiMn
_Two O _Four Lithium-containing oxides such as TiO_Two , V_Two O_Five ,
MoO_Three Oxides such as TiS _Two , Sulfides such as FeS,
Or polyacetylene, polyparaphenylene, polyani
Conductive polymers such as phosphorus and polypyrrole are used
You. Activated carbon, porous metal for electric double layer capacitors
An oxide, a porous metal, a conductive polymer, or the like is used.

[0032]

The present invention will be described below in more detail with reference to examples, but the present invention is not limited to these examples.

Example 1 Lithium aluminate

[0034]

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To di (hexafluoroisopropyl) carbonate

[0036]

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To prepare an electrolyte having a concentration of 0.3 mol / dm ³ , and the ionic conductivity was measured using an AC bipolar cell. As a result, the ionic conductivity at 25 ° C. was 0.1.
01 mS / cm. The electrolyte was impregnated into filter paper, and a combustion test was conducted by igniting a flame. However, no combustion occurred.

Example 2 A 1: 1 (volume) mixture of propylene carbonate (PC) and dimethyl carbonate (DMC) was added to the electrolyte of Example 1 in an amount of 20% with respect to the electrolyte. The conductivity was measured with an AC bipolar cell. As a result, the ionic conductivity at 25 ° C. was 1.40 mS / cm. The electrolyte was impregnated into filter paper, and a combustion test was conducted by igniting a flame. However, no combustion occurred.

Next, a half cell was prepared using this electrolyte solution and LiCoO ₂ as a positive electrode material, and a charge / discharge test of the battery was actually performed. The test cell was prepared as follows.
5 parts by weight of polyvinylidene fluoride (PVDF) as a binder with respect to the LiCoO ₂ powder 90,
And acetylene black as a conductive material in a ratio of 5 and further adding N, N-dimethylformamide,
Paste. This paste was applied on an aluminum foil and dried to obtain a positive electrode for testing. Lithium metal was used for the negative electrode. Then, a cell was assembled by using a glass fiber filter as a separator and soaking the electrolytic solution in the separator.

The constant current charge / discharge test was performed under the following conditions. Current density of 0.35 mA / c for both charging and discharging
It performed in m ^2, charging, 4.2V, discharge, 3.0V (v
s. Li / Li ⁺ ). As a result, the initial discharge capacity was 123 mAh / g (capacity of the positive electrode). The charge / discharge was repeated 20 times, but the capacity at the 20th time was 89% of the initial capacity.

Further, a half cell was prepared using this electrolyte and natural graphite as a negative electrode material, and a charge / discharge test of the battery was actually performed. The test cell was prepared as follows.
Polyvinylidene fluoride (PVDF) as a binder was mixed at a ratio of 1 to natural graphite powder 9 at a weight ratio,
Further, N, N-dimethylformamide was added to form a slurry. This slurry was applied on a nickel mesh and dried at 150 ° C. for 12 hours to obtain a test negative electrode body. Lithium metal was used for the counter electrode. Then, a half cell was assembled by using a glass fiber filter as a separator and soaking the electrolytic solution in the separator. A constant current charge / discharge test was performed under the following conditions. Both charging and discharging were performed at a current density of 0.3 mA / cm ² , charging was performed at 0.0 V, and discharging was performed at 1.5 V (vs. Li /
Li ⁺ ). As a result, the initial discharge capacity is 3
It was 30 mAh / g. The charge / discharge was repeated 20 times, but the capacity at the 20th time was 95% of the initial capacity.

Example 3 The lithium aluminate used in Example 1 was replaced with 2,2-bis (trifluoromethyl) -1,3-dioxolane

[0043]

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To prepare an electrolytic solution having a concentration of 0.5 mol / dm ³ , and the ionic conductivity was measured using an AC bipolar cell. As a result, the ionic conductivity at 25 ° C. was 0.1.
02 mS / cm.

When 10% of 1,2-dimethoxyethane was added to this electrolytic solution, the ionic conductivity was 5.2 mS / cm. The electrolyte was impregnated into filter paper, and a combustion test was conducted by igniting a flame. However, no combustion occurred.

Example 4 The lithium aluminate used in Example 1 was dissolved in methyl nonafluorobutyl ether (C ₄ F ₉ OCH ₃ ).
An electrolytic solution having a concentration of 0.2 mol / dm ³ was prepared, and the ionic conductivity was measured using an AC bipolar cell. As a result, 25
The ionic conductivity at ° C. was 0.01 mS / cm.

When 5% of 1,2-dimethoxyethane was added to this electrolytic solution, the ionic conductivity was 2.
It was 0 mS / cm. The electrolyte was impregnated into filter paper, and a combustion test was conducted by igniting a flame. However, no combustion occurred.

Comparative Example 1 LiPF ₆ was added for dissolution in di (hexafluoroisopropyl) carbonate, but did not dissolve at all.

Next, addition of LiPF ₆ at a concentration 0.2 mol / dm ³ to di (hexafluoroisopropyl) carbonate containing 20% propylene carbonate, a solution although LiPF ₆ was dissolved 2
The phases were separated. Analysis of each phase indicated that one was di (hexafluoroisopropyl) carbonate and the other was a LiPF ₆ / propylene carbonate solution.

Comparative Example 2 LiPF ₆ , LiN (CF ₃ SO ₂ ) ₂ , LiBF ₄ , Li
CF ₃ SO ₃ , LiSbF ₆ and LiClO ₄ were converted to 2,2-bis (trifluoromethyl) -1,3-
A dissolution test for dioxolan was performed. as a result,
None of the electrolytes dissolved.

[0051]

As the electrolyte of the present invention can use a flame-retardant solvent, it can be used as compared with conventional electrolytes used for electrochemical devices such as lithium batteries, lithium ion batteries, and electric double layer capacitors. Very good in terms of safety.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Mikihiro Takahashi 2805 Imafukunakadai, Kawagoe-shi, Saitama F-term in Chemical Research Laboratory, Central Glass Co., Ltd. 5H024 FF15 FF16 FF19 HH00 5H029 AJ12 AK03 AL12 AM03 AM04 AM05 AM06 EJ11 HJ02

Claims (5)

[Claims] 1. An electrochemical device using an organic electrolyte, wherein a fluorine-containing organic solvent is used as a main solvent of the organic electrolyte, and the electrolyte contains a compound having a chemical structural formula represented by the general formula (1). An electrolytic solution for an electrochemical device, comprising: Embedded image A ^{q +} is a metal ion or onium ion, M is a transition metal, a group III, group IV or group V element of the periodic table, a
Is 0 or 1, b is 0 to 8, c is 0 to 8, d is
0 to 8, p is n / q, n is 1 to 3, and q is 1 to 3, and Z is O, S, NR ⁶ , or NR ⁶ R ⁷
X is halogen; R ¹ is C ₁ -C ₁₀ alkylene;
R ² , R ³ and R ⁴ are each independently H, halogen, C ₁
Alkyl -C _10, alkyl halide C ₁ -C _10,
C ₄ -C ₂₀ aryl, or C ₄ -C ₂₀ halogenated aryl, R ⁵ is a C ₁ -C ₁₀ alkyl, a C ₁ -C ₁₀ halogenated alkyl, a C ₁ -C ₁₀ alkoxy, a C ₁ -C ₁₀ alkoxy, _{1 ~C 10}
Halogenated alkoxy, C ₄ -C ₂₀ aryl, C ₄ -C
C _{2 0} aryl halides, of C ₄ -C ₂₀ aryloxy or C ₄ -C ₂₀ halogenated aryloxy,, R ^6,
R ⁷ represents H or C ₁ -C ₁₀ alkyl, respectively. 2. M is Al, B, V, Ti, Si, Z
r, Ge, Sn, Cu, Y, Zn, Ga, Nb, Ta,
2. The electrolyte for an electrochemical device according to claim 1, wherein the electrolyte is one of Bi, P, As, Sc, Hf, and Sb. 3. The electrolytic solution for an electrochemical device according to claim 1, wherein A ^{q +} is one of a Li ion and a quaternary alkylammonium ion. 4. The fluorinated organic solvent comprises at least one of fluorine-containing carbonates, esters, ethers, lactones, nitriles, amides, and sulfones. The electrolytic solution for an electrochemical device according to any one of claims 1 to 3. 5. The electricity according to claim 1, wherein the organic electrolyte contains an organic compound containing a hetero element having a dielectric constant of 1 or more as a dissociation accelerator for the electrolyte. Electrolyte for chemical devices.