JP2000327634A - Fluorinated carbonate compound - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a new fluorinated carbonate compound excellent in flame retardancy, having chemical stability and a high dielectric constant, and useful as a solvent e.g. for a nonaqueous electrolytic solution of a lithium secondary battery. SOLUTION: This new compound is expressed by the formula, wherein (n) and (m) are each an integer of 1-5; (x) is 1 or an integer of 2(m)+1 and; R is a (substituted) (1-3C)alkyl and is e.g. 3-perfluoropropoxy-2,2,3,3- tetrafluoropropylmethyl carbonate. The compound can be synthesized by reacting a corresponding alkyl chloroformate with a fluorinated alcohol having at least one ether bond in a solvent such as methylene chloride in the presence of an amine such as trimethylamine or pyridine. Flame retardancy is improved by lengthening fluorine-containing chains. A fluorinated carbonate compound having high dielectric constant, a wide liquid phase temperature range and low viscosity and being liquid even at ordinary temperature and highly safe is obtained by introducing an ether bond in the fluorine-containing chains.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel fluorinated carbonate compound, which is excellent in flame retardancy, is chemically stable, has a high dielectric constant, and is used as a non-aqueous electrolyte for lithium secondary batteries. It relates to a fluorinated carbonate compound useful as a solvent.

[0002]

2. Description of the Related Art Carbonate compounds are widely used as solvents for non-aqueous electrolytes in lithium secondary batteries. For example, as disclosed in Japanese Patent Application Laid-Open No. Hei 2-10666, a chain form of propylene carbonate is used. A mixture of a carbonate ester and a mixture of an ethylene carbonate and a chain carbonate as disclosed in JP-A-4-162370 and U.S. Pat. No. 5,192,629 are known. I have.

However, an electrolytic solution using such a solvent is highly flammable, and may cause ignition when overcharged or an external short circuit or an internal short circuit occurs for some reason, and a more safe non-aqueous solution. The development of an electrolyte has been desired.

[0004] In response to such a demand, a chain carbonate compound substituted with a fluorine atom has been proposed as a solvent for a non-aqueous electrolyte having improved safety as compared with a conventional non-aqueous electrolyte, as disclosed in JP-A-6-219992. Is disclosed. This non-aqueous electrolyte solvent has slightly improved flame retardancy compared to unsubstituted carbonate ester as shown in Comparative Examples below.
It cannot be said that it still satisfies sufficient security.

[0005]

As described above, known solvents for non-aqueous electrolytes have a problem in flame retardancy and do not satisfy sufficient safety.

An object of the present invention is to solve the above-mentioned problems of the prior art and to provide a novel solvent for a non-aqueous electrolyte which is chemically stable and has a high dielectric constant.

[0007]

The gist of the present invention to achieve the above object is as follows.

[1] General formula (1)

[0009]

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Wherein n and m are each independently from 1 to 5
X is an integer of 1 or 2m + 1, and R is a carbon number of 1 to 1.
3 alkyl group or halogen-substituted alkyl group].

[2] The above-mentioned fluorinated carbonate compound represented by the general formula (1), wherein n is 3 or 4, m is 2 or 3, x is 2, and R is a methyl group.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION In the molecular structure, in particular, the longer the fluorine chain introduced to improve the flame retardancy, the greater its effect. However, the longer the fluorine chain, the greater the rigidity and cohesion of the molecule. Increase, causing an increase in melting point. Further, when the fluorine chain becomes longer, the dielectric constant generally lowers and the dissociation rate of the ion lowers. In extreme cases, the solubility of the salt also lowers, making the solvent unsuitable as a solvent for the electrolytic solution.

Therefore, the present invention has been achieved by considering the interposition of an ether bond in the fluorine chain. As an effect of the present invention, by increasing the degree of freedom of the fluorine chain, the increase in the melting point is suppressed, and further, the coordination force to ions due to the decrease in the charge of carbonate oxygen due to the strong electron withdrawing effect of fluorine, As a result, it is possible to prevent a decrease in salt dissociation. These points are clear from the various physical properties of the examples described later.

Furthermore, this fluorinated carbonate compound was newly discovered for the first time and is a novel compound in which a carbonate containing a fluorine atom contains an ether bond.

The novel fluorinated carbonate compound has extremely high flame retardancy, is liquid at room temperature, has a high dielectric constant, and has physical properties required as a solvent such as a nonaqueous electrolyte for a lithium secondary battery, and It is a solvent with high safety.

The fluorinated carbonate compound of the present invention comprises
It has a chemical structure represented by the general formula (1). In addition,
When used as a non-aqueous electrolyte for a lithium secondary battery, those having a chemical structure in which n is 3 or 4, m is 2 or 3, x is 2, and R is a methyl group in general formula (1) are particularly preferable. Preferably, the number of fluorine atoms is more than twice the number of hydrogen atoms.

The fluorinated carbonate compound of the present invention has good compatibility with cyclic carbonates such as ethylene carbonate and propylene carbonate or chain carbonates such as dimethyl carbonate and diethyl carbonate. The mixed solvent can well dissolve lithium salts such as hexafluorophosphoric acid, trifluoromethanesulfonic acid, perchloric acid, and fluoroalkylsulfonylimide.

As described above, since the above-mentioned fluorinated carbonate compound has extremely high flame retardancy, it is used as a solvent for a non-aqueous electrolyte of a lithium secondary battery.
A non-aqueous electrolyte having high flame retardancy can be obtained, and the safety of the lithium secondary battery can be greatly improved.

Further, the fluorinated carbonate compound is
It is chemically stable and does not react with water or oxidize in air.

Examples of the fluorinated carbonate compound include 3-perfluoropropoxy-2,2,3,3-tetrafluoropropylmethyl carbonate and 2-perfluorobutoxy-2,3,3,3-tetrafluoropropylmethyl Carbonate, 2-perfluorobutoxy-2,
There are 2-difluoroethylmethyl carbonate, 2-perfluoroisopropoxy-2,3,3,3-tetrafluoropropylmethyl carbonate and the like.

The above fluorinated carbonate compound can be synthesized, for example, as shown by the following formula (2).

[0022]

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That is, a fluorinated carbonate compound can be easily synthesized by reacting a corresponding alkyl chloroformate with a fluorinated alcohol having an ether bond in the presence of an amine such as triethylamine or pyridine. It is possible.

The above synthesis process is an example of the synthesis of a fluorinated carbonate compound, and is not limited to this.

[0025]

EXAMPLES The fluorinated carbonate compound of the present invention is 2-
A production example in the case of perfluoropropoxy-2,3,3,3-tetrafluoropropylmethyl carbonate is shown.

First, 2-perfluoropropoxy-
2,3,3,3-tetrafluoropropanol 200g
(633 mmol), 90 g of methyl chloroformate (949)
mmol) and methylene chloride (60 ml) at 10 ° C.
To 90 g (886 mmol) of triethylamine
And a mixed solution of methylene chloride and 150 ml was added dropwise over 1 hour and 30 minutes.

Next, the obtained mixed solution was stirred overnight, and then 100 ml of water was added thereto, followed by washing with water to remove generated triethylamine hydrochloride.

Next, 100 ml of dilute hydrochloric acid was added and the mixture was stirred to remove the remaining triethylamine, and liquid separation was performed. The organic layer was washed again with water, dried, and dried at 68 ° C. under a pressure of 34 mmHg.
Under reduced pressure to obtain about 205 g of 2-perfluoropropoxy-2,3,3,3-tetrafluoropropylmethyl carbonate.

When the NMR spectrum of the obtained compound was measured, a characteristic spectrum as shown in FIG. 1 was obtained. The measurement was performed in a CDCl ₃ solvent using TMS (tetramethylsilane) as a reference agent. 1H-NM
The assignment of the main peak of R is as follows.

CDCl ₃ soln, δ ppm: 3.87
(S, 3H, OCH ₃ ), 4.69 [dd, 1H, J = 2
8 Hz, J = 12 Hz, CF (CF ₃ ) CH ₂ O], 4.7
2 [dd, 1H, J = 28 Hz, J = 12 Hz, CF
(CF ₃₎ CH ₂ O].

FIG. 2 shows an IR spectrum. In the figure, the peak 1 of 2900～3000Cm ~ ¹ is the CH ₃ C
-H stretching vibration, peak 2 around 1750 cm- ¹ = C =
C = O stretching vibration of O, a plurality of peaks 3 at 1000 to 1500 cm- ¹ indicate stretching vibration of C—F bond,
0 cm- ¹ is the IR absorption attributed to the stretching vibration of COC.

From this, the existence of a carbonate group and an ether bond was confirmed, and the presence of a CF bond and a CH bond in the molecule was also confirmed.

From the above measurement results, it was identified that the compound of Example 1 was 2-perfluoropropoxy-2,3,3,3-tetrafluoropropylmethyl carbonate.

Next, 2-perfluoropropoxy-2,
The main physical property values of 3,3,3-tetrafluoropropylmethyl carbonate are shown below.

Boiling point: 152 ° C., freezing point: −48 ° C., viscosity: 1.5 cSt (at 25 ° C.), relative dielectric constant: 3.7, flash point: none (no flash).

The flash point was measured using a tag-closed flash point meter and a Cleveland open flash point meter in accordance with JIS2265.

As can be seen from the above physical properties, the dielectric constant of 2-perfluoropropoxy-2,3,3,3-tetrafluoropropylmethyl carbonate can be reduced by introducing an ether bond into the fluorine chain. Not currently used dimethyl carbonate (DM
C) The dielectric constant of a chain carbonate such as (C.
It was found to have a dielectric constant comparable to 7).

Furthermore, by introducing an ether bond, 2-perfluoropropoxy 2,3,3,3-tetrafluoropropylmethyl carbonate can be used as an electrolyte by adding lithium bis (pentafluoroethylsulfonyl) imide as an electrolyte at 1 mol / l or more. Can also be melted, its 1m
The conductivity of the ol / l solution was 0.24 mS / cm.

As described above, the compound of this example has a wide temperature range as a liquid and a low viscosity. And it turned out that the electrolytic solution using this solvent has conductivity, and has excellent physical properties and safety as an electrolytic solution solvent for a lithium secondary battery.

Table 1 shows the compounds of this example and JP-A-6-21.
It shows the flash point of the compound described in JP-A-9992 and dimethyl carbonate.

[0041]

[Table 1]

As can be seen from Table 1, the novel fluorinated carbonate compound of the present invention has very high flame retardancy.

[0043]

According to the present invention, the flame retardancy is remarkably improved by lengthening the fluorine chain, and the dielectric constant, the liquidus temperature range and the low viscosity can be realized by introducing an ether bond into the fluorine chain. Was.

According to the novel fluorinated carbonate of the present invention, it exhibits properties equal to or better than those of a conventional solvent for an electrolytic solution,
In addition, it is possible to provide an electrolyte solvent having extremely high flame retardancy. That is, the effectiveness of the ether bond was proved as a method for making the carbonate ester flame-retardant and maintaining the properties as a solvent.

The novel fluorinated carbonate compound of the present invention in which a carbonate ester containing a fluorine atom contains an ether bond has extremely high flame retardancy and is liquid even at room temperature.
It has extremely high safety and is particularly useful as a non-aqueous electrolyte for lithium secondary batteries and the like.

[Brief description of the drawings]

FIG. 1 NMR of fluorinated carbonate compound of Example
It is a spectrum diagram.

FIG. 2 is an IR spectrum of a fluorinated carbonate compound of an example.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hideaki Katayama 7-1-1, Omika-cho, Hitachi City, Ibaraki Prefecture Inside Hitachi Research Laboratory, Hitachi, Ltd. (72) Inventor Hiroyuki Yamaguchi 3--4 Muromachi, Chuo-ku, Tokyo No. 6 Kanto Kagaku Co., Ltd. F term (reference) 4H006 AA01 AB78 AB80 AB91 BM10 BM71 BP10 5H029 AJ07 AJ12 AL12 AM03 AM05 AM07 HJ02

Claims (2)

[Claims] 1. A compound of the general formula (1) Wherein n and m are each independently an integer of 1 to 5, x is an integer of 1 or 2m + 1, and R is an alkyl group having 1 to 3 carbon atoms or a halogen-substituted alkyl group. A fluorinated carbonate compound. 2. The fluorinated carbonate compound according to claim 1, wherein in the general formula (1), n is 3 or 4, m is 2 or 3, x is 2, and R is a methyl group.