JP3431641B2 - Organic electrolyte and organic electrolyte battery using the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic electrolyte solution and an organic electrolyte battery using the same.

[0002]

2. Description of the Related Art An organic electrolyte battery represented by a lithium-manganese dioxide battery using a negative electrode made of lithium, a positive electrode made of a mixture of manganese dioxide as a positive electrode active material, and an organic electrolyte has a high energy density. In addition, since it is lightweight, and has a long service life, demand for it tends to increase.

By the way, in this type of organic electrolyte battery,
In most cases, lithium or a lithium compound is used for the negative electrode, and a metal oxide such as manganese dioxide or an intercalation compound is used for the positive electrode.Since these are highly reactive, the organic electrolytic solution is not suitable for these electrode materials. Therefore, the one with low reactivity must be selected and used.

Therefore, the kind of solvent used for the organic electrolyte is considerably limited, and at present, relatively low reactive ones such as esters such as propylene carbonate and ethers such as 1,2-dimethoxyethane are used. There is.

However, relying solely on these cannot improve the output characteristics of the battery more than ever before.

Although a solvent having a heterounsaturated bond such as acetonitrile has high conductivity, it has high reactivity with a negative electrode such as lithium (Li) and lacks stability.
It is difficult to use as a practical battery because it reduces the storage properties of the battery.

[0007]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems in the conventional organic electrolytic solution and changes the structure of the solvent used in the organic electrolytic solution to provide the organic electrolytic solution and the electrode. It is an object of the present invention to provide an organic electrolytic solution battery having excellent storability by developing an organic electrolytic solution having reduced reactivity and high stability, and using the organic electrolytic solution.

[0008]

The present invention improves the stability of an organic electrolytic solution by using an organic solvent having a fluorine atom bonded to a carbon atom adjacent to an unsaturated bond as a solvent for the organic electrolytic solution. By using this organic electrolyte, the storability of the battery is improved. Further, as an organic solvent and an electrolyte of the organic electrolytic solution, a combination of an organic solvent in which a fluorine atom is bonded to a carbon atom adjacent to an unsaturated bond and a lithium salt having a fluoroalkyl group having 2 or more carbon atoms are used. This improves the safety of the battery.

The process of completing the present invention will be described in detail as follows.

The present inventors firstly used LiC as an electrolyte.
_When the conductivity of various solvent-based organic electrolytes using ₄ F ₉ SO ₃ was examined, it was found that LiC ₄ F ₉ SO ₃ / PC: DME
-Based organic electrolytic solution [L in a mixed solvent of propylene carbonate (PC) and 1,2-dimethoxyethane (DME)
iC ₄ F ₉ SO ₃ dissolved therein] has low reactivity with electrodes such as a negative electrode and a positive electrode, and has high conductivity.

Further, LiC ₄ F ₉ SO ₃ / AN: DME
-Based organic electrolytic solution [LiC ₄ F _{9 in} a mixed solvent of acetonitrile (AN) and 1,2-dimethoxyethane (DME)]
SO ₃ dissolved], LiC ₄ F ₉ SO ₃ / P
C: DME: AN-based organic electrolyte solution [LiC ₄ F ₉ S in a mixed solvent of propylene carbonate (PC), 1,2-dimethoxyethane (DME) and acetonitrile (AN)]
It has been found that those having dissolved O ₃ ] have higher conductivity, but all of them react with Li (lithium) of the negative electrode and are found to lack stability to the negative electrode. .

This is contained in acetonitrile-
Because of an unsaturated bond such as C≡N (nitrile group), a substituent adjacent to the unsaturated bond (CH _{3 in} the case of acetonitrile)
It is thought that this is because the group becomes unstable.

Actually, when the gas produced by the reaction of acetonitrile with Li was confirmed, H ₂ (hydrogen) and CH ₄
(Methane) was the main component.

[0014] This is probably because the bound CH ₃ group itself or CH bond CH ₃ group is easily cut to -C≡N.

Therefore, the inventors of the present invention, when a halogen atom is added to the carbon atom of the CH ₃ group, the bond of the carbon atom is protected by the size of the atom and the bonding force between the halogen atom and the carbon atom, and Li etc. The experiment was conducted on the assumption that the reactivity with

As a result, the organic electrolyte containing acetonitrile immediately reacts with Li to generate H ₂ and CH ₄ , whereas only one H atom in the CH ₃ group of acetonitrile is replaced with a fluorine atom. The organic electrolyte containing FCH ₂ C≡N (fluoroacetonitrile) hardly reacted with Li, and the metallic gloss of the Li surface was maintained even after storage.

From the above, it is possible to stabilize adjacent carbon atoms that have become unstable due to an unsaturated bond such as -C≡N by the fluorine atom, and reduce the reactivity between the organic electrolytic solution and Li or the like. It was then found that the stability of the organic electrolytic solution and the storability of the battery can be improved.

The above-mentioned fluorine atoms have a great effect of protecting adjacent atoms, and do not significantly impair the conductivity of the organic electrolyte.

In the organic solvent of the present invention, the atom adjacent to the unsaturated bond is a carbon atom, but it is sufficient that at least one fluorine atom is bonded to the carbon atom adjacent to the unsaturated bond, and two or more bonds are naturally formed. You may.

In the present invention, the unsaturated bond is a factor that improves the conductivity of the organic electrolyte solution. The unsaturated bond is, for example, -C≡N (nitrile group),
> C = O (carbonyl group),> S = O (sulfoxyl group), NO ₂ (nitro group) and the like.

In particular, the hetero-unsaturated bond has a large polarity and a large ionization degree of the electrolyte, and therefore has a large effect of increasing the conductivity of the organic electrolytic solution. Among them, -C≡N is particularly suitable as the unsaturated bond in the present invention because it has a particularly large polarity and is particularly excellent in the action of increasing the conductivity of the organic electrolytic solution.

Specific examples of the organic solvent having a fluorine atom bonded to the carbon atom adjacent to the unsaturated bond as described above include:
For example, fluoroacetonitrile (FCH ₂ C≡N),
Examples thereof include difluoroacetonitrile (F ₂ CHC≡N) and methyl fluoroacetate (FCH ₂ COOCH ₃ ).

In the present invention, in the preparation of the organic electrolytic solution, the organic solvent having a fluorine atom bonded to the carbon atom adjacent to the unsaturated bond can be used in combination with another organic solvent. As such an organic solvent which can be used in combination, for example, 1,2-dimethoxyethane, dimethoxymethane, dimethoxypropane, 1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, 4-methyl-
Examples thereof include ethers such as 1,3-dioxolane, propylene carbonate, ethylene carbonate, butylene carbonate, esters such as γ-butyrolactone and γ-valerolactone, and sulfolane.

In particular, in order to obtain a battery having excellent discharge characteristics at low temperature, it is preferable to use 1,2-dimethoxyethane among the above organic solvents, which has a low freezing point and a large effect of improving conductivity.

In the preparation of the organic electrolytic solution, the amount of the organic solvent in which the fluorine atom is bonded to the carbon atom adjacent to the unsaturated bond is preferably 10% by volume or more, and more preferably 30% by volume or more in the total solvent. . This is because when the organic solvent in which the fluorine atom is bonded to the carbon atom adjacent to the unsaturated bond is less than 10% by volume in the total solvent, the conductivity of the organic electrolytic solution is increased and the reactivity with the electrode is reduced. This is because the effect is not fully exerted.

Although it is possible to form the entire solvent of the organic electrolyte by using only the organic solvent in which the fluorine atom is bonded to the carbon atom adjacent to the unsaturated bond, the above-mentioned unsaturated solvent is taken into consideration in view of the conductivity at low temperature. The amount of the organic solvent in which the fluorine atom is bonded to the carbon atom adjacent to the saturated bond is 90% by volume or less, preferably 80% by volume or less in the total solvent.

When preparing the organic electrolyte,
When an ether such as 2-dimethoethane is used in combination, the amount of the ether is preferably 10 to 80% by volume, more preferably 30 to 50% by volume. In other words, if too much ether is added, the conductivity will decrease, and if too little ether will decrease the conductivity, increasing the impedance when used in a battery.

In the preparation of the organic electrolytic solution of the present invention, as the electrolyte, for example, lithium fluoroalkanesulfonate represented by LiC _n F _{2n + 1} SO ₃ and Li ₂ (C
_n F _2n ) (SO ₃ ) ₂ , LiN (C _n F _{2n + 1} S
O ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiN (CF ₃
CO) ₂ , LiC _n F _{2n + 1} CO ₂ , LiB (C
₆ H ₅ ) ₄ , LiClO ₄ , LiPF ₆ , LiA
_S F ₆ , LiSbF ₆ , and LiBF ₄ are used alone or in combination of two or more. Note that n in the chemical formula is an integer.

[0029] Among them, in the present invention, in the electrolyte is preferable because carbon atoms on 2 or more, the lithium salt is excellent in safety as a battery, in particular having a fluoroalkyl group with a carbon number of the 4 or more. Above all, the lithium salt of perfluoroalkanesulfonic acid is most preferable because it is particularly excellent in safety and can obtain battery characteristics to some extent.

Next, the main constituent members of the battery will be described.

In the present invention, the negative electrode comprises an alkali metal or a compound containing an alkali metal integrated with a current collecting material such as a stainless steel net. Examples of the alkali metal include lithium, sodium and potassium. As the compound containing an alkali metal, for example, an alloy of an alkali metal and aluminum, lead, indium, potassium, cadmium, tin, magnesium or the like,
Further, a compound of an alkali metal and a carbon material, a compound of a low potential alkali metal and a metal oxide, a compound of a sulfide and the like can be mentioned.

For the positive electrode, for example, a positive electrode active material such as manganese dioxide, vanadium pentoxide, chromium oxide, lithium cobalt oxide, lithium nickel oxide, or a conductive auxiliary agent or polytetrafluoroethylene is added to these positive electrode active materials. A mixture obtained by appropriately adding a binder or the like is used as a molded body by using a current collecting material such as a stainless steel net as a core material.

[0033]

EXAMPLES Next, the present invention will be described more specifically with reference to examples.

Example 1 PC: DME: FAN mixed solvent having a volume ratio of 1: 1: 1 [propylene carbonate (PC), 1,2-dimethoxyethane (DME), fluoroacetonitrile (FA
N) in a volume ratio of 1: 1: 1] to LiC ₄ F ₉
SO ₃ was dissolved at 0.3 mol / l to prepare an organic electrolytic solution.

A manganese dioxide mixture composed of a mixture of heat-treated manganese dioxide, carbon black and polytetrafluoroethylene was molded into a sheet having a thickness of 0.4 mm and a width of 30 mm using a stainless steel net as a core material.
A strip positive electrode with a stainless steel collector attached
It was dried at 0 ° C., and after drying, it was cooled to room temperature in a dry atmosphere.

Next, the above strip-shaped positive electrode was wrapped with a separator made of a microporous polypropylene film having a thickness of 25 μm, and a strip-shaped negative electrode obtained by crimping a sheet-shaped lithium sheet having a thickness of 0.18 mm and a width of 30 mm onto a stainless steel net was prepared. Overlap
Outer diameter of 15 mm after spirally winding into a spiral electrode body
After filling in the bottomed cylindrical battery case, spot welding of the positive electrode and negative electrode lead bodies was performed, and then the above-mentioned organic electrolytic solution was injected into the battery case.

Then, the opening of the battery case was sealed by a conventional method to produce a cylindrical organic electrolyte battery having the structure shown in FIG.

Explaining the battery shown in FIG. 1, 1 is the positive electrode and 2 is the negative electrode. However, in FIG. 1, in order to avoid complication, the stainless steel net, the current collector, and the like used in manufacturing the positive electrode 1 and the negative electrode 2 are not shown. And 3 is a separator and 4 is the above-mentioned organic electrolytic solution.

5 is a stainless steel battery case,
The battery case 5 also serves as a negative electrode terminal. An insulator 6 made of a polytetrafluoroethylene sheet is installed on the bottom of the battery case 5, and an insulator 7 made of a polytetrafluoroethylene sheet is also arranged on the inner peripheral part of the battery case 5. The spiral electrode body including the negative electrode 2 and the separator 3, the organic electrolytic solution 4, and the like are contained in the battery case 5.

Reference numeral 8 is a stainless steel sealing plate, and a gas vent hole 8a is provided at the center of the sealing plate 8. Reference numeral 9 is a polypropylene-made annular packing, 10 is a flexible thin plate made of titanium, and 11 is an annular heat-deformable member made of polypropylene.

The thermal deformation member 11 acts to change the breaking pressure of the flexible thin plate 10 by being deformed by the temperature.

Reference numeral 12 denotes a nickel-plated terminal plate made of rolled steel. The terminal plate 12 is provided with a cutting edge 12a and a gas discharge hole 12b, and gas is generated inside the battery, When the flexible thin plate 10 is deformed due to the increase of the internal pressure of the flexible thin plate 10, the cutting blade 12a destroys the flexible thin plate 10 and the gas inside the battery is discharged from the gas discharge hole 12b to the outside of the battery. It is designed to drain and prevent the battery from bursting.

Reference numeral 13 is an insulating packing, and 14 is a lead body. This lead body 14 electrically connects the positive electrode 1 and the sealing plate 8, and the terminal plate 12 comes into contact with the sealing plate 8 to make a positive electrode terminal. Acts as. Reference numeral 15 is a lead body that electrically connects the negative electrode 2 and the battery case 5.

Comparative Example 1 PC: DME: AN mixed solvent with a volume ratio of 1: 1: 1 [Propylene carbonate (PC), 1,2-dimethoxyethane (DME) and acetonitrile (AN) with a volume ratio of 1: 1). 1 mixed solvent] and 0.3% of LiC ₄ F ₉ SO ₃
Mol / l was dissolved to prepare an organic electrolytic solution.

Example 1 was repeated except that this organic electrolytic solution was used.
A cylindrical organic electrolyte battery was prepared in the same manner as in.

Comparative Example 2 PC: DME mixed solvent with a volume ratio of 1: 2 [propylene carbonate (PC) and 1,2-dimethoxyethane (DM
E) mixed solvent with a volume ratio of 1: 2] to LiC ₄ F ₉ SO
0.3 mol / l of ₃ was dissolved to prepare an organic electrolytic solution.

Example 1 was repeated except that this organic electrolytic solution was used.
An organic electrolyte battery was produced in the same manner as in.

The characteristics of the batteries of Example 1 and Comparative Example 1 produced as described above and the organic electrolyte used in the batteries were examined.

First, the organic electrolytic solution used in the battery of Example 1 and the organic electrolytic solution used in the battery of Comparative Example 1 were
0 ml each and a 0.2 mm-thick 10 mm × 40 mm lithium piece were placed in a vial, sealed and stored at 60 ° C. for 3 days, and the appearance of the lithium surface was observed. The results are shown in Table 1.

[0050]

[Table 1]

As shown in Table 1, the organic electrolyte of Comparative Example 1 containing acetonitrile reacted with lithium and turned yellow, but the organic electrolyte of Example 1 hardly reacted with lithium and had a metallic luster. It was kept.

In the organic electrolyte solution of Example 1, instead of acetonitrile, fluoroacetonitrile in which one of the hydrogen atoms bonded to the carbon atom adjacent to -C≡N of acetonitrile was replaced by a fluorine atom was used. It is considered that this is because the reactivity of the negative electrode with lithium was reduced.

Next, the battery of Example 1 and the battery of Comparative Example 1 were stored at 80 ° C. for 10 days, and the change in open circuit voltage due to storage was examined. The results are shown in Table 2. In addition, Table 2 also shows the ratio of the discharge capacity of each battery to the discharge capacity of the battery of Example 1 before storage.

[0054]

[Table 2]

As shown in Table 2, in the battery of Comparative Example 1 in which acetonitrile was used as the solvent of the organic electrolyte, the voltage dropped to about 3 V before the battery was stored, and almost no discharge was possible. This is because the lithium of the negative electrode has reacted with the organic electrolytic solution. In addition, when a plurality of batteries of Comparative Example 1 were manufactured, some of the batteries leaked liquid or the burst preventive device was activated.

On the other hand, in the battery of Example 1, 80 ° C.
Even under storage under severe conditions such as 10 days, the open circuit voltage did not decrease and sufficient discharge was possible.

Next, the results of comparing the characteristics of the battery of Example 1 and the organic electrolytic solution used for the battery with the battery of Comparative Example 2 and the organic electrolytic solution used for the battery will be shown. The organic electrolyte used in the battery of Comparative Example 2 was a PC: DME [mixed solvent of propylene carbonate (PC) and 1,2-dimethoxyethane (DME)] system. Is the most commonly adopted solvent system.

First, the organic electrolyte used in the battery of Example 1 and the organic electrolyte of the battery of Comparative Example 2 were -20 ° C. and 0 ° C.
Table 3 shows the results of examining the ionic conductivity at 20 ° C and 20 ° C.
Shown in.

[0059]

[Table 3]

As the organic electrolyte of Comparative Example 2, a solvent composition showing particularly high conductivity was selected among PC: DME systems which can obtain high conductivity, but as shown in Table 3, as shown in Table 3, The organic electrolytic solution had higher conductivity than the organic electrolytic solution of Comparative Example 2 at any temperature.

Next, the results of measuring the closed circuit voltage and the impedance of the battery of Example 1 and the battery of Comparative Example 2 are shown in Table 4.
Shown in. The closed circuit voltage is the battery voltage after energization at 3 A for 0.5 seconds, and the impedance is the value at 1 kHz and 10 kHz measured by an LCR meter.

[0062]

[Table 4]

As shown in Table 4, the battery of Example 1 had a higher closed circuit voltage and a lower impedance than the battery of Comparative Example 2 using the conventional solvent system. This result indicates that the conductivity of the organic electrolyte used in the battery of Example 1 is high.

[0064]

INDUSTRIAL APPLICABILITY As described above, in the present invention, as a solvent for the organic electrolyte, carbon atoms adjacent to unsaturated bonds are used.
By using the organic solvent having fluorine atoms bonded, it was possible to obtain an organic electrolytic solution having low reactivity with the electrode and high stability.

Further, by using the above-mentioned organic electrolytic solution, a battery having excellent storability can be obtained. further,
A battery using a combination of an organic solvent having a fluorine atom bonded to a carbon atom adjacent to an unsaturated bond and a lithium salt having a fluoroalkyl group having 2 or more carbon atoms as an organic solvent and an electrolyte of an organic electrolytic solution. Can improve the safety of.

[Brief description of drawings]

FIG. 1 is a sectional view schematically showing an example of an organic electrolyte battery according to the present invention.

[Explanation of symbols]

1 positive electrode 2 Negative electrode 3 separator 4 organic electrolyte

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsuaki Hasegawa 1 Toho-cho, Yokkaichi-shi, Mie Mitsubishi Petrochemical Co., Ltd. Yokkaichi Research Institute (72) Inventor Makio Kimura 1-place, Toho-cho, Yokkaichi-shi, Mie Mitsubishi Petrochemical Co., Ltd. Company Yokkaichi Research Institute (56) Reference JP-A-51-87726 (JP, A) JP-A-59-203368 (JP, A) JP-A-3-49157 (JP, A) (58) Fields investigated ( Int.Cl. ⁷ , DB name) H01M 6/16 H01M 10/40

Claims (5)

(57) [Claims] 1. An organic electrolytic solution comprising an organic solvent in which a fluorine atom is bonded to a carbon atom adjacent to an unsaturated bond. 2. The organic electrolytic solution according to claim 1, wherein the unsaturated bond is a heterounsaturated bond. 3. The organic electrolytic solution according to claim 2, wherein the heterounsaturated bond is —C≡N. 4. A negative electrode made of an alkali metal or a compound containing an alkali metal, a positive electrode, and 1, 2, or 3.
An organic electrolytic solution battery comprising the described organic electrolytic solution. 5. A rupture prevention device which has a negative electrode made of an alkali metal or a compound containing an alkali metal, a positive electrode, and an organic electrolyte solution and discharges gas inside the battery to the outside of the battery to prevent the battery from rupturing. An organic electrolyte battery having a carbon atom adjacent to an unsaturated bond as a solvent of the organic electrolyte solution.
An organic electrolyte battery comprising an organic solvent having a fluorine atom bonded thereto and a lithium salt having a fluoroalkyl group having 2 or more carbon atoms as an electrolyte.