JP3169248B2 - Organic electrolyte battery - 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 battery, and more particularly to an improvement in an organic electrolyte.

[0002]

2. Description of the Related Art An organic electrolyte battery typified by a lithium-manganese dioxide battery using lithium as a negative electrode, a manganese dioxide mixture as a positive electrode, and an organic electrolyte has a high energy density and a light weight. Demand tends to increase due to long life.

Recently, CF ₃ SO ₃ Li has been used as an electrolyte in order to improve the safety of batteries.

[0004]

However, the above C
Batteries using F ₃ SO ₃ Li as the electrolyte have the problem that the open circuit voltage decreases during storage.

[0005] When a compound represented by the general formula C _n F _{2n + 1} SO ₃ M (n is an integer of 2 or more and M is an alkali metal) is used as the electrolyte in the same manner as the above CF ₃ SO ₃ Li. Also, a phenomenon in which the open circuit voltage of the battery decreases during storage is observed.

[0006] Such a decrease in the open circuit voltage during storage can be suppressed to some extent by pre-discharging after assembling the battery. However, the open circuit voltage may still decrease when stored at high temperatures or for a long time. become.

[0007]

According to the present invention, an alkali metal salt containing a fluorine atom having two or more carbon atoms is used as an electrolyte and an organic electrolyte (hereinafter simply referred to as "electrolyte") is used. The present invention solves the above-mentioned problem by suppressing the decrease in the open circuit voltage of the battery during storage by incorporating alcohols into the battery.

[0008] The process of completing the present invention will be described in detail as follows.

The present inventors first examined the cause of the decrease in the open circuit voltage during storage as described above, and found that the decrease in the open circuit voltage during storage caused the active material of the positive electrode, the current collector, It has been found that this is caused by elution of the metal component from the positive electrode material such as the current collector network into the electrolytic solution.

More specifically, when the metal component is eluted from the positive electrode material, the elution itself is an oxidation reaction, and the active material of the positive electrode is partially reduced to reduce the capacity. At this time, if the current collector elutes, contact failure of the active material also occurs.

[0011] Then, when this becomes even worse, the metal component eluted into the electrolyte from the positive electrode material reacts with the alkali metal of the negative electrode and precipitates as a metal on the surface of the negative electrode. This is repeated, and the metal is deposited on the negative electrode. The battery grows and penetrates through the separator and eventually reaches the positive electrode, causing an internal short circuit in the battery, lowering the open circuit voltage of the battery and greatly reducing the capacity.

Therefore, it is considered that the above-mentioned decrease in the open circuit voltage during storage can be prevented by preventing the elution of the metal component from the positive electrode material.

The inventors of the present invention have conducted intensive studies based on the above-mentioned idea. As a result, they have used an alkali metal salt containing a fluorine atom having two or more carbon atoms as an electrolyte and contained an alcohol in the electrolyte. In this case, the present inventors have found that the metal component is prevented from being eluted from the positive electrode material into the electrolytic solution, and as a result, the decrease in the open circuit voltage during storage is suppressed, and the present invention has been completed.

Usually, when an organic electrolyte battery is manufactured in a state where an alcohol is contained in the electrolyte, the alcohol in the electrolyte reacts with the alkali metal of the negative electrode to form hydrogen as shown in the following reaction formula. Gas is generated to deteriorate the negative electrode, and the generated hydrogen gas causes blistering of the battery. Li + ROH → ROLi + 1 / 2H ₂

However, when the alkali metal salt containing a fluorine atom having two or more carbon atoms is used as the electrolyte, the reaction between alcohols and the alkali metal of the negative electrode is suppressed, and the blister of the battery and the negative electrode of the negative electrode are suppressed. Deterioration can be prevented.

To confirm this, first, LiCl
A typical electrolyte such as O ₄ , LiPF ₆ , and LiCF ₃ SO _{3 is} dissolved in a mixed solvent of propylene carbonate and 1,2-dimethoxyethane at a volume ratio of 1: 2 to 0.6 mol / l to prepare an electrolyte. In a state where 500 ppm of propylene glycol as an alcohol is mixed into the electrolyte, 10 ml of the solution is added to a vial bottle having a thickness of 0.18 mm.
After sealing with a piece of lithium having a size of 95 mm × 95 mm and leaving it at room temperature for 5 days, LiClO ₄ , LiPF ₆ ,
In all of LiCF ₃ SO ₃ , propylene glycol was reduced, and hydrogen gas was detected. It was also found that a hydroxide (probably an alcoholate) was formed on the surface of the negative electrode.

From the above, it can be seen that when a conventional general electrolyte is used, alcohols in the electrolytic solution react with the negative electrode, generating hydrogen gas and deteriorating the negative electrode.

However, when an alkali metal salt containing a fluorine atom having two or more carbon atoms is used as an electrolyte, the reaction with alcohols is greatly suppressed. For example, when the same experiment as above is performed using C ₄ F ₉ SO ₃ Li belonging to the alkali metal salt containing a fluorine atom having two or more carbon atoms, as described later in Examples, alcohols The amount of seldom changes. Then, propylene glycol is used as alcohols in 500
When a battery is manufactured using an electrolytic solution containing ppm, unexpectedly, in this battery, a decrease in open circuit voltage during storage is suppressed.

As described above, the reason why the decrease in the open circuit voltage during storage can be suppressed by including alcohols in the electrolytic solution is not always clear at present, but the alcohols may have some effect when they are stored. It is considered that this is because a protective film for suppressing elution of metal components is formed on the surface of the positive electrode material such as the positive electrode active material and the current collector.

In the present invention, an alkali metal salt containing a fluorine atom having two or more carbon atoms is used as an electrolyte. The alkali metal salt needs to contain a fluorine atom because it is contained in the alkali metal salt. If the carbon atom is not protected by at least one fluorine atom,
This is because the alkali metal salt is decomposed by the positive electrode active material.

Therefore, the fluorine atom is preferably contained as a fluoroalkyl group adjacent to the carbon atom, and the larger the number of carbon atoms bonded to the fluorine atom, the greater the effect of suppressing the reaction between the alcohol and the negative electrode. .

For example, the alkali metal salt containing a fluorine atom having two or more carbon atoms is C _n F _{2n + 1} SO ₃
In the case of M type, when n is 4 or more, even if the electrolyte contains about 500 ppm of alcohol, the reaction between the alcohol and the negative electrode hardly occurs. However,
If the molecular weight is too large, the ionic conductivity decreases and the discharge characteristics and the like deteriorate. Therefore, it is preferable to use those having 20 or less carbon atoms, particularly 13 or less carbon atoms, and especially 8 or less carbon atoms.

The carbon atom containing form is particularly preferably a fluoroalkyl group (for example, CnF _{2n + 1} ) from the viewpoint of reducing the reactivity between alcohols and the negative electrode.
Typical examples are RfSO ₃ Li, RfORf'S
O ₃ Li (where Rf is a fluoroalkyl group,
Rf 'is a fluoroalkylene group).

In the present invention, as the alcohol to be contained in the electrolytic solution, for example, aliphatic alcohols such as methanol, ethanol, ethylene glycol, propylene glycol, and propargyl alcohol, and aromatic alcohols such as phenol may be used. it can. Among them, alcohols having an unsaturated bond, particularly a triple bond, such as propargyl alcohol, have a particularly high effect, and exhibit a remarkable effect even when used in a small amount.

However, since the effects of these alcohols are reduced if the molecular weight is too large, those having 7 or less carbon atoms, particularly 5 or less carbon atoms, particularly 3 or less carbon atoms are preferable.

Alcohols in the electrolyte begin to have an effect of suppressing the decrease in open-circuit voltage during storage from about 50 ppm, and in order to obtain a more favorable effect, the amount of alcohols in the electrolyte is reduced to 100 ppm or more. In particular, when the content is 200 ppm or more, more preferable effects can be obtained. However, if the amount of alcohols in the electrolytic solution is too large, the reaction between the alcohols in the electrolytic solution and the negative electrode may occur even if an alkali metal salt containing a fluorine atom having two or more carbon atoms is used as the electrolyte. The amount of alcohol in the electrolyte is 1000
It is preferable to keep the concentration at ppm or less.

In preparing the electrolytic solution, the solvent may be
For example, 1,2-dimethoxyethane, dimethoxymethane, dimethoxypropane, 1,3-dioxolan, tetrahydrofuran, 2-methyltetrohydrofuran,
Ethers such as methyl-1,3-dioxolane, propylene carbonate, ethylene carbonate, butylene carbonate, γ-butyrolactone, γ-valerolactone, diethyl carbonate, esters such as dimethyl carbonate, and also dimethylformamide, dimethyl sulfoxide, acetonitrile Or an organic solvent such as dichloromethane or a mixture of two or more thereof. In order to obtain a battery having particularly excellent discharge characteristics, it is preferable to use ether in a solvent at 55% by volume or more, particularly at 60% by volume or more. And, as the ether, 1,
Chain ethers such as 2-dimethoxyethane, dimethoxymethane, and dimethoxypropane are particularly preferably used because they improve discharge characteristics at low temperatures.

When a metal oxide such as manganese dioxide is used as the positive electrode active material, if an ester such as propylene carbonate is used in an amount of 10% by volume or more in the solvent, the positive electrode active material and the electrolyte solvent during storage can be used. The reaction with the ether used can be suppressed, and the storage characteristics of the battery can be prevented from lowering. If the discharge characteristics at low temperatures are particularly important, a combination of propylene carbonate and 1,2-dimethoxyethane is used, and the ratio of 1,2-dimethoxyethane in the combination is 55 to 80% by volume, particularly 60 to 75% by volume. % Is preferable.

The concentration of the alkali metal salt containing a fluorine atom having two or more carbon atoms in the electrolyte is from 0.05 to 0.05.
1 mol / l is suitable, especially 0.2-0.6 mol
/ L is preferred. If the alkali metal salt containing a fluorine atom having two or more carbon atoms is contained in the electrolytic solution at the above-described concentration, in addition to the alkali metal salt, for example,
Other electrolytes such as LiClO ₄ , LiBF ₄ and LiPF ₆ may be contained in small amounts. That is, an alkali metal salt containing a fluorine atom having two or more carbon atoms may be used as the main electrolyte.

The negative electrode is made of an alkali metal or a compound containing an alkali metal. Examples of the alkali metal include lithium, sodium, and potassium. Examples of the compound containing an alkali metal include those alkali metals and aluminum, lead, and the like. Alloys of indium, gallium, cadmium, tin, magnesium, and the like, and further, compounds of an alkali metal and a carbon material or a BCN composite material are exemplified. When the compound containing the alkali metal is used for the negative electrode, the reactivity between the alcohols and the negative electrode is further reduced, so that more preferable results are obtained.

For the positive electrode, a positive electrode active material such as manganese dioxide, vanadium pentoxide, chromium oxide, lithium cobalt oxide, and lithium nickel oxide, or a conductive auxiliary such as carbon black or graphite or polyelectrolyte, A molded product is used together with a current collecting material such as stainless steel or aluminum, using a mixture to which a binder such as tetrafluoroethylene is appropriately added.

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

[0033]

【Example】

Example 1 A manganese dioxide mixture made of manganese dioxide, carbon black and polytetrafluoroethylene heat-treated at 450 ° C., having a thickness of 0.4 m using a stainless steel net as a core material
m, a belt-shaped positive electrode having a stainless steel current collector attached thereto was dried at 250 ° C. for 9 hours, and then cooled to room temperature in a dry atmosphere.

Next, this 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 made of lithium having a thickness of 0.18 mm and a width of 30 mm was stacked thereon, and spirally wound. Then, the spirally wound electrode body was filled into a cylindrical battery case with a bottom having an outer diameter of 15 mm, and spot welding of the lead body was performed.

Separately, after drying C ₄ F ₉ SO ₃ Li, 0.6 mol / l of a mixed solvent of propylene carbonate and 1,2-dimethoxyethane in a volume ratio of 1: 2 was used.
And propylene glycol was added to this solution to prepare an electrolytic solution containing 200 ppm of propylene glycol, and this electrolytic solution was injected into the battery case.

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

Referring to the battery shown in FIG. 1, reference numeral 1 denotes a positive electrode formed by molding the above-mentioned manganese dioxide mixture, and a stainless steel mesh is used as a core material in the formation. Reference numeral 2 denotes a negative electrode made of lithium, and this negative electrode 2 is produced by press-bonding to a stainless steel net. However, FIG. 1 does not show a stainless steel net, a current collector, and the like used in manufacturing the positive electrode 1 and the negative electrode 2 in order to avoid complication. Reference numeral 3 denotes a separator, and reference numeral 4 denotes the above electrolyte.

5 is a stainless steel battery case,
This battery case 5 also serves as a negative electrode terminal. An insulating material 6 made of a polytetrafluoroethylene sheet is provided on the bottom of the battery case 5, and an insulating material 7 made of a polytetrafluoroethylene sheet is also provided on the inner peripheral portion of the battery case 5. A spiral electrode body composed of 1, a negative electrode 2 and a separator 3, an electrolyte solution 4, and the like are accommodated in the battery case 5.

Reference numeral 8 denotes a sealing plate made of stainless steel, and a gas ventilation hole 8a is provided in the center of the sealing plate 8. 9 is an annular packing made of polypropylene, 10 is a flexible thin plate made of titanium, 11 is an annular heat deformable member made of polypropylene, and this heat deformable member 11 is It acts to change the burst pressure.

Reference numeral 12 denotes a nickel-plated terminal plate made of rolled steel. The terminal plate 12 has a cutting edge 12a and a gas discharge hole 12b. When the internal pressure is increased and the flexible thin plate 10 is deformed by the increase of the internal pressure, the flexible blade 10 is designed to be broken by the cutting blade 12a and discharged to the outside of the battery.

Reference numeral 13 denotes an insulating packing, and 14 denotes a lead body. The lead body 14 electrically connects the positive electrode 1 to the sealing plate 8, and the terminal plate 12 contacts the positive electrode terminal by contact with the sealing plate 8. Act as Reference numeral 15 denotes a lead body for electrically connecting the negative electrode 2 and the battery case 5.

Example 2 C ₄ F ₉ SO ₃ Li was mixed with propylene carbonate and 1,2
To a mixed solvent having a volume ratio of 1: 2 with dimethoxyethane.
6 mol / l, and propargyl alcohol was added to this solution to prepare an electrolytic solution containing 100 ppm of propargyl alcohol. The same procedure as in Example 1 was carried out except that this electrolytic solution was used. A liquid battery was manufactured.

Example 3 A cylindrical organic electrolyte battery was manufactured in the same manner as in Example 1 except that the negative electrode 2 was replaced with a lithium-aluminum alloy (98% lithium content) instead of lithium.

Example 4 A cylindrical organic electrolyte battery was manufactured in the same manner as in Example 1 except that C ₈ F ₁₇ SO ₃ Li was used instead of C ₄ F ₉ SO ₃ Li.

Comparative Example 1 CF ₃ SO ₃ Li was mixed with propylene carbonate and 1,2-
0.6 to a mixed solvent having a volume ratio of 1: 2 with dimethoxyethane.
mol / l, and propylene glycol was added to this solution to prepare an electrolytic solution containing 200 ppm of propylene glycol. This electrolytic solution was used in the same manner as in Example 1 except that this electrolytic solution was used. Was prepared.

Comparative Example 2 C ₄ F ₉ SO ₃ Li was mixed with propylene carbonate and 1,2
To a mixed solvent having a volume ratio of 1: 2 with dimethoxyethane.
An electrolytic solution was prepared by dissolving 6 mol / l, and a cylindrical organic electrolyte battery was produced in the same manner as in Example 1 except that this electrolytic solution was used.

Examples 1 to 4 and Comparative Examples 1 to 2
20 batteries were allowed to stand at room temperature for one week, and those having a battery voltage of 3.4 V or less were regarded as open circuit voltage failures, and the ratio of defective batteries (open circuit voltage failure rate) was examined. The results are shown in Table 1 as [number of open-circuit voltage defective batteries / number of test batteries].

[0048]

[Table 1]

As shown in Table 1, the batteries of Examples 1 to 4 did not have any open-circuit voltage defect, but the batteries of Comparative Examples 1 to 2
Open-cell voltage failure occurred in the battery of No. The result is that the use of C ₄ F ₉ SO ₃ Li or C ₈ F ₁₇ SO ₃ Li as the electrolyte suppresses the reaction between the alcohols and the negative electrode, and opens the circuit by containing the alcohols in the electrolyte. This indicates that occurrence of a voltage defect is suppressed.

That is, the batteries of Examples 1 to 4 and Comparative Example 1
Although the electrolyte is different from that of the above battery, the electrolyte solution contains alcohols in each case. Example 1 as described above
The batteries of Example 4 did not have the open circuit voltage failure.
C ₄ in the battery was used as the electrolyte F ₉ SO ₃ Li and C
_{Although 8} F ₁₇ SO ₃ Li suppressed the reaction between the alcohols in the electrolytic solution and the negative electrode, the open circuit voltage failure occurred in the battery of Comparative Example 1 because CF ₃ SO ₃ Li used as the electrolyte was This is because the reaction between the alcohols therein and the negative electrode could not be suppressed, resulting in deterioration of the negative electrode.

The batteries of Examples 1 to 3 and the battery of Comparative Example 2 have the same electrolyte, but the batteries of Examples 1 to 3 contain alcohols in the electrolyte. Battery 2 does not contain alcohols in the electrolyte. As described above, the batteries of Examples 1 to 3 did not have the open circuit voltage defect because the batteries of Examples 1 to 3 contained alcohols in the electrolyte.

Next, 10 ml each of the electrolyte used in the batteries of Examples 1 to 4 and the electrolyte used in the battery of Comparative Example 1 was 0.18 mm thick and 28 mm × 9.
5 mm lithium piece [However, in the case of Example 3, a lithium-aluminum alloy of the same dimensions (lithium content 98%)
%) Piece] and sealed in a vial bottle.
After standing for a day, the alcohols in the electrolyte were measured by gas chromatography. The results are shown in Table 2 as the retention rate of alcohols in the electrolytic solution [(amount of alcohols after standing for 5 days / amount of alcohols before standing) × 100].

[0053]

[Table 2]

As shown in Table 2, the electrolytes used in the batteries of Examples 1 to 4 had higher retention of alcohols than the electrolytes used in the battery of Comparative Example 1 (that is, the electrolytes were left unattended). Alcohols are less reduced), C ₄ F ₉ SO ₃ L
The use of i or C ₈ F ₁₇ SO ₃ Li suppressed the reaction between the alcohols in the electrolyte and lithium, and showed that the inclusion of the alcohols in the electrolyte did not adversely affect the inside of the battery.

Next, the following experiment was conducted to confirm that the decrease in the open circuit voltage during storage was due to the elution of the metal component from the positive electrode material.

The electrolytic solution used for the batteries of Examples 1 to 2 and Example 4 and the electrolytic solution used for the battery of Comparative Example 2 were each placed in a vial bottle in an amount of 10 ml. The positive electrode used in the battery of Comparative Example 2 and the positive electrode used in the battery of Comparative Example 2 were placed in a vial bottle, sealed, and stored at 80 ° C. for 10 days. However, the positive electrode used was cut out while leaving the current collector (stainless steel SUS430) 1 cm on each side so that it could be easily put into a vial bin.

As a result, in the electrolyte of Comparative Example 2, corrosion was observed on the stainless steel current collector, and C
r, Fe, and Mn were detected, and it was confirmed that metal components were eluted from the positive electrode active material manganese dioxide (MnO ₂ ) and the stainless steel current collector.

On the other hand, in the case of the electrolytic solutions of Examples 1 to 2 and Example 4, the elution amounts of Cr and Fe were reduced to 1/20 or less as compared with the case of Comparative Example 2, and the elution amount of Mn was reduced. The amount was less than about half.

From the above, when no alcohol is contained in the electrolyte, the metal component elutes from the positive electrode material, and when the negative electrode, for example, lithium (Li) is present,
The eluted metal ions react with lithium, and the metal deposits on the lithium surface of the negative electrode, and this is repeated, and the metal grows on the lithium of the negative electrode, penetrates through the separator, finally reaches the positive electrode, and the battery is short-circuited internally. However, it can be seen that the open circuit voltage of the battery decreases, and that the reduction of the open circuit voltage of the battery is suppressed by suppressing the elution of the metal component from the positive electrode material.

[0060]

As described above, according to the present invention, an alkaline metal salt containing a fluorine atom having two or more carbon atoms is used as an electrolyte, and an alcohol is contained in the electrolyte so that the electrolyte can be stored. The decrease in the open circuit voltage of the battery was suppressed.

[Brief description of the drawings]

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

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Negative electrode 3 Separator 4 Electrolyte

Continuation of front page (56) References JP-A-1-281677 (JP, A) JP-A-4-37063 (JP, A) JP-A-5-82138 (JP, A) JP-A-2-262246 (JP) , A) JP-A-4-32160 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 6/16 H01M 10/40

Claims (2)

(57) [Claims] 1. An organic electrolyte battery including a positive electrode containing a metal element, a negative electrode made of an alkali metal or a compound containing an alkali metal, and an organic electrolyte as a power generating element, wherein the organic electrolyte is used as two electrolytes. An organic electrolyte battery comprising the above alkali metal salt containing a fluorine atom having a carbon atom and containing an alcohol. 2. The organic electrolyte battery according to claim 1, wherein the electrolyte is C ₄ F ₉ SO ₃ Li.