JPS6124174A - Secondary cell - Google Patents

Abstract

PURPOSE:To obtain a secondary cell improved on cycle life, self-discharge, and voltage constancy at the time of discharge, by using material composed of organic solvent, supporting electrolyte and special dithiophene compound as the electrolytic liquid for the secondary cell using acetylene copolymer for its positive electrode or for both of its positive and negative electrode. CONSTITUTION:A secondary cell using acetylene high polymer for its positive electrode or for both of its positive and negative electrode uses material composed of organic solvent, supporting electrolyte and dithiophene compound expressed by a general formula as shown for its electrolytic liquid. However, it is assumed that R1 and R2 are alkyl group with carbons of 5 or less in numbers, and m and n are 0.1 or 0.2 in this formula. As said dithiophene compound, for exampla, dithiophene, 3-methyldithiophene, 3, 3'-dimethyldithiophene, 3-ethyldithiophene, 3, 3'-diethyldithiophene, etc. are used and their addition amounts are preferable to be in the range of 0.1-10g to 100g of the acethylene high polymer of the positive electrode.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a secondary battery with improved cycle life, self-discharge, and voltage flatness during discharge.

Conventionally, batteries using an acetylene polymer as both the positive and negative electrodes of the battery are well known (for example, JP-A-56-136469, JP-A-57-121168,
JP-A No. 58-38465).

However, acetylene high polymers are susceptible to gradual oxidation reactions due to oxygen in the air, which does not reduce battery performance, and electrochemically produces side reaction products and impurities during charging. It is also susceptible to oxidative deterioration due to the electrolyte itself. Therefore, when an acetylene polymer is used in a battery positive electrode, the electrolyte and solvent used must have a fairly wide electrochemical stability range, and the electrolyte must have a high level of purity. be.

Furthermore, as mentioned above, even if an electrolyte with high purity and a wide electrochemical stability range is used, when an acetylene polymer is used as the positive electrode, it will suffer from oxidative deterioration even at a relatively low oxidation potential. Decrease battery performance.

For example, if the acetylene polymer of the positive electrode reaches 3.5 V or higher in the electrolytic solution based on Li/Li+reference electrode, it becomes susceptible to deterioration reactions.

One of the reasons for this is that the acetylene polymer itself is a substance that easily deteriorates due to oxidation. Therefore, it has been a major challenge for these manufacturers to develop higher-performance batteries that have less deterioration of the electrodes themselves, less self-discharge during charging and storage, and a longer service life after repeated charging and discharging. .

In view of the above points, the present inventors conducted various studies to obtain a battery with better performance, and as a result, they found that the battery performance can be significantly improved by adding a dithiophene compound to the electrolyte. They discovered this and arrived at the present invention.

That is, the present invention provides a secondary battery using an acetylene polymer as a positive electrode or a positive electrode and a negative electrode, in which the electrolyte is an organic solvent,
The present invention relates to a secondary battery comprising a supporting electrolyte and a dithiophene compound represented by the following general formula.

[However, in the formula ', R1 and R2 are alkyl groups having 5 or less carbon atoms, and m and n are 0, 1 or 2. ] In the present invention, it is not necessarily clear why battery performance can be improved by adding a dithiophene compound to the electrolyte, but it is possible to improve battery performance by adding a dithiophene compound to the acetylene polymer electrode during charging and discharging of the battery. It is assumed that one of the causes is the formation of polymers.

Various methods have been reported for producing the acetylene polymer used in the electrode of the secondary battery of the present invention, and a specific example thereof is disclosed in Japanese Patent Publication No. 48-32581.

Japanese Patent Publication No. 56-45365, Japanese Patent Publication No. 55-129404
issue.

55-12'8419, 5'5-142012
No. 56-10428, No. 56-133133,
'l'rans Farady, Soc, , 64,8
23 (1968), J. Polymer Sci., A-
1, 7, 3419 (1969), Makromol.

Chem, , Rapid Comm, , 1,621
(1980), J.

Chern, Phys., 69(1), 1
06 (1978), SyntheticMata
ls, 4.81 (1981), but is not necessarily limited thereto.

The acetylene polymer used as the electrode in the present invention may be in any form, such as film, powder, or short fibers. The acetylene polymer may also be combined with other suitable conductive materials, such as graphite. There is no problem in mixing carbon black, a7ethylene black, metal powder, carbon fiber, etc., or adding a metal net or the like as a current collector. Further, it may be reinforced with a thermoplastic resin such as polyethylene, modified polyethylene, poly(tetrafluoroethylene), or polybutadiene.

Furthermore, in the present invention, instead of an acetylene polymer, a conductive acetylene polymer obtained by doping this acetylene polymer with a dopant in advance can also be used as the electrode. ``The method of doping the acetylene polymer with a dopant may be either chemical doping or electrochemical doping.

In the secondary battery of the present invention, the acetylene polymer is used only for the positive electrode, or for both the positive and negative electrodes. When using acetylene high polymer only for the positive electrode, L as the negative electrode.
Light metals such as i, Na, k, At, poly(
thiophene), poly(3-methyl-thiophene), poly(pyrono), poly(N-methyl-virol), polyquinoline (JP-A-57-195731), poly(paraphenylene), fired phenolic resin (JP-A-57-195731) Showa 58-6
9234), polymer fired body (JP-A-58-93176)
Conductive polymers such as No. 1) are used, but are not necessarily limited to these.

Charging and discharging of the secondary battery of the present invention correspond to electrochemical doping and undoping of cations and anions to the electrodes, respectively.

As a dopant to be electrochemically doped, (i
) PF, 7, 5bF6-, A8F,-, 5bC1
Halide anions of Va group elements such as 6-o, BF
4-halodanide anions of elements of the 1lla group, such as
anion dopants such as halogen anions such as r(technical, i) z13r-, C1-, perchlorate anions such as cto4', and (ti) Li", Na
”, alkaline earth ions such as K+, R4N” (
Examples include cations and dopants such as quaternary ammonium ions (R: hydrocarbon group having 1 to 20 carbon atoms), but are not necessarily limited to these.

Specific examples of supporting electrolytes that provide the anionic and cationic dopants mentioned above include LiPF6. L
iSbF6. LiAsF6. LiClO4, Na■.

NaPF6. NaSbF6. NaSbF6. Na
CtO4, KI, KPF6゜KSbF6j KA8
F6. KCtO4[Et3BuN)”-(BF4)”
-jC(n-Bu)4N:) "-(AgF2)"-,
((n-Bu)4N)"-(PF6)"' 1 [(n-
Bu)4N)"-CtO,"-, LiAtct4. L
iBF4. 'No2'BF4. NO”BF4.
NO2'AsF6, NaSbF6゜NO2・C1
o4. Although it is possible to use No-CtO4, it is not necessarily limited to these. These supporting electrolytes may be used alone or in combination of two or more.

Among the above-mentioned cations, an asymmetric quaternary ammonium ion whose general formula is represented by the following formula is preferred.

[In the formula, R,, R2, R, and R4 have 1 to 1 carbon atoms
6, or an aryl group. However, all R, , R2, R, and R4 are not the same group at the same time. ] Specific examples of asymmetric quaternary ammonium ions include trimethylpropylammonium, trimethylbutylammonium, trimethylhexylammonium, trimethyloxylammonium, trimethylisobutylammonium, trimethyltert-butylammonium, trimethylisopropylammonium, trimethylisobutylammonium, and trimethyl. Hexadecyl ammonium, trimethylpentylammonium, trimethylphenylamsonium, triethylbutylammonium, triethylpropylammonium, triethylmethylammonium, triethylhexylammonium, triethylphenylammonium, tripropylbutylammonium, tributylmethylammonium, triphthyl ethyl Ammonium, dipropyl diethylammonium, dibutyl diethylammonium, dibutyl dimethyl ammonium, dimethyl diphenylammonium, diethyldiphenylamsonium, dibutyl ethyl, tylammonium, dibuteterbyl ethyl methyl ammonium, Petit Prize bile ethyl methyl amsonium It will be done.

The anion dopant other than the above may be a 2-anion, and the cation dopant other than the above may be a pyrylium or pyridinium cation represented by the following formula (I): (wherein, X is oxygen atom or nitrogen atom, R' is a hydrogen atom or an alkyl group having 1 to 15 carbon atoms, and 6 to 15 carbon atoms.
7 aryl group -Rf is a halogen atom or an alkyl group having 1 to 1 carbon atoms, an aryl group having 6 to 15 carbon atoms, m is 0 when X is an oxygen atom
and when X is a nitrogen atom, it is l. n is 0 or 1
- Chiru with 5. ) or a carbonium cation represented by the following formula ■ or (I[[): R5/ and R'-C+ (I[[) [In the above formula, Rf, R2, BS are hydrogen atoms (B1,
R2゜R3 is not a hydrogen atom at the same time), alk having 1 to 15 carbon atoms, a kyl group, ally
) group, an aryl group having 6 to 15 carbon atoms, or an 10R5 group, where R represents an alkyl group having 1 to 10 carbon atoms or an aryl group having 6 to 15 carbon atoms, and R4 is hydrogen. These include atoms, alkyl groups having 1 to 15 carbon atoms, and aryl groups having 6 to 15 carbon atoms. ].

The I(F'2-anion used usually has the following general formula % formula % (): [However, in the above formula, R', R" is a hydrogen atom or a carbon number
~15 alkyl group, ary-# having 6 to 15 carbon atoms (a
ryl) 15, RII is an alkyl group having 1 to 10 carbon atoms, an aryl group having 6 to 15 carbon atoms,
is an oxygen atom or a nitrogen atom, and n is O or a positive integer of 5 or less. M is an alkali metal] is obtained by dissolving the compound (), hydrogenide salt) in a suitable organic solvent using as a supporting electrolyte. The above formula (I
Specific examples of compounds represented by I/), (Vl and (M) include H4NaHF2°Bu4N@HF2.Na
a BF2. KaHF2. Li @HP2 and the pyrylium or pyridinium cation represented by the above formula (I) are the cations represented by the formula (1) / and ct
o4-, BF4-, Atc! 4″, FeC2,t
5nCz5″, pr6″.

pct, 7, 5bp6-*AaF6', cyss
It can be obtained by dissolving in a suitable organic solvent using a salt with an anion such as O3'', HF; etc. as a supporting electrolyte. Specific examples of such salts include CH3 and the like.

Specific examples of carbonium cations represented by the above formula Q[)t or (III) include (C6H5)sC+t
(CH3), C”+ These carbonium cations are
It can be obtained by dissolving them and an anion salt (carbonium salt) in a suitable organic solvent as a supporting electrolyte. Representative examples of anions used here include BF4
-, AtC14-, AtBr5C1-, FeC1;
, 5nC43-.

pF6-, pct6″, 5bcz6-, sbF,
-, cto;, cF3so3'', etc., and specific examples of carbonium salts include (
C6H5)3C-BF4°(CH3)3C1IBF4.
HCO・htct4. HCO-BF4゜C6H5C0
・5nCZs etc. can be mentioned.

The organic solvent of the electrolyte used in the present invention includes aliphatic nitrile compounds, aromatic nitrile compounds,
ethers, esters, amides, carbonates,
Examples include sulfolane compounds and nologne compounds, preferably aliphatic nitrile compounds and aromatic nitrile compounds, particularly preferably aromatic nitrile compounds.

Specific examples of these organic solvents include tetrahydro7rane, 2-methyltetrahydrofuran, 1,4-dioxane, anisole, monoglyme, acetonitrile, propionitrile, butyronitrile, valeronitrile, 4-methyl-2-pentanone, benzonitrile, o-') lunitrile, m-tolnitrile, p-tolnitrile, α-tolnitrile, 1,2-dichloroethane, γ-butyrolactone, dimethoxyethane, methylformate, propylene carbonate, ethylene carbonate, dimethylformamide, dimethylsulfoxide, dimethylthioformamide , sulfolane, 3-methyl-sulfolane, trimethyl phosphate, triethyl phosphate, etc. Among these, preferred solvents include acetonitrile, propionitrile, phthyronitrile, valeronitrile, benzonitrile, α-tolnitrile, -Tolnitrile, m-)lunitrile, p-tolnitrile,
Particularly preferred solvents include benzonitrile, 0-tolunitrile, m-)lunitrile, and p-)lunitrile. These organic solvents may be used in any of the four directions even if used as a mixed solvent.

The concentration of the supporting electrolyte used in the secondary battery of the present invention varies depending on the type of positive electrode or long electrode used, charging/discharging conditions, operating temperature, type of electrolyte, type of organic solvent, etc., and therefore cannot be generally prescribed. Not possible, but usually 0.5
~10 mol/l. The electrolyte may be a homogeneous system or a non-uniform system and may be used in any of the four directions.

The dithiophene compound used in the present invention has the general formula [wherein R4 and R2 are alkyl groups having 5 or less carbon atoms, and m and n are 0, 1 or 2. ]. Specific examples of the dithiophene compound include dithio7ene, 3-methyldithiophene, 3,3'-dimethyldithiophene, 3-ethyldithiophene, 3,3'-diethyldithiophene, and the like.

The amount of dithiophene compound added is 0.1 to 10? It is preferable that it is within the range of . Outside this range, no significant improvement in battery performance can be expected.

Further, in the secondary battery of the present invention, the amount of dopant doped into the acetylene polymer is 1 to 15 mol per mol of repeating unit (-CH-) of the acetylene polymer. The preferred amount is 3 to 10 mol.

The amount of doping can be freely controlled by measuring the amount of electricity flowing during electrolysis. The doping may be carried out either under constant current, constant voltage or under varying conditions of current and voltage.

In the present invention, if necessary, a porous membrane made of synthetic resin such as polyethylene or polypropylene or natural fiber paper may be used as a diaphragm in all four directions.

In addition, the acetylene polymer used in the present invention undergoes a gradual oxidation reaction due to oxygen, which may reduce the performance of the battery, so the battery should be sealed and kept in a substantially oxygen-free state. desirable.

The secondary battery of the present invention has high energy density, high charge/discharge efficiency, long cycle life, low self-discharge rate, and good voltage flatness during discharge. Furthermore, the secondary battery of the present invention is lightweight, compact, and has a high energy density, so it is ideal for use in portable devices, electric vehicles, gasoline vehicles, and power storage batteries.

Hereinafter, the present invention will be explained in more detail with reference to Examples and Comparative Examples.

Example 1 [Manufacture of film-like acetylene polymer] In a glass reaction vessel with an internal volume of 500 m in a nitrogen atmosphere, 1.
．． A catalyst solution was prepared by adding 7M titanium tetrabutoxide, dissolving it in 30g of aninole, and then adding 2.7M triethylaluminum with stirring.

This reaction vessel was cooled with liquid nitrogen, and the nitrogen gas in the system was exhausted using a vacuum pump. Next, this reaction vessel was
After cooling to 0.degree. C. and keeping the catalyst solution stationary, purified acetylene gas at a pressure of 1 atmosphere was bubbled through.

Immediately, polymerization occurred on the surface of the catalyst solution, producing a film-like acetylene high polymer. Thirty minutes after the introduction of acetylene, the acetylene gas in the reaction vessel system was exhausted to stop the polymerization.

After removing the catalyst solution with a syringe under nitrogen atmosphere, -78
While keeping the temperature at ℃, the sample was washed 5 times with 100 d of purified toluene. The film-like acetylene polymer swollen with toluene was a uniform film-like swollen product in which fibrils were tightly intertwined.

Next, the swollen product was vacuum-dried to obtain a reddish-purple film with a metallic luster, a thickness of 180 μm, and a cis content of 98%. In addition, the bulk density of this film-like acetylene polymer is 0.30 g-/(f), and its electrical conductivity (DC four-probe method) is 3.2XIOΩ at 20°C.
It was α.

[Battery experiment]

Two disks with a diameter of 20 mm were cut out from the film-like acetylene polymer obtained by the above method, and a battery was constructed by using the disks as active materials for a positive electrode and a negative electrode, respectively.

The figure is a schematic cross-sectional view of a battery cell for measuring the characteristics of a non-aqueous secondary battery, which is a specific example of the present invention. sb, 1 is a platinum lead wire for the negative electrode, 2 is a platinum wire mesh current collector for the negative electrode with a diameter of 20 mm x 80 mesh 2 body, 3 is a disc-shaped negative electrode with a diameter of 20 mm, 4 is a diameter of 20 m
5 is a circular porous polypropylene diaphragm thick enough to be sufficiently impregnated with electrolyte, 5 is a disk-shaped positive electrode with a diameter of 20 mm, and 6 is a platinum wire mesh current collector for the positive electrode with a diameter of 20 mm and 80 mesh. , 7 is a positive electrode lead wire, and 8 is a screw-type Teflon container.

First, the platinum wire mesh current collector 6 for the positive electrode is placed in a Teflon container 8.
The positive electrode 5 is further placed on the positive electrode platinum wire mesh current collector 6, and the porous polypropylene diaphragm 4 is placed on top of the positive electrode platinum wire mesh current collector 6.
After stacking them and sufficiently impregnating them with the electrolytic solution, the negative electrode 3 was stacked, and the platinum wire mesh current collector 2 for the negative electrode was further placed thereon, and the Teflon container 8 was tightened to produce a battery.

As the electrolytic solution, 2 mol of Et3BuN'BF4 dissolved in distilled and dehydrated benzonitrile according to a conventional method was added to the solution 1.
0.1 ml of dithio7ene (0.11fi
) was used.

The thus prepared battery was charged in an argon atmosphere under a constant current (4.5 mA/cJ) by flowing an amount of electricity corresponding to a doping amount of 5.3 mol. Immediately after charging is completed, under constant current (5.0mA/lri)
Then, when the battery was discharged and the voltage reached 0.3V, it was charged again under the same conditions as above, and a repeated charging/discharging test was conducted. The number of repetitions of charging and discharging was recorded as 756 times.

The energy density of the fifth repetition is 119
The charging/discharging efficiency was 98 cm at W-hr/ky.

Furthermore, when the battery was left charged for 62 hours, its self-discharge rate was 2.9 inches.

Comparative Example 1 A battery was repeatedly charged and discharged in the same manner as in Example 1 except that dithiophene was not added to the electrolyte. The efficiency was 95%, and discharge became impossible after the 553rd repetition.

Also, the energy density at the fifth repetition is 117 W.
-hr/Q, the charge/discharge efficiency was 95 cm. Also,
When the battery was left charged for 62 hours, its self-discharge rate was 7.9 cm.

Example 2 A repeated experiment of charging and discharging a battery was conducted in exactly the same manner as in Example 1 except that 3,3'-dimethyldithiophene was used in place of dithiophene. The number of times charging and discharging was repeated until the charging and discharging efficiency decreased to 70% was 767 times. Also, the energy density at the fifth repetition was 119 W-hrA, and the energy density was 119 W-hrA.
The discharge efficiency was 98 cycles. It was also charged! , up to 6
When left for 2 hours, the self-discharge rate was 3.196.

Example 3 A 1 ton glass reaction vessel completely purged with nitrogen gas,
A 100-mesh stainless steel mesh was inserted, and then 10% of toluene purified according to a conventional method was used as a polymerization solvent.
01d, tetrabutoxytitanium 4.41 as catalyst
A catalyst solution was prepared by sequentially charging mmol and 11.01 mmol of triethylaluminum at room temperature. The catalyst solution was a homogeneous solution. Next, the reactor was cooled with liquid nitrogen, and the nitrogen gas in the system was exhausted using a vacuum pump.

The reactor was cooled to −78° C., and purified acetylene gas at a pressure of 1 atmosphere was blown into the reactor while the catalyst solution was left standing. The polymerization reaction was continued for 10 hours while maintaining the pressure of the acetylene gas at 1 atm. The system was agar-like with a reddish-purple color. After the polymerization was completed, unreacted acetylene gas was removed, and while the temperature of the system was maintained at -78°C, the edges were washed four times with 200-g purified toluene until the film thickness swollen with toluene was approximately 0.5 ttn. Includes stainless steel mesh
A sheet-like swollen acetylene polymer was obtained. This swollen acetylene polymer is a swollen product in which fibrous microcrystals (fibrils) with a diameter of 300 to 500X are regularly intertwined.
No powdery or lumpy polymer was produced.

This sheet-like swollen acetylene polymer containing the stainless steel mesh is sandwiched between chrome-plated ferro plates.
The mixture was pre-pressed at room temperature at a pressure of 100 kg/i and then pressed at a pressure of 15 ton/cJ to obtain a homogeneous and flexible composite with a reddish-brown metallic luster and a film thickness of 280 μm. This composite was vacuum dried for 5 hours at room temperature. This composite contained 43% by weight stainless steel mesh.

[Battery experiment]

Complex power obtained by the above method? A battery was repeatedly charged and discharged in the same manner as in Example 1, except that two disks with a diameter of 201 m were cut out and used as a positive electrode active material and a negative electrode active material.・The number of charging/discharging cycles until the discharge efficiency decreased to 70 hours was 809 times.

Also, the energy density at the fifth repetition is 119W.
-hr/kg, charge/discharge efficiency is 98% ”'C;h
It was. Furthermore, when the battery was left charged for 62 hours, its self-discharge rate was 2.9%.

Example 4 13ull, Chem, Soc, Japan
, 51, 2091 (1978).
[Battery experiment] was carried out in exactly the same manner as in Example 1, except that the negative electrode was formed into a disk shape of 20 mm diameter at a pressure of /i. As a result, one charge/discharge cycle was repeated up to 723 times. 1st
The voltage characteristics were almost the same as those during the second discharge.

The number of repetitions until the charging/discharging efficiency drops to 70% is 7.
He recorded 42 times. The energy density of this battery is 166
With W-hrAg, the charge/discharge efficiency was 93. When the battery was left charged for 62 hours, its self-discharge rate was 3.8 cm.

Example 5 In place of poly(paraphenylene) used in Example 4, J,
Polym, Sci, , Polym, Lets, ,
A battery experiment was conducted in exactly the same manner as in Example 4, except that poly(2,5-thennylene) prepared by the method described in J. Ed., 18°9 (1980) was used for the negative electrode.

As a result, the number of repetitions until the light/discharge efficiency decreased to 70 was recorded as 701 times. This battery worker.

The energy density was 158 W-hrA, and the charging/discharging efficiency was 97 arrows. Furthermore, when the battery was left charged for 62 hours, its self-discharge rate was 3.7%.

[Brief explanation of drawings]

The figure is a schematic cross-sectional view of a battery cell for measuring characteristics of a non-aqueous secondary battery, which is a specific example of the present invention. DESCRIPTION OF SYMBOLS 1... Platinum lead wire for negative electrode, 2... Platinum wire mesh current collector for negative electrode, 3... Negative electrode, 4... Porous polypropylene diaphragm, 5... Positive electrode, 6... For positive electrode Platinum mesh current collector, 7
...Positive electrode lead wire, 8...Teflon container. Patent applicant Showa Denko K.K. Hitachi Ltd. Patent attorney Sei Kikuchi -Figure-368=

Claims (1)

[Claims] 2 in which an acetylene polymer is used as a positive electrode or a positive electrode and a negative electrode.
A secondary battery characterized in that the electrolytic solution comprises an organic solvent, a supporting electrolyte, and a dithiophene compound represented by the following general formula. ▲There are mathematical formulas, chemical formulas, tables, etc.▼ [However, in the formula, R_1 and R_2 are alkyl groups having 5 or less carbon atoms, and m and n are 0, 1 or 2. ]