JPS60264050A - Secondary battery - Google Patents

Abstract

PURPOSE:To provide a secondary battery which assures high energy density, less self-discharging and high charging and discharging efficiency by using benzothiophane system polymer for the positive electrode while acethylene polymer for the negative electrode. CONSTITUTION:For the positive electrode of a secondary battery, the benzothiophane system polymer comprising the benzothiophane group indicated by the general expression (R is the alkyl group having a number of C of 5 or more, n is 0 or 4 or less) as the repetition unit is used. Moreover, for the negative electrode, the predetermined acetylene polymer is used. This positive electrode polymer resembles in the conjugated structure the cis-form polyacetylene and includes sulphur atoms and therefore it can be expected as the conductive material because of its specific electron structure. A secondary battery which shown less deterioration of electrode even after the use for a long period of time and has excellent performance can be formed by utilizing such polymer.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a secondary battery characterized by using an indithiophene polymer having a benzothio7ey group as a repeating unit as a positive electrode and an acetylene polymer as a negative electrode. be.

Conventionally, batteries using an acetylene polymer as both the positive and negative electrodes of the battery are well known (for example, JP-A No. 5
6-136469, JP-A-57-121168, JP-A-58-38465).

However, acetylene polymers are susceptible to gradual oxidation reactions caused by oxygen in the air, which not only degrades battery performance but also causes side reaction products and impurities during electrochemical charging, and in some cases electrolytic The solution itself is susceptible to oxidative deterioration, so when an acetylene polymer is used as a battery positive electrode, the electrolyte and solvent used in the electrolyte must have a fairly wide electrochemical stability range, and The liquid must have a high level of purity.

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

For example, when the acetylene polymer of the positive electrode reaches 3.5 V or more based on Li/L i + reference electrode in the electrolytic solution, it becomes susceptible to deterioration reversal.

One of the reasons for this is that the acetylene polymer itself is a substance that easily deteriorates due to oxidation. Therefore, among those in the industry, the electrode itself has little deterioration, the amount of self-discharge during charging and storage is small, and the life span of repeated charging and discharging is long.
Developing higher performance batteries has been a major challenge.

In view of the above points, the present inventors have conducted various studies and found that a secondary battery that uses a benzothiophene polymer for the positive electrode and an acetylene polymer for the negative electrode has been developed using conventional acetylene polymer for the positive electrode. The present invention has been completed based on the discovery that the performance is better than that of the secondary battery used in the previous research.

In the present invention, it has been confirmed that the benzothiophene-based polymer used as the positive electrode is extremely stable even in air compared to acetylene polymers, and is less susceptible to oxidative deterioration even in the air. Ta. For example, when we investigated the positive electrode properties of benzothiophene polymers using Lt/Li+reference electrode as the standard using a 1 mol/l solution of tiumno or -krate dissolved in propylene carbinate as an electrolyte, we found that Li/L. The benzothiophene polymer electrode is relatively stable even at 3.8V with respect to the reference electrode, and the amount of electricity discharged by and-ping is 3.8V.
f) '-More than 97% of the amount of electricity obtained was obtained.

However, when a benzothiophene-based polymer is used for both the positive and negative electrodes, the band gap of the benzothiophene-based polymer is too large, and both electrodes cannot be electrolyzed with stable repeated charging and discharging at high doping concentrations. It is difficult to obtain a liquid system.

By using a benzothiophene polymer for the positive electrode and an acetylene polymer for the negative electrode, the present invention has a high energy density, a small amount of self-discharge during charge storage, and a high charge/discharge efficiency that allows for a large amount of charge/discharge. The present invention provides an excellent battery that can be repeatedly discharged and exhibits minimal electrode deterioration even after a long period of time.

Conventionally, benzothiophene-based polymers having benzothiophene groups as repeating units have been used as electrically conductive materials because their conjugated structure is similar to cis-type polyacetylene and they also contain sulfur atoms. It is expected.

As a method for synthesizing the benzothiophene-based high polymer, the following methods can be considered, but are not necessarily limited to these methods.

([) (” (to) (However, in the formula, R is an alkyl group having 5 or less carbon atoms, and X is a halodane atom) (1) Obtain benzothiophene-based high polymer directly from monomer (I) with concentrated sulfuric acid. Method.

(11) Method for electrochemically oxidatively polymerizing mono-([)0 GiD catalyst (H2BO3, CuCl2/kLct,
, TCNQ').

A method in which Rei monomer (2) is Grignardized and polymerized using an N1+Co catalyst.

A specific example of the benzothiophene polymer used in the present invention is poly(benzothiophene).

Poly(3-methylbenzothiophene), poly(3゜3'
-dimethylbenzothiophene), poly(4-methylbenzothiophene), poly(3,4--,7methylbenzothiophene), $9 (414'-dimethylbenzothiophene), etc. Among them, poly(benzothiophene) is preferred.

In addition, various reports have been made regarding the method for producing the acetylene polymer used in the negative electrode of the secondary battery of the present invention, and specific examples thereof include Japanese Patent Publication No. 48-32581, Japanese Patent Publication No. 56
-45365, JP-A-55-129404, JP-A No. 55
-128419, 55-142012, 56-
No. 10428.

56, No.-133133, Trans Farad
y, Sac, +64 + 8'23 ('196'
8), J', PolymerSci, +A-1
．． E, 3419 (1969), Makr*mol
.

Chem-+ RapidCOMmll + 621
(1980).

J, Chem=Phys, 69(1), 106(
1978).

5ynthetic Matals, 4, 81
(1981), but the method is not necessarily limited to these.

The benzothiophene polymer used as the positive electrode and the acetylene polymer used as the negative electrode in the present invention may be in any form such as film, powder, or short fibers.

In addition, other suitable conductive materials, such as graphite, carbon black, acetylene black, metal powder, carbon fiber, etc., may be mixed with the benzothiophene polymer and acetylene polymer, and metal mesh as a current collector may be used. There is no problem in including such things. In addition, polyethylene, modified polyethylene, poly(tetrafluoroethylene),
It may be reinforced with a thermoplastic resin such as polybutanoene.

In addition, in the present invention, not only benzothiophene polymers and acetylene high polymers but also conductive benzothiophene polymers and acetylene high polymers obtained by doping these high polymers with dopants in advance can be used as electrodes. Can be used.

The doping method for doping the benzothiophene polymer and the acetylene polymer may be either chemical doping or electrochemical doping.

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 doping agent for electrochemical doping, (
i) PFM l sbF″6.AsF″6+ 5bc
a halide anion of an element of group Va such as z; B
a halide anion of a group IIIa element such as F;
Halogen anions such as I-(Ii) + BFrcc (7), anions such as perchlorate anions such as cto''4 and (11) Li'', Na
”, alkali metal ions such as K+, R4N+ (R:
Examples include cations and donocents such as quaternary ammonium ions (hydrocarbon groups having 1 to 20 carbon atoms), but are not necessarily limited to these.

The above-mentioned anion do/? Specific examples of compounds that provide dopants and cation dopants include LIPF6. L
i5bF LIAsF6. LIC1O4,Nal,
NaPF6゜Na8bF, NaAsF, NyonC
1O, Kl, KPF KSbF6+6 6 4,
61 WAIF6. Kcto4 * ((n-Bu)4N)
”・(AIFA)−*((n −Bu)4N)+・
(PF6)−+ ((n −Bu)4N)”・CA
O; *LIALCt, LiBF, No 'BF
, NO'BF4. NO2'AsF6゜4 4 2
4 No-AsFb, No□・ClO4, NO・cLo4
Examples include, but are not necessarily limited to.

These dopants may be used alone or in combination of two or more.

Examples of anions and dopants other than the above are HFi anions, and examples of anions and dopants other than the above are biryllium or pyridinium cations represented by the following formula (1): (wherein, X is An oxygen atom or a nitrogen atom, R' is a hydrogen atom or an alkyl group having 1 to 15 carbon atoms, and 6 to 16 carbon atoms.
aryl group, R'' is /N gll non-child or alkyl group having 1 to 10 carbon atoms, 6 carbon atoms
-15 aryl groups, m is 0 when X is an oxygen atom, and 1 when X is a nitrogen atom. n is 0
Or 1-5. ) Also, the cal&=um cation represented by the following formula ■ or (to): and R' -C+ (2) 1 [In the above formula, R1, R2, and BS are hydrogen atoms (R1, 12° and R3 are at the same time not a hydrogen atom), carbon number 1~
15 alkyl group, allyl group, carbon a
6 to 15 aryl group or -OR' group, where R is an alkyl group having 1 to 10 carbon atoms or 6 carbon atoms
~15 aryl group, R4 is a hydrogen atom, an alkyl group having 1 to 15 carbon atoms, and 6 to 15 carbon atoms.
is an aryl group. ].

The HFi anion used usually has the following general formula: (
to) ti is @: n2N-Hv2 00 M-HF2(V) ■〆I [However, in the above formula, R' and R'' are hydrogen atoms or have 1 carbon number
-15 alkyl group, C6-15 ary-/I/(
aryl) group, R'' is an alkyl group having 1 to 10 carbon atoms, an aryl group having 6 to 15 carbon atoms, X 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 (hydrogen fluoride salt) in a suitable organic solvent using as a supporting electrolyte.Compounds represented by the above formulas ω, (V) and (B) An example of a variant is H4N
'HF2. Bu4N”HF, +N&・I(F, ,
K-HF2. Ll-HF2 and the f-lyrium or pyridinium cation represented by the above formula (1),
The cation represented by formula (1) and czo; t BF;
*AtC1: *FeCl2.5nCti l
PFQ*pct″6.SbF; , A8F″; ,
cp, soH, HF; etc. (7) It can be obtained by dissolving in a suitable organic solvent using a salt with 7=one as a supporting electrolyte. Specific examples of such salts include the following.

Specific examples of the calzonium cation represented by the above formula (If) or (2) include (C6)I, ), C'', (
CH, ), C”.

These Cal? Nium cations can be obtained by dissolving a salt of them and an anion (calcium salt) in a suitable organic solvent as a supporting electrolyte. Representative examples of anions used here include BF″; , htct″
; + ALBrsCL-IF*Ct; l 5nC
t; # PF; vpct; ,,5bct″6.
SbF;, C11);, cv3so;, etc., and specific examples of calzonium salts include:
For example (C6H5)5C-BF4. (CH,)3C-
BF4°HCO-AtCt4. HCO-BF4. C
Examples include 6H5Co-8nC15.

The electrolytic solution for the secondary battery of the present invention is one in which the above dopant is dissolved in a non-aqueous organic solvent.

The organic solvent mentioned here is preferably one that is aprotic and has a high dielectric constant. For example, ethers.

Ketones, nitriles, amines, amides, sulfur compounds, phosphate ester compounds, sulfite ester compounds, borate ester compounds, chlorinated hydrocarbons, esters, carbonates, nitro compounds, Sulfolanes, etc. can be used, and among these, ethers and ketones.

Nitriles, phosphate ester compounds, borate ester compounds, chlorinated hydrocarbons, carbonates, and sulfolanes are preferred. Representative examples of these include tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-
Dioxane, monoglyme, acetonitrile, propionitrile, 4-methyl-2-e-enthanone, putininitrile, parellonitrile, benzonitrile, 1,2-dichloroethane, r-butyrolactone, valerolactone, dimethoxyethane, methylformate, 760 pyrenecar Examples include ester, ethylene carbonate, dimethylformamide, dimethylsulfoxide, dimethylthioformamide, ethyl phosphate, methyl phosphate, polybenzene, sulfolane, and 3-methylsulfolane. Among these, nitriles and sulfolanes are preferred, and aromatic nitriles are particularly preferred.

These organic solvents may be used alone or as a mixed solvent of two or more. Depending on the type of battery to be used, oxygen, water, photogenic solvents, etc. in these solvents may deteriorate the characteristics of the battery, so in that case, it is preferable to purify the battery according to a conventional method.

The amount of Donokund doped into the benzothiophene-based polymer of the positive electrode during charging is 4 to 8 with respect to benzothiophene.
0 mole, preferably 10 to 60 mole.

In addition, the amount of Donokunt doped into the acetylene polymer of the negative electrode is determined by the repeating unit (-C) of the acetylene polymer.
H-) It is 1 to 15 mol, preferably 3 to 10 mol, per 1 mol.

The amount of doping can be freely controlled by measuring the amount of electricity flowing during electrolysis. Doping can be done either under constant current, constant voltage, or under conditions of varying current and voltage. The current value, voltage value, doping time, etc. during doping are determined based on the bulk density 2 of the benzothiophene polymer or acetylene polymer.
area.

It cannot be unconditionally defined because it varies depending on the type of dot and the type of electrolyte.

In the secondary battery of the present invention, in addition to the electrolyte described above, a highly ion conductive organic solid electrolyte consisting of polyethylene oxide and NaI, Na5CN, etc., or a paste formed by simply mixing an electrolyte (Do Gundt) and an organic solvent, can be used. Furthermore, liquid electrolysis without using a solvent, such as 1,3-dialkylimidazolium chloride or 1-butylpyridinium chloride, can be used.
A mixture of aluminum chloride can also be used directly as a liquid electrolyte without using a solvent.

[I American Chemical
ety, + 18 1603-1605 (1979
), Inorg, Chem, 211263-1
264 (1982) r J, of Electr.
chemical society 130 (198
3) ] Electrolyte used in the secondary battery of the present invention (
The concentration of the electrolyte (Dor Gundt) cannot be determined unconditionally because it varies depending on the type of positive or negative electrode used, charge/discharge conditions 2 operating temperature, type of electrolyte, type of organic solvent, etc. It is usually in the range of 0.001 to 10 mol/l, except when used as. The electrolyte may be homogeneous or heterogeneous.

Glass or polyethylene if necessary in the present invention.

There is no problem in using a porous membrane made of synthetic resin such as polyzorogylene or natural fiber paper as the diaphragm.

The secondary battery of the present invention has a long cycle life, high energy density, and good self-discharge rate, voltage flatness, and charge/discharge efficiency. Further, the secondary battery of the present invention is lightweight,
Portable equipment and electric vehicles are small and have high energy density.

Ideal for gasoline-powered vehicles and power storage batteries.

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

Example 1 [Production of benzothiophene polymer] 2.01 g of commercially available metallic magnesium for Grignard reagent
(82.7 mmol) was placed in a 1001 J Mitsulo flask equipped with a thermometer, reflux condenser, and dropping funnel, and the inside of the flask was sufficiently purged with dry nitrogen gas. To this was added 60 d of dry purified tetrahydrofuran, and while stirring with a magnetic stirrer, 209 (82.7 mmol) of 2,7-diprompenzothiophene started to react, producing an organomagnesium compound.

After the dropwise addition was completed, the mixture was reacted on an oil bath at the reflux temperature of tetrahydrofuccine for 9 hours. At this time, the product was decomposed with acid, extracted with ether, and subjected to gastric analysis.
-fompensothiophene

Thereafter, the oil bath temperature was raised to 120° C., and tetrahydrofuscine was distilled off at normal pressure and then under reduced pressure to obtain a reddish brown oily residue.

To this oily residue, 60 m/s of dry purified anisole, Jikushikou (2,2'-bipyridine), Kelsow 9 (0,2'-bipyridine),
After adding 8 mmol) and reacting at 152°C for 2 hours,
The sample was poured into 500-m of hydrochloric acid and washed with methanol. After repeating this operation twice, it was filtered, and the filtration residue was Soxhlet-extracted with hot methanol for 13 hours and then with hot chloroform for 50 hours, and the amount insoluble in hot chloroform was 6.1 g.
It is a blackish brown fine powder, and the heat chloroform soluble part is 0.
It was 3g.

When the benzothiophene polymer thus obtained was compression molded using a 1-ton press, a slightly flexible plate-shaped molded product was obtained. This plate-shaped molded product could be easily cut with a knife without losing its shape.

[Production of acetylene polymer]

Under a nitrogen atmosphere, 1.7 ml of titanium tetrabutoxide was added to a glass reaction vessel with an internal volume of 500 ml, dissolved in 30 ml of aninol, and then 2.7 mg of triethylaluminum was added with stirring to prepare the catalyst. A solution was prepared.

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
It was washed repeatedly with purified toluene] and OOwLl five times while being kept at ℃. The film-like acetylene polymer swollen with toluene was a uniform film-like swollen product in which fibrils were tightly intertwined.

The swollen product was then vacuum-dried to obtain a reddish-purple film with a metallic luster, a thickness of 300 μm, and a cis content of 98 inches. In addition, the bulk density of this film-like acetylene polymer is 0.5jJ7tr, and its electrical conductivity (DC four-probe method) is 3.2 x 100 at 20°C.
Met.

[Battery experiment]

From the benzothiophene polymer obtained by the above method, a disk with a diameter of 201 m (bulk density -i, og, foam, weight 25
．． A battery with a diameter of 20 gourds (bulk density = 0.59 AL weight 16.0 cm) was cut out from the acetylene polymer obtained in the above method to serve as a positive electrode, and a battery was used as a negative electrode. was configured.

FIG. 1 is a schematic cross-sectional view of a battery cell for measuring the characteristics of a button-type battery, which is a specific example of the present invention, where ■ is a Ni-plated brass container, 2 is a disc-shaped negative electrode with a diameter of 20 mm, 3 is a circular porous polypropylene diaphragm with a diameter of 26 tlII++, 4 is a circular felt made of carbon fiber with a diameter of 26 mm, 5 is a disk-shaped positive electrode with a diameter of 20 gourds, and 6 is an average diameter of 2 μm.
7 is a Teflon container with a circular cross section, 8 is a Teflon ring for fixing the positive electrode, 9 is N
The i lead wire is shown.

The positive electrode was placed in the recess at the bottom of the container 1, and a circular porous Teflon sheet 6 was placed over the positive electrode, and then tightened and fixed with a Teflon ring 8.

Place the felt 4 in the recess at the top of the container 1 and overlap it with the positive electrode.
After impregnating the electrolytic solution, the negative electrode 2 was placed through the diaphragm 3, and the container 7 was tightened to produce a battery. The electrolyte was Bu4N-BF dissolved in distilled and dehydrated benzonitrile.
A 1 mol/l solution of 4 was used.

Charging was carried out for 19 minutes at a constant current (2-Om) (the doping amount was 24 molti per repeating unit of the benzothiophene polymer in the positive electrode, and 6 molti per repeating unit of the acetylene polymer in the negative electrode). After charging is completed, immediately discharge under a constant current (3.0 mφ2), and the voltage is 1.

When we conducted a repeated charging/discharging experiment in which we performed charging again under the same conditions as above when the voltage reached V, we found that 72
At the third time, the charging/discharging efficiency fell below 50%.

In this experiment, after the 5th charging was completed, 2
When a self-discharge test was conducted by opening the battery circuit for 4 hours, the amount of discharged electricity after 24 hours was 97 inches, which is the amount of electricity charged for the fifth time, and the amount of self-discharge was extremely small at 3 inches. The highest light/discharge efficiency of this battery was over 99 inches. The energy density per electrode active material was 104 W-L.

Comparative Example 1 A battery was repeatedly charged and discharged in the same manner as in Example 1, except that the same acetylene polymer used for the negative electrode in Example 1 was used for the positive and negative electrodes.

However, the doping amount in this case is equivalent to 6 molti for both the positive electrode and the negative electrode.

The number of repetitions of charging and discharging a battery is when the charging and discharging efficiency is 50
It took me 525 times to reach chi.

As a result of the self-discharge test conducted for the fifth time, 24
The amount of electricity discharged after the lapse of time is 83% of the amount of electricity charged,
This was considerably lower than the fourth charging/discharging efficiency of 97.

The highest light/discharge efficiency of this battery was 98 cm.

Energy density per electrode active material is 100 W-HJy
Met.

Comparative Example 2 A battery was repeatedly charged and discharged in the same manner as in Example 1, except that the same benzothiophene polymer used for the positive electrode in Example 1 was used for the positive and negative electrodes.

However, the doping amount in this case is equivalent to 24 molti for both the positive electrode and the negative electrode.

The number of times this battery is charged and discharged is that the charging and discharging efficiency is 5.
It took 247 times to reach zero.

As a result of performing a self-discharge test on the fifth repetition, 2
The amount of electricity discharged after 4 hours was 79 inches of the amount of electricity charged, which was extremely low compared to the fourth charging/discharging efficiency of 86 inches.

The highest light/discharge efficiency of this cell was 88%.

Comparative Example 3 Same as Example 1 except that the same benzothiophene polymer used for the positive electrode in Example 1 was used for the negative electrode, and the same acetylene polymer used for the negative electrode in Example 1 was used for the positive electrode. Repeated battery charging and discharging experiments were conducted using the same method.

In this case, the doping amount is equivalent to 6 molti for the positive electrode active material and 24 molti for the negative electrode active material.

This battery can be charged and discharged 96 times until the charging and discharging efficiency reaches 50%.

As a result of performing a self-discharge test on the fifth repetition, 2
The amount of discharged electricity after 4 hours was quite small until the battery voltage reached 0.5 V, and the charging/discharging efficiency was 23 cm.

The highest light/discharge efficiency of this battery was 73 cm.

[Brief explanation of drawings]

Is FIG. 1 a specific example of the present invention? FIG. 2 is a schematic cross-sectional view of a battery cell for measuring characteristics of a tan-type battery. 1... Container, 2... Negative electrode, 3... Diaphragm, 4...
Felt 5... Positive electrode, 6... Porous Teflon sheet, 7... Teflon container, 8... Teflon ring, 9... Ni1J-do wire. Patent Applicant Showa Denko Co., Ltd. Hitachi Ltd. Representative Patent Attorney Sei Kikuchi - JP-A Showa GO-264050 (8)

Claims (1)

[Scope of Claims] A secondary battery characterized in that a benzothiophene-based polymer having a benzothiophene group represented by the following general formula as a repeating unit is used as a positive electrode, and an acetylene polymer is used as a negative electrode. (However, in the formula, R is an alkyl group having 5 or less carbon atoms, and n is 0
．． t or a positive integer less than or equal to 4. )