JPS60264051A - Secondary battery - Google Patents

Abstract

PURPOSE:To provide a secondary battery which has a high energy density, shows less self-discharge and assures a high charging and discharging efficiency by utilizing the benzothiophane system polymer at least to the one of positive and negative electrodes. CONSTITUTION:The benzothiophane system polymer which is indicated by generatl expression (R is alkyl group with a number of C of 5 or less, n is 0 or 4 or less) and has the benzothiophane group as the repetition unit is used at least to the one of the positive and negative electrodes of a secondary battery. This polymer resembles in the conjugated structure the cis-form polyacetylene and includes the sulphur atoms. Therefore, it can be expected as the conductive material having the specific electron structure. A secondary battery which shows less deterioration of electrode even after the use for a long period of time and assures excellent performance can be formed by utilizing this polymer.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a secondary battery characterized in that a benzothiophene polymer having a benzothiophene group as a repeating unit is used for at least one of a positive electrode and a negative electrode.

Conventionally, batteries using an acetylene polymer as both the positive and negative electrodes of the battery are well known (for example, JP-A-5
6-136469, JP-A-57-1:21168, JP-A-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. The electrolyte itself is susceptible to oxidative and reductive deterioration, so the electrolyte and solvent used must have a fairly wide electrochemical stability range, and the electrolyte must have a high level of purity. be.

In addition, 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 an electrode, even at a relatively low oxidation potential, it will suffer from oxidative deterioration, resulting in poor battery performance. decrease.

For example, if the acetylene high 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 reactions.

One of the reasons for this is that the acetylene polymer itself is a substance that easily deteriorates due to oxidation. Therefore, among those involved, it is a matter of great importance to develop a high-performance battery that has little deterioration of the electrode itself, a small amount of self-discharge during storage, and a long service life after repeated charging and discharging. Met.

In view of the above points, the present inventors have conducted various studies and found that a secondary battery using a benzothiophene-based polymer for at least one of the positive electrode and the negative electrode uses a conventional acetylene polymer for the electrode. It was discovered that the performance was better than that of conventional secondary batteries, and the present invention was completed.

In the present invention, it has been confirmed that the benzothiophene polymer used as the electrode is resistant to oxidative deterioration even in the air, is much more stable than acetylene polymers, and is also less susceptible to oxidative deterioration electrochemically. Ta. For example, 1 liter of lithium perclate dissolved in propylene carbonate
Mol/! When the positive electrode characteristics of the benzothiophene-based polymer were investigated using the solution as an electrolyte and based on the L i/L 1 reference electrode, the benzothiophene-based polymer electrode had a ratio of 3.8 mm to the I, i/Lx reference electrode. However, it was relatively stable, and the amount of electricity that could be discharged by undoping was 97 times more than the amount of electricity that was obtained by doping at 3.8V.

By using a benzothiophene polymer for at least one of the positive and negative electrodes, the present invention has a high energy density, a small amount of self-discharge during storage, and a high charge/discharge rate for young trees.・It is possible to repeat the discharge,
The present invention provides an excellent battery with low electrode deterioration even after a long period of time.

Conventionally, benzothiophene-based polymers having dibenzothiophene 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 method φ can be considered, but it is not necessarily limited to these methods.

1 (1) (II) (III) (However, in the formula, R is an alkyl group having 5 or less carbon atoms.

(X-ray halogen atom) (i) A method for obtaining a benzothiophene-based polymer polymer directly from monomer (1) using m-sulfuric acid.

(ii) Method for electrochemically oxidatively polymerizing 7-mer () (iii) Catalyst () I2so4t cut, yh
tcts, TCNQ).

(1■) Convert Nanatsuma (2) into Dalignard, N1 *
C.

A method of polymerization using a system catalyst.

Specific examples of benzothiophene-based polymers used in the present invention include poly(benzothiophene) #poly(3-methylbenzothiophene), poly(3,3'-dimethylbenzothiophene), poly(4-methylbenzothiophene) )
, poly(3,4-dimethylbenzothiophene), poly(
Among them, poly(benzothiophene) is preferred.

The secondary battery of the present invention comprises a benzothiophene polymer (i
) It may be a battery used only for the positive electrode, (it) used only for the negative electrode, or (ii D used for both the positive and negative electrodes. In the case of the type (i) secondary battery, As the negative electrode of the counter electrode, other conjugated polymer compounds,
Alkali metals such as Li and Na, graphite, carbon fiber, T
l52 etc. are used. In the case of the secondary battery of type (ii), another conjugated polymer compound is used as the counter positive electrode.

Among the above-mentioned types, (i) or (
A secondary battery of the type iii) is particularly preferred, and a type (i) in which another conjugated polymer compound is used as the counter electrode is particularly preferred.

Other conjugated polymer compounds mentioned here include poly(p
-phenylene), poly(m-phenylene), polypyrrole, poly(phenylene sulfide), poly(arylenequinone), poly(azophenylene), poly(Schiff base), poly(aminoquinone), poly(penzimidazole) , polyacenequinones, and JP-A-57-
Examples include, but are not necessarily limited to, electroactive polymers, polyimides, polyacrylonitrile, thermal decomposition products of poly-α-cyanoacrylic, etc. described in No. 195731 and EP-67,444. . Among the other conjugated polymer compounds mentioned above, specific examples of poly(arylene quinones), poly(azophenylene), poly(Schiff bases), poly(aminoquinones), and poly(benzimidazoles) can be found in J. , E, KATO
N ed., translated by Hidetoshi Tsuchida, "Polymer Organic Semiconductors", Shokodo, 19'
Published in 1972), pages 87 to 112.

Among the other conjugated polymer compounds mentioned above, preferred are poly(p-)pyrrole) and polypyrrole.

Penzothiophene-based polymer used in the present invention,
and other conjugated polymer compounds used as counter electrodes (
The conjugated polymer compound (hereinafter referred to as a conjugated polymer compound) may be in any form such as a film, a powder, or a short fiber.

However, it is also possible to mix other suitable conductive materials, such as graphite, carbon black, acetylene black, metal powder, carbon fiber, etc. with the conjugated polymer compound, or to insert a metal net etc. as a current collector. There is no problem at all.

Further, it may be reinforced with a thermoplastic resin such as polyethylene, modified polyethylene, or tetrafluoroethylene.

As the positive electrode or electrode of the secondary battery of the present invention, not only a conjugated polymer compound but also a conductive conjugated polymer compound obtained by doping the conjugated polymer compound with a supporting electrolyte (dopant) is used. be able to.

The method for doping the conjugated polymer compound with a dopant 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 dopant to be electrochemically doped, (i
) PF;, sbp;, As F';, 5bct, halocanide anions of elements of the Va group, BF,'
I of elements of the lla group such as I:l Danide anion, I
Anions such as halogen anions such as -(I,-), Br-1CI, -, perchlorate anions such as CtO;
Dopants and (iD Li+, Na”, K+
Alkali metal ions such as R4N” (R: carbon number 1
Examples include cations and dopants such as quaternary ammonium ions (~20 hydrocarbon groups), etc.
It is not necessarily limited to these.

Specific examples of compounds providing the above-mentioned anionic dopants and cationic dopants include LiSF6t Li
SbF6. LiSbF6# LiCz04t NaI
5NaPF6 p NrSbF6t NaAsF6
tNaClO2, KI, KPF6°KSbF6,
s KAsF6 # KClO4e [(”-”)4N
l"(AsF6)".

((n-Bu)4N)"-(PF6)"e ((n-B
u)4N)"C1o; *1, IAAct4. LiB
F4. No2・BF4. No-BF4#NO2'A
lF6 @ NO”AsF6# NO2”Cff14
, NO''ClO4, but are not necessarily limited to these. These dopants may be used alone or in combination of two or more.

The anion dopant other than the above may be an HF anion, and the anion dopant other than the above may be a biryllium or pyridinium cation represented by the following formula (1): 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 15 carbon atoms.
aryl group, R" is halo r:, / atom or an alkyl group having 1 to 10 carbon atoms, 6 to 1 carbon atoms
5's aryl/l/ (aryl m, m is 't50 when X is an oxygen atom, and t!1 when X is a nitrogen atom.

n is 0 or 1-5. ) or the following formula (IO or (to)); and R4C+ (2) 1 [In the above formula, R' e R2e R'' is a hydrogen atom (R1゜R2, R5 are hydrogen atoms at the same time) ), an alkyl group having 1 to 15 carbon atoms, an allyl group,
an aryl group having 6 to 15 carbon atoms or a 10-group, provided that R5 represents an alkyl group having 1 to 10 carbon atoms or an aryl group having 6 to 15 carbon atoms;
R4 is a hydrogen atom, an alkyl group having 1 to 15 carbon atoms, or an aryl group having 6 to 15 carbon atoms. ].

The HF″2 anion used usually has the following general formula %(): () () [However, in the above formula, R′ and R″ are hydrogen atoms or have 1 carbon atom.
~15 alkyl group, aryl having 6 to 15 carbon atoms/l/
(aryl) group, R″′ 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] by dissolving the compound (hydrogen fluoride salt) in a suitable organic solvent using as a supporting electrolyte. Above formula (IV)
, (V) and (M) include H4N"HF2 tBu N"HF e Na
“LIP p K4HF e Li”HF2 and 4
2 2 2 The biryllium or pyridinium cation represented by the above formula (I) has a cz
o2, BP″; , AtC1; e FeC1″
4.8nCtis PF;

pct″6. sbp″6e AaF″M, CF,
It can be obtained by dissolving a salt with an anion such as So''s or HF'2 as a supporting electrolyte in a suitable organic solvent.Specific examples of such salts include 0 The above formula Ql ) or (to) carbonium
A specific example of a cation is (C4H5)IC”% (
0M3), C+.

0 0 These carbonium cations can be obtained by dissolving salts of them and anions (carbonium salts) in a suitable organic solvent as a supporting electrolyte. Representative examples of anions used here include Bl; tAlC1';
; , AtBr, Ct-, Fact″4*8nC1
; , PF″6゜pcz, 5bcz″6. sb
r''6e ``l':): * c:r, so^, etc. can be mentioned, and specific examples of calginium salts include (C6H5)3C-BF4. (CH3)3C-
BF4゜HCO-AtC44, HCO-BF4. C6H
Examples include 3CO-8nCt5.

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 T monoglyme.

Acetonitrile, propionitrile, 4-methyl-2+
'anthanone, phthyronitrile, valeronitrile, benzonitrile, 1,2-dichloroethane.

γ-butyrolactone, parerolactone, dimethoxyethane, methylformate, propylene carbonate,
Ethylene carbonate, dimethylformamide, dimethyl sulfoxide, dimethylthioformamide, ethyl phosphate, methyl phosphate, chlorobenzene, sulfolane, 3
-Methylsulfolane and the like can be mentioned. 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 used, oxygen, water, protic solvents, etc. in these solvents may deteriorate the battery characteristics, so in that case, it is preferable to purify them according to a conventional method.

During charging, it is absorbed into the benzothiophene polymer of the electrode. The amount of dopant is 4 for penzothiophene.
-80 moles, preferably 10-60 moles.

The amount of doge can be freely controlled by measuring the amount of electricity flowing during electrolysis. The doping can be carried out either under constant current, constant voltage or under varying conditions of current and voltage. The amount of current, voltage value, doping time, etc. during doping cannot be unconditionally specified because they vary depending on the type of bulk density of the benzothiophene polymer and the type of electrolyte.

Furthermore, 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.
It is also possible to use a paste or a paste obtained by simply mixing a mother chloride and an organic solvent, or a liquid electrolysis method that does not use a solvent, such as 1,3-dialkylimidazolium chloride or 1-butylpyridinium chloride. 3
A mixture of aluminum chloride can also be used directly as a liquid electrolyte without using a solvent.

(American Chemical
y, # 181603-'-1' 605 (197
9) e Inorg, Chem, 1263-12
64 (1982), J. ofElectroc.
chemical 5ociety 130 (1983
)) The concentration of the electrolyte (dopant) used in the secondary battery of the present invention varies depending on the type of positive electrode or negative electrode used, charging/discharging conditions 1 operating temperature, type of electrolyte, type of organic solvent, etc., so it is not generally specified. However, unless the electrolyte is used as it is as a liquid electrolyte, it is usually 0.001 to 10 mol/! is within the range of

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 polypropylene 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. In addition, the 2 medium battery of the present invention is lightweight,
Portable equipment and electric vehicles are small and have high energy density.

Ideal as a battery for automobiles and power storage.

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

Example 1 [Production of benzothiophenopolymer] 2.01 g of commercially available metallic magnesium for Grignard reagent
- (82.7 mmol) was placed in a 100-hole Mitsuro flask equipped with a thermometer, a reflux condenser, and a dropping funnel, and the inside of the flask was sufficiently purged with dry nitrogen gas. Add 60% of dry purified tetrahydrofuran to this, and while stirring with a magnetic stirrer, 20t (827 mmol) of 2
, 7-dipro were added dropwise. A reaction started simultaneously with the dropwise addition, and an organomagnesium compound was produced. After the dropwise addition was completed, the mixture was reacted on an oil bath at the reflux temperature of tetrahydrofuran for 9 hours.

At this time, the product was decomposed with acid, extracted with ether, and subjected to gas chromatography analysis, and 2 was found at 83 mol. after that,
The oil bath temperature was raised to 120°C, and tetrahydrofuran was distilled off under normal pressure and then reduced pressure to obtain a reddish brown oily residue.

To this oily residue, 60 mA of dry purified anisole was added, and 80 μm (0,28
After adding f remol) and reacting at 152°C for 2 hours,
Washed in 5oo- of hydrochloric acid and 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. The soluble part was 0.31.

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 poly(p-phenylene)]

Bretan Chemical Society of Japan,
51, 2091 (1978), poly(p-phenylene) powder produced by the method described in
Pressure molding was performed at a pressure of /crn2.

[Battery experiment]

A circular sample with a diameter of 20 mm was cut out from each of the benzothiophene polymer and poly(p-phenylene) obtained by the above method, and a battery was constructed using each sample as a positive electrode and a negative electrode active material.

The figure is a schematic cross-sectional view of a battery cell for measuring the characteristics of a secondary battery, which is a specific example of the present invention, and ■ indicates 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 and a mesh of 80;
3 is a circular negative electrode with a diameter of 20 mm [poly(p-phenylene)
), 4 is! 5 is a circular porous polyzoropylene diaphragm with a diameter of 20M and is thick enough to be sufficiently impregnated with the electrolyte, 5 is a circular positive electrode (benzothiophene polymer) with a diameter of 20M, 6
indicates a platinum wire mesh current collector for the positive electrode with a diameter of 20+ nm and 80 meshes, 7 indicates a positive electrode lead wire, and 8 indicates a screw-in 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, a 1.5 mol/j solution of Et3BuN-BF4 dissolved in distilled and dehydrated penzonitrile according to a conventional method was used.

Using the thus produced battery, charging was performed for 15 minutes under a constant current (4, OmAlα2) in an argon atmosphere. The doping amount per repeating unit of p-phenylene is 23 mol, and the amount of electricity is equivalent to the doping amount of 28 mol to the benzothiophene polymer). Immediately after charging, the battery was discharged under a constant current (2.0 mA/cm2), and when the battery voltage reached 0.5 V, the battery was charged again under the same conditions as above, performing a repeated charging/discharging test. As a result, the number of repetitions of charging and discharging was recorded as 522 times before the charging and discharging efficiency decreased to 50%.

Further, the charging/discharging efficiency after the fifth repetition was 99 degrees. When the battery was left charged for 62 hours, its self-discharge rate was 3.9%.

Comparative Example In Example 1, a battery was repeatedly charged and discharged in the same manner as in Example 1 except that poly(p-pherene) was used for both the positive and negative electrodes. The light/discharge efficiency was 92%, and charging became impossible after the 183rd repetition.

The fifth charging/discharging efficiency in this battery experiment was 92%. When the battery was left charged for 62 hours, its self-discharge rate was 83 cm.

Example 2 Bretan Chemical Society of Japan,
56, 985 (1983') (electrochemical synthesis of polypyrrole from -role monomer), a polypyrrole film was synthesized.

A battery was repeatedly charged and discharged in the same manner as in Example 1 except that the obtained polypyrrole film was used as the negative electrode. Charging was not possible after the 427th return.

When the battery was left charged for 62 hours, its self-discharge rate was 4.8%.

[Brief explanation of drawings]

The figure is a schematic cross-sectional view of a battery cell for measuring characteristics of a 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 Sei Kikuchi, patent attorney representing Showa Denko Co., Ltd.

Claims (1)

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