JP2588405B2 - Organic electrolyte battery using high concentration mixed solute - Google Patents

Description

The present invention relates to an organic electrolyte battery. More specifically, 2
The present invention relates to an organic electrolyte battery using an electrolyte containing a high concentration of lithium salts or more.

[Prior Art] In recent years, the miniaturization, thinning or weight reduction of electronic devices has been remarkable.
There is a great demand for weight reduction. At present, silver oxide batteries are frequently used as small and high-performance batteries, and lithium batteries have been developed and put into practical use as thin dry batteries and small and lightweight high-performance batteries. However, since these batteries are primary batteries, they cannot be repeatedly used and used for a long time. On the other hand, nickel-cadmium batteries have been put into practical use as high performance secondary batteries,
It is still unsatisfactory in terms of weight reduction.

In addition, lead storage batteries have conventionally been used in various industrial fields as large capacity secondary batteries, but the biggest disadvantage of these batteries is that they are heavy. This is fatal because lead peroxide and lead are used as electrodes. In recent years, attempts have been made to reduce the weight and improve the performance of batteries for electric vehicles, but they have not been put to practical use. However, there is a strong demand for a secondary battery having a large capacity and light weight as a storage battery.

As described above, batteries currently in practical use each have advantages and disadvantages, and are used depending on the intended use. However, there is a great need for batteries to be smaller, thinner, or lighter. As a battery meeting such needs, a polymer battery using a conductive polymer as an electrode material has recently been proposed. The battery has high performance as a secondary battery and has the possibility of lightening. In fact, a half-cell formed using an organic semiconductor such as a polyacene-based organic semiconductor or polyaniline, which is a heat-treated aromatic condensation polymer, exhibits extremely excellent characteristics.

However, there were some problems to be solved in order to promote the practical use of the battery. Among these problems, in particular, there is a problem that the volume of the battery must be increased if the battery is packaged in a practical battery size using a known electrolytic solution. This is because the battery takes in the negative ions in the electrolyte as a dopant on the positive electrode side on the high potential side, so that a sufficient amount of negative ions must be made to exist in the electrolyte in advance. As a result, the volume of the battery increases.

In order to solve this problem, it is sufficient that the concentration of the electrolyte is increased. However, when the concentration of the electrolyte is set to 1.5 mol / mol or more, the battery capacity is reduced, so that this measure is not practical.

[Problems to be Solved by the Invention] An object of the present invention is to propose an electrolyte solution most suitable for an organic electrolyte battery using a conductive polymer as a positive electrode and using lithium or a lithium alloy as a negative electrode. An object of the present invention is to provide an organic electrolyte battery.

Another object of the present invention is to provide an organic electrolyte battery which has a large capacity and a small internal resistance and can be repeatedly charged and discharged.

[Means for Solving the Problems] As a result of research on batteries of various types, the present inventor has found that the above-mentioned object is to use a conductive polymer capable of electrochemically doping and undoping anions as a positive electrode, In a battery using lithium or a lithium alloy as a negative electrode, 2
1.5 ~ 4M lithium salt in aprotic solvent
It has been found that this can be achieved by using a (molar concentration) dissolved mixed solute solution as an electrolytic solution.

As the lithium salt, various known lithium salts can be used. In particular, LiClO ₄ , LiBF ₄ , LiB (CH ₃ ) ₄ , L
iB (C ₂ H ₅ ) ₄ , LiB (C ₆ H ₅ ) ₄ , LiPF ₆ and LiAsF ₆ are preferred.

The aprotic solvent used is not particularly limited as long as the lithium salt can be dissolved to the concentration specified in the present invention. However, propylene carbonate, ethylene carbonate, sulfolane, dimethoxyethane, and mixtures thereof are particularly preferred.

The above lithium salt and aprotic solvent must be sufficiently dried and purified, and then used for preparing an electrolytic solution. Impurities, especially water, cause problems such as deterioration of the negative electrode, increase in leakage current, and increase in self-discharge.

The electrolytic solution used in the battery of the present invention is a solution in which two or more lithium salts are dissolved in an aprotic solvent at a concentration of 1.5 M to 4 M. It is desirable that at least two kinds of lithium salts are used, and the amount of the lithium salt used in the largest amount does not exceed 95% by weight, particularly 90% by weight of the total amount of lithium salts.

Although the reason is not clear, the concentration of the electrolytic solution can be increased by mixing two or more kinds of lithium salts. For example, 3M in the system of LiClO ₄ and propylene carbonate,
It is impossible to prepare an electrolytic solution having a concentration of 1 because LiClO ₄ does not dissolve. However, for example, a 3M propylene carbonate solution can be prepared using a mixed salt obtained by mixing LiBF ₄ of LiClO ₄ at a ratio of 1: 3. The characteristics of the battery using the mixed salt electrolyte are good.

Specifically describing a preferred embodiment of the present invention, LiCl
If it is a combination of O ₄ and LiBF ₄ , LiClO ₄ : LiBF ₄ = 1: 9 to 7:
It is preferable to use a weight ratio of 3 and to adjust the concentration of the electrolyte solution to a range of 1.5 to 3M. Outside the above mixture composition, the effect is small. For example, with a composition of LiClO ₄ : LiBF ₄ = 1: 20, a 2M propylene carbonate solution can be prepared, but the battery characteristics, particularly the discharge capacity, are unfavorably reduced. on the other hand,
When the composition is LiClO ₄ : LiBF ₄ = 8: 2 or more, the solubility of the mixed salt decreases, and the characteristics of the battery deteriorate. When a mixed salt of LiClO ₄ and LiBF ₄ is used, the concentration of the electrolyte is preferably in the range of 1.5 to 3M. If the concentration is lower than this, electrolyte shortage occurs as described later. At 3 M or more, the characteristics of the battery, particularly the capacity, deteriorate because the viscosity of the electrolytic solution increases.

Any combination of mixed salts may be used as long as it can be dissolved in an aprotic solvent at a concentration of 1.5 to 4M. For example, if LiPF ₆ : LiClO ₄ = 9: 1 to 3: 7, an electrolyte of 1.5 to 4 M can be prepared. Further, the characteristics of the battery of the present invention using this electrolytic solution are also good. In other systems,
For example, LiAsF ₆ -LiPF ₆ , LiClO ₄ -LiAsF ₆ , LiBF ₄ -LiPF _{6 and the} like can be mentioned.

The use of the electrolytic solution defined in the present invention can reduce the amount of the electrolytic solution required by the battery, and can produce a compact battery. This will be described later based on a specific battery configuration.

The positive electrode used in the organic electrolyte battery of the present invention is a conductive polymer that can be doped with an anion and can be undoped reversibly. As such a conductive polymer,
Examples include polyacetylene, polythiophene, aniline polymers, and polyacene-based organic semiconductors which are heat-treated aromatic condensation polymers. When used as an electrode material, stability,
And moldability is extremely important in practical use, from this viewpoint,
Polymers of polyacene-based organic semiconductors and anilines are particularly preferred.

The above polyacene-based organic semiconductor is disclosed in
No. 63, which is a heat-treated product of an aromatic condensed polymer, having an atomic ratio of hydrogen atom / carbon atom of 0.05 to 0.5, and a specific surface area of 60% by BET method.
This is an insoluble and infusible strange material having a polyacene skeleton structure of 0 m ² / g or more.

The aromatic condensation polymer as a raw material is, for example, a condensate of an aromatic hydrocarbon compound having a phenolic hydroxyl group and an aldehyde. As the aromatic hydrocarbon compound, for example, so-called phenols such as phenol, cresol and xylenol are suitable, but not limited thereto.

As the aldehyde, formaldehyde, acetaldehyde, furfural and the like can be used, and formaldehyde is preferred. The phenol aldehyde condensate may be any of a novolak type, a resol type, or a composite thereof.

The insoluble and infusible substrate in the present invention is a heat-treated product of the aromatic condensation polymer as described above, and can be produced, for example, as follows.

An inorganic salt such as zinc chloride or sodium phosphate is mixed with the above-mentioned aromatic condensation polymer. Thereby, porosity can be provided to the insoluble and infusible substrate. The amount to be mixed varies depending on the type of the inorganic salt and the shape and performance of the target electrode, but is preferably 10/1 to 1/7 by weight. Also,
When obtaining a substrate that is porous and has communication holes,
It is preferable to use the inorganic salt in an amount of 2.5 to 10 times the weight of the aromatic condensation polymer. The mixture of the inorganic salt and the aromatic condensation polymer obtained in this manner is formed into a target shape such as a film, a plate, or the like, and cured at a temperature of 50 to 180 ° C. for 2 to 90 minutes for curing and molding. I do.

The cured product thus obtained is then heated in a non-oxidizing atmosphere to a temperature of from 350 to 800C, preferably from 350 to 700C, particularly preferably from 400 to 600C. By this heat treatment, the aromatic condensation polymer undergoes a dehydrogenation dehydration reaction, and a polyacene skeleton structure is formed by the condensation reaction of the aromatic ring.

This reaction is a kind of thermal condensation polymerization, and the degree of reactivity is represented by the atomic ratio represented by hydrogen atoms / carbon atoms (hereinafter referred to as H / C) in the final product. The H / C value of the insoluble infusible substrate is 0.05 to 0.5, preferably 0.1 to 0.35. If the H / C value of the insoluble and infusible substrate is larger than 0.5, the polyacene-based skeletal structure is undeveloped, and the electric conductivity is undesirably low. On the other hand, when the value of H / C is smaller than 0.05, carbonization has progressed too much, and the performance as an electrode is low.

The obtained heat-treated body is sufficiently washed with water or diluted hydrochloric acid to remove the inorganic salt contained in the heat-treated body. Thereafter, when the substrate is dried, an insoluble infusible substrate having a specific surface area of 600 m ² / g or more by a BET method is obtained.

Aniline polymers which are preferred conductive polymers for the positive electrode include aniline or aniline derivatives such as N-methylaniline, p-aminodiphenylamine, p-toluidine, p-phenylenediamine, o-phenylenediamine, etc. Obtained by electrochemical oxidation polymerization. Practically, an aniline polymer is preferable.

As the chemical polymerization method, aniline or a water-soluble salt of aniline is oxidatively polymerized in a reaction medium containing a protonic acid and an oxidizing agent. As the water-soluble salt, salts of mineral acids such as hydrochloric acid and sulfuric acid are generally desirable. As the oxidizing agent, for example, chromates such as chromium (IV) oxide, potassium dichromate, sodium dichromate, manganese-based oxidizing agents such as potassium permanganate, and ammonium persulfate can be used. Sulfuric acid, hydrochloric acid, hydrobromic acid, tetrafluoroboric acid, hexafluorophosphoric acid,
Perchloric acid or the like can be used, and an acid that generates an anion having a large ionic radius, such as tetrafluoroboric acid, hexafluorophosphoric acid, or perchloric acid, is particularly desirable. Water is generally used as the reaction medium, but water-miscible organic solvents such as ketones, ethers or organic acids, for example, water-immiscible organic solvents such as acetone, tetrahydrofuran and acetic acid, carbon tetrachloride, and hydrocarbons Can also be used.

When an aqueous solution of an aniline or a water-soluble salt of an aniline is dissolved in a reaction medium and an aqueous solution of a protonic acid oxidizing agent is dropped at a temperature equal to or lower than the boiling point of the reaction medium, preferably equal to or lower than room temperature, the induction time is usually several minutes. The polymer precipitates immediately after passing. The polymer thus obtained still contains the protonic acid anion even after being sufficiently washed with water, and it is necessary to sufficiently wash this with an aqueous alkaline solution such as aqueous ammonia, and then wash the water again. Even if a small amount of impurities such as an excessive oxidizing agent remains, the self-discharge characteristics and cycle life of a secondary battery using a composite of an insoluble and infusible substrate and a polymer of aniline as a positive electrode active material are reduced. Cause.

The electrochemical polymerization method can be performed, for example, as follows. In a protic acid acidic solution in which anilines or a water-soluble salt of anilines are dissolved in the same reaction medium as used in the above-described chemical polymerization method, a counter electrode using an inert metal such as platinum, For example, Ag / AgCl standard electrode,
An electrolytic cell equipped with a reference electrode such as a saturated calomel standard electrode and a working electrode is prepared. The protonic acid at this time is preferably a protonic acid that generates an anion having a large ionic radius, such as tetrafluoroboric acid, hexafluorophosphoric acid, and perchloric acid, similarly to the chemical polymerization method.

Electropolymerization is performed using the above-mentioned electrolytic cell within a potential range appropriate for the reference electrode, that is, within a potential range in which only the polymerization of anilines occurs on the working electrode without causing the decomposition reaction of the solvent and the protonic acid. As the electropolymerization method, a constant current electrolysis method, a constant potential scanning method and the like are known, and any method may be used as long as the potential of the working electrode is maintained within the above-described appropriate potential width. The polymer obtained by such a method can be converted into a polymer containing no impurities by the same post-treatment as in the chemical polymerization method.

Since the electrochemically polymerized polyaniline is in the form of a film, it can be used as it is as the electrode material of the present invention by cutting it into an appropriate size. However, when polyaniline is produced by the oxidative polymerization method, the product is a powder and must be molded. In molding the polyaniline powder, the resulting electrode material must have porosity, conductivity, and mechanical strength. For this purpose, for example, there is a method of pressure-forming or sintering a composite in which a binder such as Teflon and a conductive material such as carbon black are mixed in polyaniline.

It is desirable for the electrode material to minimize the amount of the binder and the amount of the conductive material in the composite, and usually 1 to 10% based on the volume of polyaniline.

The battery action of the battery of the present invention utilizes electrochemical doping and electrochemical undoping of the above-mentioned electrolyte ions into a conductive polymer used as an electrode. That is, energy is stored by doping the conductive polymer, and is taken out as electric energy by undoping.

The doping or undoping may be performed under a constant current, a constant voltage, or under a condition where the current and the voltage change.However, the amount of the doping agent doped into the conductive polymer electrode is determined by the carbon atom of the electrode. The percentage of the number of ions to be doped per one is preferably 0.5 to 20%.

In the battery of the present invention, since the above-mentioned high-concentration electrolyte is used, the required amount of the electrolyte is small. For example, when operating a battery in the range of doping an insoluble and infusible substrate with 0 to 10% of an anion, the conventionally used Li
The electrolytic solution of ClO ₄ / propylene carbonate 1M should be at least 100 cc, and practically 200
cc to 300cc is required. The reason is that when doping the insoluble infusible substrate with anions, the anions in the electrolyte are absorbed by the insoluble infusible substrate of the positive electrode and the cations are absorbed by the negative electrode of Li or Li alloy, and the electrolyte in the electrolyte is This is because the electrolyte must be dissolved in the electrolytic solution in an amount equal to or greater than the consumed amount. However, in the case of the electrolyte of the present invention, for example, an electrolyte in which LiPF ₆ and LiBF ₄ are mixed at a ratio of 1: 1 and dissolved in propylene carbonate at a concentration of 2.5 M, at least 40 cc of the insoluble and infusible substrate is required for 1 mol of carbon. More specifically, a battery with anion doping of 0 to 10% can be obtained by using an electrolyte solution of 80 to 120 cc. That is, the battery operates with an electrolyte amount of 1/2 to 1/3 as compared with the conventional system. For this reason, the battery of the present invention can be made more compact than a conventional battery.

In particular, when a battery is assembled using polyaniline as a positive electrode material, the effect of the electrolytic solution according to the present invention is remarkable because polyaniline is a conductive polymer in which only an anion can be doped or undoped.

[Effects of the Invention] The present invention relates to a high-concentration mixed solution obtained by dissolving two or more lithium salts in an aprotic solvent in a battery using a conductive polymer as a positive electrode and lithium or a lithium alloy as a negative electrode. Provided is a practical battery that can be compactly packaged using a solute electrolyte.

[Examples] Hereinafter, the present invention will be further described with reference to examples.

Example 1 (1) An aqueous solution in which a water-soluble resol (about 60% concentration) / zinc chloride / water was mixed at a weight ratio of 10/25/4 was formed on a glass plate with a film applicator. Cover the glass plate on the formed aqueous solution and keep the water from evaporating.
The composition was cured by heating at 0 ° C. for 1 hour.

The cured film was placed in a siliconite electric furnace, heated at a rate of 40 ° C./hour under a nitrogen stream, and heat-treated to 500 ° C. Next, the heat-treated product was washed with dilute hydrochloric acid, washed with water, and then dried to obtain a film-like porosity. The thickness of the film was about 300 μm, the apparent density was about 0.35 g / cm ³ , and the film was excellent in mechanical strength. Next, the electrical conductivity of the film was measured at room temperature with a current of 4
It was 10 ^-3 S / cm when measured by the terminal method. According to elemental analysis, the atomic ratio of hydrogen atom / carbon atom was 0.27.

When the specific surface area was measured by the BET method, it was 2100 m ² /
It was an extremely large value of g.

(2) Next, a mixed salt obtained by mixing LiCl ₄ and LiBE ₄ at a weight ratio of 1: 1 in propylene carbonate which had been sufficiently dehydrated was placed so that the concentration of the solution became 2M. When this solution was stirred with a glass rod for several minutes, the solute was completely dissolved and a clear solution was obtained. The above operations were all performed under an argon stream. 0.24cm ^{3 of} the film made in (1) above
Was used as a positive electrode, a 50 μm-thick glass separator having the same area as this, a 50 μm-thick lithium negative electrode having the same area, and a stainless steel plate current collector were used to assemble a battery using the solution obtained above as an electrolyte. The combined volume of the positive electrode, separator, and negative electrode
0.32 cm ³ .

(3) The voltage immediately after assembly of this battery was 3.0 V.
Next, the battery was charged by applying a voltage of 4 V for 1 hour at room temperature from an external power supply. The voltage of the battery after charging, that is, the electromotive voltage was 4 V, and the value of the electromotive voltage did not change even after one hour from the end of the voltage application. Next, when the battery was discharged at a current of 4 mA through an external circuit, it took 2.5 hours for the battery voltage to reach 2 V.

Comparative Examples 1 to 5 A battery was assembled and the capacity was measured in exactly the same manner as in Example 1 except that the electrolytic solution shown in Table 1 was used. The results are shown in Table 1. In all cases, the capacity was lower than in Example 1.

Example 2 An electrolyte solution having the following solute composition and solute concentration was prepared using propylene carbonate as a solvent. In each case, the mixed solute was completely dissolved in propylene carbonate to obtain a transparent electrolyte. Next, a battery was prepared in the same manner as in Example 1, and the discharge capacity was measured at room temperature. The results are summarized in Table 2. In each case, high capacities were achieved.

Example 3 (1) 9.2 ml of concentrated hydrochloric acid was added to 90 g of distilled water, and aniline 10
g was dissolved to prepare an aniline hydrochloride aqueous solution. Separately, 50 ml of perchloric acid (60% aqueous solution) and potassium dichromate 10.5
An oxidizing aqueous solution in which g was dissolved was prepared, and this was added dropwise to the above-mentioned aqueous solution of aniline in hydrochloric acid at room temperature over 40 minutes with stirring. After stirring for another 15 minutes, the reaction mixture was
After stirring for 1.5 hours, the polymer was separated by filtration. After washing with stirring in distilled water, washing with stirring in 1N aqueous ammonia was performed, followed by filtration, and further washing with distilled water until the filtrate became neutral. After drying under reduced pressure at 70 ° C. for 10 hours, 5.8 g of purple aniline polymer powder was obtained. 5% by weight of polytetrafluoroethylene and 10% by weight of carbon black were added to the aniline powder obtained by the above method, and the mixture was pressed and molded to form an electrode plate having a thickness of 300 μm.

(2) Next, under the same conditions as in Example 1, namely, LiClO ₄ : L
Using 0.2cc of a 2M propylene carbonate solution of iBF ₄ = 1: 1, a polyaniline positive electrode (0.24 cm ³ , a thickness of 300 μm), a glass separator (50 μm), and a lithium negative electrode (50 μm), the volume of the battery was 0.32 cm ³ . I assembled batteries so that

(3) The voltage immediately after the assembly of this battery was 3.2 V.
Next, at room temperature, a voltage of 4 V was applied to the battery by an external power supply for 1 hour, thereby charging the battery and setting the electromotive voltage of the battery to 4 V. Next, when the battery was discharged at a current of 4 mA through an external circuit, it took 2.4 hours for the battery voltage to reach 2.7 V.

Comparative Example 6 The same polyaniline, separator and lithium anode as in Example 3 were used, except that LiCl ₄ / propylene carbonate was used.
A battery having a volume of 0.32 cm ³ was assembled using 0.2 cc of the 1 M electrolytic solution. When the capacity was measured by the same method as in Example 3,
The time required for the battery voltage to reach 2.7 V is 1.5 hours,
It was shorter than in Example 3.

Continuation of the front page (56) References JP-A-62-100951 (JP, A) JP-A-61-290773 (JP, A) JP-A-60-170163 (JP, A) JP-A-59-163766 (JP) , A)

Claims (7)

(57) [Claims] In a battery having a positive electrode made of a conductive polymer capable of electrochemically doping and undoping an anion and a negative electrode made of lithium or a lithium alloy, two or more lithium salts are added to an aprotic solvent in an amount of 1.5 to 4M. An organic electrolyte battery, wherein the dissolved mixed solute solution is used as an electrolyte. 2. The lithium salt is LiClO ₄ , LiBF ₄ , LiB (CH ₃ ) ₄ , L
_{iB (C 2 H 5) 4} , LiB (C 6 H 5) 4, LiPF 6 and an organic electrolyte battery Claims claim 1 wherein is selected from LiAsF _6. 3. The organic electrolyte battery according to claim 1, wherein the aprotic solvent is propylene carbonate, ethylene carbonate, sulfolane, dimethoxyethane, or a mixture thereof. 4. The solute in the mixed solute solution is LiClO ₄ and LiBF ₄ , the mixing ratio is 1: 9 to 7: 3 by weight, and the total concentration thereof is 1.5 to 3M. 3. The organic electrolyte battery according to claim 1, wherein 5. A heat-treated product of an aromatic condensation polymer comprising carbon, hydrogen and oxygen, wherein the conductive polymer has a hydrogen atom / carbon atom ratio of 0.05 to 0.5 and a ratio determined by the BET method. ^2. The organic electrolyte battery according to claim 1, which is an insoluble and infusible substrate containing a polyacene-based skeleton structure having a surface area of at least 600 m ² / g. 6. The organic electrolyte battery according to claim 5, wherein the aromatic condensation polymer is a condensate of phenol and formaldehyde. 7. The organic electrolyte battery according to claim 1, wherein the conductive polymer is an aniline polymer.