JPH0619982B2 - Secondary battery - Google Patents

Description

TECHNICAL FIELD The present invention relates to a secondary battery using as an electrode material a conductive material having a conductive polymer on a specific base material.

<Prior Art> In recent years, a secondary battery using a conductive polymer made of various organic materials as an electrode material has been proposed.

The conductive polymer used as the electrode material of this type of secondary battery is
Usually, the conductivity is low, but it is possible to dope and undope the dopants such as various anions and cations, and the dope treatment dramatically increases the conductivity. Then, a conductive polymer doped with anions is used as a positive electrode material, and a conductive polymer doped with cations is used as a negative electrode material, and a solution containing the above dopant is used as an electrolytic solution. A battery that can be charged and discharged is constructed by performing the chemical reversible process.

Polymers having a conjugated double bond in the main chain such as polyacetylene, polyparaphenylene, polyphenylene, polypyrrole, polyaniline, and polyparaphenylene vinylene are known as such conductive polymers, and polyacetylene is an example. In this case, polyacetylene is used as an electrode material for at least one of the positive electrode and the negative electrode, and anions such as BF ₄ ⁻ , ClO ₄ ⁻ , SbF ₆ ⁻ , PF ₆ ⁻ , or Li ⁺ , Na ⁺ , R ₄ −N ⁺ ( R represents an alkyl group) and the like is electrochemically reversibly doped and undoped.

By the way, such a conductive polymer is obtained in the form of powder, granules, lumps, or films, but in the case of powdered, granular, or lump-shaped conductive polymers, these are used as electrode materials for the non-aqueous electrolyte solution. In the case of constituting a secondary battery or a solid electrolyte secondary battery, by themselves, or after adding a suitable conductive material for improving the conductivity, and / or a thermoplastic resin for increasing the mechanical strength of the electrode to them, It takes time and effort to form an electrode by pressure forming into an electrode shape. In that respect, the conductive polymer film has a feature that it can be made into an electrode only by punching them out into the electrode size, and the electrode is relatively easy to produce.

As the conductive polymer film as described above, at present, a polyacetylene film obtained by applying a polymerization catalyst to a glass wall, blowing acetylene gas on it to form a polyacetylene film, and then peeling this film, Known are polythienylene film and polypyrrole film, etc. obtained by forming a film-like substance such as polyphenylene or polypyrrole on the electrolytic electrode by an electrochemical oxidative polymerization reaction (electrolytic oxidative polymerization), and then peeling the film from the electrode. Has been.

<Problems to be Solved by the Invention> However, when a secondary battery is constructed by using the above-mentioned conventional conductive polymer film as an electrode material of a battery, a polyacetylene film is present due to the presence of a trace amount of oxygen and moisture in the battery. Since the polymer deteriorates, the performance as an electrode deteriorates, and there is a drawback that the cycle life is significantly reduced due to a sudden increase in charging voltage and a decrease in charge / discharge efficiency during the cycle. There is a problem that the electrode manufacturing work is difficult and complicated because it is easily oxidized.

Further, in the polyphenylene film or polypyrrole film produced by the electrochemical oxidative polymerization reaction, the size of the film is regulated by the size of the electrolytic electrode, and the manufacturing method is complicated, which causes a high battery cost. Become. Furthermore, since it is difficult to obtain a thick and uniform film, when this film is used as a battery electrode, contact with the current collector deteriorates during charge / discharge cycles, and battery reaction concentrates on a part of the electrode. Therefore, there is a problem that the battery performance is deteriorated.

<Means for Solving Problems> The present inventors have formed a conductive polymer on a specific substrate,
I tried to obtain a conductive material that is stable and easy to manufacture and can make any part of it conductive in any direction, but by using it as an electrode of a secondary battery, Settled.

That is, the gist of the present invention is a secondary battery comprising a positive electrode, a negative electrode, and an electrolytic solution, wherein a conductive polymer is vaporized on a metal foam having a space capable of holding the oxidant in the presence of the oxidant. A conductive material obtained by polymerizing in a phase atmosphere and forming the conductive polymer in the space of the metal foam is used as at least one electrode material, and the porosity of the metal foam is 70 to 9
The secondary battery is 8%.

Examples of the material of the metal porous body used as the base material for holding the conductive polymer in the present invention include gold, platinum, silver, copper, nickel, stainless steel, or nickel-aluminum alloy, nickel-chromium alloy, copper-nickel alloy. , Nickel-chromium-aluminum alloy, etc. are used. When a metal foam made of gold, platinum, silver, stainless steel, nickel-chromium-aluminum alloy or the like is used, the metal foam can also be used as a current collector. This improves the adhesion between the conductive polymer and the current collector, extends the cycle life of the battery, and improves the liquid content of the electrode itself because the metal foam that is the electrode base material is a porous body. As a result, the charge / discharge efficiency of the battery is improved.

Also, the porosity of this metal foam should be 70-9 as described above.
Good battery characteristics can be obtained by setting the range to 8%. This is considered due to the following reasons. That is, in a metal foam having a porosity of less than 70%, the specific surface area (ratio of the surface area to the volume of the metal foam) becomes too small, so that the conductive polymer is in a small portion in contact with the metal foam. Further, since the liquid content also decreases, the utilization rate of the conductive polymer decreases. With a metal foam having a porosity of 70 to 98%, it is possible to obtain a secondary battery having good characteristics without such an adverse effect. If the porosity exceeds 98%, the strength required for the electrode cannot be obtained.

Further, the oxidizing agent used in the present invention is a compound having polymerizability with a monomer compound for polymerizing a conductive polymer, and is used alone or in combination of two or more kinds. Usually, a metal salt having a strong acid residue, halogen, or cyan, a peroxide, a nitrogen oxide, or the like is used. Specifically, Fe (ClO ₄ ) ₃ , Fe (BF ₄ ) ₃ , Fe ₂ (SiF ₆ ) ₃ , Cu (ClO ₄ ) ₂ , Cu (BF ₄ ) ₂ , CuSiF ₆ , FeCl ₃ , CuCl ₂ , K ₃ [Fe (CN) ₆ ], RuCl ₃ , MoCl ₅ , WCl ₆ , (NH ₄ ) _{2 S 2 O 8, K 2 S} 2 O 8, Na 2 S 2 O 8, NaBO 3, H 2 O 2, NOBF 4, NO 2 BF 4, NO 2 PF 6, NOClO 4, NOAsF 6, NOPF 6 , etc. is there.

As the monomer compound for polymerizing the conductive polymer used in the present invention, a pyrrole-based compound or a thiophene-based compound is used alone or in combination. Preferably, a pyrrole-based compound or a thiophene-based compound having no substituent at the 2,5 position of the pyrrole- or thiophene ring skeleton structure is used.

Specific examples of the pyrrole compound include pyrrole, N-methylpyrrole, N-ethylpyrrole, Nn-propylpyrrole, Nn-butylpyrrole, N-phenylpyrrole, N-toluylpyrrole, N-naphthylpyrrole,
3-methylpyrrole, 3,5-dimethylpyrrole, 3-ethylpyrrole, 3-n-propylpyrrole, 3-n-butylpyrrole, 3-phenylpyrrole, 3-toluylpyrrole, 3-naphthylpyrrole, 3-methoxypyrrole , 3,5-dimethoxypyrrole, 3-ethoxypyrrole, 3-n-propoxypyrrole, 3-phenoxypyrrole, 3-methyl-N-methylpyrrole, 3-methoxyN-methoxypyrrole, 3-chloropyrrole, 3-bromo Pyrrole, 3-methylthiopyrrole, 3-methylthio N-methylpyrrole and the like can be mentioned.

Further, as the thiophene compound, specifically, 2,2'-bithiophene, 3-methyl-2,2'-bithiophene, 3,3 '
-Dimethyl-2,2'-bithiophene, 3,4-dimethyl-2,
2'-bithiophene, 3,4-dimethyl-3 ', 4'-dimethyl-2,2'-bithiophene, 3-methoxy-2,2'-bithiophene, 3,3'-dimethoxy-2,2'-bithiophene ，
2,2 ', 5', 2 "-terthiophene, 3-methyl-2,2 ',
5 ', 2 "-terthiophene, 3,3'-dimethyl-2,2',
For example, 5 ', 2 "-terthiophene.

The method of retaining the oxidizing agent on the substrate is to retain the oxidizing agent as it is, or by dispersing or dissolving it in an appropriate medium and bringing the dispersion or solution into contact with the substrate. In order to easily retain the oxidizer on the base material, the base material is previously cleaned, degassed,
It is also possible to appropriately perform a pretreatment such as hydrophilization or lipophilicity. The oxidant may be held on all parts of the substrate, but may be held only on predetermined parts if necessary.

Although the ratio of the oxidizing agent to the monomer compound is related to the amount of the polymer produced, it is usually 0.001 to 10,000 mol times, and preferably 0.005 to 5,000 mol times.

The polymer of the monomer compound is formed on the substrate in a gas phase atmosphere. That is, it is carried out in a gas phase atmosphere in the presence of vapor of only the monomer compound, or nitrogen, argon, air, other gas or mixed gas.
The whole system can be operated under pressure, atmospheric pressure or reduced pressure, but it is usually preferable to operate under atmospheric pressure.

The reaction temperature is not specified as long as the monomer compound can be polymerized, but is usually -20 to 100 ° C, preferably 0 to 80 ° C.

The reaction time is usually 0.01 to 200 hours, preferably 0.02 to 100 hours, though it depends on the reaction temperature, the amount of the oxidizing agent, and the amount of the monomer compound.

After the polymerization reaction, a dark brown to black homogeneous polymer is formed on the portion of the substrate holding the oxidizing agent.

The oxidant is retained on the polymer once formed, and the same or different kind of the monomer compound is contacted to continue the polymerization reaction, thereby increasing the production amount of the polymer or forming two or more kinds of polymers. Can be done.

After the polymerization reaction, the monomer compound and the oxidizing agent remaining on the substrate are removed. Usually, it can be removed by immersing and washing the substrate in water, alcohol or an organic solvent. After that, the conductive material used in the secondary battery of the present invention can be obtained by drying the base material by a usual drying method.

<Operation> Since the conductive polymer is formed in the space of the metal foam by the vapor phase polymerization as described above, even if the polymerization amount of the polymer is increased to increase the capacity, the polymer is kept in the foam space. Can be maintained in a large amount, and the uniformity of the electrode film thickness can be easily maintained. In addition, since the polymer is generated and retained inside the pores of the foam, the polymer in the electrode does not peel off from the metal foam that is the base material due to shock, etc. The mechanical strength of the electrode is remarkably improved as compared with the case where the film is peeled from the electrolytic electrode and pressure-bonded to the current collector. Further, by using the metal foam also as the collector of the electrode, the adhesion between the conductive polymer and the collector is remarkably improved, and the contact state between the two is extremely deteriorated during the charge / discharge cycle. Becomes smaller.

Furthermore, since the metal foam, which is the electrode base material, is a porous body, the liquid content (electrolyte solution property) of the electrode itself is improved, and the ratio of the conductive polymer in the electrode involved in the battery reaction is increased, so Charge and discharge efficiency becomes good. In particular, since the porosity of the metal foam is set to 70 to 98%, the ratio of the surface area to the volume of the metal foam as the base material (specific surface area) is increased, and the amount of polymer produced is increased to increase the electrode capacity. Even in this case, the amount of polymer in the electrode that is in direct contact with the electrolytic solution is not significantly reduced. Therefore, the utilization rate of the conductive polymer is not significantly reduced even under severe charge / discharge conditions, and a secondary battery having high charge / discharge efficiency and good cycle life can be obtained even under these conditions.

Further, the conductive material used as the electrode material in the present invention is easy to manufacture and has excellent oxidation resistance, and there is no deterioration due to oxygen or water in the battery in the air as in the case of using a polyacetylene film, and the electrode is manufactured. Is easy and the storage stability of the electrode is good.

<Example> One side of a 70% porosity stainless steel foam was subjected to F
at room temperature to eCl ₃ · _6H 2 O- methanol saturated solution 30
After soaking minutes, air dried, and FeCl 3 · _6H 2 _O-methanol droplets remaining as droplets on a portion foam surface removed by adsorption with filter paper, homogeneously FeCl on one surface of the foam
₃ components were supported. Next, 4 ml of pyrrole was placed on the bottom of a glass container (10 cm in depth, 25 cm in width, 15 cm in height), and the foam obtained by the above treatment was hung from the top of the glass container, and the above was sealed with a glass plate to foam. The body was exposed to pyrrole vapor. By this contact, one side of the foam rapidly changed to dark green and then black, and polypyrrole was formed on one side of the foam.

After contacting for 40 hours, the foam was taken out and immersed in methanol for 30 minutes to extract and remove unreacted pyrrole and FeCl ₃ components. This operation was continued three times, and after air-drying, punched out in a predetermined size was used as a positive electrode, and lithium punched out in a predetermined size was used as a negative electrode, and the secondary battery according to the present invention as shown in FIG. (Invention Battery A) was produced. In this example, propylene carbonate was used as the electrolyte solvent, lithium tetrafluoroborate (LiBF ₄ ) was used as the electrolyte, and a separator made of polypropylene nonwoven fabric was used. As the electrolyte solvent, in addition to propylene carbonate, ethylene carbonate, acetonitrile, propionitrile, butyronitrile, benzonitrile, dioxolane, 1,4-dioxane, tetrahydrofuran, 1,2-dimethoxyethane, 1,2
-Dichloroethane, nitromethane, N, N-dimethylformamide, dimethylsulfoxide, sulfolane, methyl phosphate, ethyl phosphate, γ-butyrolactone and the like are mentioned as solvents. These solvents may be used alone or in combination of two or more. Good. Further, as the electrolyte, in addition to lithium tetrafluoroborate (LiBF ₄ ), lithium perchlorate (LiClO ₄ ), lithium hexafluorophosphate (LiPF ₆ ), lithium tetrachloroaluminate (L
iAlCl _4), tetraethylammonium tetrafluoroborate _{((C 2 H 5) 4} NBF 4), tetraethylammonium perchlorate _{((C 2 H 5) 4} NClO 4),
Lithium trifluoromethanesulfonate (LiCF ₃ S
O ₃ ), lithium bromide (LiBr), lithium iodide (LiI), or the like may be used.

Further, batteries (invention batteries B and C) having the same structure as the battery A of the present invention were prepared except that a foam of stainless steel having a porosity of 80% and 98% was used.

Further, for comparison, secondary batteries (comparative batteries D and E) having the same structure as the battery A of the present invention except that a foam of stainless steel having a porosity of 60% and 40% were used were produced. Further, a comparative battery F having the same structure as the battery A of the present invention was prepared, except that a polypyrrole film prepared by a conventional electrolytic polymerization method was pressed to a positive electrode can via a current collector and pressed to form a positive electrode.

The above six batteries were charged and discharged at a current of 0.5 mA for 1 hour and then discharged at a current of 0.5 mA until the battery voltage reached 2.5 V, which was repeated.

FIG. 2 shows changes with time in voltage during charge / discharge at the 20th cycle of the inventive batteries A to C and the comparative batteries D to F. In the figure, the solid line shows the voltage change during charging, and the dotted line shows the voltage change during discharging. As is apparent from FIG. 2, the present invention batteries A to
C has a lower charging voltage and a higher discharging voltage than the comparative batteries D to F, and has a good charge and discharge rate, and the charging and discharging efficiency of the batteries A to C of the present invention is good. The efficiencies are 92%, 93%, and 93%, respectively, while the comparative batteries D to F have 89%, 87%, and 81%, respectively.
As described above, the batteries A to C of the present invention have high charge and discharge efficiency.
In the case of the batteries A to C of the present invention, since the stainless steel foam having a large porosity of 70 to 98% is used as the electrode base material, the liquid content of the electrode is very good, and the conductivity with the stainless steel foam is high. It is considered that this is because the conductive polymer has many portions in direct contact with the electrolytic solution, and the utilization rate of the polymer is improved because many portions are in contact with the polymer. On the other hand, in Comparative batteries D and E, the comparative battery F is used because the stainless steel foam is used as the electrode base material.
As compared with Comparative example F, the liquid content is good, the utilization rate of the conductive polymer is high, and the charge / discharge efficiency is higher than that of Comparative battery F. However, the porosities of the stainless steel foams used in the comparative batteries D and E were as low as 60% and 40%, respectively, and the specific surface area of the positive electrode was reduced accordingly, and the liquid content of the positive electrode was reduced. In the polymer polymer amount of, the area where the stainless steel foam and polypyrrole are in contact is reduced, and the amount of polypyrrole in direct contact with the electrolytic solution is also reduced. Therefore, the utilization rate of polypyrrole is lower than that of the present batteries A to C. It is considered that as a result, the charging / discharging efficiency is lower than that of the batteries A to C of the present invention.

In addition, FIG. 3 shows the cycle change of the charge / discharge efficiency (%) of the batteries A to C of the present invention and the comparative batteries D to F. As is clear from the figure, the batteries A to C of the present invention have a high cycle charge of 140% and high charge / discharge efficiencies of 93%, 94%, and 93%, respectively, and have good cycle life. On the other hand, in the case of the comparative battery F, the charging / discharging efficiency is greatly deteriorated after about the 30th cycle. The reason why the cycle characteristic of the comparative battery F is such bad is that the polypyrrole film of the positive electrode is peeled off from the current collector during the charge / discharge cycle, and thus the adhesion between the positive electrode and the current collector is deteriorated. It is considered that, as a result of locally concentrating the current in the positive electrode, the utilization rate of polypyrrole in the positive electrode is significantly reduced, and the charge / discharge rate of the battery is significantly reduced. Further, in the case of the comparative batteries D and E, a relatively high charge / discharge efficiency was maintained up to the 100th cycle. Compared with the comparative product F, this uses a stainless steel foam as a positive electrode base material and current collector, and the adhesion between the stainless steel foam and the polypyrrole film polymer is good, and the liquid content of the positive electrode is also good. This is because. However, when compared with the batteries A to C of the present invention, the porosity of the above-mentioned stainless steel foam was much smaller in the comparative batteries D and E, and accordingly, as described above, the utilization rate of polypyrrole was higher than that of the batteries A to C of the present invention. Under the severe charge and discharge conditions of this experiment, current began to concentrate at the positive electrode local area after 100 cycles, and the electrolyte and solvent were decomposed and polymerized due to the rise of the charging voltage due to the deterioration of polypyrrole itself. It is thought that this is due to

In the batteries A to C of the present invention, since the positive electrode base material and the current collector are made of stainless steel foam having a porosity in the range of 70 to 98%, the utilization rate of polypyrrole is improved. It has excellent cycle characteristics.

FIG. 4 shows changes with time in the battery voltages of the batteries A to C of the present invention and the comparative batteries D and E in the 140th cycle of charging and discharging. As is clear from the figure, in the batteries A to C of the present invention, the charging voltage did not rise even in the 140th cycle, the discharge voltage curve was flat as compared with the comparative batteries D and E, and the battery was used over a long cycle. It can be seen that good cycle characteristics are maintained.

In the above description, the conductive material is used only for the positive electrode, but it is clear that the same effect can be obtained when the conductive material of the present invention is used for the negative electrode or the positive and negative electrodes.

<Effects of the Invention> According to the secondary battery of the present invention configured as described above,
Even if the thickness of the electrode is increased, the uniformity of the film thickness can be maintained, and the polymer is retained inside the pores of the metal foam that is the electrode base material, so the polymer in the electrode can peel off due to shock or the like. There is no need to improve the mechanical strength of the electrode, and the metal foam also serves as an electrode current collector to improve the adhesion between the polymer and the current collector. It is possible to significantly improve the cycle life of the battery because contact with the current collector and the battery reaction are not concentrated in a part. In addition, since a metal foam having a porosity of 70 to 98% is used as the electrode base material, even when the amount of polymer produced is increased or even under severe charge and discharge conditions,
By increasing the liquid content of the electrode, the utilization rate of the conductive polymer can be increased and the charge / discharge efficiency can be improved. As a result, excellent cycle characteristics can be obtained. Furthermore, the conductive material used as the electrode material in the present invention is easy to manufacture and has excellent oxidation resistance, so that the electrode can be easily manufactured and the storage stability of the electrode is good.

[Brief description of drawings]

FIG. 1 is a sectional view showing the structure of a battery according to an embodiment of the present invention,
FIG. 2 is a graph showing changes over time in battery voltage of the present invention battery and comparative battery during charging in the 20th cycle, FIG. 3 is a graph showing cycle characteristics of the present invention battery and comparative battery, and FIG. FIG. 6 is a graph showing changes with time in battery voltage of the battery of the present invention and the comparative battery during charge and discharge at the 140th cycle. 1 ... Positive electrode, 2 ... Negative electrode, 5 ... Positive electrode can, 6 ... Negative electrode can, 7 ... Current collector, 8 ... Foam.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Nobuyuki Yoshinaga 2-18, Keihan Hondori, Moriguchi City, Osaka Prefecture Sanyo Electric Co., Ltd. (72) Inventor Tetsumi Suzuki, 1000-1, Kamoshida-cho, Midori-ku, Yokohama (72) Inventor Kazumi Hasegawa, 1000, Kamoshida-cho, Midori-ku, Yokohama-shi, Kanagawa San Ryoshi Kasei Co., Ltd. (56) Reference JP-A-59-18578 (JP, A)

Claims (1)

[Claims] 1. A secondary battery comprising a positive electrode, a negative electrode and an electrolytic solution, in the presence of an oxidizing agent, a conductive polymer in a gas phase atmosphere on a metal foam having a space capable of holding the oxidizing agent. A conductive material obtained by polymerizing and forming the conductive polymer in the space of the metal foam is used as at least one electrode material, and the porosity of the metal foam is 70 to 98%. Next battery.