JPH09320572A - Manufacture of composite electrode, and lithium secondary battery using the composite electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a composite electrode free from dispersion of charge and discharge capacity by kneading an organic disulfide compound with polyaniline in powdery state, and adding N-methyl-2-pyrolidone thereto followed by kneading. SOLUTION: An organic disulfide compound powder in which sulfur-sulfur bonding is cleaved by electrolytic reduction to generate sulfur-metal ion bonding, and the original sulfur-sulfur bonding is regenerated by electrolytic oxidation is kneaded with polyaniline powder. N-methyl2-pyrolidone is mixed to the mixed powder followed by kneading. The resulting viscous active material ink is extended on a base, and the base is heated in reduced pressure or inert gas atmosphere to remove N-methyl-2-pyrolidone, whereby a composite film is formed. The composite electrode formed of this composite film is used as the positive electrode of a lithium secondary battery. Thus, the kneading time is shortened, and a stable lithium secondary battery can be provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a composite electrode composed of a plurality of organic compounds used in electrochemical devices such as batteries, electrochromic display devices, sensors and memories, and a composite electrode obtained by the manufacturing method. The present invention relates to a lithium secondary battery using as a positive electrode.

[0002]

2. Description of the Related Art Since the discovery of conductive polyacetylene by Shirakawa et al. In 1971, when a conductive polymer is used as an electrode material, it is possible to use a large area electrochromic device such as a battery having a light weight and a high energy density. Electrodes using conductive polymers as electrode materials have been actively studied because electrochemical elements such as biochemical sensors using microelectrodes can be expected.

Since polyacetylene is unstable and poor in practicality as an electrode, other π-electron conjugated conductive polymers have been investigated, and polyaniline, polypyrrole, polyacene,
A relatively stable polymer such as polythiophene has been developed, and a lithium secondary battery using these as a positive electrode has also been developed.

As an organic material which can be expected to have a high energy density, an organic disulfide compound has been proposed (see, for example, US Pat. No. 4,833,048). This compound is simply represented as R-S-S-R (R is an aliphatic or aromatic organic group, S is sulfur),
The S—S bond is cleaved by electrolytic reduction and reacts with a cation (M +) in the electrolytic bath to form a salt represented by R—S− · M +, which is the original R—S by electrolytic oxidation. -Return to SR. A metal-sulfur-based secondary battery in which a metal M supplying a cation (M +) and an organic disulfide-based compound are combined is proposed in the above-mentioned US patent specification. Electrodes using conductive polymers such as polyaniline, polypyrrole, polyacene, and polythiophene take in not only cations but also electrolyte solution during electrode reaction, so that the electrolyte solution not only acts as an ion transfer medium in the battery. Since it also participates in the battery reaction, it is necessary to supply an amount of electrolytic solution corresponding to the battery capacity into the battery. Then, there is a problem that the energy density of the battery is reduced accordingly.

The energy density in this case is 20 to 50 W.
There is a problem that it is about half of that of ordinary secondary batteries such as nickel-cadmium storage batteries and lead storage batteries at about h / kg. Further, regarding the proposed organic disulfide-based compound, the inventors of the above-mentioned U.S. Pat.
Electrochem Soc. , Vol. Thirteen
6, No. 9, p. 2570-2575 (198
As reported in 9), for example, [(C ₂ H ₅ ) ₂ N
In the electrolysis of CSS-] ₂ , the oxidation and reduction potentials are separated by 1 V or more, and the electron transfer process is extremely slow according to the electrode reaction theory. Therefore, in the vicinity of room temperature, a large current suitable for practical use,
For example, it is difficult to extract a current of 1 mA / cm ² or more, and there is a problem that it is limited to use at a high temperature of 100 to 200 ° C.

Therefore, in order to produce a novel electrode which is capable of high-current electrolysis (charging / discharging) even at room temperature and which is excellent in reversibility without deteriorating the feature of the organic disulphide-based compound having high energy density, at least the organic disulphide-based compound is used. A method for producing a composite electrode composed of (hereinafter abbreviated as SS compound), N-methyl-2-pyrrolidone (CH ₃ NC ₄ H ₆ O, hereinafter abbreviated as NMP) and polyaniline has been proposed.

The SS compound, NMP and polyaniline are
At room temperature, they are compatible with each other and form a uniform sticky complex, in which case the SS compound acts as an electrode reactant and imparts ionic conductivity to the complex, and polyaniline is an electrode reactant. In addition, it acts as an electrode reaction catalyst for the SS compound and imparts conductivity to the composite. That is, the potential difference between the oxidation reaction and the reduction reaction of the SS compound, which was a difference of 1 V or more, is reduced to 0.1 V or less, the electrode reaction is promoted, and good ion conduction and electron conduction are achieved in the composite electrode. Network is formed, and electrolysis (charge / discharge) with a large current even at room temperature
Becomes possible. Regarding the introduction of the electrode catalyst into the organic disulfide-based compound electrode, the above-mentioned U.S. Pat. Electrochem So
c. , Vol. 136, No. 9, p. 2570-
2575 (1989), only an organometallic compound is disclosed as an electrode catalyst, and its effect is not specifically disclosed.

The solubility of polyaniline in NMP is
Although it is about several wt% at most, when an SS compound is present, it dissolves in an equimolar amount to NMP. SS compound and N
It is extremely compatible with MP and a viscous and uniform solution can be obtained even in an equimolar amount. This is -S of SS compound
It is considered that the H group, the ═O group of NMP, and the polyaniline having the —NH group that constitutes the phenylenediamine structure in the reductive dedoping state associate with each other via a hydrogen bond or the like to form a uniform complex. Has been.

Sufficient conductivity can be obtained even with a composite electrode of an SS compound and polyaniline. However, when one kind or a combination of any one of metal, metal oxide and graphite is added as a conductive agent to the composite electrode, more conductivity can be obtained. The conductivity is further improved, and large-current electrolysis (charging / discharging) becomes possible. However, when a substance other than the electrode reactive substance is added, the energy density is lowered, so a substance capable of forming a larger amount of ionic conduction and electron conduction networks with a small addition amount is preferable.

As a substance satisfying this condition, a carbon material is suitable, and acetylene black is particularly suitable. Since carbon materials have a smaller density than metal materials and have a large volume even with a small amount of weight, it is easy to form an electron conduction network, and other carbon materials, metal materials, and metal oxides have a significantly higher energy than acetylene black. Since the density does not decrease, it can be selected according to the application.

In the method of manufacturing the composite electrode, first, S
The S compound is dissolved in NMP to prepare a solution, then polyaniline is dissolved in this solution to prepare an active material ink, and the active material ink is cast on a substrate, and then the whole is under reduced pressure or under an inert gas. The electrode is manufactured by heating in an atmosphere.

[0012]

In the conventional method for producing a composite electrode, when the polyaniline powder is added to and mixed with a solution prepared by dissolving the SS compound in NMP, the polyaniline powder is likely to aggregate. There was a problem. In NMP in which the SS compound is dissolved, polyaniline is dissolved in a nearly equimolar amount, but becomes difficult to dissolve as the saturation concentration is approached, and polyaniline aggregated particles are generated, and the active material ink containing the aggregated particles is generated. When a composite positive electrode is produced by directly casting on a substrate, it is difficult to form a homogeneous composite positive electrode, and when a lithium secondary battery is constructed,
There is a problem that the charge and discharge capacities vary.

In order to solve this problem, it has been found that when polyaniline is dissolved in NMP, agglomerated particles are reduced by stirring and kneading for 2 hours or more, but it cannot be completely eliminated. In addition, if a time of 2 hours or more is spent in the stirring and kneading step, there is a new problem that productivity is lowered.

[0014]

In order to solve the above-mentioned problems, the present invention suppresses aggregate particles of polyaniline to prepare a homogeneous composite electrode, and by using the composite electrode, the charge and discharge capacity is improved. In order to obtain a constant lithium secondary battery, the method for manufacturing the composite electrode is as follows. In the stirring and kneading step, first, an organic disulfide compound (SS compound) and polyaniline are kneaded in a powder state to obtain a homogeneous composite in advance. After preparing the powder, N-methyl-2-pyrrolidone (N
MP) is added and kneading is performed in two stages in which solvent kneading is performed. Then, a homogeneous active material ink can be prepared in a short time of about 30 minutes, and by preparing the homogeneous active material ink, a composite electrode having no variation in charge / discharge capacity can be obtained. The secondary battery has excellent capacity characteristics.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION
Sulfur bond is cleaved to generate sulfur-metal ion, and this sulfur-metal ion bond regenerates the original sulfur-sulfur bond by electrolytic oxidation. Organic disulfide compound powder, polyaniline powder, and N-methyl-2-pyrrolidone. A mixture containing at least and is kneaded.

Further, the organic disulphide compound (SS compound) powder is mixed with the polyaniline (PAn) powder in N
An active material ink mixed with -methyl-2-pyrrolidone (NMP) is cast on a substrate, and the substrate is heated under reduced pressure or an inert gas atmosphere.

In addition, an active material ink prepared by mixing an organic disulfide compound powder and a polyaniline powder with N-methyl-2-pyrrolidone is cast on a substrate and then heated in a reduced pressure or an inert gas atmosphere to produce N-methyl. -2-Pyrrolidone is removed to form a composite film.

Further, the sulfur-sulfur bond is cleaved by electrolytic reduction to produce a sulfur-metal ion, and this sulfur-metal ion bond regenerates the original sulfur-sulfur bond by electrolytic oxidation, and polyaniline. A composite electrode prepared by kneading a mixture containing at least powder and N-methyl-2-pyrrolidone is used as a positive electrode.

The SS compound is represented by the general formula (R
A compound represented by (S) y) n can be used, and R
Is an aliphatic group, an aromatic group, S is sulfur, y is an integer of 1 or more,
n is an integer of 2 or more. Examples of such compounds include dithioglycol represented by HSCH ₂ CH ₂ SH (hereinafter referred to as DTG) and 2,5-dimercapto-1,3,4 represented by C ₂ N ₂ S (SH) _2. - thiadiazole (hereinafter, referred to as DMcT), represented by _{C 3 H 3 N 3 S 3} s
-Triazine-2,4,6-trithiol (hereinafter TT
Referred to as A), 7- methyl-2 represented by _{C 6 H 6 N 4 S 3} ,
6,8 tri mercaptopurine (hereinafter, referred to as _{MTMP), C 4 H 6 N} 4 4,5- diamino-2 represented by S _2,
6-dimercaptopyrimidine (hereinafter referred to as DDPy)
Etc., and commercially available products can be used as they are. However, when producing a positive electrode for a lithium secondary battery, it is necessary to remove water as much as possible, and thus it is necessary to perform heating under reduced pressure.

A commercially available reagent can be used as NMP. As described above, when using a commercially available SS compound and removing water, it is necessary to use a dehydrating agent that does not react with NMP.

As the polyaniline, those obtained by polymerizing aniline by electrolysis or chemical oxidation are used, but from the viewpoint of solubility, the dedoped polyaniline in the reduced form is preferable. As such polyaniline, there is “Anilead” manufactured by Nitto Denko Corporation. In addition,
Polyaniline also needs to be heated under reduced pressure when producing a positive electrode for a lithium secondary battery.

In order to compound the SS compound, NMP and polyaniline, the SS compound and polyaniline are first kneaded in a powder state to prepare a mixed powder. At this time, since the SS compound may form a lump in a powder state, in some cases, it is preferable to crush the lump by previously stirring only the SS compound in a kneading vessel. When the polyaniline powder is added to the SS compound powder and mixed in the powder state, the mixing ratio of the SS compound and the polyaniline is preferably about 1 kg of polyaniline to 2 kg of the SS compound. After confirming that the composite powder of the SS compound and polyaniline is homogeneous, NMP is added and mixed by stirring to dissolve the composite powder, whereby a homogeneous active material ink is obtained. The ratio of NMP added is SS compound 2
NMP for 1 kg of polyaniline and 1 kg of polyaniline
About 8 to 16 kg is preferable. In addition, it is desirable that the above steps are performed in an inert gas atmosphere or dry air in order to prevent water from being mixed in from the outside.

Conventionally, the time required for the above kneading is about 2
Although it took more time, in the present invention, it is shortened to about 30 minutes, and the effect of improving the productivity in the process can be obtained.

[0024]

Example 2,5-dimercapto-1,3,4-thiadiazole (DMcT) monomer powder 2 kg (12 mol)
Then, 1 kg (6 mol) of "anilead" powder manufactured by Nitto Denko Corporation as polyaniline (PAn) was added and kneaded to obtain a homogeneous gray composite powder. In this composite powder,
8 kg of N-methyl-2-pyrrolidone (NMP) (80
Mol) and mixed with stirring to obtain a viscous black-purple and opaque composite active material ink. The composite active material ink is cast on a metal film substrate made of copper and having a thickness of 20 μm so as to have a thickness of 150 μm, and is heated to 80 ° C. in a closed container which is replaced with an inert gas to obtain adhesiveness. To obtain a black-purple and opaque complex. This composite was punched out into a disc having a diameter of 1.3 cm to obtain an electrode A. The above steps were all performed in dry air.

The electrode A obtained by the above method was used as a positive electrode, and metallic lithium having a thickness of 0.4 mm was used as a negative electrode.
A gelled gel electrolyte consisting of 2.5 kg of polyacrylonitrile and 22.5 kg of a propylene carbonate / ethylene carbonate (1: 1 volume ratio) solution in which 1 M LiBF ₄ was dissolved was used as a separator layer having a thickness of 0.6 mm and a diameter of 20 mm. , Total height 1.6 cm, theoretical capacity 0.5
Five 0 mAh coin-type lithium secondary batteries A were constructed.

As a comparative example, the SS compound was used as NMP.
Polyaniline was dissolved in the solution dissolved in to prepare an active material ink, and after applying this active material ink to the substrate,
By heating the whole in a vacuum or in an inert gas atmosphere, using the prepared electrodes B, five coin-type lithium secondary batteries B each having a capacity of 0.50 mAh were constructed in the same manner as the battery A. . All the above steps were performed in dry air.

5 cells of each of batteries A and B are 50 μA at 20 ° C.
After charging for 15 hours with a constant current of 50μA, 100μA,
The cells were discharged at respective currents of 500 μA and 1 mA until the battery voltage reached 2 V, and the battery capacity at that time was recorded. The results of evaluating the electrode characteristics by the capacity characteristics of the obtained battery are as shown in Tables 1 and 2.

Table 1 shows the discharge capacity (unit: mAh) of the coin type lithium secondary battery A according to this embodiment, and Table 2 shows the discharge capacity (unit: mAh) of the coin type lithium secondary battery B according to the comparative example. ) Is shown.

[0029]

[Table 1]

[0030]

[Table 2]

As is clear from the above results, the coin-type lithium secondary battery A using the electrode A according to this example has a higher capacity than the coin-type lithium secondary battery B using the electrode B according to the comparative example. It is possible to obtain a stable battery with little variation. For example, in battery B, the standard deviation of the discharge capacity at 50 μA is 0.061, whereas in battery A, it is as small as 0.0080, and the variation was suppressed. That is, by using the electrode according to the present embodiment, it is possible to suppress variations in discharge capacity and obtain a stable battery.

In this example, the electrode was prepared by adding no conductive agent, but an electrode containing a conductive agent can be prepared by the same method. Also in this case, the composite active material ink can be produced by stirring and kneading the conductive agent in a powder state, and then adding NMP and stirring and mixing. Also in the case of using a conductive agent, it is preferable to perform heating under reduced pressure in advance in order to remove water.

[0033]

INDUSTRIAL APPLICABILITY In a method for producing a composite electrode in which an organic disulphide compound powder, a polyaniline powder, and N-methyl-2-pyrrolidone are composited, components other than the solvent are mixed in powder form and kneaded with the solvent. By doing
Variation in charge / discharge capacity can be suppressed, a stable lithium secondary battery can be manufactured, and a kneading time can be shortened to about 30 minutes, so that productivity in the process can be improved.

In the examples, the electrode performance was evaluated by constructing a battery system using metallic lithium as the negative electrode.
By using the electrode of the present invention in addition to the battery, it is possible to obtain a biochemical sensor such as an electrochromic device having a fast coloring and fading speed, a glucose sensor having a fast response speed, and an electrochemical analog memory having a fast writing and reading speed. Can also be configured. Even in this case, an element sensor with stable quality can be manufactured.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tadashi Sotobe 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (4)

[Claims] 1. An organic disulfide compound powder, in which a sulfur-sulfur bond is cleaved by electrolytic reduction to generate a sulfur-metal ion, and the sulfur-metal ion bond regenerates the original sulfur-sulfur bond by electrolytic oxidation, and polyaniline. Powder and N
-A method for producing a composite electrode, which comprises kneading a mixture containing at least methyl-2-pyrrolidone. 2. An active material ink prepared by mixing an organic disulphide compound powder with N-methyl-2-pyrrolidone together with a polyaniline powder is cast on a substrate, and the substrate is heated under reduced pressure or an inert gas atmosphere. 1. The method for manufacturing the composite electrode according to 1. 3. An active material ink prepared by mixing an organic disulfide compound powder and a polyaniline powder with N-methyl-2-pyrrolidone is cast on a substrate and then heated under reduced pressure or an inert gas atmosphere to produce N-methyl. The method for producing a composite electrode according to claim 1, wherein the composite film is formed by removing 2-pyrrolidone. 4. An organic disulfide compound powder, in which a sulfur-sulfur bond is cleaved by electrolytic reduction to generate a sulfur-metal ion, and this sulfur-metal ion bond regenerates the original sulfur-sulfur bond by electrolytic oxidation, and polyaniline. Powder and N
A lithium secondary battery having a positive electrode of a composite electrode prepared by kneading a mixture containing at least methyl-2-pyrrolidone.