JPH08203530A - Combined electrode, manufacture thereof and lithium secondary battery - Google Patents

Abstract

PURPOSE: To provide an electrode with a long repetitive service life of oxidation/ reduction when it is used as the electrode of a battery, etc., made of an electro- chemical element. CONSTITUTION: A combined electrode is such one in which polyvinylpyrrolidone is added to a combined body consisting of an organic-disulfide compound, polyanyline and N-methyl-2-pyrrolidone or further to combined body including metallic oxide. And the added quantity of the polyvinylpyrrolidone is preferably in a range of wt.% from 0.1 to 30 in comparison with the total quantity consisting of those of the organic disulfide compound, polyanyline and N- methyl-2-pyrrolidone or in comparison with the total quantity consisting of those of the organic-disulfide compound, polyanyline, N-methyl-2-pyrrolidone and metallic oxide.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plurality of organic compounds used in electrochemical devices such as batteries, electrochromic display devices, sensors and memories, or a composite electrode composed of an organic compound and an inorganic compound, and a method for producing the same.

[0002]

2. Description of the Related Art Since the discovery of conductive polyacetylene by Shirakawa et al. In 1971, the use of conductive polymers as electrode materials has led to the use of lightweight, high energy density batteries, large-area electrochromic devices, and microelectrodes. Conductive polymer electrodes are being actively studied because electrochemical devices such as biochemical sensors using the same can be expected. In addition, as an organic material that can be expected to have a high energy density, US Pat.
Organic disulfide compounds have been proposed in 833,048. In addition, the inventors of the present invention have reported that Electrochim. Acta.
Vol., 1852, 1992), a polymer composite electrode in which a conductive polymer and an organic disulfide compound are composited is proposed. This polymer composite electrode has both a high voltage, which is a characteristic of a conventional conductive polymer electrode, and a high energy density, which is a characteristic of an organic disulfide compound. When this polymer composite electrode is combined with a lithium negative electrode, a lithium secondary battery having a voltage of 3 V or more and an energy density of 150 Wh / kg or more and having performance comparable to or higher than that of an ordinary secondary battery can be expected. .

[0003]

However, when such a polymer composite electrode is subjected to repeated redox (charge / discharge), there is a problem that the electrode capacity gradually decreases. A polydisulfide compound, which is generated when an organic disulfide compound is polymerized by oxidation (charging) and has poor electrical insulation and poor ion conductivity, has poor solubility in an electrolyte. On the other hand, the organic disulfide monomer produced when it is converted into a monomer by reduction (discharge) has high solubility in an electrolyte. For this reason, when redox is repeated, the monomerized disulfide partially dissolves in the electrolyte, and the dissolved monomer is polymerized at a location different from the location where the conductive polymer originally located in the electrode is present, resulting in conductivity. The electrically insulating polydisulfide compound polymerized away from the conductive polymer is isolated from the electron / ion conduction network in the polymer electrode and does not participate in the electrode reaction. Therefore, when the redox is repeated, the electrode capacity gradually decreases.

The present invention solves such a problem and does not impair the high voltage and high energy density characteristics of a polymer composite electrode in which a conductive polymer and an organic disulfide compound are composited, and the capacity can be maintained even during repeated redox. An object of the present invention is to provide a polymer composite electrode with reduced deterioration. It is another object of the present invention to provide a lithium secondary battery using the composite electrode as a positive electrode.

[0005]

In the composite electrode of the present invention, the sulfur-sulfur bond is cleaved by electrolytic reduction to generate a sulfur-metal ion (including proton) bond, and the electrolytic oxidation causes the sulfur-metal ion bond to be changed. An organic disulfide compound that regenerates the original sulfur-sulfur bond and a composite electrode containing polyaniline or a metal oxide are represented by the formula (C ₆ H ₉ NO) _n (n is an integer) as a flexibility-imparting substance. Polyvinylpyrrolidone is added.

The method for producing a composite electrode according to the present invention is a viscous substance obtained by dissolving an organic disulfide compound, polyvinylpyrrolidone represented by the formula (C ₆ H ₉ NO) _n (n is an integer) and polyaniline in N-alkyl-2-pyrrolidone. Is coated on a substrate and heated under vacuum or in an inert gas atmosphere. In addition, the method for producing the composite electrode of the present invention is that a viscous material obtained by dissolving polyvinylpyrrolidone and polyaniline in N-alkyl-2-pyrrolidone is diluted with N-alkyl-2-pyrrolidone, and the metal oxide powder is dispersed and mixed in the solution. Then, there is a step of applying this mixture onto a substrate and heating it in a vacuum or in an inert gas atmosphere. Here, in order to obtain a viscous material in which an organic disulfide compound, polyvinylpyrrolidone and polyaniline are dissolved in N-alkyl-2-pyrrolidone, first, the organic disulfide compound and polyvinylpyrrolidone are dissolved in N-alkyl-2-pyrrolidone, and then the solution is added. It is preferred to dissolve the polyaniline to obtain a viscous body.

The metal oxide is LiCoO ₂ , V
It is preferably a transition metal oxide selected from the group consisting of ₆ O ₁₃ , LiMn ₂ O ₄ , V ₂ O ₅ and LiNiO ₂ . The lithium secondary battery of the present invention includes the positive electrode, the non-aqueous electrolyte, and the negative electrode which are the above composite electrodes. N-alkyl-2-pyrrolidone has the formula R-NC ₄ H ₆ O (wherein R is
Represents a hydrogen atom or an alkyl group). As the alkyl group, a methyl group, an ethyl group and an n-butyl group are preferable. The structural formula of polyvinylpyrrolidone is shown below.

[0008]

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[0009]

[Function] Polyvinylpyrrolidone imparts appropriate flexibility to the composite electrode, enables the construction of a thin film secondary battery or other electrochemical device, and allows the composite to undergo redox (charge / discharge). , An organic disulfide compound, polyaniline, or a complex of these compounds is reduced in dissolution / dissipation in the electrolyte, and it has an effect of giving good repeated redox (charge / discharge) characteristics. further,
In a composite electrode containing a metal oxide, polyvinylpyrrolidone has a function of giving flexibility to the electrode and preventing dissipation of a disulfide compound, and at the same time, a composite electrode due to a volume change accompanying a redox reaction of a metal oxide. Has the effect of remarkably reducing the deterioration of characteristics even if the redox reaction is repeated. By using such a composite electrode according to the present invention as a positive electrode, lithium alloy such as metallic lithium, lithium-aluminum, lithium-manganese, or a carbon material capable of reversibly taking in and out lithium ions, a metal sulfide, a metal oxide, a conductive material By using the polymer for the negative electrode, a lithium secondary battery having high energy density and excellent repetitive charge / discharge cycle characteristics can be obtained.

[0010]

EXAMPLES The polyvinylpyrrolidone represented by the formula (C ₆ H ₉ NO) _n (n is an integer) used in the present invention preferably has an average molecular weight of 10,000 to 100,000. Examples of disulfide compounds include U.S. Pat.
The general formula (R (S) _y ) _n described in No. 048 (wherein R is an aliphatic group or an aromatic group, S is sulfur, y is an integer of 1 or more, and n is an integer of 2 or more). The compound represented by can be used. Dithioglycol represented by HSCH ₂ CH ₂ SH, 2,5-dimercapto-1,3,4-thiadiazyl represented by C ₂ N ₂ S (SH) ₂ , C ₃ H ₃ N
S-triazine-2,4,6-trithiol represented by ₃ S ₃ and 7-methyl-2,6,8 represented by C ₆ H ₆ N ₄ S ₃
-Trimercaptopurine, or 4,5-diamino-2,6-dimercaptopyrimidine represented by C ₄ H ₆ N ₄ S ₂ is used. In each case, a commercially available product can be used as it is. A commercially available reagent can be used as N-alkyl-2-pyrrolidone. Pyrrolidone, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, N
-Butyl-2-pyrrolidone and the like can be used.

As polyaniline, aniline polymerized by electrolysis or chemical oxidation is used. From the viewpoint of solubility, deanidized reduced polyaniline is preferable. An example of such polyaniline is “anilead” manufactured by Nitto Denko Corporation. Reduction of the polyaniline (RDI) is a polyaniline in an electronic absorption spectra of the solution was microinjected dissolved in N-methyl-2-pyrrolidone, the intensity of the absorption peak attributable to a para-substituted benzene structure appearing on the short wavelength side of the near 340nm (I _{34 0)} When,
By the ratio with the intensity (I ₆₄₀ ) of the absorption peak due to the quinonediimine structure appearing on the long wavelength side near 640 nm,
It is represented by RDI = I ₆₄₀ / I ₃₄₀ . Polyaniline having an RDI of 0.5 or less is preferably used. The degree of dedoping of polyaniline is represented by conductivity. Conductivity is 10
Polyaniline of ^-5 S / cm or less is preferably used.

As the metal oxide, any of transition metal oxides and complex oxides can be used. In particular, the electrochemical equivalent of polyaniline is 150 mAh / g.
Compounds at or above the range are preferred. Examples of such transition metal oxides include LiCoO ₂ (electrochemical equivalent = 140 to 160 mAh / g), V ₆ O ₁₃ (electrochemical equivalent = 160 to 230 mAh / g, LiMn ₂ O ₄
(Electrochemical equivalent = 100 to 120 mAh / g), V ₂ O ₅
(Electrochemical equivalent = 130 to 150 mAh / g), LiN
iO ₂ (electrochemical equivalent = 140 to 220 mAh / g) is preferable. A powdery material having an average particle size of about 1 to 10 μm is used. These transition metal oxides can be used without any trouble even if the transition metal elements are plural. For example, for LiCoO ₂ , a composite oxide in which a part of Co (cobalt) is replaced with Mn (manganese), Ni (nickel), Fe (iron), or V
A composite oxide in which a part of V of ₆ O ₁₃ is replaced with W (tungsten) can also be used.

To form a composite of an organic disulfide compound, N-alkyl-2-pyrrolidone, polyaniline and polyvinylpyrrolidone, first, an organic disulfide compound is dissolved in N-alkyl-2-pyrrolidone in which polyvinylpyrrolidone is dissolved to form a viscous body. It is performed by adding polyaniline powder and dissolving. Alternatively, after applying a viscous material in which an organic disulfide compound and polyvinylpyrrolidone are dissolved in N-alkyl-2-pyrrolidone onto polyaniline which has been formed into a film shape in advance, the whole is heated to 60 to 100 ° C. under vacuum or in an inert gas atmosphere. Thus, a composite electrode film having one surface rich in polyaniline and the other surface rich in an organic disulfide compound may be used. As the film-shaped polyaniline, a film-shaped polyaniline deposited on a substrate by an electrolytic polymerization method or a polyaniline synthesized by an electrolytic polymerization method or a chemical polymerization method is dissolved in N-alkyl-2-pyrrolidone, and then this solution is placed on the substrate. It can also be obtained by casting and removing all or part of N-alkyl-2-pyrrolidone. Polyvinylpyrrolidone is an organic disulfide compound and N-alkyl-2
ー 0.1 to the total amount of pyrrolidone and polyaniline
It is preferably 30% by weight. The ratio of the organic disulfide compound, N-alkyl-2-pyrrolidone and polyaniline is preferably about 0.5 to 5 mol of N-alkyl-2-pyrrolidone and about 0.05 to 5 mol of polyaniline with respect to 1 mol of the organic disulfide compound.

To form a composite of polyaniline, a disulfide compound, a metal oxide, N-alkyl-2-pyrrolidone and polyvinylpyrrolidone, first, the disulfide compound is dissolved in N-alkyl-2-pyrrolidone in which polyvinylpyrrolidone is dissolved to obtain a viscous liquid. Add polyaniline powder to the liquid and dissolve. Dissolve by heating if necessary. If necessary, N-alkyl-2-pyrrolidone is further added to dilute. Next, the slurry obtained by previously dispersing the metal oxide powder in N-alkyl-2-pyrrolidone is added to the diluted solution and uniformly dispersed and mixed by a homogenizer. The obtained dispersion mixture is cast on a substrate such as a glass petri dish or a carbon film, and then heated under reduced pressure to remove a part or all of N-alkyl-2-pyrrolidone to obtain a composite electrode. Polyvinylpyrrolidone is based on the total amount of organic disulfide compound, N-alkyl-2-pyrrolidone, polyaniline and metal oxide.
It is preferably 0.1 to 30% by weight. The ratio of the polyaniline and the disulfide compound is preferably about 0.1 to 5 mol of the disulfide compound with respect to 1 mol of the polyaniline. The proportion of polyaniline and metal oxide is preferably 0.5 to 5 parts by weight of metal oxide to 1 part by weight of polyaniline.

As the metal ion used when the organic disulfide compound is reduced to form a salt, a proton can be used in addition to the alkali metal ion and alkaline earth metal ion described in the above-mentioned US patent. In particular, when using lithium ions as alkali metal ions, a lithium alloy such as metallic lithium or lithium-aluminum is used as an electrode that supplies and captures lithium ions, and an electrolyte that conducts lithium ions is used.
A lithium secondary battery having a high energy density exceeding 200 Wh / kg at a voltage of about 3 V can be constructed. When a proton is used, a metal hydride such as LaNi ₅ is used as an electrode for supplying and capturing the proton, and an electrolyte for conducting the proton is used, a battery having a voltage of 1 to 2 V can be constructed. In addition to the above components, a conductive agent such as carbon, a shape-imparting agent such as synthetic rubber, a resin, or a ceramic powder or a reinforcing agent can be added to the composite electrode of the present invention, if necessary. Further, for the purpose of cross-linking polyvinylpyrrolidone to increase the film strength of the composite film and suppress the solubility of the composite film in the electrolyte, radiation may be applied after forming the composite film. Such radiation includes α rays, β rays, γ rays, electron beams, and X rays. Above all, γ-ray irradiation is effective. The irradiation amount is preferably 0.5 to 5 Mrad.

[Example 1] 1 polyvinylpyrrolidone manufactured by MERCK having an average molecular weight of 25,000 was used.
N-methyl-2-pyrrolidone (hereinafter,
Called NMP) 3,5-dimercapto-1,3 per 3 g
1.5 g (0.01 mol) of 4-thiadiazyl (hereinafter referred to as DMcT) monomer powder was dissolved to obtain a viscous yellow transparent DMcT-NMP solution. To this solution, as polyaniline, "anilead" powder manufactured by Nitto Denko Co., Ltd.
5 g (0.003 mol) was added, and the mixture was heated to 80 ° C. in a closed container substituted with an inert gas to obtain a sticky black-green viscous substance. This viscous material was printed on a titanium foil having a thickness of 35 μm to a thickness of 120 μm, and then 1 cmH
Heat treatment was performed at 80 ° C. under reduced pressure of g. 68% by weight of NMP was dissipated by heating under reduced pressure. The content of polyvinylpyrrolidone in the obtained film was 10.5% by weight based on the total amount of DMcT, polyaniline and NMP. The obtained composite film with a thickness of 25 μm was mixed with titanium foil in 1 ×.
A composite electrode A was obtained by cutting into 1 cm square.

[Comparative Example 1] DMcT monomer powder 1.5
viscous yellow transparent DMcT
-An NMP solution was obtained. To this solution, 0.5 g of "anilead" powder manufactured by Nitto Denko as polyaniline was added, and heated to 80 ° C. in a closed container substituted with an inert gas to obtain a sticky black-green viscous substance. This viscous material was printed on a titanium foil having a thickness of 35 μm to a thickness of 120 μm, and then heat-treated at 80 ° C. under a reduced pressure of 1 cmHg to obtain a composite film having a thickness of 25 μm. The composite film obtained was cut together with a titanium foil into 1 × 1 cm to obtain a composite electrode B.

Example 2 0.5 g of polyaniline powder "anilead" manufactured by Nitto Denko was added to 100 ml of NMP,
20 ml of the supernatant was cast on a glass petri dish having a diameter of 90 mm and then placed in a vacuum heater at 60 ° C. to remove NMP to obtain 0.15 g of a polyaniline film having a thickness of 20 μm. Next, DMcT-NE was prepared by dissolving 1.5 g of DMcT monomer powder in 3 g of N-ethyl-2-pyrrolidone (hereinafter, referred to as NEP) in which 10% by weight of polyvinylpyrrolidone manufactured by MERCK having an average molecular weight of 4,000 was dissolved.
P solution, DMcT = 0.0033 mol, NEP = 0.
After being cast on the polyaniline film so as to have a molar ratio of 0087 mol, the whole is 80% in an argon gas atmosphere.
A composite film having a thickness of 25 μm was obtained by heating at 0 ° C. under vacuum. This composite film was integrated with a carbon film of fluororesin and carbon black having a thickness of 50 μm by a press roller, and then cut into 1 × 1 cm to obtain an electrode C.

[Comparative Example 2] 0.5 g of polyaniline powder "Anilead" manufactured by Nitto Denko was added to 100 ml of NMP.
20 ml of the supernatant was cast on a glass petri dish having a diameter of 90 mm and then placed in a vacuum heater at 60 ° C. to remove NMP to obtain 0.15 g of a polyaniline film having a thickness of 20 μm. Next, 1.5 g of DMcT monomer powder was added to 3 g of NEP.
DMcT-NEP solution dissolved in DMcT = 0.0
033 mol, NEP = 0.0087 mol,
After casting on a polyaniline film, the whole was vacuum-heated at 80 ° C. in an argon gas atmosphere to obtain a composite film having a thickness of 25 μm. This composite film was integrated with a carbon film of fluororesin and carbon black having a thickness of 50 μm by a press roller, and then 1 × 1c
The electrode D was obtained by cutting into m.

[Example 3] DMcT monomer powder 1.5
g (0.01 mol) was dissolved in 5 g of NMP to obtain a viscous yellow transparent DMcT-NMP solution. To this solution, 2.5 g (0.015 mol) of "anilead" powder manufactured by Nitto Denko in a dedoped reduction state as polyaniline was added,
A black-purple liquid was obtained by heating to 80 ° C. in a closed container replaced with an inert gas. V ₆ average particle size 6μm of
2.5 g of O ₁₃ powder was added to ME with an average molecular weight of 25,000.
Polyvinylpyrrolidone manufactured by RCK was dispersed and mixed in 10 g of NMP in which 10% by weight was dissolved to obtain a slurry. This slurry was added to the above black-purple liquid, and mixed with a homogenizer at a rotation speed of 5,000 rpm for about 10 minutes to obtain a dispersion liquid.
A part of NMP was removed by a rotary evaporator to obtain an adhesive dispersion, which was then printed on a conductive carbon film of carbon black and fluororesin having a thickness of 50 μm so as to have a thickness of 120 μm. The obtained film was heated under reduced pressure at 80 ° C. under a vacuum degree of 20 cmHg for about 30 minutes to obtain a composite electrode film having a thickness of 25 μm. 86% by weight of NMP was dissipated by vacuum vacuum heating. The content of polyvinylpyrrolidone in the obtained film was 11.8% by weight based on the total amount of DMcT, polyaniline, V ₆ O ₁₃ and NMP. A composite electrode E was obtained by cutting the composite electrode film together with a conductive carbon film into 1 × 1 cm.

[Comparative Example 3] DMcT monomer powder 1.5
g (0.01 mol) was dissolved in 5 g of NMP to obtain a viscous yellow transparent DMcT-NMP solution. To this solution, 2.5 g (0.015 mol) of "anilead" powder manufactured by Nitto Denko in a dedoped reduction state as polyaniline was added,
A blackish purple liquid was obtained by heating to 80 ° C. in a closed container replaced with an inert gas. 2.5 g of V ₆ O ₁₃ powder having an average particle diameter of 6 μm was dispersed and mixed in 10 g of NMP to obtain a slurry. This slurry was added to the above black-purple liquid, and mixed with a homogenizer at a rotation speed of 5,000 rpm for about 10 minutes to obtain a dispersion liquid. A part of NMP was removed by a rotary evaporator to obtain an adhesive dispersion, which was then printed on a conductive carbon film of carbon black and fluororesin having a thickness of 50 μm so as to have a thickness of 120 μm. The obtained film was heated under reduced pressure at 80 ° C. under a vacuum degree of 20 cmHg for about 30 minutes to obtain a composite electrode film having a thickness of 25 μm.
Composite electrode membrane with conductive carbon film 1 x 1c
The composite electrode F was obtained by cutting into m.

Evaluation of Electrode Performance Electrodes A obtained in Examples 1, 2 and 3 and Comparative Examples 1, 2 and 3,
Flat type batteries A, B, C, D, E, and F are configured by using B, C, D, E, and F as positive electrodes, metal lithium having a thickness of 0.3 mm as a negative electrode, and a gel electrolyte having a thickness of 0.6 mm as a separator layer. did. The gel electrolyte was prepared by dissolving 1M LiBF ₄ in propylene carbonate / ethylene carbonate (1:
(1 volume ratio) with 20.7 g of a solution of polyacrylonitrile 3.
It is a gel of 0 g. These batteries were charged and discharged at a constant current of 0.2 mA at room temperature in the range of 4.5 to 2.25 V, and the discharge capacity (Q,
The unit: mAh) was measured, and the electrode performance was evaluated by the degree of decrease in discharge capacity (Q) with the progress of charge / discharge cycles. The results are shown in Table 1.

[0023]

[Table 1]

As is clear from the above results, the batteries using the composite electrodes A, C, and E of Examples 1, 2, and 3 according to the present invention have the corresponding composite electrodes B, D, and F, respectively. The decrease in discharge capacity with the progress of charge / discharge cycles is smaller than that of the battery used.

[0025]

As described above, according to the present invention, it is possible to obtain a composite electrode having a small capacity decrease with the progress of the cycle even if the redox is repeated. By using such a composite electrode as the positive electrode of a lithium secondary battery, a battery having a long charge / discharge cycle life can be obtained. Further, the electrode of the present invention,
By using this as a counter electrode, it is possible to obtain an electrochromic device having a long life of repeated coloring and fading,
It is also possible to construct an electrochemical analog memory having a long writing / reading cycle life.

Claims (6)

[Claims] 1. A sulfur-sulfur bond is cleaved by electrolytic reduction to form a sulfur-metal ion (including proton) bond,
An organic disulfide compound in which a sulfur-metal ion bond regenerates an original sulfur-sulfur bond by electrolytic oxidation, polyaniline, and a compound (C ₆ H ₉ NO) as a flexibility-imparting substance
A composite electrode comprising polyvinylpyrrolidone represented by _n (n is an integer). 2. The electrolytic reduction reduces the sulfur-sulfur bond to form a sulfur-metal ion (including proton) bond,
The organic disulfide compound, in which the sulfur-metal ionic bond regenerates the original sulfur-sulfur bond by electrolytic oxidation, polyaniline, metal oxide, and a compound (C ₆
A composite electrode comprising polyvinylpyrrolidone represented by H ₉ NO) _n (n is an integer). 3. The metal oxide is LiCoO ₂ , V ₆ O ₁₃ ,
The composite electrode according to claim 2, which is a transition metal oxide selected from the group consisting of LiMn ₂ O ₄ , V ₂ O ₅ and LiNiO ₂ . 4. The sulfur-sulfur bond is cleaved by electrolytic reduction to form a sulfur-metal ion (including proton) bond,
An organic disulfide compound in which a sulfur-metal ion bond regenerates the original sulfur-sulfur bond by electrolytic oxidation and a compound of the formula (C ₆ H ₉ N
O) _n (n is an integer), a step of dissolving polyvinylpyrrolidone and polyaniline in N-alkyl-2-pyrrolidone to obtain a viscous body, and applying the viscous body onto a substrate, under vacuum or with an inert gas. A method of manufacturing a composite electrode, comprising a step of heating in an atmosphere. 5. The sulfur-sulfur bond is cleaved by electrolytic reduction to form a sulfur-metal ion (including proton) bond,
An organic disulfide compound in which a sulfur-metal ion bond regenerates the original sulfur-sulfur bond by electrolytic oxidation and a compound of the formula (C ₆ H ₉ N
O) _n (n is an integer), a step of dissolving polyvinylpyrrolidone and polyaniline in N-alkyl-2-pyrrolidone to obtain a viscous body, a metal oxide in a solution obtained by diluting the viscous body with N-alkyl-2-pyrrolidone And a step of applying the obtained dispersion mixture onto a substrate and heating it in a vacuum or in an inert gas atmosphere. 6. A lithium secondary battery comprising a positive electrode comprising the composite electrode according to claim 1, 2 or 3, a non-aqueous electrolyte and a negative electrode.