KR20010052228A - Lithium battery and electrode - Google Patents

Abstract

The electrode comprises an electrically conductive matrix containing a disulfide group, wherein the S-S bond of the disulfide group is decomposed by electrochemical reduction and reformed by electrochemical oxidation. A plurality of carbon nanotubes are dispersed in the electroconductive matrix. The electrode can be used as the cathode of the lithium battery.

Description

[0001] Lithium battery and electrode [0002]

A battery is a type of electrochemical cell that includes a pair of electrodes and an electrolyte placed between the electrodes. One of the electrodes is referred to as the cathode where the active material is reduced during discharge. The other electrode is referred to as an anode where the other active material is oxidized during discharge. The secondary battery represents a battery capable of charging electricity after discharge.

Recently, extensive research has been conducted on the high voltage and high energy density of lithium secondary batteries. A lithium battery refers to a battery having an anode containing an active material for discharging lithium ions during discharging. The active material may be a metal lithium and an intercalated material that may include lithium between the layers.

In particular, attention has been focused on the electrode material for the cathode of a lithium secondary battery. For example, U.S. Patent No. 4,833,048 discloses a cathode containing a disulfide compound to improve energy density. This compound is represented by RSSR, wherein R is an aliphatic or aromatic organic group and S is a sulfur atom. SS bond is decomposed by electrolytic reduction in an electrolytic cell containing cation M ⁺ to form a salt represented by RS ^- · M ⁺ . This salt is converted to RSSR by electrolytic oxidation. U.S. Patent No. 4,833,048 discloses a rechargeable battery obtained by combining a disulfide compound and a metal M that feeds and captures a cation (M ⁺ ). The rechargeable battery provides an improved energy density of over 150 Wh / kg. The entire disclosure of U.S. Patent No. 4,833,048 is incorporated herein by reference.

However, the inventors of U. S. Patent No. 4,833, 048, Electrochem. Soc., Vol. 136, No. 9, pp. 2570 to 2575 (1989), the difference between the oxidation potential and the reduction potential of the disulfide compound is very large. For example, when [(C ₂ H ₅ ) ₂ NCSS-] ₂ is electrolyzed, the oxidation potential differs by more than 1 V from the reduction potential. According to the theory of electrochemical reactions, the electron transfer of disulfide compounds proceeds extremely slowly at room temperature. Therefore, it is somewhat difficult to obtain a rechargeable battery that provides a high current output of 1 mA / cm ² or more at room temperature. The operation of the battery containing the disulfide compound electrode is limited to a very high temperature range of 100-200 [deg.] C at which electron transfer can proceed faster.

U.S. Patent No. 5,324,599 describes a cathode for a lithium secondary battery containing a disulfide compound and a conductive polymer. Conductive polymers enable the battery to operate at much lower temperatures, such as room temperature. The entire contents of U.S. Patent No. 5,324,599 are incorporated herein by reference.

Japanese Patent No. 2,513,418 corresponding to Japanese Patent Laid-Open No. 5-175929 describes a cathode containing carbon nanotubes. Carbon nanotubes are obtained by electric discharge between a pair of carbon rods. Japanese Patent No. 2,513,418 does not teach disulfide compounds. The entire contents of Japanese Patent No. 2,513,418 are incorporated herein by reference.

International Patent Publication No. WO 95/07551 discloses an electrode that can be used in a lithium secondary battery containing carbon nanotubes. Carbon nanotubes are obtained by catalytic reaction. The literature also describes aggregates of carbon nanotubes unwound with an ultrasonic homogenizer. The entire contents of WO 95/07551 are incorporated herein by reference.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention there is provided a process for the preparation of an electrically conductive matrix comprising a disulfide group wherein the SS bond of the disulfide group is decomposed by electrochemical reduction and reformed by electrochemical oxidation, An electrode comprising a carbon nanotube is provided.

Preferably, the electrically conductive matrix may contain an electrically conductive polymer and an organic compound having disulfide groups. Alternatively, the electrically conductive matrix may contain an electrically conductive polymer having a mercapto group capable of forming a disulfide group.

According to a second aspect of the present invention there is provided a process for the preparation of an electrically conductive matrix comprising a disulfide group, wherein the SS bond of the disulfide group is decomposed by electrochemical reduction and reformed by electrochemical oxidation, and a plurality of There is provided a battery precursor comprising a cathode having a carbon nanotube and a cathode current collector, wherein the cathode is coated on the cathode current collector.

According to a third aspect of the present invention there is provided a process for the preparation of an electrically conductive matrix comprising a disulfide group wherein the SS bond of the disulfide group is decomposed by electrochemical reduction and reformed by electrochemical oxidation, There is provided a lithium battery including a cathode having a carbon nanotube, an anode having an active material for emitting lithium ions, and an electrolyte disposed between the cathode and the anode.

The present invention relates to an electrode, a battery precursor, and a lithium battery.

Figure 1 is a section of the homogenizer portion.

2 is a photograph of a poly (methyl methacrylate) film containing a relaxed carbon nanotube observed by a transmission electron microscope.

3 is a photograph of a poly (methyl methacrylate) membrane containing a carbon nanotube aggregate observed by a transmission electron microscope.

4 is a cross section of a laminated structure used for a lithium battery.

The electrode of the present invention comprises an electrically conductive matrix containing a disulfide group. In one embodiment, the electrically conductive matrix contains an electrically conductive polymer and an organic compound having disulfide groups. In another embodiment, the electrically conductive matrix contains an electrically conductive polymer having a mercapto group.

Disulfide groups cause electrochemical reactions at the electrodes. That is, the S-S bond of the disulfide group is decomposed by electrochemical reduction and reformed by electrochemical oxidation. When an electrode is used as a cathode for a lithium battery, the electrochemical reaction between the cathode and the anode is represented by the following reaction formula.

In the above scheme 2,

R-S-S-R is an organic compound having a disulfide group,

R is an aliphatic or aromatic organic group,

S is a sulfur.

In this example, metallic lithium is used as the anode even though the anode of the lithium battery is not limited to metal lithium. When the lithium battery is discharged, the electrochemical reduction is occurring at the cathode, the organic compound containing a disulfide group is reacted with lithium ions decompose the SS bond of the disulfide group, and RS ^- forms a salt represented by the Li ⁺ ·. During the discharge, electrochemical oxidation takes place in the anode, and metal lithium is oxidized to lithium ions.

When the lithium battery is charged, the reaction proceeds in the reverse direction.

Specifically, electrochemical oxidation occurs at the cathode, and the salt becomes R-S-S-R. Electrochemical reduction occurs in the anode, and lithium ion becomes metallic lithium.

Examples of organic compounds having disulfide groups are shown in Tables 1 and 2.

name The 2-mercaptoethyl ether Dimercaptodithiazole Dimethylethylenediamine Ethylenediamine Polyethylene imine derivative Trithiocyanuric acid

name The Piperazine 2,4-dithiopyrimidine 1,2-ethanedithiol 2-mercaptoethylsulfide

Preferably, the organic compound contains a 5- to 7-membered heterocyclic ring containing 1 to 3 heteroatoms consisting of a nitrogen atom and a sulfur atom. The heterocyclic ring may be saturated or unsaturated. Preferably, the heterocyclic ring is saturated. More preferably, the organic compound contains a thiadiazole ring, especially a 1,3,4-thiadiazole ring. For example, a dimer of 2,5-dimercapto-1,3,4-thiadiazole can be used as an organic compound containing a disulfide group.

The electrically conductive polymer used together with the organic compound containing the disulfide group preferably has a pi electron conjugated structure. Examples of such electroconductive polymers include polymers obtained by polymerizing thiophene, pyrrole, aniline, furan, benzene, and the like. More specifically, examples of polymers include polyaniline, polypyrrole, polythiophene, and polyacene. These? Electron-conjugated electroconductive polymers are reduced and oxidized to a high reversibility of 0 to ± 1.0 V against the Ag / AgCl electrode. Electroconductive polymers doped with anions such as iodine show excellent properties.

The electrically conductive matrix may have a porous fibril structure. For example, the electrically conductive polymer has a porous fibril structure, which depends on the polymerization conditions. That is, the electrically conductive polymer may have a plurality of fibril forms to form voids therebetween. The disulfide compound may be trapped in the pores formed by the fibrils. Such an electrically conductive polymer having a porous fibril structure can be obtained by polymerization at an electrode.

Also, the electrically conductive matrix may be substantially continuous without voids. These electrically conductive matrices can be obtained by standard chemical polymerization reactions.

Of the? -electrically conjugated electroconductive polymers, polymers of the following formula (1) are preferably used.

- [Ar-NH] _n -

In the above formula (1)

Ar is aryl,

n is an integer.

The aryl preferably has 6 to 20 carbon atoms, more preferably 6 to 10 carbon atoms. Aryl is phenyl, naphthalenyl, indenyl, and the like. Preference is given to polyaniline in which aryl is phenyl.

The matrix containing the above-mentioned mixture of the disulfide compound and the electrically conductive polymer can be produced by a known method such as mixing, impregnation or coating. For example, a fibril layer of an electrically conductive polymer is formed on a stainless steel substrate by electrolytic polymerization, and then a salt of the disulfide compound is impregnated into the fibril layer, thereby obtaining a composite electrode. Alternatively, the disulfide compound particles are dispersed in a solvent in which the electroconductive polymer is dissolved, and then the solvent is removed, so that an electrically conductive polymer layer is formed on the surface of the disulfide compound particles. Furthermore, electroconductive polymer particles obtained by chemical polymerization or electrolytic polymerization can be mixed with disulfide compound particles.

Alternatively, the electrode material of the present invention may contain a monomer capable of forming a π-electron conjugated electroconductive polymer, a compound having a disulfide group-containing group and a moiety capable of reversibly decomposing the SS bond of the disulfide group For example, 1,8-disulfide naphthalene). For example, when aniline is electrolytically polymerized in an electrode in the presence of 1,8-disulfide naphthalene, a composite film of polyaniline and 1,8-disulfide naphthalene is formed.

Alternatively, as a method, a dimer of a compound having a mercapto group can be used instead of a compound having a coordination structure capable of reversible decomposition of an S-S bond in a molecule. For example, a dimer of 2-mercapto-2-thiazoline is obtained and, instead of 1,8-disulfide naphthalene, this dimer is used to produce a polyaniline-2-mercapto-2-thiazoline dimeric complex membrane . Among these cases, it is preferable that the polymerization is carried out under the condition that a film having a fibril structure can be formed. In these methods, mercapto group protected compounds are used, and as a result, the electrically conductive polymer can be produced without any disturbance. In the thus obtained composite material, the disulfide compound and the electroconductive polymer form a complex, which prevents the disulfide compound from leaking from the composite membrane to the electrolyte while being used as the cathode of the rechargeable battery.

In the electrode of the present invention, a conductive polymer containing a mercapto group may be used. The conductive polymer having a mercapto group can be obtained by, for example, (1) introducing a mercapto group into a π electron conjugated conductive polymer, or (2) forming a monomer capable of forming a π electron conjugated conductive polymer having a mercapto group Followed by electrolytic polymerization.

In the method (1), as the? -Electrically conjugated conductive polymer, a conductive polymer or a derivative thereof used as the first electrode material may be used. For example, a halogenated pyrrole can be electrolytically polymerized to form a polyhalopyrrole thin film on the electrode. At this time, it is preferable to carry out the polymerization in the same manner as in the case of the first electrode material under the condition that a thin film having a fibril structure is formed. Subsequently, the halogen group is converted to a mercapto group by thiourea to form a polypyrrole having a mercapto group. Thereafter, the compound having a mercapto group is reacted with a polypyrrole having a mercapto group to form a polypyrrole having a disulfide group. As the compound having a mercapto group, a disulfide compound (having a reduced form and having an SH group) used in the first electrode material, for example, 2,5-dimercapto-1,3,4-thiadiazole, Is used. The conductive polymer in the form of a thin film having the disulfide group thus obtained can be used as a reversible electrode.

In the method (2), monomers capable of forming a? -Electron conjugated conductive polymer, monomers capable of forming a conductive polymer in which a disulfide group is introduced and used in the first electrode material (for example, thiophene and pyrrole) Can be used. By polymerizing such a monomer, a conductive polymer having a mercapto group can be obtained. For example, a thiophene derivative having a disulfide group can be obtained by reacting a thiophene having a mercapto group in a reduced form and a disulfide compound having an SH group. A thiophene derivative having the disulfide group thus obtained (for example, 2,5-dimercapto-1,3,4-thiadiazole) is used for the first electrode. The thiophene derivative is subjected to electrolytic polymerization at an electrode, whereby a conductive polymer film having disulfide groups can be formed. It is preferable that the polymerization is carried out under the condition that a film having a fibril structure is formed. The thus formed conductive polymer film acts as a reversible electrode.

In the electrode of the present invention, a plurality of carbon nanotubes are dispersed in an electrically conductive matrix. The carbon nanotubes conduct electricity along the axial direction thereof, thereby reducing the electrical resistance of the matrix. Typically, carbon nanotubes are small in resistance and conduct more electricity than electrically conducting polymers. Moreover, the presence of carbon nanotubes acting as fillers increases the mechanical strength of the matrix.

Carbon nanotubes are microtubular graphite fibers. Although carbon nanotubes are graphitic, they are somewhat different from pure graphite due to geometric constraints. Like graphite, carbon nanotubes consist of parallel layers of carbon, but rather a series of concentric tubes arranged about the longitudinal axis of the fiber rather than a multilayered flat graphite plate. Thus, due to geometric constraints on the narrow diameter of the carbon nanotubes, the graphite layer of the carbon nanotubes can not be precisely aligned with respect to the layer, such as a flat graphite layer.

Ideally, one carbon nanotube is made up of one or more seamless cylindrical shells made of graphite plates. That is, each shell consists of sp ² (trivalent) carbon atoms from a hexagonal network with no specific edges. Carbon nanotubes can be thought of as tubular crystallites of graphite. The tube is typically closed at each end by introducing a pentagon into the hexagonal network. The interlamellar space of multishell nanotubes is about 0.34 nm and is typical for turbostratic graphite, where the position of each layer relative to the next layer is not related to each other. A given nanotube is made up of different shells with helicity. In fact, different degrees of heli- city in each shell are needed to obtain an optimal fit between successive shells in the tube and to minimize inter-layer distance. Carbon nanotubes can be prepared catalytically. The method provides an uncontaminated aggregate with amorphous carbon, making the carbon nanotube the product with minimal process. The carbon nanotubes grow by contacting the catalyst particles with gaseous hydrocarbons in an atmosphere rich in hydrogen. Their diameters may be on average between 7 and 12 nm. The length is several micrometers. These are hollow tubes with a wall thickness of 2-5 nm. These walls are concentric tubes of each graphite layer that are essentially cylindrically curled. In space along the length of the fibers, some inner layers can be bent into hemispherical septa filling the hollow interior. In these neighborhoods, the walls are short distances and can be turned into nested cones. These reflect changes in the catalyst / carbon interface during the growth of the fibrils. Unlike other catalytic vapor-grown carbon fibers, they do not have pyrolytic carbons that are less textured on these surfaces.

Carbon nanotubes can be produced by condensation of carbon vapor in an arc. Carbon vapors are described in Science Vol. 273, July 26, 1996 page 483, a laser can be produced by irradiating a carbon-nickel-cobalt mixture at 1200 ° C. They usually have a wide diameter distribution from a single layer wall to several tens of layers. Some are just concentric cylindrical (or polygonal cross-section). The other is diaphragm and cone-shaped cone. Less structured carbon can be deposited simultaneously in the form of polygonal or turbostatic carbons, some of which can coat carbon nanotubes.

Carbon nanotubes produced by condensation of carbon vapor in an arc are available from Material & Electrochemical Research Corporation and Science Laboratory Incorporation of Matsushita, Japan It can be obtained commercially from the distributor. Carbon nanotubes manufactured by Material & Electro-Chemical Research Corporation have an average length of 0.199 μm to 2.747 μm and an average diameter of 18.5 nm to 38.7 nm. Carbon nanotubes also contain some non-tubular carbon particles. In one example, the carbon nanotubes have a length of 0.843 ± 0.185 μm, a diameter of 19.6 ± 3.7 nm, and an aspect ratio of 47.2 ± 11.7. Such carbon nanotubes can be used in the present invention.

As predicted from their structure and similarity to graphite, carbon nanotubes are conductive. The conductivity of each carbon nanotube is difficult to measure, but according to recent studies, the estimated resistance value is 9.5 (+/- 4.5) m? Cm, which is slightly larger than the resistance value typically measured for graphitized carbon.

The diameter of the carbon nanotubes used in the present invention is 3.5 to 200 nm, preferably 5 to 30 nm, and the length of the carbon nanotubes should be 5 times larger than the diameter, preferably 10 ² to 10 ⁴ times the diameter.

When the diameter of the carbon nanotubes exceeds 200 nm, the influence of those providing conductivity decreases. When the thickness is less than 3.5 nm, the carbon nanotubes are scattered and difficult to handle. When the length of the carbon nanotubes is less than five times the diameter, the conductivity decreases.

Each aspect ratio of the carbon nanotubes is usually 5 or more, preferably 100 or more, more preferably 1000 or more.

The carbon nanotubes used in the present invention can be obtained, for example, by using carbon nanotubes prepared by the method described in Japanese Patent Application No. 2-503334 (1990) as a raw material. This material may be used in unmodified form, or it may undergo chemical or physical treatment, and then undergoes grinding treatment. The chemical or physical treatment may be carried out before or after the grinding treatment.

Examples of the physical or chemical treatment of carbon nanotubes include nitric acid oxidation, ozone oxidation, organic plasma treatment, resin coating such as epoxy resin, and treatment of coupling agents such as organic silicon and titanium compounds. The physical treatment includes applying a sheer force to the liquid containing the carbon nanotube aggregate, thereby loosening the aggregate.

In the present invention, carbon nanotubes in the form of an aggregate can be used. Alternatively, disentangled carbon nanotubes can be used.

When electrolytic reduction is performed in the electrode prepared in the present invention in the presence of a metal ion or a proton, the S-S bond of the disulfide group of the electrode material is decomposed to form a sulfur-metal ion bond or a sulfur-proton bond. The resulting electrode undergoes electrolytic oxidation, and the sulfur-metal ionic bond or sulfur-protonic bond returns to the S-S bond. Electrolytic oxidation and electrolytic reduction involve electron transfer, which is catalyzed by carbon nanotubes in an electrically conductive matrix.

Examples of metal ions include alkali metal ions and alkaline earth metal ions. When an electrode made of the electrode material of the present invention is used as a cathode, lithium ions are used as an alkali metal ion. When an electrode made of a lithium alloy such as lithium or lithium-aluminum is used as an anode for supplying and capturing lithium ions and an electrolyte for transferring lithium ions is used, a battery having a voltage of 3 to 4 V is obtained. An electrode made of a hydrogen storage alloy such as LaNi ₅ is used as an anode for supplying and capturing a proton, and when an electrolyte for conducting a proton is used, a battery having a voltage of 1 to 2 V is obtained. In the bond between the disulfide compound and the π electron conjugated electroconductive polymer, the π electron conjugated electroconductive polymer acts as an electrode catalyst for electrolytic oxidation and reduction of the disulfide compound. In the case of? -Electrically conjugated electroconductive polymers having disulfide groups, when the disulfide group undergoes electrolytic oxidation and reduction, the electronic structure given by the conjugated? Electrons acts as an electrode catalyst. In the case of the disulfide compound alone, the difference between the oxidation potential and the reduction potential is 1 V or more. However, when an electrically conductive polymer having a bond of a? -Electron conjugated electroconductive polymer and a disulfide compound or an electrically conductive polymer having a disulfide group is used, the difference between the oxidation potential and the reduction potential is reduced to 0.1 V or less. In the disulfide compound bonded to or introduced into the? -electrically conjugated electroconductive polymer, the electrode reaction is promoted and a higher current density at room temperature is obtained in electrolysis, i.e., charging or discharging. When the electrode material of the present invention undergoes electrolytic oxidation, the? -Electron-conjugated electroconductive polymer (in the case of an electrically conductive polymer having disulfide groups, the conjugated polymer moiety) is first oxidized and the resulting oxidized form of the polymer is converted to a disulfide compound (SH or S-metal ion moieties in the case of electrically conductive polymers having disulfide groups). Thus, the oxidized form of the pi electron-conjugated polymer is returned to the reduced form and the oxidized form of the disulfide compound is produced (i. E., The disulfide group is formed). When electrolytic reduction is first performed, the electroconductive polymer is reduced and the resulting reduced form reduces the oxidized form of the disulfide compound. Thus, the reduced form of the pi -electron conjugated polymer is returned to the oxidized form, and the disulfide compound becomes the reduced form. The introduction of an electrode catalyst into the disulfide compound electrode is described in U.S. Pat. No. 4,833,048 or J. Electrochem. Soc., Vol. 136, pp. 2570-2575 (1989). However, only the organometallic compound is described as the electrode catalyst, and the effect of the electrode catalyst is not described in detail. As already described, the? Electron-conjugated polymer or the conjugated polymer moiety acts to promote electron transfer in the oxidation-reduction reaction. This acts as a catalyst in the oxidation-reduction of the disulfide, reducing the activation energy of the reaction. In addition, the? Electron-conjugated polymer or the conjugated polymer moiety increases the effective reaction area between the electrolyte and the electrode.

The lithium battery of the present invention includes an electrode in which the aforementioned electrode functions as a cathode.

The anode of the lithium battery of the present invention is not limited. The anode may contain a carbon material, and the carbon material includes natural graphite, artificial graphite, amorphous carbon, fibrous carbon, powder carbon, petroleum pitch carbon and coal coke carbon. These carbon materials are particles or fibers having a diameter of 0.01 to 10 mu m and a length of several micrometers to several millimeters.

The anode of the lithium battery may contain an alloy containing aluminum or aluminum. Examples of aluminum or alloys thereof include Al, Al-Fe, Al-Si, Al-Zn, Al-Li and Al-Zn-Si. The aluminum or its alloy is preferably a spherical or amorphous powder obtained by mechanical crushing in flake powder obtained by rapid cooling or an inert gas such as air or nitrogen. The particle size is preferably from 1 mu m to 100 mu m.

The mixing ratio of the carbon material to aluminum or aluminum alloy is 0.01 to 5 parts by weight, preferably 0.05 to 0.5 parts by weight, based on 1 part by weight of aluminum or aluminum alloy.

Alternatively, the anode may be a so-called rocking chair cell. Intercalated compounds such as graphite can insert lithium therebetween.

The electrolyte of the lithium secondary battery of the present invention is not limited as long as the electrolyte conducts lithium ions. The electrolyte may be a liquid electrolyte, a solid electrolyte, and a gel electrolyte. Preferably, the electrolyte is a solid or gel electrolyte and more preferably remains in a solid or gel state at a temperature ranging from -20 占 폚 to 60 占 폚. Alternatively, a porous separator defining the pores and made of a polymeric material may be arranged between the cathode and the anode, and a liquid electrolyte may be present in the pores thereof. The liquid electrolyte may contain a lithium salt dissolved therein. The solid electrolyte contains a lithium salt, preferably a polymer containing a lithium salt. For salt containing lithium include _{LiI, Li 3 N, LiI-} B 2 O 3, LiI · H 2 O , and _{Li-β-Al 2 O 3} .

For example, the solid electrolyte can be a complex of polyethylene oxide and a lithium salt dissolved therein. In addition, the solid electrolyte may be a poly (acrylonitrile) film containing LiClO ₄ dissolved in propylene carbonate and propylene carbonate.

The anode and the cathode may contain components for the electrolyte. For example, the composition for a solid electrolyte may comprise a polyether obtained by adding ethylene oxide and butylene oxide to a polyamine, an ion exchange compound having a layered crystal structure and a lithium salt, and such a composition may be added to a composition for an anode or a cathode Can be added and mixed.

The polyether can be obtained by the addition reaction of ethylene oxide and butylene oxide with polyamines using an alkali catalyst under a pressure of 1 to 10 atm at 100 ° C to 180 ° C. As the polyamine which is a component of the polyether, a polyethyleneimine, a polyalkylene polyamine or a derivative thereof may be used. Examples of polyalkylene polyamines include diethylenetriamine, triethylenetetramine, hexamethylenetetramine, and dipropylenetriamine. The additional number of total moles of ethylene oxide and butylene oxide is 2 to 150 moles per polyamine active hydrogen. The molar ratio of ethylene oxide (EO) to butylene oxide (BO) is 90/20 to 10/90 (= EO / BO). The average molecular weight of the polyether thus obtained is 1,000 to 5,000,000. Preferably, the polyether is contained in the solid electrode composition in an amount of 0.5 to 20 wt%. The polyether of the solid electrolyte acts as a surfactant so that the composition is uniformly dispersed.

Examples of the ion exchange compound which is a layered crystal structure include silicates such as montmorillonite, hectorite, saponite and smectite, phosphoric acid esters such as zirconium phosphate and titanium phosphate, vanadic acid, antimonic acid, tungstic acid, And clay minerals including organic cations such as ammonium salts, or substances obtained by modification with organic polar compounds such as ethylene oxide and butylene oxide.

4 is a cross section of a laminated structure used for a lithium battery. The structure 30 has a cathode 34, an anode 38 with a lithium ion-releasing active material and an electrolyte 36 arranged between the cathode 34 and the anode 38. The structure has a cathode current collector 32 in contact with the cathode 34 and an anode current collector 40 in contact with the anode 38. In the present invention, the cathode 34 comprises an electrically conductive matrix containing a disulfide group, wherein the SS bond of the disulfide group is decomposed by electrochemical reduction and regenerated by electrochemical oxidation, and a plurality of Carbon nanotubes. The cathode current collector 32, the cathode 34, the electrolyte 36, the anode 38 and the anode current collector 40 take a layered structure and are stacked on each other in this order. The electrolyte (36) may have one or more solid electrolytes and a gel electrolyte.

When the lithium secondary battery of the present invention is charged, Li is released from the S-Li bond of the cathode and an S-S bond is generated. On the anode surface or inside the anode (when the anode component and the electrolyte component are mixed), lithium is uniformly deposited. Since lithium is deposited directly from the electrolyte, it is not contaminated with impurities such as oxygen. Therefore, even when charging and discharging are repeated, the current is not easily concentrated, whereby any short circuit to the battery can be effectively prevented. The generated lithium and electrolyte during charging (electrolysis) are in contact with each other, so that the polarization decreases during discharge and a higher current can be generated. As described above, particularly effective results can be obtained when the electrolyte is mixed with the cathode and / or the anode. In this case, it is particularly effective that a compound having a lithium salt, a polyether and a layered crystal structure is used as an electrolyte.

The lithium secondary battery of the present invention can also be produced by the following method. First, a carbon nanotube aggregate is obtained by a conventional method.

The unwound carbon nanotubes can be obtained by a method including a step of applying a plurality of carbon nanotube aggregates to a liquid and a step of applying a sheer force to the liquid to unravel the carbon nanotube aggregate.

Since the viscous liquid facilitates applying a normal force by a mechanical process, the viscosity of the liquid at 25 캜 is not less than 0.8 centipoise, preferably not less than 1.0 centipoise. The viscosity of some liquids is summarized in Table 3.

Liquid Viscosity at 25 캜 (centipoise) N-methyl-2-pyrrolidone 2-propanol [ 1.671.770.545

The liquid is an organic solvent or water. The organic solvent is preferably polar. Examples of organic solvents include N-methyl-2-pyrrolidone. When water is used, preferably water contains a surfactant. The normal force can be provided by a mechanical process, and the liquid containing the aggregate passes through a narrow gap at a high velocity.

For example, a homogenizer can be used to apply a normal force. In Figure 1 the homogenizer 10 has a stator 12 with a radially inner surface 13 and a rotor 22 with a radially outer surface 23. The stator 12 and the rotor 22 share an axis. The radially inner surface 13 of the stator 12 and the radially outer surface 23 of the rotor 22 form a narrow gap with a circular arc or arc therebetween. The blade 26 is fixed to the rotor 22 and arranged in a narrow gap. When the rotor 22 rotates, the blade 26 rotates along a narrow gap.

The stator 12 is formed in at least one hole 14 in the radial direction, and the hole allows liquid to pass through. Likewise, the rotor 22 is also formed with at least one hole 24 in the radial direction, and the hole allows liquid to pass through. Typically, the liquid passes through the hole 24 in a radially outward direction and then through the hole 14 in a radially outward direction.

When the liquid has a plurality of aggregates 16, the aggregates 16 will pass through a narrow gap by the blades 26 so that normal force is applied thereto. Aggregate 16 is slowly unwound and becomes smaller particles 18.

Alternatively, the ultrasonic generator applies ultrasonic waves to the liquid containing the aggregate, whereby the aggregate is released.

Preferably, the mixture containing the loosened carbon nanotubes and the liquid medium is mixed with the organic compound containing the disulfide group and the electroconductive polymer. Alternatively, the mixture containing the loosened carbon nanotubes and the liquid medium may be mixed with an electrically conductive polymer containing a mercapto group. The liquid medium may be the same as or different from the liquid used to unwind the carbon nanotube aggregate.

A battery collector having a current collector and a cathode film stacked thereon can be fabricated by coating a composition for a cathode film on a current collector capable of being metal foil.

The structure 30 of Figure 4 may be fabricated from a battery precursor. The electrolyte 36, the anode 38 and the anode current collector 40 may be laminated to the battery precursor.

A plurality of structures 30 may be stacked on each other and packaged in a housing to produce a lithium battery. Alternatively, the plurality of structures 30 may be rolled into a generally cylindrical shape and then packaged in a housing.

The lithium secondary battery of the present invention can also be produced by the following method. Each composition of the cathode, the anode and the electrolyte is formed into a film. The cathode composition contains carbon nanotubes. The cathode film, the electrolyte film and the anode film are laminated in this order and compressed to each other, thereby obtaining a unit cell. If necessary, a battery conductive foil and lead acting as a current collector are attached to the cathode and anode of the unit cell, and the assembly is packaged, thereby producing a lithium secondary battery. Preferably, the electrolyte component is mixed with the cathode and / or the anode.

Example 1

Carbon nanotube

First, unpack the carbon nanotube aggregate. A mixture of carbon nanotubes is added to 1-methyl-2-pyrrolidone to obtain a mixture containing 1 wt% of carbon nanotubes. The mixture is added to a homogenizer of ULTRA TALUX T-25, trade name, product of IKA Japan Company Limited, located in Nakayama, Yokohama, Japan. The homogenizer dissolves the aggregate by applying normal force to the mixture. The homogenizer is the structure of Fig. In the homogenizer, the rotor is rotated 8,000 to 24,000 revolutions per minute.

Secondly, the unraveling of the carbon nanotube aggregate is confirmed by the following procedure, which is not necessary for the manufacture of electrodes containing the carbon nanotubes. 19 parts by weight of polymethylmethacrylate serving as a binder and N-methyl-2-pyrrolidone for dilution were added to a liquid mixture containing 1 part by weight of the carbon nanotube thus obtained. Polymethylmethacrylate (hereinafter referred to as PMMA) has a weight average molecular weight of 996,000 and is an Aldrich product. The liquid mixture is poured into a glass substrate and the glass substrate is placed in a vacuum oven to evaporate the solvent to produce a PMMA film containing 5 wt% of carbon nanotubes. The PMMA film is observed with a transmission electron microscope. 2 is a photograph of the result. The fibrils corresponding to the carbon nanotubes are loosened and dispersed in the PMMA matrix.

As a comparative example, a normal force is not applied to a liquid mixture containing a carbon nanotube aggregate. Specifically, a liquid mixture containing N-methyl-2-pyrrolidone and 1 wt% of carbon nanotubes is mixed with a magnetic stirrer overnight. Other PMMA membranes were prepared using the resulting liquid mixture in the same manner as described above, and the PMMA membranes were observed with a transmission electron microscope. Figure 3 is a photograph of the result. A plurality of carbon nanotube aggregates are present in the matrix.

Battery precursor

1.8 g of 2,5-dimercapto-1,3,4-thiadiazole powder is mixed with 1.2 g of polyaniline in a ball mill. 11.1 g of a liquid mixture containing 2% by weight of the dissolved carbon nanotubes in N-methyl-2-pyrrolidone was added to 2.5 g of the powder mixture, and the resulting mixture was mixed with the mortar to prepare an ink. The ink is coated on a copper foil having a thickness of 35 mu m using a doctor blade having a gap of 200 mu m. The copper foil is placed in a vacuum oven at 80 DEG C for 3 hours to dry the ink, thereby producing a battery precursor having a film with a coating thickness of about 40 mu m and a copper foil serving as a cathode.

The resistivity of the film is measured with a resistivity meter, product of Kyowa Riken under the trade name K-705RS. The resistivity of the film is 40 ohm per cm ² .

The adhesion of the film to the copper foil is measured by a grid tape test according to Japanese Industrial Standard K 5400 8.5.2. The test gave 6 to 8 points, indicating that the film adhered to the copper foil without sticking to the tape.

The hardness of a film having a thickness of 20 mu m on a copper foil is measured by scraping the surface of the film with a pencil having a hardness of 8H according to Japanese Industrial Standard K 5400 8.4.1. There is almost no damage to the film surface when scratched. Fold the membrane along the copper foil. However, the membrane is neither stripped nor cracked. The results show that the membrane is flexible, which is important for lithium battery manufacturing.

Comparative Example 1

As a comparative example, a battery precursor comprising a copper foil and a film acting as a cathode coated thereon was prepared in the same way, except that carbon nanotubes were replaced by ketjen black, an Akzo product.

The membrane resistivity was measured with the same instrument and the membrane resistivity was 50 kiloohm per cm ² .

The film adhesion is measured by the same grid-tape test according to Japanese Industrial Standard K 5400 8.5.2, and the test gives a zero point, which indicates that the film peels away from the copper foil.

A film scratch test 55 μm thick on a copper foil according to Japanese Industrial Standard K 5400 8.4.1 shows that a soft pencil of hardness HB damages the film surface. The results show that the membrane containing Ketjenblack is much more ductile than the membrane containing carbon nanotubes.

Example 2

Lithium secondary battery

Coin configuration Lithium secondary battery is manufactured. The above-mentioned battery precursor is cut into a disk configuration having a diameter of 16 mm and used as a cathode.

The gel electrolyte was obtained in the following manner. 4.8 g of lithium tetrafluoroborate was added to a mixture of 14.5 g of propylene carbonate and 25.1 g of ethylene carbonate. 5.0 g of a copolymer powder of polyacrylonitrile and polymethyl acrylate, which is a product of Scientific Polymer Product and has a weight average molecular weight of 100,000, is added to the mixture. The thus obtained mixture is stirred with a magnetic stirrer for 1 day to obtain a white polymerizable dispersion. The polymerizable dispersion is put into a dish made of stainless steel and heated to 125 캜 to obtain a colorless dispersion. Meanwhile, a pair of TEFLON plates having a thickness of 0.5 mm are placed on the glass plate at both ends of the glass substrate. A colorless, flowable polymeric dispersion is added to the glass substrate between the TEFLON plates. Another glass plate is placed on a glass plate, and the glass plate pair is cooled to room temperature. Thereafter, the glass plate is further cooled in the freezer and then warmed to room temperature again. The thus-obtained gel film is cut into a circular shape having a diameter of 18 mm.

A foil made of metal lithium is used as an anode, and a copper foil is used as an anode current collector.

A battery precursor, a gel electrolyte, an anode, and an anode current collector are stacked in this order.

A coin-shaped lithium secondary battery is subjected to repeated cycles of discharging and charging. After 100 cycles of discharging and charging, the lithium battery was found to maintain a discharge capacity of 90% or more.

The electrode of the present invention has improved electrical conductivity and mechanical strength. Compared to other carbon materials, a smaller amount of carbon nanotubes maintains the required electrical conductance and mechanical strength of the electrode.

The battery precursor of the present invention has improved adhesion to the current collector.

The electrode of the present invention is suitable for a cathode of a lithium battery, particularly a lithium secondary battery. The electrode can be used as a sensor to detect the electrical potential of the medium.

Claims (34)

An electrode comprising an electrically conductive matrix containing a disulfide group, wherein the S-S bond of the disulfide group is decomposed by electrochemical reduction and regenerated by electrochemical oxidation, and a plurality of carbon nanotubes dispersed in the electrically conductive matrix. The electrode according to claim 1, wherein the electrically conductive matrix contains an electrically conductive polymer and an organic compound having disulfide groups. 3. The electrode of claim 2, wherein the electrically conductive polymer comprises a polymer of formula (1). Formula 1 - [Ar-NH] _n - In the above formula (1) Ar is aryl, n is an integer. 3. The electrode of claim 2, wherein the electrically conductive polymer comprises polyaniline. The electrode according to claim 2, wherein the organic compound contains a 5- to 7-membered heterocyclic ring containing 1 to 3 hetero atoms consisting of a nitrogen atom and a sulfur atom. The electrode according to claim 2, wherein the organic compound contains a thiadiazole ring. The electrode according to claim 1, wherein the electroconductive matrix contains an electroconductive polymer having a mercapto group capable of forming a disulfide group. The electrode according to claim 1, which contains 0.5 to 6% by weight of carbon nanotubes, based on the sum of the electroconductive matrix and the carbon nanotubes. The electrode according to claim 1, comprising 1 to 4% by weight of carbon nanotubes, based on the sum of the electrically conductive matrix and the carbon nanotubes. The electrode according to claim 1, wherein the carbon nanotube has an average diameter of 3.5 to 200 nm and an average length of 0.1 to 500 占 퐉. The electrode according to claim 1, wherein the average diameter of the carbon nanotubes is 5 to 30 nm and the average length is 100 to 10000 times the diameter. (a) an electrically conductive matrix containing a disulfide group, wherein the SS bond of the disulfide group is decomposed by electrochemical reduction and regenerated by electrochemical oxidation, and a cathode having a plurality of carbon nanotubes dispersed in the electrically conductive matrix And (b) A battery precursor comprising a cathode current collector, wherein the cathode is coated over the cathode current collector. 13. The battery precursor of claim 12, wherein the cathode current collector and the cathode have a layered structure. 13. The battery precursor of claim 12, wherein the thickness of the cathode ranges from 5 to 500 mu m. 13. The battery precursor according to claim 12, wherein a thickness range of the cathode is 10 to 100 mu m. 13. The battery precursor of claim 12, wherein the cathode current collector is in a sheet configuration. 13. The battery precursor of claim 12, wherein the cathode current collector comprises a metallic foil. 13. The battery precursor of claim 12, wherein the electrically conductive matrix contains an electrically conductive polymer and an organic compound having disulfide groups. 19. The battery precursor of claim 18, wherein the electrically conductive polymer comprises a polymer of the following formula (I). Formula 1 - [Ar-NH] _n - In the above formula (1) Ar is aryl, n is an integer. The battery precursor according to claim 18, wherein the organic compound contains a 5- to 7-membered heterocyclic ring containing 1 to 3 heteroatoms consisting of a nitrogen atom and a sulfur atom. The battery precursor according to claim 12, wherein the electrically conductive matrix contains an electrically conductive polymer having a mercapto group capable of forming a disulfide group. The battery precursor according to claim 12, wherein the cathode contains 0.5 to 6% by weight of carbon nanotubes based on the sum of the electroconductive matrix and the carbon nanotubes. The battery precursor according to claim 12, wherein the carbon nanotubes have an average diameter of 3.5 to 200 nm and an average length of 0.1 to 500 μm. (a) an electrically conductive matrix containing a disulfide group, wherein the SS bond of the disulfide group is decomposed by electrochemical reduction and regenerated by electrochemical oxidation, and a cathode having a plurality of carbon nanotubes dispersed in the electrically conductive matrix , (b) an anode having an active material for releasing lithium ions and (c) an electrolyte disposed between the cathode and the anode. 25. The method of claim 24, (a) a cathode current collector in contact with the cathode and (b) a lithium battery further comprising an anode current collector in contact with the anode. 26. The lithium battery according to claim 25, wherein the cathode current collector, the cathode, the electrolyte, the anode, and the anode current collector have a layered structure and are stacked on each other in this order. 25. The lithium battery of claim 24, wherein the electrolyte comprises at least one solid electrolyte and a gel electrolyte. 25. The lithium battery of claim 24, wherein the electrically conductive matrix contains an electrically conductive polymer and an organic compound having disulfide groups. 29. A lithium battery according to claim 28, wherein the electrically conductive polymer comprises a polymer of the following formula (1). Formula 1 - [Ar-NH] _n - In the above formula (1) Ar is aryl, n is an integer. The lithium battery according to claim 28, wherein the organic compound contains a 5- to 7-membered heterocyclic ring containing 1 to 3 heteroatoms consisting of a nitrogen atom and a sulfur atom. 25. The lithium battery of claim 24, wherein the electrically conductive matrix contains an electrically conductive polymer having a mercapto group capable of forming a disulfide group. 25. The lithium battery according to claim 24, wherein the cathode contains 0.5 to 6% by weight of carbon nanotubes, based on the sum of the electroconductive matrix and the carbon nanotubes. The lithium battery according to claim 24, wherein the carbon nanotubes have an average diameter of 3.5 to 200 nm and an average length of 0.1 to 500 μm. 25. The lithium battery according to claim 24, wherein the cathode has a thickness ranging from 5 to 500 mu m.