WO1994015373A1 - Electrode and secondary cell which uses the electrode - Google Patents

Abstract

An electrode using carbon fibers as the carbon material, and a chargeable/dischargeable secondary cell comprising the electrode and a cathode active material of carbon material which can be doped with lithium ions and from which the ions can be removed. The carbon fibers are oriented in one direction or the fibers are mixed with electrically conductive foils or fibers. Thus a large-capacity high-output secondary cell is provided.

Description

 Akitoda

 '' Electrodes and secondary batteries using them

 Technical field

 The present invention relates to an electrode using carbon fiber and a rechargeable secondary battery using the same.

 Background art

 In recent years, with the spread of portable devices such as video cameras and notebook computers, demand for small, high-capacity secondary batteries has increased. Most of the secondary batteries currently used are nickel-metal dome batteries that use an alkaline electrolyte, but the battery voltage is as low as about 1.2 V, and it is difficult to improve the energy density. For this reason, high-energy secondary batteries have been studied using lithium metal, which is the most basic metal for the negative electrode.

However, in rechargeable batteries that use lithium metal for the negative electrode, there is the danger that lithium will grow dendrites due to repeated charging and discharging, causing a short circuit and fire. In addition, since highly active metallic lithium is used, it is inherently dangerous, and there are many problems in using it for consumer use. In recent years, lithium-ion secondary batteries using various carbon bodies have been devised as solutions to such safety problems and at the same time, capable of providing high energy unique to lithium electrodes. This method takes advantage of the fact that lithium ions are doped into a carbon body during charging and have the same potential as lithium metal, so that it can be used as a negative electrode instead of lithium metal. During discharge, the doped lithium ions are undoped from the negative electrode and return to the original carbon body. When such a carbon body doped with lithium ions is used as a negative electrode, there is no problem of dendrite formation, and there is no metallic lithium. Currently, R & D is being actively conducted. As secondary batteries utilizing the above-described doping of carbon bodies with lithium ions, Japanese Patent Application Laid-Open Nos. Sho 62-0963 and Sho 62-122066 are known. It is. Such a carbon body is generally in the form of a powder, and a polymer binder such as Teflon-vinylidene fluoride is required for electrode molding. That is, the powder can be mixed with a binder and pressed against a metal net, or the slurry can be applied on a metal foil to produce an electrode. On the other hand, in the case of carbon fiber, no electrode for a secondary battery using carbon fiber has yet been industrially implemented, and the preferred form and structure of the electrode and the technology for producing such an electrode are not described. It is completely unknown. In particular, carbon fiber electrode morphology The major technical issues are the technology, how to make electrical contact between the carbon fiber and the current collector, and the problem of electrical short between the positive and negative electrodes due to the penetration of the separator by the fluff of carbon fiber.

 However, if a non-woven fabric or a woven fabric made of carbon fibers is used, it is possible to produce an electrode without using a binder or in a small amount. Furthermore, carbon fibers are considered to be superior in terms of chemical stability to the electrolyte, structural stability against volume expansion due to doping, and repeated charge / discharge characteristics. As a secondary battery using such an electrode, Japanese Patent Application Laid-Open Nos. Sho 60-54181 and Sho 62-13991 are known. However, in the case of an electrode using carbon fiber, it is difficult to make an electrical connection with a metal as an extraction electrode. In the case of carbon powder electrodes, the powder is mixed with a binder and then pressed onto a metal net, or a slurry is applied to the metal foil. It can be connected, but in the case of carbon fiber, methods such as sandwiching the end of the carbon fiber with a net-like or foil-shaped metal collector have been tried. However, carbon fibers tend to fall apart and break easily, so workability is poor and there are problems in mechanical strength and durability. Further, there is also a problem that fluffs, which are broken fibers, penetrate the separator and electrically contact the positive electrode and the negative electrode, thereby causing an internal short circuit. Furthermore, the voltage applied to the carbon fiber was different from the voltage applied between the terminals due to the contact resistance only by sandwiching the carbon fiber between the metal collectors. This can be confirmed by the phenomenon that the potential immediately returns when the application of the voltage is stopped, that is, the so-called overvoltage increases. In addition, if the electrode is made large, the potential difference increases far from the metal collector electrode due to the resistance of the carbon fiber, and uniform doping and undoping hardly occur.

 BRIEF DESCRIPTION OF THE FIGURES

 FIG. 1 is a schematic diagram showing an example of an electrode in which a conductive foil is provided on a carbon fiber sheet.

 FIG. 2 is a schematic view showing an example of an electrode in which a conductive foil is provided on a carbon fiber sheet.

 FIG. 3 is a schematic view showing an example of an electrode in which conductive wires are arranged in a direction parallel to carbon fibers.

 FIG. 4 is a schematic view of an example of an electrode in which carbon fibers are woven into a stitch-like conductive wire. 1 to 4, 1 denotes a carbon fiber, 2 denotes a conductive wire, 3 denotes a direction of an extraction electrode, 4 denotes a carbon fiber sheet, and 5 denotes a conductive wire.

 BEST MODE FOR CARRYING OUT THE INVENTION

 The present invention has the following configurations in order to solve the above problems.

That is, the first invention of the present application relates to an electrode using a unidirectional array of carbon fibers and an electrode using the same. And a secondary battery using the same. In the present invention, a form in which carbon fibers are arranged in a uniaxial direction is excellent in packing density and handleability. In this case, it is preferable that the carbon fibers are arranged uniformly, and if the arrangement is uneven, uniform doping may be difficult to occur.

 Further, the electrode of the second invention of the present application is characterized by comprising a carbon fiber sheet and a foil or a wire having electric conductivity.

 Preferred embodiments are illustrated below with reference to the drawings.

 FIG. 1 shows an example of an electrode in which carbon fibers are arranged uniaxially and a conductive foil is arranged thereon. FIG. 3 shows an embodiment of an electrode in which carbon fibers are arranged in a uniaxial direction and the conductive wires are also arranged in the same direction as the fibers. In FIG. 3, 1 is a carbon fiber, 2 is a conductive wire typified by a metal fiber, and 3 is a direction of connection with the extraction electrode. When the carbon fibers are arranged uniaxially in this way, the conductive fibers are arranged in a direction perpendicular to the carbon fibers, and the conductive fibers are shaped so that the carbon fibers are bundled. This is a further preferred embodiment. In addition, if carbon fibers arranged in a uniaxial direction as shown in FIG. 4 are woven into a mesh-shaped conductive wire, the carbon fibers do not fall apart and the current collection efficiency is improved.

 In order to improve the electrical contact with the carbon fibers, a method of adhering uniaxially arranged sheet-like carbon fibers on an electrically conductive foil typified by a metal foil is preferable. For example, a method in which part or all of the carbon fiber is pressure-bonded to a metal foil by a roll press or the like, or a method in which a small amount of resin such as Teflon or polyvinylidene fluoride is used as a binder to form the carbon fiber. There is a method of bonding to a metal foil.

 When the electrode is wound, the arrangement direction of the carbon fibers is preferably substantially perpendicular to the winding direction. The reason is that the carbon fiber disposed inside the metal foil can be prevented from sagging during winding, the carbon fiber is not easily broken during winding, and the end of the broken fiber penetrates the separator or meanders. This is to prevent the electrodes from protruding from both ends. If you go through the separation or project from both ends, there is a risk of an electrical short circuit with the positive electrode.

 By forming the electrode in which the carbon fiber and the metal foil are integrated as described above, the contact resistance can be reduced, and the distance between the metal current collector and the carbon fiber can be reduced, so that the potential in the carbon fiber can be made more uniform. be able to. Therefore, the problems of capacity reduction due to overvoltage due to contact resistance and non-uniform doping caused by non-uniform potential in carbon fiber can be solved.

The weight of carbon fibers arranged uniaxially is 200 g Zm or less, 30 g Zm ² or more It is more preferable to use firs of 150 g Zm ² or less and 50 g Zm ² or more. If the weight is large, the carbon fiber sheet becomes thick and the resistance in the thickness direction increases, which may cause uneven doving or make it difficult to use at high output. Also, when the weight is small, the amount of carbon fiber of the active material in the entire negative electrode is reduced, so that the amount of carbon fiber that can be filled in the battery is reduced, and the energy density of the battery tends to decrease.

 The carbon fiber in the present invention is not particularly limited, and a filament obtained by firing an organic substance is generally used. Specifically, PAN-based carbon fiber obtained from polyacrylonitrile (PAN), pitch-based carbon fiber obtained from pitch such as coal or petroleum, cellulosic carbon fiber obtained from cellulose, gas obtained from low molecular weight organic matter Examples include vapor-grown carbon fibers, and in addition, carbon fibers obtained by firing polyvinyl alcohol, lignin, polychlorinated vinyl, polyamide, polyimide, phenolic resin, furfuryl alcohol, and the like may be used. Among these carbon fibers, a carbon fiber satisfying the characteristics is appropriately selected according to the characteristics of the electrode and the battery in which the carbon fibers are used.

 Among the above carbon fibers, when used for a negative electrode of a secondary battery using a non-aqueous electrolyte containing an alkali metal salt, PAN-based carbon fibers, pitch-based carbon fibers, and vapor-grown carbon fibers are preferable. . In particular, PAN-based carbon fibers are preferably used in that they have good doping of alkali metal ions, particularly lithium ions.

 It should be noted that the carbon fiber can be used in the present invention as long as the shape of the carbon fiber is maintained even after some treatment after firing. In particular, those in which the carbon fiber is pre-charged and discharged in the electrolytic solution before being incorporated into the battery are effective because the initial capacity loss (retention) peculiar to the carbon material can be reduced. . The initial capacity loss is due to the fact that some of the dopants (eg, lithium ions) doped during the first charge remain in the carbon material and are not undoped during the discharge. To increase the capacity of the secondary battery, it is effective to reduce the initial capacity loss. Since the carbon fiber itself has electrical conductivity and is a continuous body, it is suitable for performing a charge / discharge treatment in advance. As an example of a specific method, there is a method of doping or undoping carbon fibers in an electrolyte containing lithium ions.

In the second invention of this application, the form of the carbon fiber sheet is not particularly limited, but a sheet-like structure arranged in a uniaxial direction is preferable. However, sheets such as fabrics or flutes include fabrics, knits, braids, laces, nets, felts, paper, non-woven fabrics, mats, etc. It can also be.

 The diameter of the carbon fiber used in the present invention should be determined so that each form can be easily adopted.Preferably, a carbon fiber having a diameter of 1 to 50 G // m is used, and 3 to 10 / zm is used. More preferred. It is also preferable to use several types of carbon fibers having different diameters.

 Specific examples of metals used for electrically conductive foils include gold, silver, copper, platinum, rhodium, aluminum, iron, nickel, chromium, manganese, lead, zinc, tungsten, titanium, and the like. An alloy of the above metals, such as steel, may be used. In addition, the metal surface may be coated with various substances to the extent that conductivity is not impaired. These metals or their coatings are made into foils or lines and arranged together with carbon fibers in the shape shown above. When the thickness of the metal foil is increased, the amount of the active material that can be stored in the battery is reduced. Therefore, a thin foil is preferably used. The preferred thickness is around 5-10 G / zm. Copper foil is particularly preferably used in view of electric resistance, thickness and cost of metal foil. The diameter of the metal wire should be determined according to the properties, diameter, shape, etc., of the carbon fiber used so that the current collection effect can be enhanced or bundled easily, but 1 to 200 / zm Preferably, those having a level of about 5 to 100 are used. In addition, in order to increase the strength at the time of bundling, it is also a preferable embodiment to bundle several thin metal wires into a thread.

 The ratio between the carbon fiber and the conductive wire in the electrode of the present invention should be appropriately determined in consideration of the electrode characteristics and the current collection efficiency. The preferred ratios are 1 to 105% by weight and 0.2 to 25% by volume. More preferably, the weight ratio is 2 to 8% and the volume ratio is 0.4 to 2! ¾.

 In addition, carbon fibers may have a partial break of a single yarn in a fiber bundle in a fibrous or cloth form, so-called fluff may penetrate through the separator and come into contact with the positive electrode to cause an internal short circuit. In order to solve this defect, it is effective to paste some or all of the carbon fiber with resin. The resin used for the carbon fiber sizing is not particularly limited, and a general thermoplastic or thermosetting resin can be used. Among them, a fluororesin, an olefin resin, an epoxy resin, a urethane resin, an acrylic resin, a polyester resin, and the like are used alone, or a mixture of two or more thereof, and a modified product thereof is suitably used.

The method of gluing these carbon fibers with a resin is not limited in any way. For example, a polymer solution is passed through an emulsion tank or sprayed by spraying. It is achieved by the method of crunching. If the amount of the polymer coated on the carbon fiber is too small, it tends to be difficult to sufficiently suppress fluffing, and if it is too large, the function of the carbon fiber as an active material tends to be reduced.

 Therefore, the amount of the polymer to be coated is preferably in the range of 0.1 part by weight or more and 15 parts by weight or less based on 100 parts by weight of the carbon fiber. If the amount is less than 0.1 part by weight, it is difficult to prevent fluff. If the amount exceeds 15 parts by weight, the electrical properties of the carbon fiber as an anode active material are affected. If it exceeds 50 O mA per g, the initial discharge capacity tends to decrease to 70% by weight or less when not coated.

 For this reason, the coating amount is most preferably in the range of 0.5 to 10 parts by weight, and more preferably in the range of 0.5 to 8 parts by weight. As a method for attaching the polymer, when the polymer is dissolved in a water-soluble organic solvent such as N-methylpyrrolidone, the polymer is precipitated by wet coagulation in water or a mixed solution of an organic solvent and water. The method is more effective.

 The separator to be used is not particularly limited, and may be a commercially available, insulating porous film or a woven or nonwoven fabric. Examples of the separator include polyolefin, polypropylene, and polytetrafluoroethylene. , Polyethylene, polyacetal and the like are used. The thickness of the separator is preferably 200 m or less, more preferably 50 m or less, in order to reduce the internal resistance of the battery. Specifically, "Celgard" (Daicel) and "Hipore" (Asahi Kasei) can be used.

 Carbon fiber can be used as the positive electrode material of the secondary battery, but other than this, inorganic or organic compounds such as artificial or natural graphite powder, carbon fluoride, metal or metal oxide, etc. Polymer compounds and the like can be mentioned. When an inorganic compound such as a metal or a metal oxide is used as a positive electrode, a charge / discharge reaction takes place utilizing doping and undoping of a cation. In the case of an organic polymer compound, charge and discharge reactions occur due to doping and undoping of the anion. As described above, various charge / discharge reaction modes are adopted depending on the substance, and these are appropriately selected according to the required positive electrode characteristics of the battery.

Specifically, conjugated compounds such as transition metal oxides containing transition metal oxides and transition metal chalcogens, etc., polyacetylene, polyparaphenylene, polyphenylenevinylene, polyaniline, polypyrrolyl, polythiophene, etc. Positive electrodes used in ordinary secondary batteries, such as molecules, cross-linked polymers having disulfide bonds, and thionyl chloride -

Can be mentioned. Among these, in the case of a secondary battery using a non-aqueous electrolyte containing a lithium salt, transition metal oxides such as cobalt, manganese, molybdenum, vanadium, chromium, iron, copper, and titanium, and transition metal chalcogens are used. It is preferably used. In _{particular, L i C ο 0 2,} L i N i 0 2 has a high voltage, the energy density is large, most preferably used.

 The electrolytic solution of the secondary battery using the electrode of the present invention is not particularly limited, and a conventional electrolytic solution is used, and examples thereof include an acid or alkali aqueous solution and a non-aqueous solvent. Among these, propylene carbonate, ethylene carbonate, 7-butyrolactone, N-methylpyrrolidone, acetonitrile, N, N-dimethyl are used as electrolytes for secondary batteries composed of the above-mentioned non-aqueous electrolyte containing an alkali metal salt. Formamide, dimethyl sulfoxide, tetrahydrofuran, 1,3-dioxolan, methyl formate, sulfolane, oxazolidone, thionyl chloride, 1,2-dimethoxetane, diethylene carbonate, derivatives and mixtures thereof. It is preferably used. The electrolyte contained in the electrolyte is an alkali metal, particularly lithium halide, perchlorate, thiocyanate, borofluoride, phosphorus fluoride, arsenic fluoride, aluminum fluoride, trifluoromethyl. Sulfates and the like are preferably used.

 When the electrode made of carbon fiber according to the present invention is used for a non-aqueous electrolyte secondary battery containing a metal salt of alkali metal, the method utilizes doping of cations or anions to carbon fiber, and the negative electrode, It can be used for any of the positive electrodes. Among them, it is preferably used for a negative electrode of a secondary battery. In particular, when cations represented by lithium ions are doped, carbon fibers are preferably used as a negative electrode material of a high-energy battery capable of obtaining a high capacity and a low potential. Also, since it is used in a fibrous form, the contact resistance can be lower than that of carbon powder, and high current discharge is possible.

 The secondary battery using the electrode of the present invention is widely used in portable electronic devices such as video cameras, personal computers, word processors, radio-cassettes, mobile phones, etc., utilizing the features of light weight, high capacity, and high energy density. Available.

 Example

 Hereinafter, the present invention will be described more specifically with reference to examples. The present invention is not limited to the embodiment.

Example 1

The end of the carbon fiber “Tre-force” T3000 having a bundle of 1200 pieces was fixed with a conductive copper base. Five of these toe-like structures are arranged in one direction, and copper is The foil was adhered to obtain a sheet having a length of 2 Omm, a width of 5 Omm, and a thickness of about 0.3 mm. The weight of the carbon fiber sheet was 23 Omg.

 In order to measure the capacity of the above unidirectional carbon fiber array as a secondary battery, a lithium metal foil was used for the counter electrode and the reference electrode, and a 1 M solution of lithium perchlorate in propylene carbonate was used as the electrolyte. A three-pole cell was created using. The above cell was charged to 0 V with a constant current of 2 OmA, and after a 20-minute pause, discharged to 1.5 V with a constant current of 2 OmA, and the discharge capacity was determined. As a result, the capacity per weight was 304 mAh / g, and a high discharge capacity was obtained by this method.

Example 2

 (1) Creating electrodes

Thickness 15; Commercially available PAN-based carbon fiber "Tre-force" T-300 (manufactured by Toray Industries, Inc.) is uniformly arranged in a uniaxial direction on «m copper foil, and the carbon fiber weight is 100 gZm ² . An electrode made of copper foil and carbon fiber was created.

 (2) Preparation of positive electrode

Commercially available lithium carbonate (L i ₂ C 0 ₃₎ and basic cobalt carbonate

(2CoC0 „3Co (OH) ₂ ) was weighed so that the molar ratio Li / Co = l / l, mixed in a ball mill, and heat-treated at 900 for 20 hours to obtain Li C 00 ₂ This is crushed by a ball mill, and artificial graphite is used as a conductive material, polyvinylidene fluoride (PVDF) is used as a binder, and N-methylpyrrolidone is used as a solvent. LiC00 ₂ artificial graphite / PVDF = 80 by weight A positive electrode slurry was prepared by mixing to give a positive electrode slurry, which was applied to aluminum foil, dried and pressed.

 (3) Creating a battery

 The two electrodes created in (1) and (2) above are overlapped with a porous polypropylene film (Cell Guard # 2500, manufactured by Daicel Chemical Co., Ltd.) separator and rolled up to form a cylindrical electrode. I got a body. The above electrode body was immersed in a beaker type cell containing an electrolyte of propylene carbonate containing 1 M lithium perchlorate, and the electrode terminals were taken out of the copper foil and aluminum foil to obtain a secondary battery.

 (4) Battery evaluation

The charging evaluation of the secondary battery produced above was performed. The battery was charged to 4.3 V with a current density per carbon fiber weight of 40 mA / g. The discharge capacity of the secondary battery determined from the amount of charge discharged after charging was 320 raAh / g per weight of carbon fibers used in the battery. Example 3

 Commercially available PAN-based carbon fiber as carbon fiber ("Treiki" T-300, manufactured by Toray Industries, Inc.)

3K: 3 000), a commercially available polyvinylidene fluoride resin (“Neoflon” VP-850, manufactured by Daikin Chemical Co., Ltd.) was dissolved in N-methyl 2-pyrrolidone as a polymer for gluing. Used.

 After the carbon fiber is immersed in a PVDF solution, the polymer is coagulated in a 1: 1 (weight ratio) solution of water and N-methyl-2-pyrrolidone, and then dried at 150 ° C for 1 hour. Thus, carbon fibers glued with a polymer were obtained. The amount of the PVDF polymer attached was 5% by weight with respect to the carbon fibers, and the average pore size in the SEM photograph was about 15 / zm.

 In order to confirm the effect of the fluff of this glued carbon fiber on the separator, this carbon fiber was sandwiched between porous polypropylene films ("Celgard" # 2500, manufactured by Daicel Chemical Co., Ltd.). This was wound on a stainless steel rod of 3 mm0, and a line pressure of 2 kgZcm was applied for 10 minutes to evaluate the presence or absence of penetration of carbon fiber into the separator. No penetration was found.

By the method described in Example 2, those woven of carbon fiber in the reticulated Niggeru fine line as a working electrode, metallic lithium as a counter electrode and a reference electrode, using a 1 ML i C 1 0 ₄ propylene carbonate in the electrolyte, A three-pole beaker-type liquid cell was prepared. Using this cell was charged to 0 V to the reference electrode at a constant current of carbon by weight per 1 0 OmA / g (V s L i T / L i) ( doped with lithium ions), 2 0 minutes after cessation same Then, the battery was discharged (de-doped) to 1.5 V (V s L i + Z L i) to charge and discharge, and the discharge capacity was determined.

 The discharge capacity was 350 mAhZg, and the value was the same as the value when the PVDF polymer was not glued. No decrease in the discharge capacity due to the gluing was observed.

 When the carbon fiber was used as it was without gluing, the discharge capacity was 351 mAhZg, but when the presence or absence of penetration into the separator was evaluated, the carbon fiber was found in 10 to 15 places. Was found to penetrate the separator.

Example 4

 (1) Creating electrodes

Commercially available PAN-based carbon fiber "Treiki" T-300 (manufactured by Toray Industries, Inc.) 20 mg is arranged in a uniaxial direction, and the end is a nickel fine wire (diameter 100 τη) perpendicular to the fiber arrangement axis. Weave them together and bundle them as shown in Fig. 3. The weight ratio between the carbon fiber and the fine metal wire is 100: 1. (2) Charging evaluation

 The charging evaluation was performed using the electrodes. The electrolyte was evaluated in a three-electrode liquid cell using propylene carbonate containing 1 M lithium perchlorate and lithium metal foil for the counter and reference electrodes. The battery was charged to O V (vs. Li ^ / Li) at a current density of 40 niA / g per carbon fiber weight. The voltage returned after a 20-minute pause, the so-called overvoltage, was 10 mV.

Example 5

 (1) Creating electrodes

 20 mg of commercially available PAN-based carbon fiber “Treca” T-130 (manufactured by Toray Industries, Inc.) is arranged in a uniaxial direction, and the end of the carbon fiber is meshed with a nickel fine wire (see FIG. 4). Weaved using diameter 20 β τη). The weight ratio between the carbon fiber and the fine metal wire is 100: 1.

 (2) Charging evaluation

 Using the above-mentioned electrodes, charging was evaluated in the same manner as in Example 1. The overvoltage after charging was 0.5raV.

Example 6

The carbon fibers glued with PVDF polymer described in Example 3 a negative electrode, a LiCoO ₂ / artificial graphite / PVDF Example 2 Symbol placement as a positive electrode, a polypropylene porous film ( "Cell Guard"# 2 5 0 0) The coin-type secondary battery was created by overlapping the positive electrode and the negative electrode through Separet. As the electrolytic solution was used 1ML i C 1 0 ₄ propylene carbonate sulfonate.

 100 coin-type rechargeable batteries were prepared and subjected to a charge / discharge test. In each case, all of them worked normally without occurrence of defective products such as short circuits.

Example 7

 (1) Preparation and charge / discharge of carbon fiber electrode

Commercially available PAN-based carbon fiber "Treiki" M40 (manufactured by Toray Industries, Inc.) is bundled with a Ni current collector, and this is used as the working electrode. Metal lithium is used as the counter electrode and reference electrode, and MLiCIO is used as the electrolyte. ₄ / A beaker type cell was prepared using propylene carbonate.

In this cell, after doping lithium ions up to OV (vs. Li + no Li) with respect to the reference electrode at a current of lOOraA / g per carbon weight, similarly, 1.5 V (.Li ¹ / L The charge / discharge was completed by undoping until i).

 (2) Preparation and evaluation of secondary batteries

The carbon fiber that has been charged and discharged in advance in (1) above is used as the Ni mesh of the current collector. And a positive electrode prepared by the method described in Example 4 via a separator to form a carp cell. As the electrolyte, prodylene carbonate containing 1 M lithium perchlorate was used. When this battery was charged and discharged, the Coulomb efficiency was 96%, and the initial capacity loss was reduced from 3 OmAh g when no treatment was performed to 5 mAhZg by charging and discharging in advance.

 Industrial applicability

 According to the present invention, in a chargeable / dischargeable secondary battery using a carbon material capable of doping and undoping lithium ions as a negative electrode active material, an electrode in which carbon fibers are unidirectionally arranged, By using an electrode composed of a conductive foil or a fiber, a high-capacity, high-output secondary battery can be provided.

Claims

Claim scope  1. An electrode using a carbon fiber unidirectional array.  2. The electrode according to claim 1, wherein the unidirectional array is sheet-shaped. 3. The electrode according to claim 1, wherein the direction array is arranged on a metal foil.  4. The electrode according to claim 3, wherein the electrode is wound, and the arrangement direction is substantially perpendicular to the winding direction.  5. The electrode according to claim 3, wherein the electrode is wound, and the arrangement direction is substantially parallel to the winding direction.  6. The electrode according to claim 3, wherein the metal foil is a copper foil.  7. The electrode according to any one of claims 1 to 2, wherein the carbon fibers are arranged in an axial direction, and an electric conduction wire is arranged in a direction parallel or perpendicular to the fiber axial direction. 8. The electrode according to any one of claims 1 to 7, wherein the carbon fiber is glued with a resin.  9. The electrode according to claim 8, wherein the resin is thermoplastic.  10. The electrode according to claim 8, wherein the resin is a thermosetting resin.  11. The electrode according to any one of claims 8 to 10, wherein the resin is in a range of 3% by weight or more and 17% by weight or less of the carbon fiber.  12. The electrode according to any one of claims 8 to 11, wherein the resin is in a range of 5% by weight or more and 10% by weight or less of the carbon fiber.  13. The electrode according to any one of claims 8 to 12, wherein the resin is polyvinylidene fluoride.  14. The electrode according to any one of claims 1 to 13, wherein a carbon fiber which has been charged and discharged in advance is used as an active material.  15. The electrode according to any one of claims 1 to 14, wherein the electrode is used as a negative electrode.  16. A secondary battery using the electrode according to any one of claims 1 to 15.  17. The secondary battery according to claim 16, wherein a nonaqueous electrolyte containing a lithium salt and a positive electrode through which lithium can be taken in and out are used. '  18. The secondary battery according to claim 16, wherein a transition metal oxide is used for the positive electrode. 19. The transition metal oxide, L i C 00 ₂ or L i N i 0 ₂ a is claim 16 19. The secondary battery according to any one of 18.  20. 'Electrode made of carbon fiber sheet and electrically conductive foil.  21. The electrode according to claim 20, wherein the carbon fiber sheet is a woven fabric. 22. The electrode according to claim 20 or claim 21, wherein the electrically conductive foil is a metal foil.  23. The electrode according to claim 22, wherein the metal foil is a copper foil. 24. The electrode according to claims 20 to 23, wherein the weight of the carbon fiber is 30 gZm ² or more and 200 g / m ² or less. 25. carbon weight of carbon fiber is 50 g / m or more, according to claim 20 to 24, wherein the electrodes to feature that is 150 gZm ² below.  26. The electrode according to any one of claims 20 to 25, wherein the carbon fiber is glued with a resin.  27. The electrode according to claim 26, wherein the resin ranges from 3% by weight to 17% by weight of the carbon fiber.  28. The electrode according to claim 26 or claim 27, wherein the resin is polyvinylidene fluoride.  29. A secondary battery using the electrode according to any one of claims 20 to 28.  30. The secondary battery according to claim 29, wherein a non-aqueous electrolyte containing a lithium salt and a positive electrode capable of taking lithium in and out are used.  31. The secondary battery according to claim 29, wherein a transition metal oxide is used for the positive electrode. 32. The transition metal oxide, L i C o 0 ₂ or secondary battery according to any one of L i N i 0 ₂ a is claim 29-31.