JP2008235169A - Non-aqueous electrolyte system electrochemical device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a non-aqueous electrolyte system electrochemical device having a high energy density and superior in output characteristics of high discharge rate. <P>SOLUTION: The non-aqueous electrolyte system electrochemical device comprises a positive electrode 8 having an active carbon as a main component, a negative electrode 12 having a carbon material as a main component in which lithium is stored beforehand by a chemical method or an electrochemical method in the carbon material capable of storing and releasing lithium ion, and an organic solvent system electrolytic liquid containing electrolyte made of lithium salt. The carbon material of the negative electrode main component is made of two components of an easy graphitized carbon and a hard graphitized carbon and the weight ratio of the hard graphitized carbon material included in the carbon material is 3.3-33.3%. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a non-aqueous electrolyte based electrochemical device such as a hybrid capacitor.

  Chargeable / dischargeable power sources that use organic solvent electrolytes include electric double layer capacitors and lithium ion secondary batteries. Recently, hybrids that combine the positive electrode of an electric double layer capacitor and the negative electrode of a lithium ion secondary battery. Capacitors are also known. An electric double layer capacitor is an electrochemical device that accumulates and uses charges in the electric double layer formed at the interface between the polarizable electrode and the ion conductive electrolyte by using activated carbon for both the positive and negative electrodes as the polarizable electrode. It is. In an electric double layer capacitor, the withstand voltage of a single electric double layer capacitor is 1.2 V when an aqueous electrolyte is used, and when an organic electrolyte is used, although it depends on the choice of solvent and electrolyte of the electrolyte used. It has a withstand voltage of 2.7V. In this case, in order to realize an electric double layer capacitor having a larger energy capacity, it is necessary to further increase the withstand voltage of the electric double layer capacitor.

  A lithium secondary battery is composed of a positive electrode mainly composed of a lithium-containing transition metal oxide, a negative electrode mainly composed of a carbon material capable of absorbing and desorbing lithium ions, and an organic electrolyte containing a lithium salt. Lithium ions are desorbed from the positive electrode and stored in the negative electrode carbon material, lithium ions are desorbed from the negative electrode by discharge, and lithium ions are stored in the positive electrode. A lithium ion secondary battery has properties of high voltage and high capacity compared to an electric double layer capacitor, but has high resistance and has a life due to a charge / discharge cycle.

  In recent years, hybrid type capacitors using activated carbon for the positive electrode and a carbon material capable of inserting and extracting lithium ions for the negative electrode have been studied. Since the negative electrode is associated with a lithium ion insertion / desorption reaction, it moves at a base potential closer to that of lithium metal. Therefore, it is possible to increase the withstand voltage compared to the conventional electric double layer capacitor using activated carbon for the positive electrode and negative electrode. High energy can be achieved.

  Since the hybrid capacitor can achieve higher energy than the electric double layer capacitor, its application to a new application such as an uninterruptible power supply as an energy source for driving a motor such as an electric vehicle or an energy regeneration system has been studied. Capacitors are highly expected as next-generation devices.

  As a hybrid capacitor technology, Patent Document 1 proposes a secondary battery using a positive electrode mainly composed of activated carbon and a negative electrode composed of a carbon material body in which lithium is previously occluded in an easily graphitizable carbon material. A hybrid capacitor using an easily graphitized carbon material can be increased in energy because the negative electrode exhibits a more basic potential behavior, but has a problem in that it has poor discharge rate characteristics. Further, Patent Document 2 discloses a patent using non-graphitizable carbon as a negative electrode material. The main component is a polyacene organic semiconductor composed of a polyacene skeleton structure by subjecting a negative electrode to a thermal condensation reaction of a phenolic resin in an inert gas atmosphere. A non-aqueous electrolyte secondary battery using a negative electrode is proposed. Polyacene has an amorphous structure, so there is no structural change such as expansion / contraction due to insertion / extraction of lithium ions, and it has excellent cycle characteristics, and isotropic molecular structure for insertion / extraction of lithium ions Therefore, it has excellent characteristics for rapid charge and rapid discharge, but the potential of the negative electrode changes significantly with discharge. Therefore, in order to achieve high energy when used for hybrid capacitors, the doping amount of lithium is limited to the limit. There is a problem that it must be raised. When lithium is doped to the limit, there is a problem that an internal short circuit occurs through the separator due to generation of dentlite (moss-like lithium crystal) by repeated charge and discharge.

JP-A 64-14882 International Publication WO2004 / 056772 Pamphlet

  Therefore, an object of the present invention is to provide a non-aqueous electrolyte-based electrochemical device having high energy characteristics and excellent discharge rate characteristics.

  The non-aqueous electrolyte system electrochemical device of the present invention includes a positive electrode mainly composed of activated carbon, and a carbon material in which lithium is occluded in advance by a chemical method or an electrochemical method in a carbon material that can occlude and desorb lithium ions. In a non-aqueous electrolyte-based electrochemical device having a negative electrode mainly comprising a lithium salt and an organic solvent-based electrolyte containing an electrolyte comprising a lithium salt, the carbon material of the negative electrode is composed of graphitizable carbon and non-graphitizable carbon. The weight ratio of the non-graphitizable carbon material contained in the carbon material is preferably 3.3 to 33.3%, and the non-graphitizable carbon is obtained by an X-ray wide angle diffraction method. (002) plane spacing of 0.341 to 0.390 nm and at least one selected from amorphous carbon materials having a c-axis direction crystallite size (Lc) of 0.5 to 18 nm. Yes and easy graphite Carbon was selected from highly crystalline carbon materials having a (002) plane spacing of 0.340 nm or less and a c-axis direction crystallite size (Lc) of 20 to 230 nm by X-ray wide angle diffraction. It is good that there is at least one kind.

  In the present invention, activated carbon is used as the positive electrode carbon material, and a mixture of easily graphitizable carbon and non-graphitizable carbon is used as the negative electrode carbon material that absorbs and desorbs lithium ions, and includes an electrolyte made of a lithium salt. By using the organic solvent-based electrolytic solution, it is possible to provide a non-aqueous electrolyte-based electrochemical device that has high energy density and excellent output characteristics at a high discharge rate.

  Embodiments of the present invention will be described below. First, with reference to the drawings, the structure of a non-aqueous electrolyte based electrochemical device in one embodiment of the present invention will be described.

  FIG. 1 shows a non-aqueous electrolyte type electrochemical device (hybrid capacitor) according to an embodiment of the present invention, FIG. 1 (a) is a plan view thereof, FIG. 1 (b) is a front view thereof, and FIG. ) Is a front sectional view. 1 is a hybrid capacitor, 2 is a negative electrode lead plate for external extraction, 3 is a positive electrode lead plate for external extraction, 4 is an exterior film, 5 is an electrode laminate, 8 is a positive electrode, 9 is a separator, and 12 is a negative electrode is there.

  6 shows an electrode laminate 5 according to the present invention, FIG. 6 (a) is a plan view thereof, and FIG. 6 (b) is a perspective view thereof.

  As shown in FIG. 1 (c), the hybrid capacitor is connected to the electrode laminate 5 having a plurality of electrode plates and the exterior film 4 containing the electrolytic solution and the electrode laminate 5 and protrudes outside the exterior film 4. Positive electrode lead plate 3 and negative electrode lead plate 2. The exterior film 4 is formed of, for example, a bag made of a composite film with a metal foil having a thermoplastic resin disposed on the inner surface, and includes an electrode laminate 5 and an electrolyte made of a lithium salt therein. After containing the organic solvent electrolyte, it is sealed in a vacuum atmosphere.

  The perspective view of the electrode laminated body 5 accommodated in the exterior film 4 is as FIG.6 (b). The electrode laminate 5 has a positive electrode 8, a negative electrode 12, and a separator 9, and is laminated with a separator-negative electrode plate-separator-positive electrode plate-separator so that the outer side becomes the separator 9.

  Next, the manufacturing method of the positive electrode used for this electrode laminated body, a negative electrode, and a separator is demonstrated.

The positive electrode is obtained by integrating a current collector made of aluminum foil, nickel foil, or the like and an active material mainly composed of a carbon material. Carbon materials include plant materials such as wood, sawdust, coconut husk and pulp waste liquid, coal, heavy petroleum oil, or coal-based and petroleum-based pitches obtained by pyrolyzing them, petroleum coke, carbon aerogel, tar Various materials such as fossil fuel-based materials such as pitch, synthetic polymer materials such as phenolic resin, polyvinyl chloride resin, and polyvinylidene chloride are used. After carbonizing these raw materials, they were activated by gas activation method or chemical activation method. Activated carbon having a specific surface area of 700 to 3000 m ² / g (preferably 1500 to 2500 m ² / g) is used. As the conductive agent, carbon black such as acetylene black and ketjen black, natural graphite, and thermally expanded graphite carbon fiber are preferable, and it is more preferable to add about 5 to 30% by weight.

  As the binder material, polytetrafluoroethylene, polyvinylidene fluoride, fluoroolefin copolymer cross-linked polymer, polyvinyl alcohol, or the like is used, and it is preferable that the binder material is prepared by including about 3 to 20% by weight of the binder. Ethylene is preferred from the viewpoints of heat resistance, chemical resistance and sheet strength.

  On the other hand, the negative electrode is obtained by integrating a current collector made of copper foil or nickel foil and an active material. The active material is formed by adding a conductive agent and a binder to the main carbon material. As carbon materials that can be doped and dedoped with lithium ions, graphitizable carbon and non-graphitizable carbon (by weight ratio to the carbon material). 3.3 to 33.3%) is used.

  For this non-graphitizable carbon, phenol formaldehyde resin charcoal, furfuryl alcohol resin charcoal, carbon black, vinylidene chloride charcoal, cellulose charcoal, etc. are used. For graphitizable carbon, pitch coke, mesocarbon microbeads, needle coke, Bulk mesophase, fluid coke, gilsonite coke and the like can be used.

Further, according to X-ray analysis, non-graphitizable carbon has a (002) plane spacing d ₀₀₂ of 0.341 to 0.390 nm by the X-ray wide angle diffraction method, and the crystallite size in the c-axis direction ( Lc) can be an amorphous carbon material having a thickness of 0.5 to 18 nm, and graphitizable carbon has an (002) plane spacing d ₀₀₂ of 0.340 nm or less by X-ray wide angle diffraction method. A highly crystalline carbon material having a crystallite size (Lc) in the c-axis direction of 20 to 230 nm can be obtained. Furthermore, you may use 2 or more types as non-graphitizable carbon and graphitizable carbon, respectively.

  As the conductive agent, carbon black such as acetylene black and ketjen black, natural graphite, and thermally expanded graphite carbon fiber are preferable, and it is more preferable to add about 5 to 30% by weight.

  In addition, as the binder, polytetrafluoroethylene, polyvinylidene fluoride, fluoroolefin copolymer cross-linked polymer, polyvinyl alcohol, polybutadiene rubber, styrene-butadiene rubber, or the like is used. In particular, polyvinylidene fluoride is preferable from the viewpoints of heat resistance, chemical resistance, and sheet strength.

  The separator is preferably made of a material having a small thickness and high electronic insulation and ion permeability, and is not particularly limited. For example, a nonwoven fabric such as polyethylene or polypropylene, or papermaking of viscose rayon or natural cellulose is used. Preferably used.

  Next, the manufacturing method of an electrode laminated body is demonstrated with reference to drawings.

  FIG. 2 shows a positive electrode and a negative electrode according to the present invention. 2 (a) is a plan view of the positive electrode, FIG. 2 (b) is a plan view of the negative electrode after lithium metal pressure bonding, 6 is a positive lead terminal, 7 is an active material (positive electrode), 8 is a positive electrode, 10 Is a negative electrode lead terminal, 11 is an active material (negative electrode), 12 is a negative electrode, and 13 is lithium metal.

  FIG. 3 is a plan view of the separator 9 according to the present invention.

  FIG. 4 is a plan view showing a separator / positive electrode / separator set according to the present invention, wherein 8 is a positive electrode and 9 is a separator.

  FIG. 5 is a plan view showing a set of a negative electrode (lithium metal crimped) / separator / positive electrode / separator according to the present invention, wherein 9 is a separator and 12 is a negative electrode.

  First, a positive electrode as shown in FIG. 2A and a lithium metal pressure-bonded negative electrode as shown in FIG. 2B are prepared. At this time, the method of occluding lithium in the negative electrode is performed by a chemical method or an electrochemical method by pressing a lithium metal on the negative electrode according to a known technique. Next, using the separator as shown in FIG. 3, a separator / positive electrode / separator set as shown in FIG. 4 was prepared. Further, as shown in FIG. 5, the negative electrode (lithium metal crimped) / separator / positive electrode / A set of separators is produced to obtain an electrode laminate.

  Henceforth, the manufacturing method of the nonaqueous electrolyte system electrochemical device of this Embodiment is as having already demonstrated.

  Examples and comparative examples are shown below to further clarify the features of the present invention.

(Example 1) KOH activated charcoal having a specific surface area of 2500 m ² / g and carbon black were mixed at a weight ratio of 80:10, and this mixed powder was dissolved in N-methylpyrrolidone as a binder (polyvinylidene fluoride (mixed powder: binder). = 90:10) and kneaded to obtain a slurry. Next, the slurry was uniformly applied to an etched aluminum foil having a thickness of 30 μm. Thereafter, drying and rolling were performed to obtain a positive electrode sheet having a coating thickness of 100 μm. One positive electrode was cut out from the electrode obtained above so that the portion where the active material was applied was 36.5 mm × 40 mm.

Negative electrode active material of natural graphite (d ₀₀₂ : 0.335 nm, Lc: 229.1 nm) as a graphitizable carbon material and carbotron P (d ₀₀₂ : 0.38 nm, Lc: 1.1 nm) as a non-graphitizable carbon material Powder (Carbotron is a registered trademark) is mixed at a weight ratio of 80:10, then negative electrode active material powder and conductive agent carbon black are mixed at a weight ratio of 90: 5, and N-methylpyrrolidone is used as a binder in this mixed powder. Polyvinylidene fluoride dissolved in (mixed powder: binder = 95: 5) was added and kneaded to obtain a slurry.

  Next, the slurry was uniformly applied to a copper foil having a thickness of 15 μm. Then, the negative electrode sheet with a coating thickness of 35 μm was obtained by drying and rolling. The negative electrode was cut out from the electrode obtained above so that the portion coated with the active material was 38 mm × 42 mm. Next, a lithium metal foil having a thickness of 40 μm was cut out to 20 mm × 23 mm, and this lithium foil was pressure-bonded to the negative electrode.

  The negative electrode lead terminal produced as described above and the negative electrode lead plate protruding outside the exterior film were collectively ultrasonically welded. Similarly, the positive electrode lead terminal and the positive electrode lead plate protruding outside the exterior film were collectively ultrasonically welded.

The electrode laminate thus obtained was housed in an exterior film, and then an electrolyte solution was injected. As the electrolytic solution, an electrolytic solution in which LiPF ₆ was added to a solvent in which ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 1: 1 so as to have a concentration of 1 mol / l was used. After injecting the electrolyte, the outer package was sealed in a vacuum atmosphere. Lithium metal disposed on the negative electrode was ionized by electrical contact and taken into the negative electrode. It was confirmed in a system in which a lithium metal reference electrode was inserted instead of the positive electrode that lithium was occluded in the negative electrode. As a result, a multilayer hybrid capacitor (non-aqueous electrolyte based electrochemical device) was obtained.

(Example 2) In Example 1, in place of 80% by weight of natural graphite and 10% by weight of non-graphitizable carbon material, 70% by weight of natural graphite and 20% by weight of non-graphitizable carbon material were used. Thus, a laminate type non-aqueous electrolyte type electrochemical capacitor was assembled.

(Example 3) In Example 1, instead of 80% by weight of natural graphite and 10% by weight of non-graphitizable carbon material, 65% by weight of natural graphite and 25% by weight of non-graphitizable carbon material were used. Thus, a laminate type non-aqueous electrolyte type electrochemical capacitor was assembled.

(Example 4) In Example 1, in place of 80% by weight of natural graphite and 10% by weight of non-graphitizable carbon material, 87% by weight of natural graphite and 3% by weight of non-graphitizable carbon material were used. Thus, a laminate type non-aqueous electrolyte type electrochemical capacitor was assembled.

(Example 5) In Example 1, instead of natural graphite 80% by weight and non-graphitizable carbon material 10% by weight, natural graphite 60% by weight and non-graphitizable carbon material 30% by weight were used. Thus, a laminate type non-aqueous electrolyte type electrochemical capacitor was assembled.

(Comparative Example 1) In Example 1, a laminate type non-aqueous electrolyte system was used in the same manner as in Example 1 except that 90% by weight of natural graphite was used instead of 80% by weight of natural graphite and 10% by weight of non-graphitizable carbon material. An electrochemical capacitor was assembled.

(Comparative Example 2) In Example 1, instead of the natural graphite 80% by weight and the non-graphitizable carbon material 10% by weight, the non-graphitizable carbon material 90% by weight was used in the same manner as in Example 1, and the laminate type non-water An electrolyte-based electrochemical capacitor was assembled.

  The non-aqueous electrolyte-based electrochemical capacitors obtained in Examples 1 to 5 and Comparative Examples 1 and 2 were measured for capacitance, withstand voltage, direct current resistance, and rate characteristics. At this time, the battery was charged to a working voltage with a constant current, charged with a constant voltage for 30 minutes, and then charged to 2.2 V with a predetermined current. The electrostatic capacity (F) was calculated in terms of F (capacitance conversion) from the discharge current capacity (mAh), and the DC resistance was calculated from the initial IR drop. The results are shown in Table 1. In addition, the change rate (corresponding to the rate characteristic) with respect to the capacitance at the discharge rate 1C is appended to the capacitance at the discharge rates 10C and 20C.

  From the results of Table 1, Examples 1 to 3 of the non-aqueous electrolyte based electrochemical capacitor according to the present invention have the same high capacity and high breakdown voltage as Comparative Example 1, and the same DC resistance and rate as Comparative Example 2. Results with characteristics are obtained. This is because the lithium ions occluded in the non-graphitizable carbon preferentially desorb during discharge, and the rate characteristics are excellent, and the graphitized carbon with little potential behavior against lithium desorption generally lowers the negative electrode potential. Therefore, the change in the negative electrode potential behavior during discharge is small, and it is considered that a high capacity and high breakdown voltage result was obtained.

  In Example 4, in which the blending ratio of the non-graphitizable carbon is 3.3%, compared with Examples 1 to 3, the direct current resistance is large and the rate characteristics are lowered, which is a practical lower limit. Moreover, Example 5 which made the compounding ratio of non-graphitizable carbon 33.3% becomes small compared with Examples 1-3, and becomes a practical upper limit. When further high characteristics are required, the blending ratio of non-graphitizable carbon is preferably about 5 to 30%.

  From the above results, by implementing the present invention, it has become possible to produce a multilayer hybrid capacitor product having a high breakdown voltage, a high capacity, and excellent rate characteristics.

BRIEF DESCRIPTION OF THE DRAWINGS The non-aqueous-electrolyte type electrochemical device by one embodiment of this invention is shown, FIG. 1 (a) is the top view, FIG.1 (b) is a front view, FIG.1 (c) is a front sectional view. The positive electrode and negative electrode which concern on this invention are shown, Fig.2 (a) is a top view of a positive electrode, FIG.2 (b) is a top view of the lithium metal crimped negative electrode. The top view of the separator which concerns on this invention. The top view which shows the set of the separator / positive electrode / separator which concerns on this invention. The top view which shows the set of the negative electrode (lithium metal crimping completion | finish) / separator / positive electrode / separator which concerns on this invention. The electrode laminated body which concerns on this invention is shown, Fig.6 (a) is the top view, FIG.6 (b) is the perspective view.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Hybrid capacitor 2 Negative electrode lead board 3 Positive electrode lead board 4 Outer film 5 Electrode laminated body 6 Positive electrode lead terminal 7,11 Active material 8 Positive electrode 9 Separator 10 Negative electrode lead terminal 12 Negative electrode 13 Lithium metal

Claims (3)

  A positive electrode mainly composed of activated carbon, a negative electrode mainly composed of a carbon material in which lithium is occluded and desorbed in advance by a chemical method or an electrochemical method, and an electrolyte comprising a lithium salt. And a non-aqueous electrolyte-based electrochemical device having an organic solvent-based electrolyte containing the non-aqueous electrolyte, wherein the carbon material as a main component of the negative electrode comprises two components of graphitizable carbon and non-graphitizable carbon Electrolyte electrochemical device.   2. The non-aqueous electrolyte electrochemical device according to claim 1, wherein a weight ratio of the non-graphitizable carbon contained in the carbon material is 3.3 to 33.3%.   The non-graphitizable carbon has a (002) plane spacing of 0.341 to 0.390 nm and a crystallite size (Lc) in the c-axis direction of 0.5 to 18 nm according to the X-ray wide angle diffraction method. It is at least one selected from amorphous carbon materials, and the graphitizable carbon has a (002) plane spacing of 0.340 nm or less by X-ray wide angle diffraction method, and a crystallite in the c-axis direction. 3. The non-aqueous electrolyte based electrochemical device according to claim 1, wherein the electrochemical device is at least one selected from highly crystalline carbon materials having a size (Lc) of 20 to 230 nm.

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