JP2007299855A - Stacked electrochemical device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a compact stacked electrochemical device excellent in electric characteristic and reliability. <P>SOLUTION: A positive electrode plate and a negative electrode plate are stacked via a separator sheet, and part of an outer periphery of the separator sheet is stuck to the positive electrode plate and the negative electrode plate. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a multilayer electrochemical device in which a plurality of electrode plates such as an electric double layer capacitor and a lithium secondary battery are stacked via a separator.

  An electric double layer capacitor is a capacitor that uses an electric double layer generated at the interface between a polarizable electrode and an electrolyte to accumulate electric charge. The electric double layer has a very small thickness of several nanometers and is similar to activated carbon. A large capacity has been realized by using a material having a large specific surface area for a polarizable electrode (hereinafter also referred to as an active material). Electric double layer capacitors do not use hazardous materials such as heavy metals in their constituent materials, so there is no risk of environmental contamination, and because they do not involve chemical reactions like secondary batteries, they have excellent charge / discharge cycle life. There is a feature such as. For this reason, electric double layer capacitors have come to be widely used as backup power sources for microcomputers and memories as an alternative device for secondary batteries.

  In recent years, taking advantage of the characteristics of the electric double layer capacitor, new applications such as an energy source for driving a motor such as an electric vehicle or an energy regeneration system and an uninterruptible power supply device have been studied, and an electric double layer capacitor is expected. Conventionally, as a backup power source for memories, etc., an electric double layer capacitor with a rolled electrode plate or separator is mainly used. A multilayer electric double layer capacitor in which these electrode plates are laminated is suitable.

  Many devices have been devised in multilayer electrochemical devices such as electric double layer capacitors in which electrode plates are laminated. Their purpose is to cause the positive electrode and the negative electrode to be accurately stacked through the separator without generating a useless space in the case as much as possible.

  For example, as disclosed in Patent Document 1, a technique is disclosed in which electrodes and separators are folded in a folding screen and stored in an outer case. Patent Document 2 describes a technique in which a resin separator such as polyethylene is formed in a bag shape and an electrode plate is accommodated therein.

Japanese Patent Laid-Open No. 3-1455 Japanese Patent Publication No.62-31786

  However, in a stacked electrochemical device, when the electrodes and separators are in a folding screen, in order to avoid current bias in the bent part of the electrode, a part where there is no active material and a part where there is an active material Must be manufactured alternately and regularly on the positive and negative electrode substrates, which is very difficult to manufacture.

  In addition, in the case where the resin separator is made into a bag shape and the electrode is accommodated therein, if the lamination is performed after forming a bag-like separator that accommodates the electrode by heat-sealing and bonding the periphery of the electrode, the laminating displacement is caused. However, since a resin-based separator such as polyethylene or polypropylene is thermally fused by heating, fusion wrinkles are generated, and the distance between the electrodes is increased by the wrinkles, thereby deteriorating electrical characteristics. Furthermore, since the surroundings are heat-sealed and joined, there is a space that does not contribute to the capacity, and the capacity value per volume is reduced.

  The present invention has been made to solve the above-described problems, and in particular, an object of the present invention is to provide a stacked electrochemical device having excellent characteristics by devising the connection between an electrode and a separator sheet.

  In order to solve the above-mentioned problems, in the multilayer electrochemical device of the present invention, a positive electrode plate and a negative electrode plate are laminated via a separator sheet, and a part of the outer periphery of the separator sheet is the positive electrode plate and / or the negative electrode plate. It is connected with.

  Further, a part of the outer peripheral portion of the separator sheet may be bonded to the positive electrode plate and / or the negative electrode plate with a thermoplastic resin.

  In the present invention, since a part of the outer peripheral portion of the separator sheet is bonded to the positive electrode plate and / or the negative electrode plate, it is possible to use a separator made of an inexpensive material without causing wrinkles in the separator, and at a low cost. A stacked electrical device with good characteristics and high reliability can be provided.

  Further, in the electric double layer capacitor, it is possible to use a separator made of inexpensive natural cellulose, and it is possible to provide a highly reliable product with good ESR, capacitance, and self-discharge characteristics.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a diagram for explaining a multilayer electric double layer capacitor according to an embodiment of the present invention. FIG. 1 (a) is a plan view, FIG. 1 (b) is a side view, and FIG. is there. As shown in FIG. 1, the multilayer electric double layer capacitor 4 is connected to an electrode laminate 5 having an electrode plate composed of a plurality of positive and negative plates, an exterior film 3 containing an electrolytic solution, and the electrode laminate 5. And a positive electrode lead plate 2 and a negative electrode lead plate 1 that protrude to the outside of the exterior film 3. The exterior film 3 is formed of, for example, a sheet made of a composite film with a metal foil that disposes a thermoplastic resin on the inner surface, and the electrode laminate 5 and the electrolytic solution are accommodated therein. Sealed in a vacuum atmosphere. The electrode laminate 5 is formed by alternately laminating positive and negative plates through separator sheets.

  FIG. 2 is a plan view showing the positive electrode plate of the present invention. The positive electrode plate 8 has an active material 7 coated portion and an active material formed on a rectangular current collector portion of a current collector from which a protrusion located diagonally to the positive electrode lead terminal 6 and the positive electrode lead terminal is drawn. The positive electrode lead terminal 6 and the positive electrode lead terminal which are not formed are formed with a protrusion positioned diagonally to the positive electrode lead terminal 6, and the separator sheet is bonded to the lead portion of the positive electrode lead terminal 6 and the protrusion positioned diagonally to the positive electrode lead terminal. For this purpose, an adhesive material, for example, a thermoplastic resin 9 is formed.

FIG. 3 is a plan view showing the negative electrode plate of the present invention. The negative electrode plate 11 includes a negative electrode lead terminal 12 and a negative electrode lead terminal, and an active material 10 formed on a rectangular current collector portion of a current collector from which a protrusion located diagonally is drawn, and a negative electrode on which no active material is formed The lead terminal 12 and the negative electrode lead terminal are formed with protrusions positioned diagonally, and the lead-out portion of the negative electrode lead terminal 12 and the protrusions positioned diagonally with the negative electrode lead terminal are heat for bonding with the separator sheet. A plastic resin 9 is formed. In the case of an electric double layer capacitor, the negative electrode plate can be made of the same material as the positive electrode plate. As the positive electrode plate and the negative electrode plate, those obtained by integrating a current collector made of an aluminum foil or a nickel foil and an active material (polarizable electrode) mainly composed of a carbon material can be used as in the conventional case. Carbon materials include plant materials such as wood, sawdust, coconut husk and pulp waste, 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. a specific surface area of 700~3000m ² / g, in particular 1000 to 2000 ² / g are preferred. 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 a binder. Ethylene is preferred from the viewpoints of heat resistance, chemical resistance and sheet strength.

  Next, an example of a method for manufacturing the positive electrode plate and the negative electrode plate will be described. An activated carbon powder carbonized and activated with phenol resin and carbon black are kneaded with a binder, and then rolled to form a sheet. The obtained sheet is bonded to a roughened current collector foil such as aluminum or nickel using a conductive carbon paste. Furthermore, it integrates by heat-drying and makes this a positive electrode plate or a negative electrode plate. The positive electrode plate or the negative electrode plate may be produced by a method in which an active material and a current collector are overlapped and rolled to bond them together. The active material may be bonded to one side of the current collector or may be bonded to both sides. Alternatively, a positive electrode plate or a negative electrode plate can be produced by dispersing a carbon material in a solution in which a binder such as methyl cellulose or polyvinylidene fluoride is dissolved in a solvent to form a slurry, and coating the slurry on one or both sides of the current collector. Good.

  In the case of a lithium secondary battery, a combination of an electrolyte and an electrode can be appropriately selected from known ones and used. Preferably, a gel electrolyte and an electrode active material, and if necessary, a conductive agent integrated with a binder may be used. Usually, a negative electrode active material such as a carbon material, lithium metal, a lithium alloy, or an oxide material is used for the negative electrode, and a positive electrode active material such as an oxide capable of intercalating lithium ions or a carbon material is used for the positive electrode. Used.

  The positive electrode plate is produced by applying a positive electrode active material and, if necessary, a slurry in which a conductive agent and a binder are dispersed in a solution to a current collector such as aluminum. The negative electrode plate is produced by applying a slurry in which a negative electrode active material and, if necessary, a conductive agent and a binder are dispersed in a solution, to a current collector such as copper or nickel.

  In the case of an electric double layer capacitor, the separator sheet is preferably a material having a small thickness and a high electronic insulation and ion permeability, and is not particularly limited. For example, a nonwoven fabric such as polyethylene or polypropylene, or Viscose rayon, natural cellulose paper, and the like are preferably used. It is preferable to select a material according to the electrochemical device. For example, in the case of a lithium secondary battery, one or more types of polyolefins such as polyethylene and polypropylene, or two or more types (in the case of two or more types, such as a laminate of two or more layers), polyethylene terephthalate, etc. Polyesters, thermoplastic fluororesins such as ethylene-tetrafluoroethylene copolymer, and celluloses are employed.

  The adhesive material for bonding to the separator sheet, which is formed on the current collector of each of the positive electrode plate and the negative electrode plate, is not particularly limited, and is a thermosetting resin such as an epoxy resin or a silicone resin used as an adhesive. However, when a thermoplastic resin is used, a material having high solvent resistance and high adhesion to metals and resins is preferable. For example, polyfloprene, polyethylene, ionomer, and the like are preferably selected.

  FIG. 4 is a view in which a thermoplastic resin is formed on the positive electrode lead terminal and the positive electrode lead terminal of the positive electrode plate according to the embodiment of the present invention, and a separator sheet is set thereon. FIG. 5 is a view in which a thermoplastic resin is formed on the negative electrode lead terminal and the negative electrode lead terminal of the negative electrode plate according to the embodiment of the present invention, and a separator sheet is set thereon. As shown in FIG. 4, the thermoplastic resin covers the active material and the thermoplastic resin on the positive electrode plate on the positive electrode plate formed on the protrusions located diagonally between the positive electrode lead terminal 6 and the positive electrode lead terminal. The separator sheet 13 is placed, and the positive electrode plate and the separator sheet 13 are bonded by a thermoplastic resin at the bonding portion 16 by a heat press or the like to form the positive electrode unit 14. As for the negative electrode unit, as shown in FIG. 5, the negative electrode plate and the separator sheet 13 are bonded to each other by the thermoplastic resin formed on the protrusions located at the opposite corners of the negative electrode lead terminal 12 and the negative electrode lead terminal. The negative electrode unit 15 is formed by bonding at 16.

  FIG. 6 is a perspective view illustrating a state in which the positive electrode unit and the negative electrode unit according to the embodiment of the present invention are stacked, and FIG. 7 is a perspective view of an electrode laminate in which the positive electrode unit and the negative electrode unit according to the embodiment of the present invention are stacked. FIG. 8 is a perspective view of the electrode laminate after the positive and negative electrode lead plates of the present invention are attached. As shown in FIG. 6, the negative electrode unit 15 is stacked on the positive electrode unit 14. At that time, the positive electrode lead terminal 6 and the negative electrode lead terminal 12 are set so as not to overlap to prevent short circuit. A plurality of positive electrode units and a plurality of negative electrode units are alternately stacked to form an electrode stack 5 as shown in FIG. Here, the negative electrode unit 15 is laminated on the outside. Next, as shown in FIG. 8, the positive electrode lead terminals 6 are collectively connected to the positive electrode lead plate 2, and the negative electrode lead terminals 12 are collectively connected to the negative electrode lead plate 1. By housing the electrode laminate 5 in the exterior film 3, a multilayer electric double layer capacitor as shown in FIG. 1 is obtained. Here, the separator sheet is bonded to one side of each of the positive electrode plate and the negative electrode plate, but the separator sheet can be bonded to one side of the positive electrode plate or the negative electrode plate, and the other can be laminated without bonding the separator sheet. . Moreover, although the place to adhere | attach was made into the projection part located diagonally with the positive / negative electrode lead terminal, there is no restriction | limiting in particular in a place, the magnitude | size of an adhesion part, and the number of places, and a separator sheet should just be fixed.

  FIG. 9 is a plan view of a positive electrode unit according to a reference example. In the positive electrode unit 114 of the reference example, the positive electrode plate 108 is arranged at the substantially central portion of the bag-shaped separator 113, and the positive electrode lead terminal 106 not coated with the active material protrudes from the bag-shaped separator 113 and the three sides of the peripheral portion are thermally fused. It is worn and fixed.

  FIG. 10 is a diagram showing a state where the negative electrode plate is set on the positive electrode unit according to the reference example, FIG. 10 (a) is a plan view, and FIG. 10 (b) is a perspective view. The negative electrode plate 111 is disposed on the positive electrode unit 114 of the reference example so as to face the positive electrode plate, and the positive electrode lead terminal 106 and the negative electrode lead terminal 112 are set so as not to overlap to prevent short circuit.

  FIG. 11 is a perspective view of the electrode laminate according to the reference example, and FIG. 12 is a perspective view of the electrode laminate after the positive and negative electrode lead plates of the reference example are attached. In the case of the reference example, as in the case of FIGS. 7 and 8, the positive electrode units 114 and the negative electrode plates 111 are alternately laminated, and the positive electrode lead terminals 106 are collectively connected to the positive electrode lead plate 2. A multilayer electric double layer capacitor can be obtained by connecting 112 to the negative electrode lead plate 1 in a lump.

    Embodiments will be described below with reference to the drawings.

Example 1
Polyvinylidene fluoride having a specific surface area of 1500 m ² / g mixed with carbon black at a weight ratio of 8: 1 and dissolved in N-methylpyrrolidone as a binder (mixed powder: binder = 9: 1) And kneaded to obtain a slurry. Next, on the etched aluminum foil having a thickness of 30 μm, the lead terminal portion and the protruding portion of the protruding portion located diagonally to the lead terminal are removed, and the slurry is uniformly coated on both sides, and then dried to obtain the active material. A polarizable positive electrode plate or negative electrode plate having a thickness of 70 μm on both sides was obtained.

  Next, as shown in FIGS. 2 and 3, a polypropylene resin is thermally fused as a thermoplastic resin of an adhesive material to the positive and negative electrode lead terminals not coated with the active material and the protrusions located diagonally to the lead terminals. A positive electrode plate 8 and a negative electrode plate 11 were obtained. Next, as shown in FIGS. 4 and 5, a separator sheet 13 made of a natural cellulose material having a size covering the positive electrode plate and the negative electrode plate is placed on the positive and negative electrode lead terminals 6, 12 and diagonal positions thereof. The polypropylene resin and the separator sheet 13 provided on are bonded and fixed at the bonding portion 16 by heat-sealing by heat press, and the positive electrode unit 14 and the negative electrode unit 15 were produced.

  The positive electrode unit 14 and the negative electrode unit 15 obtained as described above were alternately stacked as shown in FIG. The outermost electrode plate is a negative electrode plate, and a separator sheet 13 is placed outside the negative electrode plate (negative electrode unit (separator sheet / negative electrode plate) / positive electrode unit / negative electrode unit /.. ./Negative electrode The electrode plate and the separator were laminated in the order of unit (separator sheet / negative electrode plate) / separator sheet).

  Next, the positive electrode lead terminal 6 and the positive electrode lead plate 2 of the stacked positive electrode unit as shown in FIG. 8 were ultrasonically welded together. Similarly, the negative electrode lead terminal 12 and the negative electrode lead plate 1 were ultrasonically welded together to obtain an electrode laminate 5 to which the positive and negative electrode lead plates were attached.

  As shown in FIG. 1, the electrode laminate 5 thus obtained was housed in the exterior film 3, and then an electrolyte solution was injected. As the electrolytic solution, an electrolytic solution prepared by dissolving tetraethylammonium tetrafluoroborate in propylene carbonate at a concentration of 0.7 mol / l was used. After injecting the electrolytic solution, the outer package was sealed in a vacuum atmosphere, and thus the multilayer electric double layer capacitor of Example 1 was produced.

(Example 2)
A multilayer electric double layer capacitor was produced in the same manner as in Example 1 except that polyethylene was used for the separator sheet.

(Comparative example)
The same active material as in Example 1 was used. As shown in FIGS. 9 to 12 shown as reference examples, the positive electrode plate is sandwiched between two separator sheets made of polyethylene, and the separators on the three surrounding sides other than the lead terminal lead-out side are heat-sealed to each other. The plate was accommodated in a bag-shaped separator 113 to produce a positive electrode unit 114. After the positive electrode unit 114 and the negative electrode plate 111 housed in the bag-like separator 113 were obtained as described above, the positive electrode unit 114 and the negative electrode plate 111 were alternately stacked. The outermost electrode plate is the negative electrode plate 111, and the separator sheet 113 is installed outside the negative electrode plate (separator sheet / negative electrode plate / positive electrode unit / negative electrode plate /.../ negative electrode plate / separator sheet). The electrode and the separator sheet were laminated in this order). A laminated electric double layer capacitor was produced in the same manner as in Example 1 except that the electrode laminate 105 was produced in this manner.

  The multilayer electric double layer capacitors produced by the methods of Example 1, Example 2, and Comparative Example were measured for ESR, capacitance, and self-discharge characteristics. These characteristics were measured after the sample was prepared and after applying a load (voltage) of 60 ° C., 2.7 V, 1,000 hours and cooling to room temperature.

  Here, the ESR was obtained by measuring and calculating the voltage across the multilayer electric double layer capacitor by passing an alternating current of 10 mA through the capacitor using a sine wave oscillator with an alternating current of 1 kHz. The electrostatic capacity was determined by calculating from the slope between 2.0 V and 1.5 V when the battery was charged at 2.7 V for 30 minutes and then discharged at a current of 100 mA. The self-discharge characteristic (SD) was obtained by charging the battery at 2.7 V for 1 hour, then opening the circuit, and measuring the voltage between the terminals after 24 hours.

  Table 1 shows average values of initial characteristics, ESR before and after voltage application, capacitance (Cap), and self-discharge characteristics (SD) of multilayer electric double layer capacitors manufactured by the methods of Example 1, Example 2, and Comparative Example. It is shown in 1. The ESR, capacitance (Cap), and self-discharge characteristics (SD) are average values of 10 samples prepared, and the capacitance is expressed as a relative value when the initial value of the comparative example is 1. did.

  From Table 1, when the ESR, capacitance, and self-discharge characteristics of Example 1 and Example 2 and Comparative Example are compared, the initial values are equivalent. When the volume of the comparative example was 1, the example was 0.92, and an excellent capacity characteristic per volume was obtained. This is because in the comparative example, there is a space that does not contribute to the capacity because the separator is thermally fused around the electrode.

  After voltage application, Example 1 has the smallest ESR increase and capacitance reduction rate, and shows a good value in self-discharge characteristics. As these factors, the natural cellulose separator can be dried at a higher temperature than the polyethylene separator, and the amount of water contained in the electrolytic solution is suppressed.

  Further, in the comparative example, in two of the ten samples, the voltage after 24 hours would be 2.0 V or less. As a result of disassembling and analyzing the inside, separator fusion wrinkles are generated, and it is considered that the electrical characteristics are deteriorated by the wrinkles. In Examples 1 and 2, when the separator sheet was fused and bonded to the positive electrode, the negative electrode and the polypropylene resin, no fusion wrinkle occurred, and in a high temperature load test at 60 ° C.-2.7 V / 1000 H. I think that good results were obtained.

  From the above results, it is possible to use an inexpensive natural cellulose material separator by bonding and fixing a part of the outer peripheral portion of the separator sheet by thermal fusion via a positive electrode plate and a negative electrode plate with a thermoplastic resin. It is excellent in volumetric efficiency and can improve reliability.

  In addition, by implementing the present invention, it was possible to produce a product having excellent reliability in the product of the multilayer electric double layer capacitor, and good results were obtained in ESR, capacitance, and self-discharge characteristics. In the present embodiment, an example of a multilayer electric double layer capacitor has been described. However, the present invention is not limited to a multilayer electric double layer capacitor and can be applied to a multilayer electrochemical device.

FIG. 1A is a plan view, FIG. 1B is a side view, and FIG. 1C is a cross-sectional view illustrating a multilayer electric double layer capacitor according to an embodiment of the present invention. The top view which shows the positive electrode plate of this invention. The top view which shows the negative electrode plate of this invention. The figure which formed the thermoplastic resin in the projection part located diagonally with the positive electrode lead terminal and positive electrode lead terminal of the positive electrode plate of embodiment of this invention, and set the separator sheet on it. The figure which formed the thermoplastic resin in the projection part located diagonally with the negative electrode lead terminal and negative electrode lead terminal of the negative electrode plate of embodiment of this invention, and set the separator sheet on it. The perspective view which shows the state which accumulated the positive electrode unit and negative electrode unit of embodiment of this invention. The perspective view of the electrode laminated body which laminated | stacked the positive electrode unit and negative electrode unit of embodiment of this invention. The perspective view of the electrode laminated body after the positive / negative electrode lead board attachment of this invention. The top view of the positive electrode unit by a reference example. The figure which shows the state which set the negative electrode plate on the positive electrode unit by a reference example, FIG. 10 (a) is a top view, FIG.10 (b) is a perspective view. The perspective view of the electrode laminated body by a reference example. The perspective view of the electrode laminated body after the positive / negative electrode lead board attachment of a reference example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Negative electrode lead board 2 Positive electrode lead board 3 Exterior film 4 Electric double layer capacitor 5,105 Electrode laminated body 6,106 Positive electrode lead terminal 7 Active material (positive electrode)
8,108 Positive electrode plate 9 Thermoplastic resin 10 Active material (negative electrode)
11, 111 Negative electrode plate 12, 112 Negative electrode lead terminal 13, 113 Separator sheet 113 Bag-like separator 14, 114 Positive electrode unit 15 Negative electrode unit 16 Adhesive part

Claims (2)

  A laminated electrochemical device, wherein a positive electrode plate and a negative electrode plate are laminated via a separator sheet, and a part of the outer periphery of the separator sheet is connected to the positive electrode plate and / or the negative electrode plate.   2. The multilayer electrochemical device according to claim 1, wherein a part of the outer peripheral portion of the separator sheet is bonded to the positive electrode plate and / or the negative electrode plate with a thermoplastic resin.

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