JP2013171965A - Electrochemical element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrochemical element eliminating volume expansion of the electrochemical element by suppressing decomposition of an electrolyte on the polarizable electrode surface of the electrochemical element, thereby achieving excellent long-term reliability with less deterioration in electrostatic capacity.SOLUTION: An electrochemical element 1 includes: an electrode laminate including a polarizable electrode which contains active carbon powder and is used as at least one of a positive electrode or a negative electrode, and formed by being wound or laminated between the positive electrode and the negative electrode with a separator interposed therebetween; and a nonaqueous electrolyte containing at least one electrolyte selected from the group of a quaternary ammonium salt or a lithium salt. The electrode laminate is pressed with a surface pressure of 100-400 N/cmby pressing means 8, 9.

Description

  The present invention relates to an electrochemical element such as an electric double layer capacitor used in various electronic devices, a hybrid capacitor typified by a lithium ion capacitor, or a lithium ion battery.

  As a conventional electrochemical element, for example, an electric double layer capacitor comprises an electrode laminate by laminating a polarizable electrode on the positive electrode side and a polarizable electrode on the negative electrode side with a separator interposed therebetween, and This electrode laminate is constituted by impregnating with a nonaqueous electrolytic solution. In such an electric double layer capacitor, when energization is performed for a long time at a certain voltage, gas is generated therein, and the pressure in the electric double layer capacitor is increased by the generated gas. Then, it is known that the internal stress of the generated gas causes deformation of the electrode laminate and a decrease in the capacitance or cycle life of the electric double layer capacitor.

  On the other hand, in an electric double layer capacitor, a technique is known in which a predetermined surface pressure is applied to an electrode laminate to keep the electrode laminate laminate inside the electric double layer capacitor in close contact (see, for example, Patent Document 1). . According to this technique, the deformation of the electrode laminate due to the internal stress of the generated gas as described above can be suppressed.

Moreover, the technique which makes the predetermined surface pressure added to the electrode laminated body of an electrochemical element less than 50 N / cm < ² > is known (for example, refer patent document 2).

JP 2002-289485 A (released on October 4, 2002) JP 2005-259500 A (published on September 22, 2005)

  However, as described above, a useful suppression technique for reducing the capacity and cycle life due to long-time use has not yet been established.

  Therefore, the present invention has been made to solve the above problems, and its purpose is to suppress the volume expansion of the electrochemical device by suppressing the decomposition of the electrolyte solution on the surface of the polarizable electrode of the electrochemical device. It is an object of the present invention to provide an electrochemical device excellent in long-term reliability with little decrease in capacitance.

In order to solve the above problems, the electrochemical device of the present invention uses an electrode in which a polarizable electrode containing activated carbon powder is formed on a current collector as at least one of a positive electrode and a negative electrode, and between the positive electrode and the negative electrode. An electrochemical element comprising an electrode laminate formed by winding or laminating with a separator interposed therebetween and a nonaqueous electrolyte impregnated in the electrode laminate, wherein the nonaqueous electrolyte is quaternary ammonium. It contains at least one electrolyte selected from the group of salts or lithium salts, and the electrode laminate is pressed at 100 to 400 N / cm ² .

  Moreover, it is preferable that the said separator has a cellulose fiber as a main component and contains at least 1 type of polyolefin as a composite material.

  The polyolefin is preferably polyethylene or polypropylene.

According to the present invention, by pressing the electrode laminate at 100 to 400 N / cm ² , the distance between the electrodes becomes smaller than before, the internal resistance is reduced, and the utilization rate of the electrolytic solution decomposition active point is reduced. It is considered that the decomposition of the liquid is suppressed. Therefore, it is possible to provide an electrochemical element that eliminates the volume expansion of the electrochemical element and has excellent long-term reliability with little decrease in capacitance.

It is a cross-sectional schematic diagram of the electrochemical element which shows an example of embodiment of this invention. It is a front view of the electrochemical element which shows an example of embodiment of this invention. It is a side view of the electrochemical element which shows an example of embodiment of this invention. It is a side view of the electrochemical element which shows an example of embodiment of this invention.

  An example of an embodiment of the present invention will be described with reference to FIGS. Referring to FIGS. 1 to 4, an electrochemical element 1 in this embodiment includes an electrode laminate 5 including a positive electrode 2, a negative electrode 3, and a separator 4, a lead terminal 6, an exterior 7, A pressing plate 8 and a fastening member 9 are provided.

  In the positive electrode 2 and the negative electrode 3, polarizable electrodes containing activated carbon powder are formed on one side or both sides of a current collector made of metal foil.

  A polarizable electrode containing activated carbon powder can be manufactured by a known electrode manufacturing method such as an electric double layer capacitor or a lithium ion capacitor. For example, a binder and a conductive material can be added to activated carbon derived from a raw material selected from petroleum pitch, coke, coconut shell, phenol resin, and the like.

  As the binder, polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl alcohol, carboxymethyl cellulose, polyacrylic acid, and the like are used. Among these, polytetrafluoroethylene becomes a fibrous state during kneading and becomes conductive with activated carbon. It is preferable because the material is firmly bonded and the pores of the activated carbon are not blocked.

  As the conductive material, ketjen black, conductive carbon black of acetylene black, natural graphite, artificial graphite, carbon fiber, aluminum, nickel, and other metal fibers can be used, but the conductivity is effectively improved in a small amount. Ketjen black and acetylene black are particularly preferred.

  The electrode is manufactured by molding activated carbon, a conductive material, and a binder by a known method. For example, it can be obtained by adding and mixing polytetrafluoroethylene to a mixture of activated carbon and carbon black, followed by press molding and roll molding. Further, any of a method of forming a thin coating film by applying the mixture after making it into a slurry, and a sheet-like or plate-like molded body may be used.

  In addition, when the polarizable electrode containing activated carbon powder is used for both the positive electrode 2 and the negative electrode 3, an electric double layer capacitor can be manufactured. Further, when a polarizable electrode containing activated carbon powder is used for the positive electrode 2 and an electrode using graphite powder instead of the activated carbon powder is used for the negative electrode 3, a lithium ion capacitor can be manufactured.

  The separator 4 is interposed between the positive electrode 2 and the negative electrode 3. The electrode laminate 5 is formed by laminating or winding the positive electrode 2, the negative electrode 3 and the separator 4.

  The separator 4 is preferably composed mainly of cellulose fibers, and may contain at least one kind of polyolefin as a composite material. Such polyolefin is preferably polyethylene or polypropylene.

  Each of the positive electrode 2 and the negative electrode 3 constituting the electrode laminate 5 has an exposed portion formed on the current collector foil. The exposed portion is provided, for example, so as to have a convex shape at one end of the current collector foil, and is gathered for each of the positive electrode and the negative electrode. A plate-like or rod-like lead terminal 6 is attached to the aggregate of the exposed portions by ultrasonic welding, spot welding, or the like.

  Moreover, the electrode laminated body 5 is immersed in the non-aqueous electrolyte. As the nonaqueous electrolytic solution used in the present invention, a known electrolytic solution used for an electric double layer capacitor or a lithium ion capacitor can be used. The electrolytic solution is not particularly limited, but is generally selected in consideration of the solubility of solute, the degree of dissociation, the viscosity of the solution, etc., and is preferably an electrolytic solution having a high conductivity and a high potential window.

  Examples of the non-aqueous electrolyte include cyclic carbonates, chain carbonates, chain carboxylic esters, cyclic carboxylic esters, phosphorus-containing organic solvents, sulfur-containing organic solvents, and the like.

The non-aqueous electrolyte contains one or more electrolytes selected from the group consisting of quaternary ammonium salts or lithium salts. Any quaternary ammonium salt or lithium salt can be used as long as the electrolyte can generate quaternary ammonium ions and lithium ions. It is more preferable to use one or more selected from the group consisting of quaternary ammonium salts and lithium salts. In particular, ethyl trimethyl ammonium BF ₄ , diethyl dimethyl ammonium BF ₄ , triethyl methyl ammonium BF ₄ , tetraethyl ammonium BF ₄ , spiro- (N, N ′)-bipyrrolidinium BF ₄ , ethyl trimethyl ammonium PF ₆ , diethyl dimethyl ammonium PF ₆ , triethylmethylammonium PF _6, tetraethylammonium PF _6, spiro - (N, N ') - bipyrrolidinium PF _6, tetramethyl ammonium bis (oxalato) borate, trimethyl ammonium bis (oxalato) borate, diethyl-dimethyl ammonium bis (oxalato) borate , Triethylmethylammonium bis (oxalato) borate, tetraethylammonium bis (oxalato) borate, spiro- (N, N ′) Bipyrrolidinium bis (oxalato) borate, tetramethylammonium difluorooxalatoborate, ethyltrimethylammonium difluorooxalatoborate, diethyldimethylammonium difluorooxalatoborate, triethylmethylammonium difluorooxalatoborate, tetraethylammonium difluorooxalatoborate, spiro -(N, N ′)-bipyrrolidinium difluorooxalatoborate, LiBF ₄ , LiPF ₆ , lithium bis (oxalato) borate, lithium difluorooxalatoborate and the like are preferable.

  The concentration of the electrolyte in the nonaqueous electrolytic solution is preferably at least 0.1 mol / L or more in order to reduce the internal resistance due to the electrolytic solution, and more preferably in the range of 0.5 to 1.5 mol / L. preferable.

  The electrode laminate 5 is hermetically accommodated by the exterior 7 in a state where the lead terminal 6 is pulled out. The exterior 7 is made of a flexible material so that the stress is effectively and uniformly applied to the electrode stack 5 when the electrochemical element 1 is pressed in the electrode stacking direction by an external stress from the pressing plate 8 described later. Is preferred. Specifically, the exterior 7 is preferably an aluminum laminate film.

The electrochemical element 1 is sandwiched between two pressing plates 8 and pressed in the electrode stacking direction with a predetermined surface pressure in the range of 100 to 400 N / cm ² , preferably 200 to 400 N / cm ² . As an example of a method of pressing and maintaining the electrochemical element 1 at a predetermined surface pressure, the electrochemical element 1 sandwiched between two pressing plates 8 is pressed by a press machine until a predetermined surface pressure is obtained, A method of fixing the pressing plate 8 with the fastening member 9 in a state in which the surface pressure is reached.

  The pressing plate 8 may be a metal plate such as aluminum or stainless steel, and the fastening member 9 may be a bolt and a nut.

  In the example of the present embodiment, the pressing plate 8 and the fastening member 9 are used as pressing means for the electrochemical element 1, but the invention is not limited to this, and well-known pressing means for the electrochemical element 1 can be widely used. it can. In addition, three electrochemical elements 1 stacked in the electrode stacking direction are pressed by two pressing plates 8, but the number of the electrochemical elements 1 is not particularly limited, and even if it is one, more than three. There may be many.

  Next, an example according to the electrochemical device of the present invention will be described.

1. Electrode fabrication

1.0 g of activated carbon having a specific surface area of 1800 m ² / g, 0.1 g of ketjen black, and 0.1 g of polyvinylidene fluoride are mixed and kneaded in a mortar, and an appropriate amount of N-methyl-2-pyrrolidone is added to the mixture. An adjusted slurry solution was obtained. This slurry solution was applied on one side onto a 0.04 mm thick aluminum foil and then dried at 120 ° C. for 2 hours to produce a single side electrode sheet with an electrode layer thickness of 0.08 mm. Moreover, it applied on both surfaces on 0.05 mm thickness aluminum foil, and then dried at 120 ° C. for 2 hours to prepare a double-sided electrode sheet having an electrode layer thickness of 0.08 mm. The obtained electrode sheet was formed into a prescribed size to obtain a single-sided activated carbon electrode and a double-sided activated carbon electrode. At this time, an external electrode lead-out tab having a convex shape was provided at one end of each electrode sheet.

2. Production of electrochemical devices

  The electrode laminate 5 was obtained by laminating a specified number of sheets with the single-side activated carbon electrode of the negative electrode 3 at both ends and the double-sided activated carbon electrode sandwiching a cellulose separator 4 having a thickness of 0.05 mm between the two activated carbon electrodes. External electrode lead-out tabs were assembled for each of the positive electrode 2 and the negative electrode 3, and lead terminals 6 made of an aluminum plate were attached to each by ultrasonic welding. A cellulose separator 4 having a thickness of 0.05 mm was wound around the outer periphery of the electrode laminate 5, and the electrode laminate 5 was accommodated in an exterior 7 made of an aluminum laminate film. At this time, the edge part of the exterior 7 was heat-sealed so that an opening might be provided in one side among the edge parts with four sides of the exterior 7.

  And it short-circuited by connecting with the lead wire 6 of the positive electrode 2 and the negative electrode 3 which were pulled out from the exterior 7 with a conducting wire, and it dried at 120 degreeC for 10 hours in the pressure reduction atmosphere.

Then, 1M-triethylmethylammonium BF ₄ / propylene carbonate as a non-aqueous electrolyte was injected into the exterior 7 and the electrode laminate 5 was vacuum impregnated. And the electrochemical element 1 was produced by heat-sealing and sealing the opening part of the exterior 7. In addition, the electrochemical element 1 in a present Example is an electrical double layer capacitor.
[Example 1]

The electrochemical element 1 was sandwiched between two pressing plates 8 and pressed in the electrode stacking direction with a surface pressure of 100 N / cm ² with a press machine. And the electrochemical element 1 of Example 1 was obtained by fixing the two press plates 8 with the fastening member 9. FIG.

[Example 2]

The electrochemical element 1 was sandwiched between the two pressing plates 8 and pressed in the electrode stacking direction with a surface pressure of 400 N / cm ² with a press machine. And the electrochemical element 1 of Example 2 was obtained by fixing the two press plates 8 with the fastening member 9. FIG.
[Comparative Example]

The electrochemical element 1 was sandwiched between two pressing plates 8 and pressed in the electrode stacking direction with a surface pressure of 30 N / cm ² with a press. And the electrochemical element 1 of the comparative example was obtained by fixing the two press plates 8 with the fastening member 9. FIG.

3. Evaluation test

  A voltage of 2.7 V was applied for 200 hours in a thermostat at 60 ° C. to the electrochemical devices 1 of Examples 1 and 2 and Comparative Example produced as described above.

  Table 1 shows changes in gas generation amount and capacitance in the electrochemical elements 1 of Examples 1 and 2 and Comparative Example. The amount of gas generation was evaluated based on the volume change of the electrochemical device 1 before and after the evaluation test. Further, changes in gas generation amount and capacitance were evaluated with the initial value before voltage application being 100.

  As is apparent from the results shown in Table 1, the electrochemical devices 1 of Examples 1 and 2 obtained according to the present invention have excellent effects in which volume expansion due to gas generation is suppressed and capacitance is not lowered significantly. You can see that

  In the embodiment disclosed this time, an electric double layer capacitor is used as an example of the electrochemical element 1, but as other electrochemical element 1, a lithium ion capacitor using a polarizable electrode containing activated carbon powder only for the positive electrode, etc. The so-called hybrid capacitor can also achieve the effects of the present invention.

DESCRIPTION OF SYMBOLS 1 Electrochemical element 2 Positive electrode 3 Negative electrode 4 Separator 5 Electrode laminated body 6 Lead terminal 7 Exterior 8 Pressing plate 9 Fastening member

Claims (3)

An electrode laminate in which a polarizable electrode containing activated carbon powder is formed on a current collector and used as at least one of a positive electrode and a negative electrode, and is wound or laminated with a separator interposed between the positive electrode and the negative electrode; An electrochemical device comprising a non-aqueous electrolyte impregnated in the electrode laminate,
The non-aqueous electrolyte includes at least one electrolyte selected from the group of quaternary ammonium salts or lithium salts, and the electrode laminate is pressed at 100 to 400 N / cm ^2. .   The electrochemical device according to claim 1, wherein the separator includes cellulose fiber as a main component and at least one polyolefin as a composite material.   The electrochemical device according to claim 2, wherein the polyolefin is polyethylene or polypropylene.

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