JP2006186226A - Electrochemical device and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To sufficiently improve a characteristic of an electrochemical device using nonaqueous electrolyte. <P>SOLUTION: The electrochemical device 100 is provided with a laminated body 20 having a separator 18 and a pair of electrodes 10 and 10 arranged across the separator 18, a coating bag 50 storing the laminated body 20 and nonaqueous electrolyte impregnated in the laminated body 20. Nonaqueous electrolyte comprises organic solvent and electrolyte expressed with Q<SP>+</SP>X<SP>-</SP>. Mass of water existing in the outer bag is 50 to 1,000 ppm with respect to that of nonaqueous electrolyte. Q<SP>+</SP>is quaternary ammonium cation or quaternary phosphonium cation. X<SP>-</SP>is anion selected from a group formed of BF<SB>4</SB><SP>-</SP>, PF<SB>6</SB><SP>-</SP>, AsF<SB>6</SB><SP>-</SP>, SbF<SB>6</SB><SP>-</SP>, N(RfSO<SB>3</SB>)<SB>2</SB><SP>-</SP>, C(RfSO<SB>3</SB>)<SB>3</SB><SP>-</SP>and RfSO<SB>3</SB><SP>-</SP>. Rf is a fluoro alkyl group whose number of carbons is 1 to 12. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electrochemical device and a method for producing an electrochemical device.

An electric double layer capacitor (EDLC) using nonaqueous electrolytic solutions is known. The non-aqueous electrolyte is obtained by dissolving an electrolyte in an organic solvent. For example, non-aqueous electrolysis in which triethyl monomethyl ammonium tetrafluoroborate (TEMA-BF ₄ ) is dissolved as an electrolyte in polycarbonate (PC) as an organic solvent. Liquids and the like are known.

  Such an electric double layer capacitor includes a separator and a laminated body having a pair of electrodes provided between the separators, an exterior bag that accommodates the laminated body, and a non-aqueous electrolyte impregnated in the laminated body. Yes. The electrode is obtained by laminating an active material-containing layer on a current collector.

In such an electric double layer capacitor, it has been disclosed that the moisture content of the active material-containing layer should be less than or equal to a predetermined range in order to improve the withstand voltage characteristics, suppress the decrease in capacity and increase in internal resistance, etc. (For example, refer to Patent Document 1).
JP 2004-193571 A

  In recent years, further improvement in characteristics has been demanded for electrochemical devices. For example, for an electric double layer capacitor, it is desired that the impedance and the thickness of the electrochemical device do not increase even after long-term use and that the capacitance is sufficiently maintained.

  This invention is made | formed in view of the said subject, and it aims at fully improving the characteristic of the electrochemical device using a non-aqueous electrolyte.

  As a result of investigations by the present inventors, no matter how much the water content of the polarizable electrode layer is set within a predetermined range, moisture is mixed in the outer bag due to the separator, non-aqueous electrolyte, or the like. Furthermore, the inventors have found that it is not preferable as an electrochemical device whether the moisture content in the outer package after sealing is too high or too low, and the present invention has been conceived.

The electrochemical device according to the present invention includes a separator and a laminate having a pair of electrodes provided with the separator interposed therebetween, an exterior bag that accommodates the laminate, and a non-aqueous electrolyte impregnated in the laminate. The nonaqueous electrolytic solution includes an organic solvent and an electrolyte represented by Q ⁺ X ⁻ . And the mass of the water which exists in an exterior bag is 50-1000 ppm with respect to the mass of a non-aqueous electrolyte.

Here, Q ⁺ is a quaternary ammonium cation or quaternary phosphonium cation, X ⁻ is BF ₄ ⁻ , PF ₆ ⁻ , AsF ₆ ⁻ , SbF ₆ ⁻ , N (RfSO ₃ ) ₂ ⁻ , C (RfSO ₃ ) ₃ ^−. And an anion selected from the group consisting of RfSO ₃ ^— . Rf is a C1-C12 fluoroalkyl group.

  In such an electrochemical device, an increase in impedance, a swelling of the electrochemical device, and a decrease in capacitance with the passage of time of use are sufficiently suppressed. In addition, the withstand voltage is sufficient.

  On the other hand, when the mass of water existing in the exterior body exceeds 1000 ppm of the mass of the non-aqueous electrolyte, the increase in impedance, the swelling of the electrochemical device, and the deterioration of the capacitance with the passage of use time are remarkable. The reason for this is not clear, but, for example, if the amount of water is too large, the concentration of fluorine ions generated in the non-aqueous electrolyte solution becomes too high, causing deterioration of the solvent of the electrolyte solution or deterioration of the electrode or the like. It is possible. Fluorine ions are considered to be generated by a reaction between a fluorine compound (for example, hydrogen fluoride) in a non-aqueous electrolyte and water.

  In addition, when the mass of water present in the exterior body is less than 50 ppm of the mass of the nonaqueous electrolyte, it becomes difficult to function as an electrochemical device. The reason for this is not clear, but, for example, the amount of moisture in the outer package is too low, so the fluorine ion concentration in the non-aqueous electrolyte solution becomes too low, and an electrode coating with a sufficiently low impedance is not formed on the electrode. Conceivable.

  Here, it is preferable to contain propylene carbonate as the organic solvent.

  The electrode preferably contains acetylene black and polyvinylidene fluoride. For example, as an electrode, what formed the electrode layer containing acetylene black and polyvinylidene fluoride on collectors, such as metal foil, is mentioned.

  Moreover, it is preferable that an exterior bag is what laminated | stacked the synthetic resin film, the aluminum foil, and the synthetic resin film in order from the inner side.

  When such an exterior bag is used, it is possible to prevent moisture and the like from being mixed into the electrochemical device from the outside with use, and it is easy to maintain the amount of moisture in the exterior bag.

Further, the nonaqueous electrolyte solution BF ₄ ^- as the anion preferably has an ion.

Subsequently, the method for producing an electrochemical device according to the present invention includes a preparation step and a sealing step. In the preparation step, a laminate having a separator and a pair of electrodes provided across the separator, an exterior bag, and a nonaqueous electrolytic solution in which an electrolyte represented by Q ⁺ X ⁻ is dissolved in an organic solvent are prepared. To do. In the sealing step, the outer bag is sealed after the laminate and the non-aqueous electrolyte are accommodated in the outer bag.

  In the preparation step, the water content of the non-aqueous electrolyte is adjusted so that the mass of water present in the outer bag after the sealing step is 50 to 1000 ppm with respect to the mass of the non-aqueous electrolyte after the sealing step. Keep it.

Here, Q ⁺ is a quaternary ammonium cation or quaternary phosphonium cation, X ⁻ is BF ₄ ⁻ , PF ₆ ⁻ , AsF ₆ ⁻ , SbF ₆ ⁻ , N (RfSO ₃ ) ₂ ⁻ , C (RfSO ₃ ) ₃ ^−. And an anion selected from the group consisting of RfSO ₃ ^— . Rf is a C1-C12 fluoroalkyl group.

  Thereby, the above-mentioned electrochemical device can be suitably produced.

  Here, specifically, the water content of the non-aqueous electrolyte can be adjusted by adding water to the non-aqueous electrolyte.

  According to the present invention, the characteristics of an electrochemical device using a non-aqueous electrolyte can be sufficiently improved.

  As an example of the electrochemical device according to the present embodiment, an electric double layer capacitor will be described.

  FIG. 1 is a cross-sectional view showing an electric double layer capacitor 100 according to the present embodiment.

  The electric double layer capacitor (electrochemical device) 100 mainly includes a multilayer body 20, an outer bag 50 for housing the multilayer body, and a pair of leads 60 and 62 connected to the multilayer body 20.

  The stacked body 20 is a structure in which a pair of electrodes 10 are arranged to face each other with a separator 18 interposed therebetween. Each of the electrodes 10 is a product in which an active material-containing layer 14 is provided on a current collector 12. The active material containing layers 14 and 14 are in contact with both sides of the separator 18. Leads 60 and 62 are connected to the ends of the current collectors 12 and 12, respectively, and the ends of the leads 60 and 62 extend to the outside of the outer bag 50.

  The current collector 12 is formed of a metal foil such as an aluminum foil, for example.

  The active material-containing layer 14 is formed of, for example, a mixture of an active material and a binder. As the active material, for example, acetylene black, graphite, graphite, activated carbon, or the like can be selected, or these can be mixed and used at an arbitrary ratio. As the binder, for example, a fluororesin such as polyvinylidene fluoride (PVDF) can be used.

  The separator 18 is made of an insulating porous body. Examples of the insulating porous material include cellulose nonwoven fabric.

  The laminate 20 is impregnated with a non-aqueous electrolyte. The nonaqueous electrolytic solution is mainly impregnated in the separator 18 and the active material-containing layer 14 in the electrode 10. The non-aqueous electrolyte will be described later.

  The exterior bag 50 seals the laminated body 20 and the electrolytic solution therein. The outer bag 50 is not particularly limited as long as it can prevent leakage of the electrolytic solution to the outside and entry of moisture and the like into the electric double layer capacitor 100. For example, as the outer bag 50, as shown in FIG. 1, a metal laminate film in which a metal foil 52 is coated with a synthetic resin film 54 from both sides can be used. For example, an aluminum foil can be used as the metal foil, and a film such as polypropylene can be used as the synthetic resin film.

  The leads 60 and 62 are made of a conductive material such as aluminum.

Subsequently, the non-aqueous electrolyte will be described. This nonaqueous electrolytic solution is obtained by dissolving an electrolyte in a solvent.
The electrolyte is represented by Q ⁺ X ⁻ . Here, Q ⁺ is a quaternary ammonium cation or a quaternary phosphonium cation. Examples of the quaternary ammonium cation include those obtained by quaternizing any tertiary amine with an alkyl group, a cycloalkyl group, an aryl group, an aralkyl group, or the like. For example, triethylmonomethylammonium cation, tetraethylammonium cation, ethylmethylimidazolium cation and the like.

X ⁻ is a counter anion selected from the group consisting of BF ₄ ⁻ , PF ₆ ⁻ , AsF ₆ ⁻ , SbF ₆ ⁻ , N (RfSO ₃ ) ₂ ⁻ , C (RfSO ₃ ) ₃ ⁻ , and RfSO ₃ ^−. is there. Rf is a C1-C12 fluoroalkyl group. Such anions are often produced using hydrogen fluoride as a raw material, and often contain impurities such as hydrogen fluoride that easily react with water to generate F ⁻ ions.

Preferred electrolytes are, for example, triethylmonomethylammonium tetrafluoroborate (TEMA-BF ₄ ), tetraethylammonium tetrafluoroborate (TEA-BF ₄ ), ethylmethylimidazolium tetrafluoroborate (EMI-BF ₄ ), and the like.

  The solvent is an organic solvent, and for example, propylene carbonate (PC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC) and the like can be mixed alone or in any ratio. Here, it is particularly preferable to use PC alone.

  Moreover, it is preferable that the electrolyte concentration in a nonaqueous electrolyte solution exists in the range of 0.7-3.0 mol / L.

Such a non-aqueous electrolyte further contains a trace amount of F ⁻ ions (fluorine ions) derived from the electrolyte and the like. In the electric double layer capacitor 100 according to the present embodiment, the fluorine ion concentration in the non-aqueous electrolyte impregnated in the multilayer body 20 is preferably 3 to 180 ppm by mass.

  Further, in the present embodiment, the outer bag 50 contains water. The mass of water present in the outer bag 50 is 50 to 1000 ppm with respect to the mass of the non-aqueous electrolyte. For example, the water is contained in advance in the active material-containing layer 14, the separator 18, the current collector 12, the inner wall of the outer bag 50, the nonaqueous electrolyte, and the like. Most of the water is contained in the non-aqueous electrolyte.

  In such an electric double layer capacitor 100, an increase in impedance, a swelling of an electrochemical device, and a decrease in capacitance with the passage of time of use are sufficiently reduced. In addition, the withstand voltage is sufficient.

  On the other hand, when the mass of water existing in the exterior body exceeds 1000 ppm of the mass of the non-aqueous electrolyte, the increase in impedance, the swelling of the electrochemical device, and the deterioration of the capacitance with the passage of use time are remarkable. The reason for this is not clear, but, for example, if the amount of water is too large, the concentration of fluorine ions generated in the non-aqueous electrolyte solution becomes too high, degrading the solvent of the electrolyte solution, It may be possible to corrode the lead. Fluorine ions are considered to be generated by a reaction between a fluorine compound (for example, hydrogen fluoride) in a non-aqueous electrolyte and water.

  In addition, when the mass of water present in the exterior body is less than 50 ppm of the mass of the nonaqueous electrolyte, it becomes difficult to function as an electrochemical device. Although the reason for this is not clear, for example, since the moisture content in the outer package is too low, the fluorine ion concentration in the non-aqueous electrolyte becomes too low, and the surface of the current collector 12 such as aluminum has a sufficient fluorine content. It is considered that a high passive film cannot be formed.

  Such an electric double layer capacitor 100 may be manufactured as follows. First, the laminated body 20 to which the leads 60 and 62 are connected, the exterior bag 50, and the non-aqueous electrolyte are prepared. At this time, the laminated body 20 and the exterior bag 50 are each sufficiently dried. For example, after heating in air, the moisture can be sufficiently reduced by heating in vacuum. Here, it is preferable that the moisture content of the laminated body 20 and the exterior bag 50 is about 1 ppm <x <500 ppm with respect to the mass of the nonaqueous electrolyte to be supplied into the exterior bag 50, respectively.

  In addition, the nonaqueous electrolyte solution is laminated so that the mass of water present in the exterior bag after sealing the exterior bag 50 is 50 to 1000 ppm with respect to the mass of the nonaqueous electrolyte solution after sealing. The moisture concentration is adjusted to a predetermined value according to the degree of drying of the body 20, the outer bag 50, and the like. As a specific adjustment method, for example, after the non-aqueous electrolyte is sufficiently dried, a predetermined water concentration can be obtained by adding water. In addition, for example, various types of electric double layer capacitors are prepared using non-aqueous electrolytes adjusted in advance to various moisture concentrations, and the moisture concentrations in the sealed outer bag 50 are measured. This can be determined by trial and error.

  Subsequently, the multilayer body 20 is accommodated in the exterior bag 50, a nonaqueous electrolyte is dropped into the multilayer body 20, and then the exterior bag 50 is sealed to complete the above-described electric double layer capacitor.

  In addition, the electric double layer capacitor 100 is not limited to the above-mentioned form, For example, the laminated body 20 etc. may be used.

  In addition, the above-described electrolytic solution is not limited to an electric double layer capacitor, and can be suitably used as long as it is a device such as a primary battery or a secondary battery in which an electrolyte and an electrode are in contact with each other to cause an electrochemical action.

<Example 1>
The electric double layer capacitor of Example 1 was produced as follows.

<Production of electrode>
Using acetylene black as the active material and PVDF as the binder, these were mixed so that the active material: binder = 80: 20, and the resulting mixture was kneaded with N-methylpyrrolidone to prepare a coating material. did.

  After this paint was applied on one side of the etched aluminum foil by the doctor blade method, the coating film was dried by heating the aluminum foil in air at 150 ° C. for 30 minutes and subsequently in vacuum at 150 ° C. for 8 hours. . Next, an aluminum foil was punched out into a rectangular shape having a tab portion around the coating film formation region to obtain an electrode for an electric double layer capacitor. All operations after drying were performed in a dry room with a dew point of -35 ° C or lower.

<Creating a cell>
Two punched electrodes were opposed to each other through a cellulose separator, and thermocompression bonded to obtain a laminate. Aluminum leads were welded to the tab portion of the laminate by ultrasonic welding. The laminate with the leads was put into a bag-like aluminum laminate film having two of the four sides opened, the lead was taken out from one opening, and thermocompression bonded with the lead in between. Electrolyte is dripped with respect to a laminated body from the opening part finally left of the aluminum laminated exterior bag containing a laminated body, the opening part which remained by vacuum thermocompression bonding is sealed, and Example 1 of a form like FIG. Three electric double layer capacitors were obtained. The thickness of the electric double layer capacitor was about 0.3 mm.

<Adjustment of electrolyte>
As the non-aqueous electrolyte, a PC solution containing 1.0 mol / L of TEA-BF ₄ having a fluorine ion content of 10 mass ppm and a moisture content of 10 mass ppm was used. Quantification of the fluorine ion amount was performed by ion chromatography. The water content was measured by the Karl Fischer method, specifically, the coulometric titration method.

<Example 2>
In Example 2, an electric double layer was formed in the same manner as in Example 1 except that water was further added to the nonaqueous electrolyte of Example 1 to add a nonaqueous electrolyte having a water content of 500 ppm by mass to the laminate. Three capacitors were obtained.

<Example 3>
In Example 3, using a separator made of an aramid resin, a laminate was dried and a cell was prepared in a glove box having a dew point of −80 ° C. or less in a dry argon atmosphere, and a PC solution containing 1 mol / L of TEA-BF ₄ was used. Then, three electric double layer capacitors were obtained in the same manner as in Example 1 except that a non-aqueous electrolyte having a fluorine ion content of 1 mass ppm and a water content of 10 mass ppm was dropped onto the laminate. .

<Comparative Example 1>
Comparative Example 1 was the same as Example 1 except that a nonaqueous electrolytic solution having a water content of 1000 ppm by mass was added to the laminate by adding water to the electrolytic solution of Example 1.

<Comparative example 2>
In Comparative Example 2, the same procedure as in Example 1 was performed, except that a nonaqueous electrolytic solution having a water content of 2000 ppm by mass was added to the laminate by adding water to the electrolytic solution of Example 1.

<Comparative Example 3>
In Comparative Example 3, the same procedure as in Example 1 was performed, except that a nonaqueous electrolytic solution having a moisture content of 5000 ppm by mass was added to the laminate by adding water to the electrolytic solution of Example 1.

<Comparative example 4>
In Comparative Example 2, the same procedure as in Example 1 was performed, except that a nonaqueous electrolytic solution having a water content of 20000 mass ppm was added dropwise to the laminate, with respect to the electrolytic solution of Example 1.

<Comparative Example 5>
In Comparative Example 5, an aramid resin separator was used, and the laminate was dried and a cell was prepared in a glove box having a dew point of −80 ° C. or less and a dry argon atmosphere. Furthermore, the PC solution containing 1 mol / L of TEA-BF ₄ was repeatedly washed with a non-aqueous electrolyte solution having a fluorine ion amount of 1 ppm by weight and a water content of 10 ppm by mass, Three electric double layer capacitors were obtained in the same manner as in Example 1 except that this non-aqueous electrolyte was dropped.

<Measurement of the amount of fluorine ions in the non-aqueous electrolyte and the amount of moisture in the outer bag in the electric double layer capacitor>
About the electric double layer capacitor of each example and each comparative example, the amount of fluorine ions in the non-aqueous electrolyte in the outer bag after sealing and the amount of water in the outer bag (ratio to the weight of the non-aqueous electrolyte in the outer bag) ).

  Specifically, the amount of fluorine ions is measured by opening one end of an aluminum laminate outer bag in a dry room having a dew point of −35 ° C. or less, sucking up a non-aqueous electrolyte from the laminate with a pipette, The fluorine ion concentration was measured.

  In addition, regarding the measurement of the moisture content in the outer bag, one end of the outer bag is opened in a dry room having a dew point of −35 ° C. or lower, the lead is cut, and the laminate and the non-aqueous electrolyte are placed in a predetermined amount of PC (water In a container with a known amount), sealed, and left in a thermostatic chamber in a dry room at 70 ° C. for 1 hour, after which the moisture content of the PC is obtained by the Karl Fischer method and divided by the mass of the nonaqueous electrolyte. The amount of water in the outer bag was determined.

  The results are shown in FIG. The amount of water in the outer bag after sealing is increased compared to the amount of water in the electrolyte prepared in advance. This is considered to be the influence of moisture or the like contained in the laminated body or the inner wall of the outer bag. Therefore, it is considered that the amount of fluorine ions in the non-aqueous electrolyte after sealing is also larger than the amount of non-aqueous electrolyte fluorine ions prepared in advance.

<Characteristic evaluation of electric double layer capacitor>
After measuring the initial impedance (value at 1 kHz), initial capacitance, and initial cell thickness using an electric double layer capacitor for each example and each comparative example, a current of 2.7 V was applied at 70 ° C. to 1000 The impedance, capacitance, and cell thickness after time were measured. The respective values after 1000 hours have elapsed when the initial value is set to 100 are shown in FIG.

  In Examples 1-3, compared with the other Comparative Examples 1-5, the tendency which was good also in the impedance, the electrostatic capacitance, and the thickness of the cell was shown. In Comparative Example 3, stable energization was not possible, and even an initial value could not be obtained. Thus, it was confirmed that the present invention greatly contributes to the realization of a small, thin and long-life electrochemical device.

FIG. 1 is a cross-sectional view showing an electric double layer capacitor according to an embodiment. FIG. 2 shows the fluorine ion concentration in the non-aqueous electrolyte prepared in advance for Examples 1 to 3 and Comparative Examples 1 to 3, the moisture content of the non-aqueous electrolyte prepared in advance, the moisture content in the outer bag after sealing, It is a table | surface which shows the fluorine ion concentration of the non-aqueous electrolyte after sealing, the impedance after 1000-hour electricity supply, an electrostatic capacitance, and the thickness of a cell.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Electrode, 18 ... Separator, 20 ... Laminated body, 50 ... Exterior bag, 80 ... Electrolyte, 100 ... Electric double layer capacitor (electrochemical device).

Claims (7)

An electrochemical device comprising a separator having a separator and a pair of electrodes provided with the separator interposed therebetween, an exterior bag containing the laminate, and a non-aqueous electrolyte impregnated in the laminate,
The non-aqueous electrolyte includes an organic solvent and an electrolyte represented by Q ⁺ X ⁻ ,
The electrochemical device wherein the mass of water present in the outer bag is 50 to 1000 ppm relative to the mass of the non-aqueous electrolyte.
Here, Q ⁺ is a quaternary ammonium cation or quaternary phosphonium cation, X ⁻ is BF ₄ ⁻ , PF ₆ ⁻ , AsF ₆ ⁻ , SbF ₆ ⁻ , N (RfSO ₃ ) ₂ ⁻ , C (RfSO ₃ ) ₃ ^−. And an anion selected from the group consisting of RfSO ₃ ^— . Rf is a C1-C12 fluoroalkyl group.   The electrochemical device according to claim 1, comprising propylene carbonate as the organic solvent.   The electrochemical device according to claim 1, wherein the electrode includes acetylene black and polyvinylidene fluoride.   The electrochemical device according to any one of claims 1 to 3, wherein the outer bag is a laminate of a synthetic resin film, an aluminum foil, and a synthetic resin film in order from the inside.   The electrochemical device according to claim 1, which is an electric double layer capacitor. Preparatory process for preparing a laminate having a separator and a pair of electrodes provided across the separator, an outer bag, and a non-aqueous electrolyte in which an electrolyte represented by Q ⁺ X ⁻ is dissolved in an organic solvent When,
A sealing step of sealing the outer bag after the laminate and the non-aqueous electrolyte are contained in the outer bag;
A method for producing an electrochemical device comprising:
The amount of water in the non-aqueous electrolyte solution in the preparation step so that the mass of water present in the exterior bag after the sealing step is 50 to 1000 ppm with respect to the mass of the non-aqueous electrolyte solution after the sealing step. Method of manufacturing an electrochemical device that regulates temperature.
Here, Q ⁺ is a quaternary ammonium cation or quaternary phosphonium cation, X ⁻ is BF ₄ ⁻ , PF ₆ ⁻ , AsF ₆ ⁻ , SbF ₆ ⁻ , N (RfSO ₃ ) ₂ ⁻ , C (RfSO ₃ ) ₃ ^−. And an anion selected from the group consisting of RfSO ₃ ^— . Rf is a C1-C12 fluoroalkyl group.   The method for producing an electrochemical device according to claim 6, wherein the moisture content of the non-aqueous electrolyte is adjusted by adding moisture to the non-aqueous electrolyte.

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