JP4529683B2 - Electrochemical devices - Google Patents

Description

  The present invention relates to 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 a non-aqueous electrolyte contains a small amount of fluorine ions derived from the electrolyte. When fluorine ions coexist with amines or ammonium salts, the characteristics of the electrochemical device such as a decrease in withstand voltage and an increase in impedance are reduced. It is supposed to be the cause.

And in order to improve the withstand voltage characteristic and impedance characteristic of such an electrochemical device, a non-aqueous electrolyte solution in which the amount of hydrogen fluoride and fluorine ions is reduced as much as possible is prepared, and the electrochemical device is used with this. It is said that it is preferable to manufacture (for example, refer patent document 1, 2).
JP 2000-114107 A No. 2004-47957

  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 studies by the present inventors, the non-aqueous electrolyte is accommodated in the exterior bag together with the laminate, no matter how much the fluorine ion concentration of the non-aqueous electrolyte before being accommodated in the exterior bag is set to a predetermined range. Then, the fluorine ion concentration in the non-aqueous electrolyte increases due to the influence of minute moisture that is inevitably contained in the laminated body and the inner wall of the outer bag, and further, the fluorine ions of the non-aqueous electrolyte in the outer bag. The inventors have found that an excessively low concentration or an excessively low concentration is not preferable as an electrochemical device, and arrived at the present invention.

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 contains an organic solvent, an electrolyte represented by Q ⁺ X ⁻ , and F ⁻ ions. The F ⁻ ion concentration in the non-aqueous electrolyte is 3 to 180 ppm by mass.

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 fluorine ion concentration in the non-aqueous electrolyte exceeds 180 ppm by mass, the increase in impedance, the swelling of the electrochemical device, and the deterioration of the capacitance with the passage of time of use are remarkable. The reason for this is not clear, but it is conceivable that, for example, the fluorine ion concentration is too high, so that the solvent of the electrolytic solution or the like is deteriorated or the electrode or the like is deteriorated.

  Moreover, if the fluorine ion concentration in the non-aqueous electrolyte is less than 3 mass ppm, it becomes difficult to function as an electrochemical device. The reason for this is not clear, but it is conceivable that, for example, an electrode film having a sufficiently low impedance is not formed on the electrode because the fluorine ion concentration is too low.

  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.

  Use of such an outer bag can prevent moisture and the like from being mixed into the electrochemical device from the outside during use, and maintain the fluorine ion concentration of the nonaqueous electrolytic solution impregnated in the electrode and separator. Cheap.

  A particularly typical electrochemical device is an electric double layer capacitor.

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 electrolyte 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.

  And in a preparatory process, the moisture content in a non-aqueous electrolyte solution is adjusted so that the fluorine ion concentration in the non-aqueous electrolyte solution in the exterior bag after a sealing process may be 3-180 mass ppm.

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 laminate 20 and the non-aqueous electrolyte 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 an arbitrary tertiary amine with an alkyl group, a cycloalkyl group, an aryl group, an aralkyl group, or the like. Examples thereof include tetraalkylammonium cations such as triethylmonomethylammonium cation and tetraethylammonium cation, and imidazolium cations such as ethylmethylimidazolium cation.

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 non-aqueous electrolyte solution, further, F derived from the electrolytes ^- include ionic (fluorine ion). And in the electric double layer capacitor 100 which concerns on this embodiment, the fluorine ion density | concentration in a non-aqueous electrolyte in the state sealed in the exterior bag 50 is 3-180 mass ppm.

  Further, in the present embodiment, the outer bag 50 contains water. It is preferable that the mass of the water which exists in the exterior bag 50 is 50-1000 ppm with respect to the mass of a 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 fluorine ion concentration in the non-aqueous electrolyte exceeds 180 ppm by mass, the increase in impedance, the swelling of the electrochemical device, and the deterioration of the capacitance with the passage of time of use are remarkable. The reason for this is not clear, but it is conceivable that, for example, the fluorine ion concentration is too high, so that the solvent or the like of the electrolytic solution is deteriorated or the current collector or lead such as aluminum is corroded.

  Moreover, if the fluorine ion concentration in the non-aqueous electrolyte is less than 3 mass ppm, it becomes difficult to function as an electrochemical device. The reason for this is not clear. For example, it is considered that a passive film having a sufficiently high fluorine content cannot be formed on the surface of the current collector 12 such as aluminum because the fluorine ion concentration is too low.

  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.

  For the non-aqueous electrolyte, the degree of drying of the laminate 20, the outer bag 50, etc. so that the fluorine ion concentration in the non-aqueous electrolyte after sealing the outer bag 50 is in the range of 3 to 180 ppm. The water concentration is adjusted to a predetermined value according to the above. 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, the predetermined water concentration is prepared by using various non-aqueous electrolytes previously adjusted to various water concentrations to produce various electric double layer capacitors, and measuring the fluorine ion concentration of the non-aqueous electrolyte after sealing. 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, what laminated | stacked many laminated bodies 20 etc. may be sufficient.

  In addition, even in an electrochemical device other than an electric double layer capacitor such as a primary battery or a secondary battery, the characteristics are improved when the fluorine ion concentration of the nonaqueous electrolyte in the outer bag is specified as described above. .

<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 placed in 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 sandwiched therebetween. The non-aqueous electrolyte is dropped onto the laminate from the last remaining opening of the aluminum laminate outer bag containing the laminate, and the remaining opening is sealed by vacuum thermocompression bonding. Three electric double layer capacitors of 1 were obtained. The thickness of the electric double layer capacitor was about 0.3 mm.

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

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

<Comparative Example 3>
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 determined 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 1-3, 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 (5)

A preparation step of preparing a laminate having a separator and a pair of electrodes provided with the separator interposed therebetween, an exterior 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:
Adjust the amount of water in the non-aqueous electrolyte in the preparation step so that the fluorine ion concentration in the non-aqueous electrolyte in the outer bag after the sealing step is 3 to 180 ppm by mass,
The manufacturing method of the electrochemical device which adjusts the water | moisture content of the said non-aqueous electrolyte by adding a water | moisture content with respect to the said 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 method for producing an electrochemical device according to claim 1, wherein the organic solvent contains propylene carbonate. The method for producing an electrochemical device according to claim 1, wherein the electrode contains acetylene black and polyvinylidene fluoride. The method for producing an 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 method for producing an electrochemical device according to any one of claims 1 to 4, wherein the electrochemical device is an electric double layer capacitor.

Images