JP2007049030A - Method of manufacturing electrochemical device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing an electrochemical device which can efficiently suppress an increase in impedance (internal resistance) due to generation of a gas or an increase in thickness of a case. <P>SOLUTION: The method of manufacturing an electrochemical device 100 in which a pair of electrodes and an nonaqueous electrolyte are hermetically sealed in a case 50 is provided with a voltage applying process of applying a voltage between the pair of electrodes in a state where the pair of electrodes contact the nonaqueous electrolyte. In the voltage applying process, the voltage is applied so that a formula 0.5≤C2/C1≤0.95, where C1 is electrostatic capacity of the electrochemical device at the time of start of the voltage applying process and C2 is electrostatic capacity of the electrochemical device at the time of finish of the voltage applying process. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

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

  At present, electrochemical devices in which a pair of electrodes and a non-aqueous electrolyte are sealed in a case are widely used in various fields. Examples of such an electrochemical device include an electric double layer capacitor and a lithium ion secondary battery.

  By the way, in such an electrochemical device using a non-aqueous electrolyte, if moisture remains in the case, gas is generated in the case due to a reaction between the moisture and the non-aqueous electrolyte or water electrolysis. There is a case.

  In addition, electrodes such as carbon often have large vacancies, and organic compounds such as various solvents and functional groups used in the production process of the electrode are present inside the vacancies. When an electrochemical device is used and the electrode is placed in a high temperature or high voltage energized state, the organic compound or functional group in the electrode is decomposed to generate gas.

  Normally, the case of an electrochemical device is sealed to prevent the inflow of moisture from the outside, so there is no escape route for the gas generated in this way, and the generation of gas increases the impedance (internal resistance). There is a problem that the thickness of the case increases.

In order to solve this problem, for example, in Japanese Patent Application Laid-Open No. 2002-141251, a positive electrode and a negative electrode are opposed to each other through a separator and filled together with an electrolytic solution, and then charged and discharged at least once, Then, a technique for sealing the case after replacing at least a part of the electrolytic solution with a new electrolytic solution is disclosed.
Japanese Patent Laid-Open No. 2002-141251

  However, in the above-described method, the electrolyte to be replaced is wasted and inefficient, and problems due to gas generation may not be sufficiently solved.

  This invention is made in view of the said subject, and provides the manufacturing method of the electrochemical device which can suppress the raise of the impedance (internal resistance) by generation | occurrence | production of gas, and the increase in the thickness of a case efficiently. For the purpose.

  A method for producing an electrochemical device according to the present invention is a method for producing an electrochemical device in which a pair of electrodes and a non-aqueous electrolyte are sealed in a case, wherein the pair of electrodes and the non-aqueous electrolyte are in contact with each other. A voltage applying step of applying a voltage between the pair of electrodes under the condition of being present. In the voltage application step, when the capacitance of the electrochemical device at the start of the voltage application step is C1 and the capacitance of the electrochemical device at the end of the voltage application step is C2, 0.5 ≦ (C2 / C1 ) A voltage is applied so as to satisfy ≦ 0.95.

  According to the present invention, in the voltage application step, impurities such as organic compounds and functional groups adhering to the electrode and impurities such as moisture contained in the electrolyte are sufficiently decomposed, and as a gas, the electrode and electrolyte Is discharged outside. Thereby, it can fully suppress that gas is generated from an impurity in a case after sealing.

  Here, in the case of 0.5> (C2 / C1), the electrolyte solution and the electrode deteriorate. On the other hand, when (C2 / C1)> 0.95, the impurities are not sufficiently gasified, and the generation of gas in the case during use cannot be sufficiently suppressed.

  Here, in the voltage application step, a voltage is applied between the pair of electrodes in a state where the pair of electrodes and the non-aqueous electrolyte is preliminarily sealed in the case. After the voltage application step, It is preferable to open the sealed case to discharge the gas present in the case to the outside of the case, and then seal the case again.

  In this case, it is preferable because the voltage application step can be performed in a normal environment.

  On the other hand, in the voltage application step, the pair of electrodes and the non-aqueous electrolyte are accommodated in the case, the case is formed with an opening communicating with the inside and outside of the case, and a voltage is applied between the pair of electrodes under reduced pressure. It is also preferable to seal the case after the voltage application step.

  In this case, since the generation of the gas by the application of the voltage and the exhaust of the gas from the case can be performed at the same time, the manufacturing can be performed with fewer steps.

  Moreover, it is preferable that the temperature of the electrochemical device in a voltage application process is 40-90 degreeC. Under such conditions, particularly sufficient impurity decomposition is performed.

  The nonaqueous electrochemical device is preferably an electric double layer capacitor. Moreover, it is preferable that a pair of electrodes each contain a carbon material, and the electrolytic solution contains an electrolyte and an organic solvent.

ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the electrochemical device which can suppress efficiently the raise of the impedance (internal resistance) based on generation | occurrence | production of gas and the increase in the thickness of a case is provided.

  First, an electric double layer capacitor as an example of an electrochemical device produced in the present invention will be described with reference to FIG.

  The electric double layer capacitor 100 mainly includes a multilayer body 20, a case 50 that accommodates the multilayer body in a sealed state, 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. Each active material-containing layer 14 is 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 case 50.

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

  The active material-containing layer 14 is formed of, for example, a mixture of a carbon material that becomes an active material and a binder. Examples of the carbon material include acetylene black and activated carbon.

  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 an electrolytic solution. This electrolytic solution is mainly impregnated in the separator 18 and the active material-containing layer 14 in the electrode 10.

  The electrolytic solution is a so-called non-aqueous electrolytic solution containing an electrolyte and an organic solvent.

  The electrolyte is not particularly limited, and examples thereof include onium salts such as ammonium salts, sulfonium salts, and phosphonium. Particularly suitable electrolytes include quaternary ammonium salts such as tetraethylammonium tetrafluoroborate and triethylmonomethylammonium tetrafluoroborate.

  The organic solvent is not particularly limited, and examples thereof include propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and a mixture thereof.

  The electrolyte concentration in the electrolytic solution is not particularly limited, but is preferably in the range of 0.5 to 3 mol / L.

  Such an electrolytic solution may be in a gel form. For example, a gel electrolyte solution in which an organic solvent, an electrolyte, a plasticizer, and a polymer matrix are mixed does not flow but becomes a self-supporting film-like non-aqueous electrolyte solution.

  The case 50 seals the laminate 20 and the electrolytic solution therein. The case 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 from the outside. For example, as the case 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 52, and a film such as polypropylene can be used as the synthetic resin film 54.

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

  Then, the manufacturing method of the electrochemical device which concerns on this embodiment is demonstrated.

  First, an active material such as a carbon material and a binder such as PVdF are dissolved in a solvent such as N-methylpyrrolidone to obtain a coating solution. And this coating liquid is apply | coated on the electrical power collector 12 which consists of metal foil etc., a coating film is dried, and the active material content layer 14 is formed. Then, the current collector 12 having the active material-containing layer 14 is cut into a predetermined size to obtain the electrode 10. Thereafter, the leads 60 and 62 are welded to the ends of the electrode 10. Thereby, the electrodes 10 and 10 having the leads 60 and 62 in FIG. 1 are completed. Moreover, the electrolyte solution and the separator 18 are prepared. Here, the electrode 10, the separator 18, and the electrolyte are sufficiently dried at a high temperature and under reduced pressure to remove impurities as much as possible.

  Subsequently, as shown in FIG. 2, a sheet 51B is prepared by coating the resin on both sides of the metal foil, and as shown in FIG. 3, two sheets are lowered in the middle, and one side 50a is fused by heat or ultrasonic waves. A case 50 having two sides 50b and 50c that are closed and opened is created.

  Subsequently, as shown in FIG. 3, the separator 18 is sandwiched between a pair of electrodes 10 and 10 in a vacuum container 90 in an inert atmosphere, and the central part is integrated by thermocompression bonding. A body 20 is obtained.

  Subsequently, the stacked body 20 is inserted into the case 50 from the opened side 50c. At this time, the leads 60 and 62 are projected from the open side 50 c of the case 50 to the outside. After that, the side 50c opened in the case 50 is fused by heat or ultrasonic waves, and the side 50c is closed as shown in FIG. Thereafter, a predetermined amount of electrolytic solution is supplied into the case 50 from the opened side 50b, and the laminate 20 is impregnated with the electrolytic solution.

  Thereafter, as shown in FIG. 5, the opened side 50 b is fused and closed by heat or ultrasonic waves, and the laminate 20 and the electrolytic solution are temporarily sealed in the case 50.

  Subsequently, an aging process is performed on the temporarily sealed electric double layer capacitor 100. In this aging process, a voltage application device 200 is used as shown in FIG. The voltage application device 200 includes at least a DC power source 201 that can apply a predetermined DC voltage between the electrodes 10 and 10, a capacitance measuring device 203 that can measure the capacitance between the electrodes 10 and 10, Have

  First, the voltage applying device 200 is connected to the leads 60 and 62, and the capacitance between the pair of electrodes 10 and 10 is measured by the capacitance measuring device 203 before aging to obtain C1. Thereafter, a predetermined DC voltage is applied between the electrodes 10 and 10 from the DC power source 201 under a predetermined environmental temperature. Each time a voltage is applied for a predetermined time, the capacitance between the pair of electrodes 10 and 10 is measured by the capacitance measuring device 203 to obtain C2. The voltage application is continued until 0.5 ≦ (C2 / C1) ≦ 0.95 is satisfied. The environmental temperature, that is, the temperature of the electric double layer capacitor is preferably 40 to 90 ° C.

  Here, it is preferable that the amount of energization exceeds the amount necessary for electrolyzing moisture in the cell. If the amount of water in the case 50 before aging is 5000 ppm or less based on the weight of the electrolytic solution, if the current is supplied so as to satisfy the above-mentioned conditions, the normal amount of current is sufficient for the amount of current necessary for the decomposition of the water in the case. It exceeds.

  The energization voltage is not particularly limited, but is preferably 1.23 to 4.00V.

  By this aging process, gas is generated from the electrode 10 and the electrolytic solution. Specifically, for example, decomposition of moisture in the electrolytic solution, decomposition of impurities and functional groups attached to the surface of the electrode 10, particularly an active material-containing layer (for example, an active material such as carbon) occurs, and gas Will occur. This gas stays in the temporarily sealed case 50. This aging process does not need to be performed in a reduced pressure atmosphere.

  When the aging condition is 0.5> (C2 / C1), the aging is excessive and the electrolyte and the electrode are deteriorated. On the other hand, when the aging condition is (C2 / C1)> 0.95, the aging is insufficient, and the removal of impurities such as moisture from the electrolyte and the electrode is insufficient. Gas is generated, the impedance increases remarkably, and the swelling of the cell is not sufficiently suppressed.

  After the aging, as shown in FIG. 7, the electric double layer capacitor 100 is moved into the decompression vessel 90 in an inert atmosphere, and the end of the case 50 is perforated under reduced pressure to form an opening 50h. It should be noted that instead of the opening 50h formed by drilling, the case may be partially cut and cut, and in short, the sealed case may be opened and the inside and outside of the case communicated.

  Then, the gas generated in the aging process is discharged out of the case 50 through the opening 50h.

  Thereafter, as shown in FIG. 8, 50 w around the opening 50 h in the case 50 is fused by heat or ultrasonic waves, and the laminate 20 and the electrolytic solution are again sealed in the case 50. Thereby, the electric double layer capacitor 100 is completed.

  Thus, in the present embodiment, before the electrode 10 and the electrolytic solution are finally sealed in the case 50, the condition that the change in capacitance is 0.5 ≦ (C2 / C1) ≦ 0.95. Since a voltage is applied between the electrodes 10 and 10, the impurities in the case 50 are sufficiently gasified, and the impurities can be discharged out of the case 50 as a gas. Therefore, the amount of impurities in the case 50 after the final sealing is sufficiently reduced. Thereby, even if the electric double layer capacitor 100 is used, an increase in impedance (internal resistance) and an increase in the thickness of the case due to the generation of gas are sufficiently suppressed. In addition, the electrolytic solution is not particularly wasted during the manufacturing process.

  Further, in the present embodiment, since aging is performed in a temporarily sealed state, aging is not necessary in the decompression vessel 90, and aging operation is easy.

  In addition, this invention is not limited to the said embodiment, A various deformation | transformation aspect is possible.

  For example, in the above embodiment, aging is performed on the temporarily sealed electric double layer capacitor, but the present invention is not limited to this, and as shown in FIG. 9, the laminate 20 and the electrolytic solution are accommodated in the case 50. Further, aging may be performed using the voltage applying device 200 in a state where the case 50 is not sealed, that is, the open side 50b remains and the inside and outside of the case are in communication. In this case, if the aging process is performed in the decompression vessel 90 in an inert atmosphere, gas is discharged from the opened side 50b simultaneously with the aging process, so that the number of processes can be reduced.

  In the above embodiment, aging is performed in the case 50, but aging is performed in a state where the pair of electrodes and the electrolytic solution are in contact with each other outside the case, and then the pair of electrodes and electrolytic solution after the aging is completed. It may be accommodated in the case 50 and the case 50 may be sealed.

  Moreover, the electric double layer capacitor 100 is not limited to the above-mentioned form, For example, what laminated many laminated bodies 20 etc. may be sufficient.

  In the above embodiment, the method for manufacturing the electric double layer capacitor has been described. However, the present invention is not limited to the manufacturing of the electric double layer capacitor. For example, other electrochemical methods such as a pseudo capacitor and a redox capacitor can be used. It can be applied to the manufacture of capacitors.

  Furthermore, in the description of the above embodiment, the configuration suitable for the case where the present invention is applied to the production of an electrochemical capacitor (particularly, an electric double layer capacitor) has been described, but the present invention is not limited to this, The present invention can also be applied to the production of various secondary batteries such as lithium ion secondary batteries. In this case, the active material-containing layer of the first electrode (positive electrode) 12 contains an electrode active material that can be used for the positive electrode of a secondary battery such as a lithium ion secondary battery. The active material-containing layer of the second electrode (negative electrode) 13 contains an electrode active material that can be used for the negative electrode of a secondary battery such as a lithium ion secondary battery. In this case, it is preferable to use aluminum, titanium, or the like for the current collector of the first electrode from the viewpoint of corrosion resistance. From the viewpoint of not forming an alloy with lithium, the current collector of the second electrode is made of copper, nickel, etc. Is preferably used.

(Examples A1 to A25)
(Production of electrodes)
Acetylene black having a pore area of a specific area of 50 m ² / g and a pore diameter of 1 nm or less as the active material and having a pore volume of 0.33 cm ³ / g and PVDF as the binder, the active material: binder = 70: 30 ( These were mixed so that the weight ratio), and N-methylpyrrolidone was added to the obtained mixture and kneaded to prepare a coating solution.

  This coating solution is applied on one side of an etched aluminum foil by the doctor blade method, then rolled, and this aluminum foil is heated in air at 150 ° C. for 30 minutes, and subsequently heated at 175 ° C. for 12 hours under vacuum. Was dried. Next, this aluminum foil was punched into a rectangular shape having a tab portion centered on the coating film formation region, and a pair of electrodes for an electric double layer capacitor was obtained.

(Production of cell)
The cell was produced in a low moisture environment with a dew point of −40 ° C. or lower. Two pairs of 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 openings, the lead was taken out from one opening, and the opening was thermocompression bonded with the lead sandwiched therebetween. As the electrolytic solution, an electrolytic solution obtained by dissolving tetraethylammonium tetrafluoroborate in propylene carbonate at a concentration of 1.0 M was used. Then, this electrolytic solution is dropped from the last remaining opening of the aluminum laminate outer bag containing the laminate, and the remaining opening is thermocompression bonded in a vacuum state to form an electric double layer capacitor having a form as shown in FIG. I got a lot.

(Analysis of the amount of water contained in the case)
When one electric double layer capacitor was selected and the moisture contained in the electric double layer capacitor was measured by the Karl Fischer method, it was 500 ppm in terms of electrolyte weight.

(Analysis of the amount of N-methylpyrrolidone contained in the case)
One electric double layer capacitor was selected, and the amount of N-methylpyrrolidone as a residual solvent was measured by GC-Mass. As a result, it was 150 ppm in terms of electrolyte weight.

(aging)
The electric double layer capacitor was aged under various conditions such that the impedance change (C2 / C1) before and after aging satisfied 0.5 ≦ (C2 / C1) ≦ 0.95. Specifically, in Examples A1 to A25, a voltage was applied to each electric double layer capacitor with a combination of environmental temperature, voltage, and time as shown in FIG. After aging, a part of the case was perforated in the vacuum device, and the gas in the case was exhausted, and then the perforated part was sealed by heat sealing. Thus, the electric double layer capacitor of Examples A1 to A25 corresponding to each aging condition was obtained.

(High temperature energization test)
The electric double layer capacitors of Examples A1 to A25 were subjected to continuous energization for 500 hours at 70 ° C. and 3.0 V, respectively, and this was used as a high temperature energization test. Then, the impedance change before and after the high-temperature energization test and the swelling of the case were measured.

(Comparative Examples A1 to A30)
In Comparative Examples A1 to A30, the change in impedance after the high-temperature energization test and the swelling of the case were measured in the same manner as in Example A1, except that the aging conditions were as shown in FIG. In A1 to A30 in this comparative example, the change in impedance before and after aging (C2 / C1) does not satisfy 0.5 ≦ (C2 / C1) ≦ 0.95.

  The results of Examples A1 to A25 and Comparative Examples Comparative Examples A1 to A30 are shown in FIGS.

  A combination of various temperatures, voltages, and times. When the capacitance ratio before and after aging satisfies 0.5 ≦ (C2 / C1) ≦ 0.95, the impedance change after the high-temperature energization test is 130%. The swelling of the case was not a problem. On the other hand, when the above conditions were not satisfied, the impedance after the high-temperature energization test increased significantly and the case was swollen.

(Examples B1 to B8)
In Examples B1 to B8, activated carbon having a specific surface area of 2000 m ² / g and a pore diameter of 1 nm or less and a pore volume of 0.81 cm ³ / g was used as the active material, and further 1 nm as the conductive auxiliary agent. Using acetylene black having a pore volume of 0.03 cm ³ / g having the following pore diameter, the active material: conducting aid: binder (PVDF) = 70: 5: 25 (weight ratio) Mixing and adding N-methylpyrrolidone to prepare a coating solution, supplying 100 μL of electrolyte in the case, and aging conditions as shown in FIG. 12 are the same as in Example A1 I made it. In Examples B1 to B8, the change in impedance before and after aging (C2 / C1) satisfies 0.5 ≦ (C2 / C1) ≦ 0.95.

  The amount of water contained in the case was 2000 ppm in terms of electrolyte weight. The amount of N-methylpyrrolidone contained in the case was 5000 ppm in terms of electrolyte weight.

(Comparative Examples B1 to B8)
Comparative Examples B1 to B8 were the same as Example B1 except that the aging conditions were as shown in FIG. In Comparative Examples B1 to B8, the change in impedance (C2 / C1) before and after aging does not satisfy 0.5 ≦ (C2 / C1) ≦ 0.95. These results are shown in FIG. Even when the active material was replaced with activated carbon, the same tendency as in Example 1 was exhibited.

FIG. 1 is a schematic cross-sectional view of an electric double layer capacitor. FIG. 2 is a schematic perspective view showing a method for manufacturing the electric double layer capacitor. FIG. 3 is a schematic perspective view subsequent to FIG. 2 showing the method for manufacturing the electric double layer capacitor. FIG. 4 is a schematic perspective view subsequent to FIG. 3 showing the method of manufacturing the electric double layer capacitor. FIG. 5 is a schematic perspective view subsequent to FIG. 4 showing the method of manufacturing the electric double layer capacitor. FIG. 6 is a schematic perspective view subsequent to FIG. 5 showing the method of manufacturing the electric double layer capacitor. FIG. 7 is a schematic perspective view subsequent to FIG. 6 showing the method of manufacturing the electric double layer capacitor. FIG. 8 is a schematic perspective view subsequent to FIG. 7 showing the method of manufacturing the electric double layer capacitor. FIG. 9 is a schematic perspective view subsequent to FIG. 8 showing the method of manufacturing the electric double layer capacitor. FIG. 10 is a table showing manufacturing conditions, changes in impedance after the high-temperature test, and cell swelling after the high-temperature energization test for Examples A1 to A25. FIG. 11 is a table showing manufacturing conditions, comparative impedance changes after the high temperature test, and cell swelling after the high temperature energization test for Comparative Examples A1 to A30. FIG. 12 is a table showing manufacturing conditions, impedance changes after the high-temperature test, and cell swelling after the high-temperature energization test for Examples B1 to B8 and Comparative Examples B1 to B8.

Explanation of symbols

  50: Case, 10: Electrode, 100: Electric double layer capacitor (electrochemical device).

Claims (6)

A method for producing an electrochemical device in which a pair of electrodes and a non-aqueous electrolyte are sealed in a case,
A voltage application step of applying a voltage between the pair of electrodes in a state where the pair of electrodes and the non-aqueous electrolyte are in contact with each other;
In the voltage application step, when the capacitance of the electrochemical device at the start of the voltage application step is C1 and the capacitance of the electrochemical device at the end of the voltage application step is C2, 0.5 ≦ ( C2 / C1) A method for producing an electrochemical device in which a voltage is applied so as to satisfy 0.95. In the voltage application step, a voltage is applied between the pair of electrodes in a state where the pair of electrodes and the non-aqueous electrolyte are temporarily sealed in the case in advance.
After the voltage application step, under reduced pressure, the temporarily sealed case is opened and the gas present in the case is discharged out of the case,
The method for manufacturing an electrochemical device according to claim 1, wherein the case is then sealed again. In the voltage application step, the pair of electrodes and the non-aqueous electrolyte are accommodated in the case, the case is formed with an opening that communicates the inside and outside of the case, and the pair of the pair is under reduced pressure. Apply a voltage between the electrodes,
The method for producing an electrochemical device according to claim 1, wherein the case is sealed after the voltage application step.   The method for producing an electrochemical device according to any one of claims 1 to 3, wherein the temperature of the electrochemical device in the voltage application step is 40 to 90 ° C.   The method for manufacturing an electrochemical device according to claim 1, wherein the electrochemical device is an electric double layer capacitor.   The method of manufacturing an electrochemical device according to claim 5, wherein each of the pair of electrodes includes a carbon material, and the electrolytic solution includes an electrolyte and an organic solvent.

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