JP2004193560A - Electric double layer capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology capable of suppressing changes over aging of an electric double layer capacitor and ensuring the high performance over a long term. <P>SOLUTION: The residual chlorine concentration per unit area of a foil is managed not to exceed 1.0 mg/m<SP>2</SP>. Since the chlorine concentration is managed not to exceed 1.0 mg/m<SP>2</SP>, changes of an electric double layer capacitor can be suppressed over aging and the electric double layer capacitor can maintain the high performance over a long term. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

  The present invention relates to a current collector foil used for an electric double layer capacitor.

2. Description of the Related Art An electric double layer capacitor corresponding to an electric double layer capacitor, particularly an invention focusing on the strength of a current collecting foil (aluminum foil) thereof has been known (for example, Patent Document 1).
JP-A-11-283871 (pages 2-3)

  In page 10 paragraph number [0007], line 10 to line 12 of Patent Document 1, "However, the strength of the obtained electrode body is low, and the manufacturing process of the electrode body and the lamination of the electrode body and the separator to produce a capacitor. The electrode body is likely to be damaged in the process of performing the process. "

The third page, paragraph number [0011], page 7 to line 9 of Patent Document 1 describes "a current collector for an electric double layer capacitor characterized by having a breaking energy of 3 kg · mm or more".
From this, it can be said that Patent Literature 1 is an invention in which the problem of strength is solved by increasing the impact resistance.

  The present inventors prototyped a large number of electric double layer capacitors in consideration of the strength of the electrode body, that is, the current collector foil, as in Patent Document 1, and evaluated them. As a result of this evaluation, it was found that although the strength was satisfactory, the resistance value increased more than tolerable with the use time, and the performance as a storage battery was significantly reduced.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a technique of an electric double capacitor capable of suppressing deterioration over time and exhibiting high performance over a long period of time.

  Therefore, as a result of examining various elements, it was found that chlorine remaining on the surface of the current collector foil had a great influence on aging. Since chlorine ions contained in the etching solution are factors of residual chlorine, chlorine is inevitably left on the current collector foil after etching.

This residual chlorine is generally removed by washing. In order to increase the degree of cleaning, multiple cleanings are required, and the multiple cleanings are not preferable from the viewpoint of manufacturing cost.
Thus, the present inventors have studied the concentration of residual chlorine in various ways and have succeeded in finding an allowable limit thereof.

That is, claim 1 forms a positive electrode and a negative electrode by attaching an electrode material mainly composed of activated carbon to a pair of current collecting foils, and a separator is interposed between the positive and negative electrodes and an electrolytic solution is interposed. In the electric double layer capacitor capable of performing charging and discharging through the pair of current collector foils,
An electric double layer capacitor, wherein the current collector foil used in the step of attaching an electrode material satisfies the following conditions.
-The current collector foil is subjected to an etching process using an etching solution containing chlorine ions.
The above etching treatment is performed so that the capacitance per unit surface area of the foil alone in the case of chemical conversion treatment with a coating withstand voltage of 65.5 volts falls within (1.7 to 2.3) μF / cm ^2. .
Tensile strength of the foil, that which is not less than the 9000N / cm ^2.
Chlorine concentration per unit area remaining in the foil, it, not exceed 1.0 mg / ^{m 2.}

By controlling the capacitance so that it is within (1.7 to 2.3) μF / cm ² and the chlorine concentration per unit area remaining on the foil does not exceed 1.0 mg / m ² , the electric power Aging of the heavy capacitor can be suppressed, and high performance can be exhibited over a long period of time.
By setting the tensile strength of the foil to 9000 N / cm ² or more, it is possible to avoid breakage trouble during manufacturing and reduce manufacturing cost.

Since chlorine of up to 1.0 mg / m ² is allowed to remain in the foil, cleaning is facilitated, and the cost for cleaning can be reduced.

According to claim 1, the capacitance is set to (1.7 to 2.3) μF / cm ^2, and the chlorine concentration per unit area remaining on the foil does not exceed 1.0 mg / m ^2. By managing, the aging of the electric double capacitor can be suppressed, and high performance can be exhibited over a long period of time. By setting the tensile strength of the foil to 9000 N / cm ² or more, it is possible to avoid breakage trouble during production and reduce production cost.

The best mode for carrying out the present invention will be described below with reference to the accompanying drawings. The drawings should be viewed in the direction of reference numerals.
FIG. 1 is a perspective view of an electric double-layer capacitor according to the present invention. An electric double-layer capacitor 10 has a band-shaped positive electrode 11 and a band-shaped negative electrode 12 laminated via a separator 13 and tightly wound into a container. 14 is a cylindrical electric double layer capacitor.
Reference numeral 15 denotes a sealing plate, 16 denotes a positive electrode terminal, 17 denotes a negative electrode terminal, and 18 denotes a liquid injection port for injecting an electrolytic solution.

  FIG. 2 is an enlarged cross-sectional view of the electric double layer capacitor. A positive electrode 11 includes a current collector foil 21 such as an aluminum foil and an electrode material 22 mainly composed of activated carbon adhered to the current collector foil 21 in a sheet shape. Consists of The negative electrode 12 also includes a current collecting foil 21 such as an aluminum foil and an electrode substance 22 mainly composed of activated carbon adhered to the current collecting foil 21 in a sheet shape. The electrode materials 22, 22 are also adhered to the back surfaces of the current collector foils 21, 21, but are not shown for simplicity.

Then, the electrode materials 22 and 22 are impregnated with an appropriate amount of an electrolytic solution.
When a direct current is applied to the positive electrode terminal 16 and the negative electrode terminal 17, positive and negative ions are adsorbed inside the electrode materials 22, 22 and on the surfaces of the current collecting foils 21, 21, and one forms a positive electrode and the other forms a negative electrode. At the time of discharge, a current can be extracted through the positive and negative terminals 16 and 17 due to the movement of electrons accompanying the desorption of the adsorbed ions.

FIG. 3 is a flowchart for explaining in detail the manufacturing flow of the electric double layer capacitor according to the present invention, particularly the manufacturing of the current collector foil. STxx indicates a step number.
ST01: As the current collecting foil, for example, an aluminum foil having a purity of 99.8% or more is prepared. The surface of the aluminum foil is substantially flat.

  ST02: The aluminum foil is etched in an etching solution containing hydrochloric acid. By this etching, a fine rough surface is formed on the surface of the foil. The fine rough surface serves as a wedge for retaining the electrode material to be applied later.

After the formation of the rough surface is completed, the foil is subjected to a neutralization treatment and is subjected to predetermined cleaning. The predetermined cleaning means that the cleaning is performed to such an extent that the residual chlorine concentration satisfies the control standard (1.0 mg / m ² or less). This prevents excessive cleaning work.

  ST03: As a pretreatment for measuring the capacitance, a foil piece cut out of the foil is immersed in an aqueous solution of ammonium adipate, and a chemical conversion treatment is performed by applying a voltage of 65.5 volts with a coating withstand voltage.

ST04: The capacitance C of the foil is measured.
FIG. 4 is a diagram illustrating the principle of capacitance measurement. A test vessel 30 is filled with an aqueous solution 31 of ammonium adipate, a foil piece 21 is immersed therein, and a counter electrode 32 is arranged at a position surrounding the foil piece 21. The capacitance of the foil piece 21 is measured by the capacitance meter 33 while applying electricity to the piece 21 and the counter electrode 32. This means that the capacitance C of the foil alone has been measured.

Referring back to FIG.
ST05: It is checked whether or not the capacitance C of the foil alone is in the range of (1.7 to 2.3) μF / cm ² . The basis for this range will be described later. If YES, proceed to the next step, but if NO, treat it as a rejected product.

  ST06: Measure the tensile strength TS of the foil. A test piece having a width of 10 mm and a length (50 mm + gripping allowance) is cut out from the foil, and the test piece is set on a tensile tester of JIS B 7721, whereby the tensile strength TS of the foil can be measured.

ST07: Check whether or not the tensile strength TS is 9000 N / cm ² or more. If it is less than this value, it may be broken due to tension applied at the time of winding or the like, so it is treated as a rejected product. If YES, proceed to the next step.

  ST08: The residual chlorine concentration CL of the foil is measured. Specifically, chloride ions of the foil are extracted with an aqueous sodium hydroxide solution. The extract is clarified by adding sulfuric acid, heating, and centrifuging, and then an aqueous solution of silver nitrate is added to make it opaque as silver chloride. The degree of the cloudiness is compared with a standard solution to determine the concentration.

ST09: Check whether the residual chlorine concentration CL of the foil is 1.0 mg / m ² or less. The basis for this range will be described later. If YES, proceed to the next step, but if NO, treat it as a rejected product.

ST10: The electrode substance is formed into a sheet and attached by bonding or the like only for the foil that has passed the above inspection.
ST11: Wound with the separator.
ST12: Store in a container.
ST13: Attach the sealing plate.
ST14: Inject electrolyte.
Thus, the cylindrical electric double layer capacitor shown in FIG. 1 can be obtained.

  ST03 to ST09 can be a sampling inspection. In this case, the main manufacturing flow is ST01 → ST02 → ST10 → ST11 to ST14, and ST03 to ST09 are sub-flows.

  In addition, the order of ST03 to ST09 may be changed.

An embodiment according to the present invention will be described below. Make 11 samples for comparative experiments.
1. Sample material:
1-1. Current collector foil:
1-1-1. Current collector foils for Examples 1-5 and Comparative Examples 1-6:
The raw aluminum foil was immersed in 5% hydrochloric acid heated to 40 to 50 ° C. (depending on the examples and comparative examples; individual conditions are shown in the next section), the electrolytic current density was 0.25 A / cm ² , and the quantity of electricity was The surface was etched with a 50 Hz alternating current of 25 to 40 A · min / dm ² (depending on the examples and comparative examples; individual conditions are shown in the next section).
The foil taken out of the etching bath is subjected to a cleaning treatment with an acidic aqueous solution of pH 1 heated at 30 ° C. to 50 ° C. (discrimination is described in the next section) for 30 seconds or 1 minute (discrimination is described in the next section), and further 180 ° C. And dried with warm air.

1-1-2. Individual conditions:
In Example 1, the solution temperature was 45 ° C., the amount of electricity was 35 A · min / dm ² , and the washing was performed for 1 minute with an acidic aqueous solution of pH 1 heated to 50 ° C.
In Example 2, the liquid temperature was 47 ° C., the amount of electricity was 35 A · min / dm ² , and the cleaning was the same as in Example 1.
In Example 3, the liquid temperature was 50 ° C., the amount of electricity was 35 A · min / dm ² , and the cleaning was the same as in Example 1.
In Example 4, the liquid temperature was 50 ° C., the amount of electricity was 38 A · min / dm ² , and the cleaning was the same as in Example 1.
In Example 5, the liquid temperature was 50 ° C., the amount of electricity was 40 A · min / dm ² , and the cleaning was the same as in Example 1.

In Comparative Example 1, the liquid temperature was 40 ° C., the amount of electricity was 25 A · min / dm ² , and the cleaning was the same as in Example 1.
In Comparative Example 2, the liquid temperature was 40 ° C., the amount of electricity was 28 A · min / dm ² , and the cleaning was the same as in Example 1.
In Comparative Example 3, the liquid temperature was 42.5 ° C., the amount of electricity was 40 A · min / dm ² , and the cleaning was the same as in Example 1.
In Comparative Example 4, the liquid temperature was 45 ° C., the amount of electricity was 45 A · min / dm ² , and the cleaning was the same as in Example 1.

In Comparative Example 5, the solution temperature was 50 ° C., the amount of electricity was 30 A · min / dm ² , and the washing was performed with an acidic aqueous solution of pH 1 heated to 40 ° C. for 30 seconds.
In Comparative Example 6, the liquid temperature was 50 ° C., the amount of electricity was 30 A · min / dm ² , and the cleaning was performed with an acidic aqueous solution of pH 1 heated to 30 ° C. for 30 seconds.

The following description is commonly applied to the above-described various current collector foils.
1-2. Electrode material:
90 parts by weight of activated carbon, 5 parts by weight of graphite powder and 5 parts by weight of ethylene tetrafluoride are mixed, kneaded, molded, and rolled to produce a sheet-like electrode material having a thickness of 145 μm, a width of 100 mm, and a length of 1200 mm. .
1-3. adhesive:
Conductive adhesive composed of PVA (polyvinyl alcohol), graphite and amorphous carbon

1-4. Separator:
Artificial silk separator. A porous film having a thickness of 75 μm and a width of 105 mm.
1-5. container:
Container having a diameter of 40 mm and a height of 130 mm 1-6. Electrolyte:
TEMA.BF ₄ / PC as an organic electrolyte. TEMA.BF ₄ is triethylmethylammonium tetrafluoroborate, and PC is propylene carbonate.

2. How to make a sample:
An electrode material is attached to both sides of the current collector foil using the adhesive. It is wound together with the separator, placed in a container, and injected with an electrolytic solution to produce a cylindrical electric double layer capacitor. Eleven types of samples are prepared for comparison experiments.

3. Measurement 3-1. The capacitance is measured by the above-described measuring method.
3-2. Measurement of tensile strength: Measured by the above-mentioned measuring method.
3-3. Measurement of residual chlorine concentration: Measured by the above-mentioned measuring method.

3-4. Measurement of cell resistivity:
For unused samples. A resistance meter is connected to the positive and negative terminals 16 and 17 in FIG. 1 to measure a resistance value A (Ω). This is multiplied by the area B (cm ² ) of the positive and negative electrode current collector foil to determine the cell resistivity (Ωcm ² ). That is, the cell resistivity (Ωcm ² ) = the resistance value A (Ω) × the area B (cm ² ) of the positive and negative electrode current collector foils. However, this is a value when the thickness of the electrode material is 145 μm (see 1-2.).

3-5. Measurement of resistance increase rate after 2000 hours:
After measuring the cell resistivity, a continuous application of 2.5 volts is performed in a 45 ° C. environment. After 2000 hours, the application is stopped.
Then, in a normal temperature environment, constant-pressure discharge is started while maintaining 30 amps, and the discharge ends when 2.5 volts is reduced to 1.0 volt.

  At this point, 3-4. According to the same procedure as described in the measurement of cell resistivity, a cell resistivity of 2000 hr was obtained. Calculate what percentage has increased with respect to the cell resistivity obtained in the above. This calculated value will be referred to as a resistance increase rate after 2000 hours.

3-6. Electrode peelability:
After measuring the resistance increase rate after 2000 hours, the sample is disassembled, and the foil and the electrode material are visually inspected. And, if the sheet-like electrode material remains adhered to the foil, "no peeling", if the sheet-like electrode material partially peels from the foil, "partially peeling", most of the sheet-like electrode material comes from the foil. If it was peeled, it was regarded as "peeled".

  Table 1 is a table in which, for Examples 1 to 5 and Comparative Examples 1 to 6, the capacitance, the tensile strength, the residual chlorine concentration, the cell resistivity, the resistance increase after 2000 hours, and the electrode peeling property are recorded. Various graphs are created from the values in this table and evaluated.

FIG. 5 is an evaluation graph of the rate of increase in resistance after 2000 hours, in which the horizontal axis represents the capacitance, ○ in the graph represents an example, and Δ represents a comparative example.
The resistance increase rate after 2000 hours indicates the degree of aging. The larger the aging deterioration, the larger the value. Therefore, it can be said that the smaller the value, the better. The circles are all around 15.0%, which is much smaller than the triangle.
From this graph, it can be said that the 65.5 V electrostatic capacitance only needs to be in the range of 1.7 to 2.3 μF / cm ² .

FIG. 6 is a graph showing the relationship between the capacitance and the cell resistivity. The horizontal axis represents the capacitance, ○ in the graph represents an example, and Δ represents a comparative example.
The cell resistivity is the initial specific resistance, but it goes without saying that the smaller this value is, the better. When the range of 1.7 to 2.3 μF / cm ² found in FIG. 5 is applied to FIG. 6, ○ is generally smaller than △. From this point as well, it can be said that it is appropriate to keep the 65.5 V electrostatic capacity of the foil within the range of 1.7 to 2.3 μF / cm ² .

FIG. 7 is a graph showing the relationship between the capacitance and the tensile strength. The horizontal axis represents the capacitance, 、 in the graph represents the example, and Δ represents the comparative example.
The capacitance is increased by forming a rough surface on the smooth foil surface by etching. On the other hand, the formation of a rough surface reduces the cross-sectional area of the foil and decreases the tensile strength. The graph shows that trend.

If 2.3μF / cm ² in the horizontal axis, at least 9000 N / cm tensile strength of ² can be secured. If 1.7μF / cm ² in the horizontal axis, the tensile strength of 11000N / cm ² is obtained. From this point as well, it can be said that it is appropriate to keep the 65.5 V electrostatic capacity of the foil within the range of 1.7 to 2.3 μF / cm ² .

FIG. 8 is a graph created for the evaluation of residual chlorine. The horizontal axis represents the residual chlorine concentration, and the vertical axis represents the resistance increase rate after 2000 hours.
Comparative Examples 5 and 6 indicated by Δ are not preferable because the upper layer ratio of the resistance after 2,000 hours is remarkably large. In this regard, in Examples 1 to 5 indicated by が, the upper layer ratio of the resistance after 2,000 hours is remarkably small and good. It suffices if the horizontal axis is within 1.0 mg / cm ² .
That is, it can be said that aging can be suppressed by using a foil having a residual chlorine concentration not exceeding 1.0 mg / cm ² .

From the above Table 1 and FIGS. 5 to 8, the capacitance per unit surface area of the foil alone is contained in (1.7 to 2.3) μF / cm ^2, and the chlorine concentration per unit area remaining on the foil is It was confirmed that it is important to keep the amount not to exceed 1.0 mg / m ² in order to suppress aging deterioration. Needless to say, it is necessary to control the tensile strength to 9000 N / cm ² or more in order to avoid breakage trouble during production.

Although the current collector foil is described as an aluminum foil, other metal foils may be used.
In addition, since the present invention can be applied to a flat capacitor as well as a cylindrical capacitor, the external shape of the capacitor is arbitrary.

  The electric double layer capacitor according to the present invention is suitable for a vehicle-mounted battery.

It is a perspective view of the electric double layer capacitor concerning the present invention. FIG. 3 is an enlarged cross-sectional view of the electric double layer capacitor. FIG. 2 is a flowchart illustrating in detail a production flow of an electric double layer capacitor according to the present invention, particularly production of a current collector foil. It is a capacitance measurement principle diagram. It is an evaluation graph of a resistance rise rate after 2000 hours. 5 is a graph showing a relationship between capacitance and cell resistivity. It is a graph which shows the relationship between capacitance and tensile strength. It is the graph created for the evaluation of residual chlorine.

Explanation of reference numerals

  DESCRIPTION OF SYMBOLS 10 ... Electric double layer capacitor, 11 ... Positive electrode, 12 ... Negative electrode, 13 ... Separator, 21 ... Current collecting foil (foil), 22 ... Electrode material.

Claims (1)

A positive electrode and a negative electrode are produced by attaching an electrode material mainly composed of activated carbon to a pair of current collecting foils, and a separator is interposed between the positive and negative electrodes and an electrolytic solution is interposed therebetween. In electric double layer capacitors that can be charged and discharged through foil,
An electric double layer capacitor, wherein the current collector foil used in the step of attaching an electrode material satisfies the following conditions.
-The collector foil is subjected to an etching treatment with an etching solution containing chlorine ions.
The etching treatment is performed so that the capacitance per unit surface area of the foil alone in the case where the chemical conversion treatment is performed at a coating withstand voltage of 65.5 volts falls within (1.7 to 2.3) μF / cm ² .
Tensile strength of the foil, that which is not less than the 9000N / cm ^2.
Chlorine concentration per unit area remaining in the foil, it, not exceed 1.0 mg / ^{m 2.}

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