JP2008010854A - Electric double-layer capacitor and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric double-layer capacitor capable of reducing resistance by suppressing deterioration in a positive electrode for the electric double-layer capacitor used for automobiles, or the like. <P>SOLUTION: The electric double-layer capacitor comprises: an element 1 in which a pair of positive and negative electrodes, where a polarizable electrode layer 3 mainly using activated carbon is formed on a collector 2, is wound while a separator 4 is interposed between the pair of positive and negative electrodes; and a metal case 6 in which the element 1 is stored with an electrolyte for drive. The surface of activated carbon including a part without any contact with a material, where the activated carbon in the polarizable electrode layer 3 formed in the positive electrode composes the polarizable electrode layer 3, is fluorinated by the termination section of carbon skeleton. An aluminum fluoride film is formed on the surface of the collector 2 including a part without any contact with a material, where the collector 2 composes the polarizable electrode layer 3 on the interface between the collector 2 and the polarizable electrode layer 3, thus suppressing deterioration in the positive electrode and reducing resistance. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an electric double layer capacitor used for various electronic devices, a backup power source, a regenerative power source, a power storage device and the like of a hybrid vehicle and a fuel cell vehicle, and a manufacturing method thereof.

  Conventionally, electric double layer capacitors have attracted attention and are used in many fields because of their high withstand voltage, large capacity, and high reliability of rapid charge / discharge. Such an electric double layer capacitor uses a polarizable electrode mainly composed of activated carbon for both the positive electrode and the negative electrode, and the withstand voltage of the electric double layer capacitor is 1.2 V when an aqueous electrolyte is used. When a system electrolyte is used, it is 2.5 to 3.3 V. Since the energy of the electric double layer capacitor is proportional to the square of the withstand voltage, the organic electrolyte having a higher withstand voltage is higher in energy than the aqueous electrolyte, but even in an electric double layer capacitor using an organic electrolyte The energy density is 1/10 or less of a secondary battery such as a lead storage battery.

As prior art document information related to the invention of this application, for example, Patent Document 1 is known.
Japanese Patent Laid-Open No. 10-270293

However, in the conventional electric double layer capacitor, when a voltage is applied, an F ⁻ component such as BF ₄ ⁻ or PF ₆ ⁻ used as an electrolyte anion constituting the driving electrolyte reacts with aluminum which is a positive electrode current collector. The aluminum is eluted, and the eluted aluminum adheres to the surface of the activated carbon constituting the polarizable electrode layer as aluminum fluoride (AlF ₃ ), so that the resistance value increases and the current collector deteriorates. As a result, the performance deteriorates.

  An object of the present invention is to solve such a conventional problem, and to provide an electric double layer capacitor capable of reducing resistance by suppressing deterioration of a positive electrode and a method for manufacturing the same.

  In order to solve the above problems, the present invention provides a pair of positive and negative electrodes in which a polarizable electrode layer mainly composed of activated carbon is formed on a current collector made of a metal foil, and each electrode layer is formed by interposing a separator therebetween. In an electric double layer capacitor comprising an element configured by stacking or winding in an opposed state, a case containing the element together with a driving electrolyte, and a sealing member sealing the opening of the case, The end of the carbon skeleton is fluorinated on the activated carbon surface including the portion where the activated carbon in the polarizable electrode layer formed on the positive electrode is not in contact with the material constituting the polarizable electrode layer, and the current collector In the interface between the electrode and the polarizable electrode layer, an aluminum fluoride film is formed on the surface of the current collector including a portion where the current collector is not in contact with the material constituting the polarizable electrode layer.

  In addition, as a method of manufacturing this electric double layer capacitor, the positive electrode is decompressed in a fluorine gas atmosphere and heat-treated, so that activated carbon in the polarizable electrode layer formed on the positive electrode constitutes the polarizable electrode layer. A material that constitutes the polarizable electrode layer at the interface between the current collector and the polarizable electrode layer, such that the end portion of the carbon skeleton is fluorinated on the activated carbon surface including a portion that is not in contact with the material; An aluminum fluoride film is formed on the surface of the current collector including the non-contact portion.

  As described above, the electric double layer capacitor according to the present invention is such that the activated carbon surface in the polarizable electrode layer formed on the positive electrode is fluorinated at the terminal portion of the carbon skeleton and the surface of the current collector is aluminum fluoride. Due to the structure in which the film is formed, aluminum fluoride has a strong bond between fluorine atoms and aluminum atoms, so that when the voltage is applied, aluminum, which is the current collector of the positive electrode, is prevented from eluting into the electrolyte solution, The effect that the increase in resistance can be prevented is obtained.

(Embodiment)
Hereinafter, the invention described in the entire claims of the present invention will be described by using embodiments.

  FIG. 1 is a partially cutaway perspective view showing a configuration of an electric double layer capacitor according to an embodiment of the present invention. In FIG. 1, 1 is an element, and the element 1 is a current collector made of an aluminum foil. 2 is formed by winding a pair of positive and negative electrodes formed with a polarizable electrode layer 3 mainly composed of activated carbon on the front and back surfaces 2 with a separator 4 interposed therebetween.

  5 is a lead wire connected to and drawn from the two electrodes, 6 is an aluminum metal case containing the element 1 together with a driving electrolyte (not shown), and 7 is a pair drawn from the element 1. This is a sealing rubber that has a hole through which the lead wire 5 passes and is fitted into the opening of the metal case 6 and seals by processing the opening end of the metal case 6, and a specific embodiment will be described below. However, the present invention is not limited to this.

  First, as a positive electrode and a negative electrode, high-purity aluminum foil (Al: 99.99% or more) having a thickness of 30 μm is used as a current collector 2, and the surface is roughened by electrolytic etching in a hydrochloric acid-based etching solution. did.

  Subsequently, a phenol resin-based activated carbon powder having an average particle diameter of 5 μm and carbon black and carboxymethylcellulose (hereinafter referred to as CMC) having an average particle diameter of 0.05 μm as a conductivity imparting agent in a weight ratio of 10: 2: 1. After the water-soluble binder solution mixed and dissolved is sufficiently kneaded with a kneader, methanol and water dispersion solvents are added little by little, and further kneaded to prepare a paste having a predetermined viscosity. The polarizable electrode layer 3 was formed by coating on the front and back surfaces of No. 2 and drying in air at 100 ° C. for 1 hour.

  Subsequently, the front and back surfaces of the positive electrode on which the polarization layer electrode layer 3 is formed on the front and back surfaces of the current collector 2 are heated in a fluorine gas atmosphere to reduce the activated carbon in the polarizable electrode layer 3. The end of the carbon skeleton is fluorinated on the activated carbon surface including the portion not in contact with the material constituting the polarizable electrode layer 3, and the current collector is at the interface between the current collector 2 and the polarizable electrode layer 3. An aluminum fluoride film was formed on the surface of the current collector 2 including a portion where 2 is not in contact with the material constituting the polarizable electrode layer 3. This fluorine gas treatment was performed by putting the positive electrode into a treatment chamber (not shown) and heating at 90 ° C. for 2 minutes in a fluorine gas atmosphere under a reduced pressure of 90 KPa. FIG. 2 shows a positive electrode subjected to a fluorine gas treatment compared with a positive electrode before the treatment.

2A and 2B are cross-sectional views showing the positive electrode before and after the fluorine gas treatment. In FIG. 2A, 2 is a current collector made of aluminum foil, and 2a is this current collector. An alloy layer _{3 of} Al ₂ O ₃ composition made of aluminum oxide formed on the surface of the body 2 is a polarizable electrode layer. The polarizable electrode layer 3 is composed of activated carbon 3a, conductive additive 3b, and binder 3c.

Thus, the positive electrode before the fluorine gas treatment (alloy layer 2a made of aluminum oxide and having an Al ₂ O ₃ composition is formed, and further a polarizable electrode layer 3 mainly composed of activated carbon 3a is formed thereon. ) Has an effect of reducing the contact resistance by interposing the Al ₂ O ₃ alloy layer 2a made of aluminum oxide between the polarizable electrode layer 3 and the current collector 2, but this positive electrode is used for driving. When charging and discharging is performed by immersing in the electrolytic solution, aluminum is eluted from a part of the alloy layer 2a having the Al ₂ O ₃ composition, and reacts with the fluorine component in the driving electrolytic solution to produce an AlF ₃ compound. It adheres to the surface of the activated carbon 3a. Therefore, the activated carbon area is reduced, the capacity of the electrochemical capacitor is reduced, and the AlF ₃ compound is not a good conductor, so that there is a problem that the resistance increases as the reaction proceeds. .

On the other hand, the positive electrode subjected to the fluorine gas treatment according to this embodiment is an alloy layer having an Al ₂ O ₃ composition made of aluminum oxide formed on the surface of the current collector 2 as shown in FIG. The surface of the part of the alloy layer 2a where the alloy layer 2a is not in contact with the material constituting the polarizable electrode layer 3 at the interface with the polarizable electrode layer 3 as well as the surface of the part where the 2a is exposed is fluorinated. Thus, an AlF ₃ alloy layer 2b is formed.

  In addition to the surface of the activated carbon 3a exposed from the polarizable electrode layer 3, the activated carbon 3a in the polarizable electrode layer 3 is a material constituting the polarizable electrode layer 3 (activated carbon 3a, conductive additive 3b, binder 3c). The surface of the activated carbon 3a that is not in contact with the carbon is also in a state (not shown) in which the terminal portion of the carbon skeleton is fluorinated (usually hydrogen (H) or oxygen (O)). Yes.

  In this way, the surface of the alloy layer 2a where the alloy layer 2a is not in contact with the material constituting the polarizable electrode layer 3 at the interface with the polarizable electrode layer 3, or the activated carbon 3a in the polarizable electrode layer 3 It can be considered that the fluorination of the surface of the activated carbon 3a that is not in contact with the material constituting the polarizable electrode layer 3 can be realized by performing the fluorine gas treatment under reduced pressure. It is.

  Therefore, since the positive electrode whose surface is fluorinated in this way, aluminum fluoride has a strong bond between fluorine atoms and aluminum atoms. Therefore, even if this electrode body is impregnated in the driving electrolyte and charged and discharged, the positive electrode This makes it possible to suppress the elution of aluminum, which is a current collector, and to prevent the deterioration of the capacity and resistance.

Next, the positive electrode and the negative electrode obtained in this way are made into a set of two sheets, and the element 1 is obtained by winding with the separator 4 interposed therebetween, and the element 1 is combined with the driving electrolyte. While being inserted into the metal case 6, the element 1 was impregnated with the driving electrolyte. As the driving electrolyte, tetraethylammonium ions are used as electrolyte cations, BF ₃ (C ₂ F ₅ ) ⁻ as electrolyte anions, polycarbonate having a high dielectric constant as a solvent, and 1 wt% of phosphoric acid as an additive. What was added was used.

  Next, the lead wire 5 drawn out from the element 1 inserted into the metal case 6 together with the driving electrolyte in this way is passed through the hole provided in the sealing rubber 7, and the sealing rubber 7 is inserted into the metal case 6. Then, sealing was performed by drawing and curling the vicinity of the opening of the metal case 6 to complete the electric double layer capacitor according to the present embodiment.

  The results of measuring the capacitance / resistance characteristics of the electric double layer capacitor according to this embodiment configured as described above are shown in Table 1 in comparison with a conventional product as a comparative example.

  As is clear from Table 1, the electric double layer capacitor according to the present embodiment has a configuration in which the front and back surfaces of the positive electrode on which the polarizable electrode layer is formed are covered with aluminum fluoride, so that the aluminum fluoride is a fluorine atom. Because the bond between aluminum and aluminum is strong, it is possible to prevent the electrode foil from degrading by suppressing the elution of the positive electrode current collector into the driving electrolyte when a voltage is applied. An effect is obtained.

In the present embodiment, the example in which BF ₃ (C ₂ F ₅ ) ⁻ is used as the electrolyte anion of the driving electrolyte has been described. However, the present invention is not limited to this, and PF ₃ (C ₂ F ₅ ) ₃ ⁻ , (CF ₃ SO ₂ ) ₂ N ⁻ , (C ₂ F ₅ SO ₂ ) ₂ N ⁻ , (CF ₃ SO ₂ ) ₃ C ⁻ , (Chemical Formula 1), (Chemical Formula 2) The same effect can be obtained even when any one of PF ₆ ⁻ is used, and each of the electrolyte anions is classified into the following (a) to (d), and the effects of the respective electrolyte anions are obtained. Will be described in more detail.

(A) When BF ₃ (C ₂ F ₅ ) ⁻ , PF ₃ (C ₂ F ₅ ) ₃ ^— is used (b) (CF ₃ SO ₂ ) ₂ N ⁻ , (C ₂ F ₅ SO ₂ ) ₂ N ^{_{-, (CF 3 SO 2)}} 3 C - was the case (d) PF ₆ that using the case of using (c) (Formula 1) (Formula 2) ^- first case of using, BF ₃ (C in (a) ^{_{2 F 5) -, PF 3}} (C 2 F 5) 3 - when using the electrolyte anions, BF ₄ as conventional ^- as compared with the case of using the anion, cell degradation by inhibiting hydrolysis The effect of suppression and the effect of reducing the cell resistance can be obtained.

To explain this reason, first, the conventional products BF ₄ ^- the case for using the anion is described, BF ₄ ^- Hydrolysis in the case of using an anion proceeds as shown in Equation (1) - (Equation 4) Equilibrium goes to the right and the concentration of H ⁺ and F ⁻ increases.

As the H ⁺ concentration increases, acidification in the electrolyte system proceeds. When the electrolytic solution becomes strongly acidic, decomposition (solvent decomposition reaction) of cyclic carbonate solvents (propylene carbonate, ethylene carbonate, etc.) that are generally used as solvents in the electrolytic solution of electrochemical capacitors and electric double layer capacitors proceeds. Gas generation, capacity deterioration and resistance deterioration will be caused. Since this solvent decomposition reaction is a chemical reaction, the higher the temperature, the faster the reaction rate and the greater the cell performance degradation. Further, (Equation 1) to (Equation 4) are equilibrium reactions, and it goes without saying that the in-solution equilibrium changes depending on the H ⁺ concentration.

On the other hand, when the F ⁻ concentration increases, the aluminum or aluminum oxide on the aluminum surface, which is the positive electrode current collector, tends to react with F ⁻ and changes to aluminum fluoride (mainly AlF, AlF ₃ ) (aluminum corrosion reaction). ). This aluminum corrosion reaction is shown by (Formula 5)-(Formula 8).

Since this reaction reacts slowly during use of the electrochemical capacitor cell (mainly when voltage is applied), the ratio of aluminum or aluminum oxide on the aluminum surface gradually decreases, and the ratio of aluminum fluoride gradually increases. Aluminum fluoride is very stable in organic electrolytes and is repaired if there is a fluorine source in the electrolyte even if the coating is mechanically, electrically or electrochemically destroyed. That is, the aluminum surface can be gently stabilized (passivated). In addition, since fluorine and aluminum have high binding energy, aluminum fluoride forms a very stable compound even in an acid or alkali solution. Therefore BF ₄ ^- anions are widely used in electrochemical capacitors, electric double layer capacitor.

  However, this aluminum corrosion reaction generates aluminum fluoride in the electrolyte solution and adheres to the electrode surface or separator surface, thereby covering the electrode active material surface and separator surface with non-conductive aluminum fluoride. . For this reason, there exists a subject that it becomes the factor of capacity | capacitance degradation of an electrochemical capacitor cell, and resistance degradation.

The composition of aluminum fluoride is mainly AlF and AlF ₃ , but some amount of the portion having a composition (structure) containing oxygen such as AlOF, AlO (OH), and Al (OH) ₃ should remain. Needless to say. Needless to say, even if a small amount of AlOF or the like is present, if the main composition is AlF or AlF ₃ , it functions as a good passive film.

On the other hand, when BF ₃ (C ₂ F ₅ ) ⁻ according to the present invention is used as the electrolyte anion, the following (formula 9) is obtained.

The reaction of (Formula 9) is less likely to proceed to the right side than the reaction of (Formula 1) above. That is, since the hydrolysis reaction as in the above (formula 1) to (formula 4) does not proceed easily, H ⁺ generation and F ⁻ generation can be suppressed. Therefore, it is considered that deterioration reaction can be suppressed and cell capacity deterioration, resistance deterioration, and gas generation can be suppressed. Since the generation of F ⁻ can be suppressed, the reactions as shown in the above (formula 5) to (formula 8) are less likely to proceed than in the case of the BF ₄ ⁻ anion. Therefore, it is not essential that the aluminum current collector is mainly made of aluminum fluoride in advance for practical use. However, in long-term use, it is considered that the effect of suppressing deterioration is somewhat greater when the aluminum current collector is mainly made of aluminum fluoride in advance.

_{Furthermore, BF 3 (C 2 F 5} ) - anions are BF ₄ ^- as compared to the anion, since the electrolyte solution viscosity tends high low conductivity, the effect of lower resistance can be obtained as an electrochemical capacitor cell.

_{Thus, BF 3 (C 2 F 5} ) - anions in addition to the deterioration suppressing effect of hydrolysis inhibitor, in which the effect of resistance reduction is obtained. The same effect can be obtained when PF ₃ (C ₂ F ₅ ) ₃ ^- is used.

Next, in the case of using (CF ₃ SO ₂ ) ₂ N ⁻ , (C ₂ F ₅ SO ₂ ) ₂ N ⁻ , (CF ₃ SO ₂ ) ₃ C ⁻ electrolyte anions in (b), (CF ₃ SO ₂ ) A description will be given using ₂ N ⁻ as an example.

When this electrolyte anion is applied alone to an electrochemical capacitor cell (without electrode treatment or phosphoric acid addition), there is a problem that cell capacity deterioration and resistance deterioration occur. The reason for the deterioration is presumed to be that the aluminum corrosion reaction shown in the above (formula 5) to (formula 8) occurs vigorously because a large amount of H ⁺ + F ⁻ is generated by an anion hydrolysis reaction.

  This anion hydrolysis reaction will be described using (Formula 10) to (Formula 15).

From these equations, it can be seen that as the hydrolysis reaction proceeds, the equilibrium proceeds to the right and the concentrations of F ⁻ and H ⁺ increase. For this reason, (i) aluminum corrosion reaction and (ii) solvent decomposition reaction proceed.

(I) Suppression of aluminum corrosion reaction In order to suppress the aluminum corrosion reaction, an electrode treatment in which the aluminum surface is preliminarily composed mainly of aluminum fluoride (AlF or AlF ₃ ) is particularly effective.

  When performing electrode processing on an electrode having an electrode active material, the electrode processing method needs to be a dry process. This is because in the wet process, a reaction product (mainly a non-conductor such as aluminum fluoride) adheres to the surface of the electrode active material and the separator, which causes cell capacity deterioration and resistance deterioration. For this reason, the process by dry processes, such as a plasma process and gas processing to an electrode, is needed.

When electrode processing is performed on an electrode having no electrode active material (when aluminum fluoride is formed only on the current collector aluminum before forming the active material layer), not only a dry process but also a wet process is used. Also good. In this case, the wet process does not cause the above-described capacity deterioration or resistance deterioration. The solution used in the wet process, hydrofluoric acid-containing aqueous solution or BF ₄ ^- anion, or PF ₆ ^- anion-containing electrolyte solution or the like, may be any electrolyte containing F. Preferably BF ₄ ^- anion, or PF ₆ ^- is anion-containing organic electrolyte.

Incidentally, the AlF or AlF ₃ is formed on the aluminum current collector surface, the electrode surface, for example, can be confirmed by XPS analysis (evaluation of Al2p and F1s binding energy). Handbook of X-ray Photospectron Spectroscopy (Perkin-Elmer Corporation) Appendix B. According to the Al2p binding energy obtained by XPS analysis described in Chemical States Tables, it is found that if the value is 76.3 eV, it is identified as AlF ₃ . On the other hand, it turns out that they are aluminum simple substance: 72.9eV, aluminum oxide: 74.4-74.7eV, aluminum hydroxide: 74.0-74.2eV. An element that forms a bond stronger than the bond of aluminum oxide (Al—O bond) is considered to be an element having an electronegativity higher than that of O (3.44), and corresponds to F (electronegativity: 3). .98) only (electronegativity values are those of Pauling). Therefore, it is presumed that the Al—F bond is the only bond stronger than the Al—O bond. Therefore, in order to shift to a higher energy side than the binding energy of aluminum oxide, at least an Al—F bond needs to be formed.

  From the above, it is considered that when the Al2p binding energy obtained by XPS analysis is larger than 74.7 eV, the surface composition of the aluminum current collector has aluminum fluoride and the above-mentioned corrosion reaction is suppressed.

  Essentially, if the Al2p bond energy of the film on the aluminum surface is larger than 74.7 eV, it is considered that the electrode (aluminum current collector) corrosion reaction is not limited to aluminum fluoride.

Further, if the coating composition is mainly aluminum fluoride, the upper limit of the binding energy value of aluminum oxide: 74.7 eV and the binding energy value of AlF ₃ : 75.5 eV or more, which is the central value of 76.3 eV. In other words, it can be said that the film composition is mainly aluminum fluoride.

  That is, when an unused (including after aging) electrochemical capacitor cell is disassembled and the positive electrode current collector surface is subjected to XPS analysis, the Al2p binding energy is at least 74.7 eV, preferably 75.5 eV or more. In other words, it can be regarded as according to the present invention.

  Furthermore, by XPS analysis, F1s binding energy can be evaluated, and when the energy is in the range of 686 to 687 eV, it can be seen that aluminum fluoride is formed.

The XPS analysis conditions are those described below.
Equipment Physical Electronics ESCA5400MC
X-ray anode Monochromated-AlKα (1486.6eV) 14kV 200W
Analysis area Circle with a diameter of 0.6 mm (ii) Inhibition of solvent decomposition reaction In order to suppress the solvent decomposition reaction, it is effective to add trimethyl phosphate as an additive used in the driving electrolyte. Although the details of this mechanism are not clear, it is presumed that the solvent decomposition reaction is suppressed because a thin passive film is formed on the surface of the electrode active material and the surface of the aluminum current collector.

  In addition to phosphoric acid, the additive used for the driving electrolyte includes monomethyl phosphate, dimethyl phosphate, trimethyl phosphate, phosphate ester, phosphorous acid, or salts thereof, or borate ester, Boric acid or a salt thereof can be used, and the addition amount is preferably in the range of 0.01 to 20 wt%. If the amount added is less than 0.01 wt%, a sufficiently good passive film may not be formed, and the positive electrode surface becomes acidic when a voltage is applied, and aluminum is dissolved, resulting in deterioration of the electrochemical capacitor. End up. On the other hand, if it exceeds 20 wt%, a passive film is formed on the surface of aluminum to be thicker than necessary, which causes an increase in resistance due to the passive film, which is not preferable.

  From the above, when the electrolyte anion (b) is used, (1) the surface of the aluminum current collector is covered with aluminum fluoride, and (2) the trimethyl phosphate additive is used (1) and By devising both or one of (2), the ability to suppress deterioration (improve the withstand voltage), which is the original performance of the electrolyte anion of (b), can be brought out.

  Next, the case where the electrolyte anion of (Chem. 1) and (Chem. 2) of (c) is used will be described by taking the case of using (Chem. 1) as an example.

  In this case, the same explanation as in the case of the electrolyte anion in (b) above ((i) aluminum corrosion reaction suppression and (ii) solvent decomposition reaction suppression by the formation of aluminum fluoride by electrode treatment and addition of a phosphate-based additive) In addition, since the hydrolysis reaction suppression effect shown by the electrolyte anion of the above (a) is effective, a greater deterioration suppression effect can be obtained than in the case of the electrolyte anion of the above (a) and (b) It is.

  The hydrolysis reaction of the above (Chemical Formula 1) is shown in the following (Formula 16) to (Formula 19).

When the hydrolysis reaction proceeds as in the above (formula 16) to (formula 19), H ⁺ and F ⁻ increase, so that (i) aluminum corrosion and (ii) as in the case of the electrolyte anion in (b) above. ) Solvent decomposition proceeds. In order to suppress them, it is effective to form aluminum fluoride on the surface of the aluminum current collector by electrode treatment and to add a phosphoric acid additive to the electrolytic solution.

  In addition, it is considered that the degree of reaction progressing to the right side of the above (formula 16) to (formula 19) is less than that of the above (formula 10) to (formula 15). This is presumably because the anion structure was made cyclic. Therefore, it can be presumed that the cyclic anions such as (Chemical Formula 1) and (Chemical Formula 2) have the effects shown in the suppression of hydrolysis, that is, the electrolyte anions classified in (a) above.

  From the above, when the electrolyte anion of (c) is used, (1) Degradation reaction suppression by suppressing hydrolysis reaction and (2) Deterioration suppression (improves withstand voltage) which is the original performance of anion. It has the two effects of being able to bring out the ability.

  In the structures of (Chemical Formula 1) and (Chemical Formula 2), all carbon terminal groups are shown terminated with fluorine. However, the same effect can be obtained even if part of the carbon terminal groups are replaced with hydrogen or halogen atoms. .

Finally, the case where the electrolyte anion of PF ₆ ⁻ of (d) is used will be described. This effect is that the effect of the electrolyte anion of (b) and the cell resistance can be reduced by improving the electrolyte conductivity. .

Challenge as compared to the case of anionic alone, although the withstand voltage high, dissociation of the fluorine many upon hydrolysis produces corrosion of aluminum, the cell capacity degradation, that is resistance deterioration occurs ^- the anion alone, BF ₄ ^- PF ₆ There is. Therefore, by (1) covering the surface of the aluminum current collector with aluminum fluoride, (2) using a trimethyl phosphate-based additive, (1) and (2) or by devising either one, It is possible to bring out the ability to suppress deterioration (improve the withstand voltage), which is the original performance of the electrolyte anion of PF ₆ ^{− in} (d).

Furthermore, PF ₆ ^- anion itself is small in size, negative charge is delocalized, the (b), the electrolyte anions comparison, the cell low resistance for high conductivity with low viscosity (c) It has the effect that it can aim at.

  In addition, the end part of the carbon skeleton has an activated carbon surface including a portion where the activated carbon in the polarizable electrode layer formed on the positive electrode according to claim 1 of the present invention is not in contact with the material constituting the polarizable electrode layer. Aluminum fluoride is applied to the surface of the current collector including the portion that is not in contact with the material constituting the polarizable electrode layer at the interface between the current collector and the polarizable electrode layer, as well as to be fluorinated (α) By forming the film (β), the following effects can be obtained simultaneously.

  That is, (α) increases the potential at which the activated carbon (activated carbon itself or activated carbon surface functional group) at the positive electrode and the electrolytic solution (especially anions, solvents, and hydrolysis products thereof) react electrochemically. Can be obtained (improvement of withstand voltage). This effect can be said to be an effect of suppressing deterioration when the use voltage of the single cell is set to be equal to the conventional one.

  Moreover, the effect of suppressing cell capacity deterioration and resistance deterioration due to electrode adhesion of deteriorated products due to aluminum elution can be obtained by the above (β).

  Thus, since the fluorine gas treatment to the positive electrode foil can obtain (α) and (β) at the same time, the special effect that (α) and (β) can be obtained at the same time. It is what you play.

  In addition, in order to acquire the effect by said ((alpha)) and ((beta)) simultaneously, although demonstrated using the example which performs the fluorine gas process with respect to positive electrode electrode foil, it does not restrict | limit to this method in particular.

  For example, after aluminum fluoride is first formed on the surface of the aluminum current collector by fluorine gas treatment, fluorine plasma treatment, or electrochemical treatment with a fluorine-containing solution or a fluorine-containing organic electrolyte. The activated carbon layer is formed on both sides or one side of the aluminum current collector layer with aluminum fluoride formed on the surface by coating or bonding sheet formation, and finally the activated carbon layer is treated with fluorine gas or fluorine plasma. Thus, a method of terminating the activated carbon surface functional group with a fluorine atom or the like can be considered.

  By using these methods, particularly good effects can be obtained in the following cases.

  That is, it is often difficult to set a single fluorine gas treatment condition in order to realize both (α) and (β) by simply performing fluorine gas treatment. If the above method is used in such a case, it is possible to set optimum fluorination conditions for each of (α) and (β), so that there is an effect that high mass production stability can be obtained.

  The gas composition of the fluorine gas treatment is not limited to fluorine but may be a gas composition that improves water repellency, and a mixed gas of fluorine and inert gas is preferable, and a mixed gas of fluorine and nitrogen is more preferable. In addition, as a result of examining the ratio and capacitor characteristics in detail regarding the mixed gas ratio, the ratio is more preferably in the range of fluorine partial pressure / nitrogen partial pressure = 0.26 to 0.02.

  When the fluorine partial pressure / nitrogen partial pressure ratio is 0.26 or more, during the fluorine gas treatment, the reaction heat between the fluorine gas and the activated carbon increases, the activated carbon surface area decreases, and the cell capacity decreases. If the cell resistance increases due to the formation of a fluorocarbon layer having a lower conductivity than activated carbon on the surface, the initial cell characteristics are significantly deteriorated, and a substantial cell deterioration suppressing effect cannot be obtained. Conceivable. On the other hand, when the fluorine partial pressure / nitrogen partial pressure ratio is 0.02 or less, it is considered that the effect cannot be obtained because the fluorination of the end groups on the activated carbon surface and the fluorination of the aluminum surface do not proceed sufficiently.

  In the present invention, the electrode subjected to the fluorination treatment has been mainly limited to the positive electrode, but in a broad sense, it is necessary to select at least the positive electrode. That is, although only the positive electrode is the most desirable form, the effect of suppressing deterioration is also seen in the treatment of the positive electrode and the negative electrode. This is because there is not much elution of aluminum from the negative electrode although it is less than the positive electrode. However, when the cell withstand voltage (applied voltage) is increased and tested (used), it is more effective to treat only the positive electrode with fluorine. The reason for this is considered that when the negative electrode is subjected to a fluorination treatment, the reduction potential of the negative electrode increases and the withstand voltage on the negative electrode side decreases.

  As described above, in the case of an electric double layer capacitor, in a broad sense, a capacitor using a current collector mainly made of aluminum for both positive and negative electrodes, an effect of suppressing cell deterioration can be obtained by performing fluorine treatment on at least the positive electrode. However, it is necessary to avoid performing fluorine treatment only on the negative electrode.

  These proofs can be verified, for example, by measuring the Al2p binding energy in the XPS analysis described above. Initially or after aging, or by disassembling the used electric double layer capacitor cell, the positive and negative electrode collector aluminum is subjected to XPS analysis under the same conditions as the analysis conditions described above, and the positive electrode Al2p binding energy and negative electrode If there is a significant difference in the Al2p binding energy, the Al2p binding energy of the negative electrode is higher than the Al2p binding energy of the positive electrode, and the Al2p binding energy of the negative electrode is larger than 74.7 eV, it can be regarded as being according to the present invention.

  Further, for example, XPS analysis can be used for proof that the activated carbon surface is fluorinated. After initial or after aging, or by disassembling the used electric double layer capacitor cell and conducting analysis of the activated carbon surface of the positive electrode, if one of the peaks around 287 to 290 eV showing C—F bond is obtained, it is according to the present invention. It can be regarded as a thing.

  As mentioned above, although the example of the detection method by XPS about the content by this invention was demonstrated, it cannot be overemphasized that it can detect also by other analysis methods, such as NMR.

  Needless to say, the anion species shown in the present invention can be identified by various analysis methods such as NMR, ion chromatography, FT-IR, and GC-MS.

  The electric double layer capacitor and the method for manufacturing the same according to the present invention have the effect that aluminum can be prevented from eluting into the electrolyte solution to prevent the electrode foil from deteriorating and the increase in resistance can be suppressed. It is useful as a backup power source and regenerative power for hybrid vehicles and fuel cell vehicles.

1 is a partially cutaway perspective view showing a configuration of an electric double layer capacitor according to an embodiment of the present invention. (A) Cross-sectional view showing the positive electrode before the fluorine gas treatment, (b) Cross-sectional view showing the positive electrode after the treatment

Explanation of symbols

1 element 2 current collectors 2a Al ₂ O ₃ alloy layer 2b AlF ₃ alloy layer 3 polarizable electrode layer 3a charcoal 3b conductive additive 3c binder 4 separator 5 leads 6 metal case 7 sealing rubber composition having the composition

Claims (3)

By laminating or winding a pair of positive and negative electrodes, in which a polarizable electrode layer mainly composed of activated carbon is formed on a current collector made of metal foil, with a separator interposed therebetween, with each electrode layer facing each other A polarizable electrode layer formed on at least the positive electrode in an electric double layer capacitor comprising a configured element, a case containing the element together with a driving electrolyte, and a sealing member sealing an opening of the case The end of the carbon skeleton is fluorinated on the activated carbon surface including the part where the activated carbon inside does not contact the material constituting the polarizable electrode layer, and the current collector is collected at the interface between the current collector and the polarizable electrode layer. An electric double layer capacitor in which an aluminum fluoride film is formed on the surface of a current collector including a portion where the body is not in contact with the material constituting the polarizable electrode layer. As electrolyte anions of the driving electrolyte, BF ₃ (C ₂ F ₅ ) ⁻ , PF ₃ (C ₂ F ₅ ) ₃ ⁻ , (CF ₃ SO ₂ ) ₂ N ⁻ , (C ₂ F ₅ SO ₂ ) ₂ N ^{_{-, (CF 3 SO 2)}} 3 C -, ( Formula 1), (Formula 2), PF ₆ ^- electric double layer capacitor according to claim 1 with any one of the.

A step of forming a polarizable electrode layer mainly composed of activated carbon on a current collector made of metal foil to produce a positive electrode and a negative electrode, and a pair of positive and negative electrodes as described above, and a separator interposed between each electrode layer An electric circuit including a step of fabricating an element by stacking or winding in an opposed state, a step of housing the element in a case together with a driving electrolyte, and a step of sealing an opening of the case. In the multilayer capacitor manufacturing method, at least the positive electrode is subjected to a reduced pressure treatment in a fluorine gas atmosphere so that activated carbon in the polarizable electrode layer formed on the positive electrode is not in contact with the material constituting the polarizable electrode layer. The end of the carbon skeleton is fluorinated on the activated carbon surface, and the current collector is in contact with the material constituting the polarizable electrode layer at the interface between the current collector and the polarizable electrode layer. Method of manufacturing an electric double layer capacitor which is adapted to form aluminum fluoride film on the collector surface including portions without.

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