JP2008010855A - Electrochemical capacitor and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrochemical capacitor capable of reducing resistance by suppressing deterioration in the quality of a positive electrode for the electrochemical capacitor used for automobiles, or the like. <P>SOLUTION: The electrochemical capacitor comprises: the positive electrode where a polarizable electrode layer mainly made of activated carbon is formed on a collector; an element in which negative electrodes where the electrode layer of graphite is formed on the collector are wound by interposing a separator between the negative electrodes; and a metal case in which the element is stored with an organic-based electrolyte containing a lithium ion. The front and rear of the positive electrode on which the polarizable electrode layer is formed is covered with aluminum fluoride, and Li<SP>+</SP>is used as the electrolyte cation of the organic-based electrolyte, and one of BF<SB>3</SB>(C<SB>2</SB>F<SB>5</SB>)<SP>-</SP>, PF<SB>3</SB>(C<SB>2</SB>F<SB>5</SB>)<SB>3</SB><SP>-</SP>, (CF<SB>3</SB>SO<SB>2</SB>)<SB>2</SB>N<SP>-</SP>, (C<SB>2</SB>F<SB>5</SB>SO<SB>2</SB>)<SB>2</SB>N<SP>-</SP>, (CF<SB>3</SB>SO<SB>2</SB>)<SB>3</SB>C<SP>-</SP>, and PF<SB>6</SB><SP>-</SP>of a chemical formula (1) or (2) is used as an electrolytic anion. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an electrochemical capacitor used for various electronic devices, a backup power source, a regenerative power source or a power storage for a hybrid vehicle or 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 with a higher withstand voltage has higher energy than the aqueous electrolyte, but even with 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-acid battery, and further improvement of the energy density is required.

  From such a background, an electrode mainly composed of activated carbon is used as a positive electrode, and an electrode in which lithium ions are previously occluded in a carbon material having a [002] plane spacing of 0.338 to 0.356 nm by X-ray diffraction is used. A secondary battery having an upper limit voltage of 3 V as a negative electrode has been proposed (Patent Document 1).

  In addition, a secondary battery using a carbon material in which lithium ions are occluded in advance by a chemical method or an electrochemical method in a carbon material that can occlude and desorb lithium ions has been proposed (Patent Document 2).

  Furthermore, a secondary battery having an upper limit voltage of 4 V has been proposed having a negative electrode in which a carbon material capable of inserting and extracting lithium ions is supported on a porous current collector that does not form an alloy with lithium (Patent Document 3).

In addition to the electric double layer capacitor, there is a lithium ion battery as a power source capable of charging / discharging a large current. The lithium ion battery has a feature of a high voltage and a large capacity as compared with the electric double layer capacitor, but has a high resistance and a high speed. There was a problem that the life due to the charge / discharge cycle was remarkably shorter than that of the electric double layer capacitor.
JP-A 64-14882 Japanese Patent Laid-Open No. 8-1007048 JP-A-9-55342

However, the secondary battery proposed for the purpose of improving the disadvantages of the conventional electric double layer capacitor has the advantages of high withstand voltage, large capacity, and rapid charge / discharge. BF ₄ used as an electrolyte anions constituting ^- or PF ₆ ^-, etc. F ^- component reacts with aluminum as the current collector of the positive electrode and aluminum eluted aluminum aluminum fluoride this elution (AlF ₃₎ As a result, there are problems that the resistance value increases due to adhesion to the surface of the activated carbon constituting the polarizable electrode layer, or the performance as a secondary battery deteriorates due to deterioration of the current collector.

  An object of the present invention is to solve such a conventional problem, and to provide an electrochemical 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-mentioned problems, the present invention mainly comprises a positive electrode in which a polarizable electrode layer mainly composed of activated carbon is formed on a current collector made of metal foil, and a carbon material mainly on the current collector made of metal foil. An element formed by laminating or winding a negative electrode on which an electrode layer is formed, with each electrode layer facing each other with a separator interposed therebetween, and this element together with an organic electrolyte containing lithium ions In an electrochemical capacitor comprising a housing case, the front and back surfaces of the positive electrode on which the polarizable electrode layer is formed are covered with aluminum fluoride, and Li ^{+ is used} as the electrolyte cation of the organic electrolyte, and BF _{3 is used} as the electrolyte anion. (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 ^- It is obtained by the configuration using any one.

  In addition, as a method of manufacturing this electrochemical capacitor, a step of forming a positive electrode by forming a polarizable electrode layer mainly composed of activated carbon on a current collector made of metal foil, Forming a negative electrode by forming an electrode layer mainly composed of a carbon material on the element, and laminating or winding the positive electrode and the negative electrode with a separator interposed therebetween, with each electrode layer facing each other. In the method for producing an electrochemical capacitor, comprising the steps of: preparing the element together with an organic electrolyte containing lithium ions in a case; and sealing the case opening. The front and back surfaces of the positive electrode on which the polar electrode layer is formed are coated with aluminum fluoride by performing fluorine plasma treatment.

  As described above, the electrochemical capacitor according to the present invention has a structure in which the front and back surfaces of the positive electrode on which the polarizable electrode layer is formed are covered with aluminum fluoride, and aluminum fluoride has a strong bond between fluorine atoms and aluminum atoms. It is possible to prevent the electrode foil from deteriorating by suppressing the aluminum, which is the positive electrode current collector, from eluting into the electrolyte during application. In addition, since the aluminum current collector is passivated by the electrolyte anion of the electrolytic solution, the fluorine component in the electrolytic solution does not attack the aluminum, which can suppress the increase in resistance. Is.

(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 the structure of an electrochemical capacitor according to an embodiment of the present invention, and FIGS. 2A and 2B are discharges shown for explaining the principle of the electrochemical capacitor. 1 and FIG. 2, 1 is an element, and the element 1 has a polarizable electrode layer 3 mainly composed of activated carbon on the front and back surfaces of a current collector 2 made of aluminum foil. Constructed by winding a formed positive electrode and a negative electrode having a graphite electrode layer 5 formed on the front and back surfaces of a current collector 4 made of copper foil in a set with two separators interposed therebetween It is what has been.

  7 is a lead wire connected to the two electrodes and drawn out, 8 is an aluminum metal case containing the element 1 together with the driving electrolyte 9, and 10 is a lead drawn from the element 1 as a pair. It is a sealing rubber that has a hole through which the wire 7 passes and is fitted into the opening of the metal case 8 and seals by processing the opening end of the metal case 8, and a specific embodiment will be described below. However, the present invention is not limited to this.

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

  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 having the polarizable electrode layer 3 formed on the front and back surfaces of the current collector 2 were coated with aluminum fluoride by fluorine plasma treatment. This fluorine plasma treatment was performed using apparatuses shown in the sectional view of the plasma processing chamber in FIG. 3A and the sectional view of the plasma generating chamber in FIG.

  That is, the plasma processing chamber 11 and the plasma generation chamber 12 are connected via a chamber connection hole 13, and in FIG. 3B, a mixed gas composed of argon and carbon tetrafluoride is supplied from the gas introduction hole 14. Plasma is generated by injection between the electrodes 16A and 16B connected to the high-frequency power source 15, and this plasma is supplied from the plasma lead-out hole 17 to the plasma processing chamber 11 through the plasma introduction hole 18.

  As shown in FIG. 3A, a positive electrode 19 in which a polarizable electrode layer 3 is formed on the front and back surfaces of the current collector 2 is rolled in a plasma processing chamber 11 into which plasma is introduced from the plasma introduction hole 18. The positive electrode 19 delivered from the unwinding side as the untreated positive electrode 19a is subjected to plasma treatment, and then wound up as the treated positive electrode 19b on the winding side and cut to an appropriate length. It is.

  Moreover, the said fluorine plasma processing was performed on the conditions shown in the following (Table 1), and sectional drawing of the positive electrode before this fluorine plasma processing and after a fluorine plasma processing is shown to Fig.4 (a), (b). .

As shown in FIG. 4B, the positive electrode 19 subjected to the fluorine plasma treatment as described above has an Al ₂ O ₃ composition alloy layer in contact with the current collector 2 made of aluminum foil and the activated carbon 3a. 2a is not changed before and after the fluorine plasma treatment. On the other hand, the portion where the alloy layer 2a of the Al ₂ O ₃ composition is not surrounded by the current collector 2 and the activated carbon 3a is exposed to fluorination by the fluorine plasma treatment to form the AlF ₃ alloy layer 2b. Make a change.

Accordingly, by preliminarily making the aluminum component into an AlF ₃ composition by performing plasma treatment, it is possible to suppress the elution of aluminum even when the electrode body is impregnated in the electrolytic solution and charged and discharged. Thus, deterioration of the capacity and resistance can be prevented.

That is, the positive electrode before the fluorine plasma treatment (in which an alloy layer 2a made of aluminum oxide and having an Al ₂ O ₃ composition is formed, and a polarizable electrode layer 3 mainly composed of activated carbon 3a is formed thereon) Although the alloy layer 2a composed of aluminum oxide and having an Al ₂ O ₃ composition is interposed between the polarizable electrode layer 3 and the current collector 2, there is an effect of reducing the contact resistance. When it is immersed and charged and discharged, aluminum is eluted from a part of the alloy layer 2a having the Al ₂ O ₃ composition, reacts with the fluorine component in the electrolytic solution to produce an AlF ₃ compound, and adheres to the surface of the activated carbon 3a. (FIG. 4A). 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. However, by subjecting this to fluorine plasma treatment as in this embodiment, elution of aluminum can be suppressed and deterioration of capacity and resistance can be prevented. In FIG. 4, 3b represents a conductive additive, and 3c represents a binder.

Next, as a negative electrode, a copper foil having a thickness of 15 μm was used as the current collector 4, and a graphite electrode layer 5 having a thickness of 30 μm (single-sided thickness) was formed on the front and back surfaces of the current collector 4. This graphite electrode layer 5 has a ratio of graphite: acetylene black: binder = 80: 10: 10, and the binder is polytetrafluoroethylene (hereinafter referred to as PTFE) 8): CMC (2). Configured. In addition, as a manufacturing method, CMC, acetylene black, graphite, and PTFE are added to water in this order, and a paste-like product obtained by stirring and kneading is added onto the current collector 4 using a comma coater, a die coater, or the like. After coating to a thickness of 50 μm (single-sided thickness), drying this at a temperature of 80 ° C., and pressing at a linear pressure of 75-100 kgf / cm, the thickness of 30 μm (single-sided thickness), electrode density A graphite electrode layer 5 having a thickness of 1.2 to 1.5 g / cm ³ was prepared and cut into predetermined dimensions.

Subsequently, the current collector 4 having the graphite electrode layer 5 formed on the front and back surfaces thereof, together with the Li foil, Li ⁺ as the electrolyte cation, BF ₄ ⁻ as the electrolyte anion, and ethylene carbonate having a high dielectric constant (hereinafter, referred to as a solvent). EC) and low-viscosity diethyl carbonate (hereinafter referred to as DEC) are mixed in an electrolytic solution made of a mixed solvent in a volume ratio of 1: 1, and the positive electrode of a charge / discharge device (not shown) is used as a current collector. 4, the negative electrode was connected to the Li foil.

  In this state, the potential difference between the positive electrode and the negative electrode is about 2.5 to 3 V, but constant current discharge (current collection is not preferable because Li is deposited when the electric potential difference becomes 0.004 V). When viewed from the body 4, constant current charging) was performed. Then, constant potential discharge (constant potential charging as viewed from the current collector 4) is performed for 5 hours in the state where the potential difference between the + and − electrodes is 0.004 V or until the current value becomes 1/20. Thus, a negative electrode in which lithium ions were occluded in graphite constituting the electrode layer 5 formed on the front and back surfaces of the current collector 4 was obtained.

Next, the positive electrode and the negative electrode obtained in this way are made into a set of two sheets, and an element 1 is obtained by winding with a separator interposed therebetween, and the element 1 together with the driving electrolyte 9 is obtained. While being inserted into the metal case 8, the element 1 was impregnated with the driving electrolyte 9. As the driving electrolyte 9, Li ⁺ as an electrolyte cation, BF ₃ (C ₂ F ₅ ) ⁻ as an electrolyte anion, and EC having a high dielectric constant and DEC having a low viscosity as a solvent are mixed at a weight ratio of 1: 1. The mixed solvent used was added with 1 wt% phosphoric acid as an additive.

  Next, the lead wire 7 drawn out from the element 1 inserted in the metal case 8 together with the driving electrolyte 9 in this way is passed through the hole provided in the sealing rubber 10, and the sealing rubber 10 is inserted into the metal case. After being fitted into the opening of 8, sealing was performed by drawing and curling the vicinity of the opening end of the metal case 8 to complete the electrochemical capacitor according to the present embodiment.

  The results of measuring the capacitance / resistance characteristics of the electrochemical capacitor according to the present embodiment configured as described above are shown in Table 2 in comparison with a conventional product as a comparative example.

  As is clear from Table 2, the electrochemical capacitor according to the present embodiment has a structure in which the front and back surfaces of the positive electrode on which the polarizable electrode layer is formed are covered with aluminum fluoride. Since the bonding of the atoms is strong, it is possible to prevent the electrode foil from deteriorating by suppressing the aluminum, which is the positive electrode current collector, from eluting into the electrolyte when a voltage is applied. In addition, since the aluminum current collector is passivated by the electrolyte anion and additives of the electrolytic solution, the fluorine component in the electrolytic solution does not attack the aluminum, thereby suppressing an increase in resistance. The effect of 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 9 has been described, but 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 3), (Chemical Formula 4) ) And PF ₆ ⁻ , the same effect can be obtained. Each of the electrolyte anions is classified into the following (a) to (d), and each of the electrolyte anions depends on the electrolyte anion. The effect 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 ^- when using the (c) (Formula 3), if (d) PF ₆ using (Formula 4) ^- first case of using, BF ₃ in (a) ( C ₂ F ₅ ) ⁻ , PF ₃ (C ₂ F ₅ ) ₃ ⁻ electrolyte anion, compared to the case of using BF ₄ ⁻ anion as a conventional product, cell by inhibiting hydrolysis The effect of suppressing deterioration and the effect of reducing 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, generation of H ^{+ and} generation of F ⁻ 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 the case of long-term use, it is better to keep the aluminum current collector mainly made of aluminum fluoride in advance. It is considered that there is some effect of suppressing deterioration.

_{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 Description will be made using SO ₂ ) 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 with reference to (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, plasma treatment or the like for the electrode is required.

The gas used for the plasma treatment may be any gas mainly containing fluorine atoms such as CF ₄ . From the viewpoint of preventing global warming, a gas having a smaller global warming potential such as C ₂ F ₆ , c-C ₄ F ₈ , c-C ₅ F ₈ , CFCO, etc. is desirable. It is desirable that the process conditions such as electrodes, RF power supply, etc. used in the plasma generating apparatus, RF power, pressure, gas composition, etc. generate moderately plasma containing F radicals or F 2 ⁻ ions.

From the viewpoint of stable plasma generation, it is desirable to use an argon gas together with a fluorine-containing gas such as CF ₄ . The ratio (I _F / I _Ar ) between the argon emission intensity (I _Ar (emission wavelength: λ = 697 nm)) and the fluorine emission intensity (I _F (emission wavelength: λ = 685 nm)) during plasma generation is It is desirable to make the process conditions constant. These can also be realized by changing the gas flow rate, pressure, RF power, etc. during the electrode treatment process. Thereby, conditions that enable stable electrode processing to be continuously performed on the long electrode foil are obtained.

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, PF ₆ ^- anion-containing electrolyte solution and the like, may be a electrolyte containing F. Preferably BF ₄ ^- is anion-containing organic electrolyte ^- anion or PF _6.

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, AlF ₃ is identified. 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 surface of the positive electrode current collector is subjected to XPS analysis, if the Al2p bond energy is 75.5 eV or more, 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 have the following contents.
Equipment: ESCA5400MC, Physical Electronics
X-ray anode: Monochromated-AlKα (1486.6eV) 14kV 200W
Analysis region: 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 of using the electrolyte anion of (Chemical Formula 3) and (Chemical Formula 4) of (c) will be described taking the case of using Chemical Formula 3 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 (Chemical Formula 3) 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 3) and (Chemical Formula 4) have the effects shown by the hydrolysis inhibition, that is, the electrolyte anions classified in the above (a).

  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 3) and (Chemical Formula 4), all the carbon terminal groups are shown to be terminated with fluorine. However, the same effect can be obtained even if part of the carbon terminal groups are replaced with hydrogen.

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.

  As described above, the effect of suppressing cell deterioration can be obtained by subjecting aluminum of the positive electrode current collector of the electrochemical capacitor to fluorine treatment, and further, the effect of suppressing cell deterioration can be obtained by combining with an anion and an additive. It is.

  These proofs can be verified, for example, by measuring the Al2p binding energy in the XPS analysis described above. Initial or after aging, or by disassembling the used electrochemical 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 the negative electrode Al2p If there is a significant difference in 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 higher than 74.7 eV, it can be regarded as being according to the present invention.

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

  The electrochemical 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 electrolytic solution to prevent deterioration of the electrode foil, 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 electrochemical capacitor according to an embodiment of the present invention. (A) The conceptual diagram of the discharge state shown in order to demonstrate the principle of the electrochemical capacitor, (b) The conceptual diagram of the charge state (A) Cross-sectional view showing the configuration of the plasma processing chamber used in the embodiment, (b) Cross-sectional view showing the configuration of the plasma generation chamber (A) Cross-sectional view showing a positive electrode before plasma treatment according to the embodiment, (b) Cross-sectional view showing a positive electrode after plasma treatment

Explanation of symbols

1 elements 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 5 electrode layer 6 separator 7 leads 8 metal case 9 drives the composition of the composition Electrolytic solution 10 Sealing rubber 11 Plasma processing chamber 12 Plasma generation chamber 13 Chamber connection hole 14 Gas introduction hole 15 High frequency power supply 16A, 16B Electrode 17 Plasma outlet hole 18 Plasma introduction hole 19 Positive electrode 19a Untreated positive electrode 19b Treated positive electrode

Claims (6)

A positive electrode in which a polarizable electrode layer mainly composed of activated carbon is formed on a current collector made of metal foil, and a negative electrode in which an electrode layer mainly composed of a carbon material is formed on a current collector made of metal foil. In an electrochemical capacitor comprising an element configured by stacking or winding each electrode layer facing each other with a separator interposed therebetween, and a case in which this element is accommodated together with an organic electrolyte containing lithium ions, Li ⁺ as the electrolyte cation of the organic electrolyte, BF ₃ (C ₂ F ₅ ) ⁻ , PF ₃ (C ₂ F ₅ ) ₃ ⁻ , (CF ₃ SO ₂ ) ₂ N ⁻ , (C ₂ F ₅ ) as the electrolyte anion An electrochemical capacitor using any one of SO ₂ ) ₂ N ⁻ , (CF ₃ SO ₂ ) ₃ C ⁻ , (Chemical Formula 1), (Chemical Formula 2), and PF ₆ ⁻ .
The electrochemical capacitor according to claim 1, wherein the front and back surfaces of the positive electrode on which the polarizable electrode layer is formed are covered with aluminum fluoride. The electrochemical capacitor according to claim 2, wherein the aluminum fluoride covering the front and back surfaces of the positive electrode on which the polarizable electrode layer is formed is formed by fluorine plasma treatment. The organic electrolyte solution according to claim 1, wherein 0.01 to 20 wt% of an additive composed of any one of phosphoric acid, phosphate and phosphate, or boric acid, borate and borate is added. The electrochemical capacitor as described. The electrochemical capacitor according to claim 1, wherein graphite is used as a carbon material constituting the electrode layer of the negative electrode. Forming a positive electrode by forming a polarizable electrode layer mainly composed of activated carbon on a current collector made of metal foil, and forming an electrode layer mainly composed of a carbon material on the current collector made of metal foil; A step of producing a negative electrode, a step of producing an element by laminating or winding the positive electrode and the negative electrode with a separator interposed therebetween, and each electrode layer facing each other, and the element contains lithium ions In a method for producing an electrochemical capacitor having a step of housing in a case together with an organic electrolyte and a step of sealing an opening of the case, the front and back surfaces of the positive electrode on which the polarizable electrode layer is formed are fluorine A method for producing an electrochemical capacitor which is coated with aluminum fluoride by plasma treatment.