JP2008103697A - Electrochemical capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrochemical capacitor capable of improving energy density by simple constitution. <P>SOLUTION: In a charge/discharge cycle of a hybrid capacitor 1 provided with a positive pole 2, a negative pole 3 opposed to the positive pole 2 through an interval, a separator 4 arranged between the positive pole 2 and the negative pole 3, and a cell bath 6 storing the positive pole 2, the negative pole 3 and the separator 4 and filled with an electrolyte 5 so as to dip these components into it; irreversible capacity for expanding a potential range is made to appear in the positive pole 2. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an electrochemical capacitor, and more particularly, to a hybrid capacitor having both power storage by an electric double layer and power storage by an oxidation-reduction reaction.

Conventionally, investigation and development of an electric double layer capacitor having a high output and a long life as an electric storage device mounted on a hybrid vehicle or a fuel cell vehicle have been advanced.
The electric double layer capacitor stores energy by adsorbing anions and cations on the positive electrode and the negative electrode, respectively. Stored energy is represented by CV ^2/2, by increasing the voltage, it is possible to store more energy, too high a voltage chemical reaction positive and negative electrodes (redox reaction) occurs, the electrodes Deteriorates.

For this reason, the upper limit of the voltage must be kept within a range where no chemical reaction occurs at the positive electrode and the negative electrode, so that the potential range becomes narrow and it is difficult to improve the energy density.
Therefore, in recent years, in order to improve the energy density of the electric double layer capacitor, by using a material capable of reversibly occluding and releasing lithium ions as a negative electrode material, in addition to electric double layer power storage, power storage by oxidation-reduction reaction is also possible. A hybrid capacitor having both of these has been proposed.

However, even in the case of a hybrid capacitor, the potential range of the positive electrode is narrowed due to the irreversible capacity generated at the negative electrode in the charge / discharge cycle, and thus the electric capacity of the positive electrode may not be sufficiently developed. That is, the electric capacity of the positive electrode is not fully utilized, and the energy density may not be sufficiently improved.
Therefore, in order to solve the above-described problems, for example, Patent Document 1 discloses that a positive electrode made of a polarizable electrode material mainly composed of activated carbon and a current collector made of aluminum or stainless steel, and occludes and desorbs lithium ions. A carbonaceous material in which lithium ions are occluded by a chemical method or an electrochemical method, a negative electrode comprising a current collector that does not form an alloy with lithium, and a non-aqueous electrolyte containing a lithium salt An electric double layer capacitor is disclosed.

  Patent Document 2 discloses an organic electrolyte capacitor including a positive electrode, a negative electrode, and an aprotic organic solvent solution of a lithium salt as an electrolytic solution, in which the positive electrode active material is capable of reversibly supporting lithium ions and anions. The negative electrode active material is an active material capable of reversibly carrying lithium ions, and the capacitance per unit weight of the negative electrode active material is more than three times the capacitance per unit weight of the positive electrode active material An organic electrolyte capacitor is disclosed in which the weight of the positive electrode active material is larger than the weight of the negative electrode active material, and lithium ions are supported in advance on the negative electrode.

  In the electric double layer capacitor described in Patent Document 1 and the organic electrolyte capacitor described in Patent Document 2, for example, by precharging the negative electrode, lithium ions are preliminarily occluded in the negative electrode, and electricity corresponding to irreversible capacity is obtained. Capacitance can be compensated. Therefore, the electric capacity of the positive electrode can be fully utilized, and the energy density of the capacitor can be improved.

In addition, if the amount of lithium ions stored is large, the positive electrode can develop an electric capacity due to adsorption / desorption of lithium ions, and the discharge potential of the positive electrode can be shifted to the base side to expand the potential range. Therefore, the energy density can be further improved.
Japanese Patent No. 3689948 International publication pamphlet WO2003 / 003395

However, in order to precharge the negative electrode and occlude lithium ions, a third electrode such as a lithium electrode for supplying lithium ions must be provided in the capacitor. Another problem occurs, such as an increase in size and an associated increase in costs.
This invention is made | formed in view of such a situation, The place made into the objective is providing the electrochemical capacitor which can improve an energy density with a simple structure.

In order to achieve the above object, the electrochemical capacitor of the present invention comprises a positive electrode that develops an irreversible capacity for expanding a potential range in a charge / discharge cycle, and a material that can reversibly store and release lithium ions. It has a negative electrode and an electrolytic solution made of an organic solvent containing lithium ions.
In the electrochemical capacitor of the present invention, it is preferable that the electrochemical capacitor includes a scavenger that captures a negative electrode activity inhibiting substance derived from an anion contained in the electrolytic solution due to the irreversible capacity of the positive electrode.

Further, the electrochemical capacitor of the present invention, the scavenger, to the irreversible capacity 1 mAh, it is preferable that in a ratio of ^{2 × 10 -5 mol~175 × 10 -5} mol.

  In the electrochemical capacitor of the present invention, in the charge / discharge cycle, the positive electrode can fully utilize the capacitance of the positive electrode by developing an irreversible capacity for expanding the potential range, thereby improving the energy density of the capacitor. Can be made. Further, since a lithium electrode or the like for precharging the negative electrode is not required, the capacitor can be configured simply. Furthermore, since the capacitor can be configured simply, the cost can be reduced.

FIG. 1 is a schematic configuration diagram of a hybrid capacitor showing an embodiment of an electrochemical capacitor of the present invention.
In FIG. 1, the hybrid capacitor 1 includes a positive electrode 2, a negative electrode 3 disposed opposite to the positive electrode 2 with a gap, a separator 4 interposed between the positive electrode 2 and the negative electrode 3, a positive electrode 2, a negative electrode 3 and a separator 4 are accommodated, and a cell tank 6 filled with an electrolyte solution 5 is provided so as to immerse them. The hybrid capacitor 1 is a battery cell that is employed on a laboratory scale, and industrially, the hybrid capacitor 1 is appropriately scaled up by a known technique.

The positive electrode 2 is formed by, for example, forming a mixture containing activated carbon, a conductive agent and a binder into an electrode shape and then drying the mixture.
Activated carbon is obtained, for example, by subjecting the activated carbon raw material to activation treatment.
The activated carbon raw material is not particularly limited. For example, pitch-based raw materials such as petroleum pitch, coal-based pitch, and mesophase pitch, coke-based raw materials obtained by heat-treating these pitch-based materials, palms, wood flour Plant-based raw materials such as, phenol-based resins, vinyl chloride-based resins, resorcinol-based resins, polyacrylonitrile, polybutyral, polyacetal, polyethylene, polycarbonate, polyvinyl acetate, and the like, and carbides thereof, preferably Examples thereof include pitch-based raw materials, coke-based raw materials, and synthetic resin-based raw materials (in particular, vinyl chloride-based and polyacrylonitrile), which are graphitizable carbon (soft carbon).

As the activation treatment, for example, alkaline activation treatment using potassium hydroxide (KOH), sodium hydroxide (NaOH), lithium hydroxide (LiOH), cesium hydroxide (CsOH), rubidium hydroxide (RbOH) or the like as an activator. Chemical activation treatment using zinc chloride (ZnCl ₂ ), phosphoric acid (H ₃ PO ₄ ) or the like as an activator, gas activation treatment using carbon dioxide (CO ₂ ), air or the like as an activator, and water vapor (H ₂ A steam activation treatment using O) as an activator, and the like, preferably an alkali activation treatment, and more preferably an alkali activation treatment using potassium hydroxide (KOH) as an activator. For example, in the case where the above KOH activation treatment is performed, such activation treatment is performed by pre-calcining soft carbon in a nitrogen atmosphere, for example, 500 to 800 ° C., and then in a nitrogen atmosphere at 700 to 1000 ° C., in the soft carbon 1 For example, by baking with 0.5 to 5 parts by weight of KOH with respect to parts by weight.

When the activated carbon raw material is subjected to such activation treatment, the potential of the positive electrode 2 is particularly 4 V vs. Since a relatively large irreversible capacity can be developed in the positive electrode 2 in a charge / discharge cycle of Li / Li ⁺ or more, the electric capacity of the positive electrode 2 can be fully utilized.
The blending ratio of the activated carbon thus obtained is, for example, 80 to 99% by weight in the mixture.

Examples of the conductive agent include carbon black, ketjen black, and acetylene black. Moreover, the mixture ratio of a electrically conductive agent is 0 to 20 weight% in a mixture, for example. That is, the conductive agent may or may not be blended.
Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluoroolefin copolymer crosslinked polymer, fluoroolefin vinyl ether copolymer crosslinked polymer, carboxymethyl cellulose, polyvinyl pyrrolidone, polyvinyl alcohol, and polyacryl. An acid etc. are mentioned. Moreover, the mixture ratio of a binder is 1 to 10 weight% in a mixture, for example.

And in order to shape | mold the positive electrode 2 in an electrode shape, for example, the mixture which mix | blended the above-mentioned activated carbon, a electrically conductive agent, and a binder is pressed and rolled using a roll press, for example, The electrode sheet obtained by this is used. After punching into an electrode shape, it is dried and pressed onto a metal foil to be a current collector.
Examples of the metal foil include aluminum foil, copper foil, stainless steel foil, and nickel foil.

  The negative electrode 3 is an electrode that reversibly stores and releases lithium ions, and is formed of an electrode material that can reversibly store and release lithium ions. Such an electrode material is not particularly limited. For example, a non-graphitizable carbon material (hard carbon), a graphitizable carbon material (soft carbon), or graphite is used. The negative electrode 3 is formed, for example, by forming a mixture containing hard carbon, soft carbon or graphite, a conductive agent and a binder into an electrode shape and then drying it.

Hard carbon is a general thermosetting resin such as phenol resin, melamine resin, urea resin, furan resin, epoxy resin, alkyd resin, unsaturated polyester resin, diallyl phthalate resin, furfural resin, silicone resin, xylene resin, It can be obtained by firing a urethane resin or the like.
Examples of the soft carbon include the above-mentioned soft carbon such as a pitch-based material, a coke-based material, and a synthetic resin-based material.

  Examples of graphite include pyrolytic products of condensed polycyclic hydrocarbon compounds such as natural graphite, artificial graphite, graphitized mesophase carbon microspheres, graphitized mesophase carbon fibers, graphite whiskers, graphitized carbon fibers, pitch, and coke. A graphite-type carbon material is mentioned. Such a graphite-based carbon material is preferably a powder having an average particle diameter of 25 μm or less.

The blending ratio of hard carbon, soft carbon or graphite is, for example, 80 to 99% by weight in the mixture.
Examples of the conductive agent include the above-described conductive agents. Moreover, the mixture ratio of a electrically conductive agent is 0 to 20 weight% in a mixture, for example. That is, the conductive agent may or may not be blended.

Examples of the binder include the above-described binders. Moreover, the mixture ratio of a binder is 1 to 10 weight% in a mixture, for example.
In order to mold the negative electrode 3 into an electrode shape, for example, a mixture containing hard carbon, soft carbon or graphite, a conductive agent and a binder is stirred and mixed in a solvent, and the resulting metal foil serves as a current collector. After coating on top, it is dried, punched into an electrode shape, and then dried.

Examples of the solvent include N-methylpyrrolidone, dimethylformamide, toluene, xylene, isophorone, methyl ethyl ketone, ethyl acetate, methyl acetate, ethyl acetate, dimethyl phthalate, ethanol, methanol, butanol, water, and the like.
Examples of the metal foil include the above-described metal foil.
The separator 4 is made of an insulating material such as glass fiber, silica or alumina fiber, ceramic fiber, whisker or other inorganic fiber, for example, natural fiber such as cellulose, for example, organic fiber such as polyolefin or polyester. Can be mentioned. Moreover, the separator 4 is shape | molded, for example in plate shape.

The electrolytic solution 5 is made of an organic solvent containing lithium ions, and is prepared by dissolving a lithium salt in the organic solvent.
Examples of the lithium salt include LiClO ₄ , LiCF ₃ SO ₃ , LiC (SO ₂ CF ₃ ) ₃ , LiB (C ₆ H ₅ ) ₄ , LiC ₄ F ₉ SO ₃ , LiC ₈ F ₁₇ SO ₃ , LiB [C _{6 H 3 (CF 3) 2} -3,5] 4, LiB (C 6 F 5) 4, LiB [C 6 H 4 (CF 3) -4] 4, LiBF 4, LiPF 6, LiAsF 6, LiSbF 6 , LiCF ₃ CO ₂ , LiN (CF ₃ SO ₂ ) _{2 and the} like. In the above formula, [C ₆ H ₃ (CF ₃ ) ₂ -3, 5] is the 3rd and 5th positions of the phenyl group, and [C ₆ H ₄ (CF ₃ ) -4] is the 4th position of the phenyl group. Each of which is substituted with —CF ₃ .

  Examples of the organic solvent include propylene carbonate, propylene carbonate derivatives, ethylene carbonate, ethylene carbonate derivatives, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, γ-butyrolactone, 1,3-dioxolane, dimethyl sulfoxide, sulfolane, and formamide. , Dimethylformamide, dimethylacetamide, dioxolane, phosphoric acid triester, maleic anhydride, succinic anhydride, phthalic anhydride, 1,3-propane sultone, 4,5-dihydropyran derivative, nitrobenzene, 1,3-dioxane, 1 , 4-dioxane, 3-methyl-2-oxazolidinone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydride Furan derivatives, sydnone compounds, acetonitrile, nitromethane, alkoxy ethane, and toluene. These can be used alone or in combination of two or more.

The electrolytic solution 5 is prepared so that the concentration of the lithium salt in the organic solvent is, for example, 0.5 to 5 mol / L, preferably 1 to 3 mol / L. Moreover, it prepares so that the moisture content in the electrolyte solution 5 may be 50 ppm or less, for example, Preferably, it may be 10 ppm or less so that a high withstand voltage may be obtained.
In the hybrid capacitor 1, as described above, as a method for causing the positive electrode 2 to exhibit an irreversible capacity for expanding the potential range, the potential of the positive electrode 2 is set to 4 V vs. In addition to the method of making Li / Li ⁺ or more, for example, an additive that is easily oxidatively decomposed electrochemically can be added to the electrolytic solution 5.

Examples of the additive include dimethylformamide (DMF), dimethyl sulfoxide (DMSO), LiCF ₃ SO ₄ , LiFSI, and the like. By adding such an additive to the electrolytic solution 5, the irreversible capacity can be expressed in the positive electrode 2 in the charge / discharge cycle, and thus the electric capacity of the positive electrode 2 can be fully utilized.
And in this hybrid capacitor 1, the positive electrode 2 expresses the irreversible capacity | capacitance for expanding an electric potential range in a charging / discharging cycle.

  Although there is no particular limitation on causing the positive electrode 2 to exhibit irreversible capacity, for example, the first cycle in the charge / discharge cycle of the hybrid capacitor 1 (here, one cycle is a charge / discharge in which charge and discharge are performed once each). In addition, after the constant current charging is performed at the first current value until the cell voltage applied to the positive electrode 2 and the negative electrode 3 reaches the predetermined voltage, the constant voltage is maintained at the predetermined voltage until the second current value is reached. Hold the voltage.

The magnitude of the predetermined voltage is, for example, 2.5 to 5 V, preferably 4 to 5 V (the potential of the positive electrode 2 at this time is 4 to 5 V vs. Li / Li ⁺ , preferably 4.5 ˜4.8 V vs. Li / Li ⁺ ).
As a 1st electric current value, it is 0.1-10 mA / cm < ² >, for example, Preferably, it is 1-5 mA / cm < ² >.

The second current value, 0.05~1mA / cm ^2, preferably from 0.2~0.5mA / cm ^2.
Next, the cell voltage is 0 to 4 V, preferably 1 to 3 V (the potential of the positive electrode 2 at this time is 1.5 to 4 V vs. Li / Li ⁺ , preferably 2 to 3 V vs. Li / Li ⁺ ) Is discharged at a constant current of 0.1 to 10 mA / cm ² , preferably 1 to 5 mA / cm ² . In the second and subsequent cycles, for example, the cell voltage is 0 to 5 V, preferably 1 to 5 V (the potential of the positive electrode 2 at this time is 1.5 to 5 V vs. Li / Li ⁺ , preferably 2 The battery is charged / discharged so as to be ˜4.6V vs. Li / Li ⁺ ).

Thus, in the first cycle of the charge / discharge cycle, irreversible capacity can be expressed in the positive electrode 2 by charging as described above. Therefore, in the first cycle discharge and the second and subsequent cycle charge / discharge cycles. The electric capacity of the positive electrode 2 can be fully utilized.
That is, in the conventional hybrid capacitor, the potential of the positive electrode 2 is caused by the irreversible capacity (for example, Q _Nc1 -Q _Nd1 ) generated in the negative electrode 3 as shown in FIG. As a result of the decrease in the range from V ₁ to V ₁ ′, the electric capacity of the positive electrode 2 decreases from C ₁ V ₁ (C ₁ : capacitance of the electric double layer in the positive electrode 2) to C ₁ V ₁ ′. Thus, although the positive electrode 2 originally has an electric capacity of C ₁ V ₁ , the electric capacity cannot be fully utilized, and only the electric capacity of C ₁ V ₁ ′ can be developed. It is not possible to obtain a relatively low energy density. Therefore, in such a hybrid capacitor, in order to obtain a sufficient electric capacity in the positive electrode 2 in the same manner as the negative electrode 3, a very large amount of the positive electrode 2 (activated carbon) is required, and in order to improve the energy density, It becomes a big obstacle.

Therefore, as shown in FIG. 3, the charge / discharge profile is shown by precharging the negative electrode 3 with an electric capacity corresponding to the irreversible capacity of the negative electrode 3 (for example, Q _Nc1 -Q _Nd1 ). The original electric capacity C ₁ V ₁ of the positive electrode 2 can be obtained without increasing the amount of use. In this case, a third electrode (for example, a lithium electrode) for precharging the negative electrode 3 is used as a hybrid. Since it must be provided in the capacitor 1, other inconveniences such as a complicated capacitor structure, an increase in the size of the capacitor, and an increase in costs associated therewith occur.

However, in the hybrid capacitor 1 of the present embodiment, the usage amount of the positive electrode 2 is not increased, and even if the third electrode described above is not provided, as shown in FIG. The original electric capacity C ₁ V ₁ can be obtained. That is, in the first cycle of the charge / discharge cycle, the irreversible capacity corresponding to the irreversible capacity of the negative electrode 3 is expressed in the positive electrode 2, so that the irreversible capacity of the negative electrode 3 can be compensated. Since it can be utilized, the energy density of the hybrid capacitor 1 can be improved.

Further, as shown in FIG. 5, the charge / discharge profile shows that when the irreversible capacity exceeding the irreversible capacity of the negative electrode 3 is expressed in the positive electrode 2, anion adsorption / desorption occurs in the positive electrode 2 in the charge / discharge cycle. In addition to the electric capacity C ₁ V ₁ due to the above, the electric capacity C ₁ V ₂ due to the adsorption / desorption of lithium ions is developed, the discharge potential of the positive electrode 2 is shifted to the base side, and the positive electrode 2 potential range is V ₁ + V ₂ Energy density can be further improved.

On the other hand, in the hybrid capacitor 1, due to the irreversible capacity of the positive electrode 2, a negative electrode activity inhibitor that is derived from an anion contained in the electrolyte 5 (for example, PF ₆ ⁻ contained in LiPF ₆ , etc.) is generated. There is a case.
As a process of generating the negative electrode activity inhibitor, for example, a process of generating HF due to the irreversible capacity of the positive electrode 2 will be described below.

First, when the predetermined voltage described above is applied to the positive electrode 2 and the negative electrode 3, in the electrolytic solution 5, for example, from the moisture and organic matter contained in the positive electrode 2 and the electrolytic solution 5, as shown in the following formulas (1) and (2): , Protons (H ⁺ ) are generated.
(1) 2H ₂ O → O ₂ + 4H ⁺ + 4e ⁻
(2) R−H → R + H ⁺ + e ⁻ (R is an alkyl group)
Then, the generated protons, anion contained in the electrolytic solution 5 (e.g., PF ₆ contained in LiPF ₆ ^-, etc.) and react, HF is generated (see the following formula (3)).
(3) PF ₆ ⁻ + H ⁺ → PF ₅ + HF

  A negative electrode activity-inhibiting substance such as HF may reduce the electric capacity of the negative electrode 3 and reduce the energy density of the hybrid capacitor 1. Therefore, it is preferable that the hybrid capacitor 1 includes a capturing agent or a capturing member for capturing the negative electrode activity inhibitor.

  For example, as the separator 4, a separator 4a disposed on the positive electrode 2 side and a separator 4b disposed on the negative electrode 3 side are provided, and a lithium foil 7 serving as a capturing agent (capturing member) is provided between the separators 4a and 4b. Is preferably provided. By providing the lithium foil 7, for example, even when a negative electrode activity inhibitor is generated due to the irreversible capacity of the positive electrode 2, the negative electrode activity inhibitor can be captured by the lithium foil 7.

As the lithium foil 7, a known lithium foil can be used, and for example, it is formed in a circular shape or a square shape.
The surface area of the lithium foil 7 is preferably substantially the same as the surface area of the positive electrode 2 and the negative electrode 3 or a larger area. When the surface area of the lithium foil 7 is such an area, the negative electrode activity inhibiting substance (for example, HF) can be efficiently captured.

Furthermore, the thickness is 0.01-0.1 mm, for example, Preferably, it is 0.01-0.05 mm.
The lithium foil 7 has a plurality of holes in the thickness direction. By forming such a hole, the electrolytic solution 5 can pass between the separator 4a and the separator 4b, and can be charged and discharged.

In addition, since the lithium foil 7 should just be a lithium metal, lithium powder and paste-form lithium can also be provided as a capture | acquisition agent, for example.
In addition to the lithium metal described above, the negative electrode activity inhibitor can also be captured by including in the cell tank 6 a compound having a Si—N bond (for example, perhydropolysilazane, methylpolysilazane, etc.). In this case, the negative electrode activity inhibiting substance is captured and stabilized by the compound having a Si—N bond.

Moreover, it is preferable to use carbonates such as Li ₂ CO ₃ (lithium carbonate), Na ₂ CO ₃ (sodium carbonate) and K ₂ CO ₃ (potassium carbonate) instead of lithium metal. These may be used alone or in combination of two or more.
For example, the carbonate may be disposed between the separator 4 a and the separator 4 b, and may also serve as the separator 4. Further, the carbonate may be coated on the surface of the positive electrode 2 and / or the negative electrode 3.

In order to arrange the carbonate between the separator 4a and the separator 4b, for example, powdery carbonate is added to one surface of the separator 4a or the separator 4b, and the surface and the surface of the other separator 4a (4b) are added. And sandwich the carbonate.
In order for the carbonate to also serve as the separator 4, for example, a mixture in which carbonate and a binder are blended is formed in a plate shape as in the separator 4, for example.

Examples of the binder include the above-described binders. The weight ratio of the carbonate and the binder varies depending on the carbonate used, for example, Li ₂ CO _3: PVdF (polyvinylidene fluoride) = 5-9: is preferably 1 to 5, Li ₂ CO _3: PTFE (polytetrafluoroethylene) = 5-9: is preferably 1-5.
In order to coat the carbonate on the surface of the positive electrode 2 and / or the negative electrode 3, for example, a mixture containing carbonate and a binder is stirred and mixed in a solvent, and then applied onto the positive electrode 2 and / or the negative electrode 3 After that, it is dried.

Examples of the binder include the above-described binders, and preferably a rubber-based binder (for example, styrene-butadiene rubber).
Examples of the solvent include the above-mentioned solvents, preferably NMP (N-methylpyrrolidone) and water.
The scavengers and trapping member described above, to the irreversible capacity 1mAh expressed in the positive electrode 2, it is preferably contained in an amount of ^{2 × 10 -5 mol~175 × 10 -5} mol. When the amount of the scavenger is within such a range, a further excellent energy density can be expressed.

For example, referring to the above formulas (1) to (3), 1 mol of HF is generated with the flow of 1 mol of electrons. In other words, the irreversible capacity expressed in positive electrode 2 and Q (mAh), a Faraday constant 96500 (C / mol) Then, the amount M _HF of HF generated in the hybrid capacitor 1, M _HF = 3.6 × Q × F ⁻¹ (mol).
In the case of using the Li ₂ CO ₃ as a scavenger, as shown in the following formula (4), HF is (reacts with Li ₂ CO ₃₎ is trapped in Li ₂ CO _3, LiF and H ₂ CO ₃ produces.
(4) Li ₂ CO ₃ + 2HF → 2LiF + H ₂ CO ₃

As shown in the above formula (4), 0.5 mol of Li ₂ CO ₃ is required to capture 1 mol of HF. More specifically, the required amount M _Li2CO3 of Li ₂ CO ₃ is M _Li2CO3 = 0.5 M _HF = 1.8 × Q × F ⁻¹ (mol), and when F = 96500 is substituted, M _Li2CO3 = 2 × 10 ⁻⁵ × Q (mol). That is, when Li ₂ CO ₃ is contained 2 × 10 ⁻⁵ × Qmol or more with respect to the irreversible capacity Q (mAh), HF can be sufficiently captured. As a result, since a decrease in energy density due to the negative electrode activity inhibitor (HF) can be suppressed, a further excellent energy density can be expressed.

Next, although this invention is demonstrated based on an Example and a comparative example, this invention is not limited by the following Example.
Example 1
(Positive electrode) Mesophase pitch (AR resin manufactured by Mitsubishi Gas Chemical Co., Inc.) was fired at 750 ° C. in a nitrogen atmosphere to obtain graphitizable carbon (soft carbon). Potassium hydroxide (KOH) is mixed with the obtained soft carbon at a blending weight ratio of soft carbon: KOH = 1: 4, fired at 800 ° C. in a nitrogen atmosphere (KOH activation), and then washed with pure water. As a result, KOH activated soft carbon was obtained.

Next, KOH-activated soft carbon: carbon black: PTFE (polytetrafluoroethylene) is mixed at a blending weight ratio of 85: 5: 10, and pressed and rolled using a roll press to form an electrode sheet having a thickness of 75 μm. Obtained. This electrode sheet was punched into a size of φ10 and further vacuum-dried at 100 ° C. for 12 hours to produce a positive electrode.
(Negative electrode) Hard carbon (Carbotron PS (F) manufactured by Kureha Co., Ltd.): PVdF (polyvinylidene fluoride) was mixed at a blending weight ratio of 9: 1 and sufficiently stirred in NMP (1-methyl-2-pyrrolidone). Thereafter, the film was applied to an aluminum foil to a thickness of about 50 μm, dried, then punched out to a size of φ10, and further vacuum dried at 100 ° C. for 12 hours to produce a negative electrode.
(Separator) A 400 μm thick ceramic filter (GB-100R manufactured by ADVANTEC) was punched into φ24 to produce a separator.
(Electrolyte) of LiPF ₆ ethylene carbonate / diethylene carbonate solvent: by preparing (1 1 by volume), LiPF ₆ concentration to prepare an electrolyte solution of 1 mol / L.

A test cell was assembled using one positive electrode, one negative electrode, one separator, and 1 cc of the electrolyte, and a charge / discharge test was performed under the following charge / discharge conditions. The charge / discharge curve is shown in FIG. The monopolar potential was measured based on the Li reference electrode. The unit indicated by “mAh / cc-carbon electrodes” on the horizontal axis of FIG. 6 is the sum of the positive electrode and the negative electrode (the current collector (for example, Al foil or Cu foil) carrying the positive electrode material and the negative electrode material). The capacity (mAh) per unit volume (1 cc) of the sum of the positive electrode material and the negative electrode material excluding the volume is shown.
(Charge / discharge conditions)
First cycle After constant-current charging at 1 mA / cm ² until the cell voltage reached 4.8 V, the constant voltage was maintained at 4.8 V until the current value decreased to 0.2 mA / cm ² . Next, constant current discharge was performed at 1 mA / cm ² until the cell voltage reached 2V.
The second and subsequent cycles were charged and discharged in a voltage range of 2.0 to 4.6V.
Comparative Example 1
(Positive electrode) Activated carbon (RP-15 manufactured by Kuraray Chemical Co., Ltd.): Carbon black: PTFE (polytetrafluoroethylene) is mixed at a mixing weight ratio of 85: 5: 10, and is pressed and rolled using a roll press. Thus, an electrode sheet having a thickness of 520 μm was obtained. This electrode sheet was punched into a size of φ10 and further vacuum-dried at 100 ° C. for 12 hours to produce a positive electrode.
(Negative electrode) Hard carbon (Carbotron PS (F) manufactured by Kureha Co., Ltd.): PVdF (polyvinylidene fluoride) was mixed at a blending weight ratio of 9: 1 and sufficiently stirred in NMP (1-methyl-2-pyrrolidone). Thereafter, the film was applied to an aluminum foil to a thickness of about 50 μm, dried, then punched out to a size of φ10, and further vacuum dried at 100 ° C. for 12 hours to produce a negative electrode.
(Separator) A 400 μm thick ceramic filter (GB-100R manufactured by ADVANTEC) was punched into φ24 to produce a separator.
(Electrolyte) of LiPF ₆ ethylene carbonate / diethylene carbonate solvent: by preparing (1 1 by volume), LiPF ₆ concentration to prepare an electrolyte solution of 1 mol / L.

A test cell was assembled using one positive electrode, one negative electrode, one separator, and 1 cc of the above electrolyte, and after charging at a constant current of 1 mA / cm ² until the cell voltage reached 3.8 V, the cell voltage was 1 A charge / discharge test was repeated in which a cycle of constant current discharge at 1 mA / cm ² was performed until the voltage dropped to 9 V. The charge / discharge curve is shown in FIG. The monopolar potential was measured based on the Li reference electrode. Further, the unit indicated by “mAh / cc-carbon electrodes” on the horizontal axis of FIG. 7 is the sum of the positive electrode and the negative electrode (the current collector carrying the positive electrode material and the negative electrode material (for example, Al foil or Cu foil)). The capacity (mAh) per unit volume (1 cc) of the sum of the positive electrode material and the negative electrode material excluding the volume is shown.

Discussion In Comparative Example 1, as shown in FIG. 7, the potential range of the positive electrode is about 1 V vs. Li / Li ⁺ (range potential of the positive electrode of 3~4V vs.Li/Li ⁺⁾ from about 0.5V vs. Li / Li ⁺ (the positive electrode potential is 3.5~4V vs.Li/Li ⁺ range) is smaller to.

On the other hand, in Example 1, as shown in FIG. 6, in the first charge / discharge cycle, irreversible capacity appears in the positive electrode, the potential of the positive electrode shifts to the base potential side, and the potential range of the positive electrode is about 2V. vs. Li / Li ⁺ (the positive electrode potential is 2.5~4.5V vs.Li/Li ⁺ range) has become.
That is, in the hybrid capacitor of Example 1, 2.5 to 3.5 V vs. positive electrode, which cannot be used in the hybrid capacitor of Comparative Example 1, is used. Li / Li ⁺ and 4 to 4.5 V vs. By utilizing the potential range of Li / Li ⁺ , the usage amount of the positive electrode can be reduced, so that the energy density of the entire cell is improved.
Example 2
(Positive electrode)
Mesophase pitch (AR resin manufactured by Mitsubishi Gas Chemical Co., Ltd.) was heated in the atmosphere at 350 ° C. for 2 hours, and then pre-fired at 800 ° C. for 2 hours in a nitrogen atmosphere to obtain soft carbon. The obtained soft carbon was put into an alumina crucible, and 4 parts by weight of KOH was added to 1 part by weight of the soft carbon. And soft carbon was baked with KOH at 800 degreeC by nitrogen atmosphere for 2 hours (KOH activation). Next, the KOH activated soft carbon was washed with ultrapure water. This washing was performed until the waste liquid from washing became neutral. Thereby, KOH activated soft carbon (positive electrode material) was obtained. After washing, KOH activated soft carbon was pulverized in a mortar and classified with a sieve (32 μm). The powder that did not pass through the sieve was pulverized again in a mortar and repeated classification.

Next, the obtained KOH-activated soft carbon, the conductive additive (Ketjen Black ECP manufactured by Lion Corporation), and the binder (PTFE dispersion manufactured by Daikin Industries, Ltd.) were mixed in a weight ratio of 85: 5: 10 solids. Thus, an electrode sheet having a thickness of 100 μm was obtained by kneading in a mortar and pressing and rolling using a roll press. This electrode sheet was punched out to a size of φ10, further carried into a dryer, and vacuum-dried at 120 ° C. for 12 hours. Then, after the inside of the dryer was purged with nitrogen, the electrode sheet was carried into a glove box in a dry Ar atmosphere so as not to be exposed to the atmosphere, thereby producing a positive electrode.
(Negative electrode)
Artificial graphite, soft carbon, and binder (PVdF manufactured by Kureha Co., Ltd.) were added to NMP (N-methylpyrrolidone) at a blending weight ratio of 22.5: 67.5: 10 at a room temperature (25 ° C. ˜30 ° C.) for 12 hours. The slurry (negative electrode material) obtained by stirring was applied to a copper foil, and then dried at 80 ° C. for 12 hours. The copper foil after drying was pressed and rolled with a hand press to obtain an electrode sheet with a thickness of 29 μm. This electrode sheet was punched out to a size of φ10, further carried into a dryer, and vacuum dried at 120 ° C. for 12 hours. Then, after the inside of the dryer was purged with nitrogen, the electrode sheet was carried into a glove box in a dry Ar atmosphere so that the electrode sheet was not exposed to the atmosphere, thereby producing a negative electrode.
(Separator) A 400 μm thick ceramic filter (GB-100R manufactured by ADVANTEC) was punched into φ13 to produce a separator.
(Electrolytic Solution) An electrolytic solution was prepared by preparing 1 mol / L LiPF ₆ / ethylene carbonate + diethylene carbonate solvent (1: 1 volume ratio).
(Scavenger)
Li ₂ CO ₃ powder and PTFE were mixed at a blending weight ratio of 80:20, and pressed and rolled using a roll press to obtain a sheet having a thickness of 30 μm. This sheet was punched out to a size of φ13, further carried into a dryer, and vacuum-dried at 120 ° C. for 12 hours. Then, after purging the inside of the dryer with nitrogen, the electrode sheet was carried into a glove box in a dry Ar atmosphere so as not to be exposed to the atmosphere, thereby preparing a scavenger sheet.

A test cell was assembled using one positive electrode, one negative electrode, two separators, 1.5 cc of electrolyte, and one scavenger sheet. The scavenger sheet was sandwiched between separators. And the charging / discharging test was implemented with respect to the assembled test cell on the following charging / discharging conditions.
(Charge / discharge conditions)
First cycle After constant-current charging at 1 mA / cm ² until the cell voltage reached 4.8 V, the constant voltage was maintained at 4.8 V until the current value dropped to 0.5 mA / cm ² . Next, constant current discharge was performed at 1 mA / cm ² until the cell voltage reached 2.3V.
The second and subsequent cycles were charged and discharged in a voltage range of 2.3 to 4.6V.

FIG. 8 shows a charge / discharge curve obtained by charge / discharge under the above charge / discharge conditions. The monopolar potential was measured based on the Li reference electrode. Further, the unit indicated by “mAh / cc-carbon electrodes” on the horizontal axis of FIG. 8 is the sum of the positive electrode and the negative electrode (the current collector carrying the positive electrode material and the negative electrode material (for example, Al foil or Cu foil)). The capacity (mAh) per unit volume (1 cc) of the sum of the positive electrode material and the negative electrode material excluding the volume is shown. Moreover, the irreversible capacity expressed in the positive electrode by this test was 67.2 mAh / cc-carbon electrodes.
Comparative Example 2
(Positive electrode) Activated carbon (RP-15 manufactured by Kuraray Chemical Co., Ltd.), a conductive agent (Ketjen Black ECP manufactured by Lion Co., Ltd.), and a binder (PTFE dispersion manufactured by Daikin Industries, Ltd.) as a positive electrode material, solid content 85 The electrode sheet having a thickness of 270 μm was obtained by kneading in a mortar at a blending weight ratio of 5:10 and pressing and rolling using a roll press. This electrode sheet was punched out to a size of φ10, further carried into a dryer, and vacuum dried at 120 ° C. for 12 hours. Then, after the inside of the dryer was purged with nitrogen, the electrode sheet was carried into a glove box in a dry Ar atmosphere so as not to be exposed to the atmosphere, thereby producing a positive electrode.
(Negative electrode) A non-graphitizable carbon (manufactured by Kureha Co., Ltd.) and a binder (PVdF made by Kureha Co., Ltd.) were added to NMP (N-methylpyrrolidone) at a blending weight ratio of 90:10 solids and room temperature ( The mixture was stirred at 25 ° C to 30 ° C for 12 hours. The slurry (negative electrode material) obtained by stirring was applied to a copper foil, and then dried at 80 ° C. for 12 hours. By pressing and rolling the dried copper foil with a hand press, an electrode sheet having a thickness of 25 μm was obtained. This electrode sheet was punched out to a size of φ10, further carried into a dryer, and vacuum-dried at 120 ° C. for 12 hours. Then, after the inside of the dryer was purged with nitrogen, the electrode sheet was carried into a glove box in a dry Ar atmosphere so that the electrode sheet was not exposed to the atmosphere, thereby producing a negative electrode.
(Separator) A 400 μm thick ceramic filter (GB-100R manufactured by ADVANTEC) was punched into φ24 to produce a separator.
(Electrolytic Solution) An electrolytic solution was prepared by preparing 1 mol / L LiPF ₆ / ethylene carbonate + diethylene carbonate solvent (1: 1 volume ratio).

A test cell was assembled using one positive electrode, one negative electrode, two separators, and 1.5 cc of the electrolyte. And the charging / discharging test was implemented with respect to the assembled test cell on the following charging / discharging conditions.
(Charge / discharge conditions)
The cell voltage was charged / discharged at a voltage range of 1.9 to 3.8 V and a current of 1 mA / cm ² .

FIG. 9 shows a charge / discharge curve obtained by charge / discharge under the above charge / discharge conditions. The monopolar potential was measured based on the Li reference electrode. In addition, the unit indicated by “mAh / cc-carbon electrodes” on the horizontal axis of FIG. 9 is the sum of the positive electrode and the negative electrode (the current collector carrying the positive electrode material and the negative electrode material (for example, Al foil or Cu foil)). The capacity (mAh) per unit volume (1 cc) of the sum of the positive electrode material and the negative electrode material excluding the volume is shown.
Measurement Results FIG. 10 is a graph showing the energy density in the charge / discharge cycle of Example 2. FIG. 11 is a graph showing the energy density in the charge / discharge cycle of Comparative Example 2. 10 and FIG. 11, the unit indicated by “Wh / L-carbon electrodes” is the sum of the positive electrode and the negative electrode (the current collector carrying the positive electrode material and the negative electrode material (for example, Al foil or Cu The energy (Wh) per unit volume (1 L) of the sum of the positive electrode material and the negative electrode material (electrode layer) excluding the volume of the foil) is shown.

  As shown in FIG. 10, the energy density of the test cell of Example 2 is, for example, 145.0 Wh / L-carbon electrodes in the fifth cycle in which charging / discharging is relatively stable. On the other hand, as shown in FIG. 11, the energy density of the test cell of Comparative Example 2 is, for example, 28.2 Wh / L-carbon electrodes in the fifth cycle in which charging / discharging is relatively stable.

Thereby, it was confirmed that Example 2 expresses an energy density superior to that of Comparative Example 2.
Trial calculation examples 1-2
Next, in order to confirm how the energy density of the hybrid capacitor changes depending on the amount of the scavenger added to the irreversible capacity developed at the positive electrode, trial calculation examples 1 and 2 were performed. Trial calculation examples 1 and 2 were performed by calculating the energy density in the case where the cell shown in FIG. 12 was assembled based on the energy density (measured value) of Example 2 and Comparative Example 2 under the following trial calculation conditions.
(Calculation conditions)
Trial calculation example 1 (Example 2)
Positive electrode: A positive electrode is formed by coating a positive electrode material on both sides of an Al foil.

Negative electrode: A negative electrode is formed by coating a negative electrode material on both sides of a Cu foil.
Scavenger: Li ₂ CO ₃
Shape of scavenger: Li ₂ CO ₃ powder and PTFE are mixed at a blending weight ratio of 80:20, and a sheet formed by pressing and rolling using a roll press is used as a scavenger sheet. This scavenger sheet also serves as a separator.

Electrode layer thickness T ₂ + T ₃ : 120 μm
Energy density of electrode layer: 145 Wh / L-carbon electrodes
The thickness of the separator (including the trapping agent) T ₁ varies depending on the amount of Li ₂ CO ₃ added.
Cu foil thickness T ₄ : 15 μm
Al foil thickness T ₅ : 15 μm
Trial calculation example 2 (Comparative example 2)
Positive electrode: A positive electrode is formed by coating a positive electrode material on both sides of an Al foil.

Negative electrode: A negative electrode is formed by coating a negative electrode material on both sides of a Cu foil.
Capture agent: None Thickness of electrode layer T ₂ + T ₃ : 120 μm
Energy density of electrode layer: 28.2Wh / L-carbon electrodes
Separator thickness T ₁ : 30 μm
Cu foil thickness T ₄ : 15 μm
Al foil thickness T ₅ : 15 μm
Measurement Results FIG. 13 is a graph showing changes in energy density when the addition amount (coefficient) of Li ₂ CO ₃ with respect to the irreversible capacity is changed in the trial calculation examples 1 and 2. The unit indicated by “Wh / L-cell” on the vertical axis in FIG. 13 is the unit of cell 1 (electrode layer (positive electrode material + negative electrode material) + separator + half of the separator side from the center in the thickness direction of the Cu foil + Al foil). The energy (Wh) per unit volume (1 L) of the separator side half from the center in the thickness direction is shown.

As shown in FIG. 13, the energy density of the trial calculation example 1 is 122 Wh / L-cell when the coefficient is 2 × 10 ⁻⁵ mol / mAh-cell, for example, and the coefficient is 175 × 10 ⁻⁵ mol / mAh. It is 20.5 Wh / L-cell at the time of -cell. On the other hand, since the scavenger is not contained in the cell of the trial calculation example 2, the energy density of the trial calculation example 2 is constant at 20.5 Wh / L-cell regardless of the coefficient.

Thus, the calculations Example 1, the coefficient is, when ^{2 × 10 -5 mol / mAh~175 ×} 10 -5 mol / mAh, i.e., scavenger, with respect to irreversible capacity 1mAh, 2 × 10 ^-5 mol When added at a ratio of ˜175 × 10 ⁻⁵ mol, it was confirmed that the energy density was always equal to or higher than the energy density of Trial Calculation Example 2. That is, it was confirmed that when the addition amount of the scavenger is in the above-described range, the negative electrode active material can be satisfactorily captured and a further excellent energy density can be expressed.

Test example

Test Examples 1-7
Next, Test Examples 1 to 7 were carried out in order to confirm how the electric capacity of the negative electrode changes depending on the type of scavenger.
(Positive electrode) Activated carbon (RP-15 manufactured by Kuraray Chemical Co., Ltd.), conductive agent (Ketjen Black ECP manufactured by Lion Corporation), and binder (PTFE dispersion manufactured by Daikin Industries, Ltd.) with a solid content of 85: 5: 10 The electrode sheet having a thickness of 130 μm was obtained by kneading in a mortar at a blending weight ratio of, and pressing and rolling using a roll press. This electrode sheet was punched out to a size of φ10, further carried into a dryer, and vacuum-dried at 120 ° C. for 12 hours. Then, after the inside of the dryer was purged with nitrogen, the electrode sheet was carried into a glove box in a dry Ar atmosphere so as not to be exposed to the atmosphere, thereby producing a positive electrode.
(Negative electrode) A non-graphitizable carbon (manufactured by Kureha Co., Ltd.) and a binder (PVdF made by Kureha Co., Ltd.) were added to NMP (N-methylpyrrolidone) at a blending weight ratio of a solid content of 9: 1 and room temperature ( The mixture was stirred at 25 ° C to 30 ° C for 12 hours. The slurry obtained by stirring was applied to a copper foil, and then dried at 80 ° C. for 12 hours. The dried copper foil was punched out to a size of φ10, further carried into a dryer, and vacuum-dried at 120 ° C. for 12 hours. Then, after the inside of the dryer was purged with nitrogen, the electrode sheet was carried into a glove box in a dry Ar atmosphere so that the electrode sheet was not exposed to the atmosphere, thereby producing a negative electrode.
(Separator) A 400 μm thick ceramic filter (GB-100R manufactured by ADVANTEC) was punched into φ24 to produce a separator.
(Electrolytic Solution) An electrolytic solution was prepared by preparing 1 mol / L LiPF ₆ / ethylene carbonate + diethylene carbonate solvent (1: 1 volume ratio).
(Capturing agent) For each test example, the capturing agent shown in Table 1 below was used in an amount sufficient to capture the negative electrode activity inhibitor.

A test cell was assembled using one positive electrode, one negative electrode, two separators, and 1.5 cc of the electrolyte. In addition, about the capture | acquisition agent of the test examples except the test example 1, the powdery capture agent was added to the surface of one separator, and it was pinched | interposed by the said surface and the surface of the other separator. In contrast, for the scavenger of Test Example 1, a foil-like scavenger (Li) was sandwiched between two separators. Then, the assembled test cell, the voltage range (current density: 1mA / cm ²⁾ of 0~1.5V (vs.Li/Li ⁺⁾ was subjected to a charge and discharge test with.

Discussion FIG. 14 shows changes in the capacitance of the negative electrode in the charge / discharge cycles of Test Examples 1 to 7. Note that the unit indicated by “mAh / cc-negative electrode” on the vertical axis in FIG. 14 is the unit volume of the negative electrode (negative electrode material excluding the volume of the current collector (eg, Cu foil) carrying the negative electrode material). The capacity per 1 cc) (mAh) is shown.

As shown in FIG. 14, in Test Examples 1 to 4 in which Li, Li ₂ CO ₃ , Na ₂ CO _3, and K ₂ CO ₃ are included as a scavenger, the averaged electric power is obtained even when the charge / discharge cycle is repeated. It was confirmed that the capacity could be expressed. For example, in Test Example 2, it was confirmed that an electric capacity of 140.4 mAh / cc-negative electrode was developed in the fifth cycle in which charging / discharging was relatively stable.

  That is, FIG. 14 confirmed that in Test Examples 1 to 4, it was possible to develop a more excellent energy density than Test Examples 5 to 7 in which the electric capacity of the negative electrode gradually decreased by repeating the charge / discharge cycle.

It is a schematic block diagram of the hybrid capacitor which shows one Embodiment of the electrochemical capacitor of this invention. It is a general profile of charging / discharging of the conventional hybrid capacitor. It is a charge / discharge profile of the hybrid capacitor when the negative electrode is precharged. It is a charging / discharging profile of the hybrid capacitor of this embodiment. It is a charging / discharging profile of the hybrid capacitor of this embodiment, Comprising: It is a figure which shows the case where the discharge potential of a positive electrode is shifted to the base side. 2 is a charge / discharge curve of Example 1. FIG. 3 is a charge / discharge curve of Comparative Example 1. 2 is a charge / discharge curve of Example 2. FIG. It is a charging / discharging curve of the comparative example 2. 4 is a graph showing energy density in a charge / discharge cycle of Example 2. 6 is a graph showing energy density in a charge / discharge cycle of Comparative Example 2. It is a schematic block diagram which shows the cell structure of the hybrid capacitor used in order to calculate the trial calculation data of Example 2 and Comparative Example 2. In estimation Examples 1-2 is a graph showing changes in energy density when varying the amount of Li ₂ CO ₃ with respect to irreversible capacity. It is a figure which shows the change of the electrical capacity of the negative electrode in the charging / discharging cycle of Test Examples 1-7.

Explanation of symbols

1 Hybrid Capacitor 2 Positive Electrode 3 Negative Electrode 4 Separator 5 Electrolyte 7 Lithium Foil

Claims (3)

In the charge / discharge cycle, a positive electrode that expresses an irreversible capacity for expanding the potential range;
A negative electrode made of a material capable of reversibly inserting and extracting lithium ions;
An electrochemical capacitor comprising an electrolyte solution made of an organic solvent containing lithium ions.   2. The electrochemical capacitor according to claim 1, further comprising a scavenger that captures a negative electrode activity inhibitor derived from an anion contained in the electrolyte due to the irreversible capacity of the positive electrode. 3. The electrochemical capacitor according to claim 2, wherein the scavenger is contained in a ratio of 2 × 10 ⁻⁵ mol to 175 × 10 ⁻⁵ mol with respect to the irreversible capacity of 1 mAh.

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