JP2010206018A - Electrochemical capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrochemical capacitor which can exhibit an excellent energy density and an output density by including a negative electrode containing a mixed material of soft carbon and graphite, further, the contained amount of the soft carbon being within a specified range. <P>SOLUTION: A hybrid capacitor includes a positive electrode 2 containing polarizable carbon material, a negative electrode 3 containing the mixed material of soft carbon and graphite, being capable of occluding/releasing lithium ion reversibly, and an electrolyte 6 composed of an organic solvent containing lithium ion, wherein the contained amount of the soft carbon of the negative electrode 3 is made to be 50 wt.% or less to the total amount of the soft carbon and the graphite. <P>COPYRIGHT: (C)2010,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, an electric double layer capacitor having a high output and a long life is known as an electric storage device mounted on a hybrid vehicle or a fuel cell vehicle.
In the electric double layer capacitor, both the positive electrode and the negative electrode are made of a polarizable carbon material, and when a voltage is applied between the positive electrode and the negative electrode, an anion is attracted on the positive electrode and a cation is attracted on the negative electrode, respectively. Electric double layer) is formed. The electric double layer capacitor can store energy by forming the electric double layer.

  On the other hand, in recent years, a capacitor including a positive electrode containing a polarizable carbon material and a negative electrode made of a material capable of reversibly occluding and releasing anions in an electrolytic solution has been proposed. This type of capacitor can be used both for electric storage by an electric double layer and for electric storage by an oxidation-reduction reaction at the negative electrode, and is therefore referred to as a hybrid capacitor, which is about four times as much as a conventional electric double layer capacitor. Can be obtained.

As a hybrid capacitor, for example, a ceramic filter separator, a positive electrode made of a mixture of KOH activated soft carbon, conductive carbon black and PTFE dispersion in a weight ratio of 85: 5: 10, and artificial graphite (graphite) , A hybrid capacitor comprising a negative electrode composed of a mixture of soft carbon and PVdF in a weight ratio of 22.5: 67.5: 10 and an electrolyte composed of ethylene carbonate + diethylene carbonate solvent containing LiPF ₆ is proposed. (For example, refer to Patent Document 1).

JP 2008-103697 A

However, in various fields dealing with capacitors, further improvements in energy density and power density are required.
Therefore, it is necessary to design a hybrid capacitor so that both energy density and power density are improved in a balanced manner.
An object of the present invention is that the negative electrode contains a mixed material of soft carbon and graphite, and further, when the content of the soft carbon is in a specific range, an electric energy that can exhibit excellent energy density and output density. It is to provide a chemical capacitor.

  In order to achieve the above object, the electrochemical capacitor of the present invention comprises a positive electrode containing a polarizable carbon material and a mixed material of soft carbon and graphite, and a negative electrode capable of reversibly occluding and releasing lithium ions. And an electrolytic solution made of an organic solvent containing lithium ions, and the soft carbon content of the negative electrode is 50% by weight or less based on the total amount of soft carbon and graphite.

  In the electrochemical capacitor of the present invention, it is preferable that the content of soft carbon in the negative electrode is 10 to 50% by weight with respect to the total amount of soft carbon and graphite.

  According to the electrochemical capacitor of the present invention, since the soft carbon content of the negative electrode is 50% by weight or less with respect to the total amount of soft carbon and graphite, an excellent energy density and output density can be expressed. .

It is a schematic block diagram of the hybrid capacitor which shows one Embodiment of the electrochemical capacitor of this invention. It is a graph for demonstrating the measuring method of 10 second power density. It is a graph which shows the energy density of each Example and each comparative example. It is a graph which shows the 10 second output density of each Example and each comparative example.

FIG. 1 is a schematic configuration diagram of a hybrid capacitor showing an embodiment of an electrochemical capacitor of the present invention.
The hybrid capacitor 1 includes a positive electrode 2, a negative electrode 3 opposed to the positive electrode 2 with a gap, two separators 4 interposed between the positive electrode 2 and the negative electrode 3, and a trap interposed between the separators 4. A member 7, a positive electrode 2, a negative electrode 3, a separator 4, and a cell tank 5 that accommodates the capture member 7; It has. The hybrid capacitor 1 is a battery cell employed on a lab scale, and industrially a hybrid capacitor 1 that is appropriately scaled up by a known technique is employed.

The positive electrode 2 contains a positive electrode material made of polarizable carbon. For example, an electrode sheet made of a mixture obtained by blending a positive electrode material, a conductive agent, and a polymer binder is formed into a predetermined shape (for example, a circular shape). It is formed by drying after being formed into.
The positive electrode material is obtained by, for example, activating a carbon material.
Examples of the carbon material include hard carbon and soft carbon. These can be used alone or in combination. Of these, soft carbon is preferable. In addition, in the term of the negative electrode described later, hard carbon and soft carbon will be described in detail.

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. For example, chemical activation treatment using zinc chloride (ZnCl ₂ ), phosphoric acid (H ₃ PO ₄ ) or the like as an activator, for example, gas activation treatment using carbon dioxide (CO ₂ ), air or the like as an activator, for example, Examples include steam activation treatment using steam (H ₂ O) as an activator. Among these, Preferably, an alkali activation process is mentioned, More preferably, the alkali activation process (KOH activation process) which uses potassium hydroxide (KOH) as an activator is mentioned.

In the activation process, for example, when the KOH activation process is performed, the carbon material is pre-fired at, for example, 500 to 800 ° C. and then fired together with KOH at 700 to 1000 ° C. in a nitrogen atmosphere. The amount of KOH used is, for example, 0.5 to 5 parts by weight with respect to 1 part by weight of the carbon material.
In the hybrid capacitor using the positive electrode material obtained by the activation process as the positive electrode 2, for example, the potential of the positive electrode 2 is 4 V vs. In the charge / discharge cycle of Li / Li + or more, the positive electrode 2 can exhibit a relatively large irreversible capacity. Therefore, in the discharge process, the positive electrode can be discharged to a lower potential. As a result, the electric capacity of the positive electrode 2 can be increased.

The positive electrode material is blended so that, for example, the weight ratio of the solid content is 80 to 99 wt% with respect to the total amount of the mixture.
Examples of the conductive agent include carbon black, ketjen black, and acetylene black. These can be used alone or in combination of two or more.
Moreover, a electrically conductive agent is mix | blended so that the weight ratio of solid content may be a ratio of 0-20 weight% with respect to the mixture whole quantity, for example. That is, the conductive agent may or may not be blended.

  Examples of the polymer 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. These can be used alone or in combination of two or more. Of these, PVdF is preferable.

Moreover, a polymer binder is mix | blended so that the weight ratio of solid content may become a ratio of 1 to 10 weight% with respect to the mixture whole quantity, for example.
And in order to form the positive electrode 2, the mixture which mix | blended positive electrode material, the electrically conductive agent, and the polymer binder is stirred in a solvent, and a slurry is obtained. Next, the slurry is applied to the surface of the current collector, and pressure-stretched using, for example, a roll press to obtain an electrode sheet. Next, the electrode sheet is punched into a predetermined shape (for example, a circular shape) and then dried. Thereby, the positive electrode 2 is obtained.

Although the thickness and diameter of the positive electrode 2 obtained by such a method differ depending on the scale of the hybrid capacitor 1, for example, in the lab scale, the thickness is 30 to 150 μm and the diameter is about 10 mm.
The negative electrode 3 contains a negative electrode material containing soft carbon and graphite. For example, an electrode sheet made of a mixture obtained by blending a negative electrode material and a polymer binder is formed into a predetermined shape (for example, a circular shape). Thereafter, it is formed by drying.

With soft carbon, for example, by heat treatment in an inert atmosphere, the hexagonal network surface composed of carbon atoms tends to form a relatively regular laminated structure (graphite structure) than the hexagonal network surface of hard carbon. A general term for carbon. Specifically, in an inert atmosphere, when it is heat-treated at 2000 to 3000 ° C., (002) the average plane spacing _{d 002} of face 3.40Å or less, and preferably 3.35~3.40Å crystals It is a general term for carbon forming the structure.

Specific soft carbon raw materials include, for example, pitches such as petroleum pitch, coal pitch, and mesophase pitch, such as petroleum needle coke, coal needle coke, anthracene, polyvinyl chloride, and polyacrylonitrile. Examples include graphitizable cokes. These can be used alone or in combination of two or more.
The hard carbon used as a comparative control of soft carbon is, for example, a crystal structure in which an average interplanar spacing d ₀₀₂ of (002) plane exceeds 3.40 mm when heat-treated at 2500 ° C. in an inert atmosphere. It is a general term for carbon to be formed.

  Specific raw carbon materials include, for example, phenol resin, melamine resin, urea resin, furan resin, epoxy resin, alkyd resin, unsaturated polyester resin, diallyl phthalate resin, furfural resin, resorcinol resin, silicone resin, xylene resin. Difficulty from graphitizable coke such as thermosetting resin such as urethane resin, carbon black such as thermal black, furnace black, lamp black, channel black, acetylene black, such as flue coke and gilsonite coke Examples thereof include graphitizable coke, for example, plant-based materials such as coconut palm and wood flour, such as glassy carbon.

The content of soft carbon in the negative electrode material is 50% by weight or less, preferably 10 to 50% by weight, more preferably 10 to 25% by weight, particularly preferably, based on the total amount of soft carbon and graphite. 10 to 20% by weight.
Examples of graphite include natural graphite and artificial graphite. These can be used alone or in combination of two or more. Moreover, as artificial graphite, the thermal decomposition thing obtained by heat-processing above-mentioned soft carbon is mentioned, for example. Further, graphite is preferably used in the form of powder (for example, having an average particle size of 25 μm or less).

The negative electrode material can contain a small amount of a third component such as hard carbon, for example, in addition to soft carbon and graphite, if necessary.
And the above negative electrode materials are mix | blended so that the weight ratio of solid content may become a ratio of 80 to 99 weight% with respect to the mixture whole quantity, for example.
Examples of the conductive agent include the above-described conductive agents. Moreover, a electrically conductive agent is mix | blended so that the weight ratio of solid content may be a ratio of 0-20 weight% with respect to the mixture whole quantity, for example. That is, the conductive agent may or may not be blended.

Examples of the polymer binder include the polymer binder described above, and preferably PVdF. Moreover, a polymer binder is mix | blended so that the weight ratio of solid content may become a ratio of 1 to 10 weight% with respect to the mixture whole quantity, for example.
In order to form the negative electrode 3, for example, first, a mixture in which the negative electrode material and the polymer binder are blended is stirred in a solvent to obtain a slurry. Next, the slurry is applied to the surface of the current collector, and pressure-stretched using, for example, a roll press to obtain an electrode sheet. Next, the electrode sheet is punched into a predetermined shape (for example, a circular shape) and then further dried. Thereby, the negative electrode 3 is obtained.

  Examples of the solvent include aprotic polar solvents such as N-methyl-2-pyrrolidone (NMP) and dimethylformamide (DMF), for example, protic polar solvents such as ethanol, methanol, propanol, butanol, and water, for example, Nonpolar solvents such as toluene, xylene, isophorone, methyl ethyl ketone, ethyl acetate, methyl acetate, dimethyl phthalate and the like can be mentioned. Among these, Preferably, an aprotic polar solvent is mentioned, More preferably, N-methyl-2-pyrrolidone (NMP) is mentioned.

As the current collector, for example, a metal foil such as an aluminum foil, a copper foil, a stainless steel foil, or a nickel foil can be used.
Although the thickness and diameter of the negative electrode 3 obtained by the above methods differ depending on the scale of the hybrid capacitor 1, for example, in the lab scale, the thickness is 5 to 70 μm and the diameter is about 10 mm.

Examples of the separator 4 include separators made of inorganic fibers such as glass fibers, ceramic fibers, and whiskers, natural fibers such as cellulose, and organic fibers such as polyolefin and polyester.
Moreover, although the thickness and diameter of the separator 4 differ with scales of the hybrid capacitor 1, for example, in the lab scale, the thickness is 15 to 100 μm and the diameter is about 24 mm.

The capturing member 7 is, for example, a sheet obtained by press-stretching a capturing agent for capturing a negative electrode activity inhibitor (described later) and a polymer binder.
Examples of the scavenger include alkali metal carbonates such as lithium carbonate (Li ₂ CO ₃ ), sodium carbonate (Na ₂ CO ₃ ), and potassium carbonate (K ₂ CO ₃ ). These can be used alone or in combination of two or more. Of these, lithium carbonate is preferable.

Examples of the polymer binder include the above-described polymer binder, and preferably PTFE.
In order to form the capturing member 7, for example, first, the capturing agent and the polymer binder are mixed at a mixing ratio (capturing agent: polymer binder) of 20:80 to 98: 2 by weight ratio of solid content. Preferably, it mix | blends so that it may become 50: 50-90: 10. Next, the mixture is pressurized and stretched using, for example, a roll press to obtain a capturing agent-containing sheet.

Then, the scavenger-containing sheet is punched into a predetermined shape (for example, a circular shape) and then dried. Thereby, the capture member 7 is obtained.
The electrolytic solution 6 is made of an organic solvent containing a lithium salt, and is prepared, for example, by dissolving a lithium salt in the organic solvent.
The lithium salt has an anion component containing halogen. For example, LiClO ₄ , LiCF ₃ SO ₃ , LiC (SO ₂ CF ₃ ) ₃ , 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 . These can be used alone or in combination of two or more.

  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 (DMSO), Sulfolane, formamide, dimethylformamide (DMF), dimethylacetamide (DMA), 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-methyl Tetrahydrofuran, tetrahydrofuran derivatives, sydnone compounds, acetonitrile, nitromethane, alkoxy ethane, and toluene. These can be used alone or in combination of two or more.

In order to prepare the electrolytic solution 6, for example, the concentration of the lithium salt is, for example, 0.5 to 5 mol / L, preferably 1 to 3 mol / L. The lithium salt is dissolved in an organic solvent so that the amount is, for example, 50 ppm or less, preferably 10 ppm or less.
In the hybrid capacitor 1, the negative electrode activity-inhibiting substance captured by the capturing member 7 is a substance derived from an anion contained in the electrolytic solution 6, for example, a fluorine derived from PF ₆ ⁻ contained in LiPF _6. An acid (HF) etc. are mentioned. Such a negative electrode activity-inhibiting substance is generated when, for example, an irreversible capacity for expanding the potential range of the positive electrode 2 is developed in the positive electrode 2 in a charge / discharge cycle.

The irreversible capacity at the positive electrode 2 is manifested, for example, by executing the first charge / discharge cycle as follows. Specifically, first, the cell voltage applied between the positive electrode 2 and the negative electrode 3 (between the positive electrode and the negative electrode) rises to 2.5 to 5.0 V (preferably 4.0 to 5.0 V). Up to 0.1 to 10 mA / cm ² (preferably, 1 to 5 mA / cm ² ). After charging (preferably, 0.2~0.5mA / cm ²⁾ current values 0.05~1mA / cm ² until drops, and held in the cell voltage after rising, then the cell voltage 0 A constant current discharge is performed at 0.1 to 10 mA / cm ² (preferably 1 to 5 mA / cm ² ) until the voltage drops to 4.0 V (preferably 1.0 to 3.0 V). By executing the first cycle in this manner, the irreversible capacity can be expressed in the positive electrode 2.

In the second and subsequent cycles of the charge / discharge cycle, for example, the maximum cell voltage is in the range of 4.0 to 4.8 V (preferably 4.2 to 4.6 V), and the minimum cell voltage is 0.0 to 4. A constant power discharge in the range of 0 V (preferably 2.0 to 2.4 V) is performed.
In the hybrid capacitor 1, due to the expression of irreversible capacity at the positive electrode 2, for example, when the electrolytic solution 6 contains LiPF ₆ , HF is generated as follows. Specifically, in the charging process of the first cycle, protons (H ⁺ ) are generated from moisture and organic substances contained in the positive electrode 2 and / or the electrolytic solution 6 (see the following formulas (1) and (2)).
(1) 2H ₂ O → O ₂ + 4H ⁺ + 4e ⁻
(2) R—H → R + H ⁺ + e ⁻ (R is an alkyl group)
Then, the generated protons, PF ₆ contained in the electrolytic solution 6 ^- reacted with, HF (negative electrode active inhibitor) is produced (the following formula (3) refer).
(3) PF ₆ ⁻ + H ⁺ → PF ₅ + HF
However, in the hybrid capacitor 1, the HF generated as described above can be captured by the capturing member 7 immersed in the electrolytic solution 6.
And according to this hybrid capacitor 1, since the soft carbon content of the negative electrode 3 is 50% by weight or less with respect to the total amount of soft carbon and graphite, an excellent energy density and output density can be expressed. it can.

For example, the 10-second output density of the hybrid capacitor 1 is, for example, 3000 W / L or more, preferably 10000 W / L or more.
However, as shown in FIG. 2, the 10-second power density is an xy having an x-axis for determining the value of the power density (W / L) and a y-axis for determining the value of the energy density (Wh / L). On the plane, a graph A connecting points indicating the relationship between the output density and the energy density when the discharge power value (W) of the constant power discharge in the charge / discharge cycle is changed, and a graph B satisfying the equation y = 0.0022x It is the value (W / L) of the x coordinate at the intersection with (straight line). The output density and the energy density are values per unit volume (1 L) of the sum of the volumes of the positive electrode 2 and the negative electrode 3 (excluding the volume of the current collector).

  The electrochemical capacitor of the present invention can be suitably used, for example, as various industrial products such as a drive battery mounted in an automobile (such as a hybrid vehicle), a memory backup power source for a notebook computer, a mobile phone, and the like.

Next, although this invention is demonstrated based on an Example and a comparative example, this invention is not limited by the following Example.
Examples 1-4 and Comparative Examples 1-2
1. Production of positive electrode Mesophase pitch (AR resin manufactured by Mitsubishi Gas Chemical Co., Ltd.) was heated in the atmosphere at 350 ° C. for 2 hours. Next, the heated pitch was pre-fired at 800 ° C. for 2 hours in a nitrogen atmosphere. As a result, mesophase carbon microbeads were obtained. The obtained mesophase carbon microbeads were put in an alumina crucible, and 4 parts by weight of KOH was added to 1 part by weight of mesophase carbon microbeads. Next, the mesophase carbon microbeads were activated with KOH by firing with KOH at 800 ° C. for 2 hours in a nitrogen atmosphere. Next, the mesophase carbon microbeads activated with KOH were washed with ultrapure water. Washing was performed until the waste liquid 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). Then, the grinding operation in the mortar was repeated until almost all the KOH-activated soft carbon had a particle size that could pass through the sieve.

After classification, by kneading KOH activated soft carbon powder, conductive agent (VXC72R manufactured by CABOT) and polymer binder (PVdF manufactured by Kureha Co., Ltd.) with a stirrer at a weight ratio of 75:15:10 solid content. The slurries were obtained.
Subsequently, the slurry was apply | coated to the surface of aluminum foil (current collector) using the coating machine, and the 85-micrometer-thick electrode sheet was obtained by carrying out pressure extension using the roll press. Next, the electrode sheet was punched into a circular shape having a diameter of 10 mm, and then carried into a dryer and vacuum-dried at 120 ° C. for 12 hours. 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. Through the above steps, a positive electrode was produced.
2. Production of Negative Electrode Soft carbon, graphite, and polymer binder (PVdF manufactured by Kureha Co., Ltd.) were added to an N-methyl-2-pyrrolidone (NMP) solvent at a weight ratio shown in Table 1 below, and room temperature (25 ° C. The slurry of the mixture was obtained by stirring for 12 hours at ˜30 ° C.

Next, the obtained slurry was applied to the surface of a copper foil (current collector) and subjected to pressure stretching with a roll press to obtain an electrode sheet having a thickness of 25 μm. Next, the electrode sheet was punched into a circular shape having a diameter of 10 mm, and then carried into a dryer and vacuum-dried at 120 ° C. for 12 hours. 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. The negative electrode was produced by the above operation.
3. Production of Separator A separator was produced by punching a ceramic filter (GB-100R, manufactured by ADVANTEC) into a circular shape having a diameter of 25 mm.
4). Preparation of scavenger-containing sheet Lithium carbonate (Li ₂ CO ₃ ) powder (average particle size 85.0 μm manufactured by Kishida Chemical Co., Ltd.) and polymer binder (PTFE dispersion manufactured by Daikin Industries, Ltd.) having a solid content of 80:20 A mixture thereof was obtained by kneading in a mortar in a weight ratio.

Next, the mixture was stretched under pressure using a manual roll press to obtain a sheet having a thickness of 30 μm. Next, the obtained sheet was punched into a circular shape of φ13, and then carried into a dryer and vacuum-dried at 120 ° C. for 12 hours. Then, after purging the inside of the dryer with nitrogen, a scavenger-containing sheet was prepared by carrying it into a glove box in a dry Ar atmosphere so that the sheet was not exposed to the atmosphere.
5). Preparation of Electrolytic Solution LiPF ₆ (lithium salt) was prepared by dissolving in an ethylene carbonate-diethylene carbonate mixed solvent (volume ratio 1: 1) so that the concentration was 2 mol / L.
6). Assembly of test cell A test cell was assembled using 1 positive electrode, 1 negative electrode, 2 separators, 1 scavenger-containing sheet and 1 mL of electrolyte. The scavenger-containing sheet was used in a form sandwiched between two separators.
Evaluation experiment 1. Charge / Discharge Test A charge / discharge test was carried out by the following method for each of the test cells assembled in the above Examples and Comparative Examples.
(1) 1st cycle It charged with constant current at 1 mA / cm < ² > until the cell voltage rose to 4.8V. After charging, the cell voltage was maintained at 4.8 V until the current value dropped to 0.5 mA / cm ² , and then constant current discharge was performed at 1 mA / cm ² until the cell voltage dropped to 2.3 V.
(2) Second cycle A constant current was charged at 1 mA / cm ² until the cell voltage increased to 4.6V. After charging, constant current was discharged at 1 mA / cm ² until the cell voltage dropped to 2.3V.
(3) From the 3rd cycle Onward, constant current charging was performed at 1 mA / cm ² until the cell voltage increased to 4.6V. After charging, the cell voltage was maintained at 4.6 V until the current value dropped to 0.5 mA / cm ² , and then constant power discharge was performed at a predetermined discharge power value. The discharge power value in each cycle was set to gradually increase from 1 mW to 250 mW.

  Based on the test results obtained by the charge / discharge test, the energy density and 10-second output density of each test cell were calculated. The results are shown in Table 1 and FIGS.

2. Test results According to Table 1 and FIGS. 3 to 4, in Examples 1 to 4 where the soft carbon content in the negative electrode is 50 wt% or less, Comparative Example 1 in which the negative electrode does not contain soft carbon, and It was confirmed that a higher energy density and a 10-second output density can be exhibited than Comparative Example 2 in which the soft carbon content is 75 wt%.

1 Hybrid Capacitor 2 Positive Electrode 3 Negative Electrode 6 Electrolyte

Claims (2)

A positive electrode containing a polarizable carbon material;
A negative electrode containing a mixed material of soft carbon and graphite and capable of reversibly inserting and extracting lithium ions;
An electrolyte solution composed of an organic solvent containing lithium ions,
An electrochemical capacitor, wherein the content of soft carbon in the negative electrode is 50% by weight or less based on the total amount of soft carbon and graphite.   2. The electrochemical capacitor according to claim 1, wherein the content of soft carbon in the negative electrode is 10 to 50 wt% with respect to the total amount of soft carbon and graphite.

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