JP2009043747A - Hybrid capacitor and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hybrid capacitor which can have high volume energy density and long-period cycle characteristics, and a manufacturing method thereof. <P>SOLUTION: Disclosed is an asymmetrical electrical double layer capacitor which uses a polarizing electrode made principally of active carbon as a positive electrode and a Faraday electrode using an SiLix film and capable of reversibly absorbing Li ions as a negative electrode, and uses a non-aqueous electrolyte containing Li salt as an electrolyte. The SiLix film may be formed by doping an Si film formed on metal foil with Li or may be formed directly on current collector metal foil by sputtering an Si-Li alloy target. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an asymmetric electric double layer capacitor capable of increasing the volume energy density.

An electric double layer capacitor is a capacitor that uses an electric double layer generated at the electrolyte interface in an electrolyte and positive and negative polarizable electrodes mainly composed of activated carbon, and is widely used as a memory backup power source for small devices. In recent years, it is also considered promising for medium and large-sized applications such as auxiliary power supplies and electric vehicles, and realization of electric double layer capacitors with high energy density is desired.
Here, the energy E stored in the cell capacitor, the capacitance of the capacitor C (F), using a withstand voltage V (V), is expressed by E = 1 / 2CV ^2. Therefore, the larger the electrostatic capacitance C and the withstand voltage V of the capacitor, the more advantageous for improving the energy density.
In conventional symmetrical electric double layer capacitors, a method to increase the capacitance density by increasing the surface area has been studied by examining starting materials and activation conditions when obtaining activated carbon that is the main component of the electrode. .
For example, a method is disclosed in which activated carbon having a specific surface area of 2000 m ² / g to 3500 m ² / g is obtained by firing a mixture of petroleum coke and potassium hydroxide (see, for example, Patent Document 1). .)
However, there is a limit in increasing the specific surface area of activated carbon, and there is a problem that the activated carbon becomes bulky as the specific surface area is increased, and it is difficult to improve the capacitance per volume. As for the withstand voltage, there is a problem that if the voltage is increased excessively, the electrolytic solution is electrolyzed, leading to an increase in internal resistance and a decrease in capacitance. There is a limit of about 2.7V.

An asymmetric electric double layer capacitor (hereinafter referred to as a hybrid capacitor) has been disclosed as a technique for simultaneously increasing the capacitance and withstand voltage and increasing the energy density of the capacitor (see, for example, Patent Document 2).
This consists of a polarizable electrode mainly composed of activated carbon for the positive electrode, a Faraday electrode doped with Li in advance in a carbon material capable of reversibly occluding and releasing Li, and an organic solvent containing Li salt in the electrolyte. It is characterized by using a system electrolyte. When this capacitor is charged and discharged, the anion in the electrolyte is adsorbed and desorbed at the positive electrode (polarizable electrode), and only the Li ion is occluded and desorbed at the negative electrode (Faraday electrode). In addition, since the negative electrode is preliminarily doped with Li, the potential of the negative electrode is close to that of metal Li. That is, there is already a potential difference of nearly 3 V between the positive electrode and the negative electrode before charging, and the potential difference between the positive and negative electrodes when the positive electrode (polarizable electrode) is charged to near the electrolysis voltage of the electrolyte is about 4.3 V. This corresponds to the withstand voltage of the capacitor. Moreover, since the negative electrode is a Faraday electrode, the capacitance of the hybrid capacitor is equal to the capacitance of the positive electrode, which is about twice that of a symmetric type electric double layer capacitor using a polarizable electrode for both electrodes. .
JP-A-63-78513 Japanese Patent Laid-Open No. 8-1007048

As described above, various studies have been made to improve the energy density of the hybrid capacitor, but it can be said that increasing the capacities of the positive electrode and the negative electrode is effective in order to further improve the energy density. .
However, there is a limit to the increase in the surface area of the activated carbon of the negative electrode, and the limits of the theoretical maximum capacity of 372 mAh / g and 837 mAh / ml naturally occur in the graphite of the negative electrode material.
In order to further improve the energy density of the hybrid capacitor, it is conceivable to use Si or Sn, which has been studied for secondary batteries, as a material capable of reversibly inserting and extracting Li in the negative electrode. The theoretical capacity per unit volume of carbon (graphite) is 837 mAh / ml, whereas the theoretical capacity per unit volume of Si is 9770 mAh / ml, so the volume necessary to obtain the same negative electrode capacity can be reduced. It can be expected that the volume energy density of the hybrid capacitor is improved. Further, the theoretical capacity per unit volume of Sn is 7220 mAh / ml, and it can be expected that the volume energy density of the hybrid capacitor is similarly improved.

  An object of the present invention is to provide a negative electrode for a hybrid capacitor capable of obtaining a high volume energy density and obtaining long-term cycle characteristics, and a hybrid capacitor using the negative electrode.

The present invention seeks to solve the above problem by using as a Faraday electrode capable of reversibly occluding Li ions as a negative electrode having a SiLix film formed on at least the outermost surface of the current collector metal foil. .
That is, the hybrid capacitor of the present invention uses a polarizable electrode mainly composed of activated carbon for the positive electrode, a Faraday electrode capable of reversibly occluding Li ions for the negative electrode, and an asymmetrical solution using a non-aqueous electrolyte containing a Li salt as the electrolyte. The type electric double layer capacitor is characterized in that a SiLix film is formed on at least the outermost surface of the negative Faraday electrode formed on the current collector metal foil.
In the SiLix film, x is preferably 0.3 or more and 5.5 or less.

One of the methods for manufacturing a hybrid capacitor of the present invention is to form a Si film on a current collector metal foil, then electrochemically dope Li on the surface of the Si film, and have a SiLix film at least on the outermost part. A method for producing a hybrid capacitor was obtained, in which a negative electrode was formed, the negative electrode and a positive electrode made of activated carbon were opposed to each other with a separator interposed therebetween, and a laminate cell was produced using a non-aqueous electrolyte containing a Li salt.
Further, another method of manufacturing a hybrid capacitor according to the present invention includes forming a Si-Li alloy film on a current collector metal foil, and then electrochemically doping Li on the surface of the Si-Li alloy film. A hybrid capacitor formed by forming a negative electrode having a SiLix film on the outermost surface, making the negative electrode and a positive electrode made of activated carbon face each other with a separator interposed therebetween, and producing a laminate cell using a non-aqueous electrolyte containing a Li salt It was set as the manufacturing method of this.
Furthermore, another method of manufacturing a hybrid capacitor according to the present invention is to form a negative electrode made of a SiLix film on a current collector metal foil, and to make the negative electrode and a positive electrode made of activated carbon face each other with a separator interposed therebetween. A method for producing a hybrid capacitor comprising producing a laminate cell using a nonaqueous electrolyte solution is included.
In the SiLix film, x is preferably 0.3 or more and 5.5 or less.
In these hybrid capacitor manufacturing methods of the present invention, a vapor deposition method can be used as a method of forming the Si film or the SiLix film. As the vapor deposition method, a sputtering method or a vacuum deposition method can be used.

  The hybrid capacitor of the present invention can provide a hybrid capacitor having excellent cycle characteristics by using a SiLix film having a SiLix film formed on at least the outermost surface of the metal foil as a negative electrode. Volume energy density can be improved more than a capacitor.

Here, the operation concept of the hybrid capacitor will be described. FIG. 1 shows a schematic diagram of changes in potential and electric capacity of the positive and negative electrodes when the hybrid capacitor is charged and discharged. At the time of charging / discharging, electric capacity is generated by adsorption of anions in the electrolytic solution in the positive electrode and insertion of Li ions in the electrolytic solution in the negative electrode. When charging is started, both the capacitance and potential increase at the positive electrode, and both the capacitance and potential decrease at the negative electrode. On the contrary, when the discharge is started, both the electric capacity and the potential decrease at the positive electrode, and both the electric capacity and the electric potential increase at the negative electrode.
If the capacitance at the positive and negative electrodes is Q, the capacitance at the positive and negative electrodes is C _a and C _c , and the voltage change at the positive and negative electrodes is ΔV _a and ΔV _c ,
Q = C _a ΔV _a = C _c ΔV _c (1)
If ΔV _c >> ΔV _a , C _c << C _a from equation (1). Since this capacitor has C _a and C _c arranged in series, the capacitance C _cell of the _cell is substantially equal to C _c . Therefore, the smaller the potential change when inserting Li, the more preferable the negative electrode material. Moreover, since the potential difference between the positive electrode and the negative electrode corresponds to the withstand voltage of the capacitor, a lower Li insertion potential is preferable. Since Sn has a higher Li insertion potential than graphite, the withstand voltage of the capacitor is reduced. On the other hand, Si that is sufficiently charged and Li is sufficiently doped has a Li insertion potential almost equal to that of graphite, and the potential change during insertion of Li is small. In addition, by fully doping Si in advance with Li, the irreversible capacity due to the formation of SEI (solid electrolyte interface layer) can be compensated.

A feature of the present invention is a hybrid capacitor using a polarizable electrode mainly composed of activated carbon as a positive electrode, a Faraday electrode capable of reversibly occluding lithium ions in a negative electrode, and a non-aqueous electrolyte containing a lithium salt as an electrolyte. The negative electrode is Si (including boron and phosphorus doped n-type and p-type semiconductors) or Si-Li alloy is doped with Li, or SiLix formed directly by vapor deposition or the like is used. There is to do. By doping Li or directly forming SiLix into Si or Si-Li alloy, the potential is sufficiently lowered to compensate for irreversible capacity, and the capacity of the negative electrode is sufficiently larger than that of the positive electrode, and the charge / discharge depth of the negative electrode is increased. Since it can be made small, it can be used as the negative electrode of a hybrid capacitor.
Here, x in the SiLix film is preferably 0.3 or more and 5.5 or less. When x is smaller than 0.3, the negative electrode potential cannot be lowered sufficiently, and the withstand voltage of the hybrid capacitor cannot be increased. Further, when x is greater than 5.5, the volume change during pre-doping is large, and even a slight volume change when driving the hybrid capacitor causes the Si film, Si-Li alloy film, or SiLix film to peel off from the current collector. Therefore, it is not preferable.
In SiLix, when x becomes larger than 4.4, Li precipitates. When SiLix is used as the negative electrode of a lithium ion battery, the deposited Li has an adverse effect on cycle characteristics, safety and reliability when charging and discharging are repeated, but in the case of a hybrid capacitor, the Li utilization rate is small. It doesn't matter. However, since it is preferable that Li does not precipitate in order to improve the cycle characteristics, x is preferably 0.3 or more and 4.4 or less.
In addition, since SiLix has better cycle characteristics when the volume change due to film formation or electrochemical Li doping is suppressed, x should be as small as possible, but x should be as small as possible from the viewpoint of lowering the potential. Larger is preferable. Therefore, x is more preferably 1.3 or more and 4.1 or less.

Si can cause a lithiation reaction without depositing metallic Li up to SiLi _4.4 . The amount of electricity required for this reaction is 4200 mAh per Si weight, which is the theoretical capacity of Si. The percentage of the amount of electricity required for actual Li doping with respect to this theoretical capacity is defined as the doping depth. For example, when Si is electrochemically doped with Li to form SiLi _3.3 , the doping depth is 75%, and the amount of electricity required for Li doping is 3150 mAh per Si weight.
Moreover, the Si—Li alloy produced by the vapor deposition method can be regarded as Si doped with Li in advance. For example, SiLi _0.44 alloy can be considered to have a doping depth of 10%.
The Si—Li alloy thus produced can be used as a negative electrode of a hybrid capacitor as it is, but it can also be used as a negative electrode by further lowering the potential by electrochemically pre-doping Li as necessary. In this case, the net doping depth is the sum of the doping depth calculated from the Li amount doped in advance and the doping depth calculated from the Li amount when electrochemically doping Li. For example, when SiLi _0.44 alloy is electrochemically doped with Li to form SiLi _3.3 , the doping depth is 75%, and the amount of electricity required for Li doping to Li doping is 2730 mAh per Si weight. .
Based on this definition, it can be said that the doping depth is preferably 7% or more and 123% or less in the present invention. At this time, the amount of electricity required for electrochemically doping Li into the Si film is preferably 286 mAh or more and 5155 mAh or less per negative electrode weight.

An electrochemical method can be used as a method of doping Si or Si—Li alloy with Li. Li doping by an electrochemical method can be performed by directly bonding an electrode made of Si or a Si—Li alloy and a metal Li electrode and short-circuiting both electrodes. Alternatively, an electrode made of Si or Si—Li alloy and a metal Li electrode are made to face each other through a separator, immersed in an electrolyte containing Li ions, and an electric current is applied so that the electrode made of Si or Si—Li alloy becomes a cathode. It can also be done by flowing. Since the doping of Li by bonding of metal Li electrodes is difficult to control the doping amount, the latter is preferable. The doping amount of Li can be adjusted by adjusting the time during which the current flows.
When the negative electrode potential is lowered as much as possible by doping Li electrochemically, the withstand voltage of the hybrid capacitor can be increased, so that the energy density can be improved. The Si-Li alloy film can be regarded as a Si film doped with Li in advance, and can be used as it is as a negative electrode of a hybrid capacitor. However, in some cases, the potential is further lowered by electrochemically pre-doping Li. It is effective.

  The Si or Si-Li alloy used is a Si thin film or Si-Li alloy thin film formed on a current collector made of copper foil, aluminum foil, nickel foil or the like by a vapor deposition method such as a sputtering method or a vacuum deposition method. It is preferable. According to these methods, a uniform thin film can be easily formed on the current collector, the adhesion between the current collector and the negative electrode material is improved, and the negative electrode is deteriorated due to peeling due to charge and discharge. This is because it can be made difficult. In addition to the sputtering method and the vacuum deposition method, Si or Si—Li alloy thin films formed by various vapor deposition methods such as ion plating can also be used.

  As the hybrid capacitor negative electrode material of the present invention, Si and Si—Li alloy are cited, but since the Si—Li alloy has better cycle characteristics even at a high Li utilization rate, the negative electrode film thickness can be reduced. . This is because the Si-Li alloy film has a structure in which Li is uniformly dispersed in the Si film, and volume change can be suppressed when electrochemically doping Li or when absorbing and desorbing Li as a hybrid capacitor. This is probably because of this. Therefore, the volume energy density can be increased by using the Si—Li alloy for the negative electrode.

A Si—Li alloy target for forming a Si—Li alloy film by a sputtering method can be produced by press-molding Si—Li alloy powder. The Si-Li alloy powder for producing the Si-Li alloy target has an inert atmosphere in which the dew point is controlled to -60 ° C or lower in advance in order to prevent oxidation of Li during powder production. It is produced by alloying with. About 5-40 wt% of Li is suitable for the compounding ratio of Si powder and metal Li. This corresponds to x being 0.1 to 2.7 in SiLix. If x is less than 0.1, volume expansion will increase even if Li is electrochemically doped, and the cycle characteristics of the hybrid capacitor will deteriorate, and if x is greater than 2.7, cracking will occur. This is because it becomes difficult to produce a sintered body that does not exist.
Using the obtained Si—Li alloy powder as a raw material, a Si—Li alloy target is produced by hot pressing. This Si—Li alloy target can be used for forming a SiLix film as an evaporation material for various vapor deposition methods such as a vacuum evaporation method as well as a sputtering method.
The SiLix film according to the present invention includes a SiLix film in which an oxide film is formed on part or all of the surface by air oxidation or the like.

As described above, the hybrid capacitor of the present invention is composed of a non-aqueous electrolyte containing a Li salt, using a polarizable electrode mainly composed of activated carbon for the positive electrode and a SiLix film capable of reversibly occluding lithium ions for the negative electrode.
Activated carbons that can be used for the positive electrode include coconut shell activated carbon and petroleum coke activated carbon. It is preferable to use petroleum coke activated carbon to obtain a large-capacity electric double layer capacitor.
In addition, activated carbon activation treatment methods include a steam activation treatment method, a molten KOH activation treatment method, and the like. If the activated carbon is kneaded with carbon black (conductive agent) and a binder in the presence of alcohol, formed into a sheet, and then dried, a polarizable electrode is obtained.
The polarizable electrode is preferably bonded to the current collector using a conductive adhesive or the like. As the adhesive, for example, polytetrafluoroethylene is preferable. Also, a polarizable electrode is obtained by mixing a solvent with activated carbon powder, carbon black as a conductive agent, and an adhesive to form a slurry, which is applied to the surface of the metal foil of the current collector, dried, and integrated with the current collector. It is done.

  Examples of the lithium salt of the nonaqueous electrolytic solution used for the hybrid capacitor are as follows. That is, LiClO4, LiCF3SO3, LiC (SO2CF3) 3, LiB (C6H5) 4, LiC4F9SO3, LiC8F17SO3, LiB [C6H3 (CF3) 2-3, 5] 4, LiB (C6F5) 4, LiB [C6H4 (CF3) 4] 4, LiBF4, LiPF6, LiAsF6, LiSbF6, LiCF3CO2, LiN (CF3SO2) 2. In the above formula, [C6H3 (CF3) 2-3,5] is substituted at the 3rd and 5th positions of the phenyl group, and [C6H4 (CF3) -4] is substituted at the 4th position of the phenyl group, respectively. Means what

Moreover, the following are preferably exemplified as the solvent of the non-aqueous electrolyte solution. That is, propylene carbonate, propylene carbonate derivative, ethylene carbonate, ethylene carbonate derivative, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, γ-butyrolactone, 1,3-dioxolane, dimethyl sulfoxide, sulfolane, formamide, dimethylformamide, dimethyl Acetamide, dioxolane, phosphate 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, tetrahydrofuran derivative, Denon compounds, acetonitrile, nitromethane, alkoxy ethane, toluene.
These solvents may be used alone or in combination of two or more.
[Example]

Hereinafter, the present invention will be described in detail by way of examples. In the following examples, a commercially available activated carbon electrode having a thickness of 130 μm (manufactured by Hosen Co., Ltd., activated carbon layer thickness 100 μm, current collector aluminum foil thickness 30 μm, single electrode capacity 0.42 F / cm ² ) was used as the polarizable electrode. . The thickness of the positive and negative electrodes of the hybrid capacitor was designed to be about 1:40 in terms of the maximum discharge capacity ratio of the positive and negative electrodes (in the case of a Si—Li alloy negative electrode, the thickness was about 1:20). . The capacitance of the capacitor was calculated based on the Japan Electronic Machinery Manufacturers Association (EIAJ) standard RC-2377.
The upper limit of the drive voltage _V 1 _(V), the lower limit value is set to _V 2 _(V), when the initial capacitance density was C (F / cm ^3), the energy density E per electrode volume (Wh / l ) Was calculated as in the following formula (2).
_{E = 0.5 × C × (V} 1 2 -V 2 2) × 1000/3600 ···· (2)

(Uses SiLi _2.2 film doped with activated carbon for positive electrode and 2100 mAh of Li per Si weight for negative electrode)
An electrolytic copper foil (made by Fukuda Metal Foil Powder Co., Ltd.) having a thickness of 10 μm was used, and the copper foil was cut into 15 mm × 15 mm to form a current collector substrate, and a Si target having a purity of 99.99% as a sputtering target (high Purity Chemical Co., Ltd.) was used, and a Si film was formed to 5.5 μm in an argon atmosphere of 4 mtorr using a magnetron sputtering apparatus (SH-450, ULVAC, Inc.). The negative electrode weight at this time was 2.38 mg.
After that, a copper lead was attached by spot welding, and opposed to Li foil (thickness 300 μm, manufactured by Honjo Metal Co., Ltd.) via a 50 μm-thick separator (TF4050, manufactured by Nippon Kogyo Co., Ltd.), ethylene carbonate ( EC) and dimethyl carbonate (DMC) in a volume ratio of 1: 2 in an electrolyte solution (LBG-0918, manufactured by Kishida Chemical Co., Ltd.) containing LiPF ₆ at a concentration of 1 mol / L. Under the condition of 4 mA / cm ² , Li was electrochemically doped to produce a negative electrode. The time required for Li doping is 333 min. This film is a SiLi _2.2 film, and the doping depth corresponds to 50%. The negative electrode thus produced was opposed to a 15 × 15 mm activated carbon electrode provided with an Al lead with a separator interposed therebetween to produce a hybrid capacitor element. Thereafter, using the same electrolytic solution as described above, a laminate cell was produced with an aluminum laminate film (thickness: 100 μm, manufactured by Showa Denko KK).

The produced cell was charged / discharged at a voltage of 3 to 4 V and a current density of 0.4 mA / cm ² by a charge / discharge measurement system (manufactured by Instrument Center). The initial capacitance per electrode volume (hereinafter referred to as initial capacitance density) was 29.1 F / cm ³ . Table 1 shows the energy density per electrode volume (hereinafter referred to as energy density), and Table 2 shows the capacity reduction rate after 300 cycles.

(Use a SiLi _4.0 film doped with activated carbon for the positive electrode and 3818 mAh Li per Si weight for the negative electrode)
A laminate cell was produced in the same manner as in Example 1 except that the Li doping time was changed to 605 min. This film is a SiLi _4.0 film, and the doping depth corresponds to 91%. As a result of the charge / discharge measurement, the initial capacitance density was 29.5 F / cm ³ . The energy density is shown in Table 1, and the capacity reduction rate after 300 cycles is shown in Table 2.

(Uses SiLi _2.2 film that is electrochemically doped with 1722 mAh of Li per Si weight in activated carbon for the positive electrode and SiLi _0.40 produced by sputtering for the negative electrode)
When Si powder and bulk metal Li were weighed so that the composition was SiLi _0.45 (Si-10 wt% Li), Si powder was placed on a Nb dish, and heated above the melting point of lithium on a hot plate, Bulk metal Li was placed on Si powder, Li metal was dissolved and reacted with Si powder, and mixed uniformly to obtain Si-Li alloy powder. The above steps were carried out in a glove box whose dew point was controlled to -60 ° C or lower. A sintered body was produced by hot pressing using the produced alloy powder as a raw material. The sintering conditions were 500 ° C.—in vacuum—2 hr, the press pressure was 248 kgf / cm ² , and the target diameter was 60 mm. The produced Si—Li alloy powder sintered body was bonded to a copper backing plate to obtain an Si—Li alloy target.

Using an electrolytic copper foil (made by Fukuda Metal Foil Powder Co., Ltd.) having a thickness of 18 μm, this copper foil is cut into 15 mm × 15 mm to form a current collector substrate, and using the Si—Li alloy as a sputtering target, magnetron sputtering. A Si—Li film was formed to 4.1 μm in an argon atmosphere of 0.53 Pa using an apparatus (SH-450, manufactured by ULVAC, Inc.). As a result of quantitative analysis, the Si weight of the Si—Li film was 1.12 mg. The film composition was SiLi _0.40 (Si-9 wt% Li), which was almost the same as the target composition.
Then, attaching the leads of copper of the _{SiLi 0.40} film by spot welding, the thickness of 50μm separator (TF4050, Nippon Kodoshi Co.) Li foil through (300Myumt, manufactured by Honjo Metal Co., Ltd.) and the counter I let you. Furthermore, an electrolyte solution (LBG-0918, manufactured by Kishida Chemical Co., Ltd.) containing LiPF6 at a concentration of 1 mol / L in a solvent having a volume ratio of ethylene carbonate (EC) and dimethyl carbonate (DMC) of 1: 2. A negative electrode was produced by electrochemically doping Li under conditions of a density of 0.4 mA / cm ² . The time required for Li doping was 129 min. This film is a SiLi _2.2 film, and the doping depth corresponds to 50%.

Thereafter, a laminate cell of a hybrid capacitor was produced in the same manner as in Example 1, and charge / discharge measurement was performed.
As a result of the charge / discharge measurement, the initial capacitance was 29.7 F / cm ³ . The energy density is shown in Table 1, and the capacity reduction rate after 300 cycles is shown in Table 2.
(Comparative Example 1)

(As usual, activated carbon electrodes are used for both electrodes)
Two 15 × 15 mm activated carbon electrodes were prepared, and Al leads were attached to each by spot welding. This was made to oppose on both sides of the separator, and the capacitor element was produced.
Thereafter, an electrolytic solution (CPG-00005 manufactured by Kishida Chemical Co., Ltd.) containing (C ₂ H ₅ ) ₄ NBF ₄ at a concentration of 1 mol / L in a propylene carbonate (PC) solvent was used, and an aluminum laminate film was used. A laminate cell was produced.
Voltage produced by the cell in charge and discharge measuring system 1.0～2.5V, was subjected to charge and discharge measurement at a current density of 0.4 mA / cm ^2. As a result of the charge / discharge measurement, the initial capacitance was 9.0 F / cm ³ . The energy density is shown in Table 1, and the capacity reduction rate after 300 cycles is shown in Table 2.
(Comparative Example 2)

(Use activated carbon for the positive electrode and Si film not doped with Li for the negative electrode)
A laminate cell was produced in the same manner as in Example 1 except that Li was not electrochemically doped. The produced cell was subjected to charge / discharge measurement in the same manner as in Example 1.
As a result of the charge / discharge measurement, the initial capacitance was 28.0 F / cm ³ . The energy density is shown in Table 1, and the capacity reduction rate after 300 cycles is shown in Table 2.
(Comparative Example 3)

(Use a SiLi _5.7 film doped with activated carbon for the positive electrode and 5451 mAh Li per negative electrode Si weight for the negative electrode)
A laminate cell was produced in the same manner as in Example 1 except that the time for electrochemically doping Li was 865 min. This film is a SiLi _5.7 film, and the doping depth corresponds to 130%. The produced cell was subjected to charge / discharge measurement in the same manner as in Example 1.
As a result of the charge / discharge measurement, the initial capacitance was 29.2 F / cm ³ . The energy density is shown in Table 1, and the capacity reduction rate after 300 cycles is shown in Table 2.

Table 1 shows that the hybrid capacitors of Examples 1 to 3 and Comparative Examples 2 and 3 all have a capacitance higher than the capacitance density of the activated carbon electrode of Comparative Example 1, which is higher energy than the conventional hybrid capacitor. It can be said that it is density.
From Table 2, in Examples 1 to 3, the decrease rate of capacitance density after 300 cycles was within 20%, whereas in the comparative examples 2 and 3 in which the doping amount of Li was outside the scope of claims, The capacitance density reduction rate is about 50%, which indicates that the durability of the hybrid capacitor is not sufficient.
Also, when a hybrid capacitor having an activated carbon electrode of 130 μm as the positive electrode is manufactured, if the SiLix film is used as the negative electrode, the film thickness is 4.1 μm and the cycle characteristics are good, but when the Si film is used as the negative electrode, the film thickness is the same. When the thickness is 4.1 μm, sufficient cycle characteristics cannot be obtained. In order to obtain sufficient cycle characteristics, it is necessary to increase the negative electrode capacity by lowering the Li utilization rate by setting the Si film thickness to 5.5 μm as in the embodiment of the present invention. In this case, the volume of the entire cell is increased, so that the volume energy density of the hybrid capacitor is decreased.
Therefore, the hybrid capacitor using the SiLix film as the negative electrode has good cycle characteristics and can have a higher volume energy density than the Si film.

  As described above, the hybrid capacitor of the present invention using the Si-Lix film obtained by doping Li in Si or a Si-Li alloy as the negative electrode is effective in improving the capacitance density and energy density of the capacitor.

  Since the capacitor of the present invention has a high energy density per volume energy, it can be used as a compact backup power source for various AV devices such as mobile phones and digital cameras.

It is a schematic diagram which shows the electric potential change in the case of charging / discharging.

Claims (8)

  An asymmetric electric double layer capacitor using a polarizable electrode mainly composed of activated carbon as a positive electrode, a Faraday electrode capable of reversibly occluding Li ions in a negative electrode, and a non-aqueous electrolyte containing a Li salt as an electrolyte. A hybrid capacitor characterized in that a SiLix film is formed on at least the outermost portion of a negative Faraday electrode formed on a current collector metal foil.   2. The hybrid capacitor according to claim 1, wherein x of the SiLix film is 0.3 or more and 5.5 or less.   After forming a Si film on the current collector metal foil, electrochemically doping Li on the surface of the Si film to form a negative electrode having a SiLix film at least on the outermost surface, the positive electrode comprising the negative electrode and activated carbon; A laminate capacitor is manufactured using a non-aqueous electrolyte containing a Li salt with a separator interposed therebetween, and a method for manufacturing a hybrid capacitor, comprising:   After forming a Si-Li alloy film on the current collector metal foil, the surface of the Si-Li alloy film is electrochemically doped with Li to form a negative electrode having a SiLix film at least on the outermost surface. And a positive electrode made of activated carbon facing each other with a separator interposed therebetween, and a laminate cell is produced using a non-aqueous electrolyte containing a Li salt.   Forming a negative electrode made of a SiLix film on a current collector metal foil, making the negative electrode and a positive electrode made of activated carbon face each other with a separator interposed therebetween, and producing a laminate cell using a non-aqueous electrolyte containing a Li salt A method for manufacturing a hybrid capacitor, which is characterized.   6. The method of manufacturing a hybrid capacitor according to claim 3, wherein x of the SiLix film is 0.3 or more and 5.5 or less.   6. The method for manufacturing a hybrid capacitor according to claim 3, wherein the method for forming the Si film or the SiLix film is a vapor deposition method.   The method of manufacturing a hybrid capacitor according to claim 7, wherein the vapor deposition method is a sputtering method or a vacuum deposition method.