POWER STORAGE MATERIAL AND ULTRA POWER STORAGE BODY

Abstract

A power storage material is made by using a fiber material of cellulose molecules obtained from wood, plant fibers (pulp), and the like, and capable of storing electric power of direct current and alternating current, and an ultra power storage body has the power storage material. A power storage material includes a fiber mainly including a fiber derived from at least any one of wood, plant fibers (pulp), animals, algae, microorganisms, and microbial products, and having a large number of recesses and protrusions on a surface. The fiber is preferably crystallized/amorphous fibers, is preferably an amorphous fiber having an atomic vacancy, and preferably has a specific surface area of 10 m.sup.2/g or more. Preferably, the large number of recesses and protrusions have a diameter of 1 nm to 500 nm. Preferably, the electric resistance is 100 MΩ or more, and the electric capacity is 5 mF/cm.sup.2 or more

Claims

1. A power storage material comprising a fiber mainly including a fiber derived from at least any one of wood, plant fibers or pulp, animals, algae, microorganisms, and microbial products, and having a large number of recesses and protrusions on a surface.

2. The power storage material according to claim 1, wherein the fiber comprises a crystallized fiber and an amorphous fiber.

3. The power storage material according to claim 1, wherein the fiber is an amorphous fiber having an atomic vacancy.

4. The power storage material according to claim 1, wherein the fiber has a specific surface area of 10 m.sup.2/g or more.

5. The power storage material according to claim 1, wherein the large number of recesses and protrusions have a diameter of 1 nm to 500 nm.

6. The power storage material according to claim 1, wherein electric resistance is 100 MΩ or more, and an electric capacity is 5 mF/cm.sup.2 or more.

7. An ultra power storage body comprising a power storage material according to claim 1.

8. The ultra power storage body according to claim 7, wherein the power storage material has a thin film sheet shape, the ultra power storage body comprising a pair of metal electrodes respectively provided on both sides of the power storage material to sandwich the power storage material.

9. The ultra power storage body according to claim 8, wherein the power storage body comprises a plurality of stacked bodies.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0076] FIG. 1 is a perspective view showing a molecular structure of a power storage material in accordance with an embodiment of the present invention.

[0077] FIG. 2 is a circuit diagram of an electric distributed constant circuit, showing the power storage material in accordance with the embodiment of the present invention.

[0078] FIG. 3 is an atomic force microscope (AFM) image of a surface of a sample 1 of the power storage material in accordance with the embodiment of the present invention.

[0079] FIG. 4 is a graph showing discharge characteristics of the power storage material under a constant current of 1 nA after charging the sample 1 at 1 mA and 10 V in accordance with the embodiment of the present invention.

[0080] FIG. 5 is a graph showing a relationship between a charged voltage and storage energy at the time of charging a sample 2 of the power storage material in accordance with the embodiment of the present invention.

[0081] FIG. 6 is a graph showing the frequency characteristics of a storage capacitance Cp at a series junction of the sample 2 of the power storage material in accordance with the embodiment of the present invention.

[0082] FIG. 7 is a Nyquist diagram (Cole-Cole plot) of AC impedance showing frequency characteristics of a sample 3 of the power storage material in accordance with the embodiment of the present invention.

[0083] FIG. 8 is side views and a perspective view showing a method of manufacturing a stack by an MEMS method of an ultra power storage body in accordance with the embodiment of the present invention.

DESCRIPTION OF EMBODIMENTS

[0084] Hereinafter, a power storage material and an ultra power storage body in accordance with the embodiment of the present invention will be described based on drawings and Examples.

[0085] As shown in FIG. 1, the power storage material in accordance with the embodiment of the present invention the embodiment of the present invention is a sheet material having innumerable recess and protrusion surfaces including crystallized/amorphous fibers mainly including wood fibers (pulp).

[0086] The power storage material in accordance with the embodiment of the present invention can store and discharge electricity by utilizing the electron adsorption phenomenon due to the quantum size effect that occurs in the protrusions of a large number of recesses and protrusions. The power storage material in accordance with the embodiment of the present invention is a capacitor in which innumerable recess and protrusion surfaces are each including a solid/gas electric double layer. As shown in FIG. 2, a plurality of capacitors is finitely joined in parallel to form an electric distributed constant circuit. Thus, the power storage material according to the embodiment of the present invention can store electricity instantaneously or in a relatively short time, and can store a large amount of electricity.

[0087] The following shows Examples of the power storage material and the ultra power storage body in accordance with the embodiment of the present invention. Note here that the following Examples are provided merely for describing the present invention and for reference in specific embodiments thereof, but not for limiting the scope of the present invention.

Example 1

[0088] The power storage material in accordance with the embodiment of the present invention was produced. Table 1 shows the producing method, processing method, manufacturing conditions, density of the produced ultra capacitor material, electric resistance (GΩ), and storage capacity (F/cm.sup.2) of the manufactured samples 1 to 4 of the power storage material. The amount of electricity stored was determined from the discharge curve at a constant current of 1 nA after charging at 1 mA for 4 minutes (see, for example, FIG. 4), and the electrical resistance was determined from the Nyquist diagram (see, for example, FIG. 6). Each sample 1 to 4 was produced as follows.

Sample 1

[0089] A bleached unbeaten softwood kraft pulp (degree of whiteness: 85%) in an amount of 500 g (absolute dry weight) was added to 500 mL of an aqueous solution that dissolves 780 mg of TEMPO (Sigma Aldrich) and 75.5 g of sodium bromide, and the mixture was stirred until the pulp was dispersed uniformly. A sodium hypochlorous acid solution was added to the reaction system to an amount of 6.0 mmol/g, and oxidation reaction was started. The pH in the system decreased during the reaction, but a 3M sodium hydroxide solution was gradually added to adjust the pH to 10. The reaction was ended when the sodium hypochlorous acid was consumed and the pH in the system stopped changing. Pulp was separated from the reacted mixture by filtering with a glass filter, and the pulp was fully washed with water to obtain an oxidized pulp (hereinafter referred to as “TEMPO-oxidized pulp”). The pulp yield at this time was 90%, and the time required for oxidation reaction was 90 minutes. Furthermore, a specific surface area of the obtained TEMPO-oxidized pulp was 53 m.sup.2/g.

[0090] The TEMPO-oxidized pulp obtained in the above step was adjusted to 3.0% (w/v) with water, and subjected to disintegration treatment five times using an ultra high-pressure homogenizer (20° C., 150 MPa) to obtain a dispersion liquid of the TEMPO-oxidized fine cellulose fibers (hereinafter, referred to as “TEMPO-oxidized CNF”). The obtained TEMPO-oxidized CNF had an average fiber diameter of 4 nm and an aspect ratio of 150. The amount of carboxyl groups in the obtained TEMPO-oxidized CNF was 1.42 mmol/g. The specific surface area of the obtained TEMPO-oxidized CNF was 386 m.sup.2/g.

[0091] Ion-exchanged water was added to 3% (w/v) dispersion liquid of the obtained TEMPO-oxidized CNF, and the resulting product was stirred with a homogenizer at 3000 rpm for 10 minutes to dilute the concentration to 0.5% (w/v). The dispersion liquid was depressurized with an aspirator, the dispersion liquid was degassed, and further degassed with Mazerustar KK-300SS (manufactured by Kurabo Industries Ltd.) at 2000 rpm for 2 minutes. Then, a silicon rubber mold (100 cm.sup.2) was placed on a hydrophilically treated polyethylene terephthalate film, 140 g of the dispersion liquid was poured into the film, and the film was dried at 40° C. for 48 hours to obtain a TEMPO-oxidized CNF sheet.

Sample 2

[0092] A TEMPO-oxidized CNF sheet was obtained in the same manner as in the sample 1 except that 3% (w/v) dispersion liquid in which the TEMPO-oxidized CNF produced in the same manner as in the sample 1 was dispersed was pressurized to 350° in an autoclave, treated at a constant pressure of 25 MPa, ion-exchanged water was then added thereto, the resulting product was stirred at 3000 rpm for 10 minutes by using a homogenizer, and the concentration was diluted to 0.5% (w/v).

Sample 3

[0093] Ion-exchanged water was added to the TEMPO-oxidized pulp obtained in the same manner as in the sample 1, and 20 g of the dispersion liquid adjusted to the concentration of 0.5% (w/v) was extracted by suction filtration through a 90 cm.sup.2 nylon mesh with an opening size of 63 and then dried at 40° C. for 48 hours to produce a TEMPO-oxidized pulp sheet.

Sample 4

[0094] To a biaxial kneader in which the rotation speed was adjusted to 150 rpm, 130 parts of water and a mixture obtained by dissolving 20 parts of sodium hydroxide in a mixed solvent of 10 parts of water and 90 parts of isopropanol (IPA) were added, and 100 parts of hardwood pulp (LBKP manufactured by Nippon Paper Industries Co., Ltd.) was charged in a dry mass at 100° C. for 60 minutes. The resulting product was stirred and mixed at 35° C. for 80 minutes, and subjected to mercerization treatment. While further stirring was carried out, a mixed solvent including 23 parts of water, 207 parts of IPA, and 40 parts of sodium monochloroacetate were added. Then, the resulting product was stirred for 30 minutes, the temperature was raised to 70° C. and etherification treatment was carried out for 90 minutes. After the reaction was completed, the resulting product was neutralized with acetic acid until the pH became 7, the resulting product was washed with hydrous methanol, and then deliquored, dried, and pulverized to obtain a sodium salt of the CM-pulp. The degree of substitution of carboxymethyl ether in the obtained CM-pulp was 0.17.

[0095] The CM-pulp obtained in the above step was adjusted to 3.0% (w/v) with water, and subjected to disintegrating treatment five times with an ultra high-pressure homogenizer (20° C., 150 MPa) to obtain a dispersion liquid of the CM-fine cellulose fibers (hereinafter, referred to as “CM-CNF”. The specific surface area of the obtained CM-CNF was 325 m.sup.2/g. Ion-exchanged water was added to the obtained 3.0% (w/v) dispersion liquid of the CM-CNF, and the resulting mixture was stirred with a homogenizer at 3000 rpm for 10 minutes to dilute to a concentration to 0.5% (w/v). The dispersion liquid was depressurized with an aspirator, the dispersion liquid was degassed, and further degassed with Mazerustar KK-300SS (Kurabo Industries Ltd.) at 2000 rpm for 2 minutes. Then, a silicon rubber mold (100 cm.sup.2) was placed on a hydrophilically treated polyethylene terephthalate film, 140 g of dispersion liquid was poured into the film, and the film was dried at 40° C. for 48 hours to obtain a CM-CNF sheet.

TABLE-US-00001 TABLE 1 Electric Storage Test Sample Treatment Crystal or Density resistance amount Sample type method amorphous (g/cm.sup.3) (GΩ) (mF/cm.sup.2) 1 Oxide CNF Crystal 1.5 135 15.3 sheet 2 Oxide CNF TEMPO catalytic 1.7 127 18.5 sheet oxidized material is heated to 320° C. under 25 MPa 3 Oxide pulp 1.1 50 7.8 sheet 4 Carboxymethylated 1.0 86 3.5 CNF sheet

[0096] As shown in Table 1, it was revealed that each of the power storage materials of the samples 1 to 4 had electric resistance of 50 GΩ to 135 GΩ and electric capacity of 3 F/cm.sup.2 to 19 F/cm.sup.2. In particular, since the sample 2 is amorphous, it has atomic vacancies, and when they have a positive charge, the amount of electron adsorbed increases and the amount of stored electricity increases. It was also revealed that the specific density was as low as 2 or less. It was also revealed that each of the power storage materials of the samples 1 to 4 can operate up to −269° C. to 300° C. and 500 V. In addition, withstand voltage up to 1000 V was also revealed. From these facts, it is considered that each of the power storage materials is the most suitable material for the field of heavy electricity and the atmospheric current (lightning current) storage. Furthermore, when the sample 2 was irradiated with a strong electron beam of 3 mA/m.sup.2, it was revealed that the sample 2 had withstand voltage up to 200 keV, which was twice as high as that of the carbon nanotube of 80 keV.

[0097] An atomic force microscope (AFM) image of a surface of the sample 1 is shown in FIG. 3. As shown in FIG. 3, it was revealed that the surface of the power storage material had a large number of recesses and protrusions having a diameter of 3 nm or less. Furthermore, the discharge characteristics of the sample 1 after being charged at 1 mA and 10 V under a constant current of 1 nA were measured, and the results are shown in FIG. 4. FIG. 4 also shows amorphous titania (“titania” in the figure) and an amorphous perfloride polymer (“polymer” in the figure) as comparative examples. As shown in FIG. 4, it was revealed that the amorphous titania and the amorphous polymer had a discharging time of 10 seconds or less, whereas the sample 1 showed a discharging time (storage amount) of about 2370 seconds.

Example 2

[0098] Charging was performed for 2 seconds by a constant voltage method using the power storage material of the sample 2, unlike the charging for several hours by constant current charging as in conventional Li-ion secondary batteries. The relationship between a charged voltage and storage energy at that time is measured and shown in FIG. 5. As shown in FIG. 5, it was revealed that the amount of stored electricity increased parabolically with an increase in the charging voltage in an extremely short time.

Example 3

[0099] Using the power storage material of sample 2, the storage capacity was measured by series bonding with alternating current. Copper electrodes were mechanically fixed above and below the thin film of the sample 2 having a surface area of 10 mm×30 mm, and the storage capacity was measured in the frequency range of 1 MHz to 1 MHz by a potentiostat/galvanostat. The measurement results are shown in FIG. 6.

[0100] As shown in FIG. 6, it was revealed that in the power storage material of the sample 2, power storage capacity increased logarithmically as the frequency decreased. This is because the power storage material of the embodiment of the present invention is charged and discharged at the nano-diameter fiber interface in the low frequency region, but is not charged and discharged at the fiber interface where the height difference is large in the high frequency region. A similar phenomenon of increasing electric capacity in the low frequency region is observed in amorphous titania (see, for example, Non-Patent Literature 10).

[0101] As described above, the power storage material in accordance with the embodiment of the present invention can be charged and discharged in a low frequency region by the quantum nano-size effect, and can be used as an AC capacitor for a microelectronic circuit, a noise filter, or the like.

Example 4

[0102] The frequency characteristics were measured using the power storage material of the sample 3. The measurement was carried out by mechanically fixing copper electrodes above and below the thin film of the sample 2 having a surface area of 10 mm×30 mm. A Nyquist diagram of AC impedance in the frequency range of 1 MHz to 1 GHz was measured, and the results are shown in FIG. 7.

[0103] As shown in FIG. 7, a Nyquist diagram parallel to the imaginary axis was obtained. Such AC impedance characteristics show a distributed constant circuit in which a large number of capacitors are connected in parallel to the resistor R, and show that it is one huge storage body by the electric distributed constant circuit shown in FIG. 2.

[0104] The characteristics of the power storage material in accordance with the embodiment of the present invention are shown in Table 2 in comparison with the characteristics of a commercially available Li-ion battery, an electric double layer capacitor, and a physical secondary battery (battenice) being developed. In Table 2, “O” indicates that the characteristics are relatively good, “X” indicates that the characteristics are relatively poor, and “Δ” indicates that the characteristics are average. As shown in Table 2, the power storage material in accordance with the embodiment of the present invention has superior characteristics to the Li-ion battery in terms of charging voltage, operating temperature, charging time, DC storage, ignition resistance, and environmental pollution, particularly superior characteristics to electric double layer capacitors in terms of charging voltage, operating temperature, ignition resistance, and environmental pollution, and is particularly superior to physical secondary batteries in charging voltage, operating temperature, and DC storage.

TABLE-US-00002 TABLE 2 Specific Charge Operating Charging DC Ignition Environmental gravity voltage temperature time charge resistance pollution Product of ◯ ◯ ◯ ◯ ◯ ◯ ◯ the to 1.6 to 500 −200 to present V +200° C. invention Li-ion ◯ X X X X X X battery 3 to 3.5 3 to 4.2 −10 to to 10 hr V +30° C. Electric ◯ X X ◯ ◯ Δ Δ double to 2 3 to 4 −10 to layer V +30° C. capacitor Physical ◯ X Δ ◯ Δ ◯ ◯ secondary to 5 to 1.5 −25 to battery V +85° C. (battenice)

Example 5

[0105] As shown in FIG. 8, a stacked power storage body was prepared by the MEMS method using the ultracapacitor material of the sample 2. Firstly, a Cu layer (thickness: 500 nm) was formed on a surface of a glass substrate (40×40×0.5 mm) by sputtering (see FIG. 8.1), and an Al layer was sputtered on the Cu layer (see FIG. 8.3). The glass substrate was removed, and it was used as the basic body of a storage layer for an electronic circuit. The Cu layer and the Al layer form a pair of metal electrodes. A plurality of these electrodes were stacked so as to prepare a power storage layer for an electronic circuit. In the produced stacked storage body, the storage layers for electronic circuits are joined in parallel in which the Al layer of the storage layer for electronic circuits at the top and the Cu layer of the storage layer for electronic circuits at the bottom serve as terminals. Therefore, for example, a stack in which 100 electronic circuit storage layers are stacked has capacity 100 times as much as that of a single electronic circuit storage layer.

[0106] The power storage body in accordance with the embodiment of the present invention can be used as, for example, an AC capacitor for a microelectronic circuit and a power storage body on the back surface of a solar cell panel. Furthermore, the power storage body can also be used in, for example, various backup power supply modules for lightning arresters, welding, and over-discharge prevention, and electrical and electronic boards of coupling elements, noise filters, high-sensitivity acceleration sensors, high-power transformer cutoff prevention devices, emergency power supply devices for automobiles or ships, and the like.