Manufacturing method for electrode of electricity storage device and electrode of electricity storage device

Abstract

Disclosed is a manufacturing method for an electrode of an electricity storage device. The manufacturing method includes: a working procedure of acquiring a long metal fiber by cutting an end surface of a metal foil coil; a working procedure of cutting the long metal fiber so that the average length is less than 5 mm in a state of pressing a bundle of the acquired long metal fibers or in a state of configuring the bundle of the long metal fibers in a cylinder; a working procedure of mixing a metal short fiber obtained from this with a positive electrode material or a negative electrode material constituting a positive electrode or a negative electrode of a lithium battery, to prepare slurry; a working procedure of coating a foil with the slurry; and a working procedure of forming a positive or negative electrode containing the short fibers through a working procedure of drying it to form a predetermined shape.

Claims

1. A manufacturing method for an electrode of an electricity storage device, wherein comprising: a fiber manufacturing working procedure, acquiring a long metal fiber by cutting an end surface of a coil with a cutting tool, wherein the coil is formed by winding a metal foil; a cutting working procedure, cutting the long metal fiber so that the average length is less than 5 mm in a state of pressing a bundle of the long metal fibers on a predetermined surface by using a pressing component, or in a state of configuring the bundle of the long metal fibers in a plastic tube; a slurry preparation working procedure, preparing liquid-like or gel-like slurry, wherein the slurry contains a binder, a metal short fiber manufactured by the cutting working procedure, and adsorbent powder that adsorbs electrolyte ions during charging or active substance powder that performs a chemical reaction during charging-discharging; a forming working procedure, forming the slurry into a predetermined shape; and a drying working procedure, drying the slurry formed into the predetermined shape, to form an electrode containing the short fibers.

2. The manufacturing method for the electrode of the electricity storage device according to claim 1, wherein: in the cutting working procedure, cutting the bundle of the long metal fibers together with the pressing component or the plastic tube.

3. The manufacturing method for the electrode of the electricity storage device according to claim 1, wherein: in the cutting working procedure, cutting the bundle of the long metal fibers together with the pressing component or the plastic tube.

4. The manufacturing method for the electrode of the electricity storage device according to claim 1, wherein: in the slurry preparation working procedure, mixing the short fibers into the slurry, so that the weight ratio of the short fibers relative to the entire electrode after drying in the drying working procedure is less than 8% by weight.

5. An electrode of an electricity storage device, comprising: a metal short fiber of which an average length is less than 5 mm, and adsorbent powder that adsorbs electrolyte ions during charging or active substance powder that performs a chemical reaction during charging-discharging, wherein a weight ratio of the short fibers is less than 8% by weight.

6. The electrode of the electricity storage device according to claim 5, wherein: the electrode of the electricity storage device further comprises a carbon fiber of which an average thickness is 0.5 μm or less.

7. The electrode of the electricity storage device according to claim 5, wherein: an average thickness of the electrode after removing a current collector foil is 120 μm or more.

8. An electrode of an electricity storage device, comprising: a metal short fiber, and adsorbent powder that adsorbs electrolyte ions during charging or active substance powder that performs a chemical reaction during charging-discharging, wherein the short fiber has a small diameter portion and a large diameter portion of which a diameter is more than 1.5 times greater than that of the small diameter portion, and a length of the large diameter portion is 5 times less than an average diameter of the small diameter portion.

9. The electrode of the electricity storage device according to claim 8, wherein: the average diameter of the small diameter portion of the short fiber is 30 μm or less.

10. The electrode of the electricity storage device according to claim 8, wherein: the short fibers are composed of aluminum with a purity of 99.9% or more.

11. The electrode of the electricity storage device according to claim 8, wherein: a plurality of the large diameter portions and a plurality of the small diameter portions alternately exist on one piece of the short fiber A.

12. The manufacturing method for the electrode of the electricity storage device according to claim 2, wherein: the pressing component is a plastic film with a thickness of 1 mm or less.

13. The manufacturing method for the electrode of the electricity storage device according to claim 2, wherein: in the slurry preparation working procedure, mixing the short fibers into the slurry, so that the weight ratio of the short fibers relative to the entire electrode after drying in the drying working procedure is less than 8% by weight.

14. The manufacturing method for the electrode of the electricity storage device according to claim 3, wherein: in the slurry preparation working procedure, mixing the short fibers into the slurry, so that the weight ratio of the short fibers relative to the entire electrode after drying in the drying working procedure is less than 8% by weight.

15. The manufacturing method for the electrode of the electricity storage device according to claim 12, wherein: in the slurry preparation working procedure, mixing the short fibers into the slurry, so that the weight ratio of the short fibers relative to the entire electrode after drying in the drying working procedure is less than 8% by weight.

16. The electrode of the electricity storage device according to claim 6, wherein: the an average thickness of the electrode after removing a current collector foil is 120 μm or more.

17. The electrode of the electricity storage device according to claim 9, wherein: the short fibers are composed of aluminum with a purity of 99.9% or more.

18. The electrode of the electricity storage device according to claim 9, wherein: a plurality of the large diameter portions and a plurality of the small diameter portions alternately exist on one piece of the short fiber A.

19. The electrode of the electricity storage device according to claim 10, wherein: a plurality of the large diameter portions and a plurality of the small diameter portions alternately exist on one piece of the short fiber A.

20. The electrode of the electricity storage device according to claim 17, wherein: a plurality of the large diameter portions and a plurality of the small diameter portions alternately exist on one piece of the short fiber A.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0045] FIG. 1 is a cross-sectional schematic diagram of an electrode involved according to an embodiment of the present disclosure.

[0046] FIG. 2 is a cross-sectional schematic diagram of another electrode of this embodiment.

[0047] FIG. 3 is a schematic diagram showing a preparation method for slurry of this embodiment.

[0048] FIG. 4 is a schematic diagram showing a coating method of the slurry used to manufacture the electrode of this embodiment.

[0049] FIG. 5 is a schematic diagram showing a rolling method for manufacturing the electrode of this embodiment.

[0050] FIG. 6 is a cross-sectional schematic diagram of an all-solid-state battery using the electrode of this embodiment.

[0051] FIG. 7 is a schematic diagram showing a pressurizing method for manufacturing the electrode of this embodiment.

[0052] FIG. 8 is a graph showing the characteristics of a lithium ion battery using the electrode of this embodiment.

[0053] FIG. 9 is a graph showing the cycle characteristics of the lithium ion battery using the electrode of this embodiment.

[0054] FIG. 10 is a graph showing the characteristics of the lithium ion battery using the electrode of this embodiment.

[0055] FIG. 11 is a schematic diagram showing a manufacturing method for a short fiber of an electrode according to a modification example of this embodiment.

[0056] FIG. 12 is a schematic diagram of the short fiber of the electrode according to a modification example of this embodiment.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0057] An electrode and an electricity storage device involved according to an embodiment of the present disclosure are described below with reference to the drawings. It should be noted that a lithium ion battery is mainly used as the electricity storage device for the description.

[0058] FIG. 1 and FIG. 2 show an electrode (positive electrode or negative electrode) mixed with a short fiber A of aluminum or copper with an average wire diameter of 50 μm or less.

[0059] It should be noted that FIG. 1 and FIG. 2 are diagrams for easy understanding of the structure of this embodiment. The size, thickness, length, and mixing ratio and the like of the short fiber A, active substance powder 20, a conductive aid 30, a carbon fiber CF and the like are different from the reality.

[0060] As shown in FIG. 1 and FIG. 2, the electrode is provided with the short fiber A of aluminum or copper with the average wire diameter of 50 μm or less and the active substance powder 20 that is maintained together with the short fiber A by a binder B so as to perform a chemical reaction during charging-discharging. According to the needs, the electrode is further provided with the conductive aid 30 maintained by a binder B.

[0061] [Forming of Metal Short Fiber Used as Current Collector]

[0062] For example, a pair of plastic films with a thickness of 0.1 mm to 0.3 mm is used to sandwich a bundle of metal long fibers (a long fiber of aluminum or copper) manufactured by a coil cutting method, and the bundle of the long fibers is cut into an arbitrary length. Namely, the long fiber is cut in a state that the bundle of the long fibers is pressed on a predetermined surface using a pressing component made of plastic and the like. The predetermined surface is an upper surface of a plastic film in this embodiment, but it may be an upper surface of a workbench made of plastic, metal and the like. The thickness of the plastic film may be 1 mm or less. Alternatively, in a state that the bundle of the long fiber is configured in a cylindrical plastic tube, the bundle of the long fiber is cut into an arbitrary length. The wall thickness of the plastic tube may be 0.1 mm to 0.3 mm, for example, and may be 0.5 mm or less. Namely, in a state that the bundle of the long fibers is configured in a tubular component made of plastic and the like, the bundle of the long fibers is cut. The bundle of the long fibers may be cut together with the pressing component or the tubular component. Thus, it is possible to cut the bundle of the long fibers stably and efficiently. In addition, preferably the bundle of the long fibers is relatively densely configured in the tubular component. Thus, the short fiber A with the arbitrary length is manufactured.

[0063] It should be noted that the average length of the short fiber A cut into the arbitrary length is 5 mm or less, and preferably the average length is 2 mm or less. In addition, the average wire diameter of the short fiber A is 50 μm or less, preferably 25 μm or less, and more preferably 20 μm or less.

[0064] In the coil cutting method, an aluminum or copper foil is wound into a coil shape, and an end surface of the coil is cut with a cutting tool, as to obtain a long metal fibers (metal long fiber). Then, the short fiber A is obtained by cutting the long metal fiber into the above lengths.

[0065] It should be noted that the metal fiber, the short fiber A, and the foil of this embodiment may also be comprised of other metals, such as steel, stainless steel, and brass.

[0066] [Forming of Electrode]

[0067] While the electrode shown in FIG. 1 is manufactured, as shown in FIG. 3, liquid-like or gel-like slurry S containing the short fiber A of aluminum or copper, the active substance powder 20, the conductive aid 30, and the binder B is prepared. In order to prepare this slurry S, the short fiber A of aluminum or copper, the active substance powder 20, the conductive aid 30, and the diluted binder B are mixed by using a mixing machine and the like. The weight ratios of the active substance powder 20, the conductive aid 30, and the binder B during drying may be about these weight ratios in the commercially available secondary battery. Hereinafter, the weight ratio or the mixing ratio refers to the weight ratio or the mixing ratio relative to the entire electrode dried by the drying working procedure described later. In this embodiment, the mixing ratio of the binder B is 2% by weight or more and less than 6% by weight, preferably about 4% by weight. The mixing ratio of the short fiber A is preferably 1% by weight or more and less than 8% by weight. If there are few short fibers A, the effect as the current collector is small, and if there are many short fibers A, the internal resistance is increased on the contrary. The mixing ratio of the short fiber A is preferably 2.5% by weight or more and 5.5% by weight or less. It should be noted that it may be considered that the mixing ratio of the short fiber A is most preferably 3.5% by weight or more and 5% by weight or less. While the electrode shown in FIG. 2 is manufactured, a carbon fiber CF is further added on the basis of the above to prepare the slurry S. While the carbon nanofiber CF is added, the mixing ratio thereof is preferably 1% by weight or more and less than 2% by weight. If there are few carbon nanofibers CF, the effect is not seen, and if there are many carbon nanofibers CF, the deterioration is caused in a cycle test.

[0068] The average length of the short fiber A of aluminum or copper is 5 mm or less. Therefore, in the slurry S, the short fiber A of aluminum or copper is easily mixed with other complexes. While the average length of the short fiber A is 2 mm or less, there is a tendency to be more easily mixed. If it is too short, the mutual contact between the fibers is less. Therefore, the average length of the short fiber A is preferably 1 mm or more. In addition, if the short fiber A is longer, the fibers are entangled with each other, and a fiber lump remains in the slurry S. Therefore, the average length of the short fiber A is preferably 1 mm or more and 4 mm or less.

[0069] Next, the slurry S is coated on a current collector foil (aluminum foil or copper foil) with a predetermined thickness, and pre-drying is performed in order to increase the viscosity. While the current collector foil is not used, the slurry S may be coated on a diaphragm. For example, as shown in FIG. 4, the slurry S serving as the positive electrode is coated on one surface in a thickness direction of the diaphragm SP, and the slurry S serving as the negative electrode is coated on the other surface in the thickness direction of the diaphragm SP. It is also possible to coat the slurry S serving as the positive electrode or the negative electrode on only one surface of the diaphragm SP. The pre-drying dries the binder B to an incompletely solidified state, thereby the electrode foil is easily formed into a predetermined shape. It should be noted that in this embodiment, a portion of the electrode serving as the positive electrode or the negative electrode which is integrated with the current collector foil or the diaphragm SP is called as an electrode foil sometimes.

[0070] In addition, instead of coating the current collector foil or the diaphragm SP, the slurry S of the positive electrode or the negative electrode may be formed into a sheet shape on a predetermined mold. In this case, the electrode that is the positive electrode or the negative electrode formed into the sheet shape is called as the electrode foil.

[0071] Next, the coated and dried electrode foil is pressed and pressurized. Thereby, the slurry S is formed into a predetermined thickness and the like corresponding to the size of the electrode. It should be noted that, as shown in FIG. 5, the electrode foil is pressurized by passing between a pair of rollers, thereby it is formed into the predetermined thickness.

[0072] Next, the drying working procedure of drying the formed electrode foil by vacuum drying and the like is performed. In this way, the removal of moisture in the electrode and the solidification of the binder B are performed.

[0073] Preferably the short fiber A of aluminum or copper with a purity of 99% or more is used, and more preferably the short fiber A of aluminum or copper with a purity of 99.9% or more is used. At this time, through the pressurization in FIG. 5, in a portion in which the short fibers A contact with each other, two intersected short fibers A are easily deformed by mutually biting.

[0074] Namely, in the contact portion, the short fiber A becomes flat, and thus the two intersected short fibers A bite into each other. By pressurizing, the short fibers A are brought into close contact through the active substance powder 20, so that the resistance of the contact portion between the short fibers A is reduced.

[0075] Namely, it is possible to reduce the movement resistance of electrons in the contact portion between the short fibers A, and it is beneficial to reduce the movement resistance of the electrons to input and output terminals.

[0076] It should be noted that through the working procedure of forming the slurry S into the electrode foil, and the working procedure of pressing and pressurizing the formed electrode foil and the like, the short fiber A contacting the active substance powder 20 is bent along the active substance powder 20, and the short fiber A is wound around the active substance powder 20.

[0077] [Active Substance Powder of Positive Electrode]

[0078] As the active substance powder 20 of the positive electrode, it may be any substances as long as it may be maintained on the current collector 10 by the binder B and the like or it may be maintained on the binder B solidified together with the current collector 10, and preferably it is a substance with good cycle characteristics. As an example of the active substance, a lithium cobaltate (LiCoO.sub.2), an iron phosphate-based active substance, and carbon materials such as graphite may be listed. It should be noted that a well-known active substance used for the positive electrode and negative electrode of the secondary battery may be used.

[0079] As an example, the average particle diameter of the active substance powder 20 is a value obtained by adding 10 μm to the average wire diameter of the short fiber A functioning as the current collector. For example, while the average wire diameter of the short fiber A is 20 μm, the average particle diameter of the active substance powder 20 is preferably 30 μm or less or about 30 μm. Thus, the contact area between the short fiber A functioning as the current collector and the active substance powder 20 is increased, and it helpful to improve the charging-discharging speed.

[0080] [Binder]

[0081] As the binder B, a thermoplastic resin, a polysaccharide polymer material and the like may be used. An example of a material of the binder B is a polyacrylic resin, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), a copolymer of vinylidene fluoride (VdF) and hexafluoropropylene (HFP) and the like. It should be noted that a well-known binder used for the electrode of the secondary battery and the electric double-layer capacitor may be used.

[0082] [Conductive Aid]

[0083] As the conductive aid 30, it may be any materials as long as it has the conductivity, and preferably it is a material that does not produce a chemical change due to the electrolyte or solvent. As an example of the conductive aid 30, graphite and carbon black may be listed. It should be noted that a well-known conductive aid used for the electrode of the secondary battery and the electric double-layer capacitor may be used.

[0084] [Active Substance Powder of Negative Electrode]

[0085] As the active substance powder 20 of the negative electrode, artificial graphite, natural graphite and the like are used. While they are used in the negative electrode, since a working potential on the negative electrode side is low, a Li—Al reaction occurs while the short fiber A of aluminum is used. This causes a decrease in Li and the rapid deterioration of the battery. Therefore, the short fiber A of aluminum may not be used, and the short fiber A of copper needs to be used. On the other hand, LTO (lithium titanate), which is developed in recent years and has a higher reaction potential than the Li—Al reaction, may be used as the active substance powder 20 of the negative electrode. In this case, the short fiber A of aluminum may be used for the negative electrode. It may be seen that if the short fiber A of aluminum is 1% by weight or more and less than 8% by weight (preferably 3.5% by weight or more and 5% by weight or less), and LTO is used as the active substance powder 20 of the negative electrode, the internal resistance may be greatly reduced.

[0086] [Applications of Other Devices]

[0087] The above manufacturing method for the electrode and the electrode may be applied to the electrode of the electricity storage device such as the electric double-layer capacitor, the secondary battery including the all-solid-state battery, and a hybrid capacitor including a lithium ion capacitor. For example, while the positive electrode and negative electrode of the capacitor such as the electric double-layer capacitor is manufactured, it may be manufactured by the working procedure of mixing the activated carbon functioning as the active substance powder 20, the conductive aid 30, and the diluted binder B with the short fiber A together. It is also possible to use well-known active substance powder used in the capacitor such as the electric double-layer capacitor instead of the activated carbon. While the all-solid-state battery is manufactured, it may be manufactured through the working procedure of mixing the solid electrolyte with the active substance powder 20, the conductive aid 30, the diluted binder B, and the short fiber A together.

[0088] It should be noted that while the electrode shown in FIG. 2 is manufactured, as the slurry S, in addition to the active substance powder 20, the conductive aid 30 and the binder B, it is also possible to use the slurry S containing the carbon fiber CF with an average thickness of 0.5 μm or less, preferably 0.3 μm or less. In this case, as shown in FIG. 2, the carbon fiber CF is configured between the short fibers A functioning as the current collector.

[0089] The carbon fiber CF is in contact with the short fiber A, the active substance powder 20, the conductive aid 30, and other carbon fibers CF. In this embodiment, the carbon fiber CF with an average thickness of 0.1 μm or more and less than 0.2 μm and an average length of 20 μm or more and less than 200 μm is used. In one example, the resistivity of the carbon-based conductive aid 30 is 0.1 to 0.30 Ω.Math.cm, and the resistivity of the carbon fiber CF is, for example, 5×10.sup.−5 Ω.Math.cm.

[0090] For example, even in the case that the active substance powder 20 and the short fiber A are not in direct contact, the active substance powder 20 and the short fiber A are electrically connected through the carbon fiber CF. In addition, even in the case that the active substance powder 20 is in direct contact with the short fiber A, by providing a connection with the carbon fiber CF, the electrical resistance between the active substance powder 20 and the short fiber A may be further reduced.

[0091] In this way, through the carbon fiber CF having the good conductivity, the movement resistance of the electrons between the active substance powder 20 and the short fiber A may be reduced, and it is beneficial to reduce the movement resistance of the electrons to the input and output terminals.

[0092] It should be noted that, instead of using the conductive aid 30, the slurry S containing the carbon fiber CF may be used to manufacture the electrode. In this case, the carbon fiber CF is also configured between the short fibers A functioning as the current collector, and this structure is advantageous in reducing the electrical resistance between the active substance powder 20 and the short fiber A. It should be noted that FIG. 2 is a diagram for easy understanding of the structure of this embodiment. The size, thickness, length, and mixing ratio and the like of the short fiber A, the active substance powder 20, the conductive aid 30, the carbon fiber CF and the like are different from the reality.

[0093] [Application to Coin-Type Secondary Battery]

[0094] Regarding the application of the coin-type secondary battery as the electricity storage device, for example, the structure described in Japanese Patent Application Laid-Open Publication No. 2018-106846 may be used below, to manufacture the coin-type battery by using the short fiber A of the present application to replace a blown fiber and a flutter-processed fiber in Japanese Patent Application Laid-Open Publication No. 2018-106846.

[0095] [Application to Laminated-Type Secondary Battery]

[0096] In the case of laminating an electricity storage portion composed of the positive electrode, the negative electrode, and the diaphragm into a multilayer secondary battery, it is the same as the coin-type secondary battery, the electrode structure of the embodiment may be used for only the positive electrode, only the negative electrode and both the positive electrode and the negative electrode.

[0097] [Application to all-Solid-State Battery]

[0098] The case of using in the all-solid-state battery is described below.

[0099] In the following, an all-solid-state lithium ion secondary battery is taken as an example to describe the electricity storage device (all-solid-state battery). It should be noted that this embodiment may be used for all-solid-state batteries such as an all-solid-state sodium ion secondary battery, an all-solid-state magnesium ion secondary battery, an air battery using the solid electrolyte, or the all-solid-state lithium ion secondary battery with intense expansion and contraction and using a Si (silicon) negative electrode.

[0100] An example of a schematic diagram of the structure of the all-solid-state battery is shown in FIG. 6. The all-solid-state battery is roughly provided with a positive electrode current collector 1, a positive electrode layer 2, a solid electrolyte layer 3, a negative electrode layer 4, and a negative electrode current collector 5. The positive electrode layer 2 is the electrode of the above positive electrode, and the negative electrode layer 4 is the above negative electrode.

[0101] (Current Collector Foil)

[0102] The positive electrode current collector 1 is generally a metal foil, and the metal foil may be formed by aluminum, an alloy composed of various metals and the like. The negative electrode current collector 5 generally uses a copper foil in many cases. While the active substance powder 20 of the negative electrode is composed of lithium titanate, the negative electrode current collector 5 may use the aluminum foil. In the case of the all-solid-state battery, stainless steel (SUS) with higher voltage resistance and corrosion resistance, a conductive material such as a cobalt-based alloy, other conductive materials, conductive ceramics and the like are also used sometimes.

[0103] (Positive Electrode Layer)

[0104] In order to increase the discharge capacity, the material of the active substance powder 20 of the positive electrode is preferably a substance that easily inserts the lithium ion, such as LiCoPO, LiCoO.sub.2, LiMnO.sub.4, LiFePO.sub.4 and the like. According to the needs, the conductive aid 30, the binder B, an inorganic solid electrolyte for improving the ion conductivity, and a powdered solid electrolyte 14 such as a polymer electrolyte are added, and the positive electrode layer is formed by sintering and press-forming. In this embodiment, the positive electrode layer contains the short fiber A made of aluminum, copper and the like.

[0105] (Negative Electrode Layer)

[0106] The material of the active substance powder 20 of the negative electrode is also the same as that of the positive electrode layer. In order to increase the discharge capacity, it is preferably a material that easily inserts the ion. For example, LiFePO.sub.4, Li.sub.4Ti.sub.5O.sub.12, Li.sub.4Fe.sub.4(PO.sub.4).sub.3, SiOx, Cu.sub.6Sn.sub.5, LiTiO.sub.4 and the like may be listed. The negative electrode layer is formed by mixing the active substance powder 20, the conductive aid 30, the binder B, the inorganic solid electrolyte for improving the ion conductivity, and the powdered solid electrolyte 24 such as the polymer electrolyte, and sintering and press-forming. In this embodiment, the negative electrode layer contains the short fiber A made of aluminum, copper and the like.

[0107] In the positive electrode and the negative electrode of the all-solid-state battery, the mixing ratio of the short fiber A is also 1% by weight or more and less than 8% by weight, preferably 3.5% by weight or more and 5% by weight or less. In addition, the mixing ratio of the binder B is preferably 2% by weight or more and less than 6% by weight.

[0108] (Forming of Positive Electrode Layer)

[0109] Firstly, the liquid-like or gel-like slurry S containing the short fiber A, the active substance powder 20 that generates the chemical reaction during charging-discharging, the conductive aid 30, the binder B, and the solid electrolyte 14 is prepared. The slurry S is prepared by mixing a mixture of the short fiber A of aluminum or copper, the active substance powder 20, the conductive aid 30, the diluted binder B, and the solid electrolyte 14. During the charging-discharging, the chemical reaction in which the ions such as the lithium ion are released from the active substance powder 20 of the positive electrode into the electrolyte, and the chemical reaction in which the ions such as the lithium ion enter the active substance powder 20 occur.

[0110] Next, in order to increase the viscosity of the slurry S, pre-drying is performed. The pre-drying is to dry the binder B to a state in which it is not completely solidified, so that the slurry S is easily formed into a predetermined shape. Therefore, the pre-drying may be omitted according to the viscosity of the binder B.

[0111] Next, as shown in FIG. 7, the slurry S is put into a mold, and the slurry S is pressurized. Thus, the slurry S is formed into a predetermined thickness and the like corresponding to the size of the electrode. It should be noted that the slurry S may be pressurized by enabling the slurry S to pass between a pair of rollers, thus the slurry S is formed into the predetermined thickness corresponding to the size of the electrode. Or, after the thickness of the slurry S may be adjusted with a mold or a roller, the slurry S may be cut and formed into a predetermined shape (size). Or, the slurry S may be formed into the predetermined shape by coating the slurry S on one surface in the thickness direction of the positive electrode current collector 1.

[0112] Next, the drying working procedure of drying the formed slurry S by vacuum drying and the like is performed. Thus, the binder B in the slurry S is solidified. Thus, the active substance powder 20 and the solid electrolyte 14 in the slurry S are in a state contacting with the short fiber A. It should be noted that the state of contacting does not mean that all the active substance powder 20 is in contact with the short fiber A, and even if a part of the active substance powder 20 is in contact with the short fiber A, it is the state of contacting. Similarly, even if a part of the solid electrolyte 14 is in contact with the short fiber A, it is also the state of contacting.

[0113] It should be noted that the mixing ratio of the substances in the positive electrode layer 2 in which the active substance powder 20 and the solid electrolyte 14 are added is preferably 80% by weight or more, more preferably 85% by weight or more, and further preferably 90% by weight or more. Herein, the mixing ratio of the active substance powder 20 is preferably 70% by weight or more, and more preferably 75% by weight or more. On the other hand, the mixing ratio of the solid electrolyte 14 is preferably 10% by weight or more, and more preferably 15% by weight or more. The mixing ratio of the short fiber A in the positive electrode layer 2 is preferably 3% by weight or more, more preferably about 5% by weight, and preferably less than 8% by weight. The rest is occupied by the conductive aid 30, the binder B, the carbon fiber CF and the like.

[0114] (Forming of Negative Electrode Layer)

[0115] Firstly, the liquid-like or gel-like slurry S containing the short fiber A, the active substance powder 20 that generates the chemical reaction during charging-discharging, the conductive aid 30, the binder B, and the solid electrolyte 24 is prepared. The slurry S is prepared by mixing a mixture of the short fiber A of aluminum or copper, the active substance powder 20, the conductive aid 30, the diluted binder B, and the solid electrolyte 24.

[0116] Next, in order to increase the viscosity of the slurry S, pre-drying is performed. The pre-drying is to dry the binder B to a state in which it is not completely solidified, so that the slurry S is easily formed into a predetermined shape. Therefore, the pre-drying may be omitted according to the viscosity of the binder B.

[0117] Next, as shown in FIG. 7, the slurry S is put into a mold, and the slurry S is pressurized. Thus, the slurry S is formed into a predetermined thickness and the like corresponding to the size of the electrode. It should be noted that the slurry S may be pressurized by enabling the slurry S to pass between a pair of rollers, thus the slurry S is formed into the predetermined thickness corresponding to the size of the electrode. Or, after the thickness of the slurry S may be adjusted with a mold or a roller, the slurry S may be cut and formed into a predetermined shape (size). Or, the slurry S may be formed into the predetermined shape by coating the slurry S on one surface in the thickness direction of the negative electrode current collector 5.

[0118] Next, the drying working procedure of drying the formed slurry S by vacuum drying and the like is performed. Thus, the binder B in the slurry S is solidified. Thus, the active substance powder 20 and the solid electrolyte 24 in the slurry S are in a state contacting with the short fiber A. It should be noted that the state of contacting does not mean that all the active substance powder 20 is in contact with the short fiber A, and even if a part of the active substance powder 20 is in contact with the short fiber A, it is the state of contacting. Similarly, even if a part of the solid electrolyte 24 is in contact with the short fiber A, it is also the state of contacting.

[0119] It should be noted that in the positive electrode and the negative electrode, adsorption substance powder that adsorbs electrolyte ions during charging may also be used as the active substance powder instead of the active substance powder 20.

[0120] It should be noted that the mixing ratio of the substances in the negative electrode layer 4 in which the active substance powder 20 and the solid electrolyte 24 are added is preferably 80% by weight or more, more preferably 85% by weight or more, and further preferably 90% by weight or more. Herein, the mixing ratio of the active substance powder 20 is preferably 70% by weight or more, and more preferably 75% by weight or more. On the other hand, the mixing ratio of the solid electrolyte 24 is preferably 10% by weight or more, and more preferably 15% by weight or more. The mixing ratio of the short fiber A in the negative electrode layer 4 is preferably 3% by weight or more, more preferably about 5% by weight, and preferably less than 8% by weight. The rest is occupied by the conductive aid 30, the binder B, the carbon fiber CF and the like.

[0121] (Forming of Solid Electrolyte Layer)

[0122] A mixture of the solid electrolyte 24 containing powder and the binder B is mixed to form the liquid-like or gel-like slurry, it is dried, pressurized in the mold, and pressurized with the roller and the like, to obtain the solid electrolyte layer 3 with the predetermined thickness. The solid electrolyte layer 3 may be a well-known solid electrolyte layer. In addition, the solid electrolyte layer 3 may be a well-known gel-like solid electrolyte layer.

[0123] (Forming of Electricity Storage Element)

[0124] By overlapping the positive electrode layer 2, the solid electrolyte layer 3, and the negative electrode layer 4 manufactured as described above and pressurizing, the positive electrode layer 2 and the solid electrolyte layer 3 are combined, and the solid electrolyte layer 3 and the negative electrode layer 4 are combined. In addition, according to the needs, the positive electrode current collector 1 is overlapped on the positive electrode layer 2, and the negative electrode current collector 5 is overlapped on the negative electrode layer 4. In this way, the electricity storage element BE composed of the positive electrode layer 2, the solid electrolyte layer 3, and the negative electrode layer 4 is formed. As shown in FIG. 6, by overlapping a necessary number of the electricity storage elements BE, the all-solid-state battery is formed.

[0125] (Solid Electrolyte)

[0126] The solid electrolytes 14, 24, and 34 exist in the entire battery like the electrolyte of the lithium ion battery (LiB), and the ion transfer is performed between the positive electrode layer 2 and the negative electrode layer 4. As materials of the solid electrolytes 14, 24, and 34, the following inorganic solid electrolyte and polymer solid electrolyte may be used.

[0127] As the inorganic solid electrolyte, Li (lithium) nitrides, halides, silicides and the like, for example, Li.sub.3N, Lil, Li.sub.3N-Lil-LiOH, LiSiO.sub.4, LiSoO.sub.4—Lil—LiOH, Li.sub.3PO.sub.4—Li.sub.4SiO.sub.4, Li.sub.2SiS.sub.3, may be used. In addition, a lithium-containing phosphate compound with a NASICON-type structure may be used, and a chemical formula thereof is Li.sub.xM.sub.y (PO.sub.4).sub.3. x is 1≤x≤2, y is l≤y≤2, and M may be a substance made of Al, Ti, Ge, Ga and the like. In addition, P may also be replaced with Si and B.

[0128] As the polymer solid electrolyte, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphoric acid ester polymer and the like may be used.

EMBODIMENT

[0129] An example in which the above short fiber A is applied to the positive electrode of the lithium ion battery is shown below.

[0130] The short fiber A of aluminum, the active substance powder 20 (ternary system Li (Ni.sub.aMn.sub.bCo.sub.i-a-b)O.sub.2 (NMC)), the conductive aid 30 (acetylene black (AB)), the binder B (polyvinylidene fluoride (PVDF)) diluted with a solvent (N-methylpyrrolidone (NMP)) are used to prepare the slurry S in the weight ratio (the weight ratio after the drying working procedure), so that active substance powder 20: conductive aid 30: binder B: short fiber A of aluminum is 87:5:4:4. Then, this slurry S is used, a positive electrode foil prepared as described above and a negative electrode foil without adding metal fibers such as the short fiber A are used on the aluminum foil, and LiPF.sub.6 (lithium hexafluorophosphate) is used in the electrolyte to manufacture a lithium ion battery (Embodiment 1). In addition, in the lithium ion battery of Embodiment 1, a lithium ion battery in which 1.5% by weight of carbon nanofibers CF are added to the above slurry S in the weight ratio while the positive electrode is manufactured is also manufactured (Embodiment 2). By adding 1.5% by weight of the carbon fiber CF, the weight ratio of active substance powder 20: conductive aid 30: binder B: short fiber A of aluminum is about 85.7:4.9:3.9:3.9.

[0131] In addition, in the lithium ion battery of Embodiment 1, a lithium ion battery in which the short fiber A of aluminum or copper is not added to the slurry S while the positive electrode is manufactured is also manufactured (Contrast Example 1). Without adding the short fiber A, the weight ratio of active substance powder 20: conductive aid 30: binder B is about 87.5:5.2:4.2.

[0132] In order to manufacture the negative electrode foils of Embodiment 1, Embodiment 2 and Contrast Example 1, firstly, the active substance powder 20 (natural spherical graphite), the conductive aid 30 (acetylene black (AB)), and the binder B (polyvinylidene fluoride (PVDF)) diluted with the solvent (N-methylpyrrolidone (NMP)) are used to prepare the slurry S in the weight ratio, so that the weight ratio of active substance powder 20, conductive aid 30, binder B is 90:5:5. Then, this slurry S is used to process on the copper foil in the above manner, and the negative electrode foil is manufactured.

[0133] In addition, a lithium ion battery using commercially available positive electrode foil and negative electrode foil is also manufactured (Contrast Example 2). This positive electrode foil and negative electrode foil are considered to be high-performance among the commercially available positive electrode foil and negative electrode foil. It should be noted that the material of the active substance powder of the positive electrode of Contrast Example 2 is the same as the material of the active substance powder 20 of Embodiment 1, Embodiment 2 and Contrast Example 1, and the material of the active substance powder of the negative electrode of Contrast Example 2 is the same as the material of the active substance powder 20 of Embodiment 1, Embodiment 2 and Contrast Example 1.

[0134] In order to manufacture the lithium ion batteries of Embodiment 1, Embodiment 2, Contrast Example 1, and Contrast Example 2, the positive electrode foil and the negative electrode foil are cut into predetermined sizes, and a diaphragm made of a polypropylene is sandwiched between the positive electrode foil and the negative electrode foil, and they are accommodated in a battery container formed by a laminated sheet made of a plastic material. The electrolyte is added in the battery container and the battery container is sealed, thus the lithium ion batteries of Embodiment 1, Embodiment 2, Contrast Example 1, and Contrast Example 2 are manufactured. It should be noted that the sizes of the positive electrode foil and the negative electrode foil, the size of the diaphragm, the thickness of the diaphragm, and the capacity of the battery container of Embodiment 1, Embodiment 2, Contrast Example 1, and Contrast Example 2 are substantially the same.

[0135] It should be noted that in Embodiment 1, Embodiment 2 and Contrast Example 1, the average thickness of the positive electrode (the average thickness of the positive electrode layer) after removing the thickness of the aluminum foil (current collector foil) is about 155 μm, and the thickness of the aluminum foil of the positive electrode of Embodiment 1, Embodiment 2 and Contrast Example 1 is about 15 μm. In Contrast Example 2, the average thickness of the positive electrode (the average thickness of the positive electrode layer) after removing the thickness of the aluminum foil (current collector foil) is about 90 μm, and the thickness of the aluminum foil of the positive electrode of Contrast Example 2 is about 15 μm. In Embodiment 1, Embodiment 2, Contrast Example 1, and Contrast Example 2, the average thickness of the negative electrode (the average thickness of the negative electrode layer) after removing the thickness of the copper foil (current collector foil) is about 85 μm, and the thickness of the copper foil of the negative electrode of Embodiment 1, Embodiment 2, Contrast Example 1, and Contrast Example 2 is about 15 μm.

[0136] In addition, a commercially available lithium ion battery of 5000 mAh is used as Contrast Example 3.

[0137] The lithium ion batteries of Embodiment 1, Embodiment 2, Contrast Example 1, Contrast Example 2, and Contrast Example 3 are subjected to a charging-discharge test.

[0138] FIG. 8 shows the discharging characteristics (rate characteristics) of Embodiment 1, Embodiment 2, Contrast Example 1, Contrast Example 2, and Contrast Example 3.

[0139] Since the electrode mixed with the short fiber A of aluminum has the low internal resistance, the thickness of the active material layer of the electrode may also be set to be 2 to 3 times of the usual thickness. The active material layer refers to a layer having the short fiber A, the active substance powder 20, the conductive aid 30 and the binder B, and is a layer that does not contain the current collector foil. As described above, the positive electrodes of Embodiment 1 and Embodiment 2 are manufactured for this time with a thickness of about 1.7 times greater than that of Contrast Example 2. As shown in FIG. 8, it may be seen that the discharging capacity (charging capacity) per unit area of Embodiment 1 is compared with the discharging capacity (charging capacity) per unit area of Contrast Example 2, although it also depends on a discharging current (charging current), while the discharge current (charging current) is 2 mA/cm.sup.2, it reaches about 2 times, and while the discharging current (charging current) is 3 mA/cm.sup.2, it reaches about 1.75 times.

[0140] As described above, the thickness of the positive electrode of Embodiment 1 and Embodiment 2 is about 1.7 times greater than that of the positive electrode of Contrast Example 2. Therefore, it may be seen that the battery characteristics of Embodiment 1 and Embodiment 2 shown in FIG. 8 are excellent. It should be noted that, as shown in FIG. 8, there is a tendency that the discharging capacity (charging capacity) is decreased while the discharging current (charging current) is increased. This is common as the characteristics of the secondary battery. Namely, during rapid discharging or charging, the discharging capacity or the charging capacity is decreased.

[0141] The positive electrode foil of the commercially available lithium ion battery of Contrast Example 3 forms the positive electrode containing the active substance on the aluminum foil of about 1800 cm.sup.2. 5000 mAh divided by 1800 cm.sup.2 is about 2.78 mAh/cm.sup.2. As shown in FIG. 8, the rated capacity 5000 mAh of the commercially available lithium ion battery of Contrast Example is achieved while the discharging current (charging current) is 0.2 mA/cm.sup.2. For example, while the charging-discharging of the commercially available lithium ion battery of Contrast Example 3 is performed at 2 mA/cm.sup.2 (0.72 C), the charging-discharging is repeatedly performed at a maximum capacity of about 3470 mAh. On the other hand, in the lithium ion battery of Contrast Example 2 using the commercially available positive electrode foil and negative electrode foil at the same current, the capacity thereof is about 3870 mAh. In addition, in the lithium ion battery of Embodiment 1, the capacity thereof is about 7920 mAh, and the charging-discharging may be performed at a high capacity.

[0142] Through the comparison with Contrast Example 1, it may be seen that Embodiment 1 and Embodiment 2 are excellent. Namely, compared with the discharging capacity (charging capacity) per unit area of Contrast Example 1, the discharging capacity (charging capacity) per unit area of Embodiment 1 is 1.2-1.3 times while the discharging current (charging current) is 2 mA/cm.sup.2, and it is also 1.2-1.3 times while the discharging current (charging current) is 3 mA/cm.sup.2. It should be noted that, as described above, the thicknesses of the positive electrodes of Embodiment 1, Embodiment 2 and Contrast Example 1 are the same.

[0143] If the electrode of this embodiment is used, the thickness size of one electrode may be increased. With this structure, it is possible to increase the discharging capacity (charging capacity) while the weight of the entire battery is reduced and the volume is reduced and the like.

[0144] FIG. 9 shows the cycle characteristics of the lithium ion battery of Embodiment 1 measured by setting the current during charging-discharging to 2 mAh/cm.sup.2. It may be seen that the discharging capacity (charging capacity) of the lithium ion battery of Embodiment 1 with the aluminum fiber added is decreased in an initial stage, but becomes stable at about 4.3 mAh/cm.sup.2.

[0145] In this way, the lithium ion battery manufactured by using the short fiber A of aluminum or copper in this embodiment may have about two times of the discharging capacity (charging capacity) compared to the lithium ion battery using the commercially available electrode foil. As in Contrast Example 1, only by increasing the thickness size of the positive electrode or the negative electrode, the characteristic improvement proportional to the increase in thickness may not be achieved. However, the positive electrode or the negative electrode of this embodiment using the short fiber A of aluminum or copper may obtain the characteristics that are proportional to the increase in thickness or higher. The thickness of the positive electrode of Contrast Example 2 as the common electrode is 90 μm, but in Embodiments 1 and 2, the thickness of the positive electrode after removing the thickness of the aluminum foil is 155 μm, and Embodiments 1 and 2 are 1.7 times or more of Contrast Example 2. Namely, by adding the short fiber A to the electrode as described above, the thickness of the electrode may be 120 μm or more, more preferably 150 μm or more, and at the same time, the characteristics proportional to the increase in thickness or the above characteristics may be obtained.

[0146] As shown in FIG. 10, the internal resistance of the battery with the electrode containing the short fiber A of aluminum or copper is lower than the internal resistance of the battery with the electrode without containing the short fiber A. It may be considered that the internal resistance of the battery with the electrode containing the short fiber A in this way is reduced, and the characteristics of Embodiment 1 and Embodiment 2 may be improved. FIG. 10 shows the internal resistance of the battery with the positive electrode of Embodiment 3, Embodiment 4, and Embodiment 5 and the internal resistance of the battery with the positive electrode of Contrast Example 1.

[0147] In Embodiment 3, relative to Embodiment 1, the weight ratio of the short fiber A of aluminum in the positive electrode is set to 1.22% by weight, and in Embodiment 4, relative to Embodiment 1, the weight ratio of the short fiber A of the aluminum foil in the positive electrode is set to 4.88% by weight. In addition, in Embodiment 5, relative to Embodiment 1, the weight ratio of the short fiber A of the aluminum foil in the positive electrode is set to 9.75% by weight. The weight ratio of the active substance powder 20, the conductive aid 30, and the binder B of Embodiment 3, Embodiment 4, and Embodiment 5 is slightly changed relative to the weight ratio of Embodiment 1 according to the increase or decrease of the short fiber A.

[0148] As shown in FIG. 8 and FIG. 10, if the electrode containing the short fiber A is used like this embodiment, as long as it has the same discharging capacity (charging capacity), the charging-discharging may be performed at twice the speed. In addition, the discharging capacity (charging capacity) of Embodiment 2 to which the carbon fiber CF is added is increased compared to Embodiment 1.

[0149] In this way, the electrode of this embodiment may obtain the characteristics proportional to the increase in thickness or the above characteristics. For example, while the battery is manufactured by stacking a plurality of the positive electrode foils and a plurality of the negative electrode foils, and the aluminum foil and the copper foil and the like are used as the current collector on each positive electrode foil and each negative electrode foil, the piece number of the aluminum foils and the copper foils required for manufacturing the batteries with the same capacity is reduced. This is helpful to the space saving of the battery, the light weight of the battery, and the reduction of the manufacturing cost of the battery and the like.

[0150] It should be noted that the short fiber A may also be manufactured by a method other than the coil cutting method. For example, the short fiber A may be formed by a flutter cutting method in which a cutting tool is brought into contact with a cylindrical component of aluminum or copper having a circular cross section, a milling method and the like.

[0151] In addition, it is also possible to manufacture the short fiber A with the above length by blowing a metal such as molten aluminum into a space from a micropore.

[0152] For example, as shown in FIG. 11, the molten aluminum is prepared in a closed container 40 into which a base end portion of an elbow pipe 41 made of ceramics, stainless steel and the like and bent at a front end is inserted, under a state that a front end portion of the elbow pipe 41 is exposed outside the closed container 40, while air or inert gas and the like is injected from a gas guiding pipe 40a to increase the pressure in the closed container 40, the molten aluminum rises from a rear portion of the elbow pipe 41 and reaches the front end portion.

[0153] If a nozzle 42 having a plurality of micropores 42a with a pore diameter of several μm to several mm is arranged in an opening portion 41a at the front end of the elbow pipe 41, the molten aluminum is blown into the space from the micropores 42a. As the aluminum, it is preferable to use the aluminum with a purity of 99.9% or higher in terms of easy processing, and it is more preferable to use the aluminum with a purity of 99.99% or higher. However, an alloy with other metals may also be used. The space may be filled with the air, or other inert gases such as nitrogen. It should be noted that the front end of the elbow pipe 41 may also face downward.

[0154] In an example of FIG. 11, the nozzle 42 is arranged in a mode of blowing the aluminum in an approximately horizontal direction, but the aluminum may be blown in other directions such as a direction facing downward. Thus, the aluminum coming out of the micropores 42a of the nozzle 42 is cooled while being scattered in the space, and becomes the short fibers A of aluminum.

[0155] It should be noted that while the short fibers A obtained by blowing the molten aluminum and other metals into the space from the micropores are used to manufacture the respective electrodes, the effects described later may be obtained. Firstly, the short fiber A has a shape having a large diameter portion A1 and a small diameter portion A2 as shown in FIG. 12 according to the blowing conditions. In one example, as shown in FIG. 12, the large diameter portion A1 is shorter than the small diameter portion A2, and the large diameter portion A1 has 1.5 times or more of a diameter relative to the small diameter portion A2. Namely, the large diameter portion A1 is a portion having a diameter that is 1.5 times or more greater than that of the small diameter portion A2. In one example, the length of the large diameter portion A1 is 5 times shorter than the average diameter of the small diameter portion A2, and more preferably shorter than 3 times. In FIG. 12, a plurality of the large diameter portions Al and a plurality of the small diameter portions A2 alternately exist on one piece of the short fiber A, but there is also a case that a single large diameter portion A1 and a single small diameter portion A2 exist on one piece of the short fiber A. In one example, the average diameter of the small diameter portion A2 is 10 μm or more and 30 μm or less. It should be noted that other metals may also be used to manufacture the short fiber A having the large diameter portion A1 and the small diameter portion A2.

[0156] If the short fiber A described above is used to manufacture the electrode of each of the above embodiments, the large diameter portion A1 of the short fiber A is easily exposed on the surface of the electrode. This is beneficial to reduce the electrical resistance between the short fiber A in the electrode foil and the current collector foil. In addition, while the electrode is manufactured without using the current collector foil, the large diameter portion A1 of the short fiber A is also easily exposed on the surface of the electrode foil. Therefore, while a terminal and the like are mounted on the electrode foil, the resistance between the terminal and the electrode foil is decreased.

[0157] The present disclosure is supplemented below.

[0158] (Mode of Lithium Ion Battery)

[0159] The manufacturing method for the electrode of the electricity storage device in the first aspect of the present disclosure includes: the working procedure of using the mixing machine to mix the short fiber A of the above metals (mainly aluminum or copper), the active substance powder 20, the conductive aid 30, and the binder B to prepare the slurry S; the forming working procedure of coating and forming the slurry S on a predetermined metal foil (current collector foil); and the drying working procedure of drying the slurry S formed into the predetermined shape, to from the electrode containing the short fiber A of aluminum or copper that functions as the current collector and a structural body. The description of functioning as the structural body refers to a state in which the short fiber A maintains particles such as the active substance powder 20 and the conductive aid 30 maintained on the electrode foil. In the electrode foil without containing the short fiber A, while the electrode foil is bent, the particles tend to peel off from the electrode foil. In contrast, the short fiber A is also bent flexibly while the electrode foil containing the short fiber A is bent, and the short fiber A prevents the particles from falling off.

[0160] In the above embodiment, if the slurry formed into the predetermined shape is dried and pressed with a calendaring machine, the short fibers A of aluminum or copper are connected to each other, or the short fibers A are wound around the active substance powder 20 and the conductive aid 30.

[0161] Thus, the internal resistance of the active material layer may be greatly improved, and the structure that may be two times, three times and the like thicker than the commercially available electrode is formed.

[0162] (Modes of Electric Double-Layer Capacitor and Solid-Type Battery)

[0163] The modes of these devices are also the same. In the case of the electric double-layer capacitor, the slurry S that mixes the adsorbent powder (activated carbon), the conductive aid 30, and the binder B with the above short fiber A is used, and in the case of the all-solid-state battery, the solid electrolyte is used instead of the liquid electrolyte.

DESCRIPTION OF REFERENCE SIGNS

[0164] 1-Positive electrode current collector, 2-Positive electrode layer, 3-Solid electrolyte layer, 4-Negative electrode layer, 5-Negative electrode current collector, 14, 24, 34-Solid electrolyte, 20-Active substance powder, 30-Conductive aid, A-Short fiber, Al-Large diameter portion, A2-Small diameter portion, B-Binder, S-Slurry, and CF-Carbon fiber.