Method for manufacturing electrode of power storage device and electrode of power storage device

Abstract

To provide a manufacturing method of an electrode of a high-capacity electric power storage device, the method allowing for reduction in an internal resistance and prevention of peeling of an active material from a current collector due to expansion and contraction thereof.SOLUTION: A manufacturing method of an electrode of an electric power storage device includes the steps of: obtaining a long metallic fiber by cutting the end face of a metallic foil coil with a cutting tool; cutting the long metallic fiber in such a manner that the average length of the cut long metallic fiber is 5 mm or less, while the bundle of long metallic fibers is pressed against a predetermined surface using a pressing member, or while the bundle of long metallic fibers is placed in a tube; preparing a liquid or gel-like slurry including a metallic short fiber A obtained by cutting the long metallic fiber, a binder B, and adsorbent powder on which electrolyte ions are adsorbed during charging or an active material powder 20 that chemically reacts during charging and discharging; molding the slurry into a predetermined shape; and forming an electrode including the short fibers A by drying the slurry formed into the predetermined shape.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for manufacturing an electrode of a power storage device and an electrode of a power storage device.

Background Art

[0002] Capacitors and secondary batteries are used in various fields for the purpose of energy reduction and prevention of global warming. Particularly in the automotive industry, the adoption of electric energy has accelerated the development for further improving these performances. Electric double layer capacitors have conventionally been used for backing up memories in electronic circuits to which a low voltage is applied, and have high input / output reliability compared to secondary batteries.

[0003] Therefore, in recent years, they have been used for power generation by natural energy such as sunlight and wind power, construction machinery, instantaneous low-power power supplies, and regenerative power supplies for trains. Although their use in automobiles has been considered, their characteristics and costs did not meet the requirements, and their use in this field has not been realized until recently. However, currently, electric double layer capacitors are used for electronic control brake systems, and their use for backup power supplies of automotive electrical components, starting energy supply for idling stop systems, brake control, power assist, etc. is being considered.

[0004] The structure of an electric double layer capacitor is composed of positive and negative electrode parts, an electrolytic solution, and a separator for preventing short-circuiting between the opposing positive and negative electrode parts. The electrode part is formed by applying many layers of a kneaded mixture of a polarizable electrode (currently mainly activated carbon), a binder for holding the activated carbon, and a conductive auxiliary agent (mainly fine carbon particles) onto an aluminum foil (thickness of about 20 μm) which is a current collector. Such an electric double layer capacitor is disclosed in, for example, Patent Document 1.

[0005] Charging of the electric double layer capacitor is performed by the movement of electrolyte ions in the solution and their adsorption and desorption on the surface of the micropores of the activated carbon. The electric double layer is formed at the interface where the activated carbon powder and the electrolytic solution are in contact. Incidentally, the particle size of ordinary activated carbon is, for example, about 4 to 8 μm, and the specific surface area is, for example, 1600 to 2500 m 3 / g. The electrolytic solution has cations, anions, and a solvent. As the cations, tetraethylammonium salts are used, as the anions, borate ions such as tetrafluoroborate ions are used, and as the solvent, propylene carbonate, ethylene carbonate, etc. are used.

[0006] On the other hand, a lithium-ion secondary battery (lithium-ion battery) mainly consists of a positive electrode, a negative electrode, and a separator. Generally, the positive electrode is a mixture of an active material powder, usually lithium cobaltate, a conductive aid as an additive, and a binder, which is applied to an aluminum foil with a thickness of about 20 μm as a current collector to a thickness of about 100 μm. The negative electrode is a copper foil as a current collector coated with a carbon material. These are separated by a separator such as polyethylene and immersed in an electrolytic solution to form a lithium-ion battery. Such a lithium-ion battery is disclosed in, for example, Patent Document 2.

[0007] Charging and discharging are performed by the movement of lithium ions between the positive electrode and the negative electrode. During charging, lithium ions move from the positive electrode to the negative electrode, and when the lithium ions in the positive electrode are depleted or the negative electrode can no longer store lithium ions, the charging is completed. During discharging, the reverse occurs.

[0008] On the other hand, although LiB (lithium-ion battery) is the most widely used in recent years, the electrolyte salt (usually LiPF6) contained in the electrolytic solution solvent is a flammable liquid, and there are risks such as ignition and liquid leakage. Furthermore, it is said that this organic electrolytic solution causes the decomposition of anions and various foreign molecules at the interface with the positive electrode, shortening the life of LiB. Therefore, attempts have been made to replace the electrolytic solution with a solid electrolyte, and such a battery is called an all-solid-state battery because the positive electrode layer, the negative electrode layer, and the electrolyte layer are all composed of solids. The all-solid-state battery is not limited to the constituent materials of LiB by nature, but since there are many studies on solidifying the electrolytic solution of LiB in general, it generally refers to all-solid LiB.

[0009] The advantages of all-solid-state batteries include being safe because the electrolyte layer is flame-retardant, having fewer side reactions with anions and solvent molecules and being longer-lived because only lithium ions move through the electrolyte layer, and having a wide operating temperature range because the electrolyte layer is not liquid, among others.

[0010] Also, when attempting to obtain a high-capacity and high-voltage battery using LiB, multiple single cells must be connected. However, when using a solid electrolyte layer, it is only necessary to stack the positive electrode layer, solid electrolyte layer, and negative electrode layer in that order, so there is also the advantage that it is possible to fabricate a battery with a high energy density.

[0011] The performance of the above devices is all carried out through the exchange of ions and electrons. Therefore, the capacitance, charge and discharge rate, lifespan, etc. of the device depend on how smoothly or continuously the exchange of electrons can be carried out.

[0012] On the other hand, the charge and discharge of an all-solid-state battery in which the electrolyte of a lithium-ion battery is solidified is carried out by the insertion and extraction of Li. For example, in Patent Document 3, a conductive elastic body is arranged between single cells to suppress expansion and contraction. In Patent Document 4, a buffer layer is provided around the battery. In Patent Document 5, various measures such as controlling the porosity are taken. Also, electrodes using current collectors made of metal fibers are known. For example, Patent Documents 6 and 7 can be cited.

Prior Art Documents

Patent Documents

[0013]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

[0014] (Problems of Electric Double Layer Capacitors) Electric double layer capacitors are different from secondary batteries mainly composed of lithium ion batteries in that they do not involve chemical reactions, have a short power storage time, and a fast current discharge time. Also, regarding the energy density, while lithium batteries are several hundred Wh / L, electric double layer capacitors are several tens of Wh / L, which is one digit lower. The reason electric double layer capacitors are being considered for use not as power storage but as backup power for electrical components, starting energy for idle stop systems, brake control, power assist, etc. is due to the above differences.

[0015] In recent years, electric double layer capacitors have been developed for use in large-capacity power devices such as electric vehicles and energy generation. However, in order to efficiently charge and discharge a large amount of energy to and from the capacitor, there is a problem that the capacitance must be increased and the internal resistance of the electrode part must be reduced.

[0016] (Problems of Lithium Ion Batteries) On the other hand, secondary batteries mainly composed of lithium ion batteries have a relatively high energy density and can be used for a long time, so they are used in various fields including portable devices. In recent years, they have come to be used in fields such as automobiles, heavy machinery, and energy, and there is a demand for increased size in order to increase the capacity. However, with the increase in size, there are many problems including the problem of capacity, as well as charging speed, lifespan, reliability, and manufacturing difficulty. For example, the capacity of a battery used in a mobile phone is about 15 Wh, while the capacity of a battery used in a hybrid vehicle is several tens of kWh to 100 kWh, and the difference between the two is thousands of times, and the above problems accompany this.

[0017] The reaction of a lithium-ion battery is a reversible chemical reaction. When the electrodes are charged and discharged, the active material expands and contracts. Therefore, the active material peels off from the current collector, and the charge and discharge characteristics deteriorate. That is, it is not always possible to perform 100% identical charge and discharge, and a decrease in the charge and discharge capacity occurs. Since the battery is used for several years in hybrid vehicles and electric vehicles, it is necessary to suppress the peeling of the current collector and the active material in order to prevent the above deterioration.

[0018] Also, one of the biggest problems of a lithium-ion battery is internal resistance. The internal resistance can be said to be the resistance when lithium ions move through the electrolyte between the positive and negative electrodes inside the battery. This movement resistance is the main reason why the capacity cannot be increased or the charge and discharge speed cannot be increased. Regarding increasing the size, that is, increasing the capacity, when a large amount of active material is applied to the current collector, the capacity increases, but the movement resistance of lithium ions increases. For this reason, there is a limit to the thickness of the active material layer. When the active material layer becomes thick, the charge and discharge speed becomes slow due to the movement resistance. When the coating thickness is reduced, the internal resistance is reduced and the charge and discharge speed becomes fast, but the capacity decreases. Therefore, the capacity is increased by stacking the current collectors coated with the active material multiple times, expanding the area of the current collector coated with the active material, etc.

[0019] The speed of charging and discharging is also related to the amount of lithium ions generated. If a large number of ions are created and can move at once, the charging speed and discharging speed will be fast. Since the chemical reaction of the secondary battery occurs at the interface between the electrolyte and the active material, if the contact area between the electrode and the electrolyte can be increased, the charge and discharge speed will also be improved.

[0020] Currently, in order to reduce the internal resistance, improvements have been made to additives, conductive aids, and active materials, and carbon fine particles have been pre-coated on the current collector. Also, in terms of the shape of the current collector, as described above, improvements have been made to make it as thin as possible and to form fine holes or the like in the foil to increase the surface area. Similarly, in the case of electric double layer capacitors, research and development have been carried out on improvements to activated carbon and additives, and on increasing the contact area between the current collector and the active material layer.

[0021] (Problems of all individual batteries) On the other hand, the charge and discharge of all-solid-state batteries in which the electrolyte of lithium-ion batteries is solidified is carried out by Li insertion and extraction. At this time, the crystal lattice that is the host repeats expansion and contraction. If the volume change due to this is large, the contact between the particles of the active material, solid electrolyte, and conductive aid is cut off, and the amount of effective active material decreases. In the case of all-solid-state batteries, even if charge and discharge are repeated at a current of about one-tenth to two-tenths of the battery capacity, an amount of Li close to 1 mole is inserted and extracted, and the volume expansion and contraction rate reaches nearly 10%. Therefore, various devices have been proposed to suppress the expansion and contraction.

[0022] Thus, in energy storage devices, in order to solve the problem of increasing the capacity, if the internal resistance can be reduced and the separation of the active material from the current collector due to expansion and contraction can be prevented, there is a great possibility of significant improvement.

Means for Solving the Problems

[0023] The method for manufacturing an electrode of an energy storage device according to the first aspect of the present invention is , gold A fiber forming step of obtaining the fibers, a cutting step of cutting the long metal fiber bundle so that the average length becomes 5 mm or less while pressing the long metal fiber bundle against a predetermined surface using a pressing member, or while arranging the long metal fiber bundle in a tube, a slurry forming step of forming a liquid or gel-like slurry containing the short metal fibers produced by the cutting step, an adsorbent powder that adsorbs electrolyte ions during charging or an active material powder that undergoes a chemical reaction during charge and discharge, and a binder, a forming step of forming the slurry into a predetermined shape, and a drying step of drying the slurry formed into the predetermined shape to form an electrode containing the short fibers.

[0024] The first aspect of the present invention produces short fibers used for the electrodes of the power storage device as described above. There has been a case of using a method for producing long fibers or short fibers by the aluminum melt blowing method, or a method for producing short fibers called the chatter vibration processing method, in which a metal bar is shaved while vibrating a cutting tool to produce short fibers.

[0025] However, with these methods, it is difficult to stably produce short fibers with a diameter of several tens of μm and a length of several mm. In addition, short fibers with unstable shapes may affect battery performance. We conducted a study to more stably produce such short fibers and found a method that can cut long fibers produced by the coil cutting method into arbitrary sizes. The coil cutting method is a method of producing long fibers by cutting a metal foil wound in a coil shape from its end face direction. Therefore, the cross section of the fiber has a shape such as a square, rectangle, or trapezoid having the thickness of the foil and the cutting depth, and the shape is regular. By using such short fibers with a regular cross-sectional shape and length, it is possible to improve battery performance. This method can be applied to any type of metal as long as it can be made into a foil.

[0026] The second aspect of the present invention is formed using a cutting tool having an average length of 5 mm or less made of copper An electrode of an energy storage device including short fibers and an adsorbent powder that adsorbs electrolyte ions during charging or an active material powder that undergoes a chemical reaction during charge and discharge, wherein the weight ratio of the short fibers is 1 wt% or more and 9.75 wt% less than. Alternatively, copper short fibers with an average length of 5 mm or less, an adsorbent powder to which electrolyte ions are adsorbed during charging or an active material powder that undergoes a chemical reaction during charge and discharge, and a conductive aid that is graphite, carbon black, acetylene black, or other carbon fine particles, wherein the weight ratio of the short fibers is 1 wt% or more and less than 9.75 wt%.

[0027] A third aspect of the present invention is an electrode of an energy storage device including short fibers made of metal and an adsorbent powder that adsorbs electrolyte ions during charging or an active material powder that undergoes a chemical reaction during charge and discharge, wherein the short fibers have a small diameter portion and a large diameter portion having a diameter of 1.5 times or more of the small diameter portion, and the length of the large diameter portion is shorter than 5 times the average diameter of the small diameter portion.

Advantages of the Invention

[0028] According to the present invention, it is possible to improve battery performance.

Brief Description of the Drawings

[0029] [Figure 1] It is a cross-sectional image view of an electrode according to an embodiment of the present invention. [Figure 2] It is a cross-sectional image view of another electrode of this embodiment. [Figure 3] It is a schematic view showing a method for manufacturing a slurry of this embodiment. [Figure 4] It is a schematic view showing an example of a method for applying a slurry for manufacturing an electrode of this embodiment. [Figure 5] It is a schematic view showing a rolling method for manufacturing an electrode of this embodiment. [Figure 6] It is a schematic cross-sectional view of an all-solid-state battery using an electrode of this embodiment. [Figure 7] It is a schematic view showing a pressing method for manufacturing an electrode of this embodiment. [Figure 8] It is a graph showing the characteristics of a lithium-ion battery using an electrode of this embodiment. [Figure 9] It is a graph showing the cycle characteristics of a lithium-ion battery using an electrode of this embodiment. [Figure 10] This is a graph showing the characteristics of a lithium-ion battery using the electrode of this embodiment. [Figure 11] This is a schematic diagram showing a method for manufacturing short fibers of the electrode of a modified example of this embodiment. [Figure 12] This is a schematic diagram of the short fibers of the electrode of a modified example of this embodiment.

Mode for Carrying Out the Invention

[0030] The electrode and the power storage device according to an embodiment of the present invention will be described below with reference to the drawings. Note that a lithium-ion battery is mainly used as the power storage device for the description. FIGS. 1 and 2 show an electrode (positive electrode or negative electrode) in which short fibers A of aluminum or copper with an average wire diameter of 50 μm or less are mixed. Note that FIGS. 1 and 2 are diagrams for clearly showing the configuration of this embodiment, and the sizes, thicknesses, lengths, mixing ratios, etc. of the short fibers A, the active material powder 20, the conductive assistant 30, the carbon fiber CF, etc. are different from the actual ones.

[0031] As shown in FIGS. 1 and 2, this electrode includes short fibers A of aluminum or copper with an average wire diameter of 50 μm or less, and an active material powder 20 that is held by a binder B together with the short fibers A and undergoes a chemical reaction during charge and discharge, and includes a conductive assistant 30 held by the binder B as necessary.

[0032] [Molding of Metal Short Fibers Serving as Current Collectors] A bundle of metal long fibers (aluminum or copper long fibers) produced by the coil cutting method is sandwiched between a pair of plastic films having a thickness of, for example, 0.1 mm to 0.3 mm, and the bundle of the long fibers is cut to an arbitrary length. That is, the long fibers are cut in a state where the bundle of the long fibers is pressed against a predetermined surface using a pressing member made of other thin members such as plastic, thin metal foil, paper, etc. The predetermined surface is the upper surface of the plastic film in the present embodiment, but may be the upper surface of a workbench made of plastic, metal, etc., or a thin member such as foil or paper. Preferably, the plastic film has a thickness of 1 mm or less. Alternatively, the bundle of the long fibers is cut to an arbitrary length in a state where the bundle of the long fibers is disposed in a cylindrical plastic tube. The wall pressure of the plastic tube is, for example, 0.1 to 0.3 mm, and preferably 0.5 mm or less.

[0033] That is, the bundle of the long fibers is cut in a state where the bundle of the long fibers is disposed in a tubular member made of thin members such as plastic, metal foil, paper, etc. The bundle of the long fibers may be cut together with the pressing member or the tubular member. Thereby, it becomes possible to stably and efficiently cut the bundle of the long fibers. Also, it is preferable that the bundle of the long fibers is relatively densely disposed in the tubular member. Thereby, the short fiber A having an arbitrary length is created. There may be a case where the bundle of the long fibers is cut without using the pressing member or the tubular member.

[0034] Note that the short fiber A cut to the arbitrary length has an average length of 5 mm or less, preferably an average length of 2 mm or less. Also, the short fiber A has an average wire diameter of 50 μm or less, preferably 25 μm or less, more preferably 20 μm or less.

[0035] In the coil cutting method, an aluminum or copper foil is wound into a coil shape, and a long metal fiber (metal long fiber) is obtained by cutting the end face of the coil with a cutting tool. Then, the short fiber A is obtained by cutting the long metal fiber to the above length. Note that the metal fiber, short fiber A, thin plate, or foil of the present embodiment may be made of other metals such as steel, stainless steel, brass, etc.

[0036] The short fiber A produced by the coil cutting method has, on its cross section, a side corresponding to the portion that was the surface of the foil and a side cut by the cutting tool. And between the side corresponding to the surface and the cut side, it becomes an angular, wide V-shaped, narrow V-shaped, or a shape close to a V shape. For this reason, it is expected that in each of the processes described later, the short fiber A will be easily scratched through the binder B etc. and will easily come into contact with the active material powder 20, other short fibers A, etc. Or, it is expected that the short fiber A will easily bite into other short fibers A.

[0037] [Electrode forming] When creating the electrode shown in FIG. 1, as shown in FIG. 3, a liquid or gel-like slurry S containing aluminum or copper short fiber A, active material powder 20, conductive assistant 30, and binder B is created. To create the slurry S, aluminum or copper short fiber A, active material powder 20, conductive assistant 30, and diluted binder B are kneaded using a kneader or the like. There is no problem if the weight ratio of the active material powder 20, conductive assistant 30, and binder B during drying is about these weight ratios in a commercially available secondary battery. Hereinafter, the weight ratio or compounding ratio refers to the weight ratio or compounding ratio with respect to the entire dried electrode by the drying process described later.

[0038] In this embodiment, the compounding ratio of the binder B is 2 wt% or more and less than 6 wt%, and around 4 wt% is preferable. The compounding ratio of the short fiber A is preferably 1 wt% or more and less than 8 wt%. If there is little short fiber A, the effect as a current collector is small, and if there is a lot of short fiber A, conversely, the internal resistance will increase. The compounding ratio of the short fiber A is optimally preferably 2.5 wt% or more and 5.5 wt% or less. Incidentally, the compounding ratio of the short fiber A is considered to be most preferably 3.5 wt% or more and 5 wt% or less. When creating the electrode shown in FIG. 2, carbon fiber CF is further added to the above to create the slurry S. When adding carbon fiber CF, its compounding ratio is preferably 1 wt% or more and less than 2 wt%. If there is little carbon fiber CF, the effect is not visible, and if there is a lot of carbon fiber CF, it will cause deterioration in the cycle test.

[0039] The short fibers A of aluminum or copper have an average length of 5 mm or less. Therefore, in the slurry S, the short fibers A of aluminum or copper are likely to mix with other formulations. When the average length of the short fibers A becomes 2 mm or less, there is a tendency for them to mix more easily. If they are too short, the contact between the short fibers A decreases. Therefore, it is preferable that the average length of the short fibers A is 1 mm or more. Also, if the short fibers A are long, the short fibers A become entangled with each other and fiber lumps remain in the slurry S. Therefore, optimally, the average length of the short fibers A is preferably 1 mm or more and 4 mm or less.

[0040] Subsequently, the slurry S is applied to a current collector foil (aluminum foil or copper foil) to a predetermined thickness and pre-dried to increase the viscosity. When not using a current collector foil, it is possible to apply the slurry S to a separator. For example, as shown in FIG. 4, the slurry S serving as the positive electrode is applied to one surface in the thickness direction of the separator SP, and the slurry S serving as the negative electrode is applied to the other surface in the thickness direction of the separator SP. The slurry S serving as the positive electrode or the negative electrode may be applied to only one surface of the separator SP. The pre-drying is performed until the binder B is not completely cured, thereby facilitating the shaping of the electrode foil into a predetermined shape. In this embodiment, in some cases, an electrode in which the positive electrode or the negative electrode and the current collector foil or the separator SP are integrated may be referred to as an electrode foil.

[0041] Furthermore, it is also possible to form the positive electrode or negative electrode slurry S into a sheet shape on a predetermined mold without applying it to the current collector foil or the separator SP. In this case, the electrode that is formed into a sheet shape and is the positive electrode or the negative electrode is referred to as an electrode foil.

[0042] Subsequently, the electrode foil (positive electrode or negative electrode slurry S) on which coating and drying have been performed is pressurized. Thereby, the slurry S is formed into a predetermined thickness or the like according to the size of the electrode. For example, as shown in FIG. 5, the electrode foil (positive electrode or negative electrode slurry S) is passed between a pair of rollers to be pressurized and formed into a predetermined thickness. Subsequently, a drying process is performed in which the formed electrode foil is dried by vacuum drying or the like. Thereby, the moisture in the electrode is removed and the binder B is cured.

[0043] When using short fibers A of aluminum or copper with a purity of preferably 99% or more, more preferably 99.9% or more, for example, by the pressure shown in FIG. 5, at the portion where the short fibers A are in contact with each other so as to cross, it becomes easy to deform the two crossed short fibers A so as to bite into each other.

[0044] That is, the short fiber A is flattened at the contacting portion, and thereby, the two crossed short fibers A bite into each other. By applying pressure, the short fiber A is closely contacted by the active material powder 20, leading to a reduction in the resistance at the contact portion between the short fibers A. That is, it is possible to reduce the transfer resistance of electrons at the contact portion between the short fibers A, which is advantageous for reducing the resistance for electrons to move to the input / output terminals. In addition, through the process of forming the slurry S into an electrode foil and the process of pressuring the formed electrode foil, etc., the short fiber A in contact with the active material powder 20 is bent along the active material powder 20, and the short fiber A is entangled with the active material powder 20.

[0045] [Positive electrode active material powder] As the positive electrode active material powder 20, any material that can be held by the short fiber A with a binder B or the like, or a material held by the binder B cured with the short fiber A, is acceptable, and those with excellent cycle characteristics are preferred. Examples of the active material include lithium cobaltate (LiCoO2), iron phosphate-based active materials, and carbon materials such as graphite. It is possible to use known active materials used for the positive and negative electrodes of secondary batteries.

[0046] The average particle diameter of the active material powder 20 is, as an example, a value obtained by adding 10 μm to the average wire diameter of the short fiber A that functions as a current collector. For example, when the average wire diameter of the short fiber A is 20 μm, the average particle diameter of the active material powder 20 is preferably 30 μm or less or about 30 μm. Thereby, the contact area between the short fiber A that functions as a current collector and the active material powder 20 increases, which can contribute to the improvement of the charge / discharge rate. Note that the particle diameter of the active material powder 20 may be other than the above.

[0047] [Binder] As the binder B, it is possible to use a thermoplastic resin, a polysaccharide polymer material, or the like. Examples of the material of the binder B include polyacrylic resins, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), and copolymers of vinylidene fluoride (VdF) and hexafluoropropylene (HFP). It is also possible to use known binders used for the electrodes of secondary batteries and electric double layer capacitors.

[0048] [Conductive aid] As the conductive aid 30, any material having conductivity may be used, and it is preferably a material that does not undergo chemical changes by electrolytes or solvents. Examples of the conductive aid 30 include graphite and carbon black. It is also possible to use known conductive aids used for the electrodes of secondary batteries and electric double layer capacitors. Preferably, the average particle size of the conductive aid 30 is smaller than the average particle size of the active material powder 20.

[0049] [Negative electrode active material powder] As the active material powder 20 of the negative electrode, artificial graphite, natural graphite, etc. are used. When these are used for the negative electrode, since the operating potential on the negative electrode side is low, a Li-Al reaction occurs when short fibers A of aluminum are used. This causes a decrease in Li and rapidly advances the deterioration of the battery. Therefore, short fibers A of aluminum cannot be used, and it is necessary to use short fibers A of copper. On the other hand, LTO (lithium titanate), which has been developed in recent years and has a reaction potential higher than that of the Li-Al reaction, can be used as the active material powder 20 of the negative electrode. In this case, short fibers A of aluminum can be used for the negative electrode. It has been found that when short fibers A of aluminum are used in an amount of 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 material powder 20 of the negative electrode, the internal resistance can be significantly reduced.

[0050] [Application to other devices] The above-described method for manufacturing an electrode and the electrode can be applied to electrodes of power storage devices such as electric double layer capacitors, secondary batteries including all-solid-state batteries, and hybrid capacitors including lithium ion capacitors. For example, when manufacturing the positive and negative electrodes of a capacitor such as an electric double layer capacitor, it can be manufactured through a process of kneading activated carbon that functions as the active material powder 20, the conductive assistant 30, and the diluted binder B together with the short fiber A. The active material powder 20 used in the electric double layer capacitor can also be said to be an adsorbent powder to which electrolyte ions are adsorbed during charge and discharge. Instead of activated carbon, it is also possible to use well-known active material powders used in capacitors such as electric double layer capacitors. In the case of an all-solid-state battery, it can be manufactured through a process of kneading the solid electrolyte together with the active material powder 20, the conductive assistant 30, the diluted binder B, and the short fiber A.

[0051] In addition, when creating the electrode shown in FIG. 2, as the slurry S, it is also possible to use a slurry S containing carbon fibers CF with an average thickness of 0.5 μm or less, preferably 0.3 μm or less, in addition to the active material powder 20, the conductive assistant 30, and the binder B. In this case, as shown in FIG. 2, the carbon fibers CF are arranged between the short fibers A that function as current collectors.

[0052] The carbon fibers CF are in contact with the short fibers A, the active material powder 20, the conductive assistant 30, and other carbon fibers CF. In this embodiment, carbon fibers 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 are used. In one example, the resistivity of the carbon-based conductive assistant 30 is 0.1 to 0.3 Ω·cm, while the resistivity of the carbon fibers CF is, for example, 5×10 -5 Ω·cm.

[0053] For example, even when the active material powder 20 and the short fiber A are not in direct contact, the active material powder 20 and the short fiber A are electrically connected via the carbon fibers CF. Also, even when the active material powder 20 and the short fiber A are in direct contact, the connection by the carbon fibers CF further reduces the electrical resistance between the active material powder 20 and the short fiber A. In this way, the carbon fiber CF with good conductivity can reduce the electron transfer resistance between the active material powder 20 and the short fiber A, which is advantageous for reducing the resistance of electrons moving to and from the input / output terminals.

[0054] It is also possible to manufacture the electrode using the slurry S containing the carbon fiber CF without using the conductive assistant 30. Also in this case, the carbon fiber CF is disposed between the short fibers A that function as a current collector, and this configuration is advantageous for reducing the electrical resistance between the active material powder 20 and the short fiber A. Note that FIG. 2 is a diagram for clearly showing the configuration of the present embodiment, and the sizes, thicknesses, lengths, mixing ratios, etc. of the short fiber A, the active material powder 20, the conductive assistant 30, the carbon fiber CF, etc. are different from the actual ones.

[0055] [Application to Coin-Type Secondary Battery] Hereinafter, regarding the application to a coin-type secondary battery which is an electric storage device, for example, using the structure described in JP-A-2018-106846, it is possible to manufacture a coin-type battery using the short fiber A of the present application instead of the blowing fiber and the rattling-processed fiber in JP-A-2018-106846. Note that as the electrolytic solution, a well-known electrolytic solution used for secondary batteries can be used.

[0056] [Application to Stacked-Type Secondary Battery] In the case of a secondary battery in which a power storage unit including a positive electrode, a negative electrode, and a separator is stacked in a plurality of layers, similar to the coin-type secondary battery, the electrode structure of the above-described embodiment can be used for only the positive electrode, only the negative electrode, and both the positive electrode and the negative electrode. Note that as the electrolytic solution, a well-known electrolytic solution used for secondary batteries can be used.

[0057] [Application to All-Solid-State Battery] Hereinafter, the application to an all-solid-state battery will be described. Using an example of an all-solid-state lithium-ion battery, a power storage device (all-solid-state battery) will be described. Note that this embodiment can be applied to all-solid-state batteries such as all-solid-state sodium-ion secondary batteries, all-solid-state magnesium-ion secondary batteries, all-solid-state batteries such as air batteries using solid electrolytes, or all-solid-state lithium-ion secondary batteries with a large expansion and contraction using an Si (silicon) negative electrode.

[0058] An example of a schematic diagram of the structure of an all-solid-state battery is as shown in FIG. 6. The all-solid-state battery generally has 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 corresponds to the electrode of the positive electrode described above, and the negative electrode layer 4 corresponds to the electrode of the negative electrode described above.

[0059] (Current collector foil) The positive electrode current collector 1 is generally a metal foil, and the metal foil can be formed of aluminum, an alloy composed of a plurality of metals, or the like. Generally, a copper foil is often used for the negative electrode current collector 5. When the active material powder 20 of the negative electrode is made of lithium titanate, it is possible to use an aluminum foil for the negative electrode current collector 5. In the case of an all-solid-state battery, a conductive material such as SUS (stainless steel) or a cobalt-based alloy having high voltage resistance and corrosion resistance, other conductive materials, or conductive ceramics may be used.

[0060] (Positive electrode layer) The material of the active material powder 20 of the positive electrode is preferably, for example, LiCoPO, LiCoO2, LiMnO4, LiFePO4, etc. If necessary, a conductive assistant 30, a binder B, a solid electrolyte 14 in the form of a powder such as an inorganic solid electrolyte or a polymer electrolyte for enhancing ion conductivity is added, and the positive electrode layer 2 is formed through sintering or pressure molding. In this embodiment, the positive electrode layer 2 contains short fibers A made of aluminum, copper, or the like.

[0061] (Negative electrode layer) The material of the active material powder 20 of the negative electrode is also preferably a substance that easily occludes ions in order to increase the discharge capacity, similar to the positive electrode layer 2. For example, LiFePO4, Li4Ti5O 12 , Li4Fe4(PO4)3, SiO xExamples include Cu6Sn5, LiTiO4, etc. The negative electrode layer 4 is formed by mixing these active material powders 20, conductive aids 30, binder B, and a solid electrolyte 24 in the form of a powder such as an inorganic solid electrolyte or a polymer electrolyte to increase the ionic conductivity, and then sintering or pressure molding. In this embodiment, the negative electrode layer 4 contains short fibers A made of aluminum, copper, or the like.

[0062] Also in the case of the positive electrode layer 2 and the negative electrode layer 4 of the all-solid-state battery, the mixing ratio of the short fibers A is preferably 1 wt% or more and less than 8 wt%, and most preferably 3.5 wt% or more and 5 wt% or less. Further, the mixing ratio of the binder B is preferably 2 wt% or more and less than 6 wt%.

[0063] (Forming the positive electrode layer) First, a liquid or gel-like slurry S containing short fibers A, active material powder 20 that undergoes a chemical reaction during charge and discharge, conductive aids 30, binder B, and solid electrolyte 14 is prepared. The slurry S is prepared by kneading a mixture of short fibers A of aluminum or copper, active material powder 20, conductive aids 30, diluted binder B, and solid electrolyte 14. When charge and discharge are performed, similar to a lithium-ion battery having an electrolyte solution, chemical reactions occur in which ions such as lithium ions are released from the active material powder 20 of the positive electrode into the electrolyte, and chemical reactions occur in which ions such as lithium ions are incorporated into the active material powder 20.

[0064] Subsequently, pre-drying is performed to increase the viscosity of the slurry S. Pre-drying is to dry the slurry S until the binder B is not completely cured, thereby making it easier to form the slurry S into a predetermined shape, and thus can be omitted depending on the viscosity of the binder B. Subsequently, as shown in FIG. 7, the slurry S is placed in the mold and the slurry S is pressurized. Thereby, the slurry S is formed into a predetermined thickness or the like according to the size of the electrode. Note that the slurry S can also be pressurized by passing the slurry S between a pair of rollers, and thereby the slurry S can be formed into a predetermined thickness according to the size of the electrode. After adjusting the thickness of the slurry S with a mold or rollers, it is also possible to cut the slurry S and form it into a predetermined shape (size). It is also possible to form the slurry S into a predetermined shape by applying the slurry S to one surface in the thickness direction of the positive electrode current collector 1.

[0065] Subsequently, a drying process is performed to dry the formed slurry S by vacuum drying or the like. Thereby, the binder B in the slurry S is cured. By this process, the active material powder 20 and the solid electrolyte 14 in the slurry S come into contact with the short fiber A. Note that the contacted state does not mean that all of the active material powder 20 is in contact with the short fiber A. Even if a part of the active material powder 20 is in contact with the short fiber A, it is in the contacted state. Similarly, even if a part of the solid electrolyte 14 is in contact with the short fiber A, it is in the contacted state.

[0066] Note that the mixing ratio of the active material powder 20 and the solid electrolyte 14 in the positive electrode layer 2 is preferably 80% by weight or more, more preferably 85% by weight or more, and further preferably 90% by weight or more. Among these, the mixing ratio of the active material 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 assistant 30, the binder B, the carbon fiber CF, etc.

[0067] (Forming of negative electrode layer) First, a liquid or gel-like slurry S is prepared, which contains short fiber A, active material powder 20 that undergoes a chemical reaction during charge and discharge, conductive assistant 30, binder B, and solid electrolyte 24. The slurry S is prepared by kneading a mixture of aluminum or copper short fiber A, active material powder 20, conductive assistant 30, diluted binder B, and solid electrolyte 24.

[0068] Subsequently, pre-drying is performed to increase the viscosity of the slurry S. Pre-drying dries the slurry S to a state where the binder B is not completely cured, making it easier to mold the slurry S into a predetermined shape. Therefore, it can be omitted according to the viscosity of the binder B. Subsequently, as shown in FIG. 7, the slurry S is placed in a mold and the slurry S is pressurized. Thereby, the slurry S is molded into a predetermined thickness or the like according to the size of the electrode. It is also possible to pressurize the slurry S by passing the slurry S between a pair of rollers, thereby molding the slurry S into a predetermined thickness according to the size of the electrode. After adjusting the thickness of the slurry S with a mold or rollers, it is also possible to cut the slurry S into a predetermined shape (size). It is also possible to mold the slurry S into a predetermined shape by applying the slurry S to one surface in the thickness direction of the negative electrode current collector 5.

[0069] Subsequently, a drying process is performed to dry the molded slurry S by vacuum drying or the like. Thereby, the binder B in the slurry S is cured. By this process, the active material powder 20 and the solid electrolyte 24 in the slurry S are brought into a state of contacting the short fiber A. Note that the state of contact does not mean that all of the active material powder 20 is in contact with the short fiber A. Even if a part of the active material powder 20 is in contact with the short fiber A, it is the state of contact. Similarly, even if a part of the solid electrolyte 24 is in contact with the short fiber A, it is the state of contact.

[0070] In the case of an all-solid-state capacitor that forms an electric double layer, in the positive or negative electrode, it is also possible to use an adsorbent powder on which electrolyte ions are adsorbed during charging instead of the active material powder 20.

[0071] In addition, the mixing ratio of the active material powder 20 and the solid electrolyte 24 in the negative electrode layer 4 is preferably 80% by weight or more, more preferably 85% by weight or more, and still more preferably 90% by weight or more. Among these, the mixing ratio of the active material 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%. The rest is occupied by the conductive assistant 30, the binder B, the carbon fiber CF, etc.

[0072] (Forming of the solid electrolyte layer) A liquid or gel-like slurry is created by kneading a mixture containing the powdered solid electrolyte 34 and the binder B, and a solid electrolyte layer 3 having a predetermined thickness is obtained by performing drying, pressurization in a mold, pressurization using a roller, etc. The solid electrolyte layer 3 may be a well-known solid electrolyte layer. Also, the solid electrolyte layer 3 may be a well-known gel-like solid electrolyte layer.

[0073] (Forming of the power storage element) The positive electrode layer 2, the solid electrolyte layer 3, and the negative electrode layer 4 created as described above are stacked and pressurized to bond the positive electrode layer 2 and the solid electrolyte layer 3, and to bond the solid electrolyte layer 3 and the negative electrode layer 4. Also, if necessary, the positive electrode current collector 1 is stacked on the positive electrode layer 2, and the negative electrode current collector 5 is stacked on the negative electrode layer 4. Thereby, a power storage element BE composed of the positive electrode layer 2, the solid electrolyte layer 3, and the negative electrode layer 4 is formed. By stacking the necessary number of power storage elements BE as shown in FIG. 6, a all-solid-state battery is formed.

[0074] (Solid electrolyte) The solid electrolytes 14, 24, and 34 are present throughout the battery, just like the electrolyte of a lithium-ion battery (LiB), and conduct ions between the positive electrode layer 2 and the negative electrode layer 4. As the material of the solid electrolytes 14, 24, and 34, the following inorganic solid electrolytes or polymer solid electrolytes can be used.

[0075] As the inorganic solid electrolyte, nitrides, halides, silicides, etc. of Li (lithium) such as Li3N, LiI, Li3N-LiI-LiOH, LiSiO4, LiSoO4-LiI-LiOH, Li3PO4-Li4SiO4, Li2SiS3 can be used. Also, a lithium-containing phosphate compound having a NASICON-type structure, chemical formula Li x M y (PO4)3 can be used. x is 1 ≦ x ≦ 2, y is 1 ≦ y ≦ 2, and M can be a substance composed of Al, Ti, Ge, Ga, etc. Also, P can be replaced with Si or B.

[0076] As the polymer solid electrolyte, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate esters polymers, etc. can be used.

[0077] [Examples] An example of applying the above short fiber A to the positive electrode of a lithium-ion battery is shown below. The short fiber A of aluminum and the active material powder 20 (NMC; ternary Li (Ni a Mn b Co 1-a-b)Using O2, conductive assistant 30 (AB; acetylene black), and binder B (PVDF; polyvinylidene fluoride) diluted with a solvent (NMP; N-methylpyrrolidone), slurry S was prepared at the aforementioned weight ratio (weight ratio after the drying process) such that the weight ratio of active material powder 20:conductive assistant 30:binder B:aluminum short fiber A was 87:5:4:4. Then, the slurry S was coated on an aluminum foil, and a positive electrode foil fabricated as described above and a negative electrode foil without metal fibers such as short fiber A were used, and a lithium-ion battery was created using, for example, LiPF6 (lithium hexafluorophosphate) as the electrolyte (Example 1). Also, in the lithium-ion battery of Example 1, a lithium-ion battery was created in which 1.5 wt% of carbon fiber CF was added to the aforementioned slurry S at the aforementioned weight ratio when making the positive electrode (Example 2). By adding 1.5 wt% of carbon fiber CF, the weight ratio of active material powder 20:conductive assistant 30:binder B:aluminum short fiber A became approximately 85.8:4.9:3.9:3.9.

[0078] Also, in the lithium-ion battery of Example 1, a lithium-ion battery was created in which no aluminum or copper short fiber A was added to the aforementioned slurry S when making the positive electrode (Comparative Example 1). By not adding short fiber A, the weight ratio of active material powder 20:conductive assistant 30:binder B became approximately 90.6:5.2:4.2.

[0079] For the fabrication of the negative electrode foils of Example 1, Example 2, and Comparative Example 1, first, using active material powder 20 (natural spherical graphite), conductive assistant 30 (AB; acetylene black), and binder B (PVDF; polyvinylidene fluoride) diluted with a solvent (NMP; N-methylpyrrolidone), slurry S was prepared at the aforementioned weight ratio such that the weight ratio of active material powder 20:conductive assistant 30:binder B was 90:5:5. Then, the slurry S was coated on a copper foil to fabricate the negative electrode foil as described above.

[0080] In addition, a lithium-ion battery using commercially available positive and negative foils was also fabricated (Comparative Example 2). The positive and negative foils are those that are said to be of high performance among commercially available positive and negative foils. Note that the material of the positive electrode active material powder in Comparative Example 2 is the same as the material of the active material powder 20 in Example 1, Example 2, and Comparative Example 1, and the material of the negative electrode active material powder in Comparative Example 2 is the same as the material of the active material powder 20 in Example 1, Example 2, and Comparative Example 1.

[0081] To fabricate the lithium-ion batteries of Example 1, Example 2, Comparative Example 1, and Comparative Example 2, the positive and negative foils were cut to a predetermined size, a separator made of polypropylene was sandwiched between the positive and negative foils, and these were housed in a battery container made of a laminate sheet made of a plastic material. The electrolyte was put into the battery container, and the battery container was sealed, whereby the lithium-ion batteries of Example 1, Example 2, Comparative Example 1, and Comparative Example 2 were fabricated. Note that the sizes of the positive and negative foils, the size of the separator, the thickness of the separator, and the capacity of the battery container in Example 1, Example 2, Comparative Example 1, and Comparative Example 2 are substantially the same.

[0082] Note that the average thickness (average thickness of the positive electrode layer) of the positive electrodes in Example 1, Example 2, and Comparative Example 1 excluding the thickness of the aluminum foil (current collector foil) is about 155 μm, and the thickness of the aluminum foil of the positive electrodes in Example 1, Example 2, and Comparative Example 1 is about 15 μm. The average thickness (average thickness of the positive electrode layer) of the positive electrode in Comparative Example 2 excluding the thickness of the aluminum foil (current collector foil) is about 90 μm, and the thickness of the aluminum foil of the positive electrode in Comparative Example 2 is about 15 μm. The average thickness (average thickness of the negative electrode layer) of the negative electrodes in Example 1, Example 2, Comparative Example 1, and Comparative Example 2 excluding the thickness of the copper foil (current collector foil) is about 85 μm, and the thickness of the copper foil of the negative electrodes in Example 1, Example 2, Comparative Example 1, and Comparative Example 2 is about 15 μm.

[0083] In addition, a commercially available 5000 mAh lithium-ion battery was used as Comparative Example 3. Charge and discharge tests were conducted on the lithium-ion batteries of Example 1, Example 2, Comparative Example 1, Comparative Example 2, and Comparative Example 3.

[0084] Figure 8 shows the discharge characteristics (rate characteristics) of Example 1, Example 2, Comparative Example 1, Comparative Example 2, and Comparative Example 3. For those with short aluminum fibers A mixed in, since the internal resistance is low, the thickness of the active material layer of the electrode can be increased to 2 to 3 times the normal thickness. The active material layer is a layer having short fibers A, active material powder 20, conductive assistant 30, and binder B, and does not include the current collector foil. As described above, this time, the positive electrodes of Example 1 and Example 2 were fabricated with a thickness about 1.7 times that of Comparative Example 2. As shown in Figure 8, the discharge capacity (charge capacity) per unit area of Example 1 depends on the discharge current (charge current) compared with that of Comparative Example 2, but when the discharge current (charge current) is 2 mA / cm 2 it becomes about twice, and it can be seen that when the discharge current (charge current) is 3 mA / cm 2 it becomes about 1.75 times.

[0085] As described above, since the thicknesses of the positive electrodes of Example 1 and Example 2 are about 1.7 times that of the positive electrode of Comparative Example 2, it can be seen that the battery characteristics of Example 1 and Example 2 shown in Figure 8 are excellent. In addition, as shown in Figure 8, as the discharge current (charge current) increases, the discharge capacity (charge capacity) tends to decrease. This is common as the characteristics of a secondary battery. That is, when discharging or charging rapidly, the discharge capacity or charge capacity decreases.

[0086] The positive electrode foil of the commercially available lithium-ion battery of Comparative Example 3 has a positive electrode containing an active material formed on an aluminum foil of about 1800 cm 2 . Dividing 5000 mAh by 1800 cm 2 gives about 2.78 mAh / cm 2 . As shown in Figure 8, it can be seen that the nominal capacity of 5000 mAh of the commercially available lithium-ion battery of Comparative Example 3 is realized when the discharge current (charge current) is 0.2 mA / cm 2 . For example, when it is 2 mA / cm 2When charging and discharging the commercially available lithium-ion battery of Comparative Example 3 at (0.72C), charging and discharging are repeated with a maximum capacity of about 3470 mAh. On the other hand, in the lithium-ion battery of Comparative Example 2 using commercially available positive and negative electrode foils at the same current, the capacity is about 3870 mAh. Further, in the lithium-ion battery of Example 1, the capacity is about 7920 mAh, and charging and discharging can be performed with a high capacity.

[0087] That Examples 1 and 2 are excellent is also clear from the comparison with Comparative Example 1. That is, the discharge capacity (charge capacity) per unit area of Example 1, compared with that of Comparative Example 1, is 1.2 to 1.3 times when the discharge current (charge current) is 2 mA / cm 2 and is also 1.2 to 1.3 times when the discharge current (charge current) is 3 mA / cm 2 . As described above, the thicknesses of the positive electrodes of Example 1, Example 2, and Comparative Example 1 are equivalent.

[0088] When the electrode of the present embodiment is used, the thickness dimension of one electrode can be increased. With this configuration, it is possible to increase the discharge capacity (charge capacity) while reducing the weight and volume of the entire battery.

[0089] FIG. 9 shows the cycle characteristics of the lithium-ion battery of Example 1 measured with a current of 2 mA / cm during charging and discharging. The lithium-ion battery of Example 1 containing aluminum fibers shows a decrease in discharge capacity (charge capacity) at the initial stage, but seems to settle at about 4.3 mA / cm 2 . 2

[0090] Thus, the lithium-ion battery manufactured using the aluminum or copper short fiber A of this embodiment can have a discharge capacity (charge capacity) approximately twice that of a lithium-ion battery using a commercially available electrode foil. As in Comparative Example 1, simply increasing the thickness dimension of the positive electrode or the negative electrode does not result in an improvement in characteristics proportional to the increase in thickness. However, the positive electrode or the negative electrode of this embodiment using the aluminum or copper short fiber A can obtain characteristics proportional to or greater than the increase in thickness. The thickness of the positive electrodes of Examples 1 and 2 excluding the thickness of the aluminum foil is 155 μm, compared to 90 μm of the positive electrode of Comparative Example 2, which is the normal electrode thickness. Examples 1 and 2 are 1.7 times or more that of Comparative Example 2. That is, by incorporating the short fiber A into the electrode as described above, while making the thickness of the electrode 120 μm or more, more preferably 150 μm or more, and even more preferably 200 μm or more, characteristics proportional to or greater than the increase in thickness can be obtained.

[0091] As shown in FIG. 10, the internal resistance of a battery having an electrode containing aluminum or copper short fiber A is lower than that of a battery having an electrode not containing short fiber A. It is considered that the reduction of the internal resistance of the battery having an electrode containing the short fiber A in this way leads to the improvement of the characteristics of Examples 1 and 2. FIG. 10 shows the internal resistance of the batteries having the positive electrodes of Example 3, Example 4, and Example 5 and the internal resistance of the battery having the positive electrode of Comparative Example 1.

[0092] Example 3 is obtained by setting the weight ratio of the aluminum short fiber A in the positive electrode to 1.22% by weight in Example 1. Example 4 is obtained by setting the weight ratio of the aluminum foil short fiber A in the positive electrode to 4.88% by weight in Example 1. Further, Example 5 is obtained by setting the weight ratio of the aluminum foil short fiber A in the positive electrode to 9.75% by weight in Example 1. The weight ratios of the active material powder 20, the conductive assistant 30, and the binder B in Example 3, Example 4, and Example 5 change slightly with respect to those in Example 1 according to the increase or decrease of the short fiber A.

[0093] As shown in FIGS. 8 and 10, when an electrode containing short fiber A as in this embodiment is used, if the discharge capacity (charge capacity) is the same, charging and discharging can be performed at a speed twice or more as fast. Also, in Example 2 where carbon fiber CF was added, the discharge capacity (charge capacity) is larger than that of Example 1. Further, as shown in FIG. 10, even in Example 5 in which 9.75% by weight of short fiber A was blended, the internal resistance was considerably improved compared to Comparative Example 1. Therefore, even if the blending ratio of short fiber A is less than 9.5% by weight, there is a possibility of obtaining an effect on the normal electrode of Comparative Example 1.

[0094] Thus, the electrode of this embodiment can obtain characteristics proportional to or more than the increase in thickness. For example, when a battery is made by laminating a plurality of positive electrode foils and a plurality of negative electrode foils, and aluminum foil and copper foil are used as current collectors for each positive electrode foil and each negative electrode foil, respectively, the number of aluminum foils and copper foils required to make a battery of the same capacity is reduced. This contributes to space saving of the battery, weight reduction of the battery, reduction of the manufacturing cost of the battery, etc.

[0095] Note that short fiber A can also be produced by a method other than the coil cutting method. For example, short fiber A can be formed by a chatter vibration cutting method in which a cutting tool is applied to a columnar member of aluminum or copper having a circular cross section, a milling method, or the like.

[0096] Also, it is possible to create short fiber A having the above length by blowing out a molten metal such as aluminum into the space from a fine hole. For example, as shown in FIG. 11, molten aluminum is prepared in a sealed container 40 into which the base end portion of a bent tube 41 made of ceramic, stainless steel, etc. with a bent tip is inserted. With the tip portion of the bent tube 41 protruding outside the sealed container 40, when air or an inert gas or the like is injected from a gas introduction tube 40a to increase the pressure inside the sealed container 40, the molten aluminum rises from the rear portion of the bent tube 41 and reaches the tip portion.

[0097] If a nozzle 42 having a plurality of micropores 42a with a pore diameter of several μm to several mm is set at the opening 41a at the tip of the bent pipe 41, the molten aluminum blows out from the micropores 42a into the space. As this aluminum, it is preferable to use one with a purity of 99.9% or more for facilitating the processing, and more preferably one with a purity of 99.99% or more for facilitating the processing, but it is also possible to form an alloy with other metals. The space may be filled with air, may be filled with an inert gas such as nitrogen, or may be filled with other gases. Note that the pipe 41 may not be bent, and the tip of the pipe 41 may face downward.

[0098] In the example of Fig. 11, the nozzle 42 is arranged so that aluminum blows out in a substantially horizontal direction, but aluminum may also be blown out in other directions such as downward. Thereby, the aluminum discharged from the micropores 42a of the nozzle 42 is cooled while flying in the space and becomes the short fiber A of aluminum. In the case where it is a long fiber in the state blown out from the nozzle 42, the long fiber can be cut by the above-described method to produce the short fiber A.

[0099] Note that when each of the above-described electrodes is formed using the short fiber A obtained by blowing a molten metal such as aluminum from the micropores into the space, the effects described below can be obtained. The short fiber A produced as described above has a shape having a large diameter portion A1 and a small diameter portion A2 as shown in Fig. 12 depending on 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 a diameter 1.5 times or more that of the small diameter portion A2. That is, the large diameter portion A1 is a portion having a diameter 1.5 times or more that of the small diameter portion A2. In one example, the length of the large diameter portion A1 is shorter than 5 times the average diameter of the small diameter portion A2, and more preferably shorter than 3 times. In Fig. 12, a plurality of large diameter portions A1 and a plurality of small diameter portions A1 alternately exist in one short fiber A, but there may also be a case where one short fiber A has a single large diameter portion A1 and a single small diameter portion A2. In one example, the average diameter of the small diameter portion A2 is 10 μm or more and 30 μm or less. Note that it is also possible to form a short fiber A having a large diameter portion A1 and a small diameter portion A2 using other metals.

[0100] When the electrodes of the above embodiments are fabricated using the short fiber A, the large-diameter portion A1 of the short fiber A is likely to be exposed on the surface of the electrodes. This is advantageous in reducing the resistance between the short fiber A and the current collector foil in the electrode foil. Also, when fabricating an electrode without using a current collector foil, the large-diameter portion A1 of the short fiber A is likely to be exposed on the surface of the electrode foil, so that when attaching a terminal or the like to the electrode foil, the resistance between the terminal and the electrode foil becomes small. Note that when using the short fiber A, it is expected that the electrode exhibits good functions even if the blending ratio of the short fiber in the electrode is 8% by weight or more.

[0101] The above disclosure is supplemented as follows. (Embodiment in a lithium-ion battery) The method for manufacturing an electrode of the power storage device according to the first aspect of the present invention includes a step of kneading a short fiber A of a metal (mainly aluminum or copper), an active material powder 20, a conductive assistant 30, and a binder B with a kneader to create a slurry S, a forming step of applying and molding the slurry S onto a predetermined metal foil (current collector foil), and a drying step of drying the slurry S formed into the predetermined shape to form an electrode in which the short fiber A of aluminum or copper functions as a current collector and a structural body. Functioning as a structural body means maintaining a state in which particles such as the active material powder 20 and the conductive assistant 30 are held together with the short fiber A on the electrode foil. In an electrode foil that does not contain the short fiber A, when the electrode foil is bent, particles tend to peel off from the electrode foil. In contrast, in an electrode foil containing the short fiber A, when the electrode foil is bent, the short fiber A also bends flexibly, and the short fiber A prevents the particles from falling off.

[0102] In the above embodiment, after performing the pre-drying or after drying the slurry formed into a predetermined shape, when performing the pressurization or pressing by a rolling mill as described above, the short fibers A of aluminum or copper are connected to each other, or the short fiber A is entangled with the active material powder 20 or the conductive assistant 30. This step and structure are also advantageous for significantly improving the internal resistance of the active material layer and making the thickness of the electrode twice, three times, etc. that of a commercially available electrode.

[0103] (Embodiments in an electric double layer capacitor and an all-solid-state battery) The embodiments in these devices are similar. In the case of an electric double layer capacitor, an adsorbent powder of activated carbon is used instead of the active material powder 20. In the case of an electric double layer capacitor, a slurry S in which the adsorbent powder, the conductive aid 30, and the binder B are mixed with the short fiber A is used. In the case of an all-solid-state battery, a solid electrolyte is used instead of the liquid electrolyte.

Explanation of symbols

[0104] 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 material powder 30 Conductive aid A Short fiber A1 Large-diameter part A2 Small-diameter part B Binder S Slurry CF Carbon fiber

Claims

1. An electrode for a power storage device, comprising: copper short fibers having an average length of 5 mm or less formed using a cutting tool; and an adsorbent powder to which electrolyte ions are adsorbed during charging or an active material powder that undergoes a chemical reaction during charge and discharge. The electrode for a power storage device, wherein the weight ratio of the short fibers is 1% by weight or more and less than 9.75% by weight.

2. The electrode has an active material layer including the short fibers and the adsorbent powder or the active material powder. The electrode for a power storage device according to Claim 1, wherein the average thickness of the active material layer is 120 μm or more.

3. A fiber production step of obtaining long metal fibers of aluminum or copper; A cutting step of cutting the long metal fibers so that the average length becomes 5 mm or less, with the bundle of the long metal fibers pressed against a predetermined surface using a pressing member or with the bundle of the long metal fibers disposed in a tube; A slurry production step of producing a liquid or gel-like slurry including the aluminum or copper short fibers produced by the cutting step, an adsorbent powder to which electrolyte ions are adsorbed during charging or an active material powder that undergoes a chemical reaction during charge and discharge, and a binder; A forming step of forming the slurry into a predetermined shape; A drying step of forming an electrode including the short fibers by drying the slurry formed into the predetermined shape. The method for manufacturing an electrode for a power storage device includes: In the slurry production step, mixing the short fibers into the slurry so that the weight ratio of the short fibers to the entire electrode after drying by the drying step is 1% by weight or more and less than 9.75% by weight.

4. In the cutting step, cutting the bundle of the long metal fibers together with the pressing member or the tube. The method for manufacturing an electrode for a power storage device according to Claim 3.

5. The method for manufacturing an electrode for a power storage device according to Claim 3 or 4, wherein the pressing member is a plastic film.

6. Forming short fibers made of copper or aluminum with an average length of 5 mm or less using a cutting tool, A slurry preparation step of preparing a liquid or gel-like slurry containing the formed short fibers, an adsorbent powder to which electrolyte ions are adsorbed during charging, or an active material powder that undergoes a chemical reaction during charge and discharge, and a binder, A forming step of forming the slurry into a predetermined shape, A drying step of forming an electrode containing the short fibers by drying the slurry formed into the predetermined shape, and having, In the slurry preparation step, a method for manufacturing an electrode of a power storage device in which the short fibers are mixed into the slurry so that the weight ratio of the short fibers to the entire electrode after drying by the drying step is 1% by weight or more and less than 9.75% by weight. The method for manufacturing an electrode of a power storage device according to claim 6, wherein an electrode having an average thickness of the active material layer containing the short fibers and the adsorbent powder or the active material powder of 120 μm or more is formed.

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