Method for manufacturing an electrode for an electric storage device, method for manufacturing short fibers for an electrode for an electric storage device, short fibers for an electrode for an electric storage device contained in a container, and electrode for an electric storage device

Abstract

To provide a manufacturing method of an electrode, capable of re-cutting an inner resistance and preventing an active material from being peeled from a collector by an expansion constriction.SOLUTION: A manufacturing method of an electrode of a power storage device, includes: a fiber creation step of obtaining aluminum or copper metal fiber; a mixing step of dropping the metal fiber or the metal fiber cut with a predetermined cutting tool into a solvent, and shortening a mean length of the metal fiber to 0.8 mm or less by mixing the solvent; a formation step of forming, into a predetermined shape, a liquid-like or gel-like slurry containing aluminum-made or copper-made short fiber A generated by the mixing step, a suction material powder sucked by electrolyte ions at charging, or an active material powder 20 which is chemically reacted at charging and discharging, and a binder B; and a drying step of forming an electrode including the short fiber 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 for an electricity storage device, a method for manufacturing short fibers for an electrode for an electricity storage device, short fibers for an electrode for an electricity storage device contained in a container, and an electrode for an electricity storage device. [Background technology]

[0002] Capacitors and secondary batteries are used in a variety of fields with the aim of reducing energy consumption and preventing global warming. In particular, the adoption of electrical energy in the automotive industry has accelerated development to further improve their performance. Electric double layer capacitors have conventionally been used to back up memories in electronic circuits to which low voltages are applied, and have higher input / output reliability than secondary batteries.

[0003] For this reason, in recent years they have been used in power generation using natural energy such as solar and wind power, as well as in construction machinery, power supplies for momentary sags, and regenerative power supplies for trains. Their use in automobiles has also been considered, but the characteristics and cost did not meet the requirements, and their use in this field was not realized until recently. However, electric double layer capacitors are now being used in electronically controlled brake systems, and their use as backup power sources for automotive electrical components, as starting energy supplies for idling stop systems, brake control, power assist, and more is being considered.

[0004] An electric double layer capacitor is structured to consist of positive and negative electrodes, an electrolyte, and a separator that prevents short-circuiting between the opposing positive and negative electrodes. The electrodes are formed by applying multiple layers of a mixture of polarizable electrodes (currently mainly activated carbon), a binder to hold the activated carbon, and a conductive additive (mainly fine carbon particles) onto an aluminum foil (approximately 20 μm thick) that serves as a current collector. Such an electric double layer capacitor is disclosed, for example, in Patent Document 1.

[0005] Charging of an electric double layer capacitor is achieved by electrolyte ions moving through the solution and adsorbing and desorbing onto the microporous surface of the activated carbon. An electric double layer is formed at the interface between the activated carbon powder and the electrolyte. For reference, the particle size of normal activated carbon is, for example, about 4 to 8 μm, and the specific surface area is, for example, 1600 to 2500 m 3 The electrolyte contains cations, anions, and a solvent, with tetraethylammonium salts used as cations, tetrafluoroborate ions used as anions, and propylene carbonate or ethylene carbonate used as the solvent.

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

[0007] Charging and discharging are carried out by the movement of lithium ions between the positive and negative electrodes. When charging, lithium ions move from the positive electrode to the negative electrode, and charging is completed when the positive electrode runs out of lithium ions or the negative electrode can no longer store lithium ions. When discharging, the opposite occurs.

[0008] Lithium-ion batteries (LiBs) have been the most widely used in recent years, but the electrolyte salt (usually LiPF6) contained in the electrolyte solvent is a flammable liquid, posing a risk of fire and leakage. Furthermore, this organic electrolyte is said to cause decomposition of anions and various foreign molecules at the interface with the positive electrode, shortening the lifespan of LiBs. Therefore, attempts have been made to replace the electrolyte with a solid electrolyte. Such batteries are called all-solid-state batteries because the positive electrode layer, negative electrode layer, and electrolyte layer are all solid. While the term all-solid-state battery is not limited to the materials used in LiBs, the term is often used to refer to all-solid-state LiBs, as there is currently much research being done on solidifying the electrolyte in LiBs.

[0009] The advantages of all-solid-state batteries include safety because the electrolyte layer is flame-retardant, a longer lifespan because only lithium ions move through the electrolyte layer, making side reactions with anions and solvent molecules less likely to occur, and a wider operating temperature range because the electrolyte layer is not liquid.

[0010] Furthermore, when trying to obtain a high-capacity, high-voltage battery using LiB, multiple individual cells must be connected together. However, by using a solid electrolyte layer, it is possible to simply stack the positive electrode layer, the solid electrolyte layer, and the negative electrode layer in that order, which has the advantage of making it possible to produce a battery with a high energy density.

[0011] The performance of these devices is all determined by the exchange of ions and electrons. Therefore, the electrical capacity, charge / discharge speed, and lifespan of the device depend on how smoothly and continuously the exchange of electrons can be carried out.

[0012] On the other hand, in all-solid-state batteries, where the electrolyte in lithium-ion batteries has been solidified, charging and discharging is performed by the insertion and removal of Li. For example, in Patent Document 3, a conductive elastic body is placed between the cells to suppress expansion and contraction, in Patent Document 4, a buffer layer is provided around the battery, and in Patent Document 5, various measures are taken, such as controlling the porosity. Electrodes using a current collector made of metal fibers are also known. For example, Patent Documents 6 and 7 are cited. [Prior art documents] [Patent documents]

[0013] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-086113 [Patent Document 2] Japanese Patent Application Laid-Open No. 2007-123156 [Patent Document 3] Japanese Patent Application Laid-Open No. 2008-311173 [Patent Document 4] Japanese Patent Application Laid-Open No. 2015-111532 [Patent Document 5] Patent No. 5910737 [Patent Document 6] Patent No. 6209706 [Patent Document 7] Japanese Patent Application Laid-Open No. 2018-106846 Summary of the Invention [Problem to be solved by the invention]

[0014] (Challenges with electric double layer capacitors) Electric double layer capacitors differ from secondary batteries, mainly lithium-ion batteries, in that they do not involve chemical reactions, have a short charge storage time, and a fast current release time. Furthermore, in terms of energy density, electric double layer capacitors are only a few tens of Wh / L, compared to several hundred Wh / L for lithium batteries, which is an order of magnitude lower. It is because of these differences that electric double layer capacitors are being considered for use not only in energy storage, but also as backup power sources for electrical equipment, as starting energy for idling stop systems, for brake control, and as power assist.

[0015] In recent years, electric double layer capacitors have been developed for use in large-capacity power devices such as electric vehicles and energy power generation. However, in order to efficiently transfer large amounts of energy into and out of the capacitor, it is necessary to increase the capacitance and reduce the internal resistance of the electrodes.

[0016] (Issues with lithium-ion batteries) On the other hand, secondary batteries, primarily lithium-ion batteries, have a relatively high energy density and can be used for long periods of time, making them suitable for use in a variety of fields, including mobile devices. In recent years, they have come to be used in automobiles, heavy machinery, energy, and other fields, and there is a demand for larger batteries to increase capacity. However, increasing battery size presents many challenges, including capacity, charging speed, lifespan, reliability, and manufacturing difficulties. For example, the capacity of a battery used in a mobile phone is approximately 15 Wh, while the capacity of a battery used in a hybrid vehicle is several tens to hundreds of kWh. The difference between the two is several thousand times, resulting in the aforementioned challenges.

[0017] The reaction in lithium-ion batteries is a reversible chemical reaction, and the active material expands and contracts when the electrodes are charged and discharged. This causes the active material to peel off from the current collector, degrading the charge and discharge characteristics. In other words, the battery does not always charge and discharge at the same rate, resulting in a decrease in charge and discharge capacity. In hybrid and electric vehicles, batteries are used for many years, so it is necessary to prevent the peeling of the active material from the current collector in order to prevent the above-mentioned deterioration.

[0018] Furthermore, one of the biggest issues with lithium-ion batteries is their internal resistance. Internal resistance can be thought of as the resistance to lithium ions moving through the electrolyte between the positive and negative electrodes inside the battery, or the resistance to the exchange of electrons between materials. In other words, it is caused by the adhesion between materials, the exchange of electrons between them, and the ease with which lithium ions flow through the electrolyte. In order to increase the size, i.e., the capacity, by applying a large amount of active material to the current collector, the capacity increases, but the resistance to lithium ion migration increases, so there is a limit to the thickness of the active material layer. As the active material layer becomes thicker, its internal resistance slows down the charge / discharge rate. Reducing the coating thickness reduces the internal resistance and increases the charge / discharge rate, but reduces the capacity. For this reason, capacity is increased by stacking multiple current collectors (electrode foils) coated with active material or by increasing the area of ​​the current collectors coated with active material.

[0019] The speed of charging and discharging is also related to the amount of lithium ions generated. If more ions can be generated and moved at once, the charging and discharging speeds will be faster. Since the chemical reaction in a secondary battery occurs at the interface between the electrolyte and the active material, increasing the contact area between the electrode and electrolyte will also improve the charging and discharging speeds.

[0020] To reduce internal resistance, improvements are currently being made to additives, conductive additives, and active materials, as well as pre-coating carbon particles on the current collector. The shape of the current collector has also been improved, as mentioned above, by making it as thin as possible and by forming fine holes in the foil to increase the surface area. Similarly, research and development is being conducted on electric double layer capacitors, with improvements being made to activated carbon and additives, and increasing the contact area between the current collector and the active material layer.

[0021] (Challenges for all-solid-state batteries) On the other hand, all-solid-state batteries, which use a solidified electrolyte solution in lithium-ion batteries, are charged and discharged by Li intercalation and deintercalation. During this process, the host crystal lattice repeatedly expands and contracts. If the resulting volume change is large, contact between the particles of the active material, solid electrolyte, and conductive additive is severed, reducing the amount of effective active material. In the case of all-solid-state batteries, even repeated charge and discharge at a current of about one-tenth to two-tenths of the battery capacity results in the intercalation and deintercalation of nearly one mole of Li, and the volume expansion and contraction rate reaches nearly 10%. For this reason, various methods have been proposed to suppress this expansion and contraction.

[0022] Thus, in order to solve the problem of increasing capacity in electricity storage devices, if the internal resistance can be reduced and in all-solid-state batteries, peeling of the active material from the current collector due to expansion and contraction can be prevented, there is a possibility of significant improvement. [Means for solving the problem]

[0023] Therefore, the present inventors have discovered a method for further finely grinding fibers to a length of about several millimeters during stirring in the production of electricity storage devices, and have also found that using this method can improve the characteristics of electricity storage devices.Furthermore, they have found that electricity storage devices can also be improved by using powdered metal produced by atomizing metal powder, which is produced by spraying molten metal through fine holes.

[0024] A method for manufacturing an electrode for an electricity storage device according to a first aspect of the present invention includes a fiber preparation step of obtaining aluminum or copper metal fibers; a stirring step of placing the metal fibers or the metal fibers cut with a predetermined cutting tool in a solvent and stirring the solvent to shorten the metal fibers to an average length of 0.8 mm or less; a forming step of forming a liquid or gel slurry containing the aluminum or copper short fibers produced by the stirring step, an adsorbent powder that adsorbs electrolyte ions during charging or an active material powder that chemically reacts during charging and discharging, and a binder 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.

[0025] A second aspect of the present invention relates to a method for producing short fibers for use in electrodes of an electricity storage device, the method comprising the steps of: a fiber preparation step of obtaining aluminum or copper metal fibers; a stirring step of placing the metal fibers or the metal fibers cut with a specified cutting tool in a solvent and stirring the solvent to shorten the metal fibers to an average length of 0.8 mm or less; and a shipping step of shipping the aluminum or copper short fibers produced by the stirring step in the solvent or another solvent.

[0026] The third aspect of the present invention provides short fibers for electrodes of an electricity storage device contained in a container, which comprises a solvent containing aluminum or copper short fibers having an average length of 0.8 mm or less, and a container that is resistant to the solvent and that accommodates the solvent.

[0027] The fourth aspect of the present invention provides an electrode for an electricity storage device comprising short aluminum or copper fibers having an average length of 0.8 mm or less, and an adsorbent powder that adsorbs electrolyte ions during charging or an active material powder that undergoes a chemical reaction during charging and discharging, wherein the weight ratio of the short fibers is less than 9.75% by weight.

[0028] An electrode for an electricity storage device according to a fifth aspect of the present invention is an electrode for an electricity storage device comprising a metal powder having an average particle size of 0.1 mm or less, and an adsorbent powder to which electrolyte ions are adsorbed during charging or an active material powder that undergoes a chemical reaction during charging and discharging, wherein the weight ratio of the metal powder is less than 9.75% by weight. An electrode of an electricity storage device according to a sixth aspect of the present invention is an electrode of an electricity storage device including a mixture of aluminum or copper fibers and metal powder having an average particle size of 0.1 mm or less, and an adsorbent powder to which electrolyte ions are adsorbed during charging or an active material powder that undergoes a chemical reaction during charging and discharging, The weight ratio of the mixture is less than 9.75% by weight. [Effects of the Invention]

[0029] The present invention contributes to improving battery performance by using the short fibers and metal powder described above. [Brief explanation of the drawings]

[0030] [Figure 1] FIG. 2 is a cross-sectional image diagram of an electrode according to one embodiment of the present invention. [Figure 2] FIG. 10 is a cross-sectional image diagram of another electrode according to the present embodiment. [Figure 3] 1 is an electron microscope photograph of short fibers of the present embodiment. [Figure 4] 1 is an electron microscope photograph of the metal powder of the present embodiment. [Figure 5] 1 is a schematic diagram showing a method for producing a slurry according to an embodiment of the present invention. [Figure 6] FIG. 1 is a schematic cross-sectional view of an all-solid-state battery using the electrode of the present embodiment. [Figure 7]1 is a graph showing the characteristics of a lithium ion battery using an electrode according to an embodiment of the present invention. [Figure 8] 1 is a graph showing the cycle characteristics of a lithium ion battery using an electrode according to an embodiment of the present invention. [Figure 9] 1 is a graph showing the characteristics of a lithium ion battery using the electrode of the present embodiment. [Figure 10] 1 is a graph showing the characteristics of a lithium ion battery using an electrode according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0031] An electrode and an electricity storage device according to an embodiment of the present invention will be described below with reference to the drawings. Note that the description will be made mainly using a lithium ion battery as the electricity storage device. 1 and 2 show electrodes (positive or negative electrodes) containing aluminum or copper short fibers A having an average diameter of 50 μm or less. Instead of the short fibers A, metal powder made of aluminum, copper, or a metal having conductivity equal to or less than these may be mixed in. 1 and 2 are diagrams for clearly illustrating the configuration of this embodiment, and the size, thickness, length, and compounding ratio of the short fiber A, active material powder 20, conductive additive 30, carbon fiber CF, etc. differ from the actual size, thickness, length, and compounding ratio.

[0032] 1 and 2, this electrode comprises aluminum or copper short fibers A having an average wire diameter of 50 μm or less or metal powder having an average particle size of 0.1 mm or less, active material powder 20 that is held together with the short fibers A or metal powder by binder B and undergoes a chemical reaction during charge and discharge, and optionally comprises a conductive additive 30 held by binder B. Note that when the metal powder is used instead of the short fibers A, in FIGS. 1 and 2, the metal powder will be present in place of the short fibers A, but because the shape of the metal powder is different from that of the short fibers A, the presence of the metal powder may be slightly different from that of the short fibers A.

[0033] [Short fiber molding] A bundle of metal long fibers (aluminum or copper long fibers, with an average fiber diameter of 50 μm or less, preferably 25 μm or less, and more preferably 20 μm or less) produced by the coil cutting method is sandwiched between a pair of paper or plastic films, each having a thickness of, for example, 0.1 mm to 0.3 mm, and the long fiber bundle is cut to a desired length. Specifically, the long fiber bundle is pressed against a predetermined surface using a pressing member made of plastic, thin metal foil, paper, or other thin material, and then the long fibers are cut using a cutting tool such as a cutting blade. In this embodiment, the predetermined surface is the upper surface of the plastic film, but it can also be the upper surface of a work table made of plastic, metal, or other thin material such as foil or paper. Preferably, the plastic film has a thickness of 1 mm or less. Alternatively, the long fiber bundle is placed inside a cylindrical plastic tube and then cut to a desired length. The wall thickness of the plastic tube is, for example, 0.1 to 0.3 mm, and preferably 0.5 mm or less. This allows for the production of metal fibers of a desired length, for example, 1 to 3 mm.

[0034] That is, the long fiber bundle is cut while being placed in a tubular member made of a thin material such as plastic, metal foil, or paper. The long fiber bundle may be cut together with the pressing member or the tubular member. This allows for stable and efficient cutting of the long fiber bundle. It is also preferable that the long fiber bundle be arranged relatively densely in the tubular member. There may also be cases where the long fiber bundle is cut without using a pressing member or a tubular member.

[0035] Here, in the coil cutting method, aluminum or copper foil is wound into a coil shape, and the end face of the coil is cut with a cutting tool to obtain long metal fibers (long metal fibers). The metal fibers of this embodiment or short fibers A described below may contain small amounts of other metals such as steel, stainless steel, brass, etc.

[0036] The metal fibers produced by the coil cutting method and cut as described above have a cross section with a side corresponding to the surface of the foil and a side cut with a cutting tool. The area between the side corresponding to the surface and the cut side forms a corner, a wide V-shaped cross section, a narrow V-shaped cross section, or a shape close to a V-shaped cross section. This is expected to facilitate the short fibers A pushing through the binder B and the like in each process described below, making contact with the active material powder 20, other short fibers A, etc. Alternatively, it is expected that the short fibers A will be able to easily penetrate into other short fibers A, active material powder 20, etc. The coil cutting method is a method for producing long fibers with a uniform shape by cutting a coiled metal foil from its end face. Therefore, the cross section of the fiber is a uniform shape, such as a square, rectangle, or trapezoid, that is the thickness of the foil and the cutting depth. Short fibers with uniform cross-sectional shape and length can improve battery performance. This method can also be applied to any metal that can be made into foil. This method can produce short fibers of any length as long as they can be cut, but it takes time, is difficult, and increases costs.Furthermore, there is a risk of explosion due to dust when handling the fine fibers. It is also possible to cut aluminum, copper, or the like by other methods such as chatter processing to produce the metal fibers or short fibers A. It is also possible to produce the metal fibers by using a melt-blowing method or the like that does not involve cutting.

[0037] The metal fibers obtained by the above process are placed in a planetary centrifugal mixer (mixing device) along with two or more ceramic balls with a diameter of 10 mm and a solvent (e.g., NMP) used in forming the following electrode. The planetary centrifugal mixer is then rotated at 1,000 rpm for a predetermined time (e.g., about 20 minutes) to agitate the solvent, thereby obtaining short fibers A having an average length of about 200 μm and a shape shown in Figure 3. The solvent may contain binder B described below, or may contain binder B described below and other ingredients described below. While the conditions vary depending on the type of metal, Figure 3 shows an SEM photograph of aluminum short fibers A.

[0038] The average length of the short fibers A is preferably 0.8 mm or less, more preferably 0.5 mm or less, and even more preferably 0.3 mm or less. Furthermore, as the stirring device, it is also possible to use a known stirring device that can accommodate the metal fibers and the solvent inside and can cut the metal fibers by rotating a rotating body such as a blade or inner container arranged inside. When the metal fibers are made of copper, it is possible to produce copper short fibers A by using a stirring device with a rotor such as a blade, ceramic balls, etc., without adding the solvent.

[0039] On the other hand, Figure 4 is an SEM photograph of aluminum metal powder formed by atomization. As shown in Figure 4, the metal powder formed by atomization has an irregular shape. Therefore, the particle size of each particle can be, for example, the maximum length of each particle, or the average of the maximum and minimum lengths. The average particle size can also be the average particle size of five randomly selected particles. Metals other than aluminum can also be powdered by atomization. Metal powders can also be produced by known methods other than atomization. The average particle size of the metal powder in Figure 4 is approximately 40 μm or 50 μm. Note that, to achieve the battery performance described below, the average particle size of the metal powder is preferably 10 μm or more, and more preferably 20 μm or more. To prevent clogging of the slurry applicator described below, the average particle size of the metal powder is preferably 80 μm or less, and more preferably 60 μm or less to more effectively prevent clogging. If the metal powder falls within these particle size ranges, it is expected that the metal powder will be easier to disperse in the slurry S. If the average particle size of the metal powder is 0.1 mm or less, it is possible to manufacture an electrode having the functions described below.

[0040] Furthermore, when a container containing a solvent containing short fibers A formed as described above is sold, it is possible to deliver the short fibers A to customers while preventing oxidation. This solvent may be the solvent that is added to the stirring device together with the metal fibers, or it may be another solvent. A purchaser of short fibers A in a container containing solvent can manufacture, for example, electrodes for an electricity storage device, as described below, using the short fibers A together with the solvent or the short fibers A removed from the solvent. When the solvent in the container is the solvent that is added to the stirring device together with the metal fibers, the solvent is used to manufacture electrodes, and therefore the solvent can also be used to manufacture electrodes for an electricity storage device.

[0041] [Electrode formation] To form the electrode shown in FIG. 1, as shown in FIG. 5, active material powder 20, conductive additive 30, and binder B are added to a solvent (NMP) containing short fibers A, and the mixture is stirred to form a liquid or gel-like slurry S. To prepare the slurry S, aluminum or copper short fibers A, active material powder 20, conductive additive 30, and diluted binder B are kneaded using a kneader or similar device. Instead of producing short fibers A using the stirring device, active material powder 20 and binder B can be added to a solvent containing the metal fibers and stirred to cut the metal fibers into short fibers A. The weight ratio of the active material powder 20, conductive additive 30, and binder B when dried is sufficient as long as it is approximately the same as that of commercially available secondary batteries. Hereinafter, the weight ratio (compounding ratio) refers to the weight ratio (compounding ratio) relative to the entire electrode (excluding the electrode foil) after drying in the drying process described below.

[0042] In this embodiment, the blending ratio of binder B is 1% by weight or more and less than 6% by weight, and preferably around 2 to 3% by weight. The blending ratio of short fiber A is preferably 1% by weight or more and less than 8% by weight. If the amount of short fiber A is too small, the effect on the internal resistance is small, and if the amount of short fiber A is too large, the internal resistance increases. In addition, if this range is exceeded, the weight per unit area (1 cm of current collecting foil) becomes too large. 2 This will result in a decrease in the active material powder (weight per unit area). The optimal blending ratio of short fiber A is 2.0% by weight or more and 5.5% by weight or less. It is considered that the blending ratio of short fiber A is most preferably 3.0% by weight or more and 5.5% by weight or less, but this blending ratio varies depending on the basis weight and the amount of binder. For example, when increasing the basis weight, it is better to increase the amount of short fiber A, and it is better to increase the amount of short fiber A as the amount of binder B is reduced. When preparing the electrode shown in Figure 2, carbon fiber CF is further added to the above to prepare slurry S. When carbon fiber CF is added, its blending ratio is preferably 1% by weight or more and less than 2% by weight. If the amount of carbon fiber CF is too small, the effect will not be seen, and if the amount of carbon fiber CF is too large, it may cause deterioration in cycle tests.

[0043] The aluminum or copper short fibers A have an average length of less than 1 mm, and the aluminum powder produced by atomization has an average particle size of 0.1 mm or less, so that they are easily mixed with other ingredients in the slurry S.

[0044] Next, the slurry S is applied to a current collector foil (aluminum foil or copper foil) to a predetermined thickness, followed by pre-drying, for example, to increase viscosity. Low-temperature drying may be followed by vacuum drying. This evaporates almost all of the solvent (e.g., NMP), resulting in a solidified active material via binder B. This is then press-molded to form a sheet with a positive or negative electrode placed on the current collector foil. This sheet is called an electrode foil, and the positive and negative electrodes are called positive and negative foils, respectively. If a current collector foil is not used, the slurry S can be applied to a separator. For example, the positive electrode slurry S is applied to one side of the separator in the thickness direction, and the negative electrode slurry S is applied to the other side of the separator in the thickness direction. The positive or negative electrode slurry S may be applied to only one side of the separator. The pre-drying dries the material until the binder B is not completely hardened, making it easier to form the electrode foil into the desired shape.

[0045] Furthermore, it is also possible to form the positive or negative electrode slurry S into a sheet in a predetermined mold without applying it to a current collector foil or a separator. In this case, the positive or negative electrode formed into a sheet is called an electrode foil.

[0046] The purity of the aluminum or copper of these short fibers A and metal powder is preferably 99% or more, more preferably 99.9% or more. When the above-mentioned aluminum or copper short fibers A or metal powder is used, the short fibers A or metal powder has a relatively low rigidity, so that they are slightly crushed by the active material 20 during press molding, and the active material 20 is deformed so as to bite into it.

[0047] That is, the short fibers A and the metal powder are flattened at the contacting portions, thereby bringing the short fibers A and the metal powder into closer contact with the active material powder 20, leading to a reduction in resistance to electron transfer. In one example, a drying step is performed in which the formed electrode foil is dried by vacuum drying or the like, thereby removing the moisture in the electrode and hardening the binder B, thereby completing the electrode.

[0048] [Cathode active material powder] The positive electrode active material powder 20 may be any material that can be held by short fibers A with binder B or the like, or that can be held by binder B hardened together with short fibers A, and is preferably one with excellent cycle characteristics. Examples of the positive electrode active material powder 20 include lithium cobalt oxide (LiCoO2), lithium iron phosphate (LiFePO4), lithium manganese oxide (LiMn2O4), and ternary materials containing mixtures thereof, which are commonly used in lithium ion batteries. It is also possible to use known active materials that are used for the positive and negative electrodes of secondary batteries.

[0049] [binder] Thermoplastic resins, polysaccharide polymer materials, etc. can be used as binder B. Examples of materials for binder B include polyacrylic resins, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), copolymers of vinylidene fluoride (VdF) and hexafluoropropylene (HFP), etc. It is possible to use known binders that are used in electrodes of secondary batteries and electric double layer capacitors.

[0050] [Conductive additive] The conductive additive 30 may be any material that is conductive, and is preferably a material that is not chemically changed by electrolytes or solvents. Examples include graphite and carbon black. It is also possible to use known conductive additives that are used in electrodes of secondary batteries and electric double layer capacitors.

[0051] [Negative electrode active material powder] Artificial graphite, natural graphite, and the like are used as the negative electrode active material powder 20. When these are used in the negative electrode, the operating potential on the negative electrode side is low, so when aluminum short fibers A or metal powder are used, a Li-Al reaction occurs. This causes a decrease in Li and rapid battery degradation. For this reason, aluminum short fibers A or metal powder cannot be used, and copper short fibers A or metal powder must be used. On the other hand, LTO (lithium titanate), which has been developed recently and has a higher reaction potential than the Li-Al reaction, can be used as the negative electrode active material powder 20. In this case, aluminum short fibers A or metal powder can be used as the negative electrode active material powder 20. It has been found that when aluminum short fibers A or metal powder is used in an amount of 1% by weight or more but less than 9.75% by weight, preferably less than 8% by weight, and more preferably 3.0% by weight or more but less than 5% by weight, the internal resistance can be significantly reduced when LTO or the like is used as the negative electrode active material powder 20.

[0052] [Applications for other devices] The above-described electrode manufacturing method and electrode can be applied to electrodes for 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, positive and negative electrodes for capacitors such as electric double-layer capacitors can be produced by kneading activated carbon, conductive additive 30, and diluted binder B, instead of active material powder 20, with short fiber A or metal powder. The material used in electric double-layer capacitors instead of active material powder 20 can also be considered an adsorbent powder that adsorbs electrolyte ions during charging and discharging. Well-known active material powders used in capacitors such as lithium-ion capacitors can also be used. Electrodes for all-solid-state batteries can be produced, for example, by kneading a solid electrolyte with active material powder 20, conductive additive 30, diluted binder B, and short fiber A or metal powder to form a slurry S (Figure 6). Note that electrodes such as those shown in Figures 1 and 2 can also be used in all-solid-state batteries.

[0053] 2, it is also possible to use a slurry S containing carbon fibers CF having 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 additive 30, and the binder B. In this case, as shown in FIG. 2, the carbon fibers CF are arranged between the short fibers A, and a synergistic effect can be expected in the exchange of electrons between the short fibers A or the metal powder and the active material powder 20.

[0054] The carbon fiber CF comes into contact with the short fiber A or metal powder, the active material powder 20, the conductive additive 30, and other carbon fiber CF. In this embodiment, the carbon fiber CF has 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. In one example, the resistivity of the carbon-based conductive additive 30 is 0.1 to 0.3 Ω·cm, while the resistivity of the carbon fiber CF is, for example, 5×10 -5 Ω·cm.

[0055] For example, even when the active material powder 20 and the short fibers A or the metal powder are not in direct contact with each other, the active material powder 20 and the short fibers A or the metal powder are electrically connected via the carbon fibers CF. Furthermore, even when the active material powder 20 and the short fibers A or the metal powder are in direct contact with each other, the connection by the carbon fibers CF further reduces the electrical resistance between the active material powder 20 and the short fibers A. In this way, the carbon fiber CF, which has good conductivity, can reduce the resistance to electron movement between the active material powder 20 and the short fiber A or metal powder, which is advantageous in reducing the resistance of electrons moving to the input / output terminals.

[0056] [Application to coin-type secondary batteries] The application to an electricity storage device will be exemplified below. Regarding application to a coin-type secondary battery, which is an electricity storage device, for example, it is possible to manufacture a coin-type battery using the short fiber A of the present application or metal powder instead of the blown fiber or chattered fiber in JP 2018-106846 A by using the structure described in JP 2018-106846 A.

[0057] [Application to stacked secondary batteries] In the case of a secondary battery in which a storage unit consisting of a positive electrode, a negative electrode, and a separator is stacked in multiple layers, the electrode structure of the above embodiment can be used for only the positive electrode, only the negative electrode, or both the positive electrode and the negative electrode, as in the coin-type secondary battery.

[0058] [Application to all solid-state batteries] The application to all-solid-state batteries will be described below. Hereinafter, an electricity storage device (all-solid-state battery) will be described using an example of an all-solid-state lithium ion battery. Note that this embodiment can be used for all-solid-state batteries such as all-solid-state sodium ion secondary batteries, all-solid-state magnesium ion secondary batteries, and air batteries using a solid electrolyte, or all-solid-state lithium ion batteries using a Si (silicon) negative electrode that undergo significant expansion and contraction.

[0059] An example of a schematic diagram of the structure of an all-solid-state battery is shown in Figure 6. An all-solid-state battery roughly comprises 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 aforementioned positive electrode, and the negative electrode layer 4 corresponds to the aforementioned negative electrode.

[0060] (current collecting foil) The positive electrode current collector 1 is generally a metal foil, and the metal foil can be made of aluminum, an alloy of multiple metals, or the like. Copper foil is generally used for the negative electrode current collector 5. When the negative electrode active material powder 20 is made of lithium titanate, aluminum foil can be used for the negative electrode current collector 5. In the case of all-solid-state batteries, conductive materials such as stainless steel (SUS) and cobalt-based alloys, which have high voltage resistance and corrosion resistance, other conductive materials, conductive ceramics, and the like may also be used.

[0061] (positive electrode layer) To increase discharge capacity, the material of the positive electrode active material powder 20 is preferably a substance that easily absorbs lithium ions, such as LiCoPO, LiCoO2, LiMnO4, or LiFePO4. If necessary, a conductive additive 30, a binder B, and a powdered solid electrolyte 14 such as an inorganic solid electrolyte or a polymer electrolyte for increasing ionic conductivity are added to prepare a slurry S, which is then sintered or pressure-molded to form the positive electrode layer 2. In this embodiment, the positive electrode layer 2 contains short fibers A or metal powder made of aluminum, copper, or the like.

[0062] (negative electrode layer) As with the positive electrode layer 2, the material of the negative electrode active material powder 20 is preferably a material that easily absorbs ions in order to increase the discharge capacity, such as LiFePO4, Li4Ti5O 12 , Li4Fe4(PO4)3, SiOx, Cu6Sn5, LiTiO4, etc. The negative electrode layer 4 is formed by mixing these active material powders 20, a conductive additive 30, a binder B, and a powdered solid electrolyte 24 such as an inorganic solid electrolyte or a polymer electrolyte to increase ionic conductivity to form a slurry S, and then sintering or pressure-molding the slurry S. In this embodiment, the negative electrode layer 4 contains short fibers A or metal powder made of aluminum, copper, etc.

[0063] In the case of the positive electrode layer 2 and the negative electrode layer 4 of the all-solid-state battery, the blending ratio of the short fibers A is 1% by weight or more and 9.75% by weight or less, preferably 1% by weight or more and less than 8% by weight, and optimally 3% by weight or more and 6% by weight or less. The blending ratio of the binder B is preferably 2% by weight or more and less than 5% by weight.

[0064] (Forming of positive electrode layer) First, a liquid or gel-like slurry S is prepared containing short fibers A or metal powder, active material powder 20 that chemically reacts during charge and discharge, conductive additive 30, binder B, and solid electrolyte 14. The slurry S is prepared by kneading a mixture of aluminum or copper short fibers A or metal powder, active material powder 20, conductive additive 30, diluted binder B, and solid electrolyte 14. During charge and discharge, 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 in which ions such as lithium ions are taken up by the active material powder 20.

[0065] Next, the slurry S is applied to a current collector or onto a predetermined mold or the like, and after drying at low temperature or vacuum drying, it is pressed to form an electrode sheet. The current collector (current collecting foil) coated with the slurry S is dried at low temperature and vacuum dried, and then the slurry S is passed through rollers to apply pressure to the slurry S, thereby forming the slurry S into a predetermined thickness according to the size of the electrode.The formed slurry S is then cut and formed into a predetermined shape (size).

[0066] The compounding 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 even more preferably 90% by weight or more. Among these, the compounding ratio of the active material powder 20 is preferably 70% by weight or more, and more preferably 75% by weight or more. Meanwhile, the compounding ratio of the solid electrolyte 14 is preferably 10% by weight or more, and more preferably 15% by weight or more. The compounding ratio of the short fibers 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 remaining components are the conductive additive 30, the binder B, the carbon fibers CF, etc.

[0067] (Forming of negative electrode layer) First, a liquid or gel-like slurry S is prepared containing short fibers A, active material powder 20 that chemically reacts during charging and discharging, conductive additive 30, binder B, and solid electrolyte 24. The slurry S is prepared by kneading a mixture of aluminum or copper short fibers A or metal powder, active material powder 20, conductive additive 30, diluted binder B, and solid electrolyte 24.

[0068] Next, the slurry S is applied to a current collector or onto a predetermined mold or the like, and after drying at low temperature or vacuum drying, it is pressed to form an electrode sheet. The current collector (current collecting foil) coated with the slurry S is dried at low temperature and vacuum dried, and then the slurry S is passed through rollers to apply pressure to the slurry S, thereby forming the slurry S into a predetermined thickness according to the size of the electrode.The formed slurry S is then cut and formed into a predetermined shape (size).

[0069] In the case of an all-solid-state capacitor that forms an electric double layer, it is also possible to use, in place of the active material powder 20, an adsorbent powder that adsorbs electrolyte ions during charging in the positive or negative electrode.

[0070] The compounding 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 even more preferably 90% by weight or more. Among these, the compounding ratio of the active material powder 20 is preferably 70% by weight or more, and more preferably 75% by weight or more. Meanwhile, the compounding ratio of the solid electrolyte 24 is preferably 10% by weight or more, and more preferably 15% by weight or more. The compounding ratio of the short fibers 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 remaining components are the conductive additive 30, the binder B, the carbon fibers CF, etc.

[0071] (Forming of solid electrolyte layer) A liquid or gel-like slurry is prepared by kneading a mixture containing the powdered solid electrolyte 34 and the binder B, and the slurry is then dried, pressed in a mold, pressed using a roller, or the like to obtain a solid electrolyte layer 3 having a predetermined thickness. The solid electrolyte layer 3 may be a known solid electrolyte layer. Alternatively, the solid electrolyte layer 3 may be a known gel-like solid electrolyte layer.

[0072] (Forming of storage element) The positive electrode layer 2, solid electrolyte layer 3, and negative electrode layer 4 prepared 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. If necessary, a positive electrode current collector 1 is stacked on the positive electrode layer 2, and a negative electrode current collector 5 is stacked on the negative electrode layer 4. This forms an electricity storage element BE consisting of the positive electrode layer 2, solid electrolyte layer 3, and negative electrode layer 4. An all-solid-state battery is formed by stacking the required number of electricity storage elements BE as shown in FIG. 6.

[0073] (solid electrolyte) The solid electrolytes 14, 24, and 34 are present throughout the battery, similar to the electrolyte solution in a lithium-ion battery (LiB), and transfer ions between the positive electrode layer 2 and the negative electrode layer 4. The solid electrolytes 14, 24, and 34 may be made of the following inorganic solid electrolytes or polymer solid electrolytes.

[0074] As inorganic solid electrolytes, nitrides, halides, and silicon compounds of Li (lithium) such as Li3N, LiI, Li3N-LiI-LiOH, LiSiO4, LiSoO4-LiI-LiOH, Li3PO4-Li4SiO4, and Li2SiS3 can be used. In addition, lithium-containing phosphate compounds with a Nasicon structure and compounds with the chemical formula Li x M y (PO4)3 can be used, where x is 1≦x≦2 and y is 1≦y≦2, and M can be a material composed of Al, Ti, Ge, Ga, etc. P can also be replaced with Si or B.

[0075] As the polymer solid electrolyte, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate ester polymers, etc. can be used. When short fibers A are uniformly dispersed in an electrode of an all-solid-state battery, the short fibers A structurally suppress large deformations within the electrode, and when the host crystal lattice repeatedly expands and contracts, the short fibers A prevent the active material powder 20 from losing contact with other components.

[0076] [Example] An example will be given below in which the above-mentioned metal fibers, which have been cut to a length of 1 to 3 mm as described above, are applied to the positive electrode of a lithium ion battery. The above metal fibers of aluminum and active material powder 20 (NMC; ternary Li (Ni a Mn b Co 1-a-b Slurry S was prepared using 02, a conductive additive 30 (AB; acetylene black), and a binder B (PVDF; vinylidene prefluoride) diluted with a solvent (NMP; normal methylpyrrolidone) in a weight ratio (weight ratio after drying) of 87:5:4:4 (active material powder 20:conductive additive 30:binder B:aluminum short fiber A). Then, a lithium-ion battery was fabricated using a positive electrode foil fabricated as described above by applying the slurry S to an aluminum foil, and a negative electrode foil without metal fibers such as short fiber A, using, for example, LiPF6 (lithium hexafluorophosphate) as the electrolyte (Example 1). Furthermore, a lithium-ion battery was also fabricated by adding 1.5 wt% of carbon fiber CF to the slurry S described above when fabricating the positive electrode of the lithium-ion battery of Example 1 (Example 2). By adding 1.5% by weight of carbon fiber CF, the weight ratio of the above metal fibers of active material powder 20:conductive additive 30:binder B:aluminum becomes approximately 85.8:4.9:3.9:3.9.

[0077] Furthermore, a lithium ion battery was also produced in which the aluminum or copper metal fibers were not added to the slurry S when preparing the positive electrode in the lithium ion battery of Example 1 (Comparative Example 1). By not adding the metal fibers, the weight ratio of active material powder 20:conductive additive 30:binder B was approximately 90.6:5.2:4.2.

[0078] To produce the negative electrode foils of Examples 1 and 2 and Comparative Example 1, first, a slurry S was prepared using active material powder 20 (natural spherical graphite), conductive additive 30 (AB; acetylene black), and binder B (PVDF; vinylidene prefluoride) diluted with a solvent (NMP; normal methylpyrrolidone) in a weight ratio of 90:5:5 (active material powder 20:conductive additive 30:binder B). The slurry S was then applied to copper foil to produce the negative electrode foils as described above.

[0079] A lithium-ion battery was also fabricated using commercially available positive and negative electrode foils (Comparative Example 2). These positive and negative electrode foils are said to have high performance among commercially available positive and negative electrode foils. The material of the positive electrode active material powder in Comparative Example 2 was the same as the material of the active material powder 20 in Examples 1, 2, and Comparative Example 1, and the material of the negative electrode active material powder in Comparative Example 2 was the same as the material of the active material powder 20 in Examples 1, 2, and Comparative Example 1.

[0080] To fabricate the lithium-ion batteries of Example 1, Example 2, Comparative Example 1, and Comparative Example 2, the positive and negative electrode foils were cut to a predetermined size, a separator made of polypropylene was sandwiched between the positive and negative electrode foils, and these were housed in a battery container made of a laminated sheet of plastic material. The electrolyte was poured into the battery container, and the battery container was sealed to fabricate the lithium-ion batteries of Example 1, Example 2, Comparative Example 1, and Comparative Example 2. The sizes of the positive and negative electrode foils, the size and thickness of the separator, and the capacity of the battery container were substantially the same for Example 1, Example 2, Comparative Example 1, and Comparative Example 2.

[0081] The average thickness of the positive electrodes (average thickness of the positive electrode layer) of Example 1, Example 2, and Comparative Example 1, excluding the thickness of the aluminum foil (collector foil), is approximately 155 μm, and the thickness of the aluminum foil of the positive electrodes of Example 1, Example 2, and Comparative Example 1 is approximately 15 μm. The average thickness of the positive electrode (average thickness of the positive electrode layer) of Comparative Example 2, excluding the thickness of the aluminum foil (collector foil), is approximately 90 μm, and the thickness of the aluminum foil of the positive electrode of Comparative Example 2 is approximately 15 μm. The average thickness of the negative electrodes (average thickness of the negative electrode layer) of Example 1, Example 2, Comparative Example 1, and Comparative Example 2, excluding the thickness of the copper foil (collector foil), is approximately 85 μm, and the thickness of the copper foil of the negative electrodes of Example 1, Example 2, Comparative Example 1, and Comparative Example 2 is approximately 15 μm.

[0082] In addition, a commercially available 5000 mAh lithium ion battery was used as Comparative Example 3. Charge and discharge tests were carried out on the lithium ion batteries of Example 1, Example 2, Comparative Example 1, Comparative Example 2, and Comparative Example 3.

[0083] FIG. 7 shows the discharge characteristics (rate characteristics) of Example 1, Example 2, Comparative Example 1, Comparative Example 2, and Comparative Example 3. Because aluminum containing the above-mentioned metal fibers has low internal resistance, the active material layer of the electrode can be made two to three times thicker than usual. The active material layer is a layer containing short fibers A, active material powder 20, conductive additive 30, and binder B, and does not contain a current collecting foil. As mentioned above, the positive electrodes of Examples 1 and 2 were fabricated with a thickness approximately 1.7 times that of Comparative Example 2. As shown in Figure 7, the discharge capacity (charge capacity) per unit area of ​​Example 1 is higher than that of Comparative Example 2 when the discharge current (charge current) is 2 mA / cm, although this depends on the discharge current (charge current). 2 When the discharge current (charge current) is 3mA / cm 2 It can be seen that the value is approximately 1.75 times higher when

[0084] As mentioned above, the thickness of the positive electrodes of Examples 1 and 2 is about 1.7 times that of the positive electrode of Comparative Example 2, and therefore it can be seen that the battery characteristics of Examples 1 and 2 shown in FIG. 7 are excellent. As shown in Figure 7, the discharge capacity (charge capacity) tends to decrease as the discharge current (charge current) increases. This is a general characteristic of secondary batteries. In other words, when discharging or charging is performed rapidly, the discharge capacity or charge capacity decreases.

[0085] The positive electrode foil of the commercially available lithium-ion battery of Comparative Example 3 is approximately 1800 cm 2 The positive electrode containing the active material is formed on the aluminum foil. 2 Dividing by this gives approximately 2.78mAh / cm 2 As shown in FIG. 7, the nominal capacity of the commercially available lithium ion battery of Comparative Example 3, 5000 mAh, is 0.2 mA / cm 2 For example, it can be seen that this is achieved when 2mA / cm 2 When the commercially available lithium-ion battery of Comparative Example 3 is charged and discharged at a current of 0.72 C, it is repeatedly charged and discharged at a maximum capacity of approximately 3470 mAh. On the other hand, the lithium-ion battery of Comparative Example 2, which uses commercially available positive and negative electrode foils at the same current, has a capacity of approximately 3870 mAh. Furthermore, the lithium-ion battery of Example 1 has a capacity of approximately 7920 mAh, allowing it to be charged and discharged at a high capacity.

[0086] The superiority of Examples 1 and 2 is also evident from a comparison with Comparative Example 1. That is, the discharge capacity (charge capacity) per unit area of ​​Example 1 is 2 mA / cm when the discharge current (charge current) is 2 mA / cm when compared with that of Comparative Example 1. 2 When the discharge current (charge current) is 3mA / cm, the charge current is 1.2 to 1.3 times higher. 2 As mentioned above, the thickness of the positive electrode in Example 1, Example 2, and Comparative Example 1 is the same.

[0087] By using the electrode of this embodiment, the thickness of each electrode can be increased, which makes it possible to increase the discharge capacity (charge capacity) while reducing the weight and volume of the entire battery.

[0088] FIG. 8 shows the results of charging and discharging the lithium ion battery of Example 1 at a current of 2 mAh / cm 2 The lithium-ion battery of Example 1 containing aluminum fibers exhibits a decrease in discharge capacity (charge capacity) at the initial stage, but maintains a discharge capacity of approximately 4.3 mAh / cm. 2 It seems that things will settle down.

[0089] Thus, lithium-ion batteries fabricated using the aluminum or copper metal fibers can have approximately twice the discharge capacity (charge capacity) of lithium-ion batteries using commercially available electrode foils. Simply increasing the thickness of the positive or negative electrode, as in Comparative Example 1, does not result in an improvement in performance proportional to the increase in thickness. However, the positive or negative electrodes of this embodiment using the aluminum or copper metal fibers can achieve performance proportional to or even greater than the increase in thickness. The thickness of the positive electrodes of Examples 1 and 2, excluding the aluminum foil, is 155 μm, compared to the 90 μm of the positive electrode of Comparative Example 2, which is a typical electrode thickness. Thus, Examples 1 and 2 are 1.7 times thicker than Comparative Example 2. In other words, by incorporating short fibers A into the electrode as described above, it is possible to achieve performance proportional to or greater than the increase in thickness while maintaining the electrode thickness at 120 μm or more, more preferably 150 μm or more, and even more preferably 200 μm or more.

[0090] As shown in Figure 9, the internal resistance of a battery having an electrode containing the aluminum or copper metal fibers is lower than the internal resistance of a battery having an electrode that does not contain the metal fibers. This reduction in the internal resistance of a battery having an electrode containing the metal fibers is thought to be responsible for the improved characteristics of Examples 1 and 2. Figure 9 shows the internal resistance of batteries having positive electrodes of Examples 3, 4, and 5, and the internal resistance of a battery having a positive electrode of Comparative Example 1.

[0091] In Example 3, the weight ratio of the metal fibers to the aluminum of the positive electrode in Example 1 was changed to 1.22 wt %, and in Example 4, the weight ratio of the metal fibers to the aluminum foil of the positive electrode in Example 1 was changed to 4.88 wt %. In Example 5, the weight ratio of the metal fibers to the aluminum foil of the positive electrode in Example 1 was changed to 9.75 wt %. The weight ratios of the active material powder 20, the conductive additive 30, and the binder B in Examples 3, 4, and 5 vary slightly from those in Example 1 depending on whether the metal fibers are increased or decreased.

[0092] As shown in Figures 7 and 9, when an electrode containing the metal fibers is used as in this embodiment, it becomes possible to charge and discharge at a rate more than twice as fast as that of Example 1, assuming the same discharge capacity (charge capacity). Furthermore, Example 2, in which carbon fiber CF is added, exhibits a larger discharge capacity (charge capacity) than Example 1. Furthermore, as shown in Figure 9, Example 5, in which the metal fibers are blended at 9.75 wt%, also exhibits a significant improvement in internal resistance compared to Comparative Example 1. Therefore, even if the blending ratio of the metal fibers is 9.75 wt% or less, less than 9.75 wt%, or 9.5 wt% or less, it is possible to obtain the same effect as the ordinary electrode of Comparative Example 1.

[0093] Thus, electrodes incorporating the above-mentioned metal fibers as described above can achieve characteristics proportional to or greater than the increase in thickness. For example, when a battery is made by stacking multiple positive electrode foils and multiple 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 can be reduced. This contributes to saving battery space, reducing battery weight, and reducing battery manufacturing costs.

[0094] The metal fibers can be produced by methods other than coil cutting, such as chatter vibration cutting, in which a cutting tool is applied to a cylindrical aluminum or copper member with a circular cross section, or milling. It is also possible to produce the metal fibers having the above length by blowing molten metal such as aluminum into a space through fine holes.

[0095] Further Examples An example in which the short fiber A is applied to the positive electrode of a lithium ion battery is shown below. Short aluminum fibers A with an average length of 0.5 mm or less and active material powder 20 (NMC; ternary Li (Ni a Mn b Co 1-a-b )O2, a conductive additive 30 (AB; acetylene black), and a binder B (PVDF; polyvinylidene fluoride) diluted with a solvent (NMP; normal methylpyrrolidone) were used to prepare a slurry S in the weight ratio (weight ratio after drying) of active material powder 20:conductive additive 30:binder B:aluminum short fiber A of 87:5:4:4. A lithium-ion battery was then fabricated using the slurry S and a cathode foil fabricated on aluminum foil as described above, and an anode foil without metal fibers such as short fiber A, using LiPF6 (lithium hexafluorophosphate) as the electrolyte (Example 6).

[0096] In addition, in Example 6, the slurry S was produced by mixing 4% by weight of the aluminum metal powder instead of 4% by weight of the short fiber A, and a lithium ion battery was also produced using the slurry S and a positive electrode foil produced as described above on an aluminum foil (Example 7). In addition, instead of blending 4% by weight of short fiber A in Example 6, the slurry S was prepared by blending 4% by weight of the above-mentioned metal fiber made of aluminum cut to a length of 1 to 3 mm as described above, and a lithium ion battery was also produced using the slurry S and a positive electrode foil prepared as described above on an aluminum foil (Example 8).

[0097] To produce the negative electrode foils of Examples 6 to 8, first, a slurry S was produced using an active material powder 20 (natural spherical graphite), a conductive additive 30 (AB; acetylene black), and a binder B (PVDF; polyvinylidene fluoride) diluted with a solvent (NMP; normal methylpyrrolidone) in a weight ratio of active material powder 20:conductive additive 30:binder B of 90:5:5. Then, the slurry S was used to produce a negative electrode foil on a copper foil as described above.

[0098] To fabricate the lithium-ion batteries of Examples 6 to 8, the positive and negative electrode foils were cut to a predetermined size, a separator made of polypropylene was sandwiched between the positive and negative electrode foils, and these were housed in a battery container made of a laminated sheet made of a plastic material. The electrolyte was poured into the battery container, and the battery container was sealed to fabricate the lithium-ion batteries of Examples 6 to 8. The sizes of the positive and negative electrode foils, the size and thickness of the separator, and the capacity of the battery container were substantially the same for Examples 6 to 8.

[0099] The average thickness of the positive electrodes (average thickness of the positive electrode layer) of Examples 6 to 8, excluding the thickness of the aluminum foil (current collector foil), was approximately 210 to 220 μm, and the thickness of the aluminum foil of the positive electrodes of Examples 6 to 8 was approximately 15 μm. The average thickness of the negative electrodes (average thickness of the negative electrode layer) of Examples 6 to 8, excluding the thickness of the copper foil (current collector foil), was approximately 110 to 120 μm, and the thickness of the copper foil of the negative electrodes of Examples 6 to 8 was approximately 15 μm. In Examples 6 to 8, the positive electrodes were quite thick at 210 to 220 μm, so the negative electrodes were also made thicker.

[0100] FIG. 10 shows the discharge characteristics (rate characteristics) of Examples 6 to 8. The composition and composition ratio of the positive electrode of Example 8 are the same as those of Example 1. As shown in Figure 10, the discharge capacities (charge capacities) of Examples 6 and 7 are equal to or greater than the discharge capacity (charge capacity) of Example 8. In Figure 10, the discharge capacity (charge capacity) of Examples 6 and 7 is 0.5 mA / cm compared to that of Example 8. 2 ~12.5mA / cm 2This is because the short fibers A in the positive electrode of Example 6 are shorter than the metal fibers in the positive electrode of Example 8, and therefore the short fibers A are more easily dispersed during the preparation of the above-mentioned slurry S, which may have affected the results shown in FIG.

[0101] Furthermore, when the slurry S is applied to the positive electrode foil using a known application device, the slurry S of Example 6 causes less clogging in the application device than the slurry S of Example 8. This is a great advantage in mass production, and it is possible that the same effect will be obtained in Example 7. For example, in mass production, a mass production machine called a die coater applies the slurry S through a slit or nozzle according to the coating thickness, and problems such as clogging caused by metal fibers or uneven mixing of the metal fibers with the active material 20 can occur. However, the short staple fibers A can improve or solve these problems. 10, the discharge capacity (charge capacity) of Examples 6 and 7 is equal to or greater than that of Example 8, and they have similar characteristics. Therefore, even if the blending amounts of short fiber A and metal powder in the positive electrodes of Examples 6 and 7 are changed to those of Examples 3 to 5, it is possible to achieve good discharge capacity and internal resistance similar to those of Examples 3 to 5. Furthermore, even if carbon fiber CF is added to the positive electrodes of Examples 6 and 7 as in Example 2, it is possible to achieve good discharge capacity and internal resistance similar to those of Example 2.

[0102] In Examples 1 to 8, when copper metal fibers or short fibers A are used instead of aluminum metal fibers or short fibers A to produce the negative electrode, the specific gravity of copper is three times or more that of aluminum, so the amount of copper metal fibers or short fibers A may be more than 9.75% of the amount of aluminum. However, from the viewpoint of ease of dispersion of copper metal fibers or short fibers A in the slurry S, the amount of copper metal fibers or short fibers A is preferably less than 12 wt %, and more preferably less than 10 wt %.

[0103] If the short fibers A are made of copper, copper has a lower electrical resistivity than aluminum, so there is a high possibility that the same effects as those described above can be achieved. Taking into account the difference in specific gravity between copper and aluminum, the blending ratio of copper metal fibers or short fibers A is preferably 1.5 or 2% by weight or more. Even if the blending ratio of copper metal fibers or short fibers A is 1% by weight or more, the same effects as those described above may be achieved in some cases.

[0104] When using a metal powder made of another metal such as copper instead of aluminum powder, the same effects as those described above should be achievable if the electrical resistivity of that metal is equal to or lower than that of aluminum. Taking into account the difference in specific gravity between the other metal and aluminum, the blending ratio of the metal powder made of the other metal is preferably 1.5 or 2% by weight or more. As is clear from the above explanation, it is possible to manufacture an electrode using a mixture of the above aluminum metal fibers and metal powder, a mixture of aluminum short fibers A and metal powder, a mixture of the above copper metal fibers and metal powder, or a mixture of copper short fibers A and metal powder in the same compounding ratio as the above aluminum or copper metal fibers or short fibers A, and the electrode will also have the same effect as when the above metal fibers or short fibers A are used.

[0105] Thus, compared to lithium-ion batteries using commercially available electrode foils, lithium-ion batteries fabricated using aluminum or copper short fibers A according to this embodiment can achieve superior discharge capacity (charge capacity) while increasing the electrode thickness. Simply increasing the thickness of the positive or negative electrode, as in Comparative Example 1, does not result in an improvement in characteristics proportional to the increase in thickness. However, the positive or negative electrodes of this embodiment using aluminum or copper short fibers A can achieve characteristics proportional to or even greater than the increase in thickness. Compared to the normal electrode thickness of 90 μm for the positive electrode of Comparative Example 2, the thickness of the positive electrodes of Examples 1 to 5 excluding the aluminum foil is 155 μm, which is 1.7 times or more thicker than Comparative Example 2. The electrodes of Examples 6 and 7, which have equivalent or superior performance to Examples 1 to 5, can achieve characteristics proportional to or greater than the increase in thickness by incorporating short fibers A into the electrodes as described above, while maintaining an electrode thickness of 120 μm or more, preferably 150 μm or more.

[0106] In Examples 6 to 8, the discharge capacity (charge capacity) did not improve in proportion to the increase in thickness as in Examples 1 to 5. In Examples 6 to 8, the positive electrode was quite thick, and the negative electrode may not have been thick enough to compensate for this. Other factors may also be considered. Therefore, even with the positive electrode thicknesses of Examples 6 to 8, it may be possible to obtain characteristics that are proportional to or close to the increase in thickness.

[0107] Furthermore, even when the positive electrode is thick as in Examples 6 to 8, the presence of the metal fibers, short fibers A, or metal powder prevents or makes it difficult for the slurry S to peel off from the current collector foil when the slurry S is dried. This phenomenon is thought to occur because the metal fibers, short fibers A, or metal powder uniformly dispersed in the positive electrode structurally support the thick positive electrode. In the production of Examples 1 to 8 and Comparative Example 1, if the metal fibers, short fibers A, or metal powder were not present, the ends of the electrodes would sometimes crumble into powder or needle-like shapes when the electrodes were cut, attached, etc. In other words, dispersing the metal fibers, short fibers A, or metal powder within the electrodes as described above also prevents the electrodes from crumbling into powder or needle-like shapes.

[0108] Furthermore, the lithium ion battery manufactured using the metal powder of this embodiment, like the battery using short fiber A, can have a superior discharge capacity (charge capacity) compared to lithium ion batteries using commercially available electrode foils.

[0109] The above disclosure is supplemented below. (Lithium-ion battery) The method for manufacturing an electrode for an electricity storage device according to the first aspect of the present invention includes the steps of kneading the above-mentioned metal (mainly aluminum or copper) short fibers A or metal powder, active material powder 20, conductive additive 30, and binder B in a kneader to prepare slurry S, applying the slurry S to a predetermined metal foil (current collector foil) and forming it into a desired shape, and drying and pressing the slurry S formed into the desired shape. The short fibers A improve clogging of the slits and nozzles with the slurry S and uneven application caused by the end fibers A during the application step, enabling a reduction in the internal resistance of the lithium-ion battery and an increase in the coating weight (thicker application), ultimately improving the performance of the lithium-ion battery.

[0110] In the above embodiment, when the slurry formed into a predetermined shape is dried and pressed with a rolling mill, the aluminum or copper short fibers A are connected to each other, or the short fibers A become entangled with or bite into the active material powder 20 and the conductive additive 30. This configuration can significantly improve the internal resistance of the positive or negative electrode, and is useful for making the positive or negative electrode two or three times as thick as commercially available positive or negative electrodes.

[0111] (Electric double layer capacitors and solid-state batteries) The configuration of these devices is also the same; in the case of an electric double layer capacitor, a slurry S is used in which an adsorbent powder, which is activated carbon, a conductive additive 30, and a binder B are mixed with the short fibers A, and in the case of an all-solid-state battery, a solid electrolyte is used instead of a liquid electrolyte. [Explanation of symbols]

[0112] 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 additives A. Short fiber B binder S Slurry CF Carbon Fiber

Claims

1. a fiber preparation step for obtaining aluminum or copper metal fibers; a stirring step of placing the metal fibers or the metal fibers cut by a predetermined cutting tool in a solvent and stirring the solvent to shorten the metal fibers to an average length of 0.8 mm or less; a molding step of molding a liquid or gel slurry containing aluminum or copper short fibers produced by the stirring step, an adsorbent powder that adsorbs electrolyte ions during charging or an active material powder that chemically reacts during charging and discharging, and a binder into a predetermined shape; a drying step of drying the slurry formed into the predetermined shape to form an electrode containing the short fibers.

2. 2. The method for manufacturing an electrode for an electricity storage device according to claim 1, wherein in the fiber preparation step, the metal fibers are obtained by cutting an end face of a coil formed by winding aluminum or copper metal foil with a cutting tool.

3. The method for manufacturing an electrode for an electricity storage device according to claim 1 or 2, wherein the stirring step comprises stirring the solvent in a state in which balls for accelerating cutting of the metal fibers are placed in the solvent.

4. The method for manufacturing an electrode for an electricity storage device according to claim 1 or 2, wherein the stirring step stirs the solvent by rotating a blade.

5. 5. The method for manufacturing an electrode for an electricity storage device according to claim 1, further comprising, before the stirring step, a cutting step of cutting the metal fibers while the bundle of metal fibers is pressed against a predetermined surface using a pressing member or while the bundle of metal fibers is placed in a tube.

6. The method for manufacturing an electrode for an electricity storage device according to claim 5 , wherein in the cutting step, the bundle of metal fibers is cut together with the pressing member or the tube.

7. 7. The method for manufacturing an electrode for an electricity storage device according to claim 1, wherein the slurry contains short fibers so that the weight ratio of the short fibers to the entire electrode after drying in the drying step is less than 9.75% by weight.

8. a fiber preparation step for obtaining aluminum or copper metal fibers; a stirring step of placing the metal fibers or the metal fibers cut by a predetermined cutting tool in a solvent and stirring the solvent to shorten the metal fibers to an average length of 0.8 mm or less; and a shipping step of shipping the aluminum or copper short fibers produced by the stirring step in the solvent or another solvent.

9. 9. The method for producing short fibers for electrodes of an electricity storage device according to claim 8, wherein the fiber production process involves cutting the end faces of a coil formed by winding aluminum or copper metal foil with a cutting tool to obtain the metal fibers.

10. 10. The method for producing short fibers for an electrode of an electricity storage device according to claim 8, wherein the stirring step involves stirring the solvent in a state in which balls for accelerating cutting of the metal fibers are placed in the solvent.

11. The method for producing short fibers for an electrode of an electricity storage device according to claim 8 or 9, wherein the stirring step stirs the solvent by rotating a blade.

12. The method for producing short fibers for an electrode of an electricity storage device according to any one of claims 8 to 11, further comprising a cutting step of cutting the metal fibers in a state where the bundle of metal fibers is pressed against a predetermined surface using a pressing member or in a state where the bundle of metal fibers is placed in a tube, before the stirring step.

13. The method for producing short fibers for an electrode of an electricity storage device according to claim 12 , wherein in the cutting step, the bundle of metal fibers is cut together with the pressing member or the tube.

14. a stirring step of stirring aluminum or copper metal fibers in a solvent to shorten the metal fibers to an average length of 0.8 mm or less; A method for producing a slurry for an electrode of an electricity storage device, comprising at least mixing the metal fibers, an adsorbent material powder that adsorbs electrolyte ions during charging or an active material powder that undergoes a chemical reaction during charging and discharging, and a binder to produce a liquid or gel-like slurry.

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