Electrode for power storage device using solid electrolyte, power storage device, and method for manufacturing positive electrode layer or negative electrode layer for power storage device

Abstract

To make it possible to reduce an influence of expansion and contraction of an electrode of a power storage device and maintain battery characteristics.SOLUTION: Electrodes 2, 4 of a power storage device include: a metal fiber A; adsorption material powder or active material powder 11, 21 in contact with the metal fiber A, which are an adsorbent powder that adsorbs electrolyte ions during charging / discharging or an active material powder that chemically reacts during charging / discharging; and powdery solid electrolytes 14, 24 in contact with the metal fiber A.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an electrode for an electricity storage device using a solid electrolyte, an electricity storage device, and a method for manufacturing a positive electrode layer or a negative electrode layer for an electricity storage device. [Background technology]

[0002] Secondary batteries are used in various fields for the purpose of reducing energy consumption and preventing global warming, and research and development on secondary batteries has accelerated, especially with the adoption of electrical energy in the automotive industry. In recent years, research on next-generation storage batteries has been actively conducted, including metal-air batteries, sodium-ion batteries, lithium-ion batteries, and magnesium-ion batteries.

[0003] Lithium ion batteries (hereinafter also referred to as LiBs) have a high usable voltage of 3.5 to 3.7 V compared to conventional nickel-metal hydride batteries and the like, and are the secondary batteries most widely adopted in recent years.

[0004] LiB is mainly composed of a positive electrode, a negative electrode, a separator, and an electrolyte. For example, a positive electrode is generally made by kneading an active material powder (usually a lithium-containing metal oxide) and additives such as a conductive assistant and a binder (hereinafter referred to as an active material paste) on an aluminum foil with a thickness of about 20 μm, which is a current collector, and applying this to a thickness of about 100 μm. The negative electrode is made by applying a carbon material to a copper foil, which is a current collector. These are separated by a separator such as polyethylene, and the LiB is constructed by soaking them in an electrolyte. Such a lithium-ion secondary battery is disclosed, for example, in Patent Document 1.

[0005] Charging and discharging are performed by the movement of lithium ions between the positive and negative electrodes, during charging lithium ions move from the positive electrode to the negative electrode, and charging is completed when there are no more lithium ions in the positive electrode or when the negative electrode can no longer store lithium ions.

[0006] LiBs are the most widely used in recent years, but the electrolyte solvent contains an electrolyte salt (usually LiPF 6 ) is a flammable liquid, so a structure that does not cause fires or leakage is required. Furthermore, it is said that this organic electrolyte causes decomposition of anions and various foreign molecules at the interface with the positive electrode, shortening the life of the LiB. Therefore, attempts are being 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 composed of solids. Although all-solid-state batteries are not limited to the constituent materials of LiBs, the term generally refers to all-solid-state LiBs because there is a lot of research into solidifying the electrolyte of LiBs.

[0007] The advantages of all-solid-state batteries include safety because the electrolyte layer is flame-retardant; longer life 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.

[0008] In addition, to obtain a high-capacity, high-voltage battery using LiB, multiple cells must be connected together.By using a solid electrolyte layer, it is possible to produce a battery with high energy density by simply stacking the positive electrode layer, the solid electrolyte layer, and the negative electrode layer in that order.

[0009] Because solid-state batteries have many advantages over LiBs, in recent years, much research has been done on the electrolytes and positive and negative electrodes of solid-state batteries. However, there are also problems. For example, there is the problem of capacity degradation caused by the expansion and contraction of the active material during charge and discharge cycles, and the problem of peeling of the active material from the current collector.

[0010] All-solid-state batteries are charged and discharged by Li insertion and removal, during which the host crystal lattice repeatedly expands and contracts. If the resulting volume change is large, the 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 if they are repeatedly charged and discharged at a current of about one-tenth to two-tenths of the battery capacity, nearly one mole of Li is inserted and removed, and the volume expansion and contraction rate reaches nearly 10%. For this reason, various ideas have been proposed to suppress this expansion and contraction.

[0011] To solve this problem, various ideas have been devised, such as placing a conductive elastic body between the cells to suppress expansion and contraction in Patent Document 2, providing a buffer layer around the battery in Patent Document 3, and controlling the porosity in Patent Document 4. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] JP 2007-123156 A [Patent Document 2] JP 2008-311173 A [Patent Document 3] JP 2015-111532 A [Patent Document 4] Patent No. 5910737 Summary of the Invention [Problem to be solved by the invention]

[0013] However, in the arrangement of the elastic body between the short cells in Patent Document 2, it is difficult to fill the gaps that occur due to the expansion and contraction of the positive or negative electrode and the solid electrolyte. In a structure in which an elastic body is arranged between a current collector and a solid positive electrode layer or a solid negative electrode layer, vertical expansion and contraction may be suppressed, but there is a problem with horizontal expansion and contraction, and the overall thickness increases because an elastic body layer of about 20 to 30 μm is used. Similarly, Patent Document 3 also requires the provision of a glass layer or a buffer layer, which causes problems with the overall thickness and manufacturing costs, and Patent Document 4 also requires the control of the porosity of two layers, which causes technical problems, time, and cost problems.

[0014] On the other hand, in recent years, development of LiBs using silicon as the anode has been progressing to increase capacity. However, the volume of silicon expands by about four times when it is charged. Research is also being conducted to use silicon in solid-state batteries, but the volume expansion is also an issue here.

[0015] For example, LiCoO 2 If Si is used for the anode using , the energy density is expected to be about 400Wh / kg (650Wh / L). Although development of batteries with such high energy density is underway, as mentioned above, materials expand and contract during charging and discharging. Therefore, even with this structure, it is necessary to change the binder and electrode structure.

[0016] In view of the above circumstances, an object of the present invention is to reduce the effects of expansion and contraction of electrodes in an electricity storage device and to maintain the battery characteristics. [Means for solving the problem]

[0017] The electrode of the electricity storage device of the first aspect of the present invention comprises metal fibers, an adsorbent powder to which electrolyte ions are adsorbed during charging and discharging, or an active material powder that undergoes a chemical reaction during charging and discharging, the adsorbent powder or active material powder being in contact with the metal fibers, and a powdered solid electrolyte in contact with the metal fibers. This configuration is advantageous for maintaining electrical contact between the active material powder and the solid electrolyte and the metal fibers when the electrode expands or contracts due to charging and discharging.

[0018] An electricity storage device according to a second aspect of the present invention comprises a positive electrode layer having metal fibers, an adsorbent powder to which electrolyte ions are adsorbed during charging and discharging or an active material powder that chemically reacts during charging and discharging, the adsorbent powder or active material powder being in contact with the metal fibers, and a powdered solid electrolyte being in contact with the metal fibers; a negative electrode layer having metal fibers, an adsorbent powder to which electrolyte ions are adsorbed during charging and discharging or an active material powder that chemically reacts during charging and discharging, the adsorbent powder or active material powder being in contact with the metal fibers, and a powdered solid electrolyte being in contact with the metal fibers; and a solid electrolyte layer having a powdered solid electrolyte, the solid electrolyte layer being disposed between the positive electrode layer and the negative electrode layer and in contact with the positive electrode layer and the negative electrode layer.

[0019] Since the metal fibers are elastically deformable, the positive electrode layer and the negative electrode layer are also affected by the elasticity of the metal fibers, that is, the positive electrode layer can more easily follow the expansion and contraction of the negative electrode layer, and the negative electrode layer can more easily follow the expansion and contraction of the positive electrode layer.

[0020] A manufacturing method for a positive electrode layer or a negative electrode layer of an electricity storage device according to a third aspect of the present invention includes a slurry preparation step of preparing a liquid or gel-like slurry containing at least short metal fibers having an average length of 25 mm or less, an adsorbent powder to which electrolyte ions are adsorbed during charge and discharge or an active material powder that undergoes a chemical reaction during charge and discharge, a powdered solid electrolyte, and a binder, and a step of forming the slurry into a predetermined shape.

[0021] A manufacturing method for a positive electrode layer or a negative electrode layer of an electricity storage device according to a fourth aspect of the present invention includes a slurry preparation step of preparing a liquid or gel-like slurry containing an adsorbent powder to which electrolyte ions are adsorbed during charging and discharging or an active material powder that undergoes a chemical reaction during charging and discharging, a powdered solid electrolyte, and a binder, and an introduction step of introducing the slurry between sheet-shaped metal fibers or between nonwoven fabrics of metal fibers. Effect of the Invention

[0022] According to the present invention, the influence of expansion and contraction of the electrodes of the power storage device can be reduced, and the battery characteristics can be maintained. In addition, the incorporation of conductive metal fibers improves the electrical connection between the current collector and the active material powder, and reduces the influence of expansion and contraction of the electrodes due to the elasticity of the fibers themselves. [Brief description of the drawings]

[0023] [Figure 1] FIG. 1 is a cross-sectional schematic diagram of an electricity storage device according to an embodiment that uses a solid electrolyte. [Diagram 2] 1 is a schematic diagram of a method for producing metal fibers according to an embodiment of the present invention. FIG. [Diagram 3] 1 is a schematic diagram of a method for forming a slurry according to an embodiment of the present invention. [Figure 4] 1 is a schematic diagram of another molding method of the slurry of the present embodiment. Note that these figures are for the purpose of easily illustrating the configuration of the present embodiment, and the sizes, thicknesses, lengths, etc. of the metal fibers, active material powder, conductive assistant, solid electrolyte, etc. differ from the actual sizes, thicknesses, lengths, etc. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] Hereinafter, an embodiment of the power storage device (all-solid-state battery) will be described using an all-solid-state lithium ion secondary battery as an example. 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 secondary batteries using a Si (silicon) negative electrode that expand and contract rapidly.

[0025] An example of a schematic diagram of the structure of an all-solid-state battery is shown in Figure 1. An all-solid-state battery is roughly composed of a positive electrode collector 1, a positive electrode layer 2, a solid electrolyte layer 3, a negative electrode layer 4, and a negative electrode collector 5. The positive electrode layer 2 contains, for example, a positive electrode active material, a conductive assistant, and a binder, and the negative electrode layer 4 contains, for example, a negative electrode active material, a conductive assistant, and a binder.

[0026] (current collector 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. This is because when aluminum foil is used for the negative electrode current collector 5, the formation potential of the Al-Li alloy is lower than the operating potential of the negative electrode graphite, and an Al-Li alloy is formed on the negative electrode. Therefore, if the negative electrode active material is an active material with a higher operating potential or an active material that does not react, such as lithium titanate, it is possible to use aluminum foil for the negative electrode current collector 5. In the case of an all-solid-state battery, conductive materials such as SUS (stainless steel), cobalt-based alloys, other conductive materials, conductive ceramics, etc., which have high voltage resistance and corrosion resistance, may be used.

[0027] (Positive electrode layer) The positive electrode active material powder 11 is made of a material that easily absorbs lithium ions, such as LiCoPO4 or LiCoO2, in order to increase the discharge capacity. 2 , LiMnO 4 , LiFePO 4 etc. are preferable. If necessary, a conductive assistant 12, a binder 13, and a powdered solid electrolyte 14 such as an inorganic solid electrolyte or a polymer electrolyte for increasing ionic conductivity are added, and the positive electrode layer is formed through sintering and pressure molding. In this embodiment, the positive electrode layer contains metal fibers made of aluminum, copper, etc. A method for producing the positive electrode layer will be specifically described below.

[0028] (Negative electrode layer) As with the positive electrode layer, the material of the negative electrode active material powder 21 is preferably a material that easily absorbs ions in order to increase the discharge capacity. For example, LiFePO 4 , Li 4 Ti 5 O 12 , Li 4 Fe 4 (PO 4 ) 3 , SiO x , Cu 6 Sn 5 , LiTiO 4The negative electrode layer is formed by mixing the negative electrode active material powder 21, the conductive assistant 22, the binder 23, and a powdered solid electrolyte 24 such as an inorganic solid electrolyte or a polymer electrolyte to increase the ion conductivity, and sintering or pressure molding the mixture. In this embodiment, the positive electrode layer and the negative electrode layer contain metal fibers A made of aluminum, copper, or the like. A method for producing the positive electrode layer and the negative electrode layer will be specifically described below.

[0029] [Metal fiber molding] Metal fibers can be produced by the methods described in Japanese Patent No. 6209706, JP 2018-106846 A, etc. As the metal fibers, short fibers having an average length of 25 mm or less can be used, and long fibers having an average length of more than 25 mm can also be used.

[0030] (Short fiber molding) The metal fiber A, which is a short fiber of aluminum or copper, has, for example, an average length of 25 mm or less, preferably 15 mm or less, more preferably 5 mm or less, and an average wire diameter of 50 μm or less, preferably 25 μm or less. The metal fiber A may be made of other metal materials. The metal fiber A of aluminum or copper is formed, for example, 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, or by a milling cutting method. It is also possible to form the metal fiber of aluminum or copper having the above wire diameter and length by other methods.

[0031] As another method, a coil cutting method can be used. When using the coil cutting method, first, a metal sheet is wound into a coil shape, and the end surface is cut to obtain long metal fibers. Then, the long metal fibers A are cut to the above-mentioned length to obtain short metal fibers A.

[0032] As another method, it is also possible to produce metal fibers A having the above-mentioned length by blowing a molten metal such as aluminum through fine holes into a space. For example, as shown in FIG. 2, molten aluminum is prepared in a sealed container 40 into which a rear part of a curved tube 41 made of ceramic, stainless steel, or the like and having a curved tip is inserted, and when the tip of the curved tube 41 is exposed outside the sealed container 40, air or an inert gas is injected from a gas inlet tube 40a to increase the pressure in the sealed container 40, the molten aluminum rises from the rear part of the curved tube 41 and reaches the tip. When a nozzle 42 having a plurality of fine holes 42a with a diameter of several μm to several mm is set in the opening 41a at the tip of the curved tube 41, the molten aluminum is blown out from the fine holes 42a into the space. For ease of processing, it is preferable to use aluminum with a purity of 99.9% or more, and more preferable to use aluminum with a purity of 99.99% or more, but it is also possible to use an alloy with other metals. The space may be filled with air, an inert gas such as nitrogen, or other gas.

[0033] In this embodiment, the nozzle 42 is disposed so that the aluminum is blown out in a substantially horizontal direction, but the aluminum may be blown out in another direction, such as downward. As a result, the aluminum coming out of the fine holes 42a of the nozzle 42 is cooled while flying laterally in the space, and becomes short aluminum fibers.

[0034] (Forming of long fibers) Metal fiber A, which is a long fiber of aluminum or copper, has, for example, an average length of more than 25 mm, preferably more than 35 mm, more preferably more than 45 mm, and an average wire diameter of 50 μm or less, preferably 25 μm or less. Metal fiber A may be made of other metal materials. Metal fiber A of aluminum or copper is produced, for example, by a coil cutting method. When using the coil cutting method, first, a thin metal plate is wound into a coil shape, and the end face is cut to obtain long metal fiber A. Then, the long metal fiber is cut to the above-mentioned length to obtain metal fiber A, which is a long fiber. Metal fiber A of aluminum or copper having the above-mentioned wire diameter and length can also be formed by other methods.

[0035] As another method, it is also possible to produce metal fibers A which are long fibers by blowing a metal such as molten aluminum into a space through fine holes. Metal fibers A having the above-mentioned length can be produced by using the above-mentioned device for producing short aluminum fibers and changing the conditions for blowing aluminum.

[0036] [Forming of the positive electrode layer when using metal fiber A, which is a short fiber] First, a liquid or gel-like slurry S is prepared containing metal fiber A, positive electrode active material powder 11 that chemically reacts during charging and discharging, conductive assistant 12, binder 13, and solid electrolyte 14. The slurry S is prepared by kneading a mixture of aluminum or copper metal fiber A, positive electrode active material powder 11, conductive assistant 12, diluted binder 13, and solid electrolyte 14. Since the aluminum or copper metal fiber A has an average length of 25 mm or less, the aluminum or copper metal fiber A, positive electrode active material powder 11, conductive assistant 12, and solid electrolyte 14 are easily mixed in the slurry S. When the average length of the metal fiber A is 15 mm or less, more preferably 5 mm or less, the mixture tends to be more easily mixed.

[0037] Next, pre-drying is performed to increase the viscosity of the slurry S. Pre-drying is performed to dry the binder 13 to a state where it is not completely hardened, thereby making it easier to mold the slurry S into a predetermined shape, and therefore may be omitted depending on the viscosity of the binder 13. Next, as shown in FIG. 3, the slurry S is placed in a mold and pressurized. This allows the slurry S to be molded to a predetermined thickness according to the size of the electrode. As shown in FIG. 4, the slurry S can be pressurized by passing it between a pair of rollers, thereby molding the slurry S to a predetermined thickness according to the size of the electrode. After adjusting the thickness of the slurry S using a mold or rollers, the slurry S can be cut and molded into a predetermined shape (size). The slurry S can also be molded into a predetermined shape by applying the slurry S to one surface of the positive electrode current collector 1 in the thickness direction.

[0038] Next, a drying step is performed in which the molded slurry S is dried by vacuum drying or the like. This hardens the binder 13 in the slurry S. This causes the positive electrode active material powder 11 and the solid electrolyte 14 in the slurry S to be in contact with the metal fibers A. Note that the contact state does not mean that all of the positive electrode active material powder 11 is in contact with the metal fibers A, but even if some of the positive electrode active material powder 11 is in contact with the metal fibers A, this is still the contact state. Similarly, even if some of the solid electrolyte 14 is in contact with the metal fibers A, this is still the contact state.

[0039] The content (wt%) of the positive electrode active material powder 11 and the solid electrolyte 14 in the positive electrode layer 2 is preferably 85 wt% or more, and more preferably 90 wt% or more. Among these, the content of the positive electrode active material powder 11 is preferably 70 wt% or more, and more preferably 75 wt% or more. On the other hand, the content of the solid electrolyte 14 is preferably 10 wt% or more, and more preferably 15 wt% or more. The content (wt%) of the metal fiber A in the positive electrode layer 2 is preferably 3 wt% or more, more preferably 5 wt% or more, and preferably 8% or less. The remainder is occupied by the conductive assistant 22, the binder 23, etc.

[0040] [Forming of negative electrode layer when using metal fiber A, which is a short fiber] First, a liquid or gel-like slurry S is prepared, which contains metal fibers A, negative electrode active material powder 21 that chemically reacts during charging and discharging, conductive assistant 22, binder 23, and solid electrolyte 24. The slurry S is prepared by kneading a mixture of aluminum or copper metal fibers A, negative electrode active material powder 21, conductive assistant 22, diluted binder 23, and solid electrolyte 24.

[0041] Next, pre-drying is performed to increase the viscosity of the slurry S. Pre-drying is performed to dry the binder 23 to a state where it is not completely hardened, thereby making it easier to mold the slurry S into a predetermined shape, and therefore may be omitted depending on the viscosity of the binder 23. Next, as shown in FIG. 3, the slurry S is placed in a mold and pressurized. This allows the slurry S to be molded to a predetermined thickness according to the size of the electrode. As shown in FIG. 4, the slurry S can be pressurized by passing it between a pair of rollers, thereby molding the slurry S to a predetermined thickness according to the size of the electrode. After adjusting the thickness of the slurry S using a mold or rollers, the slurry S can be cut and molded into a predetermined shape (size). The slurry S can also be molded into a predetermined shape by applying the slurry S to one surface in the thickness direction of the negative electrode current collector 5.

[0042] Next, a drying step is performed in which the molded slurry S is dried by vacuum drying or the like. This hardens the binder 13 in the slurry S. As a result, the negative electrode active material powder 21 and the solid electrolyte 24 in the slurry S are in contact with the metal fibers A. Note that the contact state does not mean that all of the negative electrode active material powder 21 is in contact with the metal fibers A, but even if some of the negative electrode active material powder 21 is in contact with the metal fibers A, this is the contact state. Similarly, even if some of the solid electrolyte 24 is in contact with the metal fibers A, this is the contact state.

[0043] In addition, in the positive electrode layer 2 and the negative electrode layer 4, instead of the active material powders 11, 21, it is also possible to use an adsorbent powder to which electrolyte ions are adsorbed during charging.

[0044] The content (wt%) of the negative electrode active material powder 21 and the solid electrolyte 24 in the negative electrode layer 4 is preferably 85 wt% or more, and more preferably 90 wt% or more. Among these, the content of the active material powder 11 is preferably 70 wt% or more, and more preferably 75 wt% or more. On the other hand, the content of the solid electrolyte 24 is preferably 10 wt% or more, and more preferably 15 wt% or more. The content (wt%) of the metal fiber A in the negative electrode layer 4 is preferably 3 wt% or more, more preferably 5 wt% or more, and preferably 8% or less. The remaining components are the conductive assistant 22, the binder 23, and the like.

[0045] [Forming of the positive electrode layer when using long metal fiber A] First, the metal fibers A are formed into a sheet shape such as a nonwoven fabric. Then, a mixture of the positive electrode active material powder 11, the conductive assistant 12, the binder 13, and the solid electrolyte 14 is kneaded to prepare a slurry, and the slurry is pushed (introduced) into the gaps between the sheet-shaped metal fibers A. The sheet-shaped metal fibers A may be pushed into the slurry. The slurry may be either before or after drying. The introduction may be performed by applying pressure. A drying step may be performed to dry the slurry after the introduction. As a result of the above, the positive electrode active material powder 11 and the solid electrolyte 14 of the slurry are in contact with the metal fibers A.

[0046] When the metal fibers A are long fibers, the sheet-shaped metal fibers A may function as a part or the whole of the positive electrode current collector 1 . In addition, when the metal fibers A, which are short fibers, are used, the positive electrode current collector 1 may be a sheet made of the metal fibers A.

[0047] When the metal fibers A, which are long fibers, are used, the content (wt%) of the positive electrode active material powder 11 and the solid electrolyte 14 in the positive electrode layer 2 is preferably 80 wt% or more, and more preferably 85 wt% or more. Among these, the content of the positive electrode active material powder 11 is preferably 65 wt% or more, and more preferably 70 wt% or more. On the other hand, the content of the solid electrolyte 14 is preferably 10 wt% or more, and more preferably 15 wt% or more. The content (wt%) of the metal fibers A in the positive electrode layer 2 is preferably 5 wt% or more, and more preferably 10 wt% or more, and preferably 12% or less. The remaining components are the conductive assistant 22, the binder 23, and the like.

[0048] [Forming of negative electrode layer when using long metal fiber A] First, the metal fibers A are formed into a sheet shape such as a nonwoven fabric. Then, a mixture of the negative electrode active material powder 21, the conductive assistant 22, the binder 23, and the solid electrolyte 24 is kneaded to prepare a slurry, and the slurry is pushed (introduced) into the gaps formed between the metal fibers A of the sheet. The sheet-shaped metal fibers A may be pushed into the slurry. The slurry may be either before or after drying. The introduction may be performed by applying pressure. A drying step may be performed to dry the slurry after the introduction. As a result of the above, the negative electrode active material powder 21 and the solid electrolyte 24 of the slurry are in contact with the metal fibers A.

[0049] When the metal fibers A are long fibers, the sheet-like metal fibers A may function as a part or the whole of the negative electrode current collector 5 . In addition, when the metal fibers A, which are short fibers, are used, the negative electrode current collector 5 may be a sheet made of the metal fibers A.

[0050] When the metal fibers A, which are long fibers, are used, the content (wt%) of the positive electrode active material powder 11 and the solid electrolyte 14 in the negative electrode layer 4 is preferably 80 wt% or more, and more preferably 85 wt% or more. Among these, the content of the positive electrode active material powder 11 is preferably 65 wt% or more, and more preferably 70 wt% or more. On the other hand, the content of the solid electrolyte 14 is preferably 10 wt% or more, and more preferably 15 wt% or more. The content (wt%) of the metal fibers A in the negative electrode layer 4 is preferably 5 wt% or more, and more preferably 10 wt% or more, and preferably 12% or less. The remaining components are the conductive assistant 22, the binder 23, and the like.

[0051] [Forming the solid electrolyte layer] A liquid or gel-like slurry is prepared by kneading a mixture containing powdered solid electrolyte 34 and binder 33, and the slurry is 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 well-known solid electrolyte layer. Alternatively, the solid electrolyte layer 3 may be a well-known gel-like solid electrolyte layer.

[0052] [Forming of storage element] The positive electrode layer 2, the solid electrolyte layer 3, and the 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. By stacking the required number of electricity storage elements BE as shown in FIG. 1, an all-solid-state battery is formed.

[0053] (Conductive assistant) In most cases, the conductive additives 12 and 22 are added to improve the conductivity of the positive and negative electrodes. Conductive powders are used as the conductive additives 12 and 22. Usually, carbon powders made of graphite, carbon black, acetylene black, etc. are used. In some cases, metal powders such as Ni, Fe, Co, Ag, etc. are added, and in other cases, WO 3 , SnO 3 In some cases, oxides such as tantalum oxide, tantalum oxide, etc. are also added. Well-known conductive additives used in secondary batteries and capacitors can be used as the conductive additives 12, 22. For example, cokes, baked organic polymer compounds, carbon fibers, carbon nanofibers with an average diameter of 0.5 μm or less, etc. can also be used.

[0054] (solid electrolyte) Like the electrolytic solution of LiB, the solid electrolytes 14, 24, and 34 are present throughout the battery and transfer ions between the positive electrode layer 2 and the negative electrode layer 4. The solid electrolytes 14, 24, and 34 can be made of the following inorganic solid electrolytes or polymer solid electrolytes.

[0055] As an inorganic solid electrolyte, Li 3 N, LiI, Li 3 N-LiI—LiOH, LiSiO 4 , LiSoO 4 -LiI-LiOH, Li 3 PO 4 -Li 4 SiO 4 , Li 2 SiS 3 Lithium nitrides, halides, and silicides such as Li (lithium) can be used. Lithium-containing phosphate compounds with a Nasicon structure and the chemical formula Li x M y (PO 4 ) 3 can be used. x is 1≦x≦2, 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.

[0056] As the polymer solid electrolyte, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate polymer, or the like can be used.

[0057] (binder) Polyethylene, ethylene vinyl acetate, polyvinylidene fluoride, etc. can be used as the resin of the heat-fusible binder 13, 23, 33. For example, cellulose ether compounds such as carboxymethyl cellulose, rubber-based binders such as styrene-butadiene copolymer rubber, etc. can also be used as the binder 13, 23, 33. In addition, well-known binders used in secondary batteries and capacitors can be used. The inventors have confirmed that a method for producing short fibers with higher diameter accuracy is possible by cutting long fibers into pieces of about several millimeters using a coil cutting method, and short fibers produced by this method are used in the present embodiment.

[0058] (Example) (Preparation of positive electrode layer) The positive electrode active material powder 11 is simply LiCoO2 As the solid electrolyte 14, the commercially available Li x M y (PO 4 ) 3 A cathode material was produced by using a cathode active material powder (particle size 5 μm), acetylene black as the conductive additive 12, and polyvinylidene fluoride diluted with NMP (n-methylpyrrolidone) as the binder 13, to which aluminum fibers having an average diameter of 20 μm and an average length of 5 mm or less (for example, 2 mm) were added, so that the weight ratio after drying was cathode active material powder 11: solid electrolyte 14: conductive additive 12: binder 13: aluminum short fiber A = 70:18:5:2:5. This was applied to an aluminum foil having a thickness of 15 μm to a thickness of 50 μm to form a positive electrode layer 2.

[0059] (Preparation of negative electrode layer) As the negative electrode active material powder 21, LiTiO 4 The powder was used, and the same solid electrolyte 24, conductive additive 22, NMP diluted binder 23, and aluminum short fibers A as those used for the positive electrode layer 2 were added to produce a negative electrode material such that the ratio of specific gravities after drying was negative electrode active material powder 21: solid electrolyte 24: conductive additive 22: binder 23: aluminum fiber A = 70:18:5:2:5. This was applied to an aluminum foil having a thickness of 15 μm to a thickness of 50 μm to form a negative electrode layer 4 .

[0060] (Preparation of solid electrolyte layer) The solid electrolyte layer 3 is made of the commercially available Li x M y (PO 4 ) 3 A solid electrolyte paste was prepared by adding polyvinylidene fluoride binder 33 diluted with NMP to this, so that the weight ratio after drying would be solid electrolyte 34:polyvinylidene fluoride binder 33=97:3. The paste was then applied to a polyimide sheet in a thickness of 50 μm to prepare solid electrolyte layer 3.

[0061] (Battery Construction) The positive electrode layer 2, the solid electrolyte layer 3, and the negative electrode layer 4 were stacked and pressed at about 200°C, and then heated at 250°C for 1 hour to produce a single cell (electricity storage element BE). A number of similar single cells were made and stacked as shown in Figure 1, with the top and bottom surfaces sandwiched and fixed between SUS (stainless steel) foils (20 μm) 6, and then sealed in a laminate container. Three single cells were stacked to produce a solid-state battery of about 200 mAh.

[0062] (Comparative Example) For comparison, an all-solid-state battery (three-layered battery, approximately 200 mAh) similar to the above was produced except that the metal fibers A were not added to the positive electrode layer 2 and the negative electrode layer 4.

[0063] (Battery characteristic evaluation) A charge / discharge test was carried out on the prototype batteries with and without metal fiber A at a voltage range of 4.2V (upper limit) and 3V (lower limit) with a constant current of 100mAh. As a result, it was found that both batteries had a capacity of approximately 180mAh, close to the theoretical capacity. Thereafter, a cycle characteristic test was carried out using these batteries under the above-mentioned conditions, and their capacity retention rate was measured. The batteries containing metal fiber (short aluminum fiber) A maintained a capacity of approximately 85%, while the batteries not containing metal fiber A had a capacity retention rate of 60%. It was confirmed that the present invention can improve the battery characteristics of an all-solid-state battery.

[0064] When the positive electrode layer 2 and the negative electrode layer 4 contain the metal fibers A, electrical contact between the positive electrode active material powder 11, the negative electrode active material powder 21, and the solid electrolytes 14, 24 and the metal fibers A is maintained even when the positive electrode layer 2 and the negative electrode layer 4 expand or contract due to charging and discharging. The electrical contact may be made via the conductive assistants 12, 22. This is thought to be why the prototype battery containing the metal fibers A had good cycle characteristics.

[0065] Here, metal fiber A is elastically deformable. Therefore, the positive electrode layer 2 and the negative electrode layer 4 are also affected by the elasticity of metal fiber A. In other words, the positive electrode layer 2 can easily follow the expansion and contraction of the negative electrode layer 4, and the negative electrode layer 4 can easily follow the expansion and contraction of the positive electrode layer 2. This is presumably one of the reasons why the prototype battery containing metal fiber A has good cycle characteristics.

[0066] It is also possible to prepare the electricity storage element BE or the all-solid-state battery while slightly compressively deforming the positive electrode layer 2 and the negative electrode layer 4. In this case, pre-deformation is imparted to the metal fibers A in the positive electrode layer 2 and the negative electrode layer 4, and the metal fibers A are elastically deformed in advance. Therefore, the positive electrode layer 2 is more likely to follow the expansion and contraction of the negative electrode layer 4, and the negative electrode layer 4 is also more likely to follow the expansion and contraction of the positive electrode layer 2.

[0067] The positive electrode layer 2 and the negative electrode layer 4, which are electrodes of the electricity storage device of the above embodiment, include metal fibers A, adsorbent powder to which electrolyte ions are adsorbed during charging and discharging or active material powder 11, 21 which undergoes a chemical reaction during charging and discharging, and powdered solid electrolyte 14, 24. The adsorbent powder or active material powder 11, 21 are in contact with the metal fibers A, and the solid electrolyte 14, 24 is also in contact with the metal fibers A. This configuration is advantageous for maintaining electrical contact between the active material powder 11, 21 and the solid electrolyte 14, 24 and the metal fibers A when the positive electrode layer 2 and the negative electrode layer 4 expand or contract due to charging and discharging.

[0068] The positive electrode layer 2 of the electricity storage device of the above embodiment includes metal fibers A, an adsorbent powder to which electrolyte ions are adsorbed during charging and discharging or a positive electrode active material powder 11 which undergoes a chemical reaction during charging and discharging, and a powdered solid electrolyte 14. The negative electrode layer 4 of the electricity storage device of the present embodiment includes metal fibers A, an adsorbent powder to which electrolyte ions are adsorbed during charging and discharging or a negative electrode active material powder 21 which undergoes a chemical reaction during charging and discharging, and a powdered solid electrolyte 24. The electricity storage device of the present embodiment includes a solid electrolyte layer 3 including a powdered solid electrolyte 34, and the solid electrolyte layer 3 is disposed between the positive electrode layer 2 and the negative electrode layer 4.

[0069] Since the metal fibers A are elastically deformable, the positive electrode layer 2 and the negative electrode layer 4 are also affected by the elasticity of the metal fibers A. In other words, the positive electrode layer 2 can more easily follow the expansion and contraction of the negative electrode layer 4, and the negative electrode layer 4 can more easily follow the expansion and contraction of the positive electrode layer 2.

[0070] In the above embodiment, the metal fibers A are short fibers having an average length of 25 mm or less, and are produced by blowing molten metal into space through the micropores 42a. This production method allows the metal fibers A, which are short fibers, to be produced easily and in large quantities. This is advantageous for reducing the production costs of electrodes and electricity storage devices.

[0071] In the above embodiment, the metal fibers A are produced as short or long fibers using a coil cutting method. This stabilizes the diameter of the metal fibers A, and thus stabilizes the aforementioned elasticity caused by the metal fibers A. This is advantageous for improving the cycle characteristics of the electricity storage device. In this embodiment, when the cross-sectional shape of the metal fibers A is not circular, the term "diameter" refers to the thickness of the metal fibers A.

[0072] In the above embodiment, when carbon fibers having a diameter of 0.5 μm or less are added as a conductive assistant, the active material powders 11, 21 and the solid electrolytes 14, 24 are electrically connected to the metal fibers A through the carbon fibers even when the active material powders 11, 21 and the solid electrolytes 14, 24 are not in direct contact with the metal fibers A. This configuration is advantageous for improving the cycle characteristics of the electricity storage device.

[0073] In the above embodiment, an example of an all-solid-state lithium ion secondary battery has been described, but the above structure can also be applied to an all-solid-state sodium ion secondary battery. In this case, NaFe 0.5 Mn 0.5 O 2For example, transition metal oxides such as carbon black, ceramic materials, etc. can be used as the negative electrode active material powder 21. For the positive electrode active material powder 11 and the negative electrode active material powder 21, known active material powders used in sodium ion secondary batteries can be used. For the inorganic solid electrolyte, NaPF 6 It is possible to use known electrolytes such as NaTFSA.

[0074] The above structure can also be applied to an all-solid-state magnesium ion secondary battery. In this case, the positive electrode active material powder 11 is MgFeSiO 4 As the positive electrode active material powder 11 and the negative electrode active material powder 21, known active material powders used in sodium ion secondary batteries can be used. In addition, as the inorganic solid electrolyte, Mg(TFSI) 2 It is possible to use known electrolytes such as the above.

[0075] The above structure can also be applied to an air battery. The above structure can also be applied to an electric double layer capacitor, which is an electricity storage device. In this case, activated carbon powder (adsorbent powder) is used instead of the positive electrode active material powder 11, and activated carbon powder (adsorbent powder) is used instead of the negative electrode active material powder 21. In addition, as the solid electrolyte layer 3, an alginate gel (Alg / EMImBF 4 Instead of the activated carbon powder, a powder of a known adsorbent material used in an electric double layer capacitor can be used, and a known electrolyte used in an electric double layer capacitor can be used.

[0076] The above structure can also be applied to a lithium ion capacitor, which is an electricity storage device. In this case, activated carbon powder (adsorbent powder) is used instead of the positive electrode active material powder 11, and a carbon-based material powder such as graphite bladed with lithium is used instead of the negative electrode active material powder 21. In addition, alginate gel (Alg / EMImBF 4 Instead of the activated carbon powder, a known adsorbent powder used in a lithium ion capacitor can be used, and a known electrolyte used in a lithium ion capacitor can be used. [Explanation of symbols]

[0077] 1 Positive electrode current collector 2 Positive electrode layer 3 Solid electrolyte layer 4. Negative electrode layer 5 Negative electrode current collector 6. SUS foil 11 Cathode active material powder 12 Conductive additives 13. Binder 14 Solid electrolyte 21 Anode active material powder 22 Conductive additives 23 Binder 24 Solid electrolyte A Metal Fiber BE Energy Storage Element

Claims

1. A conductive assistant, Metal fibers, an adsorbent powder to which electrolyte ions are adsorbed during charging and discharging, or an active material powder which undergoes a chemical reaction during charging and discharging, the adsorbent powder or active material powder being in contact with the metal fibers; a solid electrolyte in contact with the metal fibers; Equipped with An electrode for an electricity storage device using a solid electrolyte, wherein the metal fibers are intended to reduce at least one of the following: loss of contact between particles of the adsorbent powder or between particles of the active material powder, and loss of contact between particles of the conductive assistant when the adsorbent powder or the active material powder expands and contracts during charging and discharging.

2. A conductive assistant, Metal fibers, an adsorbent powder to which electrolyte ions are adsorbed during charging and discharging, or an active material powder which undergoes a chemical reaction during charging and discharging, the adsorbent powder or active material powder being in contact with the metal fibers; a solid electrolyte in contact with the metal fibers; Equipped with An electrode for an electricity storage device using a solid electrolyte, wherein the metal fiber is produced by cutting a metal member by applying a cutting tool to the metal member, or by using a coil cutting method, or by spraying molten metal into the air through fine holes.

3. A conductive assistant, Metal fibers, an adsorbent powder to which electrolyte ions are adsorbed during charging and discharging, or an active material powder which undergoes a chemical reaction during charging and discharging, the adsorbent powder or active material powder being in contact with the metal fibers; a solid electrolyte in contact with the metal fibers; An electrode for an electricity storage device using a solid electrolyte comprising the above-mentioned.

4. a positive electrode layer including at least a metal fiber, an adsorbent powder to which electrolyte ions are adsorbed during charging and discharging, or an active material powder which undergoes a chemical reaction during charging and discharging, the adsorbent powder or active material powder being in contact with the metal fiber, a powdered solid electrolyte being in contact with the metal fiber, and a conductive assistant; a negative electrode layer including at least metal fibers, an adsorbent powder to which electrolyte ions are adsorbed during charging and discharging, or an active material powder which undergoes a chemical reaction during charging and discharging, the adsorbent powder or active material powder being in contact with the metal fibers, a powdered solid electrolyte being in contact with the metal fibers, and a conductive assistant; a solid electrolyte layer having a solid electrolyte; the solid electrolyte layer is disposed between the positive electrode layer and the negative electrode layer and in contact with the positive electrode layer and the negative electrode layer; The metal fibers are intended to reduce at least one of the disruption of contact between particles of the adsorbent powder or between particles of the active material powder, and the disruption of contact between particles of the conductive assistant, when the adsorbent powder or the active material powder expands and contracts during charging and discharging, in an electricity storage device.

5. a positive electrode layer including at least a metal fiber, an adsorbent powder to which electrolyte ions are adsorbed during charging and discharging, or an active material powder which undergoes a chemical reaction during charging and discharging, the adsorbent powder or active material powder being in contact with the metal fiber, a powdered solid electrolyte being in contact with the metal fiber, and a conductive assistant; a negative electrode layer including at least metal fibers, an adsorbent powder to which electrolyte ions are adsorbed during charging and discharging, or an active material powder which undergoes a chemical reaction during charging and discharging, the adsorbent powder or active material powder being in contact with the metal fibers, a powdered solid electrolyte being in contact with the metal fibers, and a conductive assistant; a solid electrolyte layer having a solid electrolyte; the solid electrolyte layer is disposed between the positive electrode layer and the negative electrode layer and in contact with the positive electrode layer and the negative electrode layer; The metal fibers are produced by cutting a metal member with a cutting tool, or by using a coil cutting method, or by spraying molten metal into the air through fine holes in an electricity storage device.

6. a positive electrode layer including at least a metal fiber, an adsorbent powder to which electrolyte ions are adsorbed during charging and discharging, or an active material powder which undergoes a chemical reaction during charging and discharging, the adsorbent powder or active material powder being in contact with the metal fiber, a powdered solid electrolyte being in contact with the metal fiber, and a conductive assistant; a negative electrode layer including at least metal fibers, an adsorbent powder to which electrolyte ions are adsorbed during charging and discharging, or an active material powder which undergoes a chemical reaction during charging and discharging, the adsorbent powder or active material powder being in contact with the metal fibers, a powdered solid electrolyte being in contact with the metal fibers, and a conductive assistant; a solid electrolyte layer having a solid electrolyte; The solid electrolyte layer is disposed between the positive electrode layer and the negative electrode layer and is in contact with the positive electrode layer and the negative electrode layer.

7. The electricity storage device according to any one of claims 4 to 6, wherein the metal fibers are short fibers having an average length of 5 mm or less.

8. a slurry preparation step of preparing a liquid or gel-like slurry containing at least short metal fibers having an average length of 25 mm or less, an adsorbent powder to which electrolyte ions are adsorbed during charging and discharging or an active material powder that undergoes a chemical reaction during charging and discharging, a solid electrolyte, a conductive assistant, and a binder; A forming step of forming the slurry into a predetermined shape; a drying step of forming a positive electrode layer or a negative electrode layer by at least drying the slurry formed into the predetermined shape; A method for producing a positive electrode layer or a negative electrode layer of an electricity storage device having the above structure.

9. A slurry preparation process for preparing a liquid or gel-like slurry containing at least short metal fibers having an average length of 25 mm or less, the short metal fibers being prepared by cutting a metal member by applying a cutting tool to the metal member, or by using a coil cutting method, or by blowing molten aluminum into the air through fine holes, an adsorbent powder to which electrolyte ions are adsorbed during charging and discharging, or an active material powder which undergoes a chemical reaction during charging and discharging, a solid electrolyte, a conductive assistant, and a binder; A forming step of forming the slurry into a predetermined shape; a drying step of forming a positive electrode layer or a negative electrode layer by at least drying the slurry formed into the predetermined shape; A method for producing a positive electrode layer or a negative electrode layer of an electricity storage device having the above structure.

10. a slurry preparation step of preparing a liquid or gel-like slurry containing at least short metal fibers having an average length of 25 mm or less, an adsorbent powder to which electrolyte ions are adsorbed during charging and discharging or an active material powder that undergoes a chemical reaction during charging and discharging, a solid electrolyte, a conductive assistant, and a binder; a step of at least sintering the slurry to form a positive electrode layer or a negative electrode layer of a predetermined shape; A method for producing a positive electrode layer or a negative electrode layer of an electricity storage device having the above structure.

11. The method according to claim 8 or 10, wherein the metal fibers are produced by blowing molten metal into a space through fine holes.

12. The method according to claim 8 or 10, wherein the metal fibers are produced by using a chatter vibration cutting method.

13. The method according to claim 8 or 10, wherein the metal fibers are produced using a coil cutting method.

14. A manufacturing method described in any of claims 8 to 13, wherein the metal fibers are aluminum fibers having a purity of 99.9% or more.

15. The slurry is prepared using the metal fibers having an average length of 3 mm or less and an average fiber diameter of 30 μm or less, and the slurry is applied to a positive electrode current collector or a negative electrode current collector to form the slurry into the predetermined shape. The manufacturing method according to any one of claims 8 to 13.

16. The manufacturing method according to any one of claims 8 to 13, wherein carbon fibers having an average diameter of 0.5 µm or less are added in the slurry preparation step.

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