Flexible electrochemical element

Abstract

To provide a flexible electrochemical element that is capable of deformation in response to external stress, has excellent flexibility, and is composed of iron-based element electrodes.SOLUTION: The present invention provides a flexible electrochemical element that uses an electrode in which at least a portion of a fiber assembly of an iron-group metal is used as an active material, the electrochemical element being composed of the electrode, an electrolyte, and an outer casing, and that is capable of being deformed by external stress. The present invention also provides a flexible electrochemical element in which at least a portion of the surface of the iron-based metal fiber assembly in the electrochemical element is coated with a thin film of a different metal element.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a flexible electrochemical element that contains an iron-group metal fiber aggregate in an electrode and has flexibility. [Background technology]

[0002] Energy-storable electrochemical devices, such as lithium-ion secondary batteries, are used in distributed power sources and power sources for portable devices and have become indispensable in everyday life. Furthermore, the recent increase in renewable energy sources, such as wind and solar power generation, has created a primary demand for high-capacity energy storage devices for power storage. These applications necessitate the development of electrochemical devices that are free of resource issues for their components, can be manufactured and supplied at low cost, and are highly safe. While lithium-ion secondary batteries are characterized by their high energy density and are primarily used in small-capacity cells, they pose safety challenges, such as resource constraints for their constituent elements and the risk of fire from their nonaqueous electrolytes, which are composed of electrodes in a high-energy state. Iron-based electrochemical elements, which offer advantages in terms of resource issues and cost reduction, have been researched for a long time and the technology has been accumulated. In particular, iron-air batteries, which can be charged and discharged, are highly safe because they mainly use aqueous electrolytes and do not pose a risk of fire, and are expected to be large-capacity energy storage devices, and active development is underway.

[0003] Fibrous aggregates of iron-group metals are commonly known as steel wool, and steel wool is used as a cleaning material in the form of scrubbers and brushes in kitchens and industrial applications. A typical manufacturing method involves grinding metal blocks or sheets, such as iron or stainless steel, to produce wire- or ribbon-shaped cuttings. Examples of applications of steel wool in batteries include its use as a material to prevent electrolyte leakage (Patent Document 1), its use as a current collector in iron-manganese oxide rechargeable batteries (Patent Document 2), and its use as an inert conductive matrix in nickel-iron batteries (Patent Document 2). Thus, conventional applications of steel wool in electrochemical devices have been limited to its use as a liquid holder, conductive matrix, or electrode current collector; there have been no examples of steel wool being used as an electrode active material in electrochemical devices.

[0004] Electrochemical elements such as dry batteries and storage batteries typically have fixed shapes, such as rectangular blocks, cylinders, coins, or plates, and are robust enough to resist deformation under external stress. Recently, portable and wearable devices have been developed that feature flexibility, allowing them to deform under external pressure such as bending or twisting, and these components and materials are required to be mechanically flexible. Conventional electrochemical elements are difficult to adapt to these flexible devices due to their shape and robustness, limiting the types of devices they can be installed in. Furthermore, conventional electrochemical elements are limited in the amount of space they can be installed in devices, and to improve space utilization, batteries with flexible shapes that can be filled into complex shapes are needed. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Published Utility Model Patent 1720-1976 [Patent Document 2] Special Table 2022-543752 [Patent Document 3] Special Table 2016-534491 Summary of the Invention [Problem to be solved by the invention]

[0006] A flexible electrochemical element is provided which has excellent electrolyte impregnation and retention properties, is capable of deformation in response to external stress, and has excellent durability. [Means for solving the problem]

[0007] The present invention is a flexible electrochemical element that uses a fiber aggregate of an iron-group metal as an electrode, and is characterized in that the electrochemical element, which is composed of the electrode, an electrolyte, and an outer casing, can be deformed by external stress. The present invention also provides a flexible electrochemical element, characterized in that at least a portion of the surface of the iron-group element metal fiber aggregate in the electrochemical element is covered with a thin film of a different metal element.

[0008] The elements constituting the flexible electrochemical element of the present invention, the structure of the element, and the method for producing it will be described below. In the flexible electrochemical element of the present invention, the fiber assembly of iron group metal is a spongy assembly of thin wires, typified by steel wool. The iron-group metals constituting the fiber assembly of the present invention are selected from titanium (element number 22) to zinc (element number 30) in the periodic table, with chromium (element number 24), manganese (element number 25), iron (element number 26), cobalt (element number 27), nickel (element number 28), and copper (element number 29) being particularly preferred. Manganese, iron, cobalt, and nickel are even more preferred, as well as alloys primarily composed of these metal elements. Examples include various types of iron, steel, carbon steel, silicon steel, stainless steel (alloys primarily composed of chromium, nickel, and iron), nickel steel, cobalt steel, and manganese steel. Materials also include those containing heteroelements such as boron, carbon, nitrogen, oxygen, silicon, phosphorus, and sulfur, either in solid solution or unevenly distributed or precipitated as a structure within the metal. Furthermore, fibrous assemblies composed of multiple types of metal elements can also be composited. The shape of the fibers that constitute the unit structure of the iron-based element metal fiber aggregate of the present invention is cylindrical, semicircular, elliptical, triangular, square, or rectangular in cross section, with a major axis ranging from mm to several μm, a fiber length ranging from mm to m, and an aspect ratio (fiber length / major axis) of 10 or more, with no upper limit.

[0009] Iron-based element metal fiber assemblies can have a one-dimensional structure in which the fiber bundles are aligned in one direction (x direction), a two-dimensional structure in which the fiber bundles are regularized in the in-plane direction to form a woven fabric (xy plane), a three-dimensional structure in which the fiber bundles are further aligned in the thickness direction (z direction) of the two-dimensional structure to form a thick sheet, a structure in which the regularity of the directions of these fiber assemblies is disrupted, a nonwoven fabric form, or a composite structure of these. Furthermore, for the purpose of dimensional stabilization of the shape or surface treatment, these fiber assemblies can be subjected to compression, stretching, winding, ultrasonic welding, high frequency, plasma, or resistance heating treatment as necessary. The iron-based element metal fiber aggregate of the present invention has spaces inside the fiber aggregate according to the fiber shape and fiber structure, and is characterized by excellent electrolyte impregnation and liquid retention properties, which is preferable in terms of manufacturing electrochemical elements, as it allows for rapid electrolyte impregnation and long-term electrolyte retention in the element.

[0010] The electrical and magnetic properties of the iron-based element metal fiber assembly of the present invention will now be described. The fiber assembly of the present invention exhibits high electrical conductivity due to the internal and surface electrical conductivity of the constituent fibers and the formation of a conductive network between the fibers within the fiber assembly. After clamping the fiber assembly with metal clamps, electrical conductivity can be measured using the DC two-terminal method or the DC four-terminal method. The fiber assembly of the present invention has an electrical conductivity of 0.1 S / m to 10E6 S / m. Furthermore, electrical conductivity can be evaluated non-contact using an electromagnetic induction method. This method can be used to evaluate the electrical conductivity of the fiber assembly of the present invention after constructing an electrochemical device or while it is operating as a battery. Furthermore, the fiber assembly of the present invention is made of iron-based element metals, which have ferromagnetic properties, and therefore the fiber assembly exhibits high magnetic susceptibility. Magnetic susceptibility can be evaluated using a vibrating magnetometer or the like based on the principle of electromagnetic induction. The saturation magnetic susceptibility of the fiber assembly of the present invention is 200 emu / g to 10 emu / g.

[0011] The flexible electrochemical element of the present invention is constructed using an iron-based element metal fiber assembly as an electrode, and is characterized in that this electrode has flexibility against external stress and the fiber assembly structure, i.e., the electrode structure, is endowed with robustness that makes the electrochemical element less susceptible to destruction or breakage. Conventional electrochemical element electrodes are made by coating a foil, mesh, sheet, or block-shaped current collector with a high volume density of powdered electrode active material and a trace amount of binder to form a layered active material layer. This active material layer is mechanically fragile and easily peels off due to external stress. This peeling, which results in a loss of electrochemical function, has been a major obstacle to flexible elements. The flexible electrochemical element of the present invention addresses these issues of conventional elements by significantly revising the element structure and constituent materials, resulting in a flexible element with the flexibility of an electrochemical element. Therefore, the flexible electrochemical element of the present invention is significant in that it provides new functions not found in conventional electrochemical elements.

[0012] Furthermore, the present invention can use a composite material in which the surface of a core iron-based metal fiber is coated with a thin film of a material of a different element as the positive or negative electrode. That is, the present invention relates to a flexible electrochemical element characterized by using a composite material in which at least a portion of the surface of a fiber assembly of iron-based metals that constitutes the electrochemical element is coated with a thin film of a different metal element. The main purpose is to provide an element with excellent electrochemical performance by adjusting the electrochemical properties using the composite material. The heterogeneous element is preferably an iron-based metal element different from the main element constituting the core iron-based element metal fiber aggregate. The coating structure is characterized by excellent adhesion strength and electrical bonding with the core iron-based element metal, and the thin-film coating allows for adjustment of the redox potential and electrochemical performance. For example, if the core metal fiber is iron, examples of the thin-film coating include a single element or a composite element selected from zinc, copper, nickel, cobalt, manganese, chromium, vanadium, and titanium. Furthermore, if the core metal fiber is stainless steel, the core material is formed from an alloy of various elements, so iron-based element components with different composition ratios can be used as the coating material. Furthermore, in the present invention, a metal fiber aggregate coated with a thin carbon film can also be used for the purpose of adjusting the electrochemical properties by utilizing the redox potential and the adsorption and desorption of ionic components.

[0013] Further, trace components in the thin film coating material include magnesium, aluminum, indium, tin, niobium, molybdenum, ruthenium, rhodium, palladium, silver, cadmium, tantalum, tungsten, iridium, platinum, gold, lead, bismuth, rare earth elements, carbon-based materials, and mixtures thereof. The most basic structure of this composite material is a core / shell structure, with an iron-based metal fiber aggregate as the core and a surface layer (shell) with a different structure from the core. This also includes cases where the shell does not completely cover the core, i.e., where only part of the core has a shell structure. Therefore, it is possible to composite multiple metal fibers with different compositions in a specified ratio. The thickness range of the shell-structured thin film that coats the core-shell structure can be designed taking into account the film thickness fluctuations (discharge capacity or charge / discharge capacity) that occur with the redox reaction from the surface of the electrochemical element. However, in the case of electrochemical elements that only use the shell structure to adjust the electrochemical potential, even an extremely thin coating material can achieve sufficient functionality. Therefore, the coating thickness is set according to the intended function of the electrochemical element.

[0014] Thin film coating methods for this composite material include electrochemical deposition methods such as electroplating and electroless plating to form a thin coating film on a metal fiber assembly; precursor thin film formation methods in which a precursor is applied to the surface of a metal fiber assembly and then heat-treated to form a thin film of the target component; dry process film formation methods such as sputtering, vacuum deposition, CVD, and ALD to form a thin film; and thin film formation methods that combine precursor application and dry process film formation. Of these methods, electrochemical deposition methods are preferred for the iron-based element metal fiber assembly of the present invention because they can be used to coat both the surface and inner layers. For example, an electrolytic plating method can be used in which the core iron-based element metal fiber is immersed in an electrolyte solution containing ions of the other element to be coated, and electrolysis is performed using the metal fiber as an electrode to reduce and deposit the other element on the electrode surface. Alternatively, an electroless plating method can be used in which a reducing agent is present in an electrolyte solution containing ions of the other element, and the other element is reduced and deposited on the metal fiber assembly by the reaction of the reducing agent. It is possible to continuously supply a flowing electrolyte solution containing ions of different elements to be deposited on the metal fiber aggregate, adjust the type and amount of reducing agent used in electroless plating, and add trace amounts of elements such as Pd, Rh, and Pt to the metal fiber aggregate as catalysts to adjust the amount of deposition and surface morphology.

[0015] The precursor thin film formation method is a method in which a salt, complex, cluster, or fine particle of the target metal element is coated on the surface of a metal fiber aggregate by a method such as coating, immersion, or vapor deposition, and the precursor is converted into the target component by heating or radiant energy irradiation, etc. Methods that use wet processes such as coating or immersion of the precursor have the advantage of being able to coat surfaces with complex shapes, just like the electrochemical deposition method described above. On the other hand, the dry process film formation method is useful when the goal is to coat a thin film on only a portion of a surface, because the thin film has a stronger directionality than the electrochemical deposition method and a composite material with high local heterogeneity is produced due to shadowing. The present invention also encompasses electrochemical elements using fiber assemblies in which a carbon thin film is coated on a metal fiber assembly. Methods for forming this carbon thin film include dry processes such as CVD and sputtering, and wet processes such as coating, dipping, and printing of organic polymeric materials to form a precursor and then pyrolyzing the precursor to form a carbon thin film. Iron-based elements such as iron and nickel contained in the metal fibers of the substrate are believed to exhibit catalytic activity in the formation of the carbon thin film, which is beneficial for the formation of the carbon thin film. It is believed that the iron-based elements promote dehydrogenation reactions during the process of carbon formation from the precursor and the formation of structures through the arrangement of carbon elements. The carbon thin film used in the present invention is not limited to a graphite structure, but may also include amorphous structures, amorphous carbon, carbon nanotubes, and diamond structures. In the present invention, for the purpose of adjusting the surface structure, the surface of the iron-based element metal fiber aggregate can be oxidized and dissolved by a wet method to etch a part of the surface, or the surface can be oxidized to use as a fiber aggregate having an oxide surface. Furthermore, for the purpose of adjusting the electrochemical properties, the surface of the metal fiber aggregate can be reduced to adjust the surface structure before use.

[0016] The flexible electrochemical element of the present invention has a basic structure of anode / electrolyte / cathode, and is characterized in that the anode and / or cathode contain the iron-based element metal fibrous aggregate. The flexible electrochemical element of the present invention can be used as a primary battery with only a discharge function and as a secondary battery capable of repeated charge and discharge. Of these, materials that make up the positive electrode include iron oxides such as FeO, Fe2O3, Fe3O4, and FeOOH; nickel oxides such as NiO, Ni2O3, and NiOOH; cobalt oxides such as CoO, Co2O3, and CoOOH; manganese oxides such as MnO2 and MnO; oxides such as chromium oxide, vanadium oxide, copper oxide, zinc oxide, and silver oxide; and sulfides such as iron sulfide, nickel sulfide, cobalt sulfide, and copper sulfide. Materials constituting the negative electrode include, but are not limited to, iron group element metals such as iron, cobalt, nickel, stainless steel, copper, and zinc, alloys of these iron group element metals with other elements, and hydrides.

[0017] Publicly known information can be applied to the basic electrode and electrolyte configurations. The electrolyte, located between the negative and positive electrodes, is placed in the space between the electrodes and is responsible for the movement of ions between the two electrodes, thereby forming an electrochemical element. To prevent electrical connections (short circuits) between the electrodes, an ion-permeable material other than the electrolyte can be placed between the electrodes as a separator. Examples of separator materials include woven and nonwoven fabrics made from resins such as polyethylene, polypropylene, cyclic polyolefin, polyester, nylon, and vinyl chloride, as well as porous materials, cellulose, and paper. Among these, olefin-based resins such as polyethylene, polypropylene, and cyclic polyolefin are inherently hydrophobic. Therefore, to improve wettability and impregnation properties as separators for aqueous electrolyte materials, they can be hydrophilized by atmospheric plasma discharge treatment or surface oxidation with an oxidizing agent before use.

[0018] While both non-aqueous and aqueous electrolytes can be used in the present invention, aqueous electrolyte materials are often used in electrochemical elements constructed with electrodes based on iron-based metal fiber aggregates. Compared to non-aqueous electrolyte materials, aqueous electrolyte materials offer a wider range of design options for electrolyte species, concentrations, and additives, and have superior ionic conductivity. Furthermore, aqueous electrolyte materials are inherently nonflammable, making elements constructed using them highly safe. Examples of aqueous electrolyte materials include inorganic materials such as alkali metal hydroxides (e.g., potassium hydroxide, sodium hydroxide, and lithium hydroxide); ammonium salts; chlorides (e.g., potassium chloride, sodium chloride, lithium chloride, and magnesium chloride); phosphates, nitrates, carbonates, sulfates, fluorides, bromides, borates, and sulfides of various elements; and organic electrolytes (e.g., carboxylic acids, sulfonic acids, and ammonium salts); polymer electrolytes; and ionic fluids. It is also possible to add polyvinyl alcohol, polyacrylic acid, agar, gelatin, etc. to aqueous electrolytes to thicken or gel them, or to add alcohols such as ethanol or ethylene glycol as antifreeze agents. As the electrolyte gels or thickens, its flow is reduced, which prevents electrode malfunction and performance degradation of electrochemical devices due to reduced electrode wettability, and reduces leakage, thereby improving safety. The electrochemical element of the present invention has electrodes composed of iron-based element metal fiber aggregates, and the electrodes have excellent electrolyte material impregnation and retention properties, which shortens the impregnation time and reduces defects due to poor impregnation, resulting in stable and excellent element operation.

[0019] The flexible electrochemical element of the present invention is constructed with a basic unit of anode / electrolyte / cathode protected by an exterior body. A flexible exterior body is preferable to provide the necessary flexibility depending on the intended use of the flexible electrochemical element. Conventional electrochemical elements use hard materials such as metals or ceramics as exterior bodies, resulting in a rigid electrochemical element that does not change shape even under external pressure. The electrochemical element of the present invention is characterized by its flexibility, which significantly differentiates it from conventional electrochemical elements. Materials usable for the exterior body of the present invention include molded bodies and films of resin materials such as polyethylene, polypropylene, polyester, polyimide, and polyurethane, as well as natural materials such as paper, cellulose, and polyamide, and composites of these materials. Flexible metals, ceramics, and glass can also be used for the exterior body of the present invention as needed. Furthermore, electrochemical elements with reversible ductility (stretchability) similar to rubber are also possible. The flexible electrochemical element of the present invention uses an iron-based metal fiber assembly for the electrodes, which has excellent flexibility. The flexibility of the electrodes, electrolyte, and exterior body allows for high flexibility. Furthermore, in consideration of disposal and recycling of the electrochemical element of the present invention, it is possible to design an element in which the exterior is made of biodegradable resin or natural material. The electrochemical element of the present invention has an electrode material mainly composed of iron-based elements, which are naturally abundant in the earth's crust and have the characteristics of having excellent affinity with soil and little impact on the ecosystem.

[0020] Next, a method for fabricating a flexible electrochemical element of the present invention will be described. Examples of the fabrication method for the element will be described, but the invention is not limited to these. In the case of a thin, flat element, an element protected by an outer casing can be produced by placing electrodes and electrolytes on a sheet-like outer casing made of a thermoplastic resin such as polyethylene, placing an outer casing sheet on top of this, laminating the electrodes and electrolyte with the upper and lower outer casings, and then melting and sealing the outer casing resin. Alternatively, a protected element can be obtained by inserting the electrodes and electrolyte through an opening in an outer casing made of a thermoplastic resin processed into a bag shape and sealing the opening. Alternatively, a heat-shrinkable resin bag can be used to insert the electrodes and electrolyte, and then heating the bag to shrink the resin bag, thereby obtaining a protected element with a shape corresponding to the internal shape. It is also possible to inject the electrolyte after inserting the electrodes into the outer casing. For purposes such as long-term storage of the element package, it is also possible to inject the electrolyte immediately before use to activate the electrochemical element. Furthermore, when used as an air battery, a portion of the exterior body can be made of a gas-permeable material or provided with pinholes to allow air to enter the package. Alternatively, if gas is generated internally by the electrochemical element, a gas release valve can be provided in the exterior body. Furthermore, if necessary to prevent self-discharge of the electrodes, the exterior body can be made of a material with gas barrier properties. To electrically connect the metal fiber aggregate electrode or current collector of the electrochemical element of the present invention to the inside and outside of the exterior body, a rod-shaped or flat metal terminal is connected to the metal fiber aggregate and sealed in an insulating exterior body such as resin, or the metal terminal is sealed via a hermetically sealed part, or sealed via a part of the exterior body that is conductive, thereby achieving electrical connection between the inside and outside of the exterior body.

[0021] The electrochemical element of the present invention can also be used to construct a battery assembly consisting of multiple electrode domains. Here, domains using metal fiber assemblies as electrodes are spatially separated and arranged inside the exterior of the electrochemical element, with some of the domains joined via an electrically conductive or ion-conductive bond, and the unit structure of the electrochemical element is such that the positive electrode domain and the negative electrode domain are joined via an insulating and ion-permeable region. The positive electrode domain and the negative electrode domain in the unit can be arranged in either a stacked structure or an in-plane planar structure, or both.

[0022] The electrochemical element of the present invention is characterized by its excellent flexibility. The resistance of the electrochemical element can be evaluated by applying external stress (mechanical stress) to an electrochemical element sealed in an outer casing and observing the change in performance before and after the application. Examples of external stresses to be tested include bending, twisting, winding, compression, tension, dropping, falling ball, and vibration. Test conditions can be set depending on the shape of the electrochemical element and the application to which the element will be applied. Furthermore, test conditions can be set according to the intended application, such as reduced pressure conditions that mimic high altitude, aircraft, and space environments, or pressurized conditions that mimic deep-sea environments. The effects of mechanical stress on performance due to external stress can be evaluated by detecting and comparing electrochemical signals before and after the application of external stress. The effects of mechanical stress on the element can also be evaluated by evaluating the electrical resistance due to external electromagnetic induction of the iron-based element metal fiber aggregate or the magnetic susceptibility using a vibrating magnetometer. Representative exterior materials that can be used in the present invention include transparent resin materials made of polyethylene, polypropylene, etc. The transparency of these exterior materials allows for observation of structural changes, electrode denaturation, and electrolyte segregation inside the electrochemical device. This makes it possible to detect and repair device failures, and the device can be expanded to include repairability, which was not possible with conventional electrochemical devices. [Effects of the Invention]

[0023] The present invention provides an electrochemical element that is composed of electrodes containing an iron-based element metal fiber aggregate, has excellent electrolyte impregnation and retention properties, and is flexible and can be deformed in response to external stress, with excellent durability. [Brief explanation of the drawings]

[0024] [Figure 1] 1 is a cross-sectional view of a stacked electrochemical device (Example 1). [Figure 2] 2 is a top view of a planar electrochemical device (Example 3). DETAILED DESCRIPTION OF THE INVENTION

[0025] An example of the flexible electrochemical device of the present invention is shown below. [Example]

[0026] A steel wool sheet (average diameter 25 μm, roll pad, 6 cm long x 4 cm wide x 5 mm thick) was immersed in nickel electrolyte (1M nickel sulfate). A constant current electrolysis of 10 mA / cm was performed for 20 minutes using the steel wool as the negative electrode and a graphite sheet as the counter electrode, depositing nickel on the surface. The nickel-plated steel wool sheet was washed with pure water and dried at 100°C in air. The deposited nickel thin film had an average thickness of approximately 2 μm, based on the weight gain after plating. A laminate was fabricated using the nickel-plated sheet as the positive electrode, a polypropylene nonwoven fabric sheet (100 μm thick, 10 cm square, 50% porosity) with a hydrophilic surface as the separator, and a separately prepared untreated steel wool sheet as the negative electrode. A 50 μm thick, 1 cm wide, 10 cm long stainless steel sheet was ultrasonically welded to the ends of each positive and negative electrode sheet to form current extraction terminals. The positive electrode / separator / negative electrode laminate was placed in a 100 μm thick transparent polyethylene bag (10 cm square). The electrode terminals were allowed to protrude from the opening of the bag, and a 4 M potassium hydroxide solution was poured through the opening to impregnate the laminate. The untreated steel wool sheet served as the negative electrode, and the nickel-coated sheet served as the positive electrode. The laminate was pretreated by electrolysis at a constant current of 5 mA / cm² followed by electrolysis at a constant potential of 1.5 V. The opening of the polyethylene bag was then heat-sealed to form an electrochemical device. The untreated sheet served as the negative electrode, and the nickel-coated sheet served as the positive electrode. The device was discharged (at a constant current of 2 mA / cm², followed by a 0.5 V cutoff). Charging (at a constant current of 10 mA / cm², at a constant potential of 1.5 V) and discharging were then repeated, demonstrating that the device was capable of charging and discharging. The discharge capacity after five charge-discharge cycles was 145 mAh. The electrochemical element was placed on a bendable stage, sealed in a polyethylene bag, and a 10 mm diameter metal rod was placed at the center of the surface of the sealing bag. The movable stage was bent around the rod as an axis, bending the electrochemical element at a 90° angle, holding the bend for 10 seconds, and then returning the stage to its original position. This bending procedure was repeated 10 times. After the bending treatment, the electrochemical device was charged and discharged, and good charging and discharging was confirmed. The average discharge capacity over five charge and discharge cycles was 148 mAh. [Example]

[0027] The steel wool sheet used in Example 1 was immersed in a manganese electrolyte (1 M manganese sulfate) and electrolyzed at a constant current of 10 mA / cm using a graphite plate as the counter electrode, depositing a thin film of manganese metal on the surface of the steel wool sheet. After washing the manganese-coated sheet with pure water and drying at 100°C, the weight gain indicated that the average film thickness of the deposited manganese metal was approximately 5 μm. An electrode laminate was formed using the manganese-coated sheet as the positive electrode, a polypropylene separator similar to that used in Example 1, and an untreated steel wool sheet as the negative electrode. After ultrasonic welding of stainless steel sheets to the ends of both electrodes as in Example 1, the electrode laminate was placed in a polyethylene bag, and a 2 M KOH solution was poured in as the electrolyte. The opening was then melt-sealed to produce an electrochemical device. A constant-current, constant-voltage charge / constant-current, potential cutoff discharge was performed under the same conditions as in Example 1, and good charge / discharge performance of the electrochemical device composed of the manganese-coated electrode was confirmed. The discharge capacity after five charge / discharge cycles was 220 mAh. Next, the entire electrochemical element obtained was repeatedly bent 10 times at a 90-degree angle around a metal rod with a diameter of 10 mm, in the same manner as in Example 1. After this bending test, the electrochemical element was charged and discharged. As a result, the average discharge capacity over 5 cycles was 222 mAh, and no decrease in the charge and discharge capacity was observed. [Example]

[0028] An untreated steel wool sheet similar to that used in Example 1 was used, and the steel wool sheet was immersed in a zinc plating bath (0.25 M zinc chloride, 3 M ammonium chloride) and subjected to constant current electrolysis using a graphite sheet as the counter electrode to deposit a thin zinc film on the surface of the steel wool sheet. The average thickness of the thin film, calculated as metallic zinc from the weight increase of the steel wool after washing and drying after zinc coating, was 5 μm. A steel wool sheet (after constant-current electrolytic oxidation treatment) coated with a thin nickel film, which was separately prepared under the same conditions as in Example 1, was used as the positive electrode, and a steel wool sheet coated with a thin zinc film was used as the negative electrode. The positive electrode was placed on one side of a bag made of the polyethylene sheet used in Example 1, and the negative electrode was placed on the other side, with polypropylene nonwoven fabric separating the two electrodes. Stainless steel ribbon terminals ultrasonically welded to both electrodes were allowed to protrude from the bag, and 6 M KOH was injected through the opening to impregnate both electrodes. The opening of the polyethylene bag was then melt-sealed under reduced pressure to produce an electrochemical element. The electrochemical device was confirmed to have good charge / discharge performance by constant current / constant voltage charge / constant current post-potential cutoff discharge under the same conditions as in Example 1. The discharge capacity after five charge / discharge cycles was 125 mAh. Next, as in Example 1, a metal rod was contacted with the exterior surface of the polypropylene nonwoven fabric portion of the electrochemical element, and the electrochemical element was bent 90 degrees 10 times. The metal rod was then pressed against a position rotated 90 degrees in-plane (a line crossing the positive electrode / separator / negative electrode), and the electrochemical element was bent 10 times at a 90-degree angle around the metal rod. After these longitudinal and transverse bending tests, no changes were observed in the appearance of the electrochemical element. A charge-discharge test was performed under the same charge-discharge conditions as before the stress test, resulting in an average discharge capacity of 132 mAh, with no deterioration in performance observed. [Industrial Applicability]

[0029] The electrochemical element of the present invention provides a flexible electrochemical element that has excellent resistance to external stress. Furthermore, the electrochemical element of the present invention is composed of electrodes containing an iron-based element metal fiber aggregate, and this metal fiber aggregate can be obtained using inexpensive raw materials and simple manufacturing processes. The metal fiber aggregate has excellent electrolyte material impregnation and retention properties for the electrochemical element, leading to stable performance and reduced defects, making it preferable. Furthermore, the electrochemical element of the present invention has excellent flexibility, allowing it to be used in new applications involving shape changes, unlike conventional applications that are limited to fixed shapes. [Explanation of symbols]

[0030] 1 negative electrode 2 Positive electrode 3 Separator 4. Exterior body 5, 6 electrode terminals 10 negative electrode 11 Positive electrode 12 Separator 13 Exterior body 14, 15 Electrode terminal 16 Exterior body sealing part

Claims

1. This is an electrochemical element that uses a fiber aggregate of iron group metal as an electrode, and the electrochemical element, which is composed of the electrode, electrolyte, and exterior body, is a flexible electrochemical element that can be deformed by external stress.

2. 2. A flexible electrochemical element according to claim 1, wherein at least a portion of the surface of the iron-group element metal fiber aggregate is coated with a thin film of a different metal element.

Images