Method for producing a boron-containing sheet, method for producing a negative electrode, boron-containing sheet, and its use

Abstract

This invention provides a method for manufacturing a borohydride-containing sheet with improved practicality as a battery material compared to conventional methods, a method for manufacturing a negative electrode, a borohydride-containing sheet, and its applications. [Solution] The method for manufacturing a borohydride-containing sheet according to the embodiment includes the steps of: (a) preparing a substrate having a first surface and a second surface opposite to the first surface; (b) bringing a borohydride-containing material containing borohydride into contact with the substrate; and (c) heating the borohydride-containing material to a temperature of 120°C or higher while the borohydride-containing material is spread on at least one of the first and second surfaces of the substrate.

Description

Technical Field

[0001] Embodiments of the present invention relate to a method for manufacturing a boron hydride-containing sheet, a method for manufacturing a negative electrode, a boron hydride-containing sheet, and use thereof.

Background Art

[0002] Boron hydride (BH) n is a material having a structure in which boron atoms form a two-dimensional network via hydrogen atoms, and has attracted attention because it is lightweight and resource-rich (see Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The inventors of the present invention focused on whether boron hydride can be used as a negative electrode active material for a lithium ion secondary battery, and conducted repeated studies.

[0005] [[ID=4l]]The problem to be solved by the present invention is to provide a method for manufacturing a boron hydride-containing sheet, a method for manufacturing a negative electrode, a boron hydride-containing sheet, and use thereof, which have improved practicality as battery materials as compared with the prior art. [[ID=4i]]

[0006] Another problem to be solved by the present invention is to provide a method for manufacturing a boron hydride-containing sheet, a method for manufacturing a negative electrode, a boron hydride-containing sheet, and use thereof, which have a stronger internal structure as compared with the prior art.

[0007] However, the problems of the present invention are not limited to the above, and those skilled in the art can clearly understand other problems from the description of the detailed description of the invention in this specification.

Means for Solving the Problem

[0008] The present invention may include the following aspects. [1] A method for producing a boron hydride-containing sheet, comprising: (a) preparing a substrate having a first surface and a second surface opposite to the first surface; (b) contacting a boron hydride-containing material containing boron hydride with the substrate; (c) heating the boron hydride-containing material to a temperature of 120°C or higher in a state where the boron hydride-containing material is spreading on at least one of the first surface and the second surface of the substrate. A method comprising the above steps. [2] The step (c) includes: - forming a boron hydride sheet on at least one surface of the substrate by heating the boron hydride-containing material to a temperature of 120°C or higher in a state where a solution of the boron hydride-containing material is spreading on at least one surface of the substrate, or - heat-treating the boron hydride-containing material at 120°C or higher in a state where a solid boron hydride sheet is formed on at least one surface of the substrate. The method according to [1], comprising the above steps. [3] The step (b) includes: - immersing the substrate in a solution of the boron hydride-containing material, or - placing a solution of the boron hydride-containing material on at least one surface of the substrate. The method according to [1] or [2], comprising the above steps. [4] After the step (b) and before the step (c), forming a boron hydride-containing sheet on the substrate by heating the substrate to a temperature below the boiling point of the solvent in a state where the solution of the boron hydride-containing material is spreading on at least one surface. The method according to any one of [1] to [3], comprising the above steps. [5] The substrate is a metal substrate. The method according to any one of [1] to [4]. [6]A method for manufacturing a negative electrode, comprising: (d) preparing a metal substrate having a first surface and a second surface opposite to the first surface as a negative electrode current collector; (e) contacting a boron hydride-containing material containing boron hydride with the metal substrate; (f) obtaining a negative electrode in which a boron hydride-containing sheet is formed on at least one surface of the metal substrate by heating the boron hydride-containing material at a temperature of 120 ° C or higher in a state where the boron hydride-containing material spreads on at least one of the first surface and the second surface of the metal substrate; A method comprising the above. [7]A boron hydride-containing sheet, wherein: in an infrared absorption spectrum using an infrared spectrophotometer, the height I of an absorbance peak BHB and I BH satisfy [Formula 1]. [Formula 1] I BHB / I BH ≧1 (I BHB is the height of the absorbance peak near 1250 cm -1 , and I BH is the height of the absorbance peak near 2500 cm -1 .) [8]The average composition of boron hydride contained in the boron hydride-containing sheet is represented by H x B(0 <x <1), the boron hydride-containing sheet according to [7]. [9]The boron hydride contained in the boron hydride-containing sheet is substantially insoluble in the electrolytic solution LIPASTE-EDEC / 1 (manufactured by Toyama Chemical Co., Ltd.) at room temperature. The boron hydride-containing sheet according to [7] or [8].

[10] At least one direction length of the boron hydride-containing sheet is 100 μm or more, the boron hydride-containing sheet according to any one of [7] to [9].

[11] A metal substrate, A borohydride-containing sheet according to any one of [7] to

[10] , formed on the metal substrate, A laminate containing the above.

[12] The negative electrode, The device comprises an electrode current collector and a negative electrode active material layer formed on the electrode current collector, The negative electrode active material layer includes a borohydride-containing sheet as described in any one of [7] to

[10] . Negative electrode. A secondary battery having the negative electrode described in

[13]

[12] . A catalyst, neutron absorbing material, hydrogen storage material, electronic material, communication material, or fuel material, comprising a borohydride-containing sheet as described in any one of

[14] [7] to

[10] .

[15] A sheet containing hydrogen boride, A metal substrate supporting the aforementioned hydrogen boride-containing sheet, Equipped with, A negative electrode in which the boron-containing sheet and the metal substrate are bonded together by a boron-metal bond. [Effects of the Invention]

[0009] According to one aspect of the present invention, it is possible to provide a method for producing a borohydride-containing sheet with improved practicality as a battery material compared to conventional methods, a method for producing a negative electrode, a borohydride-containing sheet, and its use.

[0010] According to another aspect of the present invention, it is possible to provide a method for producing a borohydride-containing sheet having a stronger internal structure than conventional methods, a method for producing a negative electrode, a borohydride-containing sheet, and its use. [Brief explanation of the drawing]

[0011] [Figure 1] A flowchart illustrating the method for producing a hydrogen boride-containing sheet according to the embodiment. [Figure 2] A photograph of the borohydride-containing sheet prepared in Experimental Example 2. [Figure 3] Graph showing the results of mass spectrometry of the boron-containing sheets prepared in Experimental Examples 1 and 3. [Figure 4] Infrared absorption spectra of the boron-containing sheets prepared in Experimental Examples 1 and 3. [Figure 5] XRD patterns of the boron-containing sheets prepared in Experimental Examples 2 and 4. [Figure 6] X-ray absorption spectra of the boron-containing sheets prepared in Experimental Examples 1 and 3. [Figure 7] X-ray absorption spectra of the boron-containing sheets prepared in Experimental Examples 1 and 3. [Figure 8] X-ray absorption spectra of the boron-containing sheets prepared in Experimental Examples 1 and 3. [Figure 9] A cyclic voltammogram of the boron-containing sheet prepared in Experimental Example 1. [Figure 10] A table showing the results of cyclic voltammetry of the boron-containing sheet prepared in Experimental Example 1. [Figure 11] A graph showing the discharge characteristics of a battery using the borohydride-containing sheet prepared in Experimental Example 1. [Modes for carrying out the invention]

[0012] The following describes the manufacturing method of the borohydride-containing sheet, the manufacturing method of the negative electrode, the borohydride-containing sheet, and its use according to the embodiments. Note that the following embodiments represent one aspect of the present invention and are not limiting, and can be arbitrarily modified within the scope of the technical idea of ​​the present invention. Furthermore, the various configurations and features of the embodiments can be arbitrarily combined.

[0013] The following description includes speculation about the mechanism of the invention, but this is merely one example of speculation by the inventors, and the present invention is not bound by these speculations.

[0014] <1. Boric acid-containing sheet> In this specification, "boron hydride" means a compound of hydrogen and boron. Specifically, a boron hydride represented by the chemical formula HB is known. Each boron atom (B) is connected to each other through a hydrogen atom (H) to form a two-dimensional network. The boron hydride that forms a two-dimensional network can be represented, for example, by the chemical formula (HB) n (n: natural number). The boron hydride may have a two-dimensional network in which a honeycomb structure formed by boron atoms forming a six-membered ring structure is continuous, or may have a two-dimensional network in which boron atoms form other cyclic structures such as a five-membered ring structure or a seven-membered ring structure. The boron hydride may also include a compound in which a part of hydrogen has desorbed from a boron hydride having a composition of H:B = 1:1 in molar ratio. Such a compound can be represented, for example, by the chemical formula (H x B) n (0 < x < 1, n: natural number).

[0015] In this specification, "boron hydride-containing sheet" means a material that contains boron hydride and has a two-dimensionally extended sheet shape. Note that the boron hydride-containing sheet is not limited to those containing only pure boron hydride, and may include boron hydride doped with other elements other than boron and hydrogen, or other materials.

[0016] The boron hydride-containing sheet contains, for example, 10 mass% or more, 20 mass% or more, 30 mass% or more, 40 mass% or more, 50 mass% or more, 60 mass% or more, 70 mass% or more, 80 mass% or more, or 90 mass% or more of boron hydride. The boron hydride-containing sheet may be substantially composed of only boron hydride. Here, "substantially composed of only" means that it may contain inevitable impurities.

[0017] The boron hydride constituting the boron hydride-containing sheet according to this embodiment preferably has an average composition of H x B (0 < x < 1) in which at least a part of hydrogen has desorbed. Here, "average composition" means the composition averaged over the entire boron hydride-containing sheet.

[0018] Preferably, the boron-containing sheet is supported by a substrate. The substrate may be in the form of, for example, a plate, mesh, sheet, or film. The substrate may have a layered structure in which multiple substrates are laminated. The material of the substrate is not particularly limited as long as it can support the boron-containing sheet. The substrate may be, for example, a metal substrate, a plastic substrate, a glass substrate, a ceramic substrate, or a composite material. The substrate is, for example, a metal mesh member. If the substrate is a metal substrate, the type of metal is not particularly limited, but examples include elemental metals such as aluminum, copper, nickel, iron, and chromium, as well as various alloys such as steel.

[0019] According to one embodiment, a laminate is provided that includes a metal substrate and the borohydride-containing sheet formed on the metal substrate.

[0020] <1.1 Physical properties of boric acid sheets> The borohydride-containing sheet exhibits an absorbance peak height of I in the infrared absorption spectrum measured using an infrared spectrophotometer. BHB and I BH This may satisfy [Equation 1]. [Formula 1] I BHB / I BH ≥1 (I BHB It is 1250cm -1 This is the height of the nearby absorbance peak, I BH It is 2500cm -1 This is the height of the nearby absorbance peak.

[0021] I BHB / I BH For example, this could be between 1 and 10, between 2 and 5, or between 3 and 4.

[0022] In the infrared absorption spectrum of the boric acid sheet, at 1250 cm⁻¹ -1 The absorbance peak in the vicinity is attributed to the BHB bond in the boric acid sheet. Meanwhile, at 2500 cm² -1The nearby absorbance peak is attributed to the BH bond in the boric acid sheet. The inventors have found that a boric acid-containing sheet heat-treated at a high temperature of 120°C or higher exhibits a 1250 cm³ absorption rate compared to a boric acid-containing sheet that has not undergone such heat treatment. -1 2500 cm² relative to the nearby absorbance peak -1 Peak intensity ratio of nearby absorbance peaks I BHB / I BH An increasing trend was observed. This is presumed to be because, due to high-temperature heat treatment, hydrogen atoms forming BH bonds at the ends of the borohydride-containing sheet and BH bonds in defective areas of the borohydride-containing sheet preferentially detach, while hydrogen atoms forming BHB bonds that form the network structure of the borohydride-containing sheet do not detach as much as BH bonds. Thus, it is presumed that the preferential detachment of hydrogen atoms from BH bonds at the ends and defective areas reduces the number of defects in the borohydride-containing sheet. Furthermore, it is presumed that, along with the detachment of hydrogen atoms at the ends and defective areas, at least some of the remaining boron atoms bond with metal atoms (for example, metal atoms contained in the substrate supporting the borohydride sheet). In this way, it is presumed that the detachment of hydrogen leads to the formation of recombination between boron atoms or boron-metal bonds (the metal being, for example, metal atoms contained in the substrate), making the material structure of the borohydride sheet stronger and less likely to dissolve into the electrolyte.

[0023] In particular, in the boron-containing sheet according to this embodiment, the substrate supports the boron two-dimensionally, stabilizing the two-dimensional network structure of the boron. When high-temperature heat treatment is performed, the boron-containing sheet is firmly bonded to the surface of the substrate, and it is presumed that hydrogen desorption preferentially occurs from the ends and defects of the boron-containing sheet, which are areas of low stability.

[0024] Preferably, the infrared absorption spectrum of the borohydride-containing sheet is 3500 cm⁻¹. -1 It has virtually no nearby absorbance peak. Here, "3500 cm -1 "Substantially lacking nearby absorbance peaks" means 3500 cm². -1The height of the nearby absorbance peak is I OH , 1250cm -1 The height of the nearby absorbance peak is I BHB When that happens, I OH / I BHB This means ≤0.1. 3500cm -1 The nearby absorbance peak is attributed to the stretching and contracting vibrations of water molecules. It is presumed that high-temperature heat treatment removes all or most of the water molecules that were present as impurities in the borohydride-containing sheet.

[0025] As described above, boron-containing sheets subjected to high-temperature heat treatment above 120°C undergo phenomena such as hydrogen desorption, impurity removal, and improved crystallinity at high temperatures. As a result, it is presumed that compared to boron-containing sheets obtained without high-temperature heat treatment above 120°C, the number of atomic-level defects is reduced and the internal structure is strengthened. Consequently, it is presumed that the range of motion of free electrons in the crystal widens and the band gap decreases, leading to a change in the absorption spectrum.

[0026] When a boron-containing sheet is formed on the surface of a metal substrate, preferably, the X-ray absorption spectrum of the boron-containing sheet has an X-ray absorption peak at the L-shell absorption edge of the metal atom (for example, a Ni atom, but not limited to that) corresponding to the metal-boron bond (for example, a Ni-B bond, but not limited to that). In addition, the X-ray absorption spectrum of the boron-containing sheet may have a metallic tail peak at the K-shell absorption edge of the boron atom.

[0027] When a boron-containing sheet is formed on a metal substrate, chemical bonds may be formed between the metal atoms and boron atoms, potentially strengthening the structure of the boron-containing sheet. For example, it is hypothesized that when a boron solution is heated and dried on a metal substrate, chemical bonds may be formed between the metal atoms of the substrate and the boron-containing sheet. Furthermore, it is hypothesized that the formation of chemical bonds between boron and metal atoms may result in metallic behavior (a tail peak) appearing at the K-shell absorption edge of boron. This facilitates electron transfer between the metal substrate and the boron-containing sheet, making it very effective, for example, when applying the boron-containing sheet to a battery.

[0028] <1.2 Electrochemical properties of boric acid sheets> Preferably, the oxidation potential and reduction potential of the boron-containing sheet can be detected when measured by cyclic voltammetry (a three-electrode method with the working electrode being the boron-containing sheet, the counter electrode being metallic Li, and the reference electrode being metallic Li). The oxidation potential of the boron-containing sheet may be between 1.8V and 2.0V, or between 1.85V and 1.95V. The reduction potential of the boron-containing sheet may be between 1.3V and 1.4V.

[0029] Preferably, the boron contained in the boron-containing sheet is substantially insoluble in the electrolyte LIPASTE-EDEC / 1 (manufactured by Toyama Pharmaceutical Co., Ltd.) at room temperature. Here, "substantially insoluble" means that when 1 g of boron is added to 100 mL of the electrolyte and left at room temperature for 1 hour, the amount of dissolved boron is 0.1 g or less. More preferably, the boron contained in the boron-containing sheet is substantially insoluble in the electrolyte even when multiple voltage scanning cycles (e.g., 5 times) of 0.01 V to 3.00 V are repeated in cyclic voltammetry. Note that LIPASTE-EDEC / 1 (product name) is 52.8% ethylene carbonate C3H4O3 and diethyl carbonate C5H 10 This composition contains 38.8% O3 and 8.4% lithium perchlorate LiClO4.

[0030] As described above, it is presumed that the boron-containing sheet subjected to high-temperature heat treatment has fewer atomic-level defects and a stronger internal structure. Furthermore, it is presumed that hydrogen desorption of boron at high temperatures occurs at the BH bonds formed at the ends and defect areas of the boron-containing sheet's network, rather than at the BHB bonds that form the network structure of the boron-containing sheet, as described above regarding the infrared absorption spectrum. Thus, it is presumed that a boron-containing sheet with fewer defects in its network structure and high crystallinity will have a regularly packed crystalline structure and will therefore be less soluble in electrolytes.

[0031] <1.3 Shape of the boric acid sheet> The borohydride-containing sheet is preferably substantially flat, without any twisted or wavy shapes. However, the borohydride-containing sheet does not have to be perfectly flat; for example, it may have a gently curved surface in part or overall. Here, "flat shape" refers to the borohydride-containing sheet being substantially flat as a whole, and it is acceptable for there to be slight irregularities on the main surface or sides of the sheet, or for there to be some warping or distortion at the edges of the sheet.

[0032] The borohydride-containing sheet has a length (for example, the maximum length along the main surface) measured in at least one direction of 100 μm or more, 200 μm or more, 500 μm or more, or 1 mm or more. Preferably, the borohydride-containing sheet has a length (for example, the maximum length along the main surface) measured in two mutually orthogonal directions of 100 μm or more, 200 μm or more, 500 μm or more, or 1 mm or more in each direction.

[0033] The thickness of the boron-containing sheet is not particularly limited, as long as it is sufficiently small compared to its two-dimensional extent. For example, the boron-containing sheet may consist of one layer of boron, or it may have a shape in which two or more layers of boron are laminated. There is no particular upper limit on the number of layers. For example, the thickness of the boron-containing sheet may be 1 nm to 100 μm, 10 nm to 50 μm, 100 nm to 20 μm, 500 nm to 10 μm, or 1 μm to 5 μm.

[0034] The size of a borohydride-containing sheet can be determined by observing a single borohydride-containing sheet, formed as a continuous sheet, with an optical microscope and measuring the length of the sheet along a given direction.

[0035] <1.4 Applications of boric acid sheets> Next, we will explain the uses of borohydride-containing sheets. Hydrogen boride is considered a promising functional material due to its lightweight nature, abundant raw material resources, low waste burden, and recyclability. It is also attracting attention as an energy material, with practical applications such as hydrogen transport and CO2 reduction reactions confirmed, and various theoretical predictions for other functionalities being made.

[0036] <1.4.1 Use of borohydride-containing sheets as negative electrode active material> The borohydride-containing sheet according to this embodiment can be used, for example, as a negative electrode active material for a secondary battery. According to one embodiment, a negative electrode active material or negative electrode mixture for a secondary battery is provided, which includes the above-mentioned hydrogen boride-containing sheet.

[0037] A secondary battery comprises a negative electrode, a positive electrode, and an electrolyte between the negative and positive electrodes. The secondary battery may contain an electrolyte solution, or it may be an all-solid-state battery containing a solid electrolyte. The secondary battery is, for example, a lithium-ion secondary battery, but it may also be another type of secondary battery, such as a sodium-ion secondary battery.

[0038] The negative electrode comprises a negative electrode current collector and a negative electrode active material layer formed on the negative electrode current collector. The negative electrode active material layer may include the boron-containing sheet described above. For example, the negative electrode current collector is the metal substrate described above, and the negative electrode active material layer is the boron-containing sheet described above. Alternatively, the negative electrode active material layer may have a laminated structure in which the boron-containing sheet and other layers are laminated. For example, the boron-containing sheet and a known negative electrode active material such as a carbon-based material may be used in combination as the negative electrode active material.

[0039] Furthermore, the composition and materials of the positive electrode and electrolyte are not particularly limited, and any positive electrode active material and electrolyte can be used as long as they enable the lithium-ion secondary battery to function. For example, examples of positive electrode active materials include lithium metal composite oxides containing lithium and one or more metals such as cobalt, manganese, nickel, copper, vanadium, and aluminum (e.g., lithium-manganese oxides, lithium-cobalt oxides, lithium-nickel oxides, lithium-nickel-manganese-cobalt oxides, etc.). Examples of electrolytes include organic liquid electrolytes and solid electrolytes (e.g., sulfide-based solid electrolytes) which are combinations of organic solvents and lithium salts (e.g., LiPF6).

[0040] Preferably, a lithium-ion secondary battery using a boron-containing sheet as the negative electrode active material has an initial discharge capacity of 3 mAh / g or more when measured at a current value of 0.01 A / g, and preferably has an initial discharge capacity of 10 mAh / g or more, 100 mAh / g or more, 150 mAh / g or more, 200 mAh / g or more, 500 mAh / g or more, 1000 mAh / g or more, or 1200 mAh / g or more. Here, "initial discharge capacity" refers to the discharge capacity in the first charge-discharge process performed after the aging of the secondary battery. Boron is lighter than carbon materials, which are currently widely used as negative electrode active materials in lithium-ion secondary batteries, and has been expected to be a promising battery material. The discharge capacity of a lithium-ion secondary battery using a boron-containing sheet as described above is significantly larger than that of a lithium-ion secondary battery using carbon, and the application of boron-containing sheets to next-generation batteries is strongly expected. Preferably, the boron-containing sheet is bonded to the metal substrate by boron-metal bonds. This facilitates electron transfer between the borohydride-containing sheet, which acts as the negative electrode active material, and the metal substrate. Therefore, it is believed that electrons moving during the charge-discharge reaction can be efficiently transferred without the use of conductive materials or binders. As a result, it is presumed that a high discharge capacity can be obtained without the use of conductive materials.

[0041] In another embodiment, the negative electrode comprises the borohydride-containing sheet described above and a metal substrate supporting the borohydride-containing sheet, wherein the borohydride-containing sheet and the metal substrate are bonded together by boron-metal bonds. As a result, as described above, the electron transfer efficiency between the borohydride-containing sheet as the negative electrode active material and the metal substrate as the current collector can be improved. Consequently, the charge-discharge characteristics or cycle characteristics of a secondary battery using this negative electrode can be improved. This laminated structure, in which the borohydride-containing sheet and the metal substrate are bonded together by boron-metal bonds, can be formed by heating the borohydride-containing material to a temperature of 120°C or higher while the borohydride-containing material is spread on one surface of the metal substrate (details of such a manufacturing method will be described later).

[0042] <1.4.2 Other Uses> The boron-containing sheet according to this embodiment can be used, in addition to the above-mentioned applications, as a catalyst, neutron-absorbing material, hydrogen storage material, electronic material, communication material, or fuel material, or as a material constituting such functional materials. This is due to the characteristics of boron, such as the inclusion of hydrogen atoms in its structure, being lighter than graphene, and having electrical conductivity of the same order as graphene.

[0043] <2. Method for manufacturing a borohydride-containing sheet> A method for producing a borohydride-containing sheet may include the following steps (a) to (c). (a) Step of preparing a substrate having a first surface and a second surface opposite to the first surface. (b) The step of bringing a borohydride-containing material containing borohydride into contact with the substrate. (c) A step of heating the borohydride-containing material to a temperature of 120°C or higher while the borohydride-containing material is spread on at least one of the first and second surfaces of the substrate.

[0044] The inventors have found that a borohydride-containing sheet with excellent functionality can be obtained by the above method. Figure 1 is a flowchart showing an example of a method for manufacturing a borohydride-containing sheet. Figure 1 includes not only the steps corresponding to steps (a) to (c) above, but also optional steps. The above method will be described in detail below with reference to Figure 1.

[0045] In step S100, the metal boride is brought into contact with the ion exchange material. For example, the metal boride and the ion exchange material are mixed in a liquid medium. This causes an ion exchange reaction, in which the metal cations of the metal boride are converted into protons (H + As a result of being exchanged for ) hydrogen boride (HB) n It generates.

[0046] In this specification, "metal boride" means a compound of boron with one or more metal elements. For example, metal boride has a structure in which boron atoms form a two-dimensional network. For example, metal boride has a layered structure in which metal cations are inserted between boron layers formed by a two-dimensional network of boron atoms. An example of a metal boride is metal diboride represented by the compositional formula MB2. Examples of metal borides include magnesium diboride (MgB2), aluminum diboride (AlB2), tantalum diboride (TaB2), zirconium diboride (ZrB2), rhenium diboride (ReB2), chromium diboride (CrB2), titanium diboride (TiB2), vanadium diboride (VB2), and yttrium boride (YB2); multimetallic borides such as yttrium chromium boride (YCrB4); and potassium boride (K2B9, KB9, KB). 18 Other examples include metallic borides of different compositions, such as lithium boride (Li2B5). Most metal diborides have a structure in which the boron atoms form a six-membered ring, while yttrium chromium boride (YCrB4) has a structure in which the boron atoms form five-membered and seven-membered rings.

[0047] In this specification, "ion exchange material" means a material having ion exchange capacity. For example, an ion exchange material contains ions that can exchange with metal cations. Preferably, the ion exchange material contains metal cations and protons (H + It is a material that can exchange ions with metal borides. An example of an ion exchange material that is not limited to ion exchange materials is an ion exchange resin. Any ion exchange resin that can exchange ions with metal borides can be used.

[0048] Non-limiting examples of ion exchange resins include strongly acidic ion exchange resins and weakly acidic ion exchange resins. Strongly acidic ion exchange resins are polymers having sulfo groups (-SO3H) as ion exchange groups. Examples of matrix materials for such ion exchange resins include styrene polymers, divinylbenzene polymers, and styrene-divinylbenzene copolymers. Weakly acidic ion exchange resins are polymers having carboxylic acid groups (-COOH) as ion exchange groups. Examples of matrix materials for such ion exchange resins include acrylic acid-based (co)polymers and methacrylic acid-based (co)polymers.

[0049] The ion exchange reaction in step S100 preferably proceeds in a liquid. For example, the ion exchange reaction occurs when metal boride dissolved in a liquid medium comes into contact with an ion exchange material present in a solid state in the liquid medium at the solid-liquid interface. Any liquid medium can be used as long as the above ion exchange reaction proceeds. For example, any liquid medium capable of dissolving metal boride (such as a polar solvent) can be used. Examples of liquid media include inorganic solvents such as water, and organic solvents such as methanol, ethanol, acetonitrile, and N,N-dimethylformamide.

[0050] The concentration of metal boride in the reaction solution is not particularly limited, but is preferably between 0.01 g / L and 500 g / L. If the concentration of metal boride is less than 0.01 g / L, a sufficient amount of hydrogen boride may not be obtained. If the concentration of metal boride is greater than 500 g / L, excessive aggregation of the product may occur, and a sheet-like product may not be obtained.

[0051] In step S102, residues such as ion exchange resin and impurities such as reaction by-products (e.g., boric acid) are removed during or after the ion exchange reaction. The removal method is not particularly limited, and any method such as filtration, extraction, chromatography, recrystallization, or adsorption can be used. The removal of residues and impurities may be performed at any time and may be carried out in multiple steps. If the residues and impurities are negligible, step S102 may be omitted.

[0052] In step S104, the obtained hydrogen boride solution (which may contain substances other than hydrogen boride; in that case, "hydrogen boride-containing solution" would be more appropriate, but for simplicity, it is referred to here as "hydrogen boride solution") is heated to a first temperature and concentrated. The first temperature is below the boiling point of the solvent, preferably between 50°C and 80°C. A heating temperature of 50°C or higher has the advantage of promoting the volatilization of the solvent due to thermal motion. A heating temperature of 80°C or lower has the advantage of suppressing the rapid volatilization of the solvent. Heating the hydrogen boride solution until its concentration is such that it can be retained on the sample bottle wall due to improved viscosity is preferable because it allows for efficient sheet formation afterward. In step S104, the solution may be allowed to evaporate naturally without heating, or a drying method such as reduced pressure may be used. Heating and drying methods may also be used in combination. The concentration step in step S104 can be omitted, but performing the concentration step allows for efficient separation of precipitated impurities.

[0053] Step S106 involves preparing a substrate to be used for forming the boron-containing sheet. Step S106 corresponds to step (a) above. Here, the type of substrate is not particularly limited. Any substrate of any shape, material, and size can be used as long as it has a flat surface for forming the boron-containing sheet. Non-limiting examples of substrates include metal substrates, glass substrates, silicon substrates, mica substrates, HOPG (highly oriented pyrolysis graphite) substrates, SiC substrates, and SiO2 substrates. Examples of metal substrates include metal plates and metal mesh substrates (for example, stainless steel or nickel mesh substrates. It is preferable that the pore size of the mesh is smaller than the desired size of the boron-containing sheet. For example, it may be on the order of 1 mm or smaller). The presence or absence of a coating such as an oxide film is not a concern for any of the substrates. Furthermore, the term "substrate" in this specification is not limited to an independent plate-like member, but may also refer to a flat part that constitutes a part of a member having a predetermined shape, such as a container.

[0054] In step S108, the concentrated borohydride solution is spread over the surface of the substrate. Step S108 corresponds to step (b) above. The method is not particularly limited, and the borohydride solution can be spread over the surface of the substrate by, for example, the following method. • Immerse the substrate in a boric acid solution. • Place the borohydride solution onto the surface of the substrate.

[0055] If step S108 includes immersing the substrate in a borohydride solution, the entire surface of the substrate can be coated with the borohydride solution, for example, by immersing the substrate in the borohydride solution and then removing it. This allows the surface of the substrate to be filled with the borohydride solution. On the other hand, if step S108 includes placing the borohydride solution on the surface of the substrate, the entire surface of one side of the substrate can be coated with the borohydride solution, for example, by placing the substrate on a horizontal stand and pipetting the borohydride solution over the entire surface of the substrate. This allows the surface of the substrate to be filled with the borohydride solution. However, the method of filling the surface of the substrate with the borohydride solution in step S108 is not limited to the above examples. For example, any coating method such as spin coating, dip coating, bar coating, or spray coating may be used.

[0056] In step S110, a borohydride-containing sheet is formed on the substrate surface by heating the substrate, which is supporting the borohydride solution, to a second temperature. This heating treatment causes the solvent in the borohydride solution to evaporate, leaving a solid or semi-solid borohydride-containing sheet on the substrate surface. The second temperature is preferably 50°C or higher and 80°C or lower. A heating temperature of 50°C or higher has the advantage that the volatilization of the solvent is promoted by thermal motion. A heating temperature of 80°C or lower has the advantage that the rapid volatilization of the solvent is suppressed.

[0057] In step S112, the substrate on which the boron-containing sheet is formed is heated to a third temperature higher than the first and second temperatures (hereinafter also referred to as "high-temperature heat treatment"). Step S112 corresponds to step (c) above. The third temperature is between 120°C and 2500°C, for example, between 150°C and 2300°C, between 200°C and 2000°C, between 250°C and 1500°C, between 300°C and 1200°C, between 400°C and 1000°C, or between 500°C and 800°C. If the heating temperature is 120°C or higher, the structural stability of the boron-containing sheet may be improved by the desorption of hydrogen atoms in the boron. If the heating temperature is 2500°C or lower, the boron can maintain its structure.

[0058] The atmosphere for the heat treatment in step S112 is not particularly limited. For example, the heat treatment may be carried out in an inert atmosphere or in air. Heat treatment in an inert atmosphere is preferable because it can prevent oxidation of the boron-containing sheet. The pressure during the heat treatment is also not particularly limited. The heat treatment may be carried out at atmospheric pressure, or under reduced pressure or increased pressure, as long as the desired boron-containing sheet is obtained.

[0059] Step S112 allows for the elimination of hydrogen from the boric acid as described above. This reduces defects in the structure of the boric acid-containing sheet and improves its crystallinity, thereby strengthening the internal structure of the boric acid-containing sheet. Furthermore, heating at a temperature above the boiling point of water can also cause the elimination of water contained as an impurity in the boric acid-containing sheet. Additionally, high-temperature heat treatment of the boric acid-containing sheet on the substrate can firmly bond the boric acid-containing sheet to the substrate.

[0060] The above describes a method for producing a borohydride-containing sheet according to an embodiment, but this is merely an example, and the steps may be omitted, modified, or added as appropriate. For example, step S110 may be omitted, and the substrate may be heated to a third temperature while the borohydride solution covers the substrate surface.

[0061] A separately prepared borohydride-containing sheet may be used instead of the borohydride solution. For example, by placing such a borohydride-containing sheet on the substrate surface and heating it to a third temperature, the internal structure of the borohydride-containing sheet can be strengthened in the same way as described above. It is preferable to physically attach the borohydride-containing sheet to the substrate by pressing or sticking it before heating, as this can promote bonding between the borohydride-containing sheet and the substrate through high-temperature heat treatment.

[0062] In other words, step (c) may include any of the following processes: - A process to form a borohydride sheet on at least one surface of a substrate by heating the borohydride-containing material to a temperature of 120°C or higher while the borohydride-containing material solution is spread over at least one surface of the substrate. - A process of heat-treating a boron-containing material at 120°C or higher while a solid boron sheet is formed on at least one surface of the substrate.

[0063] Furthermore, when a metal substrate (for example, a metal mesh substrate) is used as the base material for forming a boron-containing sheet, it is thought that metal-boron bonds can be formed by heating the boron-containing material and the metal substrate. In particular, when the boron-containing solution is applied to the metal substrate by immersion in the boron-containing solution, the substrate surface can be filled with a sufficient amount of boron, so it is presumed that metal-boron bonds are likely to be formed. Such metal-boron bonds facilitate electron transfer between the metal substrate and the boron-containing sheet, making it particularly preferable when the boron-containing sheet is used as a battery material. In this case, heating at the third temperature described above is not necessarily required; if metal-boron bonds are formed, the heat treatment may be performed only at temperatures below 120°C.

[0064] <3. Method for manufacturing the negative electrode> The method for manufacturing the negative electrode according to this embodiment includes the following steps (d) to (f). (d) A step of preparing a metal substrate having a first surface and a second surface opposite to the first surface as a negative electrode current collector. (e) The step of bringing a borohydride-containing material containing borohydride into contact with a metal substrate. (f) A step to obtain a negative electrode in which a borohydride-containing sheet is formed on at least one surface of the metal substrate by heating the borohydride-containing material to a temperature of 120°C or higher while the borohydride-containing material is spread on at least one of the first and second surfaces of the metal substrate.

[0065] The above method is basically the same as the one described in <2. Method for Manufacturing a Boric Acid-Containing Sheet>. With this method, a metal substrate can be used as the negative electrode current collector, so a negative electrode can be easily manufactured simply by forming a boric acid-containing sheet on the metal substrate. [Examples]

[0066] The present invention will be explained below with reference to experimental examples, but the present invention is not limited to the following experimental examples.

[0067] <Experimental Example 1> Under an inert gas atmosphere, 3 g of magnesium boride (MgB2 powder, manufactured by Rare Metallic Co., Ltd.) was added to 200 mL of acetonitrile (reagent grade, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) and dissolved. Next, 120 mL of ion exchange resin (product name: Amberlite IR120B H HG, manufactured by Organo Co., Ltd.) was added to the acetonitrile solution. After stirring this magnesium boride solution at room temperature for 72 hours, the residue in the reaction mixture was filtered to obtain a yellow filtrate. The filtrate was heated at 80°C for 2 hours to partially vaporize the acetonitrile and obtain a concentrated reaction solution. Impurities precipitated during heating were removed as appropriate.

[0068] Next, the concentrated reaction solution was applied to the Ni mesh substrate by immersing it in the concentrated reaction solution and then removing it. The concentration of the concentrated reaction solution was optimized by adding anhydrous acetonitrile (acetonitrile (super-dehydrated) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., for organic synthesis), hereinafter the same) to achieve the optimal thickness on the substrate. The substrate was then evacuated using a vacuum pump. The evacuation was performed carefully by slowly opening the manual valve to prevent holes from forming on the mesh. After that, it was slowly heated using an oil bath. The heating temperature was gradually increased from room temperature to 80°C in about 1 hour. After that, it was held at 80°C for about 1 hour, and then switched to 100°C to sufficiently vaporize the acetonitrile. After confirming that a boron layer had formed on the substrate, the temperature was raised to 300°C and heated for 24 hours. As a result, a yellowish transparent boron sheet was formed on the Ni mesh substrate (hereinafter referred to as "Sample 1"). Sample 1 was a sheet with each side measuring more than 1 mm.

[0069] <Experimental Example 2> After obtaining a concentrated reaction solution in the same manner as in Experimental Example 1, a borohydride sheet was prepared without immersing the Ni mesh substrate, as described below. First, 1.0 mL of concentrated reaction solution and 9.0 mL of anhydrous acetonitrile were added to a 20 mL sample bottle. The sample bottle was then directly connected to a vacuum pump. Vacuuming was performed carefully by slowly opening the manual valve to prevent sudden pressure changes and bumping. Next, the sample was slowly heated using an oil bath. The heating temperature was gradually increased from room temperature to 80°C in about 1 hour. After maintaining this temperature for about 1 hour, the temperature was increased to 100°C to confirm the formation of a boron layer on the substrate. The temperature was then raised to 300°C and heated for 24 hours. This evaporated the solvent, and the boron sheet formed on the wall of the sample bottle was physically peeled off the wall with a spatula to create a boron sheet that maintained its sheet shape independently without the need for a substrate such as a Ni mesh substrate (hereinafter referred to as "Sample 2"). The obtained boron sheet was brown in color. Figure 2 is a photograph of the obtained boron sheet (in a crushed state).

[0070] <Experimental Example 3> A borohydride sheet was formed on a Ni mesh substrate in the same manner as in Experimental Example 1, except that the heating temperature after sufficient vaporization of acetonitrile was changed to 100°C (hereinafter referred to as "Sample 3"). The resulting borohydride sheet was pale yellow in color.

[0071] <Experimental Example 4> A borohydride sheet was formed in the same manner as in Experimental Example 2, except that the heating temperature was changed to 100°C (hereinafter referred to as "Sample 4"). The resulting borohydride sheet was yellow in color.

[0072] <Evaluation Example 1: Desorption Gas Analysis> High-temperature mass spectrometry was performed on Sample 1 and Sample 3 under the following conditions. ·Equipment used: TDS1200 II (manufactured by Denshi Kagaku) • Set temperature: Room temperature to 1200℃ (30℃ / min) • Control thermocouple: T1 • Sample stage: Quartz stage • Type of mass spectrometer: Quadrupole mass spectrometer (QMS) Ionization method: Electron ionization • Measurement mode: SIM mode (selected mass number measurement mode) • Measurement range (m / z): 2 (Integrated time: 256 ms / ch) • Sample volume: 2.47 mg (Sample 1), 1.15 mg (Sample 3)

[0073] Figure 3 shows graphs of the mass spectrometry results for Sample 1 and Sample 3. In both samples, desorption of hydrogen molecules H2 (m / z=2) was confirmed at high temperatures. Furthermore, in Sample 3, more hydrogen desorption was observed than in Sample 1 in the temperature range below 200°C. This suggests that hydrogen desorption occurred during the sample preparation process in Sample 1, which was heated to 300°C.

[0074] <Evaluation Example 2: Dissolution into Electrolyte> To investigate the durability of the electrode material, samples 1-4 were immersed in 20 mL of electrolyte (material name: LIPASTE-EDEC / 1, manufactured by Toyama Pharmaceutical Co., Ltd.) at room temperature, and the elution of the borohydride sheets into the electrolyte (change in solution color, detachment from the Ni mesh, and presence or absence of precipitation) was visually observed. As a result, samples 1 and 2 were almost insoluble in the electrolyte, while samples 3 and 4 dissolved completely in the electrolyte.

[0075] The manufacturing conditions, observed colors, and results of <Evaluation Example 2> for each sample are summarized below. [Table 1]

[0076] <Evaluation Example 3: Infrared Absorption Spectrum> The infrared absorption spectra of Sample 1 and Sample 3 were measured under the following conditions. • Equipment used: ALPHA II (manufactured by BRUKER) • Measurement method: Total internal reflection measurement using a diamond substrate (measurement is performed while the obtained sample is held down). • Measurement range: 400cm -1 ~4,000cm -1 ·Resolution: 2.05cm -1 • Total number of times: 100

[0077] Figure 4 shows the infrared absorption spectra of Sample 1 and Sample 3. The infrared absorption spectrum of Sample 3 shows a peak attributable to impurities such as water (3500 cm⁻¹) compared to the infrared absorption spectrum of Sample 1. -1 It contained many (nearby) particles. Below are the infrared absorption spectra of Sample 1 and Sample 3 at 1250 cm⁻¹. -1 Peak intensity I of the nearby BHB oscillation peak BHB , 2500cm -1 Peak intensity I of nearby BH oscillation peaks BH , and 3500cm -1 Peak intensity I of nearby OH oscillation peaks OH The relative ratios were summarized. [Table 2]

[0078] <Evaluation Example 4: X-ray Diffraction (XRD) Pattern> The XRD patterns of Sample 2 and Sample 4 were measured under the following conditions. ·Equipment used: R-AXIS RAPID II (manufactured by Rigaku) ·Radiation source: MoKα radiation (λ=0.71073Å) • Tube voltage: 40kV ·Bulb current: 30mA • Measurement range: 0° to 30° • Step width: 0.045° / step • Scanning speed: 4.5° / min (Sample 2), 90° / min (Sample 4)

[0079] Figure 5 shows the XRD patterns of Sample 2 and Sample 4. In the XRD pattern of Sample 2, a sharp peak originating from hydrogen boride was observed, while in the XRD pattern of Sample 4, the peak originating from hydrogen boride was broader compared to that of Sample 2, suggesting that Sample 2 has higher crystallinity than Sample 4.

[0080] <Evaluation Example 5: X-ray Absorption Spectrum> The X-ray absorption spectra of Sample 1 and Sample 3 were measured under the following conditions. • Equipment used: X-ray absorption spectrometer • Beamline: NanoTerasu BL08U • Measurement methods: TEY (Total Electron Yield) and PFY (Partial Fluorescence Yield) • Spectrometer: Diffraction grating • Measurement range: 180eV~230eV (BK shell absorption edge), 840eV~890eV (Ni-L shell absorption edge)

[0081] Figure 6 shows the X-ray absorption spectra (measured in TEY mode) at the Ni-L shell absorption edge for Sample 1 and Sample 3. While Sample 3 showed an absorption peak for ordinary metallic Ni, Sample 1 showed a peak attributable to the Ni-B bond in addition to the Ni absorption peak. Furthermore, in the region shown in Figure 6, the spectrum of Sample 3 closely matched that of the Ni mesh substrate.

[0082] Figure 7 shows the X-ray absorption spectra at the BK shell absorption edge of Sample 1 and Sample 3 (measured in TEY mode). Figure 8 shows the X-ray absorption spectra at the BK shell absorption edge of Sample 1 and Sample 3 (measured in PFY mode). Comparing Sample 1 and Sample 3 in both TEY and PFY modes, the absorption edge of Sample 3 rose more gradually than that of Sample 1.

[0083] <Evaluation Example 6: Cyclic Voltammetry> Cyclic voltammetry was performed on sample 1 under the following conditions. • Equipment used: VersaStat4 (manufactured by AMETEK Science Instruments) • Measurement method: Three-electrode method (working electrode: manufactured borohydride sheet, counter electrode: metallic lithium, reference electrode: metallic lithium) • Solvent: LIPASTE-EDEC / 1 (manufactured by Toyama Pharmaceutical Co., Ltd.) • Mass of sample 1: 2.4 mg • Support electrolyte: LIPASTE-EDEC / 1 (manufactured by Toyama Pharmaceutical Co., Ltd.) ·Measurement liquid temperature: 23℃ Scanning range: 0.01V~3.00V • Scanning speed: 0.1 mV / sec

[0084] Figures 9 and 10 show the cyclic voltammetry results for Sample 1. Stable behavior was observed throughout 5 cycles, and peaks for oxidation and reduction reactions were confirmed. The oxidation potential corresponding to the upward peak of approximately 1.93 V is thought to indicate the ionization reaction of lithium. The reduction potential corresponding to the downward peak of approximately 1.37 V is thought to indicate the incorporation of lithium ions into the borohydride sheet.

[0085] <Evaluation Example 7: Discharge Characteristics> The discharge characteristics of Sample 1 were measured under the following conditions. • Equipment used: HJ1020mSD8 (manufactured by MEIDEN HOKUDO) • Pretreatment: Three-electrode method (working electrode: manufactured borohydride sheet, counter electrode: metallic lithium, reference electrode: metallic lithium) ·Measurement temperature: 23℃ • Discharge rate: 0.5mA / g Voltage range: 0.01V~3.00V

[0086] Figure 11 shows the measurement results of the discharge characteristics of Sample 1. According to Figure 11, the measured discharge capacity was approximately 150 mAh / g. Thus, it was confirmed that Sample 1 exhibits a superior discharge capacity compared to conventional samples, even without the addition of conductive materials and binders.

[0087] <Interpretation of experimental results> The following describes the interpretation of the evaluation results for each of the above experimental examples 1 to 4. However, the following is merely a provisional interpretation at the time of filing, and the present invention is not bound by this interpretation.

[0088] When comparing samples 1-2, which were heated at 300°C, with samples 3-4, which were heated at 100°C, the first difference was in their appearance. Specifically, samples 1-2 were brownish, while samples 3-4 were yellowish.

[0089] According to <Evaluation Example 3>, in Sample 1, which was heat-treated at a high temperature (300°C), the absorption peaks attributed to impurities such as water were reduced compared to Sample 3, which was heat-treated at a low temperature (100°C). This result suggests that the impurities in Sample 3 were removed in Sample 1 by the high-temperature heat treatment. Also, 1250 cm -1 Nearby BHB oscillation peak and 2500 cm -1 Looking at the nearby BH oscillation peaks, the peak intensity ratio (I) in sample 1 is higher than that of sample 3. BHB / I BH The large size suggests that the number of BH bonds in the molecular structure is reduced compared to sample 3.

[0090] According to <Evaluation Example 4>, the XRD pattern of Sample 2 showed a sharper peak around 7° compared to the XRD pattern of Sample 4. This result suggests that the crystallinity of Sample 2 was improved compared to Sample 3 due to high-temperature heat treatment.

[0091] According to <Evaluation Example 5>, in Sample 1, a peak attributed to the Ni-B bond was observed at the Ni-L shell absorption edge. Furthermore, in Sample 1, the rise of the BK shell absorption edge was gentler compared to Sample 2, in which the borohydride sheet was physically attached to the substrate.

Claims

1. A method for producing a hydrogen boride-containing sheet, (a) A step of preparing a substrate having a first surface and a second surface opposite to the first surface, (b) The step of bringing a borohydride-containing material containing borohydride into contact with the substrate, (c) The step of heating the borohydride-containing material to a temperature of 120°C or higher while the borohydride-containing material is spread on at least one of the first and second surfaces of the substrate, Methods that include...

2. Step (c) is, - To form a borohydride sheet on at least one surface of the substrate by heating the borohydride-containing material to a temperature of 120°C or higher while the borohydride-containing material solution is spread on at least one surface of the substrate, or - With a solid borohydride sheet formed on at least one surface of the substrate, the borohydride-containing material is heat-treated at 120°C or higher. The method according to claim 1, including the method described in claim 1.

3. Step (b) above is: - Immerse the substrate in the solution of the borohydride-containing material, or - Placing the solution of the borohydride-containing material on at least one surface of the substrate. The method according to claim 1 or 2, including the method according to claim 1 or 2.

4. After step (b) and before step (c), the process includes forming a borohydride-containing sheet on the substrate by heating the substrate to a temperature below the boiling point of the solvent while the borohydride-containing material solution is spread over at least one surface of the substrate. The method according to claim 1 or 2, including the method according to claim 1 or 2.

5. The substrate is a metal substrate. The method according to claim 1 or 2.

6. A method for manufacturing a negative electrode, (d) A step of preparing a metal substrate having a first surface and a second surface opposite to the first surface as a negative electrode current collector, (e) The step of bringing a borohydride-containing material containing borohydride into contact with the metal substrate, (f) A step of obtaining a negative electrode in which a borohydride-containing sheet is formed on at least one of the first and second surfaces of the metal substrate by heating the borohydride-containing material to a temperature of 120°C or higher while the borohydride-containing material is spread on at least one of the first and second surfaces of the metal substrate, Methods that include...

7. A sheet containing hydrogen boride, In infrared absorption spectra obtained using an infrared spectrophotometer, the height of the absorbance peak I ＢＨＢ and I ＢＨ A borohydride-containing sheet that satisfies [Formula 1]. [Formula 1] I ＢＨＢ / I ＢＨ ≧1 (I ＢＨＢ It is 1250 cm －１ This is the height of the nearby absorbance peak, I ＢＨ It is 2500 cm －１ This is the height of the nearby absorbance peak.

8. The average composition of boron hydride contained in the borohydride-containing sheet is H ｘ represented by B(0 < x < 1), The borohydride-containing sheet according to claim 7.

9. The boron contained in the boron-containing sheet is substantially insoluble in the electrolyte LIPASTE-EDEC / 1 (manufactured by Toyama Pharmaceutical Co., Ltd.) at room temperature. A borohydride-containing sheet according to claim 7 or 8.

10. The borohydride-containing sheet has a length of 100 μm or more in at least one direction. A borohydride-containing sheet according to claim 7 or 8.

11. Metal substrate and A borohydride-containing sheet according to claim 7 or 8, formed on the metal substrate, A laminate containing the above.

12. It is the negative electrode, The device comprises an electrode current collector and a negative electrode active material layer formed on the electrode current collector, The negative electrode active material layer includes the borohydride-containing sheet described in claim 7 or 8. Negative electrode.

13. A secondary battery comprising the negative electrode described in claim 12.

14. A catalyst, neutron absorbing material, hydrogen storage material, electronic material, communication material, or fuel material comprising the borohydride-containing sheet described in claim 7 or 8.

15. A sheet containing hydrogen boride, A metal substrate supporting the aforementioned hydrogen boride-containing sheet, Equipped with, A negative electrode in which the boron-containing sheet and the metal substrate are bonded together by a boron-metallic bond.

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