Negative electrode member and battery

Abstract

To provide a negative electrode member capable of realizing a battery such as a lithium metal battery in which discharge capacity is unlikely to decrease and discharge performance is excellent, and a battery including the negative electrode member.SOLUTION: A negative electrode member of the present invention includes: a fiber sheet; and a carbon nanotube, and the fiber sheet contains organic fibers as constituent fibers. As a result of study, the applicant of the present application has found that a battery having excellent discharge performance can be realized in the case where a carbon nanotube in which an intensity ratio (g / d) between a peak value (g) of a G band derived from vibration of a graphite structure of the carbon nanotube and a peak value (d) of a D band derived from vibration of a defect part of the carbon nanotube is greater than 0.5, which is obtained by subjecting the negative electrode member having the above-described configuration to Raman spectrum measurement, is provided.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a negative electrode member usable in a battery, such as a lithium metal battery, and to a battery including the negative electrode member. [Background technology]

[0002] A negative electrode comprising a metal active material has a high theoretical capacity and a low negative electrode potential, and is therefore attracting attention as a negative electrode that can realize a battery with a high energy density (for example, a lithium metal battery).

[0003] The present applicant has previously proposed a conductive sheet as described in Japanese Patent Laid-Open Publication No. 2023-046012 (Patent Document 1) as a component capable of constituting the negative electrode of such a battery (hereinafter, sometimes referred to as a negative electrode component). This conductive sheet comprises a fiber sheet containing organic fibers as constituent fibers and a conductive material, with the conductive material being attached to the surface of the constituent fibers of the fiber sheet. Patent Document 1 also describes that carbon nanotubes can be used as the conductive material.

[0004] However, when a battery including the conductive sheet described in Patent Document 1 as a negative electrode member was prepared and the battery was charged and discharged, the discharge capacity decreased during the charge and discharge process, and the discharge performance of the battery sometimes deteriorated. This problem was particularly likely to occur in lithium metal batteries.

[0005] Therefore, as long as the negative electrode member according to the prior art is used, it has been difficult to realize a battery such as a lithium metal battery whose discharge performance is resistant to deterioration. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2023-046012 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention has been made under these circumstances, and aims to provide a negative electrode member that can realize a battery such as a lithium metal battery that is resistant to a decrease in discharge capacity and has excellent discharge performance, and also aims to provide a battery that is equipped with the negative electrode member and is resistant to a decrease in discharge capacity and has excellent discharge performance. [Means for solving the problem]

[0008] The invention of claim 1 of the present invention is "a negative electrode member comprising a fiber sheet and carbon nanotubes, wherein the fiber sheet contains organic fibers as constituent fibers, the carbon nanotubes are present on the surface of the constituent fibers of the fiber sheet, and the intensity ratio (g / d) of the peak value (g) of the G band resulting from vibration of the graphite structure of the carbon nanotubes to the peak value (d) of the D band resulting from vibration of defects in the carbon nanotubes, obtained by subjecting the negative electrode member to Raman spectroscopy, is greater than 0.5."

[0009] The invention according to claim 2 of the present invention is a product that has an air permeability of 0.1 cm as measured by the Frazier method specified in JIS L 1913 6.8.1. 3 / cm 2 / s or more.

[0010] The invention according to claim 3 of the present invention is "the negative electrode member according to claim 1, wherein the percentage of the mass of the carbon nanotubes in the mass of the negative electrode member is 0.5 to 40 mass %."

[0011] The invention according to claim 4 of the present invention is "a basis weight of 45 g / m 2 The negative electrode member according to claim 1, wherein:

[0012] The invention according to claim 5 of the present invention is "the negative electrode member according to claim 1, which has a thickness of 150 μm or less."

[0013] The invention according to claim 6 of the present invention is "a battery comprising the negative electrode member according to any one of claims 1 to 5." [Effects of the Invention]

[0014] The negative electrode member according to claim 1 of the present invention comprises a fiber sheet and carbon nanotubes, and the fiber sheet contains organic fibers as constituent fibers.

[0015] As a result of research, the applicant of the present application has found that when the negative electrode member has the above-mentioned configuration and is provided with carbon nanotubes in which the intensity ratio (g / d) between the peak value (g) of the G band resulting from the vibration of the graphite structure of the carbon nanotube and the peak value (d) of the D band resulting from the vibration of the defect portion of the carbon nanotube is greater than 0.5, the discharge capacity is less likely to decrease and a battery with excellent discharge performance can be realized.

[0016] Although the reason why this effect is exhibited has not been fully clarified, it is believed that the following effects are exhibited.

[0017] The G band is a peak derived from the graphene structure (a hexagonal lattice structure of carbon atoms) of carbon nanotubes, and refers to the parts where the carbon bonds that make up the carbon nanotubes are uniformly distributed and bonded. On the other hand, the D band is a peak derived from the parts (sometimes called defects) where the graphene structure of carbon nanotubes is interrupted.

[0018] Therefore, the larger the G band peak value (g) relative to the D band peak value (d), i.e., the higher the intensity ratio (g / d) calculated from both peak values, the lower the proportion of defects in the carbon nanotube, and the higher the electronic conductivity of the carbon nanotube is considered to be.

[0019] As will be apparent from the examples described below, it has been discovered that by using carbon nanotubes with a high intensity ratio (g / d) as the negative electrode component, it is possible to provide a battery that is less likely to experience a decrease in discharge capacity and has excellent discharge performance.

[0020] The negative electrode member according to claim 2 of the present invention has an air permeability of 0.1 cm as measured by the Frazier method. 3 / cm 2 / s or more. Air permeability is 0.1 cm 3 / cm 2 A negative electrode member having a capacity of 1000 vol / s or more also has high liquid permeability and can contribute to lowering the resistance of the battery, and therefore can provide a battery with even better discharge performance.

[0021] In the negative electrode member according to claim 3 of the present invention, the percentage of the mass of the carbon nanotubes in the mass of the negative electrode member is 0.5 to 40 mass%. When the percentage of the mass of the carbon nanotubes in the mass of the negative electrode member is 0.5 mass% or more, the negative electrode member has excellent electrical conductivity. Furthermore, when the percentage is 40 mass% or less, the carbon nanotubes are prevented from agglomerating into a film-like structure in the voids of the fiber sheet. Therefore, the voids formed between the constituent fibers are prevented from being blocked by the carbon nanotubes agglomerated into a film-like structure. As a result, the electrolyte can sufficiently penetrate into the negative electrode member, which contributes to lowering the resistance of the battery. Therefore, the negative electrode member can provide a battery with even better discharge performance.

[0022] The negative electrode member according to claim 4 of the present invention has a basis weight of 45 g / m 2 Since the negative electrode member has a small value of 0.1 to 1.0, it can contribute to lowering the resistance inside the battery, and therefore can provide a battery with even better discharge performance.

[0023] The negative electrode member according to claim 5 of the present invention has a thickness of 150 μm or less, which contributes to lowering the resistance inside the battery, and therefore is a negative electrode member that can provide a battery with even better discharge performance.

[0024] The battery according to claim 6 of the present invention includes the negative electrode member according to the present invention, and therefore has excellent discharge performance. DETAILED DESCRIPTION OF THE INVENTION

[0025] The negative electrode member of the present invention includes carbon nanotubes, which serve to impart electrical conductivity to the negative electrode member.

[0026] The intensity ratio (g / d) of the G-band peak value (g), which is derived from the vibration of the graphite structure of the carbon nanotube, to the D-band peak value (d), which is derived from the vibration of defects in the carbon nanotube, obtained by Raman spectroscopy of this carbon nanotube is greater than 0.5. The G-band is a peak derived from the graphene structure (a hexagonal lattice structure of carbon atoms) of the carbon nanotube, and represents the portions where the carbon bonds that make up the carbon nanotube are uniformly present and bonded. On the other hand, the D-band represents the portions (sometimes referred to as defects) where the graphene structure of the carbon nanotube is interrupted.

[0027] Therefore, the larger the G-band peak value (g) relative to the D-band peak value (d), i.e., the higher the intensity ratio (g / d) calculated from both peak values, the fewer defects there are in the carbon nanotube, and the longer the bonds between the carbon atoms that make up the carbon nanotube.This suggests that the carbon nanotube has high electron conductivity.

[0028] The applicant of the present application has found that by using carbon nanotubes with a high intensity ratio (g / d) and few defects, it is possible to realize a battery with excellent discharge performance and with a low drop in discharge capacity.

[0029] Although the reason why this effect is exhibited has not been fully clarified, it is believed that the following effects are exhibited.

[0030] It is generally known that if the chemical reaction occurring on the negative electrode surface during battery charging and discharging is uneven, dendrites due to the components constituting the negative electrode will form on the negative electrode surface. This dendrite formation is known to be particularly likely in batteries with metal electrodes, such as lithium metal batteries. The detachment of these dendrites from the negative electrode causes a decrease in the discharge capacity of the battery.

[0031] On the other hand, when a battery contains the negative electrode member according to the present invention, the highly electron-conductive carbon nanotubes contained in the negative electrode member uniformly distribute electrons on the negative electrode surface, which is believed to result in uniform chemical reactions occurring on the negative electrode surface during battery charge and discharge, thereby suppressing the generation of dendrites and, as a result, making it less likely that the battery's discharge capacity will decrease.

[0032] It is believed that the higher the intensity ratio (g / d), the fewer defects there are in the carbon nanotubes, the less likely the discharge capacity to decrease, and the more excellent the discharge performance of the battery that can be realized, so it is more preferably 0.8 or more, even more preferably 5 or more, and even more preferably 10 or more. Regarding the upper limit of the intensity ratio (g / d), 300 or less is realistic, 200 or less is more realistic, and 100 or less is even more realistic.

[0033] The "intensity ratio (g / d) between the peak value (g) of the G band resulting from the vibration of the graphite structure of the carbon nanotube and the peak value (d) of the D band resulting from the vibration of the defect portion of the carbon nanotube, obtained by subjecting the carbon nanotube to Raman spectrum measurement" is determined by measuring the Raman spectrum of the carbon nanotube using a 532 nm laser wavelength with a Raman spectrophotometer as described in JIS K0137:2010 "General Rules for Raman Spectroscopic Analysis," and determining the intensity ratio (g / d) of the peak value (d) of the D band resulting from the vibration of the defect portion of the carbon nanotube from the Raman spectrum of the carbon nanotube obtained by Raman spectrum measurement using a 532 nm laser wavelength. -1 The maximum peak value in the range of 1310 to 1350 cm is the G-band peak value (g). -1 The maximum peak value within this range is taken as the D band peak value (d), and the intensity ratio (g / d) is calculated.

[0034] The carbon nanotubes constituting the negative electrode member of the present invention may be single-walled carbon nanotubes or multi-walled carbon nanotubes.

[0035] The method for producing carbon nanotubes is not particularly limited, and carbon nanotubes can be produced using, for example, carbon nanotube synthesis methods such as arc discharge, laser ablation, chemical vapor deposition (CVD), etc. Among these production methods, chemical vapor deposition (CVD) is preferred because it tends to enable the mass production of high-purity carbon nanotubes.

[0036] The diameter of the carbon nanotubes is preferably 0.5 nm or more, more preferably 1 nm or more, and even more preferably 2 nm or more, so as to suppress aggregation of the carbon nanotubes and facilitate uniform distribution of the carbon nanotubes within the negative electrode member. On the other hand, if the diameter of the carbon nanotubes is too large, the conductivity of the carbon nanotubes tends to decrease, so the upper limit of the diameter of the carbon nanotubes is preferably 200 nm or less, more preferably 100 nm or less, and even more preferably 50 nm or less. In the present invention, the diameter of the carbon nanotubes can be determined by measuring the diameter (outer diameter) of 100 randomly selected carbon nanotubes using a transmission electron microscope and calculating the arithmetic mean value of the diameters of these 100 carbon nanotubes.

[0037] The fiber length of the carbon nanotubes is preferably 0.1 μm or more, more preferably 3 μm or more, and even more preferably 5 μm or more so that they are well entangled with the constituent fibers of the fiber sheet and are less likely to fall off from the fiber sheet. On the other hand, if the fiber length of the carbon nanotubes is too long, there is a risk of the carbon nanotubes breaking, so the fiber length is preferably 5000 μm or less, more preferably 1000 μm or less, and even more preferably 100 μm or less. In the present invention, the fiber length of the carbon nanotubes can be determined by measuring the fiber lengths of 100 randomly selected carbon nanotubes using a transmission electron microscope and calculating the arithmetic mean value of the diameters of these 100 carbon nanotubes.

[0038] The aspect ratio of the carbon nanotubes is preferably 100 or more, more preferably 150 or more, and even more preferably 200 or more, so that the negative electrode member has excellent conductivity due to the action of the carbon nanotubes. On the other hand, if the aspect ratio of the carbon nanotubes is too large, the carbon nanotubes may break, so the aspect ratio is preferably 100,000 or less, more preferably 70,000 or less, and even more preferably 50,000 or less. In the present invention, the aspect ratio of the carbon nanotubes means the value of (carbon nanotube fiber length (μm) / carbon nanotube diameter (μm)).

[0039] The negative electrode member of the present invention includes a fiber sheet containing organic fibers as constituent fibers in addition to carbon nanotubes. This fiber sheet provides high flexibility to the negative electrode member, and when a battery including a negative electrode incorporating this negative electrode member expands and contracts during charging and discharging or when an external force is applied to the negative electrode, the fiber sheet provides a buffering effect, preventing cracking of the negative electrode and providing a battery with excellent discharge performance and less reduction in discharge capacity.

[0040] The fiber sheet provided in the negative electrode member of the present invention may be, for example, a nonwoven fabric, a woven fabric, or a knitted fabric. Among these, a nonwoven fabric that can achieve a high porosity is preferred. When the fiber sheet is a nonwoven fabric, it may be, for example, a dry nonwoven fabric formed by a carding method or an air-laying method, a wet nonwoven fabric formed by a wet method, or a direct-spun nonwoven fabric (spunbond nonwoven fabric, melt-blown nonwoven fabric, electrospun nonwoven fabric, etc.) formed by spinning a molten resin or a solution dissolved in a solvent. Among these, the fiber sheet included in the negative electrode member of the present invention is preferably a wet nonwoven fabric, since it can provide a thin nonwoven fabric with uniform fiber distribution and high porosity.

[0041] The fiber sheet provided in the negative electrode member of the present invention contains organic fibers as constituent fibers, and examples of the organic resin that constitutes this organic fiber include polyolefin resins (polypropylene resin, polyethylene resin, polymethylpentene, polyolefin resins having a structure in which a portion of hydrocarbons is substituted with a cyano group or a halogen such as fluorine or chlorine, etc.), styrene resins, polyether resins (polyether ether ketone, polyacetal, phenolic resin, melamine resin, urea resin, epoxy resin, modified polyphenylene ether, aromatic polyether ketone, etc.), polyester resins (polyethylene terephthalate resin, polytrimethylene terephthalate resin, polybutylene terephthalate resin, polyethylene naphthalate resin, polybutylene naphthalate resin, polycarbonate resin, polyarylate resin, wholly aromatic polyester resin, unsaturated polyester resin, etc.), and the like. Examples of organic resins include ester resins, polyimide resins, polyamideimide resins, polyamide resins (aromatic polyamide resins, aromatic polyetheramide resins, nylon resins, etc.), resins containing nitrile groups (e.g., polyacrylonitrile resins), urethane resins, epoxy resins, polysulfone resins (polysulfone resins, polyethersulfone resins, etc.), fluorine-containing resins (polytetrafluoroethylene resins, polyvinylidene fluoride resins, etc.), cellulose resins (rayon fibers, etc.), polybenzimidazole resins, acrylic resins (polyacrylonitrile resins copolymerized with acrylic ester resins or methacrylic esters, modacrylic resins copolymerized with acrylonitrile and vinyl chloride or vinylidene chloride, etc.), vinylon resins (vinyl acetate resins, polyvinyl alcohol resins, etc.), and polyphenylene sulfide resins. The fiber sheet may be composed of a single organic resin or two or more organic resins.

[0042] These organic resins may be either linear or branched polymers, may be block copolymers or random copolymers, and may have any three-dimensional structure or may be crystalline or non-crystalline.

[0043] The fibers constituting the fiber sheet may be monofilaments or composite fibers. The composite fibers may be, for example, sheath-core, island-in-sea, side-by-side, orange, or bimetallic. Furthermore, the fibers may be fibrillar.

[0044] The fiber sheet preferably includes partially heat-sealed composite fibers. Fiber fusion using partially heat-sealed composite fibers allows the intersections between the constituent fibers of the fiber sheet to be integrated without using resin components other than the resin constituting the fibers, such as binders, thereby providing a highly rigid conductive sheet. In particular, if the composite fibers are partially heat-sealed, high-strength core-sheath composite fibers with high tensile strength, a negative electrode member with excellent mechanical strength, such as penetration resistance, can be provided, which is preferable. As such fibers, partially heat-sealed, high-strength polyolefin-based core-sheath composite fibers (e.g., a polypropylene core component and a high-density polyethylene sheath component) with a tensile strength of 2.0 cN / dtex or more can be used.

[0045] The fibers constituting the fiber sheet may have a cross-sectional shape that is not only perfectly circular, nearly circular, or elliptical, but also irregular cross-section fibers. Examples of irregular cross-section fibers include fibers having a cross section that is hollow, polygonal such as a triangle, alphabetic such as a Y-shape, irregular, multi-lobed, symbolic such as an asterisk, or a shape combining multiple of these shapes.

[0046] The fineness of the fibers constituting the fiber sheet is preferably 0.01 to 20 dtex, more preferably 0.02 to 15 dtex, and even more preferably 0.03 to 10 dtex, so that the fiber sheet and the negative electrode member including the fiber sheet have sufficient strength. Note that the fineness in the present invention can be measured by the method specified in Method A described in 8.5.1 of JIS L 1015 (2010) "Testing Methods for Chemical Fiber Staples."

[0047] The fiber sheet has a certain basis weight, which makes the negative electrode member easier to handle. Furthermore, a small basis weight of the fiber sheet makes it less likely that the fibers constituting the negative electrode member will impede contact between the active materials constituting the negative electrode, contributing to lowering the resistance of the battery. This makes it possible to provide a battery with even better discharge performance. For this reason, the basis weight of the fiber sheet is set to 1 to 40 g / m. 2 is preferable, and 3 to 20 g / m 2 More preferably, 4 to 15 g / m 2 The basis weight in the present invention is defined as the mass per unit area as specified in 6.2 of JIS L 1913 (2010) "Testing methods for general nonwoven fabrics."

[0048] The fiber sheet provided in the negative electrode member of the present invention contains organic fibers as constituent fibers, but may also contain fibers other than organic fibers, such as metal fibers made of metal, metal oxide fibers made of metal oxide, and carbon fibers having a larger fiber diameter and a longer fiber length than carbon nanotubes.

[0049] The percentage of the mass of fibers other than organic fibers in the mass of the fiber sheet provided in the negative electrode member of the present invention is preferably 20% by mass or less, more preferably 10% by mass or less, even more preferably 5% by mass or less, and most preferably 0% by mass, i.e., the fiber sheet is composed only of organic fibers, because the percentage of the mass of fibers other than organic fibers in the mass of the fiber sheet is higher when the mass of the organic fibers in the mass of the fiber sheet is higher, and therefore the flexibility of the negative electrode member provided with the fiber sheet is higher. Furthermore, when a battery including a negative electrode incorporating this negative electrode member expands and contracts during charging and discharging, or when an external force is applied to the negative electrode, the flexible fiber sheet can provide a buffering effect, preventing cracking in the negative electrode and providing a battery with a low discharge capacity and excellent discharge performance.

[0050] The negative electrode member of the present invention includes a fiber sheet and carbon nanotubes present on the surface of the constituent fibers of the fiber sheet. The carbon nanotubes may be present on the surface of the constituent fibers of the fiber sheet in various ways, such as by bonding the carbon nanotubes to the surface of the constituent fibers of the fiber sheet due to sheath components present on the surface of core-sheath composite fibers contained in the fiber sheet or by melting and solidifying all molten fibers having a low melting point among the constituent fibers of the fiber sheet, by bonding the carbon nanotubes to the surface of the constituent fibers of the fiber sheet due to the presence of a binder on the surface of the constituent fibers of the fiber sheet, or by bonding the carbon nanotubes to the surface of the constituent fibers of the fiber sheet by the binder, or by not containing an adhesive component such as a binder and by entangling and adhering the carbon nanotubes to the constituent fibers of the fiber sheet.

[0051] The percentage of the mass of the carbon nanotubes in the mass of the negative electrode member of the present invention is preferably 0.5% by mass or more, more preferably 1% by mass or more, and even more preferably 2% by mass or more, so that the negative electrode member has excellent conductivity. On the other hand, if the percentage of the mass of the carbon nanotubes in the mass of the negative electrode member is too high, the carbon nanotubes tend to aggregate into a film-like structure in the voids of the fiber sheet. As a result, the voids in the sheet tend to be blocked by the carbon nanotubes aggregated into a film-like structure. This may make it difficult for the electrolyte to sufficiently penetrate the inside of the negative electrode member, increasing the resistance of the battery and making it impossible to realize a battery with excellent discharge performance. Therefore, the percentage is preferably 40% by mass or less, more preferably 30% by mass or less, and even more preferably 20% by mass or less.

[0052] The negative electrode member of the present invention includes a fiber sheet and carbon nanotubes as described above, but it may be composed of only a fiber sheet and carbon nanotubes, or may contain other substances in addition to the fiber sheet and carbon nanotubes. Examples of such other substances include a binder that bonds the fiber sheet and carbon nanotubes, and conductive substances other than carbon nanotubes (graphite, carbon fiber, metals, metal oxides, conductive polymers, etc.). The conductive substance other than carbon nanotubes may be mixed with the carbon nanotubes and adhered or bonded to the fiber sheet, or the surfaces of the fibers constituting the fiber sheet may be coated with a thin metal film by plating.

[0053] The air permeability of the negative electrode member of the present invention measured by the Frazier method specified in JIS L 1913 6.8.1 is 0.1 cm. When the air permeability of the negative electrode member is large, the negative electrode member has high liquid permeability, which contributes to lowering the resistance of the battery. This allows for the provision of a battery with even better discharge performance. 3 / cm 2 / s or more is preferable, 10cm 3 / cm 2 / s or more is preferable, and 20cm 3 / cm 2 The upper limit of the air permeability of the negative electrode member is set to 400 cm / s or more, since if the air permeability of the negative electrode member is too large, the negative electrode member tends to have a sparse structure, which may result in poor handling of the negative electrode member. 3 / cm 2 / s or less is preferable, 300ccm 3 / cm 2 / s or less is preferable, and 200cm 3 / cm 2 / s or less is even more preferable.

[0054] Regarding the basis weight of the negative electrode member of the present invention, when the basis weight of the negative electrode member is small, the fibers constituting the negative electrode member are less likely to hinder contact between the active materials, which can contribute to lowering the resistance within the battery. This makes it possible to provide a battery with even better discharge performance. For this reason, the basis weight of the negative electrode member is set to 45 g / m 2 Less than 20 g / m is preferred2 Less than 15 g / m is more preferable. 2 The lower limit of the basis weight of the negative electrode member is 1 g / m because the negative electrode member has excellent handleability when the negative electrode member has a certain basis weight. 2 More than 3g / m is preferable. 2 More preferably, 4 g / m 2 The above is even more preferable.

[0055] Regarding the thickness of the negative electrode member of the present invention, if the thickness of the negative electrode member is small, the fibers constituting the negative electrode member are less likely to impede contact between the active materials, which contributes to lowering the resistance of the battery. This makes it possible to provide a battery with even better discharge performance. For this reason, the thickness of the negative electrode member is preferably 150 μm or less, more preferably 130 μm or less, and even more preferably 100 μm or less. The lower limit of the thickness of the negative electrode member is preferably 5 μm or more, more preferably 10 μm or more, and even more preferably 15 μm or more, because a certain thickness improves the handleability of the negative electrode member. The "thickness" in the present invention refers to the average value of 10 randomly selected points measured under a load of 150 kPa using an outside micrometer (measurement range: 0 to 25 mm) as specified in 3.1 of JIS B 7502 (2016) "Micrometer."

[0056] The lower the surface resistance value of the negative electrode member of the present invention, the better the conductivity of the negative electrode member, which can contribute to lowering the resistance of the battery. This allows for the realization of a battery with even better discharge performance. On the other hand, the lower the resistance value of the negative electrode member, the more conductive material, such as carbon nanotubes, the negative electrode member contains. If the amount of conductive material contained in the negative electrode member is too large, the conductive material will clog the voids in the fiber sheet that constitutes the negative electrode member. This may make it difficult for the electrolyte to sufficiently penetrate into the inside of the negative electrode member, which may increase the resistance of the battery and make it impossible to realize a battery with excellent discharge performance. Therefore, the surface resistance value of the negative electrode member is set to 1.0 × 10 -3 ~1.0×10 8 Ω / □ is preferred, 1.0×10 -2 ~1.0×10 6 Ω / □ is more preferable, 1.0×10-1 ~1.0×10 4 The surface resistivity is more preferably Ω / □. The surface resistivity is measured by the method described in JIS K 7194:1994 "Test method for resistivity of conductive plastics using four-probe method."

[0057] The negative electrode member of the present invention may be present in, for example, an electrode in which the negative electrode member is present so as to cover a layer formed of an active material in contact with the current collector, an electrode in which the negative electrode member is present so as to be sandwiched between the current collector and the layer formed of the active material, or an electrode in which the negative electrode member is present in part or all of the interior of the layer formed of the active material and at least part of the interior of the layer formed of the active material and the current collector are in contact with each other. In the case of an electrode in which the negative electrode member is present so as to cover a layer formed of an active material in contact with the current collector, or an electrode in which the negative electrode member is present so as to be sandwiched between the current collector and the layer formed of the active material, the active material may be embedded in the negative electrode member, or the layer formed of the negative electrode member and the active material layer may be completely separated. Among these, a preferred embodiment is one in which the negative electrode member is present in the electrode so as to cover a layer formed of an active material in contact with the current collector, so as to prevent the negative electrode member from impeding electrical conduction and to prevent the active material from detaching from the electrode.

[0058] Next, an example of a method for producing the negative electrode member of the present invention will be described.

[0059] First, the fiber sheet provided in the negative electrode member is prepared.

[0060] When the fiber sheet is a nonwoven fabric, a fiber web is first formed by a dry method (e.g., carding, air-laying, etc.), a wet method, or a direct spinning method, and the constituent fibers of the fiber web are then fused, entangled, or bonded to form a nonwoven fabric. Methods for fusing, entangling, or bonding the constituent fibers include, for example, a method of fusing at least a portion of the constituent fibers (e.g., core-sheath composite fibers) to fuse the fibers together, a method of entangling the fibers together using needles or a water stream, or a method of bonding the fibers together using a binder.

[0061] For the purpose of facilitating the penetration of the battery electrolyte into the negative electrode member, the fiber sheet may be hydrophilized by a known method such as activator treatment, plasma treatment, sulfonation treatment or fluorine gas treatment.

[0062] Next, carbon nanotubes are bonded or attached to the surface of the constituent fibers of the fiber sheet to produce the negative electrode member of the present invention. Methods for bonding or attaching carbon nanotubes to the surface of the constituent fibers of the fiber sheet include, for example, a method of deforming the surface of the constituent fibers of the fiber sheet by melting, solidifying, or softening to bond the carbon nanotubes to the surface of the constituent fibers of the fiber sheet, a method of bonding the carbon nanotubes to the surface of the constituent fibers of the fiber sheet using a binder, and a method of applying a carbon nanotube dispersion to the fiber sheet and entangling and attaching the carbon nanotubes to the surface of the constituent fibers of the fiber sheet.

[0063] The negative electrode member of the present invention can be used as a constituent member of the negative electrode of a battery, such as a primary battery (e.g., an alkaline primary battery or a lithium ion primary battery) or a secondary battery (e.g., a lithium metal battery, a lithium ion battery, a lithium sulfur battery, a nickel-zinc battery, a zinc metal battery, a nickel-metal hydride battery, a sodium ion battery, a potassium ion battery, a magnesium battery, or a fluoride ion battery). [Example]

[0064] Examples of the present invention will be described below, but the present invention is not limited to the following examples.

[0065] Example 1 A fiber web was prepared by a wet method by mixing 90 mass% of core-sheath composite fibers (core component: polypropylene (melting point: 168°C), sheath component: polyethylene (melting point: 135°C), fineness: 0.8 dtex, fiber length: 5 mm) and 10 mass% of polypropylene ultrafine fibers (melting point: 168°C, fineness: 0.03 dtex, fiber length: 3 mm). Thereafter, the fiber web was treated with hot air at a temperature of 140° C. to fuse only the sheath component of the core-sheath type composite fibers, thereby preparing a fused nonwoven fabric. Thereafter, the fused nonwoven fabric was subjected to a plasma treatment to hydrophilize the fused nonwoven fabric, thereby preparing a hydrophilized nonwoven fabric. The hydrophilized nonwoven fabric was then immersed in a dispersion of carbon nanotubes A (single-walled, average diameter: 2 nm, average length: 10 μm, aspect ratio: 50,000, g / d: 59), and then pulled out and dried. This caused the carbon nanotubes A to become entangled and adhere to the fiber surfaces constituting the hydrophilized nonwoven fabric, forming a negative electrode member (basis weight: 6.2 g / m 2 , Nonwoven fabric basis weight: 6.0 g / m 2 , Carbon nanotube A loading: 0.2 g / m 2 , percentage of mass of carbon nanotubes A in the mass of the negative electrode member: 3 mass%, thickness: 40 μm, airflow rate: 160 cm 3 / cm 2 / s, surface resistance: 1. 1×10 3 Ω / □, the nonwoven fabric is composed only of organic fibers) was prepared.

[0066] Example 2 A negative electrode member (weight per unit area: 6.2 g / m) was prepared in the same manner as in Example 1, except that carbon nanotubes B (multi-layer, average diameter: 20 nm, average length: 5 μm, aspect ratio: 250, g / d: 0.9) were used instead of carbon nanotubes A. 2 , Nonwoven fabric basis weight: 6.0 g / m 2 , Carbon nanotube B loading: 0.2 g / m 2 , percentage of mass of carbon nanotubes B in the mass of negative electrode member: 3 mass%, thickness: 40 μm, airflow rate: 170 cm 3 / cm 2 / s, surface resistance: 1.9 x 10 3 Ω / □, the nonwoven fabric is composed only of organic fibers) was prepared.

[0067] (Comparative Example 1) A negative electrode member (weight per unit area: 6.2 g / m) was prepared in the same manner as in Example 1, except that carbon nanotubes C (multi-layer, average diameter: 60 nm, average length: 20 μm, aspect ratio: 333, g / d: 0.5) were used instead of carbon nanotubes A. 2 , Nonwoven fabric basis weight: 6.0 g / m2 , carbon nanotube C loading: 0.2 g / m 2 , percentage of mass of carbon nanotubes C in the mass of the negative electrode member: 3 mass%, thickness: 40 μm, airflow rate: 165 cm 3 / cm 2 / s, surface resistance: 1.4 x 10 5 Ω / □, the nonwoven fabric is composed only of organic fibers) was prepared.

[0068] Example 3 A negative electrode member (basis weight: 7.3 g / m) was prepared in the same manner as in Example 1, except that the solid content concentration of the dispersion of carbon nanotubes A was changed to adjust the amount of carbon nanotubes A supported. 2 , Nonwoven fabric basis weight: 6.0 g / m 2 , Carbon nanotube A loading: 1.3 g / m 2 , percentage of mass of carbon nanotubes A in the mass of negative electrode member: 18 mass%, thickness: 43 μm, air permeability: 0.1 cm 3 / cm 2 / s, surface resistance: 8.0 x 10 1 Ω / □, the nonwoven fabric is composed only of organic fibers) was prepared.

[0069] Example 4 A fiber web was prepared by a wet method using 100 mass% core-sheath composite fibers (core component: polypropylene (melting point: 168°C) and sheath component: polyethylene (melting point: 135°C, fineness: 0.8 dtex, fiber length: 5 mm)). Thereafter, the fiber web was treated with hot air at a temperature of 140° C. to prepare a fused nonwoven fabric in which only the sheath component of the core-sheath type composite fiber was fused. Thereafter, the fused nonwoven fabric was subjected to a plasma treatment to hydrophilize the fused nonwoven fabric, thereby preparing a hydrophilized nonwoven fabric. Thereafter, the hydrophilized nonwoven fabric was immersed in a dispersion of carbon nanotubes A, and then pulled out and dried, thereby adhering carbon nanotubes A to the fiber surfaces constituting the hydrophilized nonwoven fabric, and a negative electrode member (basis weight: 42 g / m 2 , Nonwoven fabric weight: 25g / m 2 , Carbon nanotube A loading: 17 g / m 2, percentage of carbon nanotube mass in the mass of the negative electrode member: 40 mass%, thickness: 145 μm, air permeability: 0.1 cm 3 / cm 2 / s, surface resistance: 3.0 x 10 1 Ω / □, the nonwoven fabric is composed only of organic fibers) was prepared.

[0070] The physical properties of the negative electrode members of the examples and comparative examples are shown in the following Table 1. The percentage of the mass of carbon nanotubes in the mass of the negative electrode member is abbreviated as carbon nanotube mass percentage, and the air permeability measured by the Frazier method specified in JIS L 1913 6.8.1 is abbreviated as air permeability.

[0071] [Table 1]

[0072] The negative electrode members of the examples and comparative examples were evaluated by the following methods.

[0073] (Capacity evaluation of batteries using negative electrode components) (1) Preparation of the positive electrode First, a positive electrode paste having the composition shown below in (Composition of positive electrode paste) was prepared. (Positive electrode paste composition) NCM811(LiNi 0.8 Co 0.1 Mn 0.1 O2): 94.0 mass% Acetylene black: 3.0 mass% PVDF binder: 3.0 mass% Next, the obtained paste was applied onto aluminum foil and heated at 130° C. to obtain a positive electrode. The paste contained in the positive electrode is the active material, and the aluminum foil is the current collector. (2) Preparation of the negative electrode A 20 μm thick lithium metal foil was prepared, which served as both the active material and the current collector. (3) Preparation of non-aqueous electrolyte EC (ethylene carbonate): 50 vol% DEC (dimethyl carbonate): 50 vol% A non-aqueous electrolyte solution was prepared by adding 1 mol / L LiPF6 electrolyte salt and 1.0 mass% VC (vinylene carbonate) electrolyte additive to the above-mentioned electrolyte solution. (4) Preparation of separator A microporous polyolefin membrane was prepared. (5) Battery construction The positive electrode obtained in (1) above, the negative electrode obtained in (2) above, the negative electrode member prepared in the examples and comparative examples, the electrolyte prepared in (3) above, and the separator in (4) above were used. At this time, the negative electrode member prepared in the examples and comparative examples was inserted between the negative electrode obtained in (2) and the separator in (4) above to prepare a lithium metal secondary battery. (6) Battery capacity evaluation First, the lithium metal secondary batteries of the examples and comparative examples prepared in (5) were charged at a charging rate of 0.1C until the voltage of the lithium metal secondary battery reached 3.3V, and then discharged at a discharging rate of 0.1C until the voltage reached 1.4V. Next, the same charge / discharge test as above was repeated 10 times. Next, the lithium metal secondary battery after repeated charge and discharge tests was charged at a charge rate of 0.1 C until the voltage of the lithium metal secondary battery reached 3.3 V, and then discharged at a discharge rate of 0.1 C until the voltage reached 1.4 V, at which point the discharge capacity A (mAh) was measured. This discharge capacity A (mAh) was divided by the mass (g) of the negative electrode to determine the specific capacity H (mAh / g) of the negative electrode.

[0074] Table 2 below shows the specific volume of the negative electrode when the capacity of the battery was evaluated using the negative electrode members of the Examples and Comparative Examples.

[0075] [Table 2]

[0076] The results of the battery capacity evaluation showed that the battery including the negative electrode member of the Example had a higher specific capacity of the negative electrode after 10 repeated charge and discharge cycles than the battery including the negative electrode member of the Comparative Example. Therefore, it was found that by using the negative electrode member of the Example in the negative electrode, the discharge capacity of the battery is less likely to decrease, and a battery with excellent discharge performance can be provided. [Industrial Applicability]

[0077] The negative electrode member of the present invention can be used as a constituent member of the negative electrode of a battery, for example, a primary battery (e.g., an alkaline primary battery or a lithium ion primary battery) or a secondary battery (e.g., a lithium metal battery, a lithium ion battery, a lithium sulfur battery, a nickel-zinc battery, a zinc metal battery, a nickel-metal hydride battery, a sodium ion battery, a potassium ion battery, a magnesium battery, or a fluoride ion battery).

Claims

1. A negative electrode member comprising a fiber sheet and carbon nanotubes, The fiber sheet contains organic fibers as constituent fibers, the carbon nanotubes are present on the surface of the constituent fibers of the fiber sheet, the intensity ratio (g / d) of the peak value (g) of the G band derived from the vibration of the graphite structure of the carbon nanotube to the peak value (d) of the D band derived from the vibration of defects of the carbon nanotube, obtained by Raman spectroscopy, is greater than 0.5; Negative electrode member.

2. The air permeability measured by the Frazier method specified in JIS L 1913 6.8.1 is 0.1 cm ３ / cm ２ The negative electrode member according to claim 1 , wherein the negative electrode member has a capacitance of 1 / s or more.

3. 2. The negative electrode member according to claim 1, wherein the percentage of the mass of the carbon nanotubes in the mass of the negative electrode member is 0.5 to 40 mass %.

4. Weight per unit area: 45g / m ２ 2. The negative electrode member of claim 1, wherein:

5. 2. The negative electrode member according to claim 1, having a thickness of 150 μm or less.

6. A battery comprising the negative electrode member according to any one of claims 1 to 5.

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