Carbon composite materials

Abstract

This disclosure pertains to carbon composite materials. A carbon composite material capable of suppressing the reduction in the charge / discharge capacity of a battery is provided. One carbon composite material is characterized by comprising carbon material with an aspect ratio of 2.7 or higher and 7.5 or lower, and Si.

Description

Technical Field

[0001] This disclosure relates to carbon composite materials. Background Technology

[0002] Various technologies have been proposed for carbon composite materials as disclosed in Patent Documents 1-4.

[0003] [Existing Technical Documents]

[0004] [Patent Literature]

[0005] [Patent Document] Japanese Patent Publication No. 7311169

[0006] [Patent Document] Japanese Patent Application Publication No. 2002-260658

[0007] [Patent Document] Japanese Patent Application Publication No. 2024-115207

[0008] [Patent Document] International Publication No. 2020 / 218021 Summary of the Invention

[0009] In the prior art, in batteries containing Si as the negative electrode active material, the shape of Si becomes amorphous due to the expansion and contraction of Si caused by the charging and discharging of the battery. As a result, there is a problem of reduced charge and discharge capacity associated with the charging and discharging of Si-containing batteries.

[0010] This disclosure was made in view of the above-mentioned circumstances, and its main purpose is to provide a carbon composite material capable of suppressing the reduction of the charge and discharge capacity of a battery.

[0011] That is, this disclosure includes the following schemes.

[0012] <1>

[0013] A carbon composite material, characterized in that it comprises carbon material with an aspect ratio of 2.7 or more and 7.5 or less, and Si.

[0014] <2>

[0015] According to the carbon composite material described in <1>, the crystallite size of the Si, as determined by X-ray diffraction (XRD), is 1 nm to 1 μm.

[0016] <3>

[0017] According to the carbon composite material described in <1>, the Si is amorphous.

[0018] <4>

[0019] The carbon composite material according to any one of <1> to <3>, wherein the Si content in the carbon composite material is 1% to 70% by mass.

[0020] <5>

[0021] According to the carbon composite material described in <4>, the Si content in the carbon composite material is 10% to 50% by mass.

[0022] <6>

[0023] The carbon composite material according to any one of <1> to <5> has its outermost surface covered by the carbon material.

[0024] <7>

[0025] The carbon composite material according to any one of <1> to <6> is a bundle-shaped composite of multiple carbon fibers having multiple pores.

[0026] <8>

[0027] According to the carbon composite material described in <7>, the length of the carbon fiber in the short axis direction is 0.1 μm to 3 μm, and the length of the carbon fiber in the long axis direction is 1 μm to 20 μm.

[0028] <9>

[0029] According to the carbon composite material described in <7> or <8>, the Si is supported within the fine pores.

[0030] According to this disclosure, a carbon composite material can be provided that can suppress the reduction of the charge and discharge capacity of a battery. Attached Figure Description

[0031] Figure 1 This is a schematic diagram illustrating an example of a method for manufacturing a carbon composite material according to the present disclosure.

[0032] Figure 2 This is a graph showing the relationship between the aspect ratio of the carbon material and the capacity retention of the battery in the examples and comparative examples.

[0033] [Explanation of reference numerals in the attached figures]

[0034] 10… Carbon fiber raw materials

[0035] 11… carbon fiber

[0036] 12…carbon composite materials Detailed Implementation

[0037] The following describes embodiments of this disclosure. Furthermore, matters necessary for the implementation of this disclosure, other than those specifically mentioned in this specification (e.g., the general structure and manufacturing process of carbon composite materials not characterized by this disclosure), can be grasped as design matters by those skilled in the art. This disclosure can be implemented based on the content disclosed in this specification and common technical knowledge in the field.

[0038] In addition, the dimensional relationships (length, width, thickness, etc.) in the diagram do not reflect the actual dimensional relationships.

[0039] In this disclosure, an example of a method for calculating the average particle size is as follows. First, in a scanning electron microscope (SEM) image at an appropriate magnification (e.g., 50,000 to 1,000,000 times), the particle size of a given particle is calculated if it is considered spherical. This particle size calculation based on SEM observation is performed on 2 to 300 particles of the same type, and the average particle size is taken as the average particle size.

[0040] In this disclosure, a carbon composite material is provided, characterized in that it comprises carbon (C) material with an aspect ratio of 2.7 or more and 7.5 or less, and Si (silicon).

[0041] According to this disclosure, by compositing carbon materials with Si, a desired number of electron conduction paths can be maintained. Furthermore, by having an aspect ratio of 2.7 or higher for the carbon materials, the expansion direction of Si is restricted, and amorphization of Si due to expansion and contraction can be suppressed. Therefore, when using carbon composite materials as active materials, side reactions on the surface of the active material can be suppressed, and the decrease in charge / discharge capacity associated with the charging and discharging of batteries using this active material can be suppressed.

[0042] The carbon composite material disclosed herein comprises carbon materials and Si.

[0043] Carbon composite materials can be carbon composite particles or carbon composite fibers, etc.

[0044] The Si content (Si loading of carbon materials) in carbon composites can be, for example, 1% or more by mass, 10% or more by mass, 47% or more by mass, less than 70% by mass, less than 50% by mass, or less than 49% by mass. The Si content in carbon composites can be calculated using the following formula.

[0045] Si content (%) = mass of Si ÷ (mass of carbon material + mass of Si) × 100

[0046] Carbon composite materials, the outermost surface of which can be coated with carbon materials.

[0047] The aspect ratio of carbon materials should be between 2.7 and 7.5, with an upper limit of 4.2 or lower.

[0048] Regarding aspect ratio, SEM images of the cross section or surface are obtained in the state of the electrode layer containing carbon material or the powder of carbon material. 30 to 100 particles are extracted, and the average aspect ratio of 30 to 100 particles is calculated by image analysis. The average value is used as the aspect ratio of the carbon material.

[0049] The aspect ratio is expressed as a / b, where the length along the major axis of the carbon material is denoted as 'a' and the length along the minor axis is denoted as 'b'. Furthermore, in cases where the carbon material has a thickness direction, such as in the form of flakes, the thickness is taken as the length along the minor axis, 'b'.

[0050] The aspect ratio of carbon composite materials can be the same as that of carbon materials, and the aspect ratio of carbon materials can also be regarded as the aspect ratio of carbon composite materials.

[0051] The length of the long axis of the carbon material can be, for example, greater than 0.1 μm, greater than 1 μm, greater than 5.6 μm, greater than 10.6 μm, less than 100 μm, less than 20 μm, or less than 18.2 μm.

[0052] The length of the major axis of a carbon composite material can be the same as the length of the major axis of the carbon material, and the length of the major axis of the carbon material can also be regarded as the length of the major axis of the carbon composite material.

[0053] Examples of carbon materials include natural graphite, artificial graphite, activated carbon, carbon fiber, mesocarbon microbeads (MCMB), hard carbon, and soft carbon.

[0054] The shape of carbon materials is not particularly limited; they can be in the form of particles, flakes, plates, or fibers. Carbon materials can be carbon particles or carbon fibers, etc.

[0055] Carbon fiber can be obtained by carbonizing carbon fiber raw materials such as polyacrylonitrile (PAN) resin-based fibers and cellulose nanofibers. As a carbonization condition, for example, the carbon fiber raw material can be heat-treated in an inert gas atmosphere at a temperature of 1000℃ to 1500℃.

[0056] In addition, carbon fibers can be carbon materials with mesoporous structures, such as ordered mesoporous carbon (CMK-3), and carbon fibers can use carbon nanofibers and carbon nanotubes, etc.

[0057] Carbon materials can be composites of bundles of multiple carbon fibers. By being composites of bundles of multiple carbon fibers, the expansion direction of Si is further restricted, which can further suppress the amorphization that accompanies the expansion and contraction of Si.

[0058] Carbon fibers can have at least one pore or multiple pores.

[0059] The pores in carbon fibers can be continuous along the long axis.

[0060] The pore diameter of carbon fibers can be, for example, 1 nm to 20 nm.

[0061] The length (width) of the carbon fiber in the short axis direction can be, for example, 0.1 μm to 3 μm.

[0062] The length of the long axis of carbon fiber can be, for example, greater than 0.1 μm, greater than 1 μm, greater than 5.6 μm, greater than 10.6 μm, less than 100 μm, less than 20 μm, or less than 18.2 μm.

[0063] A bundle-like composite of multiple carbon fibers can be obtained, for example, by agglomeration in a poor solvent environment. For instance, by reacting the carbon fibers in xylene, a poor solvent, with vigorous stirring, it is presumed that the carbon fibers agglomerate due to the action of functional groups (such as -COOR groups) present on the surface of the carbon fibers. By passing the resulting dispersion through a slit and rapidly drying it, a bundle-like composite of multiple carbon fibers can be obtained. The resulting composite can then be cut or pulverized as needed by mechanical grinding or the like.

[0064] Si can be either amorphous or crystalline.

[0065] When Si is crystalline, the crystallite size of Si, as determined by X-ray diffraction (XRD), can range from 1 nm to 1 μm.

[0066] Si can be supported on the surface of a carbon material. When the carbon material is carbon fiber, Si can be supported on at least one of the surfaces of the carbon fibers and the pores present in the carbon fibers. Alternatively, the surface of the Si, after being supported on the carbon material, can be coated with the carbon material.

[0067] There are no particular limitations on the methods for supporting Si on carbon materials. Examples include using CVD (chemical vapor deposition), impregnating carbon materials in a molten liquid formed by melting silicon, and forming a silicon layer on carbon materials using TEOS (tetraethyl orthosilicate).

[0068] Examples of chemical vapor deposition (CVD) include thermal CVD (chemical vapor deposition using thermal decomposition), PECVD (chemical vapor deposition using plasma), and ALD (atomic layer deposition). One advantage of using thermal CVD is its ability to form uniform amorphous Si.

[0069] Examples of Si sources used in CVD include silanes (SiH4) and halosilanes (H2O). 4-x SiCl x )wait.

[0070] The Si content in carbon composites can be detected using quantitative analytical methods such as inductively coupled plasma (ICP) spectroscopy and electron probe microanalysis (EPMA).

[0071] Carbon composites can be manufactured by loading silicon onto a substrate made of carbon materials.

[0072] Figure 1 This is a schematic diagram illustrating an example of a method for manufacturing a carbon composite material according to the present disclosure.

[0073] like Figure 1 As shown, carbon composite material 12 can be manufactured by carbonizing carbon fiber raw material 10 to produce carbon fiber 11 with multiple fine pores arranged inside in the length direction, and by evaporating Si into the fine pores of carbon fiber 11.

[0074] The carbon composite material disclosed herein is used as the negative electrode active material of a battery.

[0075] A battery has a positive electrode layer, a negative electrode layer, and an electrolyte layer. It typically has a positive electrode containing the positive electrode layer and a negative electrode containing the negative electrode layer.

[0076] According to this disclosure, by using the above-described carbon composite material as the negative electrode active material of the battery, it is possible to suppress the reduction of the battery's charge and discharge capacity.

[0077] [positive electrode]

[0078] The positive electrode has a positive electrode layer and may be further equipped with a positive electrode current collector as needed.

[0079] The positive electrode layer can be disposed on one or both surfaces of the positive electrode current collector. The positive electrode can also be formed with two or more positive electrode layers on at least one surface of the positive electrode current collector to create a multilayer structure. Furthermore, when two or more positive electrode layers are formed, the types of positive electrode active materials contained in each positive electrode layer can be the same or different.

[0080] The positive electrode layer is a layer containing at least a positive electrode active material. Additionally, the positive electrode layer may, as needed, contain at least one of a conductive material and a binder.

[0081] Examples of positive electrode active materials include oxide active materials. Examples of oxide active materials include LiCoO2, LiMnO2, LiNiO2, LiVO2, and LiNi. 1 / 3 Co 1 / 3 Mn 1 / 3 O2 and LiNi 0.8 Mn 0.1 Co 0.1 O2 and other layered active substances in rock salt, LiMn2O4, Li4Ti5O 12 and Li (Ni 0.5 Mn 1.5 Spinel-type active substances such as O4, olivine-type active substances such as LiFePO4, LiMnPO4, LiNiPO4, and LiCoPO4.

[0082] The positive electrode active material is usually in the form of particles. The positive electrode active material can be primary particles or secondary particles formed by the aggregation of primary particles.

[0083] There is no particular limitation on the average particle size of the positive electrode active material. For example, it can be 0.01 μm or larger and 50 μm or smaller, or it can be 0.5 μm or larger and 30 μm or smaller.

[0084] The proportion of positive electrode active material in the positive electrode layer can be, for example, 20% by mass or more, 30% by mass or more, or 40% by mass or more. If the proportion of positive electrode active material is too low, there is a possibility that insufficient energy density may not be obtained. On the other hand, the proportion of positive electrode active material in the positive electrode layer can be, for example, 95% by mass or less, 70% by mass or less, or 60% by mass or less. If the proportion of positive electrode active material is too high, there is a possibility that the ionic conductivity and electronic conductivity in the positive electrode layer may be relatively reduced.

[0085] The positive electrode layer can contain conductive materials. By adding conductive materials, the electronic conductivity of the positive electrode layer is improved. Examples of conductive materials include carbon-based conductive materials, metal particles, and conductive polymers. Examples of carbon-based conductive materials include particulate materials such as acetylene black (AB) and Ketjen black (KB), fibrous materials such as vapor-phase carbon fiber (VGCF), carbon nanotubes (CNTs), and carbon nanofibers (CNFs).

[0086] The proportion of conductive material in the positive electrode layer can be, for example, 0.1% by mass or more. If the proportion of conductive material is too low, there is a possibility that the electron conduction pathway in the positive electrode layer is insufficient. On the other hand, the proportion of conductive material in the positive electrode layer can be, for example, 5% by mass or less. If the proportion of conductive material is too high, the proportion of positive electrode active material becomes relatively low, and there is a possibility that the energy density will decrease.

[0087] The positive electrode layer may contain an adhesive. Examples of adhesives include styrene-butadiene rubber (SBR), polyimide (PI), polyacrylic acid (PAA), acrylonitrile-butadiene rubber (NBR), butadiene rubber (BR), polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), styrene-isoprene-styrene block copolymer (SIS), and ethylene-propylene-diene copolymer (EPDM).

[0088] The proportion of binder in the positive electrode layer can be, for example, 0.5% by mass or more. If the proportion of binder is too small, it may not be sufficient to reduce the increase in resistance caused by charging and discharging. On the other hand, the proportion of binder in the positive electrode layer can be, for example, 15% by mass or less. If the proportion of binder is too large, the proportion of positive electrode active material will be relatively small, and the energy density may be lower.

[0089] The thickness of the positive electrode layer can be, for example, 0.1 μm or more and 1000 μm or less, 1 μm or more and 500 μm or less, or 30 μm or more and 200 μm or less.

[0090] The manufacturing method of the positive electrode layer is not particularly limited. For example, the following method can be used: mixing the above-mentioned positive electrode active material with a solvent to obtain a positive electrode slurry, coating the positive electrode slurry onto a positive electrode current collector, and drying it to form a positive electrode layer. During the formation of the positive electrode layer, a pressing process can be performed to press the positive electrode layer in the thickness direction. Examples of pressing processes include roll pressing and flat plate pressing.

[0091] Examples of solvents include N-methylpyrrolidone (NMP), tetrahydronaphthalene, diisobutyl ketone, butyl butyrate, mesitylene, heptane, dibutyl ether, decane, dodecane, isodecane, and toluene, and may contain two or more of these components.

[0092] Materials used for the positive current collector include, for example, stainless steel (SUS), Cr, Au, Pt, Zn, aluminum, copper, nickel, iron, titanium, and carbon. The thickness of the positive current collector is, for example, 0.1 μm or more and 100 μm or less. The shape of the positive current collector can be foil-like or plate-like. The top view shape of the positive current collector is not particularly limited; for example, it can be circular, elliptical, rectangular, or any polygonal shape. The positive current collector can also be composed of a buffer layer, an elastic layer, or a PTC (Positive Temperature Coefficient) thermistor layer disposed on its surface.

[0093] [negative electrode]

[0094] The negative electrode has a negative electrode layer and may be further equipped with a negative electrode current collector as needed.

[0095] The negative electrode layer can be disposed on one or both surfaces of the negative electrode current collector. A multilayer structure can also be formed by forming two or more negative electrode layers on at least one surface of the negative electrode current collector. Furthermore, when forming two or more negative electrode layers, the types of negative electrode active materials contained in each negative electrode layer can be the same or different.

[0096] The negative electrode layer is a layer containing at least a negative electrode active material. Additionally, the negative electrode layer may, as needed, contain at least one of a conductive material and a binder.

[0097] The negative electrode layer contains at least the carbon composite material of this disclosure as the negative electrode active material, and may further contain negative electrode active materials other than the carbon composite material as needed. As the negative electrode active material other than the carbon composite material, active materials known as negative electrode active materials of batteries can be used, such as the aforementioned carbon material.

[0098] The proportion of carbon composite material in 100% by mass of the negative electrode active material contained in the negative electrode layer can be more than 10% by mass, more than 20% by mass, more than 50% by mass, or less than 100% by mass.

[0099] The negative electrode layer may contain more than 10% by mass of negative electrode active material, more than 20% by mass of negative electrode active material, more than 50% by mass of negative electrode active material, less than 100% by mass of negative electrode active material, less than 90% by mass of negative electrode active material, or less than 74.5% by mass of negative electrode active material.

[0100] Regarding the conductive materials and adhesives that can be used in the negative electrode layer, the same conductive materials and adhesives described in the above description of the positive electrode layer can be cited.

[0101] The proportion of conductive material in the negative electrode layer can be, for example, more than 0.1% by mass and less than 5% by mass.

[0102] The proportion of binder in the negative electrode layer can be, for example, more than 0.5% by mass and less than 15% by mass.

[0103] Materials used for the negative current collector include, for example, stainless steel (SUS), aluminum, copper, nickel, iron, titanium, and carbon. Furthermore, the thickness of the negative current collector varies depending on its shape, but can range from, for example, 1 μm to 50 μm. The shape of the negative current collector can be foil-like or plate-like. The top-view shape of the negative current collector is not particularly limited; for example, it can be circular, elliptical, rectangular, or any polygonal shape. The negative current collector can also be constructed with a buffer layer, an elastic layer, or a PTC thermistor layer disposed on its surface.

[0104] [Electrolyte layer]

[0105] The electrolyte layer is a layer formed between the positive electrode layer and the negative electrode layer, and it contains at least an electrolyte. The electrolyte can be a liquid electrolyte (electrolyte).

[0106] The electrolyte layer may contain electrolytes, etc.

[0107] In the electrolyte, non-aqueous electrolytes can be used.

[0108] As a non-aqueous electrolyte, a non-aqueous electrolyte containing lithium salt and non-aqueous solvent is usually used.

[0109] Examples of lithium salts include inorganic lithium salts such as LiPF6, LiBF4, LiClO4, and LiAsF6; and organic lithium salts such as LiCF3SO3, LiN(SO2CF3)2 (Li-TFSI), LiN(SO2C2F5)2, and LiC(SO2CF3)3.

[0110] Examples of non-aqueous solvents include ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), γ-butyrolactone, sulfolane, acetonitrile (AcN), dimethoxymethane, 1,2-dimethoxyethane (DME), 1,3-dimethoxypropane, diethyl ether, tetraethylene glycol dimethyl ether (TEGDME), tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide (DMSO), and mixtures thereof. From the viewpoint of ensuring high dielectric constant and low viscosity, it can be a mixture of cyclic carbonate compounds such as EC, PC, and BC with high dielectric constant and high viscosity and chain carbonate compounds such as DMC, DEC, and EMC with low dielectric constant and low viscosity. It can also be a mixture of EC and DEC.

[0111] The concentration of lithium salt in non-aqueous electrolytes can be, for example, 0.3~5M.

[0112] A separator that can impregnate the electrolyte and prevent the positive electrode layer from contacting the negative electrode layer can be used in the electrolyte layer.

[0113] The material used for the membrane is not particularly limited as long as it is a porous membrane. Examples include resins such as polyethylene (PE), polypropylene (PP), polyester, polyvinyl alcohol, cellulose, and polyamide, with polyethylene and polypropylene being particularly suitable. Furthermore, the membrane can be a single-layer or multi-layer structure. Examples of multi-layer membranes include two-layer PE / PP membranes, or three-layer PP / PE / PP or PE / PP / PE membranes.

[0114] The diaphragm can be made of resin nonwoven fabric, glass fiber nonwoven fabric, or other nonwoven fabrics.

[0115] The thickness of the electrolyte layer can be, for example, 0.1 μm or more and 100 μm or less, or 0.1 μm or more and 50 μm or less, or 0.1 μm or more and 30 μm or less.

[0116] The battery disclosed herein may further include a restraint clamp that applies restraint pressure to the positive electrode layer, electrolyte layer, and negative electrode layer along the thickness direction. The restraint pressure may be, for example, 0.1 MPa or more, 1 MPa or more, or 5 MPa or more. On the other hand, the restraint pressure may be, for example, 100 MPa or less, 50 MPa or less, or 20 MPa or less.

[0117] [Battery]

[0118] The type of battery disclosed herein is not particularly limited, but lithium-ion batteries are typically used. Alternatively, the battery in this disclosure can be a liquid battery with an electrolyte layer containing an electrolyte solution. The liquid battery can be a non-aqueous liquid battery with an electrolyte layer containing a non-aqueous electrolyte. Furthermore, the battery in this disclosure can be a primary battery or a secondary battery, but is particularly suitable for secondary batteries. This is because it can be repeatedly charged and discharged, making it useful, for example, as a vehicle battery.

[0119] There are no particular limitations on the shape of the battery; for example, it can be coin-shaped, cylindrical, square, flat, button-shaped, flat, or stacked.

[0120] In the case of a battery stack consisting of multiple stacked batteries, the battery stack can be either unipolar or bipolar.

[0121] Batteries are used in various applications, including as power sources for hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), battery electric vehicles (BEVs), gasoline vehicles, and diesel vehicles. In particular, they can be used as power sources for driving hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), or battery electric vehicles (BEVs). Furthermore, batteries can be used as power sources for mobile bodies other than vehicles (such as railways, ships, and aircraft), and also as power sources for electrical products such as information processing devices.

[0122] Furthermore, this disclosure is not limited to the above-described embodiments. The above embodiments are illustrative examples, and technical solutions having substantially the same structure as the technical concept described in the claims of this disclosure and achieving the same effect are included within the technical scope of this disclosure.

[0123] [Example]

[0124] (Example 1)

[0125] [Preparation of carbon fiber]

[0126] PAN resin-based fibers, which are used as carbon fiber raw materials, are heat-treated at 1500°C in an inert gas (Ar) atmosphere to carbonize them, thereby preparing multiple carbon fibers with multiple fine pores.

[0127] The aspect ratio of the carbon fiber is 2.7. The length of the carbon fiber in the longitudinal direction is 5.6 μm.

[0128] [Fabrication of bundles of multiple carbon fibers]

[0129] Using the aforementioned carbon fibers, a bundle-shaped composite of multiple carbon fibers was fabricated using the following method. The carbon fibers were stirred in xylene, a poor solvent, and the resulting dispersion was passed through a slit and rapidly dried to obtain the bundle-shaped composite of multiple carbon fibers. The resulting composite was used as a carbon material.

[0130] [Fabrication of Carbon Composite Materials]

[0131] The loading of silicon-to-carbon materials was carried out using thermal CVD as follows.

[0132] Carbon material was placed in a chamber, and a gas serving as the Si source was circulated while the temperature required for thermal decomposition (700°C) was applied. This resulted in Si particles being loaded onto the surface and within the pores of the carbon material, yielding carbon composite particles (silicon-carbon composite particles). The Si composition was investigated using ICP-S spectroscopy. The Si content in the carbon composite was 48%. The XRD-based crystallite size of the Si was below the detection limit, indicating it was amorphous.

[0133] (Example 2)

[0134] In the preparation of the carbon fibers, multiple carbon fibers with a length of 10.6 μm and multiple pores, having an aspect ratio of 4.2, were used. Otherwise, the process was the same as in Example 1 to prepare a carbon composite material. The Si content in the carbon composite material was 49%. The Si crystallite size based on XRD was below the detection limit, indicating it was amorphous.

[0135] (Example 3)

[0136] In the preparation of the carbon fibers, multiple carbon fibers with a length of 18.2 μm and multiple pores, having an aspect ratio of 7.5, were used. Otherwise, the process was the same as in Example 1 to prepare a carbon composite material. The Si content in the carbon composite material was 47%. The Si crystallite size based on XRD was below the detection limit, indicating it was amorphous.

[0137] (Comparative Example 1)

[0138] In the preparation of carbon fiber, instead of preparing carbon fiber and making the above composite, spherical Si particles with a crystalline structure, an aspect ratio of 1.1, and a length of 8.2 μm in the longitudinal direction are used as a substitute for carbon composite material.

[0139] (Comparative Example 2)

[0140] In the preparation of carbon fibers, instead of multiple carbon fibers with multiple fine pores, granular activated carbon with multiple fine pores and an aspect ratio of 1.5 and a length of 8.6 μm in the longitudinal direction was prepared. The aforementioned composite material was not fabricated; the prepared activated carbon was used as is, and the process was otherwise identical to that in Example 1 to produce a carbon composite material. The Si content in the carbon composite material was 48%. The Si crystallite size based on XRD was below the detection limit, indicating it was amorphous.

[0141] (Comparative Example 3)

[0142] In the preparation of carbon fibers, instead of multiple carbon fibers with multiple fine pores, granular activated carbon with multiple fine pores and an aspect ratio of 2.2 and a length of 9.9 μm in the longitudinal direction was prepared. The aforementioned composite material was not fabricated; the prepared activated carbon was used as is, and the process was otherwise identical to that in Example 1 to produce a carbon composite material. The Si content in the carbon composite material was 49%. The Si crystallite size based on XRD was below the detection limit, indicating it was amorphous.

[0143] (Comparative Example 4)

[0144] In the preparation of carbon fibers, instead of multiple carbon fibers with multiple fine pores, fibrous activated carbon with multiple fine pores and an aspect ratio of 9.2 and a length of 40.1 μm in the longitudinal direction was prepared. The aforementioned composite was not fabricated; the prepared activated carbon was used as the carbon material. Otherwise, the process was the same as in Example 1 to prepare a carbon composite material. The Si content in the carbon composite material was 47%. The Si crystallite size based on XRD was below the detection limit, indicating it was amorphous.

[0145] [Making the negative electrode]

[0146] Artificial graphite as the first negative electrode active material, carbon composite materials prepared in Examples 1-3 and Comparative Examples 1-4 as the second negative electrode active material, SBR as the first binder, polyacrylic acid as the second binder, and carbon nanotubes as the conductive material were mixed in a mass ratio of 70%:27.5%:1%:1%:0.05%, and distilled water was added to the resulting mixture. The materials were then thoroughly mixed using a mixer to obtain a negative electrode paste. The negative electrode paste was applied to a copper foil serving as the negative electrode current collector using a doctor blade and dried at 100°C for 15 minutes to completely evaporate the water, thereby creating a negative electrode with a negative electrode layer on the negative electrode current collector. The created negative electrode was pressed using a biaxial roller press to achieve a negative electrode layer density of 1.2 g / cm³. 3 .

[0147] [The production of the positive electrode]

[0148] LiNi is used as a transition metal oxide 0.8 Mn 0.1 Co 0.1 O2 was used as the positive electrode active material. The positive electrode active material, conductive material (acetylene black), and binder (polyvinylidene fluoride) were mixed in a mass ratio of 95%:2.5%:2.5%. N-methylpyrrolidone was added as a solvent to the resulting mixture, and the materials were thoroughly mixed using a mixer to obtain a positive electrode paste. The positive electrode paste was applied to an aluminum foil serving as the positive electrode current collector using a doctor blade and dried at 80°C for 15 minutes to create a positive electrode with a positive electrode layer on the positive electrode current collector. The created positive electrode was pressed using a biaxial roller press to achieve a positive electrode layer density of 3.2 g / cm³. 3 Furthermore, the capacity ratio of the positive electrode layer to the negative electrode layer is adjusted so that the positive electrode capacity / negative electrode capacity is 1.1.

[0149] [Septum]

[0150] As a separator, a separator with a polyethylene substrate and an alumina (Al2O3) modification layer supported on the substrate is used.

[0151] Electrolyte

[0152] As the electrolyte, lithium hexafluorophosphate (LiPF6), used as a lithium salt, is prepared into a 1.2M electrolyte using an ethylene carbonate-based solvent. The membrane is then impregnated with the electrolyte.

[0153] [Battery Manufacturing]

[0154] A coin-shaped battery was made by stacking a positive electrode, a separator impregnated with electrolyte, and a negative electrode.

[0155] [Electrochemical Evaluation]

[0156] The carbon composite materials of Examples 1-3 and Comparative Examples 1-4 were evaluated using the electrochemical units (batteries) that used the carbon composite materials.

[0157] Each battery was tested using charge-discharge cycles to determine the rate of capacity retention during the cycle.

[0158] Regarding charging, a constant current of 0.3C (C being the time rate) is applied. After the battery voltage reaches 4.2V, a constant voltage is applied to charge each battery until the current value becomes 0.01C.

[0159] Regarding discharge, a constant current of 0.3C is applied to discharge each battery until the battery voltage reaches 2.5V.

[0160] A 10-minute rest period was set between charging and discharging. The capacity of each battery was measured after 20 consecutive cycles. The capacity retention of each battery was calculated by dividing the discharge capacity after 20 cycles by the discharge capacity after the first cycle. The results are shown in Table 1.

[0161]

[0162] [result]

[0163] Figure 2 This is a graph showing the relationship between the aspect ratio of the carbon material and the capacity retention of the battery in the examples and comparative examples.

[0164] like Figure 2 As shown in Table 1, it is confirmed that batteries using carbon composite materials containing carbon materials with an aspect ratio greater than 1 and Si have a higher capacity retention rate compared to batteries using Si particles.

Claims

1. A carbon composite material, characterized in that, It includes carbon materials with an aspect ratio of 2.7 or higher and 7.5 or lower, and Si.

2. The carbon composite material according to claim 1, The crystallite size of the Si, as determined by X-ray diffraction, is 1 nm to 1 μm.

3. The carbon composite material according to claim 1, The Si is amorphous.

4. The carbon composite material according to claim 1, The Si content in the carbon composite material is 1% to 70% by mass.

5. The carbon composite material according to claim 4, The Si content in the carbon composite material is 10% to 50% by mass.

6. The carbon composite material according to claim 1, The outermost surface is covered with the carbon material.

7. The carbon composite material according to claim 1, The carbon material is a bundle-shaped composite of multiple carbon fibers with multiple fine pores, the diameter of which is 1 nm to 20 nm.

8. The carbon composite material according to claim 7, The carbon fiber has a short axis length of 0.1 μm to 3 μm and a long axis length of 1 μm to 20 μm.

9. The carbon composite material according to claim 7, The Si is supported within the fine pores.

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