Carbon materials and methods for producing the same, conductive additives, dispersions, electrode compositions, electrode slurries, electrodes, and lithium-ion secondary batteries

Abstract

The present invention provides a carbon material that exhibits excellent conductivity and superior rapid discharge characteristics, battery capacity characteristics, and charge / discharge characteristics when manufacturing electrodes for electrochemical elements. [Solution] The carbon material according to the present invention is formed by a carbonaceous outer shell having a graphene structure and has pores, and has a BET specific surface area of ​​100 m². 2 / g or more 2500m 2 The range is less than or equal to / g, the total pore volume measured by nitrogen adsorption / desorption measurement is 0.30 cc / g or more, the volume ratio of pores with a diameter of 10 nm or more to the total pore volume is 30% or more, the volume ratio of macropores (pores with a diameter exceeding 50 nm) is 5% or more, and the mode pore diameter is in the mesopore region of 2 nm to 50 nm.

Description

[Technical Field]

[0001] The present invention relates to carbon materials and methods for producing the same, conductive additives, dispersions, electrode compositions, electrode slurries, electrodes, and lithium-ion secondary batteries. [Background technology]

[0002] Since its inception, lithium-ion rechargeable batteries have seen a wide range of applications in everyday life, including smartphones and electric vehicles (EVs). As a result, the manufacturing of lithium-ion rechargeable batteries faces ongoing competition in terms of cost, as well as continuous demands for higher performance in the market. For EVs, which emit less carbon dioxide (CO2), to replace gasoline-powered vehicles in order to protect the global environment, the lithium-ion rechargeable batteries they use must have high performance characteristics such as rapid discharge characteristics, long lifespan, high capacity, and charge / discharge characteristics.

[0003] Carbon materials are widely used in lithium-ion secondary batteries, where such high performance is required. For example, Patent Document 1 (Japanese Patent Application Publication No. 2004-22177) discloses a non-aqueous electrolyte secondary battery comprising a positive electrode containing a positive electrode mixture, a negative electrode, and a non-aqueous electrolyte, wherein the positive electrode mixture contains a positive electrode active material, and contains 1 to 10 parts by weight of a conductive agent per 100 parts by weight of the positive electrode active material, and the conductive agent contains flake graphite or carbon black, and the ratio of the weight of flake graphite to the sum of the weights of flake graphite and carbon black is less than 15% by weight. However, even when such carbon materials are used as conductive agents, there are problems with insufficient rapid discharge characteristics and capacity characteristics.

[0004] Patent Document 2 (Japanese Patent Publication No. 2019-091587) describes a carbon material having a graphene layered structure, with a BET specific surface area of ​​10 m². 2 / g or more 200m 2A carbon material for energy storage devices has been disclosed in which the pore volume of the carbon material, measured according to the HK method, is 0.2 mL / g or more, the pore volume of the pores with a diameter of 0.3 nm to 1.0 nm is 0.2 mL / g or more, and the DBP absorption (oil absorption) is 150 mL / 100 g or more. However, such a carbon material has problems with insufficient electrolyte retention, conductivity, rapid discharge characteristics, charge / discharge characteristics, etc.

[0005] Patent Document 3 (International Publication No. 2017 / 119428) discloses a carbon material for a secondary battery anode, comprising a carbonaceous material having an average interplanar spacing d002 of the (002) plane, determined by X-ray diffraction using CuKα rays as a radiation source, of 0.340 nm or more, and carbon black having a DBP absorption (oil absorption) of 240 mL / 100 g or more. However, such a carbon material has poor rapid discharge characteristics, and its capacity characteristics and charge / discharge characteristics are also insufficient.

[0006] Patent Document 4 (Japanese Patent Publication No. 2020-100556) describes a specific surface area of ​​80 m² measured by the BET measurement method. 2 / g or more 250m 2 A graphene powder is disclosed in which the carbon content is less than or equal to / g and the elemental ratio of oxygen to carbon (O / C) measured by X-ray photoelectron spectroscopy is between 0.09 and 0.30. However, such a carbon material has insufficient electronic and ionic conductivity, and is inferior in terms of rapid discharge properties and capacitance characteristics.

[0007] Patent Document 5 (Japanese Patent Publication No. 2017-183292) discloses a positive electrode for a non-aqueous secondary battery having an active material layer on a current collector, wherein the active material layer has a plurality of active material particles and a plurality of graphenes, the active material particles have a layered rock salt type structure, one of the graphenes is in surface contact with the plurality of active material particles and the other of the graphenes, and the oxygen concentration of the graphene is 2 atomic percent or more and 20 atomic percent or less. However, such a positive electrode for a non-aqueous secondary battery still has problems such as insufficient conductivity and inferior rapid discharge characteristics and capacity characteristics.

[0008] Patent document 6 (JP 2023-501558) discloses porous reduced graphene oxide containing mesopores and macropores with a size of 2 nm to 500 nm.

[0009] Patent Document 7 (Japanese Patent Publication No. 2021-84819) discloses a method for producing a porous carbon material, which includes a coating step of forming a precursor containing graphene on the surface of a mold made of alkaline earth metal oxide nanoparticles, and a separation and removal step of dissolving the mold with a fluorine-free acid to separate the mold from the precursor. However, the rapid discharge characteristics, capacity characteristics, and charge-discharge characteristics of the carbon material obtained by this method have not been studied, particularly when used in lithium-ion secondary batteries.

[0010] Patent Document 8 (International Publication No. 2020 / 080520) discloses a capacitor comprising at least a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode includes a positive electrode active material, and the negative electrode includes a negative electrode active material, the positive electrode active material and the negative electrode active material include a graphene porous carbon sheet, the graphene porous carbon sheet includes a graphene porous carbon material and carbon nanotubes, the graphene porous carbon material is a porous carbon material made of graphene, the current collector on the positive electrode side and the current collector on the negative electrode side are made of aluminum, the aluminum material is coated with an amorphous carbon film, and the thickness of the amorphous carbon film is 60 nm or more and 300 nm or less.

[0011] Patent document 9 (Japanese Patent Publication No. 2022-191280) describes a first substrate, Li x S yA lithium-ion battery comprising a cathode disposed on a first substrate containing a cathode mixture containing a first granular carbon (where x is 0 to 2 and y is 1 to 8), a second substrate, an anode disposed on a second substrate containing silicon particles and an anode mixture containing a second granular carbon, and an electrolyte disposed between the cathode and the anode containing a solvent and a lithium salt, wherein the first or second granular carbon comprises a carbon aggregate containing a plurality of carbon nanoparticles, each carbon nanoparticle containing graphene, the plurality of carbon nanoparticles containing graphene comprises up to 15 layers, the ratio of carbon to elements other than hydrogen in the carbon aggregate is greater than 99%, the median diameter of the carbon aggregate containing carbon nanoparticles is 0.1 μm to 50 μm, and the surface area of ​​the carbon aggregate is 10 to 300 m² when measured by the BET method using nitrogen as the adsorbate. 2 A lithium-ion battery has been disclosed in which the carbon aggregate has an electrical conductivity of 500 S / m to 20,000 S / m when compressed. However, the carbon aggregate used in such lithium-ion batteries is produced explosively in a microwave plasma with a residence time of 0.001 seconds to approximately 2.0 seconds for the raw material gas, and therefore has almost no pores.

[0012] In particular, the carbon materials described in Patent Documents 1 to 9 had room for further improvement in terms of enhancing conductivity and improving rapid discharge characteristics, capacity characteristics, and charge / discharge characteristics when used in lithium-ion secondary batteries. [Prior art documents] [Patent Documents]

[0013] [Patent Document 1] Japanese Patent Publication No. 2004-22177 [Patent Document 2] Japanese Patent Publication No. 2019-091587 [Patent Document 3] International Publication No. 2017 / 119428 [Patent Document 4] Japanese Patent Publication No. 2020-100556 [Patent Document 5] Japanese Patent Publication No. 2017-183292 [Patent Document 6] Special Publication No. 2023-501558 [Patent Document 7] Japanese Patent Publication No. 2021-84819 [Patent Document 8] International Publication No. 2020 / 080520 [Patent Document 9] Japanese Patent Publication No. 2022-191280 [Overview of the Initiative] [Problems that the invention aims to solve]

[0014] This invention has been made in view of the above circumstances, and provides a carbon material, a method for producing the same, a conductive additive, a dispersion, an electrode composition, an electrode slurry, an electrode, and a lithium-ion secondary battery, which have excellent conductivity and can improve the rapid discharge characteristics, battery capacity characteristics, and charge / discharge characteristics when used in a lithium-ion secondary battery. [Means for solving the problem]

[0015] In view of the above problems, the inventors have conducted diligent research and found that a carbon material formed by a carbonaceous outer shell having a graphene structure and having pores, having a large BET specific surface area and a large total pore volume, and having a predetermined or greater ratio of the volume of pores with a diameter of 10 nm or more to the volume of macropores (pores with a diameter exceeding 50 nm) in the total pore volume, and having a peak top diameter (mode pore diameter) in the mesopore region between 2 nm and 50 nm, exhibits excellent conductivity as a carbon material and, when used in lithium-ion secondary batteries, exhibits excellent rapid discharge characteristics at 2C maintenance rate, battery capacity characteristics and Coulomb coefficient (charge / discharge characteristics) in charge / discharge tests. In other words, the inventors have found that by increasing the electronic conductivity of the carbon material and providing high ionic conductivity with a structure that can hold a large amount of electrolyte, the rapid discharge characteristics, battery capacity characteristics and charge / discharge characteristics of lithium-ion secondary batteries can be greatly improved.

[0016] The inventors have also found that by specifying the number per unit mass and the apparent density of the carbon material, an efficient path for electron conductivity can be formed, and moreover, a large amount of electrolyte can be retained and the ionic conductivity can be highly enhanced, further improving the rapid discharge characteristics, battery capacity characteristics, and charge-discharge characteristics of the lithium-ion secondary battery. The inventors have also found that by specifying the ash content in the carbon material, the rapid discharge characteristics, battery capacity characteristics, and charge-discharge characteristics of the lithium-ion secondary battery can be further improved.

[0017] The inventors have further found that a carbon material having excellent conductivity and stability and highly enhancing the rapid discharge performance, battery capacity characteristics, and charge-discharge characteristics of the lithium-ion secondary battery can be easily manufactured by using an aggregate of a smoke compound as a template.

[0018] Based on these findings, the inventors have completed the present invention.

[0019] (1) A carbon material formed by a carbonaceous outer shell having a graphene structure and having pores, wherein the BET specific surface area is in the range of 100 m 2 / g or more and 2500 m 2 / g or less, the total pore volume measured by nitrogen adsorption and desorption measurement is 0.30 cc / g or more, the volume ratio of pores having a pore diameter of 10 nm or more in the total pore volume is 30% or more, and the volume ratio of macropores having a pore diameter exceeding 50 nm is 5% or more, and the carbon material is in the mesopore region with a mode pore diameter of 2 nm or more and 50 nm or less.

[0020] (2) The carbon material according to (1) above, wherein the intensity ratio (I 2D ) of the intensity of the G band (I G ) to the intensity of the 2D band (I G ) in Raman spectroscopic measurement is in the range of 1.0 or more and 10 or less. 2D )

[0021] (3) The number per unit mass of the carbon material is 1.0×10 16 pieces / g or more and 1.0×1019 The carbon material described in (1) or (2) above, having a concentration of 1 / g or less.

[0022] (4) A carbon material according to any one of items (1) to (3) above, wherein the apparent density, expressed as 1 / (total pore volume + 1 / true density), is 1.00 g / cc or less.

[0023] (5) The carbon material according to any one of items (1) to (4) above, wherein the ash content in the carbon material is 5000 ppm or less.

[0024] (6) A carbon material used in lithium-ion secondary batteries, as described in any one of items (1) to (5) above.

[0025] (7) A method for producing a carbon material according to any one of items (1) to (6) above, comprising a carbonaceous layer formation step of forming a carbonaceous layer on the surface of a mold made of an aggregate of a fumid compound, and a mold removal step of removing the mold.

[0026] (8) A conductive additive for battery electrodes having the carbon material described in any one of items (1) to (6) above.

[0027] (9) A dispersion comprising a carbon material described in any one of items (1) to (6) above, and a dispersion medium in which the carbon material is dispersed.

[0028] (10) An electrode composition comprising a carbon material as described in any one of items (1) to (6) above, an active material, and a binder.

[0029] (11) An electrode slurry comprising the electrode composition described in (10) above and a solvent in which the electrode composition is dispersed.

[0030] (12) An electrode containing the carbon material described in any one of items (1) to (6) above.

[0031] (13) A lithium-ion secondary battery containing the carbon material described in any one of items (1) to (6) above. [Effects of the Invention]

[0032] According to the present invention, it is possible to provide a carbon material, a method for producing the same, a conductive additive, a dispersion, an electrode composition, an electrode slurry, an electrode, and a lithium-ion secondary battery, which have excellent conductivity and can improve rapid discharge performance, battery capacity characteristics, and charge / discharge characteristics when used in a lithium-ion secondary battery. [Brief explanation of the drawing]

[0033] [Figure 1] This is a transmission electron microscope (TEM) image of an example of a carbon material according to one embodiment of the present invention, measured at an accelerating voltage of 80 kV. [Figure 2] This is a transmission electron microscope (TEM) image of an example of a carbon material according to one embodiment of the present invention, measured at an accelerating voltage of 100 kV. [Figure 3] This is a transmission electron microscope (TEM) image of an example of a carbon material according to one embodiment of the present invention, measured at an accelerating voltage of 100 kV. [Figure 4] This figure shows an example of a Raman spectrum measured for a carbon material according to one embodiment of the present invention. [Figure 5] This figure shows discharge curves with different discharge current values ​​using a test battery of Example 1 according to one embodiment of the present invention. [Figure 6] This figure shows the relationship between the amount of carbon material blended, the 2C maintenance rate, and the discharge capacity of the test battery according to the example. The left vertical axis represents the 2C maintenance rate, the right vertical axis represents the discharge capacity, and the horizontal axis represents the amount of carbon material blended. In Figure 6, ● represents the 2C maintenance rate and △ represents the discharge capacity. [Modes for carrying out the invention]

[0034] Embodiments of the present invention will be described in detail below.

[0035] <Carbon materials> The carbon material of the present invention is a carbon material formed by a carbonaceous outer shell having a graphene structure and having pores, and has a BET specific surface area of ​​10 m². 2 / g or more 2500m 2 The following characteristics apply: the volume is in the range of less than or equal to / g, the total pore volume is 0.30 cc / g or more, the volume ratio of pores with a diameter of 10 nm or more to the total pore volume is 30% or more, the volume ratio of macropores (pores with a diameter exceeding 50 nm) is 5% or more, and the mode pore diameter is in the mesopore region of 2 nm to 50 nm.

[0036] The carbon material of the present invention is formed by a carbonaceous outer shell having a graphene structure and exhibits excellent electronic conductivity. Figure 1 shows a TEM image observed using a transmission electron microscope (TEM, model number: JEM-ARM300F, manufactured by JEOL Ltd.) at an acceleration voltage of 80 kV. Graphene is a sheet-like material of sp2-bonded carbon, and as shown in Figure 1, the carbon 6-membered ring structure is linked in a planar manner, forming a honeycomb-like hexagonal lattice structure. Furthermore, the presence of a graphene structure in the carbon material of the present invention is reflected in the intensity of the 2D band (I) in the Raman spectroscopy measurement described later. 2D The intensity of the G band (I G ) intensity ratio (I G / I 2D This can also be confirmed by checking if the value becomes 0.4 or higher.

[0037] One embodiment of the carbon material of the present invention has a complex structure. Figure 2 shows a TEM image of an example of the carbon material according to this embodiment, observed using a transmission electron microscope (TEM, model number: H-7650, manufactured by Hitachi High-Technologies Corporation) at an acceleration voltage of 100kV and a magnification of 15,000x. The degree of transmission of the particles in Figure 2 also shows that the inside of the particle shape is hollow. Furthermore, in the carbon material of this embodiment, some of the branched ends of the linearly extending linked structures form ring shapes, and these ring shapes may or may not be connected to hollow particles having a carbonaceous outer shell.

[0038] One embodiment of the carbon material of the present invention has an aggregate structure composed of carbon materials having the complex structure described above. Figure 3 shows a TEM image of an example of the carbon material according to this embodiment, observed using a transmission electron microscope (TEM, JEM-2100Plus model, manufactured by JEOL Ltd.) at an acceleration voltage of 100kV and a magnification of 40,000x.

[0039] As described above, the carbon material of the present invention is formed by a carbonaceous outer shell containing a graphene structure with high electronic conductivity, and also has pores. Here, one pore enclosed in the carbonaceous outer shell is a mesopore, preferably a mesopore with a diameter of 10 nm or more. Furthermore, macropores with a diameter exceeding 50 nm are formed by the ring shape created by the linked branched structures and the inter-branch voids of aggregates, thereby obtaining a large BET specific surface area, a large total pore volume, and a high volume ratio of pores with a diameter of 10 nm or more and macropores with a diameter exceeding 50 nm. As a result, it becomes possible to impart ionic conductivity that can hold a large amount of electrolyte and enable the movement of lithium ions. In other words, the carbon material of the present invention possesses both electronic conductivity and ionic conductivity, and when used as a conductive additive in lithium-ion secondary batteries, it can significantly improve conductivity, and the rapid discharge characteristics, battery capacity characteristics, and charge / discharge characteristics can be improved.

[0040] (BET specific surface area, pore volume, mode pore diameter) The BET specific surface area of ​​the carbon material of the present invention is the BET specific surface area calculated from nitrogen adsorption as specified in JIS Z8830, and is 100m². 2 / g or more 2500m 2 A range of less than or equal to / g, preferably 100m 2 / g or more 2000m 2 A range of less than / g, more preferably 300m 2 / g or more 1800m 2 A range of less than or equal to / g, more preferably 500m 2 / g or more 1500m 2 A range of less than or equal to / g, particularly preferably 800m 2 / g or more 1200m 2The BET specific surface area of ​​the carbon material of the present invention is suitable because it can significantly enhance both electronic and ionic conductivity when it falls within this range.

[0041] The total pore volume of the carbon material of the present invention is a value measured by nitrogen adsorption / desorption measurement, preferably 0.30 cc / g or more, preferably 0.50 cc / g or more, more preferably 1.00 cc / g or more, even more preferably 1.50 cc / g or more, and particularly preferably 2.00 cc / g or more. On the other hand, the upper limit of the total pore volume of the carbon material is preferably 20.00 cc / g or less, more preferably 15.00 cc / g or less, even more preferably 10.00 cc / g or less, even more preferably 8.00 cc / g or less, and particularly preferably 7.00 cc / g or less. If the total pore volume of the carbon material is excessively low, the amount of electrolyte held in the carbon material will decrease, which is undesirable. Also, if the total pore volume of the carbon material is excessively high, the skeletal strength of the pore structure will weaken, making it impossible to maintain the pore shape, which is undesirable. In the carbon material of the present invention, when the total pore volume is as described above, the pore shape has appropriate strength and contributes to the stability of the connecting structure.

[0042] The present invention is characterized in that the mode pore diameter (M), which is the most frequent value of the pore diameter, is present in the mesopore region of the pore distribution curve between 2 nm and 50 nm. Specifically, the mode pore diameter (M) of the carbon material of the present invention is in the range of 2 nm to 50 nm, preferably 5 nm to 45 nm, more preferably 10 nm to 40 nm, even more preferably 12 nm to 30 nm, and particularly preferably 15 nm to 25 nm. When the mode pore diameter (M) of the pore distribution of the carbon material is within this range, it is preferable to achieve high ionic conductivity and electronic conductivity.

[0043] The carbon material of the present invention has a volume ratio of mesopores, which are pores with a diameter in the range of 2 nm to 50 nm, to the total pore volume, preferably 30% or more, more preferably 35% or more, even more preferably 40% or more, even more preferably 45% or more, and particularly preferably 50% or more. On the other hand, the upper limit of the volume ratio of mesopores to the total pore volume is preferably 90% or less, more preferably 85% or less, even more preferably 80% or less, even more preferably 75% or less, and particularly preferably 70% or less. When the mesopore volume of the carbon material is within this range, the linkage structure of the hollow particles has appropriate strength, contributes to the stability of the hollow particles, and maintains their shape.

[0044] The carbon material of the present invention has a volume ratio of pores with a pore diameter of 10 nm or more of 30% or more, preferably 40% or more, more preferably 50% or more, even more preferably 60% or more, and particularly preferably 70% or more. This allows for a high balance between electronic conductivity and ionic conductivity. On the other hand, the upper limit of the volume ratio of pores with a pore diameter of 10 nm or more to the total pore volume is preferably 95% or less, more preferably 90% or less, and even more preferably 85% or less.

[0045] The carbon material of the present invention has a macropore volume ratio of pores with a diameter exceeding 50 nm to the total pore volume of 5% or more, preferably 10% or more, more preferably 15% or more, even more preferably 20% or more, and particularly preferably 25% or more. On the other hand, the upper limit of the macropore volume ratio to the total pore volume is preferably 80% or less, more preferably 70% or less, even more preferably 60% or less, even more preferably 50% or less, and particularly preferably 45% or less. If the macropore volume ratio (volume ratio of pores exceeding 50 nm) of the carbon material is excessively small, the ionic conductivity is poor, and conversely, if it is excessively large, the carbonaceous strength properties are poor, so both are undesirable. In this specification, "micropore" refers to a pore with a diameter of less than 2 nm. "Mesopore" refers to a pore with a diameter between 2 nm and 50 nm. "Macropore" refers to a pore with a diameter greater than 50 nm.

[0046] In the present invention, the number of carbonaceous layers surrounding the pores is important in order to maintain a pore shape that can achieve the above-mentioned ionic conductivity and electronic conductivity. The number of carbonaceous layers in the present invention is, for example, 1 or more, preferably 1.2 or more, more preferably 1.5 or more, even more preferably 2 or more, and particularly preferably 2.2 or more, with an upper limit of, for example, 15 or less, preferably 10 or less, more preferably 8 or less, even more preferably 6 or less, and particularly preferably 5 or less. When the number of carbonaceous layers is within this range, the carbonaceous strength properties and elastic deformation are excellent, the hollow structure of the granular shape and the macropore shape formed by the linkage of the granular shapes can be maintained, and the lithium-ion secondary battery characteristics can be greatly enhanced. The number of carbonaceous layers in the carbon material is calculated specifically as described in the examples below. After laminating the carbon layers on the mold particles, the weight of the carbon layers is calculated using thermogravimetric analysis (TG). The weight of the carbon layers per unit area of ​​the mold is calculated from this weight of the carbon layers and the BET specific surface area of ​​the mold particles, and this is used as the weight of the carbon layers per unit area of ​​single-layer graphene (7.61 × 10⁻¹⁰). -4 g / m 2 This value is calculated by dividing by ).

[0047] (Structural analysis) In this invention, the state of the carbon material can be analyzed by Raman spectroscopy. An example of a Raman spectrum measured for the carbon material of this invention is shown in Figure 4. Among the Raman spectra, wavenumber 1593 cm⁻¹ is shown. -1 The peak in the surrounding region is called the G band, and this band represents the sp2 bond (aromatic ring C=C stretching motion) in carbon materials. This is the Raman spectrum at wavenumber 1356 cm⁻¹. -1 The peak present in this vicinity is called the D band, which represents sp3 bonding (CH stretching motion) in carbon materials. This band increases when sp2 bonds in the six-membered carbon ring structure of the carbonaceous layer are broken and replaced with sp3 bonds. This occurs in the Raman spectrum at wavenumber 2680 cm⁻¹. -1 The peaks in the surrounding region are called 2D bands, and they are bands that show second-order phonon scattering (CH stretching motion), and they represent the number of layers of carbon material.

[0048] Intensity of 2D bands in carbon materials (I 2D The intensity of the G band (I G ) intensity ratio (I G / I 2D The intensity ratio I is said to be an index that indicates the stacking state of graphene layers (D. Graf, et al., NANO LETTERS, 7, 238-242; (2007)). In the same paper, intensity ratio I G / I 2D It is assumed that when the value is 0.2, there is one graphene layer.

[0049] The carbon material of the present invention has a 2D band intensity (I 2D The intensity of the G band (I G ) intensity ratio (I G / I 2D The strength ratio of carbon material I is preferably 1.0 or higher, more preferably 1.2 or higher, and particularly preferably 1.4 or higher, with the upper limit being preferably in the following order: 10 or less, 5.0 or less, 4.5 or less, 4.0 or less, 3.5 or less, 3.0 or less, 2.5 or less, and 2.2 or less. G / I 2D When the value of is within this range, the strength properties and elastic deformability that maintain the hollow structure of the carbon material are balanced, and the desired rapid discharge characteristics, capacity characteristics, and durability of the lithium-ion secondary battery are greatly improved, which is preferable. G / I 2D However, if the lower limit is exceeded excessively, the graphene material is not sufficiently formed, resulting in decreased electronic conductivity and reduced discharge capacity. If the upper limit is exceeded excessively, the number of graphene layers increases, leading to reduced flexibility and decreased electrode density, resulting in reduced packing capacity. Neither of these is desirable.

[0050] (particle shape characteristics) In one embodiment, the carbon material of the present invention is preferably a linked structure in which hollow particles having the carbonaceous outer shell described above are connected in a plurality of branched structures.

[0051] The particle size distribution curve of the carbon material of the present invention was measured after immersing the unground material in a solvent for 9 minutes, and it shows the difference in cohesive force of the linked structures.

[0052] The median diameter D50 in the particle size distribution curve of the carbon material of the present invention, where half of the particles are located, is, for example, in the range of 0.5 μm to 150 μm, preferably in the range of 1 μm to 100 μm, more preferably in the range of 10 μm to 80 μm, even more preferably in the range of 15 μm to 60 μm, and particularly preferably in the range of 20 μm to 50 μm. When the median diameter D50 of the carbon material is in this range, it is preferable in that the electronic conductivity and ionic conductivity are greatly enhanced.

[0053] The particle size D10 in the particle size distribution curve of the carbon material of the present invention, where 10% of the particles are located, is, for example, in the range of 0.1 μm to 100 μm, preferably in the range of 0.5 μm to 50 μm, more preferably in the range of 1 μm to 50 μm, even more preferably in the range of 5 μm to 30 μm, and particularly preferably in the range of 10 μm to 15 μm.

[0054] The particle size D90 of the carbon material of the present invention, where 90% of the particles are located, is, for example, in the range of 5 μm to 250 μm, preferably in the range of 10 μm to 150 μm, more preferably in the range of 20 μm to 100 μm, even more preferably in the range of 30 μm to 70 μm, and particularly preferably in the range of 40 μm to 60 μm. When the D90 of the carbon material is within this range, it is preferable in that its conductivity can be greatly enhanced.

[0055] The ratio of D90 to D10 in the carbon material of the present invention is, in terms of the D90 / D10 value, for example, 100 or less, preferably 50 or less, more preferably 25 or less, even more preferably 10 or less, and particularly preferably 5 or less, with a lower limit of, for example, 1 or more, preferably 1.5 or more, more preferably 2 or more, even more preferably 2.5 or more, and particularly preferably 3 or more. If the D90 / D10 of the carbon material is excessively large, the cohesiveness will be strong and the dispersibility will be poor, which is undesirable because the conductivity and high-performance characteristics of the lithium-ion secondary battery cannot be sufficiently obtained.

[0056] The ratio of D90 to mode pore size (M) of the carbon material of the present invention (D90 / M) is the value obtained by dividing the D90 value [μm] by the mode pore size (M) [nm] and multiplying by 1000, and is, for example, in the range of 50 or less, preferably 20 or less, more preferably 10 or less, even more preferably 6 or less, and particularly preferably 4 or less. If the (D90 / M) ratio of the carbon material is excessively large, the cohesiveness will be strong and the dispersibility will be poor, which is undesirable because the conductivity and high-performance characteristics of the lithium-ion secondary battery cannot be sufficiently obtained.

[0057] (General characteristics) The carbon content of the carbon material of the present invention is, for example, 95% by weight or more, preferably 96% by weight or more, more preferably 97% by weight or more, even more preferably 98% by weight or more, and particularly preferably 99% by weight or more. If the carbon content of the carbon material is too low, the electronic conductivity will be poor and undesirable.

[0058] The oil absorption capacity of the carbon material of the present invention is, for example, the oil absorption capacity of refined linseed oil measured in accordance with JIS K5101-13-1 (Pigment Test Methods - Part 13: Oil Absorption - Section 1: Refined Linseed Oil Method), which is, for example, 100 mL / 100 g or more, preferably 300 mL / 100 g, more preferably 500 mL / 100 g or more, even more preferably 800 mL / 100 g or more, and particularly preferably 1000 mL / 100 g or more. The upper limit is, for example, 5000 mL / 100 g or less, preferably 4000 mL / 100 g or less, more preferably 3500 mL / 100 g or less, even more preferably 3000 mL / 100 g or less, and particularly preferably 2500 mL / 100 g or less.

[0059] The oil absorption capacity of the carbon material of the present invention is significantly higher than that of carbon black, which is commonly used as a conductive additive in lithium-ion secondary batteries. This allows for a large amount of electrolyte to be held not only in the space inside the hollow particles of the linked structure, but also in the gaps created in the parts surrounded by the linked outer shell and the parts surrounded by the linked aggregate structure. This enables a stable supply of lithium ions and contributes to the rapid discharge characteristics, charge-discharge characteristics, and battery capacity characteristics of lithium-ion secondary batteries. If the oil absorption capacity of the carbon material is excessively low, the amount of electrolyte that can be held is small, causing a delay in ion supply during rapid reactions and reducing the discharge capacity. Conversely, if it is excessively high, it becomes difficult to maintain the structure of the carbon material and difficult to control the amount of electrolyte held. Both are undesirable.

[0060] The electrical conductivity of the carbon material of the present invention is, at a pressure of 10 MPa, for example, in the range of 1 S / cm to 100 S / cm, preferably in the range of 5 S / cm to 70 S / cm, more preferably in the range of 10 S / cm to 50 S / cm, even more preferably in the range of 15 S / cm to 40 S / cm, and particularly preferably in the range of 20 S / cm to 30 S / cm. The electrical conductivity of the carbon material can be determined by the reciprocal of its electrical resistivity. For example, the electrical resistivity of the carbon material can be measured according to JIS K1469.

[0061] The number of carbon atoms per unit mass of the carbon material of the present invention (number density of the carbon material) is a value calculated by the method described later, for example, 1.0 × 10⁻⁶ 16 pcs / g or more 1.0×10 19 A range of pieces / g or less, preferably 5.0 × 10 16 pcs / g or more 5.0×10 18 The range is less than or equal to pieces / g, more preferably 1.0 × 10 17 pcs / g or more 3.0×10 18 The range is less than or equal to pieces / g, particularly preferably 2.0 × 10 17 pcs / g or more 2.0×10 18 The number of carbon atoms per unit mass of carbon material is within this range, which is preferable as it optimizes the retention of the electrolyte.

[0062] The carbon material of the present invention has an apparent density expressed as 1 / (total pore volume + 1 / true density), which is a value calculated using the total pore volume value described later. For example, it is 1.00 g / cc or less, preferably 0.80 g / cc or less, more preferably 0.50 g / cc or less, even more preferably 0.34 g / cc or less, and particularly preferably 0.30 g / cc or less. The lower limit is, for example, 0.01 g / cc or more, preferably 0.02 g / cc or more, more preferably 0.05 g / cc or more, even more preferably 0.10 g / cc or more, and particularly preferably 0.15 g / cc or more. When the apparent density of the carbon material is within this range, it is suitable for highly enhancing the conductivity and electrolyte retention properties of the carbon material.

[0063] The ash content in the carbon material of the present invention is, for example, 10,000 ppm or less, preferably 5,000 ppm or less, more preferably 4,000 ppm or less, even more preferably 3,500 ppm or less, even more preferably 3,000 ppm or less, and particularly preferably 2,100 ppm or less. When the ash content of the carbon material is within this range, the stability of the electrolyte is excellent, and it is suitable for improving the durability and performance of lithium-ion secondary batteries.

[0064] (Applications of carbon materials) This carbon material can be used, for example, as part of the electrode material for batteries such as lithium-ion secondary batteries, such as a conductive additive. Furthermore, this carbon material can be incorporated into conductive additives, dispersions, electrode compositions, electrode slurries, etc., and can be used as part of the material constituting electrodes for batteries or other electronic components.

[0065] The carbon material of the present invention possesses electron transfer properties due to its graphene structure, and due to its large pore volume, it retains electrolyte and has ionic conductivity for lithium ions, as well as excellent stability in the electrolyte. Therefore, when incorporated into the electrodes of a lithium-ion secondary battery, it can exert a function that assists the battery reaction in the lithium-ion secondary battery. Furthermore, one embodiment of the carbon material of the present invention is a linked structure in which hollow granular objects covered with an outer shell made of carbonaceous material containing graphene are linked together. Because there is space inside the granular objects and inside the area surrounded by the linked structure, an electrolyte containing dissolved lithium ions can penetrate and be retained, resulting in excellent ion supply during the reaction. For this reason, the carbon material of the present invention can suitably assist the secondary battery reaction.

[0066] The positive electrode material of a lithium-ion secondary battery is a lithium-containing transition metal oxide with low electronic conductivity and is a powder with a particle size distribution. In conventional methods, an electron conduction path is established by mixing a conductive additive made of carbon material, which assists electron conduction for the battery reaction, with a binder resin and then pressing and fixing it to a current collector. The materials other than the binder resin are powder particles, and the electrolyte exists in the spaces between the particles. For this reason, it has been difficult with conventional techniques to actively place the electrolyte, or in other words lithium ions, near the positive electrode material.

[0067] In contrast, this embodiment uses the carbon material described above instead of the conventionally used conductive additive. The carbon material of this embodiment has a space inside its carbonaceous outer shell, which allows it to hold an electrolyte. The carbon material of this embodiment has a larger internal space compared to carbon black, which has been conventionally used as a conductive additive. Therefore, the carbon material of this embodiment can be said to be a material that simultaneously assists in the supply of electrons and ions necessary for the battery reaction, enabling a rapid battery reaction.

[0068] <Method for manufacturing carbon materials> Next, a method for producing carbon materials according to the present invention will be described. The carbon material of the present invention can be easily produced by, for example, forming a carbonaceous layer on the surface of a mold made of an aggregate of aerosol compounds, and then removing the mold.

[0069] (Mold material) Examples of atomized compounds used as mold materials include compounds obtained by flame hydrolysis, a dry manufacturing method for inorganic materials. These compounds are suitable for use because they form aggregate structures in which primary particles are complex and elongated.

[0070] A representative example of an atomized compound is fumed silica (fumed silicon dioxide). Fumed silica, produced by flame hydrolysis, does not go through a liquid-phase process during its production, resulting in slow aggregation. Therefore, fumed silica exhibits excellent dispersibility in both the liquid phase and the compound (solid phase). Fumed silica is produced by high-temperature gas-phase hydrolysis of silicon tetrachloride in an oxyhydrogen flame. By varying production conditions such as flame temperature, oxygen and hydrogen supply ratio, raw material supply amount, and residence time, the average primary particle size can be increased from 7 nm to 40 nm, and the BET specific surface area can be increased to 50 m². 2 / g~380m 2 Particles of silicon dioxide are obtained at a density of / g.

[0071] The structure of the atomized compound used in the mold of the present invention is preferably a particulate structure. The average primary particle diameter of the atomized compound used in the mold of the present invention is, for example, 1 nm to 150 nm, preferably 5 nm to 100 nm, more preferably 10 nm to 60 nm, even more preferably 15 nm to 50 nm, and particularly preferably 20 nm to 40 nm. When the average primary particle diameter of the mold material is in this range, the pore volume of 10 nm or more in the manufactured carbon material can be significantly increased, which is advantageous. Furthermore, if the average primary particle diameter of the atomized compound is in this range, it is easy to handle, and the permeability of the raw material gas that serves as the carbon source for the carbonaceous layer is good, making it easy to achieve a uniform carbon coating.

[0072] The BET specific surface area of ​​the atomized compound used in the mold of the present invention is, for example, 1 m². 2 / g~1000m 2 / g, preferably 10m 2 / g~500m 2 / g, more comfortably 20m 2 / g~200m 2 / g, more preferably 40m 2 / g~160m 2 / g, particularly preferably 50m 2 / g~105m 2 The range is / g. When the BET specific surface area of ​​the mold material is within this range, it is preferable to significantly increase the pore volume of 10 nm or larger in the manufactured carbon material.

[0073] The BET specific surface area of ​​the manufactured carbon material depends on the BET specific surface area of ​​the mold. The ratio of volume to surface area of ​​the mold particles increases as the mean primary particle diameter decreases. Therefore, the smaller the mean primary particle diameter of the particles, the larger the surface area per unit volume, i.e., the surface area per unit mass. Consequently, by using particles of aerosol compounds with a small mean primary particle diameter, a carbon material with a large BET specific surface area can be obtained.

[0074] The aggregate structure of the atomized compound used as a template in the present invention is preferably complex and elongated, and capable of realizing a higher-order structure. For example, an aggregate structure in which the primary particle diameter has multiple branched structures and is linked together in a bead-like manner is preferred.

[0075] The carbon content of the atomized compound used as a mold in the present invention is, for example, 0.001% by weight or more, preferably 0.01% by weight or more, more preferably 0.05% by weight or more, even more preferably 0.1% by weight or more, and particularly preferably 0.5% by weight or more. The upper limit is, for example, 5% by weight or less, preferably 4% by weight or less, more preferably 3% by weight or less, even more preferably 2.5% by weight or less, and particularly preferably 2% by weight or less. When the carbon content of the atomized compound is within this range, it is preferable because it facilitates the formation of a carbonaceous layer on the mold surface.

[0076] These mold materials can be used individually or in combination of two or more types.

[0077] (Carbonaceous layer formation process) In the present invention, the formation of a carbonaceous layer on the surface of the mold material can be achieved by contacting the mold material with an organic substance that serves as a carbon source and performing a carbonization heat treatment. Contact with the carbon source and the carbonization heat treatment can be performed simultaneously or separately. Contact between the mold material and the carbon source is performed, for example, in a temperature range of room temperature to 1000°C. The carbonization heat treatment is performed in a temperature range of 400°C to 1000°C, which is the temperature at which the organic substance serving as the carbon source decomposes thermally.

[0078] As a method for bringing the carbon source into contact with the mold material, a gas-phase contact method is preferable. Here, a gas-phase contact method is a method in which an organic gas is introduced at a high temperature and brought into contact with the mold material, and one example of this is the so-called CVD (Chemical Vapor Deposition) method.

[0079] In the CVD method, it is preferable to bring an organic compound as a carbon source into contact with the mold material and to carry out the dehydrogenation reaction in a temperature range where it can proceed, specifically 400°C to 1000°C, in order to carbonize the carbon source and strongly bond it with the mold material.

[0080] As an organic compound used as a carbon source in the gas-phase contact method, it may be appropriately selected according to the intended use, but hydrocarbons such as saturated hydrocarbons, unsaturated hydrocarbons having double and / or triple bonds, alicyclic hydrocarbons, and aromatic hydrocarbons are preferably used. Saturated hydrocarbons may be either straight-chain or branched-chain, and examples include methane, ethane, and propane. Unsaturated hydrocarbons may be either straight-chain or branched-chain, and examples include ethylene, propylene, isoprene, and acetylene. Examples of alicyclic hydrocarbons include cyclopropane and cyclohexane. Examples of aromatic hydrocarbons include benzene and toluene. Among these hydrocarbons, it is desirable to use methane, ethane, acetylene, ethylene, propylene, and benzene, and from the viewpoint of precipitating highly crystalline carbon, methane, propylene, and benzene are preferred. In particular, methane is preferably used from the viewpoint of obtaining highly crystalline carbon at a high thermal decomposition temperature.

[0081] Organic compounds that can be used in the gas-phase contact process include alcohols such as methanol, ethanol, propanol, and butanol, as well as nitrogen-containing compounds such as acetonitrile and acrylonitrile.

[0082] The reaction temperature in the CVD reaction is appropriately selected according to the decomposition temperature of the organic compound used as the carbon source, but is, for example, in the range of 400°C to 1000°C, preferably 600°C to 950°C, and preferably 800°C to 900°C.

[0083] The reaction time in the CVD reaction (CVD treatment time at a predetermined heating temperature) is appropriately selected depending on the type of template material, the type of organic compound used as the carbon source, or the number of carbon layers deposited. For example, it is in the range of 0.1 to 10 hours, preferably 0.5 to 5 hours, and more preferably 1 to 3 hours. Furthermore, the product can be analyzed by applying the analytical methods disclosed herein, and the time required for sufficient carbon deposition can be appropriately set based on the results.

[0084] CVD reactions can be carried out under an inert gas atmosphere if necessary. Examples of inert gases include nitrogen, helium, neon, and argon, with argon being preferred. In the CVD method, carbon can usually be easily adsorbed or deposited on the mold material in the gas phase by heating while passing a gaseous organic compound in contact with the mold material together with a carrier gas. The type of carrier gas, flow rate, flow rate, and heating temperature can be appropriately adjusted depending on the type of organic compound used. Examples of carrier gases include the inert gases mentioned above, but a mixture with oxygen gas or hydrogen gas may also be used. Argon is preferably used as the carrier gas.

[0085] The ratio of the amount of organic compound introduced to the total amount of carrier gas and organic compound is preferably adjusted to a range of 1% to 70% by volume, more preferably 5% to 50% by volume, even more preferably 10% to 40% by volume, and particularly preferably 15% to 35% by volume, from the viewpoint of forming the optimal number of graphene layers.

[0086] (Mold removal process) The removal of the mold after the formation of the carbonaceous layer can be done by any method that removes the mold while leaving the formed carbonaceous layer, such as dissolution with an acid or alkali, and preferably dissolution with an acid.

[0087] The acid used in this invention is appropriately selected depending on the type of mold material, but examples include hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, boric acid, and hydrofluoric acid, with hydrochloric acid and hydrofluoric acid being preferred. The acid concentration used for dissolving and removing the mold is appropriately adjusted within a range that allows for the dissolution and removal of the mold. The amount of acid used is not particularly limited as long as it is within a range that allows for the dissolution and removal of the mold material, but for example, it may be 30 times or more the stoichiometric ratio or 50 times or more the stoichiometric ratio relative to the mold material.

[0088] The carbon material after mold removal can be recovered, for example, by filtration, and then washed with pure water. Washing conditions can be selected as appropriate, but the process can be terminated after confirming that the pH of the washing solution is neutral.

[0089] The carbon material, after cleaning and removal of the mold material, can be dried by heating. The heating conditions can be, for example, a drying temperature of 100°C to 200°C and a drying time of 1 to 10 hours.

[0090] (Heat treatment process) In the method for producing carbon materials of the present invention, the carbon material after removal of the mold material (separated carbonaceous layer) can be heat-treated as needed. By heat-treating the carbonaceous layer from which the mold material has been removed, the crystallinity of the carbon is enhanced and stabilized, making it possible to produce a carbon material with higher levels of conductivity, corrosion resistance, and / or a large BET specific surface area.

[0091] The conditions for the heat treatment process are not particularly limited as long as they enhance the crystallinity of the carbon. The holding temperature during the heat treatment process is, for example, in the range of 1000°C to 3000°C, preferably 1300°C to 2500°C, more preferably 1500°C to 2000°C, even more preferably 1600°C to 1900°C, and particularly preferably 1750°C to 1850°C. A heat treatment temperature within this range is preferable because it allows for the acquisition of carbon materials with higher levels of conductivity, corrosion resistance, and / or a larger BET specific surface area. The heat treatment time (holding time at the predetermined heat treatment temperature) is, for example, in the range of 0.1 hours to 10 hours, preferably 0.2 hours to 5 hours, and more preferably 0.5 hours to 5 hours. An inert gas such as argon gas can be used as the atmosphere during the heat treatment process. Furthermore, the atmospheric pressure during the heat treatment process can be, for example, atmospheric pressure or reduced pressure.

[0092] Furthermore, through the heat treatment process, functional groups that bond to carbon (mainly oxygen-containing functional groups) and carbon chains that do not form six-membered rings detach above 1000°C, forming unbonded bonds. When these unbonded bonds bond to other nearby carbon atoms, the surface of the carbon material becomes less receptive to the bonding of functional groups. By heat-treating at 1500°C or higher, preferably 1600°C or higher, the carbon material of the present invention can exhibit desirable functions such as electronic conductivity and the maintenance of internal spaces.

[0093] These heat treatments adjust structural defects in the graphene and non-graphene components that make up the carbonaceous material. These structural defects include spaces created within the aggregate structure due to the dissolution of the template material and intrusion pores created in the outer shell formed from the carbonaceous material. By changing reaction conditions such as heat treatment temperature and time, the degree of these structural defects can be adjusted. In other words, the size of the spaces within the carbon material and the size of the intrusion pores that allow the electrolyte to penetrate into the particles can be adjusted.

[0094] Thus, the carbon material of the present invention can be easily manufactured.

[0095] <Dispersion> Next, the dispersion according to the present invention will be described. The dispersion of the present invention is obtained by dispersing the above-mentioned carbon material in a dispersion medium. The dispersion may optionally contain a dispersant to improve the dispersibility of the carbon material.

[0096] The dispersion medium used in the present invention is selected according to the intended use. For example, organic or inorganic dispersants can be suitably used to maintain good dispersion of the powder in the solvent. When used in the manufacture of lithium-ion secondary batteries, polar solvents are suitably used. From the viewpoint of affinity with the binder polymer, N,N-dimethylformamide, N-methylpyrrolidone (NMP), N,N-dimethylacetamide, and water are preferred, and the inclusion of N-methylpyrrolidone (NMP) is particularly preferred. NMP is suitable for dispersing carbon materials containing graphene.

[0097] <Electrode compositions, electrode slurries, and electrodes> Next, the electrode composition, electrode slurry, and electrode according to the present invention will be described.

[0098] The electrodes containing the carbon material of the present invention, preferably electrodes for lithium-ion secondary batteries, are preferable in that they exhibit excellent fast discharge properties, capacity characteristics, and charge-discharge characteristics. To manufacture such electrodes, it is useful to use electrode compositions and electrode slurries containing the carbon material of the present invention.

[0099] (Composition for electrode) The electrode composition of the present invention comprises the carbon material, active material, and binder of the present invention.

[0100] Examples of active materials used in the present invention include the active material used in the positive electrode described later, and the active material used in the negative electrode described later. The ratio of the active material to the carbon material of the present invention is appropriately selected according to the purpose of use, and is in the range of 0.005 to 20 parts by weight of the carbon material of the present invention per 100 parts by weight of the active material, preferably 0.01 to 10 parts by weight, more preferably 0.05 to 5 parts by weight, even more preferably 0.1 to 2 parts by weight, and particularly preferably 0.5 to 1 part by weight.

[0101] Examples of binders used in the present invention include binders used in the positive electrode and binders used in the negative electrode, as described later. The amount of binder used is appropriately selected according to the purpose of use, and is in the range of, for example, 0.05 to 10 parts by weight, preferably 0.1 to 8 parts by weight, more preferably 0.5 to 6 parts by weight, even more preferably 1 to 5 parts by weight, and particularly preferably 2 to 4 parts by weight per 100 parts by weight of active material.

[0102] In addition to the carbon material, active material, and binder of the present invention, other compounding agents may be added to the electrode composition of the present invention as needed. Other compounding agents that are normally used in electrode compositions for lithium-ion secondary batteries are used, and the amount used is, for example, 20 parts by weight or less, preferably 15 parts by weight or less, more preferably 10 parts by weight or less, even more preferably 5 parts by weight or less, and particularly preferably 2 parts by weight or less, per 100 parts by weight of the active material.

[0103] Examples of mixing methods for the electrode composition of the present invention include a dry mixing method and a wet mixing method using a dispersion medium.

[0104] (Electrode slurry) The two-electrode slurry of the present invention is obtained by mixing the above-mentioned electrode composition using a wet mixing method with a dispersion medium. Any dispersion medium capable of dissolving or dispersing the binder can be used, such as the dispersion medium used for the positive electrode described later, the dispersion medium used for the negative electrode described later, and the dispersion medium used for the carbon material-containing dispersion liquid of the present invention described above. The amount of dispersion medium used can be an appropriate amount, adjusted so that the electrode slurry for the next step can be applied to the current collector.

[0105] Methods for producing the electrode slurry of the present invention include, for example, a method of mixing the carbon material of the present invention, a binder, and a dispersion medium, and then mixing in an active material. In mixing the carbon material, binder, and dispersion medium of the present invention, there are methods such as mixing the binder into a dispersion liquid containing the carbon material, and mixing the dispersion liquid containing the carbon material with a binder solution obtained by dissolving or dispersing the binder in the dispersion medium.

[0106] For mixing, known mixers and kneaders can be used. Known mixers include automatic mortars and pestles, homogenizers, planetary mixers, homodispersers, and revolving mixers, with planetary mixers being particularly preferred.

[0107] (electrode) The electrode of the present invention may be either a negative electrode or a positive electrode, and can be obtained by applying the electrode slurry to a current collector and then drying it. The current collector may be either one used for the positive electrode or one used for the negative electrode, as described later.

[0108] As a method for applying the electrode slurry onto the current collector, any known method can be used without particular limitation. Specifically, it can be applied using a manual or automatic coater such as a baker applicator, a film applicator with a micrometer, a bar coater, a doctor blade, etc. As a method for drying, any known method can be used without particular limitation, and examples include drying with warm air, hot air, low-humidity air, vacuum drying, and drying methods by irradiation with infrared rays or electron beams. After the drying process, a pressure treatment may be applied to the electrode composite layer using a die press or a roll press, etc. By the pressure treatment, the positive electrode composite layer can be favorably adhered to the current collector.

[0109] <Positive electrode> The positive electrode will be described. Generally, the positive electrode is obtained by applying a slurry in which a positive electrode active material, a conductive auxiliary agent for assisting electron conductivity, a binder, and a solvent are mixed onto a current collecting metal foil such as rolled aluminum foil to form a coating film, heating and drying to remove the solvent, and then forming it into a predetermined size and density. The carbon material of the present invention can be usefully used as a conductive auxiliary agent.

[0110] (Positive electrode active material) The positive electrode active material is a compound capable of reversible intercalation and deintercalation of lithium, and specifically, may include a lithium composite metal oxide containing one or more metals such as cobalt, manganese, nickel, or aluminum and lithium.

[0111] Specific examples of the positive electrode active material include lithium-manganese-based oxides (e.g., LiMnO2, LiMn2O4, etc.), lithium-cobalt-based oxides (e.g., LiCoO2, etc.), lithium-nickel-based oxides (e.g., LiNiO2, etc.), lithium-nickel-manganese-based oxides (e.g., LiNi 1-a Mn a O2 (where 0 < a < 1), LiMn 2-b Ni b O4 (where 0 < b < 2), etc.), lithium-nickel-cobalt-based oxides (e.g., LiNi 1-c Co cO2 (where 0 < c < 1), lithium-manganese-cobalt-based oxides (e.g., LiCo 1-d Mn d O2 (where 0 < d < 1), LiMn 2-e Co e O4 (where 0 < e < 2), etc.), lithium-nickel-manganese-cobalt-based oxides (e.g., Li(Ni f Co g Mn h )O2 (where 0 < f < 1, 0 < g < 1, 0 < h < 1, f + g + h = 1) or Li(Ni j Co k Mn m )O4 (where 0 < j < 2, 0 < k < 2, 0 < m < 2, j + k + m = 2), etc.), or lithium-nickel-cobalt-transition metal (M) oxides (e.g., Li(Ni p Co q Mn r M S )O2 (where M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, and p, q, r, and s are the atomic fractions of the respective independent elements, 0 < p < 1, 0 < q < 1, 0 < r < 1, 0 < s < 1, and p + q + r + s = 1), etc.), and any one or two or more of these compounds may be included. Among these, from the viewpoint of being able to enhance the capacity characteristics and stability of the battery, LiCoO2, LiMnO2, LiNiO2, lithium nickel manganese cobalt oxide (e.g., Li(Ni 0.6 Mn 0.2 Co 0.2 )O2, Li(Ni 0.5 Mn 0.3 Co 0.2 )O2, or Li(Ni 0.8 Mn 0.1 Co 0.1 )O2, etc.), or lithium nickel cobalt aluminum oxide (e.g., LiNi 0.8 Co 0.15 Al 0.05 O2, etc.) are preferred.

[0112] As the positive electrode active material, a lithium atom-containing oxide (olivine-type lithium-containing phosphate compound) represented by the following general formula (1) and having an olivine-type crystal structure can be used as a highly stable one.

[0113] Li 1-x M x (AO4)·····(1) (In the formula (1), M is an ion of at least one metal selected from the group consisting of Mg, Ti, V, Nb, Ta, Cr, Mn, Fe, Co, Ni, Cu, Zn, Al, Ga, Ge, and Sn; A is at least one selected from the group consisting of Si, S, P, and V; and x is a number satisfying the relationship 0 < x < 1.) ? The value of x in the general formula (1) is selected so that the valence of the entire general formula (1) becomes 0 in accordance with the valences of M and A.

[0114] Specific examples of the olivine-type lithium-containing phosphate compound include LiFePO4, LiCoPO4, LiMnPO4, Li 0.90 Ti 0.05 Nb 0.05 Fe 0.30 Co0.30Mn 0.30 PO4 and the like. Among these, LiFePO4 (lithium iron phosphate) is particularly preferable because the iron compound used as a raw material is easily available and inexpensive.

[0115] As the positive electrode active material, organic compounds such as polyaniline, polypyrrole, polyacene, disulfide-based compounds, polysulfide-based compounds, and N-fluoropyridinium salts can also be used.

[0116] The physical properties of the positive electrode active material are determined from the required items in the battery design and manufacturing process due to constraints such as the usage form of the lithium-ion battery. In the manufacture of the positive electrode material, process design and the like are carried out so as to realize its physical properties. Examples of the physical property values include powder particle size and distribution, BET specific surface area, density, and the like.

[0117] For example, the powder particle size is appropriately selected in consideration of other constituent requirements of the lithium-ion battery, but from the viewpoint of improving battery characteristics such as rate characteristics and cycle characteristics, for example, an average value of 1 μm to 30 μm is preferred, and 1 μm to 10 μm is more preferred.

[0118] These positive electrode active materials can be used individually or in combination of two or more types.

[0119] (Positive electrode: conductive additive) Since the above-mentioned positive electrode active material generally has low electronic conductivity, it is preferable to include a conductive additive to enhance electronic conductivity within the positive electrode, and the carbon material of the present invention is suitably used for this purpose. The amount of the carbon material of the present invention used is appropriately selected depending on the purpose of use, but is in the range of, for example, 0.01 to 4 parts by weight, preferably 0.05 to 3 parts by weight, more preferably 0.1 to 2 parts by weight, even more preferably 0.2 to 1.5 parts by weight, and particularly preferably 0.5 to 1.5 parts by weight, per 100 parts by weight of positive electrode active material.

[0120] In the present invention, in addition to the carbon material of the present invention described above, other conductive substances can be combined as conductive additives. Examples of other conductive substances include carbon-based materials such as graphite, carbon black, carbon nanotubes, acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; metal powders such as carbon fluoride, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0121] These other conductive materials can be used individually or in combination of two or more. The amount of other conductive materials used is appropriately selected according to the intended use and within the range of use of the carbon material of the present invention described above. The ratio of the carbon material of the present invention to the other conductive materials is appropriately selected according to the intended use and is in the range of [carbon material of the present invention]:[other conductive materials] by weight ratio, for example, 10:90 to 90:10, preferably 20:80 to 80:20, more preferably 30:70 to 70:30, and even more preferably 40:60 to 60:40.

[0122] Furthermore, among the above, the carbon material of the present invention can be made even more effective by being combined with conventionally used conductive additives. For example, carbon blacks such as acetylene black are composed of linked structural particles with a diameter of several tens of nanometers. On the other hand, carbon does not have high crystallinity, its structural length is short, and it is easily broken down, making it poor at long-distance electron transport. By combining it with the carbon material of the present invention, it is possible to realize a system that maintains electron conductivity and ion supply ability, whether the three-dimensional structure is maintained or the three-dimensional structure is flattened into a flaky graphite-like state.

[0123] (Positive electrode: Binder) The binder used is a component that helps bond the positive electrode active material, conductive additive, and electrode current collector, and is, for example, an organic polymer. Examples include fluororesins such as polyvinyl fluoride, polyvinylidene fluoride (PVDF), and polytetrafluoroethylene; nitrile group-containing polymers such as polyacrylonitrile and polyvinylidene cyanide; polyvinyl alcohol-based polymers such as polyvinyl acetate and polyvinyl alcohol; halogen-containing polymers such as polyvinyl chloride and polyvinylidene chloride; conductive polymers such as polyaniline; alkane-based polymers such as polyethylene, polypropylene, and poly-1,1-dimethylethylene; unsaturated polymers such as polybutadiene and polyisoprene; ring-containing polymers such as polystyrene, polymethylstyrene, polyvinylpyridine, and poly-N-vinylpyrrolidone; and acrylic polymers such as polymethyl methacrylate, polyethyl methacrylate, polybutyl methacrylate, polymethyl polyacrylate, polyethyl polyacrylate, polyacrylic acid, polymethacrylic acid, and polyacrylamide. Modified or derivative products of the above organic polymers may also be used.

[0124] Among these binders, fluororesins are preferred, and PVDF is particularly preferred.

[0125] These binders can be used individually or in combination of two or more types, and the amount used is appropriately selected according to the purpose of use, for example, in the range of 0.01 to 4 parts by weight, preferably 0.05 to 3 parts by weight, more preferably 0.1 to 2 parts by weight, even more preferably 0.2 to 1.5 parts by weight, and particularly preferably 0.5 to 1.5 parts by weight per 100 parts by weight of positive electrode active material. When the amount of binder used is within this range, the adhesive strength between the electrode active materials and between the electrode active materials and the conductive additive can be improved, and consequently the bonding strength with the electrode current collector can be improved, which is preferable.

[0126] (Positive electrode: slurry) The electrode formation slurry used is prepared by mixing the above-mentioned positive electrode active material, conductive additive, binder, and other compounding agents as needed, in a dispersion medium. Other compounding agents are selected appropriately according to the intended use, and those commonly used in lithium-ion secondary batteries can be used within their normal range of application.

[0127] As the dispersion medium used, for example, one that dissolves only the binder and not other materials is preferably used in order to sufficiently uniformly distribute the binder and to form a coating film of a predetermined size in the slurry. Specifically, for example, organic solvents such as dimethylformamide, N-methyl-2-pyrrolidine (NMP), dimethyl sulfoxide (DMSO), isopropyl alcohol, and acetone, or water may be used, and one of these solvents alone or a mixture of two or more solvents may be used.

[0128] When polyvinylidene fluoride (PVDF) is used as the binder, dimethylformamide or N-methyl-2-pyrrolidone (NMP) is preferred as the dispersion medium, with NMP being particularly preferred.

[0129] (Current collector and positive electrode) The positive electrode can be manufactured by applying the electrode molding slurry described above onto a current collector and drying it. Examples of current collectors include aluminum foil, nickel foil, titanium foil, and stainless steel foil, with rolled aluminum foil being particularly preferred.

[0130] For applying the electrode-forming slurry to the current collector, commonly used printing techniques can be employed. For small coating thicknesses, gravure printing is suitable, while for larger thicknesses, doctor blade printing or die printing are preferable. The coating is then heat-dried; any drying method is acceptable, and the method that achieves the desired bonding strength with the binder is preferred.

[0131] Then, when forming the positive electrode to the predetermined dimensions, industrially available cutting blades and the like, and methods thereof, are preferably used. Furthermore, in order to achieve the predetermined density, industrially available pressurizing devices and the like, and methods thereof, are preferably used as needed.

[0132] <Negative electrode> Next, the negative electrode will be described. The negative electrode is obtained, for example, by coating a slurry of a negative electrode active material, a conductive additive, a binder, and a dispersion medium onto a metal foil body for current collection, such as rolled copper foil, heating and drying to remove the solvent, and then forming it to a predetermined size and density.

[0133] (Negative electrode: active material) As the negative electrode active material, it is preferable to have a material that can bond and stabilize lithium ions with electrons flowing from the external circuit and has many stabilization sites within it. For example, materials of organic origin, whether highly crystalline or low, are both usable, and graphite, coke, amorphous carbon, hard carbon, polymer carbon, etc., can be suitably used. In this case, the principle is that lithium ions are sandwiched between graphene layers, etc., and bond with electrons to stabilize them. In addition, as another stabilization mechanism, a method of forming intermetallic compounds electrochemically can also be used, and silicon, tin, zinc, bismuth, antimony, cadmium, lead, germanium, etc., can be suitably used. In addition, other materials that exhibit a low electrochemical reaction potential, which govern the negative electrode side of lithium-ion batteries, can also be used. Suitable examples include compounds of metals with oxygen, sulfur, halogens, nitrogen, phosphorus, etc.

[0134] Specific examples of negative electrode active materials include compounds capable of reversible intercalation and deintercalation of lithium, such as carbonaceous materials like artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; and SiO2. x(0 < x ≤ 2), metal oxides such as SnO2, vanadium oxides, and lithium vanadium oxides that can be doped and undoped with lithium; composites containing the metallic compound and a carbonaceous material, such as Si-C composites or Sn-C composites, etc. can be mentioned.

[0135] As the negative electrode active material, a thin film of metallic lithium may also be used. Also, any of low-crystalline carbon and highly crystalline carbon, etc. may be used as the above carbonaceous material. Soft carbon and hard carbon are representative of low-crystalline carbon, and examples of highly crystalline carbon include amorphous, plate-like, scaly, spherical, or fibrous natural graphite or artificial graphite, kish graphite, pyrolytic carbon, mesophase pitch-based carbon fibers, mesocarbon microbeads, mesophase pitch, and high-temperature calcined carbon such as petroleum and coal-based cokes, etc.

[0136] The physical property values of the negative electrode material are determined from the required items in the design and manufacturing process of devices (such as storage batteries as an example) due to restrictive conditions such as the usage form of the lithium-ion battery. In the manufacture of the material, process design, etc. is carried out so as to realize its physical properties. Examples of physical property values include powder particle size and distribution, BET specific surface area, density, etc.

[0137] As an example, the powder particle size is appropriately selected in consideration of the balance with other constituent elements of the lithium-ion battery, but from the viewpoint of improving battery characteristics such as rate characteristics and cycle characteristics, for example, as an average value, 1 μm to 70 μm is preferable, and 3 μm to 30 μm is more preferable.

[0138] These negative electrode active materials can be used alone or in combination of two or more. The proportion of the negative electrode active material in the slurry for electrode formation is, for example, in the range of 95.5 parts by weight to 99.5 parts by weight, preferably 96 parts by weight to 99 parts by weight, more preferably 97 parts by weight to 98 parts by weight with respect to 100 parts by weight of the solid content excluding the dispersion medium. When the content of the negative electrode active material is within this range, it is suitable in terms of highly balancing the battery capacity, conductivity, and adhesiveness.

[0139] (Conductive aid) The carbon material of the present invention may be used as a carbonaceous material for the negative electrode active material, but it can be suitably used as a conductive additive for the negative electrode active material. For example, although the negative electrode active material generally has high electronic conductivity, some materials have a smooth surface, and when contact between particles is insufficient, the carbon material of the present invention can be used as a conductive additive to support electronic conductivity. Furthermore, while flake-shaped graphite and artificial graphite used as negative electrode active materials have high electronic conductivity, they have low ion storage capacity and poor ionic conductivity. By combining these with the carbon material of the present invention, it is possible to construct a good battery reaction support system that adds ionic conductivity to electronic conductivity. Moreover, even when the three-dimensional structure of the negative electrode active material is crushed and flattened like flake-shaped graphite, adding the carbon material of the present invention is suitable because it can add ionic conductivity while maintaining electronic conductivity.

[0140] The proportion of the carbon material of the present invention in the electrode forming slurry is, for example, 0.8 to 3 parts by weight, preferably 1 to 2.5 parts by weight, and more preferably 1 to 2.2 parts by weight, per 100 parts by weight of solid content excluding the dispersion medium. When the content of the carbon material of the present invention is within this range, it is preferable in that the high-speed discharge characteristics, life characteristics, capacity characteristics, and charge-discharge characteristics of the lithium-ion secondary battery can be greatly improved.

[0141] In the present invention, the carbon material of the present invention can be used in combination with other carbon materials. Examples of other carbon materials include acetylene black, Ketjen black, lamp black, furnace black, carbon black, graphite, carbon fiber, graphite fiber, nanofiber, nanotube, coke, hard carbon, amorphous carbon, and the like.

[0142] These other carbon materials can be used individually or in combination of two or more, and the amount used can be selected according to the purpose of use, and can be used within a range similar to that of the carbon material of the present invention described above. The ratio of the carbon material of the present invention to the other carbon materials is, for example, in the weight ratio of [carbon material of the present invention]:[other carbon materials], in the range of 10:90 to 90:10, preferably 20:80 to 80:20, more preferably 30:70 to 70:30, and even more preferably 40:60 to 60:40.

[0143] By combining these conventional materials with the carbon materials of the present invention, further benefits can be obtained. For example, highly linear carbon nanotubes have high electronic conductivity but low ion storage capacity. Therefore, by combining them with the carbon materials of the present invention, it is possible to construct a good battery reaction support system that adds ionic conductivity to electronic conductivity. Also, carbon blacks such as acetylene black are composed of linked structural particles with a diameter of several tens of nanometers. On the other hand, carbon does not have high crystallinity, its structural length is short, and it is easily broken down, making it poor at long-distance electron transport. Despite these properties, by combining them with the carbon materials of the present invention, it is possible to realize a system that maintains its three-dimensional structure while also possessing ion supply capabilities.

[0144] (Negative electrode: Binder) The binders used are components that help bond the electrode active material, conductive additive, and electrode current collector. Examples include fluororesins such as polyvinyl fluoride, polyvinylidene fluoride, and polytetrafluoroethylene; CN group-containing polymers such as polyacrylonitrile and polyvinylidene cyanide; polyvinyl alcohol-based polymers such as polyvinyl acetate and polyvinyl alcohol; halogen-containing polymers such as polyvinyl chloride and polyvinylidene chloride; conductive polymers such as polyaniline; alkane polymers such as polyethylene, polypropylene, and poly-1,1-dimethylethylene; unsaturated polymers such as polybutadiene and polyisoprene; ring-containing polymers such as polystyrene, polymethylstyrene, polyvinylpyridine, and poly-N-vinylpyrrolidone; acrylic polymers such as polymethyl methacrylate, polyethyl methacrylate, polybutyl methacrylate, polymethyl acrylate, polyethyl acrylate, polyacrylic acid, polymethacrylic acid, and polyacrylamide; carboxymethylcellulose; and styrene-butadiene rubber. Modified or derivative products of the above organic polymers may also be used.

[0145] Among these binders, carboxymethylcellulose and styrene-butadiene rubber are preferred.

[0146] These binders can be used individually or in combination of two or more types, and the amount used is appropriately selected according to the purpose of use, for example, in the range of 0.01 to 4 parts by weight, preferably 0.05 to 3 parts by weight, more preferably 0.1 to 2.5 parts by weight, and even more preferably 0.2 to 2 parts by weight, per 100 parts by weight of positive electrode active material. When the amount of binder used is within this range, the adhesive strength between the electrode active materials and between the electrode active materials and the conductive additive can be improved, and consequently the bonding strength with the electrode current collector can be improved, which is preferable.

[0147] These binders can be used individually or in combination of two or more types. The proportion of each binder in the electrode-forming slurry is, for example, 0.5 to 3 parts by weight, preferably 0.8 to 2.5 parts by weight, and more preferably 1 to 2.2 parts by weight, per 100 parts by weight of solids excluding the dispersion medium. When the binder content in the electrode-forming slurry is within this range, it is possible to improve the adhesion between electrode active materials and between electrode active materials and conductive additives, and consequently improve the bonding force with the electrode current collector, which is preferable.

[0148] (Negative electrode: dispersion medium) As the dispersion medium used, solvents commonly used in the art may be used, such as organic solvents like N-methyl-2-pyrrolidine (NMP), dimethyl sulfoxide (DMSO), isopropyl alcohol, and acetone, or water. One of these solvents alone or a mixture of two or more solvents may be used. The dispersion medium is used to dissolve or disperse the electrode active material, conductive additive, and binder, taking into consideration the coating thickness of the electrode forming slurry and the manufacturing yield.

[0149] (Negative electrode: slurry) The amount of dispersion medium used is adjusted so that, for example, the concentration of solids including the electrode active material, conductive additive, and binder is in the range of, for example, 10% to 90% by weight, preferably 20% to 80% by weight, more preferably 30% to 75% by weight, even more preferably 40% to 70% by weight, and particularly preferably 50% to 65% by weight.

[0150] (Current collector and negative electrode) As the current collector for the negative electrode, for example, a material that does not exhibit electrochemical reactivity to the potential generated by the negative electrode is used. Specifically, examples include copper foil, nickel foil, titanium foil, and stainless steel foil, with electrolytic copper foil and rolled copper foil being preferred.

[0151] For applying the electrode-forming slurry onto the current collector, commonly used printing techniques can be employed. For small thicknesses, gravure printing is preferable, while for larger thicknesses, doctor blade printing or die printing are more suitable.

[0152] Subsequently, the coating film is heat-dried. Any drying method is available, and a method that achieves the desired bonding strength with the binder is preferably used. Then, when forming the negative electrode to the predetermined dimensions, industrially available cutting blades and methods are preferably used. Furthermore, to achieve the predetermined density, industrially available pressurizing devices and methods are preferably used as needed.

[0153] <Lithium-ion rechargeable battery> Next, the lithium-ion secondary battery according to the present invention will be described. The lithium-ion secondary battery of the present invention is characterized by containing the carbon material of the present invention. Specifically, it includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, wherein at least one of the positive electrode and the negative electrode uses the electrode (positive electrode and / or negative electrode) of the present invention described above. On the other hand, the lithium-ion secondary battery may further selectively include a battery container that houses the electrode assembly consisting of the positive electrode, negative electrode and separator, and a sealing member that seals the battery container. On the other hand, the positive electrode and the negative electrode are the same as described above, so a detailed explanation will be omitted.

[0154] (Separator) The separator used separates the negative and positive electrodes and provides a pathway for lithium ions to move. Any separator commonly used as a separation membrane in lithium-ion secondary batteries can be used without particular limitations, but one that has low resistance to electrolyte ion movement while having excellent electrolyte impregnation ability is particularly preferred.

[0155] Specifically, porous polymer films are used, for example, porous polymer films made from polyolefins such as polyethylene, polypropylene, polybutene, polyvinyl chloride, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or laminated structures of two or more layers thereof. Alternatively, ordinary porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, may be used. Furthermore, to ensure heat resistance or mechanical strength, coated separation membranes containing ceramic components or polymeric substances may be used, and may be used selectively in single-layer or multi-layer structures.

[0156] Polyethylene and polypropylene are particularly suitable materials for porous polymer films. Polyethylene has a relatively low melting point, and when the battery temperature rises for any reason (for example, due to an unsafe condition such as a short circuit), the pores in the film become blocked by thermal melting, inhibiting the movement of driving ions, thereby stopping the reaction and ensuring safety. Polypropylene is also suitable as a material that can be stretched and made porous without the use of plasticizers.

[0157] Furthermore, polymer compounds can be applied to both sides of the separator before use. Examples of such polymer compounds include ether-based polymer compounds such as polyvinyl formal, polyethylene oxide, and crosslinked polyethylene oxide; ester-based polymer compounds such as polymethacrylate; acrylate-based polymer compounds; and fluorine-based polymer compounds such as polyvinylidene fluoride and polyvinylidene fluoride-hexafluoropropylene copolymer. Among these, it is particularly desirable to use fluorine-based polymer compounds such as polyvinylidene fluoride from the viewpoint of preventing swelling during high-temperature storage.

[0158] (electrolyte) As the electrolyte, for example, a non-aqueous electrolyte obtained by dissolving an electrolyte in an organic solvent is used.

[0159] -Electrolytes- For example, lithium salts are used as electrolytes. Examples of lithium salts include LiPF6, LiAsF6, LiBF4, LiSbF6, LiAlCl4, LiClO4, CF3SO3Li, C4F9SO3Li, CF3COOLi, (CF3CO)2NLi, (CF3SO2)2NLi, (C2F5SO2)NLi, LiN(CF3SO2)(C4F9SO2), LiC(CF3SO2)3, LiPF4(CF3)2, LiPF4(C2F5)2, LiPF4(CF3SO2)2, LiPF4(C2F5SO2)2, LiBF2(CF3)2, LiBF2(C2F5)2, LiBF2(CF3SO2)2, LiBF2(C2F5SO2)2, Licyclic 1,2-perfluoroethanedisulfonylimide, and cyclic 1,3-perfluoropropanedisulfonylimide. Among these, LiPF6, LiBF4, LiClO4, CF3SO3Li, LiN(CF3SO2)2, and LiN(C2F5SO2)2 are preferred because they are easily soluble in the solvent and exhibit a high degree of dissociation, with LiPF6 and LiBF4 being particularly preferred.

[0160] As the electrolyte, a gel-like electrolyte may be used that contains a polymer compound that swells in an organic solvent to form a retainer that holds the non-aqueous electrolyte. Including a polymer compound that swells in an organic solvent allows for high ionic conductivity, excellent charge-discharge efficiency, and prevention of battery leakage, making it preferable. The content of such polymer compound is preferably in the range of 0.1% to 10% by weight of the electrolyte.

[0161] These electrolytes can be used individually or in combination of two or more. The concentration of the electrolyte in the electrolyte solution is, for example, in the range of 5% to 15% by weight, preferably 2% to 13% by weight, and more preferably 5% to 10% by weight.

[0162] -Organic solvents- The organic solvent used in the electrolyte is not particularly limited as long as it can dissolve the electrolyte, but solvents such as cyclic carbonates; linear carbonates; esters such as γ-butyrolactone and methyl formate; ethers such as 1,2-dimethoxyethane and tetrahydrofuran; and sulfur-containing compounds such as sulfolanes and dimethyl sulfoxide are preferably used. These organic solvents can be used individually or in combination of two or more.

[0163] Among these, cyclic carbonates and linear carbonates are preferred because they have high dielectric constants and suitable viscosity and solvation capacity that affect lithium ion movement. Solvation capacity is the ability to dissociate dissolved ions; if it is too strong, it inhibits ion movement, so there is an optimal value.

[0164] Examples of cyclic carbonates include alkylene carbonates having alkylene groups with 2 to 4 carbon atoms, such as ethylene carbonate, propylene carbonate, and butylene carbonate. Among these, ethylene carbonate and propylene carbonate are preferred from the viewpoint of improving battery characteristics, and ethylene carbonate is particularly preferred.

[0165] As for the chain-like carbonates, dialkyl carbonates are preferred, and the number of carbon atoms in each constituent alkyl group is preferably 1 to 5, and particularly preferably 1 to 4. Specifically, examples include symmetric chain-like alkyl carbonates such as dimethyl carbonate, diethyl carbonate, and di-n-propyl carbonate; and dialkyl carbonates such as asymmetric chain-like alkyl carbonates such as ethyl methyl carbonate, methyl-n-propyl carbonate, and ethyl-n-propyl carbonate. Among these, dimethyl carbonate and diethyl carbonate are preferred from the viewpoint of viscosity and boiling point, and diethyl carbonate is particularly preferred.

[0166] Furthermore, practical lithium-ion batteries operate under a wide range of environmental conditions, and in particular, the physical properties of non-aqueous solvents, such as their melting and boiling points, must be kept within a certain range. Therefore, it is preferable to use a mixture of cyclic carbonates and linear carbonates. As for combinations of cyclic carbonates and linear carbonates, for example, a combination of ethylene carbonate and linear carbonate is suitable. Specifically, combinations such as ethylene carbonate and dimethyl carbonate, ethylene carbonate and diethyl carbonate, ethylene carbonate, dimethyl carbonate and diethyl carbonate, ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate, and ethylene carbonate, dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate are suitable because they have a good balance between cycle characteristics and high-power discharge characteristics.

[0167] The mixing ratio of cyclic carbonates and linear carbonates is appropriately selected according to the desired practical properties, for example, in the weight ratio of [cyclic carbonates]:[linear carbonates], it is in the range of, for example, 10:90 to 90:10, preferably 20:80 to 80:20, more preferably 30:70 to 70:30, and even more preferably 40:60 to 60:40.

[0168] As the organic solvent used in the electrolyte, fluorine-containing carbonates can also be suitably used. Specifically, examples include cyclic carbonates having one fluorine atom, chain carbonates having one fluorine atom, cyclic carbonates having two or more fluorine atoms, and chain carbonates having two or more fluorine atoms. From the viewpoint of improving battery characteristics, fluorine-containing cyclic carbonates having two or more fluorine atoms are preferred.

[0169] Specific examples of fluorine-containing cyclic carbonates having two or more fluorine atoms include, for example, cis-4,5-difluoro-1,3-dioxolan-2-one, trans-4,5-difluoro-1,3-dioxolan-2-one, and 4,4-difluoro-1,3-dioxolan-2-one.

[0170] These fluorine-containing carbonates can be used individually or in combination of two or more types.

[0171] (Manufacturing method for lithium-ion secondary batteries) A lithium-ion secondary battery according to the present invention can be manufactured, for example, by stacking a positive electrode and a negative electrode with a separator in between, winding or folding them as needed according to the battery shape, placing them in a battery container, injecting an electrolyte into the battery container, and sealing it. To prevent pressure rise inside the secondary battery, overcharge and discharge, etc., an overcurrent prevention element such as a fuse or PTC element, expanded metal, lead plates, etc. may be provided as needed. The shape of the secondary battery may be any of the following: coin type, button type, sheet type, cylindrical type, rectangular type, flat type, etc.

[0172] <Application> The carbon material of the present invention can exhibit its functionality and be effectively utilized in any electrochemical device other than the lithium-ion secondary battery described above. Specifically, it has functions such as acting as an internal conductive path in electrodes when electron transfer is involved in device reactions, providing reinforcement when electrodes undergo physical deformation, and preventing direct contact between a third material (such as a catalyst) and the reaction material by utilizing the durability of graphene when the reaction material is in an oxidized or reduced state.

[0173] Examples of usable devices include non-aqueous electrolyte batteries such as lithium-ion batteries, sodium-ion batteries, potassium-ion batteries, magnesium-ion batteries, calcium-ion batteries, aluminum-ion batteries, lithium-sulfur batteries, and lithium-air batteries; inorganic solid electrolyte batteries such as sulfide-based solid electrolytes and oxide-based solid electrolytes; polymer solid electrolyte batteries such as polyethylene oxide-based batteries; and semi-solid batteries such as polymer gel electrolyte batteries in which electrolyte is impregnated into PVDF.

[0174] These devices utilize readily graphitizable carbon, non-graphitizable carbon, graphite, lithium alloy materials such as silicon and tin, and other metallic materials such as lithium as negative electrode active materials. Similarly, lithium-containing metal oxides, particularly lithium-containing transition metal oxides with layered, spinel, or olivine structures, lithium-free metal oxides, organic positive electrode materials, charge-transfer complex positive electrode materials, sulfur, and fluoride-based materials are used as positive electrode active materials. The carbon material of the present invention is capable of effectively enhancing conductivity for any of these active materials. Furthermore, the carbon material of the present invention is also suitable as a material for lithium-sulfur batteries, as described in publications such as WO2018 / 225619, JP 2023-501679, JP 2019-517116, and JP 2022-191280.

[0175] The carbon material of the present invention can also be suitably used in organic electrolyte capacitors, aqueous electrolyte capacitors, and aqueous solution batteries. In fuel cells, it can be used in PEFCs, SOFCs, DMPCs, etc., and in particular, it can be used not only to impart conductivity to electrodes but also as a support for oxidation-reduction catalysts.

[0176] The carbon material of the present invention can be used for applications other than electrochemical devices. Other suitable applications include, for example, electronic device systems other than the above-mentioned devices such as graphene-based sensors, electromagnetic interference suppression materials, antenna modules, heat dissipation substrates, heat exchange devices, separation membranes, reverse osmosis membranes, transparent electrode materials, structural materials that take advantage of mechanical flexibility, and conductive inks and pastes. Furthermore, in response to the demand for vehicle weight reduction, which directly leads to the reduction of carbon dioxide emissions and energy conservation, the material can be suitably used in applications that contribute to weight reduction by taking advantage of its hollow shape, such as reinforcing agents for various types of rubber including tires, paints, coloring pigments, conductive fillers for various polymers, and additives for magnetic recording media. [Examples]

[0177] The present invention will be described in detail below based on examples, but the present invention is not limited to these examples. In the following description, "%", "ppm", and "parts" used to express quantities refer to weight unless otherwise specified.

[0178] Various physical properties were evaluated according to the following method.

[0179] <Basic characteristics> (Number of carbonaceous layers) The number of carbonaceous layers in the carbon material was calculated from the amount of carbon deposited during manufacturing in the examples and comparative examples. Specifically, it was determined by thermogravimetric analysis (TGA) measurement. Using STA-2500 (NETZSCH), the material was heated to 900°C at a heating rate of 5°C / min under the flow of argon gas (80 mL / min) and oxygen (20 mL / min), then cooled at a cooling rate of 20°C / min, and TG measurement was performed. Blank measurement results were subtracted from each measurement, using empty pans and under the same temperature profile conditions. A Pt pan was used for the sample obtained using MgO (Comparative Example 2), and an alumina pan was used for the others. From the carbon weight loss rate (%) obtained by TG measurement, the average number of carbon layers was calculated as follows. From the carbon weight loss rate, the weight of the carbon layer per unit mass of the mold (W) g Calculate (g-carbon / g-template) and determine the weight W of this carbon layer. g and the BET specific surface area SA of the template particles temp (g / m 2 ) Weight W of the carbon layer per unit area of ​​the mold a (g / m 2 ) was calculated. Next, W a The weight of the carbon layer per unit area of ​​single-layer graphene is W graphene (7.61 × 10 -4 g / m 2 The average number of layers was calculated by dividing by ). Average number of layers = W a / W graphene

[0180] (purity measurement) The carbon content of the carbon material was calculated by subtracting the ash content and the amount of desorbed gas at temperature (converted to percentages) from the following formula. Carbon content = 100 - 100 × (Ash content + Total gas amount calculated from desorbed gas at temperature) / Amount of carbon material

[0181] <Nitrogen adsorption / desorption measurement> (BET specific surface area, pore volume, mode pore diameter) Nitrogen adsorption and desorption measurements of carbon materials were performed using an automated specific surface area / pore size distribution analyzer (BELSORP MINI, manufactured by Microtrac-Bel Co., Ltd.). Before measurement, the samples were dried under reduced pressure at 150°C for 6 hours using BEL pre. The BET specific surface area was determined using the BET method from the adsorption isotherms obtained from the nitrogen adsorption and desorption measurements. The applicable range of the BET method was set to P / P0 = 0.05 to 0.3. Based on the adsorption and desorption isotherms, the total pore volume was measured by converting the amount of nitrogen adsorbed at a relative pressure of P / P0 = 0.99 at -196°C to the volume of liquid nitrogen density. The pore size distribution was determined by the BJH method. In addition, the mode pore size of the pore size distribution was determined.

[0182] The applicable range for each pore volume measurement is as follows. Total pore volume: P / P0 = 0.99 Volume of micropores (pores with a diameter of less than 2 nm): P / P0 = ~0.1 Volume of mesopores (pores with a diameter between 2 nm and 50 nm): P / P0 = 0.1~0.96 Volume of pores with a diameter of 10 nm or more: P / P0 = 0.79~0.99 Volume of macropores (pores with a diameter greater than 50 nm): P / P0 = 0.96~0.99

[0183] <Structural analysis> Shape indices and aggregate shape determination methods are indicators of the structural complexity of carbon materials. Shape indices are obtained by statistically analyzing various parameters obtained from image analysis of transmission electron microscope images of monodisperse materials.

[0184] (Transmission electron microscope observation) The shape of carbon materials was observed using a transmission electron microscope (JEM-2100Plus model, manufactured by JEOL Ltd.). Observation of carbon materials using a transmission electron microscope (TEM) was performed at acceleration voltages of 80kV to 100kV.

[0185] (Raman spectroscopy measurement) Raman spectroscopy of carbon materials was performed using a micro-Raman spectrometer (LabRAM HR-800, Horiba, Ltd.). A 532 nm laser was used, with the filter set to D1 and the hole size to 100 μm. The measurement range was 300 cm². -1 ~3500cm -1 The intensity of the 2D band (I) was determined from the measured Raman spectrum. 2D The intensity of the G band relative to (I G ) intensity ratio (I G / I 2D The intensity ratio of ) was calculated.

[0186] <Particle characteristics> (Particle size distribution measurement) Using a laser diffraction particle size distribution analyzer (MT3300EXII-SDC, manufactured by Microtrac-Bell Co., Ltd.), particle size distribution measurements were performed to investigate the aggregation state of primary particles in carbon materials. The measurement samples used were unground carbon materials immersed in ethanol for 9 minutes. Median diameters D50, D10, D90, D90 / D10, and D90 / M were determined in the particle size distribution curves.

[0187] <General characteristics> (Oil absorption measurement) The oil absorption of the carbon material was determined in accordance with "JIS K5101-13-1 Pigment Test Methods - Part 13: Oil Absorption - Section 1: Refined Linseed Oil Method".

[0188] (Number density) The number density (number of particles per unit mass) P of a carbon material is equal to the volume V (m³) of a single primary particle. 3 ) and the density of carbon ρ (g / m³) 3 ) can be calculated using the following formula. P = 1 / (V × ρ) Here, the carbon density ρ can be the true density of graphite, which is 2.2 g / cc. V(m 3 ) can be calculated from the following formula. V = n × (D1 - D0) 3 / 6 Here, D0 is the inner diameter of the primary particle, and D1 is the outer diameter of the primary particle. D0 can be obtained using the mode pore size (M) mentioned above. D1 can be obtained by adding twice the value obtained by multiplying D0 by the average number of stacks n and the average interplanar spacing obtained from the 002 diffraction line to the mode diameter. Alternatively, D1 may be obtained by TEM image analysis or other methods. Furthermore, for solid carbon materials, calculations can be performed with D0=0. For example, for the known DENKA BLACK Li-100, the particle outer diameter (D1) was calculated with an average primary particle diameter of 35 nm and D0=0.

[0189] (Apparent density) The apparent density of the carbon material was calculated using the total pore volume and true density from the following formula. Apparent density (g / cc) = 1 / (total pore volume + 1 / true density) The total pore volume (cc / g) was calculated using the formula P / P0 = 0.99, and the true density used was the graphite value of 2.2 g / cc.

[0190] (Measurement of ash content) The carbon material was dried under reduced pressure at 150°C for 2 hours using a vacuum dryer, then cooled and weighed in a magnetic crucible (W). s Next, it was placed in a muffle furnace and weighed after burning at 900°C for 1 hour (W i ), crucible tare (W c Subtracting the ash content ((W i -W c ) / W s We calculated the result as ×100(%).

[0191] Various performance evaluations were conducted according to the following methods.

[0192] <Evaluation of conductivity> The electrical conductivity of carbon materials was evaluated by measuring the electrical conductivity of the powder under uniaxial compression with lateral constraint. A dry sample was filled into a cylindrical container consisting of an insulating cylinder and a negative electrode. A positive electrode was inserted into the insulating cylindrical container filled with the sample, and the sample was placed on a force gauge stand, sandwiched between the negative and positive electrodes. A spring-type force gauge mounted on the force gauge stand was lowered, applying a pressure of 10 MPa to the sample in the cylindrical container and compressing it. The height of the sample after compression was measured, and the resistance value of the sample was measured using a digital multimeter connected to the positive and negative electrodes. The electrical conductivity of the powder during compression was calculated from the obtained resistance value, the filled cross-sectional area of ​​the sample, and the height of the compressed sample. The evaluation was performed according to the following criteria. ◎:18S / cm or more ○: 15S / cm or more and less than 18S / cm △: 12S / cm or more and less than 15S / cm ×: Less than 12S / cm

[0193] <Positive electrode evaluation> (High-rate characteristics) At room temperature (25°C), the test battery was charged from the open-circuit voltage to 4.2V with a constant current of 1.25mA (equivalent to 0.2C) (constant current charging). After reaching 4.2V, constant voltage charging was performed and continued until the current was 0.31mA (0.05C). Subsequently, it was discharged to 3V with a constant current of 1.25mA (equivalent to 0.2C). The charge capacity and discharge capacity at this time were determined, and the initial Coulomb rate (discharge capacity ÷ charge capacity) was calculated. Next, using the same test battery, it was charged from the open-circuit voltage to 4.2V with a constant current of 1.25mA (equivalent to 0.2C) (constant current charging). After reaching 4.2V, constant voltage charging was performed and continued until the current was 0.31mA (0.05C). Subsequently, it was discharged to 3V with a high-rate constant current of 12.5mA (equivalent to 2C). The 2C maintenance rate ((2C capacity / 0.2C capacity) × 100) (%) for each test battery was calculated from the discharge capacity of the obtained test batteries. A higher value indicates superior high-rate characteristics. The results are shown in Table 1. In addition, Figure 5 shows the discharge curves when the test battery of Example 1 was discharged at a discharge current value equivalent to 2C and a discharge current value equivalent to 0.2C.

[0194] The rapid discharge characteristics were evaluated by assessing the calculated 2C maintenance rate according to the following criteria. ◎: Over 70% ○: Over 50% up to 70% △: Over 30% up to 50% ×: 30% or less

[0195] The charging capacity characteristics were evaluated based on the average charging capacity according to the following criteria. ◎:160mAh / g or more ○: 150mAh / g or more and less than 160mAh / g △: 140mAh / g or more and less than 150mAh / g ×: Less than 140mAh / g

[0196] The discharge capacity characteristics were evaluated based on the average charge capacity according to the following criteria. ◎:140mAh / g or more ○: 130mAh / g or more and less than 140mAh / g △: 120mAh / g or more and less than 130mAh / g ×: Less than 120mAh / g

[0197] The charge and discharge characteristics were evaluated based on the initial Coulomb rate according to the following criteria. ◎: 80% or more ○: 70% or more but less than 80% △: 60% or more but less than 70% ×: Less than 60%

[0198] <Example 1> (Manufacturing of carbon materials) -CVD reaction: carbon layer formation- Fumed silica (SiO2, model number: AEROSIL(registered trademark) NX90G, average primary particle size 38 nm, BET specific surface area 71 m²) is used as a template (template material) for carbonaceous films. 2Approximately 1 g of fumed silica (manufactured by Nippon Aerosil Co., Ltd., carbon content 0.5% to 1.5%) was spread out in a quartz boat and set in the center of a quartz reaction tube of a horizontal CVD apparatus (transparent electric furnace manufactured by Ishikawa Sangyo Co., Ltd.). While flowing argon gas into the reaction tube at a flow rate of 400 mL / min, it was heated to 900°C at a heating rate of 10°C / min and held for 30 minutes. While maintaining 900°C, methane gas was flowed at a flow rate of 80 mL / min while flowing argon gas at a flow rate of 320 mL / min (raw material gas concentration 20%), and held for 90 minutes to form a carbonaceous layer. Thereafter, while flowing argon gas at a flow rate of 400 mL / min, it was cooled to room temperature, and the template on which the carbonaceous layer was formed was taken out. At this time, it was confirmed by an electron microscope that the template was an aggregate in which a plurality of primary particles had a branched structure and were connected in a bead-like manner.

[0199] -Template removal- Next, the template on which the carbonaceous layer was formed was removed by the following operation to obtain a carbon material. (1) The template on which the carbonaceous material was formed was collected in a 100 mL PFA beaker, and ultrapure water was added to the extent that the entire sample was moistened. (2) After adding 46% hydrofluoric acid, it was stirred with a stirrer for 2 hours. (3) After stopping the stirring, it was allowed to stand until the sample settled. (4) A PTFE membrane filter (47 mmφ, pore diameter 0.1 μm) was used for suction filtration from the supernatant. (5) The sample on the filter paper was washed with about 39 mL of ultrapure water and suction filtered. This operation was repeated 3 times. (6) The sample on the filter paper was collected back into the original PFA beaker. (7) The operations (2) to (6) were repeated again. (8) About 40 mL of ultrapure water was added, and it was stirred with a stirrer for 1 hour. (9) After stopping the stirring, it was allowed to stand until the sample settled. (10) The supernatant was discarded, 5% caustic soda was added, and it was stirred for 12 hours while heating to 80°C. (11) After stopping the stirring, it was allowed to stand until the sample settled. (12) Using a PTFE membrane filter (47 mmφ, pore size 0.1 μm), the supernatant was filtered by suction. (13) The sample on the filter paper was washed with ultrapure water and filtered by suction. This procedure was repeated until the filtrate (washing solution) became neutral. (14) The sample on the filter paper was collected in a Petri dish and dried in a 110°C oven for 8 hours.

[0200] -Heat treatment- The carbon material obtained above was placed in a rectangular high-temperature heating furnace (manufactured by Izumi Tech Co., Ltd.) under reduced pressure (10 -1 After heating to the Pa order, the material was heated to 1800°C under argon gas flow (10 mL / min) at a heating rate of 15°C / min and held at that temperature for 1 hour for calcination. After cooling to room temperature, the calcined carbon material was removed to obtain carbon material A containing heat-treated graphene. Using the obtained carbon material A, basic properties, nitrogen adsorption / desorption measurements, Raman spectroscopy measurements, XRD analysis, image analysis, particle size distribution measurements, TDP-MS measurements, general properties, and conductivity evaluations were performed, and the results are shown in Table 1.

[0201] (Fabrication of positive electrode) NCM (LiNi) is a ternary cathode material with an average particle size of 8 μm as the cathode active material. 0.5 Co 0.2 Mn 0.3 96.5% of O (manufactured by Kelong), 0.5% of the above-mentioned carbon material A as a conductive additive, and 3% by weight of PVDF (manufactured by Kureha Corporation) as a binder were added to N-methylpyrrolidone (NMP) as a solvent and mixed. A dispersion of carbon material A in NMP solvent was used as the conductive additive. The mixture of the active material, conductive additive, and PVDF was placed in a planetary mixer and mixed at a rotation speed of 2000 rpm while adding NMP in several batches until homogeneous, to prepare a cathode slurry. This slurry was applied to 15 μm thick aluminum foil at a constant speed using a doctor blade coating device with a micrometer. Then, it was dried in a vacuum dryer set to 110°C to obtain a cathode base. Subsequently, the cathode base was punched out using a φ15 mm punch-type die-cutting machine, pressurized with 45 kN using a cylinder-type jig, and then vacuum dried at 120°C to obtain a cathode electrode for battery integration.

[0202] (Manufacturing of lithium-ion secondary batteries) Using the positive electrode prepared as described above and metallic lithium punched to a diameter of φ16 mm in a glove box under an argon gas atmosphere, a 25 μm thick separator (microporous film made of polypropylene) was placed between the positive electrode mixture layer and the metallic lithium. A 1 M LiPF6 solution (a 1:1 mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC)) was added as the electrolyte, and the battery was crimped and sealed to produce a 2032 size coin-type test battery. After that, it was washed with ethanol and subjected to battery evaluation. The evaluation results are shown in Table 1.

[0203] <Example 2> Except for a CVD reaction time of 40 minutes, the procedure was the same as in Example 1 to obtain graphene-containing carbon material B, and a 2032-size coin-type battery was fabricated using this carbon material B. Material properties were measured, conductivity was evaluated, and battery evaluation was performed using the obtained carbon material B and the test battery, and the results are shown in Table 1.

[0204] <Example 3> Except for a CVD reaction time of 60 minutes, the procedure was the same as in Example 1 to obtain a graphene-containing carbon material C, and a 2032-size coin-type battery was fabricated using this carbon material C. Material properties were measured, conductivity was evaluated, and the battery was evaluated using the obtained carbon material C and the test battery, and the results are shown in Table 1.

[0205] <Example 4> Except for a CVD reaction time of 80 minutes, the procedure was the same as in Example 1 to obtain graphene-containing carbon material D, and a 2032-size coin-type battery was fabricated using this carbon material D. Material properties were measured, conductivity was evaluated, and the battery was evaluated using the obtained carbon material D and the test battery, and the results are shown in Table 1.

[0206] <Example 5> Except for a CVD reaction time of 130 minutes, the procedure was the same as in Example 1 to obtain a graphene-containing carbon material E, and a 2032-size coin-type battery was fabricated using this carbon material E. Material properties were measured, conductivity was evaluated, and the battery was evaluated using the obtained carbon material E and the test battery, and the results are shown in Table 1.

[0207] <Example 6> As a template, fumed silica (SiO2, model number: AEROSIL® R972, average primary particle size 25 nm, BET specific surface area 111 m²) is used. 2 Except for using graphene ( / g, carbon content 0.6%~1.2%, manufactured by Nippon Aerosil Co., Ltd.) and setting the CVD reaction time to 120 minutes, the procedure was the same as in Example 1 to obtain a graphene-containing carbon material F, and a 2032-size coin-type battery was fabricated using this carbon material F. Material properties were measured, conductivity was evaluated, and the battery was evaluated using the obtained carbon material F and the test battery, and the results are shown in Table 1.

[0208] <Comparative Example 1> The template is alumina (Al2O3, model number: RURALOX SBa200, average primary particle size 7nm, BET specific surface area 202m²). 2 A graphene-containing carbon material G was obtained by the same procedure as in Example 1, except that graphene (2032 size coin cell) was used. A 2032 size coin cell was then fabricated using this carbon material G. Material properties, conductivity evaluation, and battery evaluation were performed using the obtained carbon material G and the test cell, and the results are shown in Table 1.

[0209] <Comparative Example 2> As a template, we used magnesia (MgO, model number: Kyowa Mag MF150, average primary particle size 30 nm, BET specific surface area 129 m²). 2 Using carbon material H (manufactured by Kyowa Chemical Industry Co., Ltd.), the procedure was the same as in Example 1, except that the mold removal operation was performed as described below. A 2032-size coin-type battery was then fabricated using this carbon material H. Material properties were measured, conductivity was evaluated, and the battery was evaluated using the obtained carbon material H and the test battery. The results are shown in Table 1.

[0210] (Removal of MgO template) 1 g to 1.4 g of the template on which carbonaceous material was formed, approximately 100 g of hydrochloric acid (FUJIFILM Wako Pure Chemical Corporation, 5 mol / L), and a stir bar were placed in a Teflon (registered trademark) beaker. After stirring at room temperature for 5 hours, the sample was washed 5 times with pure water while filtering using a membrane filter (0.1 μm), and then suction filtration was performed. At this time, great care was taken to ensure that the附着物 on the filter paper did not dry. Next, the附着物 was placed in a glass beaker containing about 100 mL of acetone. This beaker was covered with aluminum foil, held at a vacuum pressure of 0.06 MPa for 2 minutes in a vacuum dryer, and then returned to normal pressure and heated in a constant temperature bath at 60 °C for 10 minutes to perform acetone substitution. The supernatant liquid in the beaker was taken out with a pipette, and the same acetone substitution operation was performed again, followed by drying under reduced pressure at 150 °C for 6 hours to obtain a carbon material H containing graphene after template removal.

[0211] <Comparative Example 3> A coin-type battery of size 2032 was fabricated in the same manner as in Example 1, except that commercially available carbon black (model number: Denka Black Li-100, manufactured by Denka Co., Ltd.) was used as the carbon material. Material property measurement, conductivity evaluation, and battery evaluation were performed, and the results are shown in Table 1.

[0212]

Table 1

[0213] From Table 1, the carbon materials A to F of the present invention are formed by a carbonaceous outer shell having a graphene structure, have pores, and the BET specific surface area is 817 m 2 / g or more and 1020 m 2It can be seen that when the pore volume is in the range of 0 / g or less, the total pore volume is in the range of 2.95 cc / g to 5.62 cc / g, the volume ratio of pores with a diameter of 10 nm or more in the total pore volume is in the range of 62% to 81%, the volume ratio of macropores (pores with a diameter exceeding 50 nm) is in the range of 16% to 43%, and the mode pore diameter is in the range of 15.8 nm to 24.4 nm and in the mesopore region of 2 nm to 50 nm, the conductivity is excellent, and the characteristics of rapid discharge characteristics, battery capacity characteristics, and charge / discharge characteristics when used in lithium-ion secondary batteries can be significantly improved (comparison between Examples 1-6 and Comparative Examples 1-3).

[0214] Regarding conductivity, carbon materials A to F of the present invention are overwhelmingly superior to carbon materials G to H of Comparative Examples 1 to 2 and carbon black of Comparative Example 3. This is because carbon materials A to F of the present invention are formed by a carbonaceous outer shell having a graphene structure with high electronic conductivity, and moreover, they have a structure in which large pores such as pores with a diameter of 10 nm or more and macropores (pores with a diameter of 50 nm or more) are connected, which is thought to have enabled the formation of efficient electron conduction paths (comparison between Examples 1 to 6 and Comparative Examples 1 to 2). Furthermore, this is also thought to be due to the formation of effective conduction paths for electron conductivity, as can be seen from the apparent density values ​​of the carbon materials of the present invention.

[0215] Regarding rapid discharge characteristics, carbon materials A to F of the present invention have significantly higher BET specific surface area, total pore volume, and mesopore volume compared to the carbon black of Comparative Example 3. This indicates a substantial improvement not only due to differences in the electronic conductivity of the carbon material itself, but also due to the addition of ionic conductivity (comparison between Examples 1 to 6 and Comparative Example 3). On the other hand, carbon materials G to H of Comparative Examples 1 to 2 exhibit inferior rapid discharge performance despite having large total pore volume and mesopore volume. This is presumed to be because the pores in carbon materials G to H are mostly pores with a diameter of less than 10 nm, with few large pores of 10 nm or more, and even fewer macropores with a diameter exceeding 50 nm (2% to 3%), resulting in no improvement in ionic conductivity (comparison between Examples 1 to 6 and Comparative Examples 1 to 2).

[0216] The difference between carbon materials A-F of the present invention and carbon materials G-H of Comparative Examples 1-2 is also the intensity of the 2D band (I) measured by Raman spectroscopy. 2D The intensity of the G band relative to (I G ) intensity ratio (I G / I 2D It can be seen that the strength ratio I is smaller for carbon materials G to H than for carbon materials A to F. G / I 2D This is also called the layering index, and the intensity ratio is I G / I 2D A value of 0.2 indicates the presence of one graphene layer, and the number of layers increases as the value increases. Therefore, it is thought that carbon materials G to H in Comparative Examples 1 to 2 could not maintain large pores such as macropores with a diameter exceeding 50 nm because they had fewer carbonaceous graphene layers surrounding the pores compared to carbon materials A to F (comparison between Examples 1 to 6 and Comparative Examples 1 to 2).

[0217] Regarding rapid discharge characteristics, it is further found that a higher oil absorption capacity of the carbon material is preferable. The carbon materials A to F of the present invention have significantly higher oil absorption values ​​than the carbon materials of Comparative Examples 1 to 3, and it is presumed that they can hold a large amount of electrolyte, thereby improving ionic conductivity (comparison of Examples 1 to 6 and Comparative Examples 1 to 3).

[0218] Regarding battery capacity characteristics, it can be seen that carbon materials A to F of the present invention are overwhelmingly superior in both charge and discharge capacity. This is likely because carbon materials A to F of the present invention possess both electronic and ionic conductivity, and differ from carbon materials G to H of Comparative Examples 1 to 2, which have almost no pores with a diameter of 10 nm or more, especially macropores with a diameter of 50 nm or more, and from the carbon black of Comparative Example 3, which is solid and has no pores (comparison between Examples 1 to 6 and Comparative Examples 1 to 3). Furthermore, the difference in the number of particles per unit mass is also thought to have affected these characteristics.

[0219] Regarding charge-discharge characteristics, it can be seen that carbon materials A to F of the present invention yield better results than carbon material G of Comparative Example 1 (comparison of Examples 1 to 6 and Comparative Example 1). Although carbon material G shows a large total pore volume exceeding 2 cc / g, most of the pores are less than 10 nm in diameter, and the volume ratio of pores with a diameter of 10 nm or more to the total pore volume is only 13%, which is thought to have affected the lithium ion migration speed.

[0220] Table 1 shows that, in the method for producing carbon materials, using a carbon-containing inorganic compound as a mold results in a greater amount of carbon deposition on the mold surface, making it preferable for the production of carbon materials (comparison of Comparative Examples 1-2 and Examples 1-6). Specifically, in a CVD reaction at 900°C for 120 minutes, Comparative Example 1 had a carbon deposition amount of 15.1% and Comparative Example 2 had 12.3% on the mold surface, but in Example 4, an equivalent or greater deposition amount (15.6%) was achieved at 900°C for 80 minutes. Although not shown in this specification, when silica with a carbon content below the detection limit was used as a mold, the carbon deposition rate was slower under similar conditions.

[0221] <Example 7> In the preparation of the positive electrode, the test battery was manufactured under the same conditions as in Example 1, except that the amount of carbon material A was set to 0.1% by weight and the amount of positive electrode material NCM was set to 96.9%.

[0222] <Example 8> In the preparation of the positive electrode, the test battery was manufactured under the same conditions as in Example 1, except that the amount of carbon material A was set to 0.3% by weight and the amount of positive electrode material NCM was set to 96.7%.

[0223] <Example 9> In the preparation of the positive electrode, the test battery was manufactured under the same conditions as in Example 1, except that the amount of carbon material A was set to 1% by weight and the amount of positive electrode material NCM was set to 96%.

[0224] <Example 10> In the preparation of the positive electrode, the test battery was manufactured under the same conditions as in Example 1, except that the amount of carbon material A was set to 2% by weight and the amount of positive electrode material NCM was set to 95%.

[0225] <Example 11> In the preparation of the positive electrode, the test battery was manufactured under the same conditions as in Example 1, except that the amount of carbon material A was set to 3% by weight and the amount of positive electrode material NCM was set to 94%.

[0226] <Example 12> In the preparation of the positive electrode, the test battery was manufactured under the same conditions as in Example 1, except that the amount of carbon material A was set to 4% by weight and the amount of positive electrode material NCM was set to 93%.

[0227] <Example 13> In the preparation of the positive electrode, the test battery was manufactured under the same conditions as in Example 1, except that the amount of carbon material A was set to 6% by weight and the amount of positive electrode material NCM was set to 91%.

[0228] Charge and discharge tests were performed on the test batteries of Example 1, Examples 7-13, and Comparative Example 3. At room temperature (25°C), a constant current of 1.25 mA (equivalent to 0.2 C) was applied to each test battery until it reached 4.2 V (constant current charging). After reaching 4.2 V, constant voltage charging was applied and continued until it reached 0.31 mA (0.05 C). Subsequently, it was discharged to 3 V with a constant current of 1.25 mA (equivalent to 0.2 C). The charge and discharge capacities at this time were determined. The results are shown in Table 2 and Figure 6. Figure 6 shows the relationship between the amount of carbon material blended, the 2C maintenance rate, and the discharge capacity in the test batteries of Example 1 and Examples 7-13.

[0229] [Table 2]

[0230] Table 2 and Figure 6 show that, within the range of carbon material content for Examples 1 and 7-13, the 2C maintenance rate of the test batteries improved when the carbon material content was between 0.1% and 2.0% by weight, and maintained its highest value when the carbon material content was between 2.0% and 4.0% by weight. However, it decreased when the carbon material content was excessively increased to 6.0% by weight. While increasing the carbon material content also increases the battery's discharge capacity, excessive increases in the carbon material content reduced the active material content, thus decreasing the electrode's discharge capacity.

[0231] <Example 14> A negative electrode test battery was manufactured by incorporating carbon material A from Example 1 into the negative electrode. A negative electrode slurry was prepared by stirring and mixing 97% artificial graphite, 1% carbon material A from Example 1, 1% carboxymethylcellulose, and 1% styrene-butadiene rubber (SBR) with distilled water as the solvent until homogeneous. The obtained slurry was coated onto a 20 μm thick copper foil, dried at 110°C, then punched out to a diameter of φ15 mm and pressurized with 30 kN to form the negative electrode. After vacuum drying the obtained negative electrode at 120°C, a 2032 size coin-type test battery with a metallic lithium counter electrode was fabricated in a glove box under an argon gas atmosphere using a 1 M LiPF6 solution (a 1:1 mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC)) as the electrolyte and a polypropylene separator.

[0232] Each test battery was energized to 0V with a constant current of 1.23mA (equivalent to 0.2C), and after reaching 0V, it was charged at a constant voltage until it reached 0.31mA (0.05C). Then, it was discharged to 1.5V with a constant current of 1.23mA. The discharge capacity at this time was determined. Next, using the same test battery, it was energized to 0V with a constant current of 1.23mA (equivalent to 0.2C), and after reaching 0V, it was charged at a constant voltage until it reached 0.31mA (0.05C). Then, it was discharged to 1.5V with a high-rate constant current of 12.3mA (equivalent to 2C). From the discharge capacity of the test battery obtained in the above evaluation test, the 2C maintenance rate ((2C capacity / 0.2C capacity) × 100) was calculated. As a result of evaluating the obtained negative electrode battery, the 2C maintenance rate was 47%.

[0233] <Comparative Example 4> In Example 1, a commercially available carbon black (model number: Denka Black Li-100, manufactured by Denka Co., Ltd.) was used as a conductive additive instead of carbon material A, and the amount of this conductive additive added to the negative electrode was set to 1%, except that a negative electrode test battery was manufactured in the same manner as in Example 14. As a result of evaluating the obtained negative electrode battery, the 2C maintenance rate was 16%.

[0234] As is clear from the above-described examples, the 2C retention rate (rapid discharge characteristics) of the battery using the carbon material of the present invention is higher than that of the battery in Comparative Example 4. This is due to the high electronic and ionic conductivity of the carbon material of the present invention. In other words, the carbon material of the present invention has a framework of highly conductive carbonaceous material containing graphene, and has space within the particles to hold electrolyte, compared to the conductive additive used in the battery of Comparative Example 4. The discharge reaction is the reaction in which lithium ions that have been desorbed during charging return to the positive electrode material. When discharge begins, electrons flow from the external circuit to the positive electrode, and these electrons and lithium ions return to the crystal structure sites of the positive electrode in a bonded form, restoring the bonded state before charging. In other words, the bonding of lithium ions and electrons and the phase change of the crystal structure of the positive electrode occur simultaneously. The phase change can be observed from the change in voltage. The "simultaneity" of this phase change is important for the high retention rate of high-rate discharge, and it has been confirmed that the carbon material of this embodiment can achieve this "simultaneity".

[0235] The present invention is not limited to the embodiments and examples described above. Various design modifications within the scope of the present invention are included.

Claims

1. A carbon material having a porosity formed by a carbonaceous outer shell having a graphene structure, BET specific surface area is 100 m ２ / g or more 2500m ２ The range is less than or equal to / g, A carbon material having a total pore volume of 0.30 cc / g or more as measured by nitrogen adsorption / desorption measurement, in which the volume ratio of pores with a diameter of 10 nm or more to the total pore volume is 30% or more, the volume ratio of macropores (pores with a diameter exceeding 50 nm) is 5% or more, and the mode pore diameter is in the mesopore region of 2 nm to 50 nm.

2. In Raman spectroscopy measurements, the intensity of the 2D band (I ２Ｄ The intensity of the G band (I) Ｇ ) intensity ratio (I Ｇ / I ２Ｄ The carbon material according to claim 1, wherein the coefficient of the carbon is in the range of 1.0 or more and 10 or less.

3. The number of carbon atoms per unit mass of the carbon material is 1.0 × 10 １６ pieces / g or more 1.0×10 １９ The carbon material according to claim 1, wherein the amount is in the range of 1 or less per gram.

4. The carbon material according to claim 1, wherein the apparent density, expressed as 1 / (total pore volume + 1 / true density), is 1.00 g / cc or less.

5. The carbon material according to claim 1, wherein the ash content in the carbon material is 5,000 ppm or less.

6. A carbon material according to claim 1, used in lithium-ion secondary batteries.

7. A method for producing a carbon material according to any one of claims 1 to 6, A carbonaceous layer formation step in which a carbonaceous layer is formed on the surface of a mold made of aggregates of atomized compounds, A mold removal step to remove the aforementioned mold, A method for producing carbon materials, including

8. A conductive additive for battery electrodes, comprising the carbon material described in any one of claims 1 to 6.

9. A dispersion comprising a carbon material according to any one of claims 1 to 6 and a dispersion medium in which the carbon material is dispersed.

10. An electrode composition comprising a carbon material according to any one of claims 1 to 6, an active material, and a binder.

11. An electrode slurry comprising the electrode composition according to claim 10 and a solvent in which the electrode composition is dispersed.

12. An electrode comprising the carbon material according to any one of claims 1 to 6.

13. A lithium-ion secondary battery comprising the carbon material described in any one of claims 1 to 6.

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