Carbon material, method for manufacturing carbon material, negative electrode, and secondary battery

Abstract

The problems addressed by the present invention are to provide a carbon material having excellent discharge load characteristics of secondary batteries and high-temperature storage recovery rate of secondary batteries and to provide a method for producing a carbon material having excellent discharge load characteristics of secondary batteries and high-temperature storage recovery rate of secondary batteries. The present invention relates to a carbon material that satisfies formula (1) and formula (2) or to a carbon material comprising a carbon material (A) that satisfies formula (3) and a carbon material (B) that satisfies formula (4).　0.1≤SAe / SAp≤1.2 (1), 1≤α≤10 (2), 0.1≤α1≤6 (3), 8≤α2≤20 (4)

Description

[Technical Field]

[0001] This invention relates to a carbon material, a method for manufacturing a carbon material, a negative electrode, and a secondary battery. [Background technology]

[0002] In recent years, with the miniaturization of electronic devices, the demand for high-capacity secondary batteries has been increasing. In particular, secondary batteries with higher energy density and superior charge / discharge characteristics compared to nickel-cadmium batteries and nickel-metal hydride batteries, especially lithium-ion secondary batteries, are attracting attention. As a lithium-ion secondary battery, non-aqueous lithium secondary batteries have been developed and put into practical use, consisting of a positive electrode and a negative electrode capable of intercalating and releasing lithium ions, and a non-aqueous electrolyte containing dissolved lithium salts such as LiPF6 and LiBF4.

[0003] While improving the performance of lithium-ion secondary batteries has been widely studied, there has been a growing demand for even higher performance in recent years. For example, Patent Document 1 discloses a negative electrode material that improves the performance of non-aqueous secondary batteries by setting the pore volume within a specific range. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] International Publication No. 2020 / 196914 [Overview of the project] [Problems that the invention aims to solve]

[0005] However, the negative electrode material disclosed in Patent Document 1 suffers from an increased specific surface area of ​​the electrode plate due to damage to the binder and active material particles when pressed at high density, resulting in poor recovery rate for high-temperature storage of secondary batteries.

[0006] This invention has been made in view of the above problems, and the object of this invention is to provide a carbon material that is excellent in discharge load characteristics of secondary batteries and high-temperature storage recovery rate of secondary batteries. Another object of this invention is to provide a method for manufacturing a carbon material that is excellent in discharge load characteristics of secondary batteries and high-temperature storage recovery rate of secondary batteries. [Means for solving the problem]

[0007] Previously, various types of negative electrode materials had been investigated, but no negative electrode material had been found that could achieve both the discharge load characteristics of a secondary battery and the high-temperature storage recovery rate of a secondary battery. The inventors of the present invention diligently studied to solve the above problem and, as a result, discovered that by using a carbon material that satisfies the two equations described later, it is possible to achieve both the discharge load characteristics of a secondary battery and the high-temperature storage recovery rate of a secondary battery, leading to the present invention.

[0008] One aspect of the present invention is: The carbon material satisfies the following equations (1) and (2). 0.1 ≤ SAe / SAp ≤ 1.2 (1) 1 ≤ α ≤ 10 (2) (In equation (1), SAp is the specific surface area of ​​the carbon material as powder, and SAe is the specific surface area of ​​the carbon material at the inflection point of the load-density when pressed as an electrode plate. In equation (2), α is the pressed density of the carbon material, 1.3 g / cm³.) 3 ~1.7g / cm 3 This is the rate of change in curvature within a given range.

[0009] Aspect 2 of the present invention is, SAp is 1.5m 2 / g~4.5m 2 The carbon material is as described in Embodiment 1, and is / g.

[0010] A third aspect of the present invention is: SAe is 0.5m 2 / g~3.5m 2 The carbon material is as described in Embodiment 1 or 2, and is / g.

[0011] Aspect 4 of the present invention is The carbon material according to any one of Aspects 1 to 3, having a volume-based average particle diameter of 5 μm to 25 μm.

[0012] Aspect 5 of the present invention is a carbon material containing a carbon material (A) satisfying the following formula (3) and a carbon material (B) satisfying the following formula (4). 0.1 ≦ α1 ≦ 6 (3) 8 ≦ α2 ≦ 20 (4) (In formula (3), α1 is the rate of change of the degree of flexion in the range of the press density of the carbon material of 1.3 g / cm 3 to 1.7 g / cm 3 . In formula (4), α2 is the rate of change of the degree of flexion in the range of the press density of the carbon material of 1.3 g / cm 3 to 1.7 g / cm 3 .)

[0013] Aspect 6 of the present invention is the carbon material according to Aspect 5, wherein the ratio Rd50 of the volume-based average particle diameter of the carbon material (A) to the volume-based average particle diameter of the carbon material (B) is 0.3 to 1.6.

[0014] Aspect 7 of the present invention is the carbon material according to Aspect 5 or 6, wherein the ratio RSAp of the specific surface area of the carbon material (A) to the specific surface area of the carbon material (B) is 2 to 15.

[0015] ]> Aspect 8 of the present invention is the carbon material according to any one of Aspects 5 to 7, wherein the ratio RTap of the tap density of the carbon material (A) to the tap density of the carbon material (B) is 0.7 to 1.4.

[0016] Aspect 9 of the the present invention is the carbon material according to any one of Aspects 5 to 8, wherein the content of the carbon material (A) is 50% by mass to 95% by mass, and the content of the carbon material (B) is 5% by mass to 50% by mass.

[0017] / / Aspect 10 of the present invention is a method for producing the carbon material according to any one of Aspects 5 to 9, including a step of mixing the carbon material (A) and the carbon material (B).

[0018] Aspect 11 of the present invention is It includes a current collector and an active material layer formed on the current collector, The active material layer is a negative electrode containing the carbon material described in any one of embodiments 1 to 9.

[0019] Aspect 12 of the present invention is A secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, This is a secondary battery in which the negative electrode is the negative electrode described in embodiment 11. [Effects of the Invention]

[0020] The carbon material of the present invention, when used as the active material for the negative electrode of a secondary battery, can achieve both good discharge load characteristics and high-temperature storage recovery rates for the secondary battery. Furthermore, the method for manufacturing the carbon material of the present invention can produce the aforementioned carbon material. [Modes for carrying out the invention]

[0021] The present invention will be described in detail below, but the present invention is not limited to the embodiments described below and can be implemented with various modifications within the scope of its gist. In this specification, when the expression "~" is used, it is used to mean an expression that includes the numerical value or physical property value before and after it.

[0022] (Carbon material) In one embodiment, the carbon material of the present invention satisfies the following formulas (1) and (2). 0.1 ≤ SAe / SAp ≤ 1.2 (1) 1 ≤ α ≤ 10 (2) In equation (1), SAp is the specific surface area of ​​the carbon material as powder, and SAe is the specific surface area of ​​the carbon material at the inflection point of the load-density when pressed as an electrode plate. In equation (2), α is the pressed density of the carbon material, 1.3 g / cm³. 3 ~1.7g / cm 3 This is the rate of change in curvature within a given range.

[0023] In this specification, "carbon material" refers to a material consisting of 90% or more by mass of carbon elements.

[0024] The carbon material of the present invention satisfies formulas (1) and (2) above, thereby ensuring a void structure suitable for lithium ion movement when the electrode plate is pressed, and suppressing an excessive increase in the specific surface area of ​​the electrode plate, thereby enabling both the discharge load characteristics of the secondary battery and the high-temperature storage recovery rate of the secondary battery.

[0025] The carbon material of the present invention preferably satisfies the following formula (1'), more preferably satisfies the following formula (1''), and even more preferably satisfies the following formula (1'') because it suppresses side reactions with the electrolyte and has excellent high-temperature storage characteristics. 0.1 ≤ SAe / SAp ≤ 1.0 (1') 0.4 ≤ SAe / SAp ≤ 0.95 (1'') 0.6 ≤ SAe / SAp ≤ 0.9 (1''')

[0026] The specific surface area (SAp) of the carbon material of the present invention is 1.5 m² due to its excellent lithium ion acceptance properties. 2 Preferably 2.0 m 2 A value of 4.5m / g or higher is more preferable, as it suppresses the increase in irreversible capacity and provides excellent initial charge-discharge efficiency. 2 Preferably less than / g, and 4.0m 2 Less than / g is preferable.

[0027] In this specification, the specific surface area SAp of the powder shall be the value measured by the BET method. Specifically, using a specific surface area measuring device, the sample is pre-dried under reduced pressure at 350°C for 15 minutes under a nitrogen flow, then cooled to liquid nitrogen temperature. A nitrogen-helium mixed gas, precisely adjusted so that the relative pressure of nitrogen to atmospheric pressure is 0.3, is used for measurement by the nitrogen adsorption BET single-point method using the gas flow method.

[0028] The specific surface area SAe of the electrode plate of the carbon material of the present invention is 0.5 m², due to its excellent rapid charge / discharge characteristics and low-temperature input / output characteristics. 2 Preferably 1.0 m2 A value of 3.5m / g or higher is more preferable, as it offers superior initial charge / discharge efficiency and initial gas suppression. 2 Preferably less than / g, and 3.0m 2 Less than / g is preferable.

[0029] In this specification, the specific surface area SAe of the electrode plate shall be the value measured by the BET method. Specifically, using a specific surface area measuring device, the sample is pre-dried under reduced pressure at 100°C for 30 minutes under a nitrogen flow, then cooled to liquid nitrogen temperature. A nitrogen-helium mixed gas, precisely adjusted so that the relative pressure of nitrogen to atmospheric pressure is 0.3, is used for measurement by the nitrogen adsorption BET single-point method using the gas flow method.

[0030] The carbon material of the present invention preferably satisfies the following formula (2') and more preferably satisfies the following formula (2'') because it maintains a suitable void structure when pressed as an electrode plate and has excellent discharge load characteristics. 2≦α≦10 (2') 3 ≤ α ≤ 10 (2'')

[0031] In this specification, the pressed density is 1.3 g / cm³. 3 ~1.7g / cm 3 The rate of change in curvature within this range is calculated from impedance response analysis. Impedance response analysis is performed using an impedance analyzer under the conditions of a frequency of 20 kHz to 10 mHz and a voltage amplitude of 10 mV. The intersection of the 45° straight line in the high-frequency region and the vertical line in the low-frequency region on the Cole-Cole plot is used to determine the ion resistance R of the active material layer of the negative electrode sheet. ion The following is obtained. Let S be the area of ​​the negative electrode sheet, L be the thickness of the active material layer of the negative electrode sheet, σ be the conductivity of the electrolyte, and ε be the porosity of the active material layer. The degree of curvature is calculated from the following formula (5). Flexibility=R ion ×(ε / 2×L)×(σ×S) (5) Using the calculated degree of flexure, the press density is 1.3 g / cm³ from the following formula (6). 3 ~1.7g / cm 3Calculate the rate of change in curvature within the specified range. [Percentage change in flexibility] = [Amount of change in flexibility] / [Amount of change in press density] (6)

[0032] The volume-based average particle size d50 of the carbon material of the present invention is preferably 5 μm or more, more preferably 8 μm or more, and even more preferably 10 μm or more, in order to suppress excessive reaction with the electrolyte and to have excellent initial charge-discharge efficiency. Furthermore, in order to suppress streaking when forming the electrode plate, it is preferably 25 μm or less, more preferably 22 μm or less, and even more preferably 20 μm or less.

[0033] In this specification, the volume-based average particle size d50 is defined as the volume-based median diameter value measured by a laser diffraction / scattering particle size distribution analyzer. Specifically, 0.01 g of the sample is suspended in 10 mL of a 0.2 mass% aqueous solution of polyoxyethylene sorbitan monolaurate, a surfactant, introduced into a laser diffraction / scattering particle size distribution analyzer, and after irradiating with 28 kHz ultrasound at an output of 60 W for 1 minute, the volume-based median diameter in the analyzer is measured.

[0034] The tap density of the carbon material of the present invention suppresses process defects such as scribing during electrode plate manufacturing, improves packing properties resulting in good rollability and easier formation of high-density negative electrode sheets. When formed into an electrode plate, the curvature of the lithium ion migration path is reduced, and the shape of the voids between particles is standardized, resulting in smoother electrolyte movement and improved rapid charge-discharge characteristics. 3 The above is preferable, 0.80 g / cm³ 3 The above is more preferable, 0.90 g / cm³ 3 The above is even more preferable, as the particles have appropriate spaces on their surface and inside, preventing them from becoming too hard, resulting in excellent electrode plate pressability, and superior rapid charge / discharge characteristics and low-temperature input / output characteristics. 3 The following is preferable: 1.30 g / cm³ 3 The following is more preferable: 1.10 g / cm³ 3 The following is even more preferable.

[0035] In this specification, tap density is determined using a powder density meter with a diameter of 1.6 cm and a volume of 20 cm³. 3 The sample is dropped into a cylindrical tap cell to fill it completely, and then tapped 1000 times with a stroke length of 10 mm. The density value is calculated from the volume and mass of the sample at that time.

[0036] The circularity of the carbon material of the present invention is preferably 0.88 or higher, more preferably 0.90 or higher, and even more preferably 0.92 or higher, as it reduces the degree of bending of lithium ion diffusion, facilitates the movement of electrolyte into the voids between particles, and results in excellent rapid charge and discharge characteristics. Furthermore, it is preferably 0.99 or lower, more preferably 0.98 or lower, and even more preferably 0.97 or lower, as it ensures good contact between carbon materials and results in excellent cycle characteristics.

[0037] In this specification, circularity is calculated by measuring the particle size distribution of the equivalent circle diameter by flow-type particle image analysis and using the following formula (9). Specifically, ion-exchanged water is used as the dispersion medium, and polyoxyethylene sorbitan monolaurate is used as the surfactant. The dispersion is then obtained by dispersing the particles using ultrasound. Subsequently, the shape of the particles is captured using a flow-type image analysis system. From images of at least 1000 particles, the circularity of particles with an equivalent circle diameter in the range of 1.5 μm to 40 μm is averaged and defined as the circularity. [Circularity] = [Perimeter of an equivalent circle with the same area as the particle projection shape] / [Actual perimeter of the particle projection shape] (9)

[0038] The cumulative pore volume of the carbon material of the present invention is preferably 0.003 mL / g or more, more preferably 0.005 mL / g or more, even more preferably 0.010 mL / g or more, preferably 0.120 mL / g or less, more preferably 0.090 mL / g or less, and even more preferably 0.070 mL / g or less, as it is moderately deformable during pressing.

[0039] In this specification, the cumulative pore volume in the range of pore diameters from 0.01 μm to 1 μm shall be the value measured by a mercury porosimeter using the mercury intrusion method. Specifically, using a mercury porosimeter, the carbon material is weighed to approximately 0.2 g, sealed in a powder cell, and pre-treated by degassing at 25°C and below 50 μm Hg for 10 minutes. Next, the pressure is reduced to 4 psia, mercury is introduced into the cell, and the pressure is increased stepwise from 4 psia to 40,000 psia, and then decreased to 25 psia. The number of steps during the pressure increase is set to 80 or more, and after an equilibrium time of 10 seconds at each step, the amount of mercury injected is measured. The pore distribution is calculated from the mercury injection curve obtained in this way using Washburn's equation. The surface tension (γ) of mercury is calculated as 485 dyne / cm, and the contact angle (ψ) is calculated as 140°. From the obtained pore distribution, the cumulative pore volume in the range of pore diameter from 0.01 μm to 1 μm is calculated.

[0040] The d10 of the carbon material of the present invention suppresses the tendency of particles to aggregate and exhibits excellent slurry stability and electrode plate strength, so a particle size of 1 μm or more is preferred, more preferably 3 μm or more, and even more preferably 5 μm or more. Furthermore, to suppress streaking during electrode plate formation, a particle size of 30 μm or less is preferred, more preferably 20 μm or less, and even more preferably 17 μm or less.

[0041] In this specification, d10 is defined as the value obtained when the particle size distribution, in which the particle frequency % is accumulated from the smallest particle size, reaches 10% in the measurement of the volume-based average particle size d50.

[0042] The d90 of the carbon material of the present invention is preferably 20 μm or more, more preferably 25 μm or more, and even more preferably 30 μm or more, as it can suppress a decrease in electrode plate strength. Furthermore, as it suppresses striating during electrode plate formation, it is preferably 100 μm or less, more preferably 70 μm or less, and even more preferably 50 μm or less.

[0043] In this specification, d90 is defined as the value obtained when the particle size distribution, in which the particle frequency % is calculated from the smallest particle size, reaches 90% in terms of cumulative particle size.

[0044] The amount of DBP (dibutyl phthalate) absorbed by the carbon material of the present invention is preferably 20 mL / 100g or more, more preferably 30 mL / 100g or more, and even more preferably 40 mL / 100g or more, as the presence of suitable voids within the particles helps to avoid a decrease in the reaction surface. Furthermore, to suppress streaking during electrode formation, it is preferably 85 mL / 100g or less, more preferably 70 mL / 100g or less, and even more preferably 65 mL / 100g or less.

[0045] In this specification, the DBP oil absorption amount shall be the value measured in accordance with ISO 4546. Specifically, the value is measured when 40g of the sample is added, the dropping rate is 4mL / min, the rotation speed is 125rpm, and the set torque is 500N·m. An example of a measuring device is the Brabender Absorbometer Type E.

[0046] In another embodiment, the carbon material of the present invention includes a carbon material (A) that satisfies the following formula (3) and a carbon material (B) that satisfies the following formula (4). 0.1 ≤ α1 ≤ 6 (3) 8 ≤ α² ≤ 20 (4) In equation (3), α1 is the pressed density of the carbon material, 1.3 g / cm³. 3 ~1.7g / cm 3 This is the rate of change in curvature within the range. In equation (4), α2 is the press density of the carbon material, 1.3 g / cm³. 3 ~1.7g / cm 3 This is the rate of change in curvature within a given range.

[0047] The carbon material of the present invention includes a carbon material (A) that satisfies formula (3) and a carbon material (B) that satisfies formula (4), making it easier to satisfy formulas (1) and (2).

[0048] (Carbon material (A)) The carbon material (A) satisfies the following equation (3). 0.1 ≤ α1 ≤ 6 (3) The carbon material of the present invention, by containing carbon material (A), plays a role in maintaining the void structure when the electrode plate is pressed, and exhibits excellent lithium ion diffusion.

[0049] The carbon material (A) is preferable to satisfy the following formula (3') and more preferable to satisfy the following formula (3'') in order to suppress excessive load when pressing the electrode plates. 0.5 ≤ α1 ≤ 5.5 (3') 1 ≤ α1 ≤ 5 (3'')

[0050] The specific surface area SAp of the carbon material (A) is 0.3 m² because it ensures a space for lithium to enter and exit, and has excellent rapid charge and discharge characteristics. 2 Preferably 0.5 m 2 More preferably 0.8m / g or more, 2 A value of 8.0 m² or more is even more preferable, as it suppresses side reactions with the electrolyte and provides excellent initial charge-discharge efficiency. 2 Preferably less than / g, and 5.0m 2 More preferably less than / g, and 2.5m 2 A value of less than / g is even more preferable.

[0051] The tap density of carbon material (A) is 0.60 g / cm³ due to its excellent packing properties when used in electrode plates. 3 The above is preferable, 0.80 g / cm³ 3 The above is more preferable, 1.00 g / cm³ 3 The above is even more preferable, as it exhibits excellent interparticle conductivity, and therefore 1.40 g / cm³ 3 The following is preferable: 1.35 g / cm³ 3 The following is more preferable: 1.30 g / cm³ 3 The following is even more preferable.

[0052] The volume-based average particle size d50 of the carbon material (A) is preferably 1 μm or more, more preferably 5 μm or more, and even more preferably 10 μm or more, in order to suppress excessive reaction with the electrolyte and to have excellent initial charge-discharge efficiency. Furthermore, in order to suppress streaking when forming the electrode plate, it is preferably 40 μm or less, more preferably 30 μm or less, and even more preferably 20 μm or less.

[0053] The circularity of the carbon material (A) is preferably 0.88 or higher, more preferably 0.90 or higher, and even more preferably 0.92 or higher, in order to secure a movement path for lithium ions in the electrolyte when used as an electrode plate and to have excellent high current density charge-discharge characteristics. It is also preferably 0.99 or lower, more preferably 0.98 or lower, and even more preferably 0.97 or lower, in order to secure a contact area between particles and to have excellent conductivity.

[0054] The d002 value of carbon material (A) is preferably 3.40 Å or less, and more preferably 3.38 Å or less, because the graphite is highly crystalline and has sufficient charge / discharge capacity. The theoretical d002 value of graphite is 3.354 Å, and highly crystalline natural graphite exhibits a d002 value close to the theoretical value. On the other hand, the d002 value of artificial graphite varies greatly depending on the type of coke used as raw material and the graphitization temperature.

[0055] The Lc of the carbon material (A) is preferably 950 Å or higher, and more preferably 1000 Å or higher, because the graphite is highly crystalline and has sufficient charge / discharge capacity.

[0056] In this specification, the d002 value is the interplanar spacing of the lattice plane (002 plane) measured by X-ray diffraction according to the Japan Society for the Promotion of Science (JSPS) method, and Lc is the crystallite size measured by X-ray diffraction according to the JSPS method. The X-ray diffraction measurement conditions are as follows. Sample: A mixture prepared by adding approximately 15% by mass of X-ray standard high-purity silicon powder to the object to be measured. X-ray:CuKα ray Measurement range: 20°≦2θ≦30° Step angle: 0.013° Sample preparation: A flat sample surface is created by filling a 0.2 mm deep recess in the sample plate with the powdered sample.

[0057] The Raman R value of the carbon material (A) is preferably 0.10 or higher, more preferably 0.15 or higher, and even more preferably 0.20 or higher, as high density makes it difficult for the crystals to orient in the plane direction, thus avoiding a decrease in charge-discharge load characteristics. Furthermore, it is preferably 0.80 or lower, more preferably 0.70 or lower, and even more preferably 0.60 or lower, as this suppresses excessive reaction with the electrolyte, thus avoiding a decrease in charge-discharge efficiency and an increase in gas generation.

[0058] In this specification, the Raman R value is defined as the 1580 cm⁻¹ value in the Raman spectrum obtained by Raman spectroscopy. -1 Nearby Peak P A Intensity I A And, 1360cm -1 Nearby Peak P B Intensity I B Measure and the intensity ratio (I B / I A The value calculated as follows will be used. In this specification, "1580cm -1 "Nearby" means 1580cm -1 ~1620cm -1 It refers to the range of "1360cm" -1 "Nearby" means 1350cm -1 ~1370cm -1 It refers to the range. Raman spectra are measured using a Raman spectrometer. Specifically, carbon material is filled into the measurement cell by free-falling, and measurements are performed while irradiating the measurement cell with argon ion laser light and rotating the measurement cell in a plane perpendicular to the laser light. The measurement conditions are as follows: Wavelength of argon ion laser light: 514.5 nm Laser power on the sample: 25mW Resolution: 4cm -1 Measurement range: 1100cm -1 ~1730cm -1 Peak intensity measurement, peak half-width measurement: background processing, smoothing processing (convolution 5 points by simple averaging)

[0059] The carbon material (A) is preferably graphite having a coating on at least a portion of its surface, more preferably graphite having carbonaceous material on at least a portion of its surface, and even more preferably graphite having amorphous carbonaceous material on at least a portion of its surface, due to its excellent lithium ion acceptance.

[0060] The content of amorphous carbonaceous material in carbon material (A) is preferably 0.1% by mass or more, more preferably 1% by mass or more, and even more preferably 3% by mass or more, in order to obtain a more uniform coating state and excellent charge acceptance properties, and is preferably 30% by mass or less, more preferably 20% by mass or less, and even more preferably 15% by mass or less, in order to obtain excellent rolling properties when forming electrode plates.

[0061] In this specification, the content of amorphous carbonaceous material in the carbon material is calculated using the following formula (10). That is, it is calculated from the mass of the carbon material and amorphous carbonaceous material before and after firing. In this calculation, the change in mass of the carbon material before and after firing is assumed to be negligible. Amorphous carbonaceous material content (mass%) = [(Amount of carbon material in amorphous carbonaceous material after firing - Amount of carbon material before firing) / Amount of carbon material before firing] × 100 (10)

[0062] (Manufacturing method for carbon material (A)) The method for manufacturing carbon material (A) is not particularly limited as long as it can be manufactured in a manner that satisfies formula (3) above, but a method is preferred in which carbon material raw material is spheroidized in the presence of a granulator, subjected to pressure treatment, and then impregnated with an amorphous carbon precursor, as this method offers high capacity and excellent input / output characteristics and cycle characteristics. Specifically, a manufacturing method including the following steps (1) to (6) is preferred. Process (1): Process for adjusting the particle size of carbon material raw materials. Process (2): Process of mixing carbon material raw materials and granulating agent. Process (3): Process for spheroidizing carbon material raw materials Step (4): Step to remove the granulating agent. Step (5): Pressurization process Step (6): Step of impregnating amorphous carbonaceous material

[0063] The following describes steps (1) to (6), but other steps may be included, and the manufacturing method is not limited to including steps (1) to (6).

[0064] (Process (1)) Step (1) is a step to adjust the particle size of the carbon material raw material.

[0065] Graphite is preferred as the raw material for the carbon material, and is more preferable than natural graphite due to its high crystallinity and excellent capacity. Artificial graphite is more preferable than natural graphite because it has even higher crystallinity, better capacity, and does not require heat treatment during manufacturing. Graphite with few impurities is preferable, and it is even more preferable to purify it as needed before use.

[0066] Examples of natural graphite include earthy graphite, scaly graphite, and flake graphite. Among these natural graphites, scaly graphite and flake graphite are preferred, with flake graphite being more preferred, due to their high degree of graphitization and low impurity content.

[0067] Examples of artificial graphite include organic materials such as coal tar pitch, coal-based heavy oil, atmospheric pressure residue, petroleum-based heavy oil, aromatic hydrocarbons, nitrogen-containing cyclic compounds, sulfur-containing cyclic compounds, polyphenylene, polyvinyl chloride, polyvinyl alcohol, polyacrylonitrile, polyvinyl butyral, natural polymers, polyphenylene sulfide, polyphenylene oxide, furfuryl alcohol resin, phenol-formaldehyde resin, and imide resin, which are graphitized by heating them to over 2500°C.

[0068] The d002 value of the carbon material raw material is preferably 3.360 Å or less, and more preferably 3.357 Å or less, because the graphite is highly crystalline and has sufficient charge / discharge capacity.

[0069] The carbon material raw material Lc is preferably 900 Å or higher, and more preferably 1000 Å or higher, because the graphite is highly crystalline and has sufficient charge / discharge capacity.

[0070] The purity of the carbon material raw material is preferably 99.0% or higher, more preferably 99.5% or higher, even more preferably 99.9% or higher, and particularly preferably 100%, as these factors contribute to superior capacity and battery safety.

[0071] In this specification, purity is defined as the value calculated from the mass of the carbon material before and after heating, obtained by accurately weighing approximately 10 g of thoroughly dried carbon material and heating it at 815°C in air for 10 hours.

[0072] The volume-based average particle size (d50) of the carbon material raw material is preferably 1 μm or more, more preferably 3 μm or more, and even more preferably 5 μm or more, due to its excellent transportability. It is preferably 150 μm or less, more preferably 130 μm or less, and even more preferably 120 μm or less, due to its excellent productivity.

[0073] The specific surface area (SA) of carbon material raw materials can be controlled by its shape, so it is 1.0 m². 2 Preferably 1.5 m 2 More preferably 2.0m / g or more, 2 A value of 30.0 m² or more is even more preferable, as it offers excellent control over irreversible capacity. 2 Preferably less than / g, and 20.0m 2 More preferably less than / g, and 10.0m 2 A value of less than / g is even more preferable.

[0074] The tap density of the carbon material raw material is 0.60 g / cm³ due to its excellent transportability. 3 The above is preferable, 0.70 g / cm³ 3 The above is more preferable, 0.80 g / cm³ 3 The above is even more preferable, as it allows for easier control during grinding, and therefore 1.40 g / cm³ is preferred. 3 The following is preferable: 1.30 g / cm³ 3 The following is more preferable: 1.20 g / cm³ 3 The following is even more preferable.

[0075] The Raman R value of the carbon material raw material is preferably 0.10 or higher, more preferably 0.15 or higher, and even more preferably 0.20 or higher, as high density makes it difficult for crystals to orient in the plane direction, thus avoiding a decrease in charge-discharge load characteristics. Furthermore, it is preferably 0.80 or lower, more preferably 0.70 or lower, and even more preferably 0.60 or lower, as this suppresses excessive reaction with the electrolyte, thus avoiding a decrease in charge-discharge efficiency and an increase in gas generation.

[0076] The method for adjusting the particle size of the carbon material raw material is not particularly limited as long as it can be adjusted to the volume-based average particle size or specific surface area described later; crushing, pulverization, and classification are acceptable. Crushing, pulverization, and classification can be carried out using known methods.

[0077] The volume-based average particle size (d50) of the carbon material raw material after particle size adjustment is preferably 1 μm or more, more preferably 2 μm or more, even more preferably 3 μm or more, preferably 20 μm or less, more preferably 15 μm or less, and even more preferably 12 μm or less, as this facilitates control of the spheroidization process.

[0078] The specific surface area (SA) of the carbon material raw material after particle size adjustment is 5.0 m² because it ensures a space for lithium ions to enter and exit, and exhibits excellent rapid charge / discharge characteristics and low-temperature input / output characteristics. 2 Preferably 7.5 m 2 More preferably 10.0 m 2 A value of 30.0 m² or more is even more preferable, as it suppresses side reactions with the electrolyte, prevents a decrease in initial charge / discharge efficiency and an increase in gas generation, and improves battery capacity. 2 Preferably less than / g, and 25.0m 2 Less than / g is more preferable, and 20.0m 2 A value of less than / g is even more preferable.

[0079] The tap density of the carbon material raw material after particle size adjustment is 0.60 g / cm³, as it exhibits excellent spheroidization during the spheroidization treatment. 3 The above is preferable, 0.70 g / cm³ 3 The above is more preferable, 0.80 g / cm³ 3 The above is even more preferable, 1.40 g / cm³3 The following is preferable, 1.30 g / cm 3 The following is more preferable, 1.20 g / cm 3 The following is even more preferable.

[0080] (Step (2)) Step (2) is a step of mixing a carbon material raw material and a granulating agent.

[0081] The granulating agent is preferably a liquid when spheroidizing the carbon material raw material. Also, the granulating agent preferably contains an organic compound that becomes amorphous carbon. Furthermore, the granulating agent preferably does not contain an organic solvent, contains an organic solvent, at least one of the organic solvents has no flash point, or contains an organic solvent and has a flash point of 5 °C or higher. When the granulating agent satisfies the above requirements, when spheroidizing the carbon material raw material, the granulating agent forms a liquid crosslink between the carbon material raw materials, and an attractive force is generated by the capillary negative pressure of the liquid crosslink and the surface tension of the liquid between the carbon material raw materials, and the distance between the carbon material raw materials can be effectively shortened.

[0082] Examples of the method of mixing the carbon material raw material and the granulating agent include, for example, a method of mixing the carbon material raw material and the granulating agent using a mixer or a kneader, a method of adding the carbon material raw material to a solution in which the granulating agent is dissolved and removing the solvent, and the like. Among these methods, since fine pores of 1 nm to 4 nm can be efficiently reduced, a method of mixing the carbon material raw material and the granulating agent using a mixer or a kneader is preferable.

[0083] The addition amount of the granulating agent can suppress the decrease in the spheroidization degree due to the decrease in the adhesion force between the carbon material raw materials, and can suppress the decrease in productivity due to the adhesion of the carbon material raw materials to the apparatus. Therefore, based on 100 parts by mass of the carbon material raw material, 0.1 part by mass or more is preferable, 1 part by mass or more is more preferable, 10 parts by mass or more is even more preferable, 1000 parts by mass or less is preferable, 100 parts by mass or less is more preferable, and 50 parts by mass or less is even more preferable.

[0084] (Step (3)) Step (3) is a step of spheroidizing the carbon material raw material. By spheroidizing the carbon material raw material, excellent rapid charge and discharge characteristics are achieved.

[0085] A preferred method for spheroidizing carbon material raw materials is one that involves applying mechanical energy to the material, as this allows for easier control of the particle shape. Examples of mechanical energy include impact, compression, friction, and shear force. These mechanical energies may be used individually or in combination of two or more types. A method for sphericalizing carbon material raw materials by applying mechanical energy can be achieved by using a device that applies mechanical energy.

[0086] When spheroidizing carbon material raw materials, the viscosity of the granulator is preferably 1 cP or higher, more preferably 5 cP or higher, even more preferably 10 cP or higher, particularly preferably 20 cP or higher, preferably 1000 cP or lower, more preferably 800 cP or lower, even more preferably 600 cP or lower, and particularly preferably 500 cP or lower. The viscosity of the granulator used when spheroidizing carbon material raw materials can be adjusted by controlling the amount of organic solvent and the temperature of the spheroidizing process.

[0087] In this specification, viscosity is defined as the value measured at 25°C using a rheometer. Shear rate 100 s -1 If the shear stress in the area is 0.1 Pa or higher, the shear rate is 100 s. -1 The value measured was at a shear rate of 100 s. -1 If the shear stress in is less than 0.1 Pa, then 1000 s -1 The value measured was at a shear rate of 1000 s. -1 If the shear stress in the sample is less than 0.1 Pa, the value measured at a shear rate that results in a shear stress of 0.1 Pa or more shall be used.

[0088] When granulating carbon material raw materials, the carbon material raw materials may be granulated in the presence of other substances. Examples of other substances include metals that can be alloyed with lithium, their oxides, amorphous carbon, and green coke.

[0089] When spheroidizing carbon material raw materials, it is preferable to perform the spheroidizing process while adhering the fine powder generated during the process to the surface of the carbon material. By adhering the fine powder generated during the spheroidizing process to the surface of the carbon material, the voids within the carbon material can be effectively reduced when the carbon material is coated with amorphous carbonaceous material or graphite material. In addition, the amount of edges that can be used as lithium ion insertion and desorption sites increases, the electrolyte can efficiently spread to the voids within the carbon material, and the low-temperature input / output characteristics and cycle characteristics are excellent. The fine powder may include not only the fine powder generated during the spherification process, but also fine powder with adjusted particle size that may be added separately.

[0090] To effectively adhere the fine powder to the carbon material surface, it is preferable to increase the adhesion between carbon material particles and carbon material particles, between carbon material particles and fine powder particles, and between fine powder particles and fine powder particles. Examples of interparticle adhesion forces include van der Waals forces and electrostatic attraction that do not involve interparticle inclusions, as well as physical and chemical bridging forces that do involve interparticle inclusions.

[0091] The van der Waals force is such that as the volume-based average particle size (d50) decreases below 100 μm, [self-weight] < [adhesion force]. Therefore, the smaller the volume-based average particle size of the carbon material raw material, the stronger the adhesion force between particles, making it more likely for fine powder to adhere to the carbon material and be encapsulated within the spherical carbon material, which is preferable.

[0092] The carbon material raw material and granulating agent may be put into the spheroidizing apparatus, and steps (2) and (3) may be carried out simultaneously.

[0093] (Step (4)) Step (4) is the step of removing the granulating agent. The granulating agent may be removed entirely or partially. When using a granulating agent containing an organic solvent, it is preferable to remove the organic solvent as well.

[0094] Methods for removing granulating agents and organic solvents include, for example, washing with a solvent and heating to cause volatilization and decomposition. Among these methods, heating to cause volatilization and decomposition is preferred because it offers superior productivity and removal efficiency.

[0095] (Step (5)) Step (5) is a pressurized treatment step.

[0096] Examples of pressurization treatments include isotropic pressurization and anisotropic pressurization. Among these pressurization treatments, isotropic pressurization is preferred because it can be controlled to satisfy equation (3).

[0097] Examples of pressurizing methods include hydrostatic isotropic pressurization using water as the pressurizing medium, pneumatic isotropic pressurization using air or other gases as the pressurizing medium, and pressurization by filling a mold and applying pressure in a constant direction with a uniaxial press.

[0098] The pressurized pressure is preferably 50 MPa or higher, more preferably 100 MPa or higher, even more preferably 150 MPa or higher, preferably 300 MPa or lower, more preferably 280 MPa or lower, and even more preferably 260 MPa or lower, as it is easier to control the pressure to satisfy equation (3).

[0099] Step (5) can be performed at any point in steps (1) to (6), but it is preferable to perform it between steps (4) and (6) because it allows for efficient pressurization after removing excess granulating agent.

[0100] (Process (6)) Step (6) is the process of impregnating amorphous carbonaceous material. By impregnating the carbon material with amorphous carbonaceous material, side reactions between the negative electrode and the electrolyte can be suppressed, resulting in high capacity and excellent low-temperature input / output characteristics and high-temperature storage characteristics. Amorphous carbonaceous material refers to carbon with a d002 value of 0.340 nm or greater.

[0101] A method of impregnating a carbon material with amorphous carbonaceous material is preferable because it suppresses excessive side reactions with the electrolyte and provides excellent initial charge-discharge efficiency. This method involves mixing the carbon material with an amorphous carbonaceous material precursor and heating it in a non-oxidizing atmosphere to convert the amorphous carbonaceous material precursor into amorphous carbonaceous material.

[0102] Methods for mixing carbon material and amorphous carbonaceous precursor include, for example, mixing the carbon material and amorphous carbonaceous precursor using a mixer or kneader, and adding the carbon material to a solution in which the amorphous carbonaceous precursor is dissolved and then removing the solvent. Among these methods, the method of mixing the carbon material and amorphous carbonaceous precursor using a mixer or kneader is preferred because it can efficiently reduce fine pores of 1 nm to 4 nm.

[0103] The atmosphere during heating is not particularly limited as long as it is a non-oxidizing atmosphere, but a nitrogen, argon, or carbon dioxide atmosphere is preferred, and a nitrogen atmosphere is more preferred, as it can suppress the formation of micropores due to oxidation. The oxygen concentration is preferably 1% by volume or less, and more preferably 0.1% by volume or less, as it is easier to control to satisfy equation (3).

[0104] The heating temperature when amorphous carbonaceous precursors are amorphous is not particularly limited as long as it does not reach a crystalline structure equivalent to that of graphite, but is preferably 500°C or higher, more preferably 600°C or higher, even more preferably 700°C or higher, preferably 2000°C or lower, more preferably 1800°C or lower, and even more preferably 1600°C or lower.

[0105] The heating time is preferably 0.1 hours or more, more preferably 1 hour or more, preferably 1000 hours or less, and more preferably 100 hours or less, as it is easy to control to satisfy equation (3).

[0106] Examples of amorphous carbonaceous precursors include tar, pitch, aromatic hydrocarbons such as naphthalene and anthracene, and thermoplastic resins such as phenolic resins and polyvinyl alcohol resins. These precursors may be used individually or in combination of two or more. Among these precursors, tar, pitch, and aromatic hydrocarbons are preferred because their carbon structure develops easily and coating can be achieved with small amounts. More preferably, those with a residual carbon content of 50% or more are preferred, and even more preferably, those with a residual carbon content of 60% or more are preferred, as they are easy to control to satisfy formula (3).

[0107] Since the ash content in the amorphous carbonaceous precursor is easy to control to satisfy formula (3), it is preferably 0.00001% by mass or more, preferably 1% by mass or less, more preferably 0.5% by mass or less, and even more preferably 0.1% by mass or less, based on 100% by mass of the amorphous carbonaceous precursor.

[0108] The metal impurity content in the amorphous carbonaceous precursor is preferably 0.1 ppm by mass or more, more preferably 1000 ppm by mass or less, more preferably 500 ppm by mass or less, and even more preferably 100 ppm by mass or less, as it is easy to control the content to satisfy formula (3).

[0109] In this specification, the metal impurity content is defined as the value obtained by dividing the total content of Fe, Al, Si, and Ca in the amorphous carbonaceous precursor by the residual carbon content.

[0110] Since the Qi (quinoline-insoluble content) in the amorphous carbonaceous precursor is easily controlled to satisfy formula (3), it is preferably 5% by mass or less, and more preferably 3% by mass or less, per 100% by mass of the amorphous carbonaceous precursor.

[0111] The carbon material obtained through steps (1) to (6) may be crushed, pulverized, or classified as necessary in order to bring the volume-based average particle size of carbon material (A) into a desired range. Crushing, pulverization, and classification can be carried out using known methods.

[0112] The content ratio of the amorphous carbonaceous material precursor in the mixture of the carbon material and the amorphous carbonaceous material precursor is preferably 0.1% by mass or more, more preferably 1% by mass or more, and still more preferably 3% by mass or more in 100% by mass of the mixture of the carbon material and the amorphous carbonaceous material precursor, because a more uniform coating state can be obtained and the charging acceptance property is excellent. Further, since it has excellent rolling property during polarization, it is preferably 30% by mass or less, more preferably 20% by mass or less, and still more preferably 15% by mass or less.

[0113] (Carbon material (B)) The carbon material (B) satisfies the following formula (4). 8 ≦ α2 ≦ 20 (4) By including the carbon material (B) in the carbon material of the present invention, the rolling property during electrode plate pressing is improved, the load applied to the particles in the electrode plate is dispersed, and the increase in the specific surface area of the electrode plate is suppressed, so that the high-temperature storage characteristics are excellent.

[0114] Since the carbon material (B) suppresses excessive particle deformation and has excellent lithium ion diffusibility, it preferably satisfies the following formula (4'), and more preferably satisfies the following formula (4''). 9 ≦ α2 ≦ 19 (4') 10 ≦ α2 ≦ 18 (4'')

[0115] The powder specific surface area S Ap of the carbon material (B) is preferably 3.0 m 2 / g or more, more preferably 4.0 m 2 / g or more, and still more preferably 5.0 m 2 / g or more. Further, since it suppresses side reactions with the electrolytic solution and has excellent initial charge-discharge efficiency, it is preferably 20.0 m 2 / g or less, more preferably 15.0 m 2 / g or less, and still more preferably 10.0 m 2 / g or less.

[0116] The tap density of the carbon material (B) is preferably 0.70 g / cm<00,000102> or more, more preferably 0.75 g / cm 3 or more, and still more preferably...3 The above is even more preferable, as it exhibits excellent interparticle conductivity, and therefore 1.30 g / cm³ 3 The following is preferable: 1.20 g / cm³ 3 The following is more preferable: 1.10 g / cm³ 3 The following is even more preferable.

[0117] The volume-based average particle size d50 of the carbon material (B) is preferably 1 μm or more, more preferably 5 μm or more, and even more preferably 10 μm or more, in order to suppress excessive reaction with the electrolyte and to have excellent initial charge-discharge efficiency. Furthermore, in order to suppress streaking when forming the electrode plate, it is preferably 40 μm or less, more preferably 30 μm or less, and even more preferably 20 μm or less.

[0118] The circularity of the carbon material (B) is preferably 0.88 or higher, more preferably 0.90 or higher, and even more preferably 0.92 or higher, in order to secure a movement path for lithium ions in the electrolyte when used as an electrode plate and to have excellent high current density charge-discharge characteristics. It is also preferably 0.99 or lower, more preferably 0.98 or lower, and even more preferably 0.97 or lower, in order to secure a contact area between particles and to have excellent conductivity.

[0119] The d002 value of carbon material (B) is preferably 3.40 Å or less, and more preferably 3.38 Å or less, because the graphite is highly crystalline and has sufficient charge / discharge capacity. The theoretical d002 value of graphite is 3.354 Å, and highly crystalline natural graphite exhibits a d002 value close to the theoretical value. On the other hand, the d002 value of artificial graphite varies greatly depending on the type of coke used as raw material and the graphitization temperature.

[0120] The Lc of the carbon material (B) is preferably 950 Å or higher, and more preferably 1000 Å or higher, because the graphite is highly crystalline and has sufficient charge / discharge capacity.

[0121] The Raman R value of the carbon material (B) is preferably 0.10 or higher, more preferably 0.15 or higher, and even more preferably 0.20 or higher, as high density makes it difficult for the crystals to orient in the plane direction, thus avoiding a decrease in charge-discharge load characteristics. Furthermore, it is preferably 0.80 or lower, more preferably 0.70 or lower, and even more preferably 0.60 or lower, as this suppresses excessive reaction with the electrolyte, thus avoiding a decrease in charge-discharge efficiency and an increase in gas generation.

[0122] (Manufacturing method for carbon material (B)) The method for manufacturing the carbon material (B) is not particularly limited as long as it can be manufactured in a manner that satisfies formula (4) above, but it is preferable to use spheroidized natural graphite as the carbon material (B) because it has good packing properties as an electrode plate and excellent capacity.

[0123] The raw material for carbon material (B) is preferably graphite, which has high crystallinity and excellent capacity. Natural graphite and artificial graphite are more preferred, with natural graphite being even more preferred because it has even higher crystallinity, even better capacity, and does not require heat treatment during manufacturing. Graphite with few impurities is preferable, and if necessary, it is even more preferable to use it after refining.

[0124] Examples of natural graphite include earthy graphite, scaly graphite, and flake graphite. Among these natural graphites, scaly graphite and flake graphite are preferred, with flake graphite being more preferred, due to their high degree of graphitization and low impurity content.

[0125] Examples of artificial graphite include organic materials such as coal tar pitch, coal-based heavy oil, atmospheric pressure residue, petroleum-based heavy oil, aromatic hydrocarbons, nitrogen-containing cyclic compounds, sulfur-containing cyclic compounds, polyphenylene, polyvinyl chloride, polyvinyl alcohol, polyacrylonitrile, polyvinyl butyral, natural polymers, polyphenylene sulfide, polyphenylene oxide, furfuryl alcohol resin, phenol-formaldehyde resin, and imide resin, which are graphitized by heating them to over 2500°C.

[0126] Regarding the method of spheroidization, a method that involves applying mechanical energy is preferred because it allows for easy control of the particle shape. Examples of mechanical energy include impact, compression, friction, and shear force. These mechanical energies may be used individually or in combination of two or more types. The method of shaping objects into spheres by applying mechanical energy can be achieved by using a device that provides mechanical energy.

[0127] During the spheroidization process, the raw materials may be granulated in the presence of other substances. Examples of other substances include metals that can be alloyed with lithium, their oxides, and green coke.

[0128] (Composition of carbon material) The carbon material (A) content is preferably 50% by mass or more, more preferably 55% by mass or more, and even more preferably 60% by mass or more, in 100% by mass of the carbon material composition, in order to ensure lithium ion diffusion paths between particles when the electrode plates are pressed and to have excellent charge-discharge characteristics at high current densities. Furthermore, in order to have excellent rolling properties when pressing the electrode plates, it is preferably 95% by mass or less, more preferably 90% by mass or less, and even more preferably 85% by mass or less.

[0129] The carbon material (B) content is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more, in 100% by mass of the carbon material composition, in order to suppress side reactions with the electrolyte due to an increase in the specific surface area of ​​the electrode plate and to have excellent high-temperature storage characteristics. Furthermore, in order to ensure a suitable void structure between particles and to have excellent rapid charge and discharge characteristics, it is preferably 50% by mass or less, more preferably 45% by mass or less, and even more preferably 40% by mass or less.

[0130] For example, the carbon material of the present invention may have a carbon material (A) content of 50% to 95% by mass and a carbon material (B) content of 5% to 50% by mass.

[0131] The carbon material of the present invention may contain other substances in addition to carbon material (A) and carbon material (B). Examples of other substances include metals that can be alloyed with lithium, their oxides, and conductive materials. The content of other substances is preferably 20% by mass or less, and more preferably 10% by mass or less, so as not to impair the original function of the carbon material.

[0132] (Manufacturing method for carbon materials) The present invention's method for producing carbon material includes a step of mixing the aforementioned carbon material (A) and the aforementioned carbon material (B). The mixing method is not particularly limited, as long as it can mix carbon material (A) and carbon material (B) to achieve the desired composition.

[0133] The ratio Rd50 ([volume-based average particle size d50 of carbon material (B)] / [volume-based average particle size d50 of carbon material (A)]) of the volume-based average particle size d50 of carbon material (A) is preferably 0.3 to 1.6, more preferably 0.4 to 1.5, and even more preferably 0.5 to 1.4. When the ratio Rd50 is within the above range, a uniform lithium ion diffusion path is ensured within the electrode plate, resulting in excellent charge-discharge characteristics at high current densities.

[0134] The ratio RSAp ([Specific surface area SAp of carbon material (B)] / [Specific surface area SAp of carbon material (A)]) of the specific surface area SAp of carbon material (A) is preferably 2 to 15, more preferably 3 to 14, and even more preferably 4 to 13. When the RSAp ratio is within the above range, excessive side reactions with the electrolyte are suppressed, resulting in excellent initial charge-discharge efficiency.

[0135] The ratio RTap([tap density of carbon material (B)] / [tap density of carbon material (A)]) of the tap density of carbon material (A) is preferably 0.7 to 1.4, more preferably 0.75 to 1.3, and even more preferably 0.8 to 1.2. When the ratio RTap is within the above range, the slurry stability during electrode plate fabrication is excellent.

[0136] (Negative electrode) The negative electrode of the present invention comprises a current collector and an active material layer formed on the current collector, wherein the active material layer contains the carbon material of the present invention. The carbon material of the present invention has the effect of acting as the active material of the negative electrode.

[0137] The method for manufacturing the negative electrode is not particularly limited as long as an active material layer can be formed on the current collector, but a method of applying a slurry containing the carbon material and binder resin of the present invention onto the current collector and drying it is preferred because it is inexpensive and has excellent productivity. A thickening agent may be further added to the slurry.

[0138] It is preferable to apply a slurry containing the carbon material and binder resin of the present invention onto a current collector, dry it, and then apply pressure to increase the density of the active material layer formed on the current collector, thereby increasing the battery capacity per unit volume of the active material layer.

[0139] The density of the active material layer is set at 1.2 g / cm³ to suppress the decrease in battery capacity caused by an increase in the thickness of the electrode plates. 3 The above is preferable, 1.5 g / cm³ 3 The above is more preferable because the amount of electrolyte held in the void decreases due to the reduction in the void within the electrode plate, the mobility of alkali ions such as lithium ions decreases, and the deterioration of rapid charge-discharge characteristics can be suppressed. 3 The following is preferable: 1.8 g / cm³ 3 The following are preferable.

[0140] (Secondary battery) The secondary battery of the present invention comprises a positive electrode, a negative electrode, and an electrolyte. The positive electrode and the negative electrode of the present invention are preferably capable of intercalating and releasing lithium ions.

[0141] (positive electrode) A known positive electrode can be used.

[0142] (electrolyte) Any known electrolyte can be used.

[0143] (Separator) In the secondary battery of the present invention, it is preferable to have a separator interposed between the positive electrode and the negative electrode. A known separator can be used.

[0144] (Application) The carbon material of the present invention can achieve both the discharge load characteristics and high-temperature storage recovery rate of secondary batteries, making it suitable for use as an active material for the negative electrode of secondary batteries, more suitable for use as an active material for the negative electrode of non-aqueous secondary batteries, and particularly suitable for use as an active material for the negative electrode of lithium-ion secondary batteries. [Examples]

[0145] The present invention will be described in more detail below using examples, but the present invention is not limited to the following examples without departing from its essence.

[0146] (Method for measuring volume-based average particle size d50) 0.01 g of the sample was suspended in 10 mL of a 0.2% by mass aqueous solution of polyoxyethylene sorbitan monolaurate (product name "Tween 20", manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), a surfactant, and introduced into a laser diffraction / scattering particle size distribution analyzer (model name "LA-920", manufactured by Horiba, Ltd.). After irradiating with 28 kHz ultrasound at an output of 60 W for 1 minute, the volume-based median diameter in the analyzer was measured, and the volume-based median diameter was defined as the volume-based average particle size d50.

[0147] (Method for measuring tap density) Using a powder density meter (model name "Tap Denser KYT-3000", manufactured by Seishin Corporation), a sample with a diameter of 1.6 cm and a volume of 20 cm³ was measured. 3 The sample was dropped into a cylindrical tap cell to fill it completely, and then tapped 1000 times with a stroke length of 10 mm. The density value calculated from the volume and mass of the sample at that time was defined as the tap density.

[0148] (Method for measuring powder specific surface area SAp) Using a specific surface area measuring device (model name "Macsorb HM Model-1210", manufactured by Mountec Co., Ltd.), the sample was pre-dried under reduced pressure at 350°C for 15 minutes under a nitrogen flow, then cooled to liquid nitrogen temperature. Using a nitrogen-helium mixed gas precisely adjusted so that the relative pressure of nitrogen to atmospheric pressure was 0.3, the specific surface area was measured by the nitrogen adsorption BET single-point method using the gas flow method, and this was defined as the powder specific surface area SAp.

[0149] (Fabrication of negative electrode sheet) To 50.00±0.02g of the carbon material obtained in the Examples and Comparative Examples, 50.00±0.02g (0.50g in terms of solid content) of a 1% by mass aqueous solution of carboxymethylcellulose sodium salt and 1.00±0.05g (0.50g in terms of solid content) of styrene-butadiene rubber aqueous dispersion with a weight-average molecular weight of 270,000 were mixed in a hybrid mixer (manufactured by Keyence Corporation) for 5 minutes, and degassed for 30 seconds to obtain a slurry. The obtained slurry is then placed on a 10 μm thick copper foil, which serves as the current collector, with a negative electrode material concentration of 10.0 ± 0.2 mg / cm³. 2 The material was dried to ensure adhesion. Further, roll pressing was performed, resulting in a density of 1.3 ± 0.03 g / cm³ of the negative electrode active material layer. 3 ~1.7±0.03 g / cm³ 3 The negative electrode sheet (electrode plate) was obtained by adjusting it to achieve this configuration.

[0150] (Fabrication of the positive electrode sheet) A slurry was obtained by mixing 85% by mass of lithium nickel-manganese-cobaltate (LiNiMnCoO2) as the positive electrode active material, 10% by mass of acetylene black as the conductive material, and 5% by mass of polyvinylidene fluoride (PVdF) as the binder in N-methylpyrrolidone. The obtained slurry is then placed on a 15 μm thick aluminum foil, which serves as the current collector, with a positive electrode material concentration of 22.5 ± 0.2 mg / cm³. 2 The material was applied and dried to ensure adhesion. Further, roll pressing was performed, and the density of the positive electrode active material layer was determined to be 2.6 ± 0.05 g / cm³. 3 The positive electrode sheet was obtained by adjusting it to achieve this.

[0151] (Fabrication of sheet-type rechargeable batteries) The obtained negative electrode sheet, polyethylene separator, and obtained positive electrode sheet were stacked in order. The resulting stack was wrapped in a cylindrical aluminum laminate film, and an electrolyte solution prepared by dissolving LiPF6 in a mixed solvent of ethylene carbonate and dimethyl carbonate (volume ratio 30:70) to a concentration of 1 mol / L was injected. After that, it was vacuum sealed to create a sheet-like non-aqueous secondary battery. Furthermore, to improve adhesion, the sheet-like secondary battery was sandwiched between glass plates and pressurized.

[0152] (Method for measuring the specific surface area SAe of the electrode plates) Using a specific surface area measuring device (model name "Macsorb HM Model-1210", manufactured by Mountec Co., Ltd.), the sample was pre-dried under reduced pressure at 100°C for 30 minutes under a nitrogen flow, then cooled to liquid nitrogen temperature. Using a nitrogen-helium mixed gas precisely adjusted so that the relative pressure of nitrogen to atmospheric pressure was 0.3, the specific surface area was measured by the nitrogen adsorption BET single-point method using the gas flow method, and the electrode plate specific surface area SAe was determined.

[0153] (Method for measuring press inflection point density) In the press load-negative electrode active material layer density curve obtained during pressing of the negative electrode sheet, the intersection point of the tangent line drawn from the zero load point in the low-density region and the tangent line drawn in the region where the density changes linearly in the high-density region was determined, and the negative electrode active material layer density corresponding to the load at the obtained intersection point was defined as the press inflection point density. During the pressing of the negative electrode sheet, displacement, deformation, and cracking of the carbon material particles constituting the negative electrode sheet occur, increasing the density of the negative electrode active material layer. The press inflection point density serves as an indicator of the changes in each of these phenomena occurring in the carbon material particles.

[0154] (Method for measuring the rate of change in curvature) Two negative electrode sheets, obtained at various press densities, were punched out into 12.5 mm diameter discs and arranged so that their active material layers faced each other. A separator (made of porous polyethylene film) impregnated with an electrolyte solution prepared by dissolving LiPF6 at a concentration of 1 mol / L in a mixed solvent of ethylene carbonate and ethyl methyl carbonate (volume ratio 30:70) was placed between the opposing negative electrode sheets to fabricate a 2016 coin-type battery. The obtained 2016 coin-type battery was left to stand at 25°C for 24 hours, after which impedance response analysis was performed. The impedance response analysis was performed using an impedance analyzer (Solartron) under the conditions of a frequency of 20kHz to 10mHz and a voltage amplitude of 10mV. The intersection of the 45° straight line in the high-frequency region and the vertical line in the low-frequency region on the Cole-Cole plot was used to determine the ion resistance R of the active material layer of the negative electrode sheet. ion The following was obtained. Let S be the area of ​​the negative electrode sheet, L be the thickness of the active material layer of the negative electrode sheet, σ be the conductivity of the electrolyte, and ε be the porosity of the active material layer. The degree of curvature was calculated from the following equation (5). Flexibility=R ion ×(ε / 2×L)×(σ×S) (5) Using the calculated degree of flexure, the press density is 1.3 g / cm³ from the following formula (6). 3 ~1.7g / cm 3 The rate of change in curvature within the specified range was calculated. [Percentage change in flexibility] = [Amount of change in flexibility] / [Amount of change in press density] (6)

[0155] (Method for measuring discharge load characteristics) The obtained sheet-shaped secondary battery underwent initial charge-discharge testing at 25°C for 3 cycles at a voltage range of 4.1V to 3.0V and a current value of 0.2C (1C is defined as the current value required to discharge the rated capacity based on the 1-hour rate discharge capacity in 1 hour; the same applies hereafter), and for 2 cycles at a voltage range of 4.2V to 3.0V and a current value of 0.2C (with an additional 2.5 hours of constant voltage charging at 4.2V during charging). Subsequently, the battery was charged at a constant current of 0.2C up to 4.2V, then charged at a constant voltage of 4.2V for another 2.5 hours, and discharged at a constant current of 3C down to 3.0V. The ratio of the discharge capacity at 3C discharge to the discharge capacity at 0.2C discharge, as shown in equation (7) below, was defined as the discharge load characteristic (%). Discharge load characteristics (%) = ([Discharge capacity at 3C discharge] / [Discharge capacity at 0.2C discharge]) × 100 (7)

[0156] (Method for measuring the recovery rate during high-temperature storage) The obtained sheet-shaped secondary battery underwent initial charge-discharge cycles at 25°C: 3 cycles at a voltage range of 4.1V to 3.0V and a current of 0.2C, and 2 cycles at a voltage range of 4.2V to 3.0V and a current of 0.2C (with an additional 2.5 hours of constant voltage charging at 4.2V during charging). Furthermore, after charging to a state of charge (SOC) of 80% at a current of 0.2C, it was stored at 60°C for 2 weeks. Thereafter, it was discharged at a current of 0.2C, and then charged and discharged again at a current of 0.2C (with an additional 2.5 hours of constant voltage charging at 4.2V during charging). The ratio of the discharge capacity after storage to the discharge capacity after initial charge-discharge, expressed by the following formula (8), was defined as the high-temperature storage recovery rate (%). High-temperature storage recovery rate (%) = ([Discharge capacity after storage] / [Discharge capacity after initial charge / discharge]) × 100 (8)

[0157] [Manufacturing Example 1] Manufacturing of carbon material (A1) Flake-shaped natural graphite with a volume-based average particle size of 100 μm was crushed to obtain graphite with a volume-based average particle size of 11 μm. 100 parts by mass of the obtained graphite was mixed with 12 parts by mass of granulator, then subjected to a spheroidizing treatment, and the granulator was further removed by heat treatment to obtain spheroidized graphite (volume-based average particle size of 16 μm, specific surface area of ​​15 m²). 2 / g, tap density 0.96g / cm³ 3) was obtained. The obtained spheroidized graphite was filled into a rubber container, the rubber container was sealed and subjected to isotropic pressurization treatment, followed by crushing and classification to obtain spheroidized graphite powder. The obtained spheroidized graphite powder was mixed with pitch (ash content 0.02 mass%, metal impurity content 20 mass ppm, Qi 1 mass%) as an amorphous carbonaceous material precursor, the furnace pressure was reduced to 10 torr or less and restored to atmospheric pressure with nitrogen, and then nitrogen was circulated to reduce the oxygen concentration in the furnace to 0.01 volume% or less and heat treatment was performed at 1300°C in an inert gas. The obtained calcined product was crushed and classified to obtain carbon material (A1). The mass ratio of spheroidized graphite to amorphous carbonaceous material in the obtained carbon material (A1) was 1:0.08. The evaluation results for the obtained carbon material (A1) are shown in Table 1.

[0158] [Manufacturing Example 2] Manufacturing of carbon material (A2) Except for changing the mixing ratio of spheroidized graphite powder and amorphous carbonaceous precursor, the procedure was carried out in the same manner as in Production Example 1 to obtain carbon material (A2). The mass ratio of spheroidized graphite to amorphous carbonaceous material in the obtained carbon material (A2) was 1:0.095. The evaluation results for the obtained carbon material (A2) are shown in Table 1.

[0159] [Manufacturing Example 3] Manufacturing of carbon material (A3) Except for changing the mixing ratio of spheroidized graphite powder and amorphous carbonaceous precursor, the procedure was carried out in the same manner as in Production Example 1 to obtain carbon material (A3). The mass ratio of spheroidized graphite to amorphous carbonaceous material in the obtained carbon material (A3) was 1:0.11. The evaluation results for the obtained carbon material (A3) are shown in Table 1.

[0160] [Manufacturing Example 4] Manufacturing of carbon material (B1) Naturally occurring flaky graphite with a volume-based average particle size of 100 μm was subjected to a spheroidizing treatment to obtain carbon material (B1). The evaluation results for the obtained carbon material (B1) are shown in Table 2.

[0161] [Manufacturing Example 5] Manufacturing of carbon material (B2) Naturally occurring flaky graphite with a volume-based average particle size of 100 μm was subjected to a spheroidizing treatment to obtain carbon material (B2). The evaluation results for the obtained carbon material (B2) are shown in Table 2.

[0162] [Manufacturing Example 6] Manufacturing of carbon material (B3) Naturally occurring flaky graphite with a volume-based average particle size of 100 μm was subjected to a spheroidizing treatment to obtain carbon material (B3). The evaluation results for the obtained carbon material (B3) are shown in Table 2.

[0163] [Example 1] A carbon material was obtained by mixing 80% by mass of carbon material (A1) and 20% by mass of carbon material (B2). The evaluation results of the obtained carbon materials are shown in Table 4.

[0164] [Examples 2-4] Except for changing the type and content of the carbon material as shown in Table 3, the procedure was carried out in the same manner as in Example 1 to obtain a carbon material. The evaluation results of the obtained carbon materials are shown in Table 4.

[0165] [Comparative Examples 1-6] Except for changing the type and content of the carbon material as shown in Table 3, the procedure was carried out in the same manner as in Example 1 to obtain a carbon material. The evaluation results of the obtained carbon materials are shown in Table 4.

[0166] [Table 1]

[0167] [Table 2]

[0168] [Table 3]

[0169] [Table 4]

[0170] As can be seen from Table 4, the carbon materials of Examples 1 to 4, which are the carbon materials of the present invention, exhibited excellent discharge load characteristics and high-temperature storage recovery rates in secondary batteries. On the other hand, the carbon materials of Comparative Examples 1 to 3, which do not satisfy the requirements of the present invention, were inferior in high-temperature storage recovery rates in secondary batteries. Similarly, the carbon materials of Comparative Examples 4 to 6, which also do not satisfy the requirements of the present invention, were inferior in discharge load characteristics and high-temperature storage recovery rates in secondary batteries. This result is thought to be because the carbon material satisfies both formulas (1) and (2), or contains carbon material (A) that satisfies formula (3) and carbon material (B) that satisfies formula (4), thereby suppressing the increase in the specific surface area of ​​the electrode plate when pressed at high density, and maintaining a good void structure within the electrode plate necessary for lithium ion diffusion.

[0171] Although various embodiments have been described above, it goes without saying that the present invention is not limited to these examples. It is clear to those skilled in the art that various modifications or alterations can be conceived within the scope of the claims, and these will naturally also fall within the technical scope of the present invention. Furthermore, the components in the above embodiments may be combined in any way without departing from the spirit of the invention.

[0172] This application is based on Japanese Patent Application No. 2022-124174 filed on August 3, 2022, and its contents are incorporated herein by reference. [Industrial applicability]

[0173] The carbon material of the present invention can achieve both the discharge load characteristics and high-temperature storage recovery rate of secondary batteries, making it suitable for use as an active material for the negative electrode of secondary batteries, more suitable for use as an active material for the negative electrode of non-aqueous secondary batteries, and particularly suitable for use as an active material for the negative electrode of lithium-ion secondary batteries.

Claims

1. comprising carbon material (A) and carbon material (B), The following equations (1) and (2) are satisfied, A carbon material in which the ratio RTap, the ratio of the tap density of carbon material (A) to the tap density of carbon material (B), is 0.7 to 1.

4. 0.1 ≤ SAe / Sap ≤ 1.2 (1) １≦α≦１０ （２） (In equation (1), SAp is the specific surface area of ​​the carbon material as powder, and SAe is the specific surface area of ​​the carbon material at the inflection point of the load-density when pressed as an electrode plate. In equation (2), α is the pressed density of the carbon material, 1.3 g / cm³. ３ ~1.7 g / cm ３ This is the rate of change in curvature within a given range.

2. Sap is 1.5m ２ / g to 4.5m ２ The carbon material according to claim 1, wherein the value is / g.

3. SAe is 0.5m ２ / g to 3.5m ２ The carbon material according to claim 1, wherein the value is / g.

4. The carbon material according to claim 1, wherein the volume-based average particle size is 5 μm to 25 μm.

5. The carbon material according to claim 1, wherein the ratio RSAp of the specific surface area of ​​carbon material (A) to the specific surface area of ​​carbon material (B) is 2 to 15.

6. The carbon material according to claim 1, wherein the cumulative pore volume of the carbon material (A) in the range of pore diameter 0.01 μm or more and 1 μm or less is 0.003 mL / g or more and 0.120 mL / g or less.

7. The material includes a carbon material (A) that satisfies the following formula (3) and a carbon material (B) that satisfies the following formula (4), A carbon material in which the ratio RTap, the ratio of the tap density of carbon material (A) to the tap density of carbon material (B), is 0.7 to 1.

4. ０．１≦α１≦６ （３） ８≦α２≦２０ （４） (In formula (3), α1 is the change rate of the degree of bending in the range of the press density of the carbon material from 1.3 g / cm ３ to 1.7 g / cm ３ . In formula (4), α2 is the change rate of the degree of bending in the range of the press density of the carbon material from 1.3 g / cm ３ to 1.7 g / cm ３ .)

8. The carbon material according to claim 7, wherein the ratio Rd50 of the volume-based average particle size of carbon material (A) to the volume-based average particle size of carbon material (B) is 0.3 to 1.

6.

9. The carbon material according to claim 7, wherein the ratio RSAp of the specific surface area of ​​carbon material (A) to the specific surface area of ​​carbon material (B) is 2 to 15.

10. The carbon material according to claim 7, wherein the cumulative pore volume of the carbon material (A) in the range of pore diameter 0.01 μm or more and 1 μm or less is 0.003 mL / g or more and 0.120 mL / g or less.

11. The carbon material according to claim 7, wherein the carbon material (A) has a content of 50% to 95% by mass, and the carbon material (B) has a content of 5% to 50% by mass.

12. A method for producing a carbon material according to claim 7, comprising the step of mixing carbon material (A) and carbon material (B).

13. It includes a current collector and an active material layer formed on the current collector, A negative electrode in which the active material layer contains the carbon material described in any one of claims 1 to 11.

14. A secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, A secondary battery wherein the negative electrode is the negative electrode described in claim 13.

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