Method for manufacturing negative electrode material for lithium ion secondary battery

Abstract

To provide a novel manufacturing method of an anode material for lithium ion secondary battery consisting of a carbon material, having a hollow structure and being improved in a high-speed charge / discharge characteristic.SOLUTION: The present invention relates to a manufacturing method of an anode material for lithium ion secondary battery including: a dispersion fluid preparing step of preparing raw material dispersion fluid containing carbon black particles of 100 pts.mass of which a DBP oil absorption amount ranges from 20 to 90 ml / 100 g and an arithmetic mean particle diameter ranges from 20 to 400 nm, a thermally curable resin of 10 to 50 pts.mass and a dispersant of 100 to 300 pts.mass; a spray dry step of drying the raw material dispersion fluid at 100 to 300°C according to a spray dry method to obtain a spray dry substance of which the particle diameter ranges from 5 to 30 μm; and a burning step of burning the spray dry substance at 800 to 3000°C to obtain the anode material for lithium ion secondary battery.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a negative electrode material for a lithium ion secondary battery.

Background Art

[0002] Lithium ion secondary batteries are mounted in many devices such as mobile phones and personal computers, and are being used in various fields because of their high capacity, high voltage, small size, and light weight.

[0003] In recent years, depending on the application, lithium ion secondary batteries may be required to have excellent high-rate charge and discharge characteristics. In order to obtain such a lithium ion secondary battery with excellent high-rate charge and discharge characteristics, attempts have been made to reduce the density of the negative electrode. When the negative electrode has a low density, the amount of electrolyte solution that can be retained near the active material particles increases, and the diffusion rate of lithium ions accepted on the surface of the active material improves, so that a lithium ion secondary battery with excellent high-rate charge and discharge characteristics can be obtained.

[0004] However, when the density of the negative electrode is reduced, there is a problem that the interparticle gaps between the particles constituting the negative electrode become too many, and the conductive path decreases. In addition, since the overvoltage portion increases, there are also problems such as a decrease in the initial efficiency and a decrease in the cycle characteristics.

[0005] Therefore, as a material that has excellent high-rate charge and discharge characteristics by reducing the density and can reduce the above problems of density reduction, particles having a hollow structure made of a carbon material can be mentioned.

[0006] Examples of the particles having a hollow structure made of a carbon material include, for example, Patent Document 1, which describes composite graphite particles that are spherical or substantially spherical, contain flaky graphite particles (A) and a carbonaceous material (B), have a hollow inside, have an average particle diameter of 5 to 25 μm, and an average aspect ratio of 5 or less.

[0007] In addition, Patent Document 2 describes a hollow sintered body including a plurality of hollow particles having an outer shell layer containing a metal material and / or a carbon material, which are fixed to each other.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Disclosure of the Invention

Problems to be Solved by the Invention

[0009] However, the demand for improving the high-rate charge and discharge characteristics of the negative electrode material for lithium-ion secondary batteries is increasing. Therefore, there is a need for a novel method for manufacturing a negative electrode material for lithium-ion secondary batteries, which is made of a carbon material, has a hollow structure, and has excellent high-rate charge and discharge characteristics.

[0010] Accordingly, an object of the present invention is to provide a novel method for manufacturing a negative electrode material for lithium-ion secondary batteries, which is made of a carbon material, has a hollow structure, and has excellent high-rate charge and discharge characteristics.

Means for Solving the Problems

[0011] Under the above technical background, the present inventors have intensively studied and found that by using carbon black particles having a DBP oil absorption amount within a specific range, granulating by a spray drying method, and then firing to form an outer shell layer of hollow particles, a negative electrode material for lithium-ion secondary batteries made of a carbon material, having a hollow structure, high sphericity, and excellent high-rate charge and discharge characteristics can be obtained, and thus the present invention has been completed.

[0012] That is, the present invention (1) prepares a raw material dispersion liquid containing 100 parts by mass of carbon black particles having a DBP oil absorption of 20 to 90 ml / 100 g and an arithmetic average particle diameter of 100 to 400 nm, 10 to 50 parts by mass of a thermosetting resin, and 100 to 300 parts by mass of a dispersion medium. A spray drying step of drying the raw material dispersion liquid at 100 to 30 °C by a spray drying method to obtain a spray dried product having a particle size of 5 to 30 μm. A firing step of firing the spray dried product at 800 to 3000 °C to obtain a negative electrode material for a lithium ion secondary battery. The present invention provides a method for manufacturing a negative electrode material for a lithium ion secondary battery, which is characterized by having the above steps.

[0013] Further, the present invention (2) provides a method for manufacturing a negative electrode material for a lithium ion secondary battery according to (1), characterized in that the circularity obtained by scanning electron microscope observation (SEM) of the negative electrode material for a lithium ion secondary battery is 0.850 or more.

[0014] Further, the present invention (3) provides a method for manufacturing a negative electrode material for a lithium ion secondary battery according to (1) or (2), characterized in that the thermosetting resin is a phenol resin.

[0015] Further, the present invention (4) provides a method for manufacturing a negative electrode material for a lithium ion secondary battery according to any one of (1) to (3), characterized in that the average particle diameter (D50) of the negative electrode material for a lithium ion secondary battery is 5.0 to 30.0 μm.

[0016] Further, the present invention (5) provides a method for manufacturing a negative electrode material for a lithium ion secondary battery according to any one of (1) to (4), characterized in that the BET specific surface area of the negative electrode material for a lithium ion secondary battery is 3.00 to 7.00 m 2 / g.

[0017] Further, the present invention (6) provides a method for manufacturing a negative electrode material for a lithium-ion secondary battery according to any one of (1) to (5), characterized in that, in a scanning electron microscope (SEM) image of a cross-section of the negative electrode material for a lithium-ion secondary battery, the ratio of the area of the void to the entire area inside the contour of the hollow particles in the negative electrode material for a lithium-ion secondary battery is 30 to 60%.

[0018] Further, the present invention (7) provides a method for manufacturing a negative electrode material for a lithium-ion secondary battery according to any one of (1) to (6), characterized in that the ratio (A / B) of the following particle density A (g / cm 3 ) obtained by mercury porosimetry of the negative electrode material for a lithium-ion secondary battery to the following particle density B (g / cm 3 ) obtained by image analysis of a scanning electron microscope (SEM) image of a cross-section of the negative electrode material for a lithium-ion secondary battery is 0.40 to 0.80. <Particle density A> Particle density A (g / cm 3 ) = C / (1 - C × D) (In the formula, C is the bulk density (g / cm 3 ) measured by filling the voids of the measurement sample with mercury in a state where almost no pressure is applied (0.51 psia) in mercury porosimetry, and D is the volume (cm 3 ) of mercury required per 1 g of the measurement sample to fill the voids by further pressurizing to 357 psia after the measurement of C.) <Particle density B> Particle density B (g / cm 3 ) = G(1 - E / (E + F)) (In the formula, E is the area of the voids inside the outer shell layer of the hollow particles in the SEM image, F is the total area of the heat-treated carbon black particles and the heat-treated binder inside the outer shell layer of the hollow particles in the SEM image, and G is the true density (g / cm 3 ) measured by filling the voids of the measurement sample with mercury in a state pressurized to 59900 psia in mercury porosimetry.)

[0019] Further, the present invention (8) provides a method for manufacturing a negative electrode material for a lithium ion secondary battery according to any one of (1) to (7), characterized in that the number ratio of hollow particles to all particles in the negative electrode material for a lithium ion secondary battery is 50% or more.

Advantages of the Invention

[0020] According to the present invention, it is possible to provide a method for manufacturing a negative electrode material for a lithium ion secondary battery, which is made of a carbon material, has a hollow structure, and has excellent high-rate charge and discharge characteristics.

Brief Description of the Drawings

[0021]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0022] The method for manufacturing a negative electrode material for a lithium ion secondary battery of the present invention includes a dispersion liquid preparation step of preparing a raw material dispersion liquid containing 100 parts by mass of carbon black particles having a DBP oil absorption of 20 to 90 ml / 100 g and an arithmetic average particle diameter of 20 to 400 nm, 10 to 50 parts by mass of a thermosetting resin, and 100 to 300 parts by mass of a dispersion medium, a spray drying step of drying the raw material dispersion liquid at 100 to 300 °C by a spray drying method to obtain a spray dried product having a particle size of 5 to 30 μm, a firing step of firing the spray dried product at 800 to 3000 °C to obtain a negative electrode material for a lithium ion secondary battery, and is characterized by having the above steps.

[0023] The method for manufacturing a negative electrode material for a lithium-ion secondary battery according to the present invention includes a dispersion preparation step, a spray drying step, and a firing step.

[0024] The dispersion preparation step is a step of preparing a raw material dispersion containing carbon black particles, a thermosetting resin, and a dispersion medium.

[0025] The carbon black particles in the dispersion preparation step are not particularly limited, and examples include furnace black and thermal black.

[0026] The DBP oil absorption amount of the carbon black particles in the dispersion preparation step is 20 to 90 ml / 100 g. When the DBP oil absorption amount of the carbon black particles is within the above range, the dispersion of the dispersion liquid is improved during spraying in spray drying, and spherical hollow particles with high roundness are easily formed. The DBP oil absorption amount of the carbon black particles is preferably 40 ml / 100 g or more in terms of incorporating a water-soluble thermosetting resin and a water solvent and easily forming a spherical structure, and is preferably 60 ml / 100 g or less in terms of facilitating spheroidization.

[0027] The arithmetic average particle diameter of the carbon black particles in the dispersion preparation step is 20 to 400 nm. When the arithmetic average particle diameter of the carbon black particles is 20 to 400 nm, a material excellent in high-rate charge and discharge characteristics is obtained while suppressing a decrease in irreversible capacity. The arithmetic average particle diameter of the carbon black particles is more preferably 100 nm or more in terms of further improving the high-rate charge and discharge characteristics, and is more preferably 300 nm or less in terms of suppressing an increase in irreversible capacity during the first charge.

[0028] The arithmetic average particle diameter of the carbon black particles is measured by observing amorphous carbon particles with a scanning electron microscope (SEM), taking the diameter of the circumscribed circle of the particles in the obtained image as the particle diameter, and using image software (WINROOF manufactured by Mitani Shosha Co., Ltd.) to calculate the average value of the particle diameters of 10,000 particles.

[0029] The average lattice plane spacing d(002) of carbon black particles in the dispersion preparation process is 0.3370 nm or more. When the average lattice plane spacing d(002) of the carbon black particles is 0.3370 nm or more, the reaction resistance on the particle surface decreases, and the high-rate charge-discharge characteristics are excellent. The average lattice plane spacing d(002) of the carbon black particles is more preferably 0.3400 nm or more in terms of further improving the high-rate charge-discharge characteristics, and particularly preferably 0.3500 nm or more in terms of further improving the high-rate charge-discharge characteristics.

[0030] The thermosetting resin in the dispersion preparation process is not particularly limited, and examples thereof include phenol resins, melamine resins, epoxy resins, etc. Among these, a water-soluble phenol resin is preferable in terms of having an affinity with an aqueous solvent and being compatible with hydrophobic carbon black. The thermosetting resin may be used alone or in combination of two or more.

[0031] The viscosity of the thermosetting resin in the dispersion preparation process at 25°C is preferably 50 to 500 mPa·s. When the viscosity of the thermosetting resin is within the above range, the affinity between the thermosetting resin and the aqueous dispersion medium increases, and a uniform dispersion is obtained. The viscosity of the thermosetting resin is preferably 60 mPa·s or more in terms of facilitating the end of uniform dispersion in visual observation, and preferably 300 mPa·s or less in terms of being able to form a uniform dispersion by easy stirring treatment.

[0032] The non-volatile content of the thermosetting resin in the dispersion preparation process is preferably 45 to 70%. When the non-volatile content of the thermosetting resin is within the above range, it is suitable as a thermosetting resin capable of bonding carbon blacks to form an outer shell layer. The non-volatile content of the thermosetting resin is preferably 50% or more in terms of being able to form an outer shell layer having practical strength, and preferably 65% or less in terms of reducing the viscosity fluctuation during the dry spray process and stabilizing the granulation quality.

[0033] The dispersion medium related to the dispersion liquid preparation step is exemplified by water. By using water as the dispersion medium, it has an appropriate affinity with the resin, making it easier to form a hollow structure while maintaining a spherical structure.

[0034] In the raw material dispersion liquid related to the dispersion liquid preparation step, the content of the thermosetting resin is 10 to 50 parts by mass with respect to 100 parts by mass of carbon black particles. When the content of the thermosetting resin is within the above range, it becomes easier to form hollow particles with high sphericity. The content of the thermosetting resin is preferably 20 parts by mass or more with respect to 100 parts by mass of carbon black particles in terms of providing binding property between carbon blacks, and is preferably 30 parts by mass or less with respect to 100 parts by mass of carbon black particles in terms of facilitating the formation of particles having sphericity while maintaining a hollow structure.

[0035] In the raw material dispersion liquid related to the dispersion liquid preparation step, the content of the dispersion medium is 100 to 300 parts by mass with respect to 100 parts by mass of carbon black particles. When the content of the dispersion medium is within the above range, it becomes easier to form a hollow structure. The content of the dispersion medium is preferably 150 parts by mass or more with respect to 100 parts by mass of carbon black particles in terms of uniformly mixing carbon black and the thermosetting resin, and is preferably 250 parts by mass or less with respect to 100 parts by mass of carbon black particles in terms of facilitating the formation of particles having sphericity.

[0036] In the raw material dispersion liquid related to the dispersion liquid preparation step, the content of the dispersion medium is 70 to 270 parts by mass with respect to a total of 100 parts by mass of carbon black particles and the thermosetting resin. When the content of the dispersion medium is within the above range, it becomes easier to generate hollow particles. The content of the dispersion medium is preferably 130 parts by mass or more with respect to a total of 100 parts by mass of carbon black particles and the thermosetting resin in terms of preventing clogging during spraying in the spray drying step, and is preferably 180 parts by mass or less with respect to a total of 100 parts by mass of carbon black particles and the thermosetting resin in terms of making the outer shell layer strength practical.

[0037] In addition to carbon black particles, thermosetting resins, and a dispersion medium, the raw material dispersion liquid related to the dispersion liquid preparation process can contain a surfactant, a dispersant, etc. as required.

[0038] In the dispersion liquid preparation process, carbon black particles and thermosetting resins, or in addition to carbon black particles and thermosetting resins, a surfactant, a dispersant, etc. used as required are mixed with a dispersion medium, and then stirred and mixed by a stirrer, ultrasonic vibration, etc. to dissolve or disperse these mixtures in the dispersion medium, thereby preparing a raw material dispersion liquid.

[0039] The viscosity of the raw material dispersion liquid at 25°C is preferably 5 to 150 mPa·s. When the viscosity of the raw material dispersion liquid is within the above range, good spraying is possible in the spray drying process. The viscosity of the dispersion liquid is preferably 10 mPa·s or more in terms of preventing clogging of the spray nozzle, and preferably 100 mPa·s or less in terms of enabling a high spraying speed.

[0040] The spray drying process is a process of drying the raw material dispersion liquid by the spray drying method at 100 to 300°C to obtain a spray-dried product with a particle size of 5 to 30 μm.

[0041] In the spray drying process, as a method of drying the raw material dispersion liquid by the spray drying method, there is no particular limitation, and as long as it is a method capable of introducing droplets of the raw material dispersion liquid into the heating part of the spray drying device, heating and drying the raw material dispersion liquid in the heating part, and evaporating and drying the dispersion medium to obtain a spray-dried product that is the dried product of the droplets of the raw material dispersion liquid, it is acceptable.

[0042] The spray drying device for performing the spray drying method is not particularly limited, and a known device can be preferably used. Examples of the spray drying device include those manufactured by Ohkawara Seisakusho (model number CL-8i), Pris Co., Ltd. (model number SB39), Yamato Scientific Co., Ltd. (model number DL410), etc.

[0043] In the spray drying process, when drying by the spray drying method, the drying temperature is 100 to 300 °C. When the drying temperature when drying by the spray drying method is within the above range, water volatilizes and a hollow structure is formed inside. The drying temperature when drying by the spray drying method is preferably 150 °C or higher in terms of rapidly volatilizing water and facilitating the formation of a hollow structure, and is preferably 200 °C or lower in terms of preventing the structural destruction of spherical particles due to the rapid drying of water.

[0044] In the spray drying process, the particle size of the droplets of the raw material dispersion liquid introduced into the spray drying apparatus is adjusted so that the particle size of the spray-dried product obtained by the spray drying method is 5 to 30 μm, preferably 10 to 20 μm.

[0045] In addition, the drying conditions of the spray drying method and the operating conditions of the spray drying apparatus in the spray drying process other than the above are appropriately selected. For example, it is possible to use an ultrasonic nozzle that sprays the nozzle by ultrasonic waves.

[0046] In the spray drying process, the particle size of the spray-dried product obtained by drying the raw material dispersion liquid by the spray drying method is 5 to 30 μm. When the particle size of the spray-dried product is within the above range, spherical particles with high roundness are obtained, and it becomes a negative electrode material for a lithium-ion secondary battery that is easy to coat as an electrode. The particle size of the spray-dried product is preferably 10 μm or more in terms of facilitating mixing with the binder, and is preferably 20 μm or less in terms of facilitating the preparation of an electrode coating film with an appropriate thickness.

[0047] And by performing the spray drying process, a spray-dried product with high sphericity of particles is obtained. In addition, the spray-dried product contains hollow particles having a hollow inside the particles. Note that the spray-dried product also contains particles that do not have a hollow.

[0048] The firing process is a process of firing the spray-dried product at 800 to 3000 °C to obtain a negative electrode material for a lithium-ion secondary battery.

[0049] In the firing process, the firing temperature when firing the spray-dried product is 800 to 3000 °C. When the firing temperature when firing the spray-dried product is 800 to 3000 °C, the Li-ion acceptance sites of the negative electrode material particles for lithium-ion secondary batteries are developed, and the charge capacity is manifested. In the firing process, when the firing temperature when firing the spray-dried product is particularly 2000 °C or higher, it becomes a negative electrode material capable of ensuring a practical charge capacity. Also, when it is 3000 °C or lower, sufficient Li-ion acceptance sites are ensured, and high-rate charge and discharge characteristics can be maintained. Further, the firing atmosphere when firing the spray-dried product is an inert gas atmosphere such as a nitrogen gas atmosphere or an argon gas atmosphere.

[0050] In the firing process, the carbon black particles in the spray-dried product are converted into heat-treated products of the carbon black particles, and the thermosetting resin is converted into carbide, whereby a negative electrode material for a lithium-ion secondary battery is obtained.

[0051] Since the shape of the negative electrode material for a lithium-ion secondary battery obtained by carrying out the method for producing a negative electrode material for a lithium-ion secondary battery of the present invention is formed using the spray-drying method, the sphericity of the particles is high. For example, FIG. 1 shows a scanning electron microscope (SEM) image of a morphological example of the particles of the negative electrode material for a lithium-ion secondary battery obtained by carrying out the method for producing a negative electrode material for a lithium-ion secondary battery of the present invention. In FIG. 1, particles with high sphericity are observed.

[0052] The roundness of the negative electrode material for a lithium-ion secondary battery obtained by performing the method for manufacturing a negative electrode material for a lithium-ion secondary battery of the present invention is preferably 0.850 or more in a scanning electron microscope (SEM) image of the negative electrode material for a lithium-ion secondary battery. When the roundness in the SEM image of the negative electrode material for a lithium-ion secondary battery is within the above range, the negative electrode material becomes closer to a spherical shape, increasing the chance of contact between the negative electrode materials and making it possible to reduce the buffering resistance. The roundness in the SEM image of the negative electrode material for a lithium-ion secondary battery is more preferably 0.880 or more in that it makes it possible to ensure sufficient contact opportunities. Also, the upper limit of the roundness in the SEM image of the negative electrode material for a lithium-ion secondary battery is not particularly limited, but is about 0.995 as the upper limit in terms of manufacturing. In the present invention, a negative electrode material for a lithium-ion secondary battery with a high sphericity is obtained, and by obtaining the roundness in the SEM image, the sphericity of the negative electrode material for a lithium-ion secondary battery can be grasped. Therefore, the higher the roundness in the SEM image, the higher the sphericity.

[0053] In the present invention, the roundness in the SEM image of the negative electrode material for a lithium-ion secondary battery is a value arbitrarily calculated using WINROOF in a scanning electron microscope (SEM) image of the negative electrode material for a lithium-ion secondary battery. Ten particles are extracted, and the roundness of each extracted particle is measured by image processing. Then, the values of the roundness of each obtained particle are averaged, and the average value is taken as the roundness in the SEM image of the negative electrode material for a lithium-ion secondary battery. The measurement of the roundness is performed by image processing calculated using WINROOF.

[0054] In the scanning electron microscope (SEM) image of the cross-section of the negative electrode material for a lithium-ion secondary battery obtained by performing the method for manufacturing a negative electrode material for a lithium-ion secondary battery of the present invention, the ratio of the area of the cavity of the hollow particle to the entire area inside the contour of the hollow particle is preferably 30 to 60%. When the area of the cavity of the hollow particle is 30 to 60% with respect to the entire area inside the contour of the hollow particle, a hollow structure capable of holding an electrolytic solution inside is formed. In the negative electrode material for a lithium-ion secondary battery of the present invention, when the ratio of the area of the cavity of the hollow particle to the entire area inside the contour of the hollow particle is 40% or more, a hollow structure is formed in which the electrolytic solution can be sufficiently retained, and when it is 50% or less, a structure capable of maintaining the hollow structure is formed. In the negative electrode material for a lithium-ion secondary battery of the present invention, the ratio of the area of the cavity of the hollow particle to the entire area inside the contour of the hollow particle in the SEM image of the cross-section is an index of the abundance of the cavity in the hollow particle.

[0055] Further, the fact that the negative electrode material for a lithium-ion secondary battery obtained by performing the method for manufacturing a negative electrode material for a lithium-ion secondary battery of the present invention contains hollow particles can also be confirmed by scanning electron microscope (SEM) observation of the cross-section of the negative electrode material for a lithium-ion secondary battery.

[0056] The hollow particles contained in the negative electrode material for a lithium-ion secondary battery obtained by performing the method for manufacturing a negative electrode material for a lithium-ion secondary battery of the present invention have an outer shell layer composed of a heat-treated product of carbon black particles and a carbide of a thermosetting resin. And a cavity is formed inside the hollow particle, that is, inside the outer shell layer. In the outer shell layer, the carbon black particles are bonded by the carbide of the thermosetting resin to maintain the shape of the outer shell layer. Note that in the outer shell layer, not all of the interparticle gaps of the carbon black particles constituting the outer shell layer are filled with the carbide of the thermosetting resin, and there are portions in the interparticle gaps of the carbon black particles that are not filled with the carbide of the thermosetting resin. Therefore, the outer shell layer has through-holes penetrating the outer shell layer. This through-hole is a hole connecting the outside of the hollow particle and the cavity inside the particle, and the electrolytic solution can enter and exit through this through-hole.

[0057] The formation of through holes in the outer shell layer is confirmed from the presence of peaks indicating pores of 200 nm or less through which mercury penetrates at a pressure of 900 psia or more in mercury porosimetry measurement.

[0058] The negative electrode material for a lithium ion secondary battery obtainable by carrying out the method for producing a negative electrode material for a lithium ion secondary battery of the present invention is an aggregate of a large number of particulate matters, and as a part thereof, includes hollow particles. Further, the negative electrode material for a lithium ion secondary battery obtainable by carrying out the method for producing a negative electrode material for a lithium ion secondary battery of the present invention is composed of a heat-treated product of carbon black particles and a carbide of a thermosetting resin, and also contains particles in which no cavities are formed.

[0059] In the negative electrode material for a lithium ion secondary battery obtainable by carrying out the method for producing a negative electrode material for a lithium ion secondary battery of the present invention, the number ratio of the hollow particles to the total number of particles is preferably 50 to 100%. When the number ratio of the hollow particles to the total number of particles in the negative electrode material for a lithium ion secondary battery is 50% or more, the effect of enhancing the high-rate charge and discharge characteristics of the hollow particles becomes greater. The number ratio of the hollow particles to the total number of particles in the negative electrode material for a lithium ion secondary battery is more preferably 60% or more, particularly preferably 70% or more, in terms of further increasing the frequency of insertion and extraction of lithium ions between the electrolyte and the active material. In the present invention, the number ratio of the hollow particles to the total number of particles in the negative electrode material for a lithium ion secondary battery is obtained by observing a cross section of a film obtained by coating the negative electrode material for a lithium ion secondary battery with an arbitrary thickness from a slurry containing 25% of a binder of polyvinylidene fluoride with a scanning electron microscope (SEM), counting the total number of particles observed in the SEM image and the number of hollow particles among them, and then calculating the number ratio of the hollow particles to the total number of particles in the negative electrode material for a lithium ion secondary battery.

[0060] The average particle diameter (D50) of the negative electrode material for a lithium-ion secondary battery obtained by carrying out the method for producing the negative electrode material for a lithium-ion secondary battery of the present invention is preferably 5.0 to 30.0 μm. When the average particle diameter (D50) of the negative electrode material for a lithium-ion secondary battery is 5.0 to 30.0 μm, a slurry suitable for coating a lithium-ion battery can be prepared. The average particle diameter (D50) of the negative electrode material for a lithium-ion secondary battery obtained by carrying out the method for producing the negative electrode material for a lithium-ion secondary battery of the present invention is 7.0 μm or more, whereby a uniform coating film without bubbles or voids is obtained, and when it is 20.0 μm or less, a uniform coating film without coarse particles is obtained. In the present invention, the average particle diameter (D50) of the negative electrode material for a lithium-ion secondary battery is the particle diameter at which the integrated particle size is 50% when measuring the volume-based integrated particle size distribution using a laser diffraction particle size distribution measuring device.

[0061] The BET specific surface area of the negative electrode material for a lithium-ion secondary battery obtained by carrying out the method for producing the negative electrode material for a lithium-ion secondary battery of the present invention is preferably 3.00 to 7.00 m 2 / g. When the BET specific surface area of the negative electrode material for a lithium-ion secondary battery is 3.00 to 7.00 m 2 / g, it has a surface capable of inserting and extracting lithium ions, and it is possible to prevent a decrease in initial efficiency due to the formation of an excessive SEI film. The BET specific surface area of the negative electrode material for a lithium-ion secondary battery of the present invention is 3.00 m 2 / g or more, whereby the surface capable of inserting and extracting lithium ions is increased, and when it is 7.00 m 2 / g or less, preferably 5.00 m 2 / g or less, it is possible to prevent the formation of an excessive SEI film. In the present invention, the specific surface area (SA) means a value calculated by the BET multipoint method in the range of relative pressure of 0.05 to 0.2 in the nitrogen adsorption isotherm using a fully automatic surface area measuring device (BELSORP-miniX manufactured by MicrotracBEL).

[0062] The total pore volume of the negative electrode material for a lithium-ion secondary battery obtained by carrying out the method for producing the negative electrode material for a lithium-ion secondary battery of the present invention is preferably 0.05 to 0.20 cm3 / g. The total pore volume of the negative electrode material for a lithium-ion secondary battery is 0.05 to 0.20 cm 3 / g, resulting in a pore structure with high electrolyte retention. The total pore volume of the negative electrode material for a lithium-ion secondary battery of the present invention is 0.05 cm 3 / g or more, resulting in a pore structure capable of retaining the electrolyte. Also, by being 0.10 m 3 / g or less, the weight per active material is maintained, and it becomes a negative electrode material for a lithium-ion secondary battery having a practical battery capacity. Note that the total pore volume of the negative electrode material for a lithium-ion secondary battery means a value calculated at a relative pressure of 0.99 in the nitrogen adsorption isotherm using a fully automatic surface area measuring device (BELSORP-miniX manufactured by MicrotracBEL).

[0063] The pore diameter (the diameter of the interparticle gaps) in the outer shell layer of the negative electrode material for a lithium-ion secondary battery obtained by performing the manufacturing method of the negative electrode material for a lithium-ion secondary battery of the present invention is preferably 10 to 200 nm. By the pore diameter (the diameter of the interparticle gaps) in the outer shell layer of the negative electrode material for a lithium-ion secondary battery being 10 to 200 nm, it becomes a negative electrode material that exhibits excellent performance. The pore diameter in the outer shell layer of the negative electrode material for a lithium-ion secondary battery obtained by performing the manufacturing method of the negative electrode material for a lithium-ion secondary battery of the present invention is 50 nm or more, which makes it easier for lithium ions to diffuse into the hollow interior, improving the high-rate charge-discharge characteristics. Also, by being 150 nm or less, the outer shell of the particles does not become sparse, and a high particle density with a high charge capacity is obtained. Note that the pore diameter in the outer shell layer of the negative electrode material for a lithium-ion secondary battery means a value calculated from the peak that appears at a mercury intrusion pressure of 900 psia or more in mercury porosimetry (Auto Pore V9510).

[0064] The tap density of the negative electrode material for a lithium-ion secondary battery obtained by performing the manufacturing method of the negative electrode material for a lithium-ion secondary battery of the present invention is preferably 0.66 to 0.81 g / cm 3 . When the tap density of the negative electrode material for a lithium-ion secondary battery is 0.66 to 0.81 g / cm 3As a result, particles having a hollow structure and a uniform shape are obtained. The tap density of the negative electrode material for a lithium ion secondary battery of the present invention is 0.69 g / cm 3 or more, which makes it easier to form a uniform coating film as particles with a uniform shape. Also, 0.78 g / cm 3 or less results in a structure in which the hollow structure is developed and a large amount of electrolyte can be retained. In the present invention, the tap density is determined by putting 5 g of graphite particle powder into a 25 ml graduated cylinder and repeating tapping 1000 times at a gap of 10 mm using a tapping type powder reduction measuring instrument (manufactured by Tsutsui Rikagaku Kikai Co., Ltd.), and then, from the value of the apparent volume and the mass of the graphite particle powder put into the graduated cylinder, the following formula: Tap density (g / cm 3 ) = mass of powder put into the graduated cylinder (g) / value of the apparent volume (cm 3 ) after repeating tapping 1000 times is meant by the value calculated by.

[0065] In the negative electrode material for a lithium ion secondary battery obtainable by carrying out the method for producing a negative electrode material for a lithium ion secondary battery of the present invention, in a scanning electron microscope (SEM) image of the cross section of the particles of the negative electrode material for a lithium ion secondary battery, the ratio of the area of the cavity of the hollow particles to the entire area inside the contour of the hollow particles is preferably 30 to 60%. When the area of the cavity of the hollow particles is 30 to 60% with respect to the entire area inside the contour of the hollow particles, a hollow structure capable of retaining the electrolyte inside is obtained. In the negative electrode material for a lithium ion secondary battery obtainable by carrying out the method for producing a negative electrode material for a lithium ion secondary battery of the present invention, when the ratio of the area of the cavity of the hollow particles to the entire area inside the contour of the hollow particles is 40% or more, a hollow structure capable of sufficiently retaining the electrolyte is obtained, and when it is 50% or less, a structure capable of maintaining the hollow structure is obtained. In the negative electrode material for a lithium ion secondary battery of the present invention, the ratio of the area of the cavity of the hollow particles to the entire area inside the contour in the SEM image of the cross section serves as an index of the abundance of the cavity in the hollow particles.

[0066] In the present invention, the ratio of the area of the cavity of the hollow particle to the area of the entire inner side of the contour of the hollow particle is determined by the following procedure. First, a coating film with an arbitrary thickness is made from a slurry containing 25% polyvinylidene fluoride for the negative electrode material of the lithium-ion secondary battery, and a scanning electron microscope (SEM) image of the cross section is obtained. Next, an arbitrary hollow particle is selected from the SEM image, and the diameter of the circumscribed circle of the selected particle is determined. When the obtained diameter of the circumscribed circle is within ±20% of the average particle diameter (D50), image analysis is performed to determine the area of the entire inner side of the contour of the selected hollow particle and the area of the cavity. Next, the ratio of the area of the cavity of the hollow particle to the area of the entire inner side of the contour of the hollow particle is calculated. Then, until 10 hollow particles with a circumscribed circle diameter within ±20% of the average particle diameter (D50) are obtained, the selection of the hollow particles and the calculation of the ratio of the area of the cavity of the hollow particle to the area of the entire inner side of the contour of the hollow particle are performed, and the obtained area ratios are averaged to obtain the ratio of the area of the cavity of the hollow particle to the area of the entire inner side of the contour of the hollow particle in the scanning electron microscope (SEM) image of the cross section of the negative electrode material for the lithium-ion secondary battery of the present invention. Note that the average particle diameter (D50) refers to the particle diameter when the integrated particle size is 50% when measuring the volume-based integrated particle size distribution using a laser diffraction particle size distribution measuring device.

[0067] In the present invention, a method for measuring the ratio of the area of the cavity of a hollow particle to the area of the entire inner side of the contour of the hollow particle will be described with reference to FIGS. 2 and 3. First, a scanning electron microscope (SEM) image of the cross-section of the negative electrode material for a lithium-ion secondary battery is obtained. Next, as shown in FIG. 2, an arbitrary hollow particle 11 is selected from the SEM image, and a circumscribed circle 12 of the selected particle (shown by a dotted line in the figure) is drawn, and the diameter 13 of the circumscribed circle is determined. Next, when the diameter 13 of the circumscribed circle of the selected hollow particle 11 is within ±20% of the average particle diameter (D50), as shown in FIG. 3, by image processing, the area of the entire inner side of the contour 14 of the hollow particle (the portion shown by diagonal lines in FIG. 3(A)) and the area of the inner side of the contour 15 of the cavity inside the hollow particle 11 (the portion shown by diagonal lines in FIG. 3(B)) are determined. Next, the ratio of the area of the inner side of the contour 15 of the cavity inside the hollow particle 11 to the area of the entire inner side of the contour 14 of the hollow particle is calculated. Then, until 10 hollow particles whose circumscribed circle diameter is within ±20% of the average particle diameter (D50) are obtained, the selection of the hollow particles and the calculation of the ratio of the area of the cavity of the hollow particle to the area of the entire inner side of the contour of the hollow particle are performed, and the obtained area ratios are averaged, and the average value is taken as the ratio of the area of the cavity of the hollow particle to the area of the entire inner side of the contour of the hollow particle. In FIGS. 2 and 3, for convenience of explanation, only the contours of the hollow particles and the cavities are shown, and the description of the heat-treated carbon black particles, the carbide of the thermosetting resin, and the inter-particle gaps in the outer shell layer is omitted.

[0068] In the negative electrode material for a lithium-ion secondary battery obtained by performing the method for producing a negative electrode material for a lithium-ion secondary battery of the present invention, the following particle density B (g / cm 3 ) with respect to the negative electrode material for a lithium-ion secondary battery obtained by mercury porosimetry measurement of the negative electrode material for a lithium-ion secondary battery 3The ratio (A / B) is preferably from 0.40 to 0.80. When the ratio (A / B) of the particle density A to the particle density B is from 0.40 to 0.80, it becomes possible to have a large cavity capable of retaining the electrolytic solution inside the particles while maintaining high diffusibility of lithium ions in the outer shell of the hollow particles. In the negative electrode material for a lithium ion secondary battery of the present invention, when the ratio (A / B) of the particle density A to the particle density B is 0.50 or more, voids through which lithium ions can easily move are maintained in the outer shell of the hollow particles, and when it is 0.70 or less, the particles can have a cavity capable of retaining the electrolytic solution inside. In the negative electrode material for a lithium ion secondary battery of the present invention, the ratio (A / B) of the particle density A to the particle density B serves as an index of the abundance of the cavities in the hollow particles.

[0069] In the present invention, the particle density A (g / cm 3 ) calculated from the pressure for filling the interparticle voids obtained by mercury porosimetry of the negative electrode material for a lithium ion secondary battery is determined by the following formula. Particle density A (g / cm 3 ) = C / (1 - C × D) (In the formula, C is the bulk density (g / cm 3 ) measured by filling the voids of the measurement sample with mercury in a state where almost no pressure is applied (0.51 psia) in mercury porosimetry, and D is the volume (cm 3 ) of mercury required per 1 g of the measurement sample for filling the voids by further applying pressure up to 357 psia after the measurement of C.) That is, the particle density A is the density before mercury penetrates into the gaps (500 nm or less) of the outer shell layer of the negative electrode material for a lithium ion secondary battery, and is the density of the hollow particles including the voids between the cavities and the outer shell.

[0070] The particle density A is determined by the following procedure. First, the measurement container of a mercury porosimeter is filled with the negative electrode material for a lithium ion secondary battery (measurement sample), the voids of the measurement sample are filled with mercury in a state where almost no pressure is applied (0.51 psia), and the bulk density C (g / cm 3) is measured. Next, by further introducing mercury by pressurizing the measurement sample in the mercury porosimeter up to 357 psia, voids of approximately 500 nm or more filled with mercury under pressurization at 357 psia are filled with mercury. Then, by further pressurizing up to 357 psia, the volume of mercury required to fill the voids, that is, after measuring the bulk density C, the volume of mercury further introduced to fill the voids filled with mercury under pressurization at 357 psia is converted per 1 g of the measurement sample, and "the volume D (cm 3 ) of mercury per 1 g of the measurement sample required to fill the voids by further pressurizing up to 357 psia after measuring C" is obtained. Next, the particle density A is calculated by "particle density A (g / cm 3 ) = C / (1 - C × D)".

[0071] In the present invention, the particle density B (g / cm 3 ) obtained by image analysis of a scanning electron microscope (SEM) image of the cross-section of the negative electrode material for a lithium-ion secondary battery is determined by the following formula. Particle density B (g / cm 3 ) = G(1 - E / (E + F)) (In the formula, E is the area of the voids in the outer shell layer in the SEM image, F is the total area of the heat-treated product of carbon black particles and the carbide (non-void part) of the thermosetting resin in the outer shell layer in the SEM image, and G is the true density (g / cm 3 ) measured by filling the voids of the measurement sample with mercury in a state pressurized to 59900 psia in mercury porosimetry.) That is, the particle density B is the density of the outer shell layer of the negative electrode material for a lithium-ion secondary battery including the voids in the outer shell layer, and is the density when it is assumed that all the particles are particles without cavities formed inside.

[0072] The particle density B is determined by the following procedure. First, obtain a scanning electron microscope (SEM) image of the cross-section of the negative electrode material for a lithium-ion secondary battery. Next, arbitrarily select hollow particles from the SEM image and determine the diameter of the circumscribed circle of the selected particles. When the obtained diameter of the circumscribed circle is within ±20% of the average particle diameter (D50), perform image analysis, draw the circumscribed rectangle of the selected hollow particle, perform monochrome image processing on the particles within the circumscribed rectangle, binarize it into black and white (voids are black), and then fill the outside of the outer contour (the contour of the hollow particle) and the inside of the inner contour (the contour of the cavity) black by image processing. Determine the total area E of the voids (black) and the area F of the non-voids (white) of the outer shell layer by image analysis. Also, measure the true density (g / cm 3 ) measured by filling the voids of the measurement sample with mercury under a pressure of 59900 psia in mercury porosimetry, and calculate the particle density using the formula "particle density (g / cm 3 ) = G(1 - E / (E + F))". Then, until 10 hollow particles with a circumscribed circle diameter within ±20% of the average particle diameter (D50) are obtained, select hollow particles and calculate the particle density, and average the obtained particle densities to obtain the particle density B calculated from the area of the void portion obtained by image analysis of the scanning electron microscope (SEM) image of the cross-section of the negative electrode material for the lithium-ion secondary battery in the negative electrode material for the lithium-ion secondary battery of the present invention.

[0073] In the present invention, a method for measuring the particle density B will be described with reference to FIGS. 2 and 4. First, a coating film with an arbitrary thickness is prepared from a slurry containing 25% polyvinylidene fluoride for a negative electrode material for a lithium-ion secondary battery, and a scanning electron microscope (SEM) image of the cross section is obtained. Next, as shown in FIG. 2, arbitrary hollow particles 11 are selected from the SEM image, a circumscribed circle 12 of the selected particles is drawn, and the diameter 13 of the circumscribed circle is obtained. Next, when the diameter 13 of the circumscribed circle of the selected hollow particle 11 is within ±20% of the average particle diameter (D50), as shown in FIG. 4, a circumscribed rectangle 25 of the selected hollow particle 11 is drawn. Next, monochrome image processing is performed on the particles within the circumscribed rectangle, binarized into black and white (voids are black), and further, the outside 24 of the outer contour and the inside 22 of the inner contour of the hollow cavity are filled with black by image processing, and the total area E of the void portions (black) and the area F of the non-void portions (white) of the outer shell layer are obtained by image analysis. Further, a negative electrode material for a lithium-ion secondary battery (measurement sample) is filled into the measurement container of a mercury porosimeter, and the voids of the measurement sample are filled with mercury under a pressure of 59900 psia, and the true density G (g / cm 3 ) is measured at a pressure of 59900 psia in mercury porosimetry. At this time, by pressurizing to 59900 psia in mercury porosimetry, the pores and internal cavities in the outer shell layer of the measurement sample are also filled with mercury. Next, the particle density is calculated by the formula "particle density (g / cm 3 ) = G(1 - E / (E + F))". Then, the selection of hollow particles and the calculation of the particle density are performed until there are 10 hollow particles whose circumscribed circle diameter is within ±20% of the average particle diameter (D50), and the obtained particle densities are averaged to obtain the particle density B. In FIGS. 2 and 4, for convenience of explanation, only the contours of the hollow particles and the contours of the cavities are shown, and the description of the heat-treated product of carbon black particles, the carbide of the thermosetting resin, and the inter-particle gaps in the outer shell layer is omitted.

[0074] The heat-treated product of carbon black particles is the main component constituting the outer shell layer of the negative electrode material for a lithium-ion secondary battery obtained by the method for manufacturing a negative electrode material for a lithium-ion secondary battery of the present invention. And since the outer shell layer of the hollow particles is formed of the heat-treated product of carbon black particles, the high-rate charge and discharge characteristics are improved.

[0075] Moreover, the negative electrode material for a lithium-ion secondary battery obtained by the method for producing a negative electrode material for a lithium-ion secondary battery of the present invention is made of a carbon material, has a hollow structure, contains hollow particles with a high sphericity, and thus has little reduction in initial efficiency, excellent cycle characteristics, and excellent high-rate charge and discharge characteristics. Since the negative electrode material for a lithium-ion secondary battery obtained by the method for producing a negative electrode material for a lithium-ion secondary battery of the present invention contains hollow particles, the formation of excessive inter-particle voids in the low-density electrode is suppressed, and a high conductive path is maintained, thereby increasing the initial efficiency and cycle characteristics, and also increasing the high-rate charge and discharge characteristics. The hollow particles contained in the negative electrode material for a lithium-ion secondary battery obtained by the method for producing a negative electrode material for a lithium-ion secondary battery of the present invention have a cavity inside, so that low density can be achieved without reducing the initial efficiency and cycle characteristics. In addition, the hollow particles contained in the negative electrode material for a lithium-ion secondary battery obtained by the method for producing a negative electrode material for a lithium-ion secondary battery of the present invention have an outer shell layer serving as a conductive path mainly composed of a heat-treated product of carbon black having many surface edge planes that mainly accept lithium ions. Therefore, the frequency of insertion and extraction of lithium ions between the electrolyte and the active material increases, and since the particle size is small, the diffusion rate of lithium ions in the active material also increases. As a result, the high-rate charge and discharge characteristics are improved.

[0076] In addition, the cavity in the hollow particles contributes to retaining the electrolyte inside the particles. Therefore, the negative electrode material for a lithium-ion secondary battery obtained by the method for producing a negative electrode material for a lithium-ion secondary battery of the present invention has an outer shell layer composed of a heat-treated product of carbon black particles and a carbide of a thermosetting resin, and contains hollow particles with a cavity formed inside, thereby improving the high-rate charge and discharge characteristics.

[0077] The initial capacity of the negative electrode material for a lithium ion secondary battery obtained by the method for producing a negative electrode material for a lithium ion secondary battery of the present invention is preferably 200 mAh / g or more. When the initial capacity of the negative electrode material for a lithium ion secondary battery is 200 mAh / g or more, it becomes possible to ensure sufficient energy density when the battery is assembled. The initial capacity of the negative electrode material for a lithium ion secondary battery obtained by the method for producing a negative electrode material for a lithium ion secondary battery of the present invention is particularly preferably 345 mAh / g or more in that it can further ensure sufficient energy density.

[0078] Examples are shown below to specifically explain the present invention, but the present invention is not limited to the examples shown below.

Examples

[0079] (Example 1) (Production of hollow particles) To 100 parts by mass of thermal black (manufactured by Cancarb, arithmetic average particle diameter 303 nm), 20 parts by mass of a water-soluble phenolic resin (manufactured by Sumitomo Bakelite) and 200 parts of water were added, and the mixture was placed in the feeder tank of a spray dryer (CL-8i manufactured by Ohkawara Seisakusho) while maintaining the raw material temperature at 40°C, and sprayed with a disk atomizer (MC-50) under the condition of a disk rotation speed of 40000 rpm. The sprayed liquid was dried with hot air at 180°C and then recovered by a cyclone, and the obtained hollow particles were fired at a temperature of 800°C and then fired at a temperature of 2400°C in a graphitization furnace to obtain hollow particles (test negative electrode material). Next, the obtained hollow particles were observed by scanning electron microscopy (SEM). The results are shown in Fig. 1.

[0080] (Example 2) Hollow particles (test negative electrode material) were prepared in the same manner as in Example 1 except that 30 parts by mass of the water-soluble phenolic resin was used.

[0081] (Example 3) Hollow particles (test negative electrode material) were prepared in the same manner as in Example 1 except that 40 parts by mass of the water-soluble phenolic resin was used.

[0082] (Comparative Example 1) To 100 parts by mass of thermal black (manufactured by Cancarb, arithmetic mean particle diameter 303 nm), 20 parts by mass of pitch (PKQL: manufactured by JFE Chemical, softening point 87 - 110°C) was added, and the mixture was put into a high-speed mixer (Mitsui Henschel Mixer FM10C / I type) and mixed at a peripheral speed of 10 m / s for 10 minutes. The obtained granulated product was fired at a temperature of 1000°C, and then fired in a graphitization furnace at a temperature of 2400°C to obtain a test negative electrode material.

[0083]

Table 1

[0084] (Analysis method) · SEM analyzer and conditions Analyzer: JSM7900F manufactured by JEOL Ltd. An electron beam accelerated at an acceleration voltage of 2 - 5 kV was applied to the sample to observe the secondary electron image. Cross-section data production apparatus: IB-19530CP manufactured by JEOL Ltd. The electrode sheet was cut into a predetermined size, and a mask was installed with respect to the processing position. By irradiating with an argon ion beam, it was cut along the edge of the mask. · Laser diffraction particle size distribution measuring apparatus and analysis conditions when obtaining the average particle diameter (D50) Analyzer: LA-960 manufactured by Horiba, Ltd. Light source: Semiconductor laser (650 nm) Distilled water or ethanol was appropriately selected, and the powder was dispersed by ultrasonic waves in a solution in which 10% by mass of an amphoteric surfactant was added to 100 parts by mass thereof. The dispersed powder was flowed into the measurement cell in the apparatus and irradiated with a laser. The particle size distribution was obtained by detecting and analyzing the scattered light with a ring-shaped detector. · Mercury porosimetry: manufactured by Shimadzu Access Co., Ltd. Analyzer: Mercury intrusion porosimeter: Autopore IV9510 type After drying the sample at 150 °C for 6 hours, approximately 0.5 g of the sample is placed in a cell, set at the low-pressure port, evacuated from atmospheric pressure to 30 μmHg, and then mercury is injected. Subsequently, the cell is transferred to the high-pressure port, and the bulk density C (g / cm 3 ) of the measurement sample powder is calculated from the amount of mercury injected into the cell in this almost non-pressurized state (0.51 psia). Subsequently, by applying pressure, the amount of mercury injected is increased, and the particle density A (g / cm 3 ) is measured from the amount of mercury when the pressure is increased to 357 psia. Further, by applying pressure, the amount of mercury injected is increased, and the density G (g / cm 3 ) is measured from the amount of mercury when the pressure is increased to 59900 psia.

[0085] (Evaluation method) (Fabrication of laminated battery) Using the working electrode and counter electrode described above, as an evaluation battery, a positive electrode (Li metal), a separator (polypropylene), and a negative electrode (test negative electrode material) are laminated in this order. Further, after attaching Ni tabs, the laminate is aluminum laminated, and the laminated battery is assembled in an inert atmosphere. The electrolyte used was a 1:1 mixed solution of ethylene carbonate (EC) and diethyl carbonate (DEC) in which 1 mol / dm 3 of the lithium salt LiPF6 was dissolved. Charging was carried out at a constant current with a current density of 0.2 mA / cm 2 . After finishing the constant current charging at a cut-off voltage of 5 mV, the potential is held constant until the lower limit current reaches 0.02 mA / cm 2 . Discharging was carried out at a constant current with a current density of 0.2 mA / cm 2 until the cut-off voltage reached 1.5 V. After 3 cycles, the discharge capacity was taken as the reversible capacity. The initial efficiency is the value (%) obtained by dividing the discharge capacity of the first cycle by the charge capacity of the first cycle. The 5C charge capacity is the charge capacity when fully charged in 12 minutes from the state of complete discharge after 3 cycles.

[0086] [Table 2] [Industrial applicability]

[0087] According to the present invention, a novel manufacturing method of a negative electrode material for a lithium ion secondary battery excellent in high-rate charge and discharge characteristics can be provided.

Explanation of Signs

[0088] 11 Hollow particle 12 Circumscribed circle 13 Diameter of the circumscribed circle 14 Outline of the hollow particle 15 Outline of the cavity 22 Inside the inner contour of the hollow cavity 24 Outside the outer contour 25 Circumscribed rectangle

Claims

1. A dispersion preparation step of preparing a raw material dispersion liquid containing 100 parts by mass of carbon black particles having a DBP oil absorption of 20 to 90 ml / 100 g and an arithmetic average particle diameter of 20 to 400 nm, 10 to 50 parts by mass of a thermosetting resin, and 100 to 300 parts by mass of an aqueous dispersion medium; A spray drying step of drying the raw material dispersion liquid at 100 to 300 °C by a spray drying method to obtain a spray dried product having a particle diameter of 5 to 30 μm; A firing step of firing the spray dried product at 800 to 3000 °C to obtain a negative electrode material for a lithium ion secondary battery; A method for manufacturing a negative electrode material for a lithium ion secondary battery, comprising the above steps.

2. The method for manufacturing a negative electrode material for a lithium ion secondary battery according to Claim 1, wherein the circularity determined by scanning electron microscope observation (SEM) of the negative electrode material for a lithium ion secondary battery is 0.850 or more.

3. The method for manufacturing a negative electrode material for a lithium ion secondary battery according to Claim 1 or 2, wherein the thermosetting resin is a phenol resin.

4. The method for manufacturing a negative electrode material for a lithium ion secondary battery according to any one of Claims 1 to 3, wherein the average particle diameter (D50) of the negative electrode material for a lithium ion secondary battery is 5.0 to 30.0 μm.

5. The BET specific surface area of the negative electrode material for the lithium ion secondary battery is 3.00 to 7.00 m ２ / g, and the method for manufacturing a negative electrode material for a lithium ion secondary battery according to any one of claims 1 to 4.

6. In the scanning electron microscope (SEM) image of the cross section of the negative electrode material for a lithium ion secondary battery, the ratio of the area of the cavity to the entire area inside the contour of the hollow particles in the negative electrode material for a lithium ion secondary battery is 30 to 60%. The method for manufacturing a negative electrode material for a lithium ion secondary battery according to any one of Claims 1 to 5.

7. The following particle density B (g / cm obtained by image analysis of a scanning electron microscope (SEM) image of the cross-section of the negative electrode material for the lithium ion secondary battery ３ ), and the following particle density A (g / cm obtained by mercury porosimetry measurement of the negative electrode material for the lithium ion secondary battery ３ ), and the ratio (A / B) is 0.40 to 0.

80. The method for manufacturing a negative electrode material for a lithium ion secondary battery according to any one of claims 1 to 6 <Particle density A> Particle density A (g / cm ３ ) = C / (1 - C × D) (In the formula, C is the bulk density (g / cm measured by filling the voids of the measurement sample with mercury in a state where it is hardly pressurized (0.51 psia) in mercury porosimetry ３ ), and D is the volume per gram of the measurement sample of mercury required to fill the voids by further pressurizing to 357 psia after the measurement of C (cm ３ ).)) <Particle density B> Particle density B (g / cm ３ ) = G(1 - E / (E + F)) (In the formula, E is the area of voids in the outer shell layer of the hollow particles in the SEM image, F is the total area of the heat-treated product of carbon black particles and the heat-treated product of the binder in the outer shell layer of the hollow particles in the SEM image, and G is the true density (g / cm ３ ) measured by filling the voids of the measurement sample with mercury in a state where the pressure is increased to 59900 psia in mercury porosimetry measurement.)

8. The method for manufacturing a negative electrode material for a lithium ion secondary battery according to any one of Claims 1 to 7, wherein the number ratio of hollow particles to all particles in the negative electrode material for a lithium ion secondary battery is 50% or more.

Images