Carbon material composition, negative electrode, and secondary battery

Abstract

The present invention relates to a carbon material composition in which the proportion of particles having a volume-based particle size distribution of 3 μm or less is 16.0-40.0%, and the maximum torque in measurement of the oil absorption amount for linseed oil is 13.0 N⋅m or less. The present invention also relates to a carbon material composition in which the proportion of particles having a volume-based particle size distribution of 3 μm or less is 16.0-40.0%, wherein the ratio (SAe / SAp) of the specific surface area SAe when the carbon material composition is formed into an electrode plate to the specific surface area SAp of the carbon material composition in powdered form is 0.70-1.00 (the specific surface area SAe is the specific surface area of the electrode plate in which the carbon material composition is used).

Description

Carbon material composition, negative electrode and secondary battery

[0001] The present invention relates to a carbon material composition, a negative electrode, and a secondary battery.

[0002] In recent years, the demand for high-capacity secondary batteries has increased with the miniaturization of electronic devices. In particular, secondary batteries, especially lithium-ion secondary batteries, have attracted attention because they have higher energy density and superior charge / discharge characteristics than nickel-cadmium batteries and nickel-metal hydride batteries. Lithium-ion secondary batteries include positive and negative electrodes that can absorb and release lithium ions, as well as LiPF ６ and LiBF ４ Non-aqueous lithium secondary batteries using a non-aqueous electrolyte solution in which lithium salts such as those mentioned above are dissolved have been developed and put to practical use.

[0003] While improvements in the performance of lithium-ion secondary batteries have been widely studied, in recent years, there has been a demand for even higher performance for lithium-ion secondary batteries. For example, Patent Document 1 discloses a negative electrode material in which the pore volume within particles per coating rate and the peak value of the voids within particles are controlled.

[0004] International Publication No. 2023 / 181705

[0005] As in Patent Document 1, by mixing a certain number or more of particles having a small particle diameter peak relative to a certain particle diameter, electrical contact between the particles is maintained, resulting in a high capacity retention rate for the battery. However, the carbon material in Patent Document 1 has the problem of deteriorating rapid charge / discharge characteristics.

[0006] The present invention has been made in view of the above problems, and an object of the present invention is to provide a carbon material composition that suppresses deterioration in rapid charge / discharge characteristics of a negative electrode using the carbon material composition and that is excellent in capacity retention rate of a battery.

[0007] As a result of extensive research to solve the above problems, the present inventors have found that by using a carbon material composition described below, it is possible to suppress deterioration of rapid charge / discharge characteristics of a negative electrode and obtain a carbon material composition that is excellent in capacity retention rate of a battery, and have thereby completed the present invention.

[0008] That is, the gist of the present invention is as follows.

[0009] A first aspect of the present invention is a carbonaceous material composition having a ratio of particles of 3 μm or less in a volumetric particle size distribution of 16.0 to 40.0% and a maximum torque of 13.0 N·m or less in a linseed oil absorption measurement.

[0010] A second aspect of the present invention is a carbonaceous material composition having a ratio of particles of 3 μm or less in a volumetric particle size distribution of 16.0 to 40.0%, wherein a ratio (SAe / SAp) of a specific surface area SAe when the carbonaceous material composition is made into an electrode plate to a specific surface area SAp of the powdered carbonaceous material composition is 0.70 to 1.00. (Here, the specific surface area SAe is the specific surface area of ​​an electrode plate using the carbonaceous material composition.) Note that the second aspect of the present invention may or may not satisfy the requirements of the carbonaceous material composition of Aspect 1, as long as it satisfies the above requirements.

[0011] A third aspect of the present invention is the carbonaceous material composition of the first or second aspect, wherein the proportion of particles having a size of 3 μm or less in the volumetric particle size distribution is 25.0 to 40.0%.

[0012] A fourth aspect of the present invention is the carbon material composition of the second or third aspect, wherein a ratio (SAe / SAp) of a specific surface area SAe when the carbon material composition is made into an electrode plate to a specific surface area SAp of the powdered carbon material composition is 0.70 to 0.89.

[0013] A fifth aspect of the present invention is the carbonaceous material composition according to any one of the first to fourth aspects, wherein the degree of circularity is 0.85 or more.

[0014] A sixth aspect of the present invention is the carbon material composition of any one of the first to fifth aspects, wherein the electrode plate using the carbon material composition is 1.54 g / cm ３ The carbon material composition is pressed with a load of 640 to 750 kgf / 5 cm.

[0015] A seventh aspect of the present invention is the carbon material composition according to any one of the first to sixth aspects, wherein the electrode plate using the carbon material composition is 1.54 g / cm ３ The carbon material composition is pressed with a load of 640 to 700 kgf / 5 cm.

[0016] Aspect 8 of the present invention is the carbon material composition of any one of Aspects 1 to 7, wherein the carbon material composition contains a carbon material (A) and a carbon material (B), the carbon material (A) and the carbon material (B) contain graphite, the carbon material (B) is a conductive additive, and the carbon material (A) is a carbon material different from the carbon material (B).

[0017] A ninth aspect of the present invention is the carbon material composition of the eighth aspect, wherein the carbon material (A) comprises graphite (A1), and the graphite (A1) is graphite coated with at least one of an amorphous carbonaceous material and a graphitic material.

[0018] A tenth aspect of the present invention is the carbon material composition of Aspect 9, wherein a total content of at least one of the amorphous carbonaceous material and the graphite material is 0.1 to 15 mass% relative to 100 mass% of the graphite (A1).

[0019] Aspect 11 of the present invention is the carbon material composition of aspect 9 or 10, wherein the tap density of the graphite (A1) is 1.00 g / cm ３ The carbon material composition is as described above.

[0020] A twelfth aspect of the present invention is the carbon material composition of any one of Aspects 9 to 11, wherein the specific surface area of ​​the graphite (A1) is 3.5 m ２ / g or less.

[0021] A thirteenth aspect of the present invention is the carbonaceous material composition according to any one of Aspects 9 to 12, wherein the graphite (A1) has a volume-based average particle size D50 of 13 μm or more and 17 μm or less.

[0022] A fourteenth aspect of the present invention is the carbon material composition of any one of Aspects 8 to 13, wherein the carbon material (A) comprises spheroidized graphite (A2).

[0023] A fifteenth aspect of the present invention is the carbon material composition of the fourteenth aspect, wherein the tap density of the spherical graphite (A2) is 0.80 g / cm ３ The carbon material composition is as described above.

[0024] A sixteenth aspect of the present invention is the carbon material composition of the fourteenth or fifteenth aspect, wherein the specific surface area of ​​the spherical graphite (A2) is 3.5 m ２ / g or more.

[0025] A seventeenth aspect of the present invention is the carbonaceous material composition according to any one of Aspects 14 to 16, wherein the volume-based average particle size D50 of the spherical graphite (A2) is 14 μm or more and 18 μm or less.

[0026] Aspect 18 of the present invention is the carbon material composition of any one of Aspects 8 to 17, wherein the carbon material (B) comprises artificial graphite (B1).

[0027] A nineteenth aspect of the present invention is the carbon material composition of the eighteenth aspect, wherein the tap density of the artificial graphite (B1) is 0.95 g / cm ３ The carbon material composition is as described above.

[0028] Aspect 20 of the present invention is the carbon material composition of aspect 18 or 19, wherein the specific surface area of ​​the artificial graphite (B1) is 2.5 m ２ / g or more.

[0029] A twenty-first aspect of the present invention is the carbonaceous material composition according to any one of Aspects 18 to 20, wherein the artificial graphite (B1) has a volume-based average particle size D50 of 7 μm or more and 12 μm or less.

[0030] A twenty-second aspect of the present invention is the carbonaceous material composition of any one of Aspects 8 to 21, wherein a ratio of the content of the carbonaceous material (B) to 100 parts by mass of the carbonaceous material (A) is 0.01 parts by mass to 30 parts by mass.

[0031] A twenty-third aspect of the present invention is the carbonaceous material composition of any one of the eighth to twenty-second aspects, wherein the tap density of the carbonaceous material composition is 0.80 g / cm ３ The carbon material composition is as described above.

[0032] A twenty-fourth aspect of the present invention is the carbonaceous material composition of any one of Aspects 8 to 23, wherein the powdery carbonaceous material composition has a specific surface area SAp of 3.0 m ２ / g or more, 5.0m ２ / g or less.

[0033] A twenty-fifth aspect of the present invention is the carbonaceous material composition according to any one of Aspects 8 to 24, wherein the linseed oil absorption of the carbonaceous material composition is 41.1 mL / 100 g or less.

[0034] A twenty-sixth aspect of the present invention is the carbonaceous material composition according to any one of Aspects 8 to 25, wherein the carbonaceous material composition has a volume-based average particle size D50 of 13 μm or more and 17 μm or less.

[0035] A twenty-seventh aspect of the present invention is a negative electrode comprising: a current collector; and an active material layer formed on the current collector; wherein the active material layer comprises the carbon material composition of any one of Aspects 1 to 26.

[0036] A twenty-eighth aspect of the present invention is a secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, wherein the negative electrode is the negative electrode of Aspect 27.

[0037] By using the carbon material composition of the present invention for the negative electrode, deterioration of rapid charge / discharge characteristics can be suppressed, and the carbon material composition of the present invention is excellent in capacity retention rate of the battery.

[0038] The present invention will be described in detail below, but these are merely examples of desirable embodiments and are not intended to limit the scope of the present invention. The term "to" in a numerical range includes the preceding and following numerical values. For example, "0 to 100% by mass" and "0% by mass to 100% by mass" mean ranges of 0% by mass or more and 100% by mass or less. Numerical ranges such as "A to B," "A or more," and "B or less" disclosed herein disclose numerical ranges in which the upper and lower limits are arbitrarily selected. "A or more" means "greater than A and / or A," and also discloses a numerical range of "greater than A." Similarly, "B or less" means "smaller than B and / or B," and also discloses a numerical range of "smaller than B."

[0039] [Carbon material composition] In the carbon material composition of the first embodiment of the present invention, the ratio of particles having a size of 3 μm or less in the volumetric particle size distribution is 16.0 to 40.0%, and the maximum torque in a linseed oil absorption measurement of the carbon material composition is 13.0 N m or less.

[0040] A carbonaceous material composition according to a second embodiment of the present invention is a carbonaceous material composition in which the proportion of particles of 3 μm or less in the volumetric particle size distribution is 16.0 to 40.0%, and the ratio (SAe / SAp) of the specific surface area SAe when the carbonaceous material composition is made into an electrode plate to the specific surface area SAp of the powdered carbonaceous material composition is 0.70 to 1.00 (here, the specific surface area SAe is the specific surface area of ​​an electrode plate using the carbonaceous material composition, and the density of the active material layer of the electrode plate is 1.54±0.03 g / cm). ３ It is preferable that the specific surface area of ​​the electrode plate is adjusted to

[0041] In this specification, the term "carbon material composition of the present embodiment" means at least one of the carbon material compositions of the above-mentioned "carbon material composition of the first embodiment of the present invention" and "carbon material composition of the second embodiment of the present invention."

[0042] The carbon material composition of this embodiment is in powder form. In the carbon material composition of this embodiment, the proportion of particles of 3 μm or less in the volumetric particle size distribution is 16.0 to 40.0%, preferably 20.0 to 40.0%, and more preferably 25.0 to 40.0%. Having the proportion of particles of 3 μm or less in the above range has the advantage of being able to improve the contact area between particles. The proportion of particles of 3 μm or less in the volumetric particle size distribution can be measured using a flow particle image analyzer.

[0043] The volume-based average particle diameter D50 of the carbon material composition is preferably 13 to 17 μm, more preferably 14 to 16 μm. Here, in order to prevent an increase in irreversible capacity and a loss of initial battery capacity, the volume-based average particle diameter D50 of the carbon material composition is preferably 15 μm or more. This can suppress process defects such as streaking during electrode plate production, and provides excellent rapid charge / discharge characteristics and low-temperature input / output characteristics.

[0044] The tap density of the carbon material composition is 0.80 g / cm ３More than this is preferred, with 0.90 to 1.50 g / cm ３ More preferably, 1.10 to 1.40 g / cm ３ By satisfying this value, process defects such as creases during electrode plate production can be suppressed, the packing property is improved, which makes it easier to form a high-density negative electrode sheet with good rollability, the degree of curvature of the lithium ion migration path when formed into an electrode body is reduced, and the shape of the voids between the particles is regular, which allows for smooth migration of the electrolyte solution and improves rapid charge / discharge characteristics.

[0045] The ratio of the tap density of the carbon material composition to the tap density of the carbon material (A) (tap density of the carbon material composition / tap density of the carbon material (A)) is preferably 0.5 or more, more preferably 1.0 to 1.5.

[0046] In the carbon material composition of the present embodiment, the maximum torque in measuring the oil absorption of linseed oil of the carbon material composition is preferably 13.0 N m or less. When the carbon material composition has this value, the solid content of the negative electrode active material layer becomes uniform, the diffusion distance between the active materials increases, and the rapid charge / discharge characteristics of the negative electrode using this carbon material become excellent.

[0047] The maximum torque in measuring the linseed oil absorption of the carbon material composition is preferably 10 to 13.0 N·m, more preferably 11.0 to 12.5 N·m.

[0048] In this specification, "maximum torque in linseed oil absorption measurement of a carbon material composition" refers to the maximum torque value during measurement in a linseed oil absorption measurement in accordance with ISO 4546. In this linseed oil absorption measurement, the torque value of the carbon material composition changes depending on the amount of linseed oil mixed in. The maximum value of the changing torque value is defined as "maximum torque in linseed oil absorption measurement." Note that 70% by volume of the linseed oil absorption showing the maximum torque is defined as "linseed oil absorption."

[0049] The linseed oil absorption of the carbonaceous material composition is preferably 41.1 mL / 100 g or less, more preferably 30.0 to 40.0 mL / 100 g.

[0050] The ratio of the maximum torque in measuring the oil absorption of linseed oil of the carbon material composition to the maximum torque in measuring the oil absorption of linseed oil of the carbon material (A) described below (maximum torque in measuring the oil absorption of linseed oil of the carbon material composition / maximum torque in measuring the oil absorption of linseed oil of the carbon material (A)) is preferably 1.0 or less, more preferably 0.7 to 0.98.

[0051] The carbon material of this embodiment preferably satisfies at least one of the following formulas (1) and (2): 0.10≦SAe / SAp≦1.00 (1) 1≦α≦10 (2) In formula (1), SAe / SAp is the ratio (SAe / SAp) of the specific surface area SAe when the carbon material composition is made into an electrode plate to the specific surface area SAp of the powdered carbon material composition. The specific surface area SAe is the specific surface area at the inflection point of the load-density curve when an electrode plate using the carbon material composition is pressed. In formula (2), α is the press density of the carbon material, 1.3 g / cm ３ ~1.7g / cm ３ In this specification, the specific surface area SAp of the powdered carbon material composition is also referred to as a powder specific surface area SAp, and the specific surface area SAe of an electrode plate made from the carbon material composition is also referred to as an electrode plate specific surface area SAe.

[0052] The powder specific surface area SAp of the carbon material composition is 3.0 m ２ / g to 5.0m ２ / g is preferred, and 3.5 to 4.5m ２ Here, the specific surface area of ​​the carbonaceous material composition is preferably 3.0 m / g, since this ensures a portion through which lithium ions can enter and exit, and the carbonaceous material composition is excellent in rapid charge / discharge characteristics and low-temperature input / output characteristics. ２ In addition, the specific surface area of ​​the carbonaceous material composition is preferably 5.0 m / g or more, because this suppresses side reactions with the electrolyte, prevents a decrease in the initial charge / discharge efficiency and an increase in the amount of gas generated, and improves the battery capacity. ２ / g or less is preferred.

[0053] The specific surface area SAe of the electrode plate of the carbon material composition is 0.5 m because it has excellent rapid charge / discharge characteristics and low-temperature input / output characteristics. ２ / g or more is preferable, and 1.0m ２ / g or more is more preferable, and 3.5 m ２ / g or less is preferable, and 3.0m ２ / g or less is more preferable.

[0054] The ratio (SAe / SAp) of the electrode plate specific surface area SAe to the powder specific surface area SAp of the carbon material composition is preferably 0.70 to 1.00, more preferably 0.70 to 0.95, even more preferably 0.70 to 0.89, particularly preferably 0.70 to 0.85, and particularly preferably 0.70 to 0.80, in order to suppress side reactions with the electrolyte and to achieve an excellent capacity retention rate.

[0055] In this specification, the specific surface area SAe of the electrode plate is a value measured by the BET method. Specifically, using a specific surface area measuring device, an electrode plate using a carbon material composition is pre-dried under reduced pressure at 100°C for 30 minutes in a nitrogen flow, cooled to the temperature of liquid nitrogen, and measured by the nitrogen adsorption BET single-point method using a gas flow method with a nitrogen-helium mixed gas accurately adjusted so that the relative pressure of nitrogen to atmospheric pressure is 0.3.

[0056] The electrode plate was prepared by applying a slurry prepared by the following method to a copper foil having a thickness of 10 μm as a current collector in a manner that the negative electrode material was 10.00 mg / cm ２ The active material layer is then coated to a width of 10 cm using a die coater, dried, cut to a width of 5 cm, and roll-pressed using a roller with a diameter of 20 cm to obtain a predetermined active material layer density. The load of the roll press is called the press load. The active material layer density is adjusted to at least 1.50 g / cm. ３ The pressing load required to achieve an active material layer density of 1.54 g / cm is preferably 600 to 1000 kgf / 5 cm, more preferably 600 to 900 kgf / 5 cm, and even more preferably 600 to 800 kgf / 5 cm. ３ The pressing load required to achieve this is preferably 640 to 750 kgf / 5 cm, and more preferably 640 to 700 kgf / 5 cm.

[0057] The slurry was prepared by mixing 50.00 g of the carbonaceous material composition of the present embodiment with 50.00 g of a 1 mass % aqueous solution of carboxymethyl cellulose sodium salt (0.50 g in terms of solid content) and 1.00 g of an aqueous dispersion of styrene-butadiene rubber having a weight-average molecular weight of 270,000 (0.50 g in terms of solid content) using a hybrid mixer for 5 minutes and degassing for 30 seconds.

[0058] The carbon material composition of the present embodiment maintains a suitable void structure when pressed into an electrode plate and has excellent discharge load characteristics. Therefore, the rate of change α of the degree of bending is preferably 1 to 7, more preferably 1 to 6, still more preferably 1 to 5, and particularly preferably 1 to 4.

[0059] In this specification, a press density of 1.3 g / cm ３ ~1.7g / cm ３ The rate of change in the degree of bending in this range is calculated by impedance response analysis. The impedance response analysis is performed using an impedance analyzer, with measurements being performed at a frequency of 20 kHz to 10 mHz and a voltage amplitude of 10 mV. The ionic resistance Rion of the active material layer of the negative electrode sheet is obtained by using the intersection of a 45° line in the high frequency region and a vertical line in the low frequency region on the Cole-Cole plot. The area of ​​the negative electrode sheet is S, the thickness of the active material layer of the negative electrode sheet is L, the conductivity of the electrolyte is σ, and the porosity of the active material layer is ε, and the degree of bending is calculated from the following formula (5): Degree of bending = Rion × (ε / 2 × L) × (σ × S) (5) Using the calculated degree of bending, the press density of 1.3 g / cm is calculated from the following formula (6). ３ ~1.7g / cm ３ The rate of change in the degree of bending is calculated in the range of [rate of change in degree of bending] = [amount of change in degree of bending] / [amount of change in press density] (6)

[0060] The circularity of the carbon material composition is preferably 0.85 or more, more preferably 0.87 or more, even more preferably 0.88 or more, and particularly preferably 0.89 or more. By satisfying the above range, the tortuosity of lithium ion diffusion is reduced, the movement of the electrolyte into the voids between the particles is smooth, and rapid charge / discharge characteristics are excellent. Furthermore, the circularity of the carbon material composition is preferably 0.99 or less, more preferably 0.95 or less, and even more preferably 0.90 or less. That is, the circularity of the carbon material composition is preferably 0.85 or more and 0.99 or less. By satisfying the above range, contact between the carbon materials can be ensured and cycle characteristics are excellent, and the circularity can be measured by the method described below.

[0061] The cumulative pore volume of the carbon material composition is preferably 0.003 to 0.120 mL / g, more preferably 0.005 to 0.090 mL / g, and even more preferably 0.010 to 0.070 mL / g. Here, the cumulative pore volume of the carbon material composition is preferably 0.003 mL / g or more and 0.120 mL / g or less, because it is moderately easy to deform when pressed.

[0062] The pellet density of the carbon material composition is 1.40 to 1.80 g / cm ３ is preferred, and 1.50 to 1.70 g / cm ３ More preferably, 1.55 to 1.60 g / cm ３ Here, since the carbon material composition is easily deformed during pressing, the pellet density of the carbon material composition is preferably 1.40 g / cm. ３ More preferably, 1.80 g / cm ３ The following is preferred:

[0063] The carbon material composition of the present embodiment is a carbon material composition containing a carbon material (A) and a carbon material (B), wherein the carbon material (A) and the carbon material (B) contain graphite, the carbon material (B) is a conductive additive, and the carbon material (A) is a different carbon material from the carbon material (B). By containing the carbon material (B), which is a conductive additive, in addition to the carbon material (A), electrical contact between carbon material particles can be maintained, and the capacity retention rate of the battery tends to be excellent.

[0064] <Carbon material (A)> (Graphite (A1)) The carbon material (A) preferably contains graphite (A1). The graphite (A1) is graphite coated with at least one of an amorphous carbonaceous material and a graphitic material.

[0065] The total content of at least one of the amorphous carbonaceous material and the graphite material relative to 100 mass% of graphite (A1) is preferably 0.1 to 15 mass%. Herein, the total content of at least one of the amorphous carbonaceous material and the graphite material relative to 100 mass% of graphite (A1) is also referred to as the coating ratio.

[0066] The coating rate (%) of graphite (A1) is preferably 0.1 to 15, more preferably 1 to 12, even more preferably 2 to 10, and even more preferably 3 to 8. Here, the coating rate (%) is preferably 0.1 or more because it allows lithium ions to move smoothly from the graphite and provides excellent rapid charge / discharge characteristics and low-temperature input / output characteristics. Furthermore, the coating rate (%) is preferably 15 or less because the proportion of graphite is sufficient and it is easy to achieve a high capacity.

[0067] In this specification, the coating ratio (%) is calculated by the following formula (1). That is, it is calculated from the mixing ratio of graphite to at least one of an amorphous carbonaceous material and a graphitic material, and the firing yield after firing. Coating ratio (%) = ([mass of sample after firing - mass of graphite] / [mass of sample after firing]) x 100 (1)

[0068] When the mixing ratio and the firing yield are unknown, the coating ratio (%) is estimated using the difference in true density between the graphite and at least one of the amorphous carbonaceous material and the graphitic material. Specifically, the crystallinity of the graphite in the carbon material is confirmed by the d002 value, and if the graphite is highly crystalline with a d002 value of 3.357 Å or less, the coating ratio (%) is estimated using the following formula (2): Coating ratio (%) = 596.72 - 264.02 × true density (2)

[0069] The theoretical d002 value of graphite is 3.354 Å, and natural graphite with high crystallinity has 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 raw coke and the graphitization temperature.

[0070] The d002 value of graphite (A1) is preferably 3.357 Å or less, more preferably 3.356 Å or less, and even more preferably 3.354 Å, because graphite is highly crystalline and has sufficient charge / discharge capacity.

[0071] The Lc of graphite (A1) is preferably 900 Å or more, more preferably 1000 Å or more, because graphite is highly crystalline and has sufficient charge / discharge capacity. The upper limit of Lc is not particularly limited, but is usually 1000 Å as the upper limit for measurement accuracy.

[0072] In this specification, the d002 value is the value of the interplanar spacing of the lattice plane (002 plane) measured by X-ray diffraction according to the Gakushin method, and Lc is the value of the crystallite size measured by X-ray diffraction according to the Gakushin method. The X-ray diffraction measurement conditions are as follows: Sample: A mixture of the measurement object and X-ray standard high-purity silicon powder, with approximately 15 mass% of the total amount added. X-ray: CuKα ray. Measurement range: 20°≦2θ≦30°. Step angle: 0.013°. Sample preparation: A powder sample was filled into a recess in a sample plate with a depth of 0.2 mm to prepare a flat sample surface.

[0073] In this specification, the true density is a value measured by a liquid phase displacement method (pycnometer method) using butanol. The true density is measured five times, and the average value is used.

[0074] The true density of graphite (A1) is 2.200 g / cm because it has excellent packing property and capacity. ３ More preferably, 2.210 g / cm ３ More preferably, 2.220 g / cm ３ The theoretical true density of graphite is 2.262 g / cm ３ is.

[0075] (Physical Properties of Graphite (A1)) The volume-based average particle diameter D50 of graphite (A1) is preferably 13 to 17 μm, more preferably 13.5 to 16.5 μm. Here, in order to prevent an increase in irreversible capacity and a loss in initial battery capacity, the volume-based average particle diameter of graphite (A1) is preferably 13 μm or more. Furthermore, in order to suppress process defects such as streaking during electrode plate production and to achieve excellent rapid charge / discharge characteristics and low-temperature input / output characteristics, the volume-based average particle diameter of graphite (A1) is preferably 17 μm or less.

[0076] In this specification, the volume-based average particle size D50 is the volume-based median diameter measured by a laser diffraction / scattering particle size distribution analyzer. Specifically, 0.01 g of a sample is suspended in 10 mL of a 0.2 mass % aqueous solution of a surfactant, polyoxyethylene sorbitan monolaurate, and the suspension is introduced into a laser diffraction / scattering particle size distribution analyzer. After irradiating the suspension with 28 kHz ultrasonic waves at an output of 60 W for 1 minute, the volume-based median diameter is measured by the laser diffraction / scattering particle size distribution analyzer.

[0077] The specific surface area (SA) of graphite (A1) is 3.5 m ２ / g or less, and 0.5 to 3.3 m ２ / g is more preferable, and 1.0 to 3.0 m ２ / g is more preferable, and 1.0m ２ / g or more 3.0m ２ Here, the specific surface area of ​​the graphite (A1) is preferably 0.5 m / g or less, because this ensures a portion through which lithium ions can enter and exit, and the graphite (A1) is excellent in rapid charge / discharge characteristics and low-temperature input / output characteristics. ２ In addition, the specific surface area of ​​graphite (A1) is preferably 3.5 m / g or more, because this suppresses side reactions with the electrolyte, prevents a decrease in the initial charge / discharge efficiency and an increase in the amount of gas generated, and improves the battery capacity. ２ / g or less is preferred.

[0078] In this specification, the specific surface area (SA) is a value measured by the Brunauer-Emmett-Teller (BET) method. Specifically, using a specific surface area measuring device, a sample is pre-dried under reduced pressure at 350°C for 15 minutes in a nitrogen stream, cooled to liquid nitrogen temperature, and measured by the nitrogen adsorption BET single-point method using a gas flow method with a nitrogen-helium mixed gas precisely adjusted so that the relative pressure of nitrogen to atmospheric pressure is 0.3.

[0079] The tap density of graphite (A1) is 1.00 g / cm ３ More preferably, 1.15 to 1.40 g / cm ３ More preferably, 1.17 to 1.35 g / cm ３ is more preferably 1.20 to 1.30 g / cm ３Here, the tap density of graphite (A1) is particularly preferably 1.00 g / cm because it can suppress process defects such as creases during electrode plate production, improves packing properties, and therefore makes it easy to form a high-density negative electrode sheet with good rollability, reduces the degree of curvature of the lithium ion migration path when formed into an electrode body, and improves the shape of the voids between the particles, thereby smoothing the migration of the electrolyte and improving the rapid charge / discharge characteristics. ３ Furthermore, since the particles have an appropriate amount of space on the surface and inside thereof, the particles do not become too hard and have excellent electrode pressability, and are excellent in rapid charge / discharge characteristics and low-temperature input / output characteristics, the tap density of graphite (A1) is 1.40 g / cm ３ The following is preferred:

[0080] In this specification, the tap density is defined as the density calculated from the volume and mass of the sample when a powder density measuring instrument is used, in which a sample is filled into a cylindrical container (chamber), the chamber is rotated to agitate the sample, and a constant pressure is applied by a piston.

[0081] The value obtained by subtracting the tap density from the pellet density of graphite (A1) is 0.10 to 0.80 g / cm ３ is preferably 0.15 to 0.60 g / cm ３ More preferably, 0.20 to 0.40 g / cm ３ Here, the difference is more preferably 0.10 g / cm because the particles can be pressed to a high density without being too hard. ３ Furthermore, since the particles have an appropriate hardness and are not excessively crushed on the electrode surface even when pressed at high density, the electrolyte moves smoothly, and the difference is preferably 0.80 g / cm or more. ３ The following is preferred:

[0082] In this specification, the value obtained by subtracting the tap density from the pellet density is calculated by the following formula (3). The value obtained by subtracting the tap density from the pellet density represents the tendency for clogging when a load is applied, and can be used as an index of particle hardness. The value obtained by subtracting the tap density from the pellet density (g / cm ３ ) = pellet density - tap density (3)

[0083] In this specification, the pellet density is a value measured by the following method. Two types of jigs, a pushing jig with a shaft of 10 mm diameter and 35 mm length and a receiving jig with a shaft of 10 mm diameter and 6 mm length, are inserted into a mold with an inner diameter of 10 mm, and then the mold is set in a device capable of measuring the load and height when clamped. A load of 15 kgf is applied using a hydraulic pump, and the jig height is measured. Thereafter, only the pushing jig is removed, 0.6 g of carbon material is added, and the pushing jig is inserted again. The mold is set on a hydraulic jack, the pressure valve is closed, and a pressure of 0.9 t / cm is applied. ２ The pressure was gently increased to 2.4 t / cm ２ After quickly applying pressure to the specified pressure, hold the pressure for 3 seconds, release the hydraulic jack, wait 60 seconds, and then loosen the pressure valve to reduce the pressure. The jig is then set back into a device capable of measuring the load and height at the time of clamping, a load of 15 kgf is applied using a hydraulic pump, and the jig height after pressurization is measured. The mass of the carbon material after pressurization is also measured, and the density calculated from the difference in the jig height and the mass is used as the pellet density. The load per unit area is calculated from the scale on the hydraulic jack, the cylinder diameter of the hydraulic jack, and the inner diameter of the mold.

[0084] The pellet density of graphite (A1) is 1.30 to 1.79 g / cm ３ is preferred, and 1.40 to 1.70 g / cm ３ Here, the pellet density is more preferably 1.30 g / cm ３ More preferably, 1.40 g / cm ３ More preferably, 1.79 g / cm ３ Preferably, 1.70 g / cm or less ３ The following is more preferred:

[0085] The circularity of graphite (A1) is preferably 0.88 to 0.99, more preferably 0.90 to 0.98, and even more preferably 0.92 to 0.97. Here, the circularity of graphite (A1) is preferably 0.88 or more, since this reduces the tortuosity of lithium ion diffusion, facilitates smooth movement of the electrolyte into the voids between particles, and provides excellent rapid charge / discharge characteristics. Furthermore, the circularity of graphite (A1) is preferably 0.99 or less, since this ensures contact between carbon materials and provides excellent cycle characteristics.

[0086] In this specification, the circularity is calculated by measuring the particle size distribution of the circle-equivalent diameter by flow particle image analysis and using the following formula (4). Specifically, a dispersion is obtained by using ion-exchanged water as a dispersion medium and polyoxyethylene sorbitan monolaurate as a surfactant and dispersing with ultrasonic waves. Then, the shape of the particles is photographed using a flow image analyzer. From images of at least 1,000 particles, the circularities of particles with circle-equivalent diameters in the range of 1.5 μm to 40 μm are averaged to obtain the circularity. [Circularity] = [Peripheral length of an equivalent circle having the same area as the projected shape of a particle] / [Actual periphery of the projected shape of a particle] (4)

[0087] (Method for Producing Graphite (A1)) The method for producing graphite (A1) is not particularly limited as long as it is a method that can produce graphite coated with at least one of an amorphous carbonaceous material and a graphitic material. For example, a method in which a raw carbonaceous material is spheroidized in the presence of a granulating agent, pressurized, and impregnated with at least one of an amorphous carbon precursor and a graphitic material precursor is preferred, as this method can make the pores in the particles dense and efficiently reduce the cumulative pore volume. Specifically, a production method including the following steps (1) to (7) is preferred. Step (1): A step of adjusting the particle size of the raw carbonaceous material; Step (2): A step of mixing the raw carbonaceous material with a granulating agent; Step (3): A step of spheroidizing the raw carbonaceous material; Step (4): A step of removing the granulating agent; Step (5): A step of pressurizing; Step (6): A step of impregnating an amorphous carbonaceous material or a graphitic material; and Step (7): A step of mixing a plurality of carbonaceous materials.

[0088] Steps (1) to (7) will be described below, but steps other than steps (1) to (7) may be included before or after each step, and the production method is not limited to steps (1) to (7).

[0089] (Step (1)) Step (1) is a step of adjusting the particle size of the carbonaceous material raw material.

[0090] The carbonaceous material is graphite, and natural graphite is preferred because it has high crystallinity and excellent capacity. Graphite with few impurities is preferred, and it is preferable to use it after purification treatment as necessary.

[0091] (Step (2)) Step (2) is a step of mixing the carbonaceous raw material and the granulating agent.

[0092] The granulating agent is preferably liquid when the carbonaceous raw material is spheronized. The granulating agent preferably contains an organic compound that becomes amorphous carbon. Furthermore, the granulating agent is preferably one that does not contain an organic solvent, one that contains an organic solvent, at least one of which has no flash point, or one that contains an organic solvent having a flash point of 5°C or higher. If the granulating agent satisfies the above requirements, the granulating agent forms a liquid bridge between the carbonaceous raw material particles when the carbonaceous raw material is spheronized, and an attractive force is generated between the carbonaceous raw material particles by the capillary negative pressure of the liquid bridge and the surface tension of the liquid, thereby effectively shortening the distance between the carbonaceous raw material particles.

[0093] (Step (3)) Step (3) is a step of spheronizing the raw carbon material. By spheronizing the raw carbon material, the rapid charge / discharge characteristics are improved.

[0094] As a method for spheronizing the carbonaceous raw material, a method for spheronizing the carbonaceous raw material by applying mechanical energy is preferred because it is easy to control the particle shape. Examples of mechanical energy include impact, compression, friction, shear force, etc. These mechanical energies may be used alone or in combination of two or more. The method for spheronizing the carbonaceous raw material by applying mechanical energy may use an apparatus for applying mechanical energy.

[0095] When a carbonaceous raw material is subjected to a spheronization treatment, it is preferable to perform the spheronization treatment while adhering the fine powder generated during the spheronization treatment to the surface of the carbonaceous material. By performing the spheronization treatment while adhering the fine powder generated during the spheronization treatment to the surface of the carbonaceous material, voids within the carbonaceous material can be effectively reduced when the carbonaceous material is coated with an amorphous carbonaceous material or a graphite material. In addition, the amount of edges available as lithium ion insertion and desorption sites increases, allowing the electrolyte to efficiently penetrate the voids within the carbonaceous material, resulting in excellent low-temperature input / output characteristics and cycle characteristics. The fine powder may not only be the fine powder generated during the spheronization treatment, but also be a fine powder with an adjusted particle size that can be added separately.

[0096] In order to effectively adhere the fine powder to the surface of the carbon material, it is preferable to strengthen the adhesive forces between carbon material particles, between carbon material particles and fine powder particles, and between fine powder particles. Examples of adhesive forces between particles include van der Waals forces and electrostatic forces that do not involve inclusions between particles, and physical crosslinking forces and chemical crosslinking forces that involve inclusions between particles.

[0097] The carbonaceous raw material and the granulating agent may be charged into the spheronizing device, and steps (2) and (3) may be carried out simultaneously.

[0098] (Step (4)) Step (4) is a step of removing the granulating agent. The granulating agent may be removed in its entirety or in part. When a granulating agent containing an organic solvent is used, it is preferable to remove the organic solvent as well.

[0099] Methods for removing the granulating agent and the organic solvent include, for example, washing with a solvent, heating to volatilize and decompose, etc. Among these methods, the heating to volatilize and decompose is preferred because of its superior productivity and removal efficiency.

[0100] (Step (5)) Step (5) is a step of pressure treatment.

[0101] Examples of the pressure treatment include isotropic pressure treatment, anisotropic pressure treatment, etc. Among these pressure treatments, isotropic pressure treatment is preferred for achieving high density.

[0102] Examples of the pressurizing means include hydrostatic isotropic pressurizing treatment using water as the pressurizing medium, pneumatic isotropic pressurizing treatment using a gas such as air as the pressurizing medium, and pressurizing treatment in which the mixture is filled into a mold and pressed in a certain direction using a uniaxial press.

[0103] The pressure to be applied is preferably 50 to 300 MPa, more preferably 100 to 280 MPa, and even more preferably 150 to 260 MPa. Here, for densification, the pressure to be applied is preferably 50 MPa or more, more preferably 100 MPa or more, and even more preferably 150 MPa or more, and is preferably 300 MPa or less, more preferably 280 MPa or less, and even more preferably 260 MPa or less.

[0104] Step (5) may be performed at any time among steps (1) to (6), but is preferably performed between steps (4) and (6) because it allows for efficient compression in a state where excess granulating agent has been removed.

[0105] (Step (6)) Step (6) is a step of attaching at least one of an amorphous carbonaceous material and a graphite material. By attaching at least one of an amorphous carbonaceous material and a graphite material to the carbon material, side reactions between the negative electrode and the electrolyte can be suppressed, resulting in high capacity, excellent low-temperature input / output characteristics, and excellent high-temperature storage characteristics. The amorphous carbonaceous material refers to carbon having a d002 value of 0.340 nm or more. The graphite material refers to graphite having a d002 value of less than 0.340 nm.

[0106] In the method of attaching at least one of an amorphous carbonaceous material and a graphitic material to a carbonaceous material, the amount of voids in the particles can be easily controlled, and therefore a method in which the carbonaceous material and at least one of an amorphous carbonaceous material precursor and a graphitic material precursor are mixed, and the mixture is heated in a non-oxidizing atmosphere to amorphously carbonize the amorphous carbonaceous material precursor and / or graphitize the graphitic material precursor is preferred.

[0107] Examples of methods for mixing a carbon material with at least one of an amorphous carbonaceous material precursor and a graphite material precursor include a method of mixing a carbon material with at least one of an amorphous carbonaceous material precursor and a graphite material precursor using a mixer or kneader, a method of adding a carbon material to a solution in which at least one of an amorphous carbonaceous material precursor and a graphite material precursor has been dissolved, and then removing the solvent, etc. Among these methods, the method of mixing a carbon material with at least one of an amorphous carbonaceous material precursor and a graphite material precursor using a mixer or kneader is preferred because it can efficiently reduce micropores of 1 nm to 4 nm.

[0108] The mixing ratio of the carbon material to at least one of the amorphous carbonaceous material precursor and the graphite material precursor may be appropriately set so as to achieve a desired coating ratio.

[0109] The atmosphere during heating is not particularly limited as long as it is a non-oxidizing atmosphere, but nitrogen, argon, and carbon dioxide are preferred, and nitrogen is more preferred, as they can suppress the generation of micropores due to oxidation. The oxygen concentration is preferably 1% by volume or less, more preferably 0.1% by volume or less. The lower limit of the oxygen concentration is not particularly limited, and is usually 0% by volume or more.

[0110] The heating temperature differs between the amorphous carbonization of an amorphous carbonaceous material precursor and the graphitization of a graphitic material precursor. The heating temperature when amorphous carbonizing an amorphous carbonaceous material precursor is not particularly limited as long as it is a temperature that does not result in a crystal structure equivalent to that of graphite, but is preferably 500 to 2000°C, more preferably 600 to 1800°C, and even more preferably 700 to 1600°C. Here, the heating temperature is preferably 500°C or higher, more preferably 600°C or higher, and even more preferably 700°C or higher, and is preferably 2000°C or lower, more preferably 1800°C or lower, and even more preferably 1600°C or lower. The heating temperature when graphitizing a graphitic material precursor is not particularly limited as long as it is a temperature that results in a crystal structure equivalent to that of graphite, but is preferably 2100 to 3300°C, more preferably 2500 to 3200°C, and even more preferably 2700 to 3100°C. Here, the heating temperature is preferably 2100°C or higher, more preferably 2500°C or higher, and even more preferably 2700°C or higher, and is preferably 3300°C or lower, more preferably 3200°C or lower, and even more preferably 3100°C or lower.

[0111] The heating time is preferably 0.1 to 1000 hours, more preferably 1 to 100 hours. Here, the heating time is preferably 0.1 hour or more, more preferably 1 hour or more, and is preferably 1000 hours or less, more preferably 100 hours or less.

[0112] Examples of amorphous carbonaceous material precursors and graphite material 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 alone or in combination of two or more. Among these precursors, tar, pitch, and aromatic hydrocarbons are preferred because they are likely to develop a carbon structure and can be coated with a small amount, and those with a residual carbon percentage of 50% or more are more preferred, and those with a residual carbon percentage of 60% or more are even more preferred.

[0113] The carbon material obtained through steps (1) to (7) may be pulverized, crushed, or classified, as necessary, in order to adjust the volume-based average particle size of the graphite (A1) to a desired range. Known methods can be used for pulverization, crushing, and classification.

[0114] (Spheroidized Graphite (A2)) The carbon material (A) preferably contains spherical graphite (A2).

[0115] The carbon material composition according to the present embodiment contains the spherical graphite (A2), and when used in combination with the graphite (A1), the carbon material composition selectively densifies the electrode when the electrode is pressed to a predetermined density. Furthermore, since the spherical graphite (A2) is unlikely to increase in surface area even when deformed during pressing, the combined use of the graphite (A1) and the spherical graphite (A2) suppresses an increase in the reaction area of ​​the electrode plate when used at a high density.

[0116] The pellet density of spherical graphite (A2) is 1.80 to 2.262 g / cm ３ Here, the pellet density of the spherical graphite (A2) is preferably 1.80 g / cm because of its excellent compressibility during pressing. ３ or more, and 1.85 g / cm ３ More preferably, 1.88 g / cm ３ More preferably, 1.90 g / cm ３ More preferably, 2.262 g / cm ３ The following is preferred:

[0117] The pellet density of the spherical graphite (A2) was 1.80 g / cm ３To achieve the above, it is preferable that the particles have an appropriate amount of voids and the scales are stacked in an appropriate manner, and therefore the spherical graphite (A2) is preferably spherical flake natural graphite.

[0118] (Physical Properties of Spheroidized Graphite (A2)) The d002 value of the spherical graphite (A2) is preferably 3.360 Å or less, more preferably 3.357 Å or less, because the more highly crystalline the graphite, the better the compressibility during pressing and the more sufficient the charge / discharge capacity. The lower limit of the d002 value is not particularly limited, but the theoretical value is 3.354 Å or more.

[0119] The Lc of the spherical graphite (A2) is preferably 900 Å or more, more preferably 1000 Å or more, because the more highly crystalline the graphite is, the better its compressibility during pressing and the more sufficient its charge-discharge capacity. The upper limit of the Lc is not particularly limited, but the upper limit of measurement is 1000 Å.

[0120] The volume-based average particle diameter D50 of the spherical graphite (A2) is preferably 14 μm to 18 μm, more preferably 14.5 to 17.5 μm. Here, in order to prevent an increase in irreversible capacity and a loss in initial battery capacity, the volume-based average particle diameter of the spherical graphite (A2) is preferably 14 μm or more. Furthermore, in order to suppress process defects such as streaking during electrode plate production and to achieve excellent rapid charge / discharge characteristics and low-temperature input / output characteristics, the volume-based average particle diameter of the spherical graphite (A2) is preferably 18 μm or less.

[0121] The specific surface area (SA) of spherical graphite (A2) is 3.5 m ２ / g or more, and 3.5 to 11.0 m ２ / g is more preferable, and 4.0 to 9.0 m ２ / g is more preferable, and 5.0 to 8.0 m ２ Here, the specific surface area of ​​the spherical graphite (A2) is preferably 3.0 m / g, because it ensures a portion through which lithium ions can enter and exit, and provides excellent rapid charge / discharge characteristics and low-temperature input / output characteristics. ２ In addition, the specific surface area of ​​the spherical graphite (A2) is preferably 11.0 m / g or more, because this suppresses side reactions with the electrolyte, prevents a decrease in the initial charge / discharge efficiency and an increase in the amount of gas generated, and improves the battery capacity. ２ / g or less is preferred.

[0122] The tap density of spherical graphite (A2) is 0.80 g / cm ３ More preferably, 0.90 to 1.30 g / cm ３ More preferably, 1.00 to 1.20 g / cm ３ Here, the tap density of the spherical graphite (A2) is more preferably 0.80 g / cm because process defects such as creases can be suppressed during the production of an electrode plate, the packing property is improved, and therefore a high-density negative electrode sheet with good rollability can be easily formed, the degree of curvature of the lithium ion migration path is reduced when the electrode body is formed, and the shape of the voids between the particles is regular, which allows smooth migration of the electrolyte and improves rapid charge / discharge characteristics. ３ Furthermore, since the particles have an appropriate amount of space on the surface and inside thereof, the particles do not become too hard and have excellent electrode pressability, and are excellent in rapid charge / discharge characteristics and low-temperature input / output characteristics, the tap density of the spherical graphite (A2) is preferably 1.30 g / cm. ３ The following is preferred:

[0123] The circularity of the spherical graphite (A2) is preferably 0.88 to 0.99, more preferably 0.90 to 0.98, and even more preferably 0.92 to 0.97. Here, the circularity of the spherical graphite (A2) is preferably 0.88 or more, because this reduces the tortuosity of lithium ion diffusion, facilitates smooth movement of the electrolyte into the voids between the particles, and provides excellent rapid charge / discharge characteristics. Furthermore, the circularity of the spherical graphite (A2) is preferably 0.99 or less, because this ensures contact between carbon materials and provides excellent cycle characteristics.

[0124] The cumulative pore volume of the spherical graphite (A2) is preferably 0.030 to 0.140 mL / g, more preferably 0.040 to 0.130 mL / g, and even more preferably 0.050 to 0.100 mL / g. Here, the cumulative pore volume of the spherical graphite (A2) is preferably 0.030 mL / g or more because it is easily deformed to a suitable degree during pressing. Furthermore, the cumulative pore volume of the spherical graphite (A2) is preferably 0.140 mL / g or less.

[0125] (Method for producing spherical graphite (A2)) The method for producing the spherical graphite (A2) is not particularly limited, but it is preferable to use flake spherical natural graphite as the spherical graphite (A2) because it has high crystallinity and excellent compressibility.

[0126] The raw material for the spherical graphite (A2) is preferably graphite, and natural graphite is preferred because it has high crystallinity and excellent capacity. Graphite with a small amount of impurities is preferred, and it is preferable to use it after purification treatment as necessary.

[0127] Examples of natural graphite include amorphous graphite, scaly graphite, flake graphite, etc. 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.

[0128] The spheronization method is preferably a method of spheronization by applying mechanical energy, since it is easy to control the particle shape. Examples of mechanical energy include impact, compression, friction, shear force, etc. These mechanical energies may be used alone or in combination of two or more. The method of spheronization by applying mechanical energy may use a device that applies mechanical energy.

[0129] During the spheronization process, the raw material may be granulated in the presence of other substances, such as metals capable of alloying with lithium, oxides thereof, raw coke, and the like.

[0130] (Composition of Carbon Material (A)) The content of graphite (A1) in the carbon material (A) is preferably 40 to 90 mass%, more preferably 45 to 85 mass%, and even more preferably 55 to 75 mass%, based on 100 mass% of the carbon material (A). Here, the content of graphite (A1) is preferably 40 mass% or more based on 100 mass% of the carbon material (A), since expansion of the electrode plate can be suppressed low. Furthermore, the content of graphite (A1) is preferably 90 mass% or less, since high initial efficiency of the secondary battery can be maintained.

[0131] The content of the spherical graphite (A2) in the carbon material (A) is preferably 10 to 60 mass%, more preferably 15 to 55 mass%, and even more preferably 25 to 45 mass%, based on 100 mass% of the carbon material (A). Here, the content of the spherical graphite (A2) in 100 mass% of the carbon material (A) is preferably 10 mass% or more, since this allows the initial efficiency of the secondary battery to be maintained high. Furthermore, the content of the spherical graphite (A2) is preferably 60 mass% or less, since this allows the expansion of the electrode plate to be suppressed low.

[0132] Examples of substances other than the graphite (A1) and the spheroidized graphite (A2) that may be contained in the carbon material (A) according to this embodiment include metals that can be alloyed with lithium, oxides thereof, conductive materials, etc. The content of other substances in the carbon material (A) is preferably 20% by mass or less in total, and more preferably 10% by mass or less, so as not to impair the inherent functions of the graphite (A1) and the spheroidized graphite (A2).

[0133] (Physical Properties of Carbon Material (A)) The volume-based average particle diameter D50 of the carbon material (A) is preferably 1 to 50 μm, more preferably 4 to 30 μm, and even more preferably 10 to 25 μm. Here, in order to prevent an increase in irreversible capacity and a loss of initial battery capacity, the volume-based average particle diameter of the carbon material (A) is preferably 1 μm or more. Furthermore, in order to suppress process defects such as streaking during electrode plate production and to achieve excellent rapid charge / discharge characteristics and low-temperature input / output characteristics, the volume-based average particle diameter of the carbon material (A) is preferably 50 μm or less.

[0134] The specific surface area (SA) of the carbon material (A) is 1.0 to 11.0 m ２ / g is preferred, and 2.0 to 9.0 m ２ / g is more preferable, and 3.0 to 8.0 m ２ Here, the specific surface area of ​​the carbon material (A) is preferably 1.0 m / g, since this ensures a portion through which lithium ions can enter and exit, and the carbon material (A) is excellent in rapid charge / discharge characteristics and low-temperature input / output characteristics. ２ In addition, the specific surface area of ​​the carbon material (A) is preferably 11.0 m / g or more, because side reactions with the electrolyte are suppressed, a decrease in the initial charge / discharge efficiency and an increase in the amount of gas generated are prevented, and the battery capacity is improved. ２ / g or less is preferred.

[0135] The tap density of the carbon material (A) is 0.70 to 1.40 g / cm ３ is preferably 0.80 to 1.30 g / cm ３ More preferably, 0.90 to 1.10 g / cm ３Here, the tap density of the carbon material (A) is more preferably 0.70 g / cm because process defects such as creases can be suppressed during the production of the electrode plate, the packing property is improved, and therefore a high-density negative electrode sheet with good rollability can be easily formed, the degree of curvature of the lithium ion migration path is reduced when the electrode body is formed, and the shape of the voids between the particles is regular, which allows smooth migration of the electrolyte and improves rapid charge / discharge characteristics. ３ Furthermore, since the particles have an appropriate amount of space on the surface and inside thereof, the particles do not become too hard and have excellent electrode pressability, and the rapid charge / discharge characteristics and low-temperature input / output characteristics are excellent. Therefore, the tap density of the carbon material (A) is 1.40 g / cm ３ The following is preferred:

[0136] The circularity of the carbonaceous material (A) is preferably 0.88 to 0.99, more preferably 0.90 to 0.98, and even more preferably 0.92 to 0.97. Here, the circularity of the carbonaceous material (A) is preferably 0.88 or more, because this reduces the tortuosity of lithium ion diffusion, facilitates smooth movement of the electrolyte into the voids between the particles, and provides excellent rapid charge / discharge characteristics. Furthermore, the circularity of the carbonaceous material (A) is preferably 0.99 or less, because this ensures contact between the carbonaceous materials and provides excellent cycle characteristics.

[0137] The cumulative pore volume of the carbon material (A) is preferably 0.003 to 0.120 mL / g, more preferably 0.005 to 0.090 mL / g, and even more preferably 0.010 to 0.070 mL / g. Here, the cumulative pore volume of the carbon material (A) is preferably 0.003 mL / g or more and 0.120 mL / g or less because it is moderately easy to deform during pressing.

[0138] The pellet density of the carbon material (A) is 1.40 to 1.80 g / cm ３ is preferred, and 1.50 to 1.70 g / cm ３ More preferably, 1.55 to 1.60 g / cm ３ Here, since the carbon material (A) is easily deformed during pressing, the pellet density of the carbon material (A) is preferably 1.40 g / cm. ３ More preferably, 1.80 g / cm ３ The following is preferred:

[0139] (Method for producing carbon material (A)) The method for producing the carbon material (A) according to this embodiment preferably includes a step of mixing the graphite (A1) and the spheroidized graphite (A2). The mixing method is not particularly limited as long as the graphite (A1) and the spheroidized graphite (A2) can be mixed to obtain a desired composition.

[0140] The ratio RD50 of the volume-based average particle diameter D50 of graphite (A1) to the volume-based average particle diameter D50 of spherical graphite (A2) ([volume-based average particle diameter D50 of spherical graphite (A2)] / [volume-based average particle diameter D50 of graphite (A1)]) is preferably 0.1 to 10, more preferably 0.2 to 5, and even more preferably 0.5 to 2. Here, the ratio RD50 is preferably 0.1 or more, more preferably 0.2 or more, and even more preferably 0.5 or more, and is preferably 10 or less, more preferably 5 or less, and even more preferably 2 or less. When the ratio RD50 is within the above range, spherical graphite (A2) can be present in the gaps between adjacent pieces of graphite (A1), or graphite (A1) can be present in the gaps between adjacent pieces of spherical graphite (A2). As a result, the presence of the spherical graphite (A2) around the graphite (A1) allows the spherical graphite (A2) to selectively deform while maintaining the shape of the graphite (A1), and even when used at high density, the spherical graphite (A2) is not broken during pressing, thereby achieving both high initial efficiency and low expansion. Furthermore, the gaps formed between the graphite (A1) and the spherical graphite (A2) absorb the volumetric changes between the graphite (A1) and the spherical graphite (A2) that accompany the absorption and desorption of lithium ions during charge and discharge. Therefore, breakage of the conductive path due to the volumetric changes between the graphite (A1) and the spherical graphite (A2) is suppressed, thereby achieving improved cycle characteristics, rapid charge and discharge characteristics, and high capacity.

[0141] The ratio RSA of the specific surface area (SA) of the graphite (A1) to the specific surface area (SA) of the spherical graphite (A2) ([specific surface area (SA) of spherical graphite (A2)] / [specific surface area (SA) of graphite (A1)]) is preferably 0.01 to 100, more preferably 0.1 to 10, and even more preferably 0.2 to 5. Here, the ratio RSA is preferably 0.01 or more, more preferably 0.1 or more, and even more preferably 0.2 or more, and is preferably 100 or less, more preferably 10 or less, even more preferably 6 or less, even more preferably 5 or less, and particularly preferably 3 or less. When the ratio RSA is within the above range, a portion for lithium ions to enter and exit is secured, resulting in excellent rapid charge / discharge characteristics and low-temperature input / output characteristics, suppression of side reactions with the electrolyte, prevention of a decrease in initial charge / discharge efficiency and an increase in the amount of gas generated, and improvement of battery capacity.

[0142] The ratio RCPV of the cumulative pore volume of graphite (A1) to the cumulative pore volume of spherical graphite (A2) ([cumulative pore volume of spherical graphite (A2)] / [cumulative pore volume of graphite (A1)]) is preferably 1 to 50, more preferably 3 to 40, and even more preferably 5 to 20. Here, the ratio RCPV is preferably 1 or more, more preferably 3 or more, and even more preferably 5 or more, and is preferably 50 or less, more preferably 40 or less, and even more preferably 20 or less. When the ratio RCPV is within the above range, the spherical graphite (A2) is selectively deformed relative to the graphite (A1) during electrode plate production, and high initial efficiency and low expansion can be achieved even when used at high density.

[0143] <Carbon Material (B)> The carbon material (B) is a conductive additive.

[0144] From the viewpoint of improving electrical conductivity, the carbon material (B) preferably contains artificial graphite (B1). Examples of the artificial graphite (B1) include those obtained by heating organic materials such as coal tar pitch, coal-based heavy oil, atmospheric residual oil, 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 to 2500°C or higher to graphitize them.

[0145] The specific surface area of ​​the artificial graphite (B1) is set to 2.5 m from the viewpoint of ensuring electrical contact between particles. ２ / g or more, and ２ / g or more is more preferable.

[0146] The volume-based average particle size D50 of the artificial graphite (B1) is preferably 7 μm to 12 μm, more preferably 8 μm to 11 μm. From the viewpoint of battery durability, it is preferably 7 μm or more. On the other hand, the average particle size of the carbon material (B) is preferably 12 μm or less from the viewpoint of ensuring electrical contact between particles.

[0147] The tap density of the artificial graphite (B1) is 0.95 g / cm from the viewpoint of improving the energy density of the battery. ３ It is preferable that the density is 1.00 g / cm or more. ３ On the other hand, the tap density of the carbon material (B) is preferably 1.20 g / cm or more from the viewpoint of ensuring electrical contact between particles. ３ Preferably, it is 0.80 g / cm or less. ３ More preferably, it is 0.50 g / cm or less. ３ It is more preferable that:

[0148] The carbon material (B) is usually fired at 2500° C. or higher. The carbon material (B) can be pulverized using a crushing type pulverizer such as a roller mill, an impact type pulverizer such as a high-speed rotary pulverizer, an air current collision type pulverizer such as a jet mill, a dry swirling flow type pulverizer, or the like.

[0149] The carbon material (B) may contain carbon nanotubes and the like in addition to the artificial graphite (B1).

[0150] <Composition of Carbon Material Composition> In the carbon material composition of the present embodiment, in order to set the maximum torque in a linseed oil absorption measurement to 13.0 N m or less, the ratio of the content of the carbon material (B) to 100 parts by mass of the content of the carbon material (A) is preferably 0.01 to 30 parts by mass, more preferably 0.1 to 25 parts by mass, and even more preferably 1.0 to 20 parts by mass.

[0151] The content of the carbon material (A) is preferably 40 to 90 mass% relative to 100 mass% of the carbon material composition, more preferably 45 to 85 mass%, and even more preferably 55 to 75 mass%. Here, the content of the carbon material (A) relative to 100 mass% of the carbon material composition is preferably 40 mass% or more, since expansion of the electrode plate can be suppressed to a low level. Furthermore, the content of the carbon material (A) is preferably 90 mass% or less, since high initial efficiency of the secondary battery can be maintained.

[0152] The content of the carbon material (B) is preferably 10 to 60 mass% relative to 100 mass% of the carbon material composition, more preferably 15 to 55 mass%, and even more preferably 25 to 45 mass%. Here, the content of the carbon material (B) relative to 100 mass% of the carbon material composition is preferably 10 mass% or more, since this allows the initial efficiency of the secondary battery to be maintained high. Furthermore, the content of the carbon material (B) is preferably 60 mass% or less, since this allows the expansion of the electrode plate to be suppressed low.

[0153] The carbon material composition according to this embodiment may contain other substances in addition to the carbon material (A) and the carbon material (B). Examples of the other substances include metals that can be alloyed with lithium, oxides thereof, and conductive materials. The total content of the other substances is preferably 20% by mass or less, and more preferably 10% by mass or less, so as not to impair the inherent functions of the carbon material (A) and the carbon material (B).

[0154] <Method for producing carbon material composition> The method for producing a carbon material composition according to this embodiment preferably includes a step of mixing the carbon material (A) and the carbon material (B). The mixing method is not particularly limited as long as the carbon material (A) and the carbon material (B) can be mixed to obtain a desired composition.

[0155] The ratio RD50 of the volume-based average particle diameter D50 of the carbonaceous material (A) to the volume-based average particle diameter D50 of the carbonaceous material (B) ([volume-based average particle diameter D50 of the carbonaceous material (B)] / [volume-based average particle diameter D50 of the carbonaceous material (A)]) is preferably 0.1 to 10, more preferably 0.2 to 5, and even more preferably 0.5 to 2. Here, the ratio RD50 is preferably 0.1 or more, more preferably 0.2 or more, and even more preferably 0.5 or more, and is preferably 10 or less, more preferably 5 or less, and even more preferably 2 or less. When the ratio RD50 is within the above range, the carbonaceous material (B) can be present in the gaps between the carbonaceous materials (A), or the carbonaceous material (A) can be present in the gaps between the carbonaceous materials (B). As a result, the presence of the carbon material (B) around the carbon material (A) allows the carbon material (B) to selectively deform while maintaining the shape of the carbon material (A), and even when used at high density, the carbon material (B) is not destroyed during pressing, achieving both high initial efficiency and low expansion. Furthermore, the gaps formed between the carbon materials (A) and (B) absorb the volumetric changes between the carbon materials (A) and (B) that accompany the absorption and release of lithium ions during charging and discharging. Therefore, disconnection of the conductive path due to the volumetric changes between the carbon materials (A) and (B) is suppressed, and improved cycle characteristics, rapid charge / discharge characteristics, and high capacity can be achieved.

[0156] The ratio RSA of the specific surface area (SA) of the carbonaceous material (A) to the specific surface area (SA) of the carbonaceous material (B) ([specific surface area (SA) of carbonaceous material (B)] / [specific surface area (SA) of carbonaceous material (A)]) is preferably 0.01 to 100, more preferably 0.1 to 10, and even more preferably 0.2 to 5. Here, the ratio RSA is preferably 0.01 or more, more preferably 0.1 or more, and even more preferably 0.2 or more, and is preferably 100 or less, more preferably 10 or less, even more preferably 6 or less, even more preferably 5 or less, and particularly preferably 3 or less. When the ratio RSA is within the above range, a portion for lithium ions to enter and exit is secured, the battery exhibits excellent rapid charge / discharge characteristics and low-temperature input / output characteristics, side reactions with the electrolyte are suppressed, a decrease in initial charge / discharge efficiency and an increase in the amount of gas generated are prevented, and the battery capacity is improved.

[0157] The ratio RCPV of the cumulative pore volume of the carbon material (A) to the cumulative pore volume of the carbon material (B) ([cumulative pore volume of carbon material (B)] / [cumulative pore volume of carbon material (A)]) is preferably 1 to 50, more preferably 3 to 40, and even more preferably 5 to 20. Here, the ratio RCPV is preferably 1 or more, more preferably 3 or more, and even more preferably 5 or more, and is preferably 50 or less, more preferably 40 or less, and even more preferably 20 or less. When the ratio RCPV is within the above range, the carbon material (B) is selectively deformed relative to the carbon material (A) during electrode plate production, and high initial efficiency and low expansion can both be achieved even when used at high density.

[0158] [Negative electrode] The negative electrode according to this embodiment includes a current collector and an active material layer formed on the current collector, and the active material layer includes the carbon material composition according to this embodiment. The carbon material composition according to this embodiment functions and effects as an active material for the negative electrode.

[0159] The method for producing the negative electrode is not particularly limited as long as it can form an active material layer on the current collector, but a method in which a slurry containing the carbon material composition according to the present embodiment and a binder resin is applied to the current collector and dried is preferred because it is inexpensive and has excellent productivity. The slurry may further contain a thickener.

[0160] It is preferable that a slurry containing the carbon material composition according to the present embodiment and a binder resin is applied to a current collector, dried, and then pressed 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.

[0161] The density of the active material layer is 1.2 to 2.0 g / cm ３ is preferred, and 1.5 to 1.8 g / cm ３ Here, the density of the active material layer is more preferably 1.2 g / cm because this can suppress a decrease in battery capacity due to an increase in the thickness of the electrode. ３ More than 1.5 g / cm is preferred. ３ Furthermore, the density of the active material layer is preferably 2.0 g / cm or less, since the amount of electrolyte solution held in the voids decreases due to the reduction in the voids in the electrode, the mobility of alkaline ions such as lithium ions decreases, and the deterioration of rapid charge / discharge characteristics can be suppressed. ３ Preferably, 1.8 g / cm or less ３The following is more preferred:

[0162] [Secondary Battery] The secondary battery according to this embodiment includes a positive electrode, a negative electrode according to this embodiment, and an electrolyte. The positive electrode and the negative electrode according to this embodiment are preferably capable of absorbing and releasing lithium ions.

[0163] [Positive Electrode] A known positive electrode can be used as the positive electrode.

[0164] [Electrolyte] Any known electrolyte can be used as the electrolyte.

[0165] [Separator] The secondary battery according to this embodiment preferably has a separator interposed between the positive electrode and the negative electrode. However, the secondary battery according to this embodiment does not exclude batteries using a solid electrolyte as the electrolyte. Known separators can be used as the separator.

[0166] The carbon material composition according to the present embodiment can maintain a high initial efficiency of a secondary battery and suppress the expansion of the electrode plate, and therefore can be suitably used as an active material for the negative electrode of a secondary battery, more suitably used as an active material for the negative electrode of a nonaqueous secondary battery, and particularly suitably used as an active material for the negative electrode of a lithium ion secondary battery.

[0167] The present invention will be specifically explained below by way of examples, but the present invention is not limited to the following examples as long as it does not depart from the gist of the invention.

[0168] (Method for measuring volume-based average particle size D50) 0.01 g of the carbon material composition obtained in each of the examples and comparative examples was suspended in 10 mL of a 0.2 mass % aqueous solution of a surfactant, polyoxyethylene sorbitan monolaurate (trade name "Tween 20"), and the suspension was introduced into a laser diffraction / scattering particle size distribution analyzer (model name "LA-920", manufactured by Horiba, Ltd.) and irradiated with 28 kHz ultrasound at an output of 60 W for 1 minute. The volume-based median diameter in the analyzer was then measured, and the volume-based median diameter was defined as the volume-based average particle size D50. The proportion of particles with a diameter of 3 μm or less in the volume-based particle size distribution was defined as the small particle rate.

[0169] (Tap Density) Using a powder density measuring device (model name "GeoPyc 1365", Micromeritics), the carbon material compositions obtained in the examples and comparative examples were filled into a cylindrical container (chamber), and a constant pressure was applied by a piston while the chamber was rotated to stir the sample, and the density calculated from the volume and mass of the sample at that time was taken as the tap density.

[0170] (Method for measuring linseed oil absorption) The linseed oil absorption was measured in accordance with ISO 4546. Specifically, a linseed oil absorption measuring device (model name "S410D", manufactured by Asahi Research Institute Co., Ltd.) was used, and 30 g of the carbon material compositions obtained in the examples and comparative examples were charged, and the measurement was performed under conditions of a linseed oil dripping rate of 4 mL / min and a rotation speed of 200 rpm. The maximum torque value during the measurement of the linseed oil absorption was taken as the maximum torque, and the dripping amount at 70% of the maximum torque was taken as the linseed oil absorption.

[0171] (Circularity) Using a flow-type particle image analyzer (FPIA-2000 manufactured by Toa Medical Electronics Co., Ltd.), the particle size distribution based on the circle-equivalent diameter of the carbon material compositions obtained in the examples and comparative examples was measured, and the average circularity was calculated. Ion-exchanged water was used as the dispersion medium, and polyoxyethylene (20) monolaurate was used as the surfactant. The circle-equivalent diameter is the diameter of a circle (equivalent circle) having the same projected area as the photographed particle image, and the circularity is the ratio of the perimeter of the equivalent circle as the numerator to the perimeter of the photographed particle projected image as the denominator. The circularities of particles with measured equivalent diameters in the range of 10 to 40 μm were averaged to obtain the circularity.

[0172] (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 carbon material compositions obtained in the examples and comparative examples were subjected to preliminary reduced pressure drying at 350°C for 15 minutes under nitrogen flow, and then cooled to liquid nitrogen temperature. Using a nitrogen-helium mixed gas accurately 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 a gas flow method, and this was defined as the powder specific surface area SAp.

[0173] (Preparation of negative electrode sheet) The carbonaceous material compositions obtained in the examples and comparative examples were used as negative electrode active materials, and the active material layer density was 1.54±0.03 g / cm ３ Specifically, 50.00±0.02 g of the carbonaceous material composition obtained in the Examples and Comparative Examples was mixed with 50.00±0.02 g (0.50 g in terms of solid content) of a 1 mass % aqueous solution of carboxymethylcellulose sodium salt and 1.00±0.05 g (0.50 g in terms of solid content) of an aqueous dispersion of styrene-butadiene rubber having a weight-average molecular weight of 270,000, and the resulting mixture was stirred for 5 minutes in a hybrid mixer (manufactured by Keyence Corporation), followed by degassing for 30 seconds to obtain a slurry.

[0174] The obtained slurry was applied to a copper foil having a thickness of 10 μm as a current collector so that the negative electrode material was 10.00±0.20 mg / cm ２ The active material layer was coated to a width of 10 cm using a die coater so that it adhered to the substrate, dried, cut to a width of 5 cm, and roll-pressed using a roller with a diameter of 20 cm until the density of the active material layer was 1.54±0.03 g / cm ３ The load of the roll press was defined as the pressing load.

[0175] (Method for measuring electrode plate specific surface area SAe) Using a specific surface area measuring device (model name "Macsorb HM Model-1210", manufactured by Mountec Co., Ltd.), the negative electrode sheet was subjected to preliminary reduced pressure drying at 100°C for 30 minutes under a nitrogen flow, and then cooled to liquid nitrogen temperature. The specific surface area was measured by the nitrogen adsorption BET single-point method using a gas flow method using a nitrogen-helium mixed gas accurately adjusted so that the relative pressure of nitrogen to atmospheric pressure was 0.3, and this was taken as the electrode plate specific surface area SAe.

[0176] (Preparation of Positive Electrode Sheet) Lithium nickel-manganese-cobalt oxide (LiNiMnCoO ２ 85% by mass of the cathode material, 10% by mass of acetylene black as a conductive material, and 5% by mass of polyvinylidene fluoride (PVdF) as a binder were mixed in N-methylpyrrolidone to obtain a slurry. The obtained slurry was applied to a 15 μm thick aluminum foil current collector so that the cathode material was 22.5±0.2 mg / cm. ２The coating was carried out using a blade coater so that the material adhered to the substrate, and then dried at 130° C. Further, roll pressing was carried out to confirm that the density of the positive electrode material was 2.60±0.05 g / cm ３ The positive electrode sheet was obtained by adjusting the temperature so that the positive electrode sheet was

[0177] (Fabrication of a Sheet-Type Secondary Battery) The negative electrode sheet, a polyethylene separator, and the positive electrode sheet were stacked in this order. The stack was wrapped in a cylindrical aluminum laminate film, and LiPF 6 was dissolved in a mixed solvent of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate (volume ratio 30:30:40). ６ After injecting an electrolyte solution containing 1 mol / L of the above-mentioned compound into the battery, the battery was vacuum sealed to prepare a sheet-shaped non-aqueous secondary battery. Furthermore, in order to improve the adhesion between the electrodes, the sheet-shaped secondary battery was sandwiched between glass plates and pressure was applied.

[0178] (Method for measuring capacity retention rate after 500 cycles of secondary battery) Initial conditioning was performed in a 25°C environment at a voltage range of 4.2 to 3.0 V and a current value of 0.2 C (the current value at which the rated capacity based on the 1-hour rate discharge capacity is discharged in 1 hour is defined as 1 C, the same applies below). After aging at 60°C, a cycle test was performed in a 45°C environment at a charge current value of 0.8 C and a discharge current value of 0.8 C. The capacity retention rate after 500 cycles was calculated from the discharge capacity at the 500th cycle using the discharge capacity at the 1st cycle as the reference, according to the following formula: Capacity retention rate after 500 cycles = (discharge capacity at the 500th cycle / discharge capacity at the 1st cycle) × 100

[0179] Using the capacity retention rate after 500 cycles of Comparative Example 1 as a reference, the rate of change in the capacity retention rate after 500 cycles of each Example and Comparative Example was calculated according to the following formula (7). This value was taken as the cycle change rate. Cycle change rate of each Example and Comparative Example = {(capacity retention rate after 500 cycles of each Example and Comparative Example - capacity retention rate after 500 cycles of Comparative Example 1) / capacity retention rate after 500 cycles of Comparative Example 1} × 100 ... formula (7)

[0180] (Method for measuring rapid charge characteristics) A sheet-like secondary battery that had not undergone charge / discharge cycles was initially charged and discharged at 25°C for three cycles at a voltage range of 4.1 V to 3.0 V and a current value of 0.2 C, and then for two cycles at a voltage range of 4.2 V to 3.0 V and a current value of 0.2 C (constant voltage charging at 4.2 V for an additional 2.5 hours during charging). The battery was then subjected to constant current charging at a current value of 0.2 C to 4.2 V, followed by constant voltage charging at 4.2 V for 2.5 hours, and constant current discharging at 3 C to 3.0 V. The ratio of the discharge capacity at 3 C discharge to the discharge capacity at 0.2 C discharge (3 C / 0.2 C) × 100 was defined as the rapid charge characteristics (%).

[0181] Using the rapid charge characteristics of Comparative Example 1 as a reference, the rate of change in the rapid charge characteristics of each Example and Comparative Example was calculated according to the following formula (8). This value was taken as the rate of change. Rate of change of each Example and Comparative Example = {(rapid charge characteristics of each Example and Comparative Example - rapid charge characteristics of Comparative Example 1) / rapid charge characteristics of Comparative Example 1} x 100 Formula (8)

[0182] [Examples 1 to 4, Comparative Examples 1 to 3] <Production of Graphite (A1)> Scaly natural graphite having a volume average particle size D50 of 100 μm was pulverized to obtain a carbonaceous raw material having a volume average particle size D50 of 11 μm. 100 parts by mass of the obtained carbonaceous raw material was mixed with 12 parts by mass of a granulating agent, and then subjected to a spheroidizing treatment. The granulating agent was then removed by a heat treatment to obtain a spheroidized carbonaceous material. The obtained spheroidized carbonaceous material was filled into a rubber container, and the rubber container was sealed and subjected to an isotropic pressure treatment at 200 MPa. The mixture was then crushed and classified to obtain a spheroidized carbonaceous powder. The obtained spheroidized carbon 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, and the pressure inside the furnace was reduced to 10 torr or less and then returned to atmospheric pressure with nitrogen. Further, nitrogen was circulated to reduce the oxygen concentration inside the furnace to 0.01 volume % or less, and heat treatment was performed at 1300°C in an inert gas. The obtained fired product was crushed and classified to obtain a carbonaceous material. The content of amorphous carbonaceous material in the obtained carbonaceous material was confirmed to be 5.5 mass% from the firing yield.

[0183] <Production of Spheroidized Graphite (A2)> Scaly natural graphite having a volume-based average particle size of 100 μm was subjected to a spheroidizing treatment to obtain spherical graphite (A2).

[0184] <Production of Carbon Material (B)> Coal tar pitch with a Qi of less than 1% by mass was coked for 24 hours and then calcined in a rotary kiln to obtain calcine coke, which was then finely pulverized to an average particle size of 8 μm using an air current collision pulverizer. This pulverized material was placed in a graphite crucible and graphitized in a graphitization furnace at 3000°C for 40 hours. The resulting graphitized material was pulverized using a dry swirling flow pulverizer to obtain carbon material (B), which is artificial graphite.

[0185] <Production of carbon material composition> A carbon material composition was obtained by mixing 100 parts by mass of a carbon material (A) containing graphite (A1) and spherical graphite (A2) with a predetermined number of parts of a carbon material (B) shown in Table 1 so as to achieve a predetermined maximum torque. The obtained carbon material composition was subjected to particle size distribution measurement, tap density measurement, and linseed oil absorption measurement, and the results are shown in Table 1. The obtained carbon material composition was also subjected to measurement of SAe / SAp, circularity, small particle rate, and press load, and the results are shown in Table 2.

[0186] <Evaluation of carbonaceous material composition> A secondary battery was produced from the negative electrode sheet produced using the obtained carbonaceous material composition. The capacity retention rate after 500 cycles and the rapid charging characteristics of the obtained secondary battery were measured. The results are shown in Table 3.

[0187]

[0188]

[0189]

[0190] The carbon material compositions of Examples 1 to 4 had a small particle ratio of 16.0 to 40.0%, a maximum torque of 13.0 N m or less, and an SAe / SAp of 0.70 to 1.00, and thus suppressed deterioration of rapid charge / discharge characteristics and were excellent in capacity retention rate of the battery.

[0191] On the other hand, the carbon material composition of Comparative Example 1 had a small particle ratio of less than 16.0%, which meant that electrical contact between the particles could not be maintained, resulting in a poor capacity retention rate of the battery. Also, the carbon material compositions of Comparative Examples 2 and 3 had a maximum torque of more than 13.0 N m, which resulted in uneven solid content in the negative electrode active material layer and an increased diffusion distance between the active materials, resulting in poor deterioration of the rapid charge / discharge characteristics of the battery.

[0192] It is clear that a person skilled in the art can conceive of various modifications and alterations within the scope of the claims, and it is understood that these also naturally fall within the technical scope of the present invention. Furthermore, the components in the above-described embodiments may be combined in any manner without departing from the spirit of the invention.

[0193] This application is based on a Japanese patent application (Patent Application No. 2024-057416) filed on March 29, 2024 and a U.S. provisional application (63 / 681,283) filed on August 9, 2024, the contents of which are incorporated by reference into this application.

Claims

1. A carbonaceous material composition having a volumetric particle size distribution in which the proportion of particles of 3 μm or less is 16.0 to 40.0%, and a maximum torque of 13.0 N·m or less in a linseed oil absorption measurement.

2. A carbonaceous material composition having a volumetric particle size distribution in which the proportion of particles of 3 μm or less is 16.0 to 40.0%, wherein the ratio (SAe / SAp) of the specific surface area SAe when the carbonaceous material composition is made into an electrode plate to the specific surface area SAp of the powdered carbonaceous material composition is 0.70 to 1.00 (here, the specific surface area SAe is the specific surface area of ​​an electrode plate using the carbonaceous material composition).

3. The carbonaceous material composition according to claim 1 or 2, wherein the proportion of particles of 3 μm or less in the volumetric particle size distribution is 25.0 to 40.0%.

4. The carbon material composition according to claim 2, wherein the ratio (SAe / SAp) of the specific surface area SAe of the carbon material composition when made into an electrode plate to the specific surface area SAp of the powdered carbon material composition is 0.70 to 0.

89.

5. The carbon material composition according to claim 1 or 2, having a circularity of 0.85 or more.

6. The electrode plate using the carbon material composition is 1.54 g / cm ３ 3. The carbon material composition according to claim 1, wherein the load required to press the carbon material composition to the desired size is 640 to 750 kgf / 5 cm.

7. The electrode plate using the carbon material composition is 1.54 g / cm ３ 3. The carbon material composition according to claim 1, wherein the load required to press the carbon material composition to the desired size is 640 to 700 kgf / 5 cm.

8. The carbon material composition according to claim 1 or 2, wherein the carbon material composition contains a carbon material (A) and a carbon material (B), the carbon material (A) and the carbon material (B) contain graphite, the carbon material (B) is a conductive additive, and the carbon material (A) is a carbon material different from the carbon material (B).

9. The carbon material composition according to claim 8, wherein the carbon material (A) contains graphite (A1), and the graphite (A1) is graphite coated with at least one of an amorphous carbonaceous material and a graphitic material.

10. The carbon material composition according to claim 9, wherein the total content of at least one of the amorphous carbonaceous material and the graphite material is 0.1 to 15 mass% relative to 100 mass% of the graphite (A1).

11. The tap density of the graphite (A1) is 1.00 g / cm ３ The carbon material composition according to claim 9 .

12. The specific surface area of ​​the graphite (A1) is 3.5 m ２ The carbon material composition of claim 9, wherein the carbon content is less than 1 / g.

13. The carbon material composition according to claim 9, wherein the graphite (A1) has a volume-based average particle size D50 of 13 μm or more and 17 μm or less.

14. The carbon material composition according to claim 8, wherein the carbon material (A) comprises spheroidized graphite (A2).

15. The tap density of the spherical graphite (A2) is 0.80 g / cm ３ The carbon material composition according to claim 14, wherein the carbon material composition is as described above.

16. The specific surface area of ​​the spherical graphite (A2) is 3.5 m ２ The carbon material composition according to claim 14, wherein the carbon material composition has a molecular weight of 1 / g or more.

17. The carbon material composition according to claim 14, wherein the volume-based average particle diameter D50 of the spherical graphite (A2) is 14 μm or more and 18 μm or less.

18. The carbon material composition according to claim 8, wherein the carbon material (B) comprises artificial graphite (B1).

19. The tap density of the artificial graphite (B1) is 0.95 g / cm ３ The carbon material composition according to claim 18, wherein 20. The specific surface area of ​​the artificial graphite (B1) is 2.5 m ２ The carbon material composition according to claim 18, wherein the carbon material composition has a molecular weight of 1 / g or more.

21. The carbon material composition according to claim 18, wherein the artificial graphite (B1) has a volume-based average particle size D50 of 7 μm or more and 12 μm or less.

22. The carbon material composition according to claim 8, wherein the ratio of the content of the carbon material (B) to the content of the carbon material (A) is 0.01 to 30 parts by mass.

23. The tap density of the carbon material composition is 0.80 g / cm ３ The carbon material composition according to claim 8 .

24. The specific surface area SAp of the powdered carbonaceous material composition is 3.0 m ２ / g or more, 5.0m ２ The carbon material composition according to claim 8, wherein the carbon material composition has a molecular weight of 1 / g or less.

25. The carbonaceous material composition according to claim 8, wherein the linseed oil absorption of the carbonaceous material composition is 41.1 mL / 100 g or less.

26. The carbon material composition according to claim 8, wherein the volume-based average particle size D50 of the carbon material composition is 13 μm or more and 17 μm or less.

27. A negative electrode comprising a current collector and an active material layer formed on the current collector, wherein the active material layer comprises the carbon material composition according to claim 1.

28. A secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, wherein the negative electrode is the negative electrode according to claim 27.

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