Carbon material, negative electrode, and secondary battery

Abstract

The present invention pertains to a carbon material in which the linseed oil absorption is 40.0 mL / 100 g or less and the frequency q(d50) of d50 in a volume-based particle size distribution is 13.0% or less.

Description

Carbon materials, negative electrodes and secondary batteries

[0001] The present invention relates to a carbon material, 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] Japanese Patent Publication No. 2021-158044 Japanese Patent Publication No. 2021-158043

[0005] According to the inventors' research, the negative electrode material for non-aqueous secondary batteries described in Patent Document 1 has a low tap density, which means that the press load during electrode plate pressing is large, damaging the negative electrode material and reducing the initial efficiency. Furthermore, the negative electrode material disclosed in Patent Document 2 has the problem that it breaks during pressing when used at high density, reducing the initial efficiency of the secondary battery. Furthermore, the negative electrode material for non-aqueous secondary batteries described in Patent Document 1 also has a high oil absorption capacity, which makes it unsuitable for batteries, such as semi-solid batteries, in which an electrolyte and a negative electrode material are mixed to form an electrode, because a large amount of electrolyte is required to form the electrode, resulting in a reduction in energy density.

[0006] The present invention has been made in consideration of these problems, and an object of the present invention is to increase the density of the negative electrode material, thereby reducing the pressing load during electrode plate pressing and reducing damage to the negative electrode material during pressing. It is possible to provide a carbon material that suppresses an increase in irreversible capacity due to damage and has excellent initial efficiency for the negative electrode. Furthermore, it is also an object of the present invention to provide a carbon material that reduces oil absorption and enables the realization of a semi-solid battery with a high energy density.

[0007] There are two independent methods for increasing the density of a negative electrode material: increasing the density of the particles themselves, and increasing the density of the powder by controlling the particle size distribution. As a result of extensive research to solve the above problem, the inventors have found that the above problem can be solved by appropriately combining the above methods and using a carbon material whose linseed oil absorption is equal to or less than a specific value, and have thus completed the present invention.

[0008] A first aspect of the present invention is a carbonaceous material having a linseed oil absorption of 40.0 mL / 100 g or less, and a frequency q(d50) of particle sizes at which the cumulative volume ratio in a volume-based particle size distribution is 50% (hereinafter also referred to as d50) of 13.0% or less.

[0009] A second aspect of the present invention is the carbonaceous material of the first aspect, wherein the carbonaceous material comprises a first carbonaceous material and a second carbonaceous material having different d50s, and the first carbonaceous material has a d50 of 25 μm or more.

[0010] A third aspect of the present invention is the carbon material of the first or second aspect, wherein the carbon material comprises a first carbon material and a second carbon material having different d50s, and the second carbon material has a d50 of 15 μm or less.

[0011] A fourth aspect of the present invention is the carbon material according to any one of the first to third aspects, wherein the carbon material is amorphous-coated graphite.

[0012] A fifth aspect of the present invention is the carbonaceous material according to any one of the first to fourth aspects, wherein a difference (d90 - d50) between a particle size at a point where a cumulative volume ratio of the carbonaceous material is 90% (hereinafter also referred to as d90) and d50 is 13.0 μm or more.

[0013] A sixth aspect of the present invention is the carbon material according to any one of the first to fifth aspects, wherein the difference (d50 - d10) between the d50 of the carbon material and the particle size at a point where the cumulative volume ratio is 10% (hereinafter also referred to as d10) is 7.0 μm or more.

[0014] A seventh aspect of the present invention is the carbon material according to any one of the first to sixth aspects, wherein the difference between d90 and d10 (d90-d10) of the carbon material is 20 μm or more.

[0015] Aspect 8 of the present invention is the carbonaceous material of any one of Aspects 1 to 7, wherein the ratio of the difference between d90 and d10 to d50 of the carbonaceous material, {(d90-d10) / d50}, is 1.05 or more.

[0016] A ninth aspect of the present invention is the carbonaceous material according to any one of the first to eighth aspects, wherein a ratio (q(d50) / q(d25)) of a frequency q(d50) of a particle size at a point where a cumulative volume ratio in a volume-based particle size distribution of the carbonaceous material is 25% (hereinafter also referred to as d25) to a frequency q(d25) of a particle size at d50 in a volume-based particle size distribution of the carbonaceous material is 3.5 or less.

[0017] A tenth aspect of the present invention is the carbonaceous material of any one of Aspects 1 to 9, wherein a ratio (q(d50) / q(d90)) of a frequency q(d50) of d50 in a volume-based particle size distribution to a frequency q(d90) of d90 in the volume-based particle size distribution of the carbonaceous material is 2.0 or less.

[0018] An eleventh aspect of the present invention is the carbonaceous material according to any one of the first to tenth aspects, wherein the frequency q(d25) of d25 in the volume-based particle size distribution of the carbonaceous material is 9.0% or less.

[0019] A twelfth aspect of the present invention is the carbonaceous material of any one of Aspects 1 to 11, wherein a ratio (q(d90) / q(d10)) of a frequency q(d90) of d90 in a volumetric particle size distribution to a frequency q(d10) of d10 in the volumetric particle size distribution of the carbonaceous material is 1.55 or greater.

[0020] A thirteenth aspect of the present invention is a negative electrode including a current collector and an active material layer formed on the current collector, the active material layer including the carbon material of any one of aspects one to twelve.

[0021] A fourteenth aspect of the present invention is a secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, wherein the negative electrode comprises the carbon material of any one of Aspects 1 to 12.

[0022] The negative electrode using the carbon material of the present invention is excellent in initial efficiency and long-term storage recovery rate.

[0023] The present invention will be described in detail below, but these are merely examples of preferred embodiments and are not intended to limit the scope of the present invention. The numerical range "to" includes the preceding and following numerical values. For example, "0% by mass to 100% by mass" means a range of 0% by mass or more and 100% by mass or less.

[0024] Numerical ranges such as "A to B," "A or more," and "B or less" disclosed herein disclose numerical ranges with arbitrarily selected upper and lower limits. "A or more" means "greater than A and / or A," and also discloses the numerical range "greater than A." Similarly, "B or less" means "smaller than B and / or B," and also discloses the numerical range "smaller than B." "dn" means the particle size at which the cumulative volume ratio of all particles is n%. For example, "d10" means that 10% of the total volume has a particle size equal to or less than this particle size. "d50" means that 50% of the total volume has a particle size equal to or less than this particle size, and is also referred to as the "average particle size." q(dn) means the frequency of particles having a particle size of dn in the particle size distribution. For example, q(d50) means the frequency of particles having a particle size of d50. dn and q(dn) can be calculated from the particle size distribution.

[0025] [Carbon material] The carbon material of this embodiment may have a linseed oil absorption of 40.0 mL / 100 g or less and a d50 frequency q(d50) in the volumetric particle size distribution of 13.0% or less. When the linseed oil absorption is 40.0 mL / 100 g or less, a high-energy battery can be obtained even in a battery in which an electrode is formed by mixing an electrolyte and a negative electrode material, such as a clay battery. In this specification, such a carbon material is also referred to as "carbon material (X)."

[0026] In this specification, the linseed oil absorption of a carbon material is a value measured in accordance with ISO 4546. Specifically, an oil absorption measuring device (model name "S410D", manufactured by Asahi Research Institute Co., Ltd.) is used, and 30 g of a sample is charged, and measurement is performed under conditions of a dropping rate of 4 mL / min and a rotation speed of 200 rpm of linseed oil. The amount of dropping at which the torque becomes 70% of the maximum torque is defined as the oil absorption.

[0027] The linseed oil absorption of the carbon material is preferably 37.0 mL / 100 g or less, more preferably 35.0 mL / 100 g or less, and even more preferably 33 mL / 100 g or less.

[0028] The carbon material (X) of this embodiment is preferably in a powder form from the viewpoint of achieving high density. The q (d50) of the carbon material (X) of this embodiment is 13.0% or less, preferably 12.5% ​​or less, more preferably 12.0% or less, even more preferably 10.0% or less, and particularly preferably 8.0% or less. By controlling q (d50) within the above range, the number of d50 particles is reduced and the ratio of large and small particles is optimized, thereby improving packing properties.

[0029] The volume-based average particle size (d50) of the carbon material (X) of this embodiment 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 size of the carbon material is preferably 1 μm or more, more preferably 4 μm or more, and even more preferably 10 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 size of the carbon material is preferably 50 μm or less, more preferably 30 μm or less, and even more preferably 25 μm or less.

[0030] The method for densifying the carbon material (X) includes the following means for controlling the particle size distribution and specific methods. Of the methods shown below, one means or a plurality of means may be used.

[0031] The first method is to widen the particle size distribution by controlling at least one of the difference between d90 and d50 (d90-d50), the difference between d50 and d10 (d50-d10), and the difference between d90 and d10 (90-d10) as follows:

[0032] The d90-d50 of the carbon material (X) is preferably 13.0 μm or more, more preferably 15.0 μm or more, more preferably 17.0 μm or more, more preferably 19.0 μm or more, more preferably 21.0 μm or more, and more preferably 23.0 μm or more. The d90-d50 of the carbon material (X) is preferably 30.0 μm or less. That is, the d90-d50 is preferably 13.0 μm or more and 30.0 μm or less. By controlling the d90-d50 within the above range, a large particle size range is ensured, which makes it easier for small particles to enter the gaps, improving the packing efficiency.

[0033] The d50-d10 of the carbon material (X) is preferably 7.0 μm or more, more preferably 9.0 μm or more, more preferably 11.0 μm or more, more preferably 13.0 μm or more, more preferably 15.0 μm or more, more preferably 15.5 μm or more, more preferably 16.0 μm or more, and more preferably 16.5 μm or more. Furthermore, the d50-d10 of the carbon material (X) is preferably 25.0 μm or less. That is, the d50-d10 is preferably 7.0 μm or more and 25.0 μm or less. By controlling the d50-d10 within the above range, the variation of small particles can be increased, thereby efficiently filling the gaps between large particles.

[0034] The d90-d10 of the carbon material (X) is preferably 20 μm or more, more preferably 25 μm or more, more preferably 30 μm or more, more preferably 35 μm or more, and more preferably 40 μm or more. The d90-d10 of the carbon material (X) is preferably 50 μm or less. That is, the d90-d10 is preferably 20 μm or more and 50 μm or less. By controlling the d90-d10 within the above range, the particles can be easily combined with each other without gaps due to a wide particle size distribution.

[0035] The ratio of the difference between d90 and d10 to the d50 of the carbonaceous material (X), {(d90-d10) / d50}, is preferably 1.05 or more, more preferably 1.15 or more, more preferably 1.20 or more, more preferably 1.30 or more, more preferably 1.40 or more, more preferably 1.50 or more, and more preferably 1.60 or more. Furthermore, the ratio of the difference between d90 and d10 to the d50 of the carbonaceous material (X), {(d90-d10) / d50}, is preferably 2.50 or less, more preferably 2.30 or less, and even more preferably 2.10 or less. That is, {(d90-d10) / d50} is preferably 1.05 or more and 2.50 or less. By controlling (d90-d10) / d50 within the above range, the balance between large and small particles is adjusted, while the spread of the overall particle size distribution is relatively increased, thereby improving the filling rate.

[0036] As a second method, there is mentioned a means for reducing the frequency of medium particles. Specifically, in addition to the above-mentioned method of controlling q(d50), there is mentioned a method of controlling at least one of the ratio (q(d50) / q(d25)) of the frequency q(d50) of d50 in the volume-based particle size distribution to the frequency q(d25) of d25 in the volume-based particle size distribution and the ratio (q(d50) / q(d90)) of the frequency q(d50) of d50 in the volume-based particle size distribution to the frequency q(d90) of d90 in the volume-based particle size distribution as follows.

[0037] The q(d50) / q(d25) of the carbon material (X) is preferably 3.5 or less, more preferably 3.0 or less, more preferably 2.5 or less, and more preferably 2.0 or less. The q(d50) / q(d25) of the carbon material (X) is preferably 1.0 or more, more preferably 1.2 or more, and more preferably 1.5 or more. That is, the q(d50) / q(d25) is preferably 1.0 or more and 3.5 or less. By controlling the q(d50) / q(d25) within the above range, the proportion of d50 is reduced and a balance with the d25 particles is achieved, which contributes to improving the density.

[0038] The q(d50) / q(d90) of the carbon material (X) is preferably 2.0 or less, more preferably 1.8 or less, more preferably 1.6 or less, and more preferably 1.4 or less. The q(d50) / q(d90) of the carbon material (X) is preferably 1.0 or more, more preferably 1.2 or more. That is, the q(d50) / q(d90) is preferably 1.0 or more and 2.0 or less. By controlling the q(d50) / q(d90) within the above range, large particles (d90) create gaps, and suppressing d50 to fill those gaps may improve the density.

[0039] A third method is to reduce the frequency of small particles. Specifically, the third method is to control at least one of the frequency q(d25) of d25 in the volume-based particle size distribution and the ratio q(d90) of the frequency q(d90) of d90 in the volume-based particle size distribution to the frequency q(d10) of d10 in the volume-based particle size distribution (q(d90) / q(d10)) as follows.

[0040] The q (d25) of the carbon material (X) is preferably 9.0% or less, more preferably 7.0% or less, and more preferably 5.0% or less. The q (d25) of the carbon material (X) is preferably 1.0% or more. That is, the q (d25) is preferably 1.0% or more and 9.0% or less. By controlling the q (d25) within the above range, the fine particles tend to aggregate, increasing the number of voids, so keeping the amount to an appropriate level contributes to improving the density.

[0041] The q(d90) / q(d10) of the carbon material (X) is preferably 1.55 or more, more preferably 1.75 or more, and even more preferably 1.95 or more. The q(d90) / q(d10) of the carbon material (X) is preferably 3.0 or less. The q(d90) / q(d10) is preferably 1.55 or more and 3.0 or less. By controlling the q(d90) / q(d10) within the above range, an excessive number of small particles tends to aggregate and reduce the filling rate, so increasing the proportion of large particles contributes to improving the density.

[0042] The carbon material of this embodiment has a tap density of 1.26 g / cm ３ Preferably, the carbon material has a tap density of 1.26 g / cm or more. ３ By satisfying the above conditions, the pressing load when forming the carbon material into a negative electrode sheet is reduced, and an increase in irreversible capacity due to damage to the negative electrode material during pressing is suppressed, and the initial efficiency tends to be excellent. The tap density of the carbon material is more preferably 1.27 g / cm ３ More preferably, 1.28 g / cm ３ More preferably, 1.29 g / cm ３ That's all.

[0043] In this specification, the tap density refers to the density measured by a compression method using a tap density measuring device (model name "GeoPyc1365", manufactured by Micromeritics) when a compressive force of 108 N is applied.

[0044] From the viewpoint of increasing design flexibility, the carbon material (X) of this embodiment preferably includes a first carbon material and a second carbon material having different volume-based average particle sizes (hereinafter also referred to as d50). From the viewpoint of increasing density, the d50 of the first carbon material is preferably 25 μm or more, more preferably 26 μm or more, and even more preferably 27 μm or more. From the viewpoint of increasing density, the d50 of the second carbon material is preferably 15 μm or less, more preferably 13 μm or less, and even more preferably 11 μm or less.

[0045] In this specification, the volume-based average particle size (d50) refers to the volume-based median diameter measured using 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 using the analyzer.

[0046] The carbon material (X) of the present embodiment preferably contains the above-mentioned first carbon material and the above-mentioned second carbon material.

[0047] When the carbon material (X) of the present embodiment contains a first carbon material and a second carbon material, the mass ratio of the first carbon material to the second carbon material (first carbon material:second carbon material) is preferably 9:1 to 5:5, and more preferably 8:2 to 6:4, in order to increase the density of the carbon material (X).

[0048] The content of the first carbon material is preferably 40 to 90 mass% relative to 100 mass% of the carbon material (X), more preferably 45 to 85 mass%, and even more preferably 55 to 75 mass%. Here, the content of the first carbon material relative to 100 mass% of the carbon material (X) is preferably 40 mass% or more, more preferably 45 mass% or more, and even more preferably 55 mass% or more, because expansion of the electrode plate can be suppressed low. Furthermore, the content of the first carbon material is preferably 90 mass% or less, more preferably 85 mass% or less, and even more preferably 75 mass% or less, because high initial efficiency of the secondary battery can be maintained.

[0049] The content of the second carbon material is preferably 10 to 60% by mass, more preferably 15 to 55% by mass, and even more preferably 25 to 45% by mass, relative to 100% by mass of the carbon material (X). Here, the content of the second carbon material is preferably 10% by mass or more, more preferably 15% by mass or more, and even more preferably 25% by mass or more, relative to 100% by mass of the carbon material (X), in order to maintain a high initial efficiency of the secondary battery. Furthermore, the content of the second carbon material is preferably 60% by mass or less, more preferably 55% by mass or less, and even more preferably 45% by mass or less, in order to suppress the expansion of the electrode plate.

[0050] The carbon material (X) according to this embodiment may contain other substances in addition to the first carbon material and the second carbon material. Examples of the other substances include metals that can be alloyed with lithium, oxides thereof, and conductive materials. The content of the other substances in the carbon material (X) is preferably 20% by mass or less in total, more preferably 10% by mass or less, so as not to impair the inherent functions of the first carbon material and the second carbon material.

[0051] When the carbon material (X) of this embodiment contains a first carbon material and a second carbon material, the ratio Rd50 of the volume-based average particle diameter (d50) of the first carbon material to the volume-based average particle diameter (d50) of the second carbon material ([volume-based average particle diameter (d50) of the second carbon material] / [volume-based average particle diameter (d50) of the first carbon material]) is preferably 0.01 to 1, more preferably 0.05 to 0.8, and even more preferably 0.1 to 0.5. When the ratio Rd50 is within the above range, the second carbon material can be present in the gaps between the first carbon material particles, or the first carbon material can be present in the gaps between the second carbon material particles. As a result, the presence of the second carbon material around the first carbon material allows the second carbon material to selectively deform while maintaining the shape of the first carbon material, and therefore the second carbon material is not destroyed during pressing even when used at high density, thereby achieving both high initial efficiency and low expansion. Furthermore, the gap formed between the first and second carbon materials absorbs the volume change between the first and second carbon materials that accompanies the absorption and release of lithium ions during charging and discharging, thereby suppressing the disconnection of the conductive path that accompanies the volume change between the first and second carbon materials, thereby achieving improved cycle characteristics, rapid charge / discharge characteristics, and high capacity.

[0052] In at least one, preferably all, of the carbon material (X), the first carbon material, and the second carbon material of this embodiment, the specific surface area (SA) of the carbon material is 0.5 to 10.0 m ２ / g is preferred, and 0.8 to 6.5 m ２ / g is more preferable, and 1.0 to 5.0 m ２ / g is more preferable, and 1.0 to 3.0 m ２ Here, the specific surface area of ​​the carbon material (A) is preferably 0.5 m / g, because 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 / g or more is preferable, and 0.8m ２ / g or more is more preferable, and 1.0m ２ Further, the specific surface area of ​​the carbon material is preferably 10.0 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 preferable, and 6.5m ２ / g or less is more preferable, and 5.0m ２ / g or less is more preferable, and 3.0m ２ / g or less is more preferable, and 2.0m ２ / g or less is even more preferable. The SA of the carbon material (X), the first carbon material, and the second carbon material of this embodiment may be the same or different.

[0053] 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.

[0054] When the carbon material (X) of the present embodiment includes a first carbon material and a second carbon material, the ratio RSA of the specific surface area (SA) of the first carbon material to the specific surface area (SA) of the second carbon material ([specific surface area (SA) of carbon material (B)] / [specific surface area (SA) of carbon 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, portions for lithium ions to enter and exit are secured, resulting in excellent rapid charge / discharge characteristics and low-temperature input / output characteristics, suppressing side reactions with the electrolyte, preventing a decrease in initial charge / discharge efficiency and an increase in the amount of gas generated, and improving battery capacity.

[0055] At least one, preferably both, of the first carbon material and the second carbon material has a tap density of 1.15 to 1.40 g / cm ３ is preferably 1.17 to 1.35 g / cm ３ More preferably, 1.20 to 1.30 g / cm ３ Here, the tap density of the carbon material is more preferably 1.15 g / cm because process defects such as creases can be suppressed during electrode plate production, 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 More preferably, 1.17 g / cm ３ More preferably, 1.20 g / cm 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 is 1.40 g / cm ３ Preferably, 1.35 g / cm or less ３ More preferably, 1.30 g / cm or less ３ It is even more preferred that: The tap densities of the first carbon material and the second carbon material may be the same or different.

[0056] At least one of, and preferably all of, the carbon material (X), the first carbon material, and the second carbon material of this embodiment is preferably amorphous-coated graphite, more preferably amorphous-coated spheroidized natural graphite, from the viewpoint of lithium ion acceptance.

[0057] The mass ratio of the spheroidized graphite particles to the amorphous carbonaceous material in at least one, preferably all, of the carbonaceous material (X), the first carbonaceous material, and the second carbonaceous material of this embodiment is preferably 1:0.3 to 1:0.01, more preferably 1:0.2 to 1:0.05, from the viewpoint of lithium ion acceptability. The mass ratios of the spheroidized graphite particles to the amorphous carbonaceous material in the carbonaceous material (X), the first carbonaceous material, and the second carbonaceous material of this embodiment may be the same or different.

[0058] In this specification, the coating ratio of the carbon material with an amorphous carbon material or graphite material in at least one, preferably all, of the carbon material (X) of this embodiment, the first carbon material, and the second carbon material is also referred to as the coating ratio. The coating ratio of at least one, preferably all, of the carbon material (X) of this embodiment, the first carbon material, and the second carbon material 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 ratio is preferably 0.1% or more, more preferably 1% or more, even more preferably 2% or more, and particularly preferably 3% or more, because it allows smooth migration of lithium ions from the graphite and provides excellent rapid charge / discharge characteristics and low-temperature input / output characteristics. Furthermore, the coating ratio is preferably 15% or less, more preferably 12% or less, even more preferably 10% or less, and particularly preferably 8% or less, because the proportion of graphite is sufficient and high capacity can be easily achieved. In this embodiment, the coating ratios of the carbon material (X), the first carbon material, and the second carbon material may be the same or different.

[0059] 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 amorphous carbonaceous material or graphitic material and the firing yield after firing. Coating ratio (%) = ([mass of sample after firing - mass of spheroidized natural graphite] / [mass of sample after firing]) x 100 (1)

[0060] When the above-mentioned mixing ratio and the above-mentioned firing yield are unknown, the coating ratio (%) is estimated using the difference in true density between the graphite and the amorphous carbonaceous material or the graphitic material. Specifically, the crystallinity of the spherical natural graphite in the carbon material (X) of this embodiment, the first carbonaceous material, or the second carbonaceous material is confirmed by the d002 value, and if the d002 value is 3.357 Å or less and the material is highly crystalline, the coating ratio (%) is estimated using the following formula (2): Coating ratio (%) = 596.72 - 264.02 × true density (2)

[0061] In at least one, preferably all, of the carbon material (X), the first carbon material, and the second carbon material of this embodiment, the theoretical d002 value of graphite is 3.354 Å, and highly crystalline natural graphite exhibits a d002 value close to the theoretical value.

[0062] In at least one, preferably all, of the carbon material (X), the first carbon material, and the second carbon material of this embodiment, the d002 value of the carbon material 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. The d002 values ​​of the carbon material (X), the first carbon material, and the second carbon material of this embodiment may be the same or different.

[0063] In at least one, preferably all, of the carbon material (X), the first carbon material, and the second carbon material of this embodiment, the Lc of the carbon material 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. The Lc of the carbon material (X), the first carbon material, and the second carbon material of this embodiment may be the same or different.

[0064] 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.

[0065] 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.

[0066] In at least one, preferably all, of the carbon material (X), the first carbon material, and the second carbon material of this embodiment, the true density of the carbon material is 2.200 g / cm 3 or less because of excellent packing property and capacity. ３ More preferably, 2.210 g / cm ３ More preferably, 2.220 g / cm ３The theoretical true density of graphite is 2.262 g / cm ３ The true densities of the carbon material (X), the first carbon material, and the second carbon material of this embodiment may be the same or different.

[0067] In at least one, preferably all, of the carbon material (X), the first carbon material, and the second carbon material of this embodiment, the value obtained by subtracting the tap density from the pellet density of the carbon material 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 More than 0.15 g / cm ３ More preferably, 0.20 g / cm 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 therefore the difference is preferably 0.80 g / cm. ３ Preferably, 0.60 g / cm or less ３ More preferably, 0.40 g / cm or less ３ The following is more preferable: The numerical values ​​obtained by subtracting the tap density from the pellet density of the carbon material (X), the first carbon material, and the second carbon material of this embodiment may be the same or different.

[0068] 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)

[0069] 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.

[0070] At least one of, preferably all of, the carbon material (X), the first carbon material, and the second carbon material of this embodiment has a pellet density of 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 than 1.40 g / cm ３ More preferably, 1.79 g / cm ３ Preferably, 1.70 g / cm or less ３ The following is more preferable: The pellet densities of the carbon material (X), the first carbon material, and the second carbon material of this embodiment may be the same or different.

[0071] The circularity of at least one, preferably all, of the carbonaceous material (X), the first carbonaceous material, and the second carbonaceous material of this embodiment 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 is preferably 0.88 or more, more preferably 0.90 or more, and even more preferably 0.92 or more, because 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 the carbonaceous material is preferably 0.99 or less, more preferably 0.98 or less, and even more preferably 0.97 or less, because this ensures contact between the carbonaceous materials and provides excellent cycle characteristics. The circularities of the carbonaceous material (X), the first carbonaceous material, and the second carbonaceous material of this embodiment may be the same or different.

[0072] 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)

[0073] In at least one, preferably all, of the carbonaceous material (X), the first carbonaceous material, and the second carbonaceous material of this embodiment, the cumulative pore volume of the carbonaceous material 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. Because the carbonaceous material is easily deformed during pressing, the cumulative pore volume of the carbonaceous material is preferably 0.003 mL / g or more, more preferably 0.005 mL / g or more, and even more preferably 0.010 mL / g or more, and is preferably 0.120 mL / g or less, more preferably 0.090 mL / g or less, and even more preferably 0.070 mL / g or less. The cumulative pore volumes of the carbonaceous material (X), the first carbonaceous material, and the second carbonaceous material of this embodiment may be the same or different.

[0074] (Method for Producing Carbon Material) The method for producing the carbon material (X) of this embodiment is not particularly limited, but it is preferable that the carbon material can be produced so that the linseed oil absorption is 40.0 mL / 100 g or less. The first carbon material and the second carbon material may be produced separately, or the first carbon material and the second carbon material may be produced together. For example, a method is preferred in which a carbon material raw material is spheroidized in the presence of a granulating agent, pressurized, and impregnated with an amorphous carbon precursor or a graphitic material precursor. Specifically, a production method including the following steps (1) to (7) is preferred. Step (1): A step of adjusting the particle size of the carbon material raw material Step (2): A step of mixing the carbon material raw material with a granulating agent Step (3): A step of spheroidizing the carbon material raw material Step (4): A step of removing the granulating agent Step (5): A step of pressurizing Step (6): A step of impregnating an amorphous carbon material or a graphitic material Step (7): A step of mixing a plurality of carbon materials

[0075] 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).

[0076] (Step (1)) Step (1) is a step of adjusting the particle size of the carbonaceous material raw material.

[0077] The carbonaceous material raw material is graphite, and natural graphite and artificial graphite are preferred because they have high crystallinity and excellent capacity, with natural graphite being more preferred because it has higher crystallinity, is more excellent capacity, and does not require heat treatment during production. Graphite with a low impurity content is preferred, and it is preferable to use it after purification treatment as necessary.

[0078] (Step (2)) Step (2) is a step of mixing the carbonaceous raw material with a granulating agent.

[0079] 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.

[0080] (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.

[0081] 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.

[0082] 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.

[0083] 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.

[0084] 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.

[0085] (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.

[0086] 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.

[0087] (Step (5)) Step (5) is a step of pressure treatment.

[0088] Examples of the pressure treatment include isotropic pressure treatment, anisotropic pressure treatment, etc. Among these pressure treatments, isotropic pressure treatment is preferred from the viewpoint of reducing the pore volume.

[0089] 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.

[0090] 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. From the viewpoint of reducing the pore volume, 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.

[0091] 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.

[0092] (Step (6)) Step (6) is a step of attaching an amorphous carbonaceous material or a graphite material. By attaching an amorphous carbonaceous material or 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 with a d002 value of 0.340 nm or more. The graphite material refers to graphite with a d002 value of less than 0.340 nm.

[0093] In the method of attaching an amorphous carbonaceous material or a graphite 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 an amorphous carbonaceous material precursor or a graphite material precursor are mixed and heated in a non-oxidizing atmosphere to amorphously carbonize the amorphous carbonaceous material precursor or graphitize the graphite material precursor is preferred.

[0094] Examples of methods for mixing the carbon material with the amorphous carbonaceous material precursor or graphite material precursor include a method of mixing the carbon material with the amorphous carbonaceous material precursor or graphite material precursor using a mixer or kneader, a method of adding the carbon material to a solution in which the amorphous carbonaceous material precursor or graphite material precursor has been dissolved, and then removing the solvent, etc. Among these methods, the method of mixing the carbon material with the amorphous carbonaceous material precursor or graphite material precursor using a mixer or kneader is preferred because it can efficiently reduce micropores of 1 nm to 4 nm.

[0095] The mixing ratio of the carbon material and the amorphous carbonaceous material precursor or the graphite material precursor may be appropriately set so as to achieve a desired coating ratio.

[0096] 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.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] The ash content in the amorphous carbonaceous material precursor or graphite material precursor is preferably 0.00001 to 1 mass% relative to 100 mass% of the amorphous carbonaceous material precursor or graphite material precursor. Here, the ash content is preferably 0.00001 mass% or more, and is preferably 1 mass% or less, more preferably 0.5 mass% or less, and even more preferably 0.1 mass% or less relative to 100 mass% of the amorphous carbonaceous material precursor or graphite material precursor.

[0101] The carbonaceous material obtained through steps (1) to (6) may be pulverized, crushed, or classified as necessary to adjust the volume-based average particle size of the carbonaceous material to a desired range. Known methods can be used for pulverization, crushing, and classification.

[0102] (Step (7)) Step (7) is a step of mixing a plurality of carbon materials. It is preferable to produce the first carbon material and the second carbon material described above in the above procedure and mix them together. Substances other than the first carbon material and the second carbon material may also be mixed. The mixing method is not particularly limited as long as the materials can be mixed to obtain the desired composition.

[0103] [Negative electrode (solid electrode)] When the negative electrode according to this embodiment is a solid electrode, it includes a current collector and an active material layer formed on the current collector, and the active material layer includes the carbon material (X) according to this embodiment. The carbon material according to this embodiment functions and effects as the active material of the negative electrode. The negative electrode, which is a solid electrode, typically includes 0 to 5 mass % of a solvent, assuming that the mass of the active material layer is 100 mass %.

[0104] The method for producing a negative electrode, which is a solid electrode, is not particularly limited as long as it can form an active material layer on a current collector, but a method in which a slurry containing a carbon material and a binder resin according to the present embodiment is applied to a current collector and dried is preferred because it is inexpensive and has excellent productivity. The slurry may further contain a thickener.

[0105] It is preferable that a slurry containing the carbon material (X) 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.

[0106] When the negative electrode is a solid electrode, 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 ３ The following is more preferred:

[0107] Furthermore, when the negative electrode is a solid electrode, the thickness of the active material layer is preferably 100 to 200 μm. The thickness of the active material layer can be measured by peeling the negative electrode active material layer from the current collector and using a micrometer. When the negative electrode is a solid electrode, the density of the active material layer can be calculated from the mass of the peeled negative electrode active material layer and the volume of the active material layer.

[0108] [Negative electrode (semi-solid electrode)] When the negative electrode according to this embodiment is a semi-solid electrode, it includes a current collector, an active material layer formed on the current collector, and an electrolyte solution, and the active material layer includes the carbon material (X) according to this embodiment. The carbon material according to this embodiment functions and effects as the active material of the negative electrode. The negative electrode, which is a semi-solid electrode, typically includes 6 to 70 mass % of the solvent, preferably 6 to 50 mass % of the solvent, and more preferably 6 to 30 mass % of the solvent, when the mass of the active material layer is taken as 100 mass %.

[0109] The method for producing a semi-solid electrode negative electrode is not particularly limited as long as it can form an active material layer on a current collector, but a method in which a slurry containing the carbon material and the electrolyte according to this embodiment is applied to the current collector is preferred because it is inexpensive and has excellent productivity. The slurry may further contain a thickener. The production method preferably does not include drying, and more preferably does not include pressing, because it is inexpensive and has excellent productivity.

[0110] When the negative electrode is a semi-solid electrode, the density of the active material layer is 1.0 to 1.4 g / cm ３ is preferable. When the negative electrode is a semi-solid electrode, the thickness of the active material layer is preferably 201 to 2000 μm. The thickness of the active material layer can be measured using a contact probe without peeling the negative electrode active material layer from the current collector. When the negative electrode is a semi-solid electrode, the density of the active material layer can be calculated from the mass of the negative electrode active material layer and the volume of the active material layer.

[0111] [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. The secondary battery may be a clay battery.

[0112] (Positive Electrode) As the positive electrode, a known positive electrode can be used.

[0113] (Electrolyte) As the electrolyte, known electrolytes can be used.

[0114] (Separator) In the secondary battery according to this embodiment, it is preferable to interpose a separator between the positive electrode and the negative electrode. However, the secondary battery according to this embodiment does not exclude the use of a solid electrolyte as the electrolyte. A known separator can be used as the separator.

[0115] The carbon material according to the present embodiment can maintain a high initial efficiency of the 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.

[0116] 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.

[0117] (Method for measuring volume-based particle sizes d10, d25, d50, and d90, and their frequencies q(d10), q(d25), q(d50), and q(d90)) 0.01 g of sample was suspended in 10 mL of a 0.2% by mass aqueous solution of surfactant polyoxyethylene sorbitan monolaurate (trade name "Tween 20"), and 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, after which measurement was performed. The volume-based median diameter in the measuring device was measured, and the volume-based median diameter was taken as the volume-based average particle size d50. The particle size distribution data obtained by measurement includes the frequency and cumulative frequency for each particle size. The particle size dn means the particle size at which the cumulative frequency is n%. The particle size dn was calculated by linear interpolation from the two closest data points (n1%, dn1) and (n2%, dn2) that sandwich the cumulative frequency n%. Similarly, the frequency q(dn) at dn was also calculated by linear interpolation from the two closest data points that sandwich dn.

[0118] (Tap Density Measurement) The tap density was measured by a compression method using a tap density measuring device (model name "GeoPyc1365", manufactured by Micromeritics). The density when a compressive force of 108 N was applied was taken as the tap density.

[0119] (Method of Measuring Specific Surface Area (SA)) Using a specific surface area measuring device (model name "Macsorb HM-1210", manufactured by Mountec Co., Ltd.), a sample was subjected to preliminary reduced pressure drying at 350°C for 15 minutes under a nitrogen flow, and then cooled to the temperature of liquid nitrogen. The specific surface area was measured by the nitrogen adsorption BET single-point method using a nitrogen-helium mixed gas that was accurately adjusted so that the relative pressure of nitrogen to atmospheric pressure was 0.3.

[0120] (Method for measuring linseed oil absorption) Linseed oil absorption was measured in accordance with ISO 4546. Specifically, an oil absorption measuring device (model name "S410D", manufactured by Asahi Research Institute Co., Ltd.) was used, and 30 g of a sample was added, and linseed oil was measured at a dropping rate of 4 mL / min and a rotation speed of 200 rpm. The amount of drop at which the torque became 70% of the maximum torque was defined as the oil absorption.

[0121] (Preparation of negative electrode sheet) The carbon materials obtained in the examples and comparative examples were used as negative electrode active materials, and the active material layer density was 1.50±0.03 g / cm ３ Specifically, 50.00±0.02 g of the carbon material 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) and degassed for 30 seconds to obtain a slurry.

[0122] 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±0.30 mg / cm ２ The active material layer was applied to a width of 5 cm using a die coater so that it would adhere, and after drying, it was roll-pressed using a roller with a diameter of 20 cm until the density of the active material layer reached 1.50±0.03 g / cm ３ The load applied during rolling was defined as the pressing load.

[0123] (Preparation of a coin-type battery) The obtained negative electrode sheet was punched into a disk with a diameter of 12.5 mm to form a negative electrode, and a lithium metal foil was punched into a disk with a diameter of 14 mm to form a counter electrode. Between the two electrodes, LiPF 5 was placed in a mixed solvent of ethylene carbonate and ethyl methyl carbonate (volume ratio 30:70). ６ A separator (made of porous polyethylene film) impregnated with an electrolyte solution containing 2% by mass of vinylene carbonate was placed in the solution to prepare a 2032 coin-type secondary battery.

[0124] (Method for measuring irreversible capacity of negative electrode of secondary battery and initial efficiency of negative electrode of secondary battery) The obtained coin-type battery was charged to 5 mV against the lithium counter electrode at a current density of 0.04 C, and further charged at a constant voltage of 5 mV until the current density reached 0.004 C. After doping lithium into the negative electrode, the battery was discharged to 1.5 V against the lithium counter electrode at a current density of 0.08 C. The difference between the charge capacity and discharge capacity at this time was defined as the irreversible capacity, and the ratio of the discharge capacity to the charge capacity ((discharge capacity / charge capacity) × 100) was defined as the initial efficiency (%).

[0125] Example 1: Scaly natural graphite with an average particle size (d50) of 100 μm was pulverized to obtain scaly natural graphite with a d50 of 26 μm. 100 parts by mass of the obtained scaly natural graphite was mixed with 12 parts by mass of liquid oil as a granulating agent, followed by spheronization. The granulating agent was then removed by heat treatment to obtain spheroidized natural graphite. The obtained spheroidized natural graphite was packed into a rubber container, sealed, and subjected to isostatic pressure treatment at 200 MPa. The resulting molded product was then crushed and classified. The obtained spheroidized natural graphite powder was mixed with pitch as an amorphous carbon precursor, which had an ash content of 0.02 mass%, a metal impurity content of 20 ppm by mass, and a Qi of 1 mass%. The furnace pressure was reduced to 10 torr or less and then returned to atmospheric pressure with nitrogen. Nitrogen was then circulated to reduce the oxygen concentration in the furnace to less than 100 ppm, and the mixture was then heat-treated at 1300°C in an inert gas atmosphere. The obtained fired product was crushed and classified to obtain a composite carbon material having a d50 of 27.5 μm and containing amorphous carbonaceous material on the surface of graphite particles. The firing yield confirmed that the mass ratio of the spherical graphite particles to the amorphous carbonaceous material (spheroidized graphite particles: amorphous carbonaceous material) in the obtained carbon material (composite carbon material) was 1:0.11. The obtained carbon material had a d10 of 15.57 μm, a q(d10) of 3.63%, a d25 of 20.93 μm, a q(d25) of 8.29%, a d50 of 27.9 μm, a q(d50) of 12.61%, a d90 of 48.11 μm, and a q(d90) of 6.48%. The tap density, oil absorption, specific surface area, press load, initial efficiency, and capacity of the obtained carbon material were measured using the methods described above. The results are shown in Tables 1 and 2.

[0126] Example 2: Spheroidized natural graphite with a d50 of 7.4 μm was packed into a rubber container, sealed, and subjected to isostatic pressure treatment at 200 MPa. The resulting molded product was then crushed and classified. The resulting spherical natural graphite powder was mixed with pitch (100% by mass) adjusted to an ash content of 0.02% by mass, a metal impurity content of 20 ppm by mass, and a Qi of 1% by mass as an amorphous carbon precursor. The furnace pressure was reduced to 10 torr or less, and the pressure was returned to atmospheric pressure with nitrogen. Further, nitrogen was circulated to reduce the oxygen concentration in the furnace to less than 100 ppm, and the mixture was heat-treated at 1300°C in an inert gas atmosphere. The resulting fired product was crushed and classified to obtain a composite carbon material with a d50 of 9.0 μm and containing amorphous carbonaceous material on the surfaces of the graphite particles. From the firing yield, it was confirmed that the mass ratio of the spheroidized graphite particles to the amorphous carbonaceous material (spheroidized graphite particles:amorphous carbonaceous material) in the obtained composite carbonaceous material was 1:0.11. The obtained carbonaceous material was mixed with the carbonaceous material obtained in Example 1 having a d50 of 27.5 μm in a mass ratio of 2:8 to obtain a carbonaceous material. The obtained carbonaceous material had a d10 of 7.98 μm, a q(d10) of 2.59%, a d25 of 14.89 μm, a q(d25) of 4.01%, a d50 of 24.73 μm, a q(d50) of 8.52%, a d90 of 47.24 μm, and a q(d90) of 5.86%. The evaluation results of the obtained carbonaceous material are shown in Tables 1 and 2.

[0127] [Example 3] A carbon material was obtained in the same manner as in Example 2, except that the carbon material obtained in Example 2 and the carbon material obtained in Example 1 with a d50 of 27.5 μm were used in a mass ratio of 3:7. The resulting carbon material had a d10 of 6.62 μm, a q(d10) of 3.30%, a d25 of 11.19 μm, a q(d25) of 3.97%, a d50 of 21.92 μm, a q(d50) of 6.45%, a d90 of 46.81 μm, and a q(d90) of 5.17%. The evaluation results of the resulting carbon material are shown in Table 1.

[0128] [Comparative Example 1] A negative electrode material with a d50 of 16.6 μm was obtained by the same procedure as in Example 1, except that flake natural graphite with an average particle size (d50) of 100 μm was pulverized to obtain flake natural graphite with a d50 of 11 μm. The resulting carbon material had a d10 of 9.91 μm, a q(d10) of 4.38%, a d25 of 12.69 μm, a q(d25) of 9.44%, a d50 of 16.58 μm, a q(d50) of 13.17%, a d90 of 29.47 μm, and a q(d90) of 5.75%. The evaluation results of the resulting negative electrode material are shown in Tables 1 and 2.

[0129] [Comparative Example 2] A negative electrode material having a d50 of 16.9 μm was obtained by the same procedure as in Comparative Example 1, except that the mass ratio of the spherical graphite particles to the amorphous carbonaceous material (spheroidized graphite particles:amorphous carbonaceous material) was 1:0.12. The resulting carbonaceous material had a d10 of 10.44 μm, a q(d10) of 4.58%, a d25 of 13.21 μm, a q(d25) of 10.09%, a d50 of 16.89 μm, a q(d50) of 14.32%, a d90 of 28.07 μm, and a q(d90) of 7.02%. The evaluation results of the resulting negative electrode material are shown in Tables 1 and 2.

[0130]

[0131]

[0132] The carbon materials of Examples 1 to 3 had reduced press loads, reduced irreversible capacity even with the same powder SA, and excellent initial efficiency. The content of amorphous carbonaceous material and heating temperature were adjusted so that the true density and Raman R value were within the specified ranges, thereby suppressing the irreversible capacity of the negative electrode and providing excellent initial efficiency. On the other hand, the carbon materials of Comparative Examples 1 and 2 had large press loads, resulting in increased irreversible capacity of the negative electrode and poor initial efficiency.

[0133] 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.

[0134] This application is based on a Japanese patent application (Patent Application No. 2024-057421) filed on March 29, 2024, the contents of which are incorporated herein by reference.

Claims

1. A carbonaceous material having a linseed oil absorption of 40.0 mL / 100 g or less, and a particle size frequency q(d50) of 50% of the cumulative volume ratio in the volume-based particle size distribution (hereinafter also referred to as d50) of 13.0% or less.

2. The carbon material according to claim 1, wherein the carbon material comprises a first carbon material and a second carbon material having different d50s, and the d50 of the first carbon material is 25 μm or more.

3. The carbon material according to claim 1, wherein the carbon material comprises a first carbon material and a second carbon material having different d50 values, and the d50 value of the second carbon material is 15 μm or less.

4. The carbon material according to any one of claims 1 to 3, wherein the carbon material is amorphous coated graphite.

5. A carbon material according to any one of claims 1 to 3, wherein the difference between the particle size at the point where the cumulative volume ratio of the carbon material is 90% (hereinafter also referred to as d90) and d50 (d90 - d50) is 13.0 μm or more.

6. A carbon material according to any one of claims 1 to 3, wherein the difference (d50 - d10) between the d50 of the carbon material and the particle size at the point where the cumulative volume ratio is 10% (hereinafter also referred to as d10) is 7.0 μm or more.

7. The carbon material according to any one of claims 1 to 3, wherein the difference between d90 and d10 (d90-d10) of the carbon material is 20 µm or more.

8. The carbon material according to any one of claims 1 to 3, wherein the ratio of the difference between d90 and d10 to the d50 of the carbon material {(d90-d10) / d50} is 1.05 or more.

9. The carbon material according to any one of claims 1 to 3, wherein the ratio (q(d50) / q(d25)) of the frequency q(d50) of the particle size at a point where the cumulative volume ratio in the volume-based particle size distribution of the carbon material is 25% (hereinafter also referred to as d25) to the frequency q(d25) of the particle size at d50 in the volume-based particle size distribution is 3.5 or less.

10. The carbon material according to any one of claims 1 to 3, wherein the ratio (q(d50) / q(d90)) of the frequency q(d50) of d50 in the volume-based particle size distribution of the carbon material to the frequency q(d90) of d90 in the volume-based particle size distribution of the carbon material is 2.0 or less.

11. The carbon material according to any one of claims 1 to 3, wherein the frequency q(d25) of d25 in the volume-based particle size distribution of the carbon material is 9.0% or less.

12. The carbon material according to any one of claims 1 to 3, wherein the ratio (q(d90) / q(d10)) of the frequency q(d90) of d90 in the volumetric particle size distribution of the carbon material to the frequency q(d10) of d10 in the volumetric particle size distribution of the carbon material is 1.55 or more.

13. A negative electrode comprising a current collector and an active material layer formed on the current collector, the active material layer comprising the carbon material according to any one of claims 1 to 3.

14. A secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, wherein the negative electrode comprises the carbon material according to any one of claims 1 to 3.

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