Graphite particles, carbon material, and secondary battery

Abstract

The present invention relates to graphite particles coated with amorphous carbon, wherein, when the particles are pressurized to a pressure of 9.81 mN and then decompressed to 0.05 mN, a value derived by dividing the particle size displacement amount observed when the pressure is released so as to reach 0.05 mN after reaching 9.81 mN by the particle size displacement amount at the time at which 9.81 mN is reached is 0.5 or greater.

Description

Graphite particles, carbon materials and secondary batteries

[0001] The present invention relates to graphite particles having excellent battery characteristics as a negative electrode active material for secondary batteries, a carbon material containing the graphite particles, and a secondary battery using a negative electrode containing the carbon material.

[0002] In recent years, the miniaturization of electronic devices has led to an increasing demand for high-capacity secondary batteries. In particular, non-aqueous secondary batteries, especially lithium-ion secondary batteries, have attracted attention because of their higher energy density and superior rapid charge / discharge characteristics compared to nickel-cadmium batteries and nickel-metal hydride batteries.

[0003] Positive and negative electrodes capable of absorbing and releasing lithium ions, and LiPF ６ and LiBF ４ Lithium ion secondary batteries using non-aqueous electrolyte solutions in which lithium salts such as those mentioned above are dissolved have been developed and are in practical use.

[0004] Various materials have been proposed as negative electrode materials for these batteries, including graphitic carbon materials such as natural graphite, artificial graphite obtained by graphitizing coke, graphitized mesophase pitch, and graphitized carbon fiber, due to their high capacity and excellent flatness of discharge potential.

[0005] Recently, non-aqueous secondary batteries, especially lithium-ion secondary batteries, have been widely used in a wide range of applications. For example, applications are expanding beyond conventional notebook computers, mobile communication devices, portable cameras, and portable game consoles to power tools, electric vehicles, and other applications. This has led to a demand for faster charging and discharging than ever before. Furthermore, lithium-ion secondary batteries with both high capacity and high cycle characteristics are desired.

[0006] However, since the theoretical capacity of carbon is 372 mAh, it is impossible to achieve a higher capacity in a carbon-based anode. Therefore, the application of various anode materials with high theoretical capacity, particularly metal particles, to anodes has been investigated (see, for example, Patent Document 1).

[0007] Japanese Patent Application Publication No. 2023-156005

[0008] As described in Patent Document 1, it is known that the mechanical properties of graphite constituting the electrode affect the performance of lithium battery negative electrodes made of active materials containing silicon (Si), which undergo volumetric changes. However, active materials containing Si, in particular, repeatedly expand and contract during charge and discharge, and it is thought that the collapse of graphite particles during this volumetric change could affect the battery's lifespan. Therefore, there is a demand for materials that can reversibly adapt to deformation.

[0009] The present invention has been made in view of the above problems, and an object of the present invention is to provide a graphite material as an electrode constituent material that can reversibly follow the volume change of the Si-containing active material in the negative electrode.

[0010] The present inventors have found that a secondary battery with excellent battery characteristics can be obtained by using specific graphite particles.

[0011] A first aspect of the present invention is graphite particles coated with amorphous carbon, wherein, when the particles are pressurized to a pressure of 9.81 mN and then released to 0.05 mN, the value obtained by dividing the amount of change in particle size observed when the pressure reaches 9.81 mN and then the pressure is released to 0.05 mN by the amount of change in particle size when the pressure reaches 9.81 mN is 0.5 or more.

[0012] A second aspect of the present invention is the graphite particles of the first aspect, which do not include a plateau in the mechanical curve when the particles are compressed up to a pressure of 9.81 mN.

[0013] A third aspect of the present invention is the graphite particles of the first or second aspect, which have a compressive modulus of elasticity of 550 MPa or more when the particles are compressed to a pressure of 9.81 mN.

[0014] A fourth aspect of the present invention is the graphite particles according to any one of the first to third aspects, wherein the displacement rate when the particles are pressurized up to a pressure of 9.81 mN is 10% or less.

[0015] A fifth aspect of the present invention is a carbon material comprising the graphite particles of any one of the first to fourth aspects, wherein the Raman R value of the carbon material is 0.4 or more and 1.0 or less.

[0016] A sixth aspect of the present invention is a carbonaceous material comprising the graphite particles of any one of the first to fourth aspects, wherein the BET specific surface area of ​​the carbonaceous material is 0.5 m ２ / g or more 3.0m ２ / g or less.

[0017] A seventh aspect of the present invention is the graphite particles according to the first or second aspect, wherein the compressive modulus of elasticity when the particles are compressed to a pressure of 9.81 mN is 150 MPa or more and 300 MPa or less.

[0018] Aspect 8 of the present invention is the graphite particles according to Aspect 1, 2 or 7, wherein the displacement rate when the particles are pressurized up to a pressure of 9.81 mN is 4% or more and 10% or less.

[0019] A ninth aspect of the present invention is a carbonaceous material comprising the graphite particles according to any one of the first, second, seventh, and eighth aspects, wherein the Raman R value of the carbonaceous material is 0.3 or more and 0.4 or less.

[0020] A tenth aspect of the present invention is a carbonaceous material comprising the graphite particles according to any one of the first, second, seventh, and eighth aspects, wherein the BET specific surface area of ​​the carbonaceous material is 0.5 m ２ / g or more 3.0m ２ / g or less.

[0021] An eleventh aspect of the present invention is a negative electrode material comprising a carbon material containing the graphite particles of any one of the first to fourth, seventh, or eighth aspects, and Si-containing particles.

[0022] A twelfth aspect of the present invention is the anode material of the eleventh aspect, further comprising a conductive additive.

[0023] A thirteenth 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 graphite particles of any one of Aspects 1 to 4, 7, or 8.

[0024] According to the specific graphite particles (A) of the present invention and the negative electrode material containing the graphite particles (A) and Si-containing particles (B), by using this as the negative electrode active material of a secondary battery, it is possible to provide a secondary battery with excellent battery characteristics.

[0025] The present invention will be described in detail below. The present invention is not limited to the following description and can be modified as desired without departing from the spirit of the present invention. In this specification, when a numerical value or physical property value is enclosed before and after "to", the value before and after the "to" is included. For example, "A to B μm" means "A μm or more and B μm or less". Numerical ranges disclosed in this specification, such as "A to B", "A or more", and "B or less", disclose numerical ranges with arbitrarily selected upper and lower limits. "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".

[0026] In this specification, particle size refers to the particle size of the powder evaluated on a volume basis. However, in the process of calculating the compressive modulus of the graphite particles, the "particle size of one graphite particle" refers to the actual measured value of one particle, not a statistical value. ５０ " is the average particle size, which is the volume-based median diameter measured by laser diffraction / scattering particle size distribution measurement. ９０ " is this d ５０ In the particle size distribution obtained when measuring the particle size, the particle size is defined as the particle size corresponding to the cumulative 90% from the smallest particle side. ｍａｘ " is this d ５０ In the particle size distribution obtained during the measurement, the particle diameter is the largest particle diameter measured.

[0027] <Graphite particles (A)> One embodiment of the present invention is graphite particles coated with amorphous carbon, which, when the particles are pressurized to a pressure of 9.81 mN and then released to 0.05 mN, exhibit a value (hereinafter also referred to as recovery rate) of 0.5 or more obtained by dividing the amount of particle size displacement observed when the pressure reaches 9.81 mN and then is released to 0.05 mN by the amount of particle size displacement at 9.81 mN. In this specification, such graphite particles are also referred to as graphite particles (A).

[0028] In terms of recovery, the recovery rate is preferably 0.55 or more, more preferably 0.60 or more, and even more preferably 0.65 or more. The graphite particles (A) are preferably particles that do not break when pressed, i.e., graphite particles that do not include a plateau in their mechanical curve when pressed up to a pressure of 9.81 mN.

[0029] In lithium battery anodes, which are made of silicon (Si)-containing active materials that undergo volumetric changes, the mechanical properties of the graphite that makes up the electrode are known to affect performance. However, because Si-containing active materials repeatedly expand and contract during charging and discharging, the destruction of graphite particles during this volumetric change is thought to affect the battery's lifespan. Therefore, there is a demand for materials that can reversibly recover from deformation.

[0030] The compressive modulus, recovery rate, and displacement rate can be calculated using a microcompression tester MCT-510 manufactured by Shimadzu Corporation by applying pressure to a single graphite particle in the direction perpendicular to the graphite particle at a predetermined loading rate, and measuring the compressive stress and compressive displacement when the maximum test force is reached and then unloaded at a predetermined unloading rate. The compressive modulus can be measured when 9.81 mN is reached, or, if a plateau is observed in the mechanical curve, by dividing the compressive stress up to the plateau by the compressive strain (= displacement in particle size at the observation point / particle size of one graphite particle observed under a microscope before compression). The "compressive modulus" herein refers to the average value of three graphite particles (A) determined by the above-mentioned measurement method. The recovery rate can be measured by dividing the displacement in particle size observed when unloading to 0.05 mN after reaching 9.81 mN by the displacement in particle size at the time of reaching 9.81 mN. The "recovery rate" herein refers to the average value of three graphite particles (A) determined by the above-mentioned measurement method. The displacement rate can be measured by dividing the particle size at which 9.81 mN is reached by the particle size before pressure application. The "displacement rate" used in this specification is the average value of three graphite particles (A) determined by the above-mentioned measurement method.

[0031] The graphite particles (A) according to one embodiment of the present invention preferably have a particle size of 10 μm or more and 25 μm or less, more preferably 12 μm or more and 20 μm or less. The particle size of a single particle is the average value of the particle sizes of three graphite particles (A) used in measuring the physical properties of a single particle.

[0032] Average Aspect Ratio The average aspect ratio, which is the ratio of the major axis to the minor axis of the graphite particles (A) contained in the carbon material, is usually 2.1 or more and 10 or less, preferably 2.3 or more and 9 or less, and more preferably 2.5 or more and 8 or less. When the aspect ratio is within the above range, spherical particles can be produced efficiently, and minute voids are formed within the obtained particles, which can mitigate volume expansion associated with charge and discharge and contribute to improving cycle characteristics.

[0033] In this specification, the aspect ratio is calculated as A / B, where A is the longest diameter of a particle when observed three-dimensionally using a scanning electron microscope and B is the shortest diameter perpendicular to A. The average aspect ratio is the average value of the aspect ratios of 50 randomly selected particles.

[0034] - Length of major axis and minor axis The length of the major axis of the graphite particles (A) is usually 100 μm or less, preferably 90 μm or less, and more preferably 80 μm or less. The length of the minor axis of the graphite particles (A) is usually 0.9 μm or more, preferably 1.0 μm or more, and more preferably 1.2 μm or more. When the lengths of the major axis and minor axis of the graphite particles (A) are within the above ranges, minute voids are easily formed within the obtained particles, which can alleviate volume expansion associated with charge and discharge and improve cycle characteristics.

[0035] (Types of Core Graphite) In this specification, graphite particles (A) before being coated with amorphous carbon are referred to as core graphite. Core graphite can be obtained, for example, by heating flake, lump, or plate-like natural graphite, petroleum coke, coal pitch coke, coal needle coke, mesophase pitch, or the like to 2500°C or higher to produce flake, lump, or plate-like artificial graphite, followed by impurity removal, pulverization, sieving, or classification, as necessary. Among these core graphites, flake, lump, or plate-like natural graphite is preferred, and flake-like natural graphite is more preferred, because it is low cost and has a high capacity.

[0036] Natural graphite is classified into flake graphite, crystal line (vein) graphite, and amorphous graphite depending on its properties (see the section on graphite in "Compilation of Powder and Granular Process Technology" (published by Industrial Technology Center, Inc. in 1974) and "HANDBOOK OF CARBON, GRAPHITE, DIAMOND AND FULLERENES" (published by Noyes PubLications)). Flaky graphite has the highest degree of graphitization at 100%, followed by flake graphite at 99.9%. Therefore, it is preferable to use these graphites.

[0037] Flake graphite, a type of natural graphite, is produced in Madagascar, China, Brazil, Ukraine, Canada, etc. Scaly graphite is mainly produced in Sri Lanka. Amorphous graphite is mainly produced in the Korean Peninsula, China, Mexico, etc.

[0038] Among these natural graphites, flake graphite and flaky graphite are preferably used in the present invention because they have advantages such as a high degree of graphitization and a low amount of impurities. Visual methods for confirming that the graphite is flaky include observing the particle surface with a scanning electron microscope; embedding particles in a resin to prepare a thin piece of resin and cutting out the particle cross section; or preparing a coating film made of particles with a cross-section polisher, cutting out the particle cross section, and then observing the particle cross section with a scanning electron microscope.

[0039] Flake graphite and scaly graphite include natural graphite that has been highly purified to exhibit nearly perfect crystallinity, and artificially formed graphite. Of these, natural graphite is preferred because it is soft and can be easily formed into a folded structure.

[0040] <Amorphous Carbon> The graphite particles (A) according to one embodiment of the present invention contain amorphous carbon, which provides excellent lithium ion acceptance.

[0041] Specifically, amorphous carbon can be obtained by heat-treating the amorphous carbon precursor as described below. The amorphous carbon precursor is preferably an amorphous carbon precursor described in the following (i) and / or (ii): (i) a carbonizable organic substance selected from the group consisting of coal-based heavy oil, direct-current heavy oil, cracked petroleum heavy oil, aromatic hydrocarbon, N-ring compound, S-ring compound, polyphenylene, organic synthetic polymer, natural polymer, thermoplastic resin, and thermosetting resin; or (ii) a carbonizable organic substance dissolved in a low-molecular-weight organic solvent.

[0042] (Physical Properties of Graphite Particles (A)) Preferred physical properties of the graphite particles (A) according to this embodiment are as follows. Examples of the graphite particles (A) include the graphite particles (A1) and (A2) described below.

[0043] Graphite particles (A1) If the compressive modulus is strong enough to withstand volume changes in the negative electrode, the graphite structure is maintained, and it is believed that the cycle characteristics, which affect the battery capacity, initial efficiency, and battery life, will be improved. The compressive modulus improves depending on the amount of amorphous carbon. Therefore, even if a natural graphite core with a relatively large specific surface area is used and the amount of amorphous carbon is increased, the coating amorphous carbon layer becomes thinner, thereby improving the compressive modulus while maintaining the capacity. Methods for increasing the specific surface area of ​​the core graphite, which is the core, include a method of mechanically treating the core graphite to be coated to increase the specific surface area, a method of chemically treating the core graphite to increase the specific surface area, and a method of granulating reduced-diameter core graphite into secondary particles to increase the specific surface area.

[0044] For the graphite particles (A1), the lower limit of the compressive elastic modulus when the particles are compressed to a pressure of 9.81 mN is preferably 530 MPa or more, more preferably 540 MPa or more, even more preferably 550 MPa or more, and particularly preferably 560 MPa or more. For the graphite particles (A1), the upper limit of the compressive elastic modulus when the particles are compressed to a pressure of 9.81 mN is preferably 800 MPa or less, more preferably 700 MPa or less.

[0045] The graphite particles (A1) are preferably graphite particles having a displacement rate of 10% or less when the particles are pressurized up to a pressure of 9.81 mN.

[0046] If the displacement rate is too high, the binder used in the electrode will be cut, and therefore, a physical property in which the graphite particles significantly shrink in response to a volume change in Si is undesirable. Therefore, the displacement rate of the graphite particles is preferably 1% or more and 10% or less, more preferably 1% or more and 8% or less, and even more preferably 1% or more and 6% or less.

[0047] Graphite particles (A2) Even if the compressive modulus is insufficient, a structure that exhibits reversibility is believed to be effective in improving battery performance, since it can follow the volume change of the negative electrode. To reduce the binder load, graphite with a low compressive modulus is believed to be able to reduce the binder load while maintaining the pressure required to operate an electrode containing a Si-containing active material. As the amorphous carbon layer becomes thicker, the compressive modulus improves, but it becomes harder and less likely to deform. As the amorphous carbon layer becomes thinner, the compressive modulus is lower, but the amorphous carbon layer becomes more flexible and its followability is believed to increase.

[0048] In the graphite particles (A2), the graphite particles preferably have a compressive modulus of 150 MPa or more and 500 MPa or less when the particles are pressed to a pressure of 9.81 mN.In order to make the electrode containing Si operate most stably, the lower limit of the compressive modulus of the graphite particles is preferably 170 MPa or more, more preferably 190 MPa or more, even more preferably 210 MPa or more, particularly preferably 230 MPa or more, and particularly preferably 250 MPa or more.The upper limit of the compressive modulus of the graphite particles is preferably 450 MPa or less, more preferably 400 MPa or less, more preferably 350 MPa, particularly preferably 300 MPa, and particularly preferably 280 MPa.

[0049] The graphite particles (A2) preferably have a displacement rate of 4% to 10% when the particles are pressurized to a pressure of 9.81 mN. In order to buffer the volume change of Si, the displacement rate is preferably 4% to 10%, more preferably 5% to 9%.

[0050] (Method for Designing Graphite Particles Satisfying Specific Mechanical Properties) The graphite particles of this embodiment usually contain core graphite coated with amorphous carbon in order to increase the acceptability of Li ions.

[0051] The recovery rate of the graphite particles depends on the intraparticle voids and the amount (hereinafter also referred to as coating amount) of the coated amorphous carbon (hereinafter also referred to as coating material). Next, consider design guidelines for graphite particles that satisfy predetermined mechanical properties. The amount of intraparticle voids can be controlled by the manufacturing method of the graphite particles. For example, it can be estimated from the internal pore volume of the product. The amorphous carbon coating rigidifies the graphite particles, which can affect their mechanical properties.

[0052] Generally, an increase in the amount of coating increases the compressive modulus of the graphite particles and tends to decrease the displacement rate. Furthermore, if the thickness of the coated amorphous carbon (coating thickness) increases locally, the graphite particles become more susceptible to cracking, which can cause a decrease in the recovery rate.

[0053] Here, we consider the interface between the liquid amorphous carbon precursor and the core graphite surface to be coated. According to the Wenzel model, as the amount of amorphous carbon precursor increases, the contact angle with the core graphite surface decreases. However, at the nanoscale, the contact angle is underestimated, and it is thought that the contact angle reaches a maximum at a certain amount as the amount of amorphous carbon precursor increases (e.g., Eric et al., Langmuir 2010 26(16), 13297-13304). In this case, it should be noted that the coating thickness increases relative to the amount of amorphous carbon precursor mixed, making it difficult to achieve the desired recovery rate. The influence of the contact angle can also be controlled by the interfacial state between the core graphite and the amorphous carbon precursor, such as the physical properties of the amorphous carbon precursor and the surface state of the core graphite.

[0054] Therefore, by adjusting the properties of the core graphite and the amorphous carbon precursor and controlling the coating thickness based on the above design guidelines, graphite particles that satisfy the desired mechanical properties can be produced.

[0055] An example of a method for calculating the coating thickness is shown below. First, the coverage coefficient is calculated from the Raman R values ​​of each of the core graphite, amorphous carbon precursor, and graphite particle. Next, the amount of coating per graphite particle is calculated from the surface area per particle of the core graphite, which is calculated from the specific surface area and average particle size of the core graphite, and the amount of coating on the graphite particle. Furthermore, the total volume of the coating is calculated from the density of the amorphous carbon. The coating area on the graphite particle is calculated from the coverage coefficient multiplied by the surface area per graphite particle, and this is then divided by the total volume of the coating to calculate the coating thickness.

[0056] <Carbon material> The preferred physical properties of the carbon material containing graphite particles (A) according to one embodiment of the present invention are as follows. In this specification, the carbon material contains a plurality of graphite particles (A). Average particle size (d50) The d50 of the carbon material containing graphite particles (A) ５０ is usually 1 μm or more and 120 μm or less, preferably 3 μm or more and 100 μm or less, more preferably 5 μm or more and 90 μm or less, and even more preferably 10 μm or more and 25 μm or less. ５０ When the d of the carbon material is within the above range, particles having a low chromaticity b* can be produced by combining with the Si-containing particles (B) during the production of the negative electrode material. ５０ When the d of the carbon material is equal to or greater than the lower limit, particles having a particle size within a range that allows an electrode to be formed with an appropriate amount of binder can be produced. ５０ When the particle diameter is equal to or less than the upper limit, the generation of streaks and unevenness due to large particles can be suppressed in the process of adding a binder, water, and an organic solvent to the particles to form a slurry and applying it during the production of a secondary battery.

[0057] Particle size (d90) d of the carbon material containing graphite particles (A) ９０ is usually 1.5 μm or more and 150 μm or less, preferably 4 μm or more and 120 μm or less, and more preferably 6 μm or more and 100 μm or less. ９０ When the d of the carbon material is equal to or greater than the lower limit, the graphite particles (A) and the Si-containing particles (B) can be efficiently combined during the production of the negative electrode material. ９０When the value is equal to or less than the upper limit, the generation of coarse particles can be suppressed when the graphite particles (A) and the Si-containing particles (B) are composited.

[0058] Particle size distribution: From the viewpoint of controlling the mechanical properties of the carbon material, the frequency of the particle size of a single particle of the graphite particles (A) contained in the carbon material (i.e., the proportion of a single particle equivalent to the graphite particles (A) satisfying the predetermined mechanical properties in the entire carbon material) is preferably 5% or more, more preferably 10% or more, and even more preferably 15% or more. Satisfaction of the predetermined mechanical properties according to the embodiment of the present invention can be confirmed through a trial in which the average value of the measured single particle properties is calculated for three graphite particles randomly selected from the carbon material. The "particle size of a single particle" refers to the average value of the average particle sizes of three graphite particles that have been confirmed to satisfy the predetermined mechanical properties, obtained through 10 trials. The frequency of particle sizes within ±10% of the particle size of a single particle contained in the carbon material is preferably 20% or more, more preferably 30% or more, and even more preferably 35% or more. The frequency of particle sizes within ±20% of the particle size of one particle contained in the carbon material is preferably 40% or more, more preferably 50% or more, even more preferably 55% or more, and most preferably 60% or more.

[0059] Particle size distribution data measured by a laser diffraction / scattering particle size analyzer includes the frequency and cumulative frequency for each particle size. Particle size dn means the particle size at which the cumulative frequency is n%. The frequency q(dn) of a particle at particle size dn is calculated by linear interpolation from the data of the two closest points on either side of dn, (dn1, q(dn1)) and (dn2, q(dn2)).

[0060] When the pore size distribution of a carbon material containing graphite particles (A) measured by mercury intrusion porosimetry has two or more peaks, the pore size at the peak top of the smallest pore size peak of the carbon material is preferably 500 nm or less, more preferably 400 nm or less, and even more preferably 300 nm or less, because the pores within the particles are small and the scales within the particles become more dense, thereby reducing the expansion of the electrode plate. The lower limit of the pore size is not particularly limited, but is usually 5 nm or more.

[0061] The cumulative pore volume (mL / g) of the carbon material containing the graphite particles (A) is preferably 0.002 to 0.120, more preferably 0.003 to 0.090, even more preferably 0.005 to 0.070, and particularly preferably 0.010 to 0.050. Here, in order to enable smooth movement of lithium ions within the electrode during charge and discharge and to achieve excellent rapid charge and discharge characteristics and low-temperature input and output characteristics, the cumulative pore volume is preferably 0.002 or more, more preferably 0.003 or more, even more preferably 0.005 or more, and particularly preferably 0.010 or more, and is preferably less than 0.120, more preferably less than 0.090, even more preferably less than 0.070, and particularly preferably less than 0.050.

[0062] In this specification, the pore size distribution is measured by mercury intrusion porosimetry. Specifically, a mercury porosimeter is used to measure a sample weighed to approximately 0.2 g, which is then sealed in a powder cell and degassed at 25 °C and 50 μmHg or less for 10 minutes for pretreatment. Next, the pressure is reduced to 4 psia, mercury is introduced into the cell, and the pressure is increased stepwise from 4 psia to 40,000 psia, and then decreased to 25 psia. The number of steps during pressure increase is 80 or more, and after each step, the amount of mercury intrusion is measured after a 10-second equilibration period. The pore size distribution is calculated from the mercury intrusion curve obtained in this manner using the Washburn equation. The surface tension (γ) of mercury is calculated as 485 dyne / cm and the contact angle (ψ) as 140°. From the obtained results, a graph is created with the pore size on the horizontal axis and the pore volume on the vertical axis. From this graph, peaks are identified, and the minimum value between the peak with the smallest pore diameter and the next peak (between the two peaks with smaller pore diameters) is identified, and the cumulative pore volume below this minimum value is taken as the cumulative pore volume (mL / g). The peak refers to the apex of the waveform, and its height (the difference in cumulative pore volume between the apex and the two adjacent minimum values) is 0.002 mL / g or more.

[0063] Tap density: The tap density of the carbon material containing graphite particles (A) is usually 0.1 g / cm ３ 1.0g / cm or more ３ or less, preferably 0.13 g / cm ３ 0.8g / cm or more ３ or less, more preferably 0.15 g / cm ３0.6g / cm or more ３ When the tap density is within the above range, minute voids are likely to be formed within the resulting particles.

[0064] In this specification, the tap density is measured using a powder density measuring instrument with a diameter of 1.5 cm and a volume capacity of 20 cm ３ After filling a cylindrical tap cell with carbon material, tapping was performed 1000 times with a stroke length of 10 mm, and the density was calculated from the volume and mass of the sample at that time.

[0065] In this specification, the specific surface area is a value measured by the BET method using nitrogen adsorption.

[0066] The spacing between (002) planes (d ００２ ) and Lc The interplanar spacing (d ００２ The Lc of the carbon material measured by wide-angle X-ray diffraction is usually 90 nm or more, preferably 95 nm or more. The interplanar spacing (d ００２ When Lc is 0.337 nm or less, the crystallinity of the graphite particles (A) contained in the carbon material is high, and particles for a secondary battery negative electrode active material with a high capacity can be obtained. Even when Lc is 90 nm or more, the crystallinity of the graphite particles (A) is high, and a negative electrode active material with a high capacity can be obtained.

[0067] In this specification, the interplanar spacing of the (002) plane and Lc are values ​​measured by wide-angle X-ray diffraction.

[0068] Raman R value: When the graphite particles (A) contain the above-described graphite particles (A1), the Raman R value of the carbon material is preferably 0.4 to 1.0, more preferably 0.4 to 0.8, even more preferably 0.4 to 0.6, and particularly preferably 0.4 to 0.5. The Raman R value can be controlled by the amount of amorphous carbon precursor mixed and the firing temperature.

[0069] When the graphite particles (A) contain the above-mentioned graphite particles (A2), the Raman R value of the carbon material is preferably 0.3 or more and 0.4 or less, and more preferably 0.35 or more and 0.4 or less.

[0070] Specific surface area by BET method The BET specific surface area of ​​the carbon material containing graphite particles (A) is 0.5 m ２ / g or more 3.0m ２ / g or less, and 1.5m ２ / g or more 3.0m ２ It is more preferable that the SiO2 content is 1 / g or less.

[0071] <Si-containing particles (B)> (Types of Si-containing particles (B)) Si-containing particles are included in the negative electrode material of this embodiment together with the graphite particles of this embodiment. Such Si-containing particles are also referred to as Si-containing particles (B). The Si-containing particles (B) may be any particles containing elemental silicon (Si), and the Si may be simple Si or a Si compound. The crystalline state of the Si-containing particles (B) may be single crystal or polycrystalline. The Si-containing particles (B) are preferably polycrystalline or amorphous, since they can be easily reduced in particle size and have improved rate characteristics.

[0072] Examples of Si compounds include Si oxides, Si nitrides, and Si carbides. Specific Si compounds represented by the general formula include SiOx, SiNx, SiCx, and SiZxOy (Z=C, N), with SiOx being preferred. The Si compound represented by the general formula SiOx is silicon dioxide (SiO ２ The value of x is usually 0 to 2, preferably 0.1 to 1.8, more preferably 0.5 to 1.5, and even more preferably 0.8 to 1.2. When x is within the above range, it is possible to achieve a high capacity and simultaneously reduce the irreversible capacity due to the bonding of Li and oxygen.

[0073] In this specification, the value of x in SiOx is a value obtained by measuring the amount of oxygen in SiOx by impulse furnace heating extraction-IR detection method under an inert gas atmosphere, measuring the amount of silicon in SiOx by ICP atomic emission spectrometry, and calculating the ratio of the amount of oxygen to the amount of silicon.

[0074] SiOx has a larger theoretical capacity than carbon materials, and amorphous Si or nano-sized Si crystals allow alkali ions such as lithium ions to easily enter and exit, making it possible to obtain a high capacity. The crystallite size is not particularly specified, and impurities may be present in the Si compound and on the surface of the compound.

[0075] (Physical Properties of Si-Containing Particles (B)) The Si-containing particles (B) preferably exhibit the following physical properties.

[0076] Average particle size (d50) of Si-containing particles (B) ５０ is usually 0.3 μm or more and 10 μm or less, preferably 0.35 μm or more and 3 μm or less, and more preferably 0.4 μm or more and 1 μm or less. ５０ When the volume expansion due to charge and discharge is within the above range, good cycle characteristics can be obtained while maintaining the charge and discharge capacity.

[0077] Specific surface area by BET method The specific surface area of ​​the Si-containing particles (B) by the BET method is usually 0.5 m ２ / g or more 120m ２ / g or less, preferably 1m ２ / g or more 100m ２ When the specific surface area of ​​the Si-containing particles (B) measured by the BET method is within the above range, the battery has high charge / discharge efficiency and discharge capacity, and lithium is quickly absorbed and released during high-rate charge / discharge, resulting in excellent rate characteristics, which is preferable.

[0078] Oxygen content The oxygen content of the Si-containing particles (B) is usually 0.01% by mass or more and 50% by mass or less, preferably 0.05% by mass or more and 45% by mass or less, based on 100% by mass of the Si-containing particles (B). The oxygen distribution state in the Si-containing particles (B) may be present near the surface, may be present inside the particles, or may be present uniformly within the particles, but is preferably present near the surface. When the oxygen content of the Si-containing particles (B) is within the above range, the strong bond between Si and O suppresses volume expansion during charge and discharge, resulting in excellent cycle characteristics, which is preferable.

[0079] In this specification, the oxygen content of the Si-containing particles (B) is a value obtained by measuring the amount of oxygen in the Si-containing particles (B) by an impulse furnace heating extraction-IR detection method under an inert gas atmosphere.

[0080] Crystallite size The Si-containing particles (B) may have a crystalline structure or may be amorphous. When the Si-containing particles (B) have a crystalline structure, the crystallite size of the (111) plane of the Si-containing particles (B) calculated by X-ray diffraction is usually 0.05 nm or more and 100 nm or less, preferably 1 nm or more and 50 nm or less. When the crystallite size of the Si-containing particles (B) is within the above range, the reaction between Si and Li ions proceeds quickly, which is preferable because it has excellent input / output properties.

[0081] In this specification, the crystallite size is a value determined by the Debye-Scherrer method from a diffraction peak attributable to the Si(111) plane centered around 2θ=28.4° observed by wide-angle X-ray diffraction.

[0082] (Method for producing Si-containing particles (B)) Commercially available Si-containing particles may be used as the Si-containing particles (B). The Si-containing particles (B) may be produced by subjecting large-particle-size Si-containing particles to mechanical energy treatment using a ball mill or the like, as described below.

[0083] Furthermore, while there is no particular limitation on the production method, Si-containing particles produced by the method described in Japanese Patent No. 3952118 can also be used as the Si-containing particles (B). For example, when producing SiOx, Si dioxide powder and metal Si powder are mixed in a specific ratio, the mixture is charged into a reactor, and the pressure is reduced to atmospheric pressure or a specific pressure, and the temperature is raised to 1000°C or higher and maintained at that temperature to generate SiO gas, which is then cooled and precipitated to obtain general formula SiOx particles (vapor deposition process). The precipitate can also be converted into particles by applying mechanical energy treatment and used.

[0084] When mechanical energy treatment is performed, for example, a device such as a ball mill, a vibration ball mill, a planetary ball mill, a tumbling ball mill, or a bead mill is used to place raw materials filled in a reactor and a moving body that does not react with the raw materials, and the raw materials are subjected to vibration, rotation, or a combination of these movements to form Si-containing particles (B) suitable for the negative electrode material according to one embodiment of the present invention.

[0085] The mechanical energy treatment time is usually 3 minutes or more, preferably 5 minutes or more, more preferably 10 minutes or more, and even more preferably 15 minutes or more, and usually 5 hours or less, preferably 4 hours or less, more preferably 3 hours or less, and even more preferably 1 hour or less. When the mechanical energy treatment time is within the above range, both improved productivity and stability of product physical properties can be achieved. From a process perspective, it is preferable that the mechanical energy treatment temperature be a temperature between the freezing point and the boiling point of the solvent.

[0086] The Si-containing particles (B) are usually prepared by first grinding the starting material as finely as possible using a dry grinder such as a ball mill, a vibration mill, a pulverizer, or a jet mill, and then wet-grinding the starting material to a final particle size. During this wet-grinding, the starting material may be mixed with a carbon material such as carbon black, ketjen black, or acetylene black and ground, and then used as is.

[0087] When wet grinding, it is preferable to select a dispersion solvent that has no or very little reactivity with the Si-containing particles (B). If necessary, a small amount of dispersant (surfactant) may be added to wet the dispersion solvent. It is also preferable to select a dispersant that has no or very little reactivity with the Si-containing particles (B).

[0088] -Type of Dispersion Solvent The type of dispersion solvent is not particularly limited, but examples include non-polar compounds having an aromatic ring and polar solvents. The type of non-polar compound having an aromatic ring is not particularly limited, but it is preferable that it is not reactive with the raw material of the Si-containing particles (B). For example, aromatic compounds that are liquid at room temperature, such as benzene, toluene, xylene, cumene, and methylnaphthalene; alicyclic hydrocarbons such as cyclohexane, methylcyclohexane, methylcyclohexene, and bicyclohexyl; and residual oils from petrochemical and coal chemical processes, such as light oil and heavy oil. Among these, xylene, methylnaphthalene, and heavy oil are preferred, with methylnaphthalene and heavy oil being more preferred, and heavy oil being even more preferred due to its high boiling point. In wet milling, increasing milling efficiency is likely to generate heat. Solvents with low boiling points may volatilize and result in high concentrations.

[0089] Preferred polar solvents are those that dissolve not only water but also organic solvents, such as NMP (N-methyl-2-pyrrolidone), GBL (γ-butyrolactone), DMF (NN dimethylformamide), methanol, ethanol, 1-propanol, 2-propanol, etc. Among these, NMP (N-methyl-2-pyrrolidone) is preferred because it is less susceptible to decomposition and has a high boiling point, and 2-propanol is preferred because it is inexpensive.

[0090] The mixing ratio of the dispersion solvent is usually 10% by mass or more and 50% by mass or less, preferably 20% by mass or more and 40% by mass or less, based on the total of 100% by mass of the Si-containing particles (B) and the dispersion solvent. When the mixing ratio of the dispersion solvent is equal to or more than the lower limit, the dispersion of the Si-containing particles (B) tends to be uniform. When the mixing ratio of the dispersion solvent is equal to or less than the upper limit, the cost tends to be reduced.

[0091] -Type of Dispersant A dispersant may be used in producing the Si-containing particles (B). Examples of dispersants include high-molecular-weight polyester acid amide amine dispersants, polyether ester acid amine salts, polyethylene glycol phosphate esters, primary to tertiary amines, and quaternary amine salts. Among these, high-molecular-weight polyester acid amide amine dispersants are preferred because they are more likely to provide a dispersion effect due to steric hindrance.

[0092] <Anode Material> One embodiment of the present invention is an anode material containing a carbon material (A) and Si-containing particles (B).

[0093] (Content ratio of carbon material (A) and Si-containing particles (B)) The content ratio of the carbon material (A) and the Si-containing particles (B) in the negative electrode material according to one embodiment of the present invention is preferably 10 to 95 mass% of the carbon material (A) and the Si-containing particles (B) and the Si-containing particles (B) are 3 to 60 mass% of the total of 100 mass% of the carbon material (A), the Si-containing particles (B), and the carbonaceous material used as needed. It is more preferable that the content ratio of the carbon material (A) is 30 to 90 mass% and the content ratio of the Si-containing particles (B) is 5 to 50 mass%. It is even more preferable that the content ratio of the carbon material (A) is 50 to 85 mass% and the content ratio of the Si-containing particles (B) is 8 to 40 mass%. When the content ratio of the carbon material (A) is not less than the above lower limit and the content ratio of the Si-containing particles (B) is not more than the above upper limit, it is easy to proceed with the composite formation of the carbon material (A) and the Si-containing particles (B). When the content of the carbon material (A) is equal to or less than the upper limit and the content of the Si-containing particles (B) is equal to or more than the lower limit, the negative electrode material according to one embodiment of the present invention can have a high capacity.

[0094] (Conductive Aid) The negative electrode material preferably further contains a conductive aid. Examples of the conductive aid include coal tar pitch, artificial graphite obtained by graphitizing a carbon-containing substance such as resin by heating it to 2500°C or higher, and carbon nanotubes. Carbon nanotubes are preferred as the conductive aid because they allow efficient contact between particles.

[0095] <Other Physical Properties of Negative Electrode Material> Preferred physical properties of the negative electrode material according to one embodiment of the present invention are as follows.

[0096] The spacing between (002) planes (d００２ The interplanar spacing (d) of the (002) plane of the carbon material (A) contained in the negative electrode material according to one embodiment of the present invention, as determined by wide-angle X-ray diffraction. ００２ The Lc of the negative electrode material according to one embodiment of the present invention, as measured by wide-angle X-ray diffraction, is usually 90 nm or more, and preferably 95 nm or more. The interplanar spacing (d ００２ When the SiO 2 content and Lc are within the above ranges, the particles for a secondary battery negative electrode active material will become a high-capacity electrode.

[0097] Tap density The tap density of the negative electrode material according to one embodiment of the present invention is usually 0.5 g / cm ３ or more, preferably 0.6 g / cm ３ More preferably, 0.8 g / cm ３ When the tap density of the negative electrode material according to one embodiment of the present invention is equal to or greater than the lower limit, the particles are spherical, sufficient continuous voids are secured within the electrode, and the mobility of Li ions in the electrolyte held in the voids increases. This tends to improve rapid charge / discharge characteristics.

[0098] Raman R value The Raman R value of the negative electrode material according to one embodiment of the present invention is usually 0.05 or more and 0.4 or less, and preferably 0.1 or more and 0.35 or less. When the Raman R value of the negative electrode material according to one embodiment of the present invention is within the above range, the crystallinity of the particle surface is well-ordered, and a high capacity can be expected.

[0099] In this specification, the Raman R value is the value at 1580 cm in the Raman spectrum obtained by Raman spectroscopy. －１ The intensity of the peak PA near 1360 cm －１ The intensity of the peak P near 1580 cm was measured, and the intensity ratio (I / I) was calculated. －１ "Around 1580-1620 cm" －１ The range is "1360 cm －１ "Around 1350-1370 cm" －１ Refers to the range of.

[0100] Raman spectra can be measured using a Raman spectrometer. Specifically, the particles to be measured are loaded into a measurement cell by gravity, and the measurement cell is irradiated with argon ion laser light while the measurement cell is rotated in a plane perpendicular to the laser light.

[0101] Specific surface area by BET method The specific surface area by BET method of the negative electrode material according to one embodiment of the present invention is usually 0.1 m ２ / g or more 40m ２ / g or less, preferably 0.7m ２ / g or more 35m ２ / g or less, more preferably 1m ２ / g or more 30m ２ / g or less. When the specific surface area measured by the BET method of the negative electrode material according to one embodiment of the present invention is equal to or greater than the above lower limit, the lithium ion acceptance during charging tends to be improved when used as a negative electrode active material. When the specific surface area measured by the BET method of the negative electrode material according to one embodiment of the present invention is equal to or less than the above upper limit, the contact area between the particles and the non-aqueous electrolyte can be suppressed when used as a negative electrode active material, and reactivity is reduced. This makes it easier to suppress gas generation and tends to make it easier to obtain a preferable battery.

[0102] ・Average particle size (d ５０ ) d of the negative electrode material according to one embodiment of the present invention ５０ is usually 1 μm or more and 50 μm or less, preferably 4 μm or more and 40 μm or less, and more preferably 6 μm or more and 30 μm or less. ５０ When the d of the negative electrode material according to one embodiment of the present invention is equal to or greater than the above lower limit, particles having a particle size within a range that allows an electrode to be formed with an appropriate amount of binder can be produced. ５０ When the particle diameter is equal to or less than the upper limit, the generation of streaks and unevenness due to large particles can be suppressed in the process of adding a binder, water, and an organic solvent to the particles to form a slurry and applying it during the production of a secondary battery.

[0103] <Method for producing carbon material> There are no particular limitations on the method for producing a carbon material, as long as it contains graphite particles coated with amorphous carbon and can produce a material that satisfies predetermined mechanical properties. For example, a method in which a carbon material is spheronized in the presence of a granulating agent, pressurized, and impregnated with an amorphous carbon precursor is preferred, as this method can densely form pores within the particles and efficiently control the cumulative pore volume. Specifically, a preferred production method includes the following steps (1) to (6): Step (1): Adjusting the particle size of the carbon material; Step (2): Mixing the carbon material with a granulating agent; Step (3): Spheronizing the carbon material; Step (4): Removing the granulating agent; Step (5): Pressurizing; Step (6): Impregnating with amorphous carbon.

[0104] Steps (1) to (6) will be described below, but steps other than steps (1) to (6) may be included before or after each step, and the production method is not limited to steps (1) to (6).

[0105] (Step (1)) Step (1) is a step of adjusting the particle size of the carbonaceous material raw material.

[0106] 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.

[0107] (Step (2)) Step (2) is a step of mixing the carbonaceous raw material and the granulating agent.

[0108] 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.

[0109] (Step (3)) Step (3) is a step of spheronizing the carbonaceous raw material.

[0110] 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.

[0111] 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 amorphous carbon or graphite. In addition, the amount of edges available as sites for lithium ion insertion and desorption increases, making it easier for the electrolyte to efficiently penetrate the voids within the carbonaceous material. 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.

[0112] 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.

[0113] The particle size of the carbon material can be controlled by the time of the spheroidizing treatment and the magnitude of the mechanical energy applied.

[0114] 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.

[0115] (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.

[0116] 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.

[0117] (Step (5)) Step (5) is a step of pressure treatment.

[0118] Examples of the pressure treatment include isotropic pressure treatment and anisotropic pressure treatment.

[0119] The pressurizing means is preferably an isotropic pressurizing treatment, and examples thereof include hydrostatic isotropic pressurizing treatment using water as a pressurizing medium, pneumatic isotropic pressurizing treatment using a gas such as air as a pressurizing medium, and pressurizing treatment in which the mixture is filled into a mold and pressed in a certain direction using a uniaxial press.

[0120] 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, since it is easy to control the pressure so that the obtained carbon material (A) satisfies formula (1), 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.

[0121] 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.

[0122] (Step (6)) Step (6) is a step of attaching amorphous carbon. By attaching amorphous carbon to the carbon material, it is possible to suppress side reactions between the negative electrode and the electrolyte. The amorphous carbon is ００２ This refers to carbon with a value of 0.340 nm or greater.

[0123] A preferred method of impregnating a carbon material with amorphous carbon involves mixing the carbon material with an amorphous carbon precursor, heating the mixture in a non-oxidizing atmosphere, and converting the amorphous carbon precursor into amorphous carbon, because this method makes it easy to control the amount of voids within the particles.

[0124] The mixing ratio of the carbon material and the amorphous carbon precursor may be appropriately set so as to achieve a desired coating ratio.

[0125] 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, with nitrogen being more preferred, as they can suppress the formation of micropores due to oxidation.

[0126] The heating temperature when converting an amorphous carbon precursor into amorphous carbon 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.

[0127] Examples of amorphous carbon 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.

[0128] The amount of amorphous carbon coating on the carbon material and the Raman R value can be controlled by adjusting the amount of amorphous carbon precursor mixed and the heating temperature.

[0129] 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.

[0130] <Method for producing a negative electrode material> The method for producing a negative electrode material according to this embodiment includes a step of mixing a carbon material (A) and Si-containing particles (B). At this time, a conductive additive may be mixed together. The mixing method is not particularly limited as long as the carbon material (A) and the Si-containing particles (B) can be mixed to obtain a desired composition.

[0131] <Applications> When the negative electrode material according to one embodiment of the present invention is used as a negative electrode active material for a secondary battery, a secondary battery with excellent battery characteristics can be realized. Therefore, the negative electrode material according to one embodiment of the present invention is useful as a negative electrode active material for a secondary battery.

[0132] [Secondary Battery] A secondary battery according to one embodiment of the present invention is a secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, wherein the negative electrode comprises a current collector and a negative electrode active material layer formed on the current collector, and the negative electrode active material layer comprises the negative electrode material according to one embodiment of the present invention. The secondary battery according to one embodiment of the present invention is typically manufactured by a method for manufacturing a secondary battery according to one embodiment of the present invention, which includes a step of forming, on a current collector, a negative electrode active material layer comprising the negative electrode material according to one embodiment of the present invention to obtain a negative electrode.

[0133] <Negative electrode> To produce a negative electrode using the negative electrode material according to one embodiment of the present invention (hereinafter, may be referred to as "negative electrode according to one embodiment of the present invention"), the negative electrode material according to one embodiment of the present invention is mixed with a binder (binding resin) and dispersed in a dispersion medium to form a slurry, which is then applied to a current collector and dried to form a negative electrode active material layer on the current collector.

[0134] The binder used has an olefinic unsaturated bond in the molecule. There are no particular restrictions on the type. Specific examples include styrene-butadiene rubber, styrene-isoprene-styrene rubber, acrylonitrile-butadiene rubber, butadiene rubber, and ethylene-propylene-diene copolymer. By using such a binder having an olefinic unsaturated bond, the swelling of the negative electrode active material layer with the electrolyte can be reduced. Among these, styrene-butadiene rubber is preferred due to its ease of availability.

[0135] As a binder having an olefinic unsaturated bond in the molecule, it is desirable that the molecular weight is large or the proportion of unsaturated bonds is high. As a binder having a large molecular weight, it is desirable that the weight average molecular weight is usually 10,000 or more, preferably 50,000 or more, and usually 1,000,000 or less, preferably 300,000 or less. As a binder having a high proportion of unsaturated bonds, it is desirable that the number of moles of olefinic unsaturated bonds per gram of the total binder is usually 2.5 × 10 －７ or more, preferably 8 x 10 －７ Above, usually 5 x 10 －６ Below 1 × 10, preferably －６ The following ranges are desirable:

[0136] It is sufficient for the binder to satisfy at least one of the molecular weight requirements and the unsaturated bond ratio requirements, but it is more preferable for it to satisfy both requirements simultaneously. If the molecular weight of the binder having an olefinic unsaturated bond is too small, the mechanical strength will be poor. If the molecular weight of the binder is too large, the flexibility will be poor. Furthermore, if the ratio of olefinic unsaturated bonds in the binder is too low, the strength improvement effect will be reduced, and if it is too high, the flexibility will be poor.

[0137] The binder having an olefinic unsaturated bond desirably has a degree of unsaturation in the range of usually 15% or more, preferably 20% or more, more preferably 40% or more, and usually 90% or less, preferably 80% or less. The degree of unsaturation represents the ratio (%) of double bonds to the repeating units of the polymer.

[0138] A binder having no olefinic unsaturated bond can also be used in combination with the binder having the above-mentioned olefinic unsaturated bond, as long as the effects of the present invention are not lost. The mixing ratio of the binder having no olefinic unsaturated bond to the amount of the binder having an olefinic unsaturated bond is usually 150% by mass or less, preferably 120% by mass or less. By using a binder having no olefinic unsaturated bond in combination, the coating property can be improved, but if the amount used is too large, the strength of the active material layer will decrease.

[0139] Examples of binders that do not have olefinic unsaturated bonds include polysaccharides such as methyl cellulose, carboxymethyl cellulose, and starch; thickening polysaccharides such as carrageenan, pullulan, guar gum, and xanthan gum; polyethers such as polyethylene oxide and polypropylene oxide; vinyl alcohols such as polyvinyl alcohol and polyvinyl butyral; polyacids such as polyacrylic acid and polymethacrylic acid or metal salts of these polymers; fluorine-containing polymers such as polyvinylidene fluoride; alkane-based polymers such as polyethylene and polypropylene, and copolymers thereof.

[0140] The mass ratio (negative electrode material / binder) of the negative electrode material to the binder (which may be a mixture of a binder having unsaturated bonds and a binder not having unsaturated bonds as described above) in the slurry is typically 90 / 10 or more, preferably 95 / 5 or more, and typically 99.9 / 0.1 or less, preferably 99.5 / 0.5 or less, in terms of dry mass ratio. If the binder ratio is too high, it is likely to result in a decrease in capacity and an increase in resistance. If the binder ratio is too low, the negative electrode plate will have poor strength.

[0141] The dispersion medium for preparing the slurry in which the negative electrode material and binder are dispersed can be an organic solvent such as alcohol or water. A conductive agent may be added to the slurry, if desired. Examples of the conductive agent include carbon black such as acetylene black, ketjen black, and furnace black, and fine powders of Cu, Ni, or alloys thereof with a particle size of 1 μm or less. The amount of the conductive agent added is typically 10% by mass or less of the negative electrode material.

[0142] The current collector to which the slurry is applied can be a conventionally known one. Specific examples include thin metal films such as rolled copper foil, electrolytic copper foil, and stainless steel foil. The thickness of the current collector is usually 4 μm or more, preferably 6 μm or more, and usually 30 μm or less, preferably 20 μm or less.

[0143] The above slurry is applied to a current collector using a doctor blade or the like, dried, and then pressed with a roll press or the like to form a negative electrode active material layer. At this time, the slurry is applied to the current collector in such a manner that the amount of negative electrode material adhered thereto is 5 to 15 mg / cm. ２ It is preferable to apply the solution so that the thickness becomes

[0144] After the slurry is applied to the current collector, it is dried at a temperature of usually 60° C. or higher, preferably 80° C. or higher, and usually 200° C. or lower, preferably 195° C. or lower, in dry air or an inert atmosphere.

[0145] The thickness of the negative electrode active material layer obtained by applying and drying the slurry after pressing is usually 5 μm or more, preferably 20 μm or more, more preferably 30 μm or more, and usually 200 μm or less, preferably 100 μm or less, more preferably 75 μm or less. If the negative electrode active material layer is too thin, it lacks practicality as a negative electrode active material layer due to the balance with the particle size of the negative electrode material, which is the negative electrode active material. If the negative electrode active material layer is too thick, it is difficult to obtain sufficient Li ion absorption and desorption function for high-density current values.

[0146] The density of the negative electrode material in the negative electrode active material layer varies depending on the application, but in applications where capacity is important, it is preferably 1.55 g / cm ３ Above, especially 1.6 g / cm ３ Further, 1.65 g / cm ３ or more, especially 1.7 g / cm ３ If the density is too low, the battery capacity per unit volume is not necessarily sufficient. If the density is too high, the rate characteristics decrease. Therefore, the density of graphite is 1.9 g / cm or more. ３ The following is preferred:

[0147] When the negative electrode according to one embodiment of the present invention is produced using the negative electrode material described above, the method and selection of other materials are not particularly limited. When a secondary battery is produced using this negative electrode, the selection of components necessary for the battery configuration, such as the positive electrode and electrolyte, that constitute the secondary battery is also not particularly limited.

[0148] <Secondary Battery> Details of a secondary battery according to one embodiment of the present invention, including a negative electrode using a negative electrode material, will be described below, taking a lithium-ion secondary battery as an example. Materials that can be used in the secondary battery according to one embodiment of the present invention, manufacturing methods, etc., are not limited to the following specific examples.

[0149] The basic structure of a secondary battery according to one embodiment of the present invention, particularly a lithium ion secondary battery, is the same as that of conventionally known lithium ion secondary batteries, and typically includes a positive electrode and a negative electrode capable of absorbing and releasing lithium ions, and an electrolyte. The negative electrode used is the negative electrode according to one embodiment of the present invention described above.

[0150] The positive electrode is formed by forming a positive electrode active material layer containing a positive electrode active material and a binder on a current collector.

[0151] Examples of the positive electrode active material include metal chalcogen compounds capable of absorbing and releasing alkali metal cations such as lithium ions during charging and discharging. Examples of the metal chalcogen compounds include transition metal oxides such as vanadium oxide, molybdenum oxide, manganese oxide, chromium oxide, titanium oxide, and tungsten oxide; transition metal sulfides such as vanadium sulfide, molybdenum sulfide, titanium sulfide, and CuS; NiPS ３ , FePS ３ Phosphorus-sulfur compounds of transition metals such as VSe ２ , NbSe ３ Selenium compounds of transition metals such as Fe ０．２５ V ０．７５ S ２ , Na ０．１ CrS ２ composite oxides of transition metals such as LiCoS ２ , LiNiS ２ and complex sulfides of transition metals such as those mentioned above.

[0152] Among these, V２ O ５ , V ５ O １３ , V.O. ２ , Cr ２ O ５ , MnO ２ , TiO, MoV ２ O ８ , LiCoO ２ , LiNiO ２ , LiMn ２ O ４ , TiS ２ , V ２ S ５ , Cr ０．２５ V ０．７５ S ２ , Cr ０．５ V ０．５ S ２ etc. are preferred, and LiCoO is particularly preferred. ２ , LiNiO ２ , LiMn ２ O ４ or lithium transition metal composite oxides in which part of these transition metals is substituted with other metals. These positive electrode active materials may be used alone or in combination.

[0153] Any known binder can be selected and used as the binder for binding the positive electrode active material. Examples include inorganic compounds such as silicate and water glass, and resins without unsaturated bonds such as Teflon (registered trademark) and polyvinylidene fluoride. Among these, resins without unsaturated bonds are preferred. If a resin with unsaturated bonds is used as the resin for binding the positive electrode active material, it may decompose during the oxidation reaction (during charging). The weight-average molecular weight of these resins is usually 10,000 or more, preferably 100,000 or more, and usually 3,000,000 or less, preferably 1,000,000 or less.

[0154] A conductive agent may be contained in the positive electrode active material layer to improve the conductivity of the electrode. There are no particular limitations on the conductive agent as long as it can be mixed in an appropriate amount with the active material to impart conductivity. Typical examples of the conductive agent include carbon powders such as acetylene black, carbon black, and graphite, and fibers, powders, and foils of various metals.

[0155] The positive electrode plate is formed by forming a slurry of the positive electrode active material and binder with a dispersant, applying the slurry to a current collector, and drying the slurry, in the same manner as in the production of the negative electrode according to the embodiment of the present invention. The positive electrode current collector may be made of aluminum, nickel, stainless steel (SUS), or the like, but is not limited thereto.

[0156] The electrolyte may be a non-aqueous electrolytic solution in which a lithium salt is dissolved in a non-aqueous solvent, or a non-aqueous electrolytic solution in the form of a gel, rubber, or solid sheet made from an organic polymer compound or the like.

[0157] The nonaqueous solvent used in the nonaqueous electrolyte solution is not particularly limited, and can be appropriately selected from known nonaqueous solvents that have been proposed as solvents for nonaqueous electrolyte solutions. Examples include chain carbonates such as diethyl carbonate, dimethyl carbonate, and ethyl methyl carbonate; cyclic carbonates such as ethylene carbonate, propylene carbonate, and butylene carbonate; chain ethers such as 1,2-dimethoxyethane; cyclic ethers such as tetrahydrofuran, 2-methyltetrahydrofuran, sulfolane, and 1,3-dioxolane; chain esters such as methyl formate, methyl acetate, and methyl propionate; and cyclic esters such as γ-butyrolactone and γ-valerolactone.

[0158] These non-aqueous solvents may be used alone or in combination of two or more. In the case of a mixed solvent, a combination of a mixed solvent containing a cyclic carbonate and a chain carbonate is preferred. It is particularly preferred that the cyclic carbonate is a mixed solvent of ethylene carbonate and propylene carbonate, since this can exhibit high ionic conductivity even at low temperatures and improve low-temperature charging load characteristics.

[0159] In particular, the content of propylene carbonate is preferably 2% by mass or more and 80% by mass or less, more preferably 5% by mass or more and 70% by mass or less, and even more preferably 10% by mass or more and 60% by mass or less, relative to the total amount of the non-aqueous solvent. If the content of propylene carbonate is lower than the above lower limit, the ionic conductivity at low temperatures decreases. If the content of propylene carbonate is higher than the above upper limit, the propylene carbonate solvated with Li ions co-intercalates between the graphite phases of the negative electrode, causing delamination and deterioration of the graphite-based negative electrode active material, resulting in a problem of insufficient capacity being obtained.

[0160] The lithium salt used in the non-aqueous electrolyte solution is not particularly limited, and can be appropriately selected from known lithium salts known to be usable for this purpose. For example, halides such as LiCl and LiBr; LiClO ４ , LiBrO ４ , LiClO ４ perhalogenates such as LiPF ６ , LiBF ４ , LiAsF ６ inorganic lithium salts such as inorganic fluoride salts such as LiCF ３ SO ３ , LiC ４ F ９ SO ３ perfluoroalkanesulfonates such as Li trifluorosulfonimide ((CF ３ SO ２ ) ２ and fluorine-containing organic lithium salts such as perfluoroalkanesulfonic acid imide salts such as LiClO ４ , LiPF ６ , LiBF ４ , is preferred.

[0161] The lithium salt may be used alone or in combination of two or more. The concentration of the lithium salt in the non-aqueous electrolyte solution is usually in the range of 0.5 mol / L or more and 2.0 mol / L or less.

[0162] When an organic polymer compound is contained in the non-aqueous electrolytic solution and the electrolyte is used in the form of a gel, rubber, or solid sheet, specific examples of the organic polymer compound include polyether polymer compounds such as polyethylene oxide and polypropylene oxide; crosslinked polymers of polyether polymer compounds; vinyl alcohol polymer compounds such as polyvinyl alcohol and polyvinyl butyral; insolubilized vinyl alcohol polymer compounds; polyepichlorohydrin; polyphosphazene; polysiloxane; vinyl polymer compounds such as polyvinylpyrrolidone, polyvinylidene carbonate, and polyacrylonitrile; and polymer copolymers such as poly(ω-methoxyoligooxyethylene methacrylate), poly(ω-methoxyoligooxyethylene methacrylate-co-methyl methacrylate), and poly(hexafluoropropylene-vinylidene fluoride).

[0163] The non-aqueous electrolyte solution may further contain a film-forming agent. Specific examples of the film-forming agent include carbonate compounds such as vinylene carbonate, vinyl ethyl carbonate, and methyl phenyl carbonate; alkene sulfides such as ethylene sulfide and propylene sulfide; sultone compounds such as 1,3-propane sultone and 1,4-butane sultone; and acid anhydrides such as maleic anhydride and succinic anhydride. Furthermore, the non-aqueous electrolyte solution may contain an overcharge inhibitor such as diphenyl ether or cyclohexylbenzene.

[0164] When these additives are used, the content of the additives in the nonaqueous electrolyte solution is usually 10% by mass or less, preferably 8% by mass or less, further preferably 5% by mass or less, and particularly preferably 2% by mass or less. If the content of the additives is too high, there is a risk of adversely affecting other battery characteristics, such as an increase in initial irreversible capacity and a decrease in low-temperature characteristics and rate characteristics.

[0165] The electrolyte may be a polymer solid electrolyte, which is a conductor of alkali metal cations such as lithium ions. Examples of the polymer solid electrolyte include the aforementioned polyether polymer compound in which a salt of Li is dissolved, and a polymer in which the terminal hydroxyl groups of polyether are substituted with alkoxide.

[0166] A porous separator such as a porous membrane or nonwoven fabric is usually interposed between the positive electrode and the negative electrode to prevent short circuits between the electrodes. In this case, the nonaqueous electrolyte is impregnated into the porous separator. The separator is made of a polyolefin such as polyethylene or polypropylene, or polyethersulfone, preferably polyolefin.

[0167] The lithium ion secondary battery to which the present invention is applied is not particularly limited in shape. Examples include a cylindrical type in which a sheet electrode and a separator are spirally wound, a cylindrical type with an inside-out structure in which a pellet electrode and a separator are combined, and a coin type in which a pellet electrode and a separator are stacked. By housing a battery of these shapes in an appropriate exterior case, it can be used in any shape, such as a coin, a cylinder, or a square.

[0168] The procedure for assembling a lithium-ion secondary battery is not particularly limited, and may be an appropriate procedure depending on the structure of the battery. For example, a battery can be constructed by placing a negative electrode on an outer case, providing an electrolyte and a separator thereon, placing a positive electrode facing the negative electrode, and crimping the battery together with a gasket and a sealing plate.

[0169] The present invention will be described in more detail below with reference to examples, although the present invention is not limited to the following examples.

[0170] Based on the contents of (Method for designing graphite particles satisfying specific mechanical properties), the particles were assumed to be spherical and were designed. The Raman R value of the core graphite alone was 0.25, the Raman R value of the amorphous carbon alone was 1.05, and the density of the core graphite was 2.2 g / cm ３ and the density of the graphite particles is assumed to be 2.1 g / cm ３ The coverage coefficient was defined by normalizing each R value. The amount of amorphous carbon precursor mixed was optimized to achieve the desired coating thickness.

[0171] (Comparative Example 1) Flake graphite (volume-based average particle size: 11.1 μm, d ９０ :21.1μm, specific surface area: 9.9m ２ / g, tap density: 0.44 g / cm ３ A granulating agent was added to the mixture, and the mixture was stirred and mixed using an agitator granulator. The resulting mixture was placed in a hybridization system and subjected to a mechanical granulation and spheronization treatment at a rotor peripheral speed of 85 m / s for 5 minutes. The granulating agent was then removed by heat treatment to obtain spherical graphite particles. The resulting spherical graphite was filled into a rubber container, the container was sealed, and subjected to an isotropic pressure treatment, followed by crushing and classification to obtain nuclear graphite. The resulting spherical graphite particles and pitch (ash content: 0.02% by mass, metal impurity content: 20 ppm by mass, Qi: 1% by mass) were mixed to satisfy predetermined mechanical properties, and heat treated at 1300°C in an inert gas to obtain a fired product. The fired product was crushed and classified to obtain a carbon material containing the graphite particles of Example 1.

[0172] Example 1 A carbon material containing graphite particles of Comparative Example 1 was produced in the same manner as in Example 1, except that the content of amorphous carbon relative to 100% by mass of the fired product was increased and the spheroidized graphite particles and pitch were mixed.

[0173] Comparative Example 2 A carbon material containing graphite particles of Comparative Example 2 was produced in the same manner as in Example 1, except that the content of amorphous carbon relative to 100% by mass of the fired product was increased compared to Example 1 and the spheroidized graphite particles and pitch were mixed.

[0174] Example 2 A carbon material containing graphite particles of Example 2 was produced in the same manner as in Example 1, except that the content of amorphous carbon relative to 100% by mass of the fired product was increased compared to Comparative Example 2 and the spheroidized graphite particles and pitch were mixed.

[0175] The cumulative pore volumes of Examples 1 and 2 and Comparative Examples 1 and 2 were all less than 0.080 ml / g.

[0176] The carbon materials containing graphite particles produced in Examples 1 and 2 and Comparative Examples 1 and 2 were evaluated as follows.

[0177] (Measurement of physical properties of single particles) Using a microcompression tester MCT-510 manufactured by Shimadzu Corporation, one graphite particle contained in the carbon materials produced in the Examples and Comparative Examples was subjected to a vertical load of 9.81 mN at a loading rate of 0.4462 mN / sec. After reaching the maximum test force, the particle was unloaded to 0.05 mN at an unloading rate of 0.4462 mN / sec. The compressive stress and compressive displacement were measured. The displacement rate at 9.81 mN was calculated by dividing the particle size at the maximum test force by the particle size before compression. The compressive modulus was calculated by dividing the compressive stress at the maximum test force, or, if a plateau is observed in the curve, before the plateau by the compressive strain (= displacement of the particle size at the observation point / particle size of one graphite particle observed under a microscope before compression). The average value calculated for three particles is shown in Table 1. The recovery rate was calculated by dividing the amount of particle size displacement observed when the load was reduced to 0.05 mN after the maximum test force was reached by the amount of particle size displacement at the time the maximum test force was reached, and the average value calculated for three particles is shown in Table 1.

[0178] (Method for measuring Raman R value) The carbon materials produced in the Examples and Comparative Examples were filled into a Raman spectrometer measurement cell by gravity, and the Raman spectrum was measured while irradiating the measurement cell with argon ion laser light (wavelength 514.5 nm) and rotating the measurement cell in a plane perpendicular to the laser light, to determine the Raman R value.

[0179] (Preparation of negative electrode) 4.875 parts by mass of silicon having an average particle size of 5 μm, 92.625 parts by mass of the carbon material produced in the examples and comparative examples, 150 parts by mass of a 1% aqueous solution of CMC (solid content 1.5 parts by mass), 2.2 parts by mass of a 45% aqueous dispersion of SBR (solid content 1 part by mass), 1.86 parts by mass of a 2.14% CNT / 3.21% CMC dispersion, and 50 parts by mass of water were added and kneaded using a hybridization mixer to obtain a slurry. The obtained slurry was applied to a copper foil having a thickness of 20 μm as a current collector at a basis weight of 7 to 8 mg / cm. ２ The active material layer was then coated so that it adhered to the substrate and dried. ３ The mixture was roll-pressed using a 250 mmφ roll press equipped with a load cell so that the negative electrode had a diameter of 12.5 mm, and then punched out into a circular shape with a diameter of 12.5 mm. The circular shape was then dried in vacuum at 120° C. for 12 hours to obtain a negative electrode for evaluation.

[0180] (Preparation of Coin Battery) The obtained negative electrode and a lithium foil as a counter electrode were stacked with a separator impregnated with an electrolyte solution in between to obtain a battery for charge / discharge tests. The electrolyte solution was a mixture of ethylene carbonate / ethyl methyl carbonate / monofluoroethylene carbonate = 30 / 60 / 10 (volume ratio) with LiPF ６ was dissolved to a concentration of 1 mol / L. ２ The battery for charge / discharge test was charged at a current density of 0.03 mA / cm until the voltage reached 5 mV, and then further charged at a constant voltage of 5 mV until the current reached 0.03 mA / cm. ２ After doping lithium into the negative electrode, the battery was charged to 0.2 mA / cm ２ The battery was discharged at a current density of 0.2 mA / cm until the voltage reached 0.7 V (initial first cycle). ２ The current density during discharge was 0.3 mA / cm ２ Charge and discharge were repeated four times under the same conditions as above (2nd to 3rd cycles). Flowing a current in the direction in which lithium was doped into the evaluation negative electrode was defined as "charging," and flowing a current in the direction in which lithium was de-doped from the evaluation negative electrode was defined as "discharging." The initial discharge capacity (mAh / g) was calculated by subtracting the mass of copper foil punched to the same area as the negative electrode from the mass of the negative electrode to calculate the mass of the negative electrode active material, and then dividing the discharge capacity at the initial 3rd cycle by the mass of the negative electrode active material. The charge / discharge efficiency at the first and third cycles was defined as the ratio of the discharge capacity to the charge capacity at the first and third cycles ((discharge capacity / charge capacity) × 100).

[0181] The evaluation results are shown in Table 1 below.

[0182]

[0183] Examples 1 and 2 and Comparative Examples 1 and 2 demonstrate that graphite particles having mechanical properties consistent with the design guidelines can be produced, and that the specified carbon material has excellent battery characteristics. Note that the single particle of Comparative Example 2 contained a plateau region in the mechanical curve.

[0184] 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.

[0185] This application is based on a Japanese patent application (Patent Application No. 2024-051879) filed on March 27, 2024, the contents of which are incorporated herein by reference.

Claims

1. Graphite particles coated with amorphous carbon, which, when the particles are pressurized to a pressure of 9.81 mN and then released to 0.05 mN, have a value of 0.5 or greater obtained by dividing the amount of particle size displacement observed when the pressure is released to 0.05 mN after reaching 9.81 mN by the amount of particle size displacement at 9.81 mN.

2. Graphite particles according to claim 1, wherein the mechanical curve does not include a plateau when the particles are compressed to a pressure of 9.81 mN.

3. Graphite particles according to claim 1, having a compressive modulus of elasticity of 550 MPa or more when the particles are compressed to a pressure of 9.81 mN.

4. Graphite particles according to claim 1, which have a displacement rate of 10% or less when the particles are compressed to a pressure of 9.81 mN.

5. A carbon material containing the graphite particles according to any one of claims 1 to 4, wherein the Raman R value of the carbon material is 0.4 or more and 1.0 or less.

6. A carbon material containing the graphite particles according to any one of claims 1 to 4, wherein the BET specific surface area of ​​the carbon material is 0.5 m ２ / g or more 3.0m ２ / g or less.

7. Graphite particles according to claim 1, having a compressive modulus of elasticity of 150 MPa or more and 300 MPa or less when the particles are compressed to a pressure of 9.81 mN.

8. Graphite particles according to claim 1, which have a displacement rate of 4% or more and 10% or less when the particles are pressurized to a pressure of 9.81 mN.

9. A carbon material containing the graphite particles according to claim 1, 2, 7 or 8, wherein the Raman R value of the carbon material is 0.3 or more and 0.4 or less.

10. A carbon material containing graphite particles according to claim 1, 2, 7 or 8, wherein the BET specific surface area of ​​the carbon material is 0.5 m ２ / g or more 3.0m ２ / g or less.

11. A negative electrode material comprising a carbon material containing the graphite particles according to any one of claims 1 to 4, and Si-containing particles.

12. The negative electrode material according to claim 11, further comprising a conductive additive.

13. A secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, wherein the negative electrode comprises the graphite particles according to any one of claims 1 to 4.

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