Negative electrode material for lithium-ion secondary battery, negative electrode for lithium-ion secondary battery, lithium-ion secondary battery, and method for producing negative electrode material for lithium-ion secondary battery

Abstract

This negative electrode material for a lithium-ion secondary battery is graphite particles in which: the compression load, which is the magnitude of pressure required to compress to a density of 1.7 g / cm3, is 3.5 kN / cm2 to 5.0 kN / cm2; and the ratio (I002 / I110) of the peak intensity of the 002 diffraction line (I002) to the peak intensity of the 110 diffraction line (I110) of a graphite crystal obtained by X-ray diffraction measurement using Cu Kα radiation on a compressed body pressed at 0.8 t / cm is 300-800.

Description

Anode material for lithium-ion secondary batteries, anode for lithium-ion secondary batteries, lithium-ion secondary battery, and method for manufacturing anode material for lithium-ion secondary batteries.

[0001] This disclosure relates to a negative electrode material for lithium-ion secondary batteries, a negative electrode for lithium-ion secondary batteries, a lithium-ion secondary battery, and a method for manufacturing a negative electrode material for lithium-ion secondary batteries.

[0002] Lithium-ion rechargeable batteries have long been widely used in electronic devices such as notebook personal computers (PCs), mobile phones, smartphones, and tablet PCs, taking advantage of their characteristics of being small, lightweight, and having high energy density. In recent years, CO2 ２ Against the backdrop of environmental problems such as global warming caused by emissions, electric vehicles such as clean electric vehicles (EVs) that run solely on batteries, hybrid electric vehicles (HEVs) that combine gasoline engines and batteries, and plug-in hybrid electric vehicles (PHEVs) are becoming more widespread, and development of lithium-ion secondary batteries (automotive lithium-ion secondary batteries) to be installed in these vehicles is progressing.

[0003] The performance of the negative electrode material significantly influences the input characteristics of lithium-ion secondary batteries. Carbon materials are widely used as negative electrode materials for lithium-ion secondary batteries. For example, highly crystalline carbon materials such as artificial graphite and spheroidal natural graphite (spheroidal natural graphite, which is spheroidized scaly natural graphite) have been proposed as materials to obtain high-density negative electrodes.

[0004] As an example of a carbon material using natural graphite, Patent Document 1 discloses a carbon material for non-aqueous secondary batteries in which carbonaceous material is contained on the surface of a granulated carbon material.

[0005] Japanese Patent Publication No. 2017-45574

[0006] The rapid growth of the EV market is driving increased demand for negative electrode materials for lithium-ion secondary batteries. Lithium-ion secondary batteries require high discharge capacity and low electrical resistance. Lithium-ion secondary batteries that use natural graphite particles as the negative electrode material can easily achieve high discharge capacity compared to, for example, batteries that use artificial graphite particles as the negative electrode material, but they also tend to have higher electrical resistance.

[0007] This disclosure aims to provide a negative electrode material for lithium-ion secondary batteries that can produce lithium-ion secondary batteries that achieve both high discharge capacity and low electrical resistance, as well as a negative electrode for lithium-ion secondary batteries containing the same, and a lithium-ion secondary battery. This disclosure also aims to provide a method for manufacturing a negative electrode material for lithium-ion secondary batteries that can produce lithium-ion secondary batteries that achieve both high discharge capacity and low electrical resistance.

[0008] Means for solving the above problem include the following embodiments: <1> Density 1.7 g / cm³ ３ The compressive load, which is the amount of pressure required to compress it to a certain level, is 3.5 kN / cm². ２ ~5.0 kN / cm ２ The peak intensity of the 002 diffraction line of the graphite crystal (I) obtained when a compressed body pressed at 0.8 t / cm is measured by X-ray diffraction using CuKα rays. ００２ ) and the peak intensity of the 110 diffraction line (I １１０ ) Ratio I ００２ / I １１０The negative electrode material for a lithium-ion secondary battery, which is graphite particles with a value of 300 to 800. <2> The spring-back rate of the graphite particles is 0.20 to 0.30, and the negative electrode material for a lithium-ion secondary battery according to <1>. Compression rate = (tap density after 250 taps - tap density after 0 taps) / tap density after 250 taps... (6) <3> The combustion start temperature determined by thermogravimetric analysis (TG) of the graphite particles in the atmosphere is 700 °C or higher, and the negative electrode material for a lithium-ion secondary battery according to <1> or <2>. <4> The content of boron atoms determined by X-ray photoelectron spectroscopy (XPS) of the graphite particles is 0.1 atomic% to 5 atomic%, and the negative electrode material for a lithium-ion secondary battery according to any one of <1> to <3>. <5> The volume average particle diameter (D50) of the graphite particles is 13 μm to 24 μm, and the negative electrode material for a lithium-ion secondary battery according to any one of <1> to <4>. <6> When the particle diameter corresponding to 10% cumulative volume from the small-diameter side and the particle diameter corresponding to 90% cumulative volume are represented as D10 and D90, respectively, in the cumulative particle size distribution of the graphite particles, the value of D90 / D10 is 2.2 to 3.3, and the negative electrode material for a lithium-ion secondary battery according to any one of <1> to <5>. <7> The specific surface area of the graphite particles determined by nitrogen adsorption measurement at 77 K is 0.5 m ２ / g to 2.0 m ２<8> A negative electrode material for a lithium-ion secondary battery according to any one of <1> to <6>, wherein the graphite particles include secondary particles formed by the aggregation of a plurality of primary particles. <9> A negative electrode for a lithium-ion secondary battery comprising a negative electrode material layer containing the negative electrode material for a lithium-ion secondary battery according to any one of <1> to <8>, and a current collector. <10> A lithium-ion secondary battery comprising the negative electrode for a lithium-ion secondary battery according to <9>, a positive electrode, and an electrolyte. <11> A method for producing a negative electrode material for a lithium-ion secondary battery, comprising the steps of: forming secondary particles formed by the aggregation of a plurality of natural graphite particles; and obtaining a negative electrode material for a lithium-ion secondary battery which is graphite particles by continuously graphitizing a composition to be graphitized containing the secondary particles. <12> A method for producing a negative electrode material for a lithium-ion secondary battery according to <11>, wherein the composition to be graphitized includes a graphitization catalyst. <13> The graphitization catalyst is having boron atoms, the method for producing a negative electrode material for a lithium-ion secondary battery according to <12>. <14> The composition to be graphitized is comprising a graphitizable binder, the method for producing a negative electrode material for a lithium-ion secondary battery according to any one of <11> to <13>. <15> The heating temperature in the continuous graphitization treatment is 2200°C to 2800°C, the method for producing a negative electrode material for a lithium-ion secondary battery according to any one of <11> to <14>.

[0009] This disclosure provides a negative electrode material for lithium-ion secondary batteries that can produce lithium-ion secondary batteries that achieve both high discharge capacity and low electrical resistance, as well as a negative electrode for lithium-ion secondary batteries containing the same, and a lithium-ion secondary battery. This disclosure also provides a method for manufacturing a negative electrode material for lithium-ion secondary batteries that can produce lithium-ion secondary batteries that achieve both high discharge capacity and low electrical resistance.

[0010] The embodiments for carrying out the present invention will be described in detail below. However, the present invention is not limited to the following embodiments. In the following embodiments, the components (including elemental steps, etc.) are not essential unless otherwise specified. The same applies to numerical values ​​and their ranges, and they do not limit the present invention.

[0011] In this disclosure, the term "process" includes not only processes that are independent of other processes, but also processes that cannot be clearly distinguished from other processes, provided that the purpose of the process is achieved. In this disclosure, numerical ranges indicated using "~" include the numbers before and after "~" as the minimum and maximum values, respectively. In numerical ranges described in stages in this disclosure, the upper or lower limit of one numerical range may be replaced by the upper or lower limit of another numerical range described in stages. Also, in numerical ranges described in this disclosure, the upper or lower limit of that numerical range may be replaced by the values ​​shown in the examples. In this disclosure, each component may contain multiple types of the corresponding substance. If multiple types of the substance corresponding to each component are present in the composition, the content or amount of each component means the total content or amount of the multiple types of substances present in the composition, unless otherwise specified. In this disclosure, each component may contain multiple types of particles. If multiple types of particles corresponding to each component are present in the composition, the particle size of each component means the value for the mixture of the multiple types of particles present in the composition, unless otherwise specified. In this disclosure, the terms “layer” or “film” include cases where, when observed, the layer or film is formed over the entire region in which it exists, as well as cases where it is formed over only a portion of the region in which it exists. In this disclosure, the term “laminated” refers to stacking layers, and two or more layers may be bonded together or detachable.

[0012] In this disclosure, the particle size distribution of the negative electrode material can be measured by a laser diffraction particle size distribution analyzer. The average particle size is the particle size (D50) at which the integration from the smallest diameter side in the volume-based particle size distribution is 50%. D90 is the particle size at which the integration from the smallest diameter side in the volume-based particle size distribution is 90%, and D10 is the particle size at which the integration from the smallest diameter side in the volume-based particle size distribution is 10%.

[0013] <<Anode Material for Lithium-ion Secondary Batteries>> The anode material for lithium-ion secondary batteries disclosed herein (hereinafter also simply referred to as "anode material") has a density of 1.7 g / cm³. ３The compressive load (hereinafter also simply referred to as "compressive load"), which is the magnitude of the pressure required to compress it to that point, is 3.5 kN / cm². ２ ~5.0 kN / cm ２ The peak intensity of the 002 diffraction line of the graphite crystal (I) obtained when a compressed body pressed at 0.8 t / cm is measured by X-ray diffraction using CuKα rays. ００２ ) and the peak intensity of the 110 diffraction line (I １１０ ) Ratio I ００２ / I １１０ These are graphite particles with an electrode orientation (hereinafter also referred to as "electrode orientation") of 300 to 800.

[0014] By using the negative electrode material disclosed herein, it is possible to manufacture lithium-ion secondary batteries that achieve both high discharge capacity and low electrical resistance. The reason for this is presumed to be as follows.

[0015] As mentioned above, lithium-ion secondary batteries that use natural graphite particles as the negative electrode material tend to achieve high discharge capacity due to their high crystallinity, but they also tend to have high electrical resistance. The reason why using natural graphite particles as the negative electrode material tends to increase electrical resistance is presumed to be that, because natural graphite particles are soft, compression to increase the density of the negative electrode causes the particles to orient in the plane of the negative electrode, blocking and obstructing the flow passages of the pores through which the electrolyte penetrates, thereby reducing the mobility of lithium ions within the negative electrode.

[0016] In contrast, the graphite particles (hereinafter also referred to as "the graphite particles") which are the negative electrode material of this disclosure, have compressive load and electrode orientation within the aforementioned ranges, and tend to have a high compressive load and low electrode orientation. With graphite particles that have a high compressive load, the graphite particles are less likely to deform even when compressed to increase the density of the negative electrode. This suppresses the in-plane orientation of the negative electrode particles, and the voids through which the flow of electrons between the graphite particles do not easily disappear, making it easier to secure a suitable flow path for the electrolyte. In other words, with graphite particles that have low electrode orientation, voids are more likely to exist within the negative electrode, and lithium ions can move more easily. Therefore, it is presumed that in a lithium-ion secondary battery using the graphite particles as the negative electrode material, even when pressed to increase the density of the negative electrode, a path for lithium ions entering and leaving the negative electrode is easily secured, and a low electrical resistance is achieved. Furthermore, because the compressive load of the graphite particles is below the upper limit and the electrode orientation is above the lower limit, the compression required to increase the density of the negative electrode ensures appropriate density and orientation of the natural graphite, thereby achieving a high discharge capacity in lithium-ion secondary batteries using these graphite particles as the negative electrode material. For these reasons, it is presumed that by using the negative electrode material of this disclosure, it is possible to manufacture lithium-ion secondary batteries that achieve both high discharge capacity and low electrical resistance.

[0017] Examples of graphite particles include graphite particles containing secondary particles formed by the aggregation of multiple natural graphite particles. Specifically, examples of graphite particles include those obtained by coating the surface of the secondary particles with a graphitizable binder and performing a graphitization treatment at a range of preferably 2200°C to 2800°C, more preferably 2400°C to 2700°C, and most preferably 2400°C to 2600°C (hereinafter also referred to as "specific granulated particles"). In other words, the graphite particles may be specific granulated particles having secondary particles formed by the aggregation of multiple natural graphite particles and a coating layer provided on at least a part of the surface of the secondary particles, which contains the graphitized binder.

[0018] By graphitizing secondary particles of natural graphite coated with a graphitizable binder at temperatures within the above range, the binder portion is graphitized, yielding graphite particles (i.e., specific granulated particles) with a compressive load within the above range and an electrode orientation within the above range. At this time, it is presumed that if the graphitization temperature is below the above upper limit, the increase in crystallinity of the binder portion due to an excessively high graphitization temperature, which would cause the particles to soften, is suppressed, and the compressive load and electrode orientation are more likely to fall within the desirable range. On the other hand, if the graphitization temperature is above the above lower limit, it is presumed that the decrease in crystallinity of the binder portion and the decrease in negative electrode capacity due to an excessively low graphitization temperature are suppressed. For this reason, the graphitization treatment temperature is preferably in the range of 2200°C to 2800°C, more preferably in the range of 2400°C to 2700°C, and most preferably in the range of 2400°C to 2600°C. Furthermore, because the specific granulated particles have compressive load and electrode orientation within the aforementioned ranges, it is possible to manufacture lithium-ion secondary batteries that achieve both high discharge capacity and low electrical resistance. In particular, since the specific granulated particles use natural graphite, lithium-ion secondary batteries using these particles as a negative electrode material achieve both high discharge capacity due to the high crystallinity of natural graphite and low electrical resistance due to the high ion mobility within the negative electrode. Below, the graphite particles, which are specific granulated particles, will be described as an example of the negative electrode material of this disclosure.

[0019] (Particle Size) The particle size of graphite particles can be measured using a laser diffraction particle size distribution analyzer (e.g., SALD3100, Shimadzu Corporation). In the cumulative particle size distribution of graphite particles obtained by the above measurement, the particle size corresponding to a cumulative 10 volume percent is D10, the particle size corresponding to a cumulative 50 volume percent is D50, and the particle size corresponding to a cumulative 90 volume percent is D90.

[0020] The D50 of the graphite particles may be between 10.0 μm and 30.0 μm. From the viewpoint of ensuring a large specific surface area and reducing resistance, the D50 of the graphite particles is preferably small in size, and may be 28.0 μm or less, 25.0 μm or less, 24.0 μm or less, or 22.0 μm or less. Conversely, if the specific surface area becomes too large, side reactions on the negative electrode surface increase, which can reduce the durability of the lithium-ion battery. From this viewpoint, the D50 of the graphite particles may be 10.0 μm or larger, 13.0 μm or larger, or 20.0 μm or larger.

[0021] The D10 of the graphite particles may be 1.0 μm to 20.0 μm, 3.0 μm to 18.0 μm, more preferably 5.0 μm to 17.0 μm, and particularly preferably 7.0 μm to 17.0 μm.

[0022] The particle size distribution D90 / D10 of the graphite particles is not particularly limited and may be 2.0 to 5.0 or 2.0 to 4.0. From the viewpoint of the stability of the slurry in the negative electrode coating process when manufacturing the negative electrode, a particle size distribution D90 / D10 of 2.2 to 3.3 is preferred. When D90 / D10 is above the lower limit, the separation of solid components in the slurry is suppressed, and when it is below the upper limit, the viscosity does not increase and the coating properties do not deteriorate.

[0023] (Electrode orientation I) ００２ / I １１０ ) The electrode orientation of these graphite particles, that is, the peak intensity of the 002 diffraction line of the graphite crystal obtained when a compressed electrode with a coating of these graphite particles pressed at a linear pressure of 0.8 t / cm is measured by X-ray diffraction using CuKα rays. ００２ ) and the peak intensity of the 110 diffraction line (I １１０ ) Ratio I ００２ / I １１０ Ratio I is 300 to 800, and from the viewpoint of obtaining a lithium-ion secondary battery that achieves both high discharge capacity and low electrical resistance, 400 to 700 is preferred, and 500 to 700 is more preferred. ００２ / I １１０ This can be determined by the method described in the examples. Ratio I ００２ / I１１０ When measuring, the components other than graphite particles, their ratios, and the manufacturing conditions for the negative electrode are the same as those described in the measurement method for electrode orientation in the examples.

[0024] (Compressive load) The compressive load of graphite particles is 3.5 kN / cm². ２ ~5.0 kN / cm ２ Therefore, from the viewpoint of obtaining a lithium-ion secondary battery with low electrical resistance, 3.6 kN / cm ２ Preferably, it is 3.7 kN / cm ２ It is more preferable that the value be greater than or equal to 3.8 kN / cm². ２ It is even more preferable that the value be greater than or equal to 4.0 kN / cm². ２ It is especially preferable that the above conditions are met.

[0025] From the perspective of obtaining a lithium-ion secondary battery with high electrical capacity, the compressive load of graphite particles should be 4.5 kN / cm. ２ The following is also acceptable: 4.2 kN / cm ２ The following is also acceptable.

[0026] In this disclosure, the compressive load of graphite particles can be determined as follows: A mold is filled with a predetermined mass (e.g., 3.0 g) of graphite particles, compressed at a constant speed (e.g., 10 mm / min), and the density of the compressed graphite particles is 1.7 g / cm³. ３ Pressure when it reaches (kN / cm ２ The compressive load of the graphite particles is defined as (1.767 cm²). In the above measurement, a mold with a diameter of 15 mm is used, and compression is performed using an Autograph (e.g., manufactured by Shimadzu Corporation). The density of the graphite particles is defined as the area of ​​the bottom of the mold (e.g., 1.767 cm²). ２ The volume and mass of the graphite particles are calculated from the distance from the bottom surface of the mold to the pressing surface of the graphite particles. A larger compressive load on the graphite particles means that deformation, breakage, etc., of the graphite particles due to pressure is less likely to occur.

[0027] (Springback Rate) The springback rate of the graphite particles is preferably 0.20 to 0.30, more preferably 0.22 to 0.28, and even more preferably 0.23 to 0.27. When the springback rate of the graphite particles is above the lower limit, damage to the graphite particles due to pressing during negative electrode manufacturing is suppressed. Furthermore, when the springback rate of the graphite particles is below the upper limit, a highly smooth negative electrode is more easily obtained, and the electrical resistance of the negative electrode is easier to reduce.

[0028] In this disclosure, the springback rate of graphite particles is the degree to which the density decreases when the pressure is released after the graphite particles have been compressed to a standard density. The greater the springback rate, the easier it is for the deformed graphite particles to return to their original state. Specifically, a mold is filled with a predetermined mass (for example, 3.0 g) of graphite particles, and the density of the graphite particles is reduced to a standard density (for example, 1.7 g / cm³). ３ The material is compressed at a constant speed (e.g., 10 mm / min) until it reaches a certain density. Then, the pressure is released, and the density after the pressure is released is measured when the elastic movement of the press surface stops. From the obtained value, the springback rate is calculated using the following formula: Springback rate = {(Reference density - Density after pressure release) / Reference density}. For the above measurement, a mold with a diameter of 15 mm is used, and compression is performed using an Autograph (e.g., manufactured by Shimadzu Corporation). The density of graphite particles is measured over the bottom area of ​​the mold (e.g., 1.767 cm²). ２ The volume and mass of the graphite particles are calculated from the distance from the bottom surface of the mold to the pressing surface of the graphite particles.

[0029] The electrode orientation, compressive load, and springback rate of graphite particles can be adjusted by changing the physical properties and composition of the raw materials for the graphite particles (e.g., natural graphite, graphitizable binders, etc.) or by changing the graphitization conditions.

[0030] (Specific surface area) The specific surface area (hereinafter also simply referred to as "specific surface area") determined by nitrogen adsorption measurement of graphite particles at 77K is 0.5 m². ２ / g to 2.0m ２ It is preferable that it be / g, and 0.6m ２ / g to 1.8m ２ It is more preferable that it be / g, and 0.6m ２ / g to 1.6m ２ It is even more preferable that the specific surface area of ​​the graphite particles is greater than or equal to the above lower limit, which has the advantage of securing sites for the absorption and release of lithium ions into the graphite particles during charging and discharging, resulting in low reaction resistance, and also has the advantage of securing contact points between particles, resulting in high electrode adhesion. Furthermore, if the specific surface area of ​​the graphite particles is less than or equal to the above upper limit, it has the advantage of suppressing side reactions of the electrolyte and having excellent durability.

[0031] The specific surface area obtained by nitrogen adsorption measurement at 77K can be determined using the BET method from the adsorption isotherm obtained from the nitrogen adsorption measurement at 77K. Specifically, the material to be measured is filled into a measurement cell, and nitrogen gas is adsorbed onto the sample obtained by heating pretreatment at 200°C while vacuum degassing using a gas adsorption device (ASAP2010, manufactured by Shimadzu Corporation). The specific surface area is determined by performing a BET analysis on the obtained sample using the five-point method.

[0032] The specific surface area of ​​graphite particles can be adjusted by the particle size distribution, particle structure, etc. Specifically, when the graphite particles are specific granulated particles, the specific surface area can be adjusted by the physical properties such as the specific surface area of ​​the natural graphite particles used as raw materials, as well as the type and amount of carbonizable binder added.

[0033] (Initiation Temperature of Combustion) The initiation temperature of combustion of graphite particles in the atmosphere, determined by thermogravimetric analysis (TG), may be 700°C or higher, 700°C to 750°C, 700°C to 730°C, or 710°C to 730°C. Graphite particles with an initiation temperature within the above range are thought to contain secondary particles formed by the aggregation of multiple primary particles. Therefore, it is presumed that lithium-ion secondary batteries that achieve both high discharge capacity and low electrical resistance will be easier to obtain. The above initiation temperature of combustion can be determined by the method described in the examples.

[0034] In this disclosure, the average interplanar spacing (d) determined by X-ray diffraction is used. ００２) is defined as a carbon material with a length of less than 0.340 nm. In this disclosure, particles in which low-crystallinity carbon is arranged on at least a portion of the surface of the graphite particles are also defined as "graphite particles". The average interplanar spacing (d) of the graphite crystals. ００２ The theoretical value of ) is 0.3354 nm, and the closer to this value, the more advanced the graphitization. From the viewpoint of the initial charge / discharge efficiency and energy density of lithium-ion secondary batteries, the average interplanar spacing (d ００２ The average interplanar spacing (d) of the graphite particles is preferably 0.33600 nm or less, more preferably 0.33596 nm or less, and even more preferably 0.33592 nm or less. From the above viewpoint, the average interplanar spacing (d) of the graphite particles is preferably 0.33600 nm or less, more preferably 0.33596 nm or less. ００２ The wavelength is preferably 0.3354 nm to 0.33600 nm, more preferably 0.3354 nm to 0.33596 nm, and even more preferably 0.3354 nm to 0.33592 nm.

[0035] Average interplanar spacing of graphite particles (d ００２ The mean interplanar spacing (d) can be calculated using Bragg's formula, based on the diffraction peak corresponding to the carbon 002 plane that appears around the diffraction angle 2θ of 24° to 27° in the diffraction profile obtained by irradiating the sample with X-rays (CuKα rays) and measuring the diffraction lines with a goniometer. ００２ The following conditions can be used for measurement: Radiation source: CuKα (wavelength = 0.15418 nm) Output: 40 kV, 20 mA Sampling width: 0.010° ​​Scanning range: 10° to 35° Scanning speed: 0.5° / min

[0036] Bragg's equation: 2dsinθ = nλ, where d is the length of one period, θ is the diffraction angle, n is the reflection order, and λ is the X-ray wavelength.

[0037] (Surface Composition) When the graphite particles are specific granulated particles, the coating layer may contain components derived from the graphitization catalyst. In other words, atoms derived from the graphitization catalyst may be present on the surface of the graphite particles. Examples of graphitization catalysts include substances that have graphitization catalytic activity such as silicon, iron, nickel, titanium, and boron, carbides of these substances, oxides of these substances, and nitrides of these substances. Among these, the graphitization catalyst is preferably a compound containing boron from the viewpoint of achieving graphitization at low temperatures. In other words, boron atoms may be present on the surface of the graphite particles.

[0038] When boron atoms are present on the surface of graphite particles, the boron content, as determined by X-ray photoelectron spectroscopy (XPS) of the graphite particles, is preferably between 0.1 atomic% and 5 atomic%. The boron content, as determined by X-ray photoelectron spectroscopy (XPS) of graphite particles, can be determined by the method described in the examples.

[0039] ≪Method for Manufacturing a Negative Electrode Material for Lithium-Ion Secondary Batteries≫ As an example of the method for manufacturing a negative electrode material for lithium-ion secondary batteries according to this disclosure, the method for manufacturing the specified granulated particles described above will be explained. The method for manufacturing the specified granulated particles includes a step of forming secondary particles by aggregating a plurality of natural graphite particles and obtaining a graphitizable composition containing the secondary particles and a graphitizable binder (hereinafter also referred to as the "graphitizable composition manufacturing step"), and a step of obtaining the specified granulated particles by graphitizing the graphitizable composition at 2200°C to 2800°C (hereinafter also referred to as the "graphitization treatment step").

[0040] The negative electrode material, which is a specific granulated particle obtained by the above manufacturing method, has compressive load and electrode orientation within the aforementioned ranges, making it possible to manufacture lithium-ion secondary batteries that achieve both high discharge capacity and low electrical resistance. Furthermore, since the above manufacturing method performs graphitization treatment at a lower heating temperature than conventional methods, it is suitable for continuous graphitization treatment. In other words, the above manufacturing method may include a step of forming secondary particles by aggregating multiple natural graphite particles, and a step of obtaining a negative electrode material for lithium-ion secondary batteries, which is graphite particles, by continuously graphitizing the composition to be graphitized containing the secondary particles. In continuous graphitization treatment, for example, a continuous graphitization furnace is used to continuously push the composition to be graphitized into the furnace, and the graphitized specific granulated particles are continuously removed from the discharge port to perform graphitization treatment of the composition to be graphitized. For this reason, it is difficult to raise the heating temperature in the graphitization treatment in continuous graphitization treatment. On the other hand, with the above manufacturing method, even if continuous graphitization treatment is applied and the continuous graphitization treatment is performed at a low heating temperature, a negative electrode material can be obtained that enables the manufacture of lithium-ion secondary batteries that have both high discharge capacity and low electrical resistance.

[0041] (Natural Graphite) Examples of natural graphite used as a raw material for the production of specific granulated particles include flaky natural graphite, flake natural graphite, plate-like natural graphite, and spheroidal natural graphite. The natural graphite used in the production of specific granulated particles may be one type alone or two or more types. From the viewpoint of ensuring that the specific surface area of ​​the resulting granulated particles is within an appropriate range, spheroidal natural graphite is preferred. Spheroidal natural graphite is a particle formed by shaping flake, flaky, or plate-like natural graphite particles into a spherical form, and does not have to be perfectly spherical.

[0042] The average particle size of the natural graphite used in the production of specific granulated particles is not particularly limited, and may range from 7 μm to 18 μm, or it may be in the range of 8 μm to 15 μm, or it may be in the range of 8 μm to 10 μm. The average particle size of the natural graphite is determined by the method described above. The average particle size of the natural graphite used in the production of specific granulated particles (hereinafter referred to as "D50") Ａ The average particle size of the obtained specific granulated particles (hereinafter referred to as "D50") relative to the given granulated particle size (also called "D50") Ｂ The ratio D50 (also known as "...") Ｂ / D50Ａ For example, this range could be 1.4 to 3.0, 1.5 to 2.7, or 1.7 to 2.2.

[0043] The specific surface area of ​​natural graphite used in the production of specific granulated particles is not particularly limited, for example, 6.0 m². ２ / g ~ 11.0m ２ The range is given as / g, and 7.0m ２ / g to 10.0m ２ It may be in the range of / g, and 8.0m ２ / g to 10.0m ２ The range may be / g. The specific surface area of ​​natural graphite is determined by the method described in the examples. Specific surface area of ​​natural graphite used in the production of specific granulated particles (hereinafter referred to as "BET" Ａ The specific surface area of ​​the obtained granulated particles relative to the "BET" (also known as "BET") Ｂ The ratio BET (also known as "...") Ｂ / BET Ａ For example, this range could be 0.05 to 0.25, or it could be 0.05 to 0.20, or 0.05 to 0.10.

[0044] The 250-tap density of natural graphite used in the production of specific granulated particles is, for example, 0.5 g / cm³. ３ ~1.0 g / cm ３ From the viewpoint of obtaining specific granulated particles in which the compressive load and electrode orientation are both within the aforementioned range, 0.60 g / cm³ is used. ３ ~1.0 g / cm ３ A range of 0.80 g / cm³ is preferred. ３ ~1.0 g / cm ３ A range of 250 taps of natural graphite is preferable for a capacity of 150 cm³. ３ A flat-bottomed test tube with markings (for example, KRS-406, manufactured by Kuramochi Scientific Instruments Co., Ltd.) contains 100 cm³ of natural graphite sample powder. ３ The density value is determined from the mass and volume of the sample powder after adding the substance, stopping the graduated flat-bottom test tube, and then dropping the graduated flat-bottom test tube from a height of 5 cm 250 times.

[0045] In the production of specific granulated particles, the content of natural graphite relative to the total of natural graphite and graphitizable binder is not particularly limited, and for example, it can be in the range of 60% to 90% by mass. From the viewpoint of obtaining specific granulated particles in which the compressive load and electrode orientation are both within the aforementioned ranges, the content of natural graphite relative to the total of natural graphite and graphitizable binder is preferably 70% to 80% by mass.

[0046] (Graphitizable Binders) The graphitizable binder used in the production of specific granulated particles is not particularly limited as long as it can be graphitized by graphitization treatment. Examples of graphitizable binders include pitch and organic polymer compounds. Examples of pitch include ethylene heavy-end pitch, petroleum pitch, coal tar pitch, asphalt decomposition pitch, pitch produced by thermal decomposition of polyvinyl chloride, etc., and pitch produced by polymerization of naphthalene etc. in the presence of a superacid. Examples of organic polymer compounds include thermoplastic resins such as polyvinyl chloride, polyvinyl alcohol, polyvinyl acetate, and polyvinyl butyral, as well as natural substances such as starch and cellulose. The graphitizable binder used in the production of specific granulated particles may be a single type or two or more types. From the viewpoint of having a high residual carbon content after graphitization and excellent product yield, pitch is preferred as the graphitizable binder used in the production of specific granulated particles.

[0047] In the production of specific granulated particles, the content of graphitizable binder relative to the total of natural graphite and graphitizable binder is not particularly limited, and for example, it can be in the range of 10% to 40% by mass. From the viewpoint of obtaining specific granulated particles in which the compressive load and electrode orientation are both within the aforementioned ranges, the content of graphitizable binder relative to the total of natural graphite and graphitizable binder is preferably 20% to 30% by mass.

[0048] (Other Components) The composition to be graphitized may contain other components besides natural graphite particles and a graphitizable binder. Examples of other components include aromatic compounds, dispersants, and graphitization catalysts. In particular, it is preferable that the composition to be graphitized contains a graphitization catalyst as another component. The inclusion of a graphitization catalyst in the composition to be graphitized enables graphitization treatment at lower temperatures. Examples of graphitization catalysts include substances that have graphitization catalytic activity such as silicon, iron, nickel, titanium, and boron, carbides of these substances, oxides of these substances, and nitrides of these substances.

[0049] Among these, graphitization catalysts containing boron atoms are preferred from the viewpoint of enabling graphitization treatment at lower temperatures. Examples of graphitization catalysts containing boron atoms include boric acid (H ３ BO ３ ), diboron trioxide (B ２ O ３ Examples include the following. When the composition to be graphitized contains a graphitization catalyst having boron atoms, the amount is not particularly limited. For example, the content of the graphitization catalyst having boron atoms relative to the entire composition to be graphitized may be 0.1% to 5% by mass, 0.5% to 4% by mass, or 0.5% to 3% by mass.

[0050] (Process for Manufacturing Graphitizable Composition) In the process for manufacturing graphitizable composition, secondary particles are formed by the aggregation of multiple natural graphite particles, and a graphitizable composition is obtained that contains the secondary particles and a graphitizable binder. Specifically, for example, natural graphite particles and a graphitizable binder are placed in a cylindrical container equipped with a stirring plate inside, and the container is rotated. The rotation of the container stirs the mixture of natural graphite particles and graphitizable binder. After stirring the mixture, secondary particles of natural graphite are formed by crushing the mixture as needed. Then, the mixture in which the secondary particles of natural graphite have been formed is subjected to heating to remove volatile components by calcining the mixture, the addition of a graphitization catalyst, etc., as needed, to obtain a graphitizable composition.

[0051] In the process of manufacturing the graphitizable composition, the heating temperature when stirring the mixture is, for example, 250°C to 350°C. The time for stirring the mixture is, for example, 1 hour to 8 hours, or 1 hour to 5 hours. It is preferable to stir the mixture in an inert gas atmosphere such as a nitrogen atmosphere. When crushing the mixture in the process of manufacturing the graphitizable composition, the crushing method is not particularly limited and can be, for example, crushing using a crushing equipment equipped with rotating blades, rotating teeth, etc., or crushing and classifying equipment equipped with rotating blades, rotating teeth, etc., in addition to a classifier. When calcining the mixture in the process of manufacturing the graphitizable composition, the heating temperature when calcining the mixture is, for example, 800°C to 1200°C, or 1000°C to 1200°C. The time for calcining the mixture is, for example, 1 hour to 10 hours, or 1 hour to 5 hours. It is preferable to calcine the mixture in an inert gas atmosphere such as a nitrogen atmosphere.

[0052] (Graphitization Treatment Process) In the graphitization treatment process, specific granulated particles are obtained by graphitizing the composition to be graphitized at 2200°C to 2800°C. In the graphitization treatment process, the heating temperature when graphitizing the composition to be graphitized is 2200°C to 2800°C as described above, and from the viewpoint of obtaining specific granulated particles capable of producing lithium-ion secondary batteries that achieve both high discharge capacity and low electrical resistance, 2400°C to 2700°C is preferred, and 2400°C to 2600°C is more preferred. In particular, when the composition to be graphitized contains a graphitization catalyst having boron atoms, graphitization proceeds more easily even at lower heating temperatures. Therefore, the heating temperature when graphitizing the composition to be graphitized may be 2200°C to 2550°C, or 2200°C to 2500°C. Furthermore, the time for graphitizing the above-mentioned composition to be graphitized can be, for example, 0.5 hours to 5 hours, or it may be 0.5 hours to 3 hours. The graphitizing treatment of the above-mentioned composition to be graphitized is preferably carried out in an inert gas atmosphere such as an argon or nitrogen atmosphere.

[0053] <<Composition for Lithium-Ion Secondary Batteries>> The composition for lithium-ion secondary batteries comprises the lithium-ion secondary battery negative electrode material of this disclosure, a binder, and a solvent. The composition for lithium-ion secondary batteries of this disclosure may be in the form of a slurry obtained by kneading the lithium-ion secondary battery negative electrode material and the binder together with the solvent. Kneading can be carried out using a dispersion device such as a disperser stirrer or a planetary kneader.

[0054] The binder used in the preparation of the negative electrode material composition for lithium-ion secondary batteries is not particularly limited. Examples of binders include styrene-butadiene copolymer (SBR), ethylenically unsaturated carboxylic acid esters such as methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, butyl methacrylate, hydroxyethyl acrylate, and hydroxyethyl methacrylate, and homopolymers or copolymers of ethylenically unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, fumaric acid, and maleic acid, as well as highly ionically conductive polymer compounds such as polyvinylidene fluoride, polyethylene oxide, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, and polymethacrylonitrile. When the negative electrode material composition for lithium-ion secondary batteries contains a binder, the binder content is not particularly limited. For example, it may be 0.5 to 20 parts by mass per 100 parts by mass of the total of the negative electrode material and binder for lithium-ion secondary batteries.

[0055] The negative electrode material composition for lithium-ion secondary batteries may contain a thickening agent. Suitable thickening agents include carboxymethylcellulose, methylcellulose, hydroxymethylcellulose, ethylcellulose, polyvinyl alcohol, polyacrylic acid or its salts, starch oxide, phosphated starch, casein, etc. When the negative electrode material composition for lithium-ion secondary batteries contains a thickening agent, the amount of the thickening agent is not particularly limited. For example, it may be 0.1 to 5 parts by mass per 100 parts by mass of the negative electrode material for lithium-ion secondary batteries.

[0056] The negative electrode material composition for lithium-ion secondary batteries may contain a conductive additive. Examples of conductive additives include carbon materials such as carbon black, graphite, and acetylene black, and inorganic compounds such as conductive oxides and conductive nitrides. When the negative electrode material composition for lithium-ion secondary batteries contains a conductive additive, the amount of the conductive additive is not particularly limited. For example, it may be 0.5 to 15 parts by mass per 100 parts by mass of the negative electrode material for lithium-ion secondary batteries.

[0057] <<Negative electrode for lithium-ion secondary battery>> The negative electrode for lithium-ion secondary battery of this disclosure includes a negative electrode material layer containing the negative electrode material for lithium-ion secondary battery of this disclosure, and a current collector. In addition to the negative electrode material layer containing the negative electrode material for lithium-ion secondary battery of this disclosure and the current collector, the negative electrode for lithium-ion secondary battery may include other components as necessary.

[0058] A negative electrode for a lithium-ion secondary battery can be manufactured, for example, by preparing the lithium-ion secondary battery negative electrode material composition described above and applying it to a current collector to form a negative electrode material layer, or by molding the lithium-ion secondary battery negative electrode material composition into a sheet, pellet, or other shape and integrating it with a current collector.

[0059] The material of the current collector is not particularly limited and can be selected from aluminum, copper, nickel, titanium, stainless steel, etc. The state of the current collector is not particularly limited and can be selected from foil, perforated foil, mesh, etc. In addition, porous materials such as porous metal (foamed metal) and carbon paper can also be used as current collectors.

[0060] When forming a negative electrode material layer by applying a lithium-ion secondary battery negative electrode material composition to a current collector, the method is not particularly limited, and known methods such as metal mask printing, electrostatic coating, dip coating, spray coating, roll coating, doctor blade method, comma coating, gravure coating, and screen printing can be employed. After applying the lithium-ion secondary battery negative electrode material composition to the current collector, the solvent contained in the lithium-ion secondary battery negative electrode material composition is removed by drying. Drying can be performed, for example, using a hot air dryer, an infrared dryer, or a combination of these devices. If necessary, the negative electrode material layer may be subjected to rolling. Rolling can be performed by methods such as a flat plate press or a calender roll.

[0061] When a negative electrode material composition for lithium-ion secondary batteries, molded into the shape of a sheet, pellet, or the like, is integrated with a current collector to form a negative electrode material layer, the method of integration is not particularly limited. For example, it can be done by rolling, flat plate pressing, or a combination of these means. The pressure applied when integrating the negative electrode material composition for lithium-ion secondary batteries with the current collector is preferably, for example, about 1 MPa to 200 MPa.

[0062] The negative electrode density of the negative electrode material layer is not particularly limited, for example, 1.1 g / cm³. ３ ~1.8 g / cm ３ Preferably, it is 1.1 g / cm³. ３ ~1.7 g / cm ３ It is more preferable that the concentration be 1.1 g / cm³. ３ ~1.6 g / cm ３ It is even more preferable that the negative electrode density be 1.1 g / cm³. ３ By doing so, the increase in electrical resistance is suppressed, and the capacitance tends to increase, reaching 1.8 g / cm³. ３ The following measures tend to suppress the degradation of input characteristics and cycle characteristics.

[0063] ≪Lithium-ion secondary battery≫ The lithium-ion secondary battery of this disclosure includes a negative electrode for the lithium-ion secondary battery of this disclosure, a positive electrode, and an electrolyte.

[0064] The positive electrode can be obtained by forming a positive electrode material layer on a current collector in the same manner as the method for producing the negative electrode described above. As the current collector, metals or alloys such as aluminum, titanium, and stainless steel can be used used used foil, perforated foil, mesh, etc.

[0065] The positive electrode material used for forming the positive electrode material layer is not particularly limited. Examples of the positive electrode material include metal compounds (metal oxides, metal sulfides, etc.) capable of doping or intercalating lithium ions, and conductive polymer materials. More specifically, lithium cobalt oxide (LiCoO ２ ), lithium nickel oxide (LiNiO ２ ), lithium manganate (LiMnO ２ ), these complex oxides (LiNi ｘ Mn ｙ Co ｚ O ２ , x + y + z = 1), complex oxides containing additive element M' (LiNi ａ Mn ｂ Co ｃ M' ｄ O ２ , a + b + c + d = 1, M': Al, Mg, Ti, Zr or Ge), spinel-type lithium manganese oxide (LiMnO ２ O ４ ), lithium vanadium compounds, V ２ O ５ , V ６ O １３ , VO ２ , MnO ２ , TiO ２ , MoV ２ O ８ , TiS ２ , V ２ S ５ , VS ２ , MoS ２ , MoS ３ , Cr ３ O ８ , Cr ２ O ５ , olivine-type LiMPO ４Examples include metal compounds such as (M: Co, Ni, Mn, Fe), conductive polymers such as polyacetylene, polyaniline, polypyrrole, polythiophene, and polyacene, and porous carbon. The positive electrode material may be a single material or two or more materials.

[0066] The electrolyte is not particularly limited; for example, a solution of lithium salt as the electrolyte in a non-aqueous solvent (a so-called organic electrolyte) can be used. Examples of lithium salts include LiClO ４ LiPF ６ LiAsF ６ LiBF ４ LiSO ３ CF ３ Examples include the following. The lithium salt may be used alone or in combination of two or more types. Examples of non-aqueous solvents include ethylene carbonate, fluoroethylene carbonate, chloroethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, cyclopentanone, cyclohexylbenzene, sulfolane, propanesultone, 3-methylsulfolane, 2,4-dimethylsulfolane, 3-methyl-1,3-oxazolidine-2-one, γ-butyrolactone, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methylpropyl carbonate, butyl methyl carbonate, ethyl propyl carbonate, butyl ethyl carbonate, dipropyl carbonate, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, methyl acetate, ethyl acetate, trimethyl phosphate ester, triethyl phosphate ester, etc. The non-aqueous solvent may be used alone or in combination of two or more types.

[0067] The state of the positive and negative electrodes in a lithium-ion secondary battery is not particularly limited. For example, the positive and negative electrodes, along with a separator placed between them as needed, may be wound in a spiral shape, or they may be stacked in a flat plate shape.

[0068] The separator is not particularly limited, and for example, a nonwoven fabric made of resin, cloth, microporous film, or a combination thereof can be used. Examples of resins include those mainly composed of polyolefins such as polyethylene and polypropylene. If the positive and negative electrodes do not come into contact due to the structure of the lithium-ion secondary battery, a separator may not be used.

[0069] The shape of lithium-ion secondary batteries is not particularly limited. Examples include laminated batteries, paper batteries, button batteries, coin batteries, stacked batteries, cylindrical batteries, and prismatic batteries.

[0070] The lithium-ion secondary battery of this disclosure is suitable as a high-capacity lithium-ion secondary battery for use in electric vehicles, power tools, power storage devices, and the like.

[0071] The present disclosure will be described in detail below with reference to examples, but the present disclosure is not limited to these examples.

[0072] [Example 1] As the natural graphite used to produce graphite particles (1), as shown in Table 1, the volume average particle size (D50) was 10.7 μm and the specific surface area was 9.5 m². ２ The bulk density after 250 taps was 0.97 g / cm³. ３ Spherical natural graphite was used. Petroleum pitch with a softening point temperature of approximately 250°C was used as a graphitizable binder for the production of graphite particles (1).

[0073] Spheroidal natural graphite and petroleum pitch were mixed in a mass ratio of 70:30 and combined in a mixer to prepare a mixed raw material. This mixed raw material was placed in a cylindrical metal pot equipped with baffles for stirring, and a lid with a gas vent was placed on top. This cylindrical pot was rotated and mixed for 1 hour in an electric furnace at 300°C in a nitrogen atmosphere, while keeping the rotation axis of the cylindrical pot horizontal, to agglomerate the mixed raw material and form secondary particles. Next, the secondary particles of the mixed raw material were crushed in a cutter mixer. The crushed secondary particles contained volatile components, so to remove these volatile components, they were calcined for 1 hour in an electric furnace at 1050°C in a nitrogen atmosphere. This calcined powder was placed in a graphite crucible and held in a high-temperature induction furnace at 2700°C in an argon atmosphere for 0.5 hours to obtain graphite particles (1).

[0074] [Example 2] As the natural graphite used to produce graphite particles (2), as shown in Table 1, the volume-average particle size (D50) was 8.7 μm and the specific surface area was 9.3 m². ２ The bulk density after 250 taps was 0.80 g / cm³. ３ Spherical natural graphite was used. Petroleum pitch with a softening point temperature of approximately 250°C was used as a graphitizable binder for the production of graphite particles (2).

[0075] A mixed raw material was prepared by blending spheroidal natural graphite and petroleum pitch in a mass ratio of 70:30 and mixing them in a mixer. This mixed raw material was placed in a cylindrical metal pot equipped with baffles for stirring, and a lid with a gas vent was placed on top. This cylindrical pot was rotated and mixed for 1 hour in an electric furnace at 300°C in a nitrogen atmosphere, while keeping the rotation axis of the cylindrical pot horizontal, to agglomerate the mixed raw material and form secondary particles. Next, the secondary particles were crushed in a cutter mixer. The resulting secondary particles contained volatile components, so to remove these volatile components, they were calcined for 1 hour in an electric furnace at 1050°C in a nitrogen atmosphere. This calcined powder was placed in a graphite crucible and held in a high-temperature induction furnace at 2800°C in an argon atmosphere for 0.5 hours to obtain graphite particles (2).

[0076] [Example 3] As the natural graphite used to produce graphite particles (3), as shown in Table 1, the volume average particle size (D50) was 15.7 μm and the specific surface area was 6.5 m².２ The bulk density after 250 taps was 0.97 g / cm³. ３ Spherical natural graphite was used. Petroleum pitch with a softening point temperature of approximately 250°C was used as a graphitizable binder for the production of graphite particles (3).

[0077] Spheroidal natural graphite and petroleum pitch were mixed in a mass ratio of 80:20 and combined in a mixer to prepare a mixed raw material. This mixed raw material was placed in a cylindrical metal pot equipped with baffles for stirring, and a lid with a gas vent was placed on top. This cylindrical pot was rotated and mixed for 1 hour in an electric furnace at 300°C in a nitrogen atmosphere, while keeping the rotation axis of the cylindrical pot horizontal, to agglomerate the mixed raw material and form secondary particles. Next, the secondary particles of the mixed raw material were crushed in a cutter mixer. The crushed secondary particles contained volatile components, so to remove these volatile components, they were calcined for 1 hour in an electric furnace at 1050°C in a nitrogen atmosphere. This calcined powder was placed in a graphite crucible and held in a high-temperature induction furnace at 2600°C in an argon atmosphere for 0.5 hours to obtain graphite particles (3).

[0078] [Example 4] As the natural graphite used to produce graphite particles (4), as shown in Table 1, the volume-average particle size (D50) was 8.7 μm and the specific surface area was 9.3 m². ２ The bulk density after 250 taps was 0.80 g / cm³. ３ Spheroidal natural graphite was used. Petroleum pitch with a softening point temperature of approximately 250°C was used as a graphitizable binder for the production of graphite particles (4).

[0079] A mixed raw material was prepared by blending spheroidal natural graphite and petroleum pitch in a mass ratio of 70:30 and mixing them in a mixer. This mixed raw material was placed in a cylindrical metal pot equipped with baffles for stirring, and a lid with a gas vent was placed on top. This cylindrical pot was rotated and mixed for 1 hour in an electric furnace at 300°C in a nitrogen atmosphere, while keeping the rotation axis of the cylindrical pot horizontal, to agglomerate the mixed raw material and form secondary particles. Next, the secondary particles were crushed in a cutter mixer. The resulting secondary particles contained volatile components, so to remove these volatile components, they were calcined for 1 hour in an electric furnace at 1050°C in a nitrogen atmosphere. This calcined powder was placed in a graphite crucible and held in a high-temperature induction furnace at 2400°C in an argon atmosphere for 0.5 hours to obtain graphite particles (4).

[0080] [Example 5] As the natural graphite used to produce graphite particles (5), as shown in Table 1, the volume-average particle size (D50) was 8.7 μm and the specific surface area was 9.3 m². ２ The bulk density after 250 taps was 0.80 g / cm³. ３ Spheroidal natural graphite was used. Petroleum pitch with a softening point temperature of approximately 250°C was used as a graphitizable binder for the production of graphite particles (5).

[0081] Spheroidal natural graphite and petroleum pitch were blended in a mass ratio of 70:30 and mixed in a mixer to prepare a mixed raw material. This mixed raw material was placed in a cylindrical metal pot equipped with baffles for stirring, and a lid with a gas vent was placed on top. This cylindrical pot was rotated and mixed for 1 hour in an electric furnace at 300°C in a nitrogen atmosphere, while keeping the rotation axis of the cylindrical pot horizontal, to agglomerate the mixed raw material and create secondary particles. Next, the secondary particles of the mixed raw material were crushed in a cutter mixer. The resulting secondary particles contained volatile components, so to remove these volatile components, they were calcined for 1 hour in an electric furnace at 1050°C in a nitrogen atmosphere. Boric acid (H) was added to this calcined powder. ３ BO ３ The boric acid was added to the total amount of the mixed raw materials in a quantity of 0.6% by mass. The calcined powder with boric acid added was placed in a graphite crucible and held in a high-temperature induction furnace under an argon atmosphere at 2400°C for 0.5 hours to obtain graphite particles (5).

[0082] [Example 6] As the natural graphite used to produce graphite particles (6), as shown in Table 1, the volume-average particle size (D50) was 8.7 μm and the specific surface area was 9.3 m². ２ The bulk density after 250 taps was 0.80 g / cm³. ３ Spheroidal natural graphite was used. Petroleum pitch with a softening point temperature of approximately 250°C was used as a graphitizable binder for the production of graphite particles (6).

[0083] Spheroidal natural graphite and petroleum pitch were blended in a mass ratio of 70:30 and mixed in a mixer to prepare a mixed raw material. This mixed raw material was placed in a cylindrical metal pot equipped with baffles for stirring, and a lid with a gas vent was placed on top. This cylindrical pot was rotated and mixed for 1 hour in an electric furnace at 300°C in a nitrogen atmosphere, while keeping the rotation axis of the cylindrical pot horizontal, to agglomerate the mixed raw material and form secondary particles. Next, the secondary particles of the mixed raw material were crushed in a cutter mixer. The resulting secondary particles contained volatile components, so to remove these volatile components, they were calcined for 1 hour in an electric furnace at 1200°C in a nitrogen atmosphere. Boric acid (H) was added to this calcined powder. ３ BO ３ The boric acid was added to the total amount of the mixed raw materials in a quantity of 2.0% by mass. The calcined powder with boric acid added was placed in a graphite crucible and held in a high-temperature induction furnace under a nitrogen atmosphere at 2400°C for 0.5 hours to obtain graphite particles (6).

[0084] [Example 7] As the natural graphite used to produce graphite particles (7), as shown in Table 1, the volume-average particle size (D50) was 8.7 μm and the specific surface area was 9.3 m². ２ The bulk density after 250 taps was 0.80 g / cm³. ３Spheroidal natural graphite was used. Petroleum pitch with a softening point of approximately 250°C was used as a graphitizable binder for the production of graphite particles (7). Spheroidal natural graphite and petroleum pitch were mixed in a mass ratio of 80:20 and mixed in a mixer to prepare a mixed raw material. This mixed raw material was placed in a cylindrical metal pot equipped with baffles for stirring, and a lid with a gas vent hole was placed on top. This cylindrical pot was rotated and mixed for 1 hour in an electric furnace at 350°C in a nitrogen atmosphere, while keeping the rotation axis of the cylindrical pot horizontal, to agglomerate the mixed raw material and form secondary particles. Next, the secondary particles of the mixed raw material were crushed in a cutter mixer. The crushed secondary particles contained volatile components, so to remove these volatile components, they were calcined for 1 hour in an electric furnace at 1050°C in a nitrogen atmosphere. This calcined powder was placed in a graphite crucible and held in a high-temperature induction furnace under an argon atmosphere at 2600°C for 0.5 hours to obtain graphite particles (7).

[0085] [Comparative Example 1] As natural graphite used in the production of graphite particles (C1), as shown in Table 2, the volume-average particle size (D50) is 19.8 μm and the specific surface area is 5.1 m². ２ The bulk density after 250 taps was 0.92 g / cm³. ３ Spheroidal natural graphite was used. To remove the volatile components of this spheroidal natural graphite, it was calcined in a nitrogen atmosphere in an electric furnace at 1050°C for 1 hour. The calcined powder was placed in a graphite crucible and held in a high-temperature induction furnace in an argon atmosphere at 3000°C for 0.5 hours to obtain graphite particles (C1).

[0086] [Comparative Example 2] As a raw material (graphitizable aggregate) used in the production of graphite particles (C2), as shown in Table 2, the volume average particle size (D50) is 12.5 μm and the specific surface area is 3.0 m². ２ The bulk density after 250 taps was 1.10 g / cm³. ３ Mosaic coke was used. To remove the volatile components of this mosaic coke, it was calcined in an electric furnace at 1050°C under a nitrogen atmosphere for 1 hour. This calcined powder was placed in a graphite crucible and held in a high-temperature induction furnace at 3000°C under an argon atmosphere for 0.5 hours to obtain graphite particles (C2).

[0087] [Comparative Example 3] As a raw material (graphitizable aggregate) used in the production of graphite particles (C3), as shown in Table 2, the volume average particle size (D50) is 12.5 μm and the specific surface area is 2.8 m². ２ The bulk density after 250 taps was 1.20 g / cm³. ３ Needle coke was used. To remove the volatile components of this needle coke, it was calcined in an electric furnace at 1050°C in a nitrogen atmosphere for 1 hour. The calcined powder was placed in a graphite crucible and held in a high-temperature induction furnace at 3000°C in an argon atmosphere for 0.5 hours to obtain graphite particles (C3).

[0088] [Comparative Example 4] As natural graphite used in the production of graphite particles (C4), as shown in Table 2, the volume-average particle size (D50) is 8.4 μm and the specific surface area is 11.9 m². ２ The bulk density after 250 taps was 0.50 g / cm³. ３ Spheroidal natural graphite was used. Petroleum pitch with a softening point temperature of approximately 250°C was used as a graphitizable binder for the production of graphite particles (C4).

[0089] Spheroidal natural graphite and petroleum pitch were blended in a mass ratio of 90:10 and mixed in a mixer to prepare a mixed raw material. To remove volatile components from this mixed raw material, it was calcined in an electric furnace at 1050°C under a nitrogen atmosphere for 1 hour. This calcined powder was placed in a graphite crucible and held in a high-temperature induction furnace at 3000°C under an argon atmosphere for 0.5 hours to obtain graphite particles (C4).

[0090] [Comparative Example 5] As natural graphite used in the production of graphite particles (C5), as shown in Table 2, the volume-average particle size (D50) is 8.4 μm and the specific surface area is 11.9 m². ２ The bulk density after 250 taps was 0.50 g / cm³. ３ Spheroidal natural graphite was used. To remove the volatile components from this spheroidal natural graphite, graphite particles (C5) were obtained by calcining it in an electric furnace at 1050°C under a nitrogen atmosphere for one hour.

[0091] In Tables 1 and 2, "-" indicates that the corresponding operation was not performed. Note that in Tables 1 and 2, the volume-average particle size (D50, "D50 of raw material" in the table), specific surface area ("Specific surface area of ​​raw material" in the table), and bulk density after 250 taps ("250-tap tap density of raw material" in the table) of the raw materials used in the production of graphite particles are values ​​obtained using the measurement method described above.

[0092]

[0093]

[0094] [Measurement and Evaluation] The graphite particles obtained in the examples and comparative examples were measured and evaluated as follows.

[0095] (Volume-average particle size, particle size distribution, specific surface area, compressive load, springback rate) The volume-average particle size (D50), particle size distribution D90 / D10, specific surface area, compressive load, and springback rate of the obtained graphite particles were determined by the measurement method described above. The results are shown in Tables 3 and 4.

[0096] (Electrode Orientation) A negative electrode for a lithium-ion secondary battery was prepared as follows, and the electrode orientation was evaluated under the conditions shown below. -Preparation of a negative electrode for a lithium-ion secondary battery- An appropriate amount of purified water was added to the obtained graphite particles (97.6 parts by mass), carboxymethylcellulose (CMC) (1.2 parts by mass), and styrene-butadiene rubber (SBR) (1.2 parts by mass) and kneaded to prepare a negative electrode material composition. Using a doctor blade coater and electrolytic copper foil, this negative electrode material composition was applied to the glossy surface of the electrolytic copper foil at a rate of 10 g / cm². ２ Coated electrodes were obtained by applying the material in the manner described above. Subsequently, the electrolytic copper foil on which the coated electrodes were formed was pre-dried in a 100°C oven dryer for 2 hours, and then roll-pressed to achieve an electrode density of 1.6 g / cm³. ３ The pressure was adjusted to achieve the desired result. Subsequently, a curing treatment was performed by drying at 120°C for 4 hours under a vacuum atmosphere to form a negative electrode material layer on the electrolytic copper foil, thereby obtaining a negative electrode for a lithium-ion secondary battery. -Evaluation of electrode orientation- The obtained negative electrode for a lithium-ion secondary battery was measured to a width of 5 cm and an area of ​​600 cm². ２The material was formed into strip-shaped sheets, and the resulting molded material was pressed with a 4t hydraulic pressure using a roll-type press. The linear pressure at this time was 4t / 5cm = 0.8t / cm. The compressed electrode, which was the pressed negative electrode, was placed in an X-ray diffraction measurement cell, and the X-ray diffraction pattern using CuKα rays was measured using an X-ray diffraction measuring device (Rigaku X-RAY DIFFRACTION METER MultiFlex) under the conditions of a scanning speed of 0.25° / min, tube voltage of 40kV, tube current of 30mA, divergence slit of 1°, scattering slit of 1°, and receiving slit of 0.3mm (2θ = 25.5° to 27.5°, 76.5° to 78.5°). The peak intensity of the 002 diffraction line of the obtained graphite crystal (I ００２ ) and the peak intensity of the 110 diffraction line (I １１０ Ratio I is the ratio of ) ００２ / I １１０ The value was determined and used as the electrode orientation. The results are shown in Tables 3 and 4.

[0097] (Boron Atom Content) The boron atom content on the surface of the graphite particles obtained in Examples 5 and 6 was measured using an XPS instrument (ULVAC-PHI PHI5000). The obtained graphite particles were attached to carbon conductive tape and introduced into the XPS analyzer. Narrow scan spectra of the detected elements were obtained, and the composition (atomic %) of each element was determined from the signal intensity. The results are shown in Table 5.

[0098] (Initiation Temperature of Combustion) For the graphite particles obtained in Examples 2 to 4 and Comparative Examples 3 to 5, the initiation temperature of combustion, determined by thermogravimetric analysis (TG) in air, was determined by the following method. A differential thermogravimetric analyzer (EXSTAR TG / DTA6200, manufactured by Seiko Instruments Inc.) was used as the measuring device, and α-alumina was used as the reference sample. Measurements were taken while 300 ml / min of dry air was flowed under the conditions of a temperature range of 30 to 1000°C and a heating rate of 2.5°C / min (20°C / min between 30 and 300°C), and a TG curve was obtained. In the obtained TG curve, the temperature at the point when the weight decreased by 1% was read as the combustion initiation temperature of the graphite particles. The results are shown in Table 6.

[0099] (Discharge Capacity) The negative electrode obtained in the electrode orientation measurement is used as the working electrode, metallic lithium is used as the counter electrode, and 1 M LiPF is used as the electrolyte. ６ A coin cell (lithium-ion secondary battery) was fabricated using a mixture of ethylene carbonate / ethyl methyl carbonate (3:7 volume ratio) and vinylene carbonate (VC) (1.0 mass%), a 25 μm thick polyethylene microporous membrane as a separator, and a 250 μm thick copper plate as a spacer. The fabricated coin cell was placed in a constant temperature bath set to 25°C and charged with a constant current of 0.1C to a voltage of 0.005V (V vs. Li / Li+), and then charged with a constant voltage of 0.005V until the current value became 0.05C. After a 30-minute pause, constant current discharge was performed with a current value of 0.2C to a voltage of 1.5V (V vs. Li / Li+), and the discharge capacity per unit amount of negative electrode material was determined. The results are shown in Tables 3 and 4. In a coin cell, charging is defined as the process where lithium ions are absorbed into the negative electrode, and discharging is defined as the process where lithium ions are released from the negative electrode.

[0100] (DC Resistance (DCR)) The DC resistance (DCR) of the lithium-ion secondary battery was measured to determine the input characteristics of the battery. Specifically, the following was done: The negative electrode for the lithium-ion secondary battery obtained in the electrode orientation measurement was used, and lithium nickel cobalt manganese oxide (LiNi) was used as the positive electrode. ０．３３ Mn ０．３３ Co ０．３３ O ２ A composite electrode comprising 94 parts by mass of ) , 3 parts by mass of carbon black, and 3 parts by mass of polyvinylidene fluoride, and an electrolyte of 1 M LiPF ６A single-layer laminated full cell (lithium-ion secondary battery) was fabricated using a mixture of ethylene carbonate / diethyl carbonate (3:7 volume ratio) and vinylene carbonate (VC) (1.0 mass%), with a 25 μm thick polyethylene microporous membrane as the separator. The above lithium-ion secondary battery (single-layer laminated full cell) was placed in a constant temperature bath set to 25°C, and three charge-discharge cycles were performed under the conditions of charging: CC / CV 0.2C 4.2V 0.02C Cut, and discharging: CC 0.2C 2.5V Cut. Subsequently, constant current charging was performed at a current value of 0.2C until the SOC reached 50%. Furthermore, the lithium-ion secondary battery was placed in a constant temperature bath set to 25°C, and constant current charging was performed for 10 seconds each under conditions of 1C, 2C, and 3C. The voltage drop (ΔV) for each constant current was measured, and the DC resistance (DCR) was measured using the following formula. The results are shown in Tables 3 and 4. DCR [Ω] = {(2C voltage drop ΔV - 1C voltage drop ΔV) + (3C voltage drop ΔV - 2C voltage drop ΔV)} / {(3C control current value I - 2C control current value I) + (2C control current value I - 1C control current value I)}

[0101]

[0102]

[0103]

[0104]

[0105] As shown in Tables 3 and 4, the graphite particles in the examples had compressive load and electrode orientation within the aforementioned ranges, and it was possible to manufacture lithium-ion secondary batteries that achieved both high discharge capacity and low electrical resistance compared to the comparative examples.

[0106] All documents, patent applications, and technical standards described herein are incorporated by reference to the same extent as if each individual document, patent application, and technical standard were specifically and individually noted to be incorporated by reference.

Claims

1. Density 1.7g / cm ３ The compressive load, which is the amount of pressure required to compress it to a certain level, is 3.5 kN / cm². ２ ~5.0 kN / cm ２ The peak intensity of the 002 diffraction line of the graphite crystal (I) obtained when a compressed body pressed at 0.8 t / cm is measured by X-ray diffraction using CuKα rays. ００２ ) and the peak intensity of the 110 diffraction line (I １１０ ) Ratio I ００２ / I １１０ A negative electrode material for lithium-ion secondary batteries, consisting of graphite particles with a density of 300 to 800.

2. The negative electrode material for a lithium-ion secondary battery according to claim 1, wherein the springback rate of the graphite particles is 0.20 to 0.

30.

3. The anode material for a lithium-ion secondary battery according to claim 1 or 2, wherein the combustion initiation temperature determined by thermogravimetric analysis (TG) of the graphite particles in the atmosphere is 700°C or higher.

4. The negative electrode material for lithium-ion secondary batteries according to any one of claims 1 to 3, wherein the boron atom content of the graphite particles, as determined by X-ray photoelectron spectroscopy (XPS), is 0.1 atomic% to 5 atomic%.

5. The negative electrode material for a lithium-ion secondary battery according to any one of claims 1 to 4, wherein the volume-average particle size (D50) of the graphite particles is 13 μm to 24 μm.

6. In the cumulative particle size distribution of the graphite particles, when the particle size corresponding to a cumulative 10% by volume from the smallest diameter side is represented as D10 and the particle size corresponding to a cumulative 90% by volume is represented as D90, the value of D90 / D10 is 2.2 to 3.3, the negative electrode material for a lithium-ion secondary battery according to any one of claims 1 to 5.

7. The specific surface area of the graphite particles determined by nitrogen adsorption measurement at 77K is 0.5 m ２ / g to 2.0 m ２ / g. The negative electrode material for a lithium ion secondary battery according to any one of claims 1 to 6.

8. The negative electrode material for a lithium-ion secondary battery according to any one of claims 1 to 7, wherein the graphite particles include secondary particles formed by the aggregation of a plurality of primary particles.

9. A negative electrode for a lithium-ion secondary battery, comprising a negative electrode material layer containing the negative electrode material for a lithium-ion secondary battery described in any one of claims 1 to 8, and a current collector.

10. A lithium-ion secondary battery comprising a negative electrode for a lithium-ion secondary battery according to claim 9, a positive electrode, and an electrolyte.

11. A method for producing a negative electrode material for a lithium-ion secondary battery, comprising the steps of: forming secondary particles by aggregating a plurality of natural graphite particles; and obtaining a negative electrode material for a lithium-ion secondary battery, which is graphite particles, by continuously graphitizing a composition to be graphitized containing the secondary particles.

12. The method for producing a negative electrode material for a lithium-ion secondary battery according to claim 11, wherein the composition to be graphitized includes a graphitization catalyst.

13. The method for producing a negative electrode material for a lithium-ion secondary battery according to claim 12, wherein the graphitization catalyst has boron atoms.

14. The method for producing a negative electrode material for a lithium-ion secondary battery according to any one of claims 11 to 13, wherein the composition to be graphitized comprises a graphitizable binder.

15. The method for manufacturing a negative electrode material for a lithium-ion secondary battery according to any one of claims 11 to 14, wherein the heating temperature in the continuous graphitization treatment is 2200°C to 2800°C.

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