Composite particles, method for manufacturing the same, and use thereof

Abstract

The present invention provides a composite particle that can achieve both high silicon utilization and oxidation inhibition during water dispersion. The composite particle of the present invention is a composite particle having a particle containing carbon material and silicon, and a coating layer containing carbon and oxygen on the surface of the particle, and has a true density of 1.80 to 1.99 g / cm 3 In the Raman spectrum, a peak exists at 450 to 495 cm ‑1 If the intensity of the peak is I Si , and the intensity of the G band is I G , then I Si / I G is 1.3 or less, and in X-ray photoelectron spectroscopy, if the atomic ratios of Si, O, and C are A Si , A O , and A C , and the ratios of SiO2 and SiO are B SiO2 , B SiO , then A Si is 0.05 or more, and I Si / I G and A C / (A C +A Si ×(B SiO2 +B SiO )) have a prescribed relationship.

Description

TECHNICAL FIELD

[0001] The present application relates to a composite particle, a method for producing the same, and use thereof. BACKGROUND

[0002] In lithium ion secondary batteries used in IT devices such as smartphones and tablet PCs, vacuum cleaners, power tools, electric bicycles, drones, and automobiles, a negative electrode active material that has both high capacity and high output is required. As the negative electrode active material, silicon (theoretical specific capacity: 4200 mAh / g) having a higher theoretical specific capacity than graphite (theoretical specific capacity: 372 mAh / g) currently in use has attracted attention.

[0003] However, silicon (Si) swells and shrinks in conjunction with electrochemical lithium insertion and extraction, and the volume at the time of swelling becomes about 3 to 4 times larger than the volume at the time of shrinking. As a result, the silicon particles can spontaneously disintegrate or peel off from the electrode, and thus it is known that the cycle characteristics of lithium ion secondary batteries using silicon are significantly low. Therefore, currently, there is active research on using silicon not only as a replacement for graphite but also as a configuration in which the degree of swelling and shrinking as a whole of the negative electrode active material is reduced. Among these, a large number of attempts have been made to composite with carbonaceous materials.

[0004] As a negative electrode active material having high capacity and long life, for example, Patent Literature 1 discloses a silicon-carbon composite material (Si-C composite material) obtained by a method in which porous carbon particles and silane gas are brought into contact at a high temperature to cause silicon to be generated inside the pores of the porous carbon. In Patent Literature 1, a material obtained by further coating the Si-C composite material with a carbon layer by a chemical vapor deposition (CVD) method is also disclosed.

[0005] PRIOR ART DOCUMENTS

[0006] Patent Literature 1: Japanese Patent Application Laid-Open No. 2018-534720 SUMMARY

[0007] PROBLEMS TO BE SOLVED BY THE INVENTION

[0008] Unlike carbon materials such as graphite used as a negative electrode active material in the past, silicon is oxidized if it comes into contact with an oxidizing agent such as oxygen or water. In the case where silicon containing silicon oxide generated by this oxidation is used as a negative electrode active material, the silicon oxide reacts with lithium to generate lithium silicate. Lithium silicate is a cause of irreversible capacity. In general, a negative electrode active material comes into contact with air and water at the time of manufacturing an electrode. In addition, sometimes a negative electrode active material, an electrode using the negative electrode active material, is stored in air. Therefore, it is preferable to use a negative electrode active material in which the oxidation of silicon is suppressed.

[0009] In the case where the material obtained by carbon-coating the Si-C composite material disclosed in Patent Document 1 by the CVD method is used as the negative electrode active material, according to the present inventors' studies, although oxidation deterioration can be suppressed, the silicon utilization and the coulombic efficiency decrease. The silicon utilization indicates the ratio of the capacity of the unit content of silicon in the negative electrode active material to the theoretical specific capacity of silicon (4200 mAh / g). If the silicon utilization is low, more Si-C composite material is required in order to increase the capacity, and therefore the silicon utilization is preferably as high as possible. It is considered that the silicon utilization decreases because if the heat treatment temperature at the time of carbon-coating is high, silicon and carbon in the Si-C composite material react to form silicon carbide. In the case where the temperature at the time of film formation by the CVD method is lowered, the decrease in the silicon utilization can be suppressed, but the carbonization is insufficient, and there is a concern that the resistance increases because the coating layer is thick.

[0010] In the case where carbon-coating is not performed, the decrease in the silicon utilization can be avoided, but the aforementioned oxidation cannot be suppressed. The Si-C composite material can be used as the negative electrode active material of a lithium ion secondary battery, and as a method of producing the negative electrode, a method of coating and drying an aqueous slurry containing the negative electrode active material on a current collector is general. In the case where the battery is evaluated in a laboratory, a small amount of the aqueous slurry is prepared, and the electrode is produced by coating in a short time, and therefore the Si-C composite material is hardly oxidized in water, and the adverse effects on the battery performance are small. However, in actual battery production, in the case where the aqueous slurry is produced in a large amount and a large-area electrode is coated, oxidation of the Si-C composite material in the aqueous slurry progresses, and for example, the degree of oxidation at the beginning of coating and at the end of coating is different, and it is conceivable that the problem of a decrease in the electrode capacity at the end of coating. In addition, hydrogen is generated at the time of oxidation in water, and therefore it is also conceivable that this hydrogen remains in the coating layer to become a cause of coating defects such as pinholes.

[0011] In the present application, the object is to provide a composite particle in which high silicon utilization is achieved in a lithium ion secondary battery, and oxidation can be suppressed at the time of dispersion of the Si-C composite material in water, that is, a composite particle composed of a Si-C composite material, in which high silicon utilization is achieved in a lithium ion secondary battery, and oxidation is difficult at the time of dispersion in water.

[0012] Means for solving the object

[0013] In Patent Literature 1, no discussion is made about the quality of carbon coating. In Patent Literature 1, as to carbon coating at 550°C, an example is disclosed in which the capacity decrease of Si-C composite is suppressed before and after carbon coating, but since there is a weight increase of 4.6%, the film layer is thick, and the resistance can be high when formed into a lithium ion secondary battery. In addition, in Patent Literature 1, no description is made about the effect of suppressing oxidation at the time of water dispersion. In order to form a high-quality carbon layer in the sense of water and oxygen barrier property, it is generally necessary to perform carbon CVD at a high temperature.

[0014] On the other hand, it is considered that if carbon and silicon are exposed to high temperature in a state of contact, silicon carbide (SiC) is generated. Since silicon carbide does not undergo lithium intercalation and extraction reaction, if the proportion of silicon carbide increases in Si-C composite, the silicon utilization rate decreases.

[0015] The present inventors have researched coating materials and coating methods in order to suppress the generation of SiC and obtain a high-quality coating layer. As a result, they have found a new composite particle in which a thin coating layer containing carbon and oxygen is provided on the surface of Si-C composite, which can improve the silicon utilization rate and suppress oxidation at the time of water dispersion, and completed the present application.

[0016] That is, the present application is constituted by, for example, the following structure.

[0017] 〔1〕

[0018] A composite particle having: a particle containing a carbon material and silicon, and a coating layer containing carbon and oxygen provided on the surface of the particle,

[0019] The true density obtained by measuring the dry density using helium gas is 1.80 g / cm 3 or more and 1.99 g / cm 3 or less,

[0020] In the Raman spectrum of the composite particle,

[0021] The peak is present in the range of 450 to 495 cm -1 ,

[0022] If the intensity of the peak is set as I Si , and the intensity of the G band (peak intensity near 1580 cm -1 ) is set as I G , I Si / I G is 1.3 or less,

[0023] If the atom number ratio based on the narrow spectrum of Si, O, and C in the X-ray photoelectron spectroscopy of the composite particle is set as A Si , A O , and AC , and the ratio of SiO2 to SiO in the Si species ratio obtained from the Si 2p spectrum state analysis is set to B SiO2 , B SiO ,

[0024] A Si is 0.05 or more,

[0025] The composite particle satisfies at least one of the following equations (1) and (2):

[0026] Y ≥ 0.75 (1)

[0027] Y ≥ -0.32X + 0.81 (2)

[0028] [In the equations (1) and (2), X = I Si / I G , and Y = A C / (A C +A Si ×(B SiO2 +B SiO ))].

[0029] 〔2〕

[0030] The composite particle according to the above item

[0031] The I Si / I G is 0.64 or less, and satisfies the equation (1).

[0032] 〔3〕

[0033] The composite particle according to the above item

[0034] The carbon material is a porous carbon, and silicon is contained in at least a part of the pores of the porous carbon.

[0035] 〔4〕

[0036] The composite particle according to any one of the above items

[0037] The thickness of the coating layer is thin to the extent that it is substantially not measurable when cross-sectional observation is performed based on an electron microscope.

[0038] 〔5〕

[0039] The composite particle according to any one of the above items

[0040] In an XRD pattern obtained by powder XRD using Cu-Kα rays, the half-value width of the peak of the Si (111) plane is 3.0° or more, the peak intensity of the SiC (111) plane / peak intensity of the Si (111) plane is 0.01 or less, and the R value of the Raman spectrum is 0.26 or more and less than 1.34.

[0041] 〔6〕

[0042] The composite particle according to any one of the items [1] to [5],

[0043] is hydrophobic.

[0044] 〔7〕

[0045] The composite particle according to any one of the items [1] to [6],

[0046] substantially does not contain graphite inside the composite particle.

[0047] 〔8〕

[0048] The composite particle according to any one of the items [1] to [7],

[0049] 50% particle diameter D50 in the cumulative particle size distribution on a volume basis V50 is 1.0 to 30.0 μm.

[0050] 〔9〕

[0051] The composite particle according to any one of the items [1] to [8],

[0052] the silicon content is 30 mass% or more and 80 mass% or less, and the oxygen content is 4.0 mass% or less.

[0053] 〔10〕

[0054] A method for producing a composite particle, comprising:

[0055] (A) bringing a silicon-containing gas into contact with a porous carbon to deposit silicon into the pores and the surface of the carbon material, thereby obtaining a Si / C particle;

[0056] (B) bringing a gas containing a hydrocarbon having an unsaturated bond into contact with the Si / C particle at 400°C or lower; and

[0057] (C) oxidizing a layer containing the hydrocarbon obtained in the step (B).

[0058] 〔11〕

[0059] The method for producing a composite particle according to the item

[10] ,

[0060] The process (A) and the process (B) are continuously performed.

[0061] 〔12〕

[0062] The composite particle manufacturing method according to the above-mentioned

[0063] The composite particle manufacturing method according to the above-mentioned

[0064] 〔13〕

[0065] The polymer-coated composite particle according to the above-mentioned

[0066] The composite particle according to the above-mentioned

[0067] 〔14〕

[0068] The negative electrode active material according to the above-mentioned

[0069] The composite particle according to the above-mentioned

[0070] 〔15〕

[0071] The negative electrode active material according to the above-mentioned

[0072] The negative electrode active material according to the above-mentioned

[0073] 〔16〕

[0074] The lithium ion secondary battery according to the above-mentioned

[0075] The negative electrode active material according to the above-mentioned

[0076] Effects of the Invention

[0077] According to the present application, it is possible to provide a composite particle with high silicon utilization rate and difficult to be oxidized when dispersed in water, a negative electrode active material for a lithium ion secondary battery using the same, and a lithium ion secondary battery. DETAILED DESCRIPTION

[0078] Next, the present application is specifically described. Unless otherwise specified, "lithium ion secondary battery" is sometimes simply referred to as "battery".

[0079] [1] Composite particle

[0080] The composite particle according to the present application is a composite particle having: a particle containing a carbon material and silicon, and a coating layer containing carbon and oxygen on the surface of the particle. That is, the composite particle according to the present application is a particle-like substance having a coating layer containing carbon and oxygen on the surface and a particle-like substance containing a carbon material and silicon inside the coating layer.

[0081] The "particle-like substance containing a carbon material and silicon" (hereinafter also referred to as "Si / C particle") means a particle-like substance containing silicon (Si) on the surface and inside of a carbon material. The carbon material is preferably porous carbon, and silicon is preferably contained in at least the fine pores of the porous carbon. The "porous carbon" means carbon having fine pores. It is preferable that fine Si domains are uniformly formed inside the carbon material. The "Si domain" means a region where silicon exists. By the Si / C particle having this configuration, expansion and contraction accompanying charge and discharge occur isotropically, and thus the charge and discharge cycle durability is improved. This configuration can be identified by performing observation of cross-sectional SEM-EDS of the composite particle. If the distribution of silicon and carbon overlaps inside the composite particle, it is known that fine Si domains below the spatial resolution of SEM-EDS are uniformly dispersed.

[0082] The Si / C particle can be obtained by, for example, bringing a silicon source such as silane (SiH4) into contact with a particle-like porous carbon to cause silicon (usually amorphous) to be deposited in the fine pores of the porous carbon. At this time, by using a porous carbon having fine pores, fine Si domains can be uniformly formed inside the particle.

[0083] The composite particle according to the present application has at least peaks in the vicinity of Raman shift = 450 to 495 cm -1 , 1350 cm -1 , and 1580 cm -1 in a Raman spectrum. In general, crystalline silicon such as a silicon wafer, particle-like silicon, and SiO x after heat treatment has a peak in the vicinity of 520 cm -1 . Amorphous silicon has a peak at a lower Raman shift than this, and thus, in the case where a peak exists in the range of 450 to 495 cm -1 , it is indicated that the composite particle has amorphous silicon. If silicon is amorphous, expansion and contraction during charge and discharge proceed more isotropically, and thus the cycle characteristics can be improved.

[0084] When the intensity of the peak at 450 to 495 cm -1 is set as I si , and the intensity of the peak in the vicinity of 1580 cm -1 (G band) is set as I G , the ratio I si / I G1.3 or less, preferably 0.94 or less, further preferably 0.64 or less, most preferably 0.54 or less.

[0085] A peak of silicon appears in the Raman spectrum, indicating the presence of silicon on the surface of the composite particles and / or in the fine pores near the surface of the Si / C particles. It is known that in the XPS described later, information from the surface of a substance to a depth of several nm is obtained, but in the Raman spectrum, information from the surface of a carbon material to a depth of about 1 μm to submicron is obtained (hereinafter, the position of the information obtained by the Raman spectrum will also be referred to as "near the surface").

[0086] The I of the composite particles Si / I G 1.3 or less indicates that the surface of the Si / C particles is not thickly covered with a component containing silicon, and indicates that the structure becomes one containing silicon and carbon. On the other hand, in the case where the proportion of silicon is very high, I Si / I G becomes a very large value compared with the above range. By I Si / I G being within the above range, expansion and shrinkage of the same degree as the inside of the Si / C particles also occurs on the surface of the Si / C particles at the time of charge and discharge, and concentration of stress of expansion and shrinkage to the surface of the Si / C particles can be avoided, and improvement of the cycle characteristics is achieved.

[0087] I Si / I G The lower limit of I is preferably 0.01. More preferably, it is 0.02. If it is less than 0.01, the thickness of the coating layer becomes large, and becomes a factor of the increase in resistance.

[0088] Further, the "peak intensity" is set to the height from the baseline to the peak apex after correction of the baseline.

[0089] I Si / I G The value of I can be changed, for example, by adjusting the reaction conditions (gas composition ratio, gas flow rate, temperature program, reaction time) of the process (A) in the manufacturing method of the composite particles described later.

[0090] In one embodiment of the present invention, the composite particles preferably have a full width at half maximum (FWHM) of 3.0° or more in the XRD pattern obtained by powder X-ray diffraction (Powder XRD) using Cu-Kα rays. A FWHM of 3.0° or more indicates that the silicon crystallites in the composite particles are small, which helps to suppress silicon degradation associated with charging and discharging. From the same viewpoint, the FWHM is preferably 4.0° or more, more preferably 5.0° or more. Furthermore, the FWHM is preferably 10.0° or less, more preferably 8.0° or less. Additionally, a peak on the Si(111) plane means a peak originating from Si and appearing around 2θ = 28°. Furthermore, the "peak intensity" used to determine the FWHM is defined as the height from the baseline to the peak apex after baseline correction.

[0091] The composite particles involved in one embodiment of the present invention increase the intensity of the D band of the Raman spectrum (1350 cm⁻¹). -1 (Near peak intensity) is set to I D The intensity I of the time and the G-band G The ratio is the R value (I). D / I G The R value is preferably 0.26 or higher and less than 1.34. If the R value is 0.26 or higher, the reaction resistance of the negative electrode using the composite particles is sufficiently low, thus improving the coulombic efficiency of the battery. On the other hand, an R value less than 1.34 means fewer defects in the carbon material. With an R value less than 1.34, the internal resistance of the battery decreases, and the rate performance is improved. From the same point of view, an R value of 0.45 or higher is more preferred, and 0.65 or higher is even more preferred. Furthermore, an R value of 1.30 or lower is more preferred, and 1.20 or lower is even more preferred.

[0092] The composite particles of the present invention have a coating on their surface containing carbon and oxygen. The composite particles have the following structural features.

[0093] If the narrow-spectrum atomic ratios of Si, O, and C in the composite particles obtained by X-ray photoelectron spectroscopy (XPS) are respectively set as A... Si A O and A C And let B be the ratio of SiO2 to SiO in the Si ratios obtained from Si2p energy spectrum state analysis. SiO2 B SiO ,

[0094] Then A Si It is greater than or equal to 0.05 and satisfies at least one of the following equations (1) and (2).

[0095] Y≥0.75(1)

[0096] Y ≥ -0.32X + 0.81 (2)

[0097] (In formulae (1) and (2), X = I Si / I G , Y = A C / (A C +A Si ×(B SiO2 +B SiO ))〕

[0098] Further, A Si +A O +A C = 1.00.

[0099] It is known that XPS is a method of obtaining insights into the kind, amount present, and chemical bond state of elements present on the surface of a substance, and obtains information from the surface of the substance to a depth of several nm.

[0100] <1>A Si

[0101] A Si less than 0.05 means that the coating is too thick. If the coating is too thick, the resistance of the composite particle rises. A Si It is preferably 0.15 or more, further preferably 0.25 or more. The analysis depth of XPS is several nm, which is very shallow, so that the fact that Si can be observed to some extent means that the coating is an extremely thin layer.

[0102] The coating contains carbon and oxygen, so that the electron conductivity is low compared with carbon coating. If the coating is too thick, the resistance rises, so that it needs to be a thin layer.

[0103] <2>A C / (A C +A Si ×(B SiO2 +B SiO ))

[0104] The value of A C / (A C +A Si ×(B SiO2 +B SiO )) is an index of the carbon concentration at a position from the surface to a depth of several nm (depth of spatial resolution in XPS) of the composite particle. This is because it is considered that Si exists in the form of an oxide such as SiO2, SiO at the surface of the composite particle, and that most of the surface of the composite particle is formed of carbon and silicon oxide such as SiO2, SiO. However, A CThe coating contains information not only about the surface but also about the carbon in the Si / C particles, so this indicator does not reflect only the carbon concentration of the coating.

[0105] A C / (A C +A Si ×(B SiO2 +B SiO A smaller value indicates a lower carbon concentration on the surface of the composite particles. If this carbon concentration decreases, the oxidation inhibition capacity decreases. That is, the composite particles are more easily oxidized.

[0106] However, as the silicon concentration near the surface of the composite particles increases, the oxidation inhibition ability is fully utilized even when the carbon concentration at the surface of the composite particles decreases. This is attributed to the fact that as the silicon concentration near the surface of the composite particles increases, i.e., as the I... Si / I G As silicon grows larger, it becomes more difficult to oxidize due to the presence of complexes between carbon from hydrocarbons and silicon oxides. That is, from A... C / (A C +A Si ×(B SiO2 +B SiO The carbon concentration index is affected by the silicon concentration near the surface of the composite particles.

[0107] Therefore, the composite particles involved in this invention satisfy the following formula (1).

[0108] Y≥0.75 (1)

[0109] In equation (1), Y = A C / (A C +A Si ×(B SiO2 +B SiO ))〕.

[0110] However, when the silicon concentration near the surface of the composite particles is relatively high (specifically, in I...), Si / I G If the value exceeds 0.2, the following equation (2) can be satisfied, or the above equation (1) can be dissatisfied.

[0111] Y≥-0.32X+0.81 (2)

[0112] In equation (2), X = I Si / I G , Y = A C / (A C +A Si ×(B SiO2 +B SiO ))〕

[0113] In the case where neither of the above-described formula (1) and (2) is satisfied, the oxidation inhibition ability of the composite particle becomes low.

[0114] Y is A C / (A C +A Si x (B SiO2 +B SiO ) is preferably 0.85 or more.

[0115] Y is A C / (A C +A Si x (B SiO2 +B SiO ) is preferably 0.98 or less.

[0116] Although the structure of the coating layer cannot be determined, it is preferred that the surface be a thin film layer in which carbon and silicon oxides are complexed.

[0117] A C / (A C +A Si x (B SiO2 +B SiO ) can be changed, for example, by adjusting the reaction temperature, reaction time, reaction pressure, or the kind or concentration of hydrocarbon in the process (B) in the manufacturing method of the composite particle described later.

[0118] The coating layer preferably contains a hydrocarbon-derived compound. In the case where the coating layer contains a hydrocarbon-derived compound, the thermal decomposition GC-MC measurement of the composite particle can be performed and judged from the fact that a hydrocarbon-derived compound is contained in the gas generated from the composite particle between 200°C and 600°C.

[0119] The coating layer can be manufactured by bringing a carbon source having an unsaturated bond into contact with the Si / C particle at a low temperature, and then oxidizing the resulting substance. Details are described later.

[0120] In the composite particle according to the embodiment of the present application, the coating is preferably thin to the extent that it is substantially undetectable in cross-sectional observation based on an electron microscope. If the coating is thin as described above, the resistance of the composite particle is low. A scanning electron microscope (SEM) does not have resolution capable of distinguishing a thickness of several nm, and thus cannot detect the thickness of a coating that is thinner. A transmission electron microscope (TEM) is sufficient in resolution, and can observe a thickness of several nm, but in the case of a TEM observation sample for a thin film including the coating, which is prepared from the composite particle, the coating of the composite particle is damaged by processing, and is destroyed, and thus the thickness of the coating cannot actually be observed using the TEM. The "substantially undetectable" refers to such a state. However, even a thin film that is substantially undetectable in cross-sectional observation based on an electron microscope can confirm the presence of the coating according to the above-described XPS and the test of the hydrophobicity of the surface described later.

[0121] The true density of the composite particle according to the present application is 1.80 g / cm 3 The above value is calculated by using helium to measure the dry density.

[0122] The true density of the composite particle according to the present application is 1.80 g / cm 3 This means that the amount of silicon filled into the pores of the carbon in the composite particle is small, and the coating is a thick layer of low-density organic matter such as tar components and polymers.

[0123] If the true density of the composite particle according to the present application is 1.80 g / cm 3 or more, and the coating is thin, the specific capacity of the composite particle can be increased and / or the resistance can be reduced. From the same viewpoint, the true density is preferably 1.85 g / cm 3 or more, and more preferably 1.88 g / cm 3 or more.

[0124] The true density of the composite particle according to the present application is 1.99 g / cm 3 or more. If the true density of the composite particle according to the present application is 1.99 g / cm 3 or more, the carbon material in the composite particle is amorphous, and the substance of the carbon material is more isotropic. The true density is lower than the literature value of the density of carbon and silicon, and thus it is considered that there is a void in the composite particle into which helium cannot intrude from the outside of the particle, and thus the cycle characteristics can be improved if the true density is in the above range. In addition, since the amount of silicon carbide in the composite particle is small, the decrease in the silicon utilization rate can be suppressed. Silicon carbide has a higher density than carbon and Si, and thus the true density becomes higher if silicon carbide is included in the composite particle. From this viewpoint, the true density is preferably 1.98 / cm 3 or more, and more preferably 1.96 g / cm 3 or more.

[0125] The true density obtained by the dry density measurement can be measured by a gas displacement method. The gas displacement method is a method of filling a container, the volume of which is measured in advance using helium gas, with a sample and helium gas in an environment maintained at a constant temperature, and calculating the true density from the volume of helium gas expelled by the sample and the mass of the sample. As a device of the gas displacement method, for example, an AccuPyc (registered trademark) II 1340 Gas Pycnometer manufactured by micromeritics Corporation can be used.

[0126] The composite particle according to one embodiment of the present application preferably has a ratio of (peak intensity of SiC (111) plane) / (peak intensity of Si (111) plane) of 0.01 or less in an XRD pattern obtained by powder X-ray diffraction measurement (powder XRD) using Cu-Ka rays. Thus, the composite particle does not contain SiC (silicon carbide) or contains SiC in a very small amount, and therefore, the utilization rate of silicon as a battery active material is increased, and the initial discharge capacity can be increased. Further, the ratio of (peak intensity of SiC (111) plane) / (peak intensity of Si (111) plane) is also referred to as I SiC(111) / I Si(111) . I SiC(111) / I Si(111) The lower limit of the ratio is more preferably 0.00, that is, the peak intensity of the SiC (111) plane is more preferably not observed. Further, the peak of the SiC (111) plane is a peak derived from SiC and appearing near 35° in terms of 2θ. In addition, the peak of the Si (111) plane is a peak derived from Si and appearing near 28° in terms of 2θ.

[0127] The composite particle according to one embodiment of the present application is preferably hydrophobic. If the composite particle is hydrophobic, the protection effect against water is increased. In addition, a polymer serving as a binder is contained in the negative electrode mixture layer. The polymer has a high affinity for the hydrophobic particle, and therefore, the particle can be dispersed more uniformly when a slurry for coating a negative electrode is manufactured.

[0128] The hydrophobic composite particle can be manufactured, for example, by using a hydrocarbon having an unsaturated bond in the process (B) described later.

[0129] As a method of measuring hydrophobicity, a method of measuring the contact angle of water with respect to the composite particle by forming the composite particle into a pellet and then measuring the contact angle of water, a method of measuring the adsorption amount of water vapor with respect to the composite particle and dividing the adsorption amount by the nitrogen adsorption amount of the same composite particle, the BET specific surface area calculated by the nitrogen adsorption method, and the like can be given.

[0130] As a method of measuring hydrophobicity, a method of observing the penetration behavior of water into a powder is easy to determine simply. The measurement can be performed, for example, by the method described in the examples.

[0131] The composite particles according to an embodiment of the present application preferably do not contain graphite inside the composite particles. The presence of graphite inside the composite particles is determined by an XRD pattern obtained by powder X-ray diffraction measurement using Cu-Ka rays. In the case where graphite is meaningfully present inside the composite particles, a peak derived from graphite, which is sharp near 26° in 2Θ, can be observed. A halo derived from carbon, silicon oxide is also observed in the vicinity, but the intensity of these patterns is low, on the other hand, graphite is observed as a very sharp peak with high intensity, and thus, when the peak of graphite is not observed, it is considered that graphite is substantially not contained inside the composite particles.

[0132] It is difficult to obtain porous graphite, and it is also difficult to distribute uniform fine pores inside graphite particles. The composite particles according to the present application preferably have fine Si domains uniformly formed inside the particles. If graphite is contained inside the composite particles, expansion and contraction at the time of charge and discharge become non-uniform inside the particles, and the cycle characteristics are degraded.

[0133] As described above, expansion and contraction at the time of charge and discharge are preferably uniform inside the particles, and thus, the shape of the composite particles according to an embodiment of the present application is preferably such that the average aspect ratio is 1.25 or less, and more preferably, a part of the particle has no corners. The composite particles are further preferably spherical (the cross section of the composite particles is circular). The aspect ratio is a value obtained by dividing the major axis of the particle by the minor axis. The aspect ratio of 1.00 indicates that the major axis and the minor axis are equal, and thus, the average aspect ratio is more preferably closer to 1.00.

[0134] The degree of sphericity can be determined by the average circularity calculated from the cross-sectional shape. The average circularity is preferably 0.95 or more and 1.00 or less. The circularity is represented by the following formula.

[0135] (Circularity) = 4π x (S / L 2 )

[0136] Here, S is the cross-sectional area of the particle [m 2 ], and L is the circumference of the particle [m].

[0137] The average aspect ratio and the average circularity described above can be calculated by analyzing an image obtained by a scanning electron microscope (SEM) using image analysis software. The analysis is performed on 100 composite particles randomly selected in the SEM photograph, and the average value of 100 (number average) is used for the determination. As the image analysis software, for example, Image J or the like is used.

[0138] The composite particles according to an embodiment of the present application preferably have a BET specific surface area of 0.1 m 2 / g or more. The BET specific surface area of 0.1 m 2 / g or more, the slurry viscosity at the time of electrode production can be made appropriate, and a good electrode can be produced. From the same viewpoint, the BET specific surface area is more preferably 0.5 m 2 / g or more, further preferably 0.9 m 2 / g or more.

[0139] The composite particles according to an embodiment of the present application preferably have a BET specific surface area of 100.0 m 2 / g or less. By having a BET specific surface area of 100.0 m 2 / g or less, the side reaction with the electrolyte solution can be reduced. From the same viewpoint, the BET specific surface area is more preferably 50.0 m 2 / g or less, further preferably 25.0 m 2 / g or less.

[0140] The BET specific surface area is usually calculated using the BET method based on the adsorption isotherm measured by a dedicated measuring device known in the technical field. As the adsorption gas, nitrogen is usually used.

[0141] The composite particles according to an embodiment of the present application preferably have a 50% particle diameter D V50 in the cumulative particle size distribution on a volume basis of 1.0 μm or more. By having a D V50 of 1.0 μm or more, the side reaction with the electrolyte solution can be reduced. Also, the handling properties of the powder are excellent, and it is easy to prepare a slurry having a viscosity and a density suitable for coating, and it is easy to increase the density at the time of forming an electrode. From this viewpoint, the D V50 is more preferably 2.0 μm or more, further preferably 3.0 μm or more, and most preferably 3.5 μm or more.

[0142] The composite particles according to an embodiment of the present application preferably have a D V50 of 30.0 μm or less. By having a D V50 of 30.0 μm or less, the diffusion length of lithium in the individual particles becomes short, and thus in addition to the excellent rate characteristics of the lithium ion battery, no streaks or abnormal unevennesses are generated at the time of coating to the current collector as a slurry. From this viewpoint, the D V50 is more preferably 20.0 μm or less, and further preferably 15.0 μm or less.

[0143] The composite particles according to an embodiment of the present application preferably have a 90% particle diameter D V90 of 50.0 μm or less. By having a D V90 of 50.0 μm or less, the diffusion length of lithium in the individual particles becomes short, and thus in addition to the excellent rate characteristics of the lithium ion battery, no streaks or abnormal unevennesses are generated at the time of coating to the current collector as a slurry. From this viewpoint, the DV90 More preferably, it is 40.0 μm or less, further preferably 30.0 μm or less, and most preferably 20.0 μm or less.

[0144] The cumulative particle size distribution of these volume bases is measured, for example, by a laser diffraction particle size distribution meter.

[0145] The composite particle according to an embodiment of the present application preferably has a silicon content of 30% by mass or more. Here, the "silicon content" of the composite particle refers to the content of silicon as an element in the silicon element and compound contained in the composite particle. If the silicon content is 30% by mass or more, the amount of silicon in the composite particle is sufficient, and the discharge capacity can be increased. From the same viewpoint, the silicon content is more preferably 35% by mass or more, and further preferably 40% by mass or more.

[0146] The composite particle according to an embodiment of the present application preferably has a silicon content of 80% by mass or less. If the silicon content is 80% by mass or less, the amount of silicon in the composite particle is not excessive, and thus the volume change caused by expansion and contraction thereof can be absorbed by carbon. From the same viewpoint, the silicon content is more preferably 75% by mass or less, and further preferably 70% by mass or less.

[0147] The silicon content in the composite particle can be determined by performing fluorescent X-ray analysis and analyzed using a fundamental parameter method (FP method) or the like. Alternatively, the composite particle can be combusted to remove carbon components, and the remaining ash after combustion can be completely dissolved in an acid or a base, and then quantified by inductively coupled plasma atomic emission spectrometry (ICP-AES).

[0148] The composite particle according to an embodiment of the present application preferably has an oxygen content of 4.0% by mass or less. If the oxygen content is 4.0% by mass or less, the irreversible capacity of the negative electrode of a lithium ion secondary battery can be reduced. From the same viewpoint, the oxygen content is more preferably 2.0% by mass or less, and further preferably 1.0% by mass or less. As a lower limit of the oxygen content, 0.2% by mass is preferable. In the case where the oxygen content is 0.2% by mass or more, high oxidation inhibition ability is exhibited.

[0149] The oxygen content in the composite particle can be determined, for example, using an oxygen-nitrogen simultaneous measurement device.

[0150] In the present application, unless otherwise specified, the oxygen content of the composite particle refers to the oxygen content of the composite particle within 2 days after production or under a non-oxidizing atmosphere. In the case where the oxygen content cannot be determined within 2 days after production due to a process or the like, the value can be regarded as equivalent to that within 2 days after production even if it is determined later, provided that the composite particle is stored under an inert atmosphere such as argon. This is because oxidation does not progress when the composite particle is stored under an inert atmosphere.

[0151] [2] Method for producing composite particles

[0152] The method for producing composite particles according to the present application has the following steps (A), (B), and (C). By the method for producing composite particles according to the present application, the aforementioned composite particles according to the present application, i.e., the composite particles described in [1] above, can be obtained.

[0153] Step (A): a step of allowing a silicon-containing gas to contact (i.e., react) with a porous carbon to deposit silicon into the pores and on the surface of the porous carbon, thereby obtaining Si / C particles

[0154] Step (B): a step of allowing a gas containing a hydrocarbon having an unsaturated bond to contact with the Si / C particles at 400°C or lower

[0155] Step (C): a step of oxidizing the substance obtained in Step (B)

[0156] In the present specification, a carbon material having pores is referred to as "porous carbon". The composite particles preferably have a structure in which silicon is contained in the particles, and therefore the porous carbon preferably has a pore volume inside that can accommodate silicon. In addition, in a nitrogen adsorption test of the carbon material (porous carbon), the pore volume at a relative pressure P / P0 of 0.99 is set as V 0.99 When V 0.99 More preferably, it is 0.25 cc / g or more and 1.50 cc / g or less.

[0157] In addition, silicon is preferably contained in the composite particles as fine domains, and therefore it is further preferable that fine pores be abundant in the porous carbon. Specifically, in a nitrogen adsorption test of the porous carbon, the pore volume at a relative pressure P / P0 of 0.01 is set as V 0.01 When V 0.01 / V 0.99 It is further preferable to be 0.45 or more, and most preferable to be 0.55 or more. The nitrogen adsorption test can be performed using a publicly known method.

[0158] As the porous carbon, for example, activated carbon, activated carbon fiber, molecular sieve carbon, or inorganic template carbon can be used. In addition, a porous carbon obtained by activating a hard carbon using water vapor or carbon dioxide can be used. It is preferable to select a porous carbon that satisfies the above conditions. The activated carbon fiber can be a pulverized particulate activated carbon fiber, or can be pulverized after the silicon is supported to form a particulate shape.

[0159] A hard carbon can be obtained, for example, by heat-treating a phenol resin at 600°C to 1400°C, preferably at 800°C to 1400°C, in an inert atmosphere.

[0160] It is preferable to perform the process (A) after adjusting the porous carbon to the desired shape or particle size distribution of the composite particles. This is because the shape and particle size of the particles hardly change in the processes (A), (B), and (C), and thus the shape and particle size distribution of the composite particles are the same as those of the porous carbon. Thus, the porous carbon used in the process (A) can also be crushed, pulverized, and sieved.

[0161] After the composite particles are produced through the processes (A), (B), and (C), the particles sometimes aggregate with each other. In this case, it is preferable to crush to restore the shape and particle size distribution of the porous carbon as a raw material. However, if excessive energy is applied at this time to pulverize the composite particles and change the particle shape, the portion of the surface of the composite particles without a coating increases, and the oxidation suppression ability becomes low, and thus this is undesirable.

[0162] The porous carbon is preferably spherical. The spherical porous carbon is more preferably obtained by carbonizing and activating a spherical phenol resin. In addition, in the spherical porous carbon, the shape can be maintained without a pulverization process, and thus this is further preferable.

[0163] As the silicon-containing gas, a silane gas can be preferably used. The silane gas can also be used in combination with an inert gas such as helium or argon or a reducing gas such as hydrogen.

[0164] The process (A) is a process in which the porous carbon is placed in a reactor, a silicon-containing gas is brought into contact with the porous carbon to deposit silicon into the pores and on the surface of the porous carbon, and Si / C particles are obtained.

[0165] The shape of the reactor is not limited. As the reactor, a static furnace, a fluidized bed furnace, a furnace having a stirring function of powder such as a rotary kiln, a roller kiln, and a continuous furnace such as a push-type furnace can be used.

[0166] The reaction temperature is not limited as long as it is a temperature at which a silicon-containing gas such as a silane gas is decomposed and silicon is precipitated in the pores of the porous carbon, but it is preferably 300°C or higher and 450°C or lower. If it is lower than 300°C, the decomposition of the silane gas does not sufficiently occur, and thus the precipitation of silicon becomes insufficient. If it exceeds 450°C, the precipitation of silicon on the surface (including the opening portion of the pores) of the porous carbon becomes significant compared to the precipitation of silicon in the pores of the porous carbon due to the decomposition of the silane gas in the pores, and the opening portion of the pores is blocked by the precipitated silicon, and thus the precipitation in the pores becomes insufficient.

[0167] Even if it is 450°C or less, decomposition of silane occurs on the surface of the porous carbon, and silicon is deposited. Generally, the surface area of the pores of the porous carbon is much larger than the external surface area, and thus the silicon deposited in the pores of the porous carbon overwhelmingly increases. When silicon is present in the pores of the porous carbon, the durability of the composite particle to stress into the composite particle accompanying expansion and contraction of silicon accompanying charging and discharging of the battery is higher than when it is present on the external surface of the porous carbon, and thus is preferable. In processing at a higher temperature, deposition at the surface of the porous carbon becomes significant, and the number of sites at which the opening of the pores is blocked increases.

[0168] The conditions such as the gas composition ratio, the gas flow rate, and the temperature program are appropriately adjusted while the properties of the composite particle are observed.

[0169] Step (B) is a step of disposing the Si / C particle obtained in Step (A) in a reactor and bringing a gas containing a hydrocarbon having an unsaturated bond into contact with the Si / C particle at 400°C or less. The coating of the composite particle involved in the present application is thin. A method of depositing carbon onto the surface such as carbon CVD forms a thick carbon coating, and thus is not suitable. It is preferable to react the Si-H group of the surface of the Si / C particle with the hydrocarbon having an unsaturated bond to form a layer containing a hydrocarbon on the surface of the Si / C particle. In the layer containing a hydrocarbon, a substance obtained by reacting hydrocarbons with each other can also be contained. As the gas of a hydrocarbon having an unsaturated bond, a gas of a hydrocarbon having a double bond or a triple bond can be used. In the case where the hydrocarbon is a compound having a low vapor pressure and not gasified at normal pressure, it is sufficient to use the hydrocarbon at a pressure lower than normal pressure. Acetylene, ethylene, propylene, and 1,3-butadiene, which are gasses at normal pressure, are preferable, and acetylene and ethylene are more preferable. At this time, a plurality of hydrocarbons can also be used. In addition, an inert gas such as helium or argon or a reducing gas such as hydrogen can also be used in combination.

[0170] In Step (B), processing at a low temperature of 400°C or less is necessary in order to react the Si-H group and the unsaturated bond. If the temperature exceeds this, the amount of the decomposed Si-H group increases, and the reaction targeted, that is, the reaction of the Si-H group of the surface of the Si / C particle with the unsaturated bond of the hydrocarbon, becomes less likely to occur. In addition, the reactivity of silicon in the Si / C particle is very high, and thus at a high temperature exceeding 400°C, the reaction of the porous carbon and silicon occurs, and silicon carbide is generated, and thus the capacity of silicon decreases.

[0171] The lower limit of the reaction temperature is not limited as long as it is a temperature at which the hydrocarbon having an unsaturated bond reacts on the surface of the Si / C particle, and if the reaction temperature is low, the reaction rate is low, and thus it is preferable to be 100°C or more, and more preferably 150°C or more.

[0172] The thickness of the layer containing hydrocarbon can be the thickness of a molecular layer of hydrocarbon or the thickness of several molecular layers. In addition, a part of the hydrocarbon can also be decomposed. Even if a part of the hydrocarbon is decomposed to become carbon, the layer containing hydrocarbon is different from carbon coating and is a material with high resistance, and thus is preferably a thin film. Therefore, the weight change before and after the process (B) is preferably small. The increase in the mass of the Si / C particles having the layer containing hydrocarbon obtained in the process (B) with respect to the mass of the Si / C particles before the process (B) is more preferably 1.0% by mass or less, and further preferably 0.5% by mass or less.

[0173] The process (C) is a process of oxidizing the substance obtained in the process (B). This process (C) is a process of introducing oxygen to the coating (more precisely, the layer containing hydrocarbon formed on the surface of the Si / C particles in the process (B)). Although the configuration of the coating is not quite clear, by containing oxygen in the coating, the oxidation inhibition ability is improved and the resistance is lowered. The oxidation can be performed by bringing the coating into contact with a gas containing oxygen (more specifically, an oxidizing gas). The gas containing oxygen preferably has an oxygen concentration of 1 to 25% by volume, more preferably 1 to 20% by volume, and further preferably 5 to 20% by volume. In this case, the oxygen is diluted with argon, nitrogen. Air can also be used as the gas containing oxygen, but in order to oxidize stably, it is preferable to adjust the humidity of the air and keep it constant.

[0174] The reaction temperature, that is, the temperature when the coating is brought into contact with the gas containing oxygen, is preferably room temperature or higher and 200°C or lower. If it exceeds 200°C, decomposition of the coating or oxidation of silicon beyond the necessary amount occurs, and thus is undesirable.

[0175] The reaction time, that is, the time when the coating is brought into contact with the gas containing oxygen, is, for example, 0.1 to 120 hours.

[0176] The process (C) can also be performed by changing the oxygen concentration to perform the oxidation treatment.

[0177] It is preferable to perform heat treatment under an inert atmosphere or under low pressure after the coating is brought into contact with the gas containing oxygen. The temperature at the time of heat treatment is preferably 400°C or lower. It is considered that by performing heat treatment at 400°C or lower, unreacted Si-H groups are decomposed and converted to silicon, and oxygen complexation to the coating can be performed stably. The heat treatment time is, for example, 0.1 to 100 hours.

[0178] The process (A) and the process (B) are preferably performed continuously. The activity of silicon on the surface of the Si / C particles obtained in the process (A) is high, and thus, if exposed to the atmosphere, oxidation progresses, and the Si-H group on the surface decreases. Therefore, it is preferable to continuously perform the processes (A) and (B) without exposure to the atmosphere (air). The time between the process (A) and the process (B) is not limited as long as the Si / C particles are not exposed to the atmosphere. For example, the process (B) can be performed after the process (A) under an inert atmosphere. In addition, the processes (A) and (B) can be performed using separate apparatuses as long as the Si / C particles obtained in the process (A) are not exposed to the atmosphere.

[0179] The process (B) and the process (C) can also be performed using separate apparatuses. In addition, the processes (B) and (C) can be performed multiple times. For example, the process (C) can be performed, followed by the process (B), or the process (C) can be performed, followed by the process (B) and then the process (C).

[0180] [3] Composite particles further having a surface coating

[0181] The composite particles according to the present application can also have a layer further outside the above-described composite particles having a Si / C particle and a coating on the surface of the Si / C particle (hereinafter also referred to as "composite particle main body"). In order to distinguish from the "coating" described above, the layer disposed further outside the composite particle main body is referred to as a "surface coating" herein.

[0182] As a method for forming the surface coating, a method in which a layer is formed on at least a part of the surface of the composite particle by carbon coating, inorganic oxide coating, or polymer coating can be given. As a method for carbon coating, a chemical vapor deposition method (CVD), a physical vapor deposition method (PVD), or the like can be given. As a method for inorganic oxide coating, a chemical vapor deposition method (CVD), a physical vapor deposition method (PVD), an atomic layer deposition method (ALD), a wet method, or the like can be given. The wet method includes a method in which a liquid in which a precursor of an inorganic oxide is dissolved and / or dispersed in a solvent is used to coat the composite particle main body, and the solvent is removed by heat treatment or the like. As a kind of polymer coating, a method in which a polymer solution is used for coating, a method in which a polymer precursor including a monomer is used for coating and polymerization is performed by the action of temperature, light, or the like, or a combination thereof can be given.

[0183] The surface coating of the composite particle can be analyzed by performing surface analysis of the composite particle. As the surface analysis, SEM-EDS, Auger electron spectroscopy, XPS, micro infrared spectroscopy, micro Raman method, or the like can be given.

[0184] In order to avoid the reaction of silicon contained in the composite particle with carbon to form silicon carbide, it is preferable to raise the temperature at the time of coating to less than 500°C, or to use a method in which the time for applying energy to the composite particle body using PVD or ALD or the like is instantaneous and does not cause the temperature of the composite particle body to rise for a long time.

[0185] As the composite particle having a surface coating, a polymer-coated composite particle is preferable. That is, the polymer-coated composite particle has, on at least a portion of the surface of the composite particle body, a surface coating of an inorganic particle-containing polymer component coating layer containing inorganic particles composed of one or more selected from graphite and carbon black and a polymer component, and the content of the polymer component is 0.1 to 10.0 mass%.

[0186] The production of the polymer-coated composite particle is preferably performed by a wet method. Specifically, it is a method in which inorganic particles composed of one or more selected from graphite and carbon black, a polymer component, and a composite particle body are mixed in a solvent and dried to remove the solvent.

[0187] At this time, it is also possible to mix after preparing a liquid in which each component is dissolved or dispersed in advance. The inorganic particles are preferably smaller than the composite particle body, and therefore it is preferable to use a liquid in which the inorganic particles are dispersed in advance. In the preparation of the liquid in which the inorganic particles are dispersed, if a shearing force is applied using a ball mill, a bead mill, or the like, the fine particles can be uniformly dispersed, and therefore this is more preferable. In the dispersion of the inorganic particles, a dispersing aid can also be appropriately added. The dispersing aid can be freely selected from publicly known dispersing aids.

[0188] The type of the polymer component is not particularly limited. For example, at least one selected from polysaccharides, cellulose derivatives, animal water-soluble polymers, derivatives of lignin, and water-soluble synthetic polymers, monosaccharides, disaccharides, oligosaccharides, amino acids, gallic acid, tannin, saccharin, salts of saccharin, and sugar alcohols such as butyne diol and sorbitol, glycerol, 1,3-butanediol, dipropylene glycol, and polyhydric alcohols can be mentioned.

[0189] The solvent is not particularly limited as long as it is a solvent capable of dissolving and dispersing the above-described materials, but water is preferable. A plurality of solvents can also be mixed. The temperature at the time of mixing is preferably 50°C to 200°C.

[0190] The temperature at the time of drying is not particularly limited as long as the polymer component does not decompose and distill off, and for example, it can be selected from 50°C to 200°C. Drying under an inert atmosphere or under vacuum can also be performed.

[0191] As needed, the obtained polymer-coated composite particle can also be subjected to a crushing step, a sieving step, and the like to remove coarse agglomerated particles.

[0192] The content of the polymer component can be confirmed, for example, by heating the polymer-coated composite particles after sufficient drying to a temperature at which the polymer component decomposes but which is lower than the temperature at which silicon, carbon oxide, etc. decomposes (for example, 300°C), and measuring the mass of the composite after decomposition of the polymer component. Specifically, in a case where the mass of the polymer-coated composite particles before heating is set as Ag, and the mass of the composite particles after heating is set as Bg, (A-B) is the content of the polymer component. The content can be calculated by {(A-B) / A} x 100.

[0193] The above measurement can be performed using thermogravimetry (TG). The measurement can be performed with high accuracy when the amount of the sample used is small, and thus is preferred.

[0194] The composite particles according to the present application are difficult to be oxidized in the coating treatment in water, that is, when a surface coating layer is formed using water by a wet method. The surface of the composite particle body can be uniformly coated.

[0195] As the effects of the surface coating layer, for example, (i) suppression of the chronological oxidation of silicon inside the composite particle, (ii) improvement of initial coulombic efficiency, and (iii) improvement of cycle characteristics can be cited.

[0196] (i) Suppression of the chronological oxidation of silicon inside the composite particle means suppression of the oxidation of silicon over time when the composite particle is exposed to an air or oxygen-containing gas atmosphere. By the presence of the surface coating layer on the surface of the composite particle, the invasion of air or oxygen-containing gas into the inside of the composite particle can be more suppressed.

[0197] (ii) Improvement of initial coulombic efficiency means reduction of the amount of lithium ions captured by the composite particle at the time of the first insertion of lithium ions into the composite particle inside a lithium ion battery. After the insertion of lithium ions into the inside of the composite particle, if an electrolyte decomposition product film (SEI <Solid Electrolyte Interface> film) is formed on the surface of the composite particle or at the lithium ion invasion site of the composite particle, the proportion of lithium ions that cannot escape from the occluded pores in the composite particle increases, and the initial coulombic efficiency decreases. At the time of the second or subsequent insertion of lithium ions, the proportion of lithium ions captured by the composite particle greatly decreases due to the presence of the SEI film. Thus, the problem is the capture of lithium ions at the time of the first insertion of lithium ions, and therefore, if a surface coating layer is present on the surface of the composite particle, the insertion of lithium ions into the pores that are easily occluded by the SEI film can be prevented, and the initial coulombic efficiency can be improved.

[0198] (iii) Improvement in cycle characteristics means suppression of capacity decrease when the composite particle is applied to a lithium ion battery and repeatedly charged and discharged. In a lithium ion battery, if charging and discharging are repeatedly performed, silicon in the composite particle reacts with fluorine, which is a component element of an electrolyte, and is eluted as a silicon fluoride compound. If silicon is eluted, the specific capacity of the composite particle decreases. If a surface coating layer is present on the surface of the composite particle, elution of silicon is suppressed, and capacity decrease of the composite particle is suppressed. In addition, by the surface coating layer, the resistance is reduced, the coulombic efficiency is improved, and the cycle characteristics are improved.

[0199] [4] Negative electrode active material

[0200] The negative electrode active material according to an embodiment of the present application contains the composite particle according to the present application. Two or more kinds of the composite particle according to the present application can be mixed and used. The negative electrode active material can further contain other components. As the other components, components generally used as a negative electrode active material of a lithium ion secondary battery can be given. For example, graphite, hard carbon, soft carbon, lithium titanate (Li4Ti5O 12 ), silicon, alloy-based active materials such as tin, and composites thereof can be given. As these components, components in a particulate form are generally used. As the components other than the composite particle, one kind or two or more kinds can be used. Among them, graphite particles and hard carbon are particularly preferable.

[0201] In the case where the negative electrode active material is formed by containing other components, the composite particle is adjusted to be 1 to 50% by mass in the negative electrode active material. It is preferable to be adjusted to be 2 to 25% by mass. By mixing and using the other components, a negative electrode active material having excellent characteristics of other carbon materials in addition to excellent characteristics of the composite particle can be formed. In the case where a plurality of materials is used as the negative electrode active material, the materials can be used after being mixed in advance, or can be sequentially added when a slurry for forming a negative electrode mixture to be described later is prepared.

[0202] As a device for mixing the composite particle and other materials, a commercially available mixer or a blender can be used. As specific examples, a mortar, a ribbon blender, a V-type mixer, a W-type mixer, a single-blade mixer, a Nauta mixer, and the like can be given.

[0203] [5] Negative electrode mixture layer

[0204] The negative electrode mixture layer according to an embodiment of the present application contains the negative electrode active material described in the [4].

[0205] The negative electrode mixture layer of the present application can be used as a negative electrode mixture layer for a lithium ion secondary battery. The negative electrode mixture layer is generally composed of a negative electrode active material, a binder, and a conductive aid as an optional component.

[0206] The manufacturing method of the negative electrode mixture layer can use, for example, a publicly known method shown below. A slurry for forming a negative electrode mixture is prepared using a negative electrode active material, a binder, a conductive aid as an optional component, and a solvent. The slurry is applied to a current collector such as a copper foil and dried. It is further vacuum-dried to remove the solvent. The resulting structure is sometimes referred to as a negative electrode sheet. The negative electrode sheet is composed of a negative electrode mixture layer and a current collector. For the negative electrode sheet, after being cut or punched into a desired shape and size, pressing is performed to increase the density of the electrode mixture layer (sometimes referred to as electrode density). If the electrode density is increased, the energy density of the battery is increased. The pressing method is not particularly limited as long as it can process into a desired electrode density, but one-axial pressing, roll pressing, and the like can be given. In the examples described later, a process in which pressing is performed after shape processing is exemplified, but shape processing can be performed after pressing. In the present application, the structure that has become a desired shape and electrode density is referred to as a negative electrode. In the negative electrode, a negative electrode in which a current collecting tab is mounted on the current collector is also included as needed.

[0207] As the binder, any binder generally used in the negative electrode mixture layer of a lithium ion secondary battery can be freely selected and used. For example, polyethylene, polypropylene, ethylene-propylene-diene rubber, butadiene rubber, styrene-butadiene rubber (SBR), butyl rubber, acrylate rubber, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), polyethylene oxide, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, carboxymethyl cellulose (CMC) and its salt, polyacrylic acid, polyacrylamide, and the like can be given. The binder can be used singly or in two or more kinds. The amount of the binder is preferably 0.5 to 30 parts by mass relative to 100 parts by mass of the negative electrode material.

[0208] The conductive aid is not particularly limited as long as it functions to impart electronic conductivity and dimensional stability (function to absorb volume change accompanying insertion and extraction of lithium) to the electrode. For example, carbon nanotube, carbon nanofiber, vapor-phase method carbon fiber (for example, "VGCF (registered trademark)-H" manufactured by Showa Denko K.K.), conductive carbon black (for example, "DENKA BLACK (registered trademark)" manufactured by Denki Kagaku K.K., "SUPER C65" manufactured by Imerys Graphite & Carbon, "SUPER C45" manufactured by Imerys Graphite & Carbon, conductive graphite (for example, "KS6L" manufactured by Imerys Graphite & Carbon, "SFG6L" manufactured by Imerys Graphite & Carbon), and the like can be given. They can be used in multiple kinds.

[0209] As the conductive aid, carbon nanotube, carbon nanofiber, or vapor-phase method carbon fiber is preferably contained, and the fiber length of these conductive aids is preferably D V50more than 1 / 2 of the length. If the length is this, the conductive aid is crosslinked between the negative active material including the composite particles, and the cycle characteristics can be improved. Also, the single-walled or multi-walled conductive aid having a fiber diameter of 15 nm or less is more preferable than other conductive aids in that the number of crosslinking increases at the same addition amount. Further, it is more preferable from the viewpoint of improving the electrode density because it is softer.

[0210] The amount of the conductive aid is preferably 1 to 30 parts by mass with respect to 100 parts by mass of the negative material.

[0211] As the solvent at the time of preparing the slurry for electrode coating, there is no particular limitation, and N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), isopropyl alcohol, tetrahydrofuran (THF), water, and the like can be cited. In the case of using water as the solvent for the binder, it is also preferable to use a viscosity increasing agent in combination. The amount of the solvent can be adjusted in such a manner that the slurry becomes a viscosity that is easy to coat on the current collector.

[0212] [6] Lithium ion secondary battery

[0213] The lithium ion secondary battery according to the present application contains the negative electrode binder layer. The lithium ion secondary battery generally contains a negative electrode composed of the negative electrode binder layer and a current collector, a positive electrode composed of a positive electrode binder layer and a current collector, at least one of a nonaqueous electrolyte and a nonaqueous polymer electrolyte present therebetween, a separator, and a battery case in which they are accommodated. The lithium ion secondary battery contains the negative electrode binder layer, and as a structure other than this, a structure known in the past can be adopted without particular limitation.

[0214] The positive electrode binder layer is generally composed of a positive material, a conductive aid, and a binder. The positive electrode in the lithium ion secondary battery can use a general structure in a general lithium ion secondary battery.

[0215] As the positive active material, there is no particular limitation as long as it is a material in which electrochemical insertion and extraction of lithium can be performed reversibly and the standard oxidation-reduction potential of these reactions is sufficiently high compared to the negative electrode reaction. For example, LiCoO2, LiNiO2, LiMn2O4, LiCo 1 / 3 Mn 1 / 3 Ni 1 / 3 O2, LiCo 0.6 Mn 0.2 Ni 0.2 O2, LiCo 0.8 Mn 0.1 Ni 0.1 O2, LiFePO4 coated with carbon, or a mixture thereof can be suitably used.

[0216] As the conductive aid, the binder, the solvent for slurry preparation, the materials mentioned in the item of the negative electrode are used. As the current collector, an aluminum foil is suitably used.

[0217] The non-aqueous electrolyte and the non-aqueous polymer electrolyte used in the lithium ion battery can use the materials known as the electrolyte of the lithium ion secondary battery. For example, a material obtained by dissolving LiClO4, LiPF6, LiAsF6, LiBF4, LiSO3CF3, CH3SO3Li or the like lithium salt in a solvent, a polymer. As the solvent, non-aqueous solvents such as ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, propylene carbonate, butylene carbonate, acetonitrile, propionitrile, dimethoxyethane, tetrahydrofuran, γ-butyrolactone, and the like; gelled polymers containing polyethylene oxide, polyacrylonitrile, polyvinylidene fluoride, polymethyl methacrylate, and the like; polymers having an ethylene oxide bond, and the like can be mentioned.

[0218] In addition, in the non-aqueous electrolyte, an additive generally used in the electrolyte of the lithium ion battery can also be added in a small amount. As this substance, for example, vinylene carbonate (VC), diphenyl, propane sulfone lactone (PS), fluoroethylene carbonate (FEC), ethylene sulfone lactone (ES), and the like can be mentioned. VC and FEC are preferably selected. As the addition amount, 0.01 to 20 mass% with respect to 100 mass% of the non-aqueous electrolyte is preferable.

[0219] As the separator, it can be freely selected from the separators used in general lithium ion secondary batteries, including combinations thereof, and polyethylene or polypropylene microporous membranes, and the like can be mentioned. In addition, a separator in which SiO2, Al2O3, or the like particles are mixed as a filler into such a separator to adhere to the surface can also be used.

[0220] As the battery case, there is no particular limitation as long as it can accommodate the positive electrode and the negative electrode and the separator and the electrolyte. In addition to the cases standardized in the industry such as battery packs, 18650 type cylindrical batteries, coin type batteries, and the like, which are commonly sold on the market, there are cases such as those packaged with an aluminum package material, and the like, and the use can be freely designed.

[0221] Each electrode can be used after being packaged after being stacked. In addition, single cells can be connected in series to be used as a storage battery, a module.

[0222] Examples

[0223] Hereinafter, examples and comparative examples will be mentioned to specifically explain the present application, but the present application is not limited to these examples.

[0224] Measurement of physical property values and battery evaluation were performed as follows.

[0225] [1] Measurement of physical property values

[0226] [1-1] X-ray Photoelectron Spectroscopy (XPS)

[0227] Using a small spatula, the sample was placed on the adhering surface of the double-sided tape attached to the Si substrate, and the double-sided tape of the base was uniformly spread in such a manner that the measuring surface was somewhat flat. The sample was spread over a range larger than the measuring range (about 100 pm in diameter). This was to ensure that only the composite particles were spread within the measuring range. With respect to this sample, the measurement was performed using the following method.

[0228] [Measurement device]

[0229] Device: PHI Quantera II (manufactured by ULVAC-PHI, Inc.)

[0230] X-ray source: Al monochromatic (25 W, 15 kV)

[0231] Analysis range: 100 pm in diameter

[0232] Electron, ion neutralization gun: ON

[0233] Photoelectron detection angle: 45 degrees

[0234] Narrow scan

[0235] Pass energy: 55 eV Step: 0.2 eV dwell time: 20 ms

[0236] Scan time: 0 (25) C, Si (50)

[0237] [Analysis method]

[0238] [Energy correction]

[0239] With respect to the narrow spectrum, the peak of the 1s of carbon was corrected to be 284.6 eV.

[0240] [C, O, Si atomic number ratio A C , A O , A Si ]

[0241] The area ratio of the narrow spectrum of C, O, and Si was calculated as the atomic number ratio. The total atomic number ratio A C , A O , A Si of C, O, and Si was 1.00.

[0242] [Si species ratio B SiO2 , B SiO , B Si ]

[0243] Regarding the Si 2p narrow spectrum, the state ratio B of Si species was calculated using the following method for peak fitting SiO2 , B SiO , B Si .

[0244] (chemical shift) Si 0 valence = 99 eV, Si 2 valence = 101 eV, Si 4 valence = 103 eV

[0245] (peak fitting method) The half-peak width and peak top were automatically adjusted by an analysis software in such a manner that the residual of the peak fitting result from the measurement result becomes minimum. In addition, the adjustment of the peak top was performed in the range of ±0.5 eV with respect to the width 3 components. The analysis software used was the software attached to the above-mentioned measurement device.

[0246] • Background subtraction method: Shirley method

[0247] • Function: Gauss-Lorentz

[0248] Si 0 valence means so-called elemental Si. Si 2 valence means SiO. Si 4 valence means SiO2. With respect to Si 1 valence and Si 3 valence, since the intensity is small, the accuracy of the peak fitting becomes low, and thus they are excluded. In Si 2 valence, silicon carbide is also generally contained, but if the peak shape of the C 1s narrow spectrum is observed, the disturbance (shoulder, tailing, etc.) of the peak shape participating in the chemical shift of 282.5-283.0 eV from silicon carbide is not observed, and thus it is considered that the amount of silicon carbide is below the detection limit. Thus, it is considered that the peak of Si 2 valence means only SiO.

[0249] [1-2] Hydrophobicity

[0250] Pure water at the same temperature as room temperature was poured into a 20 mL glass sample bottle (stem diameter x height: φ 28 mm x 61 mm) to a depth of about 1 cm. Here, 0.05 g of the composite particles was measured on a medicine wrapping paper, and the composite particles were slowly poured into the sample bottle. At this time, the pouring height of the composite particles was within 0.5-3.0 cm from the water surface. After pouring, the sample bottle was left as it was, and the penetration behavior of the water into the composite particles was observed. It was confirmed by visual observation that when the composite particles did not reach the bottom of the sample bottle even after standing for 5 minutes, it was considered to be hydrophobic. A sample that sinks in water within 5 minutes under the same conditions was considered to be hydrophilic.

[0251] [1-3] True density measurement

[0252] After the sample was vacuum-dried at 180°C for 12 hours, the sample was filled in a glove box under a dry argon atmosphere so as to be 4 to 6 of the measurement cell, and the weight of the sample was measured after the cell was vibrated for 100 times or more. Thereafter, the sample was taken out to the atmosphere, and a dry density measurement by a constant-volume expansion method using helium was performed by the following method, and the true density was calculated.

[0253] Apparatus: AccuPyc (registered trademark) II 1340 gas pycnometer measurement cell: aluminum, depth 39.3 mm, inner diameter 18 mm

[0254] Carrier gas: helium

[0255] Gas pressure: 19.5 psiG (134.4 kPaG)

[0256] Number of purges at the time of measurement: 200 times

[0257] Temperature: 25°C ± 1°C

[0258] [1-4] Raman Si peak, I Si / I G , Raman R value (I D / I G )

[0259] The measurement was performed under the following conditions.

[0260] Micro-Raman spectrometer: LabRAM (registered trademark) HR Evolution, HORIBA Ltd.

[0261] Excitation wavelength: 532 nm

[0262] Exposure time: 10 seconds

[0263] Number of accumulations: 2 times

[0264] Diffraction grating: 300 lines / mm (600 nm)

[0265] Measurement sample: The composite particles were placed on a glass specimen using a small spatula so as to be uniform. The size was made larger than the measurement range described below.

[0266] Measurement range: 80 pm vertically x 100 pm horizontally. Only the composite particles were spread within the measurement range.

[0267] Number of points: 100-point measurement was performed with 17.8 pm of vertical feed and 22.2 pm of horizontal feed,

[0268] The spectrum obtained by averaging them was obtained, and the following analysis was performed.

[0269] The Si peak in the Raman spectrum in the range of 450 to 495 cm -1 was observed.

[0270] The intensity of this Si peak was set as I si , and the ratio of the intensity of the peak near 1580 cm -1 (I G ) was set as (I Si / I G ).

[0271] The ratio of the intensity of the peak near 1350 cm -1 (I D ) to (I G ) was set as the R value (I D / I G ).

[0272] In addition, the height from the baseline to the peak top after the baseline was corrected was set as the intensity of the peak.

[0273] [1-5] Powder X-ray Diffraction Measurement (Powder XRD)

[0274] The sample was filled into a glass sample plate (window portion length x width: 18 mm x 20 mm, depth: 0.2 mm), and measurement was performed using the following method.

[0275] XRD device: SmartLab (registered trademark) manufactured by Rigaku Corporation

[0276] X-ray source: Cu-Kα ray

[0277] Kβ ray removal method: Ni filter

[0278] X-ray output: 45 kV, 200 mA

[0279] Measurement range: 10.0 to 80.0°

[0280] Scanning speed: 10.0° / minute

[0281] After background removal, Kα2 component removal, and smoothing were performed on the obtained XRD pattern using analysis software (PDXL2, manufactured by Rigaku Corporation), peak type fitting was performed, and the peak position, intensity, and half-peak width were calculated.

[0282] In addition, the Si (111) plane is a diffraction peak near 2θ = 28°, and the SiC (111) plane is a diffraction peak near 2θ = 35°.

[0283] [1-6] Particle Size Distribution Measurement

[0284] A sample of 1 cup amount of a small spatula and 2 drops of a liquid after diluting a stock solution of 32 mass% of a nonionic surfactant (SARAYA Co., Ltd. Yashino-mi detergent Hyper Power) to 100 times were added to 15 mL of water, and ultrasonic dispersion was performed for 3 minutes. With respect to the dispersion liquid, measurement was performed using the following method.

[0285] Apparatus: Laser diffraction type particle size distribution measuring device (LMS-2000e) manufactured by Seishin Enterprise Co., Ltd.

[0286] Analysis: The volume-based cumulative particle size distribution was calculated, and the 50% particle diameter D V50 (μm), the 90% particle diameter D V90 (μm) was found.

[0287] [1-7] Silicon content rate

[0288] Measurement of the silicon content rate of the sample was performed under the following conditions.

[0289] Fluorescent X-ray device: NEX CG manufactured by Rigaku Corporation

[0290] Tube voltage: 50 kV

[0291] Tube current: 1.00 mA

[0292] Sample cup: φ32 12 mL CH1530

[0293] Sample weight: 2 to 3 g

[0294] Sample height: 5 to 18 mm

[0295] The sample cup was filled with the sample, measurement was performed using the above method, and the silicon content rate in the composite particles was calculated in mass% units using the fundamental parameter method (FP method).

[0296] [1-8] Oxygen content rate

[0297] The oxygen content rate in the composite particles was calculated in mass% units using an oxygen-nitrogen analysis device EMGA (registered trademark) -920 manufactured by Horiba Seisakusho Co., Ltd. using 20 mg of the sample weighed in a nickel capsule. Argon was used as the carrier gas. By dividing the oxygen content rate in the composite particles by the silicon content rate, the oxygen content rate when the silicon content rate in the composite particles is 100 mass% was obtained in mass% units.

[0298] Measurement of the oxygen content rate was performed within 2 days after the manufacture of the composite particles.

[0299] [1-9] Scanning Electron Microscope (SEM), Energy Dispersive x-ray Spectroscopy (EDS)

[0300] The sample was mounted on a carbon tape, and observation was performed as it was in the case of particle observation. In the case of cross-sectional observation, the sample was observed after cross-sectioning using a Cross Section Polisher (registered trademark) manufactured by JEOL Ltd. Observation and measurement were performed using the following methods.

[0301] SEM: Scanning Electron Microscope Device: Regulus (registered trademark) 8220 (manufactured by Hitachi High-Tech Corporation)

[0302] EDS: XFlash (registered trademark) 5060 Flat QUAD (manufactured by Bruker Corporation)

[0303] Accelerating voltage: 1 to 20 kV

[0304] Magnification: 500 to 5000 times (appropriately selected in accordance with the size of the particles)

[0305] [1-10] BET Specific Surface Area and Pore Volume (Nitrogen Adsorption Test)

[0306] As the measuring device, a NOVA (registered trademark) 4200e manufactured by Quantachrome Corporation was used, and the sample was placed in a sample cell (9 mm x 135 mm) in such a manner that the total surface area of the sample became 2 to 60 m 2 . After drying the sample under vacuum at 300°C for 1 hour, the weight of the sample was measured, and the measurement was performed. Nitrogen was used as the gas for measurement.

[0307] The set minimum relative pressure at the time of measurement was 0.005, and the set maximum relative pressure was 0.995. The BET specific surface area of the porous carbon material was calculated using the BET multi-point method based on the adsorption isotherm data of less than 0.08 near the relative pressure of 0.005. The BET specific surface area of the composite particles was calculated using the BET multi-point method based on the adsorption isotherm data of three points near 0.1, near 0.2, and near 0.3. For the total pore volume V 0.99 , the adsorption amount at the relative pressure of 0.99 was calculated by linear approximation from the adsorption isotherm data of two points before and after the relative pressure of 0.99, and thus obtained. For the pore volume V 0.01 at the relative pressure of 0.01, the adsorption amount at the relative pressure of 0.01 was calculated by linear approximation from the adsorption isotherm data of two points before and after the relative pressure of 0.01, and thus obtained.

[0308] At this time, the density of nitrogen liquid was set to 0.808 (g / cm 3 ), the volume of 1 mole of nitrogen in the standard state was set to 22.4133 L, and the atomic weight of nitrogen was set to 14.0067, and the calculation was performed.

[0309] [1-11] Measurement of the polymer component content

[0310] The measurement was performed using the following method.

[0311] TG-DTA device: TG-DTA2000SE manufactured by NETZSCH JAPAN

[0312] Sample weight: 10 to 20 mg

[0313] Sample pan: made of alumina

[0314] Reference pan: made of alumina

[0315] Gas atmosphere: Ar

[0316] Gas flow rate: 100 mL / minute

[0317] Temperature elevation rate: 10°C / minute

[0318] Measurement temperature range: room temperature to 1000°C

[0319] The weight loss achieved by thermal decomposition from 200°C to 350°C was taken as the amount of the polymer component, and the polymer component content was calculated.

[0320] [2] Measurement of oxidation resistance of the composite particles based on the aqueous sample dispersion

[0321] A stirrer and 2 g of pure water were charged into a 20-mL glass sample bottle. 0.05 g of the sample was charged thereto, and covered with a septum made of silicone rubber. The hydrogen gas concentration in the gas phase in the sample bottle was measured while stirring with a magnetic stirrer at room temperature (20 to 26°C).

[0322] Hydrogen is generated by oxidation of silicon in the composite particles with water. Therefore, a high hydrogen gas concentration in the gas phase means that the composite particles are easily oxidized, and a low hydrogen gas concentration means that the composite particles are difficult to oxidize.

[0323] A real-time mass spectrometer was used for the measurement of the hydrogen gas concentration. For the hydrogen gas concentration, sensitivity correction was performed using the nitrogen gas concentration. In addition, the same measurement was performed in a state where the sample was not charged, and the hydrogen gas concentration calculated at this time was corrected to 0 vol%.

[0324] The sampling of the gas inside the sample bottle was performed using a capillary tube that penetrates the partition, using a real-time mass analyzer. In order to maintain the gas pressure inside the sample bottle constant, a syringe needle was inserted into the partition in addition to the capillary tube of the real-time mass analyzer, so as to be able to introduce air into the chamber.

[0325] The comparison of the hydrogen generation concentration was performed using the average hydrogen concentration from 50 minutes to 60 minutes after the start of the measurement. Since most of the air inside the sample bottle is measured immediately after the start of the measurement, the value after the lapse of time from the start of the measurement was used. Furthermore, the sampling flow rate of the real-time mass analyzer was 1 seem. In addition, the sample bottle was disposed so that the capillary tube does not come into contact with the liquid surface, so that the real-time mass analyzer does not suck in the water dispersion of the sample.

[0326] Real-time mass analyzer: OMNISTAR (registered trademark) GSD350 manufactured by PFEIFER VACUUM Co.

[0327] [3] Battery evaluation

[0328] [3-1] Production of negative electrode sheet

[0329] As the binder, styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC) were used.

[0330] Specifically, an SBR water dispersion in which SBR was dispersed at 40 mass% of the solid content and a CMC aqueous solution in which CMC powder was dissolved at 2 mass% were obtained.

[0331] As the mixed conductive aid, a conductive aid obtained by mixing carbon black (SUPER C 45 (registered trademark), manufactured by Imerys Graphite & Carbon Co.) and single-walled carbon nanotube (TUBALL (registered trademark) WPB-030, manufactured by OCSiAl Co.) at a mass ratio of 5: 1 was prepared.

[0332] The composite particles and the graphite particles were mixed so that the silicon concentration in the total amount of the negative electrode active material was 5.9 mass%, and a negative electrode active material was obtained. The negative electrode active material 96.4 parts by mass, the mixed conductive aid 0.6 parts by mass, the CMC aqueous solution of the solid content of CMC 1.5 parts by mass, and the SBR water dispersion of the solid content of SBR 1.5 parts by mass were mixed, water for viscosity adjustment was added thereto as appropriate, kneading was performed using a self-rotation and revolution mixer (manufactured by Sanky Co.), and a slurry for negative electrode active material layer formation was obtained. The slurry concentration was 45 to 55 mass%.

[0333] As the graphite particles, graphite having BET = 2.7 m 2 / g, D V10 = 7 μm, D V50= 14 μm, D V90 = 27 μm, tapped density = 0.98 g / cm 3 = 27 μm, tapped density = 0.98 g / cm

[0334] The negative electrode mixture layer was formed by uniformly applying the slurry for forming the negative electrode mixture layer onto a copper foil having a thickness of 20 μm as a current collector foil using a doctor blade having a gap of 150 μm, drying it using a hot plate, and vacuum drying it at 70°C for 12 hours, thereby forming a negative electrode mixture layer on the current collector foil. This was called a negative electrode sheet (a sheet composed of the negative electrode mixture layer and the current collector foil).

[0335] The negative electrode mixture layer density was adjusted to 1.6 g / cm 3 A negative electrode was obtained.

[0336] The electrode density (negative electrode density) of the negative electrode was calculated as follows. The mass and thickness of the negative electrode obtained by the aforementioned method were measured, and the mass and thickness of the current collector foil punched out in a 16 mmφ were measured separately, and the mass and thickness of the negative electrode mixture layer were calculated from these values, and the electrode density (negative electrode density) was calculated from these values.

[0337] [3-2] Production of a coin cell (lithium counter electrode cell)

[0338] The aforementioned negative electrode and a separator (a polypropylene microporous film) obtained by impregnating an electrolyte into a lithium foil having a thickness of 1.7 mm punched out in a 17.5 mmφ were sandwiched and stacked in a polypropylene insulating gasket (inner diameter of about 18 mm). At this time, the surface of the negative electrode mixture layer of the negative electrode was stacked so as to face the lithium foil with the separator sandwiched therebetween. This was set in a 2320 coin-type battery, sealed using a caulking machine, and formed into a test battery (lithium counter electrode cell).

[0339] The electrolyte used in the lithium counter electrode cell was a liquid obtained by mixing 100 parts by mass of a solvent obtained by mixing ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate at a ratio of 3:5:2, and 1 part by mass of vinylene carbonate (VC), and further dissolving lithium hexafluorophosphate (LiPF6) in the mixture so as to have a concentration of 1 mol / L.

[0340] [3-3] Initial charge capacity, initial discharge capacity

[0341] A lithium-polar battery was tested. Constant current (CC) charging was performed at a current value equivalent to 0.1 C from the open circuit voltage (OCV) to 0.005 V. Constant voltage (CV) charging was switched at the time point at which 0.005 V was reached. The cut-off condition was set to the time point at which the current value attenuated to equivalent to 0.005 C. The specific capacity at this time was set as the initial charge specific capacity. Subsequently, constant current discharge was performed at a current value equivalent to 0.1 C with an upper limit voltage of 1.5 V. The specific capacity at this time was set as the initial discharge specific capacity.

[0342] The test was performed in a constant temperature chamber set to 25°C. At this time, the "specific capacity" is a value obtained by dividing the capacity by the mass of the negative electrode active material. In addition, in the present test, the "current value equivalent to 1 C" refers to the current size capable of completing discharge in 1 hour based on the capacity of the negative electrode estimated from the mass of Si and carbon (including graphite) in the negative electrode active material and the theoretical specific capacity (4200 mAh / g and 372 mAh / g, respectively).

[0343] [3-4] Initial coulombic efficiency

[0344] The value expressed in percentage of the value obtained by dividing the initial discharge specific capacity by the initial charge specific capacity, (initial discharge specific capacity) / (initial charge specific capacity) x 100, was set as the initial coulombic efficiency (%).

[0345] [3-5] Silicon utilization rate

[0346] The specific capacity of silicon in the composite particles was calculated from the initial discharge specific capacity and the composition of the negative electrode active material, and the value expressed in percentage of the value obtained by dividing this value by the theoretical specific capacity of silicon (4200 mAh / g) was set as the silicon utilization rate (%). It is considered that the closer this value is to 100%, the more effectively the silicon capacity in the composite particles can be used.

[0347] The specific capacity of silicon in the composite particles was calculated from the silicon concentration (i.e., the proportion of silicon (mass %)) and the carbon concentration (i.e., the proportion of carbon (mass %)) in the negative electrode active material (the proportion of carbon (mass %) in graphite and the composite particles), the theoretical specific capacity of carbon (372 mAh / g), and the initial discharge specific capacity using the following formula.

[0348] Specific capacity of silicon in composite particles = (initial discharge specific capacity - (carbon concentration / 100) x theoretical specific capacity of carbon) / (silicon concentration / 100)

[0349] In addition, the carbon concentration and the silicon concentration in the above formula were calculated from the negative electrode active material composition and the composition of the composite particles. Furthermore, the carbon content rate in the carbon material in the composite particles was set to 100 mass %.

[0350] [Examples 1, 2, 4, 5, 7 to 11]

[0351] The porous carbon having the properties described in Table 1 was charged inside the tubular furnace, the inside of the tubular furnace was replaced with argon, and then a silicon-containing gas was introduced into the inside of the tubular furnace according to the conditions of Step (A) described in Table 1, and a reaction was performed.

[0352] Next, after the inside of the tubular furnace was replaced with argon and depressurized, the gases (hydrocarbon gas and dilution gas) described in Table 1 used in Step (B) were introduced at 300 seem to form an atmosphere of 760 torr. Thereafter, a reaction was performed according to the conditions of Step (B) described in Table 1.

[0353] Next, after the inside of the tubular furnace was replaced with argon, a gas was introduced (Steps C-1 and C-3) or filled (Step C-4) into the inside of the tubular furnace according to the conditions of Step (C) described in Table 1, and a reaction was performed, and composite particles were obtained. Step (C) was performed in the order of Step C-1, Step C-2, Step C-3, and Step C-4. As for the step not performed, "-" was written in Table 1. The structure and property values of the obtained composite particles are shown in Table 2. The evaluation results are shown in Table 3.

[0354] [Example 3]

[0355] The porous carbon having the properties described in Table 1 was charged inside the tubular furnace, the inside of the tubular furnace was replaced with argon, and then a silicon-containing gas was introduced into the inside of the tubular furnace according to the conditions of Step (A) described in Table 1, and a reaction was performed.

[0356] Next, after the inside of the tubular furnace was replaced with argon, a gas was introduced into the inside of the tubular furnace according to the conditions of Step (B) described in Table 1, and a reaction was performed.

[0357] Next, after the inside of the tubular furnace was replaced with argon, a gas was introduced (Steps C-1 and C-3) or filled (Step C-4) into the inside of the tubular furnace according to the conditions of Step (C) described in Table 1, and a reaction was performed, and composite particles were obtained. Step (C) was performed in the order of Step C-1, Step C-2, Step C-3, and Step C-4. As for the step not performed, "-" was written in Table 1. The structure and property values of the obtained composite particles are shown in Table 2. The evaluation results are shown in Table 3.

[0358] [Example 6]

[0359] [Manufacture of Inorganic Particle Dispersion Liquid]

[0360] As the inorganic particles, an inorganic particle dispersion liquid was prepared in which inorganic particles having an average particle diameter D V50Flaky graphite (KS-6, manufactured by Timcal) having a particle size of 3 μm and acetylene black (HS100, manufactured by Denki Kagaku K.K.) were used. 156 g of the flaky graphite, 40 g of the acetylene black, and 4 g of carboxymethyl cellulose were put into 800 g of water, and dispersed and mixed by using a bead mill to obtain an inorganic particle dispersion liquid (solid content 20 mass%).

[0361] [Manufacture of polymer-coated composite particle]

[0362] The composite particle obtained in Example 1 (7 g), water (1.98 g), a 2.5 mass% aqueous solution of tamarind gum (3.84 g), a 2.5 mass% aqueous solution of sorbitol (0.43 g), and the inorganic particle dispersion liquid (1.60 g) were prepared.

[0363] The water and the aforementioned aqueous solution of tamarind gum were put into a polyethylene-made capped bottle having a capacity of 105 mL, and mixed by using a revolution-rotation mixer (manufactured by Shinki Co., Ltd.) at 1000 rpm for 2 minutes. The composite particle was added, and mixed at 1000 rpm for 2 minutes. The aforementioned inorganic particle dispersion liquid was added, and mixed at 1000 rpm for 2 minutes. The aforementioned aqueous solution of sorbitol was added, and mixed at 1000 rpm for 2 minutes. The obtained slurry was spread on a SUS-made tray, and dried by using a hot air drier at 150°C for 5 hours. The dried solid content was recovered, and the agglomerated particles were crushed by using an agate mortar. The obtained composite particle was subjected to SEM observation, and it was confirmed that the flaky graphite and the acetylene black were present on the surface of the core particle, and the flaky graphite was in a protruding configuration. The content of the polymer component was 1.5 mass%.

[0364] The evaluation results of the polymer-coated composite particle are shown in Table 3. It was found that the hydrogen concentration in the gas phase in the sample aqueous dispersion container was lower than that in Example 1, and the oxidation resistance was improved as compared with the composite particle of Example 1. The oxygen content of the composite particle was slightly increased by the polymer coating, and thus the initial coulombic efficiency was slightly decreased, but the effect of improving the oxidation resistance was present.

[0365] [Comparative Examples 1 and 4]

[0366] The porous carbon having the properties described in Table 1 was charged into a tubular furnace, and after the inside of the tubular furnace was replaced with argon, a silicon-containing gas was introduced into the tubular furnace under the conditions of Process (A) described in Table 1, and a reaction was performed.

[0367] Next, after the inside of the tubular furnace was replaced with argon, the gas (hydrocarbon gas and diluent gas) was introduced into the tubular furnace according to the conditions of Step (B) described in Table 1, and the reaction was performed.

[0368] [Comparative Example 2]

[0369] The porous carbon having the properties described in Table 1 was charged into the inside of the tubular furnace, and after the inside of the tubular furnace was replaced with argon, the silicon-containing gas was introduced into the tubular furnace according to the conditions of Step (A) described in Table 1, and the reaction was performed.

[0370] Next, after the inside of the tubular furnace was replaced with argon, the gas (hydrocarbon gas and diluent gas) was introduced into the tubular furnace according to the conditions of Step (B) described in Table 1, and the reaction was performed.

[0371] Next, after the inside of the tubular furnace was replaced with argon, the gas (hydrocarbon gas and diluent gas) was introduced into the tubular furnace according to the conditions of Step (B) described in Table 1, and the reaction was performed.

[0372] [Comparative Example 3]

[0373] The porous carbon having the properties described in Table 1 was charged into the inside of the tubular furnace, and after the inside of the tubular furnace was replaced with argon, the silicon-containing gas was introduced into the tubular furnace according to the conditions of Step (A) described in Table 1, and the reaction was performed.

[0374] Next, after the inside of the tubular furnace was replaced with argon, the gas (hydrocarbon gas and diluent gas) was introduced into the tubular furnace according to the conditions of Step (B) described in Table 1, and the reaction was performed.

[0375] Next, the product was cooled to room temperature, and the composite particles were obtained. The structure and property values of the composite particles are shown in Table 2. The surface carbon coating was confirmed by cross-sectional SEM observation, and the average thickness thereof was 21 nm. The evaluation results are shown in Table 3.

[0376] [Table 1-1]

[0377]

[0378] [Table 1-2]

[0379]

[0380] [Table 1-3]

[0381]

[0382] [Table 2-1]

[0383]

[0384] [Table 2-2]

[0385]

[0386] [Table 2-3]

[0387]

[0388] [Table 3]

[0389]

[0390] Here, the average hydrogen concentration when each sample was immersed in water was measured, and the battery characteristics of the composite particles not immersed in water and the polymer-coated composite particles were evaluated.

[0391] Further, as described at the beginning of the "Problem to be Solved by the Invention", it is obvious that in the Si / C particles oxidized, the irreversible capacity becomes large and the initial coulombic efficiency becomes low, and therefore, experiments for re-exhibiting this were not performed.

[0392] In the composite particles of Examples 1 to 5 and 7 to 11 and the polymer-coated composite particles of Example 6, the hydrogen concentration in the gas phase in the sample water dispersion container was low and the oxidation resistance was high compared to the products of Comparative Examples 1, 2 and 4.

[0393] Example 5 includes a heat treatment step (step C-2) in step (C). Thus, the hydrogen concentration in the gas phase in the sample water dispersion container is lower in Example 5 than in Example 4 which does not include step C-2. C C + A Si x (B SiO2 + B SiO ) is smaller in Example 5 than in Example 4, and therefore it is considered that the oxygen content in the coating is more in Example 5. In Comparative Examples 1, 2 and 4, the hydrogen concentration is high and the oxidation resistance is low. This is because the coating is not present or is insufficient.

[0394] ​The composite particles and the polymer-coated composite particles in the examples are capable of suppressing oxidation at the time of water dispersion, and thus are considered to also have resistance to oxidation during storage in air.

[0395] In addition, with respect to battery characteristics, the composite particles of Examples 1 to 5 and 7 to 11 and the polymer-coated composite particles of Example 6 have a high silicon utilization rate compared to the products in Comparative Examples 2 and 3, and are capable of effectively using the silicon in the composite particles. In Comparative Examples 2 and 3, the reaction temperature in Step (B) is high, and silicon carbide is generated, and thus it is considered that the silicon utilization rate is low due to a decrease in the silicon capable of charge and discharge.

[0396] Industrial applicability

[0397] The composite particles of the present application are suitably used, for example, as a negative electrode active material constituting a negative electrode mixture layer of a lithium ion secondary battery or the like. The lithium ion secondary battery of the present application can be suitably used for IT devices such as smartphones and tablet PCs, vacuum cleaners, power tools, electric bicycles, drones, automobiles, and the like, which require high capacity and high output.

Claims

1. A composite particle having: a particle comprising a carbon material and silicon, the carbon material being a porous carbon, the silicon being contained in at least a part of pores of the porous carbon, and a coating layer comprising carbon and oxygen on a surface of the particle, The true density determined by using helium gas for measuring dry density was 1.80 g / cm 3 The above and 1.99 g / cm 3 The following, in a Raman spectrum of the composite particle, Peaks present at 450-495 cm -1 , If the intensity of the peak is set as I Si , and the intensity of the G band, i.e. the peak near 1580 cm -1 -1, is set as I G , then I Si / I G is 1.3 or less. If the Si, O, and C narrow-spectrum-based atomic ratios of the composite particle by X-ray photoelectron spectroscopy are set to A Si , A O , and A C , respectively, and the ratio of SiO2 and SiO in the Si species ratio obtained from Si2p energy spectrum state analysis is set to B SiO2 , B SiO , A Si is 0.05 or more, the composite particle satisfying at least one of the following equations (1) and (2): Y≥0.75 (1) Y > -0.32X + 0.81 (2) In formula (1) and (2), X = I Si / I G , Y = A C / (A C +A Si ×(B SiO2 +B SiO )) 2. The composite particle according to claim 1, The I Si / I G is 0.64 or less, and satisfies the formula (1).

3. The composite particle according to claim 1, the coating layer being thin to a degree that is substantially undetectable when cross-section observation is performed based on an electron microscope.

4. The composite particle according to claim 1, in an XRD pattern obtained by powder XRD using Cu-Ka rays, a half-value width of a peak of a Si (111) plane is 3.0° or more, a peak intensity of a (SiC (111) plane) / (peak intensity of a Si (111) plane) is 0.01 or less, and an R value of a Raman spectrum is 0.26 or more and less than 1.

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5. The composite particle according to claim 1, being hydrophobic.

6. The composite particle according to claim 1, substantially not containing graphite inside.

7. The composite particle according to claim 1, The 50% particle size D in the volume-based cumulative particle size distribution V50 is 1.0 to 30.0 μm.

8. The composite particle according to claim 1, a silicon content rate being 30 mass% or more and 80 mass% or less, and an oxygen content rate being 4.0 mass% or less.

9. A method for producing a composite particle, comprising: a step (A) of bringing a silicon-containing gas into contact with a porous carbon to deposit silicon into pores and a surface of the porous carbon, to obtain a Si / C particle; a step (B) of bringing a gas containing a hydrocarbon having an unsaturated bond into contact with the Si / C particle at 400°C or lower; and a step (C) of oxidizing a layer containing the hydrocarbon obtained in the step (B).

10. The method for producing a composite particle according to claim 9, the step (A) and the step (B) being continuously performed.

11. The method for producing a composite particle according to claim 9, the composite particle according to claim 1 being produced.

12. A polymer-coated composite particle, having the composite particle according to claim 1 and an inorganic particle-containing polymer component coating layer formed on at least a part of a surface thereof, the inorganic particle-containing polymer component coating layer containing inorganic particles composed of one or more selected from the group consisting of graphite and carbon black and a polymer component, a content rate of the polymer component being 0.1 to 10.0 mass%.

13. A negative electrode active material, containing the composite particle according to claim 1 or the polymer-coated composite particle according to claim 12.

14. A negative electrode mixture layer, containing the negative electrode active material according to claim 13.

15. A lithium ion secondary battery, containing the negative electrode mixture layer according to claim 14.

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