Negative electrode material powder for lithium ion battery

Abstract

To provide negative electrode material powder for a lithium ion battery, which is hard to ignite, is excellent in safety, and also has good water resistance.SOLUTION: There is provided negative electrode material powder for a lithium ion battery which contains a Si-containing granulated body. The Si-containing granulated body contains Si-based powder and a carbon material. The Si-based powder is a primary particle including a Si phase and a SiX compound phase. The SiX compound phase includes Si and an element X. The element X is at least one selected from the group consisting of Fe, Co, Cr, Mn, Ni, Zr, Ti, B and P. The average primary particle diameter of the Si-based powder is 0.1 μm or more, and the average secondary particle diameter of the Si-containing granulated body is 2 μm or more. The surface of the Si-based powder is covered with the carbon material and bonded with the carbon material. The carbon coated parameter A represented by the formula {58.1×average primary particle diameter (μm)+5.6×carbon amount (mass%)} of the Si-based powder is more than 15.SELECTED DRAWING: None

Description

Technical Field

[0001] This invention relates to a negative electrode material powder for lithium-ion batteries.

Background Art

[0002] Lithium-ion batteries have the advantages of high capacity, high voltage, and being miniaturizable, and are widely used as power sources for mobile phones, notebook computers, etc. In recent years, they have also received great expectations as power sources for power applications such as electric vehicles and hybrid vehicles, and their development is actively underway.

[0003] In this lithium-ion battery, lithium ions (hereinafter referred to as Li ions) move between the positive electrode and the negative electrode to perform charging and discharging. On the negative electrode side, Li ions are occluded in the negative electrode active material during charging, and Li ions are released from the negative electrode active material during discharging.

[0004] Among the above, graphite has been widely used as the negative electrode active material, but its theoretical capacity is only 372 mAh / g, and further higher capacity has been desired. Therefore, Si, which exhibits a capacity about 10 times that of graphite, has been proposed as a negative electrode active material for lithium-ion batteries. However, Si has problems in cycle characteristics when charging and discharging are repeated.

[0005] In contrast, Patent Document 1 discloses a negative electrode material for a battery in which a carbon material is formed around a silicon material with a gap therebetween using the thermal chemical vapor deposition (thermal CVD) method. Patent Document 2 discloses a negative electrode material for a lithium secondary battery having carbon on part or all of the surface of silicon oxide particles. Furthermore, Patent Document 3 discloses a carbon material in which the periphery of silicon oxide is surrounded by carbon material particles.

Prior Art Documents

Patent Documents

[0006] [Patent Document 1] Japanese Patent No. 6978947 [Patent Document 2] Japanese Patent No. 6615431 [Patent Document 3] Japanese Patent No. 5516529 [Summary of the Invention] [Problems to be Solved by the Invention]

[0007] In any of the above Patent Documents 1 to 3, in obtaining a desired negative electrode material or carbon material, carbon is coated on the surface of silicon oxide represented by SiOx, which is an active material, in the manufacturing process. However, according to the studies by the present inventors, in any of the above Patent Documents 1 to 3, it has been found that Si-based powders are likely to ignite at a relatively low temperature and are also likely to react with moisture to generate hydrogen (H2).

[0008] Therefore, an object of the present invention is to provide a negative electrode material powder for a lithium-ion battery that is difficult to ignite, has excellent safety, and also has good water resistance. [Means for Solving the Problems]

[0009] As a result of intensive studies by the present inventors on the above problems, the Si-based powder itself, which is primary particles containing an Si phase and an SiX compound phase, is coated with a carbon material, and the average primary particle diameter and the degree of coating are adjusted to satisfy specific parameters, thereby realizing good safety while being difficult to ignite, and furthermore, it has been found that good water resistance with a small amount of hydrogen generation due to reaction with moisture can be realized, and thus the present invention has been completed. As a result of further studies, it has been found that the above parameters are also related to cycle characteristics.

[0010] That is, the gist of the present invention is as follows. [1] A negative electrode material powder containing Si-containing granulated bodies, wherein the Si-containing granulated bodies contain an Si-based powder and a carbon material, The Si-based powder is primary particles containing an Si phase and an SiX compound phase, The SiX compound phase contains Si and element X, The element X is at least one selected from the group consisting of Fe, Co, Cr, Mn, Ni, Zr, Ti, B, and P, The average primary particle diameter of the Si-based powder is 0.1 μm or more, The average secondary particle diameter of the Si-containing granule is 2 μm or more, The surface of the Si-based powder is coated with the carbon material and bonded with the carbon material, The carbon-coated parameter A of the Si-based powder represented by the following formula is more than 15, and the negative electrode material powder for a lithium ion battery. Carbon-coated parameter A = 58.1 × average primary particle diameter (μm) + 5.6 × carbon content (mass%) [2] The content ratio of SiC in the Si-containing granule is less than 15%, and the negative electrode material powder for a lithium ion battery according to [1]. [3] The carbon-coated parameter A is more than 48, and the negative electrode material powder for a lithium ion battery according to [1] or [2]. [4] The average primary particle diameter of the Si-based powder is 5.0 μm or less, and the negative electrode material powder for a lithium ion battery according to any one of [1] to [3]. [5] The average secondary particle diameter of the Si-containing granule is 20 μm or less, and the negative electrode material powder for a lithium ion battery according to any one of [1] to [4]. [6] The aspect ratio of the Si-containing granule is 1.0 to 1.8, and the negative electrode material powder for a lithium ion battery according to any one of [1] to [5]. [7] The Si-based powder is primary particles further containing at least one selected from the group consisting of an SnCu compound phase and an AlCu compound phase, The SnCu compound phase contains Sn and Cu, The AlCu compound phase contains Al and Cu, The content ratio of the Si phase in the Si-based powder is 30% by mass or more, and the negative electrode material powder for a lithium ion battery according to any one of [1] to [6]. [8] The total content ratio of the SnCu compound phase and the AlCu compound phase in the Si-based powder is 0.1 to 15% by mass, and the negative electrode material powder for a lithium ion battery according to [7] above.

Advantages of the Invention

[0011] According to the present invention, it is possible to provide a negative electrode material powder for a lithium ion battery that is difficult to ignite, has excellent safety, and also has good water resistance. Therefore, when the negative electrode material powder is used as a negative electrode active material in a lithium ion battery, the safety of the lithium ion battery itself can be improved. In addition, deterioration of the lithium ion battery due to moisture can be prevented. Furthermore, by optimizing the conditions, the present invention can also improve various battery characteristics such as cycle characteristics.

Embodiments for Carrying Out the Invention

[0012] Hereinafter, embodiments of the present invention will be described. Note that the present invention is not limited to the embodiments described below. Also, "~" indicating a numerical range is used in the sense of including the numerical values described before and after it as a lower limit value and an upper limit value.

[0013] 《Negative Electrode Material Powder for Lithium Ion Battery》 The negative electrode material powder for a lithium ion battery according to this embodiment includes Si-containing granulated bodies. The Si-containing granulated bodies are granulated bodies having an average secondary particle diameter of 2 μm or more, and include Si-based powder and a carbon material. The Si-based powder is primary particles having an average primary particle diameter of 0.1 μm or more, and includes an Si phase and an SiX compound phase. The surface of the Si-based powder is coated with the carbon material, and the degree of the coating can be represented by a specific carbon coating parameter A. Also, the carbon material binds the Si-based powder, which is primary particles, to form Si-containing granulated bodies, which are secondary particles.

[0014] 〈Si-based Powder〉 The Si-based powder contained in the Si-containing granule in the present embodiment is a primary particle, and its surface is coated with a carbon material. The coating with the carbon material can be represented by a carbon coating parameter A expressed by the following formula. Carbon coating parameter A = 58.1 × average primary particle diameter (μm) + 5.6 × carbon content (mass%)

[0015] The above carbon coating parameter A has the average primary particle diameter and the carbon content of the Si-based powder as variables, and 58.1, which is the coefficient of the average primary particle diameter, and 5.6, which is the coefficient of the carbon content, are values derived from experimental results, respectively.

[0016] It has been found that when the value of this carbon coating parameter A exceeds 15, the Si-containing granule is difficult to ignite and good water resistance can be achieved. The reason for this is not clear, but it is considered that when the value of the carbon coating parameter A exceeds 15, the probability of the Si-based powder coming into direct contact with the flame decreases, resulting in difficulty in ignition. Similarly for water resistance, as the probability of the Si-based powder coming into direct contact with water decreases, the generation of hydrogen gas (H2) can be preferably suppressed. Also, for phases other than the Si phase and the SiX compound phase, oxidation due to contact with water is prevented, and unexpected reactions at the negative electrode can be prevented.

[0017] That is, from the above viewpoints, the value of the carbon coating parameter A exceeds 15, preferably 25 or more, and more preferably 35 or more.

[0018] In addition to the above, it has been found that the carbon coating parameter A in the present embodiment is also involved in the cycle characteristics when the negative electrode material powder according to the present embodiment is applied to a lithium-ion battery. Specifically, by setting the value of the carbon coating parameter A to exceed 48, good cycle characteristics can be achieved. It is considered that as the surface of the Si-based powder is coated with the carbon material to a greater extent when the value of the carbon coating parameter A exceeds 48, direct contact between the Si phase and the SiX compound phase and the electrolytic solution can be preferably prevented, and the formation and disintegration of SEI accompanying charge and discharge can be suppressed. From the viewpoint of cycle characteristics, the value of the carbon coating parameter A is preferably more than 48, more preferably 55 or more, and still more preferably 65 or more.

[0019] On the other hand, the upper limit of the value of the carbon coating parameter A is not particularly limited. However, from the viewpoint of manufacturability, adding a large amount of carbon material is not preferable, and the above value is, for example, 200 or less, may be 150 or less, and preferably 120 or less. That is, the value of the carbon coating parameter A is preferably more than 15 and 200 or less, and more preferably more than 48 and 120 or less.

[0020] The amount of carbon used for the carbon coating parameter A in this embodiment is the content ratio (mass%) of carbon with respect to the total of the Si-based powder as primary particles, the amount of carbon, and other optional components. Specifically, the amount of carbon in the Si-based powder in this specification is the carbon concentration (mass%) measured by analyzing the Si-containing granulated body using the combustion infrared absorption method.

[0021] It should be noted that whether the surface of the primary particles themselves, which are Si-based powder, is coated with a carbon material can be confirmed by transmission electron microscope (TEM) observation. Also, in the safety evaluation in the following examples, that is, in the case where the Si-containing granulated body catches fire within 10 seconds by the small gas flame ignition test, it may be determined that the above coating is not performed.

[0022] In the Si-containing granulated body in this embodiment, Si-based powders, which are primary particles whose surfaces are coated with a carbon material, are granulated by being bonded with each other by the carbon material to form secondary particles, thereby achieving various effects such as safety, water resistance, and cycle characteristics. Although the primary particles are bonded to each other by a carbon material, but only a very small part of the surface is adhered with the carbon material and cannot be said to be coated, or only the surface of the secondary particles granulated by bonding the primary particles with each other by a binder or the like is coated with the carbon material, the same effects as above cannot be obtained.

[0023] The carbon content in the above Si-based powder is preferably 1.0 to 30.0% by mass, more preferably 4.0 to 20.0% by mass, and even more preferably 6.0 to 15.0% by mass. Here, from the viewpoint of suppressing the exposure of the Si phase, SiX compound phase, etc. constituting the Si-based powder and covering a wide area, the carbon content is preferably 1.0% by mass or more, more preferably 4.0% by mass or more, and even more preferably 6.0% by mass or more. Further, from the viewpoint of suppressing the decrease in Coulomb efficiency, the carbon content is preferably 30.0% by mass or less, more preferably 20.0% by mass or less, and even more preferably 15.0% by mass or less.

[0024] The average primary particle size of the Si-based powder in this embodiment is 0.1 μm or more, preferably 0.1 to 1.0 μm, more preferably 0.2 to 0.8 μm, and even more preferably 0.3 to 0.7 μm. Here, from the viewpoints of being difficult to ignite, enhancing safety, water resistance, and reducing the amount of binder required as a negative electrode material, the average primary particle size is 0.1 μm or more, preferably 0.2 μm or more, and more preferably 0.3 μm or more. Further, from the viewpoint of reducing the absolute amount of expansion when Li is occluded and realizing good cycle characteristics, the average primary particle size is preferably 1.0 μm or less, more preferably 0.8 μm or less, and even more preferably 0.7 μm or less. Note that the average primary particle size of the Si-based powder in this specification is the median diameter (D50) obtained from the volume-based particle size distribution measured using a laser diffraction / scattering particle size distribution measuring device for the slurry before granulation of the Si-containing granulated body. Alternatively, the average primary particle size of the Si-based powder can also be obtained by image analysis of the SEM photograph of the Si-containing granulated body. Further, the average primary particle size of the Si-based powder can be adjusted by the method and conditions of pulverization, etc.

[0025] The Si phase constituting the Si-based powder in this embodiment occludes and releases Li and plays a role as a negative electrode active material. The Si phase is usually contained in the Si-based powder as Si particles. It is preferable that 95% by mass or more of the Si particles are particles composed of the Si phase. When the Si phase is other than Si particles, it can be contained as SiO2 as the Si phase.

[0026] In the Si-based powder of the present embodiment, the content ratio of the Si phase is preferably 10% by mass or more and less than 100% by mass, and more preferably 30 to 90% by mass. Here, from the viewpoint of obtaining good initial discharge capacity and initial Coulomb efficiency, the above content ratio is preferably 10% by mass or more, more preferably 20% by mass or more, further preferably 30% by mass or more, still further preferably 50% by mass or more, and most preferably 55% by mass or more. Further, since the Si-based powder contains an SiX compound phase in addition to the Si phase, the content ratio of the Si phase is less than 100% by mass. From the viewpoint of preferably obtaining the effects of phases other than the Si phase, the above content ratio is preferably 90% by mass or less, more preferably 88% by mass or less, and further preferably 86% by mass or less.

[0027] The primary particles, which are the Si-based powder in the present embodiment, contain an SiX compound phase in addition to the above Si phase. The Si-based powder may further contain at least one selected from the group consisting of an SnCu compound phase and an AlCu compound phase. Here, the SiX compound phase contains Si and element X, and element X is at least one selected from the group consisting of Fe, Co, Cr, Mn, Ni, Zr, Ti, B, and P. On the other hand, the SnCu compound phase contains Sn and Cu, and the AlCu compound phase contains Al and Cu.

[0028] The SiX compound phase in the present embodiment has poor lithium storage properties and very little expansion due to reaction with lithium ions. Therefore, the SiX compound phase plays a role of a skeleton for maintaining the structure of the electrode material. Further, since the SiX compound has high conductivity, it is also effective for ensuring conductivity between the Si phase and the conductive material.

[0029] The SiX compound phase is usually contained in the Si-based powder as SiX compound particles. It is preferable that 95% by mass or more of the SiX compound particles are particles composed of the SiX compound phase, and the particles may be composed only of the SiX compound phase. When the SiX compound phase is other than the SiX compound particles, it may be contained in the Si-based powder as an OX compound.

[0030] In the SiX compound phase in this embodiment, X is at least one element selected from the group consisting of Fe, Co, Cr, Mn, Ni, Zr, Ti, B, and P. Among them, from the viewpoints of low expansibility and high conductivity, X is preferably one or more elements selected from the group consisting of Fe, Ni, Zr, Ti, B, and P, and more preferably one or more elements selected from the group consisting of Fe, Ni, B, and P.

[0031] The SiX compound in this embodiment includes, for example, compounds represented by Si2X, SiX, and SiX2. Examples of the compound represented by Si2X include Si2Fe, Si2Ni, Si2Co, Si2Ti, Si2Zr, Si2Cr, etc. In addition, the SiX compound phase can be composed of not only one kind of compound phase, but also two or more phases such as, for example, a SiFe compound phase and a SiB compound phase or a SiP compound phase, or a SiB compound phase and a SiP compound phase.

[0032] The content ratio of the SiX compound phase in the Si-based powder in this embodiment only needs to be more than 0% by mass, and preferably 5 to 70% by mass. Here, from the viewpoint of obtaining good cycle characteristics, the above content ratio is preferably 5% by mass or more, more preferably 8% by mass or more, and further preferably 10% by mass or more. Also, the above content ratio is preferably 70% by mass or less, more preferably 50% by mass or less, and further preferably 30% by mass or less.

[0033] The SnCu compound phase and the AlCu compound phase in this embodiment may be included in the Si-based powder together with the Si phase and the SiX compound phase.

[0034] The SnCu compound phase is usually included in the Si-based powder as SnCu compound particles. The SnCu compound particles are preferably particles composed of 95% by mass or more of the SnCu compound phase, and may be particles composed only of the SnCu compound phase. The SnCu compound phase can be included in the Si-based powder as Sn and Cu in cases other than SnCu compound particles.

[0035] The AlCu compound phase is usually contained in the Si-based powder as AlCu compound particles. The AlCu compound particles are preferably particles consisting of 95% by mass or more of the AlCu compound phase, and may be particles consisting only of the AlCu compound phase. In the case other than the AlCu compound particles, the AlCu compound phase may be contained in the Si-based powder as Al and Cu.

[0036] The SnCu compound phase and the AlCu compound phase have a lower theoretical capacity than Si and a higher theoretical capacity than the SiX compound. For example, while the theoretical capacity of the SiZr compound (SiX compound) is 100 mAh / g, the theoretical capacity of the SnCu compound is about 500 mAh / g, and the theoretical capacity of the AlCu compound is about 700 mAh / g. Therefore, by including the SnCu compound phase or the AlCu compound phase in the Si-based powder, it becomes easier to secure a diffusion path for Li ions. Also, the degree of expansion due to the reaction with Li ions is smaller for the SnCu compound and the AlCu compound than for Si or Sn alone, which has a high reactivity with Li ions. Therefore, by including the SnCu compound phase or the AlCu compound phase, the adverse effect on the cycle characteristics can be suppressed to a low level. Furthermore, the SnCu compound and the AlCu compound also have the effect of enhancing conductivity, similar to the above SiX compound.

[0037] The SnCu compound phase in this embodiment may be an alloy of Sn and Cu, or may be an alloy containing other metals in addition to Sn and Cu. The AlCu compound phase in this embodiment may be an alloy of Al and Cu, or may be an alloy containing other metals in addition to Al and Cu.

[0038] In the Si-based powder of the present embodiment, the total content ratio of the SnCu compound phase and the AlCu compound phase is preferably 0.1 to 15% by mass, more preferably 0.3 to 10% by mass, and even more preferably 0.5 to 8% by mass. Here, from the viewpoint of obtaining a high discharge capacity, the above content ratio is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, and even more preferably 0.5% by mass or more. Further, from the viewpoint of the ratio of the actual discharge capacity to the theoretical capacity of the negative electrode active material, that is, the utilization rate of the active material, the above content ratio is preferably 15% by mass or less, more preferably 10% by mass or less, and even more preferably 8% by mass or less.

[0039] When the Si-based powder in the present embodiment contains at least one of the SnCu compound phase and the AlCu compound phase, the ratio of the content ratio in the Si-based powder, represented by {SiX compound phase / (SnCu compound phase + AlCu compound phase)}, is preferably 1 to 300. Here, from the viewpoint of suppressing a decrease in cycle characteristics, the above mass ratio is preferably 1 or more, more preferably 3 or more, even more preferably 5 or more, and particularly preferably 7 or more. On the other hand, from the viewpoint of obtaining a high initial discharge capacity, the above mass ratio is preferably 300 or less, more preferably 200 or less, and even more preferably 100 or less.

[0040] In addition to the Si phase, the SiX compound phase, optionally the SnCu compound phase, and optionally the AlCu compound phase, the Si-based powder in the present embodiment may further contain other compound phases within a range that does not impair the effects of the present invention. Examples of the other compound phases include SiCu compound phases and the like.

[0041] On the other hand, in the Si-based powder of the present embodiment, the smaller the total content ratio of other elements other than Si, Sn, Al, Cu, and X that constitute the Si phase, the SiX compound phase, the SnCu compound phase, and the AlCu phase, the more preferable it is, and it is more preferable that no other elements are contained. The above other elements may be included as inevitable impurities, specifically, nitrogen (N), sulfur (S), phosphorus (P), oxygen (O), etc. are mentioned. In this case, the content ratio of each element is preferably N≤0.10 mass%, S≤0.10 mass%, P≤0.10 mass%, O≤15 mass%, and the total of these is preferably 5 mass% or less.

[0042] The content ratio of the Si-based powder in the Si-containing granule is preferably 50 to 90 mass%. Here, from the viewpoint of obtaining a good discharge capacity, the above content ratio is preferably 50 mass% or more, more preferably 55 mass% or more, and still more preferably 60 mass% or more. Also, from the viewpoint of obtaining cycle characteristics, the above content ratio is preferably 90 mass% or less, more preferably 88 mass% or less, and still more preferably 86 mass% or less.

[0043] 〈Carbon material〉 The carbon material in this embodiment is a material that binds primary particles, which are Si-based powders, to each other and also coats the surface of the Si-based powder.

[0044] The carbon material may be, for example, a material obtained by firing and carbonizing part or all of a polymer material containing carbon atoms.

[0045] The content ratio (mass%) of carbon with respect to the total of the above Si-based powder, carbon material, and any other components is the amount of carbon in the carbon coating parameter A. That is, the content ratio of the carbon material contributes to the above amount of carbon, but when the Si-containing granule in this embodiment further contains a polymer material, the amount of carbon constituting such a polymer material also participates in the above amount of carbon. When two or more kinds of carbon materials are included in the Si-containing granule, or when a polymer material is also included in addition to the carbon material, the total content of carbon in them is the content ratio of carbon, that is, the amount of carbon. As described above, the above amount of carbon is preferably 1.0 to 30.0 mass%, more preferably 4.0 to 20.0 mass%, and still more preferably 6.0 to 15.0 mass%.

[0046] The average thickness of the film formed by the carbon material coating the surface of the Si-based powder is preferably 1.0 to 25 nm. Here, from the perspective of ignitability, the above average thickness is preferably 1.0 nm or more, more preferably 1.5 nm or more, further preferably 2.0 nm or more, and particularly preferably 2.5 nm or more. Also, from the perspective of capacity, the above average thickness is preferably 25 nm or less, more preferably 20 nm or less, further preferably 18 nm or less, and particularly preferably 15 nm or less. The above average thickness can be determined by observing the surface of the Si-containing granule at a magnification of 200,000 times using a transmission electron microscope (TEM) and taking the average value of the film thicknesses of the carbon material at 5 locations as the average thickness.

[0047] 〈Polymer material containing carbon atoms〉 The Si-containing granule in this embodiment may contain a polymer material containing carbon atoms. It is also preferable that the polymer material containing carbon atoms is used as a precursor of the above carbon material. That is, the Si-based powder, which is a primary particle, is coated with a polymer material containing carbon atoms, further granulated into secondary particles, and then fired. As a result, part or all of the polymer material can be carbonized, and a Si-containing granule in which the surface of the Si-based powder is coated with a carbon material and the Si-based powders are bonded with a carbon material can be obtained. When all of the above polymer material is carbonized, the Si-containing granule does not contain the polymer material, and the carbon amount in the carbon coating parameter A is all due to the carbon material.

[0048] Examples of the polymer material containing carbon atoms include phenol resin, polyvinylidene fluoride resin, polyethylene resin, polypropylene resin, polyvinyl alcohol resin, polystyrene resin, furan resin, cellulose resin, epoxy resin, polyvinyl chloride, polymethyl methacrylate resin, pitch, coke, bio-waste, polyfurfuryl alcohol resin, polyimide resin, and any combination thereof.

[0049] The above polymer material preferably has a function as a binder. From the viewpoint of binding property, the polymer material is preferably, for example, a phenol resin, a polyvinylidene fluoride resin, a polyvinyl alcohol resin, a polyimide resin, etc., and a phenol resin and a polyvinyl alcohol resin are more preferable. Further, as the phenol resin, both a novolak resin and a resol resin are preferable, but a resol resin is preferable from the viewpoint of dispersibility in a slurry. The above polymer material may be used alone or in combination of two or more.

[0050] From the viewpoint of conductivity when at least a part of the above polymer material is carbonized by heat treatment to form a carbon material, a phenol resin, a polyvinylidene fluoride resin, a polyvinyl alcohol resin, a polyimide resin are preferable, and a phenol resin and a polyvinyl alcohol resin are more preferable. Further, as the phenol resin, both a novolak resin and a resol resin are preferable, but a resol resin is preferable from the viewpoint of dispersibility in a slurry.

[0051] 〈SiC〉 The Si-containing granulated body in the present embodiment may contain SiC generated in the manufacturing process. However, since SiC is a component that leads to a decrease in capacity as a negative electrode material, its content is preferably small. The content ratio of SiC in the Si-containing granulated body is preferably less than 15%, more preferably 10% or less, and even more preferably 8% or less. The lower limit of the content ratio of SiC is not particularly limited, and the smaller the better, but it is usually 0.1% or more.

[0052] The content ratio of SiC in the Si-containing granulated body is a percentage representation of the ratio of the area of the peak derived from SiC to the area of all peaks in the obtained XRD pattern when powder X-ray diffraction (XRD) measurement is performed on the Si-containing granulated body. The above content ratio of SiC can be adjusted by the time, temperature, etc. of the heat treatment performed when coating the surface of the Si-based powder with a carbon material.

[0053] 〈Si-containing granulated body〉 The Si-containing granule in the present embodiment is a secondary granule formed by granulating Si-based powder, which is primary particles with a surface coated with a carbon material, bound by the carbon material. The average secondary particle diameter is 2 μm or more, preferably 2 to 20 μm, more preferably 3 to 18 μm, and even more preferably 4 to 15 μm. Here, from the viewpoints of being difficult to ignite, enhancing safety, water resistance, and reducing the amount of binder required as a negative electrode material, the average secondary particle diameter is 2 μm or more, preferably 3 μm or more, and more preferably 4 μm or more. Also, from the viewpoint of realizing good cycle characteristics, the average secondary particle diameter is preferably 20 μm or less, more preferably 18 μm or less, and even more preferably 15 μm or less.

[0054] Note that the average secondary particle diameter of the Si-containing granule in this specification means the average granule diameter obtained from the particle shape distribution measurement result using an image-based particle size distribution measuring device. As the image-based particle size distribution measuring device, a Morpho series device manufactured by Malvern Panalytical can be adopted. Also, the average secondary particle diameter of the Si-containing granule can be adjusted by, for example, the solid content concentration of the slurry and the pressure during drying when granulation is performed by spray-drying a slurry mixture of primary particles.

[0055] The carbon coating rate on the surface of the Si-containing granule, which is a secondary particle, is preferably 14 to 99% by mass, more preferably 30 to 95% by mass, and even more preferably 40 to 90% by mass. Here, from the viewpoint of ignitability, the carbon coating rate is preferably 14% by mass or more, more preferably 30% by mass or more, and even more preferably 40% by mass or more. Also, from the viewpoint of capacity reduction, the carbon coating rate is preferably 99% by mass or less, more preferably 95% by mass or less, and even more preferably 90% by mass or less. Note that the carbon coating rate on the surface of the Si-containing granule in this specification means the ratio occupied by carbon atoms (C) among the spectra obtained by analyzing the surface of the Si-containing granule using X-ray photoelectron spectroscopy (XPS).

[0056] In this embodiment, the aspect ratio of the Si-containing granulated particles is preferably from 1.0 to 1.8, more preferably from 1.0 to 1.5, and even more preferably from 1.0 to 1.3. Here, from the viewpoint of obtaining good cycle characteristics, the aspect ratio is preferably 1.8 or less, more preferably 1.5 or less, and even more preferably 1.3 or less. Note that the aspect ratio of the Si-containing granulated particles in this specification is a value obtained by measuring the Si-containing granulated particles using a scanning electron microscope (SEM). Specifically, with SEM, observation is carried out at a magnification of 400 times, and from the obtained image, for 10 Si-based powders, the maximum diameter D and the diameter D' perpendicular thereto are measured respectively, and the average value of the values represented by D / D' is taken as the aspect ratio. Also, the aspect ratio of the Si-containing granulated particles can be adjusted by changing the spraying pressure and the feeding speed during spray drying.

[0057] In addition to the Si-based powder, the carbon material coating the surface of the Si-based powder, the polymer material optionally containing carbon atoms, and the inadvertently contained SiC, the Si-containing granulated particles may further contain other components. Examples of other components include SiO2 and the like.

[0058] 《Method for Producing Negative Electrode Material Powder for Lithium Ion Battery》 The method for producing the negative electrode material powder for a lithium ion battery according to this embodiment is not particularly limited, but for example, includes the following steps in order. Step 1: Step of preparing primary particles containing an Si phase and an SiX compound phase Step 2: Step of wet-mixing the primary particles containing the Si phase and the SiX compound phase together with a polymer material containing carbon atoms to obtain a slurry mixture Step 3: Step of spray-drying the slurry mixture Step 4: Step of heat-treating the spray-dried mixture

[0059] Hereinafter, each step will be described in order.

[0060] 〈Step 1: Step of Preparing Primary Particles〉 Step 1 is a step of preparing primary particles containing an Si phase and an SiX compound phase. Specifically, each raw material is weighed so as to have a desired composition, and an alloy melt obtained by melting using melting means such as an arc furnace, a high-frequency induction furnace, a heating furnace, etc. is rapidly cooled, for example, by using the atomization method, whereby alloy particles composed of an Si phase and an SiX compound phase as rapidly cooled metals are obtained. When the Si-based powder contains not only the Si phase and the SiX compound phase but also the SnCu compound phase and the AlCu compound phase, by using, as the above raw materials, raw materials containing Sn, Cu, and Al in addition to Si and X, alloy particles in which the SnCu compound phase and the AlCu compound phase are dispersed in the Si phase and the SiX compound phase can also be obtained.

[0061] When the average primary particle diameter of the alloy particles obtained above is large, it may be pulverized as needed to obtain an Si-based powder with a small average primary particle diameter. On the other hand, in order to prevent the average primary particle diameter of the alloy particles from being less than 0.1 μm, for example, the particle size is measured in a timely manner while sampling during pulverization to obtain a predetermined particle size.

[0062] Also, after independently obtaining metal particles composed of the Si phase, alloy particles composed of the SiX compound phase, optionally alloy particles composed of the SnCu compound phase, and optionally alloy particles composed of the AlCu compound phase, they may be mixed to obtain an Si-based powder that is primary particles containing the desired Si phase and SiX compound phase.

[0063] In the atomization method, a gas such as N2, Ar, He, etc. is sprayed at high pressure, for example, 1 to 10 MPa, onto an alloy melt that is discharged into a spray chamber and continuously (rod-shaped) flows downward, pulverizing and cooling the melt. The cooled melt approaches a spherical shape while freely falling in the spray chamber in a semi-molten state, and powdery particles are obtained. Also, from the viewpoint of improving the cooling effect, high-pressure water may be sprayed instead of the gas. In some cases, it is also possible to obtain foiled particles by using the roll quenching method instead of the atomization method.

[0064] The particles obtained above are pulverized as needed. For pulverization, appropriate pulverization means such as ball mills, bead mills, disk mills, coffee mills, and mortar pulverization can be adopted. Adjust the pulverization conditions so as to obtain the desired average primary particle size.

[0065] When the primary particles containing the Si phase and the SiX compound phase also contain an SnCu compound phase or an AlCu compound phase in addition to the Si phase and the SiX compound phase, and the particles containing each phase are independently obtained and then mixed, the respective particles may be pulverized and then mixed, or they may be mixed and then pulverized together.

[0066] The pulverization may be wet or dry. However, when wet pulverization is adopted, solvent removal, solvent substitution, drying, etc. may be performed. Further, by changing the means and conditions of the above pulverization, the average primary particle size of the primary particles containing the Si phase and the SiX compound phase can be controlled. Also, by measuring the particle size in a timely manner while sampling during pulverization so that the average primary particle size does not become less than 0.1 μm, a predetermined particle size is obtained.

[0067] 〈Step 2: Step of obtaining a slurry mixture〉 Step 2 is a step of wet-mixing the primary particles containing the Si phase and the SiX compound phase obtained in Step 1 with a polymer material containing carbon atoms to obtain a slurry mixture.

[0068] By wet-mixing the primary particles containing the Si phase and the SiX compound phase with a polymer material containing carbon atoms and passing through the subsequent Step 3, the surface of the primary particles is coated with the polymer material, and the polymer material serves as a binder to form secondary particles in which the primary particles are bonded together. Then, by carbonizing the polymer material by firing in Step 4, an Si-containing granulated body in which the surface of the Si-based powder is coated with a carbon material and the Si-based powder is bonded with the carbon material is obtained.

[0069] As described above, examples of the polymer material containing the carbon atoms include, for example, phenol resin, polyvinylidene fluoride resin, polyethylene resin, polypropylene resin, polyvinyl alcohol resin, polystyrene resin, furan resin, cellulose resin, epoxy resin, polyvinyl chloride, polymethyl methacrylate resin, pitch, coke, bio-waste, polyfurfuryl alcohol resin, polyimide resin, and any combination thereof.

[0070] The solvent when wet-mixing the primary particles containing the Si phase and the SiX compound phase obtained in Step 1 with the polymer material containing carbon atoms is not particularly limited. When wet grinding is employed to obtain the primary particles containing the Si phase and the SiX compound phase in Step 1, the slurry may be obtained by subjecting it to Step 2 without removing the solvent used during grinding and further adding the polymer material containing carbon atoms thereto.

[0071] Examples of the solvent include ethanol, N-methyl-2-pyrrolidone, isopropyl alcohol, cyclohexane, toluene, and the like.

[0072] The mixing ratio of the primary particles containing the Si phase and the polymer material containing carbon atoms is determined such that the carbon coating parameter A in the obtained Si-based particles exceeds 15, preferably exceeds 48, and so on. That is, the appropriate mixing ratio of the polymer material containing carbon atoms varies depending on the average primary particle diameter of the primary particles containing the Si phase and the SiX compound phase.

[0073] When using, for example, a phenolic resin as the polymer material containing carbon atoms, the blending ratio of the phenolic resin is preferably 1 to 100 parts by mass, more preferably 5 to 70 parts by mass, and even more preferably 10 to 50 parts by mass with respect to 100 parts by mass in total of the Si-based powder contained in the obtained slurry mixture. Here, from the viewpoint of completely coating the surface of the Si-based powder, the blending ratio is preferably 1 part by mass or more, more preferably 5 part by mass or more, and even more preferably 10 part by mass or more. Further, from the viewpoint of obtaining a high capacity, the blending ratio is preferably 100 parts by mass or less, more preferably 70 parts by mass or less, and even more preferably 50 parts by mass or less.

[0074] The polymer material containing carbon atoms is carbonized partially or entirely by the heat treatment in Step 4 described later to obtain a carbon material.

[0075] Determine the average primary particle diameter of the Si-based powder and the mixing ratio of the Si-based powder and the polymer material containing carbon atoms so that the value of the carbon coating parameter A of the obtained Si-based powder exceeds 15.

[0076] Here, the mixing ratio can be determined with reference to the value of the carbon coating parameter B represented by the following formula.

[0077] Carbon coating parameter B = 58.1 × average primary particle diameter (μm) + 1.1 × binder addition amount (mass%) + 0.6 × binder residual carbon ratio (mass%)

[0078] In the carbon coating parameter B, the average primary particle diameter (μm) means the average primary particle diameter of the Si-based powder. The binder addition amount means the content (mass%) of the polymer material containing carbon atoms in the finally obtained Si-containing granule. The binder residual carbon ratio means the ratio (mass%) of the carbon content constituting the polymer material containing carbon atoms in the carbon content of the finally obtained Si-containing granule. That is, if the heat treatment in Step 4 described later is not performed and the surface of the Si-based powder is not coated with a carbon material, the binder residual carbon ratio is 100 (mass%).

[0079] In the carbon coating parameter B, 58.1 which is the coefficient of the average primary particle diameter of the Si-based powder, 1.1 which is the coefficient of the binder addition amount, and 0.6 which is the coefficient of the binder residual carbon rate are all values derived from experiments.

[0080] The value of the carbon coating parameter B is preferably 15 or more, more preferably 35 or more, from the viewpoints of safety and water resistance. Also, from the viewpoint of cycle characteristics, it is preferably 48 or more, more preferably 55 or more. The upper limit of the carbon coating parameter B is not particularly limited, but is usually 200 or less.

[0081] 〈Step 3: Step of spray-drying the slurry mixture〉 Step 3 is a step of spray-drying the slurry mixture obtained in Step 2, whereby granulated bodies of secondary particles in which primary particles coated with a polymer material containing carbon atoms are bonded to each other are obtained.

[0082] As the method of spray-drying, a conventionally known method can be adopted. For example, the spray-dry method can be adopted. The spray-dry method is a method in which a slurry is made into fine droplets and instantaneously dried with warm air to remove the dispersion medium, whereby secondary particles in which primary particles containing an Si phase and an SiX compound phase are granulated by being joined in a granular form by a binder are granulated. By adjusting the solid content concentration of the slurry, the pressure during drying, etc., the particle diameter of the obtained secondary particles can be controlled.

[0083] By Steps 2 and 3, the surface of the Si-based powder which is the primary particle can be made into a state where it is widely and homogeneously coated with a polymer material containing carbon atoms. Then, by subsequently performing Step 4, at least a part of the polymer material containing the carbon atoms is carbonized while maintaining the coating state. As a result, direct contact between the Si phase and the SiX compound phase and the electrolytic solution or moisture can be suppressed, and the effects of the present invention can be suitably obtained. Furthermore, since a good conductive path is also ensured, better battery characteristics are realized.

[0084] 〈Step 4: Step of heat-treating the spray-dried mixture〉 Step 4 is a step of heat-treating the mixture spray-dried in Step 3. Thereby, at least a part of the polymer material containing carbon atoms coated on the surface of the Si-based powder in Step 3 can be carbonized.

[0085] The conditions of the heat treatment are not particularly limited. For example, a heating temperature of 400 to 1100°C is preferable, 600 to 1000°C is more preferable, and 700 to 950°C is even more preferable. Here, from the viewpoint of promoting carbonization and securing a conductive path, the heating temperature is preferably 400°C or higher, more preferably 600°C or higher, and even more preferably 700°C or higher. Also, from the viewpoint of suppressing the formation of undesired compounds such as SiC, the heating temperature is preferably 1100°C or lower, more preferably 1000°C or lower, and even more preferably 950°C or lower.

[0086] The heat treatment time is not particularly limited either. For example, 0.1 to 10 hours is preferable, 0.5 to 6 hours is more preferable, and 1 to 4 hours is even more preferable. Here, from the viewpoint of promoting carbonization and carbonizing the polymer material, the heating time is preferably 0.1 hour or more, more preferably 0.5 hour or more, and even more preferably 1 hour or more. Also, from the perspective of industrial feasibility, the heating time is preferably 10 hours or less, more preferably 6 hours or less, and even more preferably 4 hours or less.

[0087] Regarding the heating temperature and heating time of the heat treatment, it has been found that by satisfying the following heat treatment parameter C within a specific range, Si-containing granulates with good battery characteristics can be obtained in addition to safety and water resistance. Heat treatment parameter C = -0.15 × heating temperature (°C) + 9.51×10 -5 × [heating temperature (°C)] 2 + 0.27 × heating time (hours)

[0088] The above heat treatment parameter C is preferably less than -15, more preferably -20 or less, and even more preferably -25 or less. Also, the lower limit is not particularly limited, but it is usually -40 or more.

[0089] The atmosphere of the heat treatment is preferably, for example, under a nitrogen atmosphere or an argon atmosphere. The pressure for heat treatment is preferably atmospheric pressure.

[0090] The method of heat treatment is not particularly limited, and examples thereof include heat treatment using a rotary kiln, heat treatment using a shuttle kiln, and the like. Among these, from the viewpoint of being able to heat-treat the powder uniformly without unevenness, heat treatment using a rotary kiln is preferable.

[0091] 《Lithium Ion Battery》 〈Negative Electrode〉 In a lithium ion battery, it is preferable to use a negative electrode using the negative electrode material powder for a lithium ion battery according to the present embodiment.

[0092] The negative electrode in the present embodiment has a conductive substrate and a conductive film laminated on the surface of the conductive substrate. The conductive film contains at least the negative electrode material powder for a lithium ion battery according to the present embodiment, and the negative electrode material powder functions as a negative electrode active material.

[0093] The above-mentioned conductive substrate functions as a current collector. Examples of its material include Cu, Cu alloy, Ni, Ni alloy, Fe, Fe-based alloy, etc. Among these, Cu and Cu alloy are preferable.

[0094] Specific forms of the conductive substrate include foil shape, plate shape, etc. Among these, from the viewpoints of being able to reduce the volume of the battery and improving the degree of freedom of shape, the foil shape is preferable.

[0095] Examples of the material of the binder used when forming the conductive film include fluororesins such as polyvinylidene fluoride (PVdF) resin and polytetrafluoroethylene, polyvinyl alcohol resin, polyimide resin, polyamide resin, polyamideimide resin, styrene-butadiene rubber (SBR), polyacrylic acid, etc. These may be used alone or in combination of two or more. Among these, polyimide resin is particularly preferable from the viewpoints of mechanical strength, resistance to volume expansion of the negative electrode active material, suppression of peeling from the conductive substrate, etc.

[0096] The conductive film may contain a conductive aid as needed. When containing a conductive aid, it becomes easier to secure a conductive path for electrons.

[0097] As the conductive aid, those conventionally known can be adopted. For example, carbon and metals can be mentioned as those with little or no volume change during charge and discharge and with characteristics not deteriorating due to charge and discharge.

[0098] The shape of carbon is not particularly limited, and examples include particulate carbon, fibrous carbon, and flaky carbon. Among them, at least one of particulate carbon and fibrous carbon is preferable from the viewpoint of forming a conductive network between Si-containing granulated bodies, and the combined use of particulate carbon and fibrous carbon is more preferable from the viewpoint of further improving cycle characteristics.

[0099] The type of carbon is not particularly limited, and examples include carbon blacks such as ketjen black, acetylene black, and furnace black, graphite, carbon nanotubes, carbon nanofibers, fullerenes, graphene, and graphene oxide. Among them, carbon black, graphite, carbon nanotubes, and fullerenes are preferable, and ketjen black and acetylene black are more preferable. These may be used alone or in combination of two or more.

[0100] Examples of particulate carbon include carbon black, graphite, hard carbon, and soft carbon. More specifically, examples of carbon black include ketjen black, acetylene black, and furnace black.

[0101] Examples of fibrous carbon include carbon nanotubes (CNT) and carbon nanofibers (CNF). As the carbon nanotubes, either single-walled carbon nanotubes (SWCNT) or multi-walled carbon nanotubes (MWCNT) can be adopted.

[0102] Examples of the metal used as the conductive aid include Ni, Cr, SUS (stainless steel) alloy, and the like.

[0103] The conductive film may contain an aggregate as necessary. When an aggregate is contained, it becomes easier to suppress the expansion and contraction of the negative electrode during charge and discharge, and the collapse of the negative electrode can be suppressed, so that the cycle characteristics can be further improved.

[0104] The negative electrode in this embodiment can be manufactured, for example, by adding a necessary amount of a negative electrode active material, a conductive aid, and an aggregate as necessary to a binder dissolved in an appropriate solvent to form a paste, applying this to the surface of a conductive substrate, drying it, and performing densification, heat treatment, etc. as necessary.

[0105] When a lithium-ion battery is configured using the negative electrode in this embodiment, the positive electrode, electrolyte, separator, etc., which are the basic components of the battery other than the above negative electrode, are not particularly limited, and conventionally known ones can be used.

[0106] 〈Positive electrode, electrolyte, etc.〉 Examples of the positive electrode include those in which a layer containing a positive electrode active material such as LiCoO2, LiNiO2, LiFePO4, LiMnO2, etc. is formed on the surface of a current collector such as an aluminum foil.

[0107] Examples of the electrolyte include an electrolytic solution in which a lithium salt is dissolved in a non-aqueous solvent. In addition, those in which a lithium salt is dissolved in a polymer, a polymer solid electrolyte in which the above electrolytic solution is impregnated in a polymer, etc. can also be used.

[0108] Specific examples of the non-aqueous solvent include ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, etc. These may be contained singly or in combination of two or more.

[0109] Specific examples of the lithium salt include, for example, LiPF6, LiBF4, LiClO4, LiCF3SO3, LiAsF6, etc. These may be included singly or in combination of two or more.

[0110] In addition, other battery components include a separator, a can (battery case), a gasket, etc. For these as well, any materials that are commonly used in lithium-ion batteries can be appropriately combined to form a battery.

[0111] The battery shape is not particularly limited and may be any shape such as cylindrical, rectangular, coin-shaped, etc., and can be appropriately selected according to its specific use.

Examples

[0112] Hereinafter, the present invention will be described more specifically using examples.

[0113] 《Examples 1 to 79 and Comparative Examples 1 to 2》 1. Preparation of Si-based powder Si, and optionally Sn, Cu, Al, Fe, Ti, Cr, Mn, Co, Ni, Zr, B, and P were weighed so that the component ratios (mass %) shown in Table 1 were obtained, and heated and melted using a high-frequency induction furnace to obtain an alloy melt. By the gas atomization method, alloy particles in which SiX compound phases were dispersed in the Si phase, or alloy particles in which SiX compound phases and SnCu compound phases or AlCu compound phases were dispersed in the Si phase were obtained from the above alloy melt. The atmosphere during alloy melt preparation and gas atomization was an argon atmosphere. Also, during gas atomization, high-pressure (4 MPa) argon gas was sprayed onto the alloy melt falling in a rod shape inside the spray chamber. Each of the obtained particles was mechanically finely pulverized using a wet bead mill to obtain a slurry in which Si-based powder was dispersed. Ethanol was used as the solvent. The composition of each phase constituting the obtained Si-based powder is as shown in "Phase ratio (mass%)" in Table 2. In Tables 1 and 2, "-" means not contained.

[0114] 2. Preparation of slurry mixture To the slurry in which the Si-based powder obtained above was dispersed, resol resin was added as a polymer material containing carbon atoms to obtain a slurry mixture. The addition amount of the resol resin was 1 to 100 parts by mass with respect to 100 parts by mass of the Si-based powder in the slurry mixture. The solid content concentration of the slurry mixture was 40% by mass.

[0115] 3. Spray drying of slurry mixture The slurry mixture obtained above was sprayed and dried by the spray drying method to obtain secondary particles in which Si-based powders whose surfaces were coated with resol resin were bound together. The conditions of the spray dryer were as follows: spray temperature: 150 °C, spray pressure: 0.3 MPa, supply rate: 1 kg / h.

[0116] 4. Heat treatment The secondary particles obtained above were put into a rotary kiln and heat-treated at the temperature and time described in Table 2 under a nitrogen atmosphere to carbonize part or all of the resol resin, thereby obtaining a negative electrode material powder for a lithium-ion battery. Table 2 also shows the value of the heat treatment parameter C represented by the following formula.

[0117] 《Evaluation: Si-based powder》 〈Average primary particle size〉 Regarding the Si-containing granulated body, the median diameter (D50) obtained from the volume-based particle size distribution measured using a laser diffraction / scattering type particle size distribution measuring device for the slurry before granulation was defined as the average primary particle size of the Si-based powder. The results are shown in Table 2.

[0118] 〈Carbon coating parameter A〉 By analyzing the Si-containing granulates using the combustion infrared absorption method, the carbon content of the Si-based powder, which is the total of the Si-based powder, the carbon material, and any other components, that is, the proportion of carbon in the entire Si-containing granulate, was determined. The results are shown in Table 2. Also shown in Table 2 are the value represented by the carbon coating parameter A, which uses this carbon content and the average primary particle diameter obtained above.

[0119] 《Evaluation: Si-containing Granulates》 〈Average Secondary Particle Diameter〉 For the Si-containing granulates, the average secondary particle diameter was determined by measuring the particle shape distribution using an image-based particle size distribution measuring device (manufactured by Malvern Panalytical, Morphologi series, Morphologi 4). The results are shown in Table 3.

[0120] 〈Aspect Ratio〉 For the Si-containing granulates, SEM observation was performed at a magnification of 400 times. From the obtained images, for 10 Si-containing granulates, the maximum diameter D and the diameter D' perpendicular to it were measured respectively, and the average value of the values represented by D / D' was taken as the aspect ratio. The results are shown in Table 3.

[0121] 〈Carbon Coating Rate〉 For the Si-containing granulates, surface analysis was performed using X-ray photoelectron spectroscopy (XPS). Among the obtained spectra, the proportion occupied by carbon atoms (C) was determined, and the carbon coating rate (mass%) on the surface of the Si-containing granulates was determined. The results are shown in Table 3.

[0122] 〈SiC Content Ratio〉 For the Si-containing granulates, powder X-ray diffraction (XRD) measurement was performed, and the ratio of the area of the peak derived from SiC to the area of all peaks in the obtained XRD pattern was determined to obtain the content ratio of SiC. The results are shown in Table 3.

[0123] 《Evaluation: Safety》 For the Si-containing granulates, a small gas flame ignition test was conducted as a Class 2 dangerous goods test under the Fire Service Act. Those that did not ignite within 10 seconds after bringing the small gas flame closer were classified as non-hazardous and marked with "○" in Table 3 as qualified, while those that ignited within 10 seconds were classified as hazardous and marked with "×" in Table 3 as unqualified.

[0124] 《Evaluation: Water Resistance》 1 g of the Si-containing granulated body was placed in 13 mL of pure water, and the total amount of hydrogen generated until 336 hours had elapsed from the start of measurement was measured using a sensor gas chromatograph. Those with a hydrogen generation amount of 100 mass ppm or less were marked as qualified with "○" in Table 3, while those exceeding 100 mass ppm were marked as unqualified with "×" in Table 3.

[0125] 《Evaluation: Battery Characteristics》 〈Fabrication of Coin-Type Battery for Charge / Discharge Test〉 100 parts by mass of the negative electrode active material for lithium ion batteries, which is a Si-containing granulated body, 5 parts by mass of acetylene black (manufactured by Denka) as a conductive assistant, and 15 parts by mass of polyimide (thermoplastic resin) as a binder were blended, and this was mixed with N-methyl-2-pyrrolidone (NMP) as a solvent to prepare a paste containing a negative electrode material. The above paste was applied to the surface of a stainless steel (SUS) 316L foil (thickness 20 μm) serving as a current collector using the doctor blade method, dried, and densified by roll pressing, and then punched out on a disk with a diameter of 11 mm to fabricate a test electrode.

[0126] Next, a Li foil (thickness 500 μm) was punched out to have substantially the same shape as the above test electrode and used as a counter electrode. The test electrode was housed in a positive electrode can, and the counter electrode was housed in a negative electrode can. A separator made of a polyolefin-based microporous membrane was placed between the test electrode and the counter electrode. Note that although the above test electrode should be the negative electrode in a lithium ion battery, when the counter electrode is a Li foil, the Li foil becomes the negative electrode and the test electrode becomes the positive electrode.

[0127] A non-aqueous electrolyte solution in which LiPF6 was dissolved at a concentration of 1 mol / l in a mixed solvent of ethylene carbonate (EC): diethyl carbonate (DEC) = 1:1 (volume ratio) was injected into the positive electrode can and the negative electrode can, and the negative electrode can and the positive electrode can were clamped and fixed to fabricate a coin-type battery for charge-discharge tests.

[0128] 〈Charge-Discharge Test〉 Regarding the fabricated coin-type battery for charge-discharge tests, constant current charge-discharge with a current value of 0.2 mA was carried out for 1 cycle. The value obtained by dividing the capacity (mAh) used during this Li insertion or release by the mass (g) of the active material was defined as the initial charge capacity or the initial discharge capacity, and the ratio of the initial discharge capacity to the initial charge capacity was determined as the initial Coulomb efficiency. The results are shown in Table 3.

[0129] Also, based on the phase ratio of the Si phase, SiX compound phase, SnCu compound phase, and AlCu compound phase in the Si-containing granulated body, the theoretical capacity of each negative electrode material (each negative electrode active material) was calculated. Then, the initial discharge capacity with respect to the above theoretical capacity was determined as the utilization rate (active material utilization rate, %) of the negative electrode active material with respect to the theoretical capacity. The results are shown in Table 3.

[0130] After the second cycle, charge-discharge tests were carried out at a 1 / 5 C rate up to 50 cycles. Here, regarding the C rate, the current value for (charging) discharging the electrode in 1 hour is defined as 1 C, so the above 1 / 5 C rate means charging or discharging in 5 hours. The ratio of the discharge capacity at the 50th cycle to the initial discharge capacity at the first cycle, that is, the discharge capacity retention rate, was evaluated as the cycle retention rate (%). The results are shown in Table 3.

[0131]

Table 1

[0132]

Table 2

[0133]

Table 3

[0134] Among the above results, especially from the comparison with the results of Comparative Examples 1 and 2, it can be seen that the negative electrode material powder for lithium ion batteries according to this embodiment is difficult to catch fire and has high safety and good water resistance. This is because the Si-based powder, which is a primary particle, has a size above a certain level and its surface is preferably coated with a carbon material, so that the Si phase, SiX compound phase, and other phases such as the optional SnCu compound phase and AlCu compound phase constituting the Si-based powder are prevented from coming into contact with the electrolyte and oxygen with a high probability.

[0135] In addition to the above, from the results of Examples 73 to 75, it can be seen that when the value of the carbon coating parameter A exceeds 48, among the battery characteristics, especially the cycle characteristics become good. Also, from the results of Examples 78 and 79, it can be seen that by setting the upper limit of the average primary particle diameter of the Si-based powder and the average secondary particle diameter of the Si-containing granule to a certain level or less, the cycle characteristics become good. From the result of Example 72, it can be seen that the aspect ratio of the Si-containing granule also contributes to the cycle characteristics. From the result of Example 77, it can be seen that the increase in the SnCu phase in the Si-based powder contributes to the cycle characteristics.

[0136] Furthermore, from the results of Examples 67 to 69 and Example 71, it can be seen that when the heat treatment temperature increases and the value of the heat treatment parameter C is -15 or more, the content ratio of SiC contained in the Si-containing granule increases, and among the battery characteristics, the utilization rate of the active material decreases. On the other hand, from the result of Example 70, it can be seen that if the heat treatment temperature is too low, sufficient carbonization does not proceed and the initial Coulomb efficiency decreases. Thus, the content ratio of SiC can be controlled by performing suitable heat treatment.

[0137] In addition to the above, from the result of Example 76, it can be seen that when the ratio of the Si phase in the Si-based powder is low, the initial Coulomb efficiency decreases.

[0138] As described above in detail, the negative electrode material powder for a lithium ion battery according to the present embodiment, the present invention is not limited to the above-described embodiments and examples, and various modifications are possible without departing from the spirit thereof.

Claims

1. A negative electrode material powder containing Si-containing granulates, wherein the Si-containing granulates contain Si-based powder and a carbon material, the Si-based powder is primary particles containing an Si phase and an SiX compound phase, the SiX compound phase contains Si and element X, the element X is at least one selected from the group consisting of Fe, Co, Cr, Mn, Ni, Zr, Ti, B, and P, the average primary particle diameter of the Si-based powder is 0.1 μm or more, the average secondary particle diameter of the Si-containing granulates is 2 μm or more, the surface of the Si-based powder is coated with and bonded by the carbon material, a negative electrode material powder for a lithium-ion battery, wherein the carbon coating parameter A represented by the following formula of the Si-based powder is more than 15. Carbon coating parameter A = 58.1 × average primary particle diameter (μm) + 5.6 × carbon content (mass%)

2. The negative electrode material powder for a lithium-ion battery according to claim 1, wherein the content ratio of SiC in the Si-containing granulates is less than 15%.

3. The negative electrode material powder for a lithium-ion battery according to claim 1 or 2, wherein the carbon coating parameter A is more than 48.

4. The negative electrode material powder for a lithium-ion battery according to claim 1 or 2, wherein the average primary particle diameter of the Si-based powder is 5.0 μm or less.

5. The negative electrode material powder for a lithium-ion battery according to claim 1 or 2, wherein the average secondary particle diameter of the Si-containing granulates is 20 μm or less.

6. The negative electrode material powder for a lithium-ion battery according to claim 1 or 2, wherein the aspect ratio of the Si-containing granulates is 1.0 to 1.

8.

7. The Si-based powder is primary particles further containing at least one selected from the group consisting of an SnCu compound phase and an AlCu compound phase, the SnCu compound phase contains Sn and Cu, the AlCu compound phase contains Al and Cu, The negative electrode material powder for a lithium-ion battery according to claim 1 or 2, wherein the content ratio of the Si phase in the Si-based powder is 30 mass% or more.

8. The negative electrode material powder for a lithium-ion battery according to claim 7, wherein the total content ratio of the SnCu compound phase and the AlCu compound phase in the Si-based powder is 0.1 to 15 mass%.

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