Negative electrode material powder for lithium ion batteries

Abstract

The present application relates to a negative electrode material powder for a lithium ion battery, comprising Si-containing granules containing a Si-based powder and a carbon material, the average primary particle diameter of the Si-based powder being 0.1 μm or more, the average secondary particle diameter of the Si-containing granules being 2 μm or more, the surface of the Si-based powder being coated with and bonded by the carbon material, and the value represented by the formula {58.1 x average primary particle diameter (μm) + 5.6 x carbon content (mass %)} of the Si-based powder exceeding 15.

Description

Technical Field

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

[0002] Lithium-ion batteries have the advantages of high capacity, high voltage, and miniaturization, and are widely used as power sources for mobile phones, laptops, and other devices. Furthermore, in recent years, their development has been actively pursued as a power source for electric vehicles, hybrid vehicles, and other similar applications.

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

[0004] Graphite is widely used as the negative electrode active material in the above-mentioned applications, but its theoretical capacity is only 372 mAh / g, and further high capacity is desired.

[0005] Therefore, Si, which can achieve approximately 10 times the capacity of graphite, has been proposed as a negative electrode active material for lithium-ion batteries.

[0006] However, Si has issues with its cycling characteristics under repeated charge and discharge cycles.

[0007] In contrast, Patent Document 1 discloses a negative electrode material for batteries in which carbon material is formed around silicon material with gaps between it using thermal CVD (thermal chemical vapor deposition). Furthermore, Patent Document 2 discloses a negative electrode material for lithium-ion batteries in which carbon is present on part or all of the surface of silicon oxide particles. Moreover, Patent Document 3 discloses a carbon material in which silicon oxide is surrounded by carbon material particles.

[0008] Existing technical documents

[0009] Patent documents

[0010] Patent Document 1: Japanese Patent No. 6978947

[0011] Patent Document 2: Japanese Patent No. 6615431

[0012] Patent Document 3: Japanese Patent No. 5516529 Summary of the Invention

[0013] The technical problem that the invention aims to solve

[0014] In any of the aforementioned patent documents 1 to 3, when obtaining the desired negative electrode material or carbon material, carbon is coated on the surface of silicon oxide, represented by SiOx, which is the active material, during the manufacturing process.

[0015] However, as the inventors have learned, in any of the aforementioned patent documents 1 to 3, Si-based powders are prone to ignition at relatively low temperatures, and thus readily react with moisture to produce hydrogen (H2).

[0016] Therefore, the purpose of this invention is to provide a negative electrode material powder for lithium-ion batteries that is not easily ignited, has excellent safety, and also has good water resistance.

[0017] Technical solutions for solving technical problems

[0018] To address the aforementioned technical problems, the inventors conducted in-depth research and found that by coating the Si-based powder itself, which consists of primary particles including the Si phase and SiX compound phase, with carbon material, and by adjusting its average primary particle size and the degree of coating to meet specific parameters, it is possible to achieve good safety by making it less prone to ignition, and further achieve good water resistance by reducing the amount of hydrogen produced due to its reaction with water, thus completing the present invention.

[0019] Further research revealed that these parameters are also related to cyclic characteristics.

[0020] That is, the main idea of ​​this invention is as follows.

[0021] [1] A negative electrode material powder for lithium-ion batteries, comprising Si-containing granules, wherein...

[0022] The Si-containing granules comprise Si-based powder and carbon materials.

[0023] The Si-based powder consists of primary particles containing both a Si phase and a SiX compound phase.

[0024] The SiX compound phase contains Si and element X.

[0025] The element X is at least one selected from the group consisting of Fe, Co, Cr, Mn, Ni, Zr, Ti, B, and P.

[0026] The average primary particle size of the Si-based powder is greater than 0.1 μm.

[0027] The average secondary particle size of the Si-containing granules is greater than 2 μm.

[0028] The surface of the Si-based powder is coated and bonded by the carbon material, and the carbon coating parameter A of the Si-based powder, expressed by the following formula, exceeds 15.

[0029] Carbon coating parameter A = 58.1 × average primary particle size (μm) + 5.6 × carbon content (mass%)

[0030] [2] According to the lithium-ion battery negative electrode material powder described in [1] above, wherein,

[0031] The SiC content in the Si-containing granules is less than 15%.

[0032] [3] According to the lithium-ion battery negative electrode material powder described in [1] or [2] above, wherein,

[0033] The carbon coating parameter A exceeds 48.

[0034] [4] The lithium-ion battery negative electrode material powder according to any one of [1] to [3] above, wherein,

[0035] The average primary particle size of the Si-based powder is less than 5.0 μm.

[0036] [5] The lithium-ion battery negative electrode material powder according to any one of [1] to [4] above, wherein,

[0037] The average secondary particle size of the Si-containing granules is less than 20 μm.

[0038] [6] The lithium-ion battery negative electrode material powder according to any one of [1] to [5] above, wherein,

[0039] The aspect ratio of the Si-containing granules is 1.0 to 1.8.

[0040] [7] The lithium-ion battery negative electrode material powder according to any one of [1] to [6] above, wherein,

[0041] The Si-based powder further comprises primary particles selected from at least one group consisting of SnCu compound phases and AlCu compound phases.

[0042] The SnCu compound phase comprises Sn and Cu.

[0043] The AlCu compound phase contains Al and Cu.

[0044] The Si phase in the Si-based powder contains more than 30% by mass.

[0045] [8] According to the lithium-ion battery negative electrode material powder described in [7] above, wherein,

[0046] The total content of the SnCu compound phase and the AlCu compound phase in the Si-based powder is 0.1-15% by mass.

[0047] Invention Effects

[0048] According to the present invention, a negative electrode material powder for lithium-ion batteries can be provided that is not easily ignited, has excellent safety, and also has good water resistance. Therefore, when this negative electrode material powder is used as a negative electrode active material in lithium-ion batteries, the safety of the lithium-ion battery itself can be improved. In addition, it can also prevent the degradation of lithium-ion batteries caused by moisture.

[0049] Furthermore, by optimizing the conditions, the present invention can also improve various battery characteristics such as cycle characteristics. Detailed Implementation

[0050] Hereinafter, embodiments of the present invention will be described. However, the present invention is not limited to the embodiments described below. Furthermore, in this specification, the symbol “~” indicating a numerical range is used to mean that the values ​​described before and after it are both lower and upper limits. Moreover, in this specification, mass% and weight% are synonymous.

[0051] Powdered Anode Material for Lithium-ion Batteries

[0052] The negative electrode material powder for lithium-ion batteries in this embodiment includes Si-containing granules.

[0053] Si-containing granules are granules with an average secondary particle size of 2 μm or more, and contain Si-based powder and carbon materials.

[0054] Si-based powder consists of primary particles with an average primary particle size of 0.1 μm or more, comprising a Si phase and a SiX compound phase. The surface of the Si-based powder is coated with the aforementioned carbon material, the degree of which can be represented by a specific carbon coating parameter A. Furthermore, through the aforementioned carbon material, the Si-based powder particles, as primary particles, are bonded together to form Si-containing granules, which are secondary particles.

[0055] <Si-based powder>

[0056] In this embodiment, the Si-based powder contained in the Si-containing granules are primary particles, and their surfaces are coated with carbon material.

[0057] The carbon coating parameter A can be represented by the following formula.

[0058] Carbon coating parameter A = 58.1 × average primary particle size (μm) + 5.6 × carbon content (mass%)

[0059] The carbon coating parameter A mentioned above uses the average primary particle size and carbon content of Si-based powder as variables, but the coefficient of average primary particle size (58.1) and the coefficient of carbon content (5.6) are values ​​derived from experimental results.

[0060] It can be seen that by making the value of the carbon coating parameter A exceed 15, the Si-containing granules are not easy to ignite and can achieve good water resistance.

[0061] The reason for this is still uncertain, but it is believed that because the carbon coating parameter A exceeds 15, the probability of Si-based powder coming into direct contact with the flame is reduced, making it difficult to ignite. Similarly, regarding water resistance, the reduced probability of Si-based powder coming into direct contact with water effectively suppresses the generation of hydrogen (H2). Furthermore, it also prevents oxidation of phases other than the Si phase and SiX compound phase due to contact with water, thus preventing unintended reactions in the negative electrode.

[0062] That is, from the above point of view, the value of carbon coating parameter A is greater than 15, preferably 25 or more, and more preferably 35 or more.

[0063] In addition to the above, it is known that the carbon coating parameter A in this embodiment is also related to the cycle characteristics when the negative electrode material powder of this embodiment is applied to a lithium-ion battery. Specifically, good cycle characteristics can be achieved by making the value of the carbon coating parameter A exceed 48. It is believed that by coating the surface of the Si-based powder with carbon material to a degree where the value of the carbon coating parameter A exceeds 48, direct contact between the Si phase, SiX compound phase and electrolyte can be appropriately prevented, and the formation / disintegration of SEI during charge and discharge can be suppressed.

[0064] From the viewpoint of cycle characteristics, the value of carbon coating parameter A is preferably greater than 48, more preferably greater than 55, and even more preferably greater than 65.

[0065] On the other hand, there is no particular upper limit to the value of the carbon coating parameter A. From a manufacturing point of view, it is not preferable to add a large amount of carbon material. The above value is, for example, 200 or less, 150 or less, and preferably 120 or less.

[0066] That is, the value of the carbon coating parameter A is preferably greater than 15 and less than 200, more preferably greater than 48 and less than 120.

[0067] In this embodiment, the carbon content used in carbon coating parameter A is the percentage (mass %) of carbon relative to the total of the Si-based powder as a primary particle, carbon content, and any other arbitrary components.

[0068] Specifically, the carbon content of the Si-based powder in this specification is the carbon concentration (mass %) determined by analyzing Si-containing granules using a combustion infrared absorption method.

[0069] It should be noted that the surface of the primary particles of the Si-based powder being coated with carbon material can be confirmed by observation using transmission electron microscopy (TEM). Furthermore, based on the safety evaluation method used in the later-described embodiments, namely the small gas flame ignition test, if the Si-containing granules ignite within 10 seconds, it can be determined that the aforementioned coating was not performed.

[0070] In this embodiment, the Si-containing granules are formed by combining Si-based powder, which is coated with carbon material as a primary particle, with the carbon material to create secondary particles, thereby achieving various effects such as safety, water resistance, and cycle characteristics.

[0071] Although primary particles are bonded together with carbon materials, the same effect cannot be obtained when carbon materials are applied to granules of primary particles whose surfaces cannot be considered covered, or to the surfaces of secondary particles granulated by bonding primary particles together with adhesives, etc.

[0072] The carbon content in the aforementioned 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. From the viewpoint of suppressing excessive exposure or coverage of the Si phase, SiX compound phase, etc., constituting the Si-based powder, the aforementioned 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. Furthermore, from the viewpoint of suppressing a decrease in coulombic efficiency, the aforementioned 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.

[0073] In this embodiment, the average primary particle size of the Si-based powder 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. From the viewpoints of difficulty in ignition, improved safety, water resistance, and reducing the amount of binder required as the negative electrode material, the aforementioned average primary particle size is 0.1 μm or more, preferably 0.2 μm or more, and more preferably 0.3 μm or more. Furthermore, from the viewpoint of reducing the absolute amount of expansion during Li insertion and achieving good cycle characteristics, the aforementioned 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.

[0074] It should be noted that the average primary particle size of the Si-based powder in this specification is the median particle size (D50) obtained from the volumetric reference particle size distribution of the slurry before granulation, measured using a laser diffraction / scattering particle size distribution measuring device for Si-containing granules. Alternatively, the average primary particle size of the Si-based powder can also be obtained by image analysis of SEM images of Si-containing granules. Furthermore, the average primary particle size of the Si-based powder can be adjusted by the pulverization method, conditions, etc.

[0075] The Si phase that constitutes the Si-based powder in this embodiment intercalates / releases Li, serving as a negative electrode active material. The Si phase is typically contained in the Si-based powder as Si particles. Preferably, the Si particles are composed of Si phase at least 95% by mass. In the case where the Si phase is not composed of Si particles, it may be contained as SiO2.

[0076] In this embodiment, the Si phase content in the Si-based powder is preferably 10% by mass or more and less than 100% by mass, more preferably 30% to 90% by mass. From the viewpoint of obtaining good initial discharge capacity and initial coulombic efficiency, the above-mentioned content is preferably 10% by mass or more, more preferably 20% by mass or more, further preferably 30% by mass or more, even more preferably 50% by mass or more, and most preferably 55% by mass or more. Furthermore, since the Si-based powder contains a SiX compound phase in addition to the Si phase, the Si phase content is less than 100% by mass. From the viewpoint of appropriately obtaining the effects brought about by phases other than the Si phase, the above-mentioned content is preferably 90% by mass or less, more preferably 88% by mass or less, and even more preferably 86% by mass or less.

[0077] In this embodiment, the primary particles of the Si-based powder, in addition to the Si phase described above, also include a SiX compound phase. The Si-based powder may further include at least one selected from the group consisting of SnCu compound phases and AlCu compound phases.

[0078] Here, the SiX compound phase comprises Si and element X, wherein element X is at least one selected from the group consisting of Fe, Co, Cr, Mn, Ni, Zr, Ti, B and P.

[0079] On the other hand, the SnCu compound phase contains Sn and Cu, while the AlCu compound phase contains Al and Cu.

[0080] In this embodiment, the SiX compound phase lacks Li intercalation capability, resulting in very little expansion due to its reaction with Li ions. Therefore, the SiX compound phase acts as a framework for maintaining the structure of the electrode material. Furthermore, the high conductivity of the SiX compound phase is also effective in ensuring conductivity between the Si phase and the conductive material.

[0081] The SiX compound phase is typically included in Si-based powders as SiX compound particles. Preferably, the SiX compound particles are composed of 95% or more of the SiX compound phase, but they can also be particles composed solely of the SiX compound phase. In the case of SiX compound particles, the SiX compound phase can be included in Si-based powders as an OX compound.

[0082] In this embodiment, X in the SiX compound phase is at least one element selected from the group consisting of Fe, Co, Cr, Mn, Ni, Zr, Ti, B, and P. From the viewpoint of low expansion 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.

[0083] Examples of SiX compounds in this embodiment include compounds represented by Si2X, SiX, and SiX2. Examples of compounds represented by Si2X include Si2Fe, Si2Ni, Si2Co, Si2Ti, Si2Zr, and Si2Cr.

[0084] It should be noted that, in addition to the case where the SiX compound phase consists of only one compound phase, it can also consist of two or more phases such as the SiFe compound phase, the SiB compound phase, the SiP compound phase, or the SiB compound phase and the SiP compound phase.

[0085] In this embodiment, the SiX compound phase in the Si-based powder contains more than 0% by mass, preferably 5 to 70% by mass. From the viewpoint of obtaining good cycling characteristics, the above-mentioned content is preferably 5% by mass or more, more preferably 8% by mass or more, and even more preferably 10% by mass or more. Furthermore, the above-mentioned content is preferably 70% by mass or less, more preferably 50% by mass or less, and even more preferably 30% by mass or less.

[0086] In this embodiment, the SnCu compound phase and AlCu compound phase can be included together with the Si phase and SiX compound phase in the Si-based powder.

[0087] SnCu compound phases are typically included in Si-based powders as SnCu compound particles. Preferably, the SnCu compound particles consist of at least 95% by mass of the SnCu compound phase, but they can also be particles consisting solely of the SnCu compound phase. In the absence of SnCu compound particles, the SnCu compound phase can be included in Si-based powders as either Sn or Cu.

[0088] AlCu compound phases are typically included in Si-based powders as AlCu compound particles. Preferably, the AlCu compound particles consist of 95% or more of the AlCu compound phase, but they can also be particles consisting solely of the AlCu compound phase. In the absence of AlCu compound particles, the AlCu compound phase can be included in Si-based powders as Al or Cu.

[0089] The theoretical capacities of SnCu and AlCu compounds are lower than those of Si but higher than those of SiX compounds. For example, the theoretical capacity of SiZr compounds (SiX compounds) is 100 mAh / g, while the theoretical capacity of SnCu compounds is around 500 mAh / g, and that of AlCu compounds is around 700 mAh / g.

[0090] Therefore, by including SnCu and AlCu compound phases in Si-based powders, the diffusion path of Li ions can be easily ensured. Furthermore, compared to Si and Sn monomers, which have high reactivity with Li ions, the expansion caused by the reaction of SnCu and AlCu compounds with Li ions is less pronounced. Therefore, by including SnCu and AlCu compound phases, the adverse effects on cycling characteristics can also be minimized. Moreover, SnCu and AlCu compounds, like the aforementioned SiX compounds, also possess the effect of improving conductivity.

[0091] In this embodiment, the SnCu compound phase can be an alloy of Sn and Cu, or an alloy containing other metals besides Sn and Cu.

[0092] In this embodiment, the AlCu compound phase can be an alloy of Al and Cu, or an alloy containing other metals besides Al and Cu.

[0093] In this embodiment, the total content of the SnCu compound phase and the AlCu compound phase in the Si-based powder 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. From the viewpoint of obtaining high discharge capacity, the above-mentioned content 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. Furthermore, from the viewpoint of the ratio of actual discharge capacity to the theoretical capacity of the negative electrode active material, i.e., the utilization rate of the active material, the above-mentioned content is preferably 15% by mass or less, more preferably 10% by mass or less, and even more preferably 8% by mass or less.

[0094] In this embodiment, when the Si-based powder contains at least one of a SnCu compound phase and an AlCu compound phase, the ratio of the Si-based powder content, expressed as {SiX compound phase / (SnCu compound phase + AlCu compound phase)}, is preferably 1 to 300. From the viewpoint of suppressing the decrease in cycling characteristics, the above-mentioned mass ratio is preferably 1 or more, more preferably 3 or more, further 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-mentioned mass ratio is preferably 300 or less, more preferably 200 or less, and further preferably 100 or less.

[0095] In this embodiment, the Si-based powder may further contain other compound phases in addition to the Si phase, SiX compound phase, any SnCu compound phase, and any AlCu compound phase, without compromising the effectiveness of the present invention.

[0096] Other compound phases, such as SiCu compound phases, can be cited.

[0097] On the other hand, in the Si-based powder of this embodiment, the smaller the total proportion of elements other than Si, Sn, Al, Cu, and X that constitute the Si phase, SiX compound phase, SnCu compound phase, and AlCu phase, the better, and it is more preferable that no other elements are present.

[0098] The aforementioned other elements may sometimes be present as unavoidable impurities, such as nitrogen (N), sulfur (S), phosphorus (P), and oxygen (O). In this case, the preferred proportions of each element are N ≤ 0.10% by mass, S ≤ 0.10% by mass, P ≤ 0.10% by mass, and O ≤ 15% by mass, and their total is preferably 5% by mass or less.

[0099] The Si-based powder content in the Si-containing granules is preferably 50 to 90% by mass. From the viewpoint of obtaining good discharge capacity, this content is preferably 50% by mass or more, more preferably 55% by mass or more, and even more preferably 60% by mass or more. Furthermore, from the viewpoint of obtaining good cycle performance, this content is preferably 90% by mass or less, more preferably 88% by mass or less, and even more preferably 86% by mass or less.

[0100] <Carbon Materials>

[0101] In this embodiment, carbon material refers to a material that, in addition to bonding the primary particles of the Si-based powder together, also coats the surface of the Si-based powder.

[0102] Carbon materials can be, for example, materials that are carbonized by firing part or all of a polymer material containing carbon atoms.

[0103] The carbon content (mass %) relative to the total of the aforementioned Si-based powder and carbon materials, and any other components, is the carbon content in carbon coating parameter A. That is, the carbon content ratio contributes to the aforementioned carbon content, but when the Si-containing granules in this embodiment also contain polymer materials, the amount of carbon constituting the polymer materials is also related to the aforementioned carbon content.

[0104] In cases where Si-containing granules contain two or more carbon materials, or polymer materials in addition to carbon materials, the total carbon content of these materials is called the carbon content ratio, or carbon amount.

[0105] As described above, the carbon content 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.

[0106] The average thickness of the carbon material film covering the surface of the Si-based powder is preferably 1.0 to 25 nm. From the viewpoint of flammability, the average thickness is preferably 1.0 nm or more, more preferably 1.5 nm or more, even more preferably 2.0 nm or more, and particularly preferably 2.5 nm or more. Furthermore, from the viewpoint of capacity, the average thickness is preferably 25 nm or less, more preferably 20 nm or less, even more preferably 18 nm or less, and particularly preferably 15 nm or less.

[0107] The average thickness can be calculated as follows: For Si-containing granules, the surface is observed using a transmission electron microscope (TEM) at a magnification of 200,000, and the average thickness of the carbon material film at 5 locations is used as the average thickness.

[0108] <Polymer materials containing carbon atoms>

[0109] The Si-containing granules in this embodiment may comprise a polymer material containing carbon atoms. The aforementioned polymer material containing carbon atoms is also preferably used as a precursor to the aforementioned carbon material.

[0110] That is, Si-based powder, which serves as primary particles, is coated with a polymer material containing carbon atoms, further granulated to form secondary particles, and then sintered. This allows for the partial or complete carbonization of the polymer material, resulting in Si-containing granules where the surface of the Si-based powder is coated with carbon material and the Si-based powder is bonded to the carbon material. It should be noted that when the polymer material is completely carbonized, the Si-containing granules do not contain polymer material, and the carbon content in the carbon coating parameter A depends entirely on the carbon material.

[0111] Examples of polymer materials containing carbon atoms include phenolic resins, polyvinylidene fluoride resins, polyethylene resins, polypropylene resins, polyvinyl alcohol resins, polystyrene resins, furan resins, cellulose resins, epoxy resins, polyvinyl chloride, polymethyl methacrylate resins, asphalt, coke, biological waste, polyfurfuryl alcohol resins, polyimide resins, and any combination thereof.

[0112] The aforementioned polymer materials preferably function as adhesives. From the viewpoint of adhesion, polymer materials such as phenolic resins, polyvinylidene fluoride resins, polyvinyl alcohol resins, and polyimide resins are preferred, with phenolic resins and polyvinyl alcohol resins being more preferred. Furthermore, as phenolic resins, phenolic varnish resins and methylphenolic resins are both preferred; from the viewpoint of dispersibility in slurries, methylphenolic resins are preferred. Only one of the aforementioned polymer materials may be used, or two or more may be used in combination.

[0113] From the viewpoint of electrical conductivity when carbon materials are produced by carbonizing at least a portion of them through heat treatment, the aforementioned polymer materials are preferably phenolic resins, polyvinylidene fluoride resins, polyvinyl alcohol resins, and polyimide resins, with phenolic resins and polyvinyl alcohol resins being more preferred. Furthermore, as phenolic resins, phenolic varnish resins and first-order phenolic resins are both preferred, and from the viewpoint of dispersibility in slurries, first-order phenolic resins are preferred.

[0114] <SiC>

[0115] The Si-containing granules in this embodiment may include SiC generated during their manufacturing process. However, SiC is a component that leads to a decrease in capacity as a negative electrode material, so its content is preferably low.

[0116] The SiC content in the Si-containing granules is preferably less than 15%, more preferably less than 10%, and even more preferably less than 8%. There is no particular limitation on the lower limit of the SiC content, but it is preferred to be less, usually more than 0.1%.

[0117] The above-mentioned SiC content ratio in the Si-containing granules is expressed as the percentage of the area of ​​the SiC peaks relative to the total peak area in the XRD pattern obtained by powder X-ray diffraction (XRD) of the Si-containing granules.

[0118] The SiC content can be adjusted by the time and temperature of the heat treatment when coating the surface of Si-based powder with carbon materials.

[0119] <Si-containing granules>

[0120] In this embodiment, the Si-containing granules are secondary particles formed by bonding and granulating primary particles, i.e., Si-based powder, whose surfaces are coated with carbon material, with the average secondary particle size being 2 μm or more, preferably 2 to 20 μm, more preferably 3 to 18 μm, and even more preferably 4 to 15 μm.

[0121] From the viewpoints of difficulty in ignition, improved safety, water resistance, and reducing the amount of binder required as a negative electrode material, the average secondary particle size is 2 μm or more, preferably 3 μm or more, and more preferably 4 μm or more. Furthermore, from the viewpoint of achieving good cycling characteristics, the average secondary particle size is preferably 20 μm or less, more preferably 18 μm or less, and even more preferably 15 μm or less.

[0122] It should be noted that the average secondary particle size of the Si-containing granules in this specification refers to the average particle size obtained from particle shape distribution measurements using an image-based particle size distribution measuring device. The image-based particle size distribution measuring device can be a Malvern Panalytical Morphologi series device.

[0123] Furthermore, the average secondary particle size of the Si-containing granules can be adjusted, for example, by spray drying a slurry mixture of primary particles, through the concentration of solid components in the slurry, the pressure during drying, etc.

[0124] The carbon coating percentage on the surface of the Si-containing granules, which are secondary particles, is preferably 14 to 99% by mass, more preferably 30 to 95% by mass, and even more preferably 40 to 90% by mass. From the viewpoint of flammability, the aforementioned carbon coating percentage is preferably 14% by mass or more, more preferably 30% by mass or more, and even more preferably 40% by mass or more. Furthermore, from the viewpoint of reducing capacity, the aforementioned carbon coating percentage is preferably 99% by mass or less, more preferably 95% by mass or less, and even more preferably 90% by mass or less.

[0125] It should be noted that the carbon coating rate of the surface of the Si-containing granules in this specification refers to the proportion of carbon atoms (C) in the spectrum obtained by analyzing the surface of the Si-containing granules using X-ray photoelectron spectroscopy (XPS).

[0126] In this embodiment, the aspect ratio of the Si-containing granules is preferably 1.0 to 1.8, more preferably 1.0 to 1.5, and even more preferably 1.0 to 1.3. Here, from the viewpoint of obtaining good cycling characteristics, the above aspect ratio is preferably 1.8 or less, more preferably 1.5 or less, and even more preferably 1.3 or less.

[0127] It should be noted that the aspect ratio of the Si-containing granules in this specification is a value obtained by measuring the Si-containing granules using a scanning electron microscope (SEM). Specifically, using an SEM at 400x magnification, for 10 Si-based powders, the maximum diameter D and the diameter D' perpendicular to it were measured, and the average value expressed as D / D' was taken as the aspect ratio. Furthermore, the aspect ratio of the Si-containing granules can be adjusted by changing the spray pressure and feed rate during spray drying.

[0128] In addition to Si-based powder, carbon materials coating the surface of Si-based powder, any polymer materials containing carbon atoms, and SiC not intentionally included, Si-containing granules may also contain other components. Examples of such other components include SiO2.

[0129] Manufacturing method of negative electrode material powder for lithium-ion batteries

[0130] The method for manufacturing the negative electrode material powder for lithium-ion batteries in this embodiment is not particularly limited, but may include, for example, the following steps in sequence.

[0131] Step 1: Preparation of primary particles containing Si phase and SiX compound phase.

[0132] Step 2: The process of wet mixing the primary particles containing Si phase and SiX compound phase with a polymer material containing carbon atoms to obtain a slurry mixture.

[0133] Step 3: The process of spray drying the above slurry mixture.

[0134] Step 4: The process of heat-treating the mixture after spray drying.

[0135] The following sections will explain each process in turn.

[0136] <Step 1: Preparation of Primary Particles>

[0137] Step 1 is the process of preparing primary particles containing Si phase and SiX compound phase.

[0138] Specifically, each raw material is measured in a manner that results in the desired composition, and melted using a melting mechanism such as an electric arc furnace, a high-frequency induction furnace, or a heating furnace. The resulting alloy melt is then rapidly cooled, for example, using an atomization method, thereby obtaining alloy particles composed of the Si phase and the SiX compound phase, which are the rapidly cooled metals.

[0139] When Si-based powder contains SnCu compound phase and AlCu compound phase in addition to Si phase and SiX compound phase, raw materials containing Sn, Cu and Al can be used as raw materials in addition to Si and X. In this way, alloy particles in which SnCu compound phase and AlCu compound phase are dispersed in Si phase and SiX compound phase can also be obtained.

[0140] If the average primary particle size of the alloy particles obtained above is large, they can be pulverized as needed to produce Si-based powder with a small average primary particle size. On the other hand, in order to ensure that the average primary particle size of the alloy particles is not less than 0.1 μm, for example, the particle size can be measured in real time while sampling during pulverization, thereby obtaining the specified particle size.

[0141] Alternatively, metal particles composed of the Si phase, alloy particles composed of the SiX compound phase, alloy particles composed of any SnCu compound phase, and alloy particles composed of any AlCu compound phase can be obtained separately and then mixed to obtain Si-based powder as primary particles containing the desired Si phase and SiX compound phase.

[0142] In the atomization method, molten alloy discharged from a spray chamber and flowing continuously (in rod-like shapes) downwards is sprayed with a high-pressure gas, such as N2, Ar, or He, at a pressure of 1 MPa to 10 MPa, which pulverizes and cools the molten liquid. The cooled molten liquid, in a semi-molten state, falls freely within the spray chamber, gradually approaching a spherical shape, resulting in powdered particles. Alternatively, from the viewpoint of improving cooling efficiency, high-pressure water can be sprayed instead of gas.

[0143] Alternatively, depending on the circumstances, a roller quenching method can be used instead of atomization to obtain foil-like particles.

[0144] The particles obtained above are then crushed as needed.

[0145] Grinding can be performed using appropriate methods such as ball mills, bead mills, disc mills, coffee grinders, and mortar and pestle grinders. The grinding conditions should be adjusted to achieve the desired average primary particle size.

[0146] When primary particles containing Si phase and SiX compound phase also contain SnCu compound phase and AlCu compound phase, after obtaining particles containing each phase independently and then mixing them, the particles can be pulverized separately before mixing, or they can be pulverized together after mixing.

[0147] The pulverization process can be either wet or dry. In the case of wet pulverization, solvent removal, solvent replacement, and drying can be performed. Furthermore, by changing the pulverization method and conditions, the average primary particle size of the primary particles containing the Si phase and SiX compound phase can be controlled. Additionally, by taking samples and measuring the particle size in real time during pulverization with an average primary particle size of not less than 0.1 μm, the specified particle size can be obtained.

[0148] <Step 2: Step to obtain the slurry mixture>

[0149] Step 2 is a process of wet mixing the primary particles containing Si phase and SiX compound phase obtained in step 1 with a polymer material containing carbon atoms to obtain a slurry mixture.

[0150] Primary particles containing Si phase and SiX compound phase are wet-mixed with a polymer material containing carbon atoms. Following step 3, the surface of the primary particles is coated with the polymer material, which acts as a binder, forming secondary particles that bond the primary particles together. Then, by further carbonizing the polymer material obtained in step 4, Si-containing granules are obtained where the surface of the Si-based powder is coated with carbon material and the Si-based powder is bonded by the carbon material.

[0151] Examples of the aforementioned carbon-containing polymer materials include, for instance, phenolic resins, polyvinylidene fluoride resins, polyethylene resins, polypropylene resins, polyvinyl alcohol resins, polystyrene resins, furan resins, cellulose resins, epoxy resins, polyvinyl chloride, polymethyl methacrylate resins, asphalt, coke, biological waste, polyfurfuryl alcohol resins, polyimide resins, and any combination thereof.

[0152] There is no particular limitation on the solvent used when wet-mixing the primary particles containing the Si phase and SiX compound phase obtained in step 1 with the polymer material containing carbon atoms. It should be noted that when wet pulverization is used to obtain the primary particles containing the Si phase and SiX compound phase in step 1, the pulverized particles can be fed into step 2 without removing the solvent used during pulverization, to which the polymer material containing carbon atoms is further added, thereby obtaining a slurry.

[0153] Examples of solvents mentioned above include ethanol, N-methyl-2-pyrrolidone, isopropanol, cyclohexane, and toluene.

[0154] The mixing ratio of primary particles containing Si phase and polymer material containing carbon atoms is determined such that the carbon coating parameter A in the resulting Si-based particles exceeds 15, preferably exceeds 48.

[0155] That is, the appropriate mixing ratio of the polymer material containing carbon atoms varies depending on the average primary particle size of the primary particles containing the Si phase and the SiX compound phase.

[0156] When using a carbon-containing polymer material, such as phenolic resin, the proportion of phenolic resin relative to 100 parts by mass of the total Si-based powder contained in the resulting slurry mixture 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. From the viewpoint of fully coating the surface of the Si-based powder, the above proportion is preferably 1 part by mass or more, more preferably 5 parts by mass or more, and even more preferably 10 parts by mass or more. Furthermore, from the viewpoint of obtaining high capacity, the above proportion 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.

[0157] The polymer material containing carbon atoms is partially or completely carbonized by heat treatment in step 4 described later, thus producing a carbon material.

[0158] The average primary particle size of the Si-based powder and the mixing ratio of the Si-based powder and the polymer material containing carbon atoms are determined in a way that makes the carbon coating parameter A of the obtained Si-based powder exceed 15.

[0159] Here, the above mixing ratio can be determined based on the value of the carbon coating parameter B, expressed in the following formula.

[0160] Carbon coating parameter B = 58.1 × average primary particle size (μm) + 1.1 × binder addition amount (mass%) + 0.6 × binder residual carbon content (mass%)

[0161] In carbon coating parameter B, the average primary particle size (μm) refers to the average primary particle size of the Si-based powder. The binder addition amount refers to the content (mass%) of the carbon-containing polymer material in the final Si-containing granules. The binder residual carbon rate refers to the proportion (mass%) of the carbon content in the final Si-containing granules that constitutes the carbon-containing polymer material. That is, assuming that the heat treatment in step 4 described later is not performed, and the surface of the Si-based powder is not coated with carbon material, the aforementioned binder residual carbon rate is 100 (mass%).

[0162] In carbon coating parameter B, the coefficients for the average primary particle size of Si-based powder (58.1), binder addition amount (1.1), and binder residual carbon rate (0.6) are all values ​​derived experimentally.

[0163] From the viewpoint of safety and water resistance, the value of the carbon coating parameter B is preferably 15 or higher, more preferably 35 or higher. Furthermore, from the viewpoint of cycling characteristics, it is preferably 48 or higher, more preferably 55 or higher. There is no particular upper limit to the carbon coating parameter B, and it is typically 200 or lower.

[0164] <Step 3: Spray drying of the slurry mixture>

[0165] Step 3 is a process of spray drying the slurry mixture obtained in step 2, thereby obtaining a granulated body of secondary particles formed by the bonding of primary particles whose surfaces are coated with a polymer material containing carbon atoms.

[0166] Spray drying can be performed using methods that are already known, such as spray drying.

[0167] Spray drying is a method in which the slurry is made into fine droplets and dried instantly with hot air to remove the dispersion medium. This process granulates the primary particles containing the Si phase and SiX compound phase into granules by binding them together with a binder.

[0168] The particle size of the secondary particles can be controlled by adjusting the concentration of solid components in the slurry and the pressure during drying.

[0169] Through steps 2 and 3, the surface of the Si-based powder, which consists of primary particles, is extensively and homogeneously coated with a polymer material containing carbon atoms. Then, step 4 is performed, whereby at least a portion of the aforementioned polymer material containing carbon atoms is carbonized while maintaining the aforementioned coating state. As a result, direct contact between the Si phase and the SiX compound phase and the electrolyte and moisture is suppressed, thus achieving the desired effects of the present invention. Furthermore, a good conductive path is ensured, thereby achieving better battery characteristics.

[0170] <Step 4: Heat treatment of the spray-dried mixture>

[0171] Step 4 is a heat treatment process for the mixture after spray drying in Step 3. This allows at least a portion of the carbon-containing polymer material coated on the surface of the Si-based powder in Step 3 to be carbonized.

[0172] The heat treatment conditions are not particularly limited, but a heating temperature of 400-1100°C is preferred, more preferably 600-1000°C, and even more preferably 700-950°C. From the viewpoint of promoting carbonization and ensuring conductive pathways, the heating temperature is preferably 400°C or higher, more preferably 600°C or higher, and even more preferably 700°C or higher. Furthermore, from the viewpoint of suppressing the formation of undesirable 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.

[0173] The heat treatment time is not particularly limited, but is preferably 0.1 to 10 hours, more preferably 0.5 to 6 hours, and even more preferably 1 to 4 hours. From the viewpoint of promoting carbonization and carbonizing the polymer material, the heating time is preferably 0.1 hours or more, more preferably 0.5 hours or more, and even more preferably 1 hour or more. Furthermore, from an industrially feasible perspective, the heating time is preferably 10 hours or less, more preferably 6 hours or less, and even more preferably 4 hours or less.

[0174] Regarding the heating temperature and heating time of heat treatment, it can be seen that by making the following heat treatment parameter C meet a specific range, Si-containing granules with good battery characteristics, in addition to safety and water resistance, can be obtained.

[0175] Heat treatment parameter C = -0.15 × heating temperature (°C) + 9.51 × 10 -5 × [Heating temperature (°C)] 2 +0.27 × heating time (hours)

[0176] The heat treatment parameter C is preferably less than -15, more preferably less than -20, and even more preferably less than -25. Furthermore, the lower limit is not particularly limited and is generally greater than -40.

[0177] The gaseous environment for heat treatment is preferably a nitrogen environment or an argon environment.

[0178] The preferred pressure for heat treatment is atmospheric pressure.

[0179] There are no particular limitations on the heat treatment method; examples include heat treatment using a rotary kiln and heat treatment using a shuttle kiln. However, from the viewpoint of being able to uniformly heat treat the powder, heat treatment using a rotary kiln is preferred.

[0180] Lithium-ion batteries

[0181] <negative electrode>

[0182] In lithium-ion batteries, it is preferable to use a negative electrode that employs the negative electrode material powder for lithium-ion batteries according to this embodiment.

[0183] The negative electrode in this 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 lithium-ion batteries of this embodiment, which functions as a negative electrode active material.

[0184] The aforementioned conductive substrate functions as a current collector. Examples of materials for this substrate include Cu, Cu alloys, Ni, Ni alloys, Fe, and Fe-based alloys, with Cu and Cu alloys being preferred.

[0185] Examples of specific conductive substrate forms include foil and plate shapes. Among these, foil is preferred from the perspective of reducing the size of the battery and increasing the degree of freedom in shape.

[0186] Materials used as adhesives in forming conductive films include, for example, polyvinylidene fluoride (PVdF) resin, polytetrafluoroethylene (PTFE) and other fluorinated resins, polyvinyl alcohol resin, polyimide resin, polyamide resin, polyamide-imide resin, styrene-butadiene rubber (SBR), and polyacrylic acid. One or more of these can be used. Among these, polyimide resin is particularly preferred from the viewpoints of mechanical strength, resistance to volume expansion of the negative electrode active material, and inhibition of peeling from the conductive substrate.

[0187] Conductive films can contain conductive additives as needed. The presence of conductive additives makes it easier to ensure the conductive path of electrons.

[0188] The conductive additive can be a conventionally known conductive additive, such as carbon or metals, which are conductive additives that do not undergo volume change during charging and discharging, or whose volume change is small and whose properties do not deteriorate due to charging and discharging.

[0189] The shape of the carbon is not particularly limited, and examples include particulate carbon, fibrous carbon, and flat carbon. From the viewpoint of forming a conductive network between Si-containing particles, at least one of particulate carbon and fibrous carbon is preferred, and from the viewpoint of further improving cycle performance, a combination of particulate carbon and fibrous carbon is more preferred.

[0190] There is no particular limitation on the type of carbon used; examples include carbon black such as Ketjen black, acetylene black, and furnace black, as well as graphite, carbon nanotubes, carbon nanofibers, fullerenes, graphene, and graphene oxide. Among these, carbon black, graphite, carbon nanotubes, and fullerenes are preferred, with Ketjen black and acetylene black being even more preferred. Only one type of carbon may be used, or two or more may be used in combination.

[0191] 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.

[0192] Examples of fibrous carbon include carbon nanotubes (CNTs) and carbon nanofibers (CNFs). Among carbon nanotubes, either single-walled carbon nanotubes (SWCNTs) or multi-walled carbon nanotubes (MWCNTs) can be used.

[0193] Metals used as conductive additives include, for example, Ni, Cr, and SUS (stainless steel) alloys.

[0194] The conductive film can contain aggregate as needed. With aggregate, it is easier to suppress the expansion and contraction of the negative electrode during charging and discharging, and to suppress the disintegration of the negative electrode, thus further improving cycle characteristics.

[0195] The negative electrode in this embodiment can be manufactured as follows: by adding a necessary amount of negative electrode active material and conductive additives and aggregates as needed to a binder dissolved in a suitable solvent, gelatinizing it, coating it on the surface of a conductive substrate and drying it, and performing compaction, heat treatment, etc. as needed.

[0196] When using the negative electrode in this embodiment to construct a lithium-ion battery, there are no particular limitations on the positive electrode, electrolyte, separator, etc., which are basic components of the battery other than the negative electrode, and conventionally known materials can be used.

[0197] <Positive electrode, electrolyte, etc.>

[0198] As the aforementioned positive electrode, an example is a positive electrode in which a layer containing positive electrode active materials such as LiCoO2, LiNiO2, LiFePO4, and LiMnO2 is formed on the surface of a current collector such as aluminum foil.

[0199] Examples of electrolytes include electrolytes in which lithium salts are dissolved in a non-aqueous solvent. Alternatively, substances in which lithium salts are dissolved in a polymer, or polymer solid electrolytes impregnated with the aforementioned electrolyte, can also be used.

[0200] Examples of non-aqueous solvents include ethylene carbonate, propylene carbonate, butyl carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate. They may contain one or more of these solvents.

[0201] Specifically, the lithium salt may include, for example, LiPF6, LiBF4, LiClO4, LiCF3SO3, and LiAsF6. It may contain one or more of these.

[0202] In addition, other components of a battery include separators, cans (battery casings), gaskets, etc. However, as long as they are materials commonly used in lithium-ion batteries, any of these materials can be appropriately combined to form a battery.

[0203] It should be noted that there are no special restrictions on the shape of the battery; it can be any shape, such as cylindrical, square, or coin-shaped, and can be selected appropriately according to its specific purpose.

[0204] Example

[0205] The present invention will be described in more detail below using examples.

[0206] Examples 1-79 and Comparative Examples 1-2

[0207] 1. Preparation of Si-based powders

[0208] Each raw material was weighed in the manner specified in Table 1, with Si and optionally Sn, Cu, Al, Fe, Ti, Cr, Mn, Co, Ni, Zr, B, and P in the proportions (mass%) listed. The mixture was then heated and melted in a high-frequency induction furnace to produce an alloy melt. Alloy particles containing SiX compound phases dispersed in the Si phase, or alloy particles containing SiX compound phases and SnCu compound phases or AlCu compound phases dispersed in the Si phase, were obtained from the alloy melt using a gas atomization method.

[0209] The ambient gas used during alloy melt production and gas atomization is argon. In addition, during gas atomization, high-pressure (4MPa) argon gas is sprayed onto the alloy melt, which falls in a rod shape in the spray chamber.

[0210] The obtained particles were mechanically finely pulverized using a wet bead mill to obtain a slurry containing Si-based powder. Ethanol was used as the solvent.

[0211] The composition of each phase constituting the obtained Si-based powder is shown in Table 2, "Specific Ratio (mass %)". It should be noted that in Tables 1 and 2, "-" indicates that the phase is not present.

[0212] 2. Preparation of slurry mixture

[0213] The slurry containing Si-based powder obtained above is further modified by adding a methyl phenolic resin as a polymer material containing carbon atoms to obtain a slurry mixture.

[0214] In the slurry mixture, the amount of methyl phenolic resin added is 1 to 100 parts by weight relative to 100 parts by weight of Si-based powder. Furthermore, the solid content concentration of the slurry mixture is 40% by weight.

[0215] 3. Spray drying of slurry mixture

[0216] The slurry mixture obtained above is sprayed and dried by spray drying method, thereby obtaining secondary particles in which Si-based powders coated with methyl phenolic resin are bonded together.

[0217] The spray drying conditions were set as follows: spray temperature: 150℃, spray pressure: 0.3MPa, and supply rate: 1kg / h.

[0218] 4. Heat treatment

[0219] The secondary particles obtained above are placed in a rotary kiln and heat-treated under nitrogen atmosphere at the temperature and time recorded in Table 2 to partially or completely carbonize the methyl phenolic resin, thereby obtaining anode material powder for lithium-ion batteries.

[0220] Table 2 also shows the values ​​of the heat treatment parameter C, expressed by the following formula.

[0221] Evaluation: Si-based powders

[0222] <Average primary particle size>

[0223] For Si-containing granules, the median particle size (D50) obtained from the volume-based particle size distribution of the slurry before granulation, measured using a laser diffraction / scattering particle size distribution measuring device, is taken as the average primary particle size of the Si-based powder. The results are shown in Table 2.

[0224] <Carbon Coating Parameter A>

[0225] By analyzing the Si-containing granules using combustion infrared absorption spectrometry, the carbon content of the Si-based powder, including the total amount of Si-based powder, carbon materials, and any other components, was determined, representing the carbon content relative to the overall Si-containing granules. The results are shown in Table 2.

[0226] In addition, the carbon content and the value of the carbon coating parameter A, which uses the average primary particle size obtained above, are also shown in Table 2.

[0227] Evaluation: Si-containing granules

[0228] <Average secondary particle size>

[0229] For Si-containing granules, the particle shape distribution was measured using an image-based particle size distribution measuring device (Malvern Panalytical, Morphologi series, Morphologi4), and the average secondary particle size was determined accordingly. The results are shown in Table 3.

[0230] Aspect Ratio

[0231] For Si-containing granules, SEM observation was performed at 400x magnification. Based on the obtained images, for 10 Si-containing granules, the maximum diameter D and the diameter D' perpendicular to it were measured respectively. The average value expressed by D / D' was taken as the aspect ratio. The results are shown in Table 3.

[0232] Carbon Coverage

[0233] For the Si-containing granulated material, the surface of the Si-containing granulated material was analyzed using X-ray photoelectron spectroscopy (XPS). The proportion of carbon atoms (C) in the obtained spectrum was determined, and the carbon coating rate (mass %) of the surface of the Si-containing granulated material was determined. The results are shown in Table 3.

[0234] 〈SiC content ratio〉

[0235] The Si-containing granulated material was subjected to powder X-ray diffraction (XRD) measurement, and the ratio of the area of the peak from SiC to the total peak area in the obtained XRD pattern was determined to obtain the SiC content ratio. The results are shown in Table 3.

[0236] 《Evaluation: Safety》

[0237] For the Si-containing granulated material, as a test for Class II dangerous substances under the Fire Service Act, a small gas flame ignition test was conducted.

[0238] Those that did not ignite within 10 seconds after approaching the small gas flame were regarded as non-dangerous and qualified, marked as "○" in Table 3, and those that ignited within 10 seconds were regarded as dangerous and unqualified, marked as "×" in Table 3.

[0239] 《Evaluation: Water resistance》

[0240] 1 g of the Si-containing granulated material was placed in 13 mL of pure water, and the total amount of hydrogen generated from the start of measurement to 336 hours was measured using a sensor gas chromatograph.

[0241] Those with a hydrogen generation amount of 100 mass ppm or less were qualified and marked as "○" in Table 3, and those exceeding 100 mass ppm were unqualified and marked as "×" in Table 3.

[0242] 《Evaluation: Battery characteristics》

[0243] 〈Fabrication of coin-type battery for charge-discharge test〉

[0244] 100 parts by mass of a negative electrode active material for a lithium ion battery as the Si-containing granulated material, 5 parts by mass of acetylene black (manufactured by Denka) as a conductive aid, and 15 parts by mass of polyimide (a thermoplastic resin) as a binder were mixed and mixed with N-methyl-2-pyrrolidone (NMP) as a solvent to prepare a paste containing a negative electrode material.

[0245] The above paste was applied to the surface of a stainless steel (SUS) 316L foil (thickness 20 μm) as a current collector using a doctor blade method, dried, densified by roll pressing, and punched into a disc with a diameter of 11 mm to fabricate a test electrode.

[0246] Next, a Li foil (500 μm thick) was punched into a shape roughly the same as the experimental electrode described above, and used as the counter electrode.

[0247] The test electrode is housed in the positive electrode container, and the counter electrode is housed in the negative electrode container. A polyolefin-based microporous membrane is placed between the test electrode and the counter electrode. Furthermore, while the test electrode should ideally 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.

[0248] A non-aqueous electrolyte containing LiPF6 at a concentration of 1 mol / L is injected into both the positive and negative electrode containers. The negative and positive electrode containers are then riveted together to create a coin-shaped battery for charge-discharge testing.

[0249] <Charge and Discharge Test>

[0250] For the coin-shaped battery used in the charge-discharge test, a constant current charge-discharge cycle of 0.2 mA was performed. The initial charge capacity or initial discharge capacity was obtained by dividing the capacity (mAh) used for Li insertion or discharge by the mass of active material (g). The ratio of the initial discharge capacity to the initial charge capacity was then calculated as the initial coulombic efficiency. The results are shown in Table 3.

[0251] Furthermore, based on the relative proportions of the Si phase, SiX compound phase, SnCu compound phase, and AlCu compound phase in the Si-containing granules, the theoretical capacity of each negative electrode material (each negative electrode active material) was calculated. Then, the initial discharge capacity relative to the above theoretical capacity was determined as the utilization rate (active material utilization rate, %) relative to the theoretical capacity of the negative electrode active material. The results are shown in Table 3.

[0252] After the second cycle, a charge-discharge test was performed at a rate of 1 / 5C, and the test was continued until 50 cycles. Here, regarding the C rate, the amount of electricity required to discharge the electrode (charge and discharge) is defined as the current value for 1 hour of (charge and discharge) discharge. Therefore, the above-mentioned 1 / 5C rate refers to charging or discharging for 5 hours.

[0253] The discharge capacity at the 50th cycle relative to the initial discharge capacity at the first cycle, i.e., the discharge capacity maintenance rate, was evaluated as the cycle maintenance rate (%). The results are shown in Table 3.

[0254]

[0255]

[0256]

[0257] Of the above results, especially the comparison with Comparative Examples 1 and 2, it can be seen that the negative electrode material powder for lithium-ion batteries of this embodiment is not easily ignited, and has high safety and good water resistance. This is believed to be because the Si-based powder, as a primary particle, has a certain or greater size, and its surface is appropriately coated with carbon material, thereby preventing other phases constituting the Si-based powder, such as the Si phase, SiX compound phase, any SnCu compound phase, AlCu compound phase, etc., from contacting the electrolyte and oxygen with a high probability.

[0258] In addition to the above, the results of Examples 73-75 show that by making the value of the carbon coating parameter A exceed 48, the battery characteristics, especially the cycle characteristics, become good.

[0259] Furthermore, the results of Examples 78 and 79 show that by keeping the upper limit of the average primary particle size of the Si-based powder and the upper limit of the average secondary particle size of the Si-containing granules below a certain value, the cycling characteristics also become good. The results of Example 72 show that the aspect ratio of the Si-containing granules also contributes to the cycling characteristics. The results of Example 77 show that the cycling characteristics are improved by increasing the SnCu phase in the Si-based powder.

[0260] Furthermore, based on the results of Examples 67-69 and Example 71, it is evident that if the heat treatment temperature is increased to a higher level, and the value of the heat treatment parameter C becomes ~15 or higher, the proportion of SiC contained in the Si-containing granules increases, resulting in a decrease in the utilization rate of the active material in the battery characteristics. On the other hand, the results of Example 70 show that when the heat treatment temperature is excessively low, sufficient carbonization cannot be achieved, leading to a decrease in the initial coulombic efficiency. Thus, by performing appropriate heat treatment, the proportion of SiC can be controlled.

[0261] In addition to the above, the results of Example 76 show that when the proportion of Si phase in the Si-based powder is low, the initial coulombic efficiency decreases.

[0262] The negative electrode material powder for lithium-ion batteries of this embodiment has been described in detail above. However, the present invention is not limited to the above embodiments and examples, and various changes can be made without departing from its spirit.

[0263] Although the present invention has been described in detail with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention. This application is based on Japanese Patent Application No. 2023-219678, filed on December 26, 2023, the contents of which are incorporated herein by reference.

Claims

1. A negative electrode material powder for lithium-ion batteries, comprising Si-containing granules, characterized in that... The Si-containing granules comprise Si-based powder and carbon materials. The Si-based powder consists of primary particles containing both a Si phase and a 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 size of the Si-based powder is greater than 0.1 μm. The average secondary particle size of the Si-containing granules is greater than 2 μm. The surface of the Si-based powder is coated with and bonded to the carbon material. The carbon coating parameter A of the Si-based powder, expressed by the following formula, exceeds 15: The carbon coating parameter A = 58.1 × average primary particle size (μm) + 5.6 × carbon content (mass%).

2. The negative electrode material powder for lithium-ion batteries according to claim 1, characterized in that, The SiC content in the Si-containing granules is less than 15%.

3. The negative electrode material powder for lithium-ion batteries according to claim 1 or 2, characterized in that, The carbon coating parameter A exceeds 48.

4. The negative electrode material powder for lithium-ion batteries according to claim 1 or 2, characterized in that, The average primary particle size of the Si-based powder is less than 5.0 μm.

5. The negative electrode material powder for lithium-ion batteries according to claim 1 or 2, characterized in that, The average secondary particle size of the Si-containing granules is less than 20 μm.

6. The negative electrode material powder for lithium-ion batteries according to claim 1 or 2, characterized in that, The aspect ratio of the Si-containing granules is 1.0 to 1.

8.

7. The negative electrode material powder for lithium-ion batteries according to claim 1 or 2, characterized in that, The Si-based powder further comprises primary particles selected from at least one group consisting of SnCu compound phases and AlCu compound phases. The SnCu compound phase comprises Sn and Cu. The AlCu compound phase contains Al and Cu. The Si phase in the Si-based powder contains more than 30% by mass.

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

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