Negative electrode material powder for lithium ion battery

Abstract

The present invention pertains to a negative electrode material powder for a lithium ion battery, the negative electrode material powder comprising a Si phase, a Si compound phase, and a Sn compound phase, and containing Si-containing granulated bodies, the Si-containing granulated bodies being obtained by aggregating the primary particles and optionally containing a binder in the range of 0-2.0 mass%, the primary particles constituting the Si-containing granulated bodies having an average particle diameter (d50) in the range of 0.1-10.0 [mu] m, the average particle diameter (d50) of the primary particles constituting the Si-containing granulated bodies being 0.1-10.0 [mu] m, and the average particle diameter (d50) of the secondary particles constituting the Si-containing granulated bodies being 0.1-10.0 [mu] m. The average particle diameter (d50) of the primary particles is smaller than 1 / 3 of the average particle diameter (d50) of the Si-containing granulated body and larger than 1 / 200.

Description

Technical Field

[0001] The present invention relates to a negative electrode material powder for a lithium ion battery. Background Art

[0002] Lithium ion batteries have the advantages of high capacitance, high voltage, and being able to be miniaturized, and are widely used as power sources for mobile phones or laptop computers, etc. In addition, in recent years, they have been highly expected as power sources for power applications such as electric vehicles or hybrid vehicles, and their development is being actively carried out.

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

[0004] Conventionally, lithium cobaltate (LiCoO 2 ) has generally been used as the active material on the positive electrode side. In addition, graphite has been widely used as the negative electrode active material. However, the theoretical capacity of the graphite as the negative electrode active material is only 372 mAh / g, and further high capacity is expected.

[0005] As an alternative to carbon-based electrode materials such as the above-mentioned graphite, metal materials such as Si (the theoretical capacity of Si is 4198 mAh / g) that can be expected to have high capacity are being studied (for example, refer to the following Patent Document 1).

[0006] Prior Art Documents

[0007] Patent Documents

[0008] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2020-126835 Summary of the Invention

[0009] Problems to be Solved by the Invention

[0010] Since Si absorbs Li through an alloying reaction with Li, large volume expansion and contraction occur with the absorption and release of Li. Therefore, if Si is used as the negative electrode active material, the particles of Si will crack or peel off from the current collector during charge and discharge, and the capacity retention characteristics during repeated charge and discharge, that is, the cycle characteristics, will deteriorate.

[0011] As a method for solving such deterioration of the cycle characteristics, it is also considered to use a Si-containing granulated body obtained by granulating nanoparticles containing a Si phase as the negative electrode material powder.

[0012] However, to form such granulated particles, a binder is required to bond the respective particles. Since the binder does not participate in the charge and discharge of Li, it reduces the charge and discharge capacity. Therefore, there is still room for improvement in enhancing battery characteristics considering initial characteristics of the battery such as initial discharge capacity and initial Coulomb efficiency, as well as cycle characteristics.

[0013] Based on the above circumstances, an object of the present invention is to provide a negative electrode material powder for a lithium ion battery that can suppress the amount of binder contained in the Si-containing granulated particles and can improve battery characteristics considering initial characteristics and cycle characteristics.

[0014] Technical means for solving the problem

[0015] In order to solve the above problems, the present inventors repeatedly conducted in-depth research. As a result, it was found that by specifying the average particle diameter of the primary particles constituting the Si-containing granulated particles, the amount of binder contained in the Si-containing granulated particles can be suppressed. The present invention has been completed based on this finding.

[0016] Moreover, the present invention provides a negative electrode material powder for a lithium ion battery, which has an Si phase, an Si compound phase, and an Sn compound phase, wherein

[0017] the negative electrode material powder contains Si-containing granulated particles,

[0018] the Si-containing granulated particles are granulated particles in which primary particles of the Si phase, the Si compound phase, and the Sn compound phase are aggregated and optionally contain a binder in the range of 0 to 2.0% by mass,

[0019] the average particle diameter (d50) of the primary particles constituting the Si-containing granulated particles is in the range of 0.1 to 10.0 μm,

[0020] the average particle diameter (d50) of the primary particles is smaller than 1 / 3 of the average particle diameter (d50) of the Si-containing granulated particles,

[0021] the average particle diameter (d50) of the primary particles is larger than 1 / 200 of the average particle diameter (d50) of the Si-containing granulated particles.

[0022] In the negative electrode material powder for a lithium ion battery thus specified, a space that allows the expansion of the Si phase is easily formed around the primary particles of the Si phase that expand as Li is absorbed. This space serves as a buffer region against the expansion of the Si phase, can suppress the collapse of the Si-containing granulated particles, and can improve cycle characteristics.

[0023] In order to form Si-containing granulates, a binder for bonding the respective particles is required. According to the research by the present inventors, if the average particle diameter (d50) of the primary particles constituting the Si-containing granulates is set within the range of 0.1 to 10.0 μm, and the average particle diameter (d50) of the same primary particles is smaller than 1 / 3 of the average particle diameter (d50) of the Si-containing granulates and larger than 1 / 200 of the average particle diameter (d50) of the Si-containing granulates, the reduction in cycle characteristics is suppressed even when the amount of the binder contained in the Si-containing granulates is suppressed to 0 to 2.0 mass%. As a result, the battery characteristics considering the initial characteristics and the cycle characteristics can be improved.

[0024] Herein, the Si compound phase can be set to be a SiX compound phase containing Si and element X, and the Sn compound phase can be set to be a SnY compound phase containing Sn and element Y. Herein, element X is one or more elements selected from the group consisting of Fe, Ni, Cr, Zr, and Ti, and element Y is one or more elements selected from the group consisting of Cu, Fe, Ni, Cr, Co, Mn, Zr, and Ti.

[0025] Moreover, when the content ratios of the Si phase, the SiX compound phase, and the SnY compound phase are represented by the following formula (1), the negative electrode material powder for a lithium ion battery can be constituted in such a manner that a + b + c = 100, 9.9 ≤ a ≤ 95, 1 ≤ b ≤ 90, and 0.1 ≤ c ≤ 50 are satisfied.

[0026] a[Si] - b[SiX] - c[SnY] … formula (1)

[0027] In the above formula (1), a, b, and c respectively represent the content ratios (mass%) of the Si phase, the SiX compound phase, and the SnY compound phase.

[0028] In this case, considering the balance between the initial characteristics and the cycle characteristics, a, b, and c in the formula (1) can respectively satisfy 29.9 ≤ a ≤ 90, 1 ≤ b ≤ 70, and 0.1 ≤ c ≤ 30.

[0029] In addition, from the viewpoint of improving the cycle characteristics, Cu can be employed as the element Y. In this case, the average particle diameter (d50) of the primary particles can be set within the range of 0.2 to 5.0 μm. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is a schematic view of the negative electrode material powder according to an embodiment of the present invention.

[0031] Figure 2 is an electron micrograph of the negative electrode material powder of the same embodiment.

[0032] Figure 3 (A) to Figure 3 (D) are explanatory diagrams of a method for manufacturing the negative electrode material powder of the same embodiment. Detailed Embodiment

[0033] Next, the negative electrode material powder for a lithium ion battery according to an embodiment of the present invention and a lithium ion battery using this negative electrode material powder as the negative electrode (hereinafter sometimes simply referred to as "battery") will be specifically described.

[0034] 1. Negative Electrode Material Powder

[0035] This negative electrode material powder has an Si phase, an Si compound phase, and an Sn compound phase as inorganic components. Moreover, in this negative electrode material powder, Si and Sn are the main constituent elements of the inorganic components.

[0036] The above Si compound phase preferably contains an SiX compound phase of Si and element X. In addition, the above Sn compound phase preferably contains an SnY compound phase of Sn and element Y. In this case, the main constituent elements of the inorganic components in this negative electrode material powder are Si, Sn, element X, and element Y. Here, element X is one or more elements selected from the group consisting of Fe, Ni, Cr, Zr, and Ti. In addition, element Y is one or more elements selected from the group consisting of Cu, Fe, Ni, Cr, Co, Mn, Zr, and Ti.

[0037] As the above inorganic components, except for inevitable elements, elements other than these main constituent elements (Si, Sn, element X, element Y) are not contained. As inevitable impurity elements, for example, nitrogen (N), sulfur (S), phosphorus (P), etc. are considered. The upper limit of each of the above inevitable impurity elements in this negative electrode material powder is N ≤ 0.10 mass%, S ≤ 0.10 mass%, and P ≤ 0.10 mass%.

[0038] This negative electrode material powder preferably contains an Si phase, an SiX compound phase, and an SnY compound phase in a phase ratio represented by the following formula (1) as its metal structure.

[0039] a[Si] - b[SiX] - c[SnY]... Formula (1)

[0040] In formula (1), a, b, and c (a + b + c = 100) respectively represent the contents (mass%) of the Si phase, the SiX compound phase, and the SnY compound phase. In this example, it is preferably satisfied that 9.9 ≤ a ≤ 95, 1 ≤ b ≤ 90, and 0.1 ≤ c ≤ 50.

[0041] It should be noted that if the proportion in the whole is 5 mass% or less, Sn monomers (Sn phase) that are not compounds may also be contained as impurities.

[0042] The Si phase is a phase mainly containing Si. Here, the meaning of the mainly contained phase is that the content ratio of Si in the Si phase is 99% by mass or more. From the viewpoint of increasing the Li absorption amount, etc., the Si phase is preferably a single phase of Si. Of course, inevitable impurities may also be contained in the Si phase.

[0043] In this negative electrode material powder, the proportion of the Si phase (the value of "a" in formula (1)) is preferably 9.9 to 95% by mass. More preferably, the proportion of the Si phase is 29.9 to 90% by mass. Here, from the viewpoint of obtaining a good initial discharge capacity, the proportion of the Si phase that absorbs Li ions is preferably 9.9% by mass or more, more preferably 10% by mass or more, further preferably 29.9% by mass or more, and even more preferably 30% by mass or more. In addition, from the viewpoint of suppressing the relative deterioration of the cycle characteristics as the proportion of the SiX compound phase decreases, the above proportion is preferably 95% by mass or less, more preferably 90% by mass or less.

[0044] On the one hand, the SiX compound constituting the SiX compound phase lacks Li absorption properties, and the expansion caused by the reaction with Li ions is very small. Therefore, the SiX compound phase plays a role of maintaining the structure of the electrode as a skeleton.

[0045] Properties such as the Li storage property or conductivity of the SiX compound sometimes vary depending on which element is selected as the above element X. Elements such as Fe, Ni, Cr, and Zr as element X are particularly excellent in the expected low expansibility and high conductivity of the SiX compound. In addition, elements X effective for improving the initial Coulomb efficiency are Ni and Ti. Element X effective for improving the discharge rate characteristics is Ti.

[0046] It should be noted that except for the case of being composed of only one compound, the SiX compound phase can also be composed of two or more compounds such as SiFe compound and SiNi compound, for example.

[0047] On the other hand, the theoretical capacity of the SnY compound constituting the SnY compound phase is lower than that of Si and higher than that of the SiX compound. For example, the theoretical capacity of the SnY compound is 150 to 600 mAh / g relative to the theoretical capacity of the SiZr compound (SiX compound) of 100 mAh / g.

[0048] In this example, via the SnY compound phase, it is easy to ensure the diffusion path of Li ions. On the other hand, the degree of expansion caused by the reaction with Li ions is smaller than that of Si or Sn monomers with higher reactivity with Li ions. Therefore, the adverse effect on the cycle characteristics due to the formation of the SnY compound can also be suppressed to a low level.

[0049] In particular, the SnCu compound formed when Cu is selected as element Y has excellent conductivity. In addition, it is effective in improving the cycle characteristics. It should be noted that in this SnY compound phase, in addition to the case where it is composed of only one compound, it may also be composed of two or more compounds.

[0050] As described above, the SiX compound phase and the SnY compound phase play different roles, and the resulting battery characteristics also change according to the ratio of these compound phases. Although the degree of the SnY compound phase is small, it expands more than the SiX compound phase by reacting with Li ions. Therefore, if the ratio of the SnY compound phase is high and the ratio of the SiX compound phase is low, the cycle characteristics deteriorate. On the other hand, if the ratio of the SiX compound phase is high and the ratio of the SnY compound phase is low, the initial discharge capacity becomes low.

[0051] In this example, the ratio of the SiX compound phase (the value of "b" in formula (1)) is preferably 1 to 90% by mass, and the ratio of the SnY compound phase (the value of "c" in formula (1)) is preferably 0.1 to 50% by mass. More preferably, the ratio of the SiX compound phase is 1 to 70% by mass and the ratio of the SnY compound phase is 0.1 to 30% by mass.

[0052] That is, as a combination of a, b, and c in formula (1), for example, it is preferably satisfied that 9.9 ≤ a ≤ 95, 1 ≤ b ≤ 90, and 0.1 ≤ c ≤ 50, and more preferably satisfied that 29.9 ≤ a ≤ 90, 1 ≤ b ≤ 70, and 0.1 ≤ c ≤ 30.

[0053] The content of each main element in the inorganic component suitable for obtaining the constituent phases as described above is as follows. In addition, in the following description, unless otherwise specified, "%" means "% by mass".

[0054] Preferably, it contains Si in the range of 50 to 95%. The more preferable range is 60 to 80%. The further preferable range is 73 to 79%. Here, from the viewpoint of obtaining a good initial discharge capacity, the content of Si is preferably 50% or more, more preferably 60% or more, and further preferably 73% or more. In addition, from the viewpoint of maintaining good cycle characteristics, the content of Si is preferably 95% or less, more preferably 80% or less, and further preferably 79% or less.

[0055] Preferably, it contains element X in the range of 1.0 to 38%. A more preferable range is 5.0 to 30%. A further preferable range is 13 to 23%. Here, from the viewpoint of obtaining good cycle characteristics, the content of element X is preferably 1.0% or more, more preferably 5.0% or more, and further preferably 13% or more. In addition, from the viewpoint of suppressing the decrease in the initial discharge capacity, the content of element X is preferably 38% or less, more preferably 30% or less, and further preferably 23% or less.

[0056] Sn is preferably in the range of 0.7 to 30%. A more preferable range is 1.0 to 10%. A further preferable range is 1.5 to 5.0%. Here, from the viewpoint of suitably obtaining the effect as a Li diffusion path, the content of Sn is preferably 0.7% or more, more preferably 1.0% or more, and further preferably 1.5% or more. In addition, from the viewpoint of suppressing the decrease in cycle characteristics due to excessive expansion of the SnY compound, the content of Sn is preferably 30% or less, more preferably 10% or less, and further preferably 5.0% or less.

[0057] Preferably, it contains element Y in the range of 1.0 to 15%. A more preferable range is 1.5 to 10%. A further preferable range is 1.5 to 4.0%. Here, from the viewpoint of suitably obtaining the effect as a Li diffusion path, the content of element Y is preferably 1.0% or more, more preferably 1.5% or more. In addition, from the viewpoint of suppressing the decrease in cycle characteristics due to excessive expansion of the SnY compound, the content of element Y is preferably 15% or less, more preferably 10% or less, and further preferably 4.0% or less.

[0058] Figure 1 Schematic diagram showing the negative electrode material powder of this example. Figure 2 It is an electron micrograph of the negative electrode material powder.

[0059] In Figure 1 1 is the negative electrode material powder, and 2 is a Si-containing granule formed by aggregating a plurality of primary particles 3. The primary particle 3 in this example is a particle obtained by separately pulverizing the Si phase, the Si compound phase, and the Sn compound phase into particle form (primary particles). Here, the above Si compound phase is preferably a SiX compound phase, and the Sn compound phase is preferably a SnY compound phase. In addition, the primary particle 3 is more preferably a particle obtained by separately pulverizing the Si phase, the Si compound phase, and the Sn compound phase into particle form, and further preferably a particle obtained by separately pulverizing the Si phase, the SiX compound phase, and the SnY compound phase into particle form.

[0060] The Si-containing granule 2 is a granule formed by aggregation of Si particles, Si compound particles, and Sn compound particles as primary particles. The Si compound particles are preferably SiX compound particles 3b, and the Sn compound particles are preferably SnY compound particles 3c. Additionally, the Si-containing granule 2 is more preferably a granule formed by aggregation of Si particles 3a, SiX compound particles 3b, and SnY compound particles 3c.

[0061] In Figure 2 the shown Si-containing granule, the dark part close to black corresponds to the Si particles 3a, the gray part corresponds to the SiX compound particles 3b, and the white part corresponds to the SnY compound particles 3c.

[0062] The average particle size (median particle size d50) of the primary particles 3 is in the range of 0.1 to 10.0 μm. Since the primary particles expand and contract in volume with the absorption and release of Li, when the particle size is large, the volume change becomes large, and the collapse of the electrode is likely to be aggravated. Therefore, in this example, the upper limit of the average particle size (d50) is specified as 10.0 μm. On the other hand, when the particle size is too small, the initial Coulomb efficiency decreases due to the increase in specific surface area, or the charge-discharge capacity decreases due to the increase in the amount of binder used to maintain the shape of the granule. Therefore, in this example, the lower limit of the average particle size (d50) is specified as 0.1 μm. A more preferable range of the average particle size (median particle size d50) of the primary particles 3 is 0.2 to 5.0 μm, and further preferably 0.2 to 3.0 μm. Additionally, regarding the average particle size of the above primary particles 3, as long as the average particle size of the whole primary particles constituting the Si-containing granule 2 is within the above range, it is acceptable, but the average particle size of the primary particles of Si particles, Si compound particles, and Sn compound particles is preferably within the above range.

[0063] It should be noted that the average particle size (d50) in this specification refers to the median particle size based on volume.

[0064] On the other hand, regarding the average particle size (d50) of the Si-containing granule 2 formed by aggregation of multiple primary particles 3, it is preferably in the range of 3 to 1000 μm, and more preferably 10 to 100 μm. Here, from the viewpoint of uniform coating when the paste-like electrode material is coated on the substrate, the above average particle size is preferably 1000 μm or less, and more preferably 100 μm or less. Additionally, from the viewpoint of processability, the above average particle size is preferably 3 μm or more, and more preferably 10 μm or more.

[0065] In addition, in this example, the average particle diameter (d50) of the primary particles 3 constituting the Si-containing granule 2 is defined to be smaller than 1 / 3 of the average particle diameter (d50) of the Si-containing granule 2. Thereby, the Si-containing granule 2 with an arbitrary component as the binder for bonding the primary particles to each other can be produced, the reduction in cycle characteristics can be suppressed, and the initial Coulomb efficiency and the initial discharge capacity can be improved at the same time. The average particle diameter of the primary particles 3 only needs to be smaller than 1 / 3 of the average particle diameter of the Si-containing granule 2, preferably 1 / 5 or less, and more preferably 1 / 10 or less.

[0066] Here, in order to further improve the cycle characteristics, the Si-containing granule 2 may contain a binder. Even in this case, the amount can be set to be less than that in the past, that is, 2.0% by mass or less based on the total mass of the Si-containing granule. Therefore, the reduction in charge-discharge capacity caused by the addition of the binder can be suppressed.

[0067] On the other hand, if the particle diameter of the granulated powder (Si-containing granule) is relatively too large, the granulated powder may aggregate in the slurry. Therefore, in this example, the average particle diameter (d50) of the primary particles 3 is defined to be larger than 1 / 200 of the average particle diameter (d50) of the Si-containing granule 2. In other words, the average particle diameter (d50) of the Si-containing granule 2 is defined to be smaller than 200 times the average particle diameter (d50) of the primary particles 3. The average particle diameter of the primary particles 3 only needs to be larger than 1 / 200 of the average particle diameter of the Si-containing granule 2, preferably 1 / 100 or more, and more preferably 1 / 50 or more.

[0068] Next, the manufacturing method of this negative electrode material powder will be described.

[0069] Each raw material is measured in an amount to achieve a specified chemical composition, and the alloy melt obtained by melting the measured raw materials and the like using a melting unit such as an electric arc furnace, a high-frequency induction furnace, or a heating furnace is quenched using an atomization method to obtain an Si alloy as a quenched alloy.

[0070] In the atomization method, a gas such as N 2 Ar, or He is sprayed onto the alloy melt that has flowed out into the spray chamber and continuously (in a rod shape) flows downward at a high pressure (for example, 1 to 10 MPa), so that the melt is cooled while being pulverized. The cooled melt becomes approximately spherical while freely falling in the spray chamber in a semi-molten state, and Si alloy particles 10 as shown in (A) are obtained. In the structure of the Si alloy particles 10 shown in the same figure, an Si phase, an SiX compound phase, and an SnY compound phase are formed, but the present invention is not limited thereto. As long as an Si phase, an Si compound phase, and an Sn compound phase are formed. Figure 3

[0071] ​Note that in the atomization method, from the viewpoint of improving the cooling effect, high-pressure water can also be sprayed instead of gas. In addition, the roll quenching method can sometimes be used instead of the atomization method to obtain a foiled Si alloy.

[0072] Next, the obtained Si alloy particles are wet-milled. As shown in Figure 3 (B), Si particles 3a, SiX compound particles 3b, and SnY compound particles 3c that exist independently as primary particles 3 are obtained.

[0073] As the wet-milling method in this example, a wet-milling method using a bead mill or the like can be adopted. In wet-milling, a solvent is used together with the Si alloy particles to be milled. As the solvent, ethanol, methanol, isopropanol, Naphtesol, etc. can be used.

[0074] If there are large differences in the amounts (proportions) of the Si phase, SiX compound phase, and SnY compound phase in the Si alloy particles 10 to be milled, the phase with a large amount is not milled, and it is easy for the particle sizes of the respective phases to differ. However, as long as the chemical composition of the Si alloy particles is adjusted so that Si, SiX compound, and SnY compound are in the above phase proportions, the average particle size of any primary particle can be easily set within the range of 0.1 to 10.0 μm by the wet-milling method, and the average particle size of the primary particles constituting the Si-containing granulated body can be set within the range of 0.1 to 10.0 μm.

[0075] Note that when manufacturing this negative electrode material powder, the following method can also be adopted instead of the above method of milling the Si alloy particles 10 having three phases inside: directly forming Si particles, SiX compound particles, and SnY compound particles from the melt, milling these particles so that they each have a specified particle size, and then mixing them.

[0076] Next, a binder is added to the slurry containing primary particles obtained as described above, if necessary. Examples of the binder include polyvinylidene fluoride (PVdF), polyvinyl alcohol (PVA), polyvinyl butyral (PVB), sodium polyacrylate (PAANa), ammonium polyacrylate (PAANH 3 ) and the like.

[0077] After that, a granulated body 2 is obtained using a spray drying method. Specifically, the above-adjusted slurry is supplied to a spray drying device while being stirred and sprayed from the tip of the nozzle of the spray drying device. Moreover, in the spray flow, that is, the fine droplets 12 (refer to Figure 3 (C)), the solvent 11 is evaporated (dried) to obtain Figure 3 the Si-containing granulated body 2 shown in (D).

[0078] 2. Battery

[0079] Next, a battery configured with a negative electrode using the negative electrode material powder of the present invention will be described.

[0080] The negative electrode has a conductive substrate and a conductive film laminated on the surface of the conductive substrate. The conductive film contains at least the above-mentioned negative electrode material powder of the present invention in a binder. In addition, if necessary, the conductive film may also contain a conductive aid. In the case of containing a conductive aid, it is easy to ensure an electron conduction path.

[0081] In addition, if necessary, the conductive film may also contain an aggregate. In the case of containing an aggregate, it is easy to suppress the expansion and contraction of the negative electrode during charge and discharge, and it is possible to suppress the collapse of the negative electrode. Therefore, the cycle characteristics can be further improved.

[0082] The above-mentioned conductive substrate functions as a current collector. As its material, for example, Cu, Cu alloy, Ni, Ni alloy, Fe, Fe-based alloy, etc. can be exemplified. Cu and Cu alloy are preferred. In addition, as the form of the specific conductive substrate, foil-like, plate-like, etc. can be exemplified. From the viewpoints of reducing the volume of the battery and improving the shape freedom, etc., foil-like is preferred.

[0083] As the material of the above-mentioned binder, for example, polyvinylidene fluoride (PVdF) resin, fluororesins such as polytetrafluoroethylene, polyvinyl alcohol resin, polyimide resin, polyamide resin, polyamideimide resin, styrene-butadiene rubber (SBR), polyacrylic acid, etc. can be suitably used. One or more of them can be used in combination. Among them, polyimide resin is particularly preferred in the sense that it has strong mechanical strength, can also well withstand the volume expansion of the active material, and can well prevent the conductive film from peeling off from the current collector due to the destruction of the binder.

[0084] As the above-mentioned conductive aid, for example, carbon blacks such as Ketjen black, acetylene black, furnace black, graphite, carbon nanotubes, fullerenes, etc. can be exemplified. One or more of them can also be used in combination. Among them, from the viewpoints of easily ensuring electron conductivity, etc., Ketjen black, acetylene black, etc. can be preferably and suitably used.

[0085] From the viewpoints of improving conductivity, electrode capacity, etc., the content of the above-mentioned conductive aid is preferably in the range of 0 to 30 parts by mass, more preferably in the range of 4 to 13 parts by mass, relative to 100 parts by mass of the negative electrode material powder of the present invention. In addition, from the viewpoints of dispersibility, ease of handling, etc., the average particle diameter (d50) of the above-mentioned conductive aid is preferably 10 nm to 1 μm, more preferably 20 to 50 nm.

[0086] As the above-mentioned aggregate, an aggregate made of a material that does not expand, contract, or expands and contracts very little during charge and discharge can be preferably used. For example, graphite, alumina, calcium oxide, zirconia, activated carbon, etc. can be exemplified. One or more of them can also be used in combination. Among them, from the viewpoints of conductivity, Li activity, etc., graphite, etc. can be preferably and suitably used.

[0087] From the viewpoint of improving cycle characteristics, etc., the content of the above-mentioned aggregate is preferably in the range of 10 to 400 parts by mass, more preferably in the range of 43 to 100 parts by mass, relative to 100 parts by mass of the negative electrode material powder. In addition, from the viewpoints of the functionality of the aggregate, control of the electrode film thickness, etc., the average particle diameter of the above-mentioned aggregate is preferably 10 to 50 μm, more preferably 20 to 30 μm. It should be noted that the average particle diameter of the above-mentioned aggregate is a value measured using a laser diffraction / scattering particle size distribution measuring device.

[0088] This negative electrode can be manufactured, for example, by the following process: adding a required amount of the negative electrode material powder to a binder dissolved in an appropriate solvent, adding a required amount of a conductive aid and an aggregate as needed to make it into a paste, coating it on the surface of a conductive substrate and drying it, and performing densification or heat treatment as needed.

[0089] When using this negative electrode to construct a lithium ion battery, the basic constituent elements of the battery other than this negative electrode, namely the positive electrode, electrolyte, separator, etc., are not particularly limited.

[0090] As the above-mentioned positive electrode, specifically, for example, a positive electrode having a layer containing a positive electrode active material such as LiCoO 2 , LiNiO 2 , LiFePO 4 , LiMnO 2 etc. formed on the surface of a current collector such as an aluminum foil can be exemplified.

[0091] As the above-mentioned electrolyte, specifically, for example, an electrolytic solution in which a lithium salt is dissolved in a non-aqueous solvent can be exemplified. In addition to this, an electrolyte in which a lithium salt is dissolved in a polymer, a polymer solid electrolyte in which the above-mentioned electrolytic solution is impregnated in a polymer, etc. can also be used.

[0092] As the above-mentioned non-aqueous solvent, specifically, for example, ethylene carbonate, propylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, etc. can be exemplified. One or more of them can also be contained.

[0093] As the above-mentioned lithium salt, specifically, for example, LiPF 6 , LiBF 4 , LiClO 4 , LiCF 3 SO3 , LiAsF 6 and so on. It may also contain one or more of them.

[0094] In addition, as other battery components, a separator, a can (battery case), a gasket, etc. can be cited. Regarding these components, as long as they are components commonly used in lithium-ion batteries, they can be appropriately combined to form a battery.

[0095] It should be noted that the battery shape is not particularly limited, and it can also be any shape such as cylindrical, square, coin-shaped, etc., and can be appropriately selected according to its specific use.

[0096] Examples

[0097] Hereinafter, the present invention will be described in more detail using examples. It should be noted that, unless otherwise specified, the % of the alloy composition is mass %.

[0098] 1. Preparation of negative electrode material powder

[0099] The following Table 1 shows the alloy compositions of 26 negative electrode material powders in the examples and 4 in the comparative examples. Each alloy composition shown in Table 1 is specified to obtain the target compositions described in Tables 2 and 3 below.

[0100] First, weigh each raw material shown in Table 1. Heat and melt each weighed raw material using a high-frequency induction furnace to make an alloy melt. By the gas atomization method, powder-like Si alloy particles are made from the above alloy melt. It should be noted that the atmosphere during the production of the alloy melt and during gas spraying is an argon atmosphere. In addition, during gas spraying, high-pressure (4 MPa) argon is sprayed onto the alloy melt that falls in a rod shape in the spraying chamber. The obtained Si alloy particles are wet-micropulverized (wet solvent: ethanol) using a bead mill to obtain a slurry containing primary particles. After adding a specified amount of PVB as a binder as shown in Tables 2 and 3, a Si-containing granule as a negative electrode material powder is made using the spray drying method.

[0101] [Table 1]

[0102]

[0103]

[0104] 2. Preparation of coin-shaped battery for charge and discharge test

[0105] 100 parts by mass of the negative electrode material powder produced as the negative electrode active material, 6 parts by mass of Ketjen black (manufactured by Lion Corporation) as the conductive assistant, and 19 parts by mass of a polyimide (thermoplastic resin) binder as the binder were blended, and they were mixed with N-methyl-2-pyrrolidone (NMP) as the solvent to prepare pastes containing the respective negative electrode material powders.

[0106] Each coin-type half cell was fabricated as follows. Here, for simplicity of evaluation, the electrode made of the negative electrode material powder was used as the test electrode, and the Li foil was used as the counter electrode. First, each paste was coated on the surface of SUS316L foil (thickness: 20 μm) serving as the negative electrode current collector by the doctor blade method to a thickness of 50 μm and dried to form each negative electrode active material layer. After formation, the negative electrode active material layer was densified by roll pressing. Thus, the test electrodes of the examples and comparative examples were fabricated.

[0107] Next, the test electrodes of the examples and comparative examples were punched into circular plates with a diameter of 11 mm to prepare each test electrode.

[0108] Next, the Li foil (thickness: 500 μm) was punched into a shape substantially the same as that of the above test electrode to prepare each counter electrode. In addition, LiPF 6 was dissolved in an equal amount mixture solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) at a concentration of 1 mol / l to prepare a non-aqueous electrolyte.

[0109] Next, each test electrode was housed in each positive electrode can, and the counter electrode was housed in each negative electrode can, and a separator made of a polyolefin-based microporous membrane was disposed between each test electrode and each counter electrode. It should be noted that each test electrode should be the negative electrode in the lithium ion battery, but when the counter electrode is the Li foil, the Li foil is the negative electrode and the test electrode is the positive electrode.

[0110] Next, the above non-aqueous electrolyte was injected into each can, and each negative electrode can and each positive electrode can were respectively riveted and fixed.

[0111] 3. Evaluation of the negative electrode material powder

[0112] 3-1. Confirmation of the constituent phases of the negative electrode material powder

[0113] The negative electrode material powders of the fabricated examples and comparative examples were subjected to XRD (X-ray diffraction) analysis, and it was confirmed that they contained an Si phase, an SiX compound phase, and an SnY compound phase. In addition, in the XRD analysis, the angle range of 120° to 20° was measured using a Co tube target.

[0114] 3-2. Calculation of the ratios of the Si phase, the SiX compound phase, and the SnY compound phase

[0115] Taking the case of Example 14 as an example, the calculation method of the proportions of the Si phase, SiX compound phase, and SnY compound phase shown in Table 2 and Table 3 below will be described.

[0116] (1) First, confirm the constituent phases in the fabricated negative electrode material powder. In the case of Example 14, the result of the above XRD analysis confirmed Si, Si 2 Fe, Sn 5 Cu 6 .

[0117] (2) When expressed as a mass% ratio, Si 2 Fe is 50.1[Si] - 49.9[Fe]. In contrast, the amount of Si that has been compounded is 17.43 × 50.1 / 49.9 = 17.50%. Therefore, the proportion of the SiX compound phase (Si 2 Fe) is the value obtained by adding the amount of compounded Si (17.50%) and the amount of Fe in Table 1 (17.43%). In this example, it is 35%.

[0118] (3) The proportion of the Si phase is the value obtained by subtracting the amount of compounded Si (17.50%) from the total Si amount in Table 1 (77.57%). In this example, it is 60%.

[0119] (4) The proportion of the SnY compound phase is the value obtained by adding the amount of Sn in Table 1 (3.05%) and the amount of Cu (1.96%). In this example, it is 5%.

[0120] [Table 2]

[0121]

[0122]

[0123] [Table 3]

[0124]

[0125]

[0126] 3 - 3. Measurement of the average particle size of primary particles

[0127] The particle size of the primary particles in the slurry after wet grinding was measured using a particle size distribution measuring device (manufactured by Nikkiso Co., Ltd., trade name: Microtrac MT3000). The diameter of the sphere having the same volume as the particle corresponding to the median (median particle size; the particle size corresponding to 50% of the cumulative curve) of the particle size distribution expressed on a volume basis was set as the average particle size (d50). The results are shown in Table 2 and Table 3.

[0128] 3-4. Measurement of Average Particle Size of Silicon-Containing Granules

[0129] The particle size of the silicon-containing granules obtained was measured using a particle image analysis device "Morphologi G3" (Malvern Panalytical). The diameter of an ideal circle (true circle) having an area equal to the projected area of the granule image (equivalent circle diameter) was calculated as the particle size of each granule, and the diameter at the median of the cumulative curve of the particle size distribution was set as the average particle size (d50). The results are shown in Tables 2 and 3. It should be noted that in Tables 2 and 3, the values of 1 / 3 times and 1 / 200 times of the average particle size of the granules are also recorded together.

[0130] 3-5. Charge-Discharge Test

[0131] Using each coin-type battery produced, a constant current charge-discharge with a current value of 0.2 mA was carried out for 1 cycle. Based on the value obtained by dividing the capacity (mAh) used when releasing Li by the active material mass (g), the initial discharge capacity C 0 (mAh / g) was calculated. In addition, the ratio of the discharge capacity to the charge capacity in the above charge-discharge cycle was obtained as a percentage of the discharge capacity / charge capacity, and the initial Coulomb efficiency (%) was obtained.

[0132] For the determination of the initial discharge capacity (mAh / g), the case where it exceeds 400 and is 500 or less is set as "◎", the case where it exceeds 350 and is 400 or less is set as "〇", the case where it exceeds 250 and is 350 or less is set as "△", and the case where it is 250 or less is set as "×", and the results are shown in Tables 2 and 3.

[0133] For the determination of the initial Coulomb efficiency, the case where it exceeds 95% is set as "◎", the case where it exceeds 80% and is 95% or less is set as "〇", the case where it exceeds 60% and is 80% or less is set as "△", and the case where it is 60% or less is set as "×", and the results are shown in Tables 2 and 3.

[0134] After the second cycle of the charge-discharge test, a charge-discharge test was carried out at a rate of 1 / 5C (C rate: the amount of electricity C required for charging (discharging) the counter electrode 0The current value for (charge) discharge for 1 hour is set as 1C. If it is 5C, then (charge) discharge for 12 minutes. If it is 1 / 5C, then (charge) discharge for 5 hours.). Then, 100 times of the above charge-discharge cycles are carried out, and the cycle characteristics are evaluated therefrom. Based on the obtained discharge capacities, the capacity retention rate (%) is calculated (discharge capacity after 100 cycles / initial discharge capacity (discharge capacity of the first cycle) × 100). Moreover, regarding the determination of the capacity retention rate, the case where it exceeds 70% is set as "◎", the case where it exceeds 50% and is 70% or less is set as "〇", the case where it exceeds 30% and is 50% or less is set as "△", and the case where it is 30% or less is set as "×", and the results are shown in Table 2 and Table 3.

[0135] In addition, the comprehensive determination shown in Table 2 and Table 3 is based on the evaluation results of the initial Coulomb efficiency, the initial discharge capacity, and the cycle characteristics. Specifically, in each of the examples and comparative examples, the case where there is no "×" evaluation in the above three characteristic evaluations is set as "qualified", and even if there is one "×" evaluation, it is set as "unqualified".

[0136] Based on the results of Table 2 and Table 3 obtained as above, the following points can be known.

[0137] Comparative Example 1 is an example where the average particle size of the primary particles is lower than the lower limit (0.1 μm), and the evaluation of the initial Coulomb efficiency is "×".

[0138] Comparative Example 2 is an example where the content of the binder exceeds the upper limit (2.0%) as the average particle size of the primary particles is small, and the evaluation of the initial discharge capacity is "×".

[0139] Comparative Example 3 is an example where the average particle size of the primary particles is higher than the upper limit (10.0 μm), and the evaluation of the cycle characteristics is "×".

[0140] Comparative Example 4 is an example where the average particle size (d50) of the primary particles is larger than 1 / 3 of the average particle size (d50) of the Si-containing granulated body (the particle size of the Si-containing granulated body is relatively small), and the evaluation of the initial discharge capacity is "×".

[0141] As described above, any of the comparative examples uses a negative electrode material containing a Si-containing granulated body, but the evaluation of the initial Coulomb efficiency, the initial discharge capacity, or the cycle characteristics is "×", and the battery characteristics considering the initial characteristics and the cycle characteristics are not sufficiently improved.

[0142] In contrast, the negative electrode material powder is composed of Si-containing granulates in which primary particles containing an Si phase, an Si compound phase, and an Sn compound phase are aggregated and which contain a binder in the range of 0 to 2.0% by mass. The average particle diameter (d50) of the primary particles constituting the Si-containing granulates is in the range of 0.1 to 10.0 μm, and this average particle diameter (d50) of the primary particles is smaller than 1 / 3 of the average particle diameter (d50) of the Si-containing granulates and larger than 1 / 200 of the average particle diameter (d50) of the Si-containing granulates. In each of the examples, there is no evaluation of "×", and the battery characteristics considering the initial Coulomb efficiency, the initial discharge capacity, and the cycle characteristics are improved.

[0143] In particular, in Examples 14 to 26 in which the proportion a of the Si phase is in the range of 29.9 ≤ a ≤ 90, the proportion b of the SiX compound phase is in the range of 1 ≤ b ≤ 70, the proportion c of the SnY compound phase is in the range of 0.1 ≤ c ≤ 30, and the average particle diameter of the primary particles is in the range of 0.2 to 4.0 μm, it can be seen that each characteristic is improved in a balanced manner.

[0144] If attention is paid to the amount of the binder, a decrease in the cycle characteristics is seen in the examples where no binder is added (Examples 8 to 10). It can be seen that, in order to improve the cycle characteristics, it is preferable to add a small amount (in the range of more than 0 and 2.0% or less) of the binder.

[0145] As described above, the negative electrode material powder for a lithium ion battery and the lithium ion battery of the present invention have been described in detail, but the present invention is not limited to the above-described embodiments and examples. For example, the negative electrode material powder of the present invention may also be composed of Si-containing granulates in which particles containing two or three of the Si phase, the SiX compound phase, and the SnY compound phase are used as primary particles, and the present invention can be variously modified without departing from its gist.

[0146] This application is based on a Japanese patent application (Japanese Patent Application No. 2022-174683) filed on October 31, 2022, the content of which is incorporated herein by reference.

Claims

1. A negative electrode material powder for a lithium-ion battery, which has an Si phase, an Si compound phase, and an Sn compound phase, Characterized in that, The negative electrode material powder contains Si-containing granulates, The Si-containing granulates are granulates in which primary particles of the Si phase, the Si compound phase, and the Sn compound phase are aggregated and optionally contain a binder in the range of 0 to 2.0% by mass, The average particle size (d50) of the primary particles constituting the Si-containing granulates is in the range of 0.1 to 10.0 μm, The average particle size (d50) of the primary particles is smaller than 1 / 3 of the average particle size (d50) of the Si-containing granulates, The average particle size (d50) of the primary particles is larger than 1 / 200 of the average particle size (d50) of the Si-containing granulates.

2. The negative electrode material powder for a lithium-ion battery according to claim 1, Characterized in that, The Si compound phase is an SiX compound phase containing Si and element X, The Sn compound phase is an SnY compound phase containing Sn and element Y, The element X is one or more elements selected from the group consisting of Fe, Ni, Cr, Zr, and Ti, The element Y is one or more elements selected from the group consisting of Cu, Fe, Ni, Cr, Co, Mn, Zr, and Ti, When the content ratios of the Si phase, the SiX compound phase, and the SnY compound phase are represented by the following formula (1), a + b + c = 100, 9.9 ≤ a ≤ 95, 1 ≤ b ≤ 90, and 0.1 ≤ c ≤ 50 are satisfied, a[Si] - b[SiX] - c[SnY]... Formula (1) In the above formula (1), a, b, and c respectively represent the content ratios (mass%) of the Si phase, the SiX compound phase, and the SnY compound phase.

3. The negative electrode material powder for a lithium-ion battery according to claim 2, Characterized in that, a, b, and c in the formula (1) respectively satisfy 29.9 ≤ a ≤ 90, 1 ≤ b ≤ 70, and 0.1 ≤ c ≤ 30.

4. The negative electrode material powder for a lithium-ion battery according to claim 2, Characterized in that, The element Y is Cu, The average particle size (d50) of the primary particles is in the range of 0.2 to 5.0 μm.

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