TWI618284B - Si alloy powder for negative active material of lithium ion battery and manufacturing method thereof - Google Patents

Abstract

The invention provides a Si alloy powder for a negative-electrode active material of a lithium ion battery with higher discharge capacitance and better cycle life, and a manufacturing method thereof. The Si alloy powder for a lithium ion battery negative electrode obtained by the present invention contains one or two or more of C: 0.01 to 0.5%, Cr, Ti, Al, and Sn in atomic%: 10 to 25% in total, and the rest Si and unavoidable impurities, and simultaneously satisfy the following formula (1) and formula (2): 0.15 ≦ Cr% / (Cr% + Ti% + Al% + Sn%) ≦ 1.00 ... (1)

(Al% + Sn%) / (Cr% + Ti% + Al% + Sn%) ≦ 0.40 ... (2).

Description

Si alloy powder for negative active material of lithium ion battery and manufacturing method thereof [Cross Reference of Related Applications]

This application claims priority based on Japanese Patent Application No. 2013-81121 filed on April 9, 2013, the disclosure content of which is incorporated herein by reference.

The invention relates to a Si alloy powder for a negative electrode of a lithium ion battery with excellent discharge capacity and cycle life, and a method for manufacturing the same.

The negative electrode active material of lithium batteries has been using powders made of carbon materials since the past, but the theoretical capacitance of carbon materials is as low as 372mAh / g, which has a limit for higher capacitance. In contrast, in recent years, the use of Sn, Al, Si and other theoretical capacitance of metal materials higher than carbon materials has been put into practical use. In particular, Si has a theoretical capacitance exceeding 4000 mAh / g, and is a promising material. However, when these metal materials are used instead of carbon as the negative electrode active material of a lithium ion battery, although a high capacitance is obtained, there is a problem of short cycle life.

For this problem, there have been various proposals for a method for improving the microstructure by forming Si alloys instead of pure Si powders because various elements are added to Si. For example, Japanese Patent Application Laid-Open No. 2012-150910 (Patent Document 1) proposes to obtain a fine eutectic structure of a Si phase and a CrSi ₂ phase by adding specific Cr, Ti, Al, and Sn.

On the other hand, in most cases, the Si alloy powder used for the negative electrode of a lithium ion battery is pulverized by a ball mill to a few μm or less to reduce the crystallinity and is used. Furthermore, for example, Japanese Patent Application Laid-Open No. 2012-178344 (Patent Document 2) or Japanese Patent Application Laid-Open No. 2012-113945 (Patent Document 3) disclose that a carbon material or a conductive powder is introduced during processing by a ball mill so that A method of compounding with Si alloy powder to achieve more excellent charge and discharge characteristics.

[Previous Technical Literature] [Patent Literature]

Patent Document 1: Japanese Patent Application Publication No. 2012-150910

Patent Document 2: Japanese Patent Application Laid-Open No. 2012-178344

Patent Document 3: Japanese Patent Application Publication No. 2012-113945

Although the above Patent Document 1 has both a fine eutectic structure and excellent discharge capacitance and cycle life, the present invention is a further improvement of this technology, and the addition of a small amount of C makes it necessary to hardly reduce the discharge capacitance. Those who have successfully increased their cycle life significantly. And according to their needs, by adding B, P, Zr, Hf, V, Nb, Ta, Mo, W, Any one or more of Mn, Fe, Co, Ni, and Cu can further improve the cycle life.

In addition, the Si phase in the present invention is a phase in which diamond is mainly composed of Si, and a phase in which Li is absorbed and released. Therefore, it also includes those in which an additional element other than Si is solid-dissolved. Moreover, the CrSi ₂ phase system in the present invention has a hexagonal crystal structure, and the space group belongs to P6 ₂ 22, which is a phase that suppresses the volume change of the Si phase during charge and discharge. Therefore, it also includes a part of which is replaced with an additional element other than Cr and Si.

Although it has been proposed as in the aforementioned Patent Documents 1 to 3, the present invention is a further improvement of this technology, and the addition of a small amount of C is necessary to substantially reduce the discharge capacitance and successfully increase the cycle life. And according to their needs, by adding one or more of B, P, Zr, Hf, V, Nb, Ta, Mo, W, Mn, Fe, Co, Ni, and Cu, the cycle life can be further improved. . As a result, a Si alloy powder for a negative-electrode active material of a lithium ion battery having a higher discharge capacity and an excellent cycle life, and a method for producing the same are provided.

According to the same aspect of the present invention, a Si alloy powder for a lithium ion battery negative electrode is provided, which contains C in an atomic% of 0.01 to 0.5%.

Any one or more of Cr, Ti, Al, and Sn: a total of 10 to 25%, and the rest of Si and unavoidable impurities, and simultaneously satisfy the following formula (1) and formula (2): 0.15 ≦ Cr% / (Cr% + Ti% + Al% + Sn%) ≦ 1.00… (1)

(Al% + Sn%) / (Cr% + Ti% + Al% + Sn%) ≦ 0.40 ... (2).

According to another aspect of the present invention, there is provided a Si alloy powder for a negative electrode of a lithium ion battery, characterized in that it contains C: 0.01 to 0.5% in atomic%, any one or more of Cr, Ti, Al, and Sn. , The total is 10 ~ 25%, and the rest of Si and unavoidable impurities are formed, and at the same time satisfy the following formula (1) and formula (2): 0.15 ≦ Cr% / (Cr% + Ti% + Al% + Sn%) ≦ 1.00 ... (1)

(Al% + Sn%) / (Cr% + Ti% + Al% + Sn%) ≦ 0.40 ... (2).

According to still another aspect of the present invention, there is provided any one of the above-mentioned Si alloy powders for a lithium ion battery negative electrode, which contain one or two of B or P in a total amount of 5% or less, and / or a total of 2% or less Any one or more of Zr, Hf, V, Nb, Ta, Mo, W, Mn, Fe, Co, Ni, and Cu.

According to still another aspect of the present invention, there is provided a method for producing a Si alloy powder for a lithium ion battery negative electrode in any of the above-mentioned states, which is characterized in that after melting a raw material of a specific composition, the cooling rate is 100 ° C / s or more. The step of rapidly condensing the alloy melt.

According to still another aspect of the present invention, a method for manufacturing a Si alloy powder for a negative electrode of a lithium ion battery is provided. It includes the step of forcibly stirring the Si alloy powder and hard balls in any of the above states in a container to crush the alloy powder.

As described above, the present invention provides a Si alloy powder for a negative-electrode active material of a lithium ion battery with a higher discharge capacity and excellent cycle life, and a method for producing the same.

Hereinafter, the present invention will be described in detail. Unless otherwise specified, "%" in this specification means atomic% (at%).

The Si alloy powder for a negative electrode active material of a lithium ion battery of the present invention contains C: 0.01 to 0.5% in atomic%, any one or more of Cr, Ti, Al, and Sn: 10 to 25% in total, and The remaining portion of Si and unavoidable impurities is preferably formed substantially from these elements and unavoidable impurities, and more preferably from these elements and unavoidable impurities.

The first feature of the present invention is that in addition to adding one or two or more of a specific amount of Cr, Ti, Al, and Sn, it is necessary to add a small amount of C, which can hardly reduce the discharge capacitance and greatly improve the cycle life. Although the detailed principle of this cycle life improvement effect is unknown, it is estimated as follows.

As described in Patent Document 1, the Si-CrSi ₂ based eutectic alloy has a significantly fine structure. The present inventors have found that in the alloy of the present invention in which a small amount of C is added to the alloy, ultrafine Cr-based carbides and / or Ti-based carbides of about 10 nm or less are minutely generated in the fine Si phase, and uniformly dispersed in the Si phase. These carbides do not react with Li. In addition, when Si atoms in the surrounding Si phase react with Li to expand the volume, since the volume of these ultrafine carbides does not change, fine cracks occur at the interface. Usually, the Si phase also cracks due to changes in the volume of Li absorbed and released. At the front end of the crack that once occurred, the stress was concentrated with the subsequent volume change, so it developed into a large crack, causing part of the Si alloy powder to fall off from the current collector, thereby deteriorating the cycle life.

On the other hand, since the ultrafine carbides are uniformly dispersed, the cracks at the interface between the Si phase and the ultrafine carbides occur in the Si phase with fine cracks everywhere. From this, it is considered that stress relaxation was caused by minute cracks in various places in the Si phase, and as a result, no large cracks occurred. Therefore, it is presumed that the Si alloy powder which is less likely to cause defects is detached from the current collector and is excellent in cycle life.

The second feature of the present invention is that B and / or P is added in a small amount as required, and the cycle life can be further improved. The detailed reason for this cycle life improvement effect is not clear, but it is estimated as follows. First, B or P has a solid solubility limit in the Si phase although it is only slightly. In addition, although these elements react with Li, compared with Si, the volume change during the reaction is small. Therefore, B and / or P, which is solid-dissolved in the Si phase, has the effect of reducing the volume change of the Si phase as Li is absorbed and released. Based on this, it is estimated that the large crack of the Si alloy powder can be suppressed and the cycle life can be improved.

The third feature of the present invention is that one or two kinds of Zr, Hf, V, Nb, Ta, Mo, W, Mn, Fe, Co, Ni, and Cu can be added in trace amounts according to their needs, thereby further improving the cycle life . The detailed reason for this cycle life improvement effect is not clear, but it is estimated as follows. First of all, in the alloy of the present application, these elements are all elements that replace the CrSi ₂ phase of Cr, and have the effect of miniaturizing the CrSi ₂ phase. It is presumed that the CrSi ₂ phase thus refined is capable of uniformly suppressing the volume change of the entire Si phase of the particles with Li absorption and release, and therefore has excellent cycle life.

On the other hand, this alloy powder can have a finer structure by applying a manufacturing method having a cooling rate of 100 ° C./s or more, which has been proposed in the past, such as an atomization method or a liquid quenching method. Further, it can be made finer by a pulverization method of various ball mills and the like which have been proposed conventionally. Further, it is also possible to use a Si alloy powder for compounding a carbon material or a conductive powder that has been proposed conventionally.

The reasons for limiting the component composition of the present invention will be described below.

(a) C: 0.01 ~ 0.5%

In the alloy of the present invention, C is an essential element that generates ultra-fine carbides in the Si phase, hardly reduces discharge capacitance, and improves cycle life. When the addition amount is less than 0.01%, the cycle life improvement effect cannot be obtained. When it exceeds 0.5%, the carbides become coarse, and conversely, the Si phase is liable to cause large cracks and deteriorate the cycle life. The amount of C added is preferably 0.02 to 0.4%, more preferably 0.03 to 0.3%.

(b) Any one or more of Cr, Ti, Al, and Sn: 10-25% in total

In the alloy of the present invention, Cr is an essential element for realizing the fine eutectic structure of the Si phase-CrSi ₂ phase, and having excellent discharge capacitance and cycle life. However, the inventors have found that Cr can be substituted with Ti, Al, or Sn within a certain range. Therefore, in the present invention, the total amount of Cr and Ti, Al, and Sn and the ratio of the total amount to the amount of Cr added are specified. First, Ti-based substituent that phase of CrSi2 ₂ Cr, CrSi ₂ lattice parameter increases, the volume of inhibition caused by the diffusion of Li in the phase expansion improve cycle life. Therefore, Ti is preferably added as required.

The part of the Al substituted Si CrSi ₂ phase, the lattice constant increased with the CrSi _2, the other part is present as the soft Al phase. Increasing the lattice constant of the CrSi ₂ phase also has the same effect as Ti. It is believed that the soft Al phase has the effect of mitigating the volume change of the Si phase that is absorbed and released by Li, and improves the cycle life. Therefore, Al is preferably added as needed. The Sn system exists as a soft Sn phase, and it is thought that the cycle life is improved by the same effect as the soft Al phase. Therefore, Sn is preferably added as needed. However, when the total content of Cr, Ti, Al, and Sn (Cr% + Ti% + Al% + Sn%) is less than 10%, a sufficient cycle life cannot be obtained, and when it exceeds 25%, a sufficient discharge capacitance cannot be obtained. The total content of Cr, Ti, Al, and Sn is preferably 13 to 23%, and more preferably 16 to 21%.

(c) 0.15 ≦ Cr% / (Cr% + Ti% + Al% + Sn%) ≦ 1.00

In order to obtain a fine eutectic structure of the Si phase-CrSi ₂ phase in the alloy of the present invention, the Cr ratio must be more than a certain amount with respect to the total content of the added Cr, Ti, Al, and Sn. That is, when Cr% / (Cr% + Ti% + Al% + Sn%) is less than 0.15, a fine eutectic structure cannot be obtained, and the cycle life is poor. Moreover, because Ti, Al, and Sn are elements that can be added according to their needs, the upper limit of Cr% / (Cr% + Ti% + Al% + Sn%) is 1.00. Cr% / (Cr% + Ti% + Al% + Sn%) is preferably in the range of 0.15 to 0.90, more preferably in the range of 0.20 to 0.80.

(d) (Al% + Sn%) / (Cr% + Ti% + Al% + Sn%) ≦ 0.40

In the alloy of the present invention, the total amount of Al and Sn must be equal to or less than the total content of Cr, Ti, Al, and Sn added. That is, when (Al% + Sn%) / (Cr% + Ti% + Al% + Sn%) exceeds 0.40, a fine eutectic structure cannot be obtained, and the cycle life is poor. (Al% + Sn%) / (Cr% + Ti% + Al% + Sn%) is preferably in the range of 0.03 to 0.3, and more preferably in the range of 0.05 to 0.25.

(e) 1 or 2 of B or P is less than 5% in total

In the alloy of the present invention, B or P is solid-dissolved in the Si phase, and is an element considered to improve the cycle life, and can be added as required. However, if the total of one or two of B or P exceeds 5%, boride or phosphide is formed, and the cycle life is deteriorated. One or two types of B or P are preferably in a range of 0.1 to 3.0%, more preferably in a range of 0.2 to 2.0%. It is better to add B as an element.

(f) Any one or more of Zr, Hf, V, Nb, Ta, Mo, W, Mn, Fe, Co, Ni, and Cu is 2% or less in total

In the alloy of the present invention, Zr, Hf, V, Nb, Ta, Mo, W, Mn, Fe, Co, Ni, and Cu are elements necessary to improve the cycle life, but Zr, Hf, V, Nb, Ta, Mo, W, Mn, Fe, When the total content of Co, Ni and Cu (Zr% + Hf% + V% + Nb% + Ta% + Mo% + W% + Mn% + Fe% + Co% + Ni% + Cu%) exceeds 2%, Silicides mainly containing these elements are generated, making it difficult to obtain a fine structure and deteriorating cycle life. The total content of Zr, Hf, V, Nb, Ta, Mo, W, Mn, Fe, Co, Ni, and Cu is preferably in the range of 0.02 to 1.50%, more preferably in the range of 0.05 to 1.00%. In addition, Fe and Mn are preferably added as elements, and more preferably added simultaneously with B.

(g) Solidification process at a cooling rate of 100 ° C / s or more

The alloy of the present invention is a eutectic alloy of Si-CrSi ₂ series. The microstructure size of eutectic alloys is generally affected by the cooling rate. As a method for solidifying at a cooling rate of 100 ° C./s or more, examples include the atomization method and the single-roller method. However, in the manufacturing steps of the alloy of the present invention, a preferable step can be made by a gas atomization method.

(h) Steps of crushing alloy powder

The negative electrode of a lithium-ion battery is usually used at a thickness of less than 100 μm. According to its battery use and design, it is used at a thinner thickness. Therefore, in order to use the alloy powder of the present invention in a negative electrode having a specific thickness, it is necessary to control the particle diameter to a thickness smaller than that of the negative electrode. Therefore, a pulverization method can be applied. This pulverization method can be applied to a general method such as a ball mill for forcibly stirring alloy powder and hard balls (also referred to as a medium), and in this step, microstructure refinement or compounding with carbon material and conductive powder can also be performed.

Examples

First, in order to discuss the impact of the amount of C added on the discharge capacitor and cycle life, the Si-19% Cr-x% C and Si-9% Cr-6% Ti-2% Al-2% Sn- x% C was evaluated (Experiment A). Next, the types and amounts of various added elements were changed, and evaluation was performed for each added amount and the upper and lower limits of the factor (Experiment B). Finally, a composite powder made of natural graphite powder or pure Zn powder was also introduced for evaluation by vibration grinding (Experiment C).

(Experiment A) [Test powder production steps]

Si alloy powders with the composition shown by Si-19% Cr-x% C and Si-9% Cr-6% Ti-2% Al-2% Sn-x% C are produced by a gas atomizer device. Furthermore, x varies in the range of 0.005 to 0.8. The base material with a dissolved amount of 1000 g was inductively melted in a refractory crucible made of alumina in an Ar atmosphere, and the melt was discharged from a fine-hole nozzle at the lower part of the crucible. Immediately after exiting the melt, it was atomized with a spray gas. The obtained powder was classified to 63 μm or less, and the charge-discharge characteristics were evaluated by the following methods.

[Charging and discharging characteristics]

To the test powder, 10% by mass of polyvinylidene fluoride (adhesive material), 10% by mass of N methylpyrrolidone (solvent), and 10% by mass of acetylene black (conductive material) were added and mixed in a mortar to form Pasty. This slurry was applied to a copper foil (current collector), dried, and then pressed with a manual press. Further, it was punched out to have a diameter of 10 mm to serve as a negative electrode. Charge and discharge characteristics were evaluated for this negative electrode and coin-type batteries using metal Li foil for the counter electrode and the reference electrode. As the electrolytic solution, an equal amount of dimethoxyethane was mixed with ethyl carbonate, and LiPF _{6 was} added as an electrolyte to a concentration of 1M.

Charge at a current value of 150 mA / g until 0 V (for the reference electrode), and then discharge at 150 mA / g to 2 V (for the reference electrode). Let this be 1 cycle and repeat 50 cycles. The discharge capacity in the first cycle was evaluated as the discharge capacity, and the discharge capacity at the 50th time was divided by the discharge capacity at the first time and multiplied by the maintenance ratio of the discharge capacity at 100 (%) to evaluate the life characteristics.

The results of Experiment A are shown in Table 1.

No. 2 to 9, No. 12 to 19 are examples of the present invention, and No. 1, 10 to 11, and 20 are comparative examples. In Comparative Examples Nos. 1 and 11, the maintenance rate was poor because the amount of C was low. Comparative Examples Nos. 10 and 20 had poor maintenance rates because the amount of C was high.

(Experiment B) [Test powder production steps]

The Si alloy powder having the composition shown in Table 2 was produced using a gas atomizing device. The base material with a dissolved amount of 1000 g was inductively melted in a refractory crucible made of alumina in an Ar atmosphere, and the melt was discharged from a fine-hole nozzle at the lower part of the crucible. Immediately after exiting the melt, it was atomized with a spray gas. After classifying the obtained powder to 63 μm or less, the obtained alloy powder and chrome steel hard balls were placed in a metal container of a vibration grinder apparatus and processed for 30 hours. Subsequently, the powder taken out from the container was used to evaluate the charge-discharge characteristics by the following method.

[Charging and discharging characteristics]

To the test powder, 10% by mass of polyvinylidene fluoride (adhesive material), 10% by mass of N methylpyrrolidone (solvent), and 10% by mass of acetylene black (conductive material) were added and mixed in a mortar to form Pasty. This slurry was applied to a copper foil (current collector), dried, and then pressed with a manual press. This was punched out to a diameter of 10 mm as a negative electrode.

Charge and discharge characteristics of the negative electrode and the coin-type battery using metal Li foil as the counter electrode and the reference electrode were evaluated. As the electrolyte system, an equivalent amount of dimethoxyethane was mixed with ethyl carbonate, and LiPF ₆ was added as the electrolyte system to a concentration of 1M. Charging was performed at a current value of 150 mA / g until 0 V (for the reference electrode), and then discharged at 150 mA / g to 2 V (for the reference electrode). Let this be 1 cycle and repeat 50 cycles. The discharge capacity in the first cycle was evaluated as the discharge capacity, and the discharge capacity at the 50th time was divided by the discharge capacity at the first time and multiplied by the maintenance ratio of the discharge capacity at 100 (%) to evaluate the life characteristics. The results of Experiment B are shown in Table 2.

Nos. 21 to 50 are examples of the present invention, and Nos. 51 to 59 are comparative examples.

Comparative Example No. 51 had a low C content, and Comparative Example No. 52 had a high C content, so the maintenance rate was poor. Comparative Example No. 53 due to Cr, Ti, Al And the total value of any one or two or more of Sn is low, so the maintenance rate is poor. In Comparative Example No. 54, since the total value of any one or more of Cr, Ti, Al, and Sn was high, the discharge capacitance was poor. In Comparative Example No. 55, since the formula (1) was low, the maintenance rate was poor. Comparative Example No. 56 had a high maintenance ratio because of the high expression (2). In Comparative Example No. 57, the total value of one or two types of B or P was high, so the maintenance rate was poor. Comparative Examples Nos. 58 and 59 have a high maintenance value due to the high combined value of any one or two of Zr, Hf, V, Nb, Ta, Mo, W, Mn, Fe, Co, Ni, and Cu. .

(Experiment C) [Test powder production steps]

The Si alloy powder of No. 26 of Experiment B was produced using a gas atomizing device. The base material with a dissolved amount of 1000 g was inductively melted in a refractory crucible made of alumina in an Ar atmosphere, and the melt was discharged from a fine-hole nozzle at the lower part of the crucible. Immediately after exiting the melt, it was atomized with a spray gas. After classifying the obtained powder to 63 μm or less, the “obtained alloy powder and natural graphite powder (80:20 by mass) and chromium steel hard balls (No. 26-1)” or “the obtained alloy powder and pure Zn powder (80:20 by mass) and chrome steel hard balls (No. 26-2) "were put into a metal container made of a vibratory grinder device and processed for 30 hours. Subsequently, the powder taken out from the container was used to evaluate the charge-discharge characteristics by the following method.

[Charging and discharging characteristics]

To the test powder, 10% by mass of polyvinylidene fluoride (adhesive material), 10% by mass of N methylpyrrolidone (solvent), and 10% by mass of acetylene black (conductive material) were added and mixed in a mortar to form Pasty. This slurry was applied to a copper foil (current collector), dried, and then pressed with a manual press. Further, it was punched out to have a diameter of 10 mm to serve as a negative electrode. Charge and discharge characteristics were evaluated for this negative electrode and coin-type batteries using metal Li foil for the counter electrode and the reference electrode. As the electrolytic solution, an equal amount of dimethoxyethane was mixed with ethyl carbonate, and LiPF _{6 was} added as an electrolyte to a concentration of 1M.

Charge at a current value of 150 mA / g until 0 V (for the reference electrode), and then discharge at 150 mA / g to 2 V (for the reference electrode). Let this be 1 cycle and repeat 50 cycles. The discharge capacity in the first cycle was evaluated as the discharge capacity, and the discharge capacity at the 50th time was divided by the discharge capacity at the first time and multiplied by the maintenance ratio of the discharge capacity at 100 (%) to evaluate the life characteristics. As a result of Experiment C, the discharge capacity of No. 26-1 was 1170 mAh / g, and the retention rate was 97%, which was excellent. In addition, the discharge capacity of No. 26-2 was 1200 mAh / g, and the retention was excellent at 97%.

From the above, it can be seen that by using a small amount of C as an essential addition in the present invention, the discharge capacitance can be hardly reduced, and the cycle life can be greatly increased. In addition, if necessary, by adding a small amount of B, P, Zr, Hf, V, Nb, Ta, Mo, W, Mn, Fe, Co, Ni, and / or Cu, the cycle life can be further improved. As a result, the Si alloy powder for a negative electrode active material of a lithium ion battery having a higher discharge capacity and an excellent cycle life, and a method for producing the same can be exhibited.

Claims (4)

A Si alloy powder for lithium ion battery negative electrode, which contains at least one of C: 0.01 to 0.5% of Cr, Ti, Al, and Sn in atomic%: a total of 10 to 25% and a total of 0 to 5% 1 or 2 of B or P, a total of 0 to 2% of any one or more of Zr, Hf, V, Nb, Ta, Mo, W, Mn, Fe, Co, Ni, and Cu, and The remaining part of Si and unavoidable impurities, and simultaneously satisfy the following formula (1) and formula (2): 0.15 ≦ Cr% / (Cr% + Ti% + Al% + Sn%) ≦ 1.00 ... (1) (Al% + Sn%) / (Cr% + Ti% + Al% + Sn%) ≦ 0.40 ... (2). If the Si alloy powder of claim 1 contains any one or both of the following, a total of 0.1 to 5% of one or two of B or P, and a total of 0.02 to 2% of Zr, Hf, V, Any one or more of Nb, Ta, Mo, W, Mn, Fe, Co, Ni, and Cu. A method for manufacturing a Si alloy powder for a lithium ion battery negative electrode, comprising melting a raw material composed of the Si alloy powder as claimed in claim 1 or 2 to obtain an alloy melt, and making the alloy melt at a cooling rate of 100 ° C / s or more Steps for rapid condensation. A method for manufacturing a Si alloy powder for a negative electrode of a lithium ion battery, comprising the steps of forcibly stirring the Si alloy powder and hard balls as claimed in claim 1 or 2 in a container to crush the aforementioned Si alloy powder.