JP2002075351A - Alloy powder for negative electrode of nonaqueous electrolyte secondary battery and method for manufacturing the alloy powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a negative electrode material for nonaqueous electrolyte secondary battery excellent in the discharge capacity and cyclic lifetime. SOLUTION: A powder of Si-X alloy (X is one or more elements to form an inter-metal compound or solid solution together with Si) whose structure includes an Si-phase having a large Li-occluding ability is manufactured by a rapid cooling solidification method with a cooling speed of 100 deg.C/sec (gas atomizing method, rapid cool rolling method, etc.). One or more easy-to-oxidize elements selected among Li elements and those oxidized easier than Li (for example, Ca, Mg, rare earth elements) is included in an amount: 0.01-1 wt.% in the alloy so that a drop of the discharge capacity due to oxygen inclusion is precluded. It may also be accepted that the solidification is followed by a heat treatment at a temperature lower than the solid phase line temperature of the alloy.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a method for storing a large amount of Li.
The present invention relates to an alloy powder for a negative electrode of a non-aqueous electrolyte secondary battery which can be released, and a method for producing the alloy powder.

[0002]

2. Description of the Related Art Production of non-aqueous electrolyte secondary batteries represented by lithium ion secondary batteries has greatly increased with the spread of portable and small-sized electric and electronic devices and the performance thereof. There is a continuing need for longer life.

[0003] In the current general non-aqueous electrolyte secondary battery,
A carbon material is mainly used as a negative electrode material. But,
In the negative electrode made of carbon material, it can not occlude Li only to the composition of LiC _6, the theoretical maximum value of the capacity and 372 mAh / g, only about 1/10 of the case of metallic lithium, a limit to the improvement of capacity There is.

[0004] Although lithium metal, which was initially used as a negative electrode material, can provide a high capacity, it does not charge or charge a battery.
When the discharge is repeated, dendrite is deposited and a short circuit occurs, so that the cycle life of charge / discharge is short, which is not practical.

As a negative electrode material for a non-aqueous electrolyte secondary battery which does not have a problem of dendrite precipitation and can increase the capacity, a proposal is made to use, for example, an intermetallic compound such as metal silicide as the negative electrode material (for example, see Japanese Patent Application Laid-Open No. -240201, 9-6365
No. 1), and a proposal to use a metal such as Al capable of forming an intermetallic compound with Li, or a metal material obtained by adding other elements such as Li, Si, and B to the metal as the negative electrode material.

[0006]

However, at present, these negative electrode materials have not been put to practical use. The main reason is that in the case of intermetallic compounds, the amount of occluded Li is small and high capacity cannot be obtained. It is considered that the volume change of the negative electrode material is large, and the negative electrode material is cracked and pulverized with repetition of the charge / discharge cycle, resulting in an extremely short cycle life.

The present invention provides a non-aqueous electrolyte which has a large amount of absorbing and releasing Li, and therefore has a high charge / discharge capacity when used as a negative electrode material of a non-aqueous electrolyte secondary battery, and is satisfactory in terms of cycle life. An object of the present invention is to provide a negative electrode material for an electrolyte secondary battery and a method for producing the same.

[0008]

Means for Solving the Problems Silicon (Si) can occlude and release Li by reversibly combining and dissociating with Li. The theoretical charge / discharge capacity of Si when used as a negative electrode material for non-aqueous electrolyte secondary batteries is 4200 mAh / g
(9800 mAh / cc: specific gravity 2.33). The theoretical maximum capacity of this Si is much larger than the theoretical maximum capacity of carbon materials currently in practical use, 372 mAh / g (844 mAh / cc: specific gravity 2.27), and the theoretical maximum capacity of metallic lithium is 3900 mAh / g.
(2100 mAh / cc: specific gravity 0.53), the discharge capacity per unit volume, which is important from the viewpoint of battery miniaturization,
Si is significantly larger. Therefore, Si can be a high capacity negative electrode material.

However, as in the case of Al, the negative electrode material made of Si has a large volume change due to the occlusion and release of Li, so it is easy to be pulverized by cracking, and the cycle life becomes extremely short. Very few attempts have been made to make the material.

The present inventors have focused on the characteristic of the extremely high theoretical capacity of the negative electrode material made of Si, and as a result of repeated investigations to improve the cycle life thereof, as a result, Si was formed into a composition that would precipitate the Si phase. It has been found that it is effective to form a structure having a phase composed of an intermetallic compound of Si and another element or a solid solution in addition to the Si phase.

In this Si alloy, the Si phase is the main Li occlusion phase, and the other phase composed of the Si intermetallic compound or solid solution is
It functions to restrain the Si phase against volume change. This other phase has no Li storage capacity or is very small compared to Si, so the charge / discharge capacity is reduced by the coexistence of other phases, but the theoretical capacity of the Si phase is as described above. Therefore, the negative electrode material exhibits a very high discharge capacity.
As a result of other phases binding the Si phase,
The volume change of the phase is suppressed, the cracking and pulverization of the negative electrode material hardly progress, and the cycle life is remarkably improved. As a result, it is possible to obtain a negative electrode material having an extremely high capacity as compared with the carbonaceous material and having a cycle life at a practical level.

However, even when such a Si alloy containing a Si phase is used as a negative electrode material of a nonaqueous electrolyte secondary battery, a predetermined discharge capacity assumed from the amount of the Si phase in the alloy cannot be obtained, and the It has been found that the capacity can be quite low. As a result of investigating this point, it was found that the alloy having the reduced discharge capacity contained a large amount of oxygen. Oxygen is inevitably mixed into the alloy during the production of the alloy, and oxidation of the alloy due to the mixing of oxygen seems to adversely affect the discharge capacity.

[0013] Then, further investigation was carried out to prevent a decrease in the discharge capacity due to oxygen. As a result, the alloy contained Li and / or an easily oxidizable element which is more easily oxidized than Li, and this element preferentially captured oxygen. As a result, it has been found that a negative electrode material having significantly improved discharge capacity can be obtained.

The present invention, which has been completed based on this finding, is an alloy powder containing a Si phase, which contains at least one kind of easily oxidizable element selected from the group consisting of Li element and elements that are more easily oxidized than Li. This is an alloy powder for a negative electrode of a non-aqueous electrolyte secondary battery. In a preferred embodiment, the oxidizable element is present at 0.01% by mass or more and 1% by mass or less,
It is selected from the group consisting of i, Ca, Mg, and rare earth elements.

The alloy powder for a negative electrode of a non-aqueous electrolyte secondary battery of the present invention can be prepared by a method of cooling a molten alloy material at a cooling rate of 100 ° C./sec or more, preferably an atomizing method, a roll quenching method, or a rotating electrode method. The solidification can be performed by a method characterized by including a step of coagulation. This manufacturing method can further include a step of subjecting the solidified alloy to a heat treatment at a temperature lower than the solidus temperature of the alloy.

According to the present invention, an alloy powder containing a Si phase, which can reversibly occlude and release a large amount of Li and can increase the capacity, is used as a negative electrode material of a nonaqueous electrolyte secondary battery. If the discharge capacity decreases when the Li and / or Li
This can be prevented by adding an easily oxidizable element (including Li) that easily forms an oxide. The mechanism has not been completely elucidated, but at present it is speculated as follows.

Generally, the production of an alloy powder is composed of steps such as melting, powder production, and heat treatment. However, in industrial practice, oxidation of the alloy due to mixing of oxygen cannot be avoided in each step. As a result, chemically stable oxides are generated in the grains and on the surface of the alloy powder. Alloys having a Si phase are no exception.

An alloy containing a Si phase contains Si, which has a low free energy of oxide formation, and thus is particularly prone to form an oxide. When this alloy powder is used as a negative electrode material of a nonaqueous electrolyte secondary battery, The oxides formed in the grains and on the surface of the alloy powder reduce the discharge capacity as described below.

The alloy containing the Si phase is composed of Si and at least one other.
It is composed of a kind of element X and is structurally Si phase and X-Si phase.
(Intermetallic compound or solid solution of element X and Si).
As described above, the element having the lowest oxide free energy among the constituent elements of this alloy is preferentially oxidized by oxygen inevitably mixed during the production, and an oxide of the element is generated. If the element having the lowest free energy of oxide generation is Si, Si in the Si phase and the X-Si phase is oxidized to form a Si oxide. If the element is X, the X element in the X-Si phase is oxidized. To form X oxide, which is present in the grains or on the surface of the alloy.

In the negative electrode material having the Si phase as the Li occlusion phase, at the time of charging, Li is combined with Si by the charging energy to form an intermetallic compound and / or an amorphous phase, so that it is occluded in the Si phase. However, when an oxide is present in an alloy containing a Si phase, Li is converted to this oxide (Si oxide or X oxide).
Since the oxide formation free energy is lower, the charging energy is first consumed by the reduction of the oxide present in the alloy with Li, and a chemically stable Li oxide is irreversibly generated. However, the amount of Li absorbed in the Si phase decreases. As a result, it is released from the Si phase during the subsequent discharge
Since the Li amount also decreases (because the occlusion amount is small), the discharge capacity of the battery decreases.

This phenomenon is basically the same regardless of whether the oxide exists at the grain boundary or the surface of the alloy powder. However, in the case of an oxide present on the surface, another adverse effect is caused because a surface oxide layer is formed. In other words, at the beginning of charging
Li reduces the surface oxide phase and covers the alloy powder surface with a chemically stable and irreversible layer of Li oxide. The Li oxide layer covering the surface of the powder acts as a barrier for the subsequent diffusion of Li into the grains and hinders the absorption of Li into the intragranular Si phase, so that the amount of Li absorbed in the Si phase decreases. As a result, the amount of Li released from the Si phase during discharge decreases, and the discharge capacity of the battery decreases.

According to the present invention, when an oxidizable element selected from Li and an element which is more easily oxidized than Li is contained in the alloy containing the Si phase, the oxidizable element is oxidized during the oxidization which cannot be avoided in the production process of the alloy powder. The oxidizable element (including Li) is preferentially oxidized to form a chemically stable and irreversible oxide of the element. This is because the oxidizable element has a lower oxide formation free energy than Si, and often lower than all the constituent elements (Si and X) of the alloy. Since the stable oxide of the easily oxidizable element is not reduced during charging, Li is consumed for the reduction of intragranular and surface oxides, forming Li oxide and reducing the amount of Li occluded. Can be prevented.
In addition, since the oxide of this easily oxidizable element is generated in the grains and on the surface of the powder during the manufacturing process of the alloy powder, a Li oxide layer serving as a barrier to inhibit Li diffusion is formed on the surface of the powder at an early stage of charging.
A decrease in the amount of Li occluded and the amount of released Li can also be prevented.

As a result, the decrease in the discharge capacity due to oxygen mixed in the production process of the alloy powder containing the Si phase can be almost completely suppressed, so that the predetermined charge / discharge capacity estimated from the amount of the Si phase in the alloy is obtained. Can be obtained, and the capacity of the nonaqueous electrolyte secondary battery can be increased.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION The alloy powder for a negative electrode of a non-aqueous electrolyte secondary battery of the present invention comprises an alloy of Si and at least one other element X (Si-X alloy). This alloy contains a Si phase, and the Si phase reversibly combines and dissociates with Li, whereby the alloy stores and releases Li. Since the Li storage capacity of the Si phase is very high, the negative electrode material exhibits a high Li storage capacity and thus a high discharge capacity even when other phases coexist.

The other element X forms an intermetallic compound and / or a solid solution phase with Si in the alloy. This intermetallic compound and / or solid solution phase restricts the Si phase to suppress the volume change of the Si phase caused by the expansion and contraction of the Si phase during occlusion and release of Li. In this case, the change in the volume of the alloy powder is suppressed, and the cracking and pulverization of the alloy powder due to the change in volume are less likely to occur, and the deterioration of the cycle life mainly caused by the pulverization of the negative electrode material is suppressed.

The other element X to be alloyed with Si in the alloy powder of the present invention is not particularly limited. Examples of other elements X include Co, Ni, Ti, V, Cr, Mn, Fe, Zn,
Examples include Al, Sn, Pb, Cu, Mo, and Nb. Of these, particularly preferred other elements are W, Zr, Co, Ni, and Ti.

The Si phase is preferably present in the alloy at a ratio of 5% by mass. If the proportion of the Si phase is too small, the discharge capacity decreases, and if the proportion of the Si phase is too large, the change in volume cannot be sufficiently suppressed, and the cycle life decreases. The composition of the alloy raw material is made Si-rich with respect to the stoichiometric ratio of the alloy system so that a Si phase is precipitated during solidification. The proportion of the Si phase can be adjusted depending on the degree of the Si richness.

The alloy powder containing a Si phase of the present invention further contains at least one oxidizable element A selected from the group consisting of Li element and oxidizable element which is easily oxidized than Li. The oxidizable element A may be Li, but is preferably an element having a lower free energy of oxide formation than Li (an element that is more easily oxidized than Li). It is advantageous. Preferred oxidizable elements in that sense are Ca, Mg, and rare earth elements (Sc, Y and lanthanoid elements).

The content of the easily oxidizable element A in the alloy is determined by converting substantially all of the oxygen that can be mixed in the alloy powder production process including the melting and solidification of the raw materials, powder production, heat treatment, etc., as a stable oxide. Any amount is sufficient as long as it is irreversibly fixed and detoxified so as not to lower the discharge capacity. Therefore, the content of the easily oxidizable element may vary depending on the amount of oxygen mixed in the production process, but it is usually preferable that the content be in the range of 0.01% by mass or more and 1% by mass or less of the alloy.

If the content of the easily oxidizable element A is too small,
Oxide generation sites are reduced, and all of the oxygen mixed in the manufacturing process cannot be fixed by generation of an oxide with an easily oxidizable element, so that the effect of improving the discharge capacity cannot be sufficiently obtained. On the other hand, if the content of the easily oxidizable element is too large,
In addition to producing oxides by reacting with oxygen, excess oxidizable elements produce stable intermetallic compounds or solid solutions with the alloying elements Si and other elements, but the amount produced is large. As a result, the electrode characteristics of the alloy, particularly the discharge capacity, are adversely affected.

The alloy powder containing the Si phase of the present invention has a predetermined composition.
It is preferable to manufacture by a method including a step of solidifying a melt of the alloy raw material adjusted to (Si + other element X + oxidizable element A) by a method in which the cooling rate is 100 ° C./sec or more.
By rapid solidification at a cooling rate of 100 ° C./sec or more, the easily oxidizable element is uniformly dispersed without segregation in the solidified alloy. Therefore, the oxidizable element preferentially reacts with oxygen mixed in the manufacturing process to form a chemically stable and irreversible oxide, thereby preventing a decrease in discharge capacity due to oxygen. Function works more effectively.

Examples of the solidification method capable of such rapid solidification include an atomizing method, a roll quenching method, a rotating electrode method, and a strip casting method. The atomization method can be any of a liquid atomization method and a gas atomization method, but the gas atomization method, which can provide a spherical powder having excellent filling properties, is more preferable. As the roll quenching method, any of a single roll and a twin roll is possible. Various methods are also known for the rotating electrode method, and any of them may be used.

The atmosphere from melting to solidification of the alloy raw material is as follows:
It is preferable to use a non-oxidizing atmosphere (eg, an inert gas atmosphere, vacuum) to avoid oxidation of the alloy. However, in the present invention, the alloy contains an easily oxidizable element, and this element can capture oxygen mixed in the manufacturing process and fix it as a stable oxide, so that adverse effects due to mixing of oxygen from the atmosphere are avoided. Can be. Therefore, it is permissible to mix a small amount of oxygen into the atmosphere, so that it is not necessary to use a costly high-purity inert gas or high vacuum.

The solidified alloy is pulverized to a powder as required. In the atomizing method or the rotating electrode method, the alloy is obtained in a powder state, so that a pulverizing step is not necessary. In the roll quenching method or the strip casting method, a flaky alloy is generally obtained, so that it is pulverized and powdered. The pulverizing step is also preferably performed in a non-oxidizing atmosphere such as an inert gas atmosphere. The alloy powder is classified if necessary to adjust the particle size.
An alloy powder suitable as a negative electrode material for a non-aqueous electrolyte secondary battery generally has an average particle size in the range of 1 to 30 μm.

The alloy powder produced by rapid solidification can be used in a solidified state, but may be subjected to a heat treatment if desired. Since the rapidly solidified alloy is in a non-equilibrium state due to a high cooling rate, not all of the oxygen mixed in during the manufacturing process becomes an oxide with an easily oxidizable element, and some of the constituent elements of the alloy ( (Si or X element). When heat treatment is performed, the oxide of such an alloy constituent element is reduced by the easily oxidizable element contained in the alloy, and becomes a chemically stable and irreversible oxide of the easily oxidizable element.

The heat treatment conditions are selected so as to be sufficient to reduce the oxides of the constituent elements of the alloy with the easily oxidizable element. The heat treatment temperature is preferably equal to or lower than the solidus temperature of the alloy so that melting of the alloy does not occur. If the heat treatment temperature is too high, the crystal grains grow and become coarse. Therefore, it is more preferable to perform the heat treatment at a temperature lower than the solidus temperature of the alloy by 50 ° C. or more. Heat treatment times typically range from 0.5 to 48 hours. The heat treatment atmosphere is preferably a non-oxidizing atmosphere (vacuum, inert gas atmosphere, or the like) in order to suppress oxidation during the heat treatment.

From the negative electrode material of the present invention, for example, a negative electrode for a non-aqueous electrolyte secondary battery can be manufactured as described below. First, an appropriate binder and a solvent thereof are mixed with an alloy powder of a negative electrode material together with a conductive powder as needed to improve conductivity. The mixture is homogenized,
The mixture is sufficiently stirred by appropriately using glass beads or the like to form a slurry. This slurry is applied to an electrode substrate (current collector) such as a rolled copper foil or a copper electrodeposited copper foil using a doctor blade or the like, dried, and then consolidated by roll rolling or the like. The negative electrode is cut to a size.

Examples of the binder include water-insoluble resins such as PVDF (polyvinylidene fluoride), PMMA (polymethyl methacrylate), and PTFE (polytetrafluoroethylene); CMC (carboxymethyl cellulose); and PVA (polyvinyl alcohol). And the like. As the solvent, depending on the binder, NMP (N-methylpyrrolidone), DM
Use an organic solvent such as F (dimethylformamide) or water.

As the conductive powder, any of carbonaceous materials (eg, carbon black, graphite) and metals (eg, Ni) can be used, but carbonaceous materials are preferred. Since the carbonaceous material can occlude Li ions between the layers, in addition to conductivity, it can contribute to the capacity of the negative electrode, and is rich in liquid retention.

When a carbonaceous material is compounded in the negative electrode, it is preferable to use the carbon material in an amount of 5% by mass or more and 80% by mass or less based on the negative electrode material of the present invention. This amount is 5% by mass
If it is less than 30, sufficient conductivity cannot be imparted, and if it exceeds 80% by mass, the capacity of the negative electrode decreases. A more preferred blending amount is 20% by mass or more and 50% by mass or less.

Using this negative electrode, a non-aqueous electrolyte secondary battery is manufactured. A typical example of the nonaqueous electrolyte secondary battery is a lithium ion secondary battery, and the negative electrode material and the negative electrode according to the present invention are suitable as the negative electrode material and the negative electrode of the lithium ion secondary battery.

The non-aqueous electrolyte secondary battery has the following basic structure:
It contains a negative electrode, a positive electrode, a separator, and a non-aqueous electrolyte. As the negative electrode, one manufactured from the negative electrode material of the present invention is used, but other positive electrodes, separators, and electrolytes are not particularly limited, and conventionally known materials or materials to be developed in the future may be appropriately used. The shape of the nonaqueous electrolyte secondary battery is not particularly limited, and may be any shape such as a cylindrical shape, a square shape, a coin shape, and a seal shape.

In the case of a lithium ion secondary battery, the positive electrode preferably uses a Li-containing transition metal compound as a positive electrode active material. Examples of Li-containing transition metal compounds are LiM _1-X M ' _X O ₂
Or LiM _2y M ' _y O ₄ (where 0 ≦ X, Y ≦ 1, M and M ′ are each Ba, Co, Ni, Mn, Cr, Ti, V, Fe, Zn, Al, I
at least one of n, Sn, Sc, and Y). However, other positive electrode materials such as transition metal chalcogenides; vanadium oxides and their Li compounds; niobium oxides and their Li compounds; conjugated polymers using organic conductive substances; chevrel phase compounds; Can also be used.

The electrolyte of a lithium ion secondary battery is generally a non-aqueous electrolyte in which a lithium salt serving as a supporting electrolyte is dissolved in an organic solvent. As the lithium salt, for example, LiCl
O ₄ , LiBF ₄ , LiPF ₆ , LiAsF ₆ , LiB (C ₆ H ₅ ), LiCF ₃ SO ₃ ,
LiCH ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , Li (CF ₂ SO ₂ ) ₂ ,
Examples thereof include LiCl, LiBr, and LiI, and one or more of them can be used.

As the organic solvent, carbonates such as propylene carbonate, ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate and diethyl carbonate are preferred. However, other various organic solvents including carboxylic acid esters and ethers can also be used.

The separator plays a role as an insulator provided between the positive electrode and the negative electrode, and also greatly contributes to retention of the electrolyte. Usually, a porous body such as polypropylene, polyethylene or a mixed cloth of both, or a glass filter is generally used.

[0047]

【Example】

[0048]

Example 1 This example illustrates the production of an alloy powder by a gas atomizing method. A molten metal obtained by high-frequency melting of alloy materials having various compositions shown in Table 1 under an argon gas atmosphere was poured into a tundish under an argon gas atmosphere. Ar
Alloy powder was produced by spraying gas. The solidification rate at this time was 10 ³ to 10 ⁵ ° C / sec as shown in Example 2.
Met. For some alloy powders, Table 1 was used in argon gas.
At 10 ° C. for 10 hours. The heat treatment temperature was 140 ° C. or lower than the solidus temperature of the alloy.

To evaluate the negative electrode performance of this alloy powder,
Average particle size 20μ obtained by classifying each alloy powder with a 45μm sieve
A negative electrode was prepared using the powder of m in the following manner. For comparison, a negative electrode was similarly produced using a conventional carbon material (graphite powder obtained by mesophase, carbonization, and graphitization of petroleum pitch and having the same average particle size as above).

The negative electrode was prepared by adding 8% by mass of polyvinylidene fluoride as a binder, 10% by mass of N-methylpyrrolidone as a solvent, and a carbon material (acetylene) as a conductive material to an alloy powder used as a negative electrode material. Black) powder was added in the same amount of 12% by mass and kneaded to form a uniform slurry. This slurry was applied to a 30 μm-thick electrolytic copper foil, dried, roll-rolled, consolidated, and then punched out using a punch having a diameter of 15 mm to obtain a disk member, which was used as a negative electrode.
The thickness of the negative electrode material layer on the copper foil was about 100 μm.

The performance of the obtained negative electrode with a single electrode was evaluated using a so-called three-electrode cell using Li metal for the counter electrode and the reference electrode. For the electrolyte, LiPF ₆ as a supporting electrolyte was mixed in a 1: 1 mixed solvent of ethylene carbonate and dimethoxyethane.
A solution dissolved at an M concentration was used. The measurement was performed at 25 ° C., and charging and discharging were performed using a device capable of maintaining an inert atmosphere such as a glove box with the dew point of the atmosphere being about −70 ° C.

Charge / discharge conditions: (1) Temperature 25 ° C. (2) Charge Discharge to 0 V (vs. reference electrode) at 1/10 C. Up to 2 V (vs. reference electrode) at 1/10 C. Discharge capacity obtained in the first cycle It is shown in Table 1.

[0053]

[Table 1] An alloy containing a Si phase can exhibit a significantly higher discharge capacity than a conventional carbon material, but it can be seen from Table 1 that the discharge capacity is further improved by adding a small amount of an oxidizable element to the alloy. .

[0054]

Example 2 This example illustrates the effect of the solidification temperature during alloy preparation. As shown in Table 2, 60% Si-0.1% Ca
-An alloy raw material having the same composition as the remaining Co was melted in the same manner as in Example 1, and alloys were prepared from the obtained molten metal by various methods shown in Table 2. The alloy obtained by the roll quenching method and the casting method (preparing an alloy by casting a molten metal in a mold) was pulverized by a ball mill in an argon gas atmosphere into powder. No heat treatment was performed.

When the microstructure of the alloy powder obtained by each method was observed, a segregation phase was observed in the alloy produced by the casting method, and the segregation phase contained Si and / or Co, which is a constituent element of the alloy, and an easily oxidizable alloy. An intermetallic compound with the Ca element was present. No segregation was observed with other solidification methods.

The cooling rate of each solidification method calculated from the interval between the dendrite secondary arms of the solidified structure was as follows: gas atomization method 10 ³ to 10 ⁵ ° C / sec roll quenching method 10 ³ to 10 ⁵ ° C / sec Rotating electrode method 10 ² ℃ / sec Casting method 30 ℃ / sec The same method as in Example 1 using a powder having an average particle diameter of 20 μm obtained by classifying the alloy powder obtained by each method with a 45 μm sieve. , And a negative electrode test was conducted. Table 2 also shows the discharge capacity obtained in the negative electrode test.

[0057]

[Table 2] As shown in Table 2, the alloy powder of the present invention produced by rapid solidification has a higher discharge capacity than an alloy powder obtained by a casting method having a cooling rate of less than 100 ° C./sec (Comparative Example). Among the rapid solidification methods, the alloy powders produced by the gas atomizing method and the roll quenching method having a high cooling rate exhibited particularly high discharge capacities. Above all, the highest discharge capacity per volume was obtained by the gas atomization method, because this alloy powder does not need to be pulverized, and there is no oxidation at the time of pulverization.

[0058]

Embodiment 3 This embodiment illustrates the influence of the heat treatment temperature.
A powder of an alloy having the same composition as in Example 2 was produced by the argon gas atomizing method described in Example 1, and heat-treated at a temperature shown in Table 3 for 10 hours in argon gas. The solidus temperature of this alloy was 1259 ° C. A negative electrode was produced and a negative electrode test was performed in the same manner as in Example 1 using the heat-treated alloy powder. The test results (discharge capacity) are also shown in Example 3.

[0059]

[Table 3] Table 3 shows that the heat treatment at a temperature lower than the solidus temperature of the alloy further increases the discharge capacity. However, when the heat treatment temperature exceeded the solidus temperature of the alloy, the discharge capacity was significantly reduced. When the microstructure of this alloy powder was observed, a segregation phase was observed. This segregation phase had almost the same appearance as the segregation phase observed in the alloy produced by the casting method of Example 2. Presumably, a liquid phase was formed during the heat treatment, and segregation occurred when the liquid phase was gradually cooled.

[0060]

According to the present invention, a small amount of an easily oxidizable element is uniformly contained in an alloy powder containing a Si phase as a negative electrode material for a non-aqueous electrolyte secondary battery having excellent discharge capacity and cycle life. Accordingly, it is possible to avoid a decrease in the discharge capacity due to mixing of oxygen during the production of the alloy powder, and to provide a negative electrode material with further improved discharge capacity at low cost.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Takayuki Nakamoto 1006 Kadoma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Inventor Harari Shimamura 1006 Kadoma Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd. (72) Inventor Koichi Kamishiro 1-8 Fuso-cho, Amagasaki City, Hyogo Prefecture Sumitomo Metal Industries, Ltd.Electronic Technology Research Laboratories (72) Inventor Yukiteru Takeshita 1-8 Fuso-cho, Amagasaki City, Hyogo Sumitomo Metal Industries, Ltd. (72) Inventor Noriyuki Nego 1-8 Fuso-cho, Amagasaki-shi, Hyogo Sumitomo Metal Industries, Ltd. Electronics Technology Laboratory F-term (reference) 4K018 AA40 BC01 KA38 5H029 AJ03 AJ05 AK03 AL11 AM03 AM04 AM05 AM07 CJ02 CJ30 DJ16 HJ00 HJ01 5H050 AA07 AA08 BA17 CA08 CA09 CB11 FA17 GA02 GA06 GA29 HA0 1 HA20

Claims (6)

[Claims] 1. An alloy powder containing a Si phase, further comprising at least one oxidizable element selected from the group consisting of a Li element and an element more easily oxidized than Li. Alloy powder for negative electrode of non-aqueous electrolyte secondary battery. 2. The alloy powder for a negative electrode of a non-aqueous electrolyte secondary battery according to claim 1, wherein the oxidizable element is contained in an amount of 0.01% by mass or more and 1% by mass or less. 3. The non-aqueous electrolyte secondary battery negative electrode alloy powder according to claim 1, wherein the oxidizable element is selected from the group consisting of Li, Ca, Mg, and a rare earth element. 4. The cooling rate of the molten alloy raw material is 100 ° C./s.
The method for producing an alloy powder for a negative electrode of a non-aqueous electrolyte secondary battery according to any one of claims 1 to 3, further comprising a step of solidifying by a method of at least ec. 5. The method according to claim 1, wherein said method is an atomizing method, a roll quenching method,
5. The method for producing an alloy powder for a negative electrode of a non-aqueous electrolyte secondary battery according to claim 4, wherein the method is a rotating electrode method. 6. The method for producing an alloy powder for a negative electrode of a non-aqueous electrolyte secondary battery according to claim 4, further comprising a step of subjecting the solidified alloy to a heat treatment at a temperature lower than the solidus temperature of the alloy.