KR20120083336A - Silicon alloy for use in materials for lithium secondary battery negative electrodes - Google Patents

Abstract

 AI: 15-40% in atomic%, Ti: 1-20%, 1 or 2 types of Ta and W: 0-3% in total, 1 or 2 or more types of Fe, Ni and Cr: 0 in total -30%, Zr: material Si alloy for lithium secondary battery negative electrode containing 0-10% and consisting of remainder Si and unavoidable impurities. The alloy is inexpensive in raw materials, has excellent cycle characteristics of lithium secondary batteries, and has excellent amorphous properties.

Description

Silicon Alloy for Lithium Secondary Battery Negative Material {SILICON ALLOY FOR USE IN MATERIALS FOR LITHIUM SECONDARY BATTERY NEGATIVE ELECTRODES}

Cross Reference of Related Application

This application claims the priority based on Japanese Patent Application No. 2009-218397 for which it applied on September 24, 2009, The whole indication of this application is integrated in this specification by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicon (Si) alloy having a high discharge capacity, a long cycle life, and excellent amorphousness, which is used for a negative electrode active material of a lithium secondary battery.

As a negative electrode active material of a lithium secondary battery, a powder made of a carbon material has been conventionally used. However, carbon materials have a low theoretical capacity of 372 mAh / g, and there is a limit to higher capacities. Therefore, in recent years, application of metal materials with a theoretical capacity higher than carbon materials, such as Sn and Si, has been examined and put into practice. Si in particular is a promising material with a theoretical capacity in excess of 4000 mAh / g. When a metallic material to replace these carbons is used as a negative electrode active material of a lithium secondary battery, a high capacity can be obtained. However, various improvements have been proposed due to a short cycle life.

For example, Japanese Patent Application Laid-Open No. 2004-95469 (Patent Document 1) discloses that when the active material phase becomes fine and the surroundings of the fine active material phase are surrounded by an inactive phase, the volume change of the active material phase during charging and discharging is suppressed, thereby improving cycle life. The cycle life is improved by the grinding process (MG method). That is, in this document, mechanically grinding (pulverizing, crushing and assembling) a negative electrode material obtained by quenching in a molten metal by using a ball mill-type apparatus (attritor, vibrating ball mill, planetary ball mill, etc.) to refine the active phase, thereby surrounding the fine active phase. Is surrounded by an inert phase, it is shown that the volume change of the active material phase during charging and discharging is suppressed and the cycle life is improved.

Moreover, in Unexamined-Japanese-Patent No. 2009-32644 (patent document 2), the alloy composition ribbon containing Si, Al, and other additive elements was produced by the liquid short-roll supercooling method, and an amorphous alloy or a microcrystalline alloy is obtained. In the alloys of Examples 12 to 14 including Fe, Ni, Cr, and Zr having a high refining effect, among the alloys described in Examples of Patent Document 2, an amorphous phase was obtained, and an ultrafine crystal of 50 nm or less was formed by heat treatment at a predetermined temperature. Getting

For reference, the compositions of Examples 12 to 14 of this Patent Document 2 are atomic%, Si is 55%, Al is 20%, Fe is 10%, Zr is 5%, Ni is 5% and Cr is 5%. Transactions, JIM, Vol. 38, No. 12 (1997), pp. 1095-1099 (Tohoku'University) (Non-Patent Document 1) are completely the same as the alloy, and the composition is known as Si-based amorphous alloy as described in this Non-Patent Document 1.

As described above, it has been known that the Si alloy for lithium secondary battery negative electrode material requires microstructure in order to improve the cycle life, and the application of the MG method and the amorphous alloy has been studied. It is considered that the method of applying the amorphous alloy is effective because there is no fear of increasing impurities such as oxygen during the treatment like the MG method. Particularly effective additive elements for obtaining amorphous alloys include Zr. For example, Non-Patent Document 1 describes that the region of Si content in which the amorphous single phase can be obtained by Zr addition is extended to 55%.

However, since Zr is a very expensive raw material compared with Si, Al, Fe, Ni, and Cr, the addition amount is inevitably suppressed as an alloying element for a lithium secondary battery negative electrode.

As described above, in the case of Patent Document 1 described above, the MG method has a problem of impurity incorporation such as oxygen or treatment cost. Also, as in Patent Document 2 and Non-Patent Document 1, the application of amorphous alloy uses an expensive raw material such as Zr. This was a problem because of the high cost.

Prior art literature

Patent literature

Patent Document 1: Japanese Patent Application Laid-Open No. 2004-95469

Patent Document 2: Japanese Patent Laid-Open No. 2009-32644

Non Patent Literature

[Non-Patent Document 1] Materials-Transactions, JIM, Vol. 38, No. 12 (1997), pp. 1095-1099 (Tohoku University)

The present inventors have found that by adding relatively inexpensive Ti as an amorphousization promoting element in place of Zr, it is possible to provide a Si-based amorphous alloy useful as a lithium secondary battery negative electrode material.

Accordingly, an object of the present invention is to provide a Si alloy having a low raw material cost, excellent cycle characteristics of a lithium secondary battery, and excellent amorphousness. It is another object of the present invention to provide a lithium secondary battery negative electrode material including such Si alloy.

According to one aspect of the invention in atomic percent

Al: 15-40%,

Ti: 1-20%

1 or 2 types of Ta and W: 0-3% in total,

1 type or 2 types or more of Fe, Ni and Cr: 0-30% in total,

Zr ： 0 ~ 10%

A Si alloy for a lithium secondary battery negative electrode material comprising a residual Si and an unavoidable impurity is provided.

According to one aspect of the invention in atomic percent

Al: 15-40%,

Ti: 1-20%

1 or 2 types of Ta and W: 0-3% in total,

1 type or 2 types or more of Fe, Ni and Cr: 0-30% in total,

Zr ： 0 ~ 10%

A lithium secondary battery negative electrode material comprising: and a Si alloy comprising residual Si and inevitable impurities is provided.

1 is an X-ray diffraction pattern of a quench ribbon to which Zr is added.
2 is an X-ray diffraction pattern of a quench ribbon to which Ti is added.
3 is an X-ray diffraction pattern of a quench ribbon without adding both Ti and Zr.

Si alloy for lithium secondary battery negative electrode material of the present invention is atomic% Al: 15-40%, Ti: 1-20%, one or two of Ta and W: 0-3% in total, Fe, Ni And one or two or more kinds of Cr: 0 to 30% in total, Zr: 0 to 10%, balance Si and unavoidable impurities, preferably substantially from these components, and more preferably only with these components. It is composed.

One of the features of the present invention is the discovery of Ti as an amorphization promoting element replacing Zr. 1 to 3 are diagrams showing the results of the amorphous forming ability of the quench alloy ribbon measured by X-ray diffraction (XRD). As shown in these figures, X-ray diffraction of a sample having an amorphous phase shows a broad halo pattern unique to the amorphous phase. In addition, in the case of a sample which is not a perfect amorphous but a mixture of amorphous and crystal, a diffraction peak having a relatively wide half value width (half the width of the diffraction peak) in addition to the halo pattern is shown. This peak is related to the amount of mixed crystal phases present, and the alloy amorphous forming ability can be evaluated with a half width.

The present inventors examined the half value width of this pattern in detail and found out that Ti addition of this alloy system was very effective. For example, FIG. 1 is an X-ray diffraction pattern of the quench ribbon to which Zr was added, and FIG. 2 is an X-ray diffraction pattern of the quench ribbon to which Ti was added. All looks clear halo pattern. 3 is an X-ray diffraction pattern of a quench ribbon without addition of Ti and Zr, and a clear halo pattern is not seen. As such, Ti was found to be an effective additive element that improves amorphous forming ability, similar to Zr. In addition, Ti has a lower raw material cost than Zr.

Hereinafter, the reason which defined the range of the Si alloy component composition of this invention is described. In addition, in the following description,% means atomic% except a special case.

Al is an essential element for promoting amorphousization, and the content thereof is 15 to 40%, preferably 18 to 30%, more preferably 20 to 26%. If the Al content is less than 15%, the effect of promoting amorphization is not sufficient, and if the Al content is more than 40%, the powder is activated and there is a fear of dust explosion.

Ti is a relatively inexpensive raw material cost to replace Zr and is an essential element for promoting amorphousization, and the content thereof is 1 to 20%, preferably 2 to 15%, and more preferably 3 to 10%. If Ti content is less than 1%, the effect of promotion of amorphousization will not be enough, and if it is more than 20%, amorphous forming ability will fall.

Ta and W are arbitrary elements for stabilizing powder production by the atomization method, and these one or two types are 3% or less in total, Preferably it is 0.2-2%, More preferably, it is 0.5- You may add in 1% of range. When the total content of Ta and W exceeds 3%, Ta and W, which are high melting point materials, are dissolved and the alloy composition is not stable.

In particular, by adding Ta and / or W in the above-described content range, the tapping of the molten alloy of the atomizing method can be smoothed. The detailed principle of this action is unclear, but the following factors are assumed. Generally, the powder prepared by atomization is Fe alloy, Ni alloy, Co alloy, Cu alloy and the like, and the specific gravity is about 8Mg / m ³ or more. In contrast, the alloy of the present invention is a Si alloy and the specific gravity is about 3Mg / m ³ .

In the atomizing method, an alloy is dissolved in crucibles such as refractory materials, and the molten metal is tapped with a nozzle below the crucible and sprayed with an inert gas or the like. At this time, the molten metal passing through the nozzle part receives the weight of the alloy molten metal remaining in the crucible and taps into the nozzle as if it is subjected to this load. Therefore, in the second half of atomization, the remaining alloy molten metal decreases in small amount and the load gradually decreases, so that tapping through the nozzle becomes unstable. This phenomenon is particularly pronounced in small Si alloys with specific gravity. By adding a small amount of Ta and / or W, which are elements having a high specific gravity, tapping through the nozzle may be smooth.

Fe, Ni, and Cr are arbitrary elements for promoting amorphousization, and 30% or less in total, preferably 10 to 28%, more preferably 15 to 25% of one or two or more of these elements as necessary. You may add in the range of. When the total content of Fe, Ni and Cr exceeds 30%, the amorphous forming ability is lowered.

Zr is an arbitrary element for promoting amorphousization, and may be added in an amount of 10% or less, preferably 4% or less, and more preferably 3% or less, as necessary. Adding more than 10% saturates the effect and increases the raw material cost.

Example

Example 1 Amorphous Constitutive  evaluation

Sample No. shown in Table 1 The component composition ribbon of 1-18 was produced with the single-roll liquid quenching apparatus. The base material was produced by arc melting in advance. The amount of melt | dissolution was 10 g, and in the case of a quenching ribbon, the nozzle diameter of the liquid quenching apparatus was about 1 mm, the diameter of the copper roll was 300 mm, and the rotation speed was 3000 rpm. The amorphous forming ability was evaluated by measuring the half value width of the X-ray diffraction pattern about the produced quench ribbon. As the X-ray diffraction sample, one having a quench ribbon attached to a glass plate was used. At this time, the surface which contacted the copper roll of the quench ribbon was made into the to-be-tested surface.

As described above, when the X-ray diffraction of the amorphous phase sample was measured, no sharp diffraction peaks caused by the crystals were observed, and a broad halo pattern peculiar to the amorphous phase was observed. In the case of a mixture of amorphous and crystal, not a perfect amorphous, a relatively wide diffraction peak of half width (half the height of the diffraction peak) was observed in addition to the halo pattern. This peak is related to the amount of mixed crystal phases present, and the amorphous forming ability of the alloy can be evaluated by the width of the half value width.

The amorphous forming ability of the alloy was determined based on the following criteria from the X-ray diffraction pattern.

(Double-circle): The clear halo pattern was seen.

(Circle): A clear halo pattern was not seen, but the half width of a main peak is 0.7 degrees or more.

X: The clear halo pattern is not seen, and the half width of the main peak is 0.7 ° or less.

Example 2: At Atomized  Tang Flowability Assessment

Sample No. shown in Table 1 Composition powders of 2, 8 to 10, 15 and 16 were prepared by the gas atomization method. In an aluminum crucible, 800 g of an induction melting furnace melt | dissolution melt | dissolved in the pressure-reduced argon atmosphere, was melted with the nozzle of nozzle diameter 3mm, and it was atomized with nitrogen gas. At this time, the shaking of the molten alloy melted out through the nozzle in the second tapping and the residue after tapping were confirmed.

Example 3: Evaluation of Explosive Properties

 Sample No. shown in Table 1 For 5 and 12, the quench ribbon was pulverized with a mortar in an argon atmosphere, classified at -45 µm, and then subjected to an explosion test to evaluate explosiveness. The explosion test was tested with a weight of 0.5 mg using the Hartmann dust explosion test apparatus.

Sample No. shown in Table 1 1-10 are exemplifications of the present invention, and sample no. 11-18 is a comparative example.

From the results shown in Table 1, it was found that the alloy composition within the scope of the present invention is excellent in amorphous forming ability. It has also been found that tapping during atomization is stabilized by the addition of Ta and / or W. Sample No. 5 and Sample No. It was found from the comparison of 12 that the explosiveness by Al was small as long as it was an alloy composition within the scope of the present invention.

Sample No. 11 is inferior in amorphous forming ability because of low Al content. Sample No. 12 has a high Al content, but has an amorphous forming ability, but a dust explosion occurs. Sample No. 13 is inferior in amorphous forming ability because Ti content is low. Sample No. Since 14 has high Ti content, amorphous forming ability is inferior. Sample No. Since 15 had a high W content, a melting glass phenomenon occurred at the time of atomization.

Sample No. Since 16 had a high Ta content, a molten metal phenomenon occurred at the time of atomization. Sample No. 17 is inferior in amorphous forming ability because the total content of Fe, Ni and Cr is high. Sample No. 18 is excellent in amorphous forming ability because of high Zr content, but there is a problem that raw material cost rises and high cost. In comparison, the sample No. It can be seen that 1 to 10 all satisfy the conditions of the present invention, promote the amorphous forming ability and stabilization of tapping at the time of atomization, and exhibit excellent melt flow properties and low explosiveness.

Thus, by using Ti as an amorphousization promoting element to replace Zr according to the present invention, the raw material cost is low, and it is possible to provide a Si alloy having excellent cycle characteristics and excellent amorphousness in a lithium secondary battery at low cost.

Claims (8)

nuclear pile,
Al: 15-40%,
Ti: 1-20%
One kind or two of Ta and W: 0-3% in total,
1 type or 2 types or more of Fe, Ni, and Cr: 0-30% in total,
Zr ： 0 ~ 10%
Si alloy for a lithium secondary battery negative electrode material, comprising a balance Si and inevitable impurities. The Si alloy according to claim 1, wherein one or two of Ta and W are contained in total of more than 0% and 3% or less. The Si alloy according to claim 1, wherein one or two or more of Fe, Ni, and Cr are contained in total of more than 0% and 30% or less. The Si alloy according to claim 1, which contains more than 0% and 10% or less of Zr. nuclear pile,
Al: 15-40%,
Ti: 1-20%
One kind or two of Ta and W: 0-3% in total,
1 type or 2 types or more of Fe, Ni, and Cr: 0-30% in total,
Zr ： 0 ~ 10%
And a Si alloy comprising a balance Si and an unavoidable impurity. 6. The lithium secondary battery negative electrode material according to claim 5, wherein the Si alloy contains one or two of Ta and W in total of more than 0% and 3% or less. 6. The lithium secondary battery negative electrode material according to claim 5, wherein the Si alloy contains one, two or more of Fe, Ni, and Cr in total of more than 0% and 30% or less. 6. The lithium secondary battery negative electrode material of claim 5, wherein the Si alloy contains greater than 0% and no greater than 10% Zr.

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